Ammonia-doped pulverized coal combustion system and combustion method

Abstract

The invention discloses a pulverized coal ammonia-doped combustion system and method, and the system comprises an ammonia gasifier which is used for receiving liquid ammonia and heating and gasifying the liquid ammonia to obtain gas ammonia; the ammonia decomposer is used for receiving gas ammonia and decomposing the gas ammonia in a high-temperature state to obtain cracked gas of hydrogen and nitrogen; the combustion chamber is used for receiving the pyrolysis gas containing hydrogen and nitrogen, pulverized coal and air and combusting the pyrolysis gas, the pulverized coal and the air in the combustion chamber to obtain high-temperature and high-pressure gas; and the air preheater is used for preheating air entering the combustion chamber. Liquid ammonia is gasified and input into the ammonia decomposer to be decomposed into hydrogen and nitrogen, then the hydrogen and the nitrogen are sprayed into the combustion chamber to be mixed with pulverized coal to be combusted, the combustion current situation of NH3 is improved, the combustion intensity and the laminar flow combustion speed of NH3 are improved, and the problem that storage, transportation and conveying are difficult is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel utilization, and in particular to a pulverized coal co-firing ammonia combustion system and a combustion method. Background Art

[0002] Pulverized coal combustion technology has been widely used at home and abroad for a long time, and has the advantages of fast combustion speed, high burnout rate, and low flue gas heat loss. As a relatively mature technology, it is widely used in large power station boilers. However, under the influence of the dual-carbon goal, it is necessary to consider the carbon emission problem of pulverized coal combustion. At present, the carbon dioxide emission of coal-fired power generation in China is about 540 grams per kilowatt-hour, and there is still considerable potential to reduce the carbon dioxide emission of coal-fired boilers in thermal power plants. In order to reduce carbon emissions, thermal power plants need to change the traditional high-carbon coal-fired power generation method and replace coal with carbon-free fuels such as biomass, hydrogen, and ammonia at the front end to achieve coal and carbon reduction. The co-firing of low-carbon fuels can not only greatly reduce carbon emissions but also make full use of the existing equipment in coal-fired power plants. It is suitable for both new units and the low-carbon transformation of existing units, and is of great significance for China to achieve a rapid and stable transition from high-carbon power to low-carbon and zero-carbon power.

[0003] Hydrogen is widely sourced and has the advantages of a wide combustion limit range, low ignition energy, and fast flame propagation speed as a zero-carbon fuel. However, one of the bottlenecks in the development of hydrogen co-firing lies in storage, transportation, and safety. Due to the low density and difficulty in liquefaction of hydrogen, the currently relatively mature high-pressure hydrogen storage requires 35 - 70 MPa, which consumes a large amount of compression work, and the mass hydrogen storage density is only about 5%, resulting in high hydrogen storage and transportation costs. Coupled with the wide explosion hazard range of hydrogen and a high probability of danger.

[0004] Compared with hydrogen, ammonia, as another zero-carbon fuel, has the advantages of easy liquefaction, high volumetric energy density, no carbon emissions, non-flammability, and high safety, and has obvious advantages in its storage and transportation. For example, under the same volume conditions, the hydrogen storage capacity of liquid ammonia is 50% higher than that of liquid hydrogen, and ammonia liquefaction is much easier than hydrogen liquefaction, making it easy to store and transport. It is a good hydrogen carrier and energy storage fuel. Since ammonia has fuel properties, its energy density is comparable to that of fossil fuels. Under certain conditions, ammonia can be directly burned, and the ideal combustion products are water and nitrogen, and there are no greenhouse gas emissions during the combustion process. As a carbon-free inorganic compound, ammonia is also the compound with the largest hydrogen content in nature. The explosion limit range of ammonia (16% - 25%) is narrower, the boiling point is higher, and the possibility of fire and explosion is lower. Ammonia has a high octane number (130) and good anti-knock performance, which is beneficial to the safety during the use of ammonia fuel.

