MXPA99001738A - Process and system to treat hum gas - Google Patents

Abstract

This invention relates to a process for treating flue gas, which includes a heat recovery step, to recover the heat from the flue gas, by means of a heat exchanger (4), and thus cool the flue gas , and a subsequent absorption step, to bring the flue gas into gas-liquid contact with an absorbent fluid (D) in the absorption towers (12, 13), so as to move at least the S02 present in the flue gas by absorption in the absorption fluid (D), this process is characterized, for example, by the provision of a stage of the addition of powder, for the spraying of a powder, which can be collected, in the absorption stage [e.g. carbon ash (H)] inside the flue gas, before the heat recovery stage. This invention makes it possible to provide a process for the treatment of flue gas in which a preliminary measurement against the S03 present in the flue gas can easily be achieved, without recourse to ammonia injection, and the flue gas can also be purified without the disadvantage of causing the injected substance to remain in the humer gas

Description

PROCESS AND SYSTEM TO TREAT SMOKE GAS FIELD OF THE INVENTION AND EXHIBITION OF THE RELATED ART This invention relates to a technique for the purification of flue gas, which contains SO2 and SO3 as sulfur oxides and, likewise, powders, such as unburned carbon (for example). example the flue gas produced by boilers that burn heavy oils). More particularly, it relates to a technique for the treatment of flue gas, in which a preventive measure against SO3, present in the flue gas, can be achieved, which can condense to produce harmful fumes of sulfuric acid, or an improvement in The dust removal capacity can be produced at low cost and with simple operation or construction of equipment. Generally, the flue gas produced, for example, from boilers that burn heavy oils, in a thermal power plant or similar, contains sulfur oxides, which include SO3 (sulfur trioxide) in addition to SO2 (sulfur dioxide) ). The ratio of SO 3 to the total amount of sulfur oxides (eg, 1,500 ppm), may vary according to the boiler combustion temperature, the type of burner, the type of the combustion catalyst and the like, but is D order several hundred in any case. That is, S03 is present in a relatively small amount, for example about 30 ppm. Consequently, an important basic consideration in the desulfurization of this type of humer gas is the ability to absorb SO2 • However, when the SO3 present in the flue gas produces fumes, they form harmful H2SO4 mists, which are highly corrosive and they constitute a factor in the formation of inlays. Also, they consist of submicron particles that can hardly be captured by mere gas-liquid contact with the absorbent fluid. For this reason, some treatment for the removal of SO3 is required in order to prevent corrosion of the equipment and the formation of scale or in order to achieve a further purification of the flue gas. Therefore, in a flue gas treatment system, for use, for example, with a boiler that burns heavy oils, it has conventionally been a common practice to inject ammonia into the flue gas, in a part upstream of the equipment. and thus capture the SO3 present in the flue gas as ammonium sulfate [(NH4) SO4]. An example of such a conventional process and system of the humer gas treatment is described below with reference to Figure 14.

In Figure 14, the reference number 1 designates an air heater (boiler secondary equipment) for heating the combustion air to be supplied to a boiler (not shown), using the heat of the exhaust gas. In this case, the apparatus or steps following this air heater 1 are within the scope of the present invention. First, in an inlet duct 2, an untreated flue gas A, leaving the air heater 1, is brought into contact with the ammonia (NH3), sprayed from a spray nozzle 2. Thus, the SO3 present in the flue gas reacts with this ammonia and the water in the flue gas to form the ammonium sulfate. Since this ammonium sulfate is present as solid particles (ie, dust) in the flue gas, the concentration of dust in the flue gas is markedly increased. (For example, when the dust concentration, before the injection of ammonia, is 180 mg / m3N, this concentration of the powder, after injection of ammonia, becomes 360 mg / m3N.) Next, the The flue gas A is introduced into a dry electrostatic precipitator 3, where the dust B is removed from it. This part of powder B, which was originally contained in flue gas A, consists essentially of unburned coal and, in the case, for example, of boilers that burn heavy oils, also contains impurities, such as vanadium and magnesium. Also, the majority of the ammonium sulfate, mentioned above, is also collected in this electrostatic precipitator 3, discharged in the powder B, and discarded, for example, as an industrial waste. Next, in order that the heat-treated flue gas C be discharged into the atmosphere, in the reheating section 5 of the gas-gas heater (GGH), as will be described later, the exhaust gas A introduces in section 4 heat recovery of this GGH, where it is subjected to heat recovery and thus cooled (heat recovery stage). For example, the temperature of the flue gas A is reduced from 160 to 100 ° C, approximately. Subsequently, at least the SO2 and some of the remaining small amount of the powder is removed from the flue gas A in the absorption towers 12 and 13 (to be described later) of a desulphurization apparatus 10 (absorption stage), heated in section 5 of reheating GGH to a temperature suitable for discharge into the atmosphere, and then discharging from a stack (not shown) into the atmosphere as treated C-flue gas. In this case, the desulphurisation apparatus 10 has a construction in which two absorption towers, 12 and 13, of the liquid column type (i.e., parallel and counter-flow absorption absorption towers) are juxtaposed above a tank 11. for storing an absorbent aqueous paste (or absorbent fluid) D and in which the flue gas is introduced successively into these absorption towers and carried in a gas-liquid contact with the aqueous paste within the tank 11 in the absorption towers respective. Each absorption tower 12 and 13 is equipped with a plurality of spray tubes 15 and 16. The aqueous paste absorbed by the circulation pumps, 17 and 18, is injected upwards from these spray tubes, 1§_ and 16, in the form of liquid columns. Also, in this case, a mist eliminator 20, to collect and remove the entrained mist, is installed downstream of the absorption towers. In the apparatus of Figure 14, the mist collected by this mist eliminator 20 accumulates in a lower hopper (not shown) and is returned to the tank 11 through a discharge pipe, which extends from the bottom of the hopper . Also, this apparatus is equipped with the so-called rotary arm air sprinkler 21, for blowing the oxidizing air into the aqueous paste in the tank 11, in the form of fine bubbles of air, while the aqueous paste is stirred, so that this absorbent aqueous paste has absorbed the sulfur dioxide, where it is brought into efficient contact with the air in the tank 11 and thus oxidizes completely to form the gypsum.

More specifically, in this apparatus, the absorbent aqueous paste, injected from the spray tubes, 15 or 16, into the absorption tower 12 or 13, flows downwards while the absorbing sulfur dioxide and the dust, as a result of the contact of the gauze humerus, and enters tank 11 where it is oxidized by contact with a large number of air bubbles-liquid gas, blown there while stirring with sprayer 21 air, and then undergoes a neutralization reaction to form the plaster. The dominant reactions that occur in the course of these treatments are represented by the following reaction formulas (1) to (3): Inlet section of the flue gas of the absorption tower SO2 + H2O ^ > H + + HSO3- (1) Tank H + + HSO3- + 1? 02 = 2H + + S0 2- (2) 2H + + SO42- + CaC? 3 + H2O ^ CaS? 4-2H2? + CO2 (3) Thus, the gypsum, a small amount of limestone (used as the absorbent) and a slight amount of powder, are suspended stably in the aqueous slurry within the tank 11. In this case, the slurry within the tank 11 (which can to be referred to later as an aqueous plaster paste S) is removed and fed to a solid-liquid separator 23, by means of an aqueous paste pump 22. This aqueous paste is filtered ep a solid-liquid separator 23, so that gypsum E with a low water content is recovered. On the other hand, a portion Fl of the solids-liquid separator filtrate is fed to a tank 26 for preparation of the slurry, by means of a filtering tank 24 and a filtering pump 25, and is reused as the constituent of water of the absorbent aqueous paste D. The tank 26 for preparing the aqueous paste is equipped with an agitator and serves to prepare the aqueous paste D absorbent by the mixture of limestone G, introduced from a silo (not shown) with the filtrate Fl fed from tank 24 of this filtrate. The absorbent aqueous paste D inside the aqueous paste preparation tank 26 is suitably fed to the tank 11 by means of an aqueous paste tank 27. In order to replenish the gradually lost water, for example due to evaporation in the absorption towers 12 and 13, the composite water (such as industrial water) is suitably supplied, for example, to the tank 11. The limestone G a powder, usually obtained by spraying the mined limestone to a particle diameter of approximately 100 μm, is used in the form. Also, in order to prevent the accumulation of impurities in the water circulating through the desulfurizing apparatus 10, the remainder of the filtrate, inside the filter tank 24 is transferred to a waste water waste process (not shown) , such as the so-called desulphurisation wastewater F2. In accordance with the process for treating the flue gas, described above, the electrostatic precipitator 3 leaving the flue gas contains little SO 3 and, therefore, the disadvantages described above are avoided. That is, if there is no ammonia injection to treat the SO3, this SO3 will condense in the equipment at the base of the dew point of the sulfuric acid and thus produce fumes, as described above. In general, most SO3 would condense into fumes as a result of cooling in section 4 of heat recovery of GGH. Consequently, at least the heat recovery section 4 of the GGH and the parts placed downstream thereof, problems, such as the corrosion of the components of the equipment and the obstruction of the flow path of the flue gas, due to the Formation of scale can arise, thus causing an increase in the cost of the equipment and the cost of maintenance.

Also, since such fumes SO3 remain in the gas treated C humerus discharged from the apparatus 10 desulfurizing a wet dust collector needs to be installed, for example, in a position downstream of absorption tower 13 and upstream of section 5 of reheating of the GGH, in order to achieve a high degree of purification of the flue gas. This also causes an increase in the cost and size of the equipment. However, if the ammonia injection is performed, as illustrated in Figure 14, the SO3 present in the flue gas is converted to ammonium sulfate in a position upstream of the electrostatic precipitator 3, as described above, and the resulting ammonium sulfate is collected as powder B in the electrostatic precipitator 3. Thus, the problems described above with SO3 are solved tentatively. In the systems of treatment of the flue gas for the boilers that burn coal, a system in which the section 4 of heat recovery of the GGH is arranged on the side upstream of the electrostatic precipitator 3, to carry out the recovery stage Heat before electrostatic powder collection (ie, the so-called high performance system) is widely employed. This system is intended to achieve high dust separation performance with a simple and small-sized equipment construction, focusing attention on the fact that, when the temperature of the flue gas is low, the performance of dust collection by capacity Unitary electrostatic precipitator is improved based on the resistivity of the powder. However, in cases where oil fuels are used, this system has few merits due to differences in properties (eg, resistance, electrical) of the dust present in the flue gas. Accordingly, it is a common practice to perform ammonia injection, mentioned above, employing a construction of equipment as illustrated in Figure 14. However, the conventional treatment process or system of the flue gas involves the following several problems due to the injection of ammonia, previously mentioned. First of all, it is necessary to buy and supply the expensive ammonia. This is disadvantageous from the point of view of the cost of the operation. Likewise, it is also necessary to lengthen the inlet duct 2, so that the ammonia can be injected and diffused. This interferes with a reduction in the size of the equipment. Also, since some of the ammonia remains on the downstream side of the electrostatic precipitator 3, the nitrogen components are contained in the waste water F2 of the desulfurization. Consequently, an embarrassing treatment for nitrogen removal, for example, by microbial denitrification, is required prior to waste disposal of the desulphurisation wastewater. This also causes an increase in the cost of operation and size of the equipment. Likewise, ammonia is also contained in the treated flue gas C and discharged to the atmosphere. The emission of ammonia is inconvenient from the point of view of the further purification of the flue gas. If the ammonia emission is regulated, some measure for the removal of ammonia (for example, the use of additional equipment) will be required. This also has a problem from the point of view of cost and similar. Likewise, ammonia is also contained in gypsum E formed as a by-product. Therefore, depending on the acceptance standards for the plaster, it may be necessary to wash this plaster in order to remove the unpleasant and similar odor. In addition, the ammonium sulfate powder remaining on the downstream side of the electrostatic precipitator 3 has a relatively small particle diameter and is not completely captured by the gas-liquid contact in the absorption towers 12 and 13. Consequently, "this Ammonium sulfate powder remains in the treated flue gas C and also has a problem from the point of view of further purification of the flue gas.Thus, the conventional treatment technique of flue gas is not satisfactory for use as a technique for the purification of this flue gas in which the increasingly higher performance has recently become 'convenient from the qualitative and quantitative standpoints and, in particular, as a simple and low-cost humer gas treatment technique for small-scale electric power plants and independent electric power plants, which have become popular in recent years. Accordingly, there is a need for further improvement in this technique of treating the flue gas.

