Spray dryer absorber and related processes

Abstract

A spray dryer absorber (SDA) system used to reduce the concentration of at least one acid compound in a gas utilizes low or no alkali-containing particulate compounds to prevent cementing during operation. The low or no-alkali-containing compounds may be supplied from external sources and/or from a particulate collection device located downstream of the SDA.

Claims

1. A system for reducing the tendency for cementing in a spray dryer absorber, comprising: at least one source of at least one gas, such at least one gas containing at least one acid compound, the concentration of which in the at least one gas has to be reduced; at least one spray dryer absorber for receiving the at least one gas and using at least one alkali-containing reagent for reacting with the at least one acid compound; at least one as-is particulate recycle line designed to supply an as-is particulate from another combustor; a particulate collection device located downstream of the at least one spray dryer absorber; and at least two means for injecting at least one particulate compound into the at least one gas in combination with the at least one alkali-containing reagent, wherein the at least one particulate compound is comprised of a low or no alkali particulate from the as-is particulate recycle line and has an alkali content that is low enough not to cause cementing in the spray dryer absorber during operation, wherein a first means of the at least two means for injecting the at least one particulate compound into the at least one gas is individually located upstream of the spray dryer absorber and wherein a second means of the at least two means for injecting the at least one particulate compound into the at least one gas is individually located in the at least one spray dryer absorber so that a combination with the individually injected at least one alkali-containing reagent is formed within the at least one spray dryer absorber due to the at least one second injection means, and wherein the low or no alkali content particulate compound is solely composed of as-is fly ash recycled directly from the particulate collection device and another combustor.

2. The system of claim 1, wherein the at least one gas comprises gas from a combustion process generated from a combustor located upstream of the at least one spray dryer absorber.

3. The system of claim 2, wherein the combustion process is conducted in a fluidized bed boiler.

4. The system of claim 3, wherein the combustion process is conducted in a circulating fluidized bed boiler.

5. The system of claim 1, wherein the alkali-containing reagent comprises a mixture of a reactivated reagent from a reactivating particulate line and a fresh reagent.

6. A method of operating a system with a spray dryer absorber to reduce the tendency for cementing in the spray dryer absorber, comprising the steps of: (A) providing at least one gas stream from at least one source, wherein the at least one gas stream contains at least one acid compound, the concentration of which in the at least one gas stream has to be reduced; (B) providing at least one spray dryer absorber designed to receive the at least one gas stream from the at least one gas source, the at least one spray dryer absorber using at least one alkali-containing reagent for reacting with the at least one acid compound; (C) providing a particulate collection device located downstream of the at least one spray dryer absorber; (D) at least one as-is particulate recycle line designed to supply an as-is particulate from the particulate collection device; and (E) providing at least two means for injecting at least one particulate compound into the at least one gas stream, wherein the at least one particulate compound is comprised of a low or no alkali particulate from the as-is particulate recycle line and has an alkali content that is low enough not to cause cementing in the spray dryer absorber during operation, wherein a first means of the at least two means for injecting the at least one particulate compound into the at least one gas is individually located upstream of the at least one spray dryer absorber, and wherein a second means of the at least two means for injecting the at least one particulate compound into the at least one gas is individually located within the at least one spray dryer absorber simultaneously with the at least one alkali-containing reagent or within the at least one spray dryer absorber downstream of the point at which the at least one alkali-containing reagent is provided the at least one spray dryer absorber so that a combination with the individually injected at least one alkali-containing reagent is formed within the at least one spray dryer absorber due to the at least one second injection means, and wherein the low or no alkali content particulate compound is solely composed of as-is fly ash recycled directly from the particulate collection device.

7. The method of claim 6, wherein there the at least one second injection means of Step (E) is located both within the at least one spray dryer absorber and thus the injection of the at least one particulate compound occurs simultaneously with providing the at least one alkali-containing reagent and within the at least one spray dryer absorber downstream of the point at which the at least one alkali-containing reagent is provided to and thus the injection of the at least one particulate compound occurs after providing the at least one alkali-containing reagent.

8. The method of claim 6, wherein the at least one gas stream comprises gas from a combustion process generated from a combustor located upstream of the at least one spray dryer absorber.

9. The method of claim 6, wherein the combustion process is conducted in a fluidized bed boiler.

10. The method of claim 9, wherein the combustion process is conducted in a circulating fluidized bed boiler.

11. The method of claim 6, wherein the alkali-containing reagent comprises a mixture of a reactivated reagent from the reactivating particulate line and a fresh reagent.

