SCR (Selective Catalytic Reduction) denitration system and method for flue gas of oil-gas co-combustion boiler

Abstract

The invention relates to the technical field of flue gas treatment, in particular to an SCR denitration system and method for flue gas of an oil-gas co-combustion boiler. The system comprises a boiler flue, and further comprises a denitration reactor and an ammonia-air mixing device, and a flue gas inlet of the denitration reactor is communicated with a flue gas outlet of the boiler flue; at least one catalyst bed layer is mounted in the denitration reactor, and a steam soot blower assembly and a sound wave soot blower assembly are arranged in the air inlet direction of each catalyst bed layer; the ammonia-air mixing device comprises an ammonia-air mixer, and an air outlet of the ammonia-air mixer is communicated with the boiler flue. The system can perform effective soot blowing on a catalyst bed layer, and prevents viscous substances carried in flue gas of an oil-gas co-combustion boiler from being attached to the surface of a catalyst to affect the activity of the catalyst; the ammonia-air mixing device is communicated with the boiler flue, so that flue gas can be mixed with ammonia gas and air before entering the reactor, and the denitration efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas treatment, and in particular to an SCR denitrification system and method for flue gas from an oil-gas mixed-firing boiler. Background Art

[0002] At present, my country's industrial boilers use coal, and all of them are unwashed raw coal as the main fuel. The combustion conditions of raw coal in the combustion boiler are poor, and the coal quality is changeable. It is difficult for the boiler to operate completely according to the designed fuel, resulting in low boiler thermal efficiency. In addition, coal-fired boilers contain a large amount of ash, which causes serious equipment blockage and wear problems when the boiler flue gas passes through the SCR catalyst bed or the downstream air preheater. With the adjustment of my country's energy structure, the vigorous promotion of coal-to-gas, coal-to-oil, and new energy development, boilers mainly using oil and gas will become an inevitable trend. Oil and gas boilers have the advantages of high efficiency and low environmental pollution, and are highly favored by people.

[0003] As people pay more attention to the environment, environmental pressure is increasing, and national environmental protection indicators are becoming more and more stringent. Among them, controlling the concentration and emission of nitrogen oxides in boiler flue gas can reduce its pollution to the atmosphere. Nitrogen oxide control technology is divided into various technologies such as low-nitrogen combustion, fuel grading, and flue gas reburning to control the generation of nitrogen oxides. Its purpose is to generate as little nitrogen oxides as possible at the source. However, these methods are far from meeting the requirements of ultra-clean emissions.

[0004] At present, denitrification technology is widely used in coal-fired boilers. The main denitrification technologies for generated nitrogen oxides include selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR) and mixed methods (SCR / SNCR). The most widely used is the selective catalytic reduction (SCR), which has high denitrification efficiency and less ammonia slip. The SCR denitrification method refers to the process of injecting a reducing agent into the flue gas under the action of a catalyst, and selectively catalytically reducing the nitrogen oxides in the flue gas at a temperature of 300-420°C for conventional medium-temperature catalysts to generate harmless nitrogen and water vapor, thereby achieving the purpose of removing nitrogen oxides.

[0005] SCR denitrification technology is widely used in coal-fired boilers in thermal power plants, and its denitrification efficiency is relatively high. However, there are few successful cases of SCR denitrification projects applied to flue gas from oil-gas mixed combustion boilers in China. Especially under 100% heavy oil combustion conditions, VOCs may be produced in the flue gas, which will become liquid and adhere to the catalyst surface at low temperatures. If the soot blowing effect is not good, long-term operation will clog the catalyst, thereby affecting the denitrification efficiency. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide an SCR denitration system and method for flue gas from an oil-gas mixed combustion boiler, so as to solve the problems of liquid VOCs adhering to and clogging the catalyst in the prior art.

[0007] The technical solution of the present invention to solve the above technical problems is as follows:

[0008] The present invention provides an SCR denitration system for flue gas of an oil-gas co-firing boiler, comprising a boiler flue, a denitration reactor and an ammonia-air mixing device, wherein the flue gas inlet of the denitration reactor is connected to the flue gas outlet of the boiler flue;

[0009] At least one catalyst bed is installed in the denitration reactor. Along the flow direction of the flue gas, a steam soot blower assembly and a sonic soot blower assembly are arranged upstream of each catalyst bed; the steam soot blower assembly and the sonic soot blower assembly are installed on the inner wall of the denitration reactor;

[0010] The ammonia-air mixing device comprises an ammonia-air mixer, and the gas outlet of the ammonia-air mixer is communicated with the boiler flue.

