A stable and efficient denitration system of a biomass boiler

Abstract

The utility model relates to flue gas denitration technical field especially relates to a kind of stable and efficient biomass boiler's denitration system of efficiency. Including: energy conversion unit, with biomass boiler connection;Heat recovery unit, with biomass boiler connection;Dust desulfurization unit, with heat recovery unit connection;Chimney, with dust desulfurization unit connection;SNCR processing unit, set between heat recovery unit and biomass boiler;Low-temperature denitration unit, set between chimney and dust desulfurization unit, and with energy conversion unit and heat recovery unit are connected;Detection control unit, for detecting the temperature of flue gas generated by biomass boiler and the concentration of NO X Of flue gas in dust desulfurization unit, and according to the temperature and the concentration of NO X Control SNCR processing unit operation and / or low-temperature denitration unit operation.The system greatly reduces the possibility of catalyst poisoning, not only solves the problem of frequent poisoning of catalyst in conventional SCR denitration, but also the way denitration efficiency is high, and the system is stable.

Description

Technical Field

[0001] This utility model relates to the field of flue gas denitrification technology, and in particular to a stable and efficient denitrification system for biomass boilers. Background Technology

[0002] Stable and efficient flue gas denitrification technology for biomass boilers has always been a challenge, and currently there is no effective and reliable denitrification method to solve this problem. This is mainly because the flue gas from biomass boilers has the following characteristics: 1. Large temperature differences in the furnace: Biomass boilers mainly include grate boilers and circulating fluidized bed boilers, with furnace temperatures of 700–760℃ and 880–950℃ respectively; 2. High hydrogen content in biomass, resulting in high moisture content in the flue gas, reaching 15%–30% or higher; 3. High mass fraction of alkali metals such as K, Na, and Ca in the flue gas dust, reaching over 8%; 4. Low but fluctuating concentrations of sulfur dioxide and nitrogen oxides: When burning pure biomass, the concentrations of sulfur dioxide and nitrogen oxides are 120–250 mg / m³. 3 Fluctuations, such as the presence of templates, wood, or bark in the fuel, can result in sulfur dioxide and nitrogen oxide concentrations in the flue gas ranging from 250 to 600 mg / m³. 3 Fluctuations. Due to the aforementioned characteristics of biomass boilers, conventional SNCR and SCR denitrification methods encounter various problems when applied to biomass boiler denitrification technology. Conventional SNCR denitrification has low efficiency and results in excessive nitrogen oxide emissions. SCR denitrification suffers from high flue gas moisture content, high alkali metal content, and large fluctuations in sulfur dioxide and nitrogen oxide concentrations. These factors lead to catalyst poisoning within a short period, requiring frequent catalyst replacement, resulting in high operating costs and unstable operation. Therefore, solutions are urgently needed. Utility Model Content

[0003] The technical problem to be solved by this utility model is to provide a stable and efficient denitrification system for biomass boilers. This system greatly reduces the possibility of catalyst poisoning, not only solving the problem of frequent catalyst poisoning in conventional SCR denitrification, but also achieving high denitrification efficiency and system stability, thus solving the problem of flue gas denitrification in biomass boilers.

[0004] To achieve the aforementioned objective, the technical solution of this utility model is as follows: a stable and efficient denitrification system for a biomass boiler, comprising:

[0005] An energy conversion unit, connected to a biomass boiler, is used to convert the heat energy generated by the biomass boiler into electrical energy.

[0006] The heat recovery unit is connected to the biomass boiler and is used to recover heat from the flue gas generated by the biomass boiler.

[0007] The dust removal and desulfurization unit is connected to the heat recovery unit and is used to perform secondary dust removal and desulfurization on the flue gas after the heat recovery unit has been treated.

[0008] The chimney is connected to the dust removal and desulfurization unit and is used to discharge the flue gas treated by the dust removal and desulfurization unit.

[0009] The SNCR treatment unit is located between the heat recovery unit and the biomass boiler and is used to perform high-temperature denitrification on the flue gas generated by the biomass boiler.

[0010] The low-temperature denitrification unit is located between the chimney and the dust removal and desulfurization unit, and is connected to both the energy conversion unit and the heat recovery unit. It is used to perform low-temperature denitrification on the flue gas treated by the dust removal and desulfurization unit.

[0011] The detection and control unit is used to detect the temperature of the flue gas generated by the biomass boiler and the NO content in the flue gas from the dust removal and desulfurization unit. X The concentration, and based on the detected temperature and NO X The concentration control of the SNCR treatment unit and / or the low-temperature denitrification unit is in operation.

[0012] Preferably, the dust removal and desulfurization unit includes a cyclone dust collector, a dry desulfurization device, and a bag filter; the cyclone dust collector is connected to a heat recovery unit and is used to remove large particulate dust from the flue gas; the bag filter is connected to a low-temperature denitrification unit; the dry desulfurization device is located between the cyclone dust collector and the bag filter and is used to remove sulfides from the flue gas.