[0005] However, due to the high latent heat of vaporization of ammonia fuel, which is as high as 1370 kJ / kg, it is necessary to absorb part of the heat during the combustion process; the combustion speed of ammonia is relatively slow, and the combustion speed at normal temperature and pressure is only 7 cm / s, which has a certain negative impact on the combustion efficiency; the minimum ignition energy of ammonia is relatively large, resulting in difficulties in ignition; in addition, the nitrogen content in ammonia is relatively high, with a mass ratio as high as 82%, posing potential problems such as excessive nitrogen oxide emissions. Coupled with the unclear combustion reaction mechanism of ammonia, pure ammonia combustion cannot be used in current coal-fired units at present, and ammonia cannot directly replace coal as the main energy source in the short term. Therefore, co-combusting ammonia with pulverized coal is the key measure for the thermal power industry to reduce CO2 emissions at present.

[0006] Developing and utilizing efficient and low-pollution combustion technologies for ammonia can be one of the effective ways to solve the substitution of fossil energy and achieve carbon emission reduction in thermal power units. At present, most of the research on ammonia combustion focuses on internal combustion engines, and there is less research on the technology development of co-firing ammonia in pulverized coal boilers. Therefore, it is very important to develop a technology process for co-firing ammonia with pulverized coal.

[0007] CN 219083064 U discloses a dielectric barrier discharge plasma ammonia burner and co-firing of ammonia with pulverized coal. Ammonia is partially converted into nitrogen and hydrogen through the dielectric barrier discharge plasma ammonia burner and then enters the power plant boiler for combustion. Due to the low reaction temperature, ammonia cannot be completely converted into hydrogen and nitrogen, resulting in some unreacted ammonia entering the combustion chamber and generating additional NO X pollution.

[0008] CN202111395722.8 discloses a coal-fired boiler for full combustion of coal mixed with hydrogen, which directly co-fires coal with hydrogen. However, hydrogen has a small energy density and has the defect of inconvenient storage and transportation. Summary of the Invention

[0009] To solve the defects of the existing technology, the main purpose of the present invention is to provide a pulverized coal co-firing ammonia combustion system and a combustion method. After liquid ammonia is vaporized, it enters an ammonia decomposer to be decomposed into hydrogen and nitrogen, and then is sprayed into the combustion chamber to be mixed with pulverized coal for combustion, which not only improves the combustion status of NH3, increases the combustion intensity and laminar combustion speed of NH3, but also solves the problems of difficult storage, transportation and conveying.

[0010] To achieve the above-mentioned invention purpose, the present invention provides a pulverized coal co-firing ammonia combustion system, including:

[0011] An ammonia vaporizer for receiving liquid ammonia and heating and vaporizing the liquid ammonia to obtain gaseous ammonia;

[0012] An ammonia decomposer for receiving gaseous ammonia and decomposing the gaseous ammonia at a high temperature to obtain a cracked gas of hydrogen and nitrogen;

[0013] A combustion chamber for receiving pyrolysis gas containing hydrogen and nitrogen, pulverized coal, and air, burning inside the combustion chamber to obtain high-temperature and high-pressure gas;

[0014] An air preheater for preheating the air entering the combustion chamber.

[0015] Further, the system further includes an ammonia superheater, which is respectively connected to an ammonia vaporizer and an ammonia decomposer, for receiving gaseous ammonia from the ammonia vaporizer and heating the gaseous ammonia to obtain high-temperature gaseous ammonia, and then entering the ammonia decomposer.

[0016] Further, the interior of the furnace of the combustion chamber is divided into a reduction zone, a main combustion zone, and a ignition zone from top to bottom.

[0017] Further, the combustion chamber is also used to receive high-temperature gaseous ammonia as a regulating gas, and the high-temperature gaseous ammonia preferably enters from the reduction zone of the combustion chamber.

[0018] Further, the preheated air is divided into primary air, secondary air, and tertiary air. The primary air, pulverized coal, and pyrolysis gas enter the ignition zone of the combustion chamber for combustion, the secondary air enters the main combustion zone of the combustion chamber for assisting combustion, and the tertiary air enters the reduction zone of the combustion chamber to fully react the unreacted ammonia.

[0019] Further, the primary air, pulverized coal, and pyrolysis gas enter the combustion chamber together through a burner. The burner is arranged on the side furnace wall of the combustion chamber and includes multiple layers of feeding channels, which sequentially include a pulverized coal and a first-layer primary air feeding channel, a pyrolysis gas feeding channel, and a second-layer primary air feeding channel from the inside to the outside.