OBJECT AND COMPENDIUM OF THE INVENTION A first object of the present invention is to provide a process for the treatment of the flue gas, in which a preventive measure against the SO 3 present in the flue gas can be easily achieved without the injection of ammonia. and the flue gas can further be purified without the disadvantage of causing the injected substance to remain in the treated flue gas. The second object of the present invention is to provide a process for the treatment of flue gas in which a preliminary measurement against the SO3 present in the flue gas and a further purification of the flue gaso can be easily and completely achieved with an operation or simpler team building. The third object of the present invention is to employ the lime-gypsum method in the absorption step to remove the SO2 and the like from the flue gas, while maintaining the gypsum purity formed as a by-product at high level or decrease in the amount of industrial waste discharged. In order to achieve the objects described above, the present inventors carried out intensive investigations and discovered the empirical fact that, even if the injection of ammonia is not carried out, the problems described above with SO3 will not arise in the treatment systems of the flue gas for boilers that burn coal exclusively. The reason for this has been found is that the flue gas produced from the exclusive coal-burning boilers contain a large amount of dust, such as fly ash (ie its content is 10 to 100 times higher compared to gas). of flue from boilers that burn oil). That is, according to the investigations made by the present inventors, it is believed that, when a powder, such as fly ash, is contained in the flue gas, the condemnation, if any, of the SO3 present in the flue gas. As a result of the cooling in section 4 of the heat recovery stage of GGH occurs only at the particle surfaces of the aforementioned dust and, therefore, the particles of H2SO4 formed by the condensation of SO3 exist in a been attached to the aforementioned dust particles, which results in no harmful smoke production (or mists of sulfuric acid). Also, it has been found from experience that, if the flue gas contains a powder in such proportion that the ratio by weight (D / S) of the amount of the powder (D) present in a unit volume of the flue gas to the amount of the SO3 (S) present in the unit volume of the flue gas, is not less than about 2, the formation of scale and the corrosion of the components of the equipment due to SO3 hardly occur. The present invention, which has been completed in accordance with the technical ideas that make epoch, obtained based on these findings (ie, the idea that a preventive measure against SO3, can be achieved by adding a powder positively to the flue gas ), solves the problems described above, to a more complete extent, by means of the features described below. According to the present invention, a process for treating the flue gas is provided to treat a chimney gauze containing at least SO2 and SO3, which comprises a powder addition step for spraying a powder into the gas of humerus, and a subsequent absorption step to bring the flue gas into gas-liquid contact with an absorbent fluid in an absorption tower, in order to remove at least the SO2 present in the flue gas by absorption in the absorbent fluid , wherein a powder addition step, for spraying the dust that can be collected in the absorption step, into the flue gas, is I provided before the heat recovery step. The first humer gas treatment process of the present invention involves the following preferred embodiments. An embodiment in which the aforementioned powder is sprayed into the flue gas, in such proportion that the weight ratio (D / S) of the amount of powder (D), which includes the powder, mentioned above, to the amount of SO3 (S) present in the flue gas, is not less than 2 (ie, D / S >; 2); An embodiment in which the powder addition stage, the aforementioned temperature of the powder, is less than the temperature of the flue gas; An embodiment in which the aforementioned powder is sprayed into the flue gas, in the form of an aqueous paste, comprising the aforementioned powder, suspended in a liquid; An embodiment in which the absorption fluid, which has undergone gas-liquid contact with the flue gas in the absorption stage, is sprayed into the flue gas, such as the aforementioned aqueous paste, so that the solid matter present in the absorption fluid can be used as the powder, mentioned above; An embodiment in which the solid matter present in the absorption fluid, which has undergone a gas-liquid contact with the flue gas in the absorption stage, is used as the aforementioned powder; and A mode in which the powder addition step is carried out by drying the aforementioned solid matter with a gas obtained by removing part of the flue gas, transporting the pneumatically dried solid material and spraying it into the flue gas. In accordance with the present invention, a second process for the treatment of flue gas is also provided, for the treatment of a flue gas containing at least SO2 and SO3, which includes a heat recovery stage, to recover the heat of the flue gas by means of a heat exchanger and thus cooling this flue gas, and a subsequent absorption step to carry the flue gas in a subsequent absorption step to bring the flue gas into a gas contact -liquid with an absorption fluid containing a calcium compound, in an absorption tower, in order to remove at least the SO2 present in the flue gas by absorption in the absorption fluid and, likewise, form the gypsum as a by-product , in which a powder addition stage, for spraying the dust that can be collected in the absorption stage, inside the flue gas, is provided before the heat recovery stage, no treatment is carried out 1 1 for the removal of dust from the flue gas, before the recovery stage and the absorption stage, so that most of the dust present in the flue gas,. together with the other powder, it can be collected in the absorption fluid, and the above process also includes the separation step, to separate the solid particles in addition to the gypsum particles, which comprises at least the dust collected in the filler. absorption, from the plaster. The second humer gas treatment process of the present invention involves the following preferred embodiments. An embodiment in which the separation step 'comprises separating the aforementioned solid particles from the gypsum particles, producing air bubbles in the absorbent fluid, in order to allow the aforementioned solid particles to have a hydrophobic surface which is Adhere to the air bubbles and thus rise, while allowing the gypsum particles to have a hydrophilic surface, to settle in the absorbent fluid; An embodiment in which the aforementioned process also includes a dust removal step, to collect this dust or the powder remaining in the flue gas, which has passed through the absorption stage, by means of a precipitator dry electrostatic or a wet precipitator (wet electrostatic precipitator); An embodiment in which a previous stage of loading, to add and thicken the powder present in the flue gas, is provided subsequent to the heat recovery stage and before the absorption stage, and the previous loading stage it is carried out by introducing the flue gas into a pre-charger, which has a discharge electrode and a dust collection electrode, which impart an electrical charge to the powder present in the flue gas, as a result of an electric discharge of the electrode of waste, allowing the charged powder to migrate to the dust collector electrode, which has an opposite sign based on the Coulomb force, and holds it in the powder collecting electrode, for a predetermined period of time; and a modality in which a thick dust removal stage, to separate some of the powder from the flue gas, which has passed through the heat recovery stage and into the absorption fluid used in the absorption stage, is provided prior to the previous loading stage. According to the present invention there is also provided a system for the treatment of flue gas, for the treatment of a flue gas containing at least SO2 and SO3, which includes a heat exchanger! to recover the heat from the flue gas and thus cool this flue gas, and an absorption tower, arranged downstream of the heat exchanger, to bring the flue gas into gas-liquid contact with an absorbent fluid, so removing at least the SO2 present in the flue gas, by absorption in the absorbent fluid, in which the powder addition element, for sprinkling a powder in the flue gas, is provided upstream of the heat exchanger. The humer gas treatment system of the present invention involves the following preferred embodiments: An embodiment in which the aforementioned powder addition element consists of nozzles for spraying the powder in the chiffon gauze in the form of an aqueous paste, comprising the powder suspended in a liquid, and the system, mentioned above, also includes a supply element for the absorbent fluid, to remove part of the gas from the humer that has undergone gas-liquid contact, with this gas of smoke in the absorption tower and its supply to the nozzles as the aqueous paste, so that the solid matter present in the absorbent fluid can be used as the powder; and A mode in which the aforementioned powder addition element consists of nozzles for sprinkling the powder in dry form within the flue gas, with the aid of a gas stream, and the aforementioned system also includes a solid-liquid separation element, to separate the solid matter from the flue gas, which has undergone gas-liquid contact with the flue gas, in the absorption tower, a drying element, to dry at least part of the solid matter separated by this solid-liquid separation element, and a pneumatic conveying element, to transport the solid matter dried by the drying element, pneumatically to the nozzles as the powder, so that the solid matter present in the absorbent fluid It can be used as the powder.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view illustrating the construction of a flue gas treatment system, according to the first embodiment of the present invention; Figure 2 is a schematic view, illustrating the construction of a flue gas treatment system, according to the second embodiment of the present invention; Figure 3 is a schematic view illustrating the construction of a flue gas treatment system, according to the third embodiment of the present invention; Figure 4 is a graph showing the data which sets out the principle of the present invention; Figure 5 is a graph showing other data that sets forth the principle of the present invention; Figure 6 is a schematic view illustrating the construction of a flue gas treatment system, according to a fourth embodiment of the present invention; Figure 7 is a schematic view, illustrating I the construction of a flue gas treatment system, according to a fifth embodiment of the present invention; Figure 8 is a schematic view, illustrating the construction of a flue gas treatment system, according to a sixth embodiment of the present invention; Figure 9 is a schematic view, illustrating the construction of a flue gas treatment system, according to a seventh embodiment of the present invention; Figure 10 is a schematic view illustrating the construction of a flue gas treatment system, according to an eighth embodiment of the present invention; Figure 11 is a schematic view, illustrating the construction of a carbon separator, to carry out the separation step of the present invention; Figure 12 is a schematic view, illustrating the construction of a flue gas treatment system, according to a ninth embodiment of the present invention; Figure 13 is a graph showing the data, which exposes the effects of the present invention; Y Figure 14 is a schematic view, illustrating the construction of an example of a conventional flue gas treatment system.

The reference characters provided in these figures are defined as follows: 1, air heater; 2. input conduit; 3. dry electrostatic precipitator; Four. heat recovery section of the gas-gas heater (heat exchanger); 5. reheating section of the gas-gas heater; 10, desulfurization apparatus; 12 and 13, absorption towers; 23, solid-liquid separator (solid-liquid separation element); 30, carbon separator; 1 40, powder addition element; 40b, nozzle; 41, diversion hopper; 42. screw feeder; 43, disintegrator (dryer element); 44. evaporative dryer cylinder; 45. fan (pneumatic conveying element), 50, thick material separator; 51. fan (pneumatic conveyor element); 60, previous loader; 61, dryer (drying element); 52, roll crusher; 63, fan (pneumatic conveyor element); 71, nozzle (powder addition element), -72. pump (absorbent fluid supply element); A, untreated flue gas; A2, gas; B, Bl and B2, powder; C, treated flue gas; Cl, gas; D, absorbent aqueous paste, (absorbent fluid that has suffered a contact with the flue gas); E, solid matter; The, solid matter (powder); G powdered limestone (powder); H coal ashes (dust); I, air and S, aqueous plaster paste.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Various embodiments of the present invention are described below with reference to the accompanying drawings. The same elements, as included in the conventional system of Figure 14, are designated by the same reference numbers and their explanation is omitted.