[0011] The beneficial effects of the present invention are that a steam soot blower assembly and a sonic soot blower assembly are arranged on the catalyst bed, which can effectively blow soot on the catalyst bed and prevent sticky substances entrained in the flue gas of the oil-gas co-firing boiler from adhering to the catalyst surface and affecting the catalyst activity; the ammonia-air mixing device is connected to the boiler flue, so that the flue gas can be mixed with ammonia and air before entering the reactor, thereby improving the efficiency of denitrification.

[0012] Based on the above technical solution, the present invention can also be improved as follows.

[0013] Further, the steam sootblower assembly includes at least one steam sootblower, and the sonic sootblower assembly includes at least one sonic sootblower.

[0014] The beneficial effect of adopting the above further technical solution is that it can improve the cleaning effect of the catalyst bed and ensure that the activity of the catalyst is not affected.

[0015] Furthermore, the catalyst bed includes a plurality of catalyst modules, and each catalyst module has 22 holes or 25 holes.

[0016] The beneficial effect of adopting the above further technical solution is that it can effectively reduce the catalyst clogging problem caused by VOCs liquid substances.

[0017] Furthermore, an ammonia injection grid is installed in the boiler flue, the ammonia injection grid is connected to the ammonia-air mixer, and the injection direction of the ammonia injection grid is toward the flue gas outlet of the boiler flue.

[0018] The beneficial effect of adopting the above further technical solution is that the ammonia-air mixed gas can be mixed with the flue gas more evenly.

[0019] Furthermore, the ammonia-air mixing device also includes an ammonia buffer tank and a dilution fan assembly, and the air outlet of the ammonia buffer tank and the air outlet of the dilution fan assembly are respectively connected to the air inlet of the ammonia-air mixer.

[0020] The beneficial effect of adopting the above further technical solution is that the ammonia content can be adjusted in real time.

[0021] Furthermore, it also includes a liquid ammonia evaporation device, the gas outlet of which is connected to the ammonia buffer tank; the liquid ammonia evaporation device is also connected to the liquid ammonia storage device and the low-pressure steam pipeline respectively.

[0022] The beneficial effect of adopting the above further technical solution is that ammonia gas can be produced by adopting a liquid ammonia evaporation device.

[0023] Furthermore, it also includes an ammonia recovery main pipe, the inlet of which is connected to the liquid ammonia storage device and the liquid ammonia evaporation device, and the ammonia recovery main pipe includes a first outlet and a second outlet, the first outlet is connected to the ammonia dilution tank, and the second outlet is connected to the boiler flue.

[0024] The beneficial effect of adopting the above further technical solution is that the ammonia recovery main pipe is set as two branches, so that part of the ammonia can be recovered and reused, avoiding the waste of ammonia.

[0025] The present invention also provides an SCR denitration method for flue gas from an oil-gas mixed-firing boiler, which uses the above-mentioned system to perform SCR denitration treatment on the flue gas from the oil-gas mixed-firing boiler, comprising the following steps:

[0026] The ammonia-air mixing device inputs ammonia-air mixed gas into the boiler flue and mixes it with the flue gas from the oil-gas co-firing boiler. The mixed flue gas enters the denitration reactor and passes through the catalyst bed to undergo a denitration reaction. The steam soot blower assembly and the sonic soot blower assembly are opened or closed according to the temperature in the denitration reactor and the pressure drop of the catalyst bed.

[0027] The above method of the present invention can prevent the clogging of the catalyst and effectively improve the denitration efficiency by using steam soot blowing and sonic soot blowing for the liquid VOCs contained in the flue gas of the oil-gas mixed-firing boiler. The process design and equipment selection of the method are reasonable, the equipment layout is compact, the footprint of the whole system is small, and the limited space on site is reasonably and effectively utilized. The relevant devices are arranged in the spare space on the structure of the oil-gas mixed-firing boiler according to local conditions, and the space and facilities required for maintenance are taken into consideration.