[0020] Further, the primary air and pulverized coal enter the combustion chamber together through a burner. The burner is arranged on the side furnace wall of the combustion chamber; the ammonia decomposer is located inside the furnace of the combustion chamber and outputs pyrolysis gas at a position above the burner.

[0021] Further, before entering the combustion chamber, the primary air participates in transporting the pulverized coal and premixes with the pulverized coal.

[0022] Further, the outlet of the pyrolysis gas feeding channel leading to the combustion chamber is rectangular or circular-rectangular.

[0023] The second aspect of the present invention also provides a method for burning pulverized coal with ammonia addition, including the following steps:

[0024] The ammonia vaporizer heats and vaporizes the liquid ammonia raw material to obtain gaseous ammonia;

[0025] The ammonia decomposer decomposes the gaseous ammonia at a high temperature to obtain pyrolysis gas of hydrogen and nitrogen;

[0026] The combustion chamber receives pyrolysis gas containing hydrogen and nitrogen, pulverized coal, and preheated air, and burns inside the combustion chamber to obtain high-temperature and high-pressure gas.

[0027] Further, the method further includes: an ammonia superheater receives gaseous ammonia and heats the gaseous ammonia to obtain high-temperature gaseous ammonia, which then enters an ammonia decomposer for decomposition.

[0028] Further, the temperature of the high-temperature gaseous ammonia is 800 - 850 °C.

[0029] Further, a part of the high-temperature gaseous ammonia enters the combustion chamber as regulating gas for reducing NO generated by pulverized coal combustion. X 。

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] The present invention uses an ammonia vaporizer to heat and vaporize liquid ammonia raw material to obtain gaseous ammonia; an ammonia decomposer decomposes the gaseous ammonia at a high temperature to obtain a cracking gas of hydrogen and nitrogen; the combustion chamber receives the cracking gas containing hydrogen and nitrogen, pulverized coal and preheated air, and burns inside the combustion chamber to obtain high-temperature and high-pressure gas. The present invention avoids the method in the prior art of vaporizing liquid ammonia and then spraying the gaseous ammonia into the combustion chamber using a nozzle. Because the ignition point of pure ammonia is relatively high, directly spraying pure ammonia may not be able to ignite or even cause the flame to go out, especially when a large amount of pure ammonia is sprayed. Therefore, in the prior art, liquid ammonia cannot be directly sprayed in a large proportion (such as 10%); while the present application adopts the method of vaporizing liquid ammonia and then entering the ammonia decomposer to decompose it into hydrogen and nitrogen and then spraying it into the combustion chamber to mix with pulverized coal and burn, which not only improves the combustion status of NH3, increases the combustion intensity and laminar burning speed of NH3, but also solves the problems of storage, transportation and conveyance.

[0032] Other features and advantages of the present invention will be described in detail through the following specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0034] Figure 1 It is a schematic diagram of a pulverized coal co-firing with ammonia combustion process (external type) provided by an embodiment of the present invention;

[0035] Figure 2 It is another schematic diagram of a pulverized coal co-firing with ammonia combustion process (internal type) provided by an embodiment of the present invention;

[0036] Figure 3 For Figure 1 it is a schematic diagram of the working principle inside the furnace of the combustion chamber in

[0037] Figures 4-5 Schematic diagram of a burner structure provided by an embodiment of the present invention.

[0038] Marking description: ammonia vaporizer 1, ammonia superheater 2, ammonia decomposer 3, combustion chamber 4 (reduction zone 4.1, main combustion zone 4.2 and ignition zone 4.3), air preheater 5, burner 6, ammonia burner 7, coal hopper 8, coal mill 9, pulverized coal blower 10, steam drum 11, circulation pump 12, superheater 13, economizer 14, condensate pump 15, condenser 16, steam turbine 17, forced draft fan 18, dust collector 19, desulfurization and denitrification device 20, induced draft fan 21, chimney 22, ash slurry pump 23, flow regulating valve 24, flue gas detection device 25.

[0039] Pulverized coal and first-layer primary air feed channel 6.1, pyrolysis gas feed channel 6.2, second-layer primary air feed channel 6.3, pyrolysis gas outlet 6.4. Specific embodiments

[0040] The following details the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

[0041] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance. Among them, the terms "first position" and "second position" are two different positions.

