JPS6274992A - Gasification of coal - Google Patents

Abstract

PURPOSE:To obtain a gas having a high heat value at low cost through improvement in gasification efficiency, by recovering CO2 from an exhaust gas of a plant comprising a combination of coal gasification ovens and recirculating CO2 into the coal gasification ovens to utilize it as a coal carrying medium and a gasifying agent. CONSTITUTION:Coal is fed from a coal feeding hopper 1 into a coal gasification oven 2 through gas stream conveyance with a CO2 gas 17 and burnt oxygen 20 to gasify the coal. The formed gas is purified in a purifying device 4, fed into a gas turbine 5, and burnt with air to utilize for electricity generation. An exhaust gas 11 of the gas turbine 5 is fed into a catalyst combustion device 12 to convert O2 contained in the exhaust gas 11 into CO2 and H2O. CO2 is absorbed in an absorption tower 14. The absorbed CO2 is released from a releasing tower 15, pressurized with a compressor 18, and recirculated into the coal feeding hopper 1 and coal gasification oven 2 to utilize it as a coal carrying medium, a gasifying agent, etc.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a coal gasification process in a plant that combines a coal gasification furnace, and in particular to CO2 in exhaust gas in a combined process that combines coal gasification and power generation. This invention relates to a coal gasification method that recirculates gas to a coal gasification furnace and effectively utilizes it for coal gasification.

[Background of the invention]

As a typical example of a coal gasification process in the prior art, a composite process that combines coal gasification and power generation will be described based on the drawings.

FIG. 4 is a system diagram showing an overview of the conventional coal gasification combined cycle power generation process. As shown in the figure, when supplying raw material coal to the coal gasifier 2, the coal in the coal supply hopper 1 is pressurized and the coal is introduced into the coal gasifier 2 by air transport. In order to prevent coal from igniting and exploding, an inert gas such as N2 gas is used as a medium for pressurizing and transporting coal. However, since N2 gas does not contribute to the gasification reaction in the coal gasifier 2 and is supplied at room temperature, the amount of heat required to heat the coal to the gasification temperature is consumed in excess, and the gasification of the coal is delayed. This is an unfavorable condition for the reaction. In other words, the amount of N2 gas required to supply 1 kg of coal is 1, 0.02 to 0.1 m' at normal pressure, and the weight of N2 gas is approximately 0.02 to 0.1 kg. Assuming that the pressure inside the furnace 2 is 30 atmospheres, approximately 0.6 to 3 kg of N2 gas is required. On the other hand, the generated gas from coal gasifier 2 is 1k of coal.
Approximately 2Nl per g! 13 gases are generated and the gasification pressure of coal is 30 atm, the N2 gas content is at least 20 atm.
% or more, and the amount of heat required to raise the temperature of this N2 coal to the gasification temperature is approximately 15% of the calorific value in the coal gasifier 2.
%. When the pressure in the coal gasifier 2 becomes high, this ratio tends to further increase. This N
The amount of heat required to raise the temperature of the 02 gas is compensated for by burning the raw material coal with the 02 gas, but this results in a decrease in coal gasification efficiency and an increase in the utility of the 02 gas. On the other hand, as the amount of N2 gas mixed into the generated gas increases, the calorific value of the generated gas decreases, leading to an increase in the number of transportation pipes to the gas usage source such as the gas turbine 5, and combustion due to poor combustion during combustion. Problems arise in that efficiency decreases and the amount of NOx generated increases. Furthermore, the N2 gas used as a medium for transporting coal is a utility that causes an increase in operating costs. Currently, N2 gas, which is a by-product of oxygen plants25, is used in most cases, but production costs are naturally allocated to N2 gas, and N2 gas is brought to a predetermined pressure for pneumatic transport of coal. There were problems such as the need for equipment and power costs to boost the pressure.

[Purpose of the invention]

The purpose of the present invention is to solve the problems of the prior art, and to replace the N2 gas, which is conventionally used as a conveying medium for pneumatically transporting raw material coal to a gasification furnace, by using exhaust gas generated from a plant. Separate and collect the CO2 gas inside and convert it into CO2
Generate gas or convert 02 gas in exhaust gas to CO
By converting the CO2-rich gas into CO2-rich gas, which is recirculated to the coal gasification furnace and used as a coal conveyance medium and gasification agent, the coal gasification efficiency is high and the heat generation is improved. The object of the present invention is to provide a coal gasification method that produces a large amount of high-quality gas, requires few utilities, and has low running costs.

