CN111006516A

CN111006516A - Gas boiler flue gas waste heat utilization system

Info

Publication number: CN111006516A
Application number: CN201911343518.4A
Authority: CN
Inventors: 莫军红; 张晓明; 王伟平; 王利平; 马强; 张素娴; 马晓华
Original assignee: Ningxia Jiyuan Juntai New Material Technology Co ltd; Ningxia Jiyuan Metallurgy Group Co ltd
Current assignee: Ningxia Jiyuan Juntai New Material Technology Co ltd; Ningxia Jiyuan Metallurgy Group Co ltd
Priority date: 2019-12-24
Filing date: 2019-12-24
Publication date: 2020-04-14

Abstract

The utility model provides a gas boiler flue gas waste heat utilization system, including gas boiler, high temperature over heater, low temperature over heater, the evaporimeter, higher level economizer, medium temperature SCR, higher level air preheater, low temperature SCR, subordinate economizer, subordinate air preheater, the draught fan, high temperature dilution fan, the ammonia evaporator, ammonia injection system equipment, air compression system, this scheme is provided with higher level economizer simultaneously, medium temperature SCR, higher level air preheater, low temperature SCR, subordinate economizer, subordinate air preheater to make higher level economizer export flue gas temperature rise to more than 300 ℃, show the medium temperature SCR desorption NOx efficiency that promotes, carry the flue gas to further denitration in the low temperature SCR again. Through the arrangement, waste heat in the flue gas is fully utilized, the efficiency of removing NOx by the medium-temperature SCR and the low-temperature SCR is greatly improved, the long-term stable standard emission of the flue gas is ensured, the whole denitration process is more efficient, safe and reliable, and good economic benefits are achieved.

Description

Gas boiler flue gas waste heat utilization system

Technical Field

The invention relates to the technical field of flue gas waste heat recovery, in particular to a gas boiler flue gas waste heat utilization system.

Background

With the national and local discharge of special emission standards of NOx, the NOx generated in the production process of ferroalloy enterprises becomes a serious factor in the standard emission of tail gas. After the gas boiler burns tail gas conveyed from the submerged arc furnace, the temperature of the flue gas at the outlet of the gas boiler is high, the temperature is still high after heat exchange is carried out through a high-temperature superheater, a low-temperature superheater and a boiler evaporator, the temperature is usually above 500 ℃, then the flue gas is sequentially subjected to denitration through an economizer and a medium-temperature SCR, but in the actual operation process, the temperature of the flue gas at the outlet of the upper-level economizer is usually between 240 ℃ and 280 ℃, and the denitration activity temperature of the medium-temperature SCR is 400 ℃, so that the denitration effect of the medium-temperature SCR is poor, NOx in the flue gas continuously exceeds the standard after denitration through the medium-temperature SCR, and even if the low-temperature SCR is arranged in the subsequent process, the NOx in the flue gas still exceeds the standard and is difficult to.

Disclosure of Invention

In view of the above, it is necessary to provide a system for utilizing waste heat of flue gas of a gas boiler.

A gas boiler flue gas waste heat utilization system comprises a gas boiler, a high-temperature superheater, a low-temperature superheater, a boiler evaporator, a higher-level economizer, a medium-temperature SCR, a higher-level air preheater, a low-temperature SCR, a lower-level economizer, a lower-level air preheater, an induced draft fan, a high-temperature dilution fan, an ammonia water evaporator, ammonia injection system equipment and an air compression system, wherein the high-temperature superheater, the low-temperature superheater and the boiler evaporator are sequentially arranged on a flue of a gas outlet of the gas boiler, an ammonia injection grid is arranged right above the higher-level economizer, one end of the higher-level economizer is connected with the boiler evaporator, the medium-temperature SCR, the higher-level air preheater, the low-temperature SCR, the lower-level economizer and the lower-level air preheater are sequentially arranged right below the other end of the economizer, one end of the induced draft fan is connected with the lower-level air preheater, the other end of the induced draft fan is connected with an external chimney, a first inlet of the ammonia water, the first outlet of the ammonia water evaporator is connected with a flue between a superior economizer and a boiler evaporator, the ammonia injection system equipment is connected with the second inlet of the ammonia water evaporator, and the air compression system is connected with the second inlet of the ammonia water evaporator.

