CN219414771U - Plasma-assisted coal-fired boiler ammonia-doped combustion and NOx ultra-low emission system - Google Patents

Abstract

The utility model discloses an ammonia-doped combustion and NOx ultra-low emission system for a plasma-assisted coal-fired boiler, comprising a boiler, an ammonia-coal mixed burner, a pulverized coal burner, an ammonia-hydrogen reburning injector, an exhaust air nozzle, an ammonia gas supply device and a plasma-thermal synergistic cracker; the outlet of the ammonia gas supply device is divided into two paths, one path is connected to the plasma-thermal synergy cracker and ammonia-hydrogen reburning injector, and the other path is connected to the ammonia-coal mixed burner; The wall is provided with ammonia-coal mixed burner, coal powder burner, ammonia-hydrogen reburning injector and burn-out air nozzle in sequence from bottom to top; ammonia-coal mixed burner and coal powder burner are arranged in the main combustion zone; ammonia-hydrogen reburning injector is set in the reburning zone; burn-out air nozzle is set in the burn-out zone. The utility model realizes that the NOx at the outlet of the furnace of the coal-fired boiler meets the ultra-low discharge requirement, the ammonia escape at the tail does not exceed the standard, and reduces the transformation cost and operation cost of the ammonia-doped combustion of the coal-fired boiler.

Description

Plasma-assisted coal-fired boiler ammonia-doped combustion and NOx ultra-low emission system

technical field

The utility model belongs to the technical field of fuel combustion, in particular to an ammonia-doped combustion and NOx ultra-low emission system for a plasma-assisted coal-fired boiler.

Background technique

With the national goal of "carbon peak carbon neutrality" put forward, the carbon reduction of coal-fired boilers in the power industry, especially the thermal power industry, has become the top priority to achieve the dual carbon goals. Among the many carbon reduction programs, the use of renewable energy to produce new zero-carbon fuels to replace or partially replace coal power generation has become a feasible technical route. As a new type of zero-carbon fuel, ammonia has the characteristics of high hydrogen content, high volume energy density and high safety. More importantly, ammonia is easier to liquefy than hydrogen for transportation and storage, so ammonia is considered to be a more potential clean fuel. Using ammonia as a substitute for fossil fuels such as coal can effectively reduce CO2 emissions in the thermal power generation industry. At the same time, ammonia combustion has some technical problems. On the one hand, ammonia combustion characteristics are poor, ignition and stable combustion are difficult, and combustion efficiency and burnout rate are low. It needs to be co-combusted with high-calorific fuel or other auxiliary combustion technologies to achieve stable and efficient self-sustained combustion and burnout of ammonia. On the other hand, ammonia itself contains a large amount of nitrogen (82.4% by mass), and it is easy to produce a large amount of NOx and other greenhouse gases during combustion. The greenhouse effect of NOx is far stronger than CO2. The advantages of fossil fuels in reducing carbon emissions.

Aiming at the problem of poor combustion characteristics of ammonia, there are currently related patents (application numbers "202110585729.X", "202210461572.4", "202210113343.3") that use technologies such as ammonia-coal mixed combustion to improve the combustion stability of ammonia. Patent "202110585729.X" utilizes pulverized coal pyrolysis furnace to generate coal gasification gas and ammonia for mixed combustion to enhance combustion intensity and stability; patent "202210461572.4" uses 25% to 35% oxygen-enriched air as a combustion aid to achieve efficient ammonia combustion, and performs staged combustion of ammonia and coal powder in the furnace, and uses CO, H2 and other combustible gases generated by the rich combustion of pure pulverized coal in the main combustion area to enhance the pulverized coal burner Combustion characteristics of the ammonia gas above; the patent "202210113343.3" uses a normally open plasma igniter in the burner to ignite the ammonia gas in the central channel first, and then ignites the concentrated coal powder, which is amplified and burned by the ammonia-coal mixed fuel step by step and then sprayed into the furnace. The above technologies have problems such as complex boiler equipment and systems, need to use other flammable fuels for cold start, high cost of combustion aids, and normally open plasma igniter electrodes are easily corroded by ammonia and have a short service life. Our previously authorized patents (grant numbers "CN 112483243 B" and "CN 113074046 B") use plasma online cracking to crack ammonia gas into ammonia-hydrogen mixed gas and use plasma combustion technology to achieve stable ammonia combustion. These two patents are mainly aimed at the fields of ammonia internal combustion engines and turbojet/turbofan aero engines.

