Regulating system for inlet temperature of flue gas denitration device of biomass boiler

Abstract

The invention discloses a biomass boiler flue gas denitration device inlet temperature adjusting system which comprises a second flue, a third flue and a fourth flue which are sequentially connected with an outlet of a hearth and are vertically arranged, an inlet of the second flue is connected with the outlet of the hearth, the second flue is communicated with the lower end of the third flue, and the fourth flue is communicated with the outlet of the hearth. The upper end of the third flue is connected with the upper end of the fourth flue through a furnace top turning flue, a temperature adjusting heat exchanger capable of reducing the temperature of flue gas, an evaporator and / or a superheater are sequentially arranged in the third flue, and a denitration device and a tail heating surface are arranged in the fourth flue. A dust remover is arranged in the furnace top turning flue, and a bypass flue capable of increasing the smoke temperature is arranged between the top of the hearth and the dust remover front flue. The boiler DCS system controls the opening degree of the regulating valve or the opening degree of the flue gas baffle according to the temperature, measured by the thermocouple, of the flue gas entering the denitration device, so that the temperature of the flue gas entering the denitration device can be regulated and controlled, and the denitration device is always in the optimal denitration temperature interval.

Description

Technical Field

[0001] The invention relates to the technical field of boilers, and in particular to a biomass-burning grate-type biomass boiler. Background Art

[0002] As an important equipment for biomass energy utilization, biomass boilers are boilers that burn biomass directly as fuel and are widely used in heating, industrial production, power generation and other fields. Biomass boilers use a variety of fuels with complex components. Compared with traditional coal-fired boilers, biomass fuels have a higher nitrogen content, so its combustion produces more nitrogen oxide (NOx) pollutants than coal-fired boilers. Nitrogen oxides are key atmospheric pollutants that directly or indirectly harm the environment, buildings, animals, plants, and humans. Therefore, before emission, the flue gas needs to be denitrated to reduce the NOx in the gas and ensure the safety of the emission gas. The current technical means for treating NOx mainly include in-furnace ammonia spray denitrification (SNCR) and catalytic reduction denitrification (SCR). Relatively speaking, the SNCR denitrification process is less efficient and needs to be arranged in the high-temperature flue gas area. Due to the particularity of the biomass boiler structure, the overall furnace bed temperature is low, generally between 700℃-800℃, and the optimal temperature window for the SNCR denitrification process is 850℃-1050℃, so the SNCR temperature window is not suitable, resulting in very low efficiency or even no effect, and the ammonia consumption is far greater than the theoretical value, which is not economical. The SCR denitrification process technology is relatively mature and reliable, and can meet the requirements of ultra-low emissions. However, it is greatly affected by the size of the boiler load and the change of the fuel type, resulting in unstable SCR denitrification efficiency. Due to the activity of the catalyst and other reasons, its operating temperature is generally 320℃~380℃. Under low load or when burning low calorific value fuel, the flue gas temperature at the SCR inlet cannot reach the flue gas temperature required by the catalyst, resulting in low catalytic reduction reaction efficiency and other problems. Some designers set a steam heater at the SCR inlet to heat the SCR inlet flue gas temperature to the activation temperature of the catalyst, thereby improving the catalyst activity and the SCR denitrification reaction efficiency, and then recover the heat through the heat exchanger, which requires the addition of a heat exchanger. The process consumes a lot of energy and heat to heat the flue gas. Therefore, such a flue gas denitrification system has a complex structure, high investment cost, and needs to consume steam during operation, and the operating cost is high. However, at high load, there will be a problem of too high flue gas temperature at the SCR inlet, and the flue gas temperature cannot be met either. The denitrification system has to be shut down, resulting in excessive NOx emissions. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a system for regulating the inlet temperature of a biomass boiler flue gas denitration device to solve the problems existing in the background technology.

