Additive suitable for biomass boiler and SCR flue gas denitration process and equipment

Abstract

The invention belongs to the field of environmental protection, and relates to an additive suitable for a biomass boiler and an SCR flue gas denitration process and equipment, the additive suitable for the biomass boiler comprises a pretreating agent capable of converting alkali metal substances in the boiler into silicate substances, and the pretreating agent comprises magnesium salt, calcium salt, aluminum salt and silicon powder; the ratio of the magnesium salt to the calcium salt to the aluminum salt to the silicon powder is (1-5): (1-5): (1-5): (0.5-2); in addition, the additive suitable for the biomass boiler, provided by the invention, further comprises a tempering protective agent which can be fused and combined with alkali metal substances in flue gas; the conditioning protective agent comprises calcium salt and silicon powder, and the ratio of the calcium salt to the silicon powder is (1-5): (0.5-2). The invention provides the additive suitable for the biomass boiler, the SCR flue gas denitration process and the SCR flue gas denitration equipment, and the additive has the characteristics of high denitration efficiency, stable operation and reliable performance, and completely meets the national requirement of ultralow emission of boiler tail gas.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection and relates to an SCR denitrification process using additives, and more particularly to an additive and SCR flue gas denitrification process and equipment suitable for biomass boilers. Background Technology

[0002] In the fields of biomass boilers and biomass power generation, the flue gas contains a large amount of alkali metals, with K2O content reaching over 20% and Na2O content reaching over 1%. This has a very adverse effect on conventional medium- and high-temperature SCR catalysts.

[0003] Alkali metals mainly refer to soluble alkali metal salts with cations such as potassium and sodium. Studies have shown that these alkali metals, during biomass combustion, form a large amount of fine-grained soot with other common substances, which passes through the SCR denitrification system along with the flue gas. As they pass through the SCR catalyst, these salt particles may adsorb and deposit in the internal pores of the catalyst, hindering the diffusion of NO and NH3 into the deeper layers of the catalyst, thus causing catalyst poisoning and deactivation. Furthermore, related studies have shown that the presence of alkali metal ions reduces the number of Brønsted acid sites on the catalyst, generating inactive KVO3; it also reduces the stability of the Brønsted acid sites, decreasing the catalytic reduction capacity of vanadium and tungsten / molybdenum. The reduction in the number and stability of the Brønsted acid sites directly leads to a decrease in NH3 and surface oxygen adsorption, thereby significantly reducing the catalyst activity. For these reasons, the SCR denitrification process is currently largely unsuitable for biomass boilers and power generation. In order to complete the task of flue gas denitrification, relevant biomass boilers and biomass power generation enterprises have to adopt non-catalytic reduction (SNCR) process, or low-carbon combustion + SNCR process, or even integrated desulfurization, denitrification and dust removal process using ceramic fiber filter tubes. These processes all have the problems of high operating costs and failure to meet ultra-low emission standards. Summary of the Invention

[0004] In order to solve the above-mentioned technical problems in the background art, the present invention provides an additive and SCR flue gas denitrification process and equipment suitable for biomass boilers, which have high denitrification efficiency, stable operation and reliable performance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] An additive suitable for biomass boilers, characterized in that: the additive for biomass boilers includes a pretreatment agent capable of converting alkali metal substances in the boiler into silicate substances, the pretreatment agent including magnesium salts, calcium salts, aluminum salts and silicon powder; the ratio of magnesium salts, calcium salts, aluminum salts and silicon powder is 1-5:1-5:1-5:0.5-2.

[0007] The fineness of the above pretreatment agent is 200-600 mesh.

[0008] The above-mentioned additives suitable for biomass boilers also include conditioning and protective agents that can melt and bond with alkali metal substances in flue gas; the conditioning and protective agents include calcium salts and silicon powder, and the ratio of calcium salts to silicon powder is 1-5:0.5-2.

[0009] The fineness of the above-mentioned conditioning and protective agent is 200-600 mesh.

[0010] Preferably, the calcium salt and silicon powder are calcined at high temperature.

[0011] An SCR flue gas denitrification process, characterized in that the SCR flue gas denitrification process includes the following steps:

[0012] 1) Formulate the additives for biomass boilers as described above, including pretreatment agents and conditioning and protection agents.

