CN111551038A

CN111551038A - Medium-temperature SCR denitration system and medium-temperature SCR denitration method for kiln tail flue gas

Info

Publication number: CN111551038A
Application number: CN202010407186.8A
Authority: CN
Inventors: 朱廷钰; 郭旸旸; 罗雷
Original assignee: Institute of Process Engineering of CAS
Current assignee: Institute of Process Engineering of CAS
Priority date: 2020-05-14
Filing date: 2020-05-14
Publication date: 2020-08-18

Abstract

The invention provides a medium-temperature SCR denitration system and a medium-temperature SCR denitration method for kiln tail flue gas. The medium-temperature SCR denitration system provided by the invention can meet the requirement of increasingly strict cement kiln tail flue gas NO_xThe emission standard can be NO at the tail of the cement kiln_xUltra-low emissions provide technical support. Cigarette with a filterGas is returned and is joined in marriage, can raise waste heat recovery device's export flue gas temperature on the one hand, and on the other hand has reduced the smoke and dust content that gets into SCR denitrification facility, reduces system deposition and catalyst poisoning when improving SCR denitration efficiency.

Description

Medium-temperature SCR denitration system and medium-temperature SCR denitration method for kiln tail flue gas

Technical Field

The invention belongs to the technical field of waste gas treatment, relates to an industrial flue gas denitration system and method, and particularly relates to a medium-temperature SCR denitration system and method for kiln tail flue gas.

Background

At present, selective non-catalytic reduction (SNCR) technology is generally adopted for denitration of cement kiln flue gas in China, and NO is_xThe removal efficiency is about 60 percent generally, and the existing emission standard can be basically met, but the SNCR denitration technology has the problems of low denitration efficiency, serious ammonia escape and the like, and is difficult to meet the further strict ultralow emission standard. The Selective Catalytic Reduction (SCR) denitration technology has mild reaction conditions and high denitration efficiency (90 percent), is widely applied to the thermal power industry, but just starts to be applied to the cement industry, mainly because the dust content of the tail flue gas of the cement kiln is as high as 80-120 g/Nm³And the dust has high CaO content and fine particle size, so that the catalyst is easy to block and poison, the service life of the catalyst is short, and the system operation cost is high.

According to the operation condition of the SCR at the tail of a cement kiln, the method can be divided into three main process routes, namely high-temperature high-dust, high-temperature medium-dust and medium-temperature medium-dust, wherein the high-temperature high-dust and the high-temperature medium-dust are applied at home and abroad, the flue gas temperature is about 300 ℃ and meets the temperature window of the current mature commercial catalyst, but the flue gas has extremely high dust content, frequent dust removal is needed to meet the requirement of stable operation of a system, a macroporous catalyst is selected, the occupied area and the investment cost are increased, the medium temperature is generally arranged behind a waste heat boiler, the higher temperature process is arranged close to the ground, the construction difficulty is low, the method has very large application potential in the cement industry, the temperature is generally about 200 ℃, the activation temperature of the conventional commercial SCR catalyst is generally more than 180 ℃, the technical route of pre-dedusting and the medium temperature SCR is adopted, although the stable, however, due to the temperature drop of the system, the temperature window of the catalyst is difficult to be completely guaranteed, so that the medium-temperature SCR denitration process suitable for the characteristics of the tail flue gas of the cement kiln is developed by combining the characteristics of cement production.

CN204555717U discloses a cement kiln tail intermediate temperature flue gas SCR denitrification device, its denitrification device is behind exhaust-heat boiler, the high temperature high dust flue gas that comes from the kiln tail preheater carries out waste heat utilization through the exhaust-heat power generation boiler, after the flue gas temperature has reduced to some extent, get into cyclone dust collector and carry out the dust collection processing, the dust concentration in the flue gas further reduces, with the reductant that reducing agent supply system supplied through to the reductant injection apparatus who arranges on the preceding pipeline of cyclone dust collector in the flue jets into the intermediate temperature denitrification device who is equipped with the catalyst and carries out the denitration. According to the process, the cyclone dust collector is arranged in front of the SCR reactor, so that dust entering the SCR reactor can be reduced, but the cement kiln smoke dust particles are fine, and the efficiency of the cyclone dust collector is limited.

CN109985522 has disclosed embedded SCR flue gas denitration reactor and method in exhaust-heat boiler for cement kiln flue gas denitration, through the vertical dilatation section that adds exhaust-heat boiler, set up a plurality of layers of catalyst layer in the dilatation section, avoid setting up SCR denitration reactor alone, reduce the system pressure drop, but because the dust concentration of going into exhaust-heat boiler flue gas is high, original exhaust-heat boiler bottom ash bucket need pass through the SCR reactor, when exhaust-heat boiler shakes and beats the deashing, SCR catalyst bed also very easily causes the jam, exhaust-heat boiler dilatation is also restricted to the boiler arrangement allowance of reality simultaneously, be difficult to realize in actual technology.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a medium-temperature SCR denitration system and a medium-temperature SCR denitration method for kiln tail flue gas, and the medium-temperature SCR denitration system provided by the invention can meet the requirement of increasingly strict NO of the kiln tail flue gas of a cement kiln_xEmission standards, especially 50mg/Nm, are currently proposed in various areas³The following emission requirements can be NO at the tail of the cement kiln_xUltra-low emissions provide technical support. According to the SCR denitration system provided by the invention, through flue gas return, on one hand, the outlet flue gas temperature of the waste heat recovery device can be raised, on the other hand, the content of smoke dust entering the SCR denitration device is reduced, and the dust deposition and the catalyst poisoning of the system are reduced while the SCR denitration efficiency is improved.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides a medium-temperature SCR denitration system for kiln tail flue gas, which is characterized in that the denitration system comprises a waste heat recovery device, a heat exchange device and an SCR denitration device, wherein a high-temperature flue gas outlet of the waste heat recovery device is connected with the heat exchange device, and an outlet of the heat exchange device and a medium-temperature flue gas outlet of the waste heat recovery device are combined into one path and then connected to the SCR denitration device.

The SCR denitration system provided by the invention can effectively reduce the abrasion and blockage of smoke dust to the SCR catalyst, reduce the poisoning and inactivation of alkali and alkaline earth metals to the catalyst, reduce the resistance of the SCR denitration system, simultaneously raise the arrangement temperature of SCR after a waste heat boiler, improve the denitration efficiency and the operation life of the SCR denitration catalyst, and realize the combination of the flue gas recirculation and the SCR denitration technology_xThe operation cost of the system is reduced while the removal is efficient.

As a preferable technical scheme of the invention, a flue gas inlet of the waste heat recovery device is connected with a kiln tail flue in an upstream system.

Preferably, the upstream system is a cement kiln, and a kiln tail flue of the cement kiln discharges smoke to enter the medium-temperature SCR denitration system.

Preferably, a bypass flue is connected to a kiln tail flue of the upstream system, and an outlet end of the bypass flue is connected to a dust removal and smoke exhaust pipeline; the high-temperature flue gas after heat exchange and dust removal is mixed with the medium-temperature flue gas discharged by the waste heat recovery device and part of kiln tail flue gas led out from the kiln tail flue in sequence and then is led into the SCR denitration device.

