JP2604430B2 - Coal gasification method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a coal gasification method, and particularly to the treatment of a waste desulfurization agent generated by a reaction when a sulfur compound in a generated gas is removed by a desulfurization agent. The present invention relates to a coal gasification method for appropriately performing detoxification treatment.

[Conventional technology]

In recent years, the use of coal as an energy source has been rapidly progressing, and a method of burning coal as fuel as it is, and a technique of gasifying and liquefying coal to use it as a non-polluting fluid fuel are expanding. In Japan, as a technology development for gasifying coal, development of a high-calorie gasification process for obtaining a raw material gas or a fuel gas and a low-calorie gasification process for power generation have been mainly advanced.
In the case of power generation, the process of gasifying coal in a spouted bed using oxygen or air and steam and discharging ash as slag is considered to be very effective in improving gasification efficiency. Can be

In this spouted bed gasification process, the temperature inside the furnace was set to 1500 ° C.
By doing the above, the ash in the coal is melted and discharged from the furnace bottom, so the gasification reaction rate of carbon in the coal is very high, and the utilization rate of carbon is said to be almost 100% . In the case of spouted bed gas, it is necessary to raise the temperature of the gasifier to discharge ash in coal as slag. Refining and introducing it to gas turbines is a key to improving power generation efficiency. When coal is gasified, sulfur in the coal is mainly H ₂ S, and if it is put into a gas turbine as it is, it causes corrosion of turbine blades. Therefore, desulfurization at a high temperature is a major issue.

Fig. 13 shows a conventional gasification power generation flow. In the spouted bed gasifier 1, the temperature of the generated gas is 1500 ° C. or higher.
The high-temperature gas leaving the gasifier passes through cyclone 7 and heat exchanger
11 and heat recovery, and then through the dust remover 12
And sulfur compounds such as hydrogen sulfide (H ₂ S) are removed.
Here, the desorbing agent reacts to form sulfide, and a gas for regenerating the sulfide is supplied from a regeneration gas supply pipe 37, and the regeneration gas enters the S recovery tower 38 from an outlet pipe 36 and is a final product. The sulfur is discharged from the recovery S outlet pipe 39. On the other hand, the refined coal gas enters the gas turbine 41 from the combustor 40 and is used for power generation.

In this way, the gas normally reproduced, because the SO _2, places a heavy load from the SO ₂ in the S recovery column for the S (sulfur), the process problems to be complicated.

The high-temperature desulfurization process using limestone as a desulfurizing agent
Various development studies have been conducted at Texaco, Squires, Westinghouse, etc., but none of them has established a process up to the treatment of limestone sulfide (CaS) that has reacted. Japanese Patent Publication No. 60-104188 discloses a desulfurization tower 25.
A method has been proposed in which the waste desulfurizing agent generated in step (1) is supplied to the slagging section of the gasification furnace and disposed of.However, since the process is a waste desulfurization treatment of a desulfurization tower installed after the gasification furnace, the process is There are drawbacks that are complicated.

[Problems to be solved by the invention]

As described above, in the related art, a high-temperature desulfurization tower is installed after a gasification furnace in order to remove a sulfur compound in a product gas. Therefore, in the high-temperature desulfurization tower, H ₂
Since S is removed as sulfide, the sulfided reactive desulfurizing agent must be regenerated. Usually, when oxygen is supplied to the sulfided catalyst to regenerate the catalyst, SO ₂ is generated as a regenerated gas. Therefore, a regeneration process for reducing the SO ₂ gas and adsorbing it as sulfur is required. Therefore, in addition to the desulfurization tower, a SO ₂ gas reduction tower and an S adsorption tower are required, so that the process is complicated and the cost is increased.

[Means for solving the problem]

The invention claimed in the present application for solving the above-mentioned problems is as follows.

(1) supplying a coal and an oxygen-containing gas smaller than the theoretical combustion oxygen amount into the gasification furnace to generate a combustible gas;
In a coal gasification method having a desulfurization step of supplying a desulfurizing agent to the generated gas to remove a sulfur component in the generated gas and a step of separating a waste desulfurizing agent from the gas after the desulfurization step,
A step of recirculating the separated desulfurizing agent to a gasification furnace to form a desulfurizing agent solid solution slag, and discharging the solution slag from the furnace bottom,
Coal gasification characterized by having a step of cooling calcium sulfide in the slag to calcium hydroxide or calcium sulfate in the step of cooling with an aqueous solution and solidifying the slag, and a separation step of separating the cooled slag from the aqueous solution Method.