Aiming at the problem of high NOx emissions from ammonia combustion, the current relevant patents (application numbers "202110354073.0", "202111366833.6", "202210327223.3" and "202210178269.3") are aimed at boiler ammonia-doped combustion systems, all using separate SNCR and SCR denitrification technologies or a combination of the two, using ammonia decomposition gasification or directly using ammonia as reduction The agent realizes the emission of NOx in the boiler tail gas up to the standard. The denitrification efficiency of SNCR technology is low, generally only about 50%, ammonia escape is difficult to control, and the denitrification efficiency of SCR technology can generally reach more than 90%. The disadvantage is that V ₂ O ₅ , WO ₃ , TiO ₂ and other catalysts need to be installed and the catalysts need to be replaced regularly, and the equipment investment and operation and maintenance costs are high. In addition, for pulverized coal combustion boilers, advanced reburning technology can also be used to reduce NOx concentration. Fuels such as natural gas, ultra-fine coal powder or biomass, and nitrogen-based reducing agents such as ammonia and urea are introduced into different positions in the reburning zone of the boiler to achieve fuel reburning while reducing NOx in flue gas. This technology has disadvantages such as various types of fuel, poor combination of reburning fuel and reducing agent, and limited NOx reduction effect.

In view of the problems in the above patents, it is necessary to develop new technologies to solve the problems of stable and efficient combustion of ammonia mixed with coal-fired boilers and how to achieve ultra-low NOx emissions more economically and effectively.

Utility model content

The utility model provides a plasma-assisted coal-fired boiler ammonia-doped combustion and NOx ultra-low emission system. On the one hand, the system described in the utility model can realize the stable and efficient mixed combustion of ammonia in a large proportion of coal-fired boilers without relying on other fuels to realize cold ^start ; SCR operating costs.

In order to achieve the above object, the utility model adopts the following technical solutions:

The system described in the utility model adopts plasma-assisted combustion, online cracking technology and ammonia-hydrogen integrated reburning and denitrification technology to realize stable and efficient ammonia combustion and ultra-low emission of NOx at the furnace outlet.

A plasma-assisted coal-fired boiler ammonia-doped combustion and NOx ultra-low emission system, including a boiler, an ammonia-coal mixed burner, a pulverized coal burner, an ammonia-hydrogen reburning injector, an exhaust air nozzle, an ammonia gas supply device, a plasma torch, a plasma-thermal synergistic cracker and a continuous online flue gas monitoring device;

The outlet pipeline of the ammonia gas supply device is divided into two paths, one path is connected to the plasma-thermal synergistic cracker and the ammonia-hydrogen reburning injector in turn, and the other path is connected to the ammonia-coal mixed burner; the plasma torch is set inside the ammonia-coal mixed burner;

The top of the boiler is connected to the tail flue, and a continuous online monitoring device for flue gas is installed in the tail flue; the furnace of the boiler is divided into the main combustion area, the reburning area and the burnout area from bottom to top;

The side wall or angle of the boiler's furnace is set up from the bottom to the top from top to top with ammonia and meal hybrid burner interfaces, coalmer burner interfaces, ammonia -hydrogen reinforcement spray interfaces, and full air spray ports; ammonia mixed burners are set on the furnace side wall or corner of the furnace of the boiler through the ammonia and meal mixed burner connector. Set on the side wall or corner of the furnace of the boiler; the ammonia hydrogen reinforcement sprayer is set on the side wall or corner of the furnace of the furnace of the boiler through the ammonia recycled spray interface;

The connection port of the ammonia-coal mixed burner and the pulverized coal burner are both arranged in the main combustion area; the connection port of the ammonia-hydrogen reburning injector is arranged in the reburning area; the burnout air nozzle is set in the burnout area.

The boiler furnace is arranged as follows:

(1) Ammonia-coal mixed burners are arranged on the lower two floors of the main combustion area, and several layers of pulverized coal burners are arranged above. Arrangement of the ammonia-coal mixed burner in the lower two floors is beneficial to increase the residence time of ammonia gas in the main combustion zone, improve the burnout rate, and improve the stable combustion effect of the boiler at low load;

(2) A layer of ammonia-hydrogen reburn injectors is arranged in the reburn area, and the main pipe is connected to the outlet of the plasma-thermal synergistic cracker after the ammonia-hydrogen reburn injectors of this layer are connected in parallel, and the ammonia-hydrogen reburn injectors use hot primary air to support combustion;

(3) Several layers of burn-off air nozzles are arranged in the burn-out area, and the burn-out air uses hot secondary air.

