An ammonia-free denitration agent for a biomass boiler and a preparation method thereof

Abstract

The application discloses a kind of ammonia-free denitration agent for biomass boiler and its preparation method, and preparation raw materials include, by mass percentage: oxidizing agent 13-18%, solubilizer 0.5-2%, dispersing agent 0.5-1%, absorbent 15-19%, activated carbon slurry 8-15%, and the balance is water.5, the incorporation of denitration agent can effectively reduce the monitored values of nitrogen oxides at the inlet and outlet of flue gas, whether mother liquor or diluted product has the effect of reducing nitrogen oxides, the use method is simple, low in cost, convenient to use, has greater economic value and broad application prospect.

Description

Technical Field

[0001] This invention relates to the field of B01D53 / 60, and more specifically to an ammonia-free denitrification agent for biomass boilers and its preparation method. Background Technology

[0002] With the continuous transformation and upgrading of energy structures at home and abroad, the proportion of renewable energy in the world's energy structure is constantly increasing. Biomass is currently the only renewable energy source that can be directly used as fuel, and it is convenient to store and has stable applications.

[0003] CN110252051B discloses a method for boiler flue gas dust removal, desulfurization, denitrification, and dioxin removal. Flue gas at a temperature of 250-350℃ is drawn from the boiler, and bicarbonate and a reducing agent are injected into the flue gas before it enters a denitrification and dust removal composite device for denitrification, dioxin removal, and dust removal. CN113144897A provides a dry denitrification agent and its application method. The dry denitrification agent includes an oxidant, urea, a catalyst, an organic accelerator, and a desiccant. When used at a temperature of 600-900℃, it can achieve a denitrification efficiency of 99%. The method is simple, low-cost, and convenient to use, possessing significant economic value and broad application prospects.

[0004] However, biomass fuels typically have high volatile matter content, high moisture content, low carbon content, low calorific value, and low sulfur and ash content. They burn quickly, are easily ignited and burn out, but have poor combustion stability. While biomass fuels produce lower concentrations of particulate matter and SOx, their ash has a low melting point and often contains high levels of alkali metals such as potassium (K) and sodium (Na), and may also contain chlorine, making them highly susceptible to corrosion and coking. Compared to coal-fired boilers, biomass boiler flue gas has higher alkali metal content and moisture content in fly ash, resulting in stronger adhesion. Furthermore, biomass boilers experience greater load fluctuations, unstable combustion, and significant temperature variations within the furnace, leading to larger fluctuations in initial nitrogen oxide emissions. Therefore, when implementing denitrification treatment in biomass power plants, it is crucial to consider issues such as the utilization of fly ash after combustion and the utilization of ammonia escape. Summary of the Invention

[0005] To address the aforementioned problems, this invention discloses an ammonia-free denitrification agent for biomass boilers. The raw materials for preparation, by mass percentage, include: 13-18% oxidant, 0.5-2% solubilizer, 0.5-1% dispersant, 15-19% absorbent, 8-15% activated carbon slurry, and the balance being water.

[0006] In one embodiment, the oxidant is a primary inorganic oxidant and / or a primary organic oxidant.

[0007] Preferably, the oxidant is a combination of a primary inorganic oxidant and a primary organic oxidant, with a mass ratio of (10-30):1.

[0008] The primary inorganic oxidant includes, but is not limited to, one or a combination of potassium permanganate, sodium perchlorate, and sodium chlorate; potassium permanganate is preferred.

[0009] The primary organic oxidant includes, but is not limited to, one or more of peracetic acid, benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, perbenzoic acid, and performic acid; preferably, peracetic acid.

[0010] In one embodiment, the solubilizer is selected from one or more of cationic solubilizers, anionic solubilizers, nonionic solubilizers, and zwitterionic solubilizers.

[0011] Preferably, the solubilizer is a nonionic solubilizer.

[0012] More preferably, the nonionic solubilizer includes, but is not limited to, one or a combination of polysorbate, polyethylene glycol, and polyoxyethylene fatty acids.

[0013] More preferably, the solubilizer is polysorbate.

[0014] In one embodiment, the dispersant is an anionic organic dispersant and / or a nonionic organic dispersant.

[0015] The anionic organic dispersants include, but are not limited to, alkylnaphthalene sulfonates, carboxylates, alkylbenzene sulfonates, and sulfates.

[0016] The nonionic organic dispersants include, but are not limited to, polycarboxylate salts, poly(meth)acrylic acid derivatives, nonylphenol polyoxyethylene ethers, etc.

[0017] Preferably, the dispersant is a sulfate salt.

