MXPA97004117A - Combusti gas washing machine - Google Patents

Abstract

The present invention relates to a spray tower (114) for removing gases and particulate matter from combustion gases, which are produced by type processing operations carried out in factories and industrial facilities. The spray tower is configured in order to minimize its total height, so that construction, operational and maintenance costs are also minimized. A tank (130) located at the base of the tower serves as a reservoir for an alkaline sludge used to remove gases and particulate matter from the combustion gases. The slurry is pumped from the tank to the sprinkler devices (116, 118) located inside the tower. An entrance (112) is located above the tank through which the combustion gases are introduced to the tower. Arranged within the tower and adjacent to the entrance is an enclosure (128) having an upper end attached to the tower and a lower end defining an opening. The sprinkler devices are located within the enclosure, preferably at approximately the same height as the entrance, so that the total height of the torch is reduced.

Description

COOLING GAS WASHING MACHINE FIELD OF THE INVENTION This invention generally relates to gas-liquid contactors used in the removal of particulate matter and acid gases from an installation and from industrial combustion gases. More particularly, this invention is directed to a spray tower, which is configured with an internal structure that allows sprinklers to be placed within the structure at approximately the same height as the entrance duct to the tower, so that Minimize the total height of the tower.

BACKGROUND OF THE INVENTION The gas-liquid contactors are widely used to remove substances such as gases and particulate matter from combustion gases produced by industrial facilities and plants. Usually of particular interest are sulfur dioxide (S02) and other acid gases produced by the combustion of fossil fuels and various industrial operations. It is known that such gases are dangerous for the environment, so that their emission into the atmosphere is tightly regulated by cleaning air statutes. The method by which such gases are removed with a spray tower or other type of liquid gas contactor is known as desulfurization of wet combustion gas. The cleaning action produced by the gas-liquid contactor is generally derived from the passage of the gas upwards through a counter-current tower to a descending liquid, which cleans the air. Wet flue gas desulfurization processes typically involve the use of calcium-based slurries or solutions based on sodium or ammonia. As used herein, a slurry is a mixture of solids and liquid, in which the solids content can be any desired level, including the extreme condition in which the sludge is taken as a moisture solid. Examples of calcium-based sludge are limestone (calcium carbonate, CaCO3) and hydrated lime sludge (calcium hydroxide, Ca (OH) 2) formed by the action of water on lime (calcium oxide, CaO). These sludges react with acid gases to form precipitates that can be collected for disposal or recirculation. The intimate contact between the alkaline sludge and the acid gases, which are present in the combustion gases, such as sulfur dioxide, hydrogen chloride (HCl), and hydrogen fluoride (HF), results in the absorption of the gases through the mud. Afterwards, the mud can be accumulated in a tank. A known type of gas-liquid contactor is a spray tower 10, an example of which is shown in cross-section in Figure 1 The spray tower 10 is generally a straight structure composed of a tower 14 equipped with an inlet duct 12 , through which the combustion gases enter the tower 14. The inlet duct 12, as well as other appropriate sections of the tower 14, are preferably formed from a high nickel alloy in order to promote its corrosion resistance . Above the inlet duct 12 is a lower group of spray nozzles 16, which introduces a spray 20 of a cleaning liquid, usually an alkaline sludge, to the tower 14. A second, upper group of spray nozzles 18 it is typically provided above the lower group of spray nozzles 16, the additional groups of spray nozzles being used as may be required for a given application. One or more pumps 26 are required to recirculate the cleaning liquid by pumping the liquid from a tank 30 to the groups of spray nozzles 16 and 18. Each group of spray nozzles 16 and 18 can be individually equipped with a pump 26 for the purpose of remove the flexibility of pumping and spraying operation to adapt to varying demands of the washing operation. The intimate contact between the spraying of liquid 20 and the combustion gases exiting through the tower 14, results in a cleaning action, by which liquid and trapped or reacted gases are collected at the bottom of tower 14 in tank 30. Clean gases, which continue to rise through tower 14, then typically they pass through a moisture scavenger 22, and are then either heated or passed directly to the atmosphere through a chimney 24. Due to structural considerations, conventionally accepted design practices typically limit the width of the pipeline. inlet 12 to about 2/3 of the diameter of the tower 14. In addition, the first group of spray nozzles 16 typically should be from about 2 to about 3 meters above the inlet duct 12, in order to provide an adequate volume of gas-liquid mass transfer time, during which the gases are absorbed by the liquid, and to prevent the liquid spraying 20 from entering the duc to input 12, which could otherwise create the development of mud and particulate matter requiring periodic removal. Conventional practices typically also limit the speed of the combustion gas within the inlet duct 12 from about 15 to about 8 meters per second, for the purpose of maintaining an adequate pressure drop and a gas distribution within the tower 14. Prior limitations generally dictate both the height of the inlet duct 12 and the position of the first group of spray nozzles 16 relative to the inlet duct 12. In view of the foregoing, it can be seen that the diameter of the tower, the height of the duct of inlet 12, and the distance of the first group of spray nozzles 16, above the inlet duct 12, all must be increased in order to adapt the increased flue gas flows through the spray tower 10. Consequently, the The total size and height of the spray tower 10 depends on the amount of combustion gases that are going to be washed. In turn, the higher sprinkler towers 10 need more powerful pumps 26 to pump the liquid to the spray nozzles 16 and 18, whose vertical height must also be increased to place the spray nozzles 16 and 18 sufficiently above the inlet duct 12. Those skilled in the art will appreciate that, in view of the considerations noted above, it may be desirable to minimize the height of a combustion gas spraying tower for the purpose of minimizing the construction, operating and maintenance costs of the tower and the washing operation.

