SI9520071A - Improved wet scrubbing method and apparatus for removing sulfur oxides from combustion effluents - Google Patents

Abstract

Sulfur oxides (SOx) are scrubbed from combustion effluents with aqueous limestone slurries single-loop, open-tower countercurrent limestone wet scrubbers. Effluent flow rates are greatly increased while L/G values and reaction tank (150) residence times are decreased. Improved entrainment eliminator design, nozzle (112) placement and spacing, and the use of a hydrocyclone (181) to separate and recycle smaller particles of limestone from the byproduct gypsum, facilitate these advantages. Limestone is reduced to very fine particles, e.g. about 8 mu or less with more than 99 % of the particle by weight less than 44 mu , and introduced into a scrubbing slurry which is contacted with SOx-laden effluent. Reactivity of the scrubbing slurry is maintained, even at reduced pH, by continuously operating a hydrocyclone to assure a molar ratio of calcium-containing to sulfur-containing compounds of greater than about 1.3 to 1 while keeping both a low chloride and low non-reactive solids content. The hydrocyclone removes large particles of calcium sulfate and provides a recycle stream (184) of fine calcium carbonate and non-reactive solids which is bled off as necessary to maintain both the desired low chloride and non-reactive solids levels.

Description

ABB ENVIRONMENTAL SYSTEMS

IMPROVED WET WASHING PROCEDURE AND SULFUR OXIDES DEVICE FROM COMBUSTION EXHAUST GASES

TECHNICAL FIELD

The present invention relates to improvements enabling the removal of sulfur oxides _(SOx) from flue gases with lower capital and operating costs.

The combustion of carbon-rich materials containing significant amounts of sulfur, including fossil fuels and waste, is regulated worldwide. The combustion of these materials produces free radicals of sulfur and oxygen, whose recombination at higher temperatures leads to the formation of various oxides, which is denoted by the common abbreviation SO _X. Legislation in force in many countries prescribes maximum amounts of sulfur oxides that can be released into the atmosphere to alleviate the problems associated with these. acid rainfall.

A number of techniques are available to limit the release of SO _X into the atmosphere. These include methods for the removal of sulfur from fuels before their combustion, methods that chemically bind sulfur during the combustion process itself, and methods by which the produced sulfur oxides from the resulting flue gases are removed. The latter include wet and dry rinse operations. Wet rinse technology is well-developed and known to be effective; however, this process requires very large processing devices, which are proportional to the overall cost.

Wet flushing SO _X removal technology is based on contacting the gaseous and liquid phases in various configurations. One of the most promising variants are single and double counter flow sprays and towers with counter flow and confluence sections.

A single circular, open tower using calcium carbonate that reacts with SO _X is the simplest to design and operate. These systems prove to be advantageous as they can operate with low pressure drop and show little tendency to deposit deposits and clog. However, the advantages resulting from their simplicity and high level of reliability are canceled out due to the size of the whole device. Because these spray towers do not have vents or fillings that can improve contact between the flue gas and the flushing solution, they are usually tall, and many spray nozzles are installed at several height levels to ensure good contact.

In open spray towers, the ability of the wash solution to absorb SO _X from gases depends on the alkalinity of the solution. Calcium carbonate is the best agent in wet flushing systems both in price and in efficiency to provide sufficient alkalinity. Unfortunately, the solubility of calcium carbonate tends to decrease with increasing alkalinity of the wash solution. Filler and partition columns enhance absorption by prolonging the retention of calcium carbonate in the zone in which gas and liquid contact, thereby providing conditions for better dissolution and, consequently, more efficient use of the rinse solution. On the other hand, open spray towers are quite high in order to provide as long a contact as possible, and are usually equipped with a number of spray nozzles located on several levels for the most efficient introduction of the wash solution into the tower.

The efficiency and economics of a single-cycle, open spray tower using a calcium carbonate wet flushing process to process SO _x- containing flue gas can be improved by reducing the tower size, providing a high level of reliability, reducing energy consumption and increasing flow of flue gas with simultaneous high reduction of SO _X.

A single-cycle, open-flush, wet-flush tower using calcium carbonate for the treatment of SO _x- containing flue gases would also be desirable to improve with greater reactivity of the flushing slurry, without, of course, any additional use of chemical additives.

BACKGROUND OF THE INVENTION

The design and operation of a limestone, countercurrent spray tower using limestone is described by Rader and Bakke in an article by Incorporating FullScale Experience into Advanced Limestone Wet FGD Designs

September 12, 1991 at IGCI * Forum, Washington, D.C. (* formerly Industrial Gas Cleaning Institute, now Institute of Clean Air Companies, Washington, DC). Open spray towers (such as without fillers, partitions or other accessories to ensure effective gas-liquid contact) are easy to dimension and provide a high level of reliability. They are especially useful in thermal power plants, where the release of chlorides can cause a number of problems, including reduced reactivity of the rinse solution and considerable corrosion of the interior of the rinse. An additional factor favoring the use of open spray towers is the low pressure loss and thus the favorable energy consumption of the blower.

So far, the use of very different reagents has been proposed, but the most preferred ones are those that are effective even without major additives and that can be purchased at low cost, stored and transported with minimal special measures. Calcium carbonate (commercially available in many forms, including limestone) is a material that meets these criteria. Proper handling translates into products that are easily deposited in the environment or sold as gypsum.

In a single-flow, counter-flow and open spray tower of the type described by Rader and Bakke, the calcium carbonate flushing suspension flows from the top down, while the flue gases containing SO _X flow from the bottom up. The authors summarize the chronological values of the individual parameters, including the gas velocity in the absorber (its minimum is 6 feet and the maximum is 15 feet per second or 2 to 5 m / s), finding that the velocity of the gas in the absorber has little effect on the liquid ratio and gas (L / G), i.e. the determining factor that determines investment and operating costs. The contact zone heights are not specified in these towers, and the characteristic values range from 6 to 15 m, which in chronological terms is an important factor in sizing an efficient system for eliminating at least 95 percent of SO _X from flue gases.

In conventional towers of this type, the ratio of slurry to gas (L / G) volume fluxes has been proven to be the only and most important parameter in the design of the device. L / G affects the cost of pumping, the costs associated with reservoirs, and other operational and economic factors. The cost of drawing limestone suspension increases in proportion to the height of the tower. It would be desirable to reduce the L / G ratio and height of the open spray tower.

Sulfur oxides (SO _X ), in principle SO2, are absorbed in the slurry and collected in a reaction vessel in which solid calcium sulfite and solid calcium sulfate are formed. The reaction vessel is purged with air to produce the desired sulfate. When the crystals reach a sufficient size, they are separated by the separation method from the rest of the contents of the reaction vessel.

In an article entitled The Bischoff Flue Gas Desulfurization Process (presented October 25-28, 1988 at the First Combined FGD and Dry SO ₂ Control Symposium, organized by EPA and EPRI),

KR Hegemann et al. describe a spray tower containing a loop with a hydrocyclone, the latter separating the slurry of gypsum from the wet rinse into a stream of coarse particles and into a stream of fine particles, introducing a stream of fine particles back into the spray tower. In U.S. Pat. No. 5,215,672 to Rogers et al. describe a process similar to that reported by Hegemann et al. in that it includes a hydrocyclone as the primary device for water removal. In this case, after separation of the fine particle stream from the coarse particle stream, including the gypsum, the water in the condensed stream of fine particles is discarded together with the particle of fine particles removed from the system. However, neither of these records indicates how the use of a hydrocyclone as a primary water removal device can contribute to improving the overall efficiency and economics of the process, reducing tower size, improving reagent utilization, providing high levels of reliability, reducing energy consumption and achieving high gaseous phase velocities at the same time as high SO _X reduction rates.

Removal of SO _X from the flue gas can also be done in filler columns. Rader and Bakke point out that these types of flushing devices show lower operating costs, but on the other hand, they have quite a few potential drawbacks. Fillers or other gas / liquid mixers can become clogged or corroded, leading to unacceptable circulation or pressure drop, resulting in long overhaul periods. Therefore, it would be useful to clean flue gases with such an open tower, which does not contain all the advantages of a filler tower, but does not contain them, and on the other hand, such a tower would be smaller than an open tower of conventional design.