(2) The coal gasification method according to (1), wherein the separation step of the waste desulfurizing agent is a step of pulverizing the slag after the cooling step with a pulverizer and then separating it from the aqueous solution.

(3) In the coal gasification method according to (1), in the step of discharging the solution slag from the furnace bottom and cooling with an aqueous solution, the aqueous solution is converted to an aqueous solution having a pH of less than 7, and calcium sulfide in the slag is reduced in the aqueous solution. A coal gasification method characterized by converting into calcium hydroxide.

(4) In the coal gasification method according to (1), in the step of discharging the solubilized slag from the furnace bottom and cooling with an aqueous solution, the aqueous solution is converted into an aqueous solution having a pH of 8 or more, and calcium sulfide in the slag is removed in the aqueous solution. A coal gasification method characterized by converting into calcium hydroxide.

[Action]

The empty tower portion of the gasification furnace is at a high temperature of 800 to 1200 ° C. When a Ca-based desulfurizing agent having high reactivity under this temperature condition is used, the sulfur compound of the product gas is desulfurized by the following reaction.

CaO (CaCO ₃ ) + H ₂ S → CaS + H ₂ O… (1) CaO (CaCO ₃ ) + COS → CaS + CO ₂ … (2) The reaction product, CaS, is collected by a dust remover and slag of the gasification furnace Into the slag. When the hot slag is quenched with cooling water, cracks are formed on the slag surface and granulated. Therefore, calcium sulfide (CaS) existing in the fracture surface of the slag reacts with water, and H ₂ S is dissolved in the cooling water as follows.

CaS + 2H ₂ O → Ca (OH) ₂ + H ₂ S (3) The reaction (3) occurs violently when the pH is 7 or less.
However, if it is below 6.5, the CaS present on the fracture surface will react completely within a short time, so if it is treated with water below pH 7 and disposed of as industrial waste as it is, no S elution reaction will occur and it can be treated as a non-polluting substance. Becomes possible.

On the other hand, the reaction (3) hardly proceeds under the condition that the pH is 8 or more, and only a part of S along the fracture surface and the crack surface causes an elution reaction. The slag treated with cooling water of pH> 8 is sent to a slag oxidation tower, and the sulfur remaining on the surface is oxidized by high-temperature combustion exhaust gas. The reaction in this case is as follows.

CaS + 2O ₂ → CaSO ₄ (4) Therefore, CaS present in the fracture surface or crack of the solution slag becomes water-insoluble calcium sulfate (CaSO ₄ ), so that there is no elution reaction of S from waste slag. .

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to Examples.

FIG. 1 is a system diagram of a coal gasifier according to one embodiment of the present invention. This apparatus comprises a gasifier 1 for gasifying coal in a spouted bed and a device attached thereto. Fine coal to be gasified is supplied from a coal supply pipe 4 to a slagging section B at the lower part of the gasification furnace, and at the same time, air or oxygen as a gasifying agent is supplied from an air supply pipe 3. Then, the coal is gasified to generate a product gas mainly composed of H ₂ and CO and sulfur compounds such as H ₂ S and COS. The ash in the coal is melted and discharged as slag 28 from the slag extraction pipe 24 to the outside of the system.

On the other hand, a degassing agent supply pipe 2 for removing sulfur compounds is provided in the empty tower portion A of the gasification furnace, and supplies a degassing agent of fine powder, for example, coal stone, ZnO, dolomite, iron oxide, and the like. In these desulfurization reactions, as in the case of coal stone, as shown in equation (1), the sulfur compound is removed as a sulfide in all cases.

The product gas desulfurized in the gasification furnace is supplied to a product gas extraction pipe 6.
Through the first cyclone 7 to separate mainly unreacted char. Unreacted char is recycled from the char supply pipe 9 to the gasification furnace. The product gas exiting the first cyclone further enters the second cyclone 8, where the mainly reacted fine powder desulfurizing agent is separated. The product gas exiting the second cyclone enters the heat exchanger 11 and is cooled to about 500 ° C., after which the fine powder desulfurizing agent is removed by the dust remover 12 and sent to the gas turbine from the purified gas outlet pipe 14.

