JPH0455238B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a coal gasification method for gasifying pulverized coal, and particularly to a method that has a high reaction rate and efficiently gasifies in a short time. [Prior Art] Conventionally, fixed bed, fluidized bed, spouted bed methods, etc. are known as coal gasification methods. Among these, in the case of the spouted bed method, the temperature is higher than the melting point of coal ash (1300~
Since the temperature is raised to 1600℃, it is easier to increase the carbon gasification rate and the yield of H ₂ and CO gas compared to other methods, and there are fewer polluting by-products, so it is suitable for synthesis gas, cast turbines, and steam. Suitable for producing raw material gas for turbine combined power generation. In the spouted bed method, coal or chia (carbon particles scattered with gas), steam, and gasifying agents such as oxygen or air are simultaneously supplied from a coal burner, and coal is supplied alone in addition to such a burner. There is a method that includes a burner. By the way, the coal gasification reaction can be roughly divided into [coal → C (char), H ₂ , CO, CO ₂ , CH ₄
…(1)] [C (char) + O ₂ → CO ₂ , CO, H ₂ …(2)] [Coal + O ₂ → CO, CO ₂ , H ₂ …(3)] Equation (1) is a thermal decomposition reaction (or carbonization). This reaction is likely to occur in the system in which a coal-only burner is added as described above. Equation (1) and (2)
As is well known, a representative example of a system in which formulas are clearly distinguished and caused to coexist is the BI-GAS process in the United States. In addition, representative examples of formula (3), where coal and gasifying agent are supplied simultaneously from a coal burner and intentionally do not distinguish between formulas (1) and (2), include the Texaco process, Shell
- There are Koppers processes, etc. In both processes, various attempts have been made to improve the carbon gasification rate (the ratio of the amount of carbon generated as gas to the amount of carbon in coal). The most typical method is the so-called chir recirculation method, in which carbon particles, i.e., chire, scattered with the gas are collected and returned to the gasification furnace for gasification. The following problems remain. That is, the cher recirculation method uses
Since it requires equipment such as pumps, tanks, and valves, it tends to complicate the gasification process and deteriorates the operability of the gasifier. In addition, there is no established means to accurately measure the amount of chard transported, making it difficult to control the amount of circulation. Especially in processes where gasification conditions vary greatly depending on the amount of cher supplied,
A large amount of equipment is required for quantitative circulation of the chartreuse. In addition, a carrier gas is required to supply the char to the gasifier, and the nitrogen used for this,
Steam, CO ₂ , a part of the produced gas, etc. do not contribute much to the gasification reaction, and it is not preferable to supply these gases to the gasification furnace more than necessary. Furthermore,
When the number of circulating chars increases, the amount of wear on the inside of the gasifier and the piping beyond the outlet of the gasifier increases. Furthermore, JP-A-57-174391 describes a coal gasification method in which unreacted carbon in molten slag is made to react more by increasing the oxygen concentration near the inner wall of the gasifier. . However, this method has a problem in that the unburned content in the slag reacts with oxygen on the furnace wall surface, causing the wall surface to become hot. [Object of the Invention] The object of the present invention is to provide a coal gasification method in which unreacted carbon can be reduced by passing pulverized coal once through a gasification furnace, and the recirculation of coal can be omitted or the amount of circulation can be significantly reduced. The purpose is to provide a method. [Summary of the Invention] The coal gasification method according to the present invention focuses on the reaction process from when coal is supplied to the gasifier until it leaves the gasifier, and is designed to complete the reaction in a short time. . That is, as a result of investigating which processes require time for the reaction, it was found that the reaction rate of coal exceeds the melting temperature of coal ash and is particularly reduced when there is not a large amount of gasifying agent. Based on this knowledge, by forming a reaction region that does not exceed the melting temperature of ash during the process of gasifying coal, the reaction time is shortened and unreacted carbon is reduced. Regarding the reaction rate, when the oxygen partial pressure is high, such as in the ejected bed method, the above equation (3) can be converted to the following:
The process can be divided into three processes: Equations (4), (5), and (6). That is, [coal (C, H, O) + O ₂ → CO ₂ , H ₂ O, coal
(C) …(4)] [Char(C)+CO ₂ →2CO…(5)] [Char(C)+H ₂ O→H ₂ +CO…(6)] Among formulas (4) to (6), Equation (4) is the fuel reaction, and (5),
The reaction is extremely fast compared to equation (6). In other words, equations (5) and (6) govern the reaction time. It is generally known that the reaction rate of coal or coal is greatly influenced by their physical and chemical properties. However, it was discovered that the properties differ not only from the inherent properties of coal but also depending on how the reaction is carried out. This fact will be explained below. Figure 1 shows the process of gasifying so-called Pacific coal by arbitrarily changing the amount of oxygen and temperature, collecting the intermediate product of gasification, char, and reacting the char with steam in a thermobalance according to equation (6). The figure shows the time required for the carbon in the char to completely gasify. As a result, it was found that the reaction completion time of the char produced at 1300-1400°C was short and it was highly reactive. On the other hand, the reactivity of the char is closely related to the physical properties of the char. Figure 2 shows the relationship between the coal reaction conditions and the specific surface area of the produced coal. As a result, 1300~
It was revealed that the specific surface area of the char produced at 1400℃ was the largest. Combining the above results, in the case of Pacific coal,
Reaction at around 1300-1400℃ can maximize the reactivity of the gasification intermediate product, and complete gasification can be achieved in a short time as long as a certain amount of gasification agent is present. It turns out that there is something. The present invention was developed by further investigating why a temperature of 1300 to 1400°C is optimal and finding that this corresponds to the melting temperature of ash in Pacific coal. The melting temperature of coal ash was measured according to JIS-8801, and the results are shown in Table 1 along with the composition of the ash.

[Embodiments of the invention]

The present invention will be specifically explained below based on the embodiment shown in FIG. FIG. 3 is a system diagram of the pulverized coal gasifier. Coal 1 is 70-80wt% less than 200 mesh
The coal is pulverized to a particle size of , and transported to the atmospheric coal hopper 20 via coal storage and pulverization equipment (not shown) by means of a bucket conveyor or gas transportation. From here, it is sent to pressurized hoppers 21 and 22, and the supply amount is controlled by coal quantitative devices 23 and 24 such as a rotary feeder or screw feeder. In addition, the hopper 20, 21, 22 and the switching valve 4
The coal supply method consisting of 0.0 and 41 is called the lock hopper method, and the hoppers 21 and 22 are at the same pressure, and both are 0.5 to 1.0 Kg/cm ² G lower than the gasifier.
Keep the pressure high. When the coal in the hopper 22 is reduced to a certain amount, the valve 41 is opened and the coal is moved from the hopper 21 to the hopper 22 by free fall. When a predetermined amount of coal has accumulated in the hopper 22, the valve 41 is closed, the pressure in the hopper 21 is lowered to normal pressure, the valve 40 is opened, and the coal is moved from the hopper 20 to the hopper 21 by free fall. Thereafter, the coal is transported to the hopper 20, the valve 40 is closed, and the pressure in the hopper 21 is increased until it becomes equal to the pressure in the hopper 22, in preparation for the next movement. By repeating the above method, coal is continuously sent to the high-pressure gasifier 29. At least two coal quantitative devices are provided as shown at 22 and 23 in order to separately supply coal to different positions of the gas furnace. The coal is allowed to fall freely from here to the ejectors 25 and 26, and is transported by the carrier gas 7.
Coal burner 27,
Send to 28th. Carrier gases include nitrogen, steam,
Air, carbon dioxide, or a part of the gas generated in the gasifier can be used, but from the viewpoint of safety against coal dust explosions and blockages in the supply pipes, it is desirable to use suffocation gas or carbon dioxide gas. Coal supplied from burners 27 and 28 to gasifier 29 is gasified by oxygen 4. This oxygen is first supplied in a constant amount corresponding to the amount of coal supplied by the flow controller 49, and then separately supplied to the upper and lower burners 27 and 28. That is, the oxygen supplied to the upper stage burner 27 passes through the supply pipe 5 and the flow rate is controlled by the flow rate controller 42, and the remaining oxygen passes through the supply pipe 6 to the lower stage burner 2.
