A garbage incineration SNCR process with ammonia and steam premixing

Abstract

The present application relates to waste incineration technical field, specifically disclose a kind of ammonia and steam premixed waste incineration SNCR process, with the medium-temperature secondary high-pressure steam (450 DEG C, 6.4MPa) generated in incineration plant and ammonia and process water are mixed, whole into the mixture is kept in superheated supersaturation state after entering lance. Utilize high-temperature high-pressure steam to provide energy, liquid is all converted into gas, then vaporized reducing agent is sprayed into hearth in high-pressure gaseous state. The present application considers that the proportion imbalance of vaporized reducing agent (ammonia) can be generated by mixing three kinds of materials (20wt% ammonia, process water, steam), by determining and calculating the dosage relationship of three kinds of materials (20wt% ammonia, process water, steam), dilution degree relationship, realize the accurate control of vaporized reducing agent (ammonia) proportion;Meanwhile, the technical problem that steam vaporization dilutes ammonia water not thoroughly is solved by using the hardware means of venturi mixer or pressure pump.

Description

Technical Field

[0001] This invention relates to the field of waste incineration technology, and more particularly to a non-steam combustion (SNCR) process for waste incineration using ammonia and steam premixing. Background Technology

[0002] SNCR, short for Selective Non-Catalytic Reduction, is a non-catalytic denitrification method that uses ammonia or urea as a reducing agent to reduce NOx in flue gas to nitrogen and water at a specific temperature. This technology has been widely used to control pollutants in high-temperature flue gas to meet existing environmental emission standards. Especially in waste-to-energy plants, SNCR systems have become a common flue gas treatment system due to their high cost-effectiveness and effectiveness in NOx removal.

[0003] In existing and publicly available literature, whether ammonia or urea is used as a reducing agent, the basic method is to prepare it as an aqueous solution and then atomize the solution with compressed air or steam before spraying it into the furnace. In schemes using steam, it is often used for preheating or mixing, replacing the atomization effect of compressed air (CN201721922888.X, CN202121801117.1, CN201110232337.1, etc.). Mechanistically, this does not vaporize the reducing agent, which remains in a droplet state. Some schemes describe using steam to vaporize the reducing agent (CN202121412947.5 and CN202020368165.5), but they do not precisely control the amount of ammonia, the amount of steam, or the degree of ammonia dilution. This leads to an imbalance in the proportion of vaporized reducing agent (ammonia), resulting in insufficient NOx removal or ammonia escape, making it difficult to truly achieve the activation of the reducing agent by steam. Summary of the Invention

[0004] The purpose of this invention is to propose a non-saturated non-combustible combustion (SNCR) process for waste incineration using ammonia and steam premixed. This process involves mixing medium-temperature, sub-high-pressure steam (450°C, 6.4 MPa) generated within the incineration plant with ammonia and process water. The mixture is then injected into a spray nozzle, maintaining it in a superheated, supersaturated state. The high-temperature, high-pressure steam provides energy, completely converting the liquid into a gas. The vaporized reducing agent is then injected into the furnace in a high-pressure, gaseous state.

[0005] This invention takes into account the potential imbalance in the proportion of vaporizing reducing agent (ammonia) that may occur when mixing three types of materials (20wt% ammonia, process water, and steam). By measuring and calculating the dosage and dilution relationship of the three types of materials (20wt% ammonia, process water, and steam), the proportion of vaporizing reducing agent (ammonia) can be precisely controlled. At the same time, hardware means such as venturi mixers or pressure pumps are used to solve the technical problem of incomplete vaporization and dilution of ammonia by steam.

[0006] To achieve this objective, the present invention adopts the following technical solution.

[0007] A non-steam combustion (SNCR) process for waste incineration using ammonia and steam premixing includes the following steps:

[0008] S1: Calculate the amount of flue gas produced and the NOx content based on the size and processing capacity of the incinerator.

[0009] S2: Analyze the ratio of NO to NO2 in the flue gas from step S1, and calculate the required flow rate of 20wt% ammonia water based on the flue gas volume and NOx content obtained from step S1.

[0010] S3: Set multiple sets of process water flow rates to dilute the required 20wt% ammonia water flow rate obtained in step S2, and select the optimal process water flow rate by detecting the subsequent NOx emission detection value and ammonia slip concentration.

[0011] S4: Calculate the steam consumption based on the energy requirement for complete vaporization of the required 20wt% ammonia water flow rate and the optimal process water flow rate.