Previous state of stroke does not reflect and does not imply a solution to achieve these improvements, the use of which would be in the removal of SO _X with an aqueous suspension of lime in a single-loop, open and countercurrent spray tower, even without the use of fillers and the related problems to achieve results which are comparable by running the process in filler columns.

In a one-cycle, counter-flow and open spray tower of the type described by Rader and Bakke, a flushing slurry containing calcium carbonate, calcium sulfate, calcium sulfite and other inert solids flows downwards, while the flue gases containing SO _X flow up. SO _X , mainly SO 2, is absorbed in a descaling rinse which is collected in a reaction vessel to form calcium sulphite and calcium sulphate. The reaction vessel is air-blown, favoring sulfate production. When the calcium sulfate crystals reach a sufficient size, they are separated by the separation method from the remaining contents of the reaction vessel. Soluble impurities such as chlorides are also removed. The construction and operation of these flushing towers is relatively economical, and the overall cost is highly dependent on the reactivity of the flushing slurry. It appears that with high concentrations of chlorides dissolved in the leaching slurry, the cost increases dramatically as calcium carbonate reactivity is significantly reduced.

The chloride content of the leaching slurry can be reduced by the additional discharge from the system. Usually it is carried out either in the reaction vessel or in the gypsum recovery process.

Downs et al., As described in U.S. Pat. 3,995,006, they pumped the slurry from the bottom of the absorbent, leading it to a hydrocyclone that separated the inflow into the stream, containing mainly fine particles of calcium sulfite, and into the stream, containing mainly relatively large particles of calcium carbonate. With the second separation of the flow with calcium sulfite, the concentrated stream of it is deposited in the surrounding area. In most cases, the discharge of large quantities of water regulates or controls the amount of accumulated chlorides in the system. However, the discharge of large quantities of water is undesirable both ecologically and economically.

Rogers et al. in U.S. Pat. No. 5,215,672 describes a process similar to that reported by Downs et al. In that it contains a hydrocyclone by which the unreacted calcium carbonate is separated from the resulting calcium salts formed by SO _x absorbed from the flue gases. After separating the stream containing fine solids from the stream containing mainly large gypsum particles, in this case water is discharged into the environment as an integral part of the concentrated stream of fine particles, together with at least a portion of fine solids. If a sufficient amount of water is removed from the system, then an additional discharge in this respect is sufficient to regulate the chloride content of the system, but a proportionally large amount of fine particles is thus eliminated from the process. Rogers et al. they propose to dispose of fine particles as waste. However, it will be apparent from the description of the present invention that the implementation of counter-strategies, despite the additional discharge of a portion of water to control the chloride content, may increase the reactivity in the system.

An article published by Rosenberg and Koch in July 1989 in the 93rd Bimonthly Report of the Stock Gas Emmissions Control Coordination Center Group describes, like Rogers et al., An FGD flue gas desulfurization process unit in the Netherlands in which hydrocyclone separates sludge gypsum from the wet wash tower into the stream containing coarse particles and into the stream containing fine particles, the latter being completely introduced back into the wash tower. With this mode of operation, the additional discharge is not carried out in the recirculation loop, but must be performed anywhere else in the system. The process diagram shown in Figure 2 of their article shows an attachment for additional discharge on the vacuum filter. By removing water from the system at this location, it is possible to control the chloride content, but this is achieved by larger amounts of water discharged than is necessary, since the water abstracted is diluted with the fresh water used to rinse the gypsum.

The prior art does not directly address the points necessary to achieve improvements could be associated with increased reactivity of the slurry in the removal of SO _X by a wet process in a single-loop, open and countercurrent spray tower.

DESCRIPTION OF THE INVENTION

The object of the invention is an improved process and apparatus for wet flushing of flue gases, especially those from solid fuel thermal power plants, for the purpose of removing sulfur oxides.

A further object of a preferred embodiment of the invention is improved singleloop, open-tower, countercurrent limestone wet scrubbers for removing _SOx.

It is a further object of the invention to allow a single circular and open spray tower to be operated with counterflow of limestone aqueous suspension at lower L / G values.

It is a further object of the invention to reduce the size of a single circular and open spray tower by countercurrent limestone aqueous suspension.

Another specific object of the invention is to increase the velocity of the flue gases through single-circular and open spray towers with the flow of limestone aqueous suspension.

It is a further object of the invention to improve the design and installation of inlet separators and water vapor removers in single and open spray columns with counterflow of limestone water suspension to effectively remove water droplets from flushed flue gases and to change their direction away from the spray tower ceiling.

It is a further object of the invention to improve the operation of single and open spray columns by countercurrent limestone aqueous suspension by shortening the retention time of gypsum crystals in the wash tower and separating them from small limestone particles in the hydrocyclone.

A further object of the preferred embodiment of the invention is to improve the operation of single and open spray towers with counterflow of limestone aqueous suspension by shortening the retention time of gypsum crystals in the wash tower and using a hydrocyclone to provide process control at a high stoichiometric ratio of calcium to sulfur, allowing utilization of calcium carbonate.

A further object of the preferred embodiment of the invention is to improve the efficiency of the process in single and open spray columns by countercurrent limestone aqueous suspension with effective contact between gas and liquid in a shorter flushing zone and using a smaller number of spray nozzle levels.

A further object of the preferred embodiment of the invention is to improve the operation of single and open spray towers with counterflow of limestone aqueous suspension by such arrangement of spray nozzles that allows reducing the amount of gas passing through the flushing zone without being purified and allowing effective contact between the gas and the liquid with a reduced number of nozzles.

It is a further object of a preferred embodiment of the invention to improve the operation of single and open spray columns with the flow of limestone aqueous suspension by maintaining high reactivity of the wash slurry, by better utilization of the limestone and by improving the efficiency of the process.

It is a further object of the invention to improve the operation of single and open spray columns with the flow of limestone aqueous suspension by providing an effective method of removing chloride from the leaching fluid.

The foregoing and other objects are defined by the invention, which enables the improvement of the process and the device for wet flushing, more specifically for flushing flue gases resulting from the combustion of sulfur-containing fuels such as coal and solid waste.

In one aspect, the invention improves the wet scrubbing process for reducing the concentration of _SOx (principally SO2) in flue gases, which takes place in the single-loop, open-tower, countercurrent limestone slurry. In the second, the present invention also enables the improvement of a device by which the improvements described above can be achieved; the device will be described in detail in the following description. In summary, the process comprises: (a) introducing a stream of flue gases containing SO _X into a vertical spray tower from the bottom up, with a velocity of the main mass of the gaseous phase greater than 4.5 and preferably less than 6 m / s; (b) introducing fine droplets of aqueous slurry of fine-grained calcium carbonate, calcium sulfate, calcium sulfite and other inert solids into the vertical portion of said tower, in contact with the gases in counter-flow, with an average mass particle size of calcium carbonate less than 6 pm, and in addition, it is 99% less than 44 [mu] m by weight, and the total molar ratio of calcium-containing to sulfur-containing compounds in the solid phase is at least from 1.1 to 1.2; (c) collecting the slurry in the reaction vessel after contact with the flue gas; (d) extracting the slurry from a reaction vessel in which its residence time is preferably equal to or less than eight hours; (e) removing water from a stream of slurry taken from a reaction vessel preferentially carried out in a hydrocyclone, forming a backflow in the upper part of the hydrocyclone containing fine particles of calcium carbonate and whose ratio of calcium-containing to sulfur-containing compounds is greater or equal to 1.3, and a stream containing calcium sulfate particles in the lower part of the hydrocyclone having an average mass size of 25 to 55 pm; (f) returning a large portion of the backflow containing calcium carbonate particles to the process; (g) the introduction of fresh calcium carbonate and other inert solids as a feed stream into the system in quantities sufficient to replace both calcium recovered from the system and not recirculated and dissolved and reacted with SO _X absorbed into the liquid phase in the spray column, with an average mass fraction of fine-grained calcium carbonate introduced into the system of less than 10 pm.