[0013] 2) The pretreatment agent obtained in step 1) is injected into the combustion chamber of the biomass boiler or into the flue above the combustion air outlet of the biomass boiler. The purpose of the pretreatment agent is to convert most of the alkali metals in the boiler into silicate substances and fix them in the bottom ash of the furnace inside the biomass boiler, so as to prevent these alkali metals from entering the flue gas too much and affecting the downstream SCR denitrification catalytic device.

[0014] 3) The conditioning and protective agent obtained in step 1) is injected into the high-temperature flue gas at the top of the biomass boiler. The purpose of the conditioning and protective agent is to mix with the high-temperature flue gas flowing through the top of the biomass boiler and to eutecticly fuse with the alkali metal substances that were not completely treated in the previous stage to form a eutectic fusion.

[0015] The amount of pretreatment agent used in step 2) above, relative to the solid-to-gas ratio of the flue gas, is 1–10 g / Nm³. 3 The flow rate of the pretreatment agent is 8–12 m / s; preferably, in step 3), the amount of conditioning and protective agent used is 0.05–0.5 g / Nm³ relative to the solid-to-gas ratio of the flue gas. 3 The flow rate of the conditioning and protective agent is 8–12 m / s.

[0016] The aforementioned SCR flue gas denitrification process also includes:

[0017] 4) The flue gas is denitrified using a denitrification catalyst to reduce nitrogen oxides in the flue gas to nitrogen; the main component of the denitrification catalyst is V2O5-WuO-TiO2; the initial activity coefficient of the denitrification catalyst is not less than 50.

[0018] An SCR flue gas denitrification device based on the SCR flue gas denitrification process described above, characterized in that: the SCR flue gas denitrification device includes a biomass boiler, a pretreatment agent addition device, a conditioning and protective agent addition device, a tail-end descending flue, a nitrogen oxide reduction device, a flue gas ash removal device, a boiler induced draft fan, and a chimney; the biomass boiler and the tail-end descending flue run parallel to each other and are connected through a flue gas channel; the tail-end descending flue is connected to the chimney through the flue gas ash removal device and the boiler induced draft fan; the interior of the tail-end descending flue... The system is equipped with an SCR medium-temperature catalyst; the flue gas ash removal equipment is connected to the tail-end descending flue and flushes the SCR medium-temperature catalyst; the pretreatment agent addition device injects pretreatment agent from outside the biomass boiler into the combustion chamber of the biomass boiler or into the flue above the combustion air inlet of the biomass boiler; the conditioning and protective agent addition device injects conditioning and protective agent from outside the biomass boiler into the top of the biomass boiler or into the flue gas passage; the nitrogen oxide reduction device injects ammonia from outside the tail-end descending flue into the tail-end descending flue.

[0019] Preferably, the pretreatment agent addition device includes a pretreatment agent fluidizing blower, a pretreatment agent fluidizing device, a pretreatment agent silo, a first rotary feeding device, a first conveying pipe, a first nozzle, a first spherical multi-point distributing device, and a first branch pipe; the pretreatment agent silo is filled with pretreatment agent; the pretreatment agent silo, the first rotary feeding device, and the pretreatment agent fluidizing device are arranged sequentially from top to bottom; the pretreatment agent silo is connected to the pretreatment agent fluidizing device through the first rotary feeding device; the pretreatment agent fluidizing blower is connected to the first nozzle sequentially through the pretreatment agent fluidizing device, the first conveying pipe, the first spherical multi-point distributing device, and the first branch pipe; the first nozzle injects pretreatment agent from outside the biomass boiler into the combustion chamber of the biomass boiler or into the flue above the combustion air inlet of the biomass boiler;

[0020] Preferably, the conditioning and protective agent addition device includes a conditioning and protective agent fluidizing blower, a conditioning and protective agent fluidizing device, a conditioning and protective agent bin, a second rotary feeding device, a second conveying pipe, a second nozzle, a second spherical multi-point distributing device, and a second branch pipe; the conditioning and protective agent bin is filled with conditioning and protective agent; the conditioning and protective agent bin, the second rotary feeding device, and the second conveying pipe are arranged sequentially from top to bottom; the conditioning and protective agent bin is connected to the second conveying pipe through the second rotary feeding device; the conditioning and protective agent fluidizing blower is connected to the second nozzle sequentially through the conditioning and protective agent fluidizing device, the second conveying pipe, the second spherical multi-point distributing device, and the second branch pipe; the second nozzle sprays the conditioning and protective agent from outside the biomass boiler to the top of the biomass boiler or into the flue gas channel;

