A flameless combustion device for coal mixed with ammonia

Abstract

The present invention discloses a flameless combustion device for coal-ammonia co-combustion, comprising: a pulverized coal pre-combustion unit, an ammonia decomposition unit, and a coal-ammonia co-combustion unit. Ammonia in the ammonia pre-combustion chamber exchanges heat with high-temperature flue gas in a high-temperature flue gas duct, and under the action of an ammonia decomposition catalyst, becomes ammonia pre-combustion gas (NH3, N2, and H2) and enters a combustion chamber. In the coal-ammonia co-combustion unit, the ammonia pre-combustion gas is first mixed with secondary air upon entering the combustion chamber; incompletely burned high-temperature flue gas enters the combustion chamber and is preliminarily mixed with the ammonia pre-combustion gas under the action of a blunt body; CO, H2, and residual coal char in the incompletely burned flue gas, as well as H2 in the ammonia pre-combustion gas, are strongly mixed with the secondary air. The flameless combustion device for coal-ammonia co-combustion not only reduces carbon dioxide emissions compared to pure coal combustion, but also enhances the stable combustion of ammonia. Furthermore, the incompletely burned flue gas produced by the pulverized coal pre-combustion chamber and the pre-combustion gas produced by the ammonia pre-combustion chamber effectively suppress the generation of nitrogen oxides.

Description

Technical Field

[0001] The present invention relates to the field of coal combustion devices, in particular to a flameless combustion device for coal mixed with ammonia. Background Art

[0002] Compared with traditional fossil fuels, ammonia (NH3) has the advantage of zero carbon emissions, so it can be used as a boiler fuel to reduce CO2 emissions on a large scale. However, ammonia combustion also has some problems. For example, when ammonia is directly injected into the boiler for combustion, ammonia combines with oxygen to produce a large amount of NO. x , and NO x The ignition temperature is high, the flammable limit range is narrow, and the flame propagation speed is slow. Therefore, the NO in ammonia combustion is suppressed. x The generation of ammonia and improving the ignition stability of ammonia have become urgent issues to be solved.

[0003] To address the high ignition temperature and poor combustion characteristics of ammonia, existing technologies typically use pyrolysis to generate N2 and H2. This utilizes H2's low ignition temperature, low lower flammability limit, wide flammability range, and stable ignition. However, existing technologies often use ammonia injection into the furnace for simultaneous combustion and pyrolysis, resulting in low pyrolysis efficiency and low H2 concentrations. Alternatively, these technologies utilize external steam as a heat source for ammonia pyrolysis, increasing external heat consumption and the heating system, thereby increasing boiler operating costs.

[0004] In the existing technology, coal mixed with ammonia combustion supplies ammonia fuel to the reduction area of ​​the burner flame through the combustion air to suppress NO x However, under the complex flow field organization of the burner outlet, it is not possible to accurately introduce the ammonia fuel into the reduction area, thus suppressing NO x The generation effect is not good, but because the ammonia fuel is directly mixed with the air, NO x The generation creates better oxygen-rich conditions.

[0005] To address the above-mentioned problems in the prior art, the present invention discloses a technical solution for a flameless combustion device for coal-ammonia co-combustion. This device can decompose ammonia into H2 in an ammonia pre-decomposition chamber before entering the combustion chamber, thereby enhancing stable combustion of ammonia. Furthermore, the incomplete combustion flue gas produced in the pulverized coal pre-combustion chamber cools down due to the heating of the ammonia, causing it to decompose, before entering the combustion chamber, effectively reducing the high-temperature conditions for the formation of nitrogen oxides during combustion. The incomplete combustion flue gas CO, H2, and residual coal char, as well as the H2 in the ammonia pre-decomposition gas, strongly mix with the secondary air, reducing the local oxygen concentration, facilitating flameless combustion, and suppressing oxygen-rich conditions for the formation of nitrogen oxides. The incomplete combustion flue gas produced in the pulverized coal pre-combustion chamber and the pre-decomposition gas (NH3, N2, and H2) produced in the ammonia pre-decomposition chamber enter the combustion chamber, creating a weakly reducing atmosphere and low-oxygen conditions, effectively suppressing the formation of nitrogen oxides. Summary of the Invention

[0006] A flameless combustion device for coal-ammonia co-combustion comprises a pulverized coal pre-combustion unit, an ammonia decomposition unit and a coal-ammonia co-combustion unit.