Preferably, the sludge is introduced with spray nozzles, the orientation of which alternately alternates in the downward and upward directions, and which are arranged at two height levels, which are 1 to 2 meters apart. It is also preferred that the overall height of the tower in the contact spray zone is less than 6 and preferably less than 4 meters, as the height has proven to be not so important for the effective elimination of 95% or more of SO _X from the flue gas. The advantage of the invention is that the diameter of the tower is relatively small so that the operating speed of the main mass of the gaseous phase passing vertically through the contact spray zone is greater than 4.5 and preferably less than 6 m / s, with the values given free cross-section of the tower, neglecting the surface occupied by the nozzles and their guides.

The increased velocity allows good suspension of the liquid in the tower without increasing the height of the tower, and also without the use of fillers or sludges to hold the slurry, making the suspended liquid more reactive due to the longer dissolution time of calcium carbonate. Hence the apparent advantage of the present invention, which is reflected in the prolongation of contact time without increasing the height of the tower, while maintaining the simplicity of design and construction, the method of operation and maintenance of the open spray tower.

In this preferred embodiment, the average particle size of the calcium carbonate in the reaction vessel ranges from 2 to 6 pm, and the average mass size of the fine-grained calcium carbonate particles introduced into the system is less than 8 pm, with a weight of at least 99 % (e.g. 99.5%) of less than 44 pm.

For all counter-flow and open spray, filler or compartmental towers, it is preferable that the mole gap between calcium-containing and sulfur-containing compounds is high in the solid phase of the washout slurry. High ratios provide the alkalinity needed to remove SO _X and improve the absorption capacity of the liquid. However, in the existing processes, high levels of depletion are not economical, since it would also lead to the excessive consumption and deposition of calcium-containing compounds, specifically calcium carbonate, in the removal of sulfur compounds and water from the system. The present invention makes it possible to operate a spray tower with a flushing slurry in which the concentration of solid calcium carbonate is significantly higher than that which is economical in other processes. Considering the operating conditions, the particle size and the gas-liquid contact, the hydrocyclone effectively increases the relative concentration of calcium available and the alkalinity in the container.

In a preferred embodiment, the spray tower comprises at least a first inlet separator, which removes significant amounts of moisture in the gases and allows the direction of flow of the gaseous phase to be changed by at least 30 ° relative to the vertical axis. Its preferred design allows the removal of most droplets less than 100 pm in diameter, by dropping off or combining them into larger droplets and eliminating them in the next separatoi. The inlet separator is preferentially used in combination with a vertical humidifier.

In a further aspect, the invention provides an improved wet process for reducing the concentration of SO _X in flue gases, comprising: (a) introducing a flue gas stream through the spray tower from the bottom up; (b) introducing fine droplets of aqueous suspension of fine-grained calcium carbonate particles, calcium sulfate, calcium sulfite and inert solids, the suspension passing through the column counterflowing with the gaseous phase flow, and the average mass fraction of calcium carbonate particles ranging from 2 to 6 pm; (c) collecting the slurry in the reaction vessel after contact with the flue gas;

(d) ensuring high reactivity of the slurry by pumping it from the reaction vessel and introducing it and treating it in a hydrocyclone, in which a back-flow containing mainly fine particles of calcium carbonate and inert substances is formed, and a flow containing mainly particles of calcium sulfates and both of these streams contain dissolved chlorides, removing solid calcium sulfate and a portion of the backflow containing calcium carbonate and inert substances from the system to remove soluble chlorides and inert solids; and (e) introducing fresh calcium carbonate into the system as a feed stream in quantities sufficient to replace both the calcium withdrawn from the process due to said separation of calcium sulphate and the one removed by said discharge of the backflow portion at keeping the average mass fraction of calcium carbonate introduced into the system less than 10 pm.

The process permits operation at such pH values that also improve reactivity. The pH of the slurry in the reaction vessel is preferably in the range of 5.0 to 6.3, more preferably in the range of 5.8 to 6.3.

It is desirable that the mole ratio of calcium-containing and sulfur-containing compounds in the backflow is greater than 1.3 and preferably higher than

1.4. It is also desirable that the concentration of suspended solids in the return stream is less than 15% and preferably lower than 5%. The process also preferably involves determining the chloride content of the slurry and releasing part of the backflow when the chloride content of the system exceeds the maximum allowable concentration. More preferably, the process also includes determining the particle density in the backflow and releasing a portion of the backflow when the solids content in the system exceeds the prescribed value. In this case, the content of inert solids is controlled.

In a further aspect, the present invention results in an improved device for wet flushing and reducing the concentration of SO _X in flue gases, comprising: (a) a spray tower with a gas phase inlet and outlet and a vertical flushing portion designed to allow passage flue gases containing SO _X from the bottom up through said flushing portion; (b) a network of spray nozzles installed in said flushing zone and designed to allow fine droplets of fine-grained calcium carbonate, calcium sulphate, calcium sulphite and inert solids to flow in and drop off through the tower with respect to the direction of flow of the gaseous phase ; (c) a reaction vessel mounted below said spray nozzle network to allow the sludge to be collected after contact with said flue gases in said vertical flushing zone, the size of said reaction vessel being such as to allow SO _X to react with calcium carbonate and to form gypsum crystals with an average particle size by mass of at least twice the size of the calcium carbonate particles introduced into the system;

(d) devices for the preparation of calcium carbonate fed to said reaction vessel, with an average particle size of less than 10 pm, with at least 99% of the particles being less than 44 pm; (e) a device for preparing a spray of a water slurry comprising at least one pump and associated tubes for pumping the slurry from the reaction vessel and supplying it to said spray nozzles located in the aforementioned flushing zone; (f) a slurry quality assurance system, including a hydrocyclone, separating said slurry in said reaction vessel and producing a stream containing small particles of calcium carbonate and inert substances, and a stream having relatively large calcium sulfate particles, a pump and associated slurry pumping tubes from a reaction vessel and its delivery to a hydrocyclone, a recycler used to transport a backflow rich in calcium carbonate particles and inert substances, from said hydrocyclone to said reaction vessel, a pipeline used to drain the flow of calcium sulfate particles from said hydrocyclone and for calcium sulphate recovery, and a discharge pipeline associated with said recycle and adapted to take away a portion of said return stream.

These improvements result in a tower that is about half as light and even twice as large in volume as existing open spray towers. The efficiency of the process is improved at the same time as its economics, the use of the reagent is improved, the high level of reliability is maintained, while the energy consumption is lower, as well as the higher gas phase velocity at the same time as the high SO _X reduction rate.

SHORT DESCRIPTION OF THE DRAWINGS

The present invention and the related advantages will be illustrated by a further detailed description, and will become even more apparent through the drawings, where:

Figure 1 is a schematic view of a preferred embodiment of the present invention, i.e. of a process for wet flushing of flue gases in a one-circle and open tower using limestone.

Figure 2 is a more detailed schematic view of a spray tower of the type shown in Figure 1.

Figure 3 is a plan view of the installation of spray nozzles at two height levels in the tower shown in Figure 2.

Figure 4 is a plan view of the installation of spray nozzles at two height levels in a spray tower of the type shown in Figure 2.

Figure 5 shows a view of the inlet separator in the spray tower shown in Figures 1 and 2.

INDUSTRIAL USE

The improvements associated with the present invention are particularly useful for the purification of flue gases formed in boilers using coal, and in some cases also effective for treating gases containing a high concentration of chlorides to be released. especially in incineration. While the advantages may be most pronounced with these devices, their usefulness is certainly not limited to the latter. With these improvements, flue gases from the combustion of materials can be effectively purified, including high carbon concentrations such as natural gas, synthesis gas, fuel oils, bitumen and residual fuel oils, industrial and household solid waste, other combustible substances, and similarly.

