MX2008002302A

MX2008002302A - Method of removing sulfur dioxide from a flue gas stream

Info

Publication number: MX2008002302A
Application number: MXMX/A/2008/002302A
Authority: MX
Inventors: Maziuk John Jr
Original assignee: Maziuk John Jr; Solvay (Societe Anonyme); Solvay Chemicals Inc
Priority date: 2005-08-18
Filing date: 2008-02-18
Publication date: 2008-09-02

Abstract

A method of removing SO2from a flue gas stream including SO2includes providing a source of trona and injecting the trona into the flue gas stream. The temperature of the flue gas is between about 600Â°F and about 900Â°F. The trona is maintained in contact with the flue gas for a time sufficient to react a portion of the trona with a portion of the SO2to reduce the concentration of the SO2in the flue gas stream.

Description

METHOD FOR EXTRACTING SULFUR DIOXIDE FROM A COMBUSTION GAS CURRENT The present invention relates to the purification of gases, and more particularly to a method for purifying combustion gases containing noxious gases, such as S02. Dry absorbent injection (DSI) with various absorbents has been used to extract S0X and other gases from the combustion gas. However, in the past DSI has generally been made at temperatures well below 400 ° F since the material of the equipment, for example baghouse means, does not withstand higher temperatures. In addition, many absorbent materials are sintered or melted at temperatures near or e 400 ° C, making them less effective for gas removal. The reaction products of many absorbent materials also adhere to equipment and ducts at higher temperatures, which requires frequent cleaning of process equipment. In order to operate at these lower temperatures, the combustion gases must often be cooled before the absorbent is injected. This represents an additional unwanted process step. Accordingly, there is a need for an absorbent injection method that is effective for the removal of SOx gases at elevated temperatures.

In one aspect, a method is provided to extract S02 from a combustion gas stream that includes S02. The method includes the provision of a trona source and the injection of trona to the flue gas stream. The temperature of the combustion gas is between t 600 ° F and t 900 ° F. The chair is kept in contact with the combustion gas for a sufficient time to react a portion of the chair with a portion of S02, in order to reduce the concentration of S02 in the flue gas stream.

In another aspect, a system is provided for the removal of S02 from a flue gas stream that includes S02. The system includes a trona source and a flue gas stream. The system also includes an injector to inject the trona into the flue gas stream. The temperature of the combustion gas is between t 600 ° F and t 900 ° F. The system also includes an area for keeping the trona in contact with the combustion gas for a sufficient time to react a portion of the trona with a portion of S02 in order to reduce the concentration of S02 in the flue gas stream. The foregoing paragraphs are provided by way of general introduction and are not intended to limit the scope of the following claims. The embodiments currently preferred, together with the further advantages, will be better understood by reference to the following detailed description taken in conjunction with the accompanying drawings. FIG. 1 is a diagram of an embodiment of a flue gas desulfurization system. FIG. 2 is a graph showing the% removal of S02 as a function of the normalized stoichiometric ratio (NSR) for trona and sodium bicarbonate. FIG. 3 is a graph showing the% removal of S02 as a function of the temperature of the combustion gas (in ° F) for an embodiment of a flue gas desulfurization system. FIG. 4 shows a perforated plate of an electrostatic precipitator after operation in an embodiment of a flue gas desulfurization system by the use of a trona. FIG. 4 shows a perforated plate of an electrostatic precipitator after operation in an embodiment of a flue gas desulfurization system by the use of sodium bicarbonate.