[0007] The pulverized coal pre-combustion unit includes a pulverized coal pre-combustion chamber.

[0008] The ammonia decomposition unit includes: a high-temperature flue gas duct, an ammonia pre-decomposition chamber, and an ammonia tank.

[0009] The coal-ammonia blending and combustion unit comprises: a fan, a flow control valve, a secondary air pipeline, a bluff body, and a combustion chamber.

[0010] After the pulverized coal is mixed with the primary air in the pulverized coal precombustion chamber, the pulverized coal undergoes pyrolysis and incomplete combustion in an oxygen-deficient environment, generating incomplete combustion flue gas (CO2, H2O, CO, H2) and residual coal char, with a flue gas temperature above 1000°C.

[0011] The high-temperature flue gas duct is led out from the coal powder precombustion chamber at one end and connected to the combustion chamber at the other end, and is used to transport the high-temperature incomplete combustion flue gas generated by the coal powder precombustion chamber to the combustion chamber.

[0012] The ammonia pre-decomposition chamber is located outside the high-temperature flue gas duct, with ammonia supplied from an ammonia tank at one end and connected to the combustion chamber at the other. The NH3 in the ammonia pre-decomposition chamber is heated by the high-temperature flue gas in the high-temperature flue gas duct. Under the action of an ammonia decomposition catalyst installed in the ammonia pre-decomposition chamber, a portion of the ammonia is pre-decomposed into N2 and H2. The resulting mixture, primarily composed of NH3, N2, and H2, becomes ammonia pre-decomposition gas and enters the combustion chamber.

[0013] The front center axis of the combustion chamber is connected to the high-temperature flue gas duct, and the front high-temperature flue gas duct of the combustion chamber is connected to the ammonia pre-decomposition chamber.

[0014] The secondary air duct inlet is located at the front end of the combustion chamber and outside the ammonia pre-decomposition chamber. It can be arranged symmetrically or asymmetrically. In a symmetrical arrangement, the secondary air is a two-way or four-way gas flow; in an asymmetrical arrangement, the secondary air is a single-way gas flow. The secondary air speed is adjusted by a fan and flow control valve. In a symmetrical arrangement, the speed is 50m / s to 100m / s; in an asymmetrical arrangement, the speed is 10m / s to 150m / s.

[0015] The blunt body is arranged at the front end of the combustion chamber and at the central axis outlet where the high-temperature flue gas duct enters the combustion chamber. The blunt body can be conical in shape to enhance the mixing effect of incomplete combustion flue gas and ammonia pre-decomposition gas, which is beneficial to promoting combustion stability and inhibiting the generation of nitrogen oxides.

[0016] The working process of the flameless combustion device for coal mixed with ammonia is as follows:

[0017] ① Pulverized Coal Precombustion Unit: In the pulverized coal precombustion chamber, after mixing with primary air, the pulverized coal undergoes pyrolysis and incomplete combustion in an oxygen-deficient environment, producing incompletely burned high-temperature flue gas. The flue gas components are CO2, H2O, CO, H2, and residual coal char. The high-temperature flue gas is discharged from the pulverized coal precombustion chamber into the high-temperature flue gas duct.

[0018] ② Ammonia decomposition unit: Ammonia is supplied from the ammonia tank to the ammonia pre-decomposition chamber. NH3 in the ammonia pre-decomposition chamber is heated by the high-temperature flue gas in the high-temperature flue gas duct. Under the action of the ammonia decomposition catalyst installed in the ammonia pre-decomposition chamber, part of the ammonia is pre-decomposed into N2 and H2. The mixed gas mainly composed of NH3, N2, and H2 becomes the ammonia pre-decomposition gas and enters the combustion chamber.

[0019] ③ Coal-ammonia co-combustion unit: The air volume in the secondary air duct is controlled by a fan and flow control valve. The secondary air introduced by the fan is transported to the combustion chamber through the secondary air duct. The secondary air duct is located outside the outlet of the ammonia pre-decomposition chamber. Therefore, when the ammonia pre-decomposition gas enters the combustion chamber, it first mixes with the secondary air, and the H2 produced by the ammonia pre-decomposition rapidly burns. The incompletely burned high-temperature flue gas enters the combustion chamber and is initially mixed with the ammonia pre-decomposition gas by the action of the blunt body. During this continuous mixing process with the secondary air, the incompletely burned flue gas CO, H2, and residual coal char react with oxygen and burn.

