MXPA98001386A - Procedure and system to treat hum gas - Google Patents

Abstract

The present invention relates to the fact that a preliminary average against the SO3 present in flue gases can easily be achieved without resorting to the injection of ammonia and this flue gas can subsequently be purified without the disadvantage of causing the injected substance to remain in the atmosphere. treated flue gas, this invention provides a process for the treatment of flue gases, which comprises an absorption stage, where the flue gas is brought into a gas-liquid contact with an absorbent fluid (D) in towers of adsorption (12, 13) and at least the SO3 present in the flue gas is removed by adsorption in the absorbent fluid (D), characterized in that a step of adding a particular powder is supplied to spray this powder, which can be collecting, in the absorption stage [for example, pulverized limestone (G)] inside the flue gas, before the absorption stage

Description

PROCEDURE 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 (for example, flue gas produced from boilers that burn heavy oils). More particularly, it refers 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, with low cost and with a simple equipment operation or construction. 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 (dioxide). sulfur). The ratio of SO 3 to the total amount of sulfur oxides (eg, 1,500 ppm) can vary according to the boiler combustion temperature, the type of burner, the type of the combustion catalyst and the like, but it is order of several by hundreds in any case. That is, SO3 is present in a relatively small amount, for example about 30 ppm. Consequently, an important basic consideration in the desulfurization of this type of flue gas is the ability to absorb SO2. However, when the SO3 present in the flue gas produces fumes, they form harmful mists of H2SO4, which are strongly corrosive and constitute a factor in the formation of scale. Likewise, they consist of submicrometric 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 position upstream of the equipment. and thus capture the SO3 present in the flue gas as ammonium sulfate [(H4) S0]. An example of such a conventional process and system for treating the flue gas is described below with reference to Figure 8. In Figure 8, reference number 1 designates an air heater (secondary boiler equipment) to heat the air. of combustion 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. Then, the exhaust gas A is introduced into a dry electrostatic precipitator 3, where the dust B, such as the fly ash, is removed from it. This powder B consists essentially of unburned coal and, in the case, for example, of boilers that burn heavy oils, furthermore it 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 discharged, for example, as an industrial waste. Next, in order that the hot, treated flue gas C be discharged to atmosphere, in the reheating section 5 of the gas-gas heater (GGH), as will be described later, the exhaust gas A introduce 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. The reheating section 5 can be omitted, according to the regulations of the exhaust gas, the height of the chimney, etc. In this process, the desulfurizing apparatus 10 has a construction in which two absorption towers, 12 and 13, of the liquid column type (ie, parallel flow and counterflow 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 sucked by the circulation pumps, 17 and 18, is injected upwards from these spray tubes, 15 and 16, into the shape of liquid columns. Also, a mist eliminator 20, to collect and remove the entrained mist, is installed downstream of the absorption towers. The mist collected by this mist eliminator 20 accumulates in a lower hopper (not shown) and is returned to the tank 11 through a drain 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 downward while the absorbing sulfur dioxide and the dust, as a result of the gas-liquid contact with the chiffon gauze, and enters the tank 11 where it is oxidized by contact with a large number of air bubbles, blown there while being agitated with the air sprinkler 21, and then undergoes a reaction of neutralization to form the plaster. The dominant reactions that occur in the course of these treatments are represented by the following reaction formulas (a) to (3): Inlet section of the flue gas of the absorption towers SO2 + H 0 • = > H + + HSO3- (!) Tank H + + HSO3- + 02"= 2H + + S0 2_ (2) 2H + + S042_ + CaC0 + H20 • = CaS04-2H20 + CO2 (3) So, the plaster, a small amount of limestone (used as the absorbent) and a slight amount of powder, are stably suspended in the slurry within the tank 11. In this process, the slurry within the tank 11 is removed and fed to a solid-liquid separator 23, by medium of a slurry pump 22. This aqueous paste is filtered in 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 solid-liquid separator filtrate is fed to a tank 26 for preparation of the aqueous paste, 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 preparation of the aqueous paste is equipped with a stirrer and serves to prepare the aqueous paste D absorbent by mixing the limestone G, introduced from a silo (not shown) with the water fed from tank 24 of the 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 limestone excavated 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 SO3, this SO3 will condense in the equipment at the base of the dew point of sulfuric acid and thus produce fumes, as described above. In general, the majority of 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 throttling of the flow path of the flue gas, due to the corrosion of the components of the equipment or the Formation of scale can arise, thus causing an increase in the cost of the equipment and the cost of maintenance. Also, since such SO3 fumes remain in the treated flue gas C discharged from the desulfurization apparatus 10, a wet dust collector needs to be installed, for example, in a downstream position of the absorption tower 13 and upstream. of section 5 of reheating 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 8, 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 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 flue gas treatment systems for boilers that burn coal, a system in which the heat recovery section 4 of the GGH is arranged on the side upstream of the electrostatic precipitator 3, to carry out the heat recovery stage before the electrostatic powder harvesting (ie, the named high performance system) is widely used. 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, electrical resistance) 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 8. However, the process or system of conventional treatment of flue gas involves the following several problems due to the injection of ammonia, mentioned above. 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. Also, it is also necessary to lengthen the conduit 2 of entry, 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 not yet regulated in Japan, but it is inconvenient from the point of view of further purification of the flue gas. If it is regulated in the future, 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 powder of ammonium sulfate remains in the treated flue gas C and also has a problem from the viewpoint of further purification of the flue gas. Thus, the technique of conventional treatment of the flue gas is not satisfactory for its use as a technique for the purification of this flue gas in which the increasingly higher performance has recently become desirable 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. Therefore, the first object of the present invention is to provide a process and system for the treatment of flue gas, in which a preventive measure against the SO3 present in the flue gas can be easily achieved without the injection of ammonia and the The flue gas can also 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 and system for the treatment of the 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 a simpler operation or construction of equipment. The third object of the present invention is to employ the cal-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 boilers that burn coal contain a large amount of dust, such as fly ash (ie, its content is 10 to 100 times higher compared to the flue gas 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 gas of 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 H2SO4 particles formed by the condensation of SO3 exist in a 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 based on these findings, solves the problems described above 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, remove at least the SO2 present in the flue gas by absorption in the absorbent fluid and collect the dust Also, according to the present invention, a process for treating the flue gas is provided to treat a flue gas containing at least SO2 and SO3, which comprises a step of adding powder to spray a powder into the flue gas. fume gas, a subsequent stage of dust collection, for introducing the flue gas into a dust collector and collecting at least the powder present in the flue gas, and a subsequent absorption step for carrying the flue gas in gas-liquid contact with an absorption fluid in an absorption tower and remove at least the SO2 present in the flue gas by absorption in the absorbent fluid. Also, according to the present invention, there is provided a process for treating the flue gas for the treatment of a flue gas containing at least SO2 and SO3, which comprises a heat recovery stage, to recover the heat from the flue gas by means of a heat exchanger and thus cooling the flue gas, and a subsequent absorption step to bring this flue gas into gas-liquid contact with an absorbent fluid in an absorption tower and remove at least the SO2 present in the flue gas by absorption in the absorbent fluid, characterized in that a powder addition stage is supplied, for spraying a powder that can be collected in the absorption stage in the flue gas, before the heat recovery stage. In the present invention, a powder addition step for spraying a powder which can be collected in an absorption tower or in a dust collector in a flue gas, is supplied before the absorption stage, using the tower of absorption or the dust collection stage used by the dust collector.

