Incineration flue gas SCR denitration system
By introducing main flue and bypass flue valves into the SCR system to control the flue gas flow path and combining it with sensor detection, the problem of SCR catalyst clogging due to ammonium bisulfate scaling was solved, achieving efficient NOx removal and flexible system operation, and reducing operating and construction costs.
Patent Information
- Application Number
- CN202422847233.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-21
- Publication Date
- 2025-10-10
- Estimated Expiration
- 2034-11-21
AI Technical Summary
In existing solid waste and hazardous waste incineration equipment, the SCR catalyst is clogged due to scaling of ammonium bisulfate, resulting in reduced denitrification efficiency, and is unable to quickly respond to instantaneous increases in NOx concentration, causing the system to be shut down for cleaning or increased operating costs.
An incineration flue gas SCR denitrification system is designed, which includes a main flue, a bypass flue and a GGH. Main and bypass flue valves are set, and NOx concentration detection sensors and temperature detection sensors are combined. The flue gas flow path is controlled by adjusting the valve opening to achieve flexible flue gas distribution and temperature management, thereby avoiding catalyst clogging.
It effectively solves the SCR catalyst clogging problem, reduces operating costs and equipment construction costs, improves system flexibility and NOx removal efficiency, and reduces heat source consumption and equipment loss.
Smart Images
Figure CN223417045U_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of flue gas denitrification, and in particular to an incineration flue gas SCR denitrification system. Background Art
[0002] The current process for incinerating solid and hazardous waste generally involves primary combustion in a rotary kiln, secondary combustion in a secondary combustion chamber, waste heat recovery in a waste heat boiler (SHB) and SNCR denitrification, rapid cooling of flue gas in a quench tower, deacidification in a dry deacidification unit, particulate removal in a bag filter, deacidification in a scrubber, particulate removal in a wet electrostatic precipitator (ESP), denitrification in an SCR unit, and chimney emissions. Because solid and hazardous waste contain multiple sources of pollution, the post-incineration flue gas requires desulfurization, denitrification, dust removal, heavy metal removal, and dioxin removal (to reduce and remove generated dioxins). Flue gas desulfurization (FGD) involves two processes: dry deacidification and wet desulfurization. To ensure that flue gas emissions meet standards, FGD often utilizes a combination of dry and wet methods.
[0003] There are two types of flue gas denitrification processes after desulfurization: SNCR (Selective Non-Catalytic Reduction Denitrification) and SCR (Selective Catalytic Reduction Denitrification). SNCR uses ammonia injection at a flue gas temperature of 850-1050°C inside the boiler, causing NOx in the flue gas to react with NH3 to produce N2 and H2O, with a denitrification efficiency of 40-60%. SCR uses ammonia injection at a flue gas temperature of 180-400°C inside the denitrification device, causing NOx in the flue gas to react with NH3 to produce N2 and H2O, with a denitrification efficiency of 70-95%.
[0004] Currently, most solid and hazardous waste incineration plants use SNCR denitrification for flue gas denitrification. As NOx emission standards become increasingly stringent, more and more solid and hazardous waste incineration plants are adding SCR denitrification devices, which is a multi-stage SNCR+SCR denitrification technology.
[0005] Taking into account factors such as operating costs, construction costs, reliability, and stability, medium-temperature or low-temperature SCR catalysts are often used. Flue gas temperatures after wet desulfurization range from 50-80°C, which is too low to reach the activation temperature of SCR catalysts. Therefore, current SCR systems for solid and hazardous waste incineration flue gas are often equipped with flue gas heating devices, such as GGH heat exchangers and external heating sources. External heating sources can use high-temperature steam or / and burners.
[0006] Therefore, the SCR device includes the following parts: GGH, ascending flue, and reactor. After desulfurization, the original flue gas first enters the GGH (heat exchanger) to exchange heat with the high-temperature flue gas after SCR denitrification, and the original flue gas is heated to 120-160°C; then the original flue gas enters the ascending flue and is heated again to 180-300°C through a steam heater or a natural gas burner. After the flue gas temperature reaches the catalyst activation temperature, it enters the reactor. In the ascending flue, an ammonia source is sprayed into the original flue gas, and NH3 and the flue gas are mixed in the ascending flue. The mixed flue gas undergoes SCR reaction on the catalyst in the reactor. The high-temperature flue gas after denitrification passes through the GGH and exchanges heat with the original flue gas. The clean flue gas after cooling is discharged from the outlet of the SCR device. The ammonia source in the SCR device is added in excess to ensure the NOx removal efficiency.
[0007] During the incineration process of solid and hazardous waste, most of the sulfur in the waste is converted to SO2, with 0.5-1.5% oxidized to SO3. The catalyst in the SCR unit not only denitrifies but, under high temperature conditions, also catalyzes the conversion of SO2 to SO3. Under the action of the high-temperature catalyst, 1-2% of SO2 is converted to SO3. The NH3 injected into the SCR unit reacts with excess SO3 to form ammonium bisulfate, which exhibits strong adhesion. Ammonium bisulfate adheres to fly ash and deposits on the catalyst surface, forming scale, which can clog the SCR catalyst pores and even the gas path, reducing or even deactivating the catalyst's denitrification efficiency and increasing flue gas pressure drop. To address catalyst fouling and clogging caused by ammonium bisulfate, the flue gas temperature must be raised to 350°C and maintained for 24-48 hours to allow for full decomposition of the ammonium bisulfate. Heating the flue gas inside the SCR unit to 350°C consumes a significant amount of heat, which can cause the SCR unit's external surfaces to overheat. After the flue gas leaves the SCR device, the excessively high temperature will not only increase the flue gas volume, but may also exceed the upper operating temperature limits of the flue, induced draft fan, and chimney. In this case, the system needs to be shut down for manual cleaning.
[0008] Increased flue gas temperature leads to larger flue gas volumes, increasing the operating load of the induced draft fan and the system's operating costs. It also increases the upper limits of the SCR unit, outlet flue, induced draft fan, and chimney, leading to equipment selection based on larger flue gas volumes and higher project construction costs. Furthermore, high flue gas temperatures place higher demands on insulation and anti-corrosion coatings for flue gases and equipment, further increasing construction costs. During operation, solid waste and hazardous waste materials exhibit volatility, and the NOx concentration in the flue gas after incineration is unstable, potentially remaining low for extended periods or exceeding the standard for shorter periods. After incineration, all flue gas passes through the SCR unit for heating and denitrification treatment, resulting in high operating costs.