Ammonia gas is fed into the furnace for combustion in two ways, one way enters the main combustion area through the ammonia-coal mixed burner and co-combusts with coal, and the other way is cracked by the plasma-thermal synergistic cracker into ammonia-hydrogen mixed gas, and then enters the furnace reburning area through the ammonia-hydrogen reburning injector for reburning and reducing NOx.

The boiler adopts ammonia-hydrogen integrated reburning denitrification technology, the excess air coefficient of the main combustion zone is <1, the excess air coefficient of the reburning zone is <1, and the excess air coefficient of the burnout zone is >1.

(1) Ammonia-coal co-combustion is carried out in the main combustion zone. In order to reduce the concentration of NOx generated in the main combustion zone, the ammonia-coal mixed burner (7) and the pulverized coal burner (8) both adopt thick-lean separation low-nitrogen burners. The excess air coefficient in the main combustion zone is 0.9-1.0, and the residence time is 0.5s-1s;

(2) In the reburning zone, the mixed combustion of ammonia-hydrogen mixture and CO, H ₂ , CH _i , NH _i and other combustible gases generated by the rich combustion in the main combustion zone reduces the NOx generated in the main combustion zone, and at the same time suppresses the formation of new NOx. The excess air coefficient in the reburning zone is 0.9-0.95, the residence time is 0.4s-0.6s, and the temperature is 1100-1300°C to control the formation of thermal NOx;

(3) The excess air coefficient in the burnout zone is 1.15 to 1.25 to ensure the burnout of pulverized coal and ammonia, and the residence time is 0.4s to 0.8s.

The ammonia-hydrogen reburning injector injects ammonia-hydrogen mixed gas into the reburning zone of the furnace to realize efficient combustion while reducing NOx generated in the main combustion zone and suppressing new NOx generation. In order to ensure the sufficient mixing of the ammonia-hydrogen mixed gas and the flue gas to improve the reburning and reduction effects, the speed of the mixed gas injected into the furnace is 80m/s-100m/s.

The plasma-thermal synergistic cracker simultaneously uses plasma cracking and thermal cracking technologies to crack ammonia gas online to produce ammonia-hydrogen mixed gas, which can reduce energy consumption and improve cracking efficiency. The cracker adopts a coaxial sleeve structure. The inner cylinder is arranged with a plasma cracking device and a catalyst as the first ammonia gas channel, and the outer cylinder is fed with high-temperature flue gas as a heat source for heating the catalyst to heat the catalyst to 400°C to 500°C.

The plasma-thermal synergistic cracker controls the ammonia cracking rate by adjusting the plasma discharge power and the high-temperature flue gas flow rate to realize the adjustment of the hydrogen ratio in the ammonia-hydrogen mixed gas at the cracker outlet, and the hydrogen ratio is continuously adjustable from 1% to 20%.

A plasma torch is arranged on the combustion air (hot primary air) channel inside the ammonia-coal mixed burner, which is used to ionize the combustion air to generate strong oxidizing components such as high-concentration O and OH radicals. When the boiler is started, the ammonia gas is first ignited and then the coal powder is ignited. The plasma torch is loaded on the combustion air side, which can avoid the rapid corrosion of the plasma torch electrode by ammonia gas and improve the service life of the equipment.

The ratio (heat ratio) of boiler mixed with ammonia gas is continuously adjustable from 0% to 30%. Among them, the proportion of ammonia gas entering the main combustion zone of the furnace through the ammonia-coal mixed burner is 90% to 95%, and the proportion of ammonia gas entering the reburning zone of the furnace through the ammonia-hydrogen reburning injector after online cracking by the plasma-thermal synergistic cracker is 5% to 10%. The inlet of the plasma-thermal synergistic cracker and the inlet of each ammonia-coal mixed burner are equipped with a flow regulating device and connected with the DCS control center.

The denitrification efficiency of the ammonia-hydrogen integrated reburning technology has been proved by tests to reach more than 80%. The main combustion zone uses a rich-lean separation low-nitrogen burner for rich combustion, which can control the NOx concentration generated in the main combustion zone to be lower than 250mg/Nm ³ (dry basis, 6% O2). The combination of the two can achieve ultra-low NOx emissions at the furnace outlet, replacing the existing SNCR and SCR technologies.

The flue gas continuous on-line monitoring device is set at the outlet of the boiler economizer, including a NOx concentration sensor and an NH3 concentration sensor for measuring the NOx and ammonia escape concentration in the flue gas at the economizer outlet, and is connected to the DCS control center.

The high-temperature flue gas is drawn from the tail flue through the furnace smoke fan and sent to the plasma-thermal synergistic cracker to heat the catalyst and then flows back to the tail flue. The outlet pipe is equipped with a flow regulating device and connected to the DCS control center.