[0042] Unless otherwise clearly defined and limited, the terms "installed", "connected", "connected to", "fixed" should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] As a relatively mature technology in China, pulverized coal combustion technology is widely used in large-scale power plant boilers. However, under the influence of the dual-carbon goal, it is necessary to consider the carbon emissions of pulverized coal combustion. In order to reduce carbon emissions, thermal power plants need to change the traditional high-carbon-emission coal-fired power generation method. By burning carbon-free fuels such as biomass, hydrogen, and ammonia at the front end as alternative fuels, coal reduction and carbon reduction can be achieved, which requires some adjustments to the traditional process of pulverized coal combustion.

[0044] The nitrogen content in ammonia fuel is too high, and there is generally a high level of unburned ammonia and nitrogen oxides in the tail gas. How to reduce nitrogen oxide emissions while ensuring stable combustion is the main bottleneck restricting the utilization of ammonia fuel. The laminar flame speed of ammonia is relatively low, and it is difficult to burn stably alone. Decomposing ammonia into hydrogen and then mixing it with hydrocarbon fuels is an effective means to improve the combustion rate of ammonia, which not only alleviates the problems of high ignition point, difficult combustion, and unstable flame when directly mixing ammonia, but also solves the transportation problem of pure hydrogen.

[0045] To solve the above technical problems, referring to Figure 1 or Figure 2 , the present invention provides a pulverized coal-ammonia co-combustion system, including:

[0046] An ammonia vaporizer 1, which is used to receive liquid ammonia and heat and vaporize the liquid ammonia to obtain gaseous ammonia;

[0047] An ammonia superheater 2, which is used to receive gaseous ammonia and heat the gaseous ammonia to obtain high-temperature gaseous ammonia;

[0048] An ammonia decomposer 3, which is used to receive high-temperature gaseous ammonia and decompose the high-temperature gaseous ammonia to obtain a cracking gas of hydrogen and nitrogen;

[0049] A combustion chamber 4, which is used to receive the cracking gas containing hydrogen and nitrogen, pulverized coal, and air, and carry out combustion inside the combustion chamber to obtain high-temperature and high-pressure gas;

[0050] An air preheater 5, which is used to preheat the air entering the combustion chamber.

[0051] In the present invention, the ammonia decomposer can be either an external type or an internal type. For example, the external type shown in Figure 1 and the internal type shown in Figure 2 . When using the internal type shown in Figure 2 , the ammonia superheater 2 may not be provided, and the ammonia decomposer 3 is directly arranged inside the furnace of the combustion chamber. The high temperature inside the furnace can heat the gaseous ammonia to make it meet the high-temperature state for cracking.

[0052] In the present invention, referring to Figure 3 , the inside of the furnace of the combustion chamber 4 is divided into a reduction zone 4.1, a main combustion zone 4.2, and an ignition zone 4.3 from top to bottom. The upper layer is the reduction zone 4.1, the middle layer is the main combustion zone 4.2, and the lower layer is the ignition zone 4.3.

[0053] In the present invention, the preheated air is divided into primary air, secondary air and tertiary air. Referring to Figure 1 and Figure 3 , in a specific embodiment, the primary air, pulverized coal and pyrolysis gas enter the ignition zone of the combustion chamber through the burner 6 and burn together. The secondary air enters the main combustion zone of the combustion chamber for combustion support. One or more groups of secondary air can be set for more complete combustion. The tertiary air enters the reduction zone of the combustion chamber to fully react the unreacted ammonia.

[0054] Preferably, referring to Figure 1 , the combustion chamber is also used to receive a part of high-temperature gaseous ammonia as regulating gas. In a specific embodiment, the regulating gas enters from the reduction zone of the combustion chamber through the ammonia burner 7 and is used to reduce NO generated by pulverized coal combustion. X , the unreacted ammonia fully reacts with the tertiary air. In a specific embodiment, referring to Figure 3 , an ammonia flow regulating valve 24 is provided on this pipeline, and the ammonia flow is adjusted according to the NO X content in the flue gas fed back by the furnace flue gas detection device 25 to reduce NOx generated by the reaction of excessive NH3 with the tertiary air.

