A denitration system and a flue gas denitration method for removing nitrogen oxides in sintering flue gas

Abstract

The present application provides a kind of denitration system for removing nitrogen oxides in sintering flue gas, including tower body, inlet flue and outlet flue;Wherein, tower body includes from bottom to top sequentially arranged dust hopper, first catalyst layer dust cleaning device, first catalyst layer, second catalyst layer, second catalyst layer soot blower, third catalyst layer dust cleaning device and third catalyst layer.The outstanding feature of the present application is that coke oven gas or natural gas is used as a denitration agent;By introducing gas denitration agent, the transportation and storage cost of denitration agent is saved, secondary pollution is avoided, and waste gas can also be effectively utilized, which achieves very good cost saving and environmental protection technical effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of environmental engineering technology, in particular to the field of flue gas treatment technology, and more particularly to a system for removing nitrogen oxides from sintering flue gas and a flue gas removal method. BACKGROUND

[0002] Sintering flue gas mainly comes from the sintering of iron ore in steel enterprises, and the main pollutants in its emissions include particulate matter, sulfur dioxide, nitrogen oxides, and dioxins. There are some outstanding problems in the existing sintering flue gas treatment process, including: 1) a single desulfurization process cannot meet the entire requirements of flue gas emission; 2) the combined desulfurization and denitrification process lacks treatment of dioxin and heavy metal pollutants; 3) adding a separate denitrification process, dioxin emission reduction process, or heavy metal pollutant treatment process after the desulfurization process will cause high investment and operating costs; 4) there are problems of easy plugging, corrosion, and high cost to varying degrees during equipment operation; 5) there is no good harmless treatment and comprehensive utilization of by-products, resulting in resource waste.

[0003] During the sintering production process of iron ore, part of the nitrogen-containing components in the sintering ingredients will be converted into nitrogen oxides, and part of the nitrogen in the air will also be oxidized into nitrogen oxides due to the high temperature of the combustion zone during the sintering process. These two types of nitrogen oxides constitute the main source of nitrogen oxides in sintering flue gas. Generally, the concentration of nitrogen oxides in the sintering production process is basically 500㎎ / Nm 3 The concentration of nitrogen oxides in the sintering production process is basically 200-400㎎ / Nm 3 between. According to the “Iron Sintering and Pelletizing Industry Air Pollutant Emission Standard” (GB 28662-2012 draft) issued by the Ministry of Environmental Protection, after January 1, 2015, the nitrogen oxide emission limit value of all steel enterprises is 300㎎ / Nm 3 (counted as NO2). In May 2017, the Ministry of Environmental Protection issued a document - the announcement of publishing 20 national pollutant emission standard revision sheets, including the “Iron Sintering and Pelletizing Industry Air Pollutant Emission Standard” (draft for comments), which proposes to revise the existing emission value of sintering flue gas from 300㎎ / Nm 3 (counted as NO2) to 100㎎ / Nm 3 (counted as NO2), and specifies the reference oxygen content for sintering as 16%. For the steel industry, finding a suitable denitrification process for sintering flue gas is a very urgent task.

[0004] For the current sintering flue gas denitration treatment field, sintering flue gas has the characteristics of large flow fluctuation, large temperature difference between each air duct, high dust content, high oxygen content, high moisture content, and high heavy metal content in dust, which greatly increases the difficulty of sintering flue gas denitration. The selective non-catalytic reduction process (SNCR) used in the field of power plant boiler flue gas denitration requires a temperature range of 900-1100℃, while the temperature of the sintering flue gas from the trolley is only 200-400℃ at the highest section, and the flue gas emission temperature after collecting by the sintering machine mother flue is generally around 150℃, which determines that the SNCR process is difficult to apply to the field of sintering flue gas denitration; the selective catalytic reduction process (SCR) used in the field of power plant boiler flue gas denitration requires a temperature range of 320-400℃, and by heating the sintering flue gas, the requirements of the SCR process can be met, but the honeycomb or flat plate catalyst used in the SCR denitration process is easy to be covered and clogged by the active surface of the catalyst under the condition of sintering flue gas, and the alkali metal in the sintering flue gas will adhere to the catalytic surface, and the heavy metal dust in the flue gas will also poison the catalyst and lose its effectiveness, which poses a great challenge to the application of the SCR denitration process in the field of sintering flue gas denitration.