COMPENDIUM OF THE INVENTION It is an object of this invention to provide a combustion gas scrubbing apparatus for the removal of particulate matter and acid gases from flue gases produced by industrial companies and facilities. It is another object of this invention that said scrubber apparatus is constructed and configured to minimize the height of the apparatus for a given combustion gas processing capacity. A further object of this invention is that the construction and material costs for the washing apparatus, as a result of its construction and configuration. Finally, it is another object of this invention that said scrubbing apparatus is equipped with an internal structure that allows the placement of spray nozzles inside the apparatus to approximately coincide with the inlet duct to the apparatus. The present invention provides a spray tower for removing gases and particulate matter from combustion gases, which are produced through processing operations of the type carried out in companies and industrial plants. The spray tower is generally composed of a tower having a lower end and an upper end, with a tank being located near the lower end of the tower. The tank serves as a reservoir for a liquid, such as an alkaline sludge, which is used to remove gases and particulate matter from the combustion gases. A pumping device is preferably provided for pumping the liquid accumulated in the tank to devices which introduce the liquid, such as by spraying, into the tower. The tower is equipped with an entrance located above the tank, through which the combustion gases are introduced to the tower. Arranged within the tower and adjacent to the inlet is an enclosure having an upper end attached to the tower and a lower end defining an opening. The enclosure may have a cylindrical shape or a tapered shape, in which the upper end of the enclosure has a larger diameter than the lower end of the enclosure. The opening is preferably located vertically below at least a portion of the inlet, so that the combustion gases introduced into the tower, through the inlet, are directed downwardly from the inlet and into the opening before the opening. climb through the tower. At least one group of spray devices is placed within the enclosure and adjacent to the opening thereof. These spray devices are placed so that the liquid will accumulate in the tank. Finally, the spray tower preferably includes a vapor removal device above the spray devices to remove liquid particles from the combustion gases flowing through the tower. An inlet is arranged at the upper end of the tower, through which clean combustion gases leave the spray tower. Since the spray tower is configured to include the enclosure, the height of the lowest group of spraying devices can be located at approximately the same height as the entrance or, if desired, below the entrance. As a result, the total height of the spray tower can be reduced to a minimum for a given height of entry, since the lowest group of spray devices do not require to be spaced a sufficient distance above the entrance to provide an adequate volume during a gas-liquid mass transfer time. As a result, the construction, operational and maintenance costs of the tower are also minimized. Other objects and advantages of this invention will be better appreciated from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing advantages and other advantages of this invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which: Figure 1 shows a cross section of a spray tower of a type known in the prior art; Figure 2 shows in cross-section a spray tower according to a first embodiment of this invention; and Figure 3 shows a cross section of a spray tower according to a second embodiment of this invention.