Preferably, the high-temperature superheater is a coiled tube type heat exchanger, the low-temperature superheater is a coiled tube type heat exchanger, and the boiler evaporator is a fin tube type boiler evaporator.

Preferably, the number of the finned tubes in the upper-stage economizer is 1/3-1/2 of the number of the finned tubes in the lower-stage economizer.

Preferably, the inlet flue gas temperature of the upper-stage economizer is T1, the T1 is 500-560 ℃, the outlet flue gas temperature of the upper-stage economizer is T2, the T2 is 300-400 ℃, the outlet flue gas temperature of the upper-stage air preheater is T3, the T3 is 240-280 ℃, the outlet flue gas temperature of the lower-stage economizer is T4, the T4 is 160-180 ℃, the outlet flue gas temperature of the lower-stage air preheater is T5, and the T5 is 115-125 ℃.

The scheme is simultaneously provided with an upper-level economizer, a medium-temperature SCR, an upper-level air preheater, a low-temperature SCR, a lower-level economizer and a lower-level air preheater, the number of fin tubes in the upper-level economizer is set to be 1/3-1/2 of the number of the fin tubes of the lower-level economizer so as to reduce the heat exchange efficiency of the upper-level economizer to the T1-temperature flue gas, the temperature of the flue gas at the outlet of the upper-level economizer is stabilized to be above 280 ℃, the high-efficiency removal of NOx in the T2-temperature flue gas by the medium-temperature SCR is ensured, the NOx removal efficiency of the medium-temperature SCR is remarkably improved, the T2-temperature flue gas after the medium-temperature SCR is conveyed to the upper-level air preheater for heat exchange, the temperature T3 at the outlet of the upper-level air preheater is 240 plus 280 ℃, then the T3-temperature flue gas is conveyed to the low-temperature SCR for further denitration. Through the setting, boiler overall structure and performance remain unchanged basically, and the thermal efficiency is not influenced, and waste heat in both make full use of flue gas obviously promotes medium temperature SCR entry flue gas temperature, low temperature SCR entry flue gas temperature again, improves medium temperature SCR, low temperature SCR desorption NOx efficiency by a wide margin, ensures that the flue gas is stable discharge to reach standard for a long time, and whole denitration process is more high-efficient, safe, reliable, has good economic benefits.

Drawings

FIG. 1 is a schematic diagram of a gas boiler flue gas waste heat utilization system.

FIG. 2 is a schematic view of a partial connection for flue gas denitration according to the present disclosure.

FIG. 3 is a schematic view of a partial connection for denitration of flue gas in a normal case.

In the figure: the system comprises a gas boiler 11, a high-temperature superheater 12, a low-temperature superheater 13, a boiler evaporator 14, an upper-stage economizer 15, a medium-temperature SCR16, an upper-stage air preheater 17, a low-temperature SCR18, a lower-stage economizer 19, a lower-stage air preheater 20, an induced draft fan 21, an ammonia water evaporator 22, an ammonia injection system device 23, an air compression system 24 and a high-temperature dilution fan 25.

Detailed Description

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.