Accordingly, even if the SO3 present in the flue gas is condensed at or after this powder addition stage, this condensation occurs only at the particle surfaces of the aforementioned powder. Therefore, 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 the harmful fumes (or mists of sulfuric acid). Also, since this powder is collected in the absorption stage or the dust collection stage, the H2SO4 particles are collected, along with the powder, in any of these stages. Consequently, neither the dust nor the H2SO4 particles remain at least in the treated flue gas. In the present invention, a powder addition step for spraying a powder, which can be collected in the absorption stage in the flue gas, can be provided before the heat recovery step using a heat exchanger. Accordingly, even if 1 SO3 present in the flue gas condenses at or after this powder addition step (e.g., as a result of cooling in the aforementioned heat recovery stage), this condensation occurs only at the particle surfaces. of the mentioned dust. Consequently, the H2SO4 particles formed by the condensation of SO3 exist in a state bound to the aforementioned dust particles, which results in a decrease in the production of harmful fumes (or mists of sulfuric acid). Also, since this powder can be collected in the absorption tower, the aforementioned H2SO4 particles, together with the powder, are collected in the absorption tower. Therefore, none of the dust and H2SO4 particles remain at least in the treated flue gas. Thus, according to the present invention, a preventive measure against the SO3 present in the flue gas can be easily achieved without recourse to ammonia injection and the flue gas can also be purified without the disadvantage of causing the injected substance 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 contains the mentioned powder, to the amount of SO3 (S), present in the flue gas , is not less than 2 (ie, D / S> 2), most of the SO3 condensation occurs on the surfaces of said powder particles and the like. This makes it possible to avoid the production of noxious fumes (or mists of sulfuric acid) with substantial certainty and to prevent SO3 from causing scale formation or corrosion, with high reliability. As a result, the injection of ammonia can be completely eliminated to carry out the following practically favorable effects: (1) The consumption of ammonia is reduced to zero, which results in a marked saving in the cost of operation. (2) The equipment for ammonia injection becomes unnecessary and the conduit does not need to be elongated especially in order to allow the ammonia to diffuse, so that a corresponding reduction in the cost of the equipment can be achieved and the size of the team (3) Since no nitrogen component is contained in desulphurisation wastewater, the need for an embarrassing treatment for nitrogen removal is eliminated prior to the disposal of the desulphurisation wastewater. 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 to 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 lime-gypsum method is used, this 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 powder or ammonium sulfate powder remains in the treated flue gas, in contrast to the prior art, the overall performance of the dust separation is improved without resorting to means 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.