The following description relates to a preferred embodiment of the process shown in Figure 1 and includes a single-cycle, open and countercurrent SO _x wet flushing tower, mainly SO2, from limestone flue gases.

Limestone is a preferred form of calcium carbonate, which can be replaced with another source if desired. In addition to its appearance in the form of limestone, calcium carbonate is found in shells of shells such as aragonite, calcite, chalk, marble, marl and travertine. It can be obtained synthetically or by excavation. In the foregoing description, the terms calcium carbonate and limestone occur alternately.

It should be emphasized that all naturally occurring forms of calcium carbonate contain smaller amounts of relatively inert materials such as free silica, magnesium carbonate or dolomite, iron oxides, aluminum oxide, and so on. In principle, it is always desirable to find very pure sources of limestone used in the wet flue gas cleaning process, but as it turns out in practice, impurities are always present in the limestone, which represent inert substances in the process. Another source of inert solids entering the process are ash particles that do not leach out in the particulate collector 10 and then accumulate in the rinse tower 100.

The limestone is finely ground, preferentially by grinding in the manner presented below, to achieve an average mass size of less than 10 pm with 99% of particles smaller than 44 μπι. The ground limestone thus forms very fine particles for wet rinsing in an open column with the flow of calcium carbonate aqueous suspension. A typical average particle size in the prior art is less than or equal to 15 pm, with only about 95% of the particles being less than 44 pm. In contrast to the prior art, it should be noted that the use of the present invention results in an average particle mass less than 8 µm, with a particle size less than 44 µm relative to the mass (e.g. 99.5%). The use of a screen with a preferential aperture size thus provides several advantages.

The process flow chart in Figure 1 shows the flue gas from a boiler in which coal is used as a fuel entering the priming device 10 for removing particulate matter, such as e.g. an electrostatic or bag filter to remove a certain proportion of particles in the gas. The purified gases then enter the flushing tower 100 through the pipeline 20, through which they flow in a bottom-up direction, or countercurrent with respect to the flow of fine droplets of fine-grained limestone, which are introduced into the system in a vertical flushing zone 110 from spray nozzles located at two altitude levels. The gaseous phase proceeds from the flushing zone 110 to the drain 120. The tower is designed so that the gaseous phase passes through the vertical flushing zone from the bottom up. The sludge slurry passing through the vertical flushing zone 110 is collected in reaction vessel 130. Reaction vessel 130 is of a size that permits the reaction of SO ₂ with calcium carbonate and the formation of such gypsum crystals, the average mass size of which is at least twice, and preferably 5 up to 10 times larger than the calcium carbonate particles introduced into the system.

The preferred embodiment of the wet process allows the aforementioned particle size difference, which is conditioned by drawing a stream of slurry from a reaction vessel in which its average residence time is about 6 hours, and by concentrating it with calcium carbonate particles (as fine particles whose mass average diameter is less than 6 pm) and with plaster removal.

In the vertical flushing zone 110, a network of spraying devices is installed. It is designed to allow the flow of fine droplets of fine-grained calcium carbonate through a tower in counterflow with respect to the direction of flow of the gaseous phase. The figure illustrates a series of spray nozzles mounted at levels 112 and 112 '. Each of the nozzles 114 (see Figure 2) is powered by guides 116, 116 'or 116'. Usually, a series of spray nozzles is installed in the spray tower at the third height level, which allows the remaining series of nozzles to be repaired or cleaned during smooth operation of the nozzles at two arbitrary height levels.

The nozzles are preferentially positioned such that the distance between the two height levels of the spray nozzles is from 1 to 2 meters, whereby the direction of flow is densified from the adjacent nozzles at the individual level alternatingly in upward and downward directions. A preferred embodiment of the invention reduces the distance between the nozzles, reduces the number of levels in operation at any time (preferably two), and increases the velocity of the gaseous phase passing vertically through the vertical flushing zone. The preferred flow profiles of the slurry, which is in the form of fine droplets, and the flue gases passing through the tower from the bottom up, are illustrated in Figure 4.

A preferred nozzle design is the centrifugal nozzle type, which produces a stream of very small droplets with an angle a ranging from 90 to about 140 °, preferably up to 120 °. One suitable nozzle is the Whirljet nozzle with a flow rate of 1134 liters per minute, manufactured by Spraying Systems Co., Wheaton, Illinois. The droplet size preferably ranges from 100 to 6000 pm, usually around 2000 pm, with these values representing Sauter's average diameter as measured by a Malve particle analyzer.

Each of the guides 116 is positioned at a certain angle relative to the other guides at the higher or lower level. In the presence of two or three altitude levels, it is preferably about 90 °.

One of the novelties and advantages of the present invention is the reduction of the residence time in the reaction vessel from 15 hours or more, as characteristic values in existing commercial installations, to 8 hours or less, more specifically to a residence time of about 6 hours. This is made possible by the increased rate of dissolution of fine calcium carbonate particles and partly by the relatively rapid production and crystallization of calcium sulfate. The sludge reactivity, on the other hand, is improved by separating calcium sulphate from calcium carbonate and recycling fine particles of calcium carbonate into the sludge contained in the reaction vessel, and by rapidly dissolving it. Reducing the holding time in the reaction vessel has a positive effect on the overall efficiency of the process, in addition to a number of advantages such as ease of process management, equipment size and quality of the by-product gypsum.

The velocity of the main mass of the gaseous phase when passing through the vertical flushing zone 110 is higher than 4.5 and preferably lower than 6 m / s. This velocity is high in a single-cycle, open spray tower with wet flushing and limestone use, and is preferably applied in combination with other innovations that allow for improved overall process efficiency. The improved spray towers of the present invention allow the purification of flue gases with a low pressure drop and with relatively smaller amounts of aqueous suspension, e.g. with lower L / G ratios.

The sulfur oxides in the flue gas are absorbed in the aqueous phase of the slurry, producing bisulfite and hydrogen ions. Bisulphite ions are partially oxidized to sulphate, producing more hydrogen ions. As the droplet becomes saturated with hydrogen ions, calcium carbonate begins to dissolve faster, leading to the formation of calcium and bicarbonate ions. The finely ground calcium carbonate is very effective for absorbing hydrogen ions, thereby improving the absorption capacity of the aqueous phase in the vertical flushing zone. The high velocities of the gaseous phase, in line with other improvements to the preferred embodiment, and the established current profile maintain good droplet suspension with a high degree of fluidization, thus allowing effective contact.

Figure 1 shows limestone milling in mill 170, cyclone-assisted classification

172, storage in the silo 174 and its introduction through an air barrier 176 into the compressed air stream in pipeline 178. By grinding the limestone just prior to its introduction into the spray tower or reaction vessel to replace the amount of calcium carbonate consumed, it is possible to achieve a defined and reproducible particle size distribution while avoiding particles larger than 44 pm. In fact, the average mass particle size of calcium carbonate after routine dry milling is 8 pm, with 99% of the particles being less than 44 pm. The absence of large limestone particles in the feed stream being introduced into the reaction vessel represents one of the essential advantages of the present invention, since it allows the reaction vessel to be significantly smaller compared to those previously used in conventional spray towers.

The introduction of air through pipeline 178 allows the supply of oxygen necessary for the oxidation of sulfite and bisulfite ions into sulfate ions. In the reaction vessel, the mixing of its contents is established by conventional means, which are not shown.

As also illustrated by the process scheme in Figure 1, the slurry is drawn from the reaction vessel 130 in order to concentrate the reactive calcium carbonate to be recirculated and to reduce the concentration of solids, which is mainly achieved by removing gypsum. Figure 1 also shows that the slurry is drawn from reaction vessel 130 via pipeline 183 to hydrocyclone 181. It is very effective in the process scheme of the present invention, as it quickly and effectively separates very fine limestone particles from larger calcium sulfate particles. The preferred average mass particle size of calcium sulfate ranges from 25 to 55 pm. Separation of smaller limestone particles produces a backflow 174 dominated by calcium carbonate and a waste stream 176 dominated by calcium sulfate. Preferably, the average mass particle size of the calcium carbonate in the reaction vessel and thus in the backflow 184 ranges from 2 to 6 pm.