[0028] The SCR denitrification method involved in the present invention will effectively solve the problems encountered in the flue gas treatment of oil and gas mixed-firing boilers, and provide technical route support for the stable operation of SCR denitrification in oil and gas mixed-firing boilers.

[0029] Furthermore, the temperature of the mixed flue gas is 280° C. to 430° C., and the volume percentage of ammonia in the ammonia-air mixed gas is less than 5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention is a schematic diagram of the structure of the SCR denitration system for flue gas from an oil-gas co-firing boiler, a denitration reactor, a boiler flue and an ammonia-air mixing device;

[0031] Figure 2 The SCR denitration system for flue gas from a mixed oil-gas boiler of the present invention includes a cross-sectional view of a catalyst bed, a steam soot blower and a sonic soot blower;

[0032] Figure 3 It is a schematic diagram of the structure of the SCR denitration system for flue gas of a mixed oil and gas boiler, a liquid ammonia evaporation device, and a liquid ammonia storage device of the present invention;

[0033] Figure 4 It is a schematic diagram of the structure of the SCR denitration system for flue gas from a mixed oil and gas boiler of the present invention, an ammonia dilution tank, and a wastewater tank;

[0034] Figure 5 This is a schematic structural diagram of an embodiment of the SCR denitration system for flue gas from a gas-oil mixed-firing boiler according to the present invention;

[0035] Figure 6 This is a schematic diagram of the catalyst structure of an embodiment of the SCR denitration system for flue gas from an oil-gas co-firing boiler of the present invention.

[0036] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0037] 1. Denitration reactor; 101. Catalyst bed; 1011. Catalyst spare layer; 102. Steam soot blower; 103. Sonic soot blower; 104. Ammonia injection grid;

[0038] 2. Ammonia-air mixing device; 201. Ammonia buffer tank; 202. Dilution fan; 203. Ammonia-air mixer;

[0039] 3. Liquid ammonia evaporation device; 301. Liquid ammonia evaporation tank;

[0040] 4. Liquid ammonia storage device; 401. Liquid ammonia storage tank;

[0041] 5. Ammonia dilution tank; 6. Wastewater pool; 7. Boiler flue; 8. Ammonia recovery main pipe. DETAILED DESCRIPTION

[0042] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0043] like Figures 1 to 6 As shown, the SCR denitration system for flue gas from an oil-gas co-firing boiler of the present invention comprises a boiler flue 7, a denitration reactor 1 and an ammonia-air mixing device 2, the flue gas inlet of the denitration reactor 1 is connected to the flue gas outlet of the boiler flue 7; at least one catalyst bed 101 is installed in the denitration reactor 1, and a steam soot blower assembly is arranged in the air inlet direction of each catalyst bed 101; a sonic soot blower assembly is also arranged in the air inlet direction of each catalyst bed 101; the ammonia-air mixing device 2 comprises an ammonia-air mixer 203, and the air outlet of the ammonia-air mixer 203 is connected to the boiler flue 7.

[0044] In the SCR denitration system for flue gas from an oil-gas co-firing boiler of the present invention, the ammonia-air mixing device 2 can provide a mixed gas of ammonia and air to the boiler flue 7, so that it is mixed with the flue gas in the denitration reactor 1, and then enters the denitration reactor 1 and passes through the catalyst bed 101 to achieve denitration treatment of the flue gas; a steam soot blowing component and a sonic soot blowing component are provided at the position of each catalyst bed 101, and steam soot blowing and sonic soot blowing can be combined to effectively solve the problem that VOCs in the flue gas of the oil-gas co-firing boiler cause clogging of the pores of the catalyst at low temperatures, thereby making the system of the present invention particularly suitable for oil-gas co-firing boilers.

[0045] Preferably, the steam sootblower assembly includes at least one steam sootblower 102; the sonic sootblower assembly includes at least one sonic sootblower 103; this can make the efficiency of steam sootblowing and sonic sootblowing higher.

[0046] As attached Figure 3 As shown, the arrangement of the steam soot blower assembly and the sonic soot blower assembly is adjusted according to the cross-sectional size of the denitration reactor 1. The steam soot blower 102 adopts a rake soot blower, which is generally arranged on the short side of the denitration reactor 1 due to its limited structural type, while the sonic soot blower 103 is arranged on the long side of the denitration reactor 1, and the interval between the sonic soot blowers 103 is generally 2 to 2.5 m.

