JPH0631359B2 - High temperature dry desulfurization method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for purifying a gas containing a sulfur compound, and more particularly to a high temperature dry desulfurization method suitable for removing hydrogen sulfide at high temperatures.

[Conventional technology]

A coal gasification process in which fossil fuels such as coal are gasified under high temperature and pressure in an oxygen-deficient state to obtain combustible gases such as hydrogen and carbon monoxide is regarded as a promising method for producing alternative energy to petroleum. However, coal contains sulfur, and when gasified, it produces sulfur compounds such as hydrogen sulfide and carbonyl sulfide in addition to the target flammable gas. These sulfides need to be separated and removed from flammable gases,
The method includes a wet method and a dry method. The wet method is an already completed technology, and various devices have been put to practical use. Since this wet method is a method of chemically absorbing sulfide into a solution and removing it, (1) it is necessary to cool the gas (crude gas) generated in the gasification furnace, which results in energy loss,
(2) There is a problem that it is necessary to regenerate the absorbing liquid and treat wastewater.

The latter dry method removes sulfides at high temperatures without cooling the generated crude gas to a low temperature and saves energy and wastewater treatment is unnecessary, so it is drawing attention as a new desulfurization method.

The method for producing a low-sulfur-content coal gasification gas described in JP-A-60-71690 is a dry method, in which a desulfurizing agent containing iron as a main component and having a particle diameter of 10 μm or less and a crude gas are 400 to 80.
The sulfide in the crude gas is fixed (reactively adsorbed) in the desulfurizing agent by contacting in the temperature range of 0 ° C. and separated. This method is more useful than the wet method, but (1) the desulfurizing agent after use has not been detoxified, (2) the sulfur concentration in the gas after purification is high, and it can be used directly as a purified gas. Has a problem.

The coal gasification process described in JP-A-60-104188, the waste desulfurizing agent after use, which is the problem in JP-A-60-71690, is charged into the high temperature part of the gasification furnace, The waste desulfurizing agent is not required to be treated and the slag is discharged smoothly in the gasification furnace. However, in this method, most of the desulfurizing agent is regenerated and repeatedly used, and a waste desulfurizing agent that cannot be used is treated in a gasification furnace.
It does not completely solve the problem in Publication No. 0. Further, there is a problem that it is difficult to separate the desulfurizing agent that can be repeatedly used from the desulfurizing agent that should be discarded in a reactor other than the fluidized bed.

[Problems to be solved by the invention]

Since the lower the sulfur concentration in the purified gas, the wider the range of utilization of the purified gas, the fixed bed system is being studied for precise high-temperature desulfurization, and in the experiment, the hydrogen sulfide concentration in the purified gas was set to 0. It is reduced to less than 5ppm. In the fixed bed system, generally, two or more reaction towers are used and one is desulfurized and the other one is regenerated, and desulfurization and regeneration are alternately repeated for continuous operation. The most difficult part of this method lies in the treatment of waste gas from regeneration (generally the sulfur adsorbed on the desulfurizing agent becomes SO ₂ when regenerated). That is, the waste gas is a tower called a reduction tower and
It is converted to sulfur and hydrogen sulfide by the reactions of (1) and (2).

SO ₂ + C = CO ₂ + S (1) SO ₂ + 3H ₂ = 2H ₂ O + H ₂ S (2) This reduction reaction requires a temperature of 700 ° C. or higher and a relatively long reaction time. After converting SO ₂ into S and H ₂ S by a reduction reaction and cooling these gases to remove S, unreacted SO ₂ and H ₂ S etc. can be removed by using the following (3) S is removed by the reaction of.

In addition, the exhaust gas from the low temperature Claus reactor is processed. As described above, the fixed bed system enables precise desulfurization, but it requires a reducing tower, a high-temperature and low-temperature Claus reactor, and an exhaust gas treatment device for the treatment of waste gas by regeneration, thus leaving a problem in operability.

In other words, the method of JP-A-60-71690 has excellent operability because it does not recycle the desulfurizing agent, but there is a problem in the treatment and purification desulfurization of the used desulfurizing agent.
Although precision desulfurization is possible with the method disclosed in the publication and the method of reusing a desulfurizing agent such as general fixed bed desulfurization, there is a problem in operability.

An object of the present invention is to provide a high-temperature dry desulfurization method which can perform precision desulfurization on crude gas and which does not require a Claus reactor or the like when regenerating a desulfurizing agent and has excellent operability.