[0012] S5: The required 20wt% ammonia flow rate obtained in step S2, the optimal process water flow rate obtained in step S3, and the amount of steam obtained in step S4 are mixed together, and the resulting mixed gas is injected into the furnace.

[0013] Preferably, in step S5, a Venturi mixer is used to mix the ammonia, process water, and steam described in step S5.

[0014] As a possible solution, in step S5, a pressure pump can also be used to pressurize the ammonia water and process water mentioned in step S5 to the same pressure as the steam and then mix them with the steam.

[0015] As one possible approach, in step S5, the injection distance and range of the mixed gas are controlled by adjusting the arrangement of the spray guns, requiring the mixed gas to be injected at least 2 meters inside the furnace.

[0016] This solution, by taking into account preconditions such as incinerator size, processing scale, and flue gas composition, determines and calculates the dosage and dilution relationships of three types of materials (20wt% ammonia, process water, and steam), thereby achieving precise control of the vaporization reducing agent (ammonia) ratio. This approach balances economic efficiency with ensuring that the NOx removal rate reaches the expected level while minimizing ammonia escape.

[0017] The technical problem of incomplete steam vaporization and dilution of ammonia water was solved by using hardware means such as Venturi mixers or pressure pumps, thereby improving the material utilization rate. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of NOx emission concentration and ammonia escape concentration under different ammonia dilution concentrations provided in one embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] This application provides a non-steam combustion (SNCR) process for waste incineration using ammonia and steam premixing. In this embodiment, the waste incineration SNCR process includes the following steps:

[0022] S1: Calculate the amount of flue gas produced and the NOx content based on the size and processing capacity of the incinerator.

[0023] In this embodiment, an incinerator with a daily processing capacity of 390 tons of municipal solid waste was set, and the measured flue gas volume V was 60885.13 Nm³. 3 / h; NOx content in flue gas M NOx 400 mg / Nm 3 The NOx emission is 400 mg / Nm³. 3 ×60885.13Nm 3 / h=24.35kg / h.

[0024] S2: Analyze the ratio of NO to NO2 in the flue gas from step S1, and calculate the required flow rate of 20wt% ammonia water based on the flue gas volume and NOx content obtained from step S1.

[0025] In this embodiment, the NO concentration accounts for 92.5% and the NO2 concentration accounts for 7.5%; therefore, the NO emission is 22.53 kg / h and the NO2 emission is 1.83 kg / h. The reaction of 20% ammonia with NO and NO2 requires calculation based on the following two reaction equations.

[0026] 4NH3 + 4NO + O2 → 4N2 + 6H2O.

[0027] 4NH3 + 2NO2 + O2 → 3N2 + 6H2O.

[0028] Therefore, the theoretically required mass flow rate of NH3 is calculated. Considering the reaction efficiency and the mass of NH3 that does not participate in the reaction, such as the volatilization and escape of ammonia, the final required amount of NH3 is 10.19 kg / h, which translates to 50.93 kg / h of 20% ammonia solution. Further considering the ammonia consumption due to certain side reactions, an additional 5% ammonia solution is needed, resulting in an actual 20wt% ammonia solution usage (m) of 53.47 kg / h.

[0029] S3: Set multiple sets of process water flow rates to dilute the required 20wt% ammonia water flow rate obtained in step S2, and select the optimal process water flow rate by detecting the subsequent NOx emission detection value and ammonia slip concentration.

[0030] Please see Figure 1 In this embodiment, four different process water flow rates were set to dilute the required 20wt% ammonia water flow rate obtained in step S2. The different dilution degree of ammonia water leads to the variation in the amount of process water used, which in turn leads to the variation in the amount of steam required to completely vaporize the mixture, and the concentration of ammonia injected into the furnace changes. Ultimately, this results in a series of changes in NOx emission detection values, denitrification efficiency, and ammonia slip concentration.

[0031] Ammonia slip and NOx emissions must meet environmental protection requirements; lower values ​​indicate lower pollutant emissions. However, a negative correlation often exists between the two, so a balance needs to be struck between them. Considering the range of fluctuations, this scheme sets ammonia slip range of 4–5 mg / Nm³. 3 This is reasonable (national standard requires less than 8mg), and the NOx emission concentration is less than 130mg / Nm³. 3 The national standard is 150mg. Therefore, the optimal process water flow rate is selected as 400kg / h in this embodiment.

