JPH0321592B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing combustible gas by partially oxidizing coal using a spouted bed gasifier, and in particular,
The present invention relates to a coal gasification method for controlling the calorific value of produced gas to be approximately constant when the amount of combustible gas produced for power generation etc. needs to be changed in a short time. Coal gasification using a spouted bed is achieved by (1) having a large specific surface area for finely pulverizing the coal and gasifying it in a short time, and (2) gasifying the coal at temperatures above the melting point of the ash in the coal. It has the following advantages: (3) the generation of fine ash particles (fly ash) can be reduced; and (3) particle hold-up within the gasifier is small, which is advantageous for load fluctuations. However, this method requires maintaining the temperature necessary to melt the ash, and each has its own problems depending on the oxygen source for partially oxidizing the coal. In other words, there are two methods: one uses air as the oxygen source for partially oxidizing coal, and the other uses oxygen production equipment to separate air into nitrogen and oxygen and use essentially only oxygen (usually oxygen concentration is 90% or more). There is.
The former method requires only compressing air in order to supply it to a pressurized gasifier, so manufacturing costs are low and the flow rate can be easily changed in a short period of time.
On the other hand, the combustible gas obtained by gasifying coal is diluted with inert gases such as nitrogen and argon in the air, resulting in a low calorific value of around 1000kcal/ ^Nm3 , and the inert gas is also heated. As a result, it is difficult to obtain the temperature necessary to melt the ash in the coal. In particular, when the produced gas is used as fuel for a gas turbine, the calorific value is close to its lower limit, so it is difficult to control the calorific value so that it does not decrease even when the load is reduced. On the other hand, in the latter method using oxygen, the generated gas calorific value is 2000 to 2700 kcal/N.
^m3 , which is an appropriate calorific value as a gas turbine fuel, and the temperature of the gasification part can easily be raised above the melting point of coal ash, but the power required for the oxygen production equipment is large and the production cost is high. In addition, in the oxygen production method using distillation separation of liquefied air under low pressure, which has the lowest oxygen production cost among large-scale oxygen production facilities, the minimum operable flow rate of the rated flow rate (varies depending on the equipment, but usually up to 70%) ) is too small, making it difficult to respond to sudden changes in flow rate. Therefore, in any method that uses air or oxygen obtained from an oxygen production facility as an oxygen source for partial oxidation of coal, the calorific value of the combustible gas produced by coal gasification cannot be used for power generation. It was difficult to do so. An object of the present invention is to provide a coal gasification method that can follow load fluctuations in a short time and can prevent changes in calorific value during load fluctuations. The present invention is based on a spouted bed gasification method using air, and focuses on combining this with oxygen production equipment. Finely pulverized coal is supplied into a spouted bed gasification furnace, and this coal is mixed with oxygen and air. In a coal gasification method in which combustible gas is produced by partial oxidation using a gasifying agent, the amount of oxygen supplied to one side is kept almost constant with respect to the amount of combustible gas produced, regardless of fluctuations in the amount of production, and The amount of air supplied on the other side is adjusted according to fluctuations in production volume, and the oxygen concentration in the flammable gas is made higher at low production loads than at high loads, so that the calorific value of the combustible gas remains almost constant at each load. By controlling to This improves load followability and at the same time enables operation at lower loads. In other words, during low loads (when production volume is small), the amount of oxygen supplied from the oxygen production equipment is kept almost constant, and the amount of air supplied is mainly reduced to reduce the amount of gasifying agent supplied to the gasifier. Increase oxygen concentration. In other words, by lowering the nitrogen concentration in the total gasification agent, the nitrogen concentration in the product gas generated in the gasifier is reduced, and the calorific value of the product gas is kept constant. In other words, the calorific value of the generated gas is controlled by the oxygen concentration of the supplied gasifying agent. FIG. 1 is a system diagram of a coal gasification power generation system suitable for applying the coal gasification method of the present invention. In FIG. 1, 1 is an oxygen production device, 2 is a compressor, and 3 is a gas turbine. , 4 is a combustor, 5 is a gasifier, 6 is a gas purification device, and 7 is a generator. Finely pulverized coal 22 and air 1 are sent to the gasifier 5.
8. Oxygen 15 is supplied, and a product gas 23 containing combustible gas is produced by a partial oxidation reaction. A small amount of steam 20 may be supplied to the gasifier 5 as needed. The coal 22 is normally transported by pneumatic current and supplied to the gasifier 5, but all or part of the air 15 and steam 20 may be used as the gas for this purpose. A portion of the nitrogen 14 may be used. The generated gas 23 becomes a purified gas 21 from which fine chires and dust are removed by the gas purification device 6, and sulfur compounds such as H ₂ S are further removed. The purified gas 21 is introduced into the combustor 4, completely combusted by the air 19, and is supplied to the gas turbine 3 as a high-temperature combustion gas 17. The gas turbine 3 drives the generator 7 to generate electric power, and at the same time drives the compressor 2 to compress normal pressure air 12 and obtain pressurized air 16. A portion of the pressurized air 16 is extracted and becomes air 18 supplied to the gasifier 5, and the rest is supplied to the combustor 4 as combustion air 19. In the oxygen production apparatus 1, oxygen 15 is separated from air 11, and nitrogen 14 is produced as a by-product. Oxygen 15 is supplied to gasifier 5. Oxygen 15 and air 18 are supplied to gasifier 5 after being pressurized by a pressurizing device (not shown). Further, the exhaust gas 13 of the gas turbine 3 is guided to a known waste heat recovery boiler (not shown) to generate steam, and this steam drives a steam turbine to generate electric power. In the coal gasification method according to the present invention, a gasification agent consisting of coal 22 and oxygen 15 and air 18 or oxygen-enriched air is supplied from a plurality of fluid supply nozzles in multiple stages in a jet gasification furnace (gasification furnace) 5. Coal 2
In a coal gasification method in which combustible gas is produced by partially oxidizing oxygen 2, oxygen 1
The supply amount (oxygen supply amount) to the gas furnace 5 of 5 is coal 2
The amount of air 18 supplied to the gasifier 5 (air supply amount) is kept almost constant regardless of the amount of air 18 supplied to the gasifier 5 (coal supply amount) when the amount of combustible gas produced is low ( When the production volume is low (when the load is low), the production volume is reduced from when the load is high (when the load is high), and the oxygen concentration of the gasifying agent is increased to keep the calorific value of the combustible gas almost constant at each load within a specified time (within a short time). is configured to control the Specifically, the supply amount of oxygen 15 is kept almost constant with respect to fluctuations in the supply amount of coal 22, and the supply amount of air 18 varies in accordance with the supply amount of coal 22. As a result, a mixed gas with a high oxygen concentration (mixed gas of air and oxygen) is supplied to the gasifier 5 during low loads, and a mixed gas with a low oxygen concentration is supplied to the gasifier 5 during high loads. Therefore, even when the load is low, the inside of the gasifier 5 is maintained at the temperature necessary for melting the ash, and the calorific value of the generated gas is controlled to be almost constant, and the gas is supplied from the oxygen production device 1 to the gasifier 5. Fluctuations in the flow rate of oxygen 15 are minimized. Next, as the gasifier 5, the inner diameter is 0.9 m and the length is approximately 20 m.
Coal having the properties shown in Table 1 was gasified by varying the feed rate using a spouted bed gasifier with a water-cooled inner wall structure and a structure in which coal ash was extracted from the bottom while being melted. , Table 2, No. 3
The results in the table were obtained. In the table, the nitrogen supply amount is the flow rate of nitrogen used for coal supply, and the air supply amount and oxygen supply amount indicate that the calorific value of the generated gas was almost constant at each coal supply amount, and stable operation was performed. This is the average flow rate at that time. Table 2 shows the higher calorific value of the produced gas as a target of 1000kcal/ ^Nm3 , and Table 3 shows the higher calorific value of the produced gas with a target of 900kcal/ ^Nm3 , and the amount of air and oxygen supplied to the gasifier 5, respectively. These are the measurement results when controlling For both the gasification conditions in Tables 2 and 3, the gasification pressure is 11 atm, and the gasification temperature is estimated from the mass balance.
The temperature was between 1680 and 1740℃.