[0009] Therefore, some devices are equipped with a bypass flue switch valve. When the NOx content in the flue gas meets the standard, it can be discharged from the bypass flue without SCR denitrification treatment. However, since the catalyst in the main path of the SCR device is in a cold state at this time, if the NOx concentration increases instantaneously, the SCR device cannot be put into use immediately, and the rapid temperature increase will cause the catalyst to exceed the temperature rise gradient, and the catalyst will crack. Utility Model Content
[0010] The present application provides an incineration flue gas SCR denitrification system, which can be used to solve the technical problem that the NOx concentration increases instantaneously and the SCR device cannot be put into use immediately.
[0011] The present application provides an incineration flue gas SCR denitrification system, the system comprising:
[0012] The flue gas SCR denitrification system includes the main flue, bypass flue and GGH (gas-to-gas heat exchanger);
[0013] Among them, one side of the GGH (gas-to-gas heat exchanger) is the high-temperature section, which includes a high-temperature inlet and a high-temperature outlet;
[0014] The other side of the GGH is the low-temperature section, which includes a low-temperature inlet and a low-temperature outlet. The raw flue gas passes through the low-temperature section, and the clean flue gas passes through the high-temperature section. Heat exchange occurs inside the GGH.
[0015] The main flue input is connected to the low-temperature inlet of GGH, and the main flue outlet is connected to the high-temperature outlet of GGH;
[0016] The input port of the bypass flue is connected to the original flue gas inlet of the SCR device, and the outlet of the bypass flue is connected to the clean flue gas outlet of the SCR device; the bypass flue is connected before the GGH low-temperature section and after the GGH high-temperature section respectively.
[0017] A main flue valve is installed at the main flue;
[0018] The bypass flue is equipped with a bypass flue valve; the bypass flue is used for flue gas to bypass the GGH, ascending flue, and reactor;
[0019] The main flue valve and the bypass flue valve are both regulating valves with an opening range of 0-100%.
[0020] Furthermore, the main flue includes an ascending flue and a reactor;
[0021] The flue gas in the ascending flue flows from bottom to top, and a flue gas heating device, an ammonium bisulfate pyrolysis heating device, an ammonia source dosing device, and an ammonia source uniform distribution device are respectively arranged in sequence; the flue gas heating device is used to heat the normal operating flue gas to the catalyst activity temperature range of 180-340℃; the ammonium bisulfate pyrolysis heating device is used to heat the ammonium bisulfate pyrolysis flue gas to 350℃.
[0022] The flue gas in the reactor is respectively provided with a flue gas uniform distribution device, a catalyst and a catalyst cleaning device from top to bottom.
[0023] Furthermore, the main flue valve includes one or two;
[0024] Assuming that two main flue valves are set, one of the first main point and the second main point can be selected for setting respectively;
[0025] The first point includes the original flue gas inlet on the GGH, the connection between the GGH and the ascending flue, the inside of the ascending flue, and between the ascending flue and the reactor; the second main point includes the connection between the reactor outlet and the GGH, and the clean flue gas outlet of the GGH;
[0026] Assuming that a main flue valve is set, it can be set at any of the six points, including the first main point and the second main point.
[0027] Furthermore, the system is also provided with a NOx concentration detection sensor; the NOx concentration detection sensor is arranged at the inlet of the flue gas SCR denitrification system and the outlet of the flue gas SCR denitrification system or the chimney; wherein the inlet of the flue gas SCR denitrification system is used to monitor the inlet NOx concentration; the outlet of the flue gas SCR denitrification system is used to monitor the outlet NOx concentration.
[0028] Furthermore, the system is also provided with a temperature detection sensor;
[0029] Temperature detection sensors can be installed at any of the following locations as needed: GGH low-temperature inlet, GGH low-temperature outlet, ammonia source dosing device outlet, before the flue gas heating device access point of the ascending flue, after the flue gas heating device access point of the ascending flue, before each layer of catalyst in the reactor, reactor outlet, GGH high-temperature outlet, and in the bypass flue;
[0030] Among them, a temperature detection sensor must be installed before the uppermost catalyst in the reactor.
[0031] Furthermore, the system is also provided with a pressure detection sensor;
[0032] The pressure detection sensor can be installed at any of the following locations as needed: GGH low-temperature inlet, GGH low-temperature outlet, ammonia source dosing device outlet, in front of the flue gas heating device access point of the ascending flue, after the flue gas heating device access point of the ascending flue, in front of each layer of catalyst in the reactor, reactor outlet, GGH high-temperature outlet, and bypass flue;
[0033] Corresponding pressure detection sensors are also provided before the top catalyst layer of the reactor and at the reactor outlet;
[0034] The total catalyst pressure drop is obtained by subtracting the pressure before the top catalyst layer of the reactor and at the reactor outlet to determine the catalyst blockage situation.
[0035] Furthermore, the system is also provided with a flow detection sensor;
[0036] The flow detection sensor is set at any of the following locations as needed: GGH low-temperature inlet or GGH high-temperature outlet, bypass flue.
[0037] Furthermore, the main flue is also provided with a main inspection valve;
[0038] Close the main flue valve and main inspection valve, and open the bypass flue valve to 100%, so that the SCR device can be inspected without shutting down the system;
[0039] The main line inspection valve is fully open when not in the inspection state;
[0040] The main line inspection valve is a regulating valve or a switching valve.