Also, where the temperature of the powder sprayed into the flue gas is less than the temperature of this flue gas, the SO3 is allowed to condense more effectively on the particle surfaces of the powder. As a result, the production of noxious SO3 mists can be prevented more satisfactorily and more easily. Likewise, where the powder is suspended in a liquid to form an aqueous paste and sprayed into the flue gas, the apparatus and device conventionally used in the desulfurization system or the like, such as a stirred tank for the preparation of an aqueous paste , the pumps of the aqueous paste and the nozzles for the spray of 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. Furthermore 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 cooling effect maintained caused by the presence of the aqueous paste liquid). Consequently, the condensation of the SO3 on the surfaces of the particles of the carbon powder H is promoted, so that the capture function of the SO3 of the carbon powder H used as the aforementioned powder is more satisfactorily performed. Also, a high degree of purification of the flue gas can also be achieved when the powder contained in the coal combustion exhaust gas (i.e., the coal dust) is used as the aforementioned powder. That is, since such coal dust has a relatively large particle diameter, in the order of several tens of microns, it can be collected in the absorption tower with a relatively high degree of collection, compared not only with the mists of the acid sulfuric, conventionally found, but also with the conventional ammonium sulfate powder. Consequently, the little carbon powder remains in the resulting treated flue gas. Similar to limestone, coal dust is a conventionally known material, which has been familiarly handled in the existing flue gas treatment systems and the existing equipment and handling techniques can be used without any modification. Thus, coal dust can be obtained and handled easily, resulting in more savings in the cost of operation and the cost of the equipment. In particular, coal dust is usually disposed as an industrial waste in exclusive power plants that burn coal and the like, so that it can be advantageously obtained without any appreciable cost. Likewise, when at least a portion of the powder, which has been collected in the dust collection stage, is again used as a powder sprayed in the flue gas, the following effects are produced in addition to the basic effects, described above . In this case, the powder (comprising the coal dust and others) is recycled as the powder that collects the SO3. Consequently, the amount of the powder (which comprises the coal dust and others) that is to be supplied recently, can be decreased and the amount of powder (comprising the coal dust and others) to be discharged from the system, it can be decreased. Likewise, when the powder (comprising the coal dust and others) to be discharged from the system is mixed with the gypsum formed, according to the lime-plaster method, as will be described below, a unique effect is produced in which that amount of powder can be reduced to a minimum, to maintain the purity of the gypsum at a high level Also, where a dust collection stage, to collect the dust present in the flue gas by means of a dry electrostatic precipitator is provided after the heat recovery stage (the heat exchanger) and before the absorption stage (the absorption tower) and at least a part of the dust collected in this dust collection stage is reused as the aforementioned powder , the following unique effects are produced, in addition to the basic effects described above. Specifically, in this case, the system represents the so-called high performance system, in which a heat exchanger is installed upstream of an electrostatic precipitator, so that the performance per unit capacity of the electrostatic precipitator is improved. Consequently, using a small-sized electrostatic precipitator, the added charcoal powder can be removed from the flue gas with a high degree of collection. Also, the powder originally contained in the untreated flue gas is also almost completely collected in this electrostatic precipitator and the absorption tower and scarcely remains in the resulting treated flue gas. Therefore, also in this case, the formation of scale and the corrosion due to SO3 are reliably prevented, for example, in the mentioned heat exchanger and the ducts placed downstream and in the hopper of the electrostatic precipitator. Likewise, the same effects as those previously described (1) to (6) are produced. Also, in this case, the powder (comprising the coal dust and others) used to capture the SO3 is recycled. Consequently, the amount of fresh coal powder to be supplied can be decreased and the amount of powder (comprising the coal dust and others) to be discharged from the system can also be decreased. In addition, even where the powder (which comprises coal dust and others) is going to be discharged from the system it is mixed with the gypsum, formed according to the lime-plaster method, as will be described later, this has a unique effect on the that the amount of the mixed powder with the plaster can be reduced to a minimum to maintain the purity of the plaster at a high level. Also, where at least part of the dust collected in the dust collection stage [ie, the powder (comprising coal dust 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 a saving in the cost of operation. Also, when powdered limestone is used as the mentioned 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 the absorption stage). with a markedly high degree of collection, in comparison not only with the mists of sulfuric acid, conventionally found, but also with the ammonium sulfate powder, conventionally found. Consequently, little limestone remains in the resulting treated flue gas. Thus, a particularly high degree of purification of the flue gas can be achieved. Likewise, limestone is a conventionally known material, which has been familiarly handled 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, which results in additional savings in the cost of operation and the cost of the equipment. The limestone also has the advantage that its addition to the flue gas does not exert an adverse influence on the operation of the entire system. Specifically, in this case, the limestone collected in the absorption tower is dissolved or suspended in the absorbent fluid and acts as an absorbent (or alkaline agent) to neutralize the absorbent fluid, thus promoting the sulfur oxide absorption reactions in otherwise. Also, where the lime-plaster method is used in which limestone is used as an absorbent and gypsum is formed from absorbed sulfur oxides, the mode in which limestone is used as dust and is added to the flue gas, does not exert an adverse influence on the purity of the gypsum, provided that the total amount of limestone aggregate is controlled as usual. In addition, aggregate limestone is converted into useful gypsum without causing any increase in the amount of industrial waste. Likewise, where the absorption step to remove the SO2 and similar from the flue gas, is carried out according to the lime-plaster method and the total amount of limestone required for use as the absorbent in this absorption stage it is added to the flue gas as the aforementioned powder, the equipment conventionally used to feed the limestone to the tank of the absorption tower, for example, by the preparation of its aqueous paste, becomes completely unnecessary. Thus, an additional saving in the cost of equipment and the like can be achieved.