DETAILED DESCRIPTION OF THE INVENTION Figures 2 and 3 illustrate combustion gas scrubbers in the form of spray towers 1 10 and 210 configured in accordance with the teachings of the present invention. As illustrated, towers 1 10 and 210 have a basic structural configuration, which is similar to that of tower 10 of the prior art shown in Figure 1. However, in accordance with this invention, towers 1 10 and 210 each include receivers or plates 128 and 228, which allow the total height of towers 110 and 210 to be minimized. As a result, the construction, operational and maintenance costs of the towers 110 and 210 are significantly reduced. Since the towers 110 and 210 are illustrated as being of a particular construction, those skilled in the art will recognize that the teachings of this invention they can be easily applied to other various structures, which serve to remove unwanted gases, steam, dust, fumes, smoke, and / or particulate matter from a volume of gas. The spray tower 110 shown in Figure 2 generally has a straight structure composed of a tower 114. As illustrated, the tower 114 has an upper section, a lower section having a greater cross section than the upper section, and a cross section tapered between and interconnecting the upper and lower sections. The lower section of the tower 114 is equipped with an inlet duct 112, which forms an opening in the perimeter of the tower 114, through which the combustion gases enter the tower 114. The source of the Combustion can be a process involving the combustion of fossil fuels or various industrial operations through which undesirable gases or particulate matter are produced. As with the prior art spray towers of the type illustrated in Figure 1, a tank or tank 130 is formed at the lower end of the tower 110, in which a liquid is maintained.

