Pure ammonia combustion circulating fluidized bed boiler system

Abstract

The invention relates to a pure ammonia combustion circulating fluidized bed boiler system which comprises an ammonia water storage tank, an ammonia water evaporator, a fluidized bed boiler hearth, a separator and an external heat exchange cracking device, the separator is connected with a high-temperature material inlet of the external heat exchange cracking device through a shunt branch, and the shunt branch is provided with a shunt valve; a heat exchange pipe is arranged in the external heat exchange cracking device, one end of the heat exchange pipe is used for introducing ammonia gas, and the other end of the heat exchange pipe is connected with an ammonia cracking gas inlet of a hearth of the fluidized bed boiler, so that mixed gas formed after cracking is fed into the hearth of the fluidized bed boiler; an air inlet is formed in the bottom of the external heat exchange cracking device, and a high-temperature material outlet is formed in one side of the external heat exchange cracking device, so that high-temperature materials after heat exchange return to the hearth of the fluidized bed boiler. According to the boiler system, the combustion rate of ammonia gas can be increased, it is guaranteed that the ammonia gas can be completely combusted, stable combustion of pure ammonia is achieved, pollutant generation is controlled, and the thermal power industry is assisted to achieve carbon reduction.

Description

Technical Field

[0001] The present invention relates to the technical field of fluidized bed boilers, and in particular to a pure ammonia combustion circulating fluidized bed boiler system. Background Art

[0002] Zero-carbon fuels such as hydrogen and ammonia have attracted widespread attention. Compared with hydrogen, ammonia has advantages such as high calorific value and easy transportation, but it also has problems such as unstable combustion and high pollutant emissions.

[0003] As a gaseous fuel, ammonia is more difficult to burn completely than natural gas, hydrogen, and other fuels. Failure to enhance ammonia combustion will result in excessive ammonia levels in flue gas, leading to not only energy waste but also serious environmental pollution.

[0004] The furnace temperature of a circulating fluidized bed boiler is generally between 800-900°C, at which ammonia burns relatively slowly. To address this issue, some designs incorporate catalysts into the furnace to promote ammonia combustion. However, after a period of operation, the catalyst deactivates, requiring replacement and disposal, increasing operating costs. Summary of the Invention

[0005] The object of the present invention is to provide a circulating fluidized bed boiler system for pure ammonia combustion, which can achieve stable and efficient combustion of ammonia through a fluidized bed method.

[0006] To achieve the above-mentioned purpose, the present invention provides a pure ammonia combustion circulating fluidized bed boiler system, which includes an ammonia storage tank, an ammonia evaporator, a fluidized bed boiler furnace and a separator. The ammonia storage tank is connected to the ammonia evaporator, and an air distribution device is provided in the fluidized bed boiler furnace. The ammonia evaporator is connected to the air distribution device to send ammonia into the fluidized bed boiler furnace. The separator is used to separate flue gas from particles, and its flue gas inlet is connected to the flue gas outlet of the fluidized bed boiler furnace. Its bottom is connected to the fluidized bed boiler furnace and is provided with a return valve to return the high-temperature material separated by the separator to the furnace; it also includes an external replacement The thermal cracking device comprises a separator connected to the high-temperature material inlet of the external heat exchange cracking device through a diversion branch, and the diversion branch is provided with a diversion valve; a heat exchange pipe is provided inside the external heat exchange cracking device, one end of the heat exchange pipe is used to introduce ammonia gas, and the other end is connected to the ammonia cracking gas inlet provided in the furnace of the fluidized bed boiler, so as to feed the mixed gas formed after cracking into the furnace of the fluidized bed boiler; an air inlet is provided at the bottom of the external heat exchange cracking device, and a high-temperature material outlet is provided on one side of the external heat exchange cracking device, so that the high-temperature material after heat exchange is returned to the furnace of the fluidized bed boiler under the fluidization action of air.

[0007] Optionally, the heat exchange tube is arranged in the transverse direction inside the external exchange thermal cracking device, the high-temperature material inlet is located at the top of the external exchange thermal cracking device and is arranged toward the ammonia inlet end of the heat exchange tube, and the high-temperature material outlet is arranged at the other end of the external exchange thermal cracking device and is located above the mixed gas output end of the heat exchange tube.

[0008] Optionally, there are multiple heat exchange tubes, and the multiple heat exchange tubes are distributed in parallel inside the external heat exchange cracking device.

[0009] Optionally, the ammonia cracking gas inlet is provided in the air distribution device or located on the upper side of the air distribution device.

[0010] Optionally, particulate material is added into the furnace of the fluidized bed boiler, and the particulate material d 50 =1-1.5 mm.