The invention is described with reference to the drawings, in which like elements are referred by equal numbers. The relationship and operation of the various elements of the present invention are comprised better through the following detailed description. Nevertheless, the embodiments of the present invention are described below only by way of example, and the invention is not limited to the embodiments illustrated in the drawings. Dry absorbent injection (DSI) has been used as a low cost alternative to dry spray or wet cleaning systems for the extraction of S02. In the DSI process, the absorbent is stored and injected dry in the combustion duct, where it reacts with the acid gas. The present invention provides a method for extracting S02 from a combustion gas stream comprising S02, preferably by injection of an absorber such as trona, into a flue gas stream for reactions with S02. The trona is a mineral that contains approximately 85-95% sodium sesquicarbonate (Na2C03 -NaHC03 • 2H20). A vast deposit of the ore trona is located in the southwest of yoming, near Green River. As used herein, the term "trona" includes other sources of sodium sesquicarbonate. However, embodiments are preferred in which the sesquicarbonate source is mine trona. The term "combustion gas" includes the exhaust gas of any kind of combustion process (including coal, oil, natural gas, crude glass material, etc.). The gas of Combustion generally includes S0 together with other acid gases such as HCl, S03 and N0X. In FIG. 1, a schematic of the process is shown. The furnace or combustor 10 is fed with a fuel source 12, such as coal, and with air 14 in order to burn the fuel source 12. From the combustor 10, the combustion gases are conducted to a heat exchanger or heater of air 40. The outlet of the heat exchanger or air heater 40 is connected to a particle collection device 50. The particle collection device 50 extracts the particles formed during the combustion process, for example fly ash, from the combustion gas before it is conducted to the gas stack 60 for ventilation. The particle collecting device 50 can be an electrostatic precipitator (ESP). Other types of particle collection devices, for example a baghouse, can also be used for the removal of solids. The baghouse contains filters to separate the particles formed during the combustion process of the combustion gas. Due to the relatively small size of the particles used in the process, the highchair can act as a pre-covered in the baghouse filter media. The S02 removal system includes a trona source 30. Preferably, the trona 30 has an average size of particles between about 10 microns and about 40 microns, more preferably between about 24 microns and about 28 microns. Preferably, the high chair is in the form of dry granules. A suitable source of trona is Trona T-200®, which is a mechanically refined trona ore product available from Solvay Chemicals, Green River, Y. The T-200® trona contains approximately 97.5% sodium sesquicarbonate and has an average particle size of approximately 24-28 microns. The S02 removal system may also include a ball mill sprayer 32 or other type of mill, to reduce and / or otherwise control the trona particle size at the site. The high chair is transported from the high chair source 30 to the injector 20. The highchair can be transported rheumatically or by any other suitable means. The highchair can be easily aerated for pneumatic transfer. The apparatus for injecting the high chair or sodium sesquicarbonate is illustrated schematically in FIG. 1. The high-injector apparatus 20 introduces the highchair into the flue gas duct section 42, which is arranged upstream of the baghouse inlet and upstream of the heat exchanger 40, in the presence of an exchanger or preheater . The highchair injection system is preferably designed to maximize contact of the trona with the S0X in the flue gas stream. Any type of injection device known in the art can be used to introduce the trona into the gas conduit. For example, injection can be achieved directly by means of an eductor driven by compressed air. The process does not require slurry equipment or reactor vessel if the trona is stored and injected dry in the combustion duct 42, where it reacts with the acid gas. However, the process can also be used with humidification of the combustion gas or wet injection of the high chair. In addition, the particles can be put together wet by an existing wet cleaning cup, if the process is used for the fine cleaning of acid mist. The temperature of the combustion gas varies with the location in the injection system and may also vary partly with time during operation. The temperature of the combustion gas in which the high chair is injected is between about 600 ° F and about 900 ° F. The chair is kept in contact with the combustion gas for a period sufficient to cause a portion of the chair to react with a portion of S02 to reduce the concentration of S02 in the flue gas stream. The temperature of the combustion gas preferably is greater than about 630 ° F, and more preferably is greater than about 700 ° C. The temperature of the combustion gas is preferably less than about 800 ° F and most preferably less than about 750 ° F. The temperature of the combustion gas is most preferably between about 700 ° F and about 750 ° F. The process can also be varied to control the temperature of the combustion gas. For example, the temperature of the combustion gas stream upstream of the trona can be adjusted to obtain the desired temperature of the combustion gas when the trona is injected. In addition, ambient air can be introduced into the flue gas stream and monitoring the temperature of the flue gas when the high chair is injected. Other possible methods of controlling the combustion gas temperature include the use of heat exchangers and / or air coolers. The process can also vary the location of the highchair injection or include multiple high-fuel injection locations. To achieve desulfurization, the trona is preferably injected at a rate with respect to the flow rate of S02 in order to provide a normalized stoichiometric ratio (NSR) between sodium and sulfur of between about 1.0 and 1.5. The NSR is a measure of the amount of reagent injected relative to the amount theoretically required. The NSR expresses the stoichiometric amount of absorbent required to react with all of the acid gas. For example, an NSR of 1.0 would mean that sufficient material was injected to theoretically produce 100% removal of SO2 in the incoming combustion gas; an NSR of 0.5 would give a theoretical yield of 50 percent removal of S02. The neutralization of S02 requires two moles of sodium per one mole of S02 present. Unlike sodium bicarbonate, the high chair does not melt at high temperatures. Rather, the sesquicarbonate undergoes rapid calcination of the sodium bicarbonate contained in sodium carbonate when heated to 275 ° F or more. It is believed that the decomposition "pochocho corn simile" creates a large and reactive surface by bringing the unreacted sodium carbonate to the surface of the particle for the neutralization of S02. The by-product of the reaction is sodium sulfate and it is combined with fly ash. The chemical reaction of the trona with the S0 is represented below: 2 [Na? CO3 • aHCQ, • 2H20]? 3Na2CO3 + 5H2O + C2 Na2C3 + SO2? NaaSQs + CO2 N3S? 3 + 32? 2? Na? S? 4 The solid reaction products of the trona and S02 (mainly sodium sulfate) and unreacted soda ash can be put together in an electrostatic precipitator or other particle collector device. Preferably, the total desulfurization is at least about 70%, more preferably at least about 80% and most preferably at least about 90%. In one embodiment, the flue gas stream also comprises S03. The trona is kept in contact with the combustion gas for a sufficient time for a portion of the trona to react with a portion of S03 to reduce the concentration of S03 in the flue gas stream. Generally, the S03 is more reactive with the absorbent than the S02, so the trona removes the S03 first. The chemical reaction of the trona with S03 is shown below: 2 [Na2CO3 • NalíCOj • 2H2O]? SNa? COj + 5H2O + CO2 The trona injection system can also be combined with other SOx removal systems such as sodium bicarbonate, lime, limestone, etc., in order to improve performance or extract other additional hazardous gases such as HCl, NOx and the like.

