HK1123005A - Method of removing sulfur dioxide from a flue gas stream - Google Patents

Description

Method for removing sulfur dioxide from flue gas stream

Technical Field

The present invention relates to the purification of gases, and more particularly to the purification of gases containing harmful gases such as SO₂The flue gas of (1).

Background

Various sorbents have been used to remove SO from flue gases using Dry Sorbent Injection (DSI)_xAnd other gases. However, DSI has typically been performed at temperatures well below 400 ° f in the past because equipment materials such as bag house media cannot withstand higher temperatures. In addition, many absorbent materials sinter or melt at temperatures near or above 400 ° f, which reduces their effectiveness in degassing. The reaction products of many absorbent materials also adhere to equipment and at higher temperaturesOn the pipes, which requires frequent cleaning of the process equipment. To operate at these lower temperatures, it is generally necessary to cool the combustion gas prior to injection of the absorbent. This is an undesirable additional process step.

Therefore, there is a need for SO removal at elevated temperatures_xAn effective absorbent injection method in the case of gas.

Disclosure of Invention

In one aspect, there is provided a process for removing sulfur from a gas containing SO₂In the flue gas stream of (A) to remove SO₂The method of (1). The method includes providing a source of trona and injecting the trona into a flue gas stream. The temperature of the flue gas is about 600F to about 900F. Maintaining the trona in contact with the flue gas for a time sufficient to contact a portion of the trona with a portion of the SO₂Reacting to reduce SO in flue gas stream₂The concentration of (c).

In another aspect, a method for recovering SO from a gas containing stream is provided₂In the flue gas stream of (A) to remove SO₂The system of (1). The system includes a source of trona and a flue gas stream. The system also includes an injector for injecting trona into the flue gas stream. The temperature of the flue gas is about 600F. to about 900F. The system also includes a zone for maintaining the trona in contact with the flue gas for a time sufficient to contact a portion of the trona with a portion of the SO₂Reacting to reduce SO in the flue gas stream₂The concentration of (c).

Drawings

The foregoing paragraphs are provided by general introduction and are not intended to limit the scope of the appended claims. The presently preferred embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

FIG. 1 is a schematic diagram of one embodiment of a flue gas desulfurization system.

FIG. 2 shows the normalization of trona and sodium bicarbonateSO as a function of the stoichiometric ratio (NSR)₂Graph with% removed.

FIG. 3 is a graph showing SO as a function of flue gas temperature (in F.) for one embodiment of a flue gas desulfurization system₂Graph with% removed.

FIG. 4 shows a perforated plate of an electrostatic precipitator after operation in one embodiment of a flue gas desulfurization system using trona.

FIG. 5 shows a perforated plate of an electrostatic precipitator after operation in one embodiment of a flue gas desulfurization system using sodium bicarbonate.

Detailed Description

The present invention is described with reference to the drawings, wherein like elements are designated by like reference numerals. The relationship and functioning of the various elements of this invention are better understood by the following detailed description. However, the embodiments of the present invention described below are merely examples, and the present invention is not limited to the embodiments shown in the drawings.

Dry Sorbent Injection (DSI) has been used for SO removal₂A low cost alternative to the spray drying or wet scrubbing system of (a). In the DSI process, the sorbent is stored and dry sprayed into the flue duct where it reacts with the acid gas. The invention provides a method of reacting SO with an absorbent, preferably by injecting an absorbent such as trona into a flue gas stream₂React to contain SO₂In the flue gas stream of (A) to remove SO₂The method of (1). The trona comprises about 85-95% sodium sesquicarbonate (Na)₂CO₃·NaHCO₃·2H₂O) in the mineral. A large deposit of mineral trona is found in southwestern wyoming near greens. As used herein, the term "trona" includes other sources of sodium sesquicarbonate. However, embodiments are preferred in which the sesquicarbonate source is mined trona. The term "flue gas" includes gases from any type of combustionExhaust gas from combustion processes (including coal, oil, natural gas, glass feedstock, etc.). The flue gas typically contains SO₂And other acidic gases such as HCl, SO₃And NO_x。