[0047] Preferably, the catalyst bed 101 includes a plurality of catalysts, each of which has 22 or 25 pores. Compared with a common boiler flue gas SCR denitration system, the catalyst used in the present invention has more pores, thereby reducing the number of pores that may be blocked.

[0048] The pressure drop of the catalyst bed 101 can be monitored by conventional means in the art. In one embodiment of the present invention, preferably, a plurality of pressure monitoring devices are installed in the denitration reactor 1, each of which is generally installed upstream of the catalyst bed 101, and the difference between the two pressure detection devices can be used to monitor the pressure drop of a single catalyst bed 101.

[0049] Preferably, a temperature monitoring device is also installed at the flue gas inlet of the denitration reactor 1.

[0050] It should be noted that the catalyst of the present invention is a commercially available catalyst that can be used for denitration. In order to make it more effective for oil-gas mixed combustion boiler flue gas, it is preferred that the composition contains anti-metal poisoning substances such as Mo to reduce and avoid the problem of catalyst poisoning caused by alkaline metals, arsenic, etc. that may be carried by flue gas.

[0051] Preferably, an ammonia spray grid 104 is also installed in the denitration reactor 1, and the ammonia spray grid 104 is connected to the ammonia-air mixer 203, and the spray direction of the ammonia spray grid 104 is toward the catalyst bed 101; by setting the ammonia spray grid 104, the ammonia-air mixture can be mixed with the flue gas more evenly.

[0052] Preferably, the ammonia-air mixing device 2 further comprises an ammonia buffer tank 201 and a dilution fan assembly, and the air outlet of the ammonia buffer tank 201 and the air outlet of the dilution fan assembly are respectively connected to the air inlet of the ammonia-air mixer 203 .

[0053] The system of the present invention also has an ammonia zone, in which a series of devices can store, evaporate, transport and recycle liquid ammonia, thereby effectively providing ammonia gas.

[0054] The ammonia area related devices specifically include a liquid ammonia evaporation device 3 and a liquid ammonia storage device 4.

[0055] The liquid ammonia storage device 4 includes at least one liquid ammonia storage tank 401, and a liquid ammonia delivery pump is provided on the liquid phase outlet pipeline of each liquid ammonia storage tank 401. Liquid ammonia can be discharged into the liquid ammonia storage tank 401 by a tank truck through a discharge compressor, or can be transported to the liquid ammonia storage tank 401 from other tank areas over a long distance through a liquid ammonia pipeline. The liquid phase outlet of the liquid ammonia storage tank 401 is located at the bottom of the tank, so that the liquid ammonia can enter the liquid ammonia evaporation device 3 by its own pressure or the liquid ammonia delivery pump.

[0056] Preferably, the design pressure of the liquid ammonia storage tank 401 is not less than 2.2 MPa, the operating pressure is controlled below 1.5 MPa, the material is low alloy steel, and the volume coefficient is not greater than 0.9.

[0057] Preferably, the liquid ammonia storage tank 401 is provided with at least three pressure gauges for remote pressure control, and is equipped with two different types of liquid level detection instruments for liquid level control.

[0058] Preferably, a cooling spray system is provided above the liquid ammonia storage tank 401 to prevent the temperature from being too high in summer, thereby causing the risk of overpressure in the liquid ammonia storage tank 401.

[0059] The liquid ammonia evaporation device 3 includes at least one liquid ammonia evaporation tank 301. Liquid ammonia is sent to the liquid ammonia evaporation tank 301 and evaporated into ammonia gas. The liquid ammonia evaporation tank 301 and the ammonia buffer tank 201 allow the ammonia gas to be mixed with the dilution air through the ammonia buffer tank 201. In this way, the pressure and flow rate of the ammonia gas can be controlled to a certain extent through the ammonia buffer tank 201, so that the ammonia-air mixture is more in line with the demand and easier to control.

[0060] In addition, the liquid ammonia evaporation device 3 is also connected to the low-pressure steam pipeline, and the low-pressure steam can be used to evaporate the liquid ammonia.