EXAMPLES A study was carried out in a commercial glass factory in Verona, CA, using an electrostatic hot-side precipitator (ESP) and without a baghouse. Natural gas was used as a source of fuel and the sulfur source came from the raw materials of the glass. The concentration of S02 in the combustion gas was 800 ppm. The used highchair was T-200 from Solvay Chemicals. The highchair was injected into the duct by means of a compressed air insufflator and a feeder with air lock. The flow rates of the highchair were measured by calibration of the rpm of the air lock with the loss of weight of the highchair in the highchair deposit. Highchair feeding rates ranged from 50 to 211 lbs / h.

EXAMPLE 1 The combustion gas was injected into the gas at a temperature of 750 ° F with NSR values of 1.0, 1.2 and 1.4. FIG. 2 shows the% extraction of S02 as a function of the standardized stoichiometric ratio (NSR) for trona. From these tests it can be seen that the trona produced S0 extraction rates of approximately 80% at an NSR of 1.2. FIG. 4 shows a perforated plate of an ESP in the glass plant after the operation of the S02 removal system for five months using trona. It can Note that the plate is relatively free from the accumulation of solids.

EXAMPLE 2 As a comparison example, sodium bicarbonate was injected under the same conditions as Example 1 with an NSR of 1.2. The result is shown in FIG.2. The% removal of S02 of 72% was significantly lower than that of trona at the same temperature and NSR. FIG. 5 shows a perforated plate of an NSP in the glass plant after the operation of the S02 extraction system by means of sodium bicarbonate. It can be seen that the plate has a significant accumulation of solids.