Preferably, a first flue valve is arranged on the bypass flue.

As a preferred technical scheme of the invention, the medium-temperature SCR denitration system further comprises a dust removal device, wherein a high-temperature flue gas outlet of the waste heat recovery device is sequentially connected with the heat exchange device and the dust removal device along the flue gas flow direction, the dust removal device is connected with a flue gas inlet of the SCR denitration device through a dust removal smoke exhaust pipeline, and a medium-temperature flue gas outlet of the waste heat recovery device is connected to the dust removal smoke exhaust pipeline; high-temperature flue gas discharged by the waste heat recovery device sequentially flows through the heat exchange device and the dust removal device and then is mixed with medium-temperature flue gas discharged by the waste heat recovery device and introduced into the SCR denitration device.

Preferably, a second flue valve is arranged on a connecting pipeline of the heat exchange device and the dust removal device.

Preferably, a third flue valve is arranged on the dust and smoke removing pipeline.

Preferably, the medium temperature flue gas outlet of the waste heat recovery device is connected to the dust and smoke removal pipeline through a three-way valve.

Preferably, the three-way valve is positioned at the front end of the third flue valve along the flow direction of the flue gas.

Preferably, two stages of heat exchange modules are longitudinally arranged in the waste heat recovery device along the flow direction of the flue gas, part of the kiln tail flue gas is led out to form high-temperature flue gas after part of heat is recovered by the primary heat exchange module, and the rest of the kiln tail flue gas enters the secondary heat exchange module to recover the rest of heat to form medium-temperature exhaust.

Preferably, the waste heat recovery device is a waste heat boiler.

Preferably, a reducing agent channel and a flue gas channel are arranged in the heat exchange device, the flue gas and the reducing agent are contacted and exchanged heat in the heat exchange device, an inlet of the reducing agent channel is connected with a reducing agent storage tank, an outlet of the reducing agent channel is connected with the SCR denitration device, an inlet of the flue gas channel is connected with a high-temperature flue gas outlet of the waste heat recovery device, and an outlet of the flue gas channel is connected with the dust removal device.

Preferably, the dust removing device comprises an electric dust remover, a bag-type dust remover, a metal filter screen dust remover, a ceramic film dust remover, a cyclone dust remover, a gravity dust remover or a tubular dust remover.

As a preferable technical solution of the present invention, at least one catalyst layer is provided inside the SCR denitration device.

Preferably, a reducing agent spraying device is arranged above the catalyst layer, and reducing agent channel outlets of the heat exchange device are respectively and independently connected with the reducing agent spraying device.

Preferably, the reducing agent spraying device is a grid type spraying device, a mixed type spraying device or a vortex type spraying device.

Preferably, a guide plate is arranged in a horizontal inlet flue of the SCR denitration device, and the guide plate is used for changing the flow direction of flue gas entering the SCR denitration device.

Preferably, the guide plate is a straight plate-shaped guide plate or an arc-shaped guide plate.

Preferably, the arc of the arc-shaped guide plate is 45 ° to 90 °, for example, 45 °, 50 °, 55 °, 60 °, 65 °, 70 °, 75 °, 80 °, 85 ° or 90 °, but not limited to the values listed, and other values not listed in the range of the values are also applicable.

Preferably, a soot blower is further arranged between the catalyst layer and the reducing agent spraying device.

Preferably, the soot blower is a steam soot blower or a sound wave soot blower.

Preferably, the steam soot blower is externally connected with a steam source.

Preferably, a flue gas outlet of the SCR denitration device is provided with a temperature detection device and a concentration detection device, the temperature detection device monitors the temperature of the exhaust gas, and the concentration detection device is used for detecting NH in the exhaust gas₃、O₂、SO₂、NO_xAnd dust concentration.

As a preferable technical scheme of the invention, the catalyst adopted by the catalyst layer is an integral catalyst of alkali-resistant and alkaline-earth metal.

Preferably, the monolithic catalyst comprises a carrier and an active component supported on the carrier.

Preferably, the active component comprises one or a combination of at least two of V, Ce, Mn, Fe or W.

Preferably, the support comprises TiO₂One or a combination of at least two of molecular sieve, mesoporous alumina or montmorillonite.

Preferably, the active ingredient is present in an amount of 0.1 to 20 wt%, and may be, for example, 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, or 20 wt%, but is not limited to the recited values, and other values not recited within the range of values are equally applicable.

Preferably, the specific surface area of the monolithic catalyst is 0-1000 m²G, may be, for example, 100m²/g、200m²/g、300m²/g、400m²/g、500m²/g、600m²/g、700m²/g、800m²/g、900m²In g or 1000m²In the following description,/g is not limited to the values listed, but other values not listed in the numerical range are equally applicable.

The monolithic catalyst preferably has a pore size of 1 to 100. mu.m, and may be, for example, 1 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm, but is not limited to the values listed, and other values not listed in this range are also applicable.

Preferably, the monolithic catalyst has a cross-sectional pore size of 0 to 10cm, for example 1cm, 2cm, 3cm, 4cm, 5cm, 6cm, 7cm, 8cm, 9cm or 10cm, but is not limited to the recited values, and other values not recited in this range are also applicable.

Preferably, the monolithic catalyst is honeycomb, plate or corrugated.

The SCR denitration system provided by the invention can be used together with the original SNCR system, the SNCR denitration is adopted in nearly 90% of the existing cement kilns, the reducing agent storage tank can be shared after the SNCR denitration is used together, the equipment investment is reduced, the number of catalyst bed layers in the SCR denitration agent device can be properly reduced, and the low-cost and high-efficiency NO removal is realized_x。

In a second aspect, the invention provides a medium-temperature SCR denitration method for kiln tail flue gas, which is implemented by using the medium-temperature SCR denitration system of the first aspect to perform medium-temperature SCR denitration treatment on kiln tail flue gas, and the denitration method includes:

kiln tail flue gas generated at the upstream enters a waste heat recovery device to recover heat therein to obtain high-temperature flue gas and medium-temperature flue gas respectively, the high-temperature flue gas is subjected to heat exchange by a heat exchange device and then mixed with the medium-temperature flue gas to be introduced into an SCR (selective catalytic reduction) denitration device, and the mixed flue gas and a reducing agent are subjected to selective catalytic reduction reaction under the action of a catalyst to realize flue gas denitration.

As a preferred technical scheme, the medium-temperature SCR denitration method specifically comprises the following steps:

the method comprises the following steps that (I) kiln tail flue gas exhausted by a cement kiln is divided into first kiln tail flue gas and second kiln tail flue gas, the first kiln tail flue gas is introduced into a waste heat recovery device, part of heat is recovered through primary heat exchange, a part of the heat is led out to form high-temperature flue gas and introduced into a heat exchange device, and the rest of the high-temperature flue gas is continuously subjected to secondary heat exchange to recover the rest of heat and then is completely exhausted to form medium-temperature flue gas;

(II) the high-temperature flue gas enters a dust removal device for dust removal after exchanging heat with a reducing agent in a heat exchange device, the high-temperature flue gas after heat exchange and dust removal is sequentially mixed with the medium-temperature flue gas and the second kiln tail flue gas to obtain returned flue gas, and the returned flue gas is introduced into an SCR denitration device;

and (III) introducing the reducing agent subjected to heat exchange in the step (II) into an SCR denitration device, and carrying out selective catalytic reduction reaction on the returned flue gas and the reducing agent under the action of a catalyst to realize flue gas denitration.