The ammonia gas supply device includes a liquid ammonia storage tank, a liquid ammonia pump, and a two-stage heat exchange evaporator. After the liquid ammonia comes out of the storage tank, it enters the two-stage heat exchange evaporator through the liquid ammonia pump. The heating heat sources are respectively power plant circulating water and low-pressure steam. The ammonia gas outlet of the second stage heat exchange evaporator is respectively connected to the ammonia main pipe in front of the ammonia-coal mixed burner and the inlet of the plasma-thermal synergistic cracker. The temperature of the ammonia gas at the outlet is 45°C-65°C.

The operation adjustment of the system described in the utility model comprises the following processes:

(1) When the coal-fired boiler is started, the ammonia gas supply device first passes the ammonia gas into the ammonia-coal mixed burner, and uses the plasma torch to activate the combustion-supporting air to ignite the ammonia gas and burn it stably;

(2) feed the pulverized coal into the ammonia-coal mixed burner, use the ammonia flame to ignite the pulverized coal, and gradually increase the input of ammonia and pulverized coal to heat up the furnace;

(3) After the furnace temperature rises, it is gradually put into the upper pulverized coal burner for combustion and the plasma torch in the ammonia-coal mixed burner is deactivated, so as to realize the high-efficiency self-sustained combustion of a large proportion of ammonia-coal mixed;

(4) Start the plasma-thermal synergistic cracker and the ammonia-hydrogen reburning injector to carry out the online cracking of ammonia and the reburning and denitrification of the ammonia-hydrogen mixture;

(5) The DCS control center receives the real-time feedback of NOx concentration and _NH3 concentration in the flue gas at the outlet of the economizer from the flue gas continuous online monitoring device, and timely adjusts the plasma discharge power of the plasma-thermal synergistic cracker and the high-temperature flue gas flow rate to adjust the ratio of ammonia-hydrogen mixture at the cracker outlet. After dynamic adjustment, the NOx concentration in the flue gas meets the ultra-low emission requirements, and the ammonia escape at the tail does not exceed the standard;

(6) When the NOx concentration or ammonia escape is too high and exceeds the limit range of the hydrogen ratio in the ammonia-hydrogen mixture controlled by the plasma-thermal synergistic cracker, adjust the ammonia flow rate at the inlet of the plasma-thermal synergistic cracker to achieve the tail gas discharge.

The utility model has the following beneficial effects:

A small proportion of ammonia gas is cracked online to produce ammonia-hydrogen mixed gas through plasma-thermal synergistic cracking technology, and ammonia-hydrogen integrated reburning denitrification is carried out by using ammonia-hydrogen reburning injector. Experiments have proved that the integrated reburning of mixed gas under reducing atmosphere is more rapid and uniform in the mixing of reburning fuel, reducing agent and NOx in flue gas. Ammonia-hydrogen integrated reburning technology, combined with thick-lean separation and low-nitrogen combustion technology can realize the NOx at the furnace outlet to meet the ultra-low emission requirements, the ammonia escape concentration will not exceed the standard, and save the operating costs of SNCR and SCR systems. In addition, the ammonia cracking by plasma-thermal cooperative cracking technology can reduce the plasma discharge power and catalyst reaction temperature, increase the cracking reaction rate, and save energy and have significant economic benefits.

Ammonia-coal mixed burners are arranged on the lower two floors of the main combustion area of the boiler, and several layers of pulverized coal burners are arranged on the top, which can realize continuous adjustment of the ammonia-doped combustion ratio from 0% to 30%, and is also beneficial to increase the residence time of ammonia gas in the main combustion area, improve the burnout rate of ammonia gas, and improve the stable combustion effect of the ammonia-coal mixed burner when the boiler is under low load. On the other hand, by adding a plasma torch to the combustion-supporting air channel inside the ammonia-coal mixed burner, the reliable ignition of ammonia gas and ignition of coal powder is realized, the problem of cold start of the boiler independent of other fuels is solved, and the strong corrosion effect of ammonia gas directly activated by the plasma torch is avoided, and the service life of the plasma torch is improved.

Description of drawings

Fig. 1 is a schematic diagram of a plasma-assisted coal-fired boiler ammonia-doped combustion and NOx ultra-low emission system of the present invention;

Fig. 2 is the structural representation of plasma-thermal synergistic cracker;

Fig. 3 is a schematic cross-sectional view of the ammonia-coal mixed burner and the plasma torch.