[0011] Optionally, the particulate material comprises fly ash particles.

[0012] Optionally, an ammonia decomposition catalyst is sprayed or arranged inside the heat exchange tube.

[0013] Optionally, the ammonia decomposition catalyst comprises a nickel-based catalyst.

[0014] Optionally, the air distribution device is a hollow structure, with an ammonia flow channel inside and an air channel outside.

[0015] Optionally, the amount of ammonia entering the external heat exchange cracking unit accounts for 5-10% of the total fuel amount, and the temperature in the heat exchange tube is maintained at 500-700°C during operation.

[0016] The pure ammonia combustion circulating fluidized bed boiler system provided by the present invention is equipped with an external heat exchange cracking device outside the fluidized bed boiler furnace. The external heat exchange cracking device is equipped with a heat exchange pipe for passing ammonia. After part of the high-temperature material diverted from the separator enters the external heat exchange cracking device, its own high temperature can be used to heat the ammonia in the heat exchange pipe, thereby decomposing part of the ammonia into nitrogen and hydrogen, and then sent into the fluidized bed boiler furnace through the ammonia cracking gas inlet. In the fluidized bed boiler furnace, hydrogen and ammonia are mixed and burned, thereby increasing the combustion rate of ammonia, ensuring that the ammonia can be completely burned, realizing stable combustion of pure ammonia, and controlling the generation of pollutants, helping the thermal power industry to achieve carbon reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic structural diagram of a pure ammonia combustion circulating fluidized bed boiler system provided in an embodiment of the present invention.

[0018] In the picture:

[0019] 1-Ammonia storage tank; 2-Ammonia evaporator; 3-Fluidized bed boiler furnace; 4-Cyclone separator; 5-Return valve; 6-Diverter valve; 7-External heat exchange cracking unit; 8-Air distribution device; 9-Ammonia cracking gas inlet; 10-Heat exchange pipe; 11-Air inlet; 12-High-temperature material inlet; 13-High-temperature material outlet. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0021] In this article, terms such as "upper, lower, inside, outside" are established based on the positional relationships shown in the drawings. Depending on the different drawings, the corresponding positional relationships may also change accordingly. Therefore, they cannot be understood as absolute limitations on the scope of protection; moreover, relational terms such as "first" and "second" are only used to distinguish one component from another with the same name, and do not necessarily require or imply any actual relationship or order between these components.

[0022] Please refer to Figure 1 , Figure 1 A schematic structural diagram of a pure ammonia combustion circulating fluidized bed boiler system provided in an embodiment of the present invention.

[0023] As shown in the figure, in a specific embodiment, the pure ammonia combustion circulating fluidized bed boiler system provided by the present invention is mainly composed of an ammonia water storage tank 1, an ammonia water evaporator 2, a fluidized bed boiler furnace 3 and a cyclone separator 4.

[0024] Among them, the ammonia storage tank 1 is mainly used to store ammonia, which is the fuel source of the pure ammonia combustion fluidized bed boiler. The ammonia storage tank 1 is connected to the ammonia evaporator 2, which is used to heat the ammonia and evaporate it into ammonia gas. The fluidized bed boiler furnace 3 is the boiler combustion chamber. Granular materials are added in the furnace. The materials are generally coal ash particles. Other particles with catalytic ammonia combustion can also be used. The material particles d 50 =1-1.5 mm.

[0025] An air distribution device 8 is installed at the bottom of the fluidized bed boiler furnace 3. Primary air is sent in from the bottom of the furnace through the blower. The ammonia evaporator 2 is connected to the air distribution device 8 to send ammonia into the fluidized bed boiler furnace 3. The cyclone separator 4 is mainly used to separate flue gas from particles. During operation, flue gas flows out from the top of the cyclone separator 4, carrying some fine particles (about 50 μm) at the same time, and coarse particles fall into the bottom of the cyclone separator 4. Its flue gas inlet is connected to the flue gas outlet of the fluidized bed boiler furnace 3. Its bottom is connected to the fluidized bed boiler furnace 3 through an inclined material chute and is provided with a return valve 5 to use the gravity of the material itself to return the high-temperature material separated by the cyclone separator 4 to the furnace.

[0026] On this basis, an external heat exchange cracking device 7 is additionally provided. The cyclone separator 4 is connected to the high-temperature material inlet 12 of the external heat exchange cracking device 7 through a diversion branch. The diversion branch is provided with a diversion valve 6. In this embodiment, the diversion valve 6 adopts a conical valve, which is mainly used to adjust the amount of material entering the external heat exchange cracking device 7.