[0018] More preferably, the sulfate ester salt is sodium dodecyl sulfate.

[0019] In one embodiment, the absorbent is selected from one or a combination of calcium hydroxide, sodium carbonate, and potassium carbonate.

[0020] Preferably, the absorbent is sodium carbonate.

[0021] More preferably, the average particle size of the sodium carbonate is 100-3000 mesh.

[0022] In one embodiment, the raw materials for preparing the activated carbon slurry, by mass percentage, include: 0.2-3% emulsifier, 1-10% activated carbon, and the balance being deionized water.

[0023] In one embodiment, the emulsifier is a cationic emulsifier and / or a nonionic emulsifier.

[0024] Preferably, the emulsifier is a combination of cationic emulsifier and nonionic emulsifier in a mass ratio of (0.5-3):1.

[0025] More preferably, the cationic emulsifier is hexadecyltrimethylammonium bromide; the nonionic emulsifier is selected from one or more combinations of polyacrylamide, polyethylene glycol, and polyethylene glycol monostearate.

[0026] More preferably, the nonionic emulsifier is polyethylene glycol, and the average molecular weight of the polyethylene glycol is 300-800, such as polyethylene glycol-400 and polyethylene glycol-600.

[0027] In one embodiment, the activated carbon is micron-sized activated carbon.

[0028] Preferably, the micron-sized activated carbon is 10-200 microns in size.

[0029] More preferably, the iodine value of the micron-sized activated carbon is greater than 600.

[0030] In one embodiment, the method for preparing the activated carbon slurry includes the following steps: dissolving an emulsifier in half of the water until it is completely dissolved; adding activated carbon to the above aqueous solution and stirring for 60–180 minutes; after mixing, adding the remaining water; emulsifying with a shear emulsifier for 0.5–2 hours; and then allowing it to stand until it does not separate into layers.

[0031] The main functions of the oxidant in ammonia-free denitrification agents are: firstly, to provide an oxygen source, enabling it to rapidly release oxygen at high temperatures to react with nitric oxide to produce nitrogen dioxide; and secondly, to provide a direct reaction between the oxidant and nitric oxide to generate nitrogen dioxide. Using a combination of primary inorganic and primary organic oxidants not only ensures the safety of the system and sufficient oxygen supply but also promotes the process by which the absorbent converts nitrogen dioxide into stable nitrates through physical and chemical adsorption. This is because adding a small amount of organic oxidant improves the dispersibility of the absorbent in the system, allowing the nano-sized absorbent to more efficiently absorb nitrogen dioxide and convert it into nitrates, thus achieving efficient NOx removal from the exhaust gas. Using a combination of cationic and nonionic emulsifiers, along with activated carbon slurry prepared from micron-sized activated carbon, allows for more efficient capture and adsorption of nitrogen monoxide and nitrogen dioxide through physical adsorption, enabling them to contact the ammonia-free denitrification agent more fully. Dispersants further increase the solubility of the oxidant and absorbent, improving the conversion efficiency of NOx to nitrates. Ultimately, the generated nitrate particles will be captured during the dust collection process, thus achieving the purpose of denitrification.

[0032] Another aspect of the present invention discloses a method for preparing the ammonia-free denitrification agent, comprising the following steps: after thoroughly stirring the solubilizer, absorbent and water, a dispersant and activated carbon slurry are added to it, and after emulsifying with a shear emulsifier for 1 to 3 hours, it is allowed to stand to prevent stratification, and then an oxidant is added to the system. After thorough stirring, the mixture is ready.

[0033] Beneficial effects

[0034] 1. Using a combination of primary inorganic and primary organic oxidants can not only ensure the safety of the system and sufficient oxygen supply, but also promote the process by which the absorbent converts nitrogen dioxide into stable nitrates through physical and chemical adsorption.

[0035] 2. This enables the nanoscale absorbent to more efficiently absorb nitrogen dioxide and convert it into nitrate, thereby achieving efficient removal of NOx from exhaust gas.

[0036] 3. Using a combination of cationic and nonionic emulsifiers, the activated carbon slurry prepared with micron-sized activated carbon can more efficiently capture and adsorb nitrogen monoxide and nitrogen dioxide through physical adsorption, allowing them to come into more complete contact with the ammonia-free denitrification agent.

[0037] 4. Dispersants can further increase the solubility of oxidants and absorbents, improving the conversion efficiency of NOx to nitrates. Ultimately, the generated nitrate particles will be captured in the dust collection stage, thus achieving the purpose of denitrification.