[0061] Preferably, a low-pressure steam U-tube and a liquid ammonia coil are provided in the liquid ammonia evaporation tank 301. After the steam heats the hot water, the condensate (drain) is discharged into the drain collecting main pipe through the drain valve on the pipeline, and then transported to the drain tank (not shown in the figure).

[0062] As for the form of the liquid ammonia evaporation tank 301, a water bath type or a steam U-coil type heating method is currently commonly used. The difference between the two methods is that the water bath type is to directly pass steam into the heat medium water medium to heat the hot water and then evaporate the liquid ammonia in the tube; the steam U-coil type is to pass steam into the heating coil at the bottom of the evaporation tank, and after indirect heat exchange with the heat medium water, it is discharged into a pit or a drain tank.

[0063] Compared with the traditional water bath type liquid ammonia evaporator, the liquid ammonia evaporation tank 301 of the present invention avoids the phenomenon of a large amount of hot mist being discharged into the air, and also avoids the risk of scalding of operators during operation.

[0064] Preferably, the design capacity of the liquid ammonia evaporation tank 301 is the ammonia consumption under the maximum operating conditions of all units, and the operating temperature is controlled at 50-70° C. The ammonia buffer tank 201 can meet the residence time of ammonia of 0.5-1 min, and the pressure is controlled between 0.15-0.4 MPa.

[0065] It also includes an ammonia recovery main pipe 8, the inlet of which is connected to the liquid ammonia storage device 4 and the liquid ammonia evaporation device 3, and the ammonia recovery main pipe 8 includes a first outlet and a second outlet, the first outlet is connected to the ammonia dilution tank 5, and the second outlet is connected to the boiler flue 7. In this way, the ammonia gas that is urgently discharged or replaced and emptied in the above-mentioned liquid ammonia storage device 4 and the liquid ammonia evaporation device 3 can be collected in a total ammonia recovery main pipe 8, and then divided into two paths, the first path is discharged into the ammonia dilution tank 5, and is absorbed by water in the ammonia dilution tank 5 to become dilute ammonia water; the ammonia water pipeline in the ammonia dilution tank 5 is discharged to the wastewater pool 6, and is pumped to the sewage treatment system by the wastewater pump; the second path enters the boiler flue 7 and mixes with NO x Through the above arrangement, part of the ammonia gas can be recovered and reused, thus avoiding a large amount of ammonia gas being wasted.

[0066] Specifically, the second route of the ammonia recovery main pipe 8 can be connected to the ammonia outlet main pipe of the ammonia buffer tank 201 and enter the boiler flue 7 together with the ammonia output from the ammonia buffer tank 201 .

[0067] Preferably, the ammonia recovery main pipe 8 is connected to the bottom of the ammonia dilution tank 5. In order to avoid siphoning in this pipe, a vacuum release valve needs to be installed on this pipe. In addition, a spray water main pipe is set at the top of the ammonia dilution tank 5, and a number of small holes are opened on the main pipe to increase the atomization effect and coverage area of ​​the water spray, thereby effectively improving the absorption rate of waste ammonia.

[0068] It should be noted that in the system of the present invention, in order to flexibly and effectively control the flow of liquid and gas phases, valves and pumps can be set on any connected pipelines as needed. The valve can be an ordinary valve, a pneumatic regulating valve, or a valve group consisting of a pneumatic regulating valve and a control valve.

[0069] The SCR denitration method for oil-gas co-firing boiler flue gas of the present invention adopts the above-mentioned system to perform SCR denitration treatment on the oil-gas co-firing boiler flue gas.

[0070] The method specifically comprises the following steps:

[0071] The ammonia-air mixing device 2 inputs ammonia-air mixed gas into the boiler flue 7 and mixes it with the flue gas of the oil-gas co-firing boiler. The mixed flue gas enters the denitration reactor 1 and passes through the catalyst bed 101 for denitration reaction. The steam soot blower assembly and the sonic soot blower assembly are opened or closed according to the temperature in the denitration reactor 1 and the pressure drop of the catalyst bed 101.