The invention adopts a process route combining flue gas recirculation and medium-temperature SCR denitration technology, when kiln tail flue gas passes through a waste heat recovery device, high-temperature flue gas firstly exchanges heat, high-concentration dust in the flue gas can be partially removed through gravity sedimentation while the flow rate of the flue gas is reduced, the high-concentration dust is led out through a flue, part of the high-temperature flue gas is led out, dust in the part of the flue gas is removed by a dust removal device, the dust is mixed with the medium-temperature flue gas discharged by the waste heat recovery device, the outlet temperature of the waste heat recovery device is raised, the mixture is mixed with the second kiln tail flue gas and then enters the SCR denitration device, a flue gas guide plate and a multilayer alkali-resistant and alkaline earth metal poisoning integral catalyst are arranged in the SCR denitration device, a humidifying tower and a raw material grinding system are optionally connected behind the denitration device, and the.

As a preferable technical scheme, in the step (I), the dust concentration in the kiln tail flue gas is 50-100 g/Nm³For example, it may be 50g/Nm³、55g/Nm³、60g/Nm³、65g/Nm³、70g/Nm³、75g/Nm³、80g/Nm³、85g/Nm³、90g/Nm³、95g/Nm³Or 100g/Nm³However, the numerical values recited are not intended to be limiting, and other numerical values not recited within the numerical range may be equally applicable.

Preferably, the temperature of the kiln tail flue gas is 280-340 ℃, for example, 280 ℃, 290 ℃, 300 ℃, 310 ℃, 320 ℃, 330 ℃ or 340 ℃, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.

Preferably, NO in the kiln tail flue gas_xThe concentration of (A) is 200-500 mg/Nm³For example, it may be 200mg/Nm³、250mg/Nm³、300mg/Nm³、350mg/Nm³、400mg/Nm³、450mg/Nm³Or 500mg/Nm³However, the numerical values recited are not intended to be limiting, and other numerical values not recited within the numerical range may be equally applicable.

Preferably, the volume flow rate of the first kiln tail flue gas is 10-90% of the total volume flow rate of the kiln tail flue gas, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90%, but not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the volume flow rate of the high-temperature flue gas accounts for 50-60% of the total volume flow rate of the first kiln tail flue gas, for example, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, or 60%, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the temperature of the high-temperature flue gas is 260 to 280 ℃, and for example, the temperature may be 260 ℃, 261 ℃, 262 ℃, 263 ℃, 264 ℃, 265 ℃, 266 ℃, 267 ℃, 268 ℃, 269 ℃, 270 ℃, 271 ℃, 272 ℃, 273 ℃, 274 ℃, 275 ℃, 276 ℃, 277 ℃, 278 ℃, 289 ℃ or 280 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the temperature of the middle-temperature flue gas is 180 to 200 ℃, for example, 180 ℃, 181 ℃, 182 ℃, 183 ℃, 184 ℃, 185 ℃, 186 ℃, 187 ℃, 188 ℃, 189 ℃, 190 ℃, 191 ℃, 192 ℃, 193 ℃, 194 ℃, 195 ℃, 196 ℃, 197 ℃, 198 ℃, 199 ℃ or 200 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

In a preferred embodiment of the present invention, in the step (ii), the dust removing efficiency of the dust removing device is 50 to 99.99%, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, but the dust removing efficiency is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.

Preferably, the dust concentration in the high-temperature flue gas subjected to heat exchange and dust removal is 1-10 mg/Nm³For example, it may be 1mg/Nm³、2mg/Nm³、3mg/Nm³、4mg/Nm³、5mg/Nm³、6mg/Nm³、7mg/Nm³、8mg/Nm³、9mg/Nm³Or 10mg/Nm³However, the numerical values recited are not intended to be limiting, and other numerical values not recited within the numerical range may be equally applicable.

Preferably, the temperature of the high-temperature flue gas after heat exchange and dust removal is 240 to 260 ℃, and may be, for example, 240 ℃, 241 ℃, 242 ℃, 243 ℃, 244 ℃, 245 ℃, 246 ℃, 247 ℃, 248 ℃, 249 ℃, 250 ℃, 251 ℃, 252 ℃, 253 ℃, 254 ℃, 255 ℃, 256 ℃, 257 ℃, 258 ℃, 259 ℃ or 260 ℃, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.

Preferably, the dust concentration in the reconstituted flue gas is 20-40 g/Nm³For example, it may be 20g/Nm³、22g/Nm³、24g/Nm³、26g/Nm³、28g/Nm³、30g/Nm³、32g/Nm³、34g/Nm³、36g/Nm³、38g/Nm³Or 40g/Nm³However, the numerical values recited are not intended to be limiting, and other numerical values not recited within the numerical range may be equally applicable.

Preferably, the temperature of the recycled flue gas is 200-260 ℃, for example, 200 ℃, 210 ℃, 220 ℃, 230 ℃, 240 ℃, 250 ℃ or 260 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the reducing agent comprises one or a combination of at least two of ammonia water, urea, liquid ammonia or organic amine.

In a preferred embodiment of the present invention, in the step (III), the flow velocity of the flue gas in the SCR denitration device is 0 to 10m/s, and may be, for example, 1m/s, 2m/s, 3m/s, 4m/s, 5m/s, 6m/s, 7m/s, 8m/s, 9m/s, or 10m/s, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned value range are also applicable.

Preferably, the system resistance of the SCR denitration device is 0 to 1000Pa, and may be, for example, 100Pa, 200Pa, 300Pa, 400Pa, 500Pa, 600Pa, 700Pa, 800Pa, 900Pa or 1000Pa, but is not limited to the above-mentioned values, and other values not mentioned in the above-mentioned range are also applicable.

Preferably, the reaction temperature of the selective catalytic reduction reaction is 200 to 260 ℃, for example, 200 ℃, 210 ℃, 220 ℃, 230 ℃, 240 ℃, 250 ℃ or 260 ℃, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the molar ratio of ammonia nitrogen involved in the selective catalytic reduction reaction is (0.5-1.5): 1, and may be, for example, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, but is not limited to the recited values, and other values not recited in the range of values are equally applicable.

Preferably, NO in the flue gas after SCR denitration treatment_xThe concentration of (A) is 30-50 mg/Nm³For example, it may be 30mg/Nm³、32mg/Nm³、34mg/Nm³、36mg/Nm³、38mg/Nm³、40mg/Nm³、42mg/Nm³、44mg/Nm³、46mg/Nm³、48mg/Nm³Or 50mg/Nm³However, the numerical values recited are not intended to be limiting, and other numerical values not recited within the numerical range may be equally applicable.

Preferably, the denitration efficiency of the SCR denitration device is 30 to 99%, and may be, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable.

The system refers to an equipment system, or a production equipment.