[Summary of the invention]

In short, the present invention aims to separate and recover CO2 gas contained in the exhaust gas discharged from the plant to generate CO2 gas in a coal gasification process in a plant combining coal gasifiers, or to generate CO2 gas in the exhaust gas. After converting the 0□ gas contained in the exhaust gas to CO2 gas, the CO2 gas contained in the exhaust gas is separated and recovered to generate CO□ gas, or the 02 gas contained in the above exhaust gas is converted to CO2 gas. Produces CO2-rich gas,
Coal gasification basically involves recirculating the separated and recovered CO2 gas or gas rich in CO□ to a coal gasification furnace and using it as a conveying medium for pneumatically transporting one coal and as a coal gasification agent. It is an effective coal gasification method that has high coal gasification efficiency, can produce high-quality gas with a high calorific value, and can also reduce utility costs.

[Embodiments of the invention]

An embodiment of the present invention will be described below in more detail with reference to the drawings. In the figures, the same reference numerals indicate the same parts (devices) or parts having the same performance.

(Example 1) FIG. 1 is a system diagram showing a coal gasification method in a composite process that combines coal gasification and power generation, which is an example of the present invention. As shown in the figure, coal is supplied to a coal supply hopper 1. The recovered recycled CO2 gas, which has been pressurized to a predetermined pressure by the compressor 18, is
The raw coal is fed under pressure into the coal supply hopper 1, and the raw coal is converted into CO2.
The coal is supplied into the coal gasifier 2 by gas airflow transport. In the coal gasifier 2, a part of the coal is combusted by C2 injected from the oxygen (02) supply line 20,
Raise the temperature to the reaction temperature to gasify the coal. in general,
The gasification temperature of coal varies depending on the reactor, but it is 800~
The temperature range is 1800°C. In this temperature range, the following gasification reaction occurs within the coal gasifier 2.

Carbonization, pyrolysis coal Coal char (C) Ten hydrocarbons (C
nHm) +820 thermal decomposition CnHIII-1 → H2, CH,, C:, tH + l + H
2+ 1/20□→H20 CH, +202→CO□+2N20 Coal char (C) + H, O-→H2+GO coal char (
C) +GO□-→2CO Then, the CO2 gas supplied together with the coal reacts with the above-mentioned coal char (C) to gasify the coal char and convert it into CO gas.

C+CO,←2CO Furthermore, since this CO2 gas directly reacts with the coal char, it promotes the gasification of 0 minutes in the coal char, which is difficult to gasify, and has the function of improving the coal gasification efficiency. Therefore, when CO2 gas is used, the generated gas generated by gasification of coal is diluted by the gas entrained by airflow transport of one coal, and the calorie content of the generated gas does not decrease.

The generated gas leaving the coal gasification furnace 2 is recovered by a heat exchanger 3, passes through a gas purification device 4, de-sulfurizes and de-sulfurizes the gas, and is led to a gas turbine 5 where it is combusted with air to generate electricity. The exhaust gas from the gas turbine 5 is exhausted from the stack 7 after its heat is recovered by the waste heat recovery boiler 6 . The exhaust gas after this waste heat recovery is guided to the catalytic combustion device 12 through the exhaust gas bypass 11, and the generated gas is further introduced from the inlet of the gas turbine 5 to the catalytic combustion device 12 through the generated gas line 19.
02 in the exhaust gas is converted into CO2 and 20. What is the exhaust gas composition at the outlet of the gas turbine 5?

00212%, H2O6%, 0210%, and 8272%, and 8 minutes is not included because it is a gas after desulfurization. The generated gas for catalytic combustion is a gas whose main components are N2 and CO1CO2, and the exhaust gas composition after catalytic combustion is approximately 25% CO2, 15% H2O, and 60% N2.
becomes. After this gas is cooled in a heat recovery device 1i13, it is introduced into a CO2 absorption tower 14, where it is converted into monoethanolamine (MEA) or notyldiethanolamine (MD
E
O2 is absorbed.

CO2 gas is released from the CO2 release tower 15. This released CO□ gas is pressurized by a compressor 18.