In accordance with the present invention, a humer gas treatment system is provided for the treatment of a flue gas containing at least SO2 and SO3, which is an absorption tower for carrying the flue gas in contact with the flue gas. gas-liquid with an absorption fluid and remove at least the SO2 present in the flue gas by absorption in the absorbent fluid, and a powder addition element, to spray a powder into the flue gas, which is provided with current above the absorption tower. In accordance with the present invention, a humer gas treatment system is also provided to treat a flue gas containing at least SO2 and SO3, which comprises a heat exchanger for recovering heat from the flue gas and thus cooling this flue gas, and an absorption tower disposed downstream of the heat exchanger to bring the flue gas into gas-liquid contact with the absorbent fluid and remove at least the SO2 present in the flue gas by absorption in the flue gas. the absorbent fluid, characterized in that the powder addition element, for spraying this powder into the flue gas, is provided upstream of the heat exchanger. In the humer gas treatment system of the present invention, it is possible to employ a mode in which a dry electrostatic precipitator is supplied, to collect the dust present in the flue gas, downstream of the heat exchanger and upstream of the the absorption tower, and at least a part of the dust collected by this electrostatic precipitator is reused as the aforementioned 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 schematic view illustrating the construction of the flue gas treatment system, according to the fourth embodiment of the present invention; Figure 5 - is a schematic view illustrating the construction of a flue gas treatment system, according to the fifth embodiment of the present invention; Figure 6 is a graph showing the data which illustrate the principle of the present invention; Figure 7 is a graph showing other data illustrating the principle of the present invention; and Figure 8 is - a schematic view illustrating the construction of a conventional treatment system for flue gas.

DETAILED DESCRIPTION OF THE PREFERRED ODALITIES 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 8, are designated by the same reference numbers and their explanation is omitted. First Mode The first embodiment of the present invention is explained with reference to Figure 1. This embodiment differs from the conventional flue gas treatment system of Figure 8 in that the step of ammonia injection is omitted, an addition element of powder (not shown) for spraying a powder in the flue gas, is provided before the electrostatic precipitator 3 and a stage for spraying powder [eg, the powder contained in the combustion exhaust gas of the coal (i.e. called carbon powder H)] in the flue gas A, using the powder addition element, is provided before the powder collection stage, which uses the electrostatic precipitator 3.

Like coal dust H, entities mentioned, for example, the coal dust collected by the electrostatic precipitators included in the humer gas treatment system of an exclusive electric power plant, which burns coal, can be used. 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 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 transporting the slurry is one consisting of a stirred tank, for dispersing the powder in a liquid to form an aqueous slurry, an aqueous slurry pump 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 transporting it inside 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 desulfurizing 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 slight 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 gas-gas heating device (GGH).

Even when the carbon powder H, used as the above-mentioned determined powder, is sprayed in the form of an aqueous paste, this carbon powder H can be added in such proportion that the weight ratio (D / S) of the The amount of powder (D) present in a unit volume of the flue gas at the amount of SO3 (S) present in a unit volume of the flue gas satisfies the relationship shown in Figure 7, described below. For example, when it is necessary to increase the degree of SO3 removal to 70%, the D / S value should not be less than 25. For example, when the SO3 concentration is 50 mg / m3 / N, the Coal dust H must be used in such quantity that the amount of the total powder in the flue gas is not less than 1250 mg / m3H. For example, even where the powder H of carbon used as the determined powder, mentioned above, is sprayed in the form of an aqueous paste, it can be added in such a low ratio, so 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 is, for example, not less than 2 (ie D / S) > 2). For example, when the SO3 concentration is 50 mg / m3N, the coal dust H can be added in an amount of not less than 100 mg / m3 / N. In this way, the effects described above of the powder are 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 particle surfaces of the powder (comprising the carbon powder mentioned above 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 carbon powder has a relatively large particle diameter, of the order of 10 μm, most of them can be collected in an electrostatic precipitator 3 with a relatively high degree of collection and the rest that has not been collected in the electrostatic precipitator 3, it can be collected in the absorption towers 12 and 13 of the desulfurizing apparatus 10 almost completely, in comparison not only with the mists of sulfuric acid conventionally found, but also with the ammonium sulfate powder conventionally found . Thus, little carbon dust remains in the resulting treated C-flue gas. The carbon powder 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, 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 condensed on the surfaces of the coal dust and the like and has been collected in the absorption towers, 12 and 13, together with the coal dust and the like, which finally suffers the reaction of neutralization (3), previously described, with the limestone, for example, in tank 11 of the absorption tower, to supply a part of the gypsum formed as a by-product. In this embodiment, a part Bl of the powder (comprising the powder which has been sprayed into the flue gas and the powder present in the flue gas) which has been collected in a powder collection stage using the electrostatic precipitator 3, it is recycled as a powder of the present invention, to be sprayed in the flue gas. A part Bl of the powder that has been collected in the electrostatic precipitator 3 is supplied into the powder silo 30, mixed with the powder H of fresh coal in the powder silo 30, and then sprayed in an upstream position of the powder. electrostatic precipitator 3 by the powder addition element again. Thus, a part Bl of the powder is recycled. In this embodiment, the powder, such as the fly ash that is contained in the untreated flue gas A, discharged from the air heater 1, as well as the coal dust H, which is supplied from the outside, is included. in the powder that is going to be sprayed in the flue gas. Also, in this embodiment, the other part B2 of the powder that has been collected by the electrostatic precipitator 3 is uniformly mixed with the gypsum E, which has been produced as a by-product in the desulfurizing apparatus 10 and discharged out of the system. In this embodiment, it is preferable that the total amount of powder to be sprayed be such as the minimum amount required to satisfy the D / S ratio defined above. Also, it is also preferable that the amount of powder Bl to be recycled is increased to its limit, in which the sprayed powder has the ability to capture the SO3, and that the quantities of the carbon powder H to be added and the B2 powder to be discharged is reduced to its minimum required levels. In this way, the amount of powder B2 to be mixed with the plaster E can be minimized to maintain the purity of the plaster E at a high level and the amount of carbon powder H to be added can be decreased to facilitate the handling of coal dust H. Thus, in accordance with this embodiment, scale formation and corrosion due to SO3 are reliably prevented in section 4 of heat recovery of the GGH and the conduits placed there downstream. Likewise, the following favorable effects occur practically (1) to (9). (1) The consumption of ammonia is reduced to zero, which results in a marked saving in the cost of operation. (2) Equipment for the injection of ammonia becomes unnecessary and the conduit does not need to be lengthened especially in order to allow 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 the prior art, 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 carbon powder 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 tangon for the preparation of a paste water, aqueous paste pumps and spray nozzles for the aqueous paste, can be used without any modification. This is advantageous from the point of view of the cost of the system 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) In this embodiment, the carbon powder H which is used as the aforementioned powder capable of collecting the SO3, is recycled. Consequently, this embodiment has unique effects in that the amount of the fresh coal powder to be supplied may decrease and that the amount of the powder B2 to be mixed with the plaster E, may be reduced to a minimum to improve the purity of the product. E. gypsum (9) In this modality, because the powder B2 is mixed with the plaster E, the amount of powder that is going to be discharged as industrial waste can be zero. Consequently, the cost of the operation can be reduced. When the high purity of the gypsum is regulated, some or all of the B2 powder may not be mixed with the plaster E.