12. The method of claim 6, wherein the method further comprises a third injection means in Step (E) that is located within the at least one spray dryer absorber downstream of the point at which the at least one alkali-containing reagent is provided to and thus the injection of the at least one particulate compound occurs after the reaction of the at least one alkali-containing reagent with the at least one acid compound.

13. A system for reducing the tendency for cementing in a spray dryer absorber, comprising: at least one source of at least one gas, such at least one gas containing at least one acid compound, the concentration of which in the at least one gas has to be reduced; at least one spray dryer absorber for receiving the at least one gas and using at least one alkali-containing reagent for reacting with the at least one acid compound; a particulate collection device located downstream of the at least one spray dryer absorber; at least one as-is particulate recycle line designed to supply an as-is particulate from a another combustor; and at least two means for injecting at least one particulate compound into the at least one gas in combination with the at least one alkali-containing reagent, wherein the at least one particulate compound is comprised of a low or no alkali particulate from the as-is particulate recycle line and has an alkali content that is low enough not to cause cementing in the spray dryer absorber during operation, wherein one of the at least two means for injecting the at least one particulate compound into the at least one gas is individually located in the at least one spray dryer absorber so that a combination with the individually injected at least one alkali-containing reagent is formed within the at least one spray dryer absorber, wherein one of the at least two means for injecting the at least one particulate compound into the at least one gas in combination with the at least one alkali-containing reagent is located upstream of the spray dryer absorber, and wherein the low or no alkali content particulate compound is solely composed of as-is fly ash recycled directly from the particulate collection device and another combustor.

14. The system of claim 13, wherein the at least one gas comprises gas from a combustion process generated from a combustor located upstream of the at least one spray dryer absorber.

15. The system of claim 14, wherein the combustion process is conducted in a fluidized bed boiler.

16. The system of claim 13, wherein the alkali-containing reagent comprises lime slurry, fly ash, or a mixture thereof.

17. The system of claim 13, wherein the system further comprises: at least three means for injecting at least one particulate compound into the at least one gas in combination with the at least one alkali-containing reagent, wherein the at least one particulate compound is comprised of a low or no alkali particulate from the as-is particulate recycle line to prevent cementing in the spray dryer absorber during operation, wherein one of the at least three means for injecting the at least one particulate compound into the at least one gas in combination with the at least one alkali-containing reagent is located upstream of the spray dryer absorber, wherein one of the at least three means for injecting the at least one particulate compound into the at least one gas in combination with the at least one alkali-containing reagent is located within the spray dryer absorber, and wherein one of the at least three means for injecting the at least one particulate compound into the at least one gas in combination with the at least one alkali-containing reagent is located downstream of the spray dryer absorber.

18. A system for reducing the tendency for cementing in a spray dryer absorber, comprising: at least one source of at least one gas, such at least one gas containing at least one acid compound, the concentration of which in the at least one gas has to be reduced, wherein the at least one gas comprises a gas from a combustion process; at least one spray dryer absorber for receiving the at least one gas and using at least one alkali-containing reagent for reacting with the at least one acid compound; a particulate collection device located downstream of the at least one spray dryer absorber; at least one as-is particulate recycle line designed to supply an as-is particulate from a another combustor; and at least one means for injecting at least one particulate compound into the at least one gas in combination with the at least one alkali-containing reagent, wherein the at least one particulate compound is comprised of a no alkali particulate from the as-is particulate recycle line and has no alkali content so as to not cause cementing in the spray dryer absorber during operation, wherein one of the at least one means for injecting the at least one particulate compound into the at least one gas is individually located in the at least one spray dryer absorber so that a combination with the individually injected at least one alkali-containing reagent is formed within the at least one spray dryer absorber, and wherein the low or no alkali content particulate compound is solely composed of as-is fly ash recycled directly from the particulate collection device and another combustor.