[0055] Preferably, referring to Figure 1 , before entering the combustion chamber, the primary air participates in transporting the pulverized coal. For example, the pulverized coal passes through the coal hopper 8 and the coal mill 9 and is mixed with air and then sent to the combustion chamber by the pulverized coal fan 10 to enter the combustion chamber and burn together with the pyrolysis gas.

[0056] In the present invention, referring to Figure 1 and Figure 4 , the burner 6 is arranged on the side furnace wall of the combustion chamber and includes multiple layers of feed channels, which successively include a pulverized coal and a first-layer primary air feed channel 6.1, a pyrolysis gas feed channel 6.2 and a second-layer primary air feed channel 6.3 from the inside to the outside. Since hydrogen has a low ignition point, stable flame and high heat, it is easier to ignite and the flame is more stable here compared with traditional pulverized coal burners.

[0057] Preferably, the outlet of the pyrolysis gas feed channel 6.2 leading to the combustion chamber is rectangular or circular-rectangular, making the structure more compact, reducing heat loss to a certain extent and shortening the flame travel; for example Figure 5 the rectangular outlet 6.4 on the pyrolysis gas feed channel 6.2 shown in

[0058] Preferably, referring to Figure 1, a small part of the high-temperature and high-pressure gas discharged from the combustion chamber sequentially passes through the ammonia superheater 2 and the ammonia vaporizer 1 to provide the energy required for ammonia decomposition. Most of the high-temperature and high-pressure gas is used to heat the steam drum 11 (generating superheated high-pressure steam for power generation by the steam turbine 17), and then passes through the economizer 14 to preheat the high-pressure condensate and enters the air preheater 5 to preheat the air entering the combustion chamber, further recovering heat.

[0059] It can be understood that with reference to Figure 1 , cold air is introduced through the air blower 18 at the inlet of the air preheater 5. The outlet of the air preheater is also connected to the dust collector 19 to remove dust from the discharged gas. After passing through the desulfurization and denitrification device 20, it is discharged into the atmosphere through the induced draft fan 21 from the chimney 22. The slag discharged from the bottom of the combustion chamber 4 and the fine ash and flushing water discharged from the dust collector 19 enter the ash yard together through the ash pump 23.

[0060] In the present invention, the ammonia decomposer can be an external type or an internal type. For example Figure 1 the external type shown in Figure 2 and Figure 1 the internal type shown in Figure 2 . When the external type shown in Figure 2 is adopted, the primary air, pulverized coal and pyrolysis gas enter the ignition zone of the combustion chamber through the burner and burn together. When the internal type shown in Figure 2 is adopted, the primary air and pulverized coal enter the combustion chamber through the burner together, and the burner is arranged on the side furnace wall of the combustion chamber; the ammonia decomposer is located inside the combustion chamber furnace and outputs pyrolysis gas above the burner.

[0061] The second aspect of the present invention also provides a pulverized coal and ammonia co-combustion method, including the following steps:

[0062] The ammonia vaporizer heats and vaporizes the liquid ammonia raw material to obtain gaseous ammonia;

[0063] The ammonia decomposer decomposes the gaseous ammonia at a high temperature to obtain a pyrolysis gas of hydrogen and nitrogen;

[0064] The combustion chamber receives the pyrolysis gas containing hydrogen and nitrogen, pulverized coal and preheated air, and burns inside the combustion chamber to obtain high-temperature and high-pressure gas.

[0065] In the present invention, the method further includes: the ammonia superheater receives gaseous ammonia and heats it to obtain high-temperature gaseous ammonia and then enters the ammonia decomposer for decomposition.

[0066] In the present invention, the temperature of the high-temperature gaseous ammonia is 800 - 850 °C.

[0067] In the present invention, calculated by volume ratio, the decomposed pyrolysis gas contains hydrogen (75%) and nitrogen (25%).

[0068] The following details the process of pulverized coal and ammonia co-combustion of the present invention through examples.