Second Mode Next, the second embodiment of the present invention is explained with reference to Figure 2. In this embodiment, a powder addition element for spraying this powder in a position upstream of the absorption towers 12 and 13 , is installed, and a powder, such as limestone G, described above, which is obtained by spraying this limestone (CaC? 3) is sprayed into the flue gas A as a powder of the present invention by the powder addition element. Also, in this embodiment, the powdered charcoal powder 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 tank 26 for preparing the slurry and the pump 27 for the slurry, shown in Figure 1, are omitted, and the filtrate Fl is returned directly to the tank 11 of the absorption towers. The total amount of the limestone required for use as the absorbent in the absorption stage in the desulfurizing apparatus 10 and in the gypsum formation, is added to the flue gas as the aforementioned powder, so that the adsorbent is supplied. indirectly to the aqueous slurry within the tank 11 of the desulphurizing apparatus 10. In this case, the quantity of the limestone G required for use as the absorbent is basically in stoichiometric proportion to the amount of sulfur oxides present in the flue gas . When the flue gas A comprises a common combustion exhaust gas (e.g., flue gas produced from an oil fuel, 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 powder (D) present in the unit volume of the flue gas to the amount of SO3 (S) present in a unit volume of the flue gas, is equal to approximately 28. At both, in this modality, the effects, previously described, of the powder are positively and satisfactorily produced, so that a preventive measure can be achieved against the SO3 present in the flue gas or the construction of the eguipus, without recourse to the injection of the ammonia More specifically, even if the SO3 present in the flue gas condenses, the majority of this condensation occurs on the surfaces of particles of the powder (comprising the aforementioned limestone, 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 limestone has a relatively large particle diameter, of the order of 100 μm, therefore, they can be collected in the absorption towers 12 and 13 of the desulfurizing apparatus 10, with markedly high levels of collection, in comparison not only with the mists of sulfuric acid, conventionally found, but also with the ammonium sulfate powder, conventionally found. Therefore, little limestone remains in the resulting treated C-flue gas. The limestone collected in the absorption towers 12 and 13 is dissolved or suspended in the aqueous paste which circulates, and acts as the aforementioned absorbent (or alkaline agent) to neutralize the aqueous slurry and form the gypsum as a by-product. On the other hand, the sulfuric acid, which has condensed on the surfaces of the limestone and the like and has been collected together with the limestone and the like, finally suffers the neutralization reaction (3), previously described, with the stone limestone, for example, in tank 11 of the absorption towers, to supply a part of the gypsum formed as a by-product. Also, in this embodiment, therefore, the formation and corrosion due to SO3, are reliably impeded, and the same effects as the effects (1) to (7) described previously in relation to the first mode, occur. Also, in this embodiment, the total amount of limestone required for use in the absorption stage in the desulfurizing apparatus 10 is supplied as the aforementioned powder and the aqueous paste preparation tank and pump 27 of this paste aqueous, conventionally used, are omitted. Thus, this modality has a unique effect in that the further reduction in the cost of the equipment and the size of the equipment can be achieved. Third Mode The third embodiment of the present invention is explained with reference to Figure 3. This mode differs from the conventional flue gas treatment system of Figure 8, in which the injection step of ammonia is omitted and in which one element of powder addition (not shown) for spraying a powder, is installed in an upstream position of the heat recovery section 4 of the GGH and a stage for spraying a powder [eg, the powder contained in the exhaust gas of the combustion of the coal (i.e., so-called coal dust H)] within the flue gas A, using the aforementioned powder addition element, provided before the heat recovery step, using the recovery section 4 heat, mentioned above. The same effects as the effects (1) to (7), previously described in relation to the first modality, occur. In addition, the following effect (8) is also produced in this mode. (8) The arrangement and construction of the electrostatic precipitator 3 and other apparatus and the construction of the desulphurizing apparatus 10 can be exactly the same as in the conventional system illustrated in Figure 8, except for the element of adding the carbon powder H. Consequently, this embodiment has a unique effect in that the existing humer gas treatment system can be adapted very easily for the application of the present invention. Figure 6 shows the actual measured data illustrating the principle of the present invention (in particular, the addition of coal dust). These data indicate the relationship between the SO3 gas concentration at the GGH inlet (or the heat recovery section inlet) and the SO3 mist concentration at the GGH outlet (or the outlet of the GGH outlet). reheating) (ie, the degree of SO3 removal) when the concentration of the carbon powder in the flue gas is used as a parameter. In Figure 6, the solid data points show the data actually measured with which the deposition of the mists of sulfuric acid on the internal surfaces of the apparatus, such as section 4 heat recovery, was observed with the naked eye, while the open data points showed the data actually measured with which the deposition of mists of sulfuric acid was not observed. It can be seen from these data that about 90% of the SO3 was still removed at a D / S value of about 1.5, no deposit of SO3 mists on the equipment surfaces was observed, and the amount of SO3 mists that remain in the effluent flue gas was as small as about 10%. Therefore, it is obvious that, if the coal dust is added to the flue gas, for example, in such proportion that the D / S is not less than about 2, the mists of the SO3 will be almost completely removed and will hardly remain in The treated flue gas, and the corrosion or scale formation due to the deposit of mists, can be impeded with high reliability. Since the above-described fog removal effect of coal dust is a physical phenomenon in which SO3 is allowed to condense on the surfaces of the particles present in the flue gas, powders in addition to coal dust (e.g. powdered limestone) will produce similar effects.