[0021] Preferably, the nitrogen oxide reduction device includes a storage tank, a transfer pump, a liquid ammonia evaporator or ammonia vaporizer, a dilution fan, a transfer pipeline, and an ammonia injection grid; the storage tank is filled with ammonia water or liquid ammonia; the storage tank is connected to the transfer pipeline via the transfer pump and the liquid ammonia evaporator or ammonia vaporizer; the dilution fan is connected to the transfer pipeline; the ammonia injection grid is placed in the tail descending flue; the transfer pipeline extends from the outside of the tail descending flue into the tail descending flue and is connected to the ammonia injection grid; the ammonia injection grid injects ammonia gas into the tail descending flue;

[0022] Preferably, the flue gas ash removal equipment includes a boiler flue gas dust removal device, an air compressor, and a soot blower; the tail descending flue is connected to the boiler induced draft fan through the flue gas dust removal device; the soot blower is placed in the tail descending flue; the boiler flue gas dust removal device is connected to the soot blower through the air compressor; the opening of the soot blower faces the SCR medium-temperature catalyst in the tail descending flue and sends the airflow treated by the flue gas dust removal device to the SCR medium-temperature catalyst.

[0023] The advantages of this invention are:

[0024] This invention provides an additive suitable for biomass boilers and an SCR flue gas denitrification process and equipment. The additive for biomass boilers includes a pretreatment agent capable of reacting with alkali metals in the boiler to convert them into silicates. It also includes a conditioning and protective agent capable of eutectic fusion with the surface of soot particles in high-temperature flue gas to form a eutectic fusion body. The pretreatment agent used in this invention employs powders such as magnesium salts, calcium salts, aluminum salts, and silica powder, which can react with alkali metals in the boiler combustion chamber to generate silicates. The conditioning and protective agent used in this invention employs powders such as calcium salts and silica powder, which can combine with alkali metals in high-temperature flue gas to form a eutectic fusion body. This invention utilizes the sequential action of pretreatment agents and conditioning and protective agents, taking advantage of their reactivity at different temperatures. These agents are sequentially introduced into the high-temperature combustion zone and high-temperature tail flue zone of a biomass boiler, where they chemically react or eutecticly fuse with alkali metals. This ultimately blocks the adsorption and deposition of alkali metals on the SCR denitrification catalyst in the downstream stage, eliminating 100% of the harmful effects of alkali metals on the SCR denitrification catalyst and ensuring the long-term stable operation of the medium- and high-temperature SCR denitrification system in the biomass boiler. Given the low cost of the pretreatment agents and conditioning agents, this method can ensure the normal operation of the SCR denitrification system in biomass boilers under low-cost conditions, thus filling the technological gap in medium- and high-temperature SCR denitrification technology for biomass boilers in my country and creating technical conditions for achieving conventional, low-cost, and high-efficiency flue gas denitrification in the biomass boiler field. Compared with existing non-reduction combustion (SNCR) processes, low-carbon combustion + SNCR processes, and even various denitrification technologies such as integrated desulfurization, denitrification, and dust removal processes using ceramic fiber filter tubes, this invention boasts high denitrification efficiency, stable operation, and reliable performance, fully meeting national requirements for ultra-low emissions from boiler exhaust. Furthermore, this invention utilizes powdered materials, enabling rapid dispersion of both pretreatment agents and conditioning agents in the flue gas, ensuring high reaction and binding efficiency with alkali metals. This equipment has a long service life, requires minimal maintenance, and does not increase system resistance. By sequentially applying pretreatment agents and conditioning agents, this invention achieves a near 100% reaction and conversion rate of alkali metals in flue ash. Moreover, the system is inexpensive and easy to use, demonstrating significant technological advantages and outstanding practical value, making it worthy of widespread promotion in the biomass boiler field. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall structure of the SCR flue gas denitrification equipment provided by the present invention;

[0026] Figure 2 This is a schematic diagram of the spherical multi-point fabric distribution device used in this invention;

[0027] in:

[0028] 1-Biomass boiler; 2-Bottom ash of furnace; 3-Tail-end descending flue; 4-Boiler flue gas dust removal device; 5-Boiler induced draft fan; 6-Chimney; 7-Steam turbine generator; 11-Pretreatment agent fluidizing blower; 12-Pretreatment agent fluidizing device; 13-Pretreatment agent; 14-Pretreatment agent silo; 15-First rotary feeding device; 16-First conveying pipeline; 17-First nozzle; 18-First spherical multi-point feeding device; 19-First branch pipe; 21-Conditioning and protective agent fluidizing blower; 22-Conditioning and protective agent fluidizing fan; 23-Preservative fluidization device; 24-Preservative storage tank; 25-Second rotary feeding device; 26-Second conveying pipeline; 27-Second nozzle; 28-Second spherical multi-point distribution device; 29-Second branch pipe; 31-Ammonia water or liquid ammonia; 32-Storage tank; 33-Transfer pump; 34-Liquid ammonia evaporator or ammonia water vaporizer; 35-Dilution fan; 36-Transfer pipeline; 37-Ammonia spraying grid; 41-Air compressor; 42-Soot blower; 43-SCR medium-temperature catalyst. Detailed Implementation

[0029] The present invention achieves the above objectives through the following specific processing methods:

[0030] See Figure 1 This invention provides an SCR flue gas denitrification device, including a biomass boiler 1, a pretreatment agent addition device, a conditioning and protective agent addition device, a tail-end descending flue 3, a nitrogen oxide reduction device, a flue gas ash removal device, a boiler induced draft fan 5, and a chimney 6; the biomass boiler 1 and the tail-end descending flue 3 run parallel to each other and are connected through a flue gas channel; the tail-end descending flue 3 is connected to the chimney 6 through the flue gas ash removal device and the boiler induced draft fan 5; an SCR medium-temperature catalyst 43 is installed inside the tail-end descending flue 3; the flue gas ash removal device is connected to the tail-end descending flue 3 and flushes the SCR medium-temperature catalyst 43; the pretreatment agent addition device injects pretreatment agent from outside the biomass boiler 1 into the combustion chamber of the biomass boiler 1 or into the flue above the combustion air inlet of the biomass boiler 1; the conditioning and protective agent addition device injects conditioning and protective agent from outside the biomass boiler 1 into the top of the biomass boiler 1 or into the flue gas channel; the nitrogen oxide reduction device injects ammonia gas from outside the tail-end descending flue 3 into the tail-end descending flue 3.

[0031] in:

[0032] The pretreatment agent addition device includes a pretreatment agent fluidizing blower 11, a pretreatment agent fluidizing device 12, a pretreatment agent silo 14, a first rotary feeding device 15, a first conveying pipe 16, a first nozzle 17, a first spherical multi-point distributing device 18, and a first branch pipe 19; the pretreatment agent silo 14 is filled with pretreatment agent 13; the pretreatment agent silo 14, the first rotary feeding device 15, and the pretreatment agent fluidizing device 12 are arranged sequentially from top to bottom; the pretreatment agent silo 14 is connected to the pretreatment agent fluidizing device 12 through the first rotary feeding device 15; the pretreatment agent fluidizing blower 11 is connected to the first nozzle 17 sequentially through the pretreatment agent fluidizing device 12, the first conveying pipe 16, the first spherical multi-point distributing device 18, and the first branch pipe 19; the first nozzle 17 injects pretreatment agent 13 from outside the biomass boiler 1 into the combustion chamber of the biomass boiler 1 or into the flue above the combustion air inlet of the biomass boiler 1.

[0033] The conditioning and protective agent addition device includes a conditioning and protective agent fluidizing blower 21, a conditioning and protective agent fluidizing device 22, a conditioning and protective agent bin 24, a second rotary feeding device 25, a second conveying pipe 26, a second nozzle 27, a second spherical multi-point distributing device 28, and a second branch pipe 29; the conditioning and protective agent bin 24 is filled with conditioning and protective agent 23; the conditioning and protective agent bin 24, the second rotary feeding device 25, and the second conveying pipe 26 are arranged sequentially from top to bottom; the conditioning and protective agent bin 24 is connected to the second conveying pipe 26 through the second rotary feeding device 25; the conditioning and protective agent fluidizing blower 21 is connected to the second nozzle 27 sequentially through the conditioning and protective agent fluidizing device 22, the second conveying pipe 26, the second spherical multi-point distributing device 28, and the second branch pipe 29; the second nozzle 27 sprays the conditioning and protective agent 23 from outside the biomass boiler 1 to the top of the boiler 1 or into the flue gas channel;

[0034] The nitrogen oxide reduction device includes a storage tank 32, a transfer pump 33, a liquid ammonia evaporator or ammonia vaporizer 34, a dilution fan 35, a transfer pipeline 36, and an ammonia injection grille 37. The storage tank 32 is filled with ammonia water or liquid ammonia 31. The storage tank 32 is connected to the transfer pipeline 36 through the transfer pump 33 and the liquid ammonia evaporator or ammonia vaporizer 34. The dilution fan 35 is connected to the transfer pipeline 36. The ammonia injection grille 37 is placed in the tail descending flue 3. The transfer pipeline 36 extends from the outside of the tail descending flue 3 into the tail descending flue 3 and is connected to the ammonia injection grille 37. The ammonia injection grille 37 injects ammonia gas into the tail descending flue 3.