The gas for the carrier medium of 1 coal is re-circulated W1 through the C○2 line 17 to the coal supply hopper 1 and the coal gasifier 2;
Used as a coal gasifier or barge gas. The effects of CO2 gas on coal gasification reactions are as described above, but from a safety perspective, it is well known that the explosion range due to a mixture of CO2 gas and flammable gas is narrower than that of N2 gas. This is extremely advantageous.

In the method of this embodiment, the product gas produced by the coal gasifier 2 does not contain as much as 20 to 30% N2, unlike when N2 gas is used as the coal conveyance medium. , N2 gas is only included due to the N content originally contained in coal, and the generated gas contains 1 to 1
It contains only about 3%, so even if high-temperature combustion is performed in the gas turbine 5, the generation of NOx can be significantly reduced.

Figure 3 shows CO2 gas and N2 gas as coal conveyance media.
Generated gas calorific value (kcal/Nm
3) Carbon utilization rate (%) a and cold gas efficiency (%)
This shows the relationship b. As shown in the figure.

As the ratio of 02/coal increases, that is, as the gasification temperature of 1 coal increases, the CO2 reaction is accelerated, and both the carbon utilization rate (%) and cold gas efficiency (%) are higher than in the case of N2 gas. Also, the calorific value (kcal/Nm3) of the generated gas is 0□/
Regardless of the ratio of coal, the use of CO2 gas has higher calories.

Note that the sensible heat of the gas combusted by the catalytic combustion device 12 is recovered as steam by the heat recovery device 13, and is led to the steam turbine 8 together with the steam of the waste heat recovery boiler 6 of the gas turbine 5, where it is converted into electricity. .

(Example 2) Another example of the present invention is shown in FIG. The composite process that combines coal gasification and power generation shown in the figure is similar to that described in Example 1 above.
In the combined process shown in FIG.
After the pressure is increased by , in the catalytic combustion device 12, the produced gas is used to convert 02 in the exhaust gas into CO□ to generate a CO2-rich gas, which is used as a coal conveying medium and a gasification agent. CO of the complex process shown in the figure
2, the CO2 absorption device composed of the absorption tower 14 and the CO2 release tower 15 has been removed.

Then, the exhaust gas leaving the catalytic combustion device 12 is transferred to the heat exchanger 2
3 and a gas condenser 24 to remove moisture, the exhaust gas has a composition of 00230% and N2 70%.

The exhaust gas having this composition is passed through the heat exchanger 23 again to raise the temperature,
The coal is supplied to a coal supply hopper 1 and a coal gasifier 2.

Since the method of this example contains about 70% N2 in the exhaust gas, it is disadvantageous in terms of coal gasification efficiency, calories of the produced gas, NOx generation, etc. compared to the method of Example 1 described above. However, since a CO□ absorption device is not required, the equipment cost and running cost are reduced accordingly. Note that since the recirculated exhaust gas rich in CO is heated and used as a coal conveyance medium and a gasification agent, it is possible to reduce the loss of the sensible heat component of the supplied gas. Furthermore, in the composite process of this example, 02 in the exhaust gas is
Since a catalytic combustion device is used as the combustion device for converting to O2, operation at high pressure is possible, and the capacity of the compressor used for boosting the pressure can be reduced or eliminated. In addition, compared to the conventional method using N2 gas, the CO2-rich exhaust gas contains less N2, so it goes without saying that the coal gasification efficiency improves and the calorific value of the generated gas increases. .

In this example, rather than coal gasification using air,
Gasification with oxygen is more effective. In other words, in the case of coal gasification using air, the generated gas has already been diluted with N2 in the air, so the calorific value of the generated gas is at the lowest value of the combustible range in the gas turbine.
There is a possibility that the amount of N2 becomes less than 0 kcal/Nm3, and therefore it becomes necessary to preheat the combustion air, so it is necessary to suppress excess N2 as much as possible. therefore.

If O2 gas is used for coal gasification, the excess N2 content can be lowered, and the gasification efficiency can be improved due to the sensible heat possessed by the recirculated gas containing CO2. It is possible to prevent a decrease in the strength of the generated gas. In addition, in the case of coal gasification by air oxidation, there is no need to install an oxygen plant, so the equipment cost is reduced accordingly, but it is necessary to separately prepare inert gas (N2) as a purge gas. , the utility will increase.

〔Effect of the invention〕

As explained in detail above, the coal gasification process in a plant combining the coal gasifier of the present invention has the following excellent effects.