On the other hand, the reactive desulfurizing agent collected by the second cyclone is recycled from the dust supply pipe 10 to the slag forming section B, and the reactive desulfurizing agent collected by the dust remover is recycled from the waste desulfurizing agent supply pipe 16 to the slag forming section. . A purified gas is used as a transport gas for the reacted desulfurizing agent, the amount of which is adjusted by the control valve 13, and the reactive desulfurizing agent is supplied to the slag forming section by the pressure pump 15. Here, after CaS is dissolved in the slag, when the high-temperature slag is rapidly cooled by the cooling water 5, cracks are formed in the slag surface and water granulated. The slag particle size here is usually 5 to 10 mm. The slag and the circulating cooling water pass through the cooling water discharge pipe 17 and are cooled by the cooler 27 before entering the slag separator 20. Here, the slag is crushed by the slag crusher 23 so that cracks are eliminated and the slag becomes 1 mm or less. The pH of the circulating cooling water is detected by a pH adjuster 21 installed in the slag separator, and this signal is sent to a liquid control valve 18. The pH of the circulating cooling water is controlled to 6.5 or less with an acidic liquid. Finally, the slag crushed to 1 mm or less is discharged out of the system from the slag extraction pipe 24, and the pH-adjusted cooling water is circulated to the lower part of the gasifier through the cooling water return pipe 22.
By treating the solution slag containing CaS in such a way, it becomes possible to dispose of the slag as a non-polluting substance, and gasification and desulfurization can be performed in the furnace,
Desulfurization cost can be reduced.

FIG. 2 is a system diagram of a coal gasifier showing another embodiment of the present invention, in which a desulfurization tower 25 is installed after the gasifier of the coal gasifier of FIG. The waste desulfurizing agent generated in the gasification furnace is supplied from the waste desulfurization agent supply pipe 26 to the slag forming section of the gasification furnace, and the generated slag is treated in the same manner as in FIG. 1 with cooling water having a pH of 6.5 or less. Thereby, the elution of S from the waste slag can be almost completely prevented.

FIG. 5 shows the results of immersion experiments performed on slag in which CaS was solubilized while changing the pH to determine the amount of S eluted per unit slag weight. When pH is 7, S of CaS existing in the fracture surface
Since it takes time for the elution amount to reach equilibrium, in the embodiment shown in FIG. 1, even if the slag is 1 mm or less, if the slag is discarded as it is, it is predicted that S elution will occur, which is not desirable. When the pH of the cooling water is set to 4, the S component present in the slag fracture surface elutes into the cooling water in a short time, and the slag thus treated can be directly discarded as a non-polluting substance. This means that if the pH of the cooling water is less than 7,
This is because the reaction represented by the formula (3) quickly proceeds to the right. The S content dissolved in the cooling water is returned to the lower part of the gasification furnace together with the circulating cooling water, and when the cooling water is heated in the gasification furnace, H ₂ S gas is supplied to the gasification furnace except for the saturated elution S content at that temperature. It is released and will be removed again by the desulfurizing agent.

FIG. 6 shows the relationship between the pH of the cooling water and the amount of S eluted. pH 7
It can be seen that the S elution amount of CaS present on the fracture surface rapidly increases when the pH is smaller, and becomes almost constant when the pH becomes 6 or less.

FIG. 7 shows the relationship between the slag particle size and the amount of S eluted at a cooling water pH of 6. When the particle size is large, the amount of S eluted is small because the specific surface area is small, but it takes time to completely elute S on the slag surface because part of S elutes from the cracked part of the slag. When the particle size is 1 mm or less, the amount of S eluted shows a substantially constant value, and it is considered that all the S components on the surface are eluted.

FIG. 8 shows the results obtained by injecting sulfides such as CaS and FeS into the slag forming section of the gasification furnace to form a solid solution in the slag, and immersing the generated slag in water to determine the amount of S eluted. . pH =
7. Assuming that the S elution rate when the slag particle size is 5 to 10 mm is 100, the S elution amount is 1 or less when the pH is 4 and the particle size is 1 mm or less, indicating that there is almost no S elution.

FIG. 9 shows the relationship between H ₂ S dissolved in cooling water and temperature. If the temperature of the slag separator is set to 40 ° C or lower, the solubility of H ₂ S is large, so the S component eluted from the slag surface elutes and exists in the form of H‖S. When returned to the gasification furnace, the cooling water It can be seen that the H ₂ S eluted and the eluted H ₂ S was released to the gasifier.