[0035] The flue gas ash removal equipment includes a boiler flue gas dust removal device 4, an air compressor 41, and a soot blower 42; the tail descending flue 3 is connected to the boiler induced draft fan 5 through the flue gas dust removal device 4; the soot blower 42 is placed in the tail descending flue 3; the boiler flue gas dust removal device 4 is connected to the soot blower 42 through the air compressor 41; the opening of the soot blower 42 faces the SCR medium-temperature catalyst 43 in the tail descending flue 3 and sends the airflow treated by the flue gas dust removal device 4 to the SCR medium-temperature catalyst 43.

[0036] This invention provides an SCR flue gas denitrification process, which includes a pretreatment agent treatment stage, a conditioning and protective agent treatment stage, and an ammonia denitrification treatment stage. The specific method of each stage is as follows:

[0037] 1) Pretreatment stage

[0038] The pretreatment agent 13, prepared in the pretreatment agent bin 14, is injected into the combustion chamber of the biomass boiler 1 or into the flue above the combustion air inlet at an appropriate location via pneumatic conveying. Utilizing the high-temperature reactivity of magnesium salts, calcium salts, aluminum salts, silica powder, and alkali metals in the pretreatment agent with the flue gas, most of the alkali metals are converted into silicate substances and fixed in the bottom ash 2 of the furnace. This reduces the formation of low-melting-point substances such as alkali metals (KCl and K2SO4) in the flue gas during combustion, significantly increasing the melting temperature of the flue gas ash. This prevents coking of internal boiler components and reduces the workload of the subsequent conditioning and protection system. Furthermore, the high-melting-point components in the pretreatment agent 13 have a certain scouring effect, removing adhering substances from the surfaces of internal boiler components such as water-cooled walls and grates, keeping the surfaces smooth and clean, increasing heat transfer, and improving boiler efficiency.

[0039] Pretreatment agent 13 is mainly composed of magnesium salts, calcium salts, aluminum salts, and silica powder, supplemented with small amounts of other active reactive substances. These substances are all inexpensive and readily available. Pretreatment agent 13 not only possesses a high ash melting point but also exhibits the characteristic of chemically reacting with alkali metals under high-temperature conditions, ultimately converting most of the alkali metals into silicate substances. These silicate substances can be used as admixtures in cement and concrete, improving the strength, durability, and engineering performance of building materials. The dosage of pretreatment agent 13 is 1–10 g / Nm³ based on the solid-to-gas ratio with the flue gas. 3 The range is determined. The fineness of the pretreatment agent 13 is controlled within the range of 200 to 600 mesh. The pretreatment agent 13 is injected into the combustion chamber throat of the biomass boiler 1 via pneumatic conveying, with the distance from the throat controlled within the range of 1 to 3 meters.

[0040] See Figure 1The pretreatment agent addition device consists of a pretreatment agent fluidizing blower 11, a pretreatment agent fluidizing device 12, a pretreatment agent silo 14, a first rotary feeding device 15, a first conveying pipe 16, a first nozzle 17, a first spherical multi-point distribution device 18, and a first branch pipe 19. The pretreatment agent addition device employs dense-phase conveying, with the solid-to-gas ratio controlled at 0.8–2 kg / Nm³. 3 Within the specified range. Both the first conveying pipe 16 and the first nozzle 17 are made of highly wear-resistant materials, and the medium flow velocity is controlled within the range of 8–12 m / s. See also... Figure 2 The function of the spherical multi-point distribution device is to distribute the pretreatment agent 13 delivered from the first conveying pipe 16 to multiple first branch pipes 19 via the first spherical multi-point distributor 18, and disperse it into the flue gas through the first nozzle 17, where it is fully mixed with the flue gas and reacts or combines with the soot. The first spherical multi-point distributor 18 has a spherical structure, with the interfaces of each branch pipe evenly distributed on the spherical surface; the first spherical multi-point distributor 18 is made of wear-resistant steel with a thickness controlled within the range of 10-20mm to ensure long-term use; the diameter of the branch pipes on the first spherical multi-point distributor 18 is controlled within the range of 50-100mm.