It flows to 8. In this case, the distribution ratio of coal and oxygen to each burner 27, 28 is important for gasification efficiency, and the distribution method will be explained in more detail later. The coal gasifier 29 includes a gasification region 30, a heat recovery region 31, and a slag cooling region 50. The gasification region will be very hot and cannot be constructed with a metal container, so it will be covered with a refractory material 52. In addition, prevention of heat loss due to radiation from here,
For the purpose of increasing particle residence time, the diameters at the top and bottom are smaller than the diameter near the burner. In the gasification region 30, gas rich in H ₂ and CO is generated by the reactions of equations (4) to (6) above. On the other hand, coal ash is molten slag9
The slag adheres to the surface of the refractory material 52, flows downward by gravity, and falls into the slag cooling area 50 through the slag tap hole 53. Water is stored in the slag cooling area, where the molten slag 9 is rapidly cooled and solidified, and further falls into the slag tank 32.
A switching valve 43 is provided between the gasifier 29 and the slag tank 32, and is kept open during normal times. Therefore, the inside of the slag tank 32 is also filled with water. When a certain amount of water-cooled slag accumulates in the slag tank or after a certain period of time has elapsed, one switching valve 43 is closed, the other switching valve 44 is opened, and both water and water-cooled slag are poured into the slag separator 33. In the slag separator 33, the water-cooled slag 9 is separated from the water by a diamond. When the slag tank 32 is empty, the switching valve 44 is closed and water is allowed to flow from the cooling water circulation pump 35 through the pipe 54 to equalize the pressure in the tank 32 with that of the gasifier. After that, valve 53 is closed, and valve 4 is closed.
3 is opened so that the slag 9 accumulates in the tank 32. Since the water stored in the slag cooling area 50 is warmed by the heat of the molten slag 9, the switching valve 46 is opened at an appropriate time, the water flows to the slag separator, and is cooled by the water cooling pipe 34. The cooled water is pressurized to the gasifier pressure by the cooling water circulation pump 35, and is then passed through the pipe 14 again to the slag cooling area 50 of the gasifier.
supply to. By constantly circulating the cooling water in this way, the water in the slag cooling area is kept at a constant temperature. Since this water gradually steams over a long period of operation, the reduced amount of water is replenished from the pipe 16 in a timely manner. The gas produced in the gasification zone of the gasifier ascends through the gasifier and enters the heat recovery zone 31 . A water-cooled pipe is provided in this area, and water is flowed through this pipe to generate steam by heat exchange with gas sensible heat. Therefore, the temperature of the gas at the outlet of the gasifier 29 is between 400 and 900°C.
The temperature drops to around ℃. This gas is led to the cyclone 36 through the pipe 11, and the dust contained in the gas is separated. The gas from which dust has been removed is pipe 1
2 to lead to the next gas treatment step (not shown). The gas treatment process differs depending on the use of the gas, but usually includes a heat exchanger, a dust removal device such as a secondary cyclone or a cleaning tower, and a desulfurization device for removing H ₂ S or CO ₂ . Dust such as ash and char collected by the cyclone 36 is stored in dust hoppers 37 and 38. The method of discharging the dust 13 is similar to the method of supplying coal and discharging slag, and after a certain amount has accumulated in the hopper 38,
The switching valve 47 is closed, the pressure in the hopper 38 is set to normal pressure, the switching valve 48 is opened, and the feeder 38 extracts the material. When the discharge is finished, switch valve 39
is closed, the pressure in the hopper 38 is increased to the same pressure as the cyclone 36, and the switching valve 37 is opened to store dust in the hopper 38. By repeating the above,
Dust is continuously discharged out of the system. Both water-cooled slag 18 and dust 13 are sent to an ash treatment facility and ash storage (not shown). In the above pulverized coal gasification method, the method of supplying coal and oxygen and controlling the temperature inside the gasifier will be explained in more detail. As mentioned above, the coal is transferred to the upper burner 2 of the gasification region.
7 and the lower burner 38 separately.
The ratio of supply to the upper and lower stages is most preferably 1:1 in order to reduce operational factors and simplify control. That is, the coal metering devices 23 and 24 are installed so that all the coal to be supplied flows evenly to the upper and lower burners.