As described above, the desulfurizing agent of the sulfur compound generated by the desulfurization reaction is blown into the slag forming section of the gasification furnace to form a solid solution in the slag, and the slag generated by using the present invention is subjected to a pollution-free treatment. Therefore, it has the feature that it can be treated as industrial waste.

FIG. 3 is a system diagram of a coal gasifier showing still another embodiment of the present invention. This equipment uses waste desulfurizer (CaS)
Is dissolved in the slag in the slag forming section B of the gasification furnace 1, and the first slag is rapidly cooled in the cooling step 5 during cooling.
The description is omitted because it is the same as that of the embodiment shown in FIG. When the high-temperature slag is rapidly cooled by the cooling water 5, a crack is formed in the slag surface and the slag is granulated. The slag particle size here is usually 5 to 10 mm, and the slag and the circulating cooling water enter the slag separator 20 through the cooling water discharge pipe 17. Here, the circulating cooling water detects the pH with a pH adjuster 21 installed in the slag separator, sends this signal to a liquid control valve 18, and sends a basic liquid having a pH of 8 or more sent from a basic liquid supply pipe 19. For example, the pH of the circulating cooling water is controlled to 8 or more with a potassium hydroxide or sodium hydroxide solution. The slag treated here is sent from the slag discharge pipe 24 to the separator 45, and the treated slag 28a is separated by the screen. The circulating cooling water is returned to the slag separator 20 through the cooling water pipe 46.

On the other hand, the treated slag passes through the slag pipe 47 and the slag oxidation tower.
It is sent to 32 and oxidized. Here, the gas or oil fuel sent from the fuel pipe 29 is burned by the air from the air pipe 30 to generate exhaust gas containing high-temperature residual oxygen, thereby causing the reaction of equation (4). The temperature here is usually above 300 ° C,
The reaction of formula (4) proceeds by the residual oxygen in the exhaust gas, the combustion gas is discharged out of the system through the exhaust gas pipe 31, and the treated slag is discarded from the waste slag pipe 33 to the outside of the system.

Normally, when a calcium-based waste desulfurizing agent or reactive desulfurizing agent is blown into slag, CaS forms a double salt compound of silicon oxide and aluminum oxide, which are mostly slag components, so it is a stable substance. It may be present as CaS, and reacts with water to elute S component. However, slag can be treated as waste by performing the above-described treatment.

FIG. 4 is a view showing still another embodiment of the present invention, in which a purified gas is used as a fuel for the oxidation treatment tower. In this embodiment, since a part of the purified gas is introduced from the branch pipe 34 as fuel for the slag processing tower, there is no need to supply fuel from the other. Therefore, there is no need to install a fuel tank or the like necessary for the slag oxidation tower, and the use of clean purified gas can reduce the cost of slag treatment.

It can be seen that when the pH of the slag in which CaS was solubilized as shown in FIG. 5 was changed and the pH was increased to 12 in the immersion experiment, the CaS elution reaction hardly occurred. Therefore, even if this circulating cooling water is blown as waste water, no pollution problem occurs.

In the relationship diagram between the pH of the cooling water and the amount of S eluted in FIG.
As a result of immersing the S-solubilized slag for 30 days, it can be seen that if the pH is increased to 8 or higher, the S elution reaction from the cross section of the slag breaks hardly occurs.

FIG. 10 shows the S elution mechanism at the fracture surface of the CaS solid solution slag. Free CaS that does not form a double salt compound in the slag reacts with water (H ₂ O) and elutes as hydrogen sulfide (H ₂ S aq.) In the aqueous solution. In addition, H ₂ O penetrates from cracks generated when the slag is quenched and reacts with free CaS inside the slag to cause S elution. CaS is expressed by the equation (3) due to the reaction with H ₂ O. (OH) which is hardly soluble in water
To produce the _2, thus alkali treatment (pH> 12) was S elution amount be discarded slag can be greatly reduced.

FIG. 11 shows the result of oxidizing slag treated at pH> 12 with combustion exhaust gas containing oxygen. The rate at which S existing as free CaS on the slag fracture surface is oxidized,
In other words, the SO ₄ generation rate is 10
It turns out that it becomes 0%, and it turns out that the slag heating time can be considerably shortened at about 600 ° C. Free CaS
When this is oxidized in this way, it finally becomes non-polluting and water-insoluble calcium sulfate in the slag as shown in the equation (4). Therefore, there is no problem even if this treated slag is discarded.