First Modality The first embodiment of the present invention is explained with reference to Figure 1. This embodiment differs from the conventional humer gas treatment system of Figure 14 in that the injection step of ammonia is omitted., a powder addition element (not shown) for spraying a powder in the flue gas, is installed in a position upstream of the heat recovery section 4 of the GGH, and a step for sprinkling a powder [eg, the powder contained in the combustion exhaust gas of the coal (ie the so-called coal dust H)] in the flue gas A, using the aforementioned powder addition element, is provided before the recovery stage of heat, using section 4 of heat recovery, mentioned above. As the coal ashes H, mentioned above, it is possible to use, for example, the coal ashes, collected by the electrostatic precipitator, included in the system for the treatment of the flue gas of an exclusive power plant, which burn coal. Such coal dust is usually disposed as an industrial waste and, therefore, can be obtained cheaply, substantially at a single expense of transport costs. As the aforementioned powder addition element, any suitable element, for example, designated for pneumatic transport or transport of aqueous paste, can be used. An example of the powder addition element that can be used, designated for pneumatic transport, is one consisting of a blower or air compressor and a line of pipe to transport the powder in an air stream, and a fixed nozzle for Disperse and inject the pneumatically transported powder into the flue gas conduit. An example of a powder addition element, which can be used, designed for the transport of the slurry is one consisting of a stirred tank I, to disperse the powder in a liquid to form an aqueous slurry, a pump of the aqueous paste for pressurizing and transporting the aqueous paste formed in the stirred tank, and a fixed nozzle for dispersing and injecting the pressurized aqueous paste and transported within the flue gas conduit. When the powder is sprayed in the form of an aqueous paste, it is preferable that the liquid constituting the aqueous paste be evaporated immediately by the heat of the flue gas, so that it efficiently achieves the effect of capturing SO3 on the surfaces of the dust particles. The common water (for example industrial water) is suitable for use as this liquid. Since the temperature of the flue gas A is as high as 160 ° C, the water in the sprayed aqueous paste will evaporate immediately. The solids content of the aqueous leg can be of the same order as the solids content of the absorbent aqueous paste in the desulfurization apparatus 10 (for example, from about 20 to 30% by weight). The test calculations made by the present inventors indicate that, even where the powder is sprayed in the form of an aqueous paste, its amount may be relatively insufficient to the flue gas, as will be described later. Therefore, the temperature of the flue gas will be reduced only several degrees centigrade and thus will not exert an adverse influence on the subsequent heat recovery in the (GGH). That is, even when the ashes H of coal, used as the powder, is sprayed in the form of an aqueous paste, it can be added in a low proportion, so that the. I weight ratio (D / S) of the amount of powder (D) present in a unit volume of the flue gas to the amount of SO3 (S) present in a unit volume of the flue gas is, for example, not less than 2 (ie, D / S _> 2). For example, when the concentration of SO3 is 50 mg / m3 / N, the carbon powder H should be used in such an amount that the amount of total powder in the flue gas is not less than 100 mg / m3H. [ In this way, the function described above of the powder is positively and satisfactorily produced, so that a preventive measure against SO3 present in the flue gas can be achieved with low cost and with a simple operation or construction of equipment, without resorting to the injection of ammonia. More specifically, even if the SO3 present in the flue gas condenses, for example, as a result of cooling in the heat recovery section 4 of the GGH, most of this condensation occurs on the surfaces of dust particles (comprising the aforementioned carbon ash, and others) present in the flue gas. Consequently, the H2SO4 particles formed by the condensation of SO3 exist in a state bound to the aforementioned particles of the powder, which results in little production of noxious fumes (or mists of sulfuric acid). Also, since the aggregate coal ash has a relatively large particle diameter, of the order of 10 μm, most of them can be collected in the absorption towers, 12 and 13, of the desulfurization apparatus 10 with a relatively high degree of collection, in: comparison not only with the sulfuric acid mist, conventionally found, but also with the conventionally found ammonium sulfate powder. Therefore, the coal ashes remain poorly in the resulting treated C-flue gas. The coal ash collected in the absorption towers, 12 and 13, is dissolved or suspended in the circulating aqueous paste, and is finally contained in the gypsum E, j formed as a by-product. However, its content is as low as a percentage that it does not cause problems in most cases. On the other hand, the sulfuric acid, which has been formed by the condensation of SO3, on the surfaces of the coal ash and the like, and has been collected together with these ashes "of caron and the like, finally suffer the neutralization reaction (3), previously described, with the limestone, for example, in tank 11 of the absorption towers, to supply a part of the gypsum formed as a by-product, thus, in accordance with this mode, the formation of inlays and inlays. corrosion, due to SO3, are reliably prevented, in section 4 heat recovery of GGH, and the conduits placed downstream of the same.They also produce the following favorable effects: (1) The consumption of ammonia is reduced to zero, which results in a marked saving in the cost of operation. (2) The ammonia injection equipment becomes unnecessary and the conduit does not need to be lengthened especially in order to allow the ammonia to diffuse, so that a corresponding reduction in the cost of the equipment and the size of the equipment can be achieved (3) Since no nitrogen component is contained in desulphurisation wastewater, the need for an embarrassing treatment for nitrogen removal is eliminated before disposing of desulphurisation wastewater F2. From this point of view, a reduction in the cost of the equipment and the size of the equipment can also be achieved. (4) The amount of ammonia contained in the treated flue gas discharged into the atmosphere is reduced to zero. This not only contributes greatly to a further purification of the flue gas, but also makes it easy to comply with the ammonia emission regulations in the future. (5) Gypsum formed as a by-product does not contain ammonia. Consequently, the plaster does not need to be washed in order to remove an unpleasant and similar odor. (6) Since no sulfuric acid mist comprising ammonium sulfate dust and powder remains in the treated flue gas, in contrast to prior art I, the overall dust separation performance of the system is improved without resorting to elements, such as a wet dust collector, installed on the downstream side of the absorption tower. This also contributes to a further purification of the flue gas. (7) When the coal ashes H, used as the aforementioned powder, is sprayed in the form of an aqueous paste, the apparatus and device conventionally used in the desulfurization system or the like, such as a stirred tank for the preparation of a Aqueous paste, slurry pumps and nozzles for spraying the slurry, can be used without any modification. This is advantageous from the point of view of the cost of the equipment and the operability of the system. In addition, this makes it easier to disperse the powder uniformly in the flue gas, as compared to pneumatic transport, so that problems due to SO3 can be prevented more efficiently. Also, in this case, the coal dust particles H are maintained at a lower temperature, due to the cooling effect caused by the evaporation of the liquid from the slurry in the flue gas (or the maintenance of the cooling effect, caused by the presence of the liquid in the aqueous paste). Consequently, the condemnation of SO3 on the particle surfaces of the coal dust H is promoted, so that the SO3 capture function of the coal dust H, used as the aforementioned powder, is more satisfactorily performed. (8) Likewise, in this embodiment, the arrangement and construction of the dry electrostatic precipitator 3 and other apparatuses and the construction of the desulphurization apparatus 10, can be exactly the same as in the conventional system illustrated in Figure 14, except for the element of addition of coal ash H. Consequently, this embodiment has a unique effect in that the existing flue gas treatment system can be adapted very easily for the application of the present invention.

Figure 4 shows the data actually measured, which demonstrate the principle of the present invention (in particular, the addition of coal ash). These data indicate the relationship between the concentration of the SO3 gas at the GGH inlet (or the heat recovery section inlet) and the concentration of SO3 mist at the GGH outlet (or the outlet of the GGH). the reheat section) (ie, the degree of SO3 removal), when the concentration of the coal ash in the flue gas is used as a parameter. In Figure 4, the solid data points show the actually measured data, with which the deposition of the sulfuric acid mist on the internal surfaces of the apparatus, such as the heat recovery section 4t, was observed with the naked eye , as long as the open data points show the actually measured data, with which the deposit of the sulfuric acid mist is not observed. It can be seen from these data that about 90% of the SO3 was removed, even at a D / S value of about I 1.5, no deposit of the SO3 mist over the surfaces of the equipment was observed and the amount The SO3 mist remained in the effluent flue gas was as small as 10%. Accordingly, it is obvious that, in accordance with the present invention, in which coal ash is added to the flue gas, for example, in such proportion that D / S is not less than about 2, the SO3 mist will be removed almost completely and will remain sparingly in the treated flue gas, and the formation of corrosion and fouling due to mist deposition can be prevented, with high reliability. Since the effect that removes the mist, described above, from coal ash is a physical phenomenon, in which SO3 is allowed to condense on the surfaces of the particles present in the flue gas, other powders, besides the ashes of coal (for example, powdered limestone) will produce similar effects.

Second Modality Next, the second embodiment of the present invention is explained with reference to Figure 2. Basically, this embodiment is similar to the first embodiment in which coal ash is used as the powder of the present invention and sprayed on an upstream position of the heat recovery section 4 of the GGH. However, this embodiment is characterized in that a dry electrostatic precipitator is installed on the downstream side of the heat recovery section 4 and a dust collection stage for collecting the dust present in the flue gas by means of this electrostatic precipitator. 3, is supplied subsequent to the heat recovery step, using the aforementioned heat recovery section 4, and prior to the absorption step, using the desulfurization apparatus 10. Likewise, in this embodiment, the Coal ashes can be sprayed into the flue gas for pneumatic transport, or they can be sprayed in the form of an aqueous paste. Also, this embodiment is constructed in such a way that at least part of the dust collected in the powder collection stage, using the electrostatic precipitator 3, is reused as the powder of the present invention, which is sprayed in one position. upstream of the heat recovery section 4 '. Specifically, in this case, the part Bl of the powder collected in the electrostatic precipitator 3 is first fed to the silo 30 of the powder, where fresh coal ashes are added. Then, this powder is recycled by the use of the previously described powder addition element to spray it again in a current position, above the heat recovery section 4. In this mode, therefore, the powder sprayed in one position! upstream of the heat recovery section 4 contains, in addition to the coal ash H, supplied externally, the powder (for example, the fly ash) originally present in the untreated flue gas A, which leaves the heater 1 air. Also, in this embodiment, the remainder B2 of the powder collected in the dry electrostatic precipitator 3 is homogeneously mixed with the gypsum E, formed in the desulfurization apparatus 10, as a by-product and discharged out of the system. In this embodiment, it is preferred that the total amount of the spray powder is the minimum amount required (eg, such an amount as to cause the D / S ratio, defined above, to have a value of approximately 2). Likewise, it is also preferred that the amount of the recycled powder Bl be increased to its limit, in which the sprayed powder has the capacity to capture the SO3, and the quantities of fresh coal ash H and the powder B2 discharged are decreased to its minimum levels required. Thus, the amount of the powder B2 mixed with the plaster E will be reduced to a minimum to maintain the purity of the plaster E at a high level, and the amount of added fresh coal ash can be decreased to facilitate the handling of the coal ash H Also in this embodiment, the function, previously described, of the powder is positively and satisfactorily performed in the same manner as in the first embodiment, so that a preventive measure against the SO3 present in the flue gas can be achieved, at a Low cost and with simple operation and equipment construction without resorting to ammonia injection. Likewise, the construction of this mode represents the high-performance system, previously described, in which the heat recovery section 4 is disposed upstream of the electrostatic precipitator 3, so that the unitary capacity of the electrostatic precipitator 3 is improved. Consequently, using the small size electrostatic precipitator 3, the added carbon ash H can be removed from the flue gas with a high degree of collection. In addition, the powder originally contained in the untreated flue gas A is also collected almost completely in this electrostatic precipitator 3 and the absorption towers 12 and 13 of the desulfurization apparatus 10, and remains poorly in the resulting treated flue gas C .

Therefore, also in this embodiment, the formation of scale and corrosion, due to SO3, are also reliably impeded, for example, in the section; 4 heat recovery of the GGH, and the conduits placed downstream thereof and in the hopper of the electrostatic precipitator 3. Likewise, the same effects as those (1) to (7), previously described, in relation to the first mode , are produced. Furthermore, in this embodiment, the powder (comprising the coal ash H and others) used to capture the SO3 is recycled. This has a unique effect in that the amount of fresh coal ash H supplied can be decreased and also the amount of the powder B2 mixed with the gypsum E can be minimized to maintain the purity of the gypsum E at a high level. , In addition, since powder B2 is mixed with gypsum E, the amount of dust discharged as industrial waste can be reduced to zero. This also contributes, for example, to savings in the cost of operation. It goes without saying that, if the plaster, which has a higher purity is desired, all or part of the powder B2 will not be mixed with the plaster E.