19. A system for reducing the tendency for cementing in a spray dryer absorber, comprising: at least one source of at least one gas, such at least one gas containing at least one acid compound, the concentration of which in the at least one gas has to be reduced; at least one spray dryer absorber for receiving the at least one gas and using at least one alkali-containing reagent for reacting with the at least one acid compound; a particulate collection device located downstream of the at least one spray dryer absorber; at least one as-is particulate recycle line designed to supply an as-is particulate from a another combustor; and at least three means for injecting at least one particulate compound into the at least one gas in combination with the at least one alkali-containing reagent, wherein the at least one particulate compound is comprised of a low or no alkali particulate from the as-is particulate recycle line and has an alkali content that is low enough not to cause cementing in the spray dryer absorber during operation, wherein one of the at least three means for injecting the at least one particulate compound into the at least one gas in combination with the at least one alkali-containing reagent are individually located near to one another in the at least one spray dryer absorber so that a combination with the individually injected at least one alkali-containing reagent is formed within the at least one spray dryer absorber, wherein one of the at least three means for injecting the at least one particulate compound into the at least one gas in combination with the at least one alkali-containing reagent is located upstream of the spray dryer absorber, wherein one of the at least three means for injecting the at least one particulate compound into the at least one gas in combination with the at least one alkali-containing reagent is located within the at least one spray dryer absorber downstream of the point at which the at least one alkali-containing reagent is provided to and thus the injection of the at least one particulate compound occurs after the providing of the at least one alkali-containing reagent, wherein the low or no alkali content particulate compound is solely composed of as-is fly ash recycled directly from the particulate collection device and another combustor, and wherein the alkali-containing reagent comprises lime slurry, fly ash, or a mixture thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a simplified schematic illustration of a system according to the present invention when the alkali-containing reagent is injected into the gas stream from a source external to the gas stream, e.g. when the alkali-containing reagent is lime slurry; and

(2) FIG. 2 is a simplified schematic illustration of a system according to the present invention when the alkali-containing reagent is introduced from the same source as the gas stream, e.g. when the alkali-containing reagent is fly ash from the combustor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

(3) Referring to the drawings generally, wherein like reference numerals designate the same or functionally similar elements throughout the several drawings, and to FIG. 1 in particular, the present invention relates to a spray dryer absorber (SDA) method and apparatus used to reduce the concentration of at least one acid compound contained in a gas. The SDA is provided downstream of a source of the gas.

(4) In one embodiment, shown in FIG. 1, the system includes a source 1 of a gas containing at least one acid compound, the concentration of which in the gas has to be reduced; an SDA 2; a particulate collection device 3, e.g., fabric filter (baghouse) or electrostatic precipitator (ESP), and a stack 4. The gas source 1 can be a chemical reactor, a combustor, a boiler, etc. A gas stream 5 from the gas source 1 travels through the SDA 2, the particulate collection device 3 and on to the stack 4, from where it is released to the atmosphere. An alkali-containing reagent 6a, such as lime slurry, from an external source is injected into the gas stream 5 in the SDA 2 for reacting with the at least one acid compound in the gas stream 5. A low or no alkali-containing particulate compound, such as fly ash from another combustor, or sand, is injected into the gas stream 5 through injecting means which may be provided at one or more locations. A first location 7a may be provided upstream of the SDA 2. A second location 7b may be provided directly into the SDA 2 simultaneously with the injection of the alkali-containing reagent 6a. A third location 7c may be provided directly into the SDA 2, but downstream of the location where injection of the alkali-containing reagent 6a occurs. It is understood that any combination of locations 7a, 7b or 7c of the means for injecting the low or no alkali-containing particulate compound may be used in the practice of the present invention.

(5) A portion of the particulate matter comprising fly ash, unreacted lime and reaction products collected in the particulate collection device 3 may be mixed in a hydrator 9 with water 10 for reactivating the unreacted lime and returning it to the SDA 2 via line 8 for introduction along with the alkali-containing reagent 6a. If the alkali content in the material collected in the particulate collection device 3 is low enough not to cause cementing when wetted, it can be recycled via line 11 and injected into the gas stream 5 alone or in combination with the low or no alkali-containing particulate compound through any combination of the injecting means locations 7a, 7b and 7c. The material may be recycled as-is from the particulate collection device 3 along the recycle line 11. The purpose of the recycle, as well as that of injecting the low or no alkali-containing particulate compound, is to use these particles to dilute the alkali-containing reagent for reducing its cementing potential. This improves reliability of the SDA and/or allows reducing its size.