In Figure 1, 1 is a liquid ammonia storage tank, 2 is a liquid ammonia pump, 3 is two-stage thermal evaporator, 4 is a plasma-thermal collaborator, 5 is furnace smoke, 6 is ammonia hydrogen reinforcement sprayer, 7 is ammonia and coal mixed burners, 8 is coal burner, 9 is full air spray port, 10 is the main combustion area, and 12 is re-burning zone. , 14 is a plasma torch, 15 is a continuous online monitoring device for flue gas, and 16 is a coal -provincial machine.

In Fig. 2, 4-1 is a high-temperature flue gas channel, 4-2 is a first ammonia gas channel, 4-3 is a catalyst, and 4-4 is a plasma discharge device;

In Fig. 3, 7-1 is the combustion-supporting air channel, 7-2 is the second ammonia gas channel, 7-3 is the thick air powder channel, and 7-4 is the light air powder channel.

Detailed ways

Embodiments of the utility model will be described in detail below with reference to the accompanying drawings. The embodiments described in the accompanying drawings are only exemplary, and are only used to explain the utility model, but cannot be construed as limiting the utility model.

The utility model proposes a plasma-assisted coal-fired boiler ammonia-doped combustion and NOx ultra-low emission system, as shown in Figure 1, the system uses plasma-assisted combustion, online cracking technology and ammonia-hydrogen integrated reburning and denitrification technology to achieve stable and efficient ammonia combustion and ultra-low emission of NOx at the furnace outlet. Continuous online monitoring device 15.

The liquid ammonia storage tank 1 is sequentially connected to the liquid ammonia pump 2 and the inlet of the two-stage heat exchange evaporator 3 . The outlet pipeline of the two-stage heat exchange evaporator 3 is divided into two paths, one path is connected to the plasma-thermal synergistic cracker 4 and the ammonia-hydrogen reburning injector 6 in sequence, and the other path is connected to the ammonia-coal mixed burner 7 .

The side wall or corner of the furnace of the boiler 10 is sequentially provided with an ammonia-coal mixed burner 7 , a pulverized coal burner 8 , an ammonia-hydrogen reburning injector 6 and an overfired air nozzle 9 from bottom to top. The top of the boiler is connected to the tail flue, and an economizer 16 and a flue gas continuous on-line monitoring device 15 are arranged in sequence in the tail flue. The interior of the furnace of the boiler 10 is sequentially divided into a main combustion zone 11 , a reburning zone 12 and a burnout zone 13 from bottom to top. In the furnace height direction of the boiler 10, the furnace side wall or corner of the boiler 10 is sequentially provided with an ammonia-coal mixed burner 7 connection port, a pulverized coal burner 8 connection port, an ammonia-hydrogen reburning injector 6 connection port and an overfired air nozzle 9. The ammonia-coal mixed burner 7 is arranged on the furnace side wall or corner of the boiler 10 through the connecting port of the ammonia-coal mixed burner. The pulverized coal burner 8 is arranged on the furnace side wall or corner of the boiler 10 through the pulverized coal burner connection port. The ammonia-hydrogen reburn injector 6 is arranged on the furnace side wall or corner of the boiler 10 through the ammonia-hydrogen reburn injector connection port.

The connecting ports of the ammonia-coal mixed burner and the pulverized coal burner are both arranged in the main combustion zone 11 . The connection port of the ammonia-hydrogen reburning injector is set in the reburning zone 12 . The overburning air nozzle 9 is arranged in the overburning area 13 . The plasma torch 14 is arranged inside the ammonia-coal mixed burner 7 .

As shown in Figure 1, the furnace of the boiler 10 is arranged as follows:

(1) Ammonia-coal mixed burners 7 are arranged on the lower two floors of the main combustion area 11, and several layers of pulverized coal burners 8 are arranged above. Arranging the ammonia-coal mixed burner 7 on the lower two floors is beneficial to increase the residence time of ammonia gas in the main combustion zone 11, improve the burnout rate, and improve the stable combustion effect of the boiler at low load;

(2) A layer of ammonia-hydrogen reburn injectors 6 is arranged in the reburn area 12. After the ammonia-hydrogen reburn injectors 6 are connected in parallel, the main pipe is connected to the outlet of the plasma-thermal synergistic cracker 4, and the ammonia-hydrogen reburn injectors 6 use hot primary air to support combustion;

(3) Several layers of overburning air nozzles 9 are arranged in the overburning area 13, and the overburning air uses hot secondary air.

Ammonia gas is fed into the furnace for combustion in two ways, one way is passed through the ammonia-coal mixed burner 7 and enters the main combustion zone 11 for co-combustion with coal, and the other way is cracked by the plasma-thermal synergistic cracker 4 into ammonia-hydrogen mixed gas, and then enters the furnace reburning zone 12 through the ammonia-hydrogen reburning injector 6 for reburning and reducing NOx.