Referring to fig. 1 and 2, the invention provides a gas boiler flue gas waste heat utilization system, which comprises a gas boiler 11, a high-temperature superheater 12, a low-temperature superheater 13, a boiler evaporator 14, an upper coal economizer 15, a medium-temperature SCR16, an upper air preheater 17, a low-temperature SCR18, a lower coal economizer 19, a lower air preheater 20, an induced draft fan 21, an ammonia evaporator 22, ammonia injection system equipment 23, an air compression system 24 and a high-temperature dilution fan 25, wherein the high-temperature superheater 12, the low-temperature superheater 13 and the boiler evaporator 14 are sequentially arranged on a flue of a flue gas outlet of the gas boiler 11, an ammonia injection grid is arranged right above the upper coal economizer 15, one end of the upper coal economizer 15 is connected with the boiler evaporator 14, the medium-temperature SCR16, the upper air preheater 17, the low-temperature SCR18, the lower coal economizer 19 and the lower air preheater 20 are sequentially arranged right below the other end of the upper coal economizer 15, draught fan 21 one end is connected with subordinate air preheater 20, the draught fan 21 other end is connected with outside chimney, the first entry of ammonia evaporator 22 is connected with higher level economizer 15 one side through high temperature dilution fan 25, the first export of ammonia evaporator 22 is connected through the flue between ammonia injection grid and higher level economizer 15, boiler evaporator 14, ammonia

injection system equipment

23 and 22 second entry linkage of ammonia evaporator,

air compression system

24 and 22 second entry linkage of ammonia evaporator.

Specifically, the high-temperature superheater 12 absorbs high-temperature heat in flue gas at the outlet of the gas boiler 11 and further heats saturated steam from the low-temperature superheater 13, one end of the high-temperature superheater 12 is connected with a steam turbine through a main steam pipeline to convey the superheated steam to the steam turbine for power generation, the low-temperature superheater 13 absorbs heat in the flue gas after heat exchange through the high-temperature superheater 12 and further heats the saturated steam from a steam drum, the boiler evaporator 14 absorbs heat in the flue gas after heat exchange through the low-temperature superheater 13 and heats hot water from the upper-level economizer 15 into saturated steam, after heat exchange is performed on the heat in the flue gas at the outlet of the gas boiler 11 through the high-temperature superheater 12, the low-temperature superheater 13 and the boiler evaporator 14, the inlet flue gas temperature T1 of the upper-level economizer 15 is 560 ℃., the economizer 15 absorbs heat in the flue gas at the temperature T1, the hot water from the lower economizer 19 is further heated, the temperature T2 of the flue gas at the outlet of the upper economizer 15 is 300-400 ℃ after the heat exchange of the flue gas with the temperature T1 is carried out by the upper economizer 15, the flue gas with the temperature is conveyed to the intermediate-temperature SCR16 for denitration, the high-efficiency removal of NOx in the flue gas can be realized because the temperature T2 of the flue gas is just in the range of the high-efficiency denitration activity temperature of the intermediate-temperature SCR16 catalyst, the flue gas after the NOx removal by the intermediate-temperature SCR16 is conveyed to the upper air preheater 17, the upper air preheater 17 absorbs the heat in the flue gas after the NOx removal by the intermediate-temperature SCR, the temperature T3 of the flue gas at the outlet of the upper air preheater 17 is 240-280 ℃, the flue gas with the temperature is conveyed to the low-temperature SCR18 for carrying out the denitration, the temperature of the flue gas is just in the range of the higher activity temperature of the low-temperature denitration catalyst, the residual NOx in the flue gas is further removed by the SCR18, and, the lower-level economizer 19 absorbs heat in flue gas with the temperature of T3, cold water in the lower-level economizer 19 is heated into hot water, the temperature T4 of flue gas at the outlet of the lower-level economizer 19 is 160- On the ammonia injection grid in the flue, rethread static mixer makes ammonia saturated steam and the 15 entry flue gas intensive mixings of higher level economizer, it includes ammonia water spray gun, ammonia water main pipe and a plurality of aqueous ammonia branch pipes, ammonia water pump, aqueous ammonia regulation distributor, PLC the control unit etc. of connecting on the pipeline to spout ammonia system equipment 23, spout ammonia system equipment 23 and carry the aqueous ammonia to the aqueous ammonia evaporimeter 22 second entry in, air compression system 24 is air compressor, with air transport to the aqueous ammonia evaporimeter 22 second entry in to make aqueous ammonia and air intensive mixing, in order to improve aqueous ammonia atomization effect, increase the evaporation rate of moisture in the aqueous ammonia.