[0069] Example 1

[0070] Adopt Figure 1 The pulverized coal-ammonia co-combustion system shown in the figure. The method of pulverized coal-ammonia co-combustion in this example is as follows:

[0071] S1: Liquid ammonia (25°C, 1 Mpa) is vaporized in an ammonia vaporizer (16°C, 0.75 Mpa);

[0072] S2: Ammonia (gaseous) is superheated to 800 - 850°C in an ammonia superheater and then enters an ammonia decomposer;

[0073] S3: Part of the gaseous ammonia is cracked into hydrogen and nitrogen in an ammonia decomposer (800 - 850°C, 0.7 Mpa). The cracked gas (0.7 MPa) enters the nozzle at high speed through a nozzle and is mixed with pulverized coal at the burner position and then sprayed into the combustion chamber together. Another part of the high-temperature ammonia gas enters the furnace as a regulating gas through an ammonia burner to reduce the NO generated by the combustion of pulverized coal; X , and the unreacted ammonia fully reacts with the tertiary air. An ammonia flow regulating valve is provided on this pipeline, and the ammonia flow at the inlet of the ammonia burner is adjusted according to the NOX content in the flue gas feedback by the furnace flue gas detection device to reduce the NOx generated by the reaction of excessive NH3 with the tertiary air;

[0074] S4: Air (NTP) is heated to 326°C by an air preheater and then divided into two paths. One path (primary air) is used to transport pulverized coal through a coal mill and is premixed with pulverized coal and then enters the combustion chamber for combustion. The other path (secondary air) enters the combustion chamber through a spray gun to assist combustion;

[0075] S5: Pulverized coal passes through a coal hopper and a coal mill, is mixed with air, and is sent to the combustion chamber by a pulverized coal fan to enter the combustion chamber for combustion together with the cracked gas coming out of the ammonia decomposer;

[0076] S6: The high-temperature and high-pressure gas discharged from the combustion chamber (1500°C, 4 Mpa, volume ratio composition includes H2: 12%, N2: 58%, CH4: 1.6%, CO: 28.2%) is divided into two parts. One part sequentially passes through the ammonia superheater and the ammonia vaporizer to heat the liquid ammonia to 800 - 850°C and then cools down to 150 - 200°C, is mixed with the cooling waste gas leaving the furnace, and is discharged into the chimney after dust removal, denitrification, and desulfurization. The other part generates superheated high-pressure steam through a steam drum (to start a steam turbine to generate electricity), then enters and sequentially passes through a economizer (to preheat high-pressure condensate), an air preheater (to preheat air), is mixed with the other part of the cooling waste gas, and then enters a tail gas treatment device and is discharged into the atmosphere.

[0077] In this embodiment, 30% ammonia is mixed with pulverized coal (300 kg of liquid ammonia is configured for 1000 kg of pulverized coal). The liquid ammonia is heated to 800 °C and cracked into 75% hydrogen and 25% nitrogen under the action of a nickel-based catalyst. The residual ammonia is ≤0.1%, and 21.9 kcal of heat is absorbed. The main reaction is:

[0078] 2NH3 = 3H2 + N2 - 21.9 kcal

[0079] Compared with pulverized coal combustion, 30% ammonia is co-fired in this embodiment. The ammonia is completely cracked into nitrogen and hydrogen at 800 °C. The high-temperature gas generated after combustion contains methane and carbon monoxide. The NOx in the coal-fired furnace can be maintained at approximately the same level as that of pulverized coal combustion, verifying the feasibility of using the ammonia-hydrogen mixture produced by high-temperature cracking of ammonia as fuel.

[0080] At the same time, through calculation, it is found that after 30% ammonia is mixed with pulverized coal in this embodiment, the mass of CO2 in the high-temperature and high-pressure gas discharged after combustion is basically unchanged compared with that before ammonia mixing, but the concentration of CO2 decreases from 8% to 6.81%. The NO X emission decreases from 0.3% to 0.019% (the hydrogen generated after ammonia decomposition combines with oxygen to form water and does not release CO2, but the accumulation of nitrogen is caused by the consumption of excess oxygen, resulting in a decrease in the CO2 concentration). At the same time, nearly 40% more high-pressure steam is generated compared with before ammonia mixing (increasing from 72 kg / h to 102 kg / h). This means that a coal-fired power plant of the same scale can increase power generation by nearly 12 - 16% after ammonia mixing while reducing the CO2 / NOx emission concentration, with remarkable effects.

[0081] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limiting the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is impossible to list all the implementation manners here. All obvious changes or variations derived from the technical solutions of the present invention are within the spirit scope covered by the present invention.

