A method for peak shaving of a pulverized coal boiler

Abstract

The application discloses a coal powder boiler peak regulation method, which comprises the following steps: modifying the coal powder into high-temperature gas-solid fuel by using a coal powder preheating combustion method; and setting a heat exchange surface in the preheating burner, and heating the boiler feed water before the boiler feed water enters an economizer. The method solves the problem of poor combustion stability of the boiler at low load, increases the temperature of the boiler feed water, reduces the heat absorption amount of the economizer from the flue gas, reduces the temperature drop range of the flue gas through the economizer, increases the flue gas temperature at the inlet of the SCR, and ensures that the SCR denitration system works in a safe and efficient temperature range.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of combustion and power generation, in particular to a coal-fired boiler peak shaving method. BACKGROUND

[0002] Based on the energy structure and the installed capacity of the power grid in China, realizing deep flexible peak shaving of coal-fired power plant boilers so that the power grid can maximize the consumption of renewable energy generation has become a problem that needs to be solved for coal-fired power plant boilers at present.

[0003] However, the existing coal-fired power plant boilers face serious technical challenges when peak shaving, such as narrow stable operating load range, poor low-load stable combustion, high pollutant emissions, etc. When the boiler is deeply peak shaved, as the load of the boiler decreases, the combustion stability becomes poor, and the minimum stable combustion load of the boiler is generally higher than 40%. At the same time, due to the decrease in load, the flue gas temperature at the outlet of the furnace decreases, and the flue gas passes through the tail heating surface and then enters the SCR denitration system to remove NO x X. In order to ensure the normal denitration efficiency of the SCR, the inlet flue gas temperature of the SCR reactor is required to be between 280-410℃, but the inlet flue gas temperature of the SCR is usually lower than the allowable temperature under ultra-low load of the boiler, which causes damage to the catalyst in the SCR and low denitration efficiency, which cannot meet the requirements of ultra-low NO x X emission. Poor low-load combustion stability and low SCR inlet temperature under low load are two key factors that limit the deep peak shaving of the boiler. SUMMARY

[0004] The purpose of the present application is to provide a coal-fired boiler deep peak shaving method, which can be used for deep peak shaving of boiler units that burn coal powder, semi-coke, residual carbon, coal slime, solid waste fly ash and other powder fuels, and can effectively adapt to the consumption of renewable energy generation under the double carbon target.

[0005] The technical solution of the present application is as follows:

[0006] A coal-fired boiler peak shaving method, comprising: using a coal powder preheating combustion method to modify the coal powder into a high-temperature gas-solid fuel; and simultaneously setting a heat exchange surface in the preheating combustor to heat the boiler feedwater before it enters the economizer.

[0007] Further, the coal powder preheating combustion method for modifying the coal powder into a high-temperature gas-solid fuel comprises: the coal powder is converted into a high-temperature gas / solid fuel after being modified by the preheating combustor, and the temperature of the high-temperature gas / solid fuel is higher than 800℃.

[0008] Further, the high-temperature gas / solid fuel is discharged from the top of the preheating burner and sprayed into the furnace of the boiler, the high-temperature gas / solid fuel is combusted and released heat in the furnace of the boiler, the flue gas generated is heated by the heating surface in the furnace and the tail heating surface of the boiler, and then enters the economizer, in which part of the heat of the flue gas is transferred to the boiler feed water, and the flue gas temperature is further reduced and then enters the SCR unit.

[0009] Further, the flue gas temperature is reduced to higher than 280℃ before entering the SCR unit.

[0010] Further, the heating of the boiler feed water before entering the economizer includes that the boiler feed water enters the economizer through the boiler feed water pipe and exchanges heat with the flue gas in the economizer; the boiler feed water entering the economizer is divided into two routes, one route of the boiler feed water enters the heating surface in the preheating burner through the first water circulation loop, and the boiler feed water is heated by the heat in the preheating burner and then enters the economizer, and the other route of the boiler feed water directly enters the economizer through the second water circulation loop.

[0011] Further, when the boiler is operated at a load lower than 30%, the boiler feed water enters the heating surface in the preheating burner through the first water circulation loop, the temperature of the boiler feed water is increased by 50-70℃ by the heat in the preheating burner, and then enters the economizer, so that the flue gas temperature before entering the SCR unit is higher than 280℃.

[0012] Further, when the boiler is operated at a high load, part of the boiler feed water directly enters the economizer through the second water circulation loop; the high load refers to a load higher than or equal to 30%.