Compared with the prior art, the invention has the beneficial effects that:

(1) the high-efficiency medium-temperature SCR denitration system provided by the invention can meet the requirement of increasingly strict cement kiln tail flue gas NO_xEmission standards, especially 50mg/Nm, are currently proposed in various areas³The following emission requirements can be NO at the tail of the cement kiln_xUltra-low emissions provide technical support.

(2) The flue gas recycling method adopted by the invention can raise the temperature of the flue gas at the outlet of the waste heat boiler, reduce the content of smoke dust entering the medium-temperature SCR denitration device, improve the SCR denitration efficiency and reduce the system dust deposition and the catalyst poisoning.

Drawings

Fig. 1 is a schematic structural diagram of a medium-temperature SCR denitration system according to an embodiment of the present invention.

Wherein, 1-kiln tail flue; 2-a first flue valve; 3-a reducing agent storage tank; 4-a bypass flue; 5-a waste heat recovery device; 6-heat exchange device; 7-a second flue valve; 8-a dust removal device; 9-a three-way valve; 10-a third flue valve; 11-an SCR denitration device; 12-reducing agent spray device.

Detailed Description

It is to be understood that in the description of the present invention, the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be taken as limiting the present invention. Furthermore, the terms "first", "second", etc. are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first," "second," etc. may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified.

It should be noted that, in the description of the present invention, unless otherwise explicitly specified or limited, the terms "disposed," "connected" and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art through specific situations.

The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.

In a specific embodiment, the invention provides a medium-temperature SCR denitration system for kiln tail flue gas, which is shown in fig. 1 and comprises a waste heat recovery device 5, a heat exchange device 6 and an SCR denitration device 11, wherein a high-temperature flue gas outlet of the waste heat recovery device 5 is connected with the heat exchange device 6, and an outlet of the heat exchange device 6 and a medium-temperature flue gas outlet of the waste heat recovery device 5 are combined into one path and then connected to the SCR denitration device 11.

The flue gas inlet of the waste heat recovery device 5 is connected with the kiln tail flue 1 in the upstream system. Illustratively, in the embodiment, the upstream system can be selected as a cement kiln, and the kiln tail flue 1 of the cement kiln discharges smoke into the medium-temperature SCR denitration system. A bypass flue 4 is connected to the kiln tail flue 1 of the upstream system, and the outlet end of the bypass flue 4 is connected to a dust removal and smoke exhaust pipeline; the high-temperature flue gas after heat exchange and dust removal is mixed with the medium-temperature flue gas discharged by the waste heat recovery device 5 and part of kiln tail flue gas led out from the kiln tail flue 1 in sequence and then is led into the SCR denitration device 11. The bypass flue 4 is provided with a first flue valve 2.

The medium-temperature SCR denitration system further comprises a dust removal device 8, a high-temperature flue gas outlet of the waste heat recovery device 5 is sequentially connected with the heat exchange device 6 and the dust removal device 8 along the flow direction of flue gas, the dust removal device 8 is connected with a flue gas inlet of the SCR denitration device 11 through a dust removal smoke exhaust pipeline, and a medium-temperature flue gas outlet of the waste heat recovery device 5 is connected to the dust removal smoke exhaust pipeline; the high-temperature flue gas discharged by the waste heat recovery device 5 sequentially flows through the heat exchange device 6 and the dust removal device 8 and then is mixed with the medium-temperature flue gas discharged by the waste heat recovery device 5 and then is introduced into the SCR denitration device 11. A second flue valve 7 is arranged on a connecting pipeline between the heat exchange device 6 and the dust removal device 8, a third flue valve 10 is arranged on a dust removal and smoke discharge pipeline, a middle-temperature flue gas outlet of the waste heat recovery device 5 is connected to the dust removal and smoke discharge pipeline through a three-way valve 9, and the three-way valve 9 is positioned at the front end of the third flue valve 10 along the flow direction of flue gas. It should be noted that, the limitation of the installation position and the number of the flue valves in the present invention is only an exemplary arrangement manner for assisting the conventional process flow of the denitration system, and the present invention does not have a specific requirement and a specific limitation thereon, and those skilled in the art can select an appropriate installation position and installation number of the valves according to the usage scenario and the system scale of the denitration system.

Two stages of heat exchange modules are longitudinally arranged in the waste heat recovery device 5 along the flow direction of the flue gas, part of the kiln tail flue gas is led out after part of heat is recovered by the first stage heat exchange module to form high temperature flue gas, and the rest of the kiln tail flue gas enters the second stage heat exchange module to recover the rest heat to form medium temperature exhaust. In the present embodiment, the waste heat recovery device 5 may be selected as a waste heat boiler.

A reducing agent channel and a flue gas channel are arranged inside the heat exchange device 6, the flue gas and the reducing agent are contacted and exchanged heat in the heat exchange device 6, an inlet of the reducing agent channel is connected with the reducing agent storage tank 3, an outlet of the reducing agent channel is connected with the SCR denitration device 11, an inlet of the flue gas channel is connected with a high-temperature flue gas outlet of the waste heat recovery device 5, and an outlet of the flue gas channel is connected with the dust removal device 8. The dust removing device 8 can be selected from one of an electric dust remover, a bag-type dust remover, a metal filter screen dust remover, a ceramic film dust remover, a cyclone dust remover, a gravity dust remover or a tubular dust remover.

At least one catalyst layer is arranged in the SCR denitration device 11, a reducing agent spraying device 12 is arranged above the catalyst layer, and reducing agent channel outlets of the heat exchange device 6 are respectively and independently connected with the reducing agent spraying device 12. The reducing agent spray device 12 may be selected from one of a grid type spray device, a hybrid type spray device, or a vortex type spray device. A guide plate is arranged in a horizontal inlet flue of the SCR denitration device 11 and used for changing the flow direction of flue gas entering the SCR denitration device 11. The guide plate can be a straight guide plate or an arc guide plate. A soot blower is also arranged between the catalyst layer and the reducing agent spraying device 12. The soot blower can be selected as a steam soot blower or a sound wave soot blower, and the sound wave soot blower is preferred under the working condition of low dust concentration. If a steam soot blower is selected, the steam soot blower also needs to be externally connected with a steam source. The flue gas outlet of the SCR denitration device 11 is provided with a temperature detection device and a concentration detection device, and the temperature detection device is used for detecting NH in discharged flue gas by monitoring the temperature of the discharged flue gas₃、O₂、SO₂、NO_xAnd dust concentration.