[Means for solving problems]

The present invention relates to a high temperature dry desulfurization method for removing a sulfur compound from a high temperature crude gas generated by gasifying a fossil fuel in a gasification furnace, in which the crude gas and the first desulfurizing agent are contacted in the first stage, The solid portion produced as a by-product in the contacting step is returned to the gasification furnace, and the crude gas that has undergone the treatment in the first step is contacted with the second desulfurizing agent in the second step to purify the crude gas, and after use The waste gas generated when the second desulfurizing agent is treated with an oxidizing agent and regenerated is returned to the gasification furnace, and the sulfur compound is discharged from the gasification furnace together with the slag.

[Action]

In order to satisfy both operability and precision desulfurization, the present invention uses a two-stage desulfurization system. That is, in the first stage, for example, calcium-based fine particles such as CaCO ₃ and Ca (CH) ₂ are supplied as a first desulfurizing agent to a high-temperature gasification furnace and decomposed into CaO, which is then converted into the gasification furnace or the crude gas. H ₂ S, COS, CS _{2 in} crude gas while entrained in air flow
To react with a sulfur compound such as to produce CaS. Ca
A crude gas containing a solid portion such as S, unreacted CaO and unreacted coal (chair) by-produced in the gasification furnace is separated into a solid portion and a crude gas by a solid separator. The separated solid portion is oxidized in a newly provided oxidation tower to convert CaS to CaSO ₄ , and the charge is converted into gas such as CO ₂ and ash, and then returned to the gasification furnace together with the gas generated in the oxidation tower, or It is returned directly to the gasification furnace without conversion, and CaSO ₄ , ash, etc. are dissolved in molten ash (slag) in the gasification furnace and discharged from the gasification furnace as a solid solution.

In the first stage, Ca under a high temperature of about 900 ° C to 1300 ° C
If the method of desulfurizing the fine powder of O and the sulfur compound by contacting them in the gas stream layer is used, the amount of the first desulfurizing agent, that is, the amount of calcium-based fine particles to be fed into the gasification furnace is controlled against the load fluctuation of the gasification furnace. The responsiveness to load changes is improved. Also, the sulfur content adsorbed and separated from the crude gas is CaS.
After being fixed in the particles as O ₄ , it is dissolved in the slag in the coarse gas furnace, flows down to the water tank at the bottom of the gasification furnace, is cooled, and is discharged to the outside of the system, so that it can be treated as a pollution-free substance.

When this first-stage desulfurization is carried out by the gas-bed reaction as described above, the desulfurization rate is about 60 to 90%, so that the crude gas after the first-stage desulfurization is again introduced into the second-stage desulfurization tower. In the second-stage desulfurization tower, a fixed bed filled with a second desulfurizing agent carrying cobalt, zinc, and iron-based metal oxides is formed and crude gas is introduced. Since the solid layer has good contact with the solid layer,
More than 95% of the sulfur compounds in the introduced crude gas are removed. That is, in the two-stage desulfurization, 99% or more desulfurization is possible. Since the second desulfurizing agent used in this second step has an equilibrium desulfurization rate with the crude gas to be desulfurized, the type of the second desulfurizing agent is selected according to the purpose.

The second desulfurizing agent in the second stage is regenerated and reused, but all the waste gas generated at the time of regeneration is returned to the gasification furnace, which is a reducing atmosphere, and the reaction of the formula (2) is performed in the gasification furnace. By H ₂ S
Convert to. That is, one of the features of the present invention is to reduce SO ₂ to H ₂ S in a gasification furnace without using a reduction tower, a Claus reaction tower or the like for treating waste gas to be regenerated as in the conventional method. Is.

In this way, the sulfur content adsorbed in the second stage is regenerated by SO
_2, and although is reduced to H _{2 S} by returning to the gasifier again, this H _{2 S} is desulfurized in the form of CaS or the like by first desulfurization agent, said as, summer and the solid separated solid portion Then, it is melted in the slag in the gasification furnace and discharged to the outside of the system. In addition, the desulfurization in the second stage is to reduce the concentration of sulfur content in the product gas according to the purpose, that is, to perform precision desulfurization, and here, a processing device for discharging the sulfur content out of the system (reduction tower) , Klaus tower, etc.) will significantly improve drivability. In the present invention, it can be said that substantial desulfurization (discharge of sulfur content in crude gas to the outside of the system) is performed by the first desulfurizing agent in the first stage.