[0072] Further preferably, before the flue gas treatment is carried out, the temperature of the flue gas needs to be measured first. The flue gas temperature measurement point is located at the flue gas inlet of the denitrification reactor 1, that is, the temperature of the flue gas after mixing with ammonia and air is measured. When the temperature is outside the allowable ammonia injection range, the temperature signal will automatically close the quick shut-off valve for ammonia to enter the ammonia-air mixing device 2. The ammonia from the ammonia zone and the air delivered by the dilution fan assembly are fully mixed in the ammonia-air mixing device 2, and the ammonia concentration in the mixed gas is controlled to be less than 5% by the ammonia flow regulating valve group, and then sprayed into the boiler flue 7. After the injected ammonia-air mixed gas is evenly mixed with the flue gas, it enters the denitrification reactor 1, and an oxidation-reduction reaction occurs in the catalyst bed 101. The catalyst bed 101 in the denitrification reactor 1 is generally adjusted according to the denitrification efficiency and the inlet NO x Set one or two layers of value, and add another layer as a backup.

[0073] Regarding the control of opening or closing the steam soot blower assembly and the sonic soot blower assembly, specifically, when the boiler load is high, the flue gas temperature of the denitration reactor 1 is high, and the VOCs that may be contained in the boiler flue gas are in the gas phase and will not block the catalyst. Under this condition, the catalyst bed 101 can be cleaned by starting the sonic soot blower assembly alone for sonic soot blowing. If the boiler has a low load for a long time, or the pressure drop of the catalyst bed 101 is large, the steam soot blower assembly can be started alone for steam soot blowing. At this time, the pressure drop change of the catalyst bed 101 is monitored at the same time. If there is no significant drop or it cannot be restored to the original pressure drop, the sonic soot blower assembly can be started at the same time on this basis to improve the cleaning effect of the catalyst bed and ensure the performance of the catalyst.

[0074] Preferably, the temperature of the mixed flue gas is 280° C. to 430° C., and the volume percentage of ammonia in the ammonia-air mixed gas is less than 5%.

[0075] The present invention is described in detail below through specific examples.

[0076] Example

[0077] like Figure 1 , 2 As shown in Figures 5 and 6, this embodiment uses the system of the present invention to perform SCR denitration treatment on the flue gas of the oil-gas co-firing boiler. Among them, the catalyst bed 101 in the denitration reactor 1 is two layers, and is arranged at intervals. Steam soot blower assemblies and sonic soot blower assemblies are arranged on the two catalyst beds 101. The steam soot blower assembly includes two steam soot blowers 102, and the two steam soot blowers 102 are arranged at equal intervals; the sonic soot blower assembly includes three sonic soot blowers 103, and the three sonic soot blowers 103 are arranged at equal intervals.

[0078] As attached Figure 3 As shown, the arrangement of the soot blowers is adjusted according to the cross-sectional size of the denitrification reactor 1. The steam soot blower 102 adopts a rake-type soot blower. Due to its limited structural type, the steam soot blower 102 is generally arranged on the short side of the reactor, and the sonic soot blower 103 is arranged on the long side. The interval between the sonic soot blowers 103 is generally 2 to 2.5 m.

[0079] In this embodiment, a 25-hole honeycomb catalyst is selected. The ash concentration in the flue gas of a mixed oil and gas boiler is generally low, at the milligram level. However, considering that the flue gas may carry sticky substances, a honeycomb catalyst with a denser number of holes cannot be selected. When preparing the catalyst formula, anti-poisoning components are added to increase the tolerance of the catalyst. In addition, sufficient margin is considered when designing the catalyst to increase the stability of the denitrification system operation.

[0080] In addition, in this embodiment, a catalyst standby layer 1011 is installed in the denitration reactor 1 , and the catalyst standby layer 1011 is closest to the flue gas inlet of the denitration reactor 1 .

[0081] In order to effectively monitor the pressure reduction of each catalyst bed layer 101 and the catalyst standby layer 1011 , a pressure gauge is installed at a corresponding position on the upper side of each layer in the denitration reactor 1 .

[0082] In this embodiment, the dilution fan assembly includes two dilution fans 202, and both dilution fans 202 are connected to the ammonia-air mixer 203. An ammonia regulating valve group is provided on the pipeline connecting the ammonia buffer tank 201 and the ammonia-air mixer 203, which can control the ammonia flow rate. The second branch of the ammonia recovery main pipe 8 is connected to the pipeline between the ammonia buffer tank 201 and the ammonia-air mixer 203, so that part of the ammonia can be recovered and reused. A pressure gauge and a thermometer are installed in the ammonia buffer tank 201 to measure the ammonia pressure and temperature therein.