[0038] 5. The addition of denitrification agents can effectively reduce the monitoring values ​​of nitrogen oxides at the flue gas inlet and outlet. Both the mother liquor and the diluted finished product have the effect of reducing nitrogen oxides. The method of use is simple, the cost is low and the use is convenient, which has great economic value and broad application prospects. Detailed Implementation

[0039] This embodiment discloses an ammonia-free denitrification agent for biomass boilers. The raw materials for preparation, by mass percentage, are: 15% oxidant, 1% solubilizer, 0.8% dispersant, 17% absorbent, 10% activated carbon slurry, and the balance being water.

[0040] The oxidant is a combination of potassium permanganate and peracetic acid in a mass ratio of 20:1.

[0041] The solubilizer is polysorbate-80.

[0042] The dispersant is sodium dodecyl sulfate.

[0043] The absorbent is sodium carbonate, purchased from Tangshan Tengzhan Trading Co., Ltd., and is of industrial grade with a particle size of 400 mesh.

[0044] The raw materials for preparing the activated carbon slurry, by mass percentage, are: 1.8% emulsifier, 8.2% activated carbon, and the balance being deionized water.

[0045] The emulsifier is a combination of cetyltrimethylammonium bromide and polyethylene glycol-400 in a mass ratio of 1:1.

[0046] The activated carbon is micron-sized activated carbon, purchased from Gongyi Fengxiang Water Treatment Materials Co., Ltd., with an average particle size of 75 microns (200 mesh) and an iodine value of 650-1000.

[0047] The method for preparing the activated carbon slurry is as follows: Dissolve the emulsifier in half of the water until it is completely dissolved. Add activated carbon to the above aqueous solution and stir for 90 minutes. After mixing, add the remaining water and emulsify using a shear emulsifier for 1 hour. Let it stand until it does not separate into layers.

[0048] Another aspect of this embodiment discloses a method for preparing the ammonia-free denitrification agent. After the solubilizer, absorbent and water are thoroughly stirred, a dispersant and activated carbon slurry are added. After emulsifying with a shear emulsifier for 2 hours, the mixture is allowed to stand to prevent stratification. Then, an oxidant is added to the system and stirred thoroughly until homogeneous.

[0049] Performance testing

[0050] 1. Experimental Method: The denitrification agent is designed to be added at the air preheater outlet flue, where it reacts fully with nitrogen oxides in the flue gas through atomized spraying. Changes in nitrogen oxide emissions are observed, and the amount of SNCR denitrification urea used is gradually reduced while ensuring compliance with environmental emission standards.

[0051] 2. Installation of temporary test equipment:

[0052] The manufacturer needs to provide one 304 stainless steel atomizing spray gun; one gear metering pump for testing; liquid piping fittings; and other installation accessories. Compressed air piping needs to be connected to the vicinity of the spray gun placement point at the air preheater outlet; a DN25 pipe diameter is sufficient. We will cooperate with the manufacturer to carry out on-site installation work and connect the power and compressed air supply.

[0053] 3. Experimental Procedure:

[0054] First, transport the denitrification agent to the designated location.

[0055] Connect the compressed air hose to the gas end of the spray gun and the liquid outlet hose of the pump to the liquid end of the spray gun. After connecting, turn on the pump and compressed air and adjust them to achieve the optimal atomization state.

[0056] The spray gun should be placed on the south side of the flue on the east side of the air preheater outlet. A hole needs to be drilled in advance and a pipe welded on to facilitate the placement and fixation of the spray gun.

[0057] Under normal production conditions and relatively stable NOx emissions from the flue gas duct, the NOx monitoring value at the flue gas inlet was 72 mg / Nm³ during the statistical blank period. 3 The NOx monitoring value at the export end was 43 mg / Nm³. 3 Urea dosage was 845 kg / h. The mother liquor test began at 10:07 AM, with the denitrification agent pump flow rate set at 253 kg / h. After approximately 5 minutes, the NOx level at the flue gas inlet gradually decreased. After 10 minutes of reaction, the NOx level at the flue gas inlet was recorded as 42 mg / Nm³. 3 The NOx monitoring value at the export end was 27 mg / Nm³. 3 The urea dosage was 820 kg / h. The dosage was manually reduced by 100 kg / h, and monitoring continued for ten minutes. The NOx monitoring value stabilized at approximately 42 mg / Nm³. 3 Around 10:00 AM, continue the experiment to gradually reduce the amount of denitrifying agent, until the minimum amount of denitrifying agent used to monitor NOx emissions at the outlet is 111 kg / h and the amount of urea is 690 kg / h, and stabilize for a period of time.