〔Example〕

First, the overall configuration of an embodiment of the present invention will be described with reference to FIG. In the coal gasification furnace 1, raw material coal, air as a gasifying agent, and a calcium-based first desulfurizing agent are supplied from a supply pipe 6 and a desulfurizing agent input pipe 7. H in the gasification furnace 1
The produced gas such as ₂ or CO comes into contact with the first desulfurizing agent, and the sulfide in the produced gas is fixed in the first desulfurizing agent as CaS or the like. While further contacting the solid portion and the produced gas, they pass through the gas transport pipe 8 and reach the solid separator composed of the dust remover 2. The solid portion is separated from the crude gas in the dust remover 2, moves through the solid moving pipe 9, and enters the oxidation tower 3. In the oxidation tower 3, an oxidant composed of N ₂ and O ₂ is introduced from the outside of the system through an oxidant supply pipe 10 to oxidize the solid portion into sulfate, and at the same time, the solid portion is melted to melt sulfate. Discharged from the oxidation tower 3,
On the other hand, the combustion gas is returned to the gasification furnace 1. Alternatively, as shown in the figure, all the substances produced in the oxidation tower 3 are returned from the return pipe 11 into the gasification furnace 1, and the solid portion is melted in the slag and discharged from the slag discharge pipe 20.

On the other hand, the crude gas passing through the dust remover 2 passes through the pipe 12 and the valve 1
It passes through 3 to reach the fixed bed desulfurization tower 4. Here, the crude gas is contacted with the filled second desulfurizing agent to be precisely desulfurized, and then is sent through the valve 14 from the purified gas transportation pipe 19 to the subsequent equipment (not shown) constituting the plant.

In order to enable continuous operation of the fixed bed desulfurization tower 4, two or more towers are installed, and regeneration is carried out in the other desulfurization towers not undergoing desulfurization. That is, the regeneration gas supply pipe 1 is attached to the desulfurization tower 5 in which the valves 13 'and 14' are closed and the inflow of the crude gas from the dust remover 2 is stopped.
5 from the valve 16 'via the supply oxidizing agent of the oxygen-containing a regeneration gas, adsorbed sulfur is oxidized to SO ₂ is removed as waste gas to the second desulfurization agent, the valve 17' through, the The waste gas is returned to the gasification furnace 1 via the gas recycle pipe 18. Conversely, when regenerating the second desulfurizing agent in the fixed bed desulfurization tower 4, the valves 13 and 14 are closed, the valves 16 and 17 are opened, and the regeneration gas is supplied from the regeneration gas supply pipe 15. .

Next, embodiments of the present invention will be described in detail. Finely pulverized coal and air or oxygen-enriched air which is a gasifying agent are supplied into the coal gasification furnace 1, and a temperature of 1300 to
Partial combustion of coal in the range of about 1600 ℃ CO,
It produces gases such as H ₂ , CO ₂ , and H ₂ S. At the same time, the ash content in the coal is melted and the slag is discharged from the slag extraction pipe 20 at the bottom of the gasification furnace 1 to the outside of the system. The high-temperature crude gas in which the produced gas and the unreacted coal (chair) are mixed is heated in the coal gasification furnace 1 while being recovered, and then exits from the top of the gasification furnace 1.

Here, at the high temperature, which is the first desulfurizing agent of the first stage, H ₂ S and C
Substances that react with OS, CS _2, etc., such as Ca-based and Fe
A fine powder of a Cu-based, Cu-based, Zn-based, dolomite, or the like is supplied to the inner region of the gasification furnace 1 at a temperature below the temperature at which it does not melt. This fine powder has a particle size that can be sufficiently scattered at the gas flow velocity in the gasification furnace 1, and the supply amount thereof is 1
The amount of sulfur is 0.5 to 5 times, preferably 1.0 to 2.0 times the stoichiometric value. First fine powder supplied
When the desulfurization agent is Ca-based CaCO ₃ , for example, the melting point is 1300.
The temperature of the first desulfurizing agent supplied to an atmosphere region at a temperature lower than this is decomposed by heat to CaO, and mainly reacts with H ₂ S, COS, CS ₂ etc. generated in the gasification furnace 1. It becomes CaS, and fixes the sulfur compound in the crude gas in the fine powder, that is, in the first desulfurizing agent. The fine powder containing CaS is entrained in the crude gas and reaches the dust remover 2. Where CaCO
_Since the decomposition temperature of ₃ is 825 ° C, a temperature range of 900 ° C to 1300 ° C is preferable for effective reaction. On the other hand, with respect to changes in the load, that is, changes in the coal treatment amount, the amount of the first desulfurizing agent of the fine powder to be supplied is changed in consideration of the coal treatment amount or the sulfur concentration in the gasification furnace 1.