[0041] Furthermore, when the operating conditions change, as the NOx concentration changes, the adjustment methods of the main flue valve and the bypass flue valve are shown in Table 1:
[0042] Table 1: Changes in various parameters after NOx concentration changes
[0043]
[0044] Under the premise of ensuring that NOx emissions meet the standards, when the NOx concentration in the flue gas increases or decreases, the main flue valve and the bypass flue valve opening are adjusted to control different flue gas volumes to pass through the main flue for heating and denitrification and directly discharge through the bypass flue; under the premise of ensuring that the inlet temperature of the SCR reactor is stable, as the flue gas volume increases or decreases, the heat source consumption of the flue gas heating device increases or decreases accordingly;
[0045] When ammonium bisulfate fouling and clogging occur on the catalyst, the main and bypass flue valves are adjusted to control a small amount of flue gas from passing through the SCR unit's main path while ensuring NOx emissions meet standards. The main flue gas from the SCR unit is heated to 350°C using a heating device or an ammonium bisulfate pyrolysis heating device, achieving efficient pyrolysis of ammonium bisulfate while simultaneously undergoing the SCR reaction to remove NOx. After pyrolysis of ammonium bisulfate, the flue gas leaves the SCR unit, mixes with the bypass flue gas, and is discharged through the induced draft fan and chimney. Raising a small amount of flue gas to the 350°C pyrolysis temperature consumes less heat.
[0046] Furthermore, the main valve opening and the bypass valve opening are adjusted according to the NOx concentration, and the adjustment range is shown in the following table:
[0047]
[0048]
[0049] The main valve opening and the bypass valve opening are adjusted according to the outlet NOx concentration and the inlet NOx concentration so that the outlet NOx concentration meets the emission standards.
[0050] The utility model reduces the main flue gas volume, can reduce the heat source consumption for flue gas heating, catalyst loss, etc., and save the operating cost of the device; low main flue gas volume will also reduce the total exhaust flue gas temperature, the lower the working flue gas volume will be, the lower the construction cost of devices such as induced draft fans and chimneys will be.
[0051] Since the amount of main flue gas is small, the flue gas temperature is relatively low after mixing with the bypass flue gas, and the operating flue gas volume is also relatively low. The low-temperature flue gas is not easy to exceed the upper limit of the operating temperature of the flue, induced draft fan and chimney, and can also effectively reduce the construction cost of the flue, induced draft fan and chimney, while saving the operating cost of the equipment; the low flue gas temperature will also have lower requirements for the insulation and anti-corrosion layer of the flue and equipment, which can reduce the insulation and anti-corrosion construction cost. BRIEF DESCRIPTION OF THE DRAWINGS
[0052] Figure 1 This is a schematic diagram of the process flow of solid waste and hazardous waste incineration in the existing technology;
[0053] Figure 2 Schematic diagram of the SCR process flow provided in the embodiment of the present application;
[0054] Figure 3 A schematic diagram of the SCR process flow provided for the first embodiment;
[0055] Figure 4 This is a schematic diagram of the SCR process flow provided for the second embodiment. DETAILED DESCRIPTION
[0056] In order to make the objectives, technical solutions and advantages of this application clearer, the implementation methods of this application will be further described in detail below with reference to the accompanying drawings.
[0057] The flue gas SCR denitrification system includes the main flue, bypass flue and GGH (gas-to-gas heat exchanger);
[0058] Among them, one side of the GGH (gas-to-gas heat exchanger) is the high-temperature section, which includes a high-temperature inlet and a high-temperature outlet;
[0059] The other side of the GGH is the low-temperature section, which includes a low-temperature inlet and a low-temperature outlet. The raw flue gas passes through the low-temperature section, and the clean flue gas passes through the high-temperature section. Heat exchange occurs inside the GGH.
[0060] The main flue input is connected to the low-temperature inlet of GGH, and the main flue outlet is connected to the high-temperature outlet of GGH;
[0061] The bypass flue's input port is connected with the raw flue gas inlet, and the bypass flue's output port is connected with the clean flue gas outlet; the bypass flue is connected before the low-temperature section of the GGH and after the high-temperature section of the GGH respectively.
[0062] The main flue is provided with a main flue valve;
[0063] The bypass flue is provided with a bypass flue valve; the bypass flue is used for flue gas bypass circulation, bypassing the GGH, the rising flue and the reactor;
[0064] The main flue valve and the bypass flue valve are both regulating valves, and the opening degree range is 0-100%.
[0065] The main flue comprises the rising flue and the reactor;
[0066] The flue gas in the rising flue flows from bottom to top, and the flue gas heating device, the ammonium bisulfate pyrolysis heating device, the ammonia source adding device and the ammonia source uniform distribution device are arranged in the rising flue in sequence; the flue gas heating device is used for heating the normal operation flue gas to the catalyst activity temperature interval of 180-340 DEG C; the ammonium bisulfate pyrolysis heating device is used for heating the ammonium bisulfate pyrolysis flue gas to 350 DEG C.
[0067] The flue gas in the reactor flows from top to bottom, and the flue gas uniform distribution device, the catalyst and the catalyst soot blowing device are arranged in the reactor.
[0068] The main flue valve comprises one or two;
[0069] If two main flue valves are provided, they are arranged at any one of the first main point and the second main point respectively; the first point comprises the GGH raw flue gas inlet, the connection between the GGH and the rising flue, the inside of the rising flue and the connection between the rising flue and the reactor; the second main point comprises the connection between the reactor outlet and the GGH and the GGH clean flue gas outlet;
[0070] If one main flue valve is provided, it is arranged at any one of the six points of the first main point and the second main point.
[0071] The flue gas SCR denitration system is provided with a NOx concentration detection sensor; the NOx concentration detection sensor is arranged at the inlet of the flue gas SCR denitration system and the outlet of the flue gas SCR denitration system or the chimney; the inlet of the flue gas SCR denitration system is used for monitoring the inlet NOx concentration; the outlet of the flue gas SCR denitration system is used for monitoring the outlet NOx concentration.
[0072] The flue gas circulation speed in the main flue ranges from 3 m / s to 15 m / s according to the equipment requirement; the main flue cavity is square according to the field layout and the catalyst shape; the flue gas overcurrent material is carbon steel or 304.
[0073] The flue flow velocity in the bypass flue is 11-15m / s; the bypass flue cavity adopts a circular flue; the flue gas flow material is carbon steel and 304.
[0074] Temperature detection sensors are installed at any of the following locations as needed: GGH low-temperature inlet, GGH low-temperature outlet, ammonia source dosing device outlet, in front of the flue gas heating device access point of the ascending flue, after the flue gas heating device access point of the ascending flue, in front of each layer of catalyst in the reactor, reactor outlet, GGH high-temperature outlet, and in the bypass flue; among them, a temperature detection sensor must be installed in front of the uppermost catalyst in the reactor.
