JPH0551804B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a pulverized coal-fired boiler, and in particular to a method for gasifying pulverized coal as auxiliary fuel to a pulverized coal burner at the time of startup of the pulverized coal-fired boiler and during load fluctuations. This relates to a pulverized coal-fired boiler that uses coal gasified fuel.

[Background of the invention]

In recent years, in Japan, due to the tight supply of heavy oil, in order to correct our dependence on oil, we have been converting the fuel from conventional heavy oil-fired combustion to coal-fired combustion, and in particular, the large capacity of coal-fired boilers is increasing in commercial boilers. A thermal power plant is being built.

However, coal fuel has poor fuel properties compared to petroleum fuel and gas fuel, so _NOx contained in exhaust gas
In particular, in order to reduce _NOx , fire division, exhaust gas recirculation, two-stage combustion, and in-furnace denitration are adopted to achieve slow combustion and reduce _NOx . It is also being done.

In these coal-fired thermal power plants, there are few cases in which the boiler load is always operated at full load, and the load is increased or decreased from 75% load to 50% load to 25% load, or the boiler is operated on a daily basis. Daily startup and shutdown, such as stopping operation on a weekly basis,
Weekly Start Stop (hereinafter simply referred to as DSS) operation, Weekly Start Stop (hereinafter simply referred to as WSS)
A transition is being made to thermal power plants that operate and handle intermediate loads.

On the other hand, in pulverized coal-fired boilers that perform DSS operation and WSS operation, the entire load is not operated only with pulverized coal from startup to full load. Gas fuels such as light oil, heavy oil, and LNG are used for startup.

This is because at startup, exhaust gas and heated air for mill warming cannot be obtained from the boiler, and therefore the mill cannot be operated.

In addition, light oil, heavy oil, gas fuel, etc. are used because the turndown ratio of the mill cannot be maintained at low loads, and the ignitability of pulverized coal itself is poor.

For example, when using light oil or heavy oil at startup, the boiler is fired using light oil as fuel from the time of startup until 15% load, and from 15% load to 40% load, the fuel is changed from light oil to heavy oil and fired. When the load exceeds % load, heavy oil and pulverized coal are co-fired, the amount of heavy oil fuel is gradually reduced, and the amount of pulverized coal fuel is increased to increase the co-firing ratio of pulverized coal, thereby transitioning to actual pulverized coal firing.

In addition, when lowering the boiler load from 100% load in DSS or WSS operation, the exhaust gas temperature is rising, unlike when the boiler itself is started, so pulverized coal must be burned from 100 to 30% load. It is a pulverized coal-fired boiler, and when the load is below 30%, the fuel is switched to heavy oil or light oil.

In this way, pulverized coal-fired boilers require auxiliary fuel such as light oil, heavy oil, gas fuel, etc. of about 10% of the combustion capacity because the pulverized coal itself has poor ignitability during startup and load changes. A fuel system is also required.

FIG. 6 is a schematic diagram showing a typical fuel system and flue duct system of a conventional pulverized coal-fired boiler.

The fuel-like air in the air doubt 1 is pressurized by the forced draft fan 2, heated by the exhaust gas from the exhaust gas duct 4 in the air preheater 3, and then sent from the air doubt 1 and wind box 5 to the pulverized coal-fired boiler 6. Supplied.

On the other hand, the exhaust gas combusted in the pulverized coal-fired boiler 6 passes through the air preheater 3 and the exhaust gas doubt 4, is pressurized by the induced draft fan 6, and is discharged into the atmosphere.

On the other hand, the mill 7 receives cooling air from the forced draft fan 2 outlet of the air duct 1, high-temperature air from the air preheater 3 outlet,
Alternatively, it is warmed by heated gas from the heated gas pipe 8 such as exhaust gas from the exhaust gas duct 4.

When the warming of the mill 7 is completed, the coal 9 is supplied to the coal hopper 10, the coal feeder 11, and the mill 7, and is supplied to the pulverized coal burner 13 through the pulverized coal pipe 12.