[0005] The characteristics of sintering flue gas determine that the common SCR and SNCR processes are difficult to be used in the field of sintering flue gas denitration. The SNCR process is difficult to find a suitable temperature range in the sintering flue gas emission process; the SCR process itself can be used for sintering flue gas denitration, but because of the high dust content in the sintering flue gas and the high content of heavy metals and alkali metals in the dust, the SCR denitration catalyst is easily poisoned, so these two process technologies are difficult to make achievements in the field of sintering flue gas denitration.

[0006] CN102188906A discloses a sintering flue gas denitration system and method without ammonia denitration agent, which uses CO in the flue gas composition to reduce NOX in the flue gas through heating to achieve the effect of denitration. However, due to the high reduction activation temperature of CO and the unstable concentration of CO in the flue gas, it will inevitably cause fluctuations in the denitration efficiency, which is difficult to adapt to the future emission standard of 100㎎ / Nm 3 (16% of sintering reference oxygen, calculated as NO2).

[0007] CN104930533B discloses a flue gas reheating device for sintering flue gas denitration, which sets a burner on the inlet flue of the denitration system, and then heats the inlet flue gas of the denitration system through the circulating flue gas to meet the temperature requirements of the denitration system.

[0008] CN107281932A discloses a process method for sintering flue gas denitrification by using steel slag sensible heat and effective components, which mainly uses the sensible heat of steel slag to heat the sintering flue gas to the temperature range required by the denitrification system, and then uses an ammonia-based denitrification agent to complete the sintering flue gas denitrification process.

[0009] The above-mentioned several inventions consider the reheating process required by the sintering flue gas, provide a good technical route for the technical progress of sintering flue gas denitrification, and also verify the difficulties and severe forms faced by the current sintering flue gas denitrification field. However, due to the environmental protection form and production cost pressure faced by the steel industry, how to select a low-cost, high-efficiency and stable denitrification process is a difficult problem to be solved in the field of sintering flue gas denitrification. SUMMARY

[0010] Therefore, in order to solve the above-mentioned defects, the present application provides a denitrification system for removing nitrogen oxides in sintering flue gas and a flue gas denitrification method. The flue gas denitrification method of the present application uses coke oven gas or natural gas as a denitrification agent. The denitrification system of the present application can realize online replacement of the catalyst, and realize the best denitrification rate through control of the operating conditions.

[0011] Specifically, the denitrification system of the present application comprises a tower body, an inlet flue and an outlet flue; wherein the tower body comprises, from bottom to top, a dust accumulation hopper, a first catalyst layer dust removal device, a first catalyst layer, a second catalyst layer, a second catalyst layer soot blower, a third catalyst layer dust removal device and a third catalyst layer;

[0012] The dust accumulation hopper is used to receive the flue dust peeled off from the surface of the first catalyst layer by the first layer catalyst layer dust removal device;

[0013] The second catalyst layer soot blower is used to clean the dust deposited on the surface of the second catalyst layer;

[0014] The third catalyst layer serves as a standby catalyst layer;

[0015] The inlet flue is arranged at the upper part of the dust accumulation hopper and in contact with the side surface of the tower body, and the inlet flue further comprises a denitrification agent uniform distribution device and a flue gas rectifier installed at the connection between the inlet flue and the tower body.

[0016] Further, the denitrification agent uniform distribution device is a gas distributor.

[0017] Further, the second layer catalyst soot blower is an ultrasonic soot blower.

[0018] Further, the denitration agent uniform distribution device and the flue gas rectifying device are provided with an inlet online detection equipment connecting hole for installing an inlet online detection equipment probe.

[0019] Further, the first catalyst layer and / or the third catalyst layer can be replaced online.