The boiler adopts ammonia-hydrogen integrated reburning denitrification technology, the excess air coefficient of the main combustion zone 11 is <1, the excess air coefficient of the reburning zone 12 is <1, and the excess air coefficient of the burnout zone 13 is >1.

(1) Ammonia-coal co-combustion is carried out in the main combustion zone 11. In order to reduce the NOx concentration generated in the main combustion zone 11, the ammonia-coal mixed burner 7 and the pulverized coal burner 8 both adopt thick-lean separation low-nitrogen burners. The excess air coefficient in the main combustion zone is 0.9-1.0, and the residence time is 0.5s-1s;

(2) The reburning zone 12 uses ammonia-hydrogen mixed gas and CO, H ₂ , CH _i , NH _i and other combustible gases generated by the rich combustion of the main combustion zone 11 to reduce NOx generated in the main combustion zone 11, while suppressing the formation of new NOx. The excess air coefficient in the reburning zone 12 is 0.9-0.95, the residence time is 0.4s-0.6s, and the temperature is 1100°C-1300°C to control the generation of thermal NOx;

(3) The excess air ratio in the burnout zone 13 is 1.15 to 1.25 to ensure the burnout of pulverized coal and ammonia, and the residence time is 0.4s to 0.8s.

The ammonia-hydrogen reburning injector 6 injects ammonia-hydrogen mixed gas into the furnace reburning zone 12 to achieve high-efficiency combustion while reducing NOx generated in the main combustion zone and suppressing new NOx formation. In order to ensure the sufficient mixing of the ammonia-hydrogen mixed gas and the flue gas to improve the reburning and reduction effects, the speed of the mixed gas injected into the furnace is 80m/s-100m/s.

The plasma-thermal cooperative cracker 4 simultaneously uses plasma cracking and thermal cracking technologies to crack ammonia gas online to produce ammonia-hydrogen mixed gas, which can reduce energy consumption and improve cracking efficiency. As shown in FIG. 2, the cracker 4 adopts a coaxial sleeve structure, including an inner cylinder and an outer cylinder. A plasma discharge device 4-4 and a catalyst 4-3 are arranged inside the inner cylinder. The inner cylinder is used as the first ammonia gas channel 4-2. The space between the outer cylinder and the inner cylinder is a high-temperature flue gas channel 4-1. High-temperature flue gas is introduced into the high-temperature flue gas channel 4-1 as a heating source for the catalyst, and the catalyst is heated to 400°C-500°C. For example, the plasma discharge device 4-4 is arranged on the inner wall of the inner cylinder, and the first ammonia gas channel 4-2 and the catalyst 4-3 are located inside the plasma discharge device 4-4.

The plasma-thermal synergistic cracker 4 controls the ammonia cracking rate by adjusting the discharge power (100kW-500kW) of the plasma discharge device 4-4 and the high-temperature flue gas flow rate to realize the adjustment of the hydrogen ratio in the ammonia-hydrogen mixed gas at the cracker outlet, and the hydrogen ratio is continuously adjustable from 1% to 20%.

As shown in Figure 3, a plasma torch 14 is arranged on the combustion air (hot primary air) channel 7-1 inside the ammonia-coal mixed burner 7, which is used to ionize the combustion air to generate strong oxidizing components such as high concentrations of O and OH radicals. The plasma torch 14 is loaded on the side of the combustion-supporting air, which can avoid the rapid corrosion of the plasma torch electrode by ammonia gas and improve the service life of the equipment. Inside the ammonia-coal mixed burner 7 are arranged a plasma torch 14, a combustion-supporting air channel 7-1, a second ammonia channel 7-2, a concentrated air powder channel 7-3 and a light air powder channel 7-4; the combustion-supporting air channel 7-1 is located in the inner center of the ammonia-coal mixed burner 7, the plasma torch 14 is arranged on the combustion-supporting air channel 7-1, and a circle of evenly distributed second ammonia channels 7-2 is arranged on the outside of the combustion-supporting air channel 7-1. Wind powder passage 7-3 and light wind powder passage 7-4.

The ratio (heat ratio) of boiler mixed with ammonia gas is continuously adjustable from 0% to 30%. Among them, the proportion of ammonia gas entering the main combustion zone of the furnace through the ammonia-coal mixed burner 7 is 90% to 95%, and the proportion of ammonia gas entering the reburning zone of the furnace through the ammonia-hydrogen reburning injector 6 after online cracking through the plasma-thermal synergistic cracker 4 is 5% to 10%. The inlet of the plasma-thermal synergistic cracker 4 and the inlet of each ammonia-coal mixed burner 7 are provided with a flow regulating device, and the flow regulating device is connected with the DCS control center.

