Low-NOx combustion system and method based on ammonia decomposition staged combustion

Abstract

The invention discloses a low NOx combustion system and method based on ammonia decomposition staged combustion, the low NOx combustion system based on ammonia decomposition staged combustion comprises an ammonia storage tank, an ammonia decomposition device, an air source and a combustion device, the combustion device comprises a first-stage combustion area and a second-stage combustion area, an outlet of the ammonia decomposition device is connected with a gas inlet of the first-stage combustion area, and an outlet of the second-stage combustion area is connected with a gas outlet of the second-stage combustion area; an air source is connected with gas inlets of the first-stage combustion area and the second-stage combustion area through an air pump, the first-stage combustion area is a rich combustion area, and the second-stage combustion area is a lean combustion area. By utilizing the system, liquid ammonia is decompressed and then enters the ammonia decomposition device to be decomposed into mixed gas of ammonia gas, hydrogen and nitrogen; the mixed gas and air are mixed into primary air, the primary air enters the first-stage combustion area to be combusted, and the remaining air enters the second-stage combustion area from the secondary air inlet to be combusted. By combining ammonia decomposition and rich-fuel-lean-fuel staged combustion technologies, stable combustion of ammonia is achieved, NOx emission is reduced, and ammonia escape is prevented.

Description

Technical Field

[0001] The present invention belongs to the field of clean combustion technology, and particularly relates to a low NOx based on ammonia decomposition and staged combustion. x Combustion systems and methods. Background Art

[0002] The combustion of fossil fuels and the resulting carbon dioxide emissions have become an important energy and environmental issue. Among them, hydrogen energy, as an ideal energy carrier, has attracted extensive attention and research from academia and industry due to its wide source, high calorific value, and no carbon dioxide emissions during combustion, which is very environmentally friendly. However, the extreme reaction properties of hydrogen have brought about problems such as difficulty in storage and transportation and combustion hazards, which have limited the large-scale application of hydrogen fuel in industrial production.

[0003] As a hydrogen-carrying fuel, ammonia has a hydrogen content of up to 17.6 wt%. Its volume energy density is much higher than that of hydrogen. It has the advantages of wide sources, easy storage and transportation, high thermal efficiency, relatively safe operation and compatibility with ordinary materials. In addition, direct combustion of ammonia does not have the problem of carbon dioxide emissions. Therefore, using ammonia to replace traditional fossil fuels for production is considered to be one of the cutting-edge technologies for achieving large-scale carbon emission reduction. In recent years, the production process of ammonia has become more mature, which provides better technical support and economic guarantee for the industrial application of ammonia. However, the combustion of ammonia fuel has the disadvantages of low combustion intensity and NO x In addition to the problem of high emissions, incomplete combustion will also lead to excessive unburned ammonia emissions.

[0004] Ammonia decomposition gas as fuel can effectively improve the combustion intensity of ammonia, while rich-lean staged combustion can significantly reduce the NO generated by ammonia combustion. x The combination of the two can simultaneously solve the low combustion intensity of ammonia and NO x For example, Chinese patent CN112902163A discloses a hydrogen-doped low-nitrogen combustion system and method based on ammonia decomposition, which solves the problems of low heat release rate, poor combustion stability and NO x The problem of high emissions is solved. However, the ammonia decomposition device described in the patent is equipped with a nitrogen removal device, which has a complex structure and adds additional costs. In addition, although injecting ammonia into the second combustion zone can reduce NO x However, the temperature at the end of the flame is low, making ammonia escape more likely.

[0005] In order to solve the above problems, the present invention proposes a low NO x Combustion systems and methods. Summary of the invention

[0006] The purpose of the present invention is to provide a low NOx based on ammonia decomposition staged combustion xCombustion system and method, by combining ammonia decomposition with rich-lean staged combustion technology, to achieve stable combustion of ammonia and reduce NO x Emissions and prevention of ammonia escape.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A low NOx based on ammonia decomposition staged combustion x The combustion system specifically includes an ammonia storage tank, an ammonia decomposition device, an air source and a combustion device. The combustion device includes a primary combustion zone and a secondary combustion zone. The outlet of the ammonia decomposition device is connected to the gas inlet of the primary combustion zone. The air source is connected to the gas inlets of the primary combustion zone and the secondary combustion zone through an air pump. The primary combustion zone is a rich combustion zone, and the secondary combustion zone is a lean combustion zone. A burner is arranged at the front end of the primary combustion zone. The secondary combustion zone is arranged with a secondary air inlet, and the position of the inlet is adjustable.