[0041] 2) Conditioning and Protective Agent Treatment Stage

[0042] Similar to the pretreatment stage, the conditioning and protective agent stage also involves pneumatically conveying the conditioning and protective agent 24 into the top of the biomass boiler 1, where it mixes with the medium- and high-temperature flue gas flowing through the area. Under the medium- and high-temperature environment and a certain solid-to-gas ratio in the boiler's tail flue, the conditioning and protective agent 23 rapidly undergoes eutectic fusion with the surface of the soot particles in the flue gas, forming a eutectic fusion body. Once this eutectic fusion body is formed, its physicochemical properties change significantly, losing the original adhesiveness and adhesion of the soot; moreover, the size and shape of the soot particles also increase significantly, making it impossible for them to penetrate the micropores of the catalyst. Therefore, the conditioning and protective agent 23 plays a crucial role in protecting the surface of the SCR catalyst from being covered and blocked. Under the protection of the conditioning and protective agent, the SCR catalyst can maintain its reactivity for a long period.

[0043] Conditioning and protective agent 23 is mainly composed of calcined calcium salts and silica powder. The powder particles exhibit a porous surface, high surface activity, and good diffusion in flue gas. These substances are inexpensive and readily available. The dosage of conditioning and protective agent 23 is 0.05–0.5 g / Nm³ based on the solid-to-gas ratio of the flue gas. 3 The range is determined. The fineness of the conditioning and protective agent 23 is controlled within the range of 200 to 600 mesh. The conditioning and protective agent 23 is injected into the top flue of the biomass boiler 1 via pneumatic conveying.

[0044] See Figure 1 The conditioning and protective agent addition device consists of a conditioning and protective agent fluidizing blower 21, a conditioning and protective agent fluidizing device 22, a conditioning and protective agent silo 24, a second rotary feeding device 25, a second conveying pipe 26, a second nozzle 27, a second spherical multi-point distribution device 28, and a second branch pipe 29. The conditioning and protective agent addition device adopts dense-phase conveying, with the solid-to-gas ratio controlled at 0.8–2 kg / Nm³. 3 Within the range. The second conveying pipe 26 and the second nozzle 27 are both made of highly wear-resistant materials, and the medium flow velocity is controlled within the range of 8 to 12 m / s.

[0045] It should be noted that the addition of pretreatment agents and conditioning and protective agents can also improve the usability of the ash and slag ultimately emitted by biomass boilers.

[0046] 3) Ammonia denitrification treatment stage

[0047] The SCR denitrification catalyst 43 is arranged in the temperature range of 260–420℃ within the tail-end downdraft flue 3 of the biomass boiler 1. When the tail-end flue duct size is small, the flue gas in this area can also be drawn out and arranged in a "back basket" configuration for arranging the SCR denitrification catalyst 43. The denitrification catalyst 43 uses 2–3 layers of SCR medium-temperature catalyst, with the reaction window controlled within the temperature range of 280–350℃; the main component of the SCR medium-temperature catalyst 43 is V2O5-WuO-TiO2, with an initial activity coefficient of not less than 50. Furthermore, the number of pores in the SCR medium-temperature catalyst 43 is controlled within the range of 10 to 20 pores, or a plate-type catalyst can be used. The denitrification agent used is traditional ammonia. Ammonia 31 can be converted into a gaseous state through a liquid ammonia evaporator or ammonia water vaporizer 34. Then, it is diluted with air or nitrogen at a ratio of 1:20 and enters the ammonia injection grid 37 through the conveying pipeline 36. There, it mixes and reacts with the medium- and high-temperature flue gas, reducing nitrogen oxides (NOx) in the flue gas to nitrogen (N2) under the action of the SCR medium-temperature catalyst. It should be noted that this is a typical traditional SCR medium-temperature denitrification method in the ammonia denitrification stage, which will not be elaborated upon here.