Third Mode The third embodiment of the present invention is explained with reference to Figure 3. This embodiment is similar to the first embodiment in which an addition element, of powder for spraying a powder, is installed in a position upstream of the section 4 of heat recovery of the GGH and, using this powder addition element, a powder prepared by spraying the limestone (CaC? 3) (for example the limestone G, mentioned above), is sprayed into the flue gas A, as the powder of the present invention. Likewise, in this embodiment, the pulverized limestone can be sprayed into the flue gas by pneumatic conveying, or it can be sprayed in the form of an aqueous paste. Also, in this embodiment, the aqueous paste preparation tank 26 and the aqueous paste pump 27, shown in Figure 14, are omitted and the filtrate Fl is returned directly to the tank 11 of the absorption towers. The total amount of limestone required for use as the absorbent in the absorption stage in the desulfurization apparatus 10 and in the formation of the gypsum, as a by-product, is added to the flue gas as the powder, mentioned above, in a upstream position of the heat recovery section 4, so that the absorbent is indirectly supplied to the aqueous slurry within the tank 11 of the desulfurizing apparatus 10. In this case, the amount of the limestone G required for use as the Absorbent is basically in stoichiometric ratio to the amount of sulfur oxides present in the flue gas. When a flue gas A comprises the common combustion exhaust gas (for example the flue gas produced from a fuel oil oil, such as a heavy oil), the test calculations made by the present inventors have revealed that the ratio by weight (D / S) of the amount of the powder (D) present in the unit volume of the flue gas to the amount of the SO3 (S) present in the unit volume of the flue gas, is equal to approximately 28. Therefore, both, in this mode, the function, previously described, of the powder is positively and satisfactorily performed, so that a preliminary measurement against the SO3 present in the flue gas can be achieved with low cost and with a simple operation and construction of the equipment without resorting to ammonia injection. More specifically, even if the SO3 present in the flue gas is condensed, for example as a result of cooling in the heat recovery section 4 of the GGH, most of this condensation occurs on the particle surfaces of the powder (comprising the limestone, mentioned above, and others) present in the flue gas. Consequently, the particles of H2SO4 formed by the condensation of SO3 exist in a state bound to the aforementioned particles of the powder, resulting in little production of harmful fumes (or sulfuric acid mist). Likewise, the aggregate limestone has a larger particle diameter, of the order of 100 μm and, therefore, can be collected in the absorption towers 12 and 13 of the desulfurization apparatus 10, with a markedly higher degree of collection, in Comparison not only with the sulfuric acid mist, conventionally found, but also with the ammonium sulfate powder, conventionally found. Consequently, the limestone scarcely remains in the resulting treated flue C gas. The limestone collected in the absorption towers, 12 and 13, is dissolved or suspended in the circulating aqueous paste, and acts as the aforementioned absorbent (or alkaline agent) to neutralize the aqueous slurry to form the gypsum as a by-product. On the other hand, the sulfuric acid that has been formed by the condensation of SO3 on the surfaces of the limestone and the like, and has been collected together with the limestone and the like, is finally subjected to the neutralization reaction (3), previously described, with the limestone, for example, in tank 11 of the absorption towers, to supply a part of the gypsum formed as a by-product. Therefore, also in this embodiment, scale formation and corrosion due to SO3 are reliably prevented, for example, in section 4 heat recovery of the GGH and the conduits placed downstream. In addition, the same effects, as effects (1) to (7), previously described in relation to the first modality, occur. Likewise, in this embodiment, the total amount of the limestone required for use in the absorption step in the desulfurization apparatus 10, is supplied as the aforementioned powder, and the aqueous paste preparation tank 26, used conventionally, and pump 27 are omitted. Thus, this modality has a unique effect in that a further reduction in the cost of the equipment and the size of the equipment can be achieved. Figure 5 shows the data actually measured, which demonstrate the principle of the present invention (in particular, the addition of limestone). These data indicate the relationship between the amount of limestone aggregate and the proportion of SO3 gas removed by condensation on the limestone particle surfaces, when an aqueous slurry composed of limestone powder and water (with a concentration about 20-30% by weight) is simply sprayed into the flue gas containing about 3.7 to 11.5 ppm SO3 and no subsequent heat recovery is made from the flue gas. These data reveal that SO3 can be effectively removed by simply spraying an aqueous slurry of limestone into the flue gas. Consequently, it can be seen that, according to the present invention, in which heat recovery is carried out after the addition of a powder, in order to allow the SO3 to condense positively, a high degree of SO3 removal can be achieved. even at a low value of D / S.

FOURTH MODE Next, a fourth embodiment of the present invention will be explained with reference to FIGURE 6. It will be understood that the detailed illustration of the construction of the desulfurization apparatus 10 is omitted in FIGS. 6 to 8. Also in this embodiment, a The powder addition element 40, for spraying a powder, is installed in a position upstream of the heat recovery section 4 of the GGH. However, the part Rl of the solid matter E, consisting essentially of the gypsum formed as a by-product in the desulfurization apparatus 10, is pneumatically transported to the aforementioned powder addition element 40, while drying with an Al gas, obtained by removing part of the flue gas A and the resulting gypsum, in dry form, is sprayed into the flue gas A as the powder of the present invention. More specifically, the solid matter E dehydrated and separated in the solid-liquid separator 23 is divided by a partition hopper 41 in the part El required for the adjustment of the mentioned weight ratio (D / S) in the flue gas A and the rest E2. This residue E2 of solid matter E is handled in the manner conventionally known for the gypsum formed as a by-product. On the other hand, the divided part of the solid matter E is introduced into a disintegrator 43 at a predetermined flow rate, for example, by means of a screw feeder 42, it disintegrates, it is dried in a drying cylinder by evaporation. , and then supplied to the powder addition element 40. The disintegrator 43, mentioned above, is a rotary disintegrator. A rotary disintegrator is a type of impact disintegrator, in which a muddy material is dispersed in a gas by means of impact rods coaxially attached to a rotating disk, like the blades of a blower, and discharged and transported in a suspended state . When a hot gas and a wet material are treated there, they are sprayed and dried there! weather. I An Al gas, obtained by removing part of the gas from the flue A by means of a drying fan 45, is introduced into the aforementioned disintegrator 43. Next, this gas, together with the disintegrated solid matter, is supplied to the powder addition element 40, by means of a drying cylinder 44 by evaporation. In this case, the gas Al comprises a hot gas, obtained by removing part of the flue gas A in a downstream position from a fan 46 of flue gas (not shown in Figure 1, and the like) which is usually installed in the side downstream of the electrostatic precipitator 3. The powder addition element 40 comprises a nozzle 40b, through which the gas Al which has passed through the evaporative drying cylinder 44 and the solid matter powder therein is injected into the conduit 40a for the gas of humero A under the pressure exerted by the dryer fan 45. In this embodiment, the nozzle 40b comprises a small diameter tube connected to the wall of the duct 40a, in order to open its internal space, as shown in Figure 6. Without However, it will be understood that the present invention is not limited to this embodiment. In this embodiment, the El part of the solid matter E, consisting essentially of the gypsum formed as a by-product in the desulfurization apparatus 10, is diverted and introduced into the disintegrator 43, where the solid matter El disintegrates into a powder and dries by heat exchange with the introduced gas Al. Powdered solid matter The, which has been dried in the disintegrator 43 to some extent, is more completely by the heat exchanger with the Al gas, while being transported pneumatically through a evaporative drying cylinder 44. Next, the dry solid matter El, together with the Al gas, is sprayed into the flue gas A by the powder addition element 40 in a downstream position of the heat recovery section 4 . The solid matter powder El and the gas Al, which are sprayed into the flue gas A in this manner, has a temperature of about 100 ° C, which is less than the temperature of the flue gas A (ie about 160 ° C). Likewise, in this mode, therefore, the function, previously described, of the powder is performed positively and satisfactorily, so that a preventive measure against the SO3 present in the flue gas can be achieved with low cost and with a simple operation and construction of equipment, without resorting to the injection of ammonia. More specifically, even if the SO3 present in the flue gas condenses, for example, as a result of cooling in the heat recovery section 4 of GGH, the majority of this condensation occurs at the particle surfaces of the powder (comprising the solid matter, aforementioned, and others) present in the flue gas. Consequently, the H2SO4 particles formed by the condensation of SO3 exist in a state bound to the aforementioned particles of the powder, resulting in little production of harmful fumes (or sulfuric acid mist). Also, the gypsum particles, which form the main constituent of the aggregate solid matter El, have a particle diameter greater in the order of 20 to 40 μm and, therefore, can be collected in the desulfurization apparatus 10, with a high degree of collection, compared not only with the sulfuric acid mist, conventionally found, but also with the ammonium sulfate powder, conventionally found. Accordingly, the gypsum particles remain poorly in the resulting treated humer gas C. The solid matter The collected in the desulfurizing apparatus 10 is dissolved or suspended in the circulating aqueous pulp, and returns as solid matter present in the aqueous pulp. . On the other hand, the sulfuric acid that has been formed by the condensation of SO3 on the surfaces of the solid matter El and the like, and have been collected together with these particles subjected to the neutralization reaction, previously described with the limestone in the apparatus of desulfurization 10 to supply part of the gypsum formed as a by-product. Therefore, also in this mode, scale formation and corrosion due to SO3 are reliably prevented, for example, in section 4 of! heat recovery of the GGH and the ducts placed downstream. Likewise, the same effects are produced as the effects (1) to (6), previously described in relation to the first modality. Also, in this embodiment, the solid matter The present in the aqueous slurry within the desulfurization apparatus 10 is supplied as the aforementioned powder, so the costs of the raw material and the trant for the powder are not required at all. Thus, this modality has the unique effect that a further reduction in cost can be achieved in comparison, for example, with the first mode in which coal ash is supplied as dust. According to the construction of the equipment of this embodiment, the D / S ratio in the flue gas can be adjusted to a value of about 10, for example, using the following operating conditions. As can be seen from the actually measured data, which have been previously shown, it has been confirmed that problems due to SO3 fog can be prevented at a D / S value of about 10.

Flow regime of flue gas A: 110 x 104m3N / h Concentration of SO3 in flue gas A: 20 ppm Temperature of gas Al (at the inlet of disintegrator 43): 154 ° C Gas temperature Al (at the outlet of cylinder 44 for evaporative drying): 100 ° C Gas flow rate Al: 4,300 m3N / h Flow regime of solid matter based on deviated gypsum, El: 880 kg / h Fifth Mode Next, a fifth embodiment of the present invention will be explained, with reference to Figure 7. Similarly to the fourth embodiment, this embodiment is such that the powder addition element 40, for spraying a powder, is installed in a upstream position of the heat recovery section 4 of the GGH. However, the El part of the solid material e, which consists essentially of the gypsum formed as a by-product in the desulfurization apparatus 10, is pneumatically conveyed to the aforementioned powder addition element 40, while drying with part of the flue gas treated C and the resulting gypsum, in dry form, is sprayed into the flue gas A as the powder of the present invention. More specifically, this embodiment is the same as the fourth embodiment, except that the gas Cl, obtained by removing part of the treated flue gas C, by means of a drying fan 51, is used as the drying gas introduced into the disintegrator 43. This embodiment is preferred where the concentration of SO3 in the flue gas A is low. Also in this mode, the function, previously described, of the powder is performed positively and satisfactorily, so that a previous measurement against the SO3 present in the flue gas, can be achieved at low cost and with a simple operation and construction of equipment , without resorting to! the injection of ammonia. Thus, the same effects are produced to those described above in relation to the fourth embodiment. According to the construction of the equipment of this embodiment, the D / S ratio in the flue gas can be adjusted to a value of approximately 4, for example, using the following operating conditions. As can be seen from the actually measured data, which have been previously shown, it has been confirmed that problems due to SO3 can be prevented at a D / S value of about 4.

Flow regime of flue gas A: 110 x 104m3N / h Concentration of SO3 in flue gas A: 20 ppm Temperature of gas Al (at the entrance of the disintegrator 43): 103 ° C Gas temperature Al (at the outlet of the 44 evaporative drying cylinder 44): 80 ° C Gas flow rate Al: 2,000 m N / h Flow regime of the solid matter based on the gypsum deviated, The: 175 kg / h Sixth Mode Next, a sixth embodiment of the present invention will be explained with reference to Figure 8. This embodiment is the same as the fourth embodiment, except that the rotary cylinder type dryer (i.e. the rotary dryer) 61 and the crushed roll 62, are used in place of the disintegrator 43 and the drying cylinder 44 by evaporation. In this case, the solid matter El, based on the gypsum, in wet form, is introduced into the dryer 61 at its upstream end, moves downstream with the rotation of the dryer 61 and is discharged in dry form. Then, this gypsum-based solid material Rl, in dry form, is introduced into the roll crusher 62 and crushed there. The crushed solid matter R1 is dispersed in a gas, conveyed to the powder addition element 40, and sprayed into the flue gas A as the powder of the present invention, while remaining in the dry form. On the other hand, an Al gas dryer, obtained by removing part of the flue gas A, is introduced in the rotary dryer 61 at its downstream end, it is put in contact with the solid matter The gypsum base, in order to dry it , and is discharged from the upstream end of the rotary dryer 61. In this case, the Al gas dryer, discharged from the rotary dryer 61, it is supplied to the exit side of the roll crusher 62 by means of a fan 63 and functions as a gas to pneumatically transport the solid matter to the gypsum base, in dry form, and is then added to the flue gas A together with solid matter Gypsum based. Thus, the Al gas dryer is finally returned to the Al flue gas. Likewise, in this mode, the previously described function of the powder is positively and satisfactorily performed, so that a preliminary measurement against the SO 3 present in the flue gas can be made. achieve at low cost and with a simple operation and construction of equipment, without recourse to ammonia injection. Thus, the same effects as those described above in relation to the fourth mode are produced. According to the construction of the equipment of this embodiment, the D / S ratio in the flue gas can be adjusted to a value of about 10, for example, using the following operating conditions.