[0075] GGH is used for heat exchange between raw flue gas and clean flue gas, and is an air-to-air plate heat exchanger or heat pipe heat exchanger.
[0076] Pressure detection sensors are set at any of the following positions as needed: GGH low-temperature inlet, GGH low-temperature outlet, ammonia source dosing device outlet, in front of the flue gas heating device access point of the ascending flue, after the flue gas heating device access point of the ascending flue, in front of each layer of catalyst in the reactor, reactor outlet, GGH high-temperature outlet, bypass flue; and pressure detection sensors are respectively set in front of the top catalyst in the reactor and at the reactor outlet; the total pressure drop of the catalyst is obtained by subtracting the pressure in front of the top catalyst in the reactor and at the reactor outlet.
[0077] The flow detection is arranged at the following positions of the SCR device: GGH low-temperature inlet or GGH high-temperature outlet, bypass flue.
[0078] In an SCR flue gas denitrification method, when the operating conditions change, during the monitoring process, as the NOx concentration changes, the adjustment method of the main flue valve and the bypass flue valve is shown in Table 1.
[0079] Table 1: Changes in various parameters after NOx concentration changes
[0080]
[0081] The bypass and main flue gas flows are detected by flow sensors; the mixed temperature of the main and bypass flue gases is detected by a temperature sensor; the NOx concentration is detected by a NOx concentration sensor; and the system pressure drop is detected by a pressure sensor. The system pressure drop is the pressure difference between the GGH raw flue gas inlet and the GGH clean flue gas outlet.
[0082] While ensuring NOx emissions meet standards, when NOx concentration in the flue gas increases or decreases, the main and bypass flue valves are adjusted to control the flue gas volume, allowing it to pass through the SCR unit's main flue for heating and denitrification, and then be discharged directly through the SCR unit's bypass flue. The main flue gas from the SCR unit is heated to 180-300°C using a conventional flue gas heating device for SCR reaction to remove NOx. The denitrified main flue gas is then mixed with the bypass gas and discharged through the induced draft fan and chimney.
[0083] Reducing the main flue gas volume can reduce the heat source consumption for flue gas heating, catalyst loss, etc., saving equipment operating costs; low main flue gas volume will also reduce the total exhaust flue gas temperature, the lower the operating flue gas volume will be, and the construction cost of equipment such as induced draft fans and chimneys will also be lower.
[0084] When ammonium bisulfate fouling and clogging the catalyst, the main and bypass flue valves are adjusted to ensure that NOx emissions meet standards, allowing a small amount of flue gas to pass through the SCR unit's main path. A conventional heating device and / or an ammonium bisulfate pyrolysis heating device are used to raise the SCR unit's main flue gas temperature to 350°C, achieving efficient pyrolysis of ammonium bisulfate while simultaneously performing the SCR reaction to remove NOx. After pyrolysis of ammonium bisulfate, the flue gas leaves the SCR unit, mixes with the bypass flue gas, and is discharged through the induced draft fan and chimney. Raising a small amount of flue gas to the 350°C pyrolysis temperature consumes less heat. Since the amount of main flue gas is small, the flue gas temperature is relatively low after mixing with the bypass flue gas, and the operating flue gas volume is also relatively low. The low-temperature flue gas is not easy to exceed the upper limit of the operating temperature of the flue, induced draft fan and chimney, and can also effectively reduce the construction cost of the flue, induced draft fan and chimney, while saving the operating cost of the equipment; the low flue gas temperature will also have lower requirements for the insulation and anti-corrosion layer of the flue and equipment, which can reduce the insulation and anti-corrosion construction cost.
[0085] Corresponding to different working conditions, the opening degrees of the main flue valve and the bypass flue valve are shown in Table 2.
[0086] Table 2: Valve adjustment table for different working conditions:
[0087]
[0088] As shown in Table 2, once the outlet NOx concentration does not meet the emission standards, adjustments need to be made. If the outlet NOx concentration meets the emission standards, the system pressure drop, main flue valve opening, and bypass flue valve opening can all be maintained at the current status.
[0089] Specifically, when the outlet NOx concentration exceeds the standard, there is no need to continue observing the inlet NOx concentration. Instead, the main flue valve opening should be gradually increased, while the bypass flue valve opening should be gradually reduced until the outlet NOx concentration meets the standard.
[0090] If the outlet NOx concentration meets the standard and the system operates 100% of the time, the status quo can be maintained, with the main flue valve opening at 0% and the bypass flue valve opening at 100%. This means that the flue gas does not pass through the main flue, resulting in no catalyst or ammonia consumption.
[0091] The various working conditions are described in detail below.
[0092] Under operating condition 1, when the hazardous solid waste is stable and contains no or very low levels of nitrogen (specifically nitrogen that generates NOx during combustion), and after sufficient combustion, the flue gas NOx level can be maintained within the standard for a long period of time (100% compliance), the flue gas bypass valve is opened, the regulating valve opening is 100%, and the main flue valve is closed. The flue gas is discharged directly from the bypass flue, and the main flow from the SCR unit is stopped. This completely eliminates the heat source consumed by flue gas heating and extends the service life of the catalyst. At this point, the flue gas temperature is lowest, the operating flue gas volume is minimum, and the flue gas resistance is minimal, effectively reducing the power load on the induced draft fan.
[0093] Operating Condition 2: When hazardous solid waste is unstable and contains 0-0.5% N (specifically, N that produces NOx during combustion), after sufficient combustion, the NOx content in the flue gas can be maintained within the standard for a long time (90-99% of the time). When NOx occasionally exceeds the standard, the flue gas bypass valve is opened, adjusting the valve opening to 20-99%, and the main flue valve opening to 1-50%. Most of the flue gas is discharged from the SCR device bypass flue, and a small amount of flue gas is denitrified from the main path of the SCR device. The denitrified flue gas is mixed with the bypass flue gas and discharged. The main flue gas passes through a conventional flue gas heating device to heat this portion of the flue gas to the catalyst activation temperature range. When NOx does not exceed the standard, ammonia source can be omitted. When the NOx concentration increases and exceeds the standard, a small amount of ammonia source is added to achieve standard emissions. This can effectively reduce the heat source consumption for flue gas heating and extend the service life of the catalyst. At this time, the flue gas temperature is low, the operating flue gas volume is low, and the flue gas resistance is small, which effectively reduces the power load of the induced draft fan.