Figure 1 illustrates a preferred embodiment of the present invention in which the backflow is concentrated by calcium carbonate particles and the use of hydrocyclone 181 also allows recirculation of process water. Preferred average mass sizes of calcium carbonate particles are in the range of 2 to 6 pm. The average mass particle size of calcium sulfate ranges from 25 to 55 pm.

The reaction vessel 130 is located below the nozzle network and thus allows the sludge to be collected after contacting it with flue gases in the vertical flushing zone 110. The size of the reaction vessel 130 is such as to allow SO ₂ to react with calcium carbonate and to form gypsum crystals whose average mass size it is at least twice, and preferably 5 to 10 times larger than the calcium carbonate particles introduced into the process.

Due to the difference in particle size between calcium carbonate and gypsum, and by other means that enable gypsum separation and calcium carbonate concentration, as will be explained below, the concentration of calcium carbonate solids in comparison with counter current systems is increased by 20 to 50%. A further advantage of the present invention over the prior art systems is the higher stoichiometric ratio of calcium-containing and sulfur-containing compounds in the slurry of at least 1.3 and preferably 1.4 or more. This system includes at least one pump 182 and associated pipeline 183 for pumping the slurry from the reaction vessel and introducing it into the hydrocyclone.

The sulfur oxides in the flue gas are absorbed into the aqueous phase of the slurry in the vertical flushing zone 110 and react with the available hydroxyl ions, forming bisulfite ions that can be partially oxidized to the sulfate already in the vertical flushing zone 110 itself, and almost complete oxidation takes place. in the reaction vessel 130. Sufficient alkalinity is mainly provided by the dissolution of calcium carbonate to produce bicarbonate and hydroxyl ions, and this process takes place both in the flushing zone 110 and in the reaction vessel 130. Oxygen purging, which is a conventional operation in the art is used for the purpose of sufficient mass conversion of sulfite ions, although the source of oxygen is partly represented by the flue gases themselves in the vertical flushing zone 110. The reaction partly proceeds in droplets, and mainly in the reaction vessel 130 in which the slurry is collected. One of the novelties and major advantages of the present invention is the reduction of the residence time in the reaction vessel from 15 hours, which is a characteristic value for existing commercial systems, to 6 hours. Reducing the holding time in the reaction vessel offers more benefits, including ease of operation, the size of process equipment and better quality of the by-product gypsum.

The pH of the slurry in reaction vessel 130 preferably ranges from 5.0 to 6.3, more preferably in the range of 5.8 to 6.3. Higher pH values provide a higher degree of alkalinity in the aqueous phase of the slurry, and thus a higher capacity of the aqueous phase to absorb SO ₂ . The invention also has the advantage that calcium carbonate is introduced into the system in the form of fine particles and, as will be explained later, also recirculated in the form of fine particles, thus providing a higher degree of alkalinity. Low PH values, which are generally used by prior art systems, otherwise accelerate the rate of dissolution of calcium carbonate, but on the other hand, due to the lower alkalinity, inhibit the absorption of SO ₂ in the wash zone. The use of the small particle size of the present invention allows for a higher degree of alkalinity even at pH values lower than desirable, thereby largely eliminating the effect of pH on the sludge absorption capacity.

Together with the reaction vessel 130 and the network of spray nozzles housed in the vertical flushing zone 110, slurry means including at least one pump 122 and associated piping 124 are used, and are used to draw slurry from reaction vessel 110 and supply these into the nozzle network in the flushing zone.

Figure 1 shows grinding of limestone at mill 170, classification by cyclone 172, storage in silo 174 and introduction through compressed air 176 into the compressed air stream in pipeline 178, which is connected directly to the spray tower 100 or to the flue gas pipeline 20. Alternatively, the limestone from silo 174 may be mixed in the vessel and pumped into the reaction vessel 130. By grinding the limestone just prior to its introduction into the process, it is possible to control very precisely the particle size of the ground material. Particle size is a critical parameter of the present invention. Preferably, the average mass particle size of the calcium carbonate introduced into the system to replace that calcium carbonate that has reacted with soluble chlorides or SO _X in the gypsum, as will be explained later, is 8 pm or less, wherein 99% or more of particles less than 44 pm.

The introduction of air through pipeline 178 allows the supply of oxygen necessary for the oxidation of calcium sulfite to calcium sulfate. In the reaction vessel, the mixing of its contents is established by conventional means, which are not shown.

Together with the reaction vessel 130, the system under code 180 is used to ensure the appropriate slurry quality. In order to maintain the high reactivity of the system, calcium carbonate, as described above, is supplied in the form of finely ground particles, and the use of hydrocyclone 181 permits separation of the slurry stream exhausted from the reaction vessel. 130, in a return stream containing mainly calcium carbonate particles and a waste stream containing gypsum particles. Hydrocyclone 181 separates the slurry from the reaction vessel into a backflow 184 containing mainly small particles of calcium carbonate and inert substances, and a stream containing mainly relatively large particles of calcium sulfate. Preferably, the average particle size of calcium carbonate and inert matter ranges from 1 to 8 μιη, and more preferably from 2 to about 6 pm. The average mass particle size of calcium sulfate ranges from 25 to 55 pm. The preferred average mass particle size of calcium sulfate is at least twice, and more preferably 5 to 10 times the size of the calcium carbonate particles. The system comprises at least one pump 182 and associated pipeline 183 for pumping the slurry from the reaction vessel and supplying it to the hydrocyclone.

The recirculation pipeline 184 extends from the hydrocyclone 181 to the reaction vessel 130 and serves to transport a backflow containing mainly calcium carbonate particles from the hydrocyclone. An important component of the system is the discharge of a part of the return stream from the recirculation pipeline 184. The discharge pipeline 185 is connected to the recirculation pipeline 184 and is adapted for the discharge of a part of the return stream from the recirculation line. It is preferable to monitor the concentration of chlorides dissolved in the slurry in pipeline 183 or anywhere else in the system and to regulate the discharge of part of the backflow from pipeline 185 so that the chloride content of the slurry moves within the prescribed range, e.g. below 30,000 mg / l, and preferably below 20,000 mg / l. Higher concentrations of chlorides inhibit the dissolution of calcium carbonate and lower the alkalinity of the leaching slurry. In stream 185, the concentration of chlorides is highest and equal to the concentration of them in the reaction vessel, so that the sampling point shown in the figure represents the best location for the release of chlorides from the system.

It may well be that inert substances in reaction vessel 130 entering the system with fresh calcium carbonate or flue gases in the inlet 20 and in the form of relatively small particles, the average mass size of which is from 4 to 12 pm, accumulate in 184, and their concentration in the reaction vessel 130 increases. Monitoring of the concentration of inert particles in the return stream can be carried out in a chemical manner (ie by analysis of characteristic spices, eg silica, iron or others) or in a physical manner ( i.e., by determining the particle size distribution, by analyzing the total concentration of particulate matter, or by some other appropriate method). An important advantage of the present invention is that by adjusting the appropriate discharge flow 185, it is possible to adjust the concentration of chlorides, to control the concentration of inert solids in the reaction vessel, or to simultaneously control both parameters. Preferably, this control is performed by increasing or decreasing the volume flow rate 185 so that the chloride and inert particle contents are within the prescribed limits. Preferably, the concentration of inert solids in the reaction vessel 130 is less than 20% by weight and preferably lower than 15% of all solids.

The particulates thus removed from the reaction vessel via pipeline 185 may be discarded together with the discharged aqueous phase, separated or treated otherwise, and thus made suitable for deposition or potential use. It is also possible to appropriately process the aqueous phase of discharge from the system, making it suitable for deposition in the environment or for any other use. The purpose of the present invention is not to limit in any way the potential methods of treating current 185, but merely to emphasize that there are numerous methods by which said current can be properly treated, e.g. separated into fractions, completely or partially recycled, and so on. A more detailed description of methods and means for treating stream 185 goes beyond the purpose of the present invention.