Under normal conditions, the number of the finned tubes in the upper economizer 15 is the same as that of the finned tubes in the lower economizer 19, the upper economizer 15 absorbs the temperature in the flue gas after heat exchange by the boiler evaporator 14, the outlet flue gas temperature T2' of the upper economizer 15 is usually 240-280 ℃, the requirement of the medium-temperature SCR16 catalyst for the activity temperature of 280-400 ℃ is difficult to meet, the NOx removal efficiency of the medium-temperature SCR16 is low, and the NOx emission in the flue gas exceeds the standard, in order to solve the problem, the scheme is simultaneously provided with the upper economizer 15, the medium-temperature SCR16, the upper air preheater 17, the low-temperature SCR18, the lower economizer 19 and the lower air preheater 20, the number of the finned tubes in the upper economizer 15 is set to be 1/3-1/2 of the number of the finned tubes of the lower economizer 19, so as to reduce the heat exchange efficiency of the upper economizer 15 on the T1 temperature flue gas, and further to enable the outlet flue gas temperature T2 of the upper economizer 15 to rise to be above 300 ℃, ensuring that the middle-temperature SCR16 efficiently removes NOx in flue gas with the temperature of T2, remarkably improving the efficiency of removing NOx by the middle-temperature SCR16, conveying the flue gas with the temperature of T2 subjected to middle-temperature SCR16 into the upper-level air preheater 17 for heat exchange, conveying the flue gas with the temperature of T3 at the outlet of the upper-level air preheater 17 into the low-temperature SCR18 for further denitration, thereby realizing the standard reaching emission of NOx in the flue gas, conveying the flue gas with the temperature of T3 subjected to low-temperature SCR18 into the lower-level economizer 19, wherein the temperature of T3 at the inlet of the lower-level economizer 19 is remarkably increased, is higher than 60 ℃ than the temperature of T3 ' at the inlet under the normal condition, the temperature of T4 at the outlet of the lower-level economizer 19 is within 10 ℃ of the temperature of T4 ' at the outlet of the lower-level economizer 19, the temperature of T48 at the inlet of the lower-level economizer 19 is higher than the temperature of T4 at the outlet of the lower-level economizer by more than 85 ℃ at the temperature of the inlet of the lower-level economizer under the lower-level economizer (about 40 ') of the lower-, the heat exchange efficiency of the lower-level economizer 19 is remarkably improved, the temperature T4 of the flue gas at the outlet of the lower-level economizer 19 is 160-180 ℃, the flue gas with the temperature T4 after heat exchange by the lower-level economizer 19 is conveyed into the lower-level air preheater 20, and the temperature T5 of the flue gas at the outlet of the lower-level air preheater 20 is equivalent to the temperature T5' of the flue gas at the outlet of the lower-level air preheater 20 under the normal condition.

Further, the high-temperature superheater 12 is a serpentine tube heat exchanger, the low-temperature superheater 13 is a serpentine tube heat exchanger, and the boiler evaporator 14 is a fin tube boiler evaporator.

Further, the number of the finned tubes in the upper-stage economizer 15 is 1/3-1/2 of the number of the finned tubes in the lower-stage economizer 19, so that the heat exchange efficiency of the upper-stage economizer 15 is reduced, and the temperature T2 of the flue gas at the outlet of the upper-stage economizer 15 is further improved.

Further, the inlet flue gas temperature of the upper-stage economizer 15 is T1, the T1 is 500-.