[0094] Condition 3, when the hazardous solid waste material is unstable and contains 0-1% N element (specifically N element that will produce NOx when burning), after sufficient combustion, NOx in the flue gas often exceeds the standard (1-90% time standard operation), open the flue gas bypass valve, adjust the valve opening 10-90%, the main road flue valve opening 10-90%, most of the flue gas can be bypassed from the SCR device and discharged, or can be denitrified from the main road of the SCR device, and the final mixed flue gas goes to the induced draft fan and the chimney. The main road flue gas passes through the conventional flue gas heating device, and the part of the flue gas is heated to the catalyst activation temperature interval; when NOx does not exceed the standard, a small amount of ammonia source is added to maintain the reliability of the ammonia source addition device, while the instant NOx exceeds the standard; when the NOx concentration increases and exceeds the standard, the ammonia source is added according to the amount to achieve the standard emission. It can reduce catalyst consumption and flue gas heating heat source consumption. At this time, the flue gas temperature is low, the flue gas volume is low, and the flue gas resistance is small, effectively controlling the power load of the induced draft fan.
[0095] Condition 4, when the hazardous solid waste material is slightly stable and contains 0.5-2% N element (specifically N element that will produce NOx when burning), after sufficient combustion, NOx in the flue gas continuously exceeds the standard (100% time exceeds the standard, exceeds the emission concentration by 1-100%) without SCR denitrification treatment, open the flue gas bypass valve opening 1-50%, the main road flue valve opening 10-99%, most of the flue gas is denitrified through the main road of the SCR device, and the remaining small part of the flue gas is directly discharged from the bypass flue of the SCR device, and the final mixed flue gas goes to the induced draft fan and the chimney. The main road flue gas passes through the conventional flue gas heating device, and the part of the flue gas is heated to the catalyst activation temperature interval; add ammonia source to achieve standard emission. It can reduce catalyst consumption and flue gas heating heat source consumption. At this time, the flue gas temperature is slightly low, the flue gas volume is slightly low, and the flue gas resistance is slightly small, and the power load of the induced draft fan is slightly low.
[0096] Condition 5, when the hazardous solid waste material is stable and contains more than 1% N element (specifically N element that will produce NOx when burning), after sufficient combustion, NOx in the flue gas needs to be completely denitrified by the SCR device to ensure that the outlet meets the standard (100% time exceeds the standard, exceeds the emission concentration by more than 100%), close the flue gas bypass valve, the main road flue valve opening 100%, the flue gas is completely denitrified from the main road of the SCR device, and the denitrified flue gas is sent to the induced draft fan and the chimney, and the internal flow of the bypass flue is stopped. The main road flue gas passes through the conventional flue gas heating device, and the part of the flue gas is heated to the catalyst activation temperature interval; add ammonia source to achieve standard emission.
[0097] Under Condition 6, when the pressure differential across the reactor or across the single-layer catalyst bed in the SCR unit's main circuit exceeds the design value, this indicates ammonium bisulfate fouling and clogging on the catalyst surface, necessitating pyrolysis of ammonium bisulfate. Open the SCR unit's bypass valve to 10-90% and the main flue gas valve to 99-10%. Minimize the amount of flue gas entering the SCR unit's main circuit while ensuring that the exhaust flue gas meets NOx standards. The flue gas entering the SCR unit's main circuit is heated to 350°C for 24-48 hours using a conventional flue gas heating device and / or an ammonium bisulfate pyrolysis heating device to achieve complete decomposition of the ammonium bisulfate. At 350°C, the SCR reaction can proceed simultaneously, achieving equally high NOx removal efficiency. During the pyrolysis of ammonium bisulfate, adjust the main and bypass valve openings based on NOx concentrations to maintain a low gas volume passing through the SCR unit. After the high-temperature flue gas from the main road leaves the device, it is mixed with the bypass flue gas to cool down and then discharged through the induced draft fan and chimney.
[0098] In operating condition 7, when NOx levels in the flue gas at the SCR unit outlet consistently exceed the standard, the main flue gas valve opening is gradually increased, while the flue gas bypass valve opening is gradually decreased. This increases the amount of flue gas denitrified by the SCR unit's main flue gas and reduces the amount of flue gas discharged directly from the SCR unit's bypass flue gas. The flue gas is then mixed and directed to the induced draft fan and chimney. The main flue gas passes through a conventional flue gas heating device to raise the temperature to the catalyst activation temperature range. Ammonia is then added to achieve flue gas denitrification. When NOx levels in the flue gas at the SCR unit outlet reach the required emission concentration limit, the system can switch to operating conditions 1-6.
[0099] When NOx concentration testing is not performed on the inlet flue gas of the SCR device, control can be performed based solely on the outlet NOx. When the outlet flue gas NOx concentration meets the standard, the main valve opening is gradually reduced, and the bypass valve opening is gradually increased, reducing the amount of flue gas undergoing denitrification treatment in the main flow of the SCR device and increasing the amount of flue gas directly discharged from the SCR device bypass flue until the NOx concentration in the flue gas at the outlet of the SCR device reaches the standard emission value.
[0100] Compared to existing high-temperature pyrolysis processes, this method significantly reduces heat source consumption for flue gas heating. The low exhaust temperature prevents it from exceeding the upper operating temperature limits of the flue, induced draft fan, and chimney. Low operating flue gas volume also effectively reduces construction costs for the flue, induced draft fan, and chimney, while also saving on equipment operating costs. The lower flue gas temperature also reduces requirements for insulation and anti-corrosion coatings on the flue and equipment, reducing insulation and anti-corrosion construction costs. Table 3 compares the effectiveness of this utility model with existing technologies.