[0020] Further, the first catalyst layer and / or the third catalyst layer adopts a fixed bed catalyst, the first catalyst layer and / or the third catalyst layer adopts an inclined plate arrangement, a catalyst loading port is arranged at the uppermost end of the inclined direction of the first catalyst layer and / or the third catalyst layer, a catalyst unloading port is arranged at the lowermost end of the inclined direction of the first catalyst layer and / or the third catalyst layer, and the catalyst particles in the first catalyst layer and / or the third catalyst layer can be completely discharged through the catalyst unloading port under the action of gravity to realize online replacement of the first catalyst layer and / or the third catalyst layer.

[0021] Further, the second catalyst layer adopts a corrugated plate type or honeycomb type catalyst layer.

[0022] Further, the denitration system adopts a lower inlet and upper outlet mode or an upper inlet and lower outlet mode.

[0023] Further, the tower body is provided with an accumulated ash hopper at the bottom, the flue inlet is provided with the flue gas rectifying device at the connection with the tower body, and the denitration agent uniform distribution device is arranged in the flue inlet.

[0024] The treated flue gas sequentially passes through the denitration agent uniform distribution device, the flue gas rectifying device and enters the tower body from the flue inlet; the treated flue gas is fully mixed with the denitration agent and then enters the tower body, passes through the first catalyst layer, the second catalyst layer and the third catalyst layer, and is finally discharged from the flue outlet.

[0025] The denitration agent is in a gaseous form and is introduced into the denitration system through a pipeline from the denitration agent uniform distribution device.

[0026] The application also provides a method for flue gas denitration using the aforementioned denitration system, and the method has the following prominent features: coke oven gas or natural gas is used as a denitration agent, that is, the existing waste gas is effectively utilized, other denitration agents in the prior art are not needed, the cost of the denitration agent can be saved, and the utilization of the waste gas realizes the technical effect of green environmental protection.

[0027] Further, the temperature of the first catalyst layer is controlled at 60-600 DEG C, preferably 80-550 DEG C, and most preferably 100-500 DEG C during the denitration process.

[0028] Further, in the denitration process, the second catalyst layer does not need a separate heating system or device, and is heated by the heat released in the redox reaction process, with the temperature controlled at 100-550 DEG C, preferably 120-500 DEG C, and most preferably 130-450 DEG C. This is also a prominent feature of the present application, which can save the cost of heat sources and effectively utilize the heat energy generated in the redox reaction to heat the second catalyst layer.

[0029] Further, in the denitration process, the third catalyst layer is controlled at a temperature of 100-550 DEG C, preferably 120-500 DEG C, and most preferably 130-450 DEG C.

[0030] Further, in the denitration process, coke oven gas or natural gas is used as the denitration agent, and the commonly used amino denitration agent in the prior art is not needed, which can greatly reduce the operation cost of the denitration system, and can also avoid the secondary pollution caused by the nitrogen-containing products of the amino denitration agent. At the same time, the denitration agent is in the form of gas, which can be transported by pipeline, which is clean, convenient, and can save the transportation and storage cost of the denitration agent.

[0031] The present application has the advantages of

[0032] 1. Coke oven gas or natural gas is used as the denitration agent, and the commonly used amino denitration agent in the prior art is not needed, which can greatly reduce the operation cost of the denitration system;

[0033] 2. Since the system and method of the present application use a gas type denitration agent, the transportation of the denitration agent in the entire denitration process can be realized by pipeline, which is convenient for system control and saves the transportation cost of the denitration agent;

[0034] 3. In the preferred embodiment of the present application, an online detection device probe is arranged in the outlet flue to collect the parameters of the exhaust gas, and the opening degree of the denitration agent pipeline valve is controlled by these parameters to adjust the composition and concentration of the denitration agent, so as to ensure the safety of the denitration system, realize the maximum denitration rate of the system design, and make the exhaust gas meet the national environmental protection index requirements;