[0013] Further, the first water circulation loop always ensures a feed water amount to prevent dry burning of the heating surface in the preheating burner.

[0014] Further, the boiler has the heating surface in the furnace and the tail heating surface.

[0015] According to an embodiment of one aspect of the present application, the coal powder is modified into high-temperature gas / solid fuel by using the coal powder preheating combustion technology, the reactivity of the fuel is improved, the problem of poor combustion stability of the boiler at a low load is solved, and stable combustion of the coal powder boiler at a load of 20% is realized; meanwhile, the heating surface is arranged in the preheating burner, the temperature of the boiler feed water is increased before entering the economizer, the heat absorption amount of the flue gas by the economizer is reduced, the temperature reduction range of the flue gas passing through the economizer is reduced, the SCR inlet flue gas temperature is increased, and the SCR inlet temperature of the coal powder boiler at a load of 20% is higher than 280℃.

[0016] The present application has the following beneficial effects:

[0017] 1) After the coal powder is modified at high temperature, the fuel reactivity is improved, and the problem of poor combustion stability of the boiler at low load is solved;

[0018] 2) The boiler feed water is heated in the preheating burner, the feed water temperature is increased, the heat absorption amount of the flue gas by the economizer is reduced, the temperature drop of the flue gas through the economizer is reduced, the SCR inlet flue gas temperature is increased, and the SCR denitration system is ensured to work in a safe and efficient temperature range. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 A schematic diagram of a coal powder boiler deep peak shaving method;

[0020] In the figure, 1 is a preheating burner, 2 is a boiler, 3 is a tail flue, 4 is an economizer, and 5 is an SCR unit. DETAILED DESCRIPTION

[0021] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments. However, the following embodiments are only used to explain the present application, and the protection scope of the present application should include the entire content of the claims, and through the description of the following embodiments, those skilled in the art can fully realize the entire content of the claims of the present application.

[0022] Figure 1 A schematic diagram of a coal powder boiler deep peak shaving method. As shown in Figure 1 A coal powder boiler deep peak shaving device used in a coal powder boiler deep peak shaving method, including a preheating burner 1, a boiler 2, a tail flue 3, an economizer 4 and an SCR unit 5. The preheating burner 1 outlet is connected to the boiler 2. The boiler 2 outlet is connected to the tail flue 3. The tail flue 3 can be arranged in a vertical single column, and the flue gas flows from top to bottom. The economizer 4 and the SCR unit 5 are arranged in the tail flue 3 in sequence along the flue gas flow direction. The boiler feed water pipe is divided into two routes before entering the economizer 4: a first water circulation loop and a second water circulation loop. The first water circulation loop enters the heating surface in the preheating burner 1, and then connects the inlet of the economizer 4, and the second water circulation loop directly connects the inlet of the economizer 4.

[0023] The preheating burner 1 is used for preheating the pulverized coal, and is of a circulating fluidized bed structure.

[0024] In one of the embodiments of the coal-fired boiler deep peak shaving method provided by the present application, the preheating burner 1 is connected with the boiler 2, the pulverized coal is converted into high-temperature coal gas and part of high-temperature solid fuel which is not gasified after being preheated and modified by the preheating burner 1. Figure 1 The high-temperature coal gas and part of the high-temperature solid fuel which is not gasified are referred to as high-temperature gas / solid fuel. The high-temperature gas / solid fuel is discharged from the top of the preheating burner 1 and then sprayed into the boiler 2. The high-temperature gas / solid fuel is combusted and heat-released in the furnace of the boiler 2, and the flue gas generated is heat-exchanged with the heating surface in the furnace and the tail heating surface of the boiler 2, and then enters the economizer 4. The flue gas in the economizer 4 transfers part of the heat to the boiler feed water, and then enters the SCR unit 5 after the temperature of the flue gas is further reduced. The boiler feed water enters the economizer 4 through the boiler feed water pipe and is heat-exchanged with the flue gas. The boiler feed water before entering the economizer 4 is divided into two routes, one of which enters the heating surface in the preheating burner 1 through the first water circulation loop, is heated by the heat in the preheating burner and then enters the economizer 4, and the other of which directly enters the economizer 4 through the second water circulation loop.