(1) Separate and recover CO2 gas in the exhaust gas of the plant,
Alternatively, by performing combustion treatment, relatively high temperature gas rich in CO2 is used as a transport medium for supplying coal to a coal gasifier, so CO2 is reduced in the coal gasifier.
The two gases react with high efficiency as coal gasifying agents, and therefore the coal gasification efficiency can be significantly increased, and the cold gas efficiency and carbon utilization rate can be significantly improved.

(2) Unlike when inert gas (N2) is used as a transport medium for coal, the product gas produced by the coal gasification reaction is not diluted significantly by N7, so the calorie content of the product gas is reduced. The calorific value of coal gasification can be kept high, which is the original calorific value of coal gasification.

(3) Since the N2 content in the gas produced by coal gasification can be reduced, the amount of N08 generated during combustion in, for example, a gas turbine can be suppressed. This allows the design temperature of the gas turbine to be increased, leading to improved power generation efficiency.

(4) Inert gas (N2), which is a utility, can be used to supply the necessary coal transportation medium and gasification agent by using the gas generated from the coal gasifier and the exhaust gas from the combined process. can reduce the use of Therefore, when using the 02 plant, excess N2, which is the by-product gas,
It has the advantage of being able to lead the product outside the system and sell it as a product.

[Brief explanation of drawings]

Figure 1 is a system diagram showing a coal gasification method in a combined process combining coal gasification and power generation, cited as Example 1 of the present invention, and Figure 2 is a coal gasification method cited as Example 2 of the present invention. Figure 3 is a system diagram showing a coal gasification method in a combined process that combines gasification and power generation.
Figure 4 is a graph showing a comparison of the generated gas calorific value and gasification efficiency when using 02 gas and when using N2 gas, which is the conventional technology. FIG. 2 is a system diagram showing a coal gasification method in a combined process that combines power generation. 1... Coal supply hopper 2... Coal gasifier 3.
...Heat exchanger 4...Gas purification equipment S...
Gas turbine 6...Waste heat recovery boiler 7...Stack 8...Steam turbine 9...G
T9 electric machine 10... ST generator 11... Exhaust gas bypass 12... Catalytic combustion device 13... Heat recovery device 14... CO2 absorption tower 15... CO
□Discharge tower 16...Exhaust gas reduction line 17...
CO2 line 18...Compressor 19...
・Produced gas line 20...Oxygen supply line 21・
... Slag removal hopper 22 ... Slag discharge line 23 ... Heat exchanger 24
... Gas condenser 25 ... Oxygen plant agent Junnosuke Nakamura 1F2 diagram

Claims (1)

[Claims] 1. In a coal gasification process in a plant that combines a coal gasifier, CO_2 gas contained in the exhaust gas discharged from the plant is separated and recovered to produce CO_2 gas, or the above-mentioned O contained in exhaust gas
After converting 2 gas into CO_2 gas, the CO_2 gas contained in the exhaust gas is separated and recovered to generate CO_2 gas, or the O_2 gas contained in the exhaust gas is converted to CO_2 gas.
A means for converting into O_2 gas to generate CO_2-rich gas is provided, and further the separated and recovered CO_2 gas or CO_2-rich gas is recirculated to the coal gasification furnace for pneumatic transportation of raw coal. A coal gasification method characterized by gasifying coal by providing a means for use as a conveying medium and a coal gasifying agent. 2. The coal gasification method according to claim 1, wherein the coal gasification process is a coal gasification combined power generation process that combines coal gasification and power generation. 3. CO contained in exhaust gas emitted from plants
3. The coal gasification method according to claim 1 or 2, wherein the means for separating and recovering the two gases is a process using an amine-based CO_2 absorption liquid. 4. O_2 contained in exhaust gas discharged from the plant
The coal gasification method according to any one of claims 1 to 3, wherein the means for converting gas into CO_2 gas is a catalytic combustion process. 5. O_2 contained in exhaust gas discharged from the plant
The means for converting gas into CO_2 gas mixes a part of the generated gas produced by the coal gasifier into the exhaust gas,
A coal gasification method according to any one of claims 1 to 4, characterized in that the method is based on a catalytic combustion process. 6. Claim 1, characterized in that the exhaust gas discharged from the plant is exhaust gas at the gas turbine outlet.
The coal gasification method according to any one of Items 1 to 5.