Flow regime of flue gas A: 110 x 104m3N / h Concentration of SO3 in flue gas A: 20 ppm Temperature of gas Al (at the inlet of disintegrator 43): 155 ° C Gas temperature Al (at the outlet of cylinder 44 for evaporative drying): 120 ° C Gas flow rate Al: 6,700 m3N / h Flow regime of solid matter based on deviated gypsum, El: 875 kg / h Seventh Mode Next, a seventh embodiment of the present invention will be explained with reference to Figure 9. This embodiment is such that a nozzle 71 for spraying the powder in the form of an aqueous paste (i.e., the powder addition element) ) is installed in a position upstream of the heat recovery section 4 of the GGH, and an aqueous paste (or fluid to absorbent) DI, removed from the tank 11 of the absorption tower of the desulfurization apparatus 10 by means of a pump 72 (i.e. the absorption fluid supply element) is sprayed on the flue gas of flue A.

Also, in this embodiment, when the ratio D / S in the flue gas A is adjusted to a predetermined value by spraying the aqueous slurry DI in an amount corresponding to the concentration of the SO3 in the flue gas A, the function, previously described, the dust is performed positively and satisfactorily, so that a preliminary measure against the SO3 present in the flue gas can be achieved at low cost and with simple operation and construction of equipment, without recourse to ammonia injection. Thus, the same effects are produced as those described above in relation to the fourth embodiment. More specifically, since the water, which constitutes the aforementioned aqueous slurry DI, is immediately evaporated by the heat of the flue gas A, the aforementioned aqueous slurry, DI, can perform the same function as in the case where the Solid matter, based on gypsum, which constitutes the aqueous paste DI, is sprayed into the flue gas A in dry form (ie, the function of capturing SO3). Also, when the aforementioned aqueous slurry is sprayed into the flue gas, the particles of the solid matter (i.e., the powder particles of the present invention) are maintained at a lower temperature, due to the cooling effect produced by the evaporation of the liquid from the aqueous slurry in the flue gas (or the maintenance of the cooling effect produced by the presence of the liquid in the slurry), as previously described. Consequently, the condensation of SO3 on the surfaces of these particles is promoted, so the capture function of SO3 is more satisfactorily performed. Also, this embodiment is constructed in such a way that part of the absorption fluid DI within the desulfurization apparatus is removed and sprayed directly into the flue gas in a position upstream of the GGH and thus has a unique effect in that the construction of the equipment It is highly simplified and, therefore, the big advantage is gained from the cost point of view. More specifically, an embodiment in which, for example, the coal ash is sprayed in the form of an aqueous paste and an additional apparatus, such as a tank, is required for the preparation of an aqueous paste and a storage element for the coal ash, and an embodiment in which gypsum-based solid matter is dried and sprayed into the flue gas (e.g., the fourth embodiment, described above) requires an additional apparatus, such as a dryer, to dry the solid matter based on plaster. However, this equipment does not require such an apparatus at all. It will be understood that the present invention is not limited to the first to seventh embodiments described above, but can also be practiced in various other ways. For example, the powder of the present invention is not limited to limestone, coal ash and gypsum, but any powder that allows SO3 to condense on its particle surfaces and can be collected in an electrostatic precipitator can also be used. common or the absorption tower of a desulfurization device. Nevertheless, the limestone, coal ash and gypsum, mentioned above, are familiar materials, which have been conventionally managed in the humer gas treatment systems, and the existing equipment and handling techniques can be used without any modification. Thus, they have the advantages that can be obtained and easily handled, and that do not exert an adverse influence on the operation of the whole system and, on the contrary, the problem of supplying the limestone to the absorption tower tank can be omit, as previously described. Also, in order to promote the condensation of SO3 on the particle surfaces of the powder, a powder (or its aqueous paste) having a temperature lower than that of the flue gas (for example, a powder (or an aqueous it can be sprayed into the flue gas, which has been forcedly cooled, as required). This allows the SO3 to condense more effectively on the particle surfaces of the powder, so that the production of the detrimental SO3 mist can be prevented more satisfactorily and more easily.

Also, the powder of the present invention may comprise, for example, both limestone and coal ash, and they may be added in admixture or separately. Even though limestone alone is used, it can be added in such a way that only part of it required to capture the SO3 is sprayed into the flue gas and the rest is supplied directly to the absorption tower tank of the desulfurization apparatus , as usual. Also, it goes without saying that, although the rotary cylinder type dryer, described in relation to the sixth embodiment (Figure 8) is used for drying purposes in a manner in which the solid matter, consisting essentially of gypsum, formed as a by-product in the desulfurization apparatus (or the absorption step) is dried and sprayed into the flue gas as the powder of the present invention, the Cl part of the treated flue gas C can be used as the drying gas, as described above in relation to the fifth modality (Figure 7). Also, as the drying element for drying the solid matter, based on the gypsum, mentioned above, a dryer of the indirect heating type is used, in which the gypsum-based solid matter is dried, for example, by the heat of the steam supplied from the outside of the flue gas treatment system.

Also, it is not necessary to say that the absorption stage or the absorption tower of the present invention is not limited to the modalities previously described. For example, the absorption tower may comprise a single absorption tower and various types of absorption towers (or gas-liquid contact apparatus), which includes the packed tower, spray tower and the types of bubble towers, may be employed In addition, the present invention is not limited to the use of a calcium compound (eg limestone) as the absorbent, and the desulfurization process can use, for example, sodium hydroxide or magnesium hydroxide. Although the present invention produces particularly excellent effects when used for flue gases from boilers using various oil fuels, such as heavy oils, Orimulsion, VR and CWM / heavy oils, similar effects can also be obtained when applied, by example, to boilers that burn coal / heavy oils. Even in boilers that burn coal, a fuel oil can be burned, for example, at the time of starting or during test operations. The present invention can be effectively applied to such cases.

Eighth Mode An eighth embodiment of the present invention will be explained with reference to Figure 10. In Figure 10, the detailed illustration of the construction of the desulfurization apparatus 10 is omitted. This embodiment differs from the conventional treatment system of the flue gas of Figure 14, in which the ammonia injection step and the dust removal step, which uses the electrostatic precipitator 3, are omitted and in that the addition element of powder (not shown) for spraying a powder, installed in an upstream position of the heat recovery section-4 of the GGH and a step for spraying a powder, comprising the powdered limestone (CaC? 3), for example the limestone G, mentioned above) in the flue gas A by the use of the aforementioned powder addition element (i.e., a powder addition stage) is provided before the heat recovery step using the section 4 of heat recovery, mentioned above. Also, in this embodiment, a dust removal step to collect a small amount of powder or the powder Bl remaining in the flue gas, which has passed through the absorption stage in the desulfurization apparatus 10, by means of of a dry electrostatic precipitator 3a, is then provided with the reheat stage, which uses the reheat section 5, and a carbon separator 30 is installed to separate the powder (e.g., the unburned carbon) B2 and the highly pure gypsum E from the aqueous paste S of gypsum, formed in the desulfurization apparatus 10 and its discharge. The carbon separator 30 functions to carry out the separation step of the present invention, to separate solid particles in addition to the gypsum particles, which comprises the powder (mainly unburned carbon) collected in the absorbent aqueous paste D within of desulphurisation 10, so it will not be mixed with the gypsum formed as a by-product. In this embodiment, the carbon separator 30 is installed in place of the liquid solid separator 23 used in the conventional humer gas treatment system of Figure 14. More specifically, in this embodiment there is no dust removal prior to the stage. of absorption, most of the dust (for example the unburned carbon) originally contained in the flue gas, together with the added powder (in this case, the limestone), is collected in the aqueous paste within the absorption towers of the desulfurizing apparatus 10, so that the aqueous plaster paste S removed from the absorption tower tank contains a greater amount of foreign matter (ie particles of the mentioned powder) than in the prior art. Therefore, in order to obtain the highly pure plaster, it is necessary to separate the mentioned powder, which constitutes the foreign material. In this embodiment, this separation step is carried out very simply using a carbon separator 30 based on the flotation process. As shown in Figure 11, the aforementioned carbon separator 30 consists, for example, of a bubble tower 31, in which the aqueous paste S of gypsum is introduced, a circulation pump 32, to circulate the aqueous paste inside the bubble tower 31, an air injector 33, installed on the delivery side of the circulation pump 32, to blow the air I into the circulating aqueous paste, a withdrawal line 34, which is from the delivery side of the circulation pump 32, a flow control valve 35, installed in the withdrawal line 34, a sensor 36 for detecting the liquid level of the bubble tower 31, a level controller 37 to regulate the opening of the flow control valve 35 based on the sensing signal of the sensor 36 and thus maintain the liquid level of the bubble tower 31 within predetermined limits, a solid-liquid separator 38 to effect the separation of solid liquid from the aqueous paste withdrawn through the withdrawal line 34, a withdrawal line 39, to remove the aqueous paste from the top of the bubble tower 31, and a solid-liquid separator 40 to effect the separation of solid-liquid from the aqueous paste withdrawn through the withdrawal line 39. The upper part of the bubble tower 31 is equipped with an overflow channel 31a, and the level of the liquid controlled by the level controller 37 is adjusted in a slightly greater position than this overflow slot 31a. Thus, an aqueous paste containing the powder in high concentration, flows past this overflow channel 31a and is withdrawn through the withdrawal line 39. More specifically, the air I, injected by the injector 33, is introduced in the tower 31 of bubbles in the form of are bubbles, which rise to the surface of the aqueous paste within the bubble tower 31. During this process, the powder (for example the unburned carbon) present in the aqueous paste S of gypsum, the lime comprises solid particles which have a hydrophobic surface, adhere to the air bubbles, move upwards together with them, and it rises to the surface of the aqueous paste. On the other hand, gypsum particles that have a hydrophilic surface, do not adhere to air bubbles, but are oppositely settled by gravity and are cumulated at the bottom of the bubble tower. Consequently, the aqueous paste withdrawn through the withdrawal line 34 contains solid matter based on gypsum with a high concentration, while the aqueous paste withdrawn through the withdrawal line 39, contains the solid matter based on powder with a high concentration. In this regard, experiments carried out by the present inventors have revealed that a simple treatment can separate the powder with a degree of removal thereof not less than 90%. As an alternative method to produce air bubbles within the bubble tower 31, these air bubbles can be produced, for example, by stirring the aqueous paste inside the bubble tower 31, instead of injecting air into it. Now, the powder addition element for carrying out the powder addition step of the present invention will be explained. As this element of powder addition, any suitable element, for example, designed! for pneumatic transport or transport of aqueous paste, can be used. An example of a usable powder addition element, designed for pneumatic transport, is one consisting of a blower or air compressor and a line of pipe to transport the powder in an air stream, and a fixed nozzle to disperse and inject the pneumatically transported powder into the flue gas conduit. An example of a usable powder addition element, designed for the transport of the slurry, is one consisting of a stirred tank to disperse the powder in a liquid to form an aqueous slurry, an aqueous slurry pump, for pressurizing and transporting the slurry formed in the stirred tank, and a fixed nozzle for dispersing and injecting the pressurized slurry 5 and transported within the flue gas duct. When the powder is sprayed in the form of an aqueous paste, it is preferable that the liquid constituting the aqueous paste be evaporated immediately by the heat of the flue gas, in order to efficiently achieve the effect of capturing SO3 on the particle surfaces. of the dust. The common water (for example industrial water) is suitable for use as this liquid. Since the temperature of the flue gas A is as high as about 160 ° C, the water 5 in the sprayed aqueous paste will evaporate instantaneously. The solid content of the aqueous paste can be of the same order as the solid content of the aqueous paste I I I in the desulfurization apparatus 10 (for example, 20 to 30% by weight). The test calculations made by the present inventors indicate that, even when the powder is sprayed in the form of an aqueous paste, its amount may be Be relatively smaller in the flue gas, as I will describe later. Therefore, the temperature of the flue gas will be reduced by only several degrees centigrade and thus will not exert an adverse influence on the subsequent heat recovery in the GGH. That is, even though the limestone G used as the powder to provide a preventive measure against the SO3 is sprayed in the form of an aqueous paste, it can be added in such a low ratio that the weight ratio (D / S) of the amount of powder (D) present in a volume unit of the flue gas to the amount of SO3 (S) present in a volume unit of the flue gas is, for example, not less than 2 (ie, D / S) > 2). As will be described later, most of the limestone G added to the flue gas in this manner is collected in the absorption towers and functions as the absorbent in the desulphurization apparatus 10. Therefore, the total amount of the limestone required for use in the absorption stage in the desulfurization apparatus 10 and in the formation of the gypsum as a by-product, can be added to the flue gas as the aforementioned powder, in a position upstream of section 4 of heat recovery, so that the absorbent material will be indirectly supplied to the aqueous slurry within the tank 11 of the desulfurizing apparatus 10. This makes it possible to omit the. tank 26 for preparing the slurry and pump 27 for the slurry, shown in Figure 14, and thus achieving a further simplification of the construction of the equipment.