[0004] The technical solution adopted by the present invention to achieve the above-mentioned purpose is: A system for regulating the inlet temperature of a flue gas denitrification device of a biomass boiler comprises a boiler DCS control system, a furnace, a second flue, a third flue and a fourth flue which are sequentially connected to the outlet of the furnace, the second flue, the third flue and the fourth flue are all arranged vertically, the inlet of the second flue is connected to the outlet of the furnace, the second vertical flue is connected to the lower end of the third vertical flue, the upper ends of the third flue and the fourth flue are connected through a furnace top turning flue, an evaporator and / or a superheater are arranged in the third flue, a denitrification device and a tail heating surface are sequentially arranged in the fourth flue according to the direction of flue gas flow; a dust collector is arranged in the furnace top turning flue, and the dust collector divides the furnace top turning flue into a flue before the dust collector and a flue before the denitrification device, and is characterized in that: a temperature regulating heat exchanger capable of reducing the flue gas temperature is arranged in the third flue and located above the evaporator and the superheater, and a bypass flue capable of increasing the flue gas temperature is arranged between the top of the furnace and the flue before the dust collector.

[0005] In the above-mentioned biomass boiler flue gas denitrification device inlet temperature regulation system, a flue gas damper is provided in the bypass flue, the flue gas damper is connected to the electric actuator, and the electric actuator is connected to the boiler DCS control system; a water channel and a flue gas channel are provided in the temperature regulating heat exchanger, and the flue gas in the third flue can pass through the flue gas channel; the inlet end of the water channel is connected to the water inlet pipe, and the outlet end of the water channel is connected to the water outlet pipe; the water inlet pipe is provided with a water inlet pipe valve, and the water outlet pipe is provided with a water outlet pipe valve, and the water inlet pipe valve and the water outlet pipe valve are both connected to the boiler DCS control system.

[0006] In the above-mentioned biomass boiler flue gas denitrification device inlet temperature regulating system, the heat source medium of the temperature regulating heat exchanger is flue gas, and the heat receiving medium is water.

[0007] In the above-mentioned biomass boiler flue gas denitrification device inlet temperature regulating system, the heat source medium of the temperature regulating heat exchanger is flue gas, and the heated medium can also be heat exchange oil or other heat exchange medium.

[0008] Furthermore, a temperature control circuit is connected between the water inlet pipe and the water outlet pipe, a regulating valve is arranged in the temperature control circuit, and the regulating valve is connected to the boiler DCS control system.

[0009] By adopting the above technical solution, a bypass flue is set between the top of the furnace and the flue before the dust collector. The flue gas entering from the third flue and the bypass flue is first dedusted by the dust collector, and the dust-free flue gas then enters the denitrification device for reaction, so as to avoid the denitrification device being affected by the alkali metals in the fly ash, which may cause the catalyst to be poisoned and ineffective. In the third flue, a thermostatic heat exchanger is set at the upper part of the evaporator and the superheater. The thermocouple set in the flue before the denitrification device feeds back the measured flue gas temperature to the boiler DCS system. After being processed by the boiler DCS system, the boiler DCS system can control the opening of the regulating valve or the opening of the flue gas damper, thereby adjusting the flue gas temperature entering the denitrification device, so that the denitrification device is always in the optimal denitrification temperature range. By closing the water inlet pipe valve and the water outlet pipe valve, the thermostatic heat exchanger can be exited from the thermostatic operation, and by closing the flue gas damper, the bypass flue can be exited from the thermostatic operation.

[0010] In the above-mentioned biomass boiler flue gas denitrification device inlet temperature regulating system, the tail heating surface is the heating surface of the economizer and the air preheater.

[0011] Furthermore, a thermocouple is provided in the flue before the denitration device, and the thermocouple is connected to the boiler DCS control system.