[0032] S4: Calculate the steam consumption based on the energy requirement for complete vaporization of the required 20wt% ammonia water flow rate and the optimal process water flow rate.

[0033] Considering that the energy for the complete vaporization of the required 20wt% ammonia water flow rate and the optimal process water flow rate is entirely provided by medium-temperature, sub-high-pressure steam (450℃, 6.4MPa), the temperature of the mixed liquid is generally 20℃ and the pressure is 1.1MPa; after mixing with steam, the temperature of the vaporized mixture becomes 253℃ and the pressure is slightly greater than 3MPa (this condition is the supersaturation temperature of water, used to ensure complete vaporization of the liquid).

[0034] Please see Figure 1When the optimal process water flow rate is 400 kg / h and the 20 wt% ammonia water dosage is 53.47 kg / h, the steam dosage can be determined to be 1055.37 kg / h through simple energy conservation calculation.

[0035] S5: The required 20wt% ammonia flow rate obtained in step S2, the optimal process water flow rate obtained in step S3, and the amount of steam obtained in step S4 are mixed together, and the resulting mixed gas is injected into the furnace.

[0036] By precisely controlling the flow rate of 20wt% ammonia water, the optimal process water flow rate, and the amount of steam used, the input ammonia resources can be utilized to the maximum extent, ensuring that the reaction of the reducing agent ammonia is sufficient to meet the expected NOx removal rate while limiting ammonia escape to an acceptable range.

[0037] Preferably, in step S5, a Venturi mixer is used to mix the ammonia, process water, and steam described in step S5.

[0038] As a possible solution, in step S5, a pressure pump can also be used to pressurize the ammonia water and process water mentioned in step S5 to the same pressure as the steam and then mix them with the steam.

[0039] The key to vaporization lies in the mixing of steam and diluted ammonia. The pressure difference between the steam (6.4 MPa) and the diluted ammonia (1.1 MPa) is too large. Two feasible methods exist: Firstly, a Venturi mixer is used, where high-speed steam injection creates a vacuum in a specific area, naturally drawing the diluted ammonia into the mixer and completing the mixing of the gas and diluted ammonia. Secondly, a pressure pump is used to pressurize the diluted ammonia to the same pressure as the steam, and then the mixture is piped in.

[0040] As one possible approach, in step S5, the injection distance and range of the mixed gas are controlled by adjusting the arrangement of the spray guns, requiring the mixed gas to be injected at least 2 meters inside the furnace.

[0041] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A non-linear combustion (SNCR) process for waste incineration using ammonia and steam premixing, characterized in that, Includes the following steps: S1: Calculate the amount of flue gas produced and the NOx content based on the size and processing capacity of the incinerator; S2: Analyze the ratio of NO to NO2 in the flue gas in step S1, and calculate the required 20wt% ammonia water flow rate based on the flue gas volume and NOx content obtained in step S1. S3: Set multiple sets of process water flow rates to dilute the required 20wt% ammonia water flow rate obtained in step S2, and select the optimal process water flow rate by detecting the subsequent NOx emission detection value and ammonia slip concentration. S4: Calculate the steam consumption based on the energy requirement of fully vaporizing the required 20wt% ammonia water flow rate and the optimal process water flow rate; wherein, the steam quality used is medium-temperature sub-high-pressure steam at 450℃ and 6.4MPa. S5: The required 20wt% ammonia water flow rate obtained in step S2, the optimal process water flow rate obtained in step S3, and the steam consumption obtained in step S4 are mixed together, and the resulting mixed gas is injected into the furnace; wherein, when using a 390-ton-per-day municipal solid waste incinerator, the optimal 20wt% ammonia water flow rate is 53.47 kg / h, the process water flow rate is 400 kg / h, and the steam consumption is 1055.37 kg / h; Furthermore, in step S5, a Venturi mixer is used to mix the ammonia water, process water, and steam mentioned in step S5; the temperature of the vaporized mixture is 253°C and the pressure is greater than 3MPa, ensuring that the liquid is completely vaporized.

2. The SNCR process for waste incineration with ammonia and steam premixing according to claim 1, characterized in that, In step S5, a pressure pump is used to pressurize the ammonia water and process water mentioned in step S5 to the same pressure as the steam, and then mix them with the steam.

3. The SNCR process for waste incineration with ammonia and steam premixing according to claim 1, characterized in that, In step S5, the spray distance and range of the mixed gas are controlled by adjusting the arrangement of the spray guns, requiring the mixed gas to be sprayed at least 2 meters inside the furnace.

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