In this case, the filtrate Fl can be treated, for example, by returning it directly to the tank 11 of the absorption towers, or part thereof can be used as the liquid required to spray the limestone G in the form of an aqueous slurry. Also, in this case, the amount of limestone G required for use as the absorbent, is basically in a stoichiometric ratio to the quantity | of sulfur oxides present in the flue gas. When the flue gas A comprises the common combustion exhaust gas (for example, the flue gas produced from a fuel oil such as a heavy oil), the test calculations made by the present inventors have revealed that the weight ratio ( D / S) of the amount of powder (D) present in a unit volume of the flue gas to the amount of SO3 (S) present in a unit volume of the flue gas, has a sufficient value of approximately 28. According to the treatment of the flue gas of this mode, the function, previously described, of the powder, is performed positively and satisfactorily, so a preventive measure against the SO3 present in the flue gas can be achieved at low cost and with a simple operation and construction of equipment, without resorting to ammonia injection.

More specifically, even if the SO3 present in the flue gas is condensed, for example, as a result of cooling in the heat recovery section 4 of GGH, the majority of this condensation occurs on the particle surfaces of the powder present in the flue gas (that is, the dust that comprises the limestone aggregate there and the dust originally contained therein). Consequently, the H2SO4 particles formed by the condensation of SO3 exist in a state bound to the aforementioned particles of the powder, resulting in little production of harmful fumes (or sulfuric acid mist). Also, since the added limestone and the dust present in the flue gas have a relatively large particle diameter of the order of 10 to 100 μm, they can be collected in the absorption towers, 12 and 13, of the desulfurization apparatus 10, with a relatively high degree of collection, in comparison not only with the sulfuric acid mist, conventionally found, but also with the ammonium sulfate powder, conventionally found. In consecuense, they barely remain in the resulting treated C flue gas. Especially in this embodiment, a dust removal step to collect a slight amount of dust or the powder remaining in the flue gas that has passed through the absorption step in the desulfurization apparatus 10, such as solid matter Bl by means of the dry electrostatic precipitator 3a, so that the aggregate powder (i.e., the limestone in the case) and the powder (mainly unburned carbon) are barely contained in the treated C-flue gas. Thus, a very high degree of purification of the flue gas can be achieved from the point of view of dust removal capacity. The limestone collected in the towers ofI 0 absorption, 12 and 13, is dissolved or suspended in the circulating aqueous paste, and acts as the aforementioned absorbent (or alkaline agent) to neutralize the aqueous paste and form the gypsum as a by-product. On the other hand, the sulfuric acid that has been formed by the condensation of SO3 on the surfaces of the limestone and the like, and has been collected together with the limestone and the like, suffers finally the neutralization reaction (3) previously described. , with the limestone, for example, in tank 11 of the absorption towers, to supply a part of the gypsum formed as a by-product. I Thus, according to this embodiment, the formation of scale and corrosion, due to SO3, is reliably prevented in the heat recovery section 4 of the GGH and the conduits placed downstream of it.

Likewise, a variety of practically favorable effects are produced. That is, not only the same effects as those described previously (1) to (6) are produced, but also the following effects. (8) In this embodiment, when the limestone used as the powder is sprayed in the form of an aqueous paste, the apparatus and devices conventionally used in the desulfurization system or the like, such as a stirred tank for the preparation of an aqueous slurry, slurry pumps and nozzles for spraying the slurry can be used without any modification. This is advantageous from the point of view of the cost of the equipment and the operability of the system. In addition, this makes it easier to disperse the powder uniformly in the flue gas, as compared to pneumatic transport, so problems due to SO3 can be prevented more efficiently. Also, in this case, the particles of the limestone G are kept at lower temperatures due to the cooling effect produced by the evaporation of the liquid from the slurry in the flue gas (or the maintenance of the cooling effect produced by the presence of the liquid of the aqueous paste). Consequently, the condensation of SO3 on the particle surfaces of limestone G is promoted, so the function of capturing the SO3 of the limestone G used as the powder, is performed more satisfactorily. (9) Also, in this embodiment, the powder removal stage, which uses an electrostatic precipitator, disposed upstream of the absorption stage and the heat recovery stage are removed and the powder (for example uncharged coal) is removed. originally contained in the flue gas, together with the added powder, is collected in the absorption towers of the desulfurization apparatus 10. This can provide a marked reduction in cost compared to the conventional system in which an electrostatic precipitator 3 in size Large and expensive is installed independently on the upstream side of the desulfurization apparatus. When compared with the conventional system of Figure 14, the system of this embodiment includes an additional apparatus, such as an electrostatic precipitator 3a, installed on the downstream side of the desulfurization apparatus and the carbon separator 30. However, the Reduction mentioned in the cost can be achieved in this case. The reason for this is that the carbon separator 30 is an apparatus that has a simple construction, as previously described, and causes only a slight increase in the cost of the equipment and the cost of operation, compared to the costly 3 electrostatic precipitator. of large size, which has been required in the conventional system. Also, the electrostatic precipitator 3a installed on the upstream side of the desulfurization apparatus involves a significantly lower load, and may thus be of small size, compared to the aforementioned conventional electrostatic precipitator 3. Also, it will be understood that this electrostatic precipitator 3a is required especially when a high dust removal capacity is desired. (10) Likewise, this embodiment also has the advantage that, since the powder (for example the unburnt carbon), which constitutes the material outside the gypsum, is separated by the separation step carried out in the carbon separator 30 , described above, highly pure gypsum can be obtained despite the construction involving the positive removal of dust in the absorption towers of the desulfurization apparatus 10.

Ninth Mode Next, a ninth embodiment of the present invention will be explained with reference to Figure 12. It will be understood that the detailed illustration of the construction of the desulfurization apparatus 10 will be omitted in Figure 12. This embodiment is basically similar to the octave wherein the limestone is sprayed as the powder of the present invention in a position upstream of the heat recovery section 4 of the GGH. However, this embodiment is characterized in that, instead of the mentioned electrostatic precipitator 3a, a preparatory separator 50 and a pre-loader 60 are installed in order to achieve the highest dust removal capacity. The preparatory separator 50 may comprise, for example, a separator of solid particles, of the type of bent plate. It is installed on the downstream side of the heat recovery section 4 and used to carry out the primary dust removal step of the present invention, to remove some of the dust from the flue gas. More specifically, this preparatory separator 50 is equipped, for example, with a plurality of plates (not shown) bent in a zigzag configuration and arranged in the flow path of the flue gas. Thus, the solid particles, ie said powder) flow together with the gas constituting the flue gas and are hit against the surfaces of these bent plates and thus fall into a recovery hopper 51. The mentioned bent plates can be washed by supplying the washing water as required. The solid particles accumulated in the recovery hopper 51, together with the wash water, are transferred to the absorption tank 11 of the desulfurization apparatus 10 by gravity and introduced into the aqueous paste (or absorbent fluid) used in the absorption stage. . The pre-charger 60 is installed at the inlet of an absorption tower of the desulphurization apparatus 10 (in this case, at the top of the absorption tower 12 of parallel flow), and comprises a simple apparatus for carrying out the stage of prior loading of the present invention. More specifically, this apparatus has a discharge electrode and an electrode that collects dust (not shown), and collects the solid particles present in the flue gas (ie the mentioned powder) temporarily, imparting an electrical charge to the solid particles, as a result of corona discharge from the discharge electrode and allows the charged solid particles to migrate to the dust collection electrode, which has an opposite sign based on the Coulomb force. Next, an impact is periodically supplied to the dust collection electrode, by means of a hammer-type device (not shown), so that the solid particles collected are swept and separated in the absorption tower. The collected solid particles aggregate and swell while they are held in the powder collection electrode for a predetermined period of time. Although it is difficult to collect the relatively fine solid particles in the absorption towers of the desulfurization apparatus 10, this pre-filler 60 thickens such solid particles and enables them to be collected in the absorption towers, so the dust removal capacity of the apparatus of desulfurization 10 is improved. 5 According to the treatment of the flue gas of this mode, the following unique effect is produced, in addition i of the effects described above, in relation to the eighth modality. That is, the dust removal charge of the desulfurization apparatus 10 is decreased by the primary dust removal stage 0, which uses the primary separator. 50 and the dust removal capacity of the desulfurization apparatus 10 is improved by the pre-loading step using the pre-charger 60. Consequently, despite the construction using the non-expensive electrostatic precipitator, which has a common structure, the High removal capacity can be achieved in the entire treatment system. Also, in this embodiment, the dust separated from the flue gas comprises only the powder B2, discharged 0 from the carbon separator 30, and is, therefore, recovered in a simple position. Consequently, this modality has the advantage of facilitating the operation of dust recovery.

It will be understood that, similarly to the electrostatic precipitator i, used in the eighth embodiment, the aforementioned primary separator 50 and the pre-loader 60 can not be used, depending on the desired dust removal capacity (i.e. the treated flue gas C). Also, depending on the desired removal capacity, it is also possible, for example, to install the pre-loader 60 only while the primary spacer 60 is omitted. In any case, this primary spacer 50 and 0 the pre-loader 60 have a simple structure and they involve a low operating cost, in comparison with the large-sized dry electrostatic precipitator, which has been installed independently on the upstream side of a conventional desulfurization apparatus. 5 Consequently, this can provide a reduction in cost, while maintaining high dust removal capacity. Figures 4, 5 and 13 show the data actually measured, demonstrating the effects of the powder of the present invention. In the fractional notation of Figure 4, the denominator represents the D / S ratio and the numerator represents the concentration of the coal ash. It can be seen from the data in Figure 4 that approximately 90% of the SO3 was still stirred at a D / S value of about 1.5, without observing SO3 fog deposition on the equipment surfaces, and the amount of The SO3 fog remaining in the effluent flue gas was as small as 10%. Accordingly, it is obvious that, according to the present invention, in which a powder is added to the flue gas, for example, in such proportion that D / S is not less than about 1, SO3 mist will be removed. almost completely and will hardly remain in the treated flue gas or the corrosion or formation of scale, due to the deposition of the fog, can be impeded with high reliability. Since the effect of fog removal, described above, "of coal ash is a physical phenomenon in which SO3 is allowed to condense on the surfaces of" the particles present in the flue gas, Other powders besides charcoal ash (eg powdered limestone and solid gypsum based material) will produce similar effects. 0 Likewise, the data in Figure 5 reveal that the SO3 can be effectively removed in a simple way by spraying an aqueous slurry of limestone into the flue. Accordingly, it can be seen that, in accordance with the present invention, in which heat recovery is effected after the addition of a powder, in order to allow the SO3 to condense positively, a high degree of SO3 removal can be achieved. be achieved even at a low value of D / S. The data in Figure 13 shows the results of a real service test, in which the limestone was pneumatically transported and sprayed into the flue gas in a position upstream of the GGH (and downstream of the electrostatic precipitator) in the fume gas treatment system of the actual electric power plant. The test conditions employed are as follows. Boiler capacity: 220 MW Type of GGH: type Lj ungstrom Desulfurization tower absorption tower: parallel packed grid tower Electrostatic precipitation on the upstream side of the desulfurization device? : Yes Flow regime of flue gas: 1,100,000 m3N / h Concentration of SO3 in untreated flue gas: 15-20 ppm Concentration of dust at the inlet of desulfurization apparatus: 20-70 mg / m3N Quantity of limestone added: 200-2,000 mg / m3 / N.