In another specific embodiment, the invention provides a medium-temperature SCR denitration method for kiln tail flue gas, which specifically comprises the following steps:

(1) kiln tail flue gas Q discharged from cement kiln₀The medium dust concentration is 50-100 g/Nm³At a temperature of 280-340 ℃, NO_xThe concentration of (A) is 200-500 mg/Nm³At the tail of the kiln, flue gas Q₀Before entering the waste heat recovery device 5, the kiln tail flue gas Q is treated₀Divided into first kiln tail flue gas Q₁And second kiln tail flue gas Q₂First kiln tail flue gas Q₁Volume flow of the flue gas Q at the tail of the kiln₀10-90% of total volume flow, and first kiln tail flue gas Q₁The waste heat recovery device 5 is introduced to recover part of heat through primary heat exchange and then a part of heat is led out to form high-temperature flue gas Q₃Then the high-temperature flue gas Q is introduced into a heat exchange device 6₃The volume flow of the flue gas accounts for the flue gas Q at the tail of the first kiln₁50-60% of total volume flow and high-temperature flue gas Q₃The temperature of (A) is 260-280 ℃; the rest partContinuously carrying out secondary heat exchange to recover residual heat and then completely discharging to form medium-temperature flue gas Q₄Middle temperature flue gas Q₄The temperature of (A) is 180-200 ℃;

(2) the reducing agent storage tank 3 is used for introducing a reducing agent into the heat exchange device 6, the reducing agent comprises one or the combination of at least two of ammonia water, urea, liquid ammonia or organic amine, and the high-temperature flue gas Q₃The high-temperature flue gas Q enters a dust removal device 8 for dust removal after exchanging heat with a reducing agent in a heat exchange device 6, the dust removal efficiency of the dust removal device 8 is 50-99.99%, and the high-temperature flue gas Q after heat exchange and dust removal₃The dust concentration in the dust is 1-10 mg/Nm³The temperature is 240-260 ℃, and the high-temperature flue gas Q after heat exchange and dust removal₃Sequentially mixing with medium-temperature flue gas Q₄And second kiln tail flue gas Q₂Mixing to obtain the recycled flue gas Q₅Returning and mixing the flue gas Q₅The dust concentration in the dust is 20-40 g/Nm³The temperature is 200-260 ℃, and the recycled flue gas Q is₅Introducing an SCR denitration device 11;

(3) introducing the reducing agent subjected to heat exchange in the step (2) into an SCR denitration device 11, wherein the flow speed of flue gas in the SCR denitration device 11 is 0-10 m/s, the system resistance of the SCR denitration device 11 is 0-1000 Pa, and returning flue gas Q₅The flue gas denitration is realized by the selective catalytic reduction reaction between the catalyst and a reducing agent under the action of the catalyst, and the adopted catalyst is 0.1-20 wt% of V, Ce, Mn, Fe or W loaded TiO₂The monolithic catalyst is a monolithic catalyst of molecular sieve, mesoporous alumina or montmorillonite, and the specific surface area of the monolithic catalyst is 0-1000 m²The pore diameter is 1-100 mu m, the pore diameter of the cross section is 0-10 cm, and the monolithic catalyst is honeycomb, plate or corrugated;

the reaction temperature of the selective catalytic reduction reaction is 200-260 ℃, the molar ratio of ammonia nitrogen participating in the reaction is (0.5-1.5): 1, and the denitration efficiency of the SCR denitration device 11 is 30-99%.

Example 1

The embodiment provides a medium-temperature SCR denitration method for kiln tail flue gas, which is used for SCR denitration of kiln tail flue gas exhausted by a 3000t/d novel dry-process cement kiln, and the denitration method specifically comprises the following steps:

(1) kiln tail flue gas Q discharged from cement kiln₀Has a volume flow of 368240Nm³H kiln tail flue gas Q₀The medium dust concentration is 50g/Nm³At a temperature of 280 ℃ and NO_xAt a concentration of 200mg/Nm³At the tail of the kiln, flue gas Q₀Before entering the waste heat recovery device 5, the kiln tail flue gas Q is treated₀Divided into first kiln tail flue gas Q₁And second kiln tail flue gas Q₂First kiln tail flue gas Q₁Volume flow of the flue gas Q at the tail of the kiln ₀10 percent of the total volume flow, namely the flue gas Q at the tail of the first kiln₁Has a volume flow of 36824g/Nm³And the second kiln tail flue gas Q₂Has a volume flow of 331416g/Nm³；

First kiln tail flue gas Q₁The waste heat recovery device 5 is introduced to recover part of heat through primary heat exchange and then a part of heat is led out to form high-temperature flue gas Q₃Then the high-temperature flue gas Q is introduced into a heat exchange device 6₃The volume flow of the high-temperature flue gas Q accounts for 50 percent of the total volume flow of the flue gas at the tail of the first kiln, and 2 percent of flue gas loss and high-temperature flue gas Q are caused by considering the influence of system air leakage₃Has a volume flow of 18043.76g/Nm³High temperature flue gas Q₃At a temperature of 260 ℃; the rest part is continuously subjected to secondary heat exchange to recover the residual heat and then is completely discharged to form medium-temperature flue gas Q₄Middle temperature flue gas Q₄At a temperature of 180 ℃, medium temperature flue gas Q₄Has a volume flow of 18043.76g/Nm³；

(2) A reducing agent storage tank 3 is used for introducing a reducing agent into a heat exchange device 6, wherein the reducing agent is ammonia water, and high-temperature flue gas Q₃The high-temperature flue gas Q enters a dust removal device 8 for dust removal after exchanging heat with a reducing agent in a heat exchange device 6, the dust removal efficiency of the dust removal device 8 is 50 percent, and the high-temperature flue gas Q after heat exchange and dust removal₃The dust concentration in (1) is 10mg/Nm³The temperature is 240 ℃, and the high-temperature flue gas Q after heat exchange and dust removal₃Sequentially mixing with medium-temperature flue gas Q₄And second kiln tail flue gas Q₂Mixing to obtain the recycled flue gas Q₅Returning and mixing the flue gas Q₅The dust concentration in (1) is 40g/Nm³At the temperature of 260 ℃, returning the smoke Q₅Introducing an SCR denitration device 11;

(3) introducing the reducing agent subjected to heat exchange in the step (2) into an SCR denitration device 11, wherein the flue gas flow in the SCR denitration device 11The speed is 1m/s, the system resistance of the SCR denitration device 11 is 100Pa, and the returned flue gas Q₅The catalyst and a reducing agent are subjected to selective catalytic reduction reaction under the action of the catalyst to realize flue gas denitration, and the adopted catalyst is 0.14 wt% of V-loaded TiO₂The specific surface area of the monolithic catalyst was 55.1m²The pore diameter is 0.5 mu m, the pore diameter of the cross section is 1cm, and the monolithic catalyst is of a honeycomb structure;

the reaction temperature of the selective catalytic reduction reaction is 260 ℃, the molar ratio of ammonia nitrogen participating in the reaction is 0.5:1, and the denitration efficiency of the SCR denitration device 11 is 37%.