[0020] The beneficial effects brought by the present invention are:

[0021] 1. Effectively improve the thermal stability of coal mixed with ammonia combustion.

[0022] In the present invention, the high-temperature flue gas flowing in the high-temperature flue gas duct heats the ammonia in the ammonia predecomposition chamber, causing most of the ammonia to thermally decompose. Ammonia is decomposed into H2 in the ammonia predecomposition chamber. H2 has a low lower combustion limit and a low ignition temperature. The ammonia predecomposition gas containing H2 enters the combustion chamber and is mixed and burned with the incompletely burned flue gas, effectively improving the thermal stability of the combustion. At the same time, H2 is a clean fuel and achieves zero carbon emissions. Compared with the prior art of decomposing while burning in the furnace, ammonia predecomposition has higher decomposition efficiency and more stable combustion.

[0023] 2. Effectively inhibit the formation of nitrogen oxides. The conditions for the formation of nitrogen oxides are high temperature and rich oxygen.

[0024] In terms of controlling high temperature: the present invention does not require the use of external heat to thermally decompose ammonia, but instead makes full use of the heat of high-temperature flue gas to heat and decompose ammonia. The cooled flue gas is sprayed into the combustion chamber, effectively alleviating the generation conditions of nitrogen oxides at high temperatures.

[0025] In terms of controlling oxygen enrichment: in the present invention, the secondary air pipeline is arranged at the periphery of the outlet of the ammonia pre-decomposition chamber, so the ammonia pre-decomposition gas is first mixed with the secondary air when entering the combustion chamber. Since the H2 in the ammonia pre-decomposition gas has a strong ability to combine with oxygen and a fast reaction speed, the speed at which N2 in the ammonia pre-decomposition gas combines with oxygen is reduced, thereby suppressing the oxygen-enriched generation conditions of nitrogen oxides. In the present invention, after the pulverized coal is mixed with the primary air in the pulverized coal pre-combustion chamber, the pulverized coal undergoes pyrolysis and incomplete combustion in an oxygen-deficient environment, generating incompletely burned high-temperature flue gas that is sent to the combustion chamber and initially mixed with the ammonia pre-decomposition gas under the action of a blunt body, also in an oxygen-deficient environment. In the process of continuous mixing with the secondary air, the incompletely burned flue gas CO, H2 and residual coal char, as well as H2 in the ammonia pre-decomposition gas, react more easily with oxygen than N2 in the ammonia pre-decomposition gas, thereby reducing the local oxygen concentration, facilitating the realization of a flameless combustion state, and further suppressing the oxygen-enriched generation conditions of nitrogen oxides. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 System diagram of a flameless combustion device for coal-ammonia combustion

[0027] Figure 2 Schematic diagram of the front end layout of the combustion chamber

[0028] Figure 3 Schematic diagram of the mixing effect of incomplete combustion flue gas and ammonia pre-decomposition gas in the combustion chamber

[0029] The following are marked in the figure: 1. Pulverized coal precombustion chamber, 2. High-temperature flue gas duct, 3. Ammonia tank, 4. Ammonia predecomposition chamber, 5. Fan, 6. Flow control valve, 7. Secondary air pipeline, 8. Blunt body, 9. Combustion chamber DETAILED DESCRIPTION

[0030] A flameless combustion device for coal-ammonia co-combustion comprises a pulverized coal pre-combustion unit, an ammonia decomposition unit and a coal-ammonia co-combustion unit.

[0031] The pulverized coal pre-combustion unit includes a pulverized coal pre-combustion chamber 1. The ammonia decomposition unit includes a high-temperature flue gas duct 2, an ammonia pre-combustion chamber 4, and an ammonia tank 3. The coal-ammonia co-combustion unit includes a fan 5, a flow control valve 6, a secondary air duct 7, a bluff body 8, and a combustion chamber 9.

[0032] The high-temperature flue gas duct 2 has one end leading out from the pulverized coal precombustion chamber 1 and the other end connected to the combustion chamber 9, and is used to transport the high-temperature incomplete combustion flue gas generated by the pulverized coal precombustion chamber 1 to the combustion chamber 9.