As is evident from these test results, a degree of SO3 removal of not less than 90% can be achieved by adding limestone in the flue gas in a position upstream of the GGH, for example, in such proportion that D / S does not be less than about 10. In this test, the concentration of the powder in the treated flue gas (i.e., the flue gas at the outlet of the desulfurization apparatus) was measured at the same time. Although the concentration at the outlet of the desulfurization apparatus increases slightly as a result of the addition of the limestone it is not greater than about 30 mg / m3N. Thus, it can be seen that a sufficiently high dust removal capacity can be achieved by installing a dry electrostatic precipitator, small in size, or the like, on the downstream side of the desulfurization apparatus. It will be understood that the present invention is not limited to the eighth and ninth modes, described above, and j that it may also be practiced in various other ways. For example, the electrostatic precipitator installed on the downstream side of the desulfurization apparatus 10 can be replaced by a wet precipitator (wet electrostatic precipitator or electrostatic precipitator). However, since a wet precipitator cools the flue gas, it must be installed on the side upstream of the reheat section 5. Also, the powder of the present invention is not limited to limestone, since coal ash and gypsum can also be used. In addition, any powder that allows the SO3 to condense on its particle surfaces can also be used and can be collected in a common electrostatic precipitator or the absorption tower of a desulfurization apparatus. However, the limestone, coal ash and gypsum, mentioned above, are the familiar materials that have been conventionally handled in the flue gas treatment systems, and the existing equipment and handling techniques can be used without any modification. Thus, they have the advantages that can be easily obtained and managed, and that do not exert an adverse influence on the operation of the whole system and, on the contrary, the problem of supplying the limestone to the tank of the absorption tower can be omitted, as previously described. On the other hand, this embodiment has the disadvantage that, when the coal ash, for example, is added as the powder of the present invention, the powder (ie the material foreign to the gypsum) present in the flue gas, introduced in the the desulfurization apparatus increases correspondingly, resulting in a corresponding increase in the load imposed on the carbon separator 30. From this point of view, therefore, it is preferable to use the limestone or gypsum as the powder of the present invention. When gypsum is used, this can be done, for example, by spraying the gypsum E recovered from the desulfurization apparatus 10, while drying as required, and adding it to the flue gas by pneumatic transport, or removing part of the pulp. Aqueous gypsum S within the absorption tower tank of the desulfurization apparatus 10 and rolling it directly into the flue gas at a position upstream of the heat recovery section 4 of the GGH. Also, in order to promote the condensation of SO3 on the particle surfaces of the powder, a powder (or its aqueous paste) having a lower temperature than that of the flue gas (for example a powder (or its aqueous paste) which it has been forcedly cooled, as required) it can be sprayed into the flue gas. This allows the SO3 to condense more effectively on the particle surfaces of the powder, so the production of the SO3 mist can be prevented more satisfactorily and more easily. Also, the powder of the present invention may comprise, for example, both limestone and coal ash, and they may be added in admixture or separately. Even when limestone is used alone, it can be added in such a way that only part of it, required to capture the SO3, is sprayed into the flue gas and the rest is supplied directly to the absorption tower tank of the - desulfurization, as usual . Furthermore, it is not necessary to say that the construction of the absorption stage or absorption tower of the present invention is not limited to the modalities described above. For example, the absorption tower may comprise a single absorption tower and several types of tower I absorption (or gas-liquid contact devices) that include the packed tower, spray tower and 0 bubble tower, can be used. Although the present invention produces particularly excellent effects when used for boiler flue gases using several fuel oils, such as heavy oil, Ormionium VR and CWM / heavy oil, similar effects can also be obtained when applied, for example, to boilers that burn coal / heavy oils. Even in boilers that burn coal exclusively, a fuel oil can be burned, for example, at the time of starting or during the test operations. The present invention can be effectively applied to such cases. As described above, in the present invention, a step of adding powder to spray a powder that can be collected in the absorption stage in the flue gas, is provided before the heat recovery step, which uses a heat exchanger. Consequently, even if the SO3 present in the fuel gas condenses at or after this stage of powder addition (for example, as a result of cooling in the heat recovery stage), this condensation occurs only at the particle surfaces. of the 5 mentioned dust. Consequently, the H2SO4 particles formed by the condensation of SO3 exist in a state bound to the aforementioned particles of the powder, which results in a decrease in the production of harmful fumes (or sulfuric acid mist). Also, since this powder 0 can be collected in the absorption tower, the mentioned H2SO4 particles, together with the powder, can be collected in the absorption tower. Consequently, dust and H2SO4 particles barely remain in the treated flue gas. Thus, according to the present invention, a preliminary measurement against the SO3 present in the flue gas can be easily achieved without resorting to ammonia injection and the flue gas can be further purified without the disadvantages of causing the injected or remain in the treated flue gas. Especially, when the mentioned powder is sprayed in such proportion that the weight ratio (D / S) of the amount of powder (D), which includes the aforementioned powder, To the amount of SO3 present in the flue gas, is not less than 2 (ie, D / S _> 2), most of the SO3 condensation occurs on the particle surfaces of the powder, mentioned above , and similar. This makes it possible to avoid the production of harmful fumes (or sulfuric acid mist) with substantial certainty and to prevent SO3 from causing fouling or corrosion, with high reliability. Also, in the present invention it is possible to carry out at least no independent treatment for removal of dust from the flue gas, by means of an electrostatic precipitator, before the heat recovery stage and the absorption stage, so that the Most of the powder present in the flue gas, together with the added powder, can be collected in the absorbent fluid, and provide a separation step to separate the solid particles in addition to the gypsum particles, which comprises at least the collected dust in the absorption fluid, from the plaster. Consequently, removal of the powder from the flue gas is also effected in the absorption stage. Thus, a further simplification of the equipment or operation and a further reduction in cost can be achieved in comparison with the conventional process of treatment of the flue gas, which involves the removal of the dust using an electrostatic precipitator of large and expensive size, installed on the side upstream of the absorption stage. Furthermore, since the powder (for example the unburnt carbon) constituting the material foreign to the gypsum, is separated in the separation stage, the highly pure gypsum can be obtained in spite of the construction involving the positive removal of the dust in the the absorption stage. The various effects of the present invention, which include those described above, can be summarized as follows: (1) The consumption of ammonia is reduced to zero, resulting in a marked saving in the cost of the operation. (2) Equipment for the injection of ammonia becomes unnecessary and the necessary conduit will not be elongated especially in order to allow ammonia to diffuse, so a corresponding reduction in the cost of the equipment and the size of the ammonia can be achieved. equipment. (3) Since no nitrogen component is contained in the desulphurisation waste water, the need for an embarrassing treatment for the removal of nitrogen is eliminated prior to the disposal of the desulphurisation waste water. From this point of view, a reduction in the cost of the equipment and the size of the equipment can also be achieved. (4) The amount of ammonia contained in the treated flue gas and discharged into the atmosphere is reduced to zero. This not only contributes greatly to a further purification of the flue gas, but also makes it easy to comply with the ammonia emission regulations in the future. (5) When the chalk-lime method is used, the gypsum formed as a by-product does not contain ammonia.

Consequently, the plaster does not need to be washed, for example, in order to remove the unpleasant odor. (6) Since no powder comprising sulfuric acid mist and ammonium sulfate powder remains in the treated flue gas, in contrast to the prior art, the general ability to remove dust from the system is improved without recourse to an element, such as a wet dust precipitator, installed on the downstream side of the absorption tower. This also contributes to a further purification of the flue gas. 5 (7) A marked reduction in cost can be achieved, compared to the prior art, in which a I large and expensive electrostatic precipitator is installed on the upstream side of the desulfurization apparatus. 0 Especially, when the process of treating the flue gas is provided with a dust removal step to collect the aforementioned dust or the powder remaining in the flue gas, which has passed through the absorption stage, by means of of a dry electrostatic precipitator or a wet electrostatic precipitator, or when the humer gas treatment process is provided with a pre-charge step, to add and swell the mentioned powder or the powder present in the flue gas and also with a primary dust removal step, to remove some of the dust from the flue gas by means of a bent plate type primary separator and to introduce it into the absorption fluid used in the absorption step, not just a reduction in the cost can be achieved, compared to the prior art, but also the general ability of dust removal in the system can be improved. (8) The present invention also has the advantage that, since the powder (for example the unburned carbon) constituting the material foreign to the gypsum, is separated in the separation step described above, the highly pure gypsum can be obtained at Despite the construction that involves the positive removal of dust in the absorption stage. Also, when the temperature of the powder sprayed into the flue gas becomes smaller than that of the flue gas SO3 is allowed to condense more efficiently on the particle surfaces of the powder, so that the production of the harmful SO3 mist may be prevented more satisfactorily and more easily. Also, when the powder is suspended in a liquid and sprayed in the form of an aqueous paste, the apparatus and devices conventionally used in a desulfurization system or the like, such as a stirred tank for the preparation of an aqueous paste, an aqueous paste and nozzles for spraying the aqueous paste can be used without any modification. This is advantageous from the point of view of the cost of the equipment and the operability of the system. In addition, this makes it easier to disperse the powder uniformly in the flue gas, as compared to pneumatic transport, so problems due to SO3 can be prevented more efficiently. Likewise, in this embodiment, the coal ash particles H are kept at a lower temperature, due to the cooling effect produced by the evaporation of the liquid from the aqueous paste in the flue gas (or the maintenance of the cooling effect produced by the presence of the liquid of the aqueous paste). Consequently, the condensation of SO3 on the particle surfaces of the powder is promoted, so the SO3 capture function of the powder is more satisfactorily performed. Also, a high degree of purification of the flue gas can be achieved, even when the dust contained in the exhaust gas from the combustion of the coal (ie, the coal ashes) is used as the aforementioned powder. More specifically, since coal ash has a relatively large particle diameter, in the order of several tens of microns, it can be collected in the absorption towers with a relatively high degree of collection, compared not only with sulfuric acid mist, conventionally found, but also with ammonium sulfate powder, conventionally found. As a result, coal ash remains only in the resulting treated flue gas. Similarly, similar to limestone, coal ash is familiar material that has been conventionally handled in flue gas treatment systems, and existing equipment and handling techniques can be used without modification. Thus, coal ash can be obtained and easily handled, resulting in a further reduction in the cost of operation and the cost of the equipment. In particular, coal ash is usually disposed as an industrial waste in thermal electric power plants, which burn coal exclusively, and the like, and can therefore be advantageously obtained almost free of charge. On the other hand, when a dust collection stage, to collect the dust present in the flow gas by means of a dry electrostatic precipitator, it is immediately installed to the heat recovery stage (i.e., the heat exchanger) and before the absorption stage (ie, the absorption tower), and at least part of the dust collected in this dust collection stage is reused as the aforementioned powder, the following unique effect is produced in addition to the basic effects before described. That is, the construction of this embodiment represents the so-called high performance system, in which a heat exchanger is disposed upstream of an electrostatic precipitator, so that the unitary capacity of the electrostatic precipitator is improved. Consequently, using the small-sized electrostatic precipitator, the aggregate carbon ash can be removed from the flue gas with a high degree of collection. In addition, the powder originally contained in the untreated flue gas is also collected almost completely in this electrostatic precipitator and the absorption tower, and remains poorly in the resulting treated flue gas. Thus, also in this embodiment, scale formation and corrosion due to SO3 are reliably impeded in the heat exchanger mentioned, the ducts placed downstream thereof and the hopper of the electrostatic precipitator. Likewise, the same effects, as those previously described (1) to (6), are produced. Also, in this embodiment, the powder (comprising coal ash and others) used to capture the SO3 is recycled. This has a unique effect in that the amount of fresh coal ash supplied can be decreased and, likewise, the amount of the powder (comprising coal ashes and others) discharged out of the system, can also be decreased. Consequently, as will be described below, this modality has a unique effect in that, even when the powder (comprising the coal ashes and others) to be discharged from the system is mixed with the gypsum formed, according to the method of lime-plaster, the amount of such powder can be reduced to a minimum to maintain the purity of the plaster at a high level. Also, when at least part of the dust collected in the dust collection stage (i.e., the powder (comprising coal ashes and others) to be discharged from the system) is mixed with the gypsum formed as a by-product, According to the lime-plaster method, the amount of dust discharged as industrial waste can be reduced to zero. This also contributes, for example, to savings in the cost of operation. On the other hand, when the powdered limestone is used as the aforementioned powder, this aggregate limestone has a large particle diameter, of the order of 100 μm and, therefore, can be collected in the absorption tower (or stage). of absorption) with a markedly higher degree of collection, compared not only with sulfuric acid mist, conventionally found, but also with ammonium sulfate powder, conventionally found. Consequently, the limestone scarcely remains in the resulting treated flue gas C. Thus, a particularly high degree of purification of the flue gas can be achieved. Also, limestone is a familiar material, which has been conventionally managed in the humer gas treatment systems, and existing equipment and handling techniques can be used without any modification. Thus, limestone can be obtained and easily handled, resulting in a further reduction in the cost of operation and the cost of the equipment. Likewise, limestone has the advantage that, when added to flue gas, it does not have an adverse influence on the operation of the entire system. That is, in this case, the limestone collected in the absorption tower dissolves or suspends in the absorption fluid, and acts as the absorbent (or alkaline agent) to neutralize the absorbent fluid. Thus, on the contrary, limestone promotes the reaction for the absorption of sulfur oxides. Likewise, when the lime-plaster method, where the limestone is used as the absorbent, in order to form the gypsum from the absorbed sulfur oxides, as a by-product, is used, the modality in which the limestone is added to the flue gas as the powder, does not exert an adverse influence on the purity of the gypsum, as long as the total amount of the aggregate limestone is controlled in the usual way. In addition, aggregate limestone is converted into useful gypsum without causing an increase in the amount of industrial waste. Likewise, when the absorption stage to absorb the SO3 and other sulfur oxides, present in the flue gas, is carried out, according to the lime-plaster method and the total amount of the limestone required for the use As the absorbent in this absorption step is added to the flue gas as the aforementioned powder, the equipment, conventionally used, for example, to form the limestone in an aqueous paste and supply it to the tank of the absorption tower becomes unnecessary . This can provide, for example, a further reduction in the cost of the equipment. On the other hand, when the solid matter present in the absorbent fluid, which has been subjected to the gas-liquid contact with the flue gas (i.e., the solid matter consists essentially of the gypsum formed as a by-product, according to the method of chalk-lime) is used as the aforementioned powder, the aggregate solid matter usually has a large particle diameter, in the order of 20 to 40 μm and, therefore, can be collected in the absorption tower (or absorption stage). ) with a high degree of collection, in comparison not only with the sulfuric acid mist, conventionally found, but also with the ammonium sulfate powder, conventionally found. As a result, the solid matter hardly remains in the resulting treated humer gas 5. Thus, the particularly high degree of purification of the flue gas can also be achieved. Likewise, the same effects, as those previously described (1) to (6), are produced. Also, since the solid matter, which consists essentially of a by-product formed in the absorption stage is used as the powder, this embodiment has a unique effect in that the addition of the powder does not cause any reduction in the purity of the mentioned byproduct. and, therefore, the purity of the by-product can be maintained at a particularly high level. Likewise, the solid matter (eg gypsum) present in the absorption fluid is a familiar material which has been conventionally handled in the flue gas treatment systems and existing equipment and the handling techniques can be used. without any modification. Thus, a further reduction in the cost of operation and the cost of the equipment can be achieved. j Especially when the absorbent fluid, of the aqueous paste type, which contains solid matter consisting essentially of a by-product (for example gypsum), formed by contact with the flue gas in the absorption tower (or absorption stage), is sprayed directly on the Smoke gas as an aqueous paste containing the powder of the present invention, this embodiment has a unique effect in that the construction of the equipment is highly simplified and, therefore, a great advantage is gained from the cost point of view. More specifically, an embodiment in which, for example, the coal ash is sprayed in the form of an aqueous paste and requires an additional apparatus, such as a tank, for the preparation of an aqueous paste and a storage element for the carbon ash, and an embodiment in which the solid matter present in the absorption fluid is dried and sprayed into the flue gas and requires an additional apparatus, such as a dryer, to dry the solid matter. However, this equipment does not require such an appliance in any way.