Example 2

The embodiment provides a medium-temperature SCR denitration method for kiln tail flue gas, which is used for SCR denitration of kiln tail flue gas exhausted by a 3200t/d novel dry-process cement kiln, and the denitration method specifically comprises the following steps:

(1) kiln tail flue gas Q discharged from cement kiln₀Has a volume flow of 436320Nm³H kiln tail flue gas Q₀The medium dust concentration is 60g/Nm³At a temperature of 290 ℃ NO_xHas a concentration of 223mg/Nm³At the tail of the kiln, flue gas Q₀Before entering the waste heat recovery device 5, the kiln tail flue gas Q is treated₀Divided into first kiln tail flue gas Q₁And second kiln tail flue gas Q₂First kiln tail flue gas Q₁Volume flow of the flue gas Q at the tail of the kiln₀40 percent of the total volume flow, namely the flue gas Q at the tail of the first kiln₁Has a volume flow of 174528g/Nm³And the second kiln tail flue gas Q₂Has a volume flow of 261792g/Nm³；

First kiln tail flue gas Q₁The waste heat recovery device 5 is introduced to recover part of heat through primary heat exchange and then a part of heat is led out to form high-temperature flue gas Q₃Then the high-temperature flue gas Q is introduced into a heat exchange device 6₃The volume flow of the high-temperature flue gas Q accounts for 53 percent of the total volume flow of the flue gas at the tail of the first kiln, and 2 percent of flue gas loss and high-temperature flue gas Q are caused by considering the influence of system air leakage₃Has a volume flow of 90649.8g/Nm³High temperature flue gas Q₃The temperature of (2) is 265 ℃; the rest part is continuously subjected to secondary heat exchange to recover the residual heat and then is completely discharged to formWarm flue gas Q₄Middle temperature flue gas Q₄At 185 ℃ and medium temperature flue gas Q₄Has a volume flow of 80387.6g/Nm³；

(2) A reducing agent storage tank 3 is used for introducing a reducing agent into a heat exchange device 6, wherein the reducing agent is urea, and high-temperature flue gas Q₃The high-temperature flue gas Q enters a dust removal device 8 for dust removal after exchanging heat with a reducing agent in a heat exchange device 6, the dust removal efficiency of the dust removal device 8 is 78 percent, and the high-temperature flue gas Q after heat exchange and dust removal is subjected to heat exchange₃The dust concentration in (1) is 7mg/Nm³The temperature is 245 ℃, and the high-temperature flue gas Q after heat exchange and dust removal₃Sequentially mixing with medium-temperature flue gas Q₄And second kiln tail flue gas Q₂Mixing to obtain the recycled flue gas Q₅Returning and mixing the flue gas Q₅Has a dust concentration of 35g/Nm³At 250 ℃, returning the mixed flue gas Q₅Introducing an SCR denitration device 11;

(3) introducing the reducing agent subjected to heat exchange in the step (2) into an SCR denitration device 11, wherein the flow speed of flue gas in the SCR denitration device 11 is 3m/s, the system resistance of the SCR denitration device 11 is 300Pa, and the returned flue gas Q₅The catalyst is an integral catalyst of 3.21 wt% of Ce supported molecular sieve, and the specific surface area of the integral catalyst is 324.4m²The pore diameter is 35 mu m, the pore diameter of the cross section is 3.8cm, and the monolithic catalyst is of a honeycomb structure;

the reaction temperature of the selective catalytic reduction reaction is 250 ℃, the molar ratio of ammonia nitrogen participating in the reaction is 0.7:1, and the denitration efficiency of the SCR denitration device 11 is 61%.

Example 3

The embodiment provides a medium-temperature SCR denitration method for kiln tail flue gas, which is used for carrying out SCR denitration on kiln tail flue gas exhausted by a 3500t/d novel dry-process cement kiln, and the denitration method specifically comprises the following steps:

(1) kiln tail flue gas Q discharged from cement kiln₀Has a volume flow of 528530Nm³H kiln tail flue gas Q₀The medium dust concentration is 70g/Nm³At a temperature of 300 ℃ NO_xAt a concentration of 300mg/Nm³At the tail of the kiln, flue gas Q₀Entering the waste heatBefore the recovery device 5, the kiln tail flue gas Q is treated₀Divided into first kiln tail flue gas Q₁And second kiln tail flue gas Q₂First kiln tail flue gas Q₁Volume flow of the flue gas Q at the tail of the kiln₀50 percent of the total volume flow, namely the flue gas Q at the tail of the first kiln₁Has a volume flow of 264265g/Nm³And the second kiln tail flue gas Q₂Has a volume flow of 264265g/Nm³；

First kiln tail flue gas Q₁The waste heat recovery device 5 is introduced to recover part of heat through primary heat exchange and then a part of heat is led out to form high-temperature flue gas Q₃Then the high-temperature flue gas Q is introduced into a heat exchange device 6₃The volume flow of the kiln tail smoke gas accounts for 55 percent of the total volume flow of the first kiln tail smoke gas, 2 percent of smoke gas loss and high-temperature smoke gas Q are caused by considering the influence of system air leakage₃Has a volume flow of 142438.8g/Nm³High temperature flue gas Q₃At a temperature of 270 ℃; the rest part is continuously subjected to secondary heat exchange to recover the residual heat and then is completely discharged to form medium-temperature flue gas Q₄Middle temperature flue gas Q₄At a temperature of 190 ℃ and medium temperature flue gas Q₄Has a volume flow of 116540.9g/Nm³；

(2) A reducing agent storage tank 3 is used for introducing a reducing agent into a heat exchange device 6, wherein the reducing agent is liquid ammonia and high-temperature flue gas Q₃The high-temperature flue gas Q after heat exchange and dust removal with a reducing agent in the heat exchange device 6 enters the dust removal device 8 for dust removal, the dust removal efficiency of the dust removal device 8 is 85 percent, and the high-temperature flue gas Q after heat exchange and dust removal is subjected to heat exchange₃The dust concentration in (1) is 5mg/Nm³The temperature is 250 ℃, and the high-temperature flue gas Q after heat exchange and dust removal₃Sequentially mixing with medium-temperature flue gas Q₄And second kiln tail flue gas Q₂Mixing to obtain the recycled flue gas Q₅Returning and mixing the flue gas Q₅The dust concentration in (1) is 30g/Nm³At the temperature of 240 ℃, returning the smoke Q₅Introducing an SCR denitration device 11;

(3) introducing the reducing agent subjected to heat exchange in the step (2) into an SCR denitration device 11, wherein the flow speed of flue gas in the SCR denitration device 11 is 5m/s, the system resistance of the SCR denitration device 11 is 500Pa, and returning flue gas Q₅The catalyst and a reducing agent are subjected to selective catalytic reduction reaction under the action of the catalyst to realize flue gas denitration, and the adopted catalyst is Mn-loaded mesoporous oxidation with the weight percent of 8.31 percentAn aluminum monolithic catalyst having a specific surface area of 512.1m²The aperture is 50 mu m, the aperture of the cross section is 4.6cm, and the monolithic catalyst is of a plate structure;

the reaction temperature of the selective catalytic reduction reaction is 240 ℃, the molar ratio of ammonia nitrogen participating in the reaction is 1:1, and the denitration efficiency of the SCR denitration device 11 is 70%.