The dust remover 2 separates solid parts such as chas, CaS, and CaO in the crude gas. The separated solid portion may be directly returned to the gasification furnace 1 and dissolved in the slag and discharged to the outside of the furnace, but the following method is preferable for the following reason. That is, the solid portion collected by the dust remover 2 is oxidized in the oxidation tower 3. When a Ca-based one is used as the first desulfurizing agent, the agent after desulfurization is mainly CaS. This CaS has a melting point of 2400 ° C.
As described above, since the slag can be contained in a state of being mixed with foreign substances without being melted, S may be eluted when the slag is discarded. Also in the Fe-based, Cu-based, and Zn-based first desulfurizing agents, in the case of a compound of a metal sulfide such as FeS, Cu ₂ S, and ZnS, there is a concern that S may be eluted from the slag. Therefore, by oxidizing the agent after desulfurization, CaSO ₄ , FeSO ₄ , ZnSO ₄ , CuSO ₄
It is effective to change to a relatively stable substance having a low melting point such as No. ₄ or the like. Especially for CaSO ₄ , the melting point is 1450 ° C.
It is possible to lower the temperature by about 950 ° C compared to CaS, and gasifier 1
It can be easily melted in and dissolved in slag in the form of solid solution. In the case of the Fe-based, Cu-based, and Zn-based first desulfurizing agents, the melting point will be 1000 ° C. or less when in the form of sulfate, so the oxidation tower 3
It is possible to melt these inside and discharge them into the aquarium.

On the other hand, the crude gas leaving the dust remover 2 still contains sulfur compounds such as hydrogen sulfide. This crude gas is introduced into the fixed-bed desulfurization tower 4, is brought into contact with the second desulfurization agent filled in the tower 4 to be desulfurized, and then sent from the inside of the purified gas transport pipe. In this desulfurization tower 4, a reaction adsorbent carrying a metal oxide, for example, TiO ₂ carrier, cobalt oxide, nickel oxide, molybdenum oxide, iron oxide (FeO, Fe ₂ O ₃ , F).
The second desulfurizing agent carrying e ₃ O ₄ ) or the like is filled.
The selection of the second desulfurizing agent is made according to the intended use of the final purified gas. That is, when it is sufficient to reduce hydrogen sulfide to a concentration of several tens of ppm, a second desulfurizing agent carrying oxides of cobalt, nickel, iron, etc. is used. The second desulfurizing agent may be used.

Two or more fixed-bed desulfurization towers are usually used, and desulfurization and regeneration are performed alternately, and the second desulfurizing agent is repeatedly used. FIG. 1 shows a desulfurization tower 4 during desulfurization and a desulfurization tower 5 during regeneration. To regenerate the second desulfurizing agent, the valves 13 ′ and 14 ′ are closed, the introduction of the crude gas from the pipe 12 is stopped, the valves 16 ′ and 17 ′ are opened, and the regeneration gas supply pipe 15 is used. By supplying an oxidizing agent such as a mixed gas of nitrogen and oxygen or a mixed gas of nitrogen, oxygen and water vapor, and oxidizing the second desulfurizing agent in the desulfurizing tower 5 to be regenerated, the second desulfurizing agent is adsorbed to the second desulfurizing agent. The sulfur content is changed to SO ₂ and desorption is performed. Since there is a condition for the second desulfurizing agent to form a sulfate compound depending on the metal species supported on the second desulfurizing agent, the temperature, the pressure and the regenerating gas composition at the time of regeneration, this is not generated. That is, the regeneration gas is prepared by adjusting the amounts of nitrogen, oxygen and water vapor within the concentration range where sulfur is separated as SO ₂ from the second desulfurizing agent. Waste gas discharged from the regenerating desulfurization tower is returned to the gasification furnace 1 through the entire amount of the gas recycle pipe 18. SO ₂ in the waste gas returned to the high temperature gasification furnace 1 is reduced by carbon and hydrogen in the gasification furnace 1 to produce Sx, H ₂ S, COS, CS.
It becomes ₂ . That is, by returning the waste gas generated by the regeneration of the second desulfurizing agent into the reducing atmosphere of the gasification furnace 1, the reducing tower and the Claus reaction tower become unnecessary, and the operability is remarkably improved.
The waste gas can be directly returned to the gasification furnace 1 because the sulfur compound in the crude gas generated in the first stage is removed.

Experimental Example Pulverized coal with a particle size of 74 μm or less and 80 wt% was supplied to the gasification furnace 1 shown in FIG. 1 at 50 kg / h, and air was supplied at 135 Nm ³ / h as a gasifying agent while gasifying at 1600 ° C. , A first desulfurizing agent and CaC for performing desulfurization in the first stage
O ₃ the gasification furnace 1 top at 940 g / h 1,200-13
It was supplied in the temperature range of 00 ° C.