[0013] Preferably, the low-temperature denitrification unit includes a heater, a low-temperature denitrification device, and a waste heat recovery device; the heater is connected to both the energy conversion unit and the bag filter, and is used to heat the flue gas treated by the bag filter using the thermal energy of the energy conversion unit; the low-temperature denitrification device is connected to the heater and performs low-temperature SCR denitrification on the flue gas heated by the heater; the waste heat recovery device is connected to the heat recovery unit and recovers heat from the flue gas treated by the low-temperature denitrification device, and transfers the recovered heat to the heat recovery unit.

[0014] Preferably, it also includes an induced draft fan; the induced draft fan is connected to the waste heat recovery device and sends the flue gas into the chimney.

[0015] Preferably, the heater heats the flue gas to 180°C~220°C.

[0016] Preferably, the detection and control unit includes a controller, a temperature sensor, and an online nitrogen oxide concentration monitor; the controller is electrically connected to the SNCR treatment unit, the low-temperature denitrification device, the temperature sensor, and the online nitrogen oxide concentration monitor; there are at least two temperature sensors, which are respectively installed at the connection between the SNCR treatment unit and the biomass boiler and in the heater; the online nitrogen oxide concentration monitor is installed in the cyclone dust collector.

[0017] Preferably, the energy conversion unit includes a steam turbine and a generator; the steam turbine is connected to a biomass boiler and converts the thermal energy provided by the biomass boiler into kinetic energy; the generator is connected to the steam turbine and converts the kinetic energy of the steam turbine into electrical energy; and the heater is connected to the steam turbine.

[0018] Preferably, the heat recovery unit includes an economizer and an air preheater; the economizer is connected to the SNCR processing unit; the air preheater is connected to the economizer; and the cyclone dust collector is connected to the air preheater.

[0019] Preferably, the SNCR treatment unit performs high-temperature SNCR denitrification on the flue gas.

[0020] The beneficial effects of this utility model are reflected in:

[0021] (1) The low-temperature denitrification device in the system provided by this utility model denitrifies the flue gas at a temperature of 180℃ to 220℃. At this operating temperature, the catalyst in the low-temperature denitrification device has good activity, and the denitrification efficiency can reach more than 90%. Moreover, since it is used on the clean flue gas after dust removal and desulfurization, the possibility of catalyst poisoning is greatly reduced, solving the problem of frequent catalyst poisoning in conventional SCR denitrification. In addition, the system provided by this utility model has high denitrification efficiency and system stability, which is of great significance to the development of biomass boiler flue gas denitrification technology and solves the problem of biomass boiler flue gas denitrification.

[0022] (2) The system provided by this utility model can basically meet the nitrogen oxide emission concentration requirements of SNCR denitrification when the biomass boiler is under high load. At this time, SCR does not need to participate in the reaction. Or when the biomass boiler fuel changes greatly and the NOx emission concentration exceeds the efficiency of SNCR denitrification alone, a low-temperature SCR denitrification system can be used as a supplement to meet the nitrogen oxide emission requirements. When the denitrification efficiency is not reached, supplementing SCR will greatly improve the denitrification efficiency. When the boiler is running at low load, the furnace temperature is low and SNCR denitrification fails. SCR low-temperature denitrification should be used in all cases. Since SCR low-temperature denitrification is performed on the clean flue gas after desulfurization and dust removal, the probability of catalyst poisoning is greatly reduced and the service life is greatly extended. It can be used for 3 to 5 years or longer, thereby reducing the frequency of replacing the low-temperature catalyst, saving operating costs, and the denitrification efficiency of the flue gas is over 90%. Attached Figure Description

[0023] Figure 1 This is a framework diagram of the system of this utility model. Detailed Implementation

[0024] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present utility model, and not all of them. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present utility model.

[0025] like Figure 1 As shown, this utility model provides a stable and efficient denitrification system for biomass boilers.

[0026] Example 1

[0027] When the biomass boiler is running at high load:

[0028] The SNCR treatment unit performs high-temperature SNCR denitrification on the flue gas generated by the biomass boiler, which can basically meet the denitrification requirements of the biomass boiler.

[0029] After denitrification, the flue gas is transported to the heat recovery unit. After passing through the economizer and air preheater to recover heat from the flue gas, the flue gas is transported to the dust removal and desulfurization unit. The flue gas undergoes secondary dust removal and desulfurization treatment through the cyclone dust collector, dry desulfurization device and bag dust collector in the dust removal and desulfurization unit.