FOURTH MODE Next, the fourth embodiment of the present invention is explained with reference to FIGURE 4. Basically, this embodiment is similar to the third embodiment in that the carbon powder is used as the powder of the invention and sprayed on a upstream position of the heat recovery section 4 of the GGH. However, this embodiment is characterized in that the dry electrostatic precipitator 3 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 precipitator electrostatic 3 is supplied after the heat recovery step, with the use of the mentioned heat recovery section 4, and before the absorption step using the desulphurization apparatus 10. Also in this embodiment, the carbon powder can be sprayed into the flue gas by pneumatic transport, or it can be sprayed in the form of an aqueous paste. Also, this embodiment is constructed in such a way that at least a part Bl of the powder collected in the powder collection stage, with the use of the electrostatic precipitator 3, is reused as a powder of the present invention, which is sprayed in a upstream position of heat recovery section 4. Specifically, in this case, part Bl of the powder collected in the electrostatic precipitator 3 is first fed to a powder silo 30, where the powder H of fresh coal is added there. Then, this powder is recycled using the powder addition element, previously described, to spray again in a position upstream of the heat recovery section 4. Therefore, in this embodiment, the powder sprayed in the upstream position of the heat recovery section 4 contains, in addition to the externally supplied carbon powder H, powder (eg fly ash) originally present in the flue gas A untreated, leaving the air heater 1. Also, in this embodiment, the remainder B2 of the powder collected in the dry electrostatic precipitator is homogeneously mixed with the gypsum E formed in the desulfurizing apparatus 10 as a by-product and discharged out of the system. In this embodiment, it is preferable that the total amount of the spray powder is the minimum amount required (for example, such an amount as to cause the D / S ratio, defined above, to have a value of about 2). Likewise, it is also preferred that the amount of recycled powder Bl be increased to its limit at which the sprayed powder has the ability to capture SO3 and the amounts of powder H of added fresh coal and the B2 powder discharged is decreased to its levels. minimum required. In this way, the amount of powder B2 mixed with the gypsum E, can be minimized to maintain the purity of the gypsum E at a high level and the amount of powder H of added fresh coal can be decreased to facilitate handling of the powder H of carbon. Also in this modality, the effects, previously described, of the powder are produced, positively and satisfactorily, in the same way as in the third modality, so that a preventive measure against the SO3 present in the flue gas, can be achieved with low cost and with a single operation or construction of equipment without resorting to the injection of ammonia. Also, the system of this embodiment represents the high performance system, previously described, in which the heat recovery section 4 is installed upstream of the electrostatic precipitator 3, so that the performance per unit capacity "of the electrostatic precipitator 3 Consequently, by using a small-sized electrostatic precipitator 3, the aggregate carbon powder H can be removed from the high-collection flue gas, and the dust 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 it remains poorly in the resulting treated C flue gas. Therefore, also in this embodiment, the formation of scale and corrosion due to SO3 are reliably prevented, for example, in section 4 of heat recovery of the GGH and the conduits placed downstream 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 modality, occur. Also, in this embodiment, the powder (comprising the coal dust H and others) used to capture the SO3 is recycled. This has a unique effect in that the amount of the powder H of fresh coal supplied can be decreased and, also, the amount of the powder B2 mixed with the plaster E can be minimized to maintain the purity of the plaster E at a high level. . Also, since powder B2 is mixed with gypsum R, the amount of dust discharged as industrial waste can be reduced to zero. This also contributes, for example, to a saving in the cost of the operation. Needless to say, if a plaster with a higher purity is desired, all or part of the powder B2 may not be mixed with this plaster E.