[0033] The ammonia pre-decomposition chamber 4 is arranged outside the high-temperature flue gas duct 2, with ammonia supplied from the ammonia tank 3 at one end and connected to the combustion chamber 9 at the other end. The ammonia pre-decomposition chamber 4 is filled with an ammonia decomposition catalyst.

[0034] The front end center axis of the combustion chamber 9 is connected to the high-temperature flue gas duct 2 , and the front end high-temperature flue gas duct 2 of the combustion chamber 9 is connected to the ammonia pre-decomposition chamber 4 .

[0035] The inlet of the secondary air pipeline 7 is located at the front end of the combustion chamber 9 and outside the ammonia pre-decomposition chamber 4. A symmetrical arrangement is possible, with the secondary air being a four-way gas. The secondary air speed is adjusted by a fan and flow control valve. When arranged symmetrically, the speed is 50 m / s to 100 m / s.

[0036] The bluff body 8 is arranged at the front end of the combustion chamber 9 and at the central axis outlet where the high-temperature flue gas duct 2 is connected to the combustion chamber 9. The bluff body 8 is conical.

[0037] The working process of a flameless combustion device for coal mixed with ammonia is as follows:

[0038] ① Pulverized Coal Precombustion Unit: In pulverized coal precombustion chamber 1, after mixing with primary air, the pulverized coal undergoes pyrolysis and incomplete combustion in an oxygen-deficient environment, producing incompletely burned high-temperature flue gas composed of CO₂, H₂O, CO, H₂, and residual coal char. The high-temperature flue gas is discharged from pulverized coal precombustion chamber 1 into high-temperature flue gas duct 2, with a flue gas temperature exceeding 1000°C.

[0039] ② Ammonia decomposition unit: Ammonia is supplied from the ammonia tank 3 to the ammonia pre-decomposition chamber 4. NH3 in the ammonia pre-decomposition chamber 4 is heated by the high-temperature flue gas in the high-temperature flue gas duct 2. Under the action of the ammonia decomposition catalyst in the ammonia pre-decomposition chamber 4, part of the ammonia is pre-decomposed into N2 and H2. The mixed gas mainly composed of NH3, N2, and H2 becomes the ammonia pre-decomposition gas and enters the combustion chamber 9.

[0040] ③ Coal-ammonia co-combustion unit: The air volume in secondary air duct 7 is controlled by flow control valve 6. Secondary air introduced by fan 5 is transported through secondary air duct 7 to combustion chamber 9. Secondary air duct 7 is located outside the outlet of ammonia pre-decomposition chamber 4. Therefore, upon entering combustion chamber 9, the ammonia pre-decomposition gas first mixes with the secondary air, and the H2 produced by the ammonia pre-decomposition rapidly burns. The incompletely burned high-temperature flue gas enters combustion chamber 9 and is initially mixed with the ammonia pre-decomposition gas by the action of blunt body 8. During this continuous mixing process with the secondary air, the incompletely burned flue gas CO, H2, and residual coal char react with oxygen and burn.

[0041] The flameless combustion device for mixing coal with ammonia not only reduces carbon dioxide emissions from pure coal combustion, but also decomposes ammonia into H2 in the ammonia pre-decomposition chamber 4 before being fed into the combustion chamber 9, enhancing the stable combustion of ammonia. Furthermore, the incomplete combustion flue gas produced in the pulverized coal pre-combustion chamber 4 heats the ammonia, causing it to decompose and cool down before entering the combustion chamber 9, effectively reducing the high-temperature conditions for the formation of nitrogen oxides during combustion. The incomplete combustion flue gas CO, H2, and residual coal char, as well as the H2 in the ammonia pre-decomposition gas, strongly mix with the secondary air, reducing the local oxygen concentration and facilitating the flameless combustion state. At the same time, it creates a weakly reducing atmosphere and low-oxygen conditions, suppressing the oxygen-rich conditions for the formation of nitrogen oxides.