[0027] The external heat exchange cracking unit 7 primarily utilizes high-temperature materials to decompose ammonia into nitrogen and hydrogen under the action of a catalyst. The unit is equipped with heat exchange tubes 10, which are sprayed or otherwise coated with an ammonia decomposition catalyst, including but not limited to nickel-based catalysts. The high-temperature materials flow from top to bottom into the external heat exchange cracking unit 7, where they are heated by heat exchange tubes 10. One end of heat exchange tube 10 is used to introduce ammonia gas, while the other end is connected to an ammonia cracking gas inlet 9 located in the fluidized bed boiler furnace 3, delivering the resulting mixed gas after cracking.

[0028] An air inlet 11 is provided at the bottom of the external heat exchange cracking device 7, and a high-temperature material outlet 13 is provided on one side of the external heat exchange cracking device 7 so that the high-temperature material after heat exchange is returned to the fluidized bed boiler furnace 3 under the fluidization effect of air.

[0029] Specifically, the number of heat exchange tubes 10 can be multiple, and the multiple heat exchange tubes 10 are distributed in parallel in the transverse direction inside the external heat exchange cracking device 7. The high-temperature material inlet 12 is located at the top of the external heat exchange cracking device 7 and is set biased towards the ammonia inlet end of the heat exchange tube 10. The high-temperature material outlet 13 is set at the other end of the external heat exchange cracking device 7 and is located above the mixed gas output end of the heat exchange tube 10. The ammonia cracking gas inlet 9 of the fluidized bed boiler furnace 3 can be set in the air distribution device 8 or on the upper side of the air distribution device 8.

[0030] The furnace of this pure ammonia-combustion circulating fluidized bed boiler system is filled with a large amount of particulate matter, exhibiting excellent heat transfer performance and high thermal inertia. An air distribution device 8 is installed at the bottom of the furnace, with secondary air inlets arranged along the height of the furnace. Ammonia water is heated in the ammonia evaporator 2, converted into ammonia gas, which is then fed into the air distribution device 8. The air distribution device 8 is a hollow structure with an internal ammonia flow channel and an external air channel. Air enters the furnace through the primary air duct at the bottom of the furnace and passes through the air distribution device 8. Within the furnace, the ammonia gas mixes with the air and burns, transferring heat to the particulate matter filling the furnace. Simultaneously, the flue gas generated by the combustion fluidizes the particles within the furnace. The flue gas and particles move upward and enter the cyclone separator 4, where gas-solid separation is completed. The gas enters the tail flue from the top of the cyclone separator 4, while the solid particles enter the bottom of the cyclone separator 4. Some of the solid particles return to the furnace through the return valve 5, while some pass through the diverter valve 6 and enter the external heat exchange cracking unit 7.

[0031] The high-temperature solid particles entering the external heat exchange cracking unit 7 account for approximately 5% of the total material. Heat exchange tubes 10 are installed in the external heat exchange cracking unit 7. The interior of the heat exchange tubes 10 can be sprayed with a nickel-based catalyst or other catalyst. During operation, the temperature inside the heat exchange tubes should be maintained at 500-700°C. The mixed gas formed after ammonia cracking is fed into the furnace air distribution device 8 or the fuel inlet located above the air distribution device 8, where it mixes with air and ammonia and then burns. The temperature inside the external heat exchange cracking unit 7 is controlled by the diverter valve 6, which controls the high-temperature material entering the device. An air inlet 11 is installed at the bottom of the external heat exchange cracking unit 7. Under the action of fluidization, the heat-exchanged material returns to the furnace.

[0032] During operation, the furnace temperature is between 800-900℃; the temperature difference between the upper and lower parts should not exceed 30℃; the oxygen concentration at the flue gas outlet is between 3.0-4.5%; the fluidization wind speed in the furnace is 2.5-3.5 m / s; the average pressure drop of the upper dilute phase bed is at least 30Pa / m; the solid particles d 50 =1-1.5 mm. The amount of ammonia entering the external thermal cracking unit 7 should account for 5-10% of the total fuel. The ammonia content in the flue gas should be less than 500 ppm.

[0033] The above embodiment is merely a preferred embodiment of the present invention and is not intended to be limiting. Based on this, targeted adjustments can be made according to actual needs to achieve different implementations. For example, other types of separators can be used in place of the cyclone separator 4, and so on. Due to the numerous possible implementations, we will not provide a detailed description here.