A schematic of the process is shown in figure 1. A furnace or burner 10 is supplied with a fuel source 12 (e.g., coal) and then with air 14 to combust the fuel source 12. The combustion gases are directed from the burner 10 to a heat exchanger or air heater 40. The outlet of the heat exchanger or air heater 40 is connected to a particle collection device 50. The particle collection device 50 removes particles, such as fly ash, generated during the combustion process from the flue gas before the flue gas is directed to a gas stack 60 for exhaust. The particulate collection device 50 may be an electrostatic precipitator (ESP). Other types of particle collection devices, such as baghouses, may also be used to remove solids. The baghouse contains a filter for separating the flue gas from particles produced during combustion. Due to the relatively small particle size used in the present process, trona may act as a precoat on baghouse filter media.

SO₂The removal system includes a source of trona 30. Trona 30 preferably has an average particle size of about 10 microns to about 40 microns, most preferably about 24 microns to about 28 microns. The trona is preferably in dry particulate form. A suitable trona source is T-200 ® trona, a mechanically refined trona ore product available from Solvay Chemicals, Green River, WY. The T-200 ® trona contains about 97.5% sodium sesquicarbonate and has an average particle size of about 24-28 microns. SO (SO)₂The removal system may also include a ball mill 32 or other type of mill to reduce and/or control the particle size of the trona in situ.

Trona is delivered to the injector 20 from a trona source 30. Trona may be transported pneumatically or by any other suitable method. Trona can be easily blown for pneumatic transport. The equipment for spraying trona or sodium sesquicarbonate is schematically shown in figure 1. The trona injection apparatus 20 introduces trona into a flue gas duct section 42, which flue gas duct section 42 is disposed upstream of the baghouse inlet and the heat exchanger 40 (if the heat exchanger is a heat exchanger)Or if a preheater is present). The trona injection system is preferably designed to mix the trona with the SO in the flue gas stream_xContact of (a) is maximized. Any type of injection device known in the art may be used to introduce trona into the gas line. For example, injection may be achieved directly by a compressed air driven injector.

If trona is stored and dry sprayed into its flue 42 where it reacts with acid gas, the process does not require slurry equipment or a reaction vessel. However, the method may also be used with humidification of flue gas or wet injection of trona. Furthermore, if the method is used for clean scrubbing of acid mist, the particles can be collected wet by the presence of a wet scrubber vessel.

The temperature of the flue gas varies with position in the injection system and may also vary slightly with time during operation. The temperature of the flue gas where the trona is injected is about 600F. to about 900F. Maintaining the trona in contact with the flue gas for a time sufficient to contact a portion of the trona with a portion of the SO₂Reacting to reduce SO in the flue gas stream₂The concentration of (c). The temperature of the flue gas is preferably greater than about 630 deg.F, and most preferably greater than about 700 deg.F. The temperature of the flue gas is preferably less than about 800F, and most preferably less than about 750F. The temperature of the flue gas is most preferably from about 700F to about 750F.

The process can also be modified to control the temperature of the flue gas. For example, the flue gas temperature upstream of the trona may be adjusted to obtain the desired flue gas temperature where the trona is injected. Further, ambient air may be introduced into the flue gas stream and the flue gas temperature monitored where the trona is injected. Other possible methods of controlling the flue gas temperature include the use of heat exchangers and/or air coolers. The method may also vary the trona injection location or include multiple locations for trona injection.

To achieve desulfurization, trona is preferably used in a ratio to SO₂A flow rate to provide a normalized stoichiometric ratio (N) of sodium to sulfur of about 1.0 to 1.5SR). NSR is a measure of the amount of reactant injected relative to the amount theoretically required. NSR represents the stoichiometric amount of absorbent required to react with all acid gases. For example, an NSR of 1.0 refers to injection of sufficient material to theoretically one hundred percent remove SO from the inlet flue gas₂(ii) a An NSR of 0.5 means that fifty percent of the SO is theoretically removed₂. SO being present per mole₂Two moles of sodium are required for SO₂And (4) neutralizing.