Example 4

The embodiment provides a medium-temperature SCR denitration method for kiln tail flue gas, which is used for SCR denitration of kiln tail flue gas exhausted by a 4500t/d novel dry-process cement kiln, and the denitration method specifically comprises the following steps:

(1) kiln tail flue gas Q discharged from cement kiln₀Has a volume flow of 571420Nm³H kiln tail flue gas Q₀The medium dust concentration is 80g/Nm³At a temperature of 320 ℃ NO_xAt a concentration of 315mg/Nm³At the tail of the kiln, flue gas Q₀Before entering the waste heat recovery device 5, the kiln tail flue gas Q is treated₀Divided into first kiln tail flue gas Q₁And second kiln tail flue gas Q₂First kiln tail flue gas Q₁Volume flow of the flue gas Q at the tail of the kiln₀80 percent of the total volume flow, namely the flue gas Q at the tail of the first kiln₁Has a volume flow of 457136g/Nm³And the second kiln tail flue gas Q₂Has a volume flow of 114284g/Nm³；

First kiln tail flue gas Q₁The waste heat recovery device 5 is introduced to recover part of heat through primary heat exchange and then a part of heat is led out to form high-temperature flue gas Q₃Then the high-temperature flue gas Q is introduced into a heat exchange device 6₃The volume flow of the high-temperature flue gas Q accounts for 58 percent of the total volume flow of the flue gas at the tail of the first kiln, and 2 percent of flue gas loss and high-temperature flue gas Q are caused by considering the influence of system air leakage₃Has a volume flow of 259836.1g/Nm³High temperature flue gas Q₃At a temperature of 275 ℃; the rest part is continuously subjected to secondary heat exchange to recover the residual heat and then is completely discharged to form medium-temperature flue gas Q₄Middle temperature flue gas Q₄The temperature of the flue gas is 195 ℃, and the medium temperature flue gas Q₄Has a volume flow of 188157.2g/Nm³；

(2) The reducing agent storage tank 3 is introduced into the heat exchange device 6Reducing agent which is organic amine and high-temperature flue gas Q₃The high-temperature flue gas Q after heat exchange and dust removal with the reducing agent in the heat exchange device 6 enters the dust removal device 8 for dust removal, the dust removal efficiency of the dust removal device 8 is 95 percent, and the high-temperature flue gas Q after heat exchange and dust removal₃The dust concentration in (1) is 3mg/Nm³The temperature is 255 ℃, and the high-temperature flue gas Q after heat exchange and dust removal₃Sequentially mixing with medium-temperature flue gas Q₄And second kiln tail flue gas Q₂Mixing to obtain the recycled flue gas Q₅Returning and mixing the flue gas Q₅The dust concentration in (1) is 25g/Nm³At 220 ℃, returning the prepared flue gas Q₅Introducing an SCR denitration device 11;

(3) introducing the reducing agent subjected to heat exchange in the step (2) into an SCR denitration device 11, wherein the flow speed of flue gas in the SCR denitration device 11 is 7m/s, the system resistance of the SCR denitration device 11 is 700Pa, and returning flue gas Q₅The denitration catalyst and a reducing agent are subjected to selective catalytic reduction reaction under the action of a catalyst to realize flue gas denitration, the adopted catalyst is a monolithic catalyst of 14.13 wt% Fe-supported montmorillonite, and the specific surface area of the monolithic catalyst is 764.3m²The aperture is 73 mu m, the aperture of the cross section is 7.3cm, and the monolithic catalyst is of a plate structure;

the reaction temperature of the selective catalytic reduction reaction is 220 ℃, the molar ratio of ammonia nitrogen participating in the reaction is 1.2:1, and the denitration efficiency of the SCR denitration device 11 is 86%.

Example 5

The embodiment provides a medium-temperature SCR denitration method for kiln tail flue gas, which is used for carrying out SCR denitration on kiln tail flue gas exhausted by a 5000t/d novel dry-process cement kiln, and the denitration method specifically comprises the following steps:

(1) kiln tail flue gas Q discharged from cement kiln₀Has a volume flow of 627430Nm³H kiln tail flue gas Q₀The medium dust concentration is 100g/Nm³At a temperature of 340 ℃ NO_xAt a concentration of 500mg/Nm³At the tail of the kiln, flue gas Q₀Before entering the waste heat recovery device 5, the kiln tail flue gas Q is treated₀Divided into first kiln tail flue gas Q₁And second kiln tail flue gas Q₂First kiln tail flue gas Q₁Volume flow of the flue gas Q at the tail of the kiln₀Total volumetric flow rate of 90%, namely the flue gas Q at the tail of the first kiln₁Has a volume flow of 564687g/Nm³And the second kiln tail flue gas Q₂Has a volume flow of 62743g/Nm³；

First kiln tail flue gas Q₁The waste heat recovery device 5 is introduced to recover part of heat through primary heat exchange and then a part of heat is led out to form high-temperature flue gas Q₃Then the high-temperature flue gas Q is introduced into a heat exchange device 6₃The volume flow of the high-temperature flue gas Q accounts for 60 percent of the total volume flow of the flue gas at the tail of the first kiln, and 2 percent of flue gas loss and high-temperature flue gas Q are caused by considering the influence of system air leakage₃Has a volume flow of 332036g/Nm³High temperature flue gas Q₃The temperature of (2) is 280 ℃; the rest part is continuously subjected to secondary heat exchange to recover the residual heat and then is completely discharged to form medium-temperature flue gas Q₄Middle temperature flue gas Q₄At a temperature of 200 ℃ and medium temperature flue gas Q₄Has a volume flow of 221357.3g/Nm³；

(2) A reducing agent storage tank 3 is used for introducing a reducing agent into a heat exchange device 6, wherein the reducing agent is ammonia water, and high-temperature flue gas Q₃The high-temperature flue gas Q after heat exchange and dust removal with a reducing agent in the heat exchange device 6 enters the dust removal device 8 for dust removal, the dust removal efficiency of the dust removal device 8 is 99 percent, and the high-temperature flue gas Q after heat exchange and dust removal is subjected to heat exchange₃The dust concentration in (1 mg/Nm)³The temperature is 260 ℃, and the high-temperature flue gas Q after heat exchange and dust removal₃Sequentially mixing with medium-temperature flue gas Q₄And second kiln tail flue gas Q₂Mixing to obtain the recycled flue gas Q₅Returning and mixing the flue gas Q₅The dust concentration in (1) is 20g/Nm³At the temperature of 200 ℃, returning the smoke Q₅Introducing an SCR denitration device 11;

(3) introducing the reducing agent subjected to heat exchange in the step (2) into an SCR denitration device 11, wherein the flow speed of flue gas in the SCR denitration device 11 is 10m/s, the system resistance of the SCR denitration device 11 is 1000Pa, and the returned flue gas Q₅The catalyst and a reducing agent are subjected to selective catalytic reduction reaction under the action of the catalyst to realize flue gas denitration, and the adopted catalyst is 19.83 wt% of W-loaded TiO₂The specific surface area of the monolithic catalyst is 981.6m²The aperture is 100 mu m, the aperture of the section is 10cm, and the monolithic catalyst is of a corrugated structure;

the reaction temperature of the selective catalytic reduction reaction is 200 ℃, the molar ratio of ammonia nitrogen participating in the reaction is 1.5:1, and the denitration efficiency of the SCR denitration device 11 is 99%.

The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims

1. The medium-temperature SCR denitration system for kiln tail flue gas is characterized by comprising a waste heat recovery device, a heat exchange device and an SCR denitration device, wherein a high-temperature flue gas outlet of the waste heat recovery device is connected with the heat exchange device, and an outlet of the heat exchange device and a medium-temperature flue gas outlet of the waste heat recovery device are combined into one path and then connected into the SCR denitration device.