[0101] Table 3: Effect comparison table
[0102] Serial number name Original pyrolysis system This pyrolysis system 1 Pyrolysis flue gas flow 100％ part 2 Bypass flue gas flow 0 part 3 Heat source consumption of flue gas heating device big Small 4 Ammonia consumption big Small 5 Catalyst service life High consumption Low consumption 6 Temperature of main and bypass flue gas after mixing high Low 7 Ammonium bisulfate blockage cleaning effect good good 8 Device insulation and anti-corrosion costs high Low 9 Construction costs high Low 10 System pressure drop high Low 11 Running costs high Low
[0103] Furthermore, the flue gas heating device can be a steam heat exchanger, using high-temperature steam to indirectly heat the flue gas. Alternatively, the flue gas heating device can be a burner, using natural gas, fuel gas, oil, or other raw materials as fuel. The high-temperature combustion generates a large amount of heat, which directly mixes with the flue gas to achieve the flue gas heating effect. The flue gas heating device can be one or more units, and can be a combination of a steam heat exchanger and a burner.
[0104] Furthermore, the ammonium bisulfate pyrolysis and heating device is a steam heat exchanger or burner. The steam heat exchanger uses high-temperature steam to indirectly heat the flue gas. The burner fuel includes natural gas, fuel gas, oil, and other raw materials. The high-temperature combustion generates a large amount of heat, which directly mixes with the flue gas to achieve the flue gas heating effect. The ammonium bisulfate pyrolysis and heating device can be one or more.
[0105] Furthermore, based on the outlet NOx concentration, while ensuring that NOx emissions meet the standards, the amount of flue gas flowing through the main path of the SCR device is minimized; the main flue valve and the bypass flue valve are set in a chain adjustment manner with the NOx concentration in the flue gas.
[0106] Furthermore, the main flue valve and the bypass flue valve are adjusted in a linked manner with the flue gas volume and the NOx concentration in the flue gas.
[0107] Furthermore, the temperature of the flue gas entering the catalyst is interlocked with the conventional flue gas heating device to ensure that the temperature of the flue gas entering the catalyst reaches the catalyst active temperature range of 180-340°C.
[0108] Furthermore, the temperature of the flue gas entering the catalyst is linked to the ammonium bisulfate pyrolysis heating device to ensure that the temperature of the flue gas entering the catalyst reaches 350°C.
[0109] Furthermore, if there is a requirement for the exhaust gas temperature of the SCR device, the exhaust gas temperature after the SCR device is interlocked with the main flue valve and the bypass flue valve for adjustment.
[0110] Furthermore, if there are requirements for the flue gas temperature and NOx concentration discharged from the SCR device, the flue gas temperature and NOx concentration after the SCR denitrification device are interlocked with the main flue valve and the bypass flue valve.
[0111] Please refer to Table 1 and Table 2 for the specific contents of the above chain adjustment settings, which will not be repeated here.
[0112] Furthermore, the main flue valve and the bypass flue valve are regulating valves with an opening of 0-100%; they are any one of a single-axis flue baffle, a multi-axis flue baffle, a louver-type baffle, a rotary flue baffle, a plug-in flue baffle, a butterfly valve, and a gate valve; and the actuator is any one of electric, pneumatic or hydraulic drive.
[0113] Furthermore, a main service valve is added to the main flue of the SCR device. By closing the main flue valve and the main service valve, and leaving the bypass flue valve 100% open, the SCR device can be serviced without shutting down the system. The main service valve is fully open when not in service mode. The main service valve can be either a regulating valve or an on-off valve. Its actuation mechanism is electrically, pneumatically, hydraulically, or manually driven. The valve can be a single-axis flue damper, a multi-axis flue damper, a louvered damper, a rotary flue damper, a plug-in flue damper, a butterfly valve, or a gate valve.
[0114] Furthermore, in order to prevent the appearance of white smoke plumes at the chimney outlet due to the flue gas temperature being too low, a flue gas heating device is added to the bypass flue; or a flue gas heating device is added to the main flue before the SCR device and the bypass flue to heat the flue gas in advance during normal operation, or to be used for chimney whitening purposes.
[0115] Furthermore, when the incineration flue gas is not subjected to a wet deacidification process, GGH can be retained or removed.
[0116] The SCR flue gas denitrification system provided by the utility model is suitable for removing non-high concentration NOx, and is particularly suitable for situations where the NOx concentration fluctuates.
[0117] Furthermore, during the SCR flue gas denitrification process, catalysts can be added to improve the denitrification efficiency of the main flue gas entering the SCR device. While ensuring the total flue gas denitrification efficiency, the flue gas volume entering the main flue of the SCR device can be reduced and the flue gas volume entering the bypass flue can be increased, thereby reducing the flue gas heating heat source and the outlet flue gas temperature.
[0118] The effects of the present invention are further described below with reference to two embodiments.
[0119] First embodiment
[0120] A company in Yantai, Shandong Province uses a 35,000 t / a solid waste comprehensive utilization device for the group's internal solid waste and hazardous waste incineration treatment. The process flow includes: rotary kiln, secondary combustion chamber, waste heat boiler, quenching tower, dry deacidification tower, bag filter, wet deacidification device, SCR device, induced draft fan and chimney.
[0121] The SCR unit consists of a primary steam heater, a gas heating system (GGH), a secondary steam heater, an ammonia injection device, an ammonia source distribution device, a flue gas distribution device, and a catalyst. The catalyst is a low-temperature catalyst, the flue gas heating device is an indirect steam heater, and the GGH utilizes a gas-to-gas plate-type indirect heat exchanger. The SCR unit lacks a bypass and a heating device for ammonium bisulfate pyrolysis, ignoring the high-temperature pyrolysis requirements of ammonium bisulfate.
[0122] The flue gas from the wet deacidification device has a temperature of 50-80℃. It first passes through the first-level steam heater to heat it to 120-140℃, then passes through the GGH heat exchange to heat it to 160-190℃, and then passes through the second-level steam heater to heat it to 200-240℃. It enters the catalyst for NOx removal reaction. The flue gas temperature after denitrification is 190-220℃. Finally, it passes through the GGH to cool it to 150-170℃ and is discharged to the induced draft fan and chimney.