EXAMPLE 3 Trona was injected into combustion gas at an NSR of 1.5 in a temperature range of 750 ° F to 805 ° F. FIG. 3 shows the% extraction of S02 as a function of the combustion gas temperature. From these tests it can be seen that the high chair produced S02 extraction rates of up to 91% and was effective for a wide range of elevated temperatures. From the previous examples it can be seen that the trona is more effective than sodium bicarbonate for the removal of S02 from a flue gas stream at high temperatures. Consequently, the system can use less absorbent material than a sodium bicarbonate system to obtain the same sulfur reduction. In addition, it can be seen that the high chair had good activity for a wide range of high temperatures. Finally, the S02 extraction system using trona had much lower accumulation of solids in the ESP perforated plates than a system using sodium bicarbonate. The embodiments described above and shown herein are illustrative and not restrictive. The scope of the invention is indicated by the claims rather than by the foregoing description and the accompanying drawings. The invention can be carried out in other specific embodiments without departing from the spirit of the invention. Accordingly, these and other changes that are included in the scope of the claims are intended to be embraced therein.

Claims

NOVELTY OF THE INVENTION Having described the invention as above, property is claimed as contained in the following: CLAIMS

1. A method for extracting S02 from a flue gas stream comprising S0, characterized in that it comprises: - providing a trona source; - injecting the trona into the flue gas stream, wherein the temperature of the combustion gas is between about 600 ° F and about 900 ° F; and - keeping the chair in contact with the combustion gas for a sufficient time for a portion of the trona to react with a portion of S02 to reduce the concentration of S02 in the flue gas stream.

2. The method according to claim 1, characterized in that the average particle size of the trona is less than about 40 microns.

3. The method according to claim 1, characterized in that the average particle size of the trona is between about 10 microns and about 40 microns.

4. The method according to claim 1, characterized in that the average particle size of the trona is between approximately 24 microns and approximately 28 microns.

The method according to claim 1, characterized in that the temperature of the combustion gas is greater than about 630 ° F.

6. The method according to claim 1, characterized in that the temperature of the combustion gas is greater than about 700 ° F.

The method according to claim 1, characterized in that the temperature of the combustion gas is less than about 800 ° F.

The method according to claim 1, characterized in that the temperature of the combustion gas is less than about 750 ° F.

The method according to claim 1, characterized in that the temperature of the combustion gas is between about 700 ° F and about 750 ° C.

The method according to claim 1, characterized in that the trona is injected at a rate with respect to the flow rate of S02 to provide a stoichiometric normalized ratio of sodium to sulfur of between about 1.0 and 1.5.

11. The method according to claim 1, characterized in that the high chair is injected as dry material.

The method according to claim 1, characterized in that, furthermore, it comprises milling the trona to a desired particle size at a location close to the flue gas stream.

The method according to claim 1, characterized in that, furthermore, it comprises attaching a reaction product of the trona and S02 in an electrostatic precipitator.

The method according to claim 1, characterized in that the combustion gas stream also comprises S03, which further comprises keeping the trona in contact with the combustion gas for a sufficient time to react a portion of the trona with a S03 portion to reduce the concentration of S0 in the flue gas stream.

15. A method for extracting S02 from a combustion gas stream comprising S02, characterized in that it comprises: providing a trona source having an average particle size between about 10 microns and about 40 microns; injecting the chair as dry granular material into the flue gas stream, where the temperature of the flue gas is between about 600 ° F and about 900 ° F, and - keeping the chair in contact with the flue gas for a time sufficient to react a portion of the trona with a portion of S02 in order to reduce the concentration of S02 in the flue gas stream.

16. The method according to claim 15, characterized in that the average particle size of the trona is between approximately 24 microns and approximately 28 microns.

The method according to claim 15, characterized in that the temperature of the combustion gas is between about 700 ° F and about 750 ° F.

18. The method according to claim 15, characterized in that the trona is injected at a rate with respect to the flow rate of S02 to provide a stoichiometric ratio normalized between sodium and sulfur of between about 1.0 and 1.5.

19. The method according to claim 15, characterized in that, further, it comprises adjusting the combustion gas temperature upstream of the trona in order to obtain the temperature of the desired combustion gas where the trona is injected. The method according to claim 19, characterized in that the adjustment also comprises introducing ambient air into the combustion gas stream and monitoring the temperature of combustion gas where the trona is injected. The method according to claim 19, characterized in that the adjustment also comprises controlling the flow of a material through a heat exchanger in communication with the combustion gas.