Fifth Modality Next, it is explained to fifth embodiment of the present invention with reference to Figure 5. This embodiment is similar to the third embodiment in which a powder addition element for spraying this powder is installed in a position upstream of the section 4 heat recovery of the GGH and, using this powder addition element, a powder prepared by pulverizing 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. Also in this embodiment, powdered 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 slurry preparation tangue 26 and the slurry pump 27, shown in Figure 8, are omitted and the Fl filtrate is returned directly to the tanga 11 of the absorption towers. The total amount of the limestone required for use as the absorbent in the absorption stage in the desulfurizing apparatus 10 and in the formation of the gypsum, is added to the flue gas as the aforementioned powder, in a position upstream of the section 4 of heat recovery, 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 limestone G required for use as the absorbent, is basically in a proportion stoichiometric to the amount of the sulfur oxides present in the flue gas. When the flue gas A comprises a common combustion exhaust gas (e.g., flue gas produced from an oil fuel, 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 powder (D) present in the unit volume of the flue gas to the amount of SO3 (S) present in a unit volume of the flue gas is equal to approximately 28. Therefore, , in this modality, the previously described effects of the dust are positively and satisfactorily produced, so that a preventive measure against the SO3 present in the flue gas can be achieved at low cost and with an operation or construction of the equipment. simple, 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, most of this condensation occurs in the surfaces of the dust particles. (which includes 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, which results in little production of noxious fumes (or mists of sulfuric acid). Likewise, the aggregate limestone has a large particle diameter, of the order of 100 μm and, therefore, can be collected in the absorption towers 12 and 13 of the desulphurizing apparatus 10, with a markedly high degree of collection, in comparison not only with the mists of sulfuric acid, conventionally found, but also with the ammonium sulfate powder, conventionally found. Accordingly, little limestone remains in the resulting treated C-flue 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 condensed on the surfaces of the limestone and the like, and has been collected together with the limestone and the like, finally undergoes the neutralization reaction (3), previously described, with the limestone , for example, in tank 11 of the absorption towers to supply part of the gypsum formed as a by-product. Also in this modality, therefore, the formation of scale 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 (7), previously described in relation to the first modality. Also, in this embodiment, the total amount of limestone required for use in the absorption step in the desulphurization apparatus 10 is supplied as the aforementioned powder and the aqueous paste preparation tank 26 used conventionally and the pump of the aqueous paste, are omitted. Thus, this modality has the unique effect that a further reduction in the cost of the equipment and the size of the equipment can be achieved. Figure 7 shows the measured data actually illustrating 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 removed by condensation on limestone particle surfaces when an aqueous slurry composed of powdered limestone and water (with a concentration of around 20 to 30% by weight) was simply sprayed into the flue gas containing about 3.7 to 11.5 ppm SO3 and a subsequent heat recovery of the flue gas was not performed. These data reveal that SO3 can be effectively removed simply by spraying an aqueous slurry of limestone into the flue gas. Accordingly, it can be seen that, in accordance with the principle of the present invention, in which the heat recovery is carried out after the addition of a powder in order to allow SO3 to condense positively, a high degree of SO3 removal can be achieved. achieve even at a low D / S value. It will be understood that the present invention is not limited to the modalities described above, since it can also be practiced in several other ways. For example, the powder of the present invention is not limited to limestone and coal dust, but any powder that allows SO3 to condense on the surfaces of the particles and can be collected in a common electrostatic precipitator can be used. or the absorption tower of a desulfurization apparatus. However, the aforementioned limestone and coal dust are conventionally known materials, which have been familiarly handled in the flue gas treatment systems, and 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 limestone to the absorption tower tank can be avoided. , as previously described. Also, in order to promote the condensation of SO3 on the surfaces of the powder particles, a powder (or its aqueous paste) having a lower temperature than that of the flue gas [eg, a powder (or its aqueous paste ) which has been forcedly cooled, as required] can be sprayed into the flue gas. This allows the SO3 to condense more effectively on the particle surfaces of the powder, so that the production of the harmful SO3 mists can be prevented more satisfactorily and more easily. Also, the powder of the present invention can comprise both limestone and coal dust, and can be added as a mixture or separately. Even when the limestone is used alone, it can be added in such a way that only its part, required to capture the SO3, is sprayed into the flue gas and the rest is supplied directly to the absorption tower of the desulfurizing apparatus as It is usual Also, in the first embodiment, instead of recycling the powder comprising a powder which has been collected in the electrostatic precipitator 3 as a powder of the present invention, all dust can be discharged as industrial waste as usual. Also, it is not necessary to say that the construction of the stage or the absorption tower, according to the invention, is not limited to the described modalities. For example, the absorption tower can be a single absorption tower and various types of towers (or gas-liquid contact apparatus) which include the packed tower, spray tower and bubble tower can be used. Furthermore, the present invention is not limited to the use of a calcium compound (eg, limestone) as the absorbent, but also a desulfurizing process using, for example, sodium hydroxide or magnesium hydroxide may be employed. Although the present invention produces particularly excellent effects when used for boiler flue gases which employ various oil fuels, such as heavy oil, oil emulsions, heavy oils VR and CWM. Similar effects can also be obtained when applied, for example, to boilers that burn coal / heavy oils. Even in boilers that exclusively burn coal, an oil fuel can be burned, for example, at the time of start-up or during test operations. The present invention can be effectively applied to such cases.