2. A medium-temperature SCR denitration system according to claim 1, wherein a flue gas inlet of the waste heat recovery device is connected with a kiln tail flue in an upstream system;

preferably, the upstream system is a cement kiln, and a kiln tail flue of the cement kiln discharges smoke to enter the medium-temperature SCR denitration system;

preferably, a bypass flue is connected to a kiln tail flue of the upstream system, and an outlet end of the bypass flue is connected to a dust removal and smoke exhaust pipeline; the high-temperature flue gas after heat exchange and dust removal is mixed with the medium-temperature flue gas discharged by the waste heat recovery device and part of kiln tail flue gas led out from the kiln tail flue in sequence and then is led into the SCR denitration device;

preferably, a first flue valve is arranged on the bypass flue.

3. A medium-temperature SCR denitration system according to claim 1 or 2, further comprising a dust removal device, wherein a high-temperature flue gas outlet of the waste heat recovery device is sequentially connected with the heat exchange device and the dust removal device along a flue gas flow direction, the dust removal device is connected with a flue gas inlet of the SCR denitration device through a dust removal smoke exhaust pipeline, and a medium-temperature flue gas outlet of the waste heat recovery device is connected to the dust removal smoke exhaust pipeline; the high-temperature flue gas discharged by the waste heat recovery device sequentially flows through the heat exchange device and the dust removal device and is mixed with the medium-temperature flue gas discharged by the waste heat recovery device and then is introduced into the SCR denitration device;

preferably, a second flue valve is arranged on a connecting pipeline between the heat exchange device and the dust removal device;

preferably, a third flue valve is arranged on the dust and smoke removing pipeline;

preferably, a medium-temperature flue gas outlet of the waste heat recovery device is connected to a dust and smoke removal pipeline through a three-way valve;

preferably, along the flow direction of the flue gas, the three-way valve is positioned at the front end of the third flue valve;

preferably, two stages of heat exchange modules are longitudinally arranged in the waste heat recovery device along the flow direction of the flue gas, part of the kiln tail flue gas is led out to form high-temperature flue gas after part of heat is recovered by the primary heat exchange module, and the rest of the kiln tail flue gas enters the secondary heat exchange module to recover the rest of heat to form medium-temperature exhaust;

preferably, the waste heat recovery device is a waste heat boiler;

preferably, a reducing agent channel and a flue gas channel are arranged in the heat exchange device, the flue gas and the reducing agent are contacted and exchanged heat in the heat exchange device, an inlet of the reducing agent channel is connected with a reducing agent storage tank, an outlet of the reducing agent channel is connected with an SCR denitration device, an inlet of the flue gas channel is connected with a high-temperature flue gas outlet of a waste heat recovery device, and an outlet of the flue gas channel is connected with a dust removal device;

4. A medium-temperature SCR denitration system according to any one of claims 1 to 3, wherein at least one catalyst layer is arranged inside the SCR denitration device;

preferably, a reducing agent spraying device is arranged above the catalyst layer, and reducing agent channel outlets of the heat exchange device are respectively and independently connected with the reducing agent spraying device;

preferably, the reducing agent spraying device is a grid type spraying device, a mixed type spraying device or an eddy current type spraying device;

preferably, a guide plate is arranged in a horizontal inlet flue of the SCR denitration device, and the guide plate is used for changing the flow direction of flue gas entering the SCR denitration device;

preferably, the guide plate is a straight plate-shaped guide plate or an arc-shaped guide plate;

preferably, the radian of the arc-shaped guide plate is 45-90 degrees;

preferably, a soot blower is further arranged between the catalyst layer and the reducing agent spraying device;

preferably, the soot blower is a steam soot blower or a sound wave soot blower;

preferably, the steam soot blower is externally connected with a steam source;

5. A medium-temperature SCR denitration system according to any one of claims 1 to 4, wherein the catalyst used in the catalyst layer is an alkali and alkaline earth metal-resistant monolithic catalyst;

preferably, the monolithic catalyst comprises a carrier and an active component loaded on the carrier;

preferably, the active component comprises one or a combination of at least two of V, Ce, Mn, Fe or W;

preferably, the support comprises TiO₂One or the combination of at least two of molecular sieve, mesoporous alumina or montmorillonite;

preferably, the content of the active ingredient is 0.1-20 wt%;

preferably, the specific surface area of the monolithic catalyst is 0-1000 m²/g；

Preferably, the aperture of the monolithic catalyst is 1-100 μm;

preferably, the cross-sectional aperture of the monolithic catalyst is 0-10 cm;

preferably, the monolithic catalyst is honeycomb, plate or corrugated.

6. A medium-temperature SCR denitration method for kiln tail flue gas is characterized in that a medium-temperature SCR denitration system of any one of claims 1 to 5 is adopted to carry out medium-temperature SCR denitration treatment on the kiln tail flue gas, and the denitration method comprises the following steps:

7. A medium-temperature SCR denitration method according to claim 6, wherein the medium-temperature SCR denitration method specifically comprises the following steps:

(II) the high-temperature flue gas enters a dust removal device for dust removal after exchanging heat with a reducing agent in a heat exchange device, the high-temperature flue gas after heat exchange and dust removal is sequentially mixed with the medium-temperature flue gas and the second kiln tail flue gas to obtain returned flue gas, and the returned flue gas Q5 is introduced into an SCR denitration device;

8. A medium-temperature SCR denitration method according to claim 7, wherein in the step (I), the dust concentration in the kiln tail flue gas is 50-100 g/Nm³；

Preferably, the temperature of the kiln tail flue gas is 280-340 ℃;

preferably, NO in the kiln tail flue gas_xThe concentration of (A) is 200-500 mg/Nm³；

Preferably, the volume flow of the first kiln tail flue gas accounts for 10-90% of the total volume flow of the kiln tail flue gas;

preferably, the volume flow of the high-temperature flue gas accounts for 50-60% of the total volume flow of the first kiln tail flue gas;

preferably, the temperature of the high-temperature flue gas is 260-280 ℃;

preferably, the temperature of the medium-temperature flue gas is 180-200 ℃.

9. An intermediate-temperature SCR denitration method according to claim 7 or 8, wherein in the step (II), the dust removal efficiency of the dust removal device is 50-99.99%;

preferably, the dust concentration in the high-temperature flue gas subjected to heat exchange and dust removal is 1-10 mg/Nm³；

Preferably, the temperature of the high-temperature flue gas subjected to heat exchange and dust removal is 240-260 ℃;

preferably, the dust concentration in the reconstituted flue gas is 20-40 g/Nm³；

Preferably, the temperature of the returned flue gas is 200-260 ℃;

10. A medium-temperature SCR denitration method according to any one of claims 7 to 9, wherein in the step (III), the flow velocity of flue gas in the SCR denitration device is 0-10 m/s;

preferably, the system resistance of the SCR denitration device is 0-1000 Pa;

preferably, the reaction temperature of the selective catalytic reduction reaction is 200-260 ℃;

preferably, the ammonia nitrogen molar ratio participating in the selective catalytic reduction reaction is (0.5-1.5): 1;

preferably, NO in the flue gas after SCR denitration treatment_xThe concentration of (A) is 30-50 mg/Nm³；

Preferably, the denitration efficiency of the SCR denitration device is 30-99%.