[0034] Pure ammonia combustion generally suffers from the problem of low fuel burnout rate, and a large amount of unburned ammonia is contained in the flue gas, which not only causes a large amount of energy waste but also brings serious environmental pollution. The fluidized bed boiler of the present invention contains a large amount of high-temperature materials, which can improve the burnout rate of ammonia. After the ammonia is decomposed, it mainly becomes hydrogen and nitrogen. With the combustion-supporting effect of hydrogen, the fuel burnout rate is further improved, and finally ammonia is completely burned. This not only realizes pure ammonia combustion, but also effectively improves ammonia combustion efficiency and reduces ammonia concentration in the flue gas, truly achieving zero carbon emissions for fluidized bed boilers, which can effectively promote the large-scale utilization of ammonia fuel and promote the transformation and upgrading of the energy industry.

[0035] The above describes in detail the pure ammonia combustion circulating fluidized bed boiler system provided by the present invention. This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are intended only to facilitate understanding of the core concepts of the present invention. It should be noted that those skilled in the art will be able to make various improvements and modifications to the present invention without departing from the principles of the present invention, and such improvements and modifications fall within the scope of protection of the claims.

Claims

1. A pure ammonia combustion circulating fluidized bed boiler system, comprising an ammonia storage tank (1), an ammonia evaporator (2), a fluidized bed boiler furnace (3) and a separator, wherein the ammonia storage tank (1) is connected to the ammonia evaporator (2), an air distribution device (8) is provided in the fluidized bed boiler furnace (3), the ammonia evaporator (2) is connected to the air distribution device (8) to feed ammonia gas into the fluidized bed boiler furnace (3), the separator is used to separate flue gas from particles, the flue gas inlet of the separator is connected to the flue gas outlet of the fluidized bed boiler furnace (3), the bottom of the separator is connected to the fluidized bed boiler furnace (3) and is provided with a return valve (5) to return the high-temperature material separated by the separator to the furnace, characterized in that: The invention also includes an external heat exchange cracking device (7), wherein the separator is connected to the high-temperature material inlet (12) of the external heat exchange cracking device (7) through a diversion branch, and the diversion branch is provided with a diversion valve (6); a heat exchange pipe (10) is provided inside the external heat exchange cracking device (7), one end of the heat exchange pipe (10) is used to introduce ammonia gas, and the other end is connected to the ammonia cracking gas inlet (9) of the fluidized bed boiler furnace (3), so as to feed the mixed gas formed after cracking into the fluidized bed boiler furnace (3); an air inlet (11) is provided at the bottom of the external heat exchange cracking device (7), and a high-temperature material outlet (13) is provided on one side of the external heat exchange cracking device (7), so that the high-temperature material after heat exchange is returned to the fluidized bed boiler furnace (3) under the fluidization effect of air.

2. The pure ammonia combustion circulating fluidized bed boiler system according to claim 1, characterized in that: The heat exchange tube (10) is arranged in the interior of the external heat exchange cracking device (10) in a transverse direction, the high-temperature material inlet (12) is located at the top of the external heat exchange cracking device (7) and is arranged toward the ammonia inlet end of the heat exchange tube (10), and the high-temperature material outlet (13) is arranged at the other end of the external heat exchange cracking device (7) and is located above the mixed gas output end of the heat exchange tube (10).

3. The pure ammonia combustion circulating fluidized bed boiler system according to claim 2, characterized in that: There are multiple heat exchange tubes (10), and the multiple heat exchange tubes (10) are distributed in parallel inside the external heat exchange cracking device (7).

4. The pure ammonia combustion circulating fluidized bed boiler system according to claim 3, characterized in that: The ammonia cracking gas inlet (9) is provided on the air distribution device (8) or on the upper side of the air distribution device (8).

5. The pure ammonia combustion circulating fluidized bed boiler system according to claim 1, characterized in that: Granular material is added into the fluidized bed boiler furnace (3), and the granular material d 50 =1-1.5 mm.

6. The pure ammonia combustion circulating fluidized bed boiler system according to claim 5, characterized in that: The particulate material includes fly ash particles.

7. The pure ammonia combustion circulating fluidized bed boiler system according to claim 1, characterized in that: An ammonia decomposition catalyst is sprayed or arranged inside the heat exchange tube (10).

8. The pure ammonia combustion circulating fluidized bed boiler system according to claim 7, characterized in that: The ammonia decomposition catalyst includes a nickel-based catalyst.

9. The pure ammonia combustion circulating fluidized bed boiler system according to claim 1, characterized in that: The air distribution device (8) is a hollow structure, with an ammonia flow channel inside and an air channel outside.

10. The pure ammonia combustion circulating fluidized bed boiler system according to any one of claims 1 to 9, characterized in that: The amount of ammonia entering the external heat exchange cracking device (7) accounts for 5-10% of the total fuel amount, and the temperature in the heat exchange tube is maintained at 500-700°C during operation.

Images