Unlike sodium bicarbonate, trona does not melt at high temperatures. In contrast, sodium sesquicarbonate undergoes flash calcination of the contained sodium bicarbonate to sodium carbonate when heated at or above 275 ° f. It is believed that the "popcorn-like" decomposition proceeds with SO by bringing unreacted sodium carbonate to the particle surface₂Neutralization results in a large active surface. The by-product of the reaction is sodium sulfate and is collected with the fly ash. Trona and SO₂The chemical reaction of (a) is as follows:

2[Na₂CO₃·NaHCO₃·2H₂O]→3Na₂CO₃+5H₂O+CO₂

Na₂CO₃+SO₂→Na₂SO₃+CO₂

Na₂SO₃+1/2O₂→Na₂SO₄

trona and SO may be collected in an electrostatic precipitator or other particle collection device₂And the solid reaction product of (b) (mainly sodium sulfate) and unreacted soda ash. The overall desulfurization rate is preferably 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 contains SO₃. Maintaining the trona in contact with the flue gas for a time sufficient to contact a portion of the trona with a portion of the SO₃Reacting to reduce SO in the flue gas stream₃The concentration of (c). AndSO₂in contrast, SO₃It is generally more reactive with the absorbent and thus trona will remove SO first₃. Trona and SO₃The chemical reaction of (a) is as follows:

2[Na₂CO₃·NaHCO₃·2H₂O]→3Na₂CO₃+5H₂O+CO₂

Na₂CO₃+SO₃→Na₂SO₄+CO₂

the trona injection system may also be used with other SO' s_xRemoval systems, e.g. combinations of sodium bicarbonate, lime, limestone, etc., to improve performance or remove additional harmful gases such as HCl, NO_xAnd the like. Examples

A hot side electrostatic precipitator (ESP) was used in a commercial glassworks by Verona, CA without a baghouse for the study. Natural gas is used as a fuel source and the sulfur source is from the glass feedstock. SO in flue gas₂The concentration of (2) was 800 ppm. The trona used was T-200 ® from Solvay Chemicals. Trona was injected in the pipe using a compressed air blower and airlock feeder. Trona flow was measured by calibrating the air lock rpm with the trona weight loss in the trona storage bin. The trona feed rate was varied from 50 lbs/hr to 211 lbs/hr.

Example 1

Trona was injected into the flue gas at temperatures of 750 ° f with NSR values of 1.0, 1.2, and 1.4. FIG. 2 shows SO as a function of Normalized Stoichiometric Ratio (NSR) of trona₂Removal% of the residue. From these experiments it can be seen that trona gave an SO of about 80% at an NSR of 1.2₂The removal rate was determined. FIG. 4 shows SO₂Removal system perforated plates of ESPs in glass plants after five months of operation using trona. It can be seen that the plate is relatively free of solids buildup.

Example 2

As a comparative exampleFor example, sodium bicarbonate was sprayed under the same conditions as in example 1 when the NSR was 1.2. The results are shown in FIG. 2. 72% SO₂Removal of% SO significantly lower than trona at the same temperature and NSR₂Removal% of the residue. FIG. 5 shows the operation of SO with sodium bicarbonate₂The perforated plate of the ESP in the glass plant after the system was removed. It can be seen that the plate had significant solids buildup.

Example 3

The trona is injected into the flue gas at a temperature of 750 ° F to 805 ° F at an NSR of 1.5. FIG. 3 shows SO as a function of flue gas temperature₂Removal% of the residue. From these experiments it can be seen that trona gave SO of up to 91%₂Removal rates and effectiveness over a wide range of high temperatures.