Claims

1. A flameless combustion device for coal-ammonia co-combustion, comprising: The pulverized coal pre-combustion unit, the ammonia decomposition unit, and the coal-ammonia co-combustion unit are characterized in that: the pulverized coal pre-combustion unit includes: a pulverized coal pre-combustion chamber (1); the ammonia decomposition unit includes: a high-temperature flue gas duct (2), an ammonia pre-combustion chamber (4); the coal-ammonia co-combustion unit includes: a secondary air duct (7), a blunt body (8), and a combustion chamber (9); the ammonia pre-combustion chamber (4) is arranged outside the high-temperature flue gas duct (2) and is heated by the high-temperature flue gas duct (2); an ammonia decomposition catalyst is filled in the ammonia pre-combustion chamber (4); one end of the high-temperature flue gas duct (2) is led out from the pulverized coal pre-combustion chamber (1), and the other end is connected to the combustion chamber (9); the inlet of the secondary air duct (7) is arranged at the front end of the combustion chamber (9) and outside the ammonia pre-combustion chamber (4); the blunt body (8) is arranged at the front end of the combustion chamber (9) and at the outlet where the high-temperature flue gas duct (2) is connected to the central axis of the combustion chamber (9), and the blunt body is conical.

2. The flameless combustion device for coal-ammonia co-combustion according to claim 1, characterized in that: The ammonia decomposition unit further comprises an ammonia tank (3); one end of the ammonia pre-decomposition chamber (4) is supplied with ammonia from the ammonia tank (3); the other end of the ammonia pre-decomposition chamber (4) is connected to the combustion chamber; the front end center axis of the combustion chamber (9) is connected to the high-temperature flue gas duct (2); the front end of the high-temperature flue gas duct (2) of the combustion chamber (9) is connected to the outside of the ammonia pre-decomposition chamber (4).

3. The flameless combustion device for coal-ammonia co-combustion according to claim 1, characterized in that: The coal-ammonia co-combustion unit further comprises: a fan (5) and a flow control valve (6); the air volume of the secondary air pipeline (7) is controlled by the flow control valve (6), and the secondary air introduced by the fan (5) is transported to the combustion chamber (9) through the secondary air pipeline (7); the secondary air pipeline (7) is arranged symmetrically or asymmetrically, and the secondary air is a two-way gas or a four-way gas in the symmetrical arrangement, and a single-way gas in the asymmetrical arrangement; the secondary air speed is adjusted by the fan (5) and the flow control valve (6), and the speed is 50m / s to 100m / s in the symmetrical arrangement; and the speed is 100m / s to 150m / s in the asymmetrical arrangement.

4. A flameless combustion device for coal-ammonia co-combustion according to any one of claims 1 to 3, characterized in that: The working process of the flameless combustion device for coal mixed with ammonia combustion is as follows: ① Pulverized coal pre-combustion unit: In the pulverized coal pre-combustion chamber (1), after the pulverized coal is mixed with the primary air, the pulverized coal undergoes pyrolysis and incomplete combustion in an oxygen-deficient environment, generating incompletely burned high-temperature flue gas. The high-temperature flue gas is discharged from the pulverized coal pre-combustion chamber (1) into the high-temperature flue gas duct (2), and the flue gas temperature is above 1000°C. ② Ammonia decomposition unit: Ammonia is supplied from the ammonia tank (3) to the ammonia pre-decomposition chamber (4); NH3 in the ammonia pre-decomposition chamber (4) is heated by the high-temperature flue gas in the high-temperature flue gas duct (2), and part of the ammonia is pre-decomposed into N2 and H2 under the action of the ammonia decomposition catalyst loaded in the ammonia pre-decomposition chamber (4). The mixed gas mainly composed of NH3, N2, and H2 becomes ammonia pre-decomposition gas and enters the combustion chamber (9); ③ Coal-ammonia co-combustion unit: The air volume of the secondary air duct (7) is controlled by the flow control valve (6), and the secondary air introduced by the fan (5) is transported to the combustion chamber (9) through the secondary air duct (7); the secondary air duct (7) is arranged at the periphery of the outlet of the ammonia pre-decomposition chamber (4), and the ammonia pre-decomposition gas is first mixed with the secondary air when entering the combustion chamber (9), and the H2 generated by the ammonia pre-decomposition is quickly burned; the incomplete combustion high-temperature flue gas enters the combustion chamber (9), and is preliminarily mixed with the ammonia pre-decomposition gas under the action of the blunt body (8); in the process of continuous mixing with the secondary air, the incomplete combustion flue gas CO, H2 and residual coal char react with oxygen and burn.

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