(6) In another embodiment, shown in FIG. 2, the system includes a source 1 of a gas containing at least one acid compound, which content in the gas has to be reduced; a spray dryer absorber (SDA) 2, a particulate collection device 3 and a stack 4. The gas source 1 can again be a chemical reactor, a combustor, a boiler, etc. The gas stream 5 from the gas source 1 travels through the SDA 2, the particulate collection device 3 and to the stack 4, from where it is released to the atmosphere. An alkali-containing reagent 6b originates from the same source as the gas stream 5; e.g., it may be an alkali-containing fly ash from the combustor. (This may be the case when firing a fuel with low sulfur content and/or high alkali content, as in certain types of coal and oil shale. Another example of ash particles being capable of serving as a reagent in the SDA for reducing acid compounds in the flue gas is ash from a fluidized bed boiler, in particular from a circulating fluidized bed (CFB) boiler. This type of boiler typically utilizes limestone, which has as its predominant component calcium carbonate, fed to the furnace for in-furnace capture of SO.sub.2 generated in the combustion process.) Water 10 is sprayed into the gas stream 5 in the SDA 2 for reactivating the alkali-containing fly ash, which then reacts with the at least one acid compound in the gas stream 5.

(7) A low or no alkali-containing particulate compound, such as fly ash from another combustor, is injected into the gas stream 5 through the injecting means 7a upstream of the SDA 2 or the injecting means 7b in the SDA 2 simultaneously with injecting water 10 or the injecting means 7c in the SDA 2 downstream of injecting water 10 or any combination of the means 7a, 7b and 7c. A portion of the fly ash collected in the particulate collection device 3 may be mixed in the hydrator 9 with water 10 for reactivating the unreacted lime in the ash and returned to the SDA 2 via line 8 for introduction into the SDA along with the water 10. If the alkali content in the material collected in the particulate collection device 3 is low enough not to cause cementing when wetted, it can be recycled via line 11 and injected into the gas stream 5 alone or in combination with the low or no alkali-containing particulate compound through any combination of the injecting means 7a, 7b and 7c. The material may be recycled as-is from the particulate collection device 3 along the recycle line 11. The purpose of the recycle, as well as that of injecting the low or no alkali-containing particulate compound, is to use these particles to dilute the alkali-containing reagent for reducing its cementing potential. This improves reliability of the SDA and/or allows reducing its size.

(8) As is noted above, the at least one low or no alkali-containing particulate compound can be injected upstream of the point, or points, where the alkali-containing reagent 6a or water 10 is injected into the SDA 2 (means 7a in FIG. 1 and FIG. 2, accordingly). This is a preferred location for injecting the low or no alkali-containing particulate compound since it improves the mixing of the compound with the reagent thus reduces the potential for cementing in the SDA 2. However, if required due to equipment constraints, the particulate compound can be injected concurrently with (means 7b) or downstream of (means 7c) the point, or points, at which the alkali-containing reagent 6a or water 10 is injected into the SDA 2.

(9) Another aspect of the present invention relates to a method of operating a system with a spray dryer absorber comprising the steps of: (A) providing at least one gas stream from at least one source, wherein the at least one gas stream contains at least one acid compound, which content has to be reduced; (B) providing a spray dryer absorber designed to receive the at least one gas stream from the at least one gas source, the spray dryer absorber using at least one alkali-containing reagent for reacting with the at least one acid compound; (C) providing at least one means for introducing at least one particulate compound into the at least one gas stream, wherein the at least one particulate compound has a low or no alkali content; and (D) providing at least one particulate collection device collecting particulate matter in the at least one gas stream prior to its leaving the system.

(10) In general, the acid compounds may be SO.sub.2 and other sulfur compounds, such as SO.sub.3 and H.sub.2SO.sub.4, as well as non-sulfur compounds, such as hydrogen chloride (HCl). The alkali-containing reagent may be calcium-based, sodium-based, etc.

(11) In addition to cost reduction benefits, reducing the size of a spray dryer absorber (SDA) opens up the potential for using SDAs in spatially confined applications where larger equipment would be difficult or impossible to use. For example, the size reduction can be beneficial when retrofitting existing units.

(12) Although the invention has been described in detail with particular reference to certain embodiments detailed herein, other embodiments can achieve the same results. For example, the present invention may be applied in new construction involving SDAs, or to the repair, replacement, and modification or retrofitting of existing SDAs. Variations and modifications of the present invention will be obvious to those skilled in the art and the present invention is intended to cover in the appended claims all such modifications and equivalents covered by the scope of the following claims.