Claims (14)

1. CLAIMS 1. A process for the treatment of flue gas, in which flue gases containing at least SO2 and SO3 are treated, this process includes a stage of heat recovery, to recover the heat of the gas by means of a heat exchanger and thus cooling this flue gas, and a subsequent absorption stage, to bring the flue gas into gas-liquid contact with an absorbent fluid, in an absorption tower, in order to remove at or minus the SO2 present in the flue gas by absorption in
2. I the absorbent fluid, in which a powder addition stage is supplied, for spraying a powder, which can be collected in the absorption stage, into the flue gas, before the heat recovery step, this powder it sprays into the flue gas, in the form of an aqueous paste, comprising said powder suspended in a liquid, and the absorbent fluid, which was subjected to the contact of gas-liquid with the flue gas, in the absorption stage. , it is sprayed into the flue gas, like an aqueous paste, of
3. So that the solid matter, present in the absorption fluid, can be used as said powder. 2. A process for the treatment of flue gas, 5 in which flue gases containing at least SO2 and SO3, including a heat recovery stage, are treated to recover the heat from the flue gas by means of a heat exchanger and thus cooling this flue gas, and a subsequent absorption step, to bring the flue gas into gas-liquid contact with the absorbent fluid in an absorption tower, so as to remove at least SO2 present in the flue gas by absorption in the absorbent fluid, in which a powder addition stage is supplied, for spraying a powder, which can be collected in the absorption stage, into the flue gas, before the step of heat recovery, this powder is sprayed into the flue gas, in the form of an aqueous paste comprising said powder suspended in a liquid and in such proportion that the weight ratio (D / S) of the total amount of the powder ( D), which includes the first powder m The amount of SO3 (S) present in the flue gas is not less than 2, and the absorption fluid, which has been subjected to the gas-liquid contact with the flue gas, in the absorption stage. , it is sprayed into the flue gas as an aqueous paste, so that the solid matter present in the absorption fluid can be used as said powder. 3. A process for the treatment of flue gas, in which flue gases containing at least SO2 and SO3, including a heat recovery stage, are treated to recover the heat from the flue gas by means of of a heat exchanger, and thus cooling this flue gas, and a subsequent absorption step, to bring the flue gas into gas-liquid contact with the absorbent fluid in an absorption tower, so as to remove at least SO2 present in the flue gas by absorption in the absorbent fluid, in which a powder addition stage is supplied, for spraying a powder, which can be collected in the absorption stage, into the flue gas, before the step of heat recovery, and the solid matter present in the absorbent fluid, which has been subjected to gas-liquid contact with the flue gas in the absorption stage, is used as said powder.
4. 4. A process for the treatment of flue gas, in which flue gases containing at least SO2 and SO3, including a heat recovery stage, are treated to recover the heat from the flue gas by means of of a heat exchanger, and thus cooling this flue gas, and a subsequent absorption step, to bring the flue gas into gas-liquid contact with the absorbent fluid in an absorption tower, so as to remove at least SO2 present in the flue gas by absorption in the absorbent fluid, in which a powder addition stage is supplied, for spraying a powder, which can be collected in the absorption stage, into the flue gas, before the step of heat recovery, the powder is sprayed into the flue gas, in such proportion that the ratio by weight (D / S) of the total amount of powder (D), which includes the first mentioned powder, to the amount of SO3 ( S), present in the flue gas, is not less than 2; and the solid matter, present in the absorption fluid, which has been subjected to gas-liquid contact with the flue gas in the absorption stage, is used as said powder.
5. 5. A process for the treatment of flue gas, as claimed in claim 3, wherein, in the powder addition stage, the temperature of the powder becomes lower than the temperature of the flue gas.
6. 6. A process for the treatment of flue gas, as claimed in claim 4, wherein in the powder addition stage, the temperature of the powder becomes lower than the temperature of the flue gas.
7. 7. A process for the treatment of flue gas, as claimed in any of claims 3 to 6, wherein the stage of powder addition is carried out by drying the solid matter with a gas obtained by removing part of the flue gas. , transporting the pneumatically dried solid matter, and rolling it in the flue gas.
8. 8. A process for the treatment of flue gas, in which flue gases containing at least SO2 and SO3, including a heat recovery stage, are treated to recover the heat from the flue gas by means of of a heat exchanger, and thus cooling this flue gas, and a subsequent absorption step, to bring the flue gas into gas-liquid contact with the absorbent fluid containing a calcium compound in an absorption tower, for thus remove at least the SO2 present in the flue gas, by absorption in the absorption fluid and, likewise, form the gypsum as a by-product, in which a stage of powder addition is supplied, to sprinkle a powder that can be To collect in the absorption stage, in the flue gas, before the heat recovery stage, no independent treatment is carried out for the removal of the natural dust contained in the flue gas, before the recovery stage of the heat and the absorption stage, so that most of the powder present in the flue gas, together with the first mentioned powder, can be collected in the absorption fluid, and the process further includes a separation step, to separate the solid particles furthermore. of gypsum particles, which comprises at least the dust collected in the I! Absorption fluid from the plaster.
9. 9. A process for the treatment of flue gas, as claimed in claim 8, wherein the step of The separation comprises the separation of the solid particles from the gypsum particles, by the production of air bubbles in the absorbent fluid, in order to allow the solid particles, which have a hydrophobic surface, to adhere to the air bubbles and raise, while allowing 0 that the gypsum particles, which have a hydrophilic surface, remain in the absorption fluid.
10. 10. A process for the treatment of flue gas, as claimed in claim 8 or 9, which also includes a step of removing natural powder content, to collect the powder content or the first mentioned powder that remain in the flue gas, which has passed through the absorption stage by means of a dry electrostatic precipitator or a wet precipitator.
11. 11. A process for the treatment of flue gas, as claimed in claim 8 or 9, wherein a pre-charge step is provided, to add and swell the contained powder or the first mentioned powder present in the gas of humero, then to the stage of | heat recovery and before the absorption stage, and this pre-charging stage is carried out by introducing the flue gas in a pre-charger, which has a discharge electrode and a dust collection electrode, imparting an electric charge to the powder contained or to the first mentioned powder, present in the flue gas, as a result of an electric discharge from the discharge electrode, which allows the charged powder or charged primary powder to migrate to the dust collection electrode, which has a opposite sign, based on the Coulomb force, and retain it in the dust collection electrode for a predetermined period of time.
12. 12. A process for the treatment of flue gas, as claimed in claim 11, wherein the step of preparing for dust removal, to separate some of the contained powder or the first mentioned powder from the flue gas, which has passed through the heat recovery stage and has been introduced into the absorption fluid used in the absorption stage, it is provided before the pre-loading stage.
13. 13. A system for the treatment of flue gas, which treats flue gases containing at least SO2 and SO3, which includes a heat exchanger to recover heat from the flue gas and thus cool this flue gas, and an absorption tower, arranged downstream of the heat exchanger, to bring the flue gas in gas-liquid contact with the absorption fluid, I so as to remove at least the SO2 present in the flue gas by the absorption inside. of the absorbent fluid, in which the powder addition element, for sprinkling a powder in the flue gas, is provided upstream of the heat exchanger, this powder addition element consists of nozzles for sprinkling the powder within the a flue, in the form of an aquepaste, comprising the powder suspended in a liquid, and the system further includes a supply element for the absorbent fluid, for removing part of the flue gas, ; which has been subjected to gas-liquid contact with the flue gas in the absorption tower and supplied to the nozzles as the aquepaste, so that the solid matter present in the absorption fluid can be used as said powder.
14. 14. A system for the treatment of flue gas, which treats flue gases containing at least SO2 and SO3, which includes a heat exchanger, to recover heat from the flue gas and thus cool this gas of a flue, and an absorption tower, arranged downstream of the heat exchanger, to bring the flue gas into a gas-liquid contact with the absorbent fluid, in order to remove at least the SO2 present in the flue gas from the flue gas. the absorption in the absorbent fluid, in which the powder addition element, to spray a powder in the flue gas, it is provided upstream of the heat exchanger, this powder addition element consists of nozzles for sprinkling the powder in dry form in the flue gas with the help of a gas stream, and the system further includes a separating element of solid-liquid, to separate the solid matter from the flue gas, which has been subjected to gas-liquid contact with the flue gas in the absorption tower, a drying element, to dry at least part of the solid matter separated by the solid-liquid separation element, and a pneumatic conveying element, for pneumatically transporting the dried solid matter by the drying element to the nozzle as said powder, so that the solid matter present in the absorption fluid can be used as said powder.