[0058] When the finished product is diluted at a 1:1 ratio and tested, the minimum usage of the denitrification agent is 253 kg / h (equivalent to 126.5 kg / h of mother liquor), which can reduce the nitrogen oxide value at the flue gas inlet to 50 mg / Nm³. 3 This replaces the back-end SCR system. It reduces urea usage by 105 kg / h. (During the experiment, the nitrogen oxide levels at the flue gas inlet flued significantly, hovering around 30 mg / Nm³.) 3 The range was approximately the same. Monitoring data were similar when the denitrification agent usage was 380 kg / h and 253 kg / h. Increasing the denitrification agent flow rate did not result in a significant decrease in nitrogen oxides.

[0059] Experimental data:

[0060]

[0061]

[0062]

[0063] Summary of Experimental Conclusions

[0064] 1. A denitrification agent mother liquor usage of 253 kg / h reduces urea usage by 135 kg / h, effectively lowering the inlet nitrogen oxide level of the flue gas to below 50, thus replacing the downstream SCR system. A denitrification agent mother liquor usage of 110 kg / h reduces urea usage by 155 kg / h, effectively lowering the outlet nitrogen oxide level of the flue gas to below 50, thus assisting the downstream SCR system.

[0065] 2. After diluting the denitrification agent mother liquor at a 1:1 ratio, the minimum usage rate tested was 253 kg / h (equivalent to 126.5 kg / h of mother liquor), which could reduce the nitrogen oxide value at the flue gas inlet to 50 mg / Nm³. 3 This replaces the back-end SCR system. It reduces urea usage by 105 kg / h. (During the experiment, the nitrogen oxide levels at the flue gas inlet flued significantly, hovering around 30 mg / Nm³.) 3 (The range of motion, left and right.)

[0066] 3. The addition of denitrification agents can effectively reduce the monitoring values ​​of nitrogen oxides at the flue gas inlet and outlet. Both the mother liquor and the diluted finished product have the effect of reducing nitrogen oxides.

[0067] 4. During the test, the nitrogen oxide monitoring value at the flue gas inlet flue gas flue gas flue gas showed large fluctuations. The possible reason is that the cross-sectional area of ​​the flue gas duct was too large, and the atomization effect of a single spray gun could not achieve full coverage, resulting in some unreacted flue gas escaping. The test results can be improved by increasing the number of spray guns to achieve full coverage of the area.

Claims

1. An ammonia-free denitrification agent for biomass boilers, characterized in that, The raw materials for preparation, by mass percentage, include: 13-18% oxidant, 0.5-2% solubilizer, 0.5-1% dispersant, 15-19% absorbent, 8-15% activated carbon slurry, and the balance being water; The absorbent is sodium carbonate; Wherein, the oxidant is a combination of a primary inorganic oxidant and a primary organic oxidant; wherein; The mass ratio of the primary inorganic oxidant to the primary organic oxidant is (10-30):1; The primary inorganic oxidant is selected from one or more combinations of potassium permanganate, sodium perchlorate, and sodium chlorate; the primary organic oxidant is selected from one or more of peracetic acid, benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, perbenzoic acid, and performic acid. The activated carbon slurry is prepared from 0.2-3% emulsifier, 1-10% micron-sized activated carbon, and the remainder deionized water by weight of the total slurry. The emulsifier is a combination of cationic and nonionic emulsifiers; The preparation method of the ammonia-free denitrification agent includes the following steps: after thoroughly stirring the solubilizer, absorbent and water, a dispersant and activated carbon slurry are added, and after emulsifying with a shear emulsifier for 1 to 3 hours, the mixture is allowed to stand to prevent stratification, and then an oxidant is added to the system. After thorough stirring, the mixture is ready.

2. The ammonia-free denitrification agent according to claim 1, characterized in that, The mass ratio of the cationic emulsifier to the nonionic emulsifier is (0.5-3):

1.

3. The ammonia-free denitrification agent according to claim 1, characterized in that, The cationic emulsifier is hexadecyltrimethylammonium bromide; the nonionic emulsifier is selected from one or more combinations of polyacrylamide, polyethylene glycol, and polyethylene glycol monostearate.

4. The ammonia-free denitrification agent according to claim 1, characterized in that, The average particle size of the micron-sized activated carbon is 10-200 micrometers.

5. The ammonia-free denitrification agent according to claim 1, characterized in that, The method for preparing the activated carbon slurry includes the following steps: dissolving the combination of the cationic emulsifier and the nonionic emulsifier in half of the water until it is completely dissolved; adding activated carbon to the aqueous solution and stirring for 60-180 minutes; after mixing, adding the remaining water; emulsifying with a shear emulsifier for 0.5-2 hours; and allowing it to stand until it does not separate into layers.

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