[0025] The principle of the present application is that: the pulverized coal first enters the preheating burner 1, the preheating burner is a circulating fluidized bed structure, the pulverized coal is preheated and modified by partial gasification in the preheating burner 1, the coal is modified into high-temperature gas / solid fuel by preheating modification, the temperature of the high-temperature gas / solid fuel is higher than 800 DEG C, and it is a mixture of gas fuel and solid fuel, so this fuel has the characteristics of gas fuel combustion, at the same time, the coke pore opens, the graphitization degree decreases, the active defect site increases, and the reaction activity of the fuel is greatly improved. The combustion of high-temperature gas / solid fuel is dominated by homogeneous reaction, which is more similar to the combustion of gas fuel, solving the problems of stable combustion and low efficiency under low load, and realizing high-efficiency and stable combustion of the pulverized coal boiler under 20% load through the above method. When the boiler 2 operates below 30% load, the boiler feed water enters the heating surface in the preheating burner 1 through the first water circulation loop, and the temperature of the boiler feed water is increased by 50-70 DEG C by using the heat in the preheating burner, and then enters the economizer 4, the increase of the temperature of the boiler feed water reduces the heat transfer temperature difference between the flue gas side and the water side in the economizer 4, reduces the temperature drop of the flue gas in the economizer 4, can maintain the flue gas temperature before entering the SCR unit 5 higher than 280 DEG C, and ensure the safety of the catalyst in the SCR unit 5 and the efficient removal of NO x X. In order to ensure that the exhaust gas temperature of the boiler 2 under full load does not exceed the standard, when the boiler 2 operates under high load (load greater than or equal to 30%), part of the boiler feed water enters the economizer 4 directly through the second water circulation loop, and the proportion of the boiler feed water passing through the first water circulation loop and the second water circulation loop is flexibly adjusted according to the SCR inlet flue gas temperature and the boiler exhaust gas temperature, it is worth noting that a certain amount of feed water is always ensured in the first water circulation loop to prevent dry burning of the heating surface in the preheating burner 1.

[0026] In the present application, the heating surface is added in the pulverized coal preheating burner to heat the boiler feed water. The heating surface in the preheating burner is a membrane wall, the membrane wall is used as the shell of the preheating burner, and the boiler feed water flows in the membrane wall and absorbs the heat in the preheating burner.

[0027] Some parts of the present application which are not described in detail belong to the known technology of those skilled in the art. The above-described embodiments only describe the preferred embodiments of the present application, and the preferred embodiments do not describe all the details and do not limit the application to the specific embodiments described. Without departing from the design spirit of the present application, various modifications and improvements of the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method for peak shaving in a pulverized coal boiler, characterized in that, include: The pulverized coal is modified into a high-temperature gas-solid fuel by using a pulverized coal preheating combustion method; at the same time, a heat exchange surface is set in the preheating burner to heat the boiler feedwater before it enters the economizer. The method of modifying pulverized coal into high-temperature gaseous / solid fuel by pulverized coal preheating and combustion includes: pulverized coal is preheated and modified by a preheating burner and then converted into high-temperature gaseous / solid fuel, wherein the temperature of the high-temperature gaseous / solid fuel is higher than 800°C. After being discharged from the top of the preheating burner, the high-temperature gas / solid fuel is injected into the furnace of the boiler. The high-temperature gas / solid fuel burns and releases heat in the furnace of the boiler. The generated flue gas enters the economizer after heat exchange through the heating surface in the furnace and the tail heating surface. In the economizer, part of the heat of the flue gas is transferred to the boiler feedwater. After the flue gas temperature is further reduced, it enters the SCR unit. The heating of boiler feedwater before it enters the economizer includes: boiler feedwater entering the economizer through the boiler feedwater pipe and exchanging heat with flue gas in the economizer; the boiler feedwater entering the economizer is divided into two paths, one path of boiler feedwater enters the heating surface in the preheating burner through the first water circulation loop, and the boiler feedwater is heated by the heat in the preheating burner before entering the economizer, and the other path of boiler feedwater enters the economizer directly through the second water circulation loop. When the boiler is running at a load below 30%, all the boiler feedwater enters the heating surface in the preheating burner through the first water circulation loop. The heat in the preheating burner is used to raise the boiler feedwater temperature by 50~70℃ before it enters the economizer, maintaining the flue gas temperature above 280℃ before entering the SCR unit. When the boiler is operating at high load, part of the boiler feedwater enters the economizer directly through the second water circulation loop; the high load refers to a load ≥ 30%.

2. The method according to claim 1, characterized in that, The first water circulation loop always ensures a constant water supply to prevent the heating surfaces in the preheating burner from drying out.

3. The method according to claim 1, characterized in that, The heat exchange surface is a membrane wall, which is used as the outer shell of the preheating burner. Boiler feedwater flows in the membrane wall and absorbs heat from the preheating burner.

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