Fig. 12 shows that calcium sulfide (CaS) generated by the reaction of equation (1) is blown into the slag forming part of the gasification furnace to form a solid solution in the slag, and the generated slag is immersed in water to elute S. The results of determining the amount are shown. 30 slags treated with pH = 7 cooling water
Assuming that the S elution rate after immersion for 100 days is 100, p
In the treatment result at H = 12, the value was reduced to 9 and further oxidized, the S elution amount became 1 or less, and it was found that there was almost no S elution.

As described above, the desulfurizing agent of the sulfur compound generated by the desulfurization reaction is blown into the slag forming section of the gasification furnace to form a solid solution in the slag, and the slag generated by using the present invention is subjected to a pollution-free treatment. Therefore, it has the feature that it can be treated as industrial waste.

〔The invention's effect〕

According to the coal gasification method of the present invention, the sulfur component in the product gas is removed in the gasification furnace using the desulfurization agent, and the waste desulfurization agent after desulfurization is removed from the slag in the slag forming section in the gasification furnace. After solid solution, it is treated with water of a specific pH to make it harmless.
Inexpensive and non-polluting coal gasification treatment can be achieved without providing a specially expensive treatment device.

[Brief description of the drawings]

1, 2, 3, and 4 are system diagrams of a coal gasifier according to an embodiment of the present invention, respectively, and FIG.
Sulfur elution amount experiment diagram of slag in which S was dissolved in various pH aqueous solutions, Fig. 6 shows the relationship between the pH of the aqueous solution and the sulfur elution amount from the slag, and Fig. 7 shows the slag particle size and sulfur elution. FIG. 8 is a graph showing the relationship between aqueous solution pH, slag particle size and sulfur elution amount, FIG. 9 is a graph showing the relationship between aqueous solution temperature and H ₂ S elution amount, FIG.
Fig. 0 is an explanatory diagram of the sulfur elution mechanism at the fracture surface of CaS solid solution slag, Fig. 11 is an explanatory diagram of the slag oxidation treatment result after treatment at pH 12 or more, and Fig. 12 is aqueous solution treatment, oxidation treatment and sulfur elution FIG. 13 is an explanatory diagram of the prior art. DESCRIPTION OF SYMBOLS 1 ... Gasification furnace, 2 ... Desulfurizer supply pipe, 3 ... Air supply pipe, 4 ... Coal supply pipe, 5 ... Cooling water, 7 ... First cyclone, 8 ... Second cyclone, 10 …… Dust supply pipe,
12 ... dust collector, 16 ... waste desulfurizing agent supply pipe, 19 ... acid liquid supply pipe, 21 ... pH adjuster, 22 ... cooling water return pipe, 28 ... slag.

Claims (4)

(57) [Claims] 1. A process for supplying a coal and an oxygen-containing gas having less than the theoretical combustion oxygen amount into a gasification furnace to generate a flammable gas, and supplying a desulfurizing agent to the generated gas to obtain sulfur in the generated gas. In a coal gasification method having a desulfurization step of removing components and a step of separating a waste desulfurization agent from gas after the desulfurization step, the separated desulfurization agent is recirculated to a gasification furnace to form a desulfurization agent solid solution slag. And the step of discharging the solution slag from the furnace bottom and cooling with an aqueous solution, the step of changing the calcium sulfide in the slag to calcium hydroxide or calcium sulfate to solidify the slag, and the step of cooling the slag from the aqueous solution And a separation step of separating. 2. The coal gasification method according to claim 1, wherein the step of separating the waste desulfurizing agent is a step of pulverizing the slag after the cooling step with a pulverizer and then separating it from the aqueous solution. 3. The method for coal gasification according to claim 1, wherein the solution solubilized slag is discharged from the furnace bottom and cooled with an aqueous solution, wherein the aqueous solution is converted to an aqueous solution having a pH of less than 7, and the slag is mixed with the aqueous solution. A coal gasification method comprising converting calcium sulfide of the present invention into calcium hydroxide. 4. The method for coal gasification according to claim 1, wherein the step of discharging the solubilized slag from the furnace bottom and cooling with an aqueous solution comprises converting the aqueous solution to an aqueous solution having a pH of less than 8 and removing the slag in the aqueous solution. A coal gasification method comprising converting calcium sulfide of the present invention into calcium hydroxide.