For the purpose of removing acid gases and particulate matter from combustion gases, the liquid is typically an alkaline sludge, usually composed of lime (calcium oxide, CaO), or limestone (CaC03) suspended in water, although they are known and other types of cleaning liquids can be used. A pump 126 is fluidly interconnected with the tank 130 for the purpose of supplying the sludge from the tank 130 to groups of spray nozzles 116 and 118 within the tower 114. The spray nozzles 116 and 118 produce a mud spray 120 inside the tower 114, in order to provide an intimate contact between the spray 120 and the combustion gases that rise through the tower 114. The result is a cleaning action, by which the sludge and the trapped or reacted gases are collected in the bottom of the tower 114 in the tank 130. Since in figure 2 the spray nozzles are shown, it is foreseeable that other types of devices for the introduction of mud to the tower 113, including atomizers and trays, can be used. Also located above the entrance duct 112 and within the upper section of the tower 114 is a steam eliminator 122 of any known type, suitable in the art. Above the steam eliminator 122 is a chimney 124, through which gases can pass from the spray tower 110 and can be heated or passed directly into the atmosphere. By themselves, the individual structures are generally conventional or of a type known in the art, and, therefore, do not cover the subject matter of this invention. Neither the above structures constitute a limitation to the scope of the present invention. In accordance with this invention, the plate 128 is disposed adjacent the inlet duct 1 12 and inside the tower 1 14, generally within the lower section of the tower 1 14. The plate 128 may have a cylindrical shape, although other forms can be used. The plate 128 is attached at its upper end to the wall of the tower 1 14, while its lower end is suspended above the tank 130. The lower end of the plate 128 defines an opening, through which the combustion introduced into the tower 1 14, through the inlet duct 1 12, can flow towards the upper section of the tower 1 14. As shown, the opening is arranged completely below the inlet duct 1 12, although it is predictable that the lower end of the plate 128 may end adjacent to the inlet duct 1 12. Preferably, the opening towards the plate 128 lies in a horizontal plane, so that the combustion gases will enter the tower 1 14 throughout the perimeter of plate 128. As a result, the distribution of combustion gas within tower 1 14 is significantly improved, and thus promotes the gas-liquid mass transfer characteristics of tower 1 14. U n lower group 1 16 of the spray nozzles 1 16 and 1 18 is located inside the plate 128 and at about the same height as the inlet duct 112. As noted above, the lower bank of spray nozzles 116 introduces the alkaline sludge towards the tower 114 in the form of a spray 120. A second upper group 118 of the spray nozzles 116 and 118 is provided above the lower group of spray nozzles 116 and within the upper section of the tower 114. Additional groups may be used of spray nozzles, as required, to provide an adequate flow of sludge to remove unwanted components from the combustion gases. The clean gases then continue to rise through the tower 114 and pass through the steam eliminator 122, where the liquid particles are removed from the gases. Then, the gases continue towards the chimney 124 and into the atmosphere. As described above, the plate 128 serves to reduce the height of the tower 114 by allowing the lower group of spray nozzles 116 to be placed significantly closer to the inlet duct 112 than is possible with the prior art spray towers. For example, when the prior art spray towers require that the lowest group of spray nozzles be placed at least about 2 meters above the inlet duct, the lower group of spray nozzles 116 of this invention are located at approximately the same height as the entrance duct 112, thereby reducing the total height of the tower 114 by approximately 2 meters. The plate 128 is also beneficial in that it promotes the distribution of combustion gas within the tower 114 by introducing the combustion gases along the entire perimeter of its lower end. Consequently, the height of the entrance duct 112 can also be reduced to a minimum, since there is a reduced tendency of the combustion gases to stratify the wall of the tower 114 opposite the entrance, which could otherwise result in a less homogeneous distribution of the combustion gases within the tower 114. Furthermore, since the inlet duct 112 is not directly subjected to the alkaline sludge, it can be formed of a carbon steel instead of an alloy with a high nickel content more expensive, as conventionally required in the prior art.

An additional advantage of the spray tower 110 of this invention is that an activated lower pump 26 can be used, since the vertical distance between the tank 130 and the spray nozzle groups 116 and 118 is reduced. Although a lateral pressure drop of slightly higher gas results from the presence of the plate 128, the operating costs incurred for this effect are more than offset by the lowest possible operating costs by the reduced heights of the tower 114 and the spray nozzles 116 and 118. In the Figure 3 illustrates a second embodiment of this invention. As with the first embodiment, the spray tower 210 of Figure 3 has a straight construction comprised of a tower 214. As above, a lower section of the tower 214 is equipped with an inlet duct 212, through which the exhaust gases of combustion enters the tower 214, and a tank 230 is formed at the lower end of the tower 210 where an alkaline slurry is maintained. Located within the upper section of tower 214 is a steam eliminator 222 and a chimney 224. In contrast to the first embodiment of Figure 2, the upper and lower sections of tower 214 are generally of the same size and shape. . Accordingly, and in accordance with this second embodiment of the invention, the plate 228 is formed to have a tapered configuration, the lower end of the plate 228 being smaller in cross section than the upper end of the plate 228. As with the above, the plate 228 is attached at its upper end to the wall of the tower 214, while its lower end is suspended above the tank 230. The lower end of the plate 228 defines an opening through which the gases of combustion, introduced into the tower 214 through the inlet duct 212, can flow into the upper section of the tower 214. A lower group 216 of the spray nozzles 216 and 218 is located within the plate 228 at approximately the same height as the inlet duct 212, while a top group 218 of the spray nozzles 216 and 218 is located in the upper section of the tower 214. A pump (not shown) serves for Bearing the sludge from tank 230 to groups of spray nozzles 216 and 218 within tower 214 and plate 228.