[0083] In this embodiment, the liquid ammonia storage device 4 includes two liquid ammonia storage tanks 401, one for use and one for backup. The capacity of the liquid ammonia storage tank 401 meets the storage days required for the liquid ammonia consumption under the BMCR operating conditions of all units. The determination of the storage days is related to the transportation method of the liquid ammonia. If the liquid ammonia is transported by pipeline, the storage capacity is generally set to 5 days; if it is transported by tank truck, the storage capacity is generally set to 7 days.

[0084] The liquid ammonia evaporation device 3 includes two liquid ammonia evaporation tanks 301. A pneumatic regulating valve is provided on the pipeline in front of the liquid ammonia evaporation tank 301. The liquid ammonia evaporation tank 301 is in the form of a steam U-shaped coil to heat the heat medium water. A regulating valve is provided on the steam pipeline to interlock the control with the heat medium water temperature. The heated heat medium water is maintained at 50-70°C and the pressure is maintained at 0.25-0.4MPa. The liquid ammonia evaporation tank 301 vaporizes the liquid ammonia in the pipe into ammonia gas, which enters the ammonia buffer tank 201.

[0085] The system working process of this embodiment is as follows:

[0086] The liquid ammonia transported from the pipeline enters the liquid ammonia storage tank 401 for storage. The liquid ammonia in the liquid ammonia storage tank 401 is transported to the liquid ammonia evaporation tank 301 by the pressure of the liquid ammonia storage tank 401 itself (when the ambient temperature is low in winter, it can be transported by a liquid ammonia delivery pump). A U-shaped steam coil is arranged at the bottom of the liquid ammonia evaporation tank 301 to heat the heat medium water in the shell side, and liquid ammonia is introduced into the tube side. The liquid ammonia is evaporated into gaseous ammonia by heating the tube side and then enters the ammonia buffer tank 201. The amount of liquid ammonia entering the liquid ammonia evaporation tank 301 is controlled by the pneumatic regulating valve in front of the liquid ammonia evaporation tank 301 to maintain the ammonia buffer tank 201 at a certain operating pressure.

[0087] Ammonia enters the ammonia-air mixer 203 through the regulating valve group, and after being fully mixed with the dilution air from the dilution fan 202, the ammonia is diluted to a concentration below 5%, and then sprayed into the boiler flue 7 through the ammonia spray grid 104. The ammonia-air mixed gas entering the boiler flue 7 is mixed with the boiler flue gas and enters the denitration reactor 1. The temperature of the denitration reactor 1 is generally controlled between 300 and 420°C, and the minimum ammonia spray temperature is 280°C. The flue gas undergoes an oxidation-reduction reaction in the catalyst bed 101 to generate N2 and H2O, thereby removing NO in the flue gas. x , so as to achieve the boiler flue gas emission standards.

[0088] Three sets of temperature transmitters are installed at the inlet of denitrification reactor 1 to monitor the flue gas temperature. The pneumatic valve in the ammonia regulating valve group is interlocked with this thermometer to control ammonia spraying only after the minimum ammonia spraying temperature is reached. x The concentration and flue gas volume are controlled by DCS interlocking, so that the NO x The concentration meets environmental protection requirements.

[0089] The waste liquid and waste gas discharged from the liquid ammonia storage tank 401 and the liquid ammonia evaporation tank 301 are collected in the ammonia recovery main pipe 8. The ammonia recovery main pipe 8 is connected to a certain distance below the liquid level of the ammonia dilution tank 5. An ammonia leakage alarm is set on the top of the ammonia dilution tank 5. The ammonia leakage alarm signal is interlocked with the dilution spray water pneumatic valve. When ammonia escapes from the top of the ammonia dilution tank 5, the alarm will be triggered, and then the spray water replenishment valve will be interlocked to open, so as to absorb the volatilized waste ammonia gas and finally enter the wastewater pool 6 through the bottom drain port of the ammonia dilution tank 5.

[0090] When the oil-gas mixed-firing boiler is burning 100% PFO, 90% PGO and 100% natural gas, the NO in the flue gas at the inlet of the denitrification reactor is x Content (maximum) ≤ 250mg / Nm 3 In the case of the SCR denitration method of the embodiment of the present invention, the flue gas NO at the outlet of the denitration reactor is x Content ≤25mg / Nm 3 (dry basis, O2, 3%); the ammonia escape rate at the outlet of the denitrification reactor is 3ppm (dry basis, 3% O2), which meets the environmental emission requirements.