[0008] Ammonia passes through the pressure reducing valve from the ammonia storage tank 1 and is controlled by adjusting the valve opening. It then enters the ammonia decomposition device 2 for decomposition to produce a mixture of ammonia, hydrogen and nitrogen. The mixed gas is mixed with the air pumped in by the air pump 3 to form a primary air, and is sprayed into the combustion device 4 by the burner 5 for combustion. The burner 5 may be a swirl structure to promote the mixing of fuel and air and optimize the combustion process. Another air enters the combustion device 4 from the secondary air inlet 6, and is mixed with the remaining combustible gas after the primary air is burned, and continues to burn. The air flow in the above process is controlled by adjusting the valve opening. The combustion chamber is divided into two areas: the primary combustion zone 7 and the secondary combustion zone 8. Rich combustion is carried out in the primary combustion zone 7. There is insufficient air and incomplete fuel combustion, which can reduce NO x Lean-burn combustion is carried out in the secondary combustion zone 8 with excess air to burn out the remaining combustible gas.

[0009] A low NO x The combustion method utilizes the above-mentioned low NO based on ammonia decomposition staged combustion x Combustion system, the specific steps are as follows: (1) After decompression, liquid ammonia enters the ammonia decomposition device and is decomposed into a mixture of ammonia, hydrogen and nitrogen; (2) The mixed gas is mixed with air to form primary air and then enters the primary combustion zone for combustion; (3) The remaining air enters the secondary combustion zone through the secondary air inlet for combustion.

[0010] Furthermore, the decomposition ratio of ammonia in the mixed gas entering the primary combustion zone is 0.0-1.0.

[0011] Furthermore, the catalyst used in the ammonia decomposition device is Ru / Al 2 O 3 .

[0012] Furthermore, the global equivalence ratio is 0.4-0.8. The equivalence ratio is the ratio of the theoretical amount of air required for complete combustion of the fuel to the actual amount of air supplied. Rich combustion means that the actual amount of air contained in the combustible mixture is less than the required theoretical amount of air. Lean combustion means that the actual amount of air contained in the combustible mixture exceeds the required theoretical amount of air.

[0013] Furthermore, the equivalence ratio of the primary combustion zone is 1.0-2.0.

[0014] Furthermore, the temperature of the primary air entering the primary combustion zone is 400-800 K.

[0015] Furthermore, the temperature of the secondary air entering the secondary combustion zone is 400-800 K.

[0016] Further, the combustion pressure is 8-16 atm.

[0017] By adjusting the above parameters, the combustion stability is improved, NO x Emissions are reduced and ammonia slip is prevented.

[0018] The beneficial effects of the present invention are: (1) The present invention provides a low NOx system based on ammonia decomposition and staged combustion. x The combustion system and method use the ammonia decomposition gas generated by the ammonia decomposition device as fuel, and the air provides oxygen, which enters the combustion device in two ways for combustion. The fuel is burned in the primary combustion zone at a specific equivalence ratio to reduce NO x The gas generated in the primary combustion zone enters the secondary combustion zone, mixes with the secondary air, and burns out to prevent ammonia from escaping.

[0019] (2) The ammonia decomposition device is used to generate ammonia decomposition gas as fuel, which effectively improves the shortcomings of pure ammonia fuel, such as the narrow flammability limit range and low flame propagation speed, and improves combustion stability and combustion thermal efficiency.

[0020] (3) By adjusting the ammonia decomposition ratio and combustion parameters and designing the combustion device structure, the ammonia combustion rate and combustion stability are improved, and NO in the flue gas is reduced. x and ammonia emissions.

[0021] (4) The operating range of ammonia decomposition combustion is expanded through adjustable rich-lean staged combustion. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A low NOx fuel based on ammonia decomposition and staged combustion x Schematic diagram of the combustion system structure; where: 1-ammonia storage tank; 2-ammonia decomposition device; 3-air pump; 4-combustion device; 5-burner; 6-secondary air inlet; 7-primary combustion zone; 8-secondary combustion zone. DETAILED DESCRIPTION

[0023] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0024] The present invention provides a low NOx based on ammonia decomposition staged combustion x Combustion system such as Figure 1 As shown, it includes an ammonia storage tank 1, the outlet of the ammonia storage tank 1 is connected to the inlet of the ammonia decomposition device 2, the outlet of the ammonia decomposition device 2 is connected to the inlet of the burner 5 set at the front end of the combustion device 4, and the outlet of the air pump 3 is divided into two gas paths, one of which is mixed with the ammonia decomposition gas at the outlet of the ammonia decomposition device 2 and enters the primary combustion zone 7 through the inlet of the burner 5, and the other air enters the secondary combustion zone 8 through the secondary air inlet 6. Valves are set in each connecting pipeline to control the ammonia flow rate and equivalence ratio.