[0048] The liquid ammonia evaporator or ammonia water vaporizer 34 uses a steam heater or an electric heater as the heating equipment; the ammonia injection grille 37 adopts a stainless steel tube bundle type or a porous pipe, which can uniformly mix ammonia with flue gas to ensure the thoroughness of the denitrification reaction. The catalyst soot blowing system consists of an air compressor 41 and a soot blower 42. After being pressurized by the air compressor 41, the purging medium passes through the soot blower 42, impacting the SCR medium-temperature catalyst and blowing away the soot deposited on its surface and in the internal pores of the SCR medium-temperature catalyst to maintain sufficient contact between the SCR medium-temperature catalyst and the flue gas. The purging medium is dry air, pure nitrogen, or clean flue gas after dust removal. The pressure of the purging medium is controlled within the range of 0.1 to 0.6 MPa. The air compressor 41 adopts an oil-free screw air compressor or a Roots blower and is equipped with necessary sound insulation devices. The soot blower 42 is an electric telescopic rake soot blower; the soot blower 42 is frequency-controlled, and the stroke speed is controlled within the range of 1 to 10 m / min. It can adjust the stroke speed according to the overall differential pressure of the denitrification device.

Claims

1. An additive suitable for biomass boilers, characterized in that: The additives applicable to biomass boilers include pretreatment agents that can convert alkali metal substances in the boiler into silicate substances. The pretreatment agents include magnesium salts, calcium salts, aluminum salts, and silicon powder. The ratio of magnesium salts, calcium salts, aluminum salts, and silicon powder is 1-5:1-5:1-5:0.5-2.

2. The additive for biomass boilers according to claim 1, characterized in that: The fineness of the pretreatment agent is 200-600 mesh.

3. The additive for biomass boilers according to claim 1 or 2, characterized in that: The additives suitable for biomass boilers also include conditioning and protective agents that can melt and bond with alkali metal substances in flue gas; the conditioning and protective agents include calcium salts and silicon powder, and the ratio of calcium salts to silicon powder is 1-5:0.5-2.

4. The additive for biomass boilers according to claim 3, characterized in that: The fineness of the conditioning and protective agent is 200-600 mesh.

5. An SCR flue gas denitrification process, characterized in that: The SCR flue gas denitrification process includes the following steps: 1) Formulate the additives for biomass boilers as described in claim 4, wherein the additives for biomass boilers include pretreatment agents and conditioning and protection agents; 2) The pretreatment agent obtained in step 1) is injected into the combustion chamber of the biomass boiler (1) or into the flue above the combustion air outlet of the biomass boiler (1). The pretreatment agent converts the alkali metal substances in the flue gas into silicate substances and fixes them in the bottom ash (2) of the furnace inside the biomass boiler (1). 3) The conditioning and protective agent obtained in step 1) is sprayed into the top of the biomass boiler (1). The conditioning and protective agent is mixed with the medium and high temperature flue gas flowing through the top of the biomass boiler (1) and eutectic fusion occurs to generate eutectic fusion.

6. The SCR flue gas denitrification process according to claim 5, characterized in that: In step 2), the amount of pretreatment agent used relative to the solid-to-gas ratio of the flue gas is 1–10 g / Nm³. 3 The flow rate of the pretreatment agent is 8–12 m / s; preferably, the amount of conditioning and protective agent used in step 3) is 0.05–0.5 g / Nm³ relative to the solid-gas ratio of the flue gas. 3 The flow rate of the conditioning and protective agent is 8–12 m / s.

7. The biomass boiler SCR flue gas denitrification process according to claim 5 or 6, characterized in that: The biomass boiler SCR flue gas denitrification process also includes: 4) The medium-high temperature flue gas after step 3) is denitrified using a denitrification catalyst (43) to reduce nitrogen oxides in the flue gas to nitrogen; the main component of the denitrification catalyst (43) is V2O5-WuO-TiO2; the initial activity coefficient of the denitrification catalyst (43) is not less than 50.