In addition, 14 is an auxiliary fuel burner that burns auxiliary fuel such as light oil, heavy oil, gas fuel, etc. when starting the pulverized coal-fired boiler 6 and when the load is low, 15 is an auxiliary fuel pipe, 16 is an auxiliary fuel storage tank, 17, 18 is a damper that controls the temperature of the heated gas pipe 8.

However, in the pulverized coal-fired boiler 6, it is necessary to heat the boiler 6 and the mill 7 with auxiliary fuel from the auxiliary fuel burner 14 in order to maintain thermal stability, and the startup time is lower than that of heavy oil-fired or gas-fired boilers. It takes too much time and the auxiliary fuel burner 14,
There is a disadvantage that layered equipment such as the auxiliary fuel pipe 15 and the auxiliary fuel tank 16 is expensive.

[Purpose of the invention]

The present invention attempts to eliminate such conventional drawbacks, and its purpose is to use coal gas fuel made from pulverized coal as an auxiliary fuel as a substitute for the auxiliary fuel that was conventionally necessary. Our goal is to provide a pulverized coal-fired boiler that can be operated with only pulverized coal.

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention provides a coal gasification device near a pulverized coal-fired boiler for gasifying a part of pulverized coal with a gasifying agent such as air or oxygen.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

Fig. 1 is a schematic configuration diagram of a pulverized coal-fired boiler according to an embodiment of the present invention, Fig. 2 is a system diagram of a coal gasifier using oxygen as the gasifying agent, and Fig. 3 is a system diagram of a coal gasifier using air as the gasifying agent. A system diagram of a coal gasifier, FIG. 4 is an enlarged view of a pulverized coal burner using a combustion catalyst, and FIG. 5 is an enlarged view of the coal gasifier.

In FIG. 1, numerals 1 to 18 indicate the same parts as the conventional one.

19 is a pulverized coal pipe for gasification that supplies pulverized coal from the mill 7, 20 is a coal gasifier, 21 is a gasifier pipe, and 22 is a pulverized coal gas auxiliary fuel that is supplied from the coal gasifier 20 to the pulverized coal burner 13. The coal gasification auxiliary fuel pipe 23 is a coal ash slag pipe.

In FIG. 1, coal 9, which is the fuel for the pulverized coal boiler 6, is supplied to the mill 7 from a coal supply line,
The pulverized coal is pulverized by a pulverized coal burner 13 into pulverized coal having a grain size suitable for fuel. In this case, the particle size of the powdered coal must be 70% or more of 200 mesh pass. This pulverized coal is sent to the pulverized coal-fired boiler 6 by using a part of the preheated air from the air preheater 3 of the pulverized coal boiler 6 as pneumatic transport air from the heated gas pipe 8, and then sent to the pulverized coal burner 13. A part of this pulverized coal is led to a coal gasifier 20 through a pulverized coal pipe 19 for coal gasification, and is pulverized by partial oxidation using a gasifying agent such as oxygen or air from a gasifying agent pipe 21. The coal is gasified to generate auxiliary fuel, and the coal gasification auxiliary fuel pipe 22
The pulverized coal is supplied to the pulverized coal burner 13 from the pulverized coal. Furthermore, at this time,
The ash content in the pulverized coal is discharged from the coal gasifier 20 as coal ash slag through the coal ash slag pipe 23 . On the other hand, the coal gas generated by the coal gasifier 20 is a gas whose main components are H ₂ and CO.
The pulverized coal is supplied as auxiliary fuel to the pulverized coal burner 13 through the pulverized coal burner 13.

In this manner, the pulverized coal-fired boiler 6 of the present invention supplies coal gas obtained by gasifying pulverized coal from the coal gasifier 20 to the pulverized coal burner 1 through the coal gasification auxiliary fuel pipe 22.
By supplying the pulverized coal to the pulverized coal 3, the pulverized coal-fired boiler 6 can be started using only pulverized coal.

Furthermore, since the engine can be started using only pulverized coal, the auxiliary fuel piping 15 and auxiliary fuel tank 16 for oil, gas, etc. can be eliminated, and auxiliary fuel other than pulverized coal can be saved.

Figure 2 shows a system diagram of a coal gasifier using oxygen as the gasifying agent. The case shown in Figure 2 is when oxygen is used as the gasifying agent. This oxygen is produced using electric power that can be easily obtained from thermal power plants. , can be easily obtained by the pressure swing method.