[0025] The specific steps are: Ammonia passes through the pressure reducing valve from the ammonia storage tank 1 and is controlled by adjusting the valve opening. It then enters the ammonia decomposition device 2 for decomposition to produce a mixture of ammonia, hydrogen and nitrogen. The mixed gas is mixed with the air pumped in by the air pump 3 to form a primary air, and is sprayed into the combustion device 4 by the burner 5 for combustion. The burner 5 may be a swirl structure to promote the mixing of fuel and air and optimize the combustion process. Another air enters the combustion device 4 from the secondary air inlet 6, and is mixed with the remaining combustible gas after the primary air is burned, and continues to burn. The air flow in the above process is controlled by adjusting the valve opening. The combustion chamber is divided into two areas: the primary combustion zone 7 and the secondary combustion zone 8. Rich combustion is carried out in the primary combustion zone 7. There is insufficient air and incomplete fuel combustion, which can reduce NO x Lean-burn combustion is carried out in the secondary combustion zone 8 with excess air to burn out the remaining combustible gas.

[0026] In the following examples, the flow rate of ammonia entering the ammonia decomposition device is set to 108 SLM, and the catalyst used in the ammonia decomposition device is Ru / Al 2 O 3 , placed in the catalyst bed of the ammonia decomposition device, and its synthesis method is shown in Chinese patent CN113058595A.

[0027] Example 1 A low NOx based on ammonia decomposition and staged combustion provided by the present invention x Combustion system for low NO x The burning method comprises the following steps: (1) After decompression, liquid ammonia enters the ammonia decomposition device and is decomposed into a mixture of ammonia, hydrogen and nitrogen; (2) The mixed gas is mixed with air to form primary air and enters the primary combustion zone for combustion; (3) The remaining air enters the secondary combustion zone through the secondary air inlet for combustion.

[0028] The ammonia decomposition ratio is 0.2, the primary air temperature is 400 K, the secondary air temperature is 600 K, the combustion pressure is 12 atm, the global equivalence ratio is 0.5, and the equivalence ratio of the primary combustion zone is 1.2.

[0029] Example 2 A low NOx based on ammonia decomposition and staged combustion provided by the present invention x Combustion system for low NO x The burning method comprises the following steps: (1) After decompression, liquid ammonia enters the ammonia decomposition device and is decomposed into a mixture of ammonia, hydrogen and nitrogen; (2) The mixed gas is mixed with air to form primary air and enters the primary combustion zone for combustion; (3) The remaining air enters the secondary combustion zone through the secondary air inlet for combustion.

[0030] The ammonia decomposition ratio is 0.2, the primary air temperature is 600 K, the secondary air temperature is 600 K, the combustion pressure is 12 atm, the global equivalence ratio is 0.6, and the equivalence ratio of the primary combustion zone is 1.3.

[0031] Example 3 A low NOx based on ammonia decomposition and staged combustion provided by the present invention x Combustion system for low NO x The burning method comprises the following steps: (1) After decompression, liquid ammonia enters the ammonia decomposition device and is decomposed into a mixture of ammonia, hydrogen and nitrogen; (2) The mixed gas is mixed with air to form primary air and enters the primary combustion zone for combustion; (3) The remaining air enters the secondary combustion zone through the secondary air inlet for combustion.

[0032] The ammonia decomposition ratio is 0.2, the primary air temperature is 800 K, the secondary air temperature is 400 K, the combustion pressure is 12 atm, the global equivalence ratio is 0.4, and the equivalence ratio of the primary combustion zone is 1.5.

[0033] Example 4 A low NOx based on ammonia decomposition and staged combustion provided by the present invention x Combustion system for low NO x The burning method comprises the following steps: (1) After decompression, liquid ammonia enters the ammonia decomposition device and is decomposed into a mixture of ammonia, hydrogen and nitrogen; (2) The mixed gas is mixed with air to form primary air and enters the primary combustion zone for combustion; (3) The remaining air enters the secondary combustion zone through the secondary air inlet for combustion.

[0034] The ammonia decomposition ratio is 0.2, the primary air temperature is 600 K, the secondary air temperature is 600 K, the combustion pressure is 16 atm, the global equivalence ratio is 0.5, and the equivalence ratio of the primary combustion zone is 1.3.