The process scheme of the present invention also includes a recovery slurry 186 for sludge containing calcium sulfate slurry, said pipeline serving to drain the slurry of calcium sulfate from a hydrocyclone in which calcium sulfate particles present are larger than calcium carbonate particles.

Figure 1 shows a preferred embodiment of the invention, where the backflow 184 is introduced back into the reaction vessel 130. According to the invention, such a mode of operation is an advantage, which is expressed in the drastic increase in the alkalinity of the aqueous suspension droplets coming into contact with the flue gases containing SO _X . The direct use of a hydrocyclone backflow containing a high concentration of fine calcium carbonate particles has a high pH value and a high stoichiometric ratio of calcium to sulfur, allowing the treatment of flue gases containing sulfur oxides in very short contact times.

The stoichiometric ratio of calcium-containing and sulfur-containing compounds in backflow 184 preferably ranges from 1.2 to 2.0, more preferably 1.3 to 1.4. The concentration of suspended solids in the backflow generally ranges from 1 to 10 weight percent, preferably from 2 to 6%. Separation of most of the calcium sulfate from the limestone by hydrocyclone 182, in addition to increasing said stoichiometric ratio and alkalinity, also reduces the concentration of particulate matter in the slurry.

One of the advantages associated with the combination of techniques used in the process of the present invention is the high stoichiometric ratio of calcium-containing and sulfur-containing compounds in the reaction vessel, which ranges from 1.1 to 1.6, preferably from 1.2 to 1.3. This property of the process, while using very small amounts of calcium carbonate, enables better overall process efficiency and more economical use of equipment and reagents.

The concentration of particulate matter in stream 183 flowing from reaction vessel 130 is in the range of 10 to 20%, preferably between 13 and 17%. The concentration of particulate matter in stream 186 preferentially ranges from 30 to 55%. Stream 186 is introduced to the filter 188 or other suitable device that allows sludge drainage. Solid gypsum is of high quality and can be used as a construction material. The filtrate is discharged by pipeline 189 and can be recirculated into the reaction vessel 130 and may be partially or completely discarded, the advantage of the invention being that it is not necessary to discharge it to control the chloride content of the system.

The inlet separator 140 effectively removes water droplets from the purified flue gases and changes the direction of the gas phase flow. The high velocities of the gaseous phase enabled by the present invention could cause abrasion of the spray tower ceiling 102 and commercial design humidifiers. It is not possible to use a more efficient humidifier instead of an inlet separator 140 because there is no high-efficiency humidifier available at a gas phase phase of 4.5 to 6 m / s, and commercially available systems are prone to slow drainage and watering, thus increasing the risk of clogging and low reliability. Therefore, the inlet separator 140 is designed for the specific operating conditions dictated by the present invention.

The inlet separator 140 preferably removes a significant amount of inlet moisture and changes the direction of the flue gas flow by at least 30 ° relative to the vertical axis of the tower and provides a more uniform velocity profile of the gaseous phase when passing through a vertical humidifier 150. In its preferred embodiment, most (by weight) ) droplets with diameters below 100 µm are eliminated by dripping or combining them into larger droplets, which are subsequently eliminated from the gaseous phase in the next moisture stripper.

The inlet separator 140 is preferentially followed by a vertical humidifier, indicated in figure 150. The flow direction of the gaseous phase changes almost vertically from the vertical separator to almost completely horizontal. This has a number of advantages, including the reduction of particle collisions in the slurry to the ceiling 102 of the spray tower, thereby also preventing the formation of deposits that would otherwise increase over time to scale in larger pieces whose the diameter would be a meter or more, thus damaging the nozzle guides, falling into the reaction vessel 130 and finally clogging the nozzles at elevation levels 112 and 112 '. In addition, the inlet separator 140 also provides a very efficient operation of the vertical humidifier 150 with a nearly horizontal gas phase flow. The highly efficient horizontal gas flow stripper 150 allows for good drainage and thus the operation of the process at higher speeds than would otherwise be permitted by a similarly designed vertical gas stream stripper. It also allows for the convincing removal of very small droplets of moisture in the horizontal flow of the gaseous phase. The high degree of moisture removal is an important feature of the present invention, although not necessarily the original one, since the horizontal gas flow phase humidifiers are often used in FGD systems and other industrial processes that require highly efficient moisture removal. However, the originality of the present invention is that the combination of an inlet separator 140 with a high-efficiency humidifier 150 while providing a relatively uniform velocity profile in the humidifier and by combining very small droplets into larger ones in the inlet separator prior to their final elimination from the gaseous phase in the humidifier allows for superior purging of flue gas.

Figure 5 shows a preferred embodiment of an improved inlet separator 140 that effectively removes most of the smaller droplets (those whose diameter is less than 100 pm) and changes the direction of vertical flue gas flow away from the upper walls of the tower. The inlet separator 140 is also illustrated in Figure 2, where it is positioned at an angle γ relative to the horizontal of the spray tower 100. This angle is preferably located in the range of 10 to 45 °, e.g. 20 °.

The single-pass inlet separator 140 consists of separating wings 142 which secrete droplets by means of collisions and change the direction of the gas flow in such a way that it is best suited for the further removal of vapors. The individual wings 142 are positioned at an angle δ with respect to the lower edge of the wing assembly 144, 144 ', 144 ”, etc.. The wings of this type are parallelogram shapes with lengths from 0.15 to 0.23 meters in the shorter dimension and from 0.6 to 1.5 meters in the longer dimension. The distance between the individual wings varies from 40 to 70% of the shorter wing dimension. Preferably, the angle δ ranges from 20 to 40 °, but the more accurate value depends on the angle δ and the desired rate of change in the direction of the flue gas flow.

Wing assemblies 144, etc., are designed and installed to allow efficient drainage. The individual assembly is, as shown, designed in the form of clips. The assemblies 144, etc., are preferably oriented in the mutual arrangement at an angle Θ which typically ranges from 125 to 145 ° and preferably around 140 °. The construction of the inlet separatoy is supported by traverses 146 whose length is equal to the length of the wing assembly. Other modes of support are also available.

The structure of the inlet separator 140 permits the direct cleaning of the wings by means of fixed conduits 147, which have spray nozzles 148 which direct jet-shaped water directly to the wings from the bottom as well as from the top, in the form of jets of tiny droplets. The flushing of the wings is performed by the individual use of a particular line or by the sequential operation thereof together with others. Washable water of adequate quality is supplied in sufficient quantities to reduce the proportion of salt deposited on the wings of the separatoi. The use of high quality rinsing water and frequent cleaning while draining well, provided by the construction of batch blades 144, etc., in the form of cups, allow the separatoy to operate with virtually no deposit formation.

Another advantage of the present invention is that the separation efficiency of the first inlet separator 140 may be lower compared to the multiple passage separators used in the prior art, since its ability to change the direction of flow of the gaseous phase from vertical to horizontal the use of a high-performance, vertical humidifier 150. Although the efficiency of the inlet separator is lower than that desired in wet flushing towers, it causes a small pressure drop, e.g. lower than 3.8 mm water column, but also has other advantages such as ease of cleaning, high drainage rate, ability to operate at high gas phase velocities, and directing the gas phase flow in the direction of the high performance 150 vapor remover and away from the upper walls of the tower . The humidifier 150 is preferably composed of wings arranged e.g. in a zig-zag sequence.

The cleaned and dried flue gases are discharged into the atmosphere through the chimney 160. Alternatively, the flue gases may also be heated in the vertical configuration gas exchanger described in U.S. Pat. No. 08 / 257,158 (patent agent number 1930-P0020) filed by the authors of the patent submitted on 9 June 1994.

The combination of enhancements of the present invention enables the construction of a single circular, wet-rinse spray tower, wherein the weight of the empty tower is only about half that of the existing, open spray towers. The difference in the size of the process equipment and the improved SO _X absorption capacity of the sludge, conditioned by its properties, compared to conventional systems, allow for an improvement of the overall process efficiency by about 30% or more. The overall process efficiency is calculated on the basis of the amount of money required to remove the SO _X unit from the untreated flue gas, thus covering investment and operating costs.