Claims

1. A pulverized coal blended with ammonia combustion system, characterized in that: Comprising: An ammonia vaporizer for receiving liquid ammonia and heating and vaporizing the liquid ammonia to obtain gaseous ammonia; An ammonia decomposer for receiving gaseous ammonia and decomposing the gaseous ammonia at a high temperature to obtain a cracked gas of hydrogen and nitrogen; A combustion chamber for receiving the cracked gas containing hydrogen and nitrogen, pulverized coal and air, and burning inside the combustion chamber to obtain high-temperature and high-pressure gas; An air preheater for preheating the air entering the combustion chamber.

2. The pulverized coal ammonia-blended combustion system according to claim 1, wherein: It further includes an ammonia superheater, which is connected to the ammonia vaporizer and the ammonia decomposer respectively, for receiving the gaseous ammonia from the ammonia vaporizer and heating the gaseous ammonia, and then entering the ammonia decomposer after obtaining high-temperature gaseous ammonia.

3. The pulverized coal ammonia-blended combustion system according to claim 2, wherein: The inside of the furnace of the combustion chamber is divided into a reduction zone, a main combustion zone and a ignition zone from top to bottom; Preferably, the combustion chamber is further used for receiving high-temperature gaseous ammonia as a regulating gas, and the high-temperature gaseous ammonia preferably enters from the reduction zone of the combustion chamber.

4. The pulverized coal and ammonia co-combustion system according to claim 2 or 3, characterized in that: The preheated air is divided into primary air, secondary air and tertiary air. The primary air, pulverized coal and cracked gas enter the ignition zone of the combustion chamber for combustion, the secondary air enters the main combustion zone of the combustion chamber for assisting combustion, and the tertiary air enters the reduction zone of the combustion chamber to fully react the unreacted ammonia.

5. The pulverized coal ammonia-blended combustion system according to any one of claims 1 to 4, characterized in that: The primary air, pulverized coal and cracked gas enter the combustion chamber together through a burner. The burner is arranged on the side furnace wall of the combustion chamber and includes multiple layers of feeding channels, which are, from the inside to the outside, the pulverized coal and the first-layer primary air feeding channel, the cracked gas feeding channel and the second-layer primary air feeding channel.

6. The pulverized coal ammonia-blended combustion system according to any one of claims 2-4, characterized in that: The primary air and pulverized coal enter the combustion chamber together through a burner. The burner is arranged on the side furnace wall of the combustion chamber; the ammonia decomposer is located inside the furnace of the combustion chamber and outputs the cracked gas above the burner.

7. The pulverized coal co-firing with ammonia combustion system according to claim 5 or 6, characterized in that: Before entering the combustion chamber, the primary air participates in transporting the pulverized coal and premixes with the pulverized coal; and / or, The outlet of the cracked gas feeding channel leading to the combustion chamber is rectangular or circular-rectangular.

8. The pulverized coal ammonia-blended combustion system according to any one of claims 1-7, characterized in that: A part of the high-temperature and high-pressure gas discharged from the combustion chamber sequentially passes through the ammonia superheater and the ammonia vaporizer to provide the energy required for ammonia decomposition. Another part of the high-temperature and high-pressure gas heats the steam drum, generates superheated high-pressure steam, generates electricity through a steam turbine, then preheats the high-pressure condensate water and enters the air preheater to preheat the air.

9. A method for pulverized coal combustion with ammonia addition using the system according to any one of claims 1-8, characterized in that, Including the following steps: The ammonia vaporizer heats and vaporizes the liquid ammonia raw material to obtain gaseous ammonia; The ammonia decomposer decomposes the gaseous ammonia at a high temperature to obtain a cracked gas of hydrogen and nitrogen; The combustion chamber receives the cracked gas containing hydrogen and nitrogen, pulverized coal and preheated air, and burns inside the combustion chamber to obtain high-temperature and high-pressure gas.

10. The pulverized coal ammonia-blended combustion method according to claim 9, characterized in that: The method further includes: the ammonia superheater receives gaseous ammonia and heats the gaseous ammonia, and then enters the ammonia decomposer for decomposition after obtaining high-temperature gaseous ammonia; Preferably, the temperature of the high-temperature gaseous ammonia is 800-850 °C.

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