[0035] Example 5 A low NOx based on ammonia decomposition and staged combustion provided by the present invention x Combustion system for low NO x The burning method comprises the following steps: (1) After decompression, liquid ammonia enters the ammonia decomposition device and is decomposed into a mixture of ammonia, hydrogen and nitrogen; (2) The mixed gas is mixed with air to form primary air and enters the primary combustion zone for combustion; (3) The remaining air enters the secondary combustion zone through the secondary air inlet for combustion.

[0036] The ammonia decomposition ratio is 0.5, the primary air temperature is 600 K, the secondary air temperature is 600 K, the combustion pressure is 12 atm, the global equivalence ratio is 0.5, and the equivalence ratio of the primary combustion zone is 1.4.

[0037] Example 6 A low NOx based on ammonia decomposition and staged combustion provided by the present invention x Combustion system for low NO x The burning method comprises the following steps: (1) After decompression, liquid ammonia enters the ammonia decomposition device and is decomposed into a mixture of ammonia, hydrogen and nitrogen; (2) The mixed gas is mixed with air to form primary air and enters the primary combustion zone for combustion; (3) The remaining air enters the secondary combustion zone through the secondary air inlet for combustion.

[0038] The ammonia decomposition ratio is 0.8, the primary air temperature is 600 K, the secondary air temperature is 600 K, the combustion pressure is 12 atm, the global equivalence ratio is 0.4, and the equivalence ratio of the primary combustion zone is 1.6.

[0039] Comparative Example 1 The difference from Example 2 is that the equivalence ratio of the primary combustion zone is 0.6, and there are only steps (1) and (2), i.e., primary air intake.

[0040] Comparative Example 2 Different from Example 5, the equivalence ratio of the primary combustion zone is 0.5, and there are only steps (1) and (2), i.e., primary air intake.

[0041] Comparative Example 3 Different from Example 6, the equivalence ratio of the primary combustion zone is 0.4, and there are only steps (1) and (2), i.e., primary air intake.

[0042] The NO obtained by the above Examples 1-6 and Comparative Examples 1-3 x The emissions are shown in Table 1.

[0043] Table 1 NO of Examples 1-6 and Comparative Examples 1-3 x Emissions The NO obtained in the above comparative example x The emission is obtained under single-stage combustion conditions. By comparing the data in the table, it can be found that compared with single-stage combustion, the low NO x Combustion system and method can burn out fuel and significantly reduce NO while ensuring stable combustion x Emissions.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low NOx based on ammonia decomposition staged combustion x Combustion system, characterized in that: It includes an ammonia storage tank, an ammonia decomposition device, an air source and a combustion device. The combustion device includes a primary combustion zone and a secondary combustion zone. The outlet of the ammonia decomposition device is connected to the gas inlet of the primary combustion zone. The air source is connected to the gas inlets of the primary combustion zone and the secondary combustion zone through an air pump. The primary combustion zone is a rich combustion zone, and the secondary combustion zone is a lean combustion zone. A burner is arranged at the front end of the primary combustion zone. A secondary air inlet is arranged in the secondary combustion zone, and the inlet position is adjustable.

2. A low NO x The combustion method is characterized by: Utilize the low NO based on ammonia decomposition staged combustion as claimed in claim 1 x Combustion system, the specific steps are as follows: (1) After decompression, liquid ammonia enters the ammonia decomposition device and is decomposed into a mixture of ammonia, hydrogen and nitrogen; (2) The mixed gas is mixed with air to form primary air and then enters the primary combustion zone for combustion; (3) The remaining air enters the secondary combustion zone through the secondary air inlet for combustion.

3. Low NO according to claim 2 x A combustion method, characterized in that: The catalyst used in the ammonia decomposition device is Ru / Al2O3.

4. Low NO according to claim 2 x A combustion method, characterized in that: The decomposition ratio of ammonia in the mixed gas entering the primary combustion zone is 0.0-1.

0.

5. Low NO according to claim 2 x A combustion method, characterized in that: The global equivalence ratio is 0.4-0.

8.

6. Low NO according to claim 2 x A combustion method, characterized in that: The equivalence ratio of the primary combustion zone is 1.0-2.

0.

7. The low NO according to claim 2 x A combustion method, characterized in that: The temperature of the primary air entering the primary combustion zone is 400-800 K.

8. The low NO according to claim 2 x A combustion method, characterized in that: The residual air temperature entering the secondary combustion zone is 400-800 K.

9. The low NO according to claim 2 x A combustion method, characterized in that The combustion pressure is 8-16 atm.

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