A cyclone and a bag filter are used for the dust remover 2 to separate a solid portion and a gas portion, and the separated solid portion is oxidized in the oxidizing tower 3 with an oxidant composed of a mixed gas of oxygen and nitrogen,
It returned to the gasification furnace 1. On the other hand, the crude gas that passed through the dust remover 2 passed through the fixed bed desulfurization tower 4 for precision desulfurization. Further, a mixed gas of nitrogen and oxygen was sent to the other desulfurization tower 5 in the regeneration step as an oxidizing agent for regeneration, and the waste gas was returned to the reduction zone of the gasification furnace 1. The fixed-bed desulfurization tower 4 was filled with a second desulfurizing agent in which cobalt oxide was carried on a titanium oxide carrier, and the temperature was 450.
℃, the space velocity is 10000 h ^-1 operation, the desulfurization tower 5 of the regeneration process gas with an oxygen concentration of 3% space velocity 10000 ^-1
I shed it. As a result, the sulfur concentration in the gas at the outlet of the gasification furnace 1 was 874 ppm, and the concentration at the outlet of the deduster 2 was 349 ppm, and at the outlet of the fixed bed desulfurization tower 4, it was 33 ppm.
In addition, the slag discharged from the gasification furnace 1 contained 2.3% of sulfur, and no sulfur was found to be eluted in the slag elution test.

When used as a gas for a fuel cell, it is necessary to reduce the sulfur concentration in the purified gas to 0.5 ppm or less.
In this case, particles of zinc oxide or ZnFe ₂ O ₄ may be used as the second desulfurizing agent in the fixed bed desulfurization tower. However, since the regeneration level becomes more severe, the gas desulfurized by the two-step method described above is led to a desulfurization tower filled with a zinc-based desulfurizing agent installed in the third stage, and the sulfur concentration of several tens of ppm is 0.5 p
It drops below pm. That is, a three-stage desulfurization method is preferable.

〔The invention's effect〕

According to the present invention, since the two-stage desulfurization is performed by the first desulfurizing agent and the second desulfurizing agent, it is possible to perform precise desulfurization on the crude gas, and at the time of regenerating the desulfurizing agent, a reduction tower or a Claus reaction for treating the waste gas Since no tower is required, high-temperature dry desulfurization with excellent operability is possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. 1 ... Gasification, 2 ... Dust remover, 3 ... Oxidation tower, 4 ... Fixed bed desulfurization tower (during desulfurization), 5 ... Fixed bed desulfurization tower (during regeneration), 18 ... Gas recycling pipe.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jinichi Tomuro 4026 Kuji Town, Hitachi City, Ibaraki Prefecture, Hitachi Research Institute Ltd. (72) Sadao Takahashi 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Atsushi Morihara 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitate Manufacturing Co., Ltd. Hitachi Research Laboratory (72) Inventor Eiji Kida 6-9 Takaracho, Kure City, Hiroshima Prefecture Bab Kotsk Hitachi Ltd. Kure Factory (72) Inventor Akio Ueda, 8 Takara-cho, Kure-shi, Hiroshima, Bab Kotsk Hitachi Co., Ltd. Kure Laboratory (72) Inventor Shigehito Takamoto, 8 Takara-cho, Kure, Hiroshima Pref.

Claims (4)

[Claims] 1. A high temperature dry desulfurization method for removing a sulfur compound from a high temperature crude gas generated by gasifying a fossil fuel in a gasification furnace, wherein a crude gas and a first desulfurizing agent are contacted in a first step, The solid portion by-produced in this contact step is returned to the gasification furnace, and the crude gas that has undergone the treatment in the first step is contacted with the second desulfurizing agent in the second step to purify the crude gas for use. A high-temperature dry process characterized in that the waste gas generated when the second desulfurizing agent is later reacted with an oxidizing agent to regenerate the waste gas is returned to the gasification furnace, and the sulfur compound is discharged from the gasification furnace together with the slag. Desulfurization method. 2. The solid gas separator according to claim 1, wherein the contact between the crude gas and the first desulfurizing agent in the first step is carried out in the form of fine particles of the first desulfurizing agent in an air-transport state. A high temperature dry desulfurization method in which solid gas separation is performed and the crude gas and the second desulfurizing agent in the second stage are brought into solid gas contact as the fixed layer. 3. The high temperature dry desulfurization method according to claim 1 or 2, wherein the solid portion produced in the first step is oxidized into a sulfate and then returned to the gasification furnace. 4. The oxidant for regenerating the second desulfurizing agent after use is an oxygen-containing gas according to claim 1, 2, or 3, and the oxygen partial pressure of the oxidant is set to the second value. A high-temperature dry desulfurization method in which sulfur is separated from the desulfurization agent as SO ₂ .