[0012] By adopting the above technical solution, the boiler DCS control system receives the flue gas temperature entering the denitrification device measured by the thermocouple, and can control the opening of the flue gas damper and the water inlet pipe valve / water outlet pipe valve / regulating valve, thereby regulating the flue gas temperature entering the denitrification device. Beneficial Effects

[0013] A bypass flue is arranged between the top of the furnace and the flue in front of the dust collector. The flue gas entering from the third flue and the bypass flue is firstly removed by the dust collector, and the dust-free flue gas then enters the denitrification device for reaction, so as to avoid the denitrification device being affected by the alkali metals in the fly ash, which may cause the catalyst to be poisoned and ineffective. A temperature-regulating heat exchanger is arranged in the third flue, located above the evaporator and the superheater. The thermocouple arranged in the flue in front of the denitrification device feeds back the measured flue gas temperature to the boiler DCS system. After being processed by the boiler DCS system, the boiler DCS system can control the opening of the regulating valve or the opening of the flue gas damper, so as to adjust the flue gas temperature entering the denitrification device, so that the denitrification device is always in the optimal denitrification temperature range, meeting the requirements of the SCR denitrification reaction; it solves the problem that the boiler combustion condition is unstable due to factors such as fuel changes, and the flue gas temperature at the SCR inlet does not meet the flue gas temperature required by the catalyst due to the size of the boiler load, resulting in low catalytic reduction reaction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the present invention.

[0015] In the figure: 1 furnace, 2 bypass flue, 3 flue gas damper, 4 boiler DCS control system, 5 second flue, 6 superheater, 7 evaporator, 8 third flue, 9 temperature control heat exchanger, 10 flue before dust collector, 11 dust collector, 12 thermocouple, 13 flue before denitrification device, 14 water inlet pipe, 14-1 water inlet pipe valve, 15 water outlet pipe, 15-1 water outlet pipe valve, 16 temperature control circuit, 16-1 regulating valve, 17 denitrification device, 18 fourth flue, 19 economizer 2, 20 secondary air preheater, 21 primary air preheater, 22 economizer 1, 23 flue gas outlet. DETAILED DESCRIPTION

[0016] In order to clearly illustrate the technical features of the present invention, the present invention is further described below through non-limiting embodiments in conjunction with the accompanying drawings. Embodiment 1:

[0017] Please see Figure 1 A biomass boiler flue gas denitrification device inlet temperature regulating system comprises a boiler DCS control system 4, a furnace 1, a second flue 5, a third flue 8, and a fourth flue 18 connected to the outlet of the furnace 1 in sequence, the second flue 5, the third flue 8, and the fourth flue 18 are all arranged vertically, the inlet of the second flue 5 is connected to the outlet of the furnace 1, the second flue 5 is connected to the lower end of the third flue 8, the upper end of the third flue 8 is connected to the fourth flue 18 through a furnace top turning flue, and a superheater 6 and an evaporator 7 are arranged in sequence in the third flue 8 according to the flue gas flow direction; the fourth flue 1 8 is arranged in sequence according to the direction of flue gas flow. In the present embodiment, the rear heating surface is the heating surface of the economizer and the air preheater. In the fourth flue 18, a denitrification device 17, an economizer 2 19, a secondary air preheater 20, a primary air preheater 21 and an economizer 1 22 are arranged in sequence according to the direction of flue gas flow. A dust collector 11 is arranged in the furnace top turning flue, and the dust collector 11 divides the furnace top turning flue into a dust collector front flue 10 and a denitrification device front flue 13. A thermocouple 12 is arranged in the denitrification device front flue 13, and the thermocouple 12 is connected to the boiler DCS control system 4.