Example 1:

referring to fig. 3, in a normal situation, the number of the fin tubes in the upper-stage economizer 15 is the same as the number of the fin tubes in the lower-stage economizer 19, the inlet flue gas temperature T1' of the upper-stage economizer 15 is 500-, preferably, the temperature T3 ' is 204 ℃, the temperature T3 ' flue gas is delivered to the low-temperature SCR18 for denitration, the catalyst activity temperature in the low-temperature SCR18 is greater than 200 ℃, and the temperature T3 ' is only between 200 and 210 ℃, so that the denitration efficiency of the low-temperature SCR18 is low, NOx in the flue gas still exceeds the standard after denitration by the medium-temperature SCR16 and the low-temperature SCR18, the temperature T3 ' flue gas with NOx removed by the low-temperature SCR18 is delivered to the lower-level economizer 19, the temperature T4 ' at the outlet of the lower-level economizer 19 is 155 and 165 ℃, preferably, the temperature T4 ' is 163 ℃, the difference between the temperature T3 ' at the inlet of the lower-level economizer 19 and the temperature T4 ' at the outlet thereof is 41 ℃, the temperature T4 ' flue gas is delivered to the lower-level air preheater 20 for heat exchange, the temperature T5 ' at the outlet of the lower-level air preheater 20 is 105 and 115 ℃, and preferably, the temperature T5 ' is 110 ℃.

Example 2:

referring to fig. 2, in the present application, the number of fin tubes in the upper economizer 15 is 1/3-1/2 of the number of fin tubes in the lower economizer 19, the inlet flue gas temperature T1 of the upper economizer 15 is 500-560 ℃, preferably, the temperature T1 is 527 ℃, the outlet flue gas temperature T2 of the upper economizer 15 is 300-400 ℃, preferably, the temperature T2 is 353 ℃, the difference between the inlet flue gas temperature T1 of the upper economizer 15 and the outlet flue gas temperature T2 thereof is 174 ℃, when the flue gas with the temperature T2 is conveyed to the intermediate-temperature SCR16, the temperature of the flue gas with the temperature T2 is within the active temperature range of the intermediate-temperature catalyst, the efficiency of the SCR16 for removing NOx is remarkably improved, the NOx content of the flue gas conveyed to the low-temperature SCR18 subsequently is remarkably reduced, the flue gas with the temperature T2 of the flue gas removed by the intermediate-temperature SCR16 is conveyed to the upper air preheater 17, and the air preheater 17 absorbs the heat in the flue gas with the temperature T2, the outlet flue gas temperature T3 is 240-280 ℃, preferably, the T3 is 264 ℃, the T3 temperature flue gas is conveyed to the low-temperature SCR18 for denitration, the T3 flue gas temperature is within the low-temperature catalyst activity temperature range, the NOx removal efficiency of the low-temperature SCR18 is obviously improved, so that the high-efficiency removal of NOx in the flue gas is realized, the NOx in the flue gas meets the emission standard, the T3 temperature flue gas subjected to NOx removal through the low-temperature SCR18 is conveyed to the lower-level economizer 19, the outlet flue gas temperature T4 of the lower-level economizer 19 is 160-180 ℃, preferably, the T4 is 176 ℃, the difference between the inlet flue gas temperature T3 of the lower-level economizer 19 and the outlet flue gas temperature T4 is 88 ℃, the outlet flue gas temperature T4 temperature flue gas is conveyed to the lower-level air preheater 20 for heat exchange, the outlet flue gas temperature T5 of the lower-level air preheater 20 is 115-125 ℃, preferably, and the T5 is 120.