8. An SCR flue gas denitrification device based on the SCR flue gas denitrification process according to claim 7, characterized in that: The SCR flue gas denitrification equipment includes a biomass boiler (1), a pretreatment agent addition device, a conditioning and protective agent addition device, a tail-end descending flue (3), a nitrogen oxide reduction device, a flue gas ash removal device, a boiler induced draft fan (5), and a chimney (6); the biomass boiler (1) and the tail-end descending flue (3) run parallel to each other and are connected through a flue gas channel; the tail-end descending flue (3) is connected to the chimney (6) through the flue gas ash removal device and the boiler induced draft fan (5); the tail-end descending flue (3) is equipped with an SCR medium-temperature catalyst (43); the flue gas denitrification equipment includes a biomass boiler (1), a pretreatment agent addition device, a conditioning and protective agent addition device, a tail-end descending flue (3), ... The gas ash removal equipment is connected to the tail descending flue (3) and flushes the SCR medium-temperature catalyst (43); the pretreatment agent addition device injects pretreatment agent from outside the biomass boiler (1) into the combustion chamber of the biomass boiler (1) or into the flue above the combustion air outlet of the biomass boiler (1); the conditioning and protective agent addition device injects conditioning and protective agent from outside the biomass boiler (1) into the furnace top of the biomass boiler (1) or into the flue gas channel; the nitrogen oxide reduction device injects ammonia from outside the tail descending flue (3) into the tail descending flue (3).

9. The SCR flue gas denitrification equipment according to claim 8, characterized in that: The pretreatment agent addition device includes a pretreatment agent fluidizing blower (11), a pretreatment agent fluidizing device (12), a pretreatment agent silo (14), a first rotary feeding device (15), a first conveying pipe (16), a first nozzle (17), a first spherical multi-point distribution device (18), and a first branch pipe (19); the pretreatment agent silo (14) is filled with pretreatment agent (13); the pretreatment agent silo (14), the first rotary feeding device (15), and the pretreatment agent fluidizing device (12) are arranged sequentially from top to bottom; the pretreatment agent... The silo (14) is connected to the pretreatment agent fluidization device (12) through the first rotary feeding device (15); the pretreatment agent fluidization blower (11) is connected to the first nozzle (17) in sequence through the pretreatment agent fluidization device (12), the first conveying pipe (16), the first spherical multi-point material distribution device (18) and the first branch pipe (19); the first nozzle (17) injects pretreatment agent (13) from outside the biomass boiler (1) into the combustion chamber of the biomass boiler (1) or into the flue above the combustion air outlet of the biomass boiler (1).

10. The SCR flue gas denitrification equipment according to claim 9, characterized in that: The conditioning and protective agent addition device includes a conditioning and protective agent fluidizing blower (21), a conditioning and protective agent fluidizing device (22), a conditioning and protective agent silo (24), a second rotary feeding device (25), a second conveying pipe (26), a second nozzle (27), a second spherical multi-point distribution device (28), and a second branch pipe (29); the conditioning and protective agent silo (24) is filled with conditioning and protective agent (23); the conditioning and protective agent silo (24), the second rotary feeding device (25), and the second conveying pipe (26) are arranged from top to bottom in the following order. The conditioning and protective agent silo (24) is connected to the second conveying pipe (26) via the second rotary feeding device (25); the conditioning and protective agent fluidizing blower (21) is connected to the second nozzle (27) via the conditioning and protective agent fluidizing device (22), the second conveying pipe (26), the second spherical multi-point feeding device (28), and the second branch pipe (29); the second nozzle (27) sprays the conditioning and protective agent (23) from outside the biomass boiler (1) to the top of the biomass boiler (1) or into the flue gas channel; Preferably, the nitrogen oxide reduction device includes a storage tank (32), a transfer pump (33), a liquid ammonia evaporator or ammonia vaporizer (34), a dilution fan (35), a transfer pipe (36), and an ammonia injection grid (37); the storage tank (32) is filled with ammonia water or liquid ammonia (31); the storage tank (32) is connected to the transfer pipe (36) through the transfer pump (33) and the liquid ammonia evaporator or ammonia vaporizer (34); the dilution fan (35) is connected to the transfer pipe (36); the ammonia injection grid (37) is placed in the tail descending flue (3); the transfer pipe (36) extends from the outside of the tail descending flue (3) into the tail descending flue (3) and is connected to the ammonia injection grid (37); the ammonia injection grid (37) injects ammonia gas into the tail descending flue (3); Preferably, the flue gas ash removal equipment includes a boiler flue gas dust removal device (4), an air compressor (41), and a soot blower (42); the tail descending flue (3) is connected to the boiler induced draft fan (5) through the flue gas dust removal device (4); the soot blower (42) is placed in the tail descending flue (3); the boiler flue gas dust removal device (4) is connected to the soot blower (42) through the air compressor (41); the opening of the soot blower (42) faces the SCR medium-temperature catalyst (43) in the tail descending flue (3) and sends the airflow treated by the flue gas dust removal device (4) to the SCR medium-temperature catalyst (43).

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