This oxygen does not need to be particularly highly purified, and its purity may be determined in consideration of separation cost. Pulverized coal for coal gasification from the mill 7 shown in FIG. is supplied to This pulverized coal is supplied to the coal gasifier 20 by airflow transport and blown into the coal gasifier 20 by the recycled gas from the gas recycle line 33 from the generated gas storage tank 26 . It is also possible to use N ₂ , steam, etc. as the gas for this airflow transport, but N ₂ requires a reduction in the calorific value of the generated gas, and steam requires drainage treatment during cooling, so this recycled gas method is not suitable. is preferred.

Moreover, this coal gas is supplied to the pulverized coal burner 13 together with pulverized coal, so that the coal gasifier 20
It is used as a starting fuel for the engine and does not require any other starting fuel or heat source. The coal gasifier 20 may be started by ignition using a conventional ignition device 27 such as an electric igniter. The pulverized coal and recycled gas injected into the coal gasifier 20 are partially combusted by the oxidizing agent O ₂ that is simultaneously injected into the coal gasifier 20, and the temperature varies depending on the type of coal, but is approximately 1200°C to 1400°C. Produce coal gas at °C. The reaction is coal CaH ₂ OcSa thermal decomposition ---→ C + H ₂ + CnHn (gas) + H ₂ O + endothermic C + O ₂ → CO ₂ + exothermic C + 1/2O ₂ → CO + exothermic gas (H ₂ + CO + H ₂ O) + O ₂ → There are various reactions such as H ₂ O + CO ₂ + exothermic reaction, but the final gas composition is determined by the balance of temperature and substances due to the equilibrium reaction of CO + H ₂ OCO ₂ + H ₂ , with H ₂ and CO as the main components. coal gas is obtained. Therefore, the recycled gas has almost the same function as an inert gas, and has little effect on the reaction gas composition.

In addition to the composition resulting from the above reaction, trace amounts of H ₂ S, COS, and NH ₃ are included as gases produced from the S and N components in the coal.

An example of the composition of coal-generated gas when using Bird's Rock coal is shown below.

CO 59.8Vol% H ₂ 25.6Vol% CO ₂ 5.3Vol% H ₂ O 4.5Vol% Others (N _2, etc.) 4.8Vol% The calorific value is approximately 2500 kcal/Nm ³ .

This coal gas is extracted from the furnace top of the coal gasifier 20 and sent to the heat recovery boiler 28.
After being cooled to 200 to 250°C, unreacted coal coal is collected by a dust removing device 29 such as a multi-cyclone, and then enters a gas cooler 30, cooled to room temperature with cooling water, and then enters a pressure booster 31 to separate the mist. Vessel 32
The gas passes through and is stored in the gas storage tank 26. The dust collected by the dust storage device 29 is recycled to the coal gasification device 20 by the recycled gas in the gas recycling line 33. On the other hand, the ash in the coal becomes molten in the coal gasifier 20, cools and solidifies in the lower part of the furnace of the coal gasifier 20, is extracted from the bottom, and enters the slag hopper 34.

A pressure detector 35 is attached to the gas storage tank 26, and the coal gasifier 20 is started and stopped according to the upper and lower limits of the pressure in the gas storage tank 26, so that the gas storage tank 26 is always maintained.
Inside, the pressure of coal gas necessary for starting the pulverized coal-fired boiler 6 is maintained. That is, the upper limit value is the design pressure of the gas storage tank 26, and the lower limit value is:
The amount of coal gas required to start the pulverized coal-fired boiler 6,
The gas pressure is set to be maintained, and the coal gasifier 20 is started at this lower limit value and stopped at the upper limit value. By taking this method,
The start-up of the pulverized coal-fired boiler 6 becomes easier, and
It is sufficient to operate the coal gasifier 20 at a constant capacity, and the operation of the coal gasifier 20 is also simplified.

Note that when this method is used, the amount of heat generated is approximately
2500 kcal/Nm ³ of gas can be produced from coal.