[0123] The interior of the induced draft fan is equipped with fiberglass anti-corrosion, which can withstand temperatures up to 170°C. The interior of the chimney is equipped with high-temperature anti-corrosion, which can withstand temperatures up to 250°C.
[0124] After prolonged operation, ammonium bisulfate scale forms on the SCR catalyst surface, clogging the catalyst channels. Because the original SCR unit design didn't consider the possibility of ammonium bisulfate clogging the catalyst, it lacked a heating device for ammonium bisulfate pyrolysis, requiring manual cleaning only when the unit is shut down.
[0125] In order to solve the above problems, the SCR denitrification device needs to be modified. The modification contents are as follows:
[0126] 1. Add an SCR device bypass between the first-stage steam heater and the GGH raw flue gas inlet, connect the bypass flue to the GGH clean flue gas outlet, and install a flue valve on the bypass;
[0127] 2. Add a burner after the secondary steam heater in the ascending flue, using natural gas as the fuel heat source. Considering the need for air flow mixing and distribution, add two natural gas burners and arrange them symmetrically.
[0128] 3. Add a main flue valve to the flue between the natural gas burner and the catalyst;
[0129] 4. Set up interlocking adjustment between the NOx concentration and flue gas temperature at the outlet of the SCR device and the main flue valve and bypass flue valve.
[0130] When ammonium bisulfate fouling and clogging the catalyst requires pyrolysis, the bypass flue valve is opened 40-60%, and the main flue valve is opened 40-90%. The main flue gas from the SCR unit is heated to above 350°C through the GGH, a secondary steam heater, and an ammonium bisulfate pyrolysis heating device (two natural gas burners) and maintained at this temperature for 48 hours to fully decompose and remove scale deposits on the catalyst surface. The pyrolysis flue gas is simultaneously treated with a catalyst for denitrification, then cooled to 220-240°C by the GGH. It is then mixed with the bypass flue gas and cooled to 160-170°C before being discharged to the induced draft fan for pressurization and discharge out the chimney.
[0131] The exhaust gas temperature does not exceed the upper temperature limit of the induced draft fan, so there is no need to repurchase the induced draft fan or replace the anti-corrosion, saving project transformation costs.
[0132] The exhaust gas temperature is low, the operating flue gas volume is small, the power load of the induced draft fan is low, and the operating cost is saved. It is expected that the power consumption of the flue gas transmission of the SCR device will be reduced by 20-50%.
[0133] The amount of flue gas is small, and the amount of natural gas used for heating is small, saving 40-80% of natural gas consumption.
[0134] The plant's flue gas has a low NOx concentration, but fluctuating levels can result in NOx exceeding the standard. In actual operation, the NOx concentration at the SCR device outlet is linked to the main and bypass flue valves. This ensures that the outlet meets the standard with the bypass valve opening at 50-80% and the main flue valve opening at 20-50%. Most of the flue gas flows through the bypass, while the remaining flue gas enters the main flue. After heating and denitrification, the remaining flue gas is discharged from the main flue. The flue gases are then mixed and discharged to the induced draft fan and chimney.
[0135] The exhaust gas temperature is as low as 140-155℃, the flue gas volume is small under working conditions, the power load of the induced draft fan is low, and the operating cost is saved. It is expected that the electricity consumption for flue gas transmission of the SCR device will be saved by 30-70%.
[0136] The flue gas volume is small, and the steam consumption of the secondary steam heater can be reduced by 50-80%, saving operating costs. The steam consumption of the primary steam heater before the flue gas bypass is not reduced.
[0137] Second embodiment
[0138] A Ningxia company uses a 25t / d solid waste and hazardous waste incineration unit for internal incineration. The process includes a rotary kiln, secondary combustion chamber, waste heat boiler, quench tower, dry deacidification tower, bag filter, wet deacidification unit, induced draft fan, wet electrostatic precipitator, SCR unit, and chimney. Local particulate matter emission limits are extremely strict, so the wet electrostatic precipitator was installed.
[0139] The SCR unit includes a gas heating system (GGH), a flue gas heating device, an ammonia injection device, an ammonia source distribution device, a flue gas distribution device, and a catalyst. The catalyst is a low-temperature catalyst, the flue gas heating device is a natural gas heater, and the GGH utilizes a heat pipe-type indirect gas-to-gas heat exchanger. The SCR unit has a bypass, and the main and bypass valves are on-off valves without adjustable opening. There is no heating device for the ammonium bisulfate pyrolysis process, and the high-temperature pyrolysis requirements of ammonium bisulfate have not been considered.
[0140] The flue gas from the wet electrostatic precipitator has a temperature of 50-80℃. It first passes through the GGH and is heated to 120-140℃. Then it passes through the natural gas burner and is heated to 200-220℃. It enters the catalyst for NOx removal reaction. After denitrification, the flue gas temperature is 190-210℃. Finally, it passes through the GGH and is cooled to 130-150℃ before being discharged to the induced draft fan and chimney.
[0141] The interior of the chimney is made of fiberglass for corrosion protection and is temperature resistant to 200°C.
[0142] After prolonged operation, ammonium bisulfate scale forms on the SCR catalyst surface, clogging the catalyst channels. The design failed to consider the possibility of ammonium bisulfate clogging the catalyst, and a heating device for ammonium bisulfate thermal decomposition was not included. When catalyst blockage occurs, manual cleaning is required during system shutdown.
[0143] In order to solve the above problems, the SCR denitrification device needs to be modified. The modification contents are as follows:
[0144] 1. Replace the original main flue valve and bypass flue valve from on-off valve to regulating valve;
[0145] 2. Set up interlocking adjustment between the NOx concentration and flue gas temperature at the outlet of the SCR device and the main flue valve and bypass flue valve;
[0146] 3. No additional ammonium bisulfate pyrolysis heating device is installed. The original natural gas burner is reused and the temperature of the flue gas entering the catalyst is linked to the load setting of the natural gas burner.