In addition to the reconfigured plate 228, the spray tower 210 of the second embodiment also differs from the spray tower 110 of the first embodiment by the inclusion of a chamfered section 234 within the tank 230, from which the sludge is expelled to feed one or more of the spray nozzles 232 located between the lower section of the tower 214 and the plate 228. A pump 238 is provided to pump the sludge from the chamfered section 234 toward the spray nozzle 232. A valve 240 is provided, through which a portion of the sludge may be supplied to a drainage device (not shown) of a type known in the art, for the purpose of extracting solid precipitates, such as gypsum (CaS04 »2H20), from the slurry. Since an alkali is added to the tank 230 and not to the chamfered section 234, the sludge expelled from the chamfered section 234 has a low pH. As such, the spray nozzle 232 serves to absorb sulfur dioxide and reduce the pH of the sludge, in order to allow the limestone to be more easily dissolved. If the gypsum is the desired byproduct of the mud, the gypsum will be of superior purity, and the total alkali consumption of the scrubbing process will be less. The spray tower 210 preferably includes aerators 230, which help to distribute oxygen and solids in the slurry within the tank 230. As is known in the art, the sulfur dioxide absorbed by the sludge reacts with the water in the sludge to form sulphites (S03") Oxygen can be introduced through a blower or other suitable device (not shown) in order to promote the oxidation of sulphites to form sulfates (S04"), which can then react with the calcium-based sludge to form gypsum as a by-product of easy sale of the washing operation. As before, it can be seen that the plate 228 of the second embodiment serves to reduce the height of the tower 214, allowing the lower group of spray nozzles 216 to be placed adjacent the inlet duct 212. The plate 228 also provides the other benefits observed with the first embodiment of this invention, including the improved distribution of combustion gases within the tower 214, a reduced height of the inlet duct, and the ability to form the inlet duct 212 of a carbon steel. In addition, the spray tower 210 is characterized in that the limestone is more readily dissolved and at a lower pH for the mud solution, resulting in a plaster of higher purity as a by-product and a lower total consumption of alkali. Since the invention has been described in terms of preferred embodiments, it is evident that other forms may be adapted by one skilled in the art, such as by incorporating the novel aspects of this invention into spray towers and other gas-liquid contactors, the which differ structurally from those shown in the figures. Accordingly, the scope of the invention will be limited only by the following claims.

Claims (8)

1 .- A washing apparatus for removing gases and particulate matter in combustion gases, the washing apparatus comprising: a passage having a lower end and an upper end; an entrance to the passage through which combustion gases are introduced into the passage; an enclosure disposed adjacent to the entrance and into the passage, the enclosure having an upper end attached to the passage and a lower end defining an opening for the combustion gases introduced into the passage through the inlet, the opening being disposed below the at least a portion of the inlet, the upper end of the enclosure having a larger diameter than the lower end of the enclosure; means for introducing a fluid into the enclosure to remove gases and particulate matter from the combustion gases; and an outlet disposed at the upper end of the passage through which the gases escape the passage.

2. - A washing apparatus according to claim 1, wherein the introduction means are located within the enclosure at an elevation no greater than the entrance to the passage.

3. A washing apparatus according to claim 1, wherein the passage circumscribes the enclosure in order to form a circumferential gap between them, the washing apparatus further comprises means for introducing a fluid into the circumferential gap between the enclosure and the passage.

4. A washing apparatus according to claim 1, wherein the opening in the enclosure is arranged completely below the entrance.

5. A washing apparatus according to claim 1, further comprising second means for introducing a fluid, these second introduction means being located in the passage above the enclosure.

6. - A scrubbing apparatus according to claim 1, further comprising means for eliminating steam from the gases flowing through the passage.

7. A washing apparatus according to claim 1, further comprising a tank located at the lower end of the passage, and means for pumping fluids accumulated in the tank to the introduction means.

8. A washing apparatus according to claim 7, further comprising means for removing solids from the fluids before the fluids are delivered to the introduction means.