[0091] In the description of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0092] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0093] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0094] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0095] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" 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 or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0096] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An SCR denitrification system for flue gas from a gas-oil mixed combustion boiler, comprising a boiler flue (7) characterized in that: It also includes a denitration reactor (1) and an ammonia-air mixing device (2), wherein the flue gas inlet of the denitration reactor (1) is connected to the flue gas outlet of the boiler flue (7); At least one catalyst bed (101) is installed in the denitration reactor (1); along the flow direction of the flue gas, a steam soot blower assembly and a sonic soot blower assembly are arranged upstream of each catalyst bed (101); the steam soot blower assembly and the sonic soot blower assembly are installed on the inner wall of the denitration reactor (1); The ammonia-air mixing device (2) comprises an ammonia-air mixer (203), and the gas outlet of the ammonia-air mixer (203) is connected to the boiler flue (7).

2. The SCR denitration system for flue gas from oil-gas mixed-firing boilers according to claim 1 is characterized in that: The steam sootblower assembly includes at least one steam sootblower (102).

3. The SCR denitration system for flue gas from oil-gas mixed-firing boilers according to claim 1 is characterized in that: The sonic sootblower assembly comprises at least one sonic sootblower (103).

4. The SCR denitration system for flue gas from an oil-gas co-firing boiler according to any one of claims 1 to 3, characterized in that: The catalyst bed (101) comprises a plurality of catalyst modules, and each catalyst module has 22 holes or 25 holes.

5. The SCR denitration system for flue gas from an oil-gas co-firing boiler according to any one of claims 1 to 3, characterized in that: An ammonia injection grid (104) is also installed in the boiler flue (7). The ammonia injection grid (104) is connected to the ammonia-air mixer (203). The injection direction of the ammonia injection grid (104) is toward the flue gas outlet of the boiler flue (7).

6. The SCR denitration system for flue gas from an oil-gas co-firing boiler according to any one of claims 1 to 3, characterized in that: The ammonia-air mixing device (2) further comprises an ammonia buffer tank (201) and a dilution fan assembly, wherein the air outlet of the ammonia buffer tank (201) and the air outlet of the dilution fan assembly are respectively connected to the air inlet of the ammonia-air mixer (203).

7. The SCR denitration system for flue gas from oil-gas mixed-firing boilers according to claim 6, characterized in that: It also comprises a liquid ammonia evaporation device (3), the gas outlet of the liquid ammonia evaporation device (3) being in communication with the ammonia buffer tank (201); the liquid ammonia evaporation device (3) is also in communication with the liquid ammonia storage device (4) and the low-pressure steam pipeline respectively.

8. The SCR denitration system for flue gas from oil-gas mixed-firing boilers according to claim 7, characterized in that: The invention also comprises an ammonia recovery main pipe (8), the inlet of which is connected to the liquid ammonia storage device (4) and the liquid ammonia evaporation device (3), and the ammonia recovery main pipe (8) comprises a first outlet and a second outlet, the first outlet is connected to the ammonia dilution tank (5), and the second outlet is connected to the boiler flue (7).

9. An SCR denitrification method for flue gas from oil-gas mixed combustion boilers, characterized in that: The system according to any one of claims 1 to 8 is used to perform SCR denitrification treatment on the flue gas of an oil-gas mixed combustion boiler, comprising the following steps: The ammonia-air mixing device (2) inputs ammonia-air mixed gas into the boiler flue (7) and mixes it with the flue gas of the oil-gas co-firing boiler. The mixed flue gas enters the denitration reactor (1) and passes through the catalyst bed (101) to undergo a denitration reaction. The steam soot blower assembly and the sonic soot blower assembly are controlled to be opened or closed according to the temperature in the denitration reactor (1) and the pressure drop of the catalyst bed (101).

10. The SCR denitrification method for flue gas from oil-gas mixed-firing boilers according to claim 9, characterized in that: The temperature of the mixed flue gas is 280° C. to 430° C., and the volume percentage of ammonia in the ammonia-air mixed gas is less than 5%.

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