[0030] At this point, after passing through cyclone dust collectors, semi-dry desulfurization, and baghouse dust collectors, the flue gas temperature of the biomass boiler is approximately 110℃, while the dust content is relatively low (generally less than 10 mg / Nm³). 3 Furthermore, the sulfur dioxide content is also relatively low (generally less than 50 mg / Nm³). 3 Therefore, the heater and cryogenic denitrification device of the cryogenic denitrification unit do not need to be turned on, as they meet emission requirements.

[0031] In practical applications, heat is generally absorbed by the demineralized water through heat exchange with the outside of the flue gas conveying pipeline. The recovered heat is then transferred to the economizer of the heat recovery unit through the circulation of the demineralized water, thereby increasing the feedwater temperature, improving boiler thermal efficiency, reducing energy consumption, and extending boiler life.

[0032] When the biomass boiler fuel fluctuates significantly, and the online NOx concentration monitor of the detection control unit detects that the NOx emission concentration at the cyclone dust collector exceeds the efficiency of a single SNCR denitrification process, the controller activates the heater and low-temperature denitrification device of the low-temperature denitrification unit. The heater uses steam from the turbine of the energy conversion unit as a heat source to heat the flue gas until the temperature sensor at the heater detects that the flue gas temperature exceeds 180°C. At this point, the flue gas enters the low-temperature denitrification device, which performs low-temperature SCR denitrification on the heated flue gas. After low-temperature SCR denitrification, the flue gas passes through the waste heat recovery device of the low-temperature denitrification unit for heat recovery, and the recovered heat is transferred to the heat energy recovery unit. The induced draft fan then sends the denitrified flue gas into the chimney, where it is discharged.

[0033] In this way, the low-temperature denitrification unit can supplement the flue gas denitrification treatment unit as an alternative to the SNCR treatment unit. This not only meets the nitrogen oxide emission requirements, but also greatly improves the denitrification efficiency of the flue gas when the SNCR treatment unit is insufficient.

[0034] Example 2

[0035] When the boiler is at low load:

[0036] When the biomass boiler is running at low load, the temperature of the flue gas decreases. The temperature sensor at the connection between the SNCR treatment unit and the biomass boiler detects that the temperature of the flue gas is lower than the temperature of the SNCR reaction zone of the SNCR treatment unit. At this time, SNCR fails, and the controller turns on the heater and the low-temperature denitrification device of the low-temperature denitrification unit to denitrify the flue gas using the low-temperature SCR denitrification method.

[0037] The flue gas generated by the biomass boiler is passed through the economizer and air preheater for heat recovery in sequence, and then the flue gas is sent to the dust removal and desulfurization unit. The flue gas undergoes secondary dust removal and desulfurization treatment through the cyclone dust collector, dry desulfurization device and bag dust collector in the dust removal and desulfurization unit.

[0038] At this point, the flue gas from the biomass boiler, after passing through cyclone dust collectors, semi-dry desulfurization, and baghouse dust collectors, reaches a temperature of approximately 110℃. The heater uses steam from the turbine in the energy conversion unit as a heat source to heat the flue gas until the temperature sensor at the heater detects that the flue gas temperature exceeds 180℃. At this point, the flue gas enters the low-temperature denitrification unit, where it undergoes low-temperature SCR denitrification. The flue gas after low-temperature SCR denitrification passes through the waste heat recovery device in the low-temperature denitrification unit for heat recovery, and the recovered heat is transferred to the heat energy recovery unit. An induced draft fan then sends the denitrified flue gas into the chimney, where it is discharged. The waste heat recovery device typically uses the demineralized water heat exchange principle.

[0039] In practical applications, the low-temperature denitrification device is equipped with a honeycomb-shaped denitrification catalyst layer. The surface of the catalyst layer is coated with catalyst, thereby increasing the contact area between the flue gas and the catalyst and improving denitrification efficiency. The catalyst is generally a commercially available catalyst for flue gas denitrification, such as a manganese-based catalyst.

[0040] By monitoring the flue gas emitted from the chimney, it was found that the activity was better at a flue gas temperature of around 180℃, with a denitrification efficiency exceeding 90%. Compared to the high-dust, high-sulfur flue gas environment of medium- and high-temperature catalysts, low-temperature catalysts operate in a clean flue gas environment, reducing the likelihood of catalyst blockage, extending catalyst lifespan, and significantly reducing operating costs. Because the flue gas temperature is lower than the catalyst's reaction temperature, this portion of the flue gas needs to be heated before entering the low-temperature denitrification system, thus requiring additional steam or other heating methods.

[0041] As can be seen from Examples 1 and 2, compared with independent SNCR denitrification, the system provided by this utility model has multiple denitrification functions that can be switched, which not only has higher denitrification efficiency for flue gas, but also can better adapt to changes in boiler load.