In the embodiment, the difference between the inlet flue gas temperature T1 of the upper-level economizer 15 and the outlet flue gas temperature T2 is 174 ℃, while the difference between the inlet flue gas temperature T1 'of the upper-level economizer 15 and the outlet flue gas temperature T2' of the upper-level economizer 15 in the embodiment 1 is 262 ℃, so that the heat exchange efficiency of the upper-level economizer 15 in the embodiment is obviously lower than that of the upper-level economizer 15 in the embodiment 1, but the outlet flue gas temperature T2 of the upper-level economizer 15 is increased to 353 ℃, and is just in the active temperature range of the medium-temperature catalyst, so that the denitration efficiency of the medium-temperature SCR16 is greatly improved, and the problem of low denitration efficiency of the medium-temperature SCR16 at present is solved; in the embodiment, the flue gas temperature T3 at the inlet of the low-temperature SCR18 is 264 ℃, the flue gas temperature T3 'at the inlet of the low-temperature SCR18 in the embodiment 1 is 204 ℃, and the flue gas temperature T3 is obviously higher than that of T3', so that the NOx removal efficiency of the low-temperature SCR18 is obviously improved; in this embodiment, the difference between the inlet flue gas temperature T3 of the lower-stage economizer 19 and the outlet flue gas temperature T4 thereof is 88 ℃, while the difference between the inlet flue gas temperature T3 'of the lower-stage economizer 19 and the outlet flue gas temperature T4' thereof in embodiment 1 is 41 ℃, and the heat exchange efficiency of the lower-stage economizer 19 in this embodiment is obviously higher than that of the lower-stage economizer 19 in embodiment 1, so that the recovery and reuse of the waste heat in the flue gas with the temperature of T3 by the lower-stage economizer 19 are obviously improved; through the arrangement, the waste heat in the flue gas with the temperature of T1 is fully utilized, the flue gas temperature T2 at the inlet of the medium-temperature SCR16 and the flue gas temperature T3 at the inlet of the low-temperature SCR18 are obviously improved, the NOx removal efficiency of the medium-temperature SCR16 and the low-temperature SCR18 is greatly improved, the long-term stable standard emission of the flue gas is ensured, the whole denitration process is safer and more reliable, and good economic benefits are achieved.

The modules or units in the device of the embodiment of the invention can be combined, divided and deleted according to actual needs.

While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims

1. A gas boiler flue gas waste heat utilization system which characterized in that: the system comprises a gas boiler, a high-temperature superheater, a low-temperature superheater, a boiler evaporator, an upper coal economizer, a medium-temperature SCR, an upper air preheater, a low-temperature SCR, a lower coal economizer, a lower air preheater, an induced draft fan, a high-temperature dilution fan, an ammonia water evaporator, ammonia injection system equipment and an air compression system, wherein the high-temperature superheater, the low-temperature superheater and the boiler evaporator are sequentially arranged on a flue of a flue gas outlet of the gas boiler, an ammonia injection grid is arranged right above the upper coal economizer, one end of the upper coal economizer is connected with the boiler evaporator, the medium-temperature SCR, the upper air preheater, the low-temperature SCR, the lower coal economizer and the lower air preheater are sequentially arranged right below the other end of the upper coal economizer, one end of the induced draft fan is connected with the lower air preheater, the other end of the induced draft fan is connected with an external chimney, a first inlet of the ammonia water evaporator is connected with one side of the upper, the first outlet of the ammonia water evaporator is connected with a flue between a superior economizer and a boiler evaporator, the ammonia injection system equipment is connected with the second inlet of the ammonia water evaporator, and the air compression system is connected with the second inlet of the ammonia water evaporator.

2. The gas boiler flue gas waste heat utilization system of claim 1, characterized in that: the high-temperature superheater is a coiled tube type heat exchanger, the low-temperature superheater is a coiled tube type heat exchanger, and the boiler evaporator is a fin tube type boiler evaporator.

3. The gas boiler flue gas waste heat utilization system of claim 1, characterized in that: the number of the finned tubes in the upper-stage economizer is 1/3-1/2 of the number of the finned tubes in the lower-stage economizer.

4. The gas boiler flue gas waste heat utilization system of claim 1, characterized in that: the inlet flue gas temperature of the upper economizer is T1, the T1 is 500-plus 560 ℃, the outlet flue gas temperature of the upper economizer is T2, the T2 is 300-plus 400 ℃, the outlet flue gas temperature of the upper air preheater is T3, the T3 is 240-plus 280 ℃, the outlet flue gas temperature of the lower economizer is T4, the T4 is 160-plus 180 ℃, the outlet flue gas temperature of the lower air preheater is T5, and the T5 is 115-plus 125 ℃.