As another example of carrying out the present invention, a case where air is used as an oxidizing agent is shown in FIG.
An example of the composition of the generated gas when Ermelo coal is used is shown below.

Table 2 CO 19.1Vol% H ₂ 8.0Vol% CO ₂ 6.7Vol% H ₂ O 5.7Vol% H ₂ 60.4Vol% Others (H ₂ S, etc.) 0.1Vol% The calorific value is approximately 800 kcl/Nm ³ .

In this method, the gas volume per unit of heat becomes large, and it is not economical to store the generated gas. For this reason, the inventors developed a catalytic combustion pulverized coal burner 1.
3, this pulverized coal burner 13 and an air oxidation type coal gasifier 20 are combined to make it possible to supply coal gas fuel for starting a boiler when air is used as a gasifying agent.

That is, the gas emitted from the coal gasifier 20 passes through a heat recovery boiler 28 and an air preheater 37, is cooled to approximately 250°C to 350°C, is removed by a dust remover 29, and is then sent to the pulverized coal-fired boiler 6 as fine powder. It is supplied to the charcoal burner 13. A gas-air mixer 39 is installed upstream of this pulverized coal burner 13, and is mixed with air necessary for combustion. The amount of combustion air is roughly equivalent to that of fuel gas, and the gas temperature after mixing is 150℃ to 200℃.
becomes. In addition, the gas after mixing has CO and H ₂ temperatures approximately half, and CO is less than 10% and H ₂ is less than 4.0%, which can be outside the explosive range for each component.

This gas-air mixture is supplied to the fuel gas nozzle 40 of the combustion catalyst pulverized coal burner 13 shown in Fig. 4, and is spontaneously ignited by the combustion catalyst 41 installed at the tip, generating combustion gas at 1200°C to 1400°C. , a pulverized coal fire 42 is generated. On the other hand, the mixture of pulverized coal and air supplied from the pulverized coal nozzle 43 comes into contact with the ignition flame 42 and ignites, producing a main flame 44. This combustion catalyst type pulverized coal burner 13 is
Not only for starting, but also for stabilizing combustion or as a burner for responding to load fluctuations, combustion may be performed constantly. In this case, the coal gasifier 20 does not need to be started and stopped frequently, and is operated in accordance with the operating conditions of the pulverized coal-fired boiler 6. Incidentally, the combustion catalyst 41 is heated at approximately 80°C to 100°C with _H2 gas and CO2 gas.
For gas, it is 200-250℃, and for mixed gas, it is controlled by the ignition temperature of _H2 , and ignites sufficiently at 150℃-200℃.

FIG. 5 shows an example of the structure of the coal gasifier of the present invention.

The coal gasifier 20 has a structure lined with a refractory material 45, and includes a gasification section 46 and a slag cooling section 47. The gasification section 46 includes a pulverized coal supply nozzle 48 and a chia nozzle 4 of the recycling line 33.
9 are installed. In addition, the slag cooling section 4
7 is attached with a start-up burner 50 and an ignition device 27, and has a built-in slag cooling nozzle 52 for cooling and solidifying molten slag 51 produced during gasification.

Pulverized coal is sent by pneumatic transport to the coal gasifier 20, which is heated to a predetermined temperature by the start-up burner 50 using startup fuel or recycled gas from the gas storage tank 26; The gas mixture is supplied from the pulverized coal nozzle 48 to the gasification unit 46 together with the gasifying agent oxygen or air, and is ignited by the temperature inside the coal gasifier 20 . In the gasification section 46, the pulverized coal becomes coal gas through the above-mentioned reaction, and is extracted from the gas outlet nozzle 53 at the top of the furnace, accompanied by unreacted coal, to proceed to the subsequent process. On the other hand, the ash content in the coal is heated above the melting temperature and becomes molten slag, which is produced in the gasification section 4.
It enters the slag cooling section 47 from the slag tap section 54 at the bottom of the slag 6. The melting temperature of this coal ash varies depending on the type of coal, but is in the range of 1200°C to 1600°C. The temperature of the coal gasifier 20 is set by the melting temperature of this coal, and is approximately 150% lower than the melting temperature.
Set the temperature higher by ℃~200℃. This temperature is regulated by the amount of oxygen or air.