[0042] Because the low-temperature denitrification system is used when nitrogen oxide concentrations are high and SNCR alone cannot meet emission requirements, it operates continuously compared to the standalone application of SCR. This significantly extends the lifespan of the low-temperature SCR catalyst, reducing the frequency of catalyst replacement. Furthermore, since low-temperature denitrification is applied to the purified flue gas after dust removal and desulfurization, the possibility of catalyst poisoning is greatly reduced. Therefore, the operating costs of the hybrid denitrification system provided by this invention are reduced in actual operation.

[0043] In addition, since the low-temperature denitrification device performs low-temperature SCR denitrification on flue gas and operates only in a low-temperature environment, the possibility of catalyst poisoning is greatly reduced, solving the problem of frequent catalyst poisoning in conventional SCR denitrification. Moreover, the service life of the catalyst is greatly extended, thereby reducing the frequency of replacing the low-temperature catalyst and saving operating costs.

[0044] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A stable and efficient denitrification system for a biomass boiler, characterized in that, include: An energy conversion unit, connected to a biomass boiler, is used to convert the heat energy generated by the biomass boiler into electrical energy. The heat recovery unit is connected to the biomass boiler and is used to recover heat from the flue gas generated by the biomass boiler. The dust removal and desulfurization unit is connected to the heat recovery unit and is used to perform secondary dust removal and desulfurization on the flue gas after the heat recovery unit has been treated. The chimney is connected to the dust removal and desulfurization unit and is used to discharge the flue gas treated by the dust removal and desulfurization unit. The SNCR treatment unit is located between the heat recovery unit and the biomass boiler and is used to perform high-temperature denitrification on the flue gas generated by the biomass boiler. The low-temperature denitrification unit is located between the chimney and the dust removal and desulfurization unit, and is connected to both the energy conversion unit and the heat recovery unit. It is used to perform low-temperature denitrification on the flue gas treated by the dust removal and desulfurization unit. The detection and control unit is used to detect the temperature of the flue gas generated by the biomass boiler and the NO content in the flue gas from the dust removal and desulfurization unit. X The concentration, and based on the detected temperature and NO X The concentration control of the SNCR treatment unit and / or the low-temperature denitrification unit is in operation.

2. The denitrification system for a stable and efficient biomass boiler according to claim 1, characterized in that, The dust removal and desulfurization unit includes a cyclone dust collector, a dry desulfurization device, and a bag filter. The cyclone dust collector is connected to the heat recovery unit and is used to remove large particulate dust from the flue gas. The bag filter is connected to the low-temperature denitrification unit. The dry desulfurization device is located between the cyclone dust collector and the bag filter and is used to remove sulfides from the flue gas.

3. The denitrification system for a stable and efficient biomass boiler according to claim 2, characterized in that, The low-temperature denitrification unit includes a heater, a low-temperature denitrification device, and a waste heat recovery device. The heater is connected to both the energy conversion unit and the bag filter, and is used to heat the flue gas treated by the bag filter using the thermal energy of the energy conversion unit. The low-temperature denitrification device is connected to the heater and performs low-temperature SCR denitrification on the flue gas heated by the heater. The waste heat recovery device is connected to the heat recovery unit and recovers heat from the flue gas treated by the low-temperature denitrification device, and transfers the recovered heat to the heat recovery unit.

4. The denitrification system for a stable and efficient biomass boiler according to claim 3, characterized in that, It also includes an induced draft fan; the induced draft fan is connected to a waste heat recovery device and sends the flue gas into the chimney.

5. A stable and efficient denitrification system for a biomass boiler according to claim 3 or 4, characterized in that, The heater heats the flue gas to 180°C~220°C.

6. A stable and efficient denitrification system for a biomass boiler according to claim 3 or 4, characterized in that, The detection and control unit includes a controller, a temperature sensor, and an online nitrogen oxide concentration monitor; the controller is electrically connected to the SNCR treatment unit, the low-temperature denitrification device, the temperature sensor, and the online nitrogen oxide concentration monitor; there are at least two temperature sensors, which are respectively installed at the connection between the SNCR treatment unit and the biomass boiler and in the heater; the online nitrogen oxide concentration monitor is installed in the cyclone dust collector.

7. The denitrification system for a stable and efficient biomass boiler according to claim 4, characterized in that, The energy conversion unit includes a steam turbine and a generator; the steam turbine is connected to a biomass boiler and converts the thermal energy provided by the biomass boiler into kinetic energy; the generator is connected to the steam turbine and converts the kinetic energy of the steam turbine into electrical energy; and the heater is connected to the steam turbine.

8. The denitrification system for a stable and efficient biomass boiler according to claim 4, characterized in that, The heat recovery unit includes an economizer and an air preheater; the economizer is connected to the SNCR treatment unit; the air preheater is connected to the economizer; and the cyclone dust collector is connected to the air preheater.

9. The denitrification system for a stable and efficient biomass boiler according to claim 4, characterized in that, The SNCR treatment unit performs SNCR denitrification on the flue gas.

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