The foregoing interpretation is intended to teach the average practitioner how to apply the teachings of the present invention in practice, but is not intended to explain all possible modifications and variations that will become apparent to the skilled person after reading the explanation. However, all such obvious modifications and variations are intended to be included within the scope of the invention as defined by the following claims. They are designed to cover all the elements and stages to which we refer, in any arrangement or sequence, and which effectively lead to the intended goal, unless otherwise stated in the text.

Claims (32)

PATENT APPLICATIONS 1. A process for reducing the SO _X content of a flue gas by a wet process in a single-cycle, open spray tower with the flow of limestone aqueous suspension, characterized in that it comprises: (a) passing a stream of flue gases containing SO _X through a vertical spray tower from the bottom up, with a velocity of the main mass of the gaseous phase exceeding 4.5 m / s; (b) introducing fine droplets of aqueous suspension of fine-grained calcium carbonate, calcium sulfate and inert solids into the vertical portion of the spray tower, the droplets of the aqueous suspension passing through the spray tower counter-flowing and contacting the flue gases; (c) collecting the aqueous suspension in the reaction vessel after contact with the flue gas; (d) withdrawing the slurry from the reaction vessel; (e) treating the slurry exhausted from the reaction vessel by an effective method of providing backflow, comprising in particular calcium carbonate particles, and an additional stream containing calcium sulfate particles; (f) returning a significant proportion of the calcium carbonate containing backflow to the process; and (g) introducing fresh calcium carbonate as a feed stream in such quantities as to replace both non-recirculating calcium and one which reacts in the flushing zone with the SO _X absorbed in the liquid phase. Method according to claim 1, characterized in that the average size of the very fine calcium carbonate particles in the feed stream of the aqueous suspension is less than or equal to 8 pm. Method according to claim 1, characterized in that the pH value of the feed stream of the aqueous suspension is in the range of 5.0 to 6.3. Method according to claim 1, characterized in that the velocity of the main mass of the gaseous phase through the spray tower is up to 6 m / s. Method according to claim 1, characterized in that a single-pass inlet separator is located in the spray tower, which effectively removes water droplets and changes the direction of the flue gas stream so as to enable the vertically mounted water vapor remover to operate effectively. Method according to claim 5, characterized in that a vertically mounted water vapor remover and inlet separator are housed in the spray tower, the latter changing the direction of the flue gas flow relative to the vertical by at least 30 °. Method according to claim 1, characterized in that the slurry, exhausted from the reaction vessel, is introduced into a hydrocyclone producing a backflow whose molar separation between calcium-containing and sulfur-containing compounds is greater than 1.3 and contains in particular fine particles calcium carbonate with an average mass up to 6 pm and a sludge stream containing mainly relatively large calcium sulfite particles with an average size between 25 and 55 pm. A method according to claim 1, characterized in that the average residence time of the aqueous suspension in the reaction vessel is less than 8 hours. 9. A process according to claim 1, characterized in that a part of the back-flow slurry is introduced into the reaction vessel with a concentration of solids below 10% and a molar ratio of calcium-containing and sulfur-containing compounds of at least 1.3. A process according to claim 9, characterized in that the mole ratio of the calcium-containing and sulfur-containing compounds in the return stream is greater than 1.4. Process according to claim 9, characterized in that the backflow contains less than 5% suspended solids. A method according to claim 1, characterized in that the aqueous slurry of limestone is introduced by spray nozzles arranged at two altitudes at a distance of less than two meters, wherein the direction of the flow of the aqueous suspension from adjacent nozzles alternately changes up and down directions. Method according to claim 1, characterized in that the average particle size of the calcium carbonate in the reaction vessel is from 2 to 6 pm, and the average mass particle size of the introduced calcium carbonate is less than 8 pm, with 99% by weight particles smaller than 44 pm. A process according to claim 1, characterized in that the pH of the slurry in the reaction vessel is in the range of 5.8 to 6.3. 15. A process for reducing the SO _X content of a flue gas by a wet process in a single-cycle, open column with the flow of limestone aqueous suspension, characterized in that it comprises: (a) passing a stream of flue gases containing SO _X through a vertical spray tower from the bottom up, with a velocity of the main mass of the gaseous phase ranging from 4.5 to 6 m / s; (b) introducing fine droplets of aqueous suspension of fine-grained calcium carbonate, calcium sulphate and inert solids into the vertical portion of the spray tower, contacting the droplets of the aqueous suspension in counter-current with flue gases; (c) collecting the aqueous suspension in the reaction vessel after contact with the flue gas; (d) withdrawing the slurry from a reaction vessel in which the slurry averages less than 8 hours; (e) treating the slurry exhausted from the reaction vessel by an effective method of providing backflow containing calcium carbonate particles and an additional stream containing calcium sulfate particles; (f) returning a significant proportion of the calcium carbonate containing backflow to the process; and (g) introducing fresh calcium carbonate as feed stream in such quantities as to replace both non-recirculating calcium carbonate and reacting in the flushing zone with SO _X absorbed in the liquid phase, with an average mass Calcium carbonate particle size in the feed stream less than 10 pm. 16. The method of claim 15, wherein the pH value of the feed stream of the aqueous suspension is in the range of 5.0 to 6.3. Process according to claim 16, characterized in that the pH of the slurry in the reaction vessel is in the range of 5.8 to 6.3. 18. A method according to claim 15, characterized in that there is a single-pass inlet separator in the spray tower that effectively removes water droplets and changes the direction of the flue gas stream so as to allow the vertically mounted water vapor remover to operate effectively. A method according to claim 18, characterized in that a vertically mounted water vapor remover and inlet separator are housed in the spray tower, the latter changing the direction of the flue gas flow relative to the vertical by at least 30 °. 20. The method according to claim 15, characterized in that the slurry, exhausted from the reaction vessel, is introduced into a hydrocyclone producing a backflow whose molar separation between calcium-containing and sulfur-containing compounds is greater than 1.3 and contains in particular fine particles calcium carbonate with an average mass up to 8 pm, and a sludge stream containing mainly relatively large calcium sulfite particles with an average size between 25 and 55 pm. 21. A process according to claim 20, characterized in that a portion of the backwater slurry with a molar ratio of calcium-containing and sulfur-containing compounds of at least 1.3 is introduced into the reaction vessel. Process according to claim 21, characterized in that the molar ratio of calcium-containing and sulfur-containing compounds in the return stream is greater than 1.4, and the return stream contains less than 5% suspended solids. Process according to claim 15, characterized in that the calcium carbonate is ground immediately before the aqueous suspension is prepared so that 99% of the calcium carbonate particles are less than 44 pm or their average mass size is less than 8 pm, while the average mass the size of the calcium carbonate particles in the reaction vessel ranges from 2 to 6 pm. 24. A process for reducing the SO _X content of a flue gas by a wet process in a single-cycle, open column with the flow of limestone aqueous suspension, characterized in that it comprises: (a) passing a stream of flue gases containing SO _X through a vertical spray tower from the bottom up; (b) introducing fine droplets of aqueous suspension of fine-grained calcium carbonate with an average size up to 6 pm, calcium sulfate and inert solids into the vertical part of the spray tower, the droplets of aqueous suspension having a molar ratio of calcium-containing and sulfur-containing, 1.1-sulfur-containing, splicing depending on the direction of flow of the gaseous phase, they pass through the tower counter-current and contact with the flue gases; (c) after contact with the flue gas, collecting the aqueous suspension in a reaction vessel in which the pH ranges from 5.0 to 6.3; (d) extracting the slurry from a reaction vessel in which the slurry averages less than 6 hours; (e) treatment of slurry depleted from the reaction vessel in a hydrocyclone producing a backflow dominated by fine calcium carbonate particles with an average particle size below 6 pm and an additional stream dominated by calcium sulfate particles with an average particle size between 25 and 55 pm; (f) returning at least a portion of the backflow whose molar ratio between calcium-containing and sulfur-containing compounds is at least 1.4 and containing in particular fine particles of calcium carbonate into the process; and (g) introducing fresh calcium carbonate as feed stream in such quantities as to replace both non-recirculating calcium carbonate and reacting in the flushing zone with SO _X absorbed in the liquid phase, with an average mass Calcium carbonate particle size in the feed stream less than 8 pm. A method according to claim 24, characterized in that there is a single-pass inlet separator in the spray tower that changes the direction of the flue gas flow to allow the vertically mounted water vapor remover to operate effectively. 