In the conventional gasifier, the molten slag from the slag tap section 54 is dripped into the lower part of the slag cooling section 47 filled with water, and is taken out as granulated slag as a mixture with water. For this reason, ammonia, fine slag, etc. get mixed into the water, so large-scale slag separation equipment and wastewater treatment equipment are installed. In the present invention, cooling water from a cooling gas (steam, N ₂ , air, etc.) line 55 is sprayed onto the molten slag flowing down to the lower part of the slag tap portion 54 to blow the slag out and cool it. Since the solidified slag is cooled using a dry cooling method, the system is simplified. This dry cooling method was adopted because the molten slag solidifies at a very high temperature of 1200℃ or higher, and the cooling temperature difference to solidify slag is small at 150℃ to 200℃, so it is almost instantaneous. Since it can solidify on the surface and turn into solid slag in airflow, it is possible to prevent the problem of scattered slag adhering to the wall surface. In addition, the reason why this method could not be adopted in the conventional gasifier 20 is that the gasifier pressure was high and the solid particles were extracted by mixing them in water and extracting them. This was because we were concerned that this cooling gas would cool the slug tap, causing solidification and blockage at the tap. In the case of this apparatus, these problems can be solved by operating at a relatively low pressure, and if the pressure is low, the start-up burner can be used to heat the slug tap section.

As mentioned above, by installing a coal gasification device near a pulverized coal-fired boiler, it is possible to use only utilities such as electricity and cooling water that can be easily obtained within the power plant from coal, which is the main fuel for power generation. Since coal gas fuel can be obtained without providing additional utilities, auxiliary fuels such as oil and LNG, which conventionally accounted for 10% of the total combustion heat, are no longer needed.

Further, a storage tank for auxiliary fuel and an auxiliary fuel combustion system device are not required.

Furthermore, since conventional coal gasification equipment can be applied to the coal gasification equipment as is, by simply installing a storage tank, the coal gasification equipment can be started and stopped by the pressure in this tank. The coal gasifier can be operated at a constant rate without any problems, and the boiler startup operation is also simplified. Furthermore, the generated gas in this storage tank can be used as a starting fuel for the coal gasifier, and no other fuel is required.

In addition, by applying a catalytic fuel type pulverized coal burner and using the generated gas at a high temperature as auxiliary fuel for the pulverized coal-fired boiler, an ignition device for the boiler is not required and it is possible to respond to load fluctuations.

Furthermore, by applying the slab dry cooling method, a waste water treatment device is not required, and the device becomes simpler.

〔Effect of the invention〕

The present invention has a coal gasifier that gasifies pulverized coal near the pulverized coal-fired boiler, so it can be operated from startup to full load using only pulverized coal.
There is no need for auxiliary fuel such as oil or LNG for startup or load changes.

[Brief explanation of the drawing]

1 to 5 show embodiments of the present invention, and FIG. 1 is a schematic configuration diagram showing the fuel system and flue duct system of a pulverized coal-fired boiler according to the embodiment of the present invention, and FIG. 2 Figure 3 is a system diagram of a coal gasifier that uses oxygen as a gasifier, Figure 3 is a diagram of a coal gasifier that uses air as a gasifier, and Figure 4 is an enlarged view of a pulverized coal burner that uses a combustion catalyst. , FIG. 5 is an enlarged view of a coal gasifier, and FIG. 6 is a schematic configuration diagram showing a fuel system and a flue system in a conventional pulverized coal-fired boiler. 6...pulverized coal-fired boiler, 7...mill, 9...coal, 12...pulverized coal pipe, 13...pulverized coal burner,
19...Pulverized coal pipe for gasification, 20...Coal gasifier, 21...Gasifying agent piping.

Claims (1)

[Claims] 1 Coal is crushed into pulverized coal in a mill, and this pulverized coal is supplied from the mill through a pulverized coal pipe to a pulverized coal burner of a boiler for combustion, in which a part of the pulverized coal is placed near the pulverized coal-fired boiler. A pulverized coal-fired boiler characterized by being equipped with a coal gasifier that gasifies with a gasifying agent such as air or oxygen.