The denitrification efficiency of the ammonia-hydrogen integrated reburning technology can reach more than 80%. The main combustion zone 11 uses a rich-lean separation low-nitrogen burner for rich combustion, which can control the NOx concentration generated in the main combustion zone 11 to be lower than 250mg/Nm ³ (dry basis, 6% O2).

The flue gas continuous online monitoring device 15 is set at the outlet of the boiler economizer 16, including a NOx concentration sensor and an NH ₃ concentration sensor for measuring NOx and ammonia escape concentrations in the flue gas at the economizer outlet, and is connected to the DCS control center.

The temperature of the high-temperature flue gas is 700°C to 800°C, and it is led out from the tail flue through the outlet pipe (the specific outlet position is determined according to the layout of the heating surface of different types of boilers) and sent to the plasma-thermal synergistic cracker 4 through the furnace smoke fan 5. After heating the catalyst, it flows back to the tail flue. The outlet pipe is equipped with a flow regulating device, and the flow regulating device is connected to the DCS control center.

The ammonia supply device includes a liquid ammonia storage tank 1, a liquid ammonia pump 2, and a two-stage heat exchange evaporator 3. The two-stage heat exchange evaporator 3 includes a first-stage heat-exchange evaporator and a second-stage heat-exchange evaporator. After the liquid ammonia comes out of the liquid ammonia storage tank 1, it enters the first-stage heat exchange evaporator through the liquid ammonia pump 2, and the first-stage heat exchange evaporator and the second-stage heat exchange evaporator are connected in series. The heating heat sources of the first-stage heat exchange evaporator and the second-stage heat exchange evaporator respectively adopt power plant circulating water and low-pressure steam. The ammonia gas outlet of the second-stage heat exchange evaporator is respectively connected to the ammonia gas main pipe in front of the ammonia-coal mixed burner 7 and the inlet of the plasma-thermal synergistic cracker 4. The temperature of the ammonia gas at the outlet is 45°C to 65°C.

The operation adjustment method of the system described in the utility model includes the following processes:

(1) When the coal-fired boiler is started, the ammonia gas supply device first passes the ammonia gas into the ammonia-coal mixed burner 7, and uses the plasma torch 14 to activate the combustion-supporting air to ignite the ammonia gas and stably burn it;

(2) pulverized coal is passed into ammonia-coal mixed burner 7, utilizes ammonia flame to ignite pulverized coal, gradually increases ammonia and pulverized coal intake to heat up the furnace;

(3) Gradually drop into the pulverized coal burner 8 above after the furnace temperature rises to burn and deactivate the plasma torch 14 in the ammonia-coal mixed burner 7 to realize the high-efficiency self-sustained combustion of a large proportion of ammonia-coal mixed;

(4) start the plasma-thermal synergistic cracker 4 and the ammonia-hydrogen reburning injector 6, carry out the on-line cracking of ammonia and the reburning denitrification of ammonia-hydrogen mixed gas;

(5) The DCS control center receives the NOx concentration and _NH3 concentration in the flue gas at the outlet of the economizer 16 fed back in real time by the flue gas continuous on-line monitoring device 15, adjusts the plasma discharge power of the plasma-thermal synergistic cracker 4 and the high-temperature flue gas flow rate in time to adjust the ratio of ammonia-hydrogen mixture at the cracker outlet, and realizes the NOx concentration in the flue gas after dynamic adjustment to meet the ultra-low emission requirements (NOx≤50mg/Nm ^dry basis, 6% O2), and the ammonia escape at the tail does not exceed the standard;

(6) When the NOx concentration or ammonia escape is too high and exceeds the limit range of the ratio of hydrogen in the ammonia-hydrogen mixture controlled by the plasma-thermal synergistic cracker 4, adjust the ammonia flow rate at the inlet of the plasma-thermal synergistic cracker 4 to achieve the discharge of tail gas up to the standard.

The above descriptions are only preferred embodiments of the utility model, and are not intended to limit the utility model. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the utility model shall be included within the protection scope of the utility model.