From the above experiments it can be seen that SO is removed from a flue gas stream at high temperatures₂Trona is more effective than sodium bicarbonate. Thus, to achieve the same sulfur reduction, the system may use less absorbent material than the sodium bicarbonate system. In addition, it can be seen that trona has good performance over a wide range of high temperatures. Finally, SO using trona compared to systems using sodium bicarbonate₂The removal system has much less solids buildup in the perforated plate of the ESP.

The embodiments described above and shown herein are exemplary and non-limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description and accompanying drawings. The present invention may be embodied in other specific forms without departing from its spirit. Accordingly, these and any other changes that come within the scope of the claims are intended to be embraced therein.

Claims (21)

1. One from containing SO₂In the flue gas stream of (A) to remove SO₂The method of (1), comprising:

-providing a source of trona;

-injecting the trona into the flue gas stream, wherein the flue gas has a temperature of about 600 ° f to about 900 ° f; and

-maintaining said trona in contact with said flue gas for a sufficient time to allow a portion of said trona to contact a portion of said SO₂Reacting to reduce the SO in the flue gas stream₂The concentration of (c).

2. The method of claim 1, wherein the mean particle size of the trona is less than about 40 microns.

3. The method of claim 1, wherein the mean particle size of the trona is from about 10 microns to about 40 microns.

4. The method of claim 1, wherein the mean particle size of the trona is about 24 microns to about 28 microns.

5. The method of claim 1, wherein the temperature of the flue gas is greater than about 630 ° f.

6. The method of claim 1, wherein the temperature of the flue gas is greater than about 700 ° f.

7. The method of claim 1, wherein the temperature of the flue gas is less than about 800 ° f.

8. The method of claim 1, wherein the temperature of the flue gas is less than about 750 ° f.

9. The method of claim 1, wherein the temperature of the flue gas is from about 700 ° f to about 750 ° f.

10. The method of claim 1, wherein the trona is in a relative relationship to the SO₂The flow rate is injected at a rate to provide a normalized stoichiometric ratio of sodium to sulfur of about 1.0 to 1.5.

11. The method of claim 1, wherein the trona is sprayed as a dry substance.

12. The method of claim 1, further comprising milling the trona to a desired average particle size at a location proximate to the flue gas stream.

13. The method of claim 1, further comprising collecting the trona and the SO in an electrostatic precipitator₂The reaction product of (1).

14. The method of claim 1, wherein the flue gas stream further comprises SO₃The method further comprises maintaining the trona in contact with the flue gas for a time sufficient to contact a portion of the trona with a portion of the SO₃Reacting to reduce the SO in the flue gas stream₃The concentration of (c).

15. One from containing SO₂In the flue gas stream of (A) to remove SO₂The method of (1), comprising:

providing a source of trona having an average particle size of about 10 microns to about 40 microns;

injecting the trona as dry particulate matter into the flue gas stream, wherein the flue gas has a temperature of about 600F to about 900F; and

maintaining said trona in contact with said flue gas for a time sufficient to allow a portion of said trona to contact a portion of said SO₂Reacting to reduce the SO in the flue gas stream₂The concentration of (c).

16. The method of claim 15, wherein the mean particle size of the trona is about 24 microns to about 28 microns.

17. The method of claim 15, wherein the temperature of the flue gas is from about 700 ° f to about 750 ° f.

18. The method of claim 15, wherein the method comprisesTrona to the SO₂The flow rate is injected at a rate to provide a normalized stoichiometric ratio of sodium to sulfur of about 1.0 to 1.5.

19. The method of claim 15, further comprising adjusting the temperature of the flue gas upstream of the trona to obtain a desired flue gas temperature where the trona is injected.

20. The method of claim 19, wherein the conditioning further comprises introducing ambient air into the flue gas stream and monitoring flue gas temperature where the trona is injected.

21. The method of claim 19, wherein the conditioning further comprises controlling material flow through a heat exchanger in communication with the flue gas.