[0018] A thermostatic heat exchanger 9 is arranged in the third flue 8, located above the evaporator 7. A water channel and a flue gas channel are arranged in the thermostatic heat exchanger 9. The flue gas in the third flue 8 can pass through the flue gas channel. The heat source medium of the thermostatic heat exchanger 9 is flue gas, and the heat medium is water. The heating surface of the thermostatic heat exchanger 9 absorbs the heat in the flue gas to heat the water and reduce the flue gas temperature. The inlet end of the water channel is connected to the water inlet pipe 14, and the outlet end of the water channel is connected to the water outlet pipe 15. The water inlet pipe 14 is provided with a water inlet pipe valve, and the water outlet pipe 15 is provided with a water outlet pipe valve. The water inlet pipe valve 14-1 and the water outlet pipe valve are both connected to the boiler DCS control system 4. A thermostatic circuit 16 is connected between the water inlet pipe 14 and the water outlet pipe 15. A regulating valve 16-1 is arranged in the thermostatic circuit 16, and the regulating valve 16-1 is connected to the boiler DCS control system 4. In this embodiment, the heated working medium is water, which can be circulating water inside the boiler or water from other external sources. For unconventional designs, other heat exchange media such as heat transfer oil can also be used according to the user's process flow.

[0019] A bypass flue 2 is arranged between the top of the furnace 1 and the dust collector front flue 10 , a flue gas damper 3 is arranged in the bypass flue 2 , the flue gas damper 3 is connected to an electric actuator, and the electric actuator is connected to a boiler DCS control system 4 .

[0020] Boiler flue gas process: The flue gas passes through the furnace 1, the second flue gas channel, and the third flue gas channel in sequence. In the third flue gas channel, it flushes the superheater 6, the evaporator 7, and the temperature-regulating heat exchanger 9 in sequence, and then enters the tail convection heating surface through the furnace top turning flue. The flue gas is dedusted by the dust collector 11 in the turning flue. On the tail convection heating surface, it passes through the denitrification device 17, the economizer 2 19, the secondary air preheater 20, the primary air preheater 21, and the economizer 1 22 in sequence, and then is discharged from the flue gas outlet 23.

[0021] Flue gas temperature control principle: When the flue gas temperature rises due to the burning of fuel with a high calorific value or the burning is more intense or the boiler load is higher or other reasons, the thermocouple 12 arranged in the flue 13 before the denitrification device will measure the flue gas temperature entering the denitrification device 17 in real time, and feed it back to the boiler DCS control system through the signal cable. When the flue gas temperature in the flue 13 before the denitrification device exceeds the design value, the boiler DCS control system will display an alarm, and at the same time, the boiler DCS control system will control the water inlet pipe valve 14-1, the water outlet pipe valve, and the regulating valve 16-1 to all open (It can also be opened manually) to increase the flow rate of the heat-absorbing medium entering the temperature-regulating heat exchanger 9, thereby increasing its heat absorption and reducing the flue gas temperature; when the thermocouple 12 measures that the flue gas temperature in the flue 13 before the denitrification device has dropped to the designed range, the signal is fed back to the boiler DCS control system through the signal cable, and the boiler DCS control system controls the regulating valve 16-1 to reduce the opening (it can also be adjusted manually) to ensure that the flow rate of the heat-absorbing medium entering the temperature-regulating heat exchanger 9 is appropriate, thereby stably controlling the flue gas temperature in the flue 13 before the denitrification device and maximizing the reaction efficiency of the denitrification device 17.

[0022] When the boiler furnace 1 burns fuel with low calorific value or the combustion condition is poor or the boiler load is low or other reasons cause the flue gas temperature to drop (such as when the boiler is started or shut down), the thermocouple 12 arranged on the flue 13 in front of the denitrification device will measure the flue gas temperature entering the denitrification device 17 in real time, and feed it back to the boiler DCS control system through the signal cable. When the flue gas temperature in the flue 13 in front of the denitrification device is lower than the design value, the boiler DCS control system will display an alarm, and at the same time, the boiler DCS system controls the water inlet pipe valve 14-1 and the water outlet pipe valve to be completely closed (can also be closed manually); then the boiler DCS control The system controls the flue gas damper 3 on the bypass flue 2 to open, and directly introduces the high-temperature flue gas in the furnace 1 into the flue 10 before the dust collector, and increases the flue gas temperature in the flue 10 before the dust collector by adding a large amount of high-temperature flue gas; when the thermocouple 12 measures that the flue gas temperature in the flue 13 before the denitrification device has risen to the designed range, the signal is fed back to the boiler DCS control system through the signal cable, and the boiler DCS control system controls the flue gas damper 3 to reduce the opening (it can also be adjusted manually) to reduce the high-temperature flue gas entering the flue 10 before the dust collector, thereby stably controlling the flue gas temperature in the flue 13 before the denitrification device, and the reaction efficiency of the denitrification device 17 is the highest. Embodiment 2:

[0023] Based on the inlet temperature regulation system of a biomass boiler flue gas denitrification device in the first embodiment, the heat source medium of the temperature regulating heat exchanger 9 is flue gas, and the heat receiving medium is heat exchange oil. Of course, other heat exchange mediums can also be used. The rest of the structure is the same as the first embodiment.

[0024] Unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] Except for the technical features described in the specification, all other technical features are known technologies to those skilled in the art.

[0026] The embodiments listed above are only for the purpose of understanding the present invention and are not limitations on the technical solutions described in the present invention. Ordinary technicians in the relevant fields can make various changes or deformations based on the technical solutions described in the claims. All equivalent changes or deformations should be included in the scope of protection of the claims of the present invention.

Claims

1. A biomass boiler flue gas denitrification device inlet temperature regulating system, comprising a boiler DCS control system, a furnace, a second flue, a third flue, and a fourth flue connected to the furnace outlet in sequence, the second flue, the third flue, and the fourth flue are all arranged vertically, the inlet of the second flue is connected to the furnace outlet, the second vertical flue is connected to the lower end of the third vertical flue, the upper ends of the third flue and the fourth flue are connected through a furnace top turning flue, an evaporator and / or a superheater are arranged in the third flue, a denitrification device and a tail heating surface are arranged in sequence in the fourth flue according to the flue gas flow direction; a dust collector is arranged in the furnace top turning flue, and the dust collector divides the furnace top turning flue into a dust collector front flue and a denitrification device front flue, characterized in that: A temperature regulating heat exchanger is arranged in the third flue, located above the evaporator and the superheater, and a bypass flue is arranged between the top of the furnace and the flue before the dust collector.

2. The biomass boiler flue gas denitrification device inlet temperature adjustment system according to claim 1 is characterized in that: A flue gas damper is provided in the bypass flue, the flue gas damper is connected to the electric actuator, and the electric actuator is connected to the boiler DCS control system; a water channel and a flue gas channel are provided in the temperature regulating heat exchanger, and the flue gas in the third flue can pass through the flue gas channel; the inlet end of the water channel is connected to the water inlet pipe, and the outlet end of the water channel is connected to the water outlet pipe; a water inlet pipe valve is provided on the water inlet pipe, and a water outlet pipe valve is provided on the water outlet pipe, and both the water inlet pipe valve and the water outlet pipe valve are connected to the boiler DCS control system.

3. The biomass boiler flue gas denitrification device inlet temperature adjustment system according to claim 2 is characterized in that: The heat source medium of the temperature-regulating heat exchanger is flue gas, and the heated medium is water.

4. The biomass boiler flue gas denitrification device inlet temperature adjustment system according to claim 2 is characterized in that: The heat source medium of the temperature regulating heat exchanger is flue gas, and the heated medium is heat exchange oil or other heat exchange medium.

5. The biomass boiler flue gas denitrification device inlet temperature adjustment system according to claim 2 is characterized in that: A temperature regulating circuit is connected between the water inlet pipe and the water outlet pipe. A regulating valve is arranged in the temperature regulating circuit. The regulating valve is connected to the boiler DCS control system.

6. The biomass boiler flue gas denitrification device inlet temperature adjustment system according to claim 1 is characterized by: The tail heating surface is the heating surface of the economizer and the air preheater.

7. The biomass boiler flue gas denitration device inlet temperature regulating system according to claim 1 or 2 or 3 or 4 or 5 or 6, characterized in that: A thermocouple is arranged in the flue before the denitration device, and the thermocouple is connected to the boiler DCS control system.

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