[0147] When ammonium bisulfate fouling and clogging the catalyst requires thermal decomposition, the bypass flue valve is opened 50-80%, and the main flue valve is opened 20-50%. The main flue gas from the SCR unit is heated to over 350°C through the GGH and natural gas burner and held at this temperature for 48 hours to fully decompose and clean the scale on the catalyst surface. Simultaneously, the flue gas passes through the catalyst for denitrification, then passes through the GGH and is cooled to 200-260°C. It is then mixed with the bypass flue gas and cooled to 120-180°C before being discharged from the chimney.
[0148] The exhaust gas temperature is lower than the upper temperature limit of the chimney's corrosion resistance, so the chimney does not need to replace the corrosion protection, saving project renovation costs.
[0149] There is no need to add a new ammonium bisulfate heating device, and the original natural gas combustion is reused, saving project transformation costs.
[0150] The exhaust gas temperature is low, the operating flue gas volume is small, the power load of the induced draft fan is low, and the operating cost is saved. It is expected that the power consumption of flue gas transmission of the SCR device will be saved by 30-60%.
[0151] The amount of flue gas is small, and the amount of natural gas used for heating is small, which can save 50-80% of natural gas consumption.
[0152] The plant's flue gas has a low NOx concentration, but fluctuating levels can result in NOx exceeding the standard. In actual operation, the NOx concentration at the SCR device outlet is linked to the main and bypass flue valves. This ensures that the bypass valve opening is 70-90% and the main flue valve opening is 10-30% when the outlet meets the standard. The majority of the flue gas flows through the bypass, while a small portion enters the main flue. After heating and denitrification, the flue gas is discharged from the main flue. The flue gases are then mixed and discharged to the induced draft fan and chimney.
[0153] The exhaust gas temperature is as low as 110-130℃, the flue gas volume is small under working conditions, the power load of the induced draft fan is low, and the operating cost is saved. It is expected that the electricity consumption for flue gas transmission of the SCR device will be saved by 40-70%.
[0154] The amount of flue gas is small, and the consumption of natural gas burners can be reduced by 50-80%, saving operating costs.
[0155] It should be noted that the above content only illustrates the technical idea of the utility model and cannot be used to limit the protection scope of the utility model. For ordinary technicians in this technical field, they can make several improvements and modifications without departing from the principles of the utility model. These improvements and modifications all fall within the protection scope of the claims of the utility model.
[0156] The above-described embodiments of the present application do not constitute a limitation on the scope of protection of the present application.
Claims
1. An incineration flue gas SCR denitrification system, characterized in that: The system comprises: The flue gas SCR denitrification system includes the main flue, bypass flue and GGH; Among them, one side of the GGH is the high-temperature side, which includes a high-temperature inlet and a high-temperature outlet; The other side of the GGH is the low-temperature side, which includes a low-temperature inlet and a low-temperature outlet. The main flue inlet is connected to the low-temperature inlet of the GGH, and the main flue outlet is connected to the high-temperature outlet of the GGH. The input port of the bypass flue is connected to the raw flue gas inlet of the SCR device, and the outlet of the bypass flue is connected to the clean flue gas outlet of the SCR device; the bypass flue is connected before the GGH low-temperature section and after the GGH high-temperature section respectively; A main flue valve is installed at the main flue; The bypass flue is provided with a bypass flue valve; The main flue valve and the bypass flue valve are both regulating valves with an opening range of 0-100%.
2. The system according to claim 1, wherein: The main flue includes the ascending flue and the reactor; In the rising flue, flue gas is sequentially provided with a flue gas heating device, an ammonium bisulfate pyrolysis heating device, an ammonia source dosing device, and an ammonia source uniform distribution device. The flue gas in the reactor is respectively provided with a flue gas uniform distribution device, a catalyst and a catalyst cleaning device from top to bottom.
3. The system according to claim 2, characterized in that The main flue valve includes one or two; Assuming that two main flue valves are set, one of the first main point and the second main point can be selected for setting respectively; The first point includes the original flue gas inlet on the GGH, the connection between the GGH and the ascending flue, the inside of the ascending flue, and between the ascending flue and the reactor; the second main point includes the connection between the reactor outlet and the GGH, and the clean flue gas outlet of the GGH; Assuming that a main flue valve is set, it can be set at any of the six points, including the first main point and the second main point.
4. The system according to claim 3, characterized in that The system is also provided with a NOx concentration detection sensor; the NOx concentration detection sensor is arranged at the inlet of the flue gas SCR denitrification system and the outlet of the flue gas SCR denitrification system or the chimney; the inlet of the flue gas SCR denitrification system is used to monitor the inlet NOx concentration; the outlet of the flue gas SCR denitrification system is used to monitor the outlet NOx concentration.
5. The system according to claim 1, wherein: The system is further provided with a temperature detection sensor; Temperature detection sensors can be installed at any of the following locations as needed: GGH low-temperature inlet, GGH low-temperature outlet, ammonia source dosing device outlet, before the flue gas heating device access point of the ascending flue, after the flue gas heating device access point of the ascending flue, before each layer of catalyst in the reactor, reactor outlet, GGH high-temperature outlet, and in the bypass flue; Among them, a temperature detection sensor must be installed before the uppermost catalyst in the reactor.
6. The system according to claim 1, wherein: The system is further provided with a pressure detection sensor; The pressure detection sensor can be installed at any of the following locations as needed: GGH low-temperature inlet, GGH low-temperature outlet, ammonia source dosing device outlet, in front of the flue gas heating device access point of the ascending flue, after the flue gas heating device access point of the ascending flue, in front of each layer of catalyst in the reactor, reactor outlet, GGH high-temperature outlet, and bypass flue; Corresponding pressure detection sensors are also provided before the top catalyst layer of the reactor and at the reactor outlet; The total catalyst pressure drop is obtained by subtracting the pressure before the top catalyst layer of the reactor and at the reactor outlet.
7. The system according to claim 1, wherein: The system is further provided with a flow detection sensor; The flow detection sensor is set at any of the following locations as needed: GGH low-temperature inlet or GGH high-temperature outlet, bypass flue.
8. The system according to claim 3, wherein: The main flue is also equipped with a main inspection valve; Close the main flue valve and main inspection valve, and open the bypass flue valve to 100%, and then perform maintenance on the SCR device without shutting down the system; The main line inspection valve is fully open when not in the inspection state; The main line inspection valve is a regulating valve or a switching valve.