Claims (18)

1. A method for the treatment of flue gases, which contain at least SO2 and SO3, this process comprises a step of adding a particular powder and spraying this powder into the flue gas, and a subsequent stage of absorption , to bring this flue gas into a gas-liquid contact with an absorbent liquid in an absorption tower, and to remove at least the SO2 present in the flue gas by absorption within the absorbent fluid and collect said dust.

2. A process for the treatment of flue gases, which contain at least SO2 and SO3, this process comprises a step of adding a particular powder and spraying this powder into the flue gas, a subsequent stage of collection of powder, to introduce the flue gas into a dust collector and collect at least the determined powder present in the flue gas, and a subsequent absorption stage, to bring the flue gas into gas-liquid contact with a absorbent fluid in an absorption tower, and remove at least the SO2 present in the flue gas, by absorption within the absorbent fluid.

3. A process for the treatment of flue gases which contain at least SO2 and SO3, this process comprises a heat recovery step, to recover the heat from the flue gas by means of a heat exchanger and thus cool this flue gas, and a subsequent absorption step to bring the flue gas into gas-liquid contact with an absorbent fluid in an absorption tower, and remove at least the 502 present in the flue gas by absorption in the absorbent liquid, characterized in that a step of adding a particular powder is supplied to spray this powder, which can be collected in the absorption stage inside the flue gas, before of this stage of heat recovery.

4. A method for the treatment of flue gases, as claimed in claim 3, wherein the determined powder is sprayed in such a proportion so the weight ratio (D / S) of the amount of powder (D), containing said determined powder mentioned to the amount of the 503 (S), present in the flue gas, is not less than 2 (ie, D / S > 2).

5. A method for the treatment of flue gases, as claimed in any of claims 1 to 3, wherein in the step of adding the determined powder, the temperature of this powder is lower than the temperature of the flue gas.

6. A method for the treatment of flue gases, as claimed in any of claims 1 to 3, wherein the determined powder is sprayed into the flue gas in the form of an aqueous paste, prepared by suspending this powder in a liquid.

7. A method for the treatment of flue gases, as claimed in any of claims 1 or 2, in which the powder contained in the combustion exhaust gas of the coal is used as said determined powder.

8. A method for the treatment of flue gases, as claimed in claim 2, in which at least a part of the determined powder, which has been collected in the dust collection stage, is reused as the determined powder that is going to spray into the flue gas in the step of adding this determined powder.

9. A method for the treatment of flue gases, as claimed in claim 3, in which the powder contained in the combustion exhaust gas of the coal is used as said determined powder.

10. A method for the treatment of flue gases, as claimed in claim 9, wherein the powder collecting step for collecting the dust present in the flue gas by means of a dry electrostatic precipitator is provided after the heat recovery stage and before the absorption stage, and at least a part of the dust collected in the powder collection stage is reused as said determined powder.

11. A process for the treatment of flue gases, as claimed in claim 2 or 10, in which the absorption step is carried out according to the lime-plaster method, wherein an absorbent fluid, having limestone suspended therein as an absorbent, it is used to form the gypsum as a by-product, and at least a part of the dust collected in the powder precipitation stage is mixed with the gypsum formed as a by-product in the absorption stage and download outside the system.

12. A method for the treatment of flue gases, as claimed in any of claims 1 to 3, wherein the powdered limestone is used as said determined powder.

13. A method for the treatment of flue gases, as claimed in claim 12, in which the absorption step is carried out according to the lime-plaster method, wherein an absorbent fluid, having the limestone suspended therein, as an absorbent, it is used to form the gypsum as a by-product, and the total amount of the limestone required for use as the absorbent in the absorption stage is added to the flue gas as said determined powder, so that the absorber is indirectly supplied to the absorbent fluid.

14. A system for the treatment of flue gases, to treat a flue gas containing at least SO2 and SO3, this process comprises an absorption tower, to bring the flue gas into contact with gas-liguid with a absorbing fluid and removing at least S02 / - present in the flue gas, by absorption into the absorbent fluid, and a particular powder addition element, for spraying this powder into the flue gas, is provided upstream of the absorption tower.

15. A system for the treatment of flue gases, as claimed in claim 14, in which a dust collector, for collecting the determined powder in the flue gas, is provided in a position upstream of the absorption tower, and A particular powder addition element, for spraying this powder into the flue gas, is provided in an upstream position of the dust collector.

16. A system for the treatment of flue gases, as claimed in claim 15, wherein at least a part of the determined powder, which has been collected in the dust collector, is recycled as the powder determined to be sprayed into the flue gas by the addition element of this determined powder.

17. A system for the treatment of flue gas, as claimed in claim 14, wherein a heat exchanger, for recovering heat from the flue gas and thus cooling this flue gas, is provided in an upstream position of the absorption tower and downstream of the powder addition element determined.

18. A system for the treatment of flue gases, as claimed in claim 17, in which a dry electrostatic precipitator, for collecting the dust present in the flue gas containing said determined powder, is provided downstream of the heat exchanger and upstream of the absorption tower, and at least a part of the dust collected by the electrostatic precipitator is reused as said determined powder.