【table】

【table】

[Table] Table 2 shows that when coal supply decreased by approximately 24%, oxygen supply decreased by only 67%. Therefore, it is shown that the change in oxygen flow rate is within the reduction range (reduction limit of 70%) that can be accommodated by existing oxygen production equipment. As a result
It was possible to reduce the load from 100% to 25% in about 30 minutes. In addition, the change in the generated gas calorific value due to such load fluctuations is within the allowable change range of the calorific value required for a 1000kcal/ ^Nm3 gas turbine.
It was within 20 kcal/Nm ³ (2%). In Table 3, the generated gas calorific value is as low as 900 kcal/Nm ³ , but the change in oxygen supply amount with respect to load fluctuations is smaller than in Table 2. In other words, when coal supply decreases by approximately 17%, oxygen supply decreases by 83%.
It is only reduced to a lesser extent. As a result, the time required to reduce the load from 100% to 20% was approximately 20 minutes. In addition, for such load fluctuations, the change in generated gas calorific value is within the allowable change range of calorific value required for a 900kcal/ ^Nm3 gas turbine.
It was extremely stable within 15kcal/ ^Nm3 . As described above, according to the present invention, by keeping the oxygen supply amount almost constant regardless of fluctuations in the production amount of combustible gas and adjusting the air supply amount according to fluctuations in the production amount, the coal supply amount can be reduced. It is possible to produce a generated gas that has a stable calorific value against changes in . Furthermore, compared to conventional gasification methods that use only oxygen, the oxygen production equipment needs to be smaller, reducing costs. At the same time, changes in the amount of oxygen produced by the oxygen production equipment are smaller, improving load followability. do.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a coal gasification power generation system showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Oxygen production device, 2...Compressor, 3...Gas turbine, 4...Combustor, 5...Gasifier, 6...Gas purification device, 7...Generator, 15...Oxygen, 18...Air.

Claims (1)

[Claims] 1 Coal in which coal and a gasifying agent consisting of oxygen and air or oxygen-enriched air are supplied from multiple stages and multiple fluid supply nozzles into an spouted bed gasifier, and the coal is partially oxidized to produce combustible gas. In the gasification method, the amount of oxygen supplied is kept almost constant regardless of the amount of coal supplied with respect to the amount of combustible gas produced;
The air supply amount is decreased when the production amount of the combustible gas is at a low load compared to when the production amount is at a high load, and the oxygen concentration of the gasification agent is increased so that the calorific value of the combustible gas is approximately constant at each load. A coal gasification method characterized in that the coal gasification is controlled within a predetermined time.