All you have to do is activate it. For example, the number of revolutions of the coal feeders should be the same. On the other hand, the amount of oxygen supplied corresponds to the amount of coal supplied. By the way, it is known that the following two efficiencies representing the performance of the gasifier are most strongly influenced by the ratio α of the supply amount of oxygen to coal. Carbon gasification rate ηe = Gasified carbon amount / Carbon amount in coal Cold gasification rate η _G = Gas calorific value x Gas generation amount / Coal calorific value x Coal supply amount And oxygen amount / Coal amount = α is The target is often the location where η _G is the largest, and although it depends on the type of coal, it is usually 0.7<α<1.0 (Kg/Kg). In the case of Pacific coal used in this example, α=0.82 (Kg/
Kg). When the amount of coal supplied is determined in this manner, the total amount of oxygen supplied is determined, and is controlled by the controller 49. Thereafter, oxygen is separately supplied to the upper stage burner 27 and the lower stage burner 28. In this case, the amount of oxygen supplied to the upper burner 27 is controlled so that the temperature near the upper burner in the gasification region of the gasifier 29 does not exceed the melting temperature of the ash. This control method constantly monitors the temperature near the burner 27 using a thermometer 51 installed at the same height as the upper burner 27, for example.
The controller 52 sends a signal to the controller 42 of the upper oxygen supply pipe 5 to adjust the flow rate of oxygen so that the temperature does not exceed the melting temperature of the ash. Note that the remaining oxygen supplied to the upper burner 27 is supplied to the lower burner 28 . In this embodiment, the total amount of oxygen supplied to the gasifier and the amount of oxygen supplied to the upper stage are controlled by controllers 49 and 42, respectively. In the case of Pacific Coal, the coal is placed in the upper row and the lower row 1:1.
Total oxygen amount/total coal supply amount = 0.82 (Kg/
Kg), upper stage oxygen supply amount / upper stage coal supply amount =
When it is set to 0.36 to 0.38 (Kg/Kg), the upper burner 27
It was confirmed that the temperature in the vicinity should be kept at 1310°C, a value that does not exceed the melting temperature of ash. Therefore, in this case,
Lower stage oxygen supply amount/lower stage coal supply amount is 1.26 to 1.28
(Kg/Kg), and the temperature exceeds the melting temperature of ash.
The temperature is 1880℃. Under such operating conditions, the reaction progresses in the gasification region of the gasification furnace 29 as follows. Since the coal supplied from the upper burner 27 is gasified under conditions with a low carbon content, it is converted into chia containing a considerable amount of carbon, but since this chia was generated under conditions that do not exceed the melting temperature of ash, as described above, Extremely reactive. therefore here
If a gasifying agent such as H ₂ O or CO ₂ is present, it will be gasified in a short time according to equations (5) and (6). On the other hand, the coal supplied to the lower stage reacts under conditions where the amount of oxygen/the amount of coal is greater than the usual ratio, so it is completely gasified in an extremely short time. At this time, since excess oxygen is supplied, the gas generated from this includes CO, _H2, and other gases.
Contains considerable amounts of CO ₂ and H ₂ O. Since the gas generated in the lower stage ascends through the gasifier, the char generated in the upper stage can react with the gas containing CO ₂ and H ₂ O produced from the lower stage as a gasifying agent. As the reaction of the char progresses, the amount of unreacted carbon decreases, and the particles that turn into ash adhere to the furnace wall while floating in the gasifier area, or the lower burner 2
Most of the molten slag finally becomes molten slag 9 and falls into the slag cooling area. The ash that has not been turned into molten slag is scattered with the gas, and is separated and collected by the cyclone 36. Table 2 and FIG. 4 show comparison values between the test results of the coal gasification method according to this example and the results of the conventional method.

[Table] Coal supply amount x Carbon in coal
Gas generation amount x gas calorific value
2) Cold gas efficiency =

Claims (1)

[Claims] 1. In a coal gasification method in which pulverized coal is supplied to a burner of a gasification furnace and gasified in an air stream with oxygen or air and steam, the supply of pulverized coal is transferred to a gasification reaction area of the gasification furnace. The ratio of the amount of oxygen supplied to the upper stage burner to the amount of pulverized coal supplied is set to a value that does not exceed the melting temperature of pulverized coal ash, and the ratio of the amount of oxygen supplied to the upper stage burner to the amount of pulverized coal supplied is set to a value that does not exceed the melting temperature of pulverized coal ash. A coal gasification method characterized in that the ratio to the amount of coal is set larger than that of the upper stage burner, and the temperature near the lower stage burner is set to be equal to or higher than the melting temperature of pulverized coal ash.