26. The method according to claim 24, characterized in that the aqueous suspension of the limestone is introduced by spray nozzles arranged at two height levels at a distance of less than two meters, the alternating direction of the flowing water suspension from adjacent nozzles alternately in up-and-down directions. Process according to claim 24, characterized in that the calcium carbonate is ground immediately before the aqueous suspension is prepared so that 99% of the calcium carbonate particles are less than 44 pm or their average mass size is less than 8 pm while the average mass the size of the calcium carbonate particles in the reaction vessel ranges from 2 to 6 pm. 28. A process for reducing the SO _X content of a flue gas by a wet process in a single-cycle, open spray tower with the flow of limestone aqueous suspension, characterized in that it comprises: (a) passing a stream of flue gases containing SO _X through a vertical spray tower from the bottom up, with a velocity of the main mass of the gaseous phase exceeding 4.5 m / s; (b) introducing fine droplets of aqueous suspension of fine-grained calcium carbonate, calcium sulfate and inert solids into the vertical portion of the spray tower so that the droplets of the aqueous suspension in the spray tower are contacted with the flue gas by counter-current and said aqueous slurry is introduced by means of spray nozzles arranged at two altitudes at a distance of less than two meters, alternating alternately in the upward and downward directions of the flowing water suspension from adjacent nozzles; (c) collecting the aqueous suspension in the reaction vessel after contact with the flue gas; (d) withdrawing the slurry from the reaction vessel; (e) treating the slurry depleted from the reaction vessel by an effective method of providing backflow, comprising in particular calcium carbonate particles, and an additional stream containing calcium sulfate particles; (f) returning at least a portion of the calcium carbonate-dominated backflow to the process; and (g) introducing fresh calcium carbonate as a feed stream in such quantities as to replace both non-recirculating calcium and one which reacts in the flushing zone with the SO _X absorbed in the liquid phase. 29. A process for reducing the concentration of SO _X in flue gases by wet flushing, characterized in that it comprises: (a) passing a stream of flue gases containing SO _X through a vertical spray tower from the bottom up; (b) introduction of fine droplets of aqueous suspension of fine-grained calcium carbonate, calcium sulphate, calcium sulphite and inert solids so that the droplets of the aqueous suspension in contact with the flue gas flow with the counter-flow gases, the average mass fraction of calcium carbonate ranges from 1 to 8 p.m .; (c) collecting the aqueous suspension in the reaction vessel after contact with the flue gas; (d) providing a high reactivity of the aqueous limestone suspension by pumping the slurry from the reaction vessel and treating said slurry in a hydrocyclone, where a backflow dominated by fine calcium carbonate particles and an additional flow dominated by calcium sulfate particles, both streams contain dissolved chlorides, while calcium sulfate is deposited as solid waste and part of the return stream is also discharged from the system for the purpose of removing either soluble chlorides or inert solids, or both; and (f) introducing fresh calcium carbonate as a feed stream in such quantities as to replace both calcium carbonate converted to calcium sulfate and one removed from the partial-flow backflow system with an average mass Calcium carbonate particle size in the feed stream less than 10 pm. 30. A process for reducing the concentration of SO _X in flue gases, characterized in that it comprises: (a) a spray tower with a flue gas inlet, a flue gas outlet and a vertical flushing zone, the tower being designed such that the gaseous phase passes through said flushing zone from the bottom up; (b) the arrangement of the spray nozzles in said flushing zone, the nozzles being designed to allow fine droplets of fine-grained calcium carbonate, calcium sulfate, calcium sulfite and inert solids to pass through the spray tower with respect to the direction of the spray tower gaseous phases countercurrent; (c) supply of calcium carbonate with an average particle size below 8 pm; (d) a reaction vessel located beneath said spray nozzle network, allowing the collection of water slurry after contact with the flue gases in said flushing zone, the reaction vessel being sufficiently large so that in the reaction of SO _X with calcium carbonates are formed by calcium sulphate crystals with an average particle weight of at least twice the average particle size of the calcium carbonate in the feed stream; (e) pumping the water slurry out of the reaction vessel and delivering the aqueous suspension to the spray nozzles located in the flushing zone; and (f) maintaining a low content of chlorides in the aqueous slurry contained in the reaction vessel by pumping it and introducing it into the hydrocyclone, forming a back-flow comprising mainly small particles of calcium carbonate and a secondary stream containing relatively large calcium sulphate particles, further by determining the chloride content of the backflow and by releasing as much of the backflow from the system as dictated by the measured chloride concentration. 31. A process for reducing the concentration of SO _X in flue gases by wet flushing, characterized in that it comprises: (a) passing a stream of flue gases containing SO _X through a vertical spray tower; (b) introducing fine droplets of aqueous suspension of fine-grained calcium carbonate, calcium sulphate, calcium sulphite and inert solids, which flow counter to the direction of the flue gas flow through the spray tower, with the pH of the aqueous suspension in the reaction vessel ranging from 5.0 to 6.3; (c) collecting the slurry in the reaction vessel; (d) maintaining a low content of chlorides in the aqueous slurry contained in the reaction vessel by pumping it and introducing it into the hydrocyclone, producing a back-flow containing mainly small particles of calcium carbonate and seconds containing a relative flow large particles of calcium sulfate, further by determining the chloride content of the backflow and by releasing as much of the backflow from the system as dictated by the measured chloride concentration; e. Returning a portion of the backflow whose molar ratio between calcium-containing and sulfur-containing compounds is greater than 1.3 to the reaction vessel; (f) pumping in the hydrocyclone of a secondary stream, mainly calcium sulphate, formed for the purpose of recovering the latter; and (g) introducing fresh calcium carbonate as a feed stream in such quantities as to replace the amount of calcium carbonate consumed or withdrawn from the system, with an average particle size by mass of less than 10 pm in the feed stream. 32. A device for wet removal of SO _X from flue gases, characterized in that it comprises: (a) a spray tower with a flue gas inlet, a flue gas outlet and a vertical flushing zone, the tower being designed such that the gaseous phase passes through said flushing zone from the bottom up; (b) in the types of spray nozzles in said flushing zone, the nozzles being designed to allow the introduction of tiny droplets of calcium carbonate aqueous suspension passing through the spray column in a countercurrent flow direction; (c) a reaction vessel located below said spray nozzle network, allowing the collection of water slurry after contact with the flue gases in said flushing zone, the reaction vessel being sufficiently large so that the reaction of SO ₂ with calcium carbonates are formed by gypsum crystals with an average particle size by weight of at least twice the average particle size of the calcium carbonate in the feed stream; (d) Devices for providing sufficient amounts of calcium carbonate with an average particle size below 10 μηι to be introduced into the reaction vessel; (e) sludge pumping aids including at least one pump and associated pipelines for transporting the aqueous suspension from the reaction vessel to the spray nozzles located in said flushing zone; and (f) an aqueous suspension quality assurance system, including a hydrocyclone, which separates said aqueous suspension in said reaction vessel into a stream dominated by small calcium carbonate particles and into a stream dominated by relatively large calcium sulfate particles, at least one pump and sludge pumping tubes from the reaction vessel and introducing them into the hydrocyclone, a recycle for transporting backflow, comprising, in particular, calcium carbonate particles, from said hydrocyclone into said reaction vessel, a discharge pipeline connected to said recycle and adapted for disposal said recycle stream, and a pipeline leading from said hydrocyclone to recover calcium sulphate slurry.