Claims (9)

1. A plasma-assisted coal-fired boiler ammonia-doped combustion and NOx ultra-low emission system, characterized in that it comprises a boiler (10), an ammonia-coal mixed burner (7), a pulverized coal burner (8), an ammonia-hydrogen reburning injector (6), an overburning air nozzle (9), an ammonia gas supply device, a plasma torch (14), a plasma-thermal synergistic cracker (4) and a continuous online flue gas monitoring device (15); The outlet pipeline of the ammonia gas supply device is divided into two paths, one path is connected to the plasma-thermal synergistic cracker (4) and the ammonia-hydrogen reburning injector (6) in sequence, and the other path is connected to the ammonia-coal mixed burner (7); the plasma torch (14) is arranged inside the ammonia-coal mixed burner (7); The top of the boiler (10) is connected to a tail flue, and a flue gas continuous online monitoring device (15) is arranged in the tail flue; the interior of the furnace of the boiler (10) is sequentially divided into a main combustion zone (11), a reburning zone (12) and a burnout zone (13) from bottom to top; The side wall or corner of the furnace of the boiler (10) is sequentially provided with an ammonia-coal mixed burner connection port, a pulverized coal burner connection port, an ammonia-hydrogen reburning injector connection port and a burn-off air nozzle (9); the ammonia-coal mixed burner (7) is arranged on the furnace side wall or corner of the boiler (10) through the ammonia-coal mixed burner connection port; the pulverized coal burner (8) is arranged on the furnace side wall or corner of the boiler (10) through the pulverized coal burner connection port; (6) The ammonia-hydrogen reburning injector connection port is arranged on the furnace side wall or corner of the boiler (10); Both the ammonia-coal mixed burner connection port and the pulverized coal burner connection port are arranged in the main combustion area (11); the ammonia-hydrogen reburning injector connection port is arranged in the reburning area (12); and the burn-out air nozzle (9) is set in the burn-out area (13). 2. The system according to claim 1, wherein the ammonia gas supply device comprises a liquid ammonia storage tank (1), a liquid ammonia pump (2) and a two-stage heat exchange evaporator (3); the two-stage heat exchange evaporator (3) includes a first-stage heat exchange evaporator and a second-stage heat exchange evaporator; the liquid ammonia storage tank (1) is sequentially connected to the liquid ammonia pump (2) first-stage heat-exchange evaporator and the inlet of the second-stage heat-exchange evaporator; Device (4) and ammonia-hydrogen reburning injector (6), the other way is connected with ammonia-coal mixed burner (7). 3. system according to claim 1, it is characterized in that, described plasma-thermal synergistic cracker (4) comprises inner cylinder and outer cylinder, and outer cylinder is coaxially sleeved outside inner cylinder, and inner cylinder is arranged with plasma discharge device (4-4) and catalyst (4-3), and inner cylinder is provided with first ammonia channel (4-2), and the space between outer cylinder and inner cylinder is high-temperature flue gas passage (4-1). 4. The system according to claim 1, characterized in that, the ammonia-coal mixed burner (7) is internally arranged with a plasma torch (14), a combustion-supporting air channel (7-1), a second ammonia gas channel (7-2), a thick air powder channel (7-3) and a light air powder channel (7-4); ) is arranged in a circle of evenly distributed second ammonia gas channels (7-2), the periphery of the second ammonia gas channel (7-2) is supported by a casing, and the thick air powder channel (7-3) and the light air powder channel (7-4) are arranged in sequence on the outside of the casing. 5. The system according to claim 1, characterized in that, the furnace of the boiler (10) is arranged as follows: (1) Ammonia-coal mixed burners (7) are arranged on the lower two floors of the main combustion zone (11), and several layers of pulverized coal burners (8) are arranged above; (2) One deck of ammonia-hydrogen reburn injectors (6) is arranged in the reburn area (12), and the main pipe after the parallel connection of this layer of ammonia-hydrogen reburn injectors (6) is connected with the outlet of the plasma-thermal synergistic cracker (4); (3) Several layers of burn-off air nozzles (9) are arranged in the burn-out area (13). 6. system according to claim 1, is characterized in that, boiler economizer (16) is positioned at tail flue, and described flue gas continuous on-line monitoring device (15) is arranged on boiler economizer (16) outlet, and described flue gas continuous on-line monitoring device (15) comprises NOx concentration sensor and NH _{Concentration} sensor. 7. The system according to claim 6, characterized in that the NOx concentration sensor and the _NH3 concentration sensor are both connected to the DCS control center. 8. The system according to claim 1, characterized in that the tail flue is connected to the furnace smoke blower (5), the plasma-thermal synergistic cracker (4) and the tail flue through an outlet pipe, and the outlet pipe is provided with a flow regulating device. 9. The system according to claim 8, wherein the flow regulating device is connected to a DCS control center.