[0035] 4. The sintering flue gas denitration method of the present application is a method for removing NOx in sintering flue gas by using coke oven gas or natural gas as a denitration agent XThe new process can solve the problem of sintering flue gas denitration with low investment cost and operation cost, the denitration process changes the situation that the traditional selective catalytic reduction process (SCR process) or selective non-catalytic reduction process (SNCR process) must use amino denitration agent, completely solves the problem of sintering flue gas denitration from the practicability, safety and economy of the denitration system, and the investment cost of the denitration system of the application is at least 1 / 3 lower than that of the traditional SCR denitration process, and the operation cost is reduced by more than half. And the denitration system occupies a small area, and the system construction can be carried out near the sintering flue gas machine head electric precipitator, and can be carried out overhead, and does not occupy the maintenance area of the electric precipitator;

[0036] 5、The denitration system of the application creatively uses coke oven gas as a denitration agent, and the temperature of the flue gas is first raised by catalytic oxidation in the denitration tower to reach the temperature interval required for the reduction reaction. Under this temperature condition, part of the denitration agent composition in the denitration agent which is not catalytically oxidized by oxygen in the flue gas has extremely strong reactivity, and on the surface of the second and third catalysts, the NO X The forced reduction becomes harmless N2.

[0037] 6、The denitration system provided by the application does not need to be matched with a heat exchanger, and does not need to be matched with a combustion boiler for flue gas heating, which is also the first in the field of flue gas denitration. The application adjusts the concentration of the denitration agent composition in the sintering flue gas, controls the heat release rate of the oxidation reaction in the denitration tower, realizes the temperature rise of the sintering flue gas, greatly reduces the initial construction investment of the denitration system equipment, greatly simplifies the operation control logic of the denitration system, and finally realizes the denitration problem of the sintering flue gas in the steel industry with a very simple process flow and reliable system equipment.

[0038] 7、The denitration system provided by the application can maximize the catalytic performance of the catalyst, and through system design, the deposition of dust in the sintering flue gas on the surface of the catalyst can be overcome, the service life of the catalyst can be improved, and the waste catalyst can be recycled and reused. The application has broad market prospects in the field of sintering flue gas denitration, and has a profound influence in the field of sintering flue gas denitration in China. BRIEF DESCRIPTION OF DRAWINGS

[0039] In the drawings, like reference numerals designate like or similar parts throughout the several views, and the reference numerals are the same or similar unless otherwise specified. The drawings schematically illustrate the various embodiments discussed in the present application by way of example and not limitation. These drawings are not necessarily drawn to scale.

[0040] Figure 1 is a specific embodiment of the present application;

[0041] Ash hopper-1, inlet flue-2, denitration agent uniform distribution device-3, flue gas rectifier-4, first catalyst layer ash removal device-5, first catalyst layer-6, second catalyst layer-7, second catalyst layer soot blower-8, third catalyst layer ash removal device-9, third catalyst layer-10, outlet flue-11. DETAILED DESCRIPTION

[0042] In the following, only certain exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present application. Therefore, the drawings and the description are considered to be exemplary in nature rather than limiting.

[0043] Figure 1 For a preferred embodiment of the present application, a denitration system for removing nitrogen oxides in sintering flue gas, according to the present application, comprises a tower body, an inlet flue 2 and an outlet flue 11, the tower body comprising, from bottom to top, an ash hopper 1, a first catalyst layer ash removal device 5, a first catalyst layer 6, a second catalyst layer 7, a second catalyst layer soot blower 8, a third catalyst layer ash removal device 9 and a third catalyst layer 10; wherein the ash hopper 1 is used to receive the flue gas dust peeled off from the surface of the first catalyst layer 6 by the first catalyst layer ash removal device 5; the second catalyst layer soot blower 8 is used to clean the dust deposited on the surface of the second catalyst layer 7; the third catalyst layer 10 serves as a backup catalyst layer; wherein the flue gas rectifier is arranged at the connection between the inlet flue 2 and the tower body.

[0044] Preferably, an induced draft fan is arranged in the outlet flue 11, for forming a negative pressure in the tower body, which helps the airflow to flow from the inlet flue 2 to the outlet flue 11.

[0045] Preferably, the first catalyst layer 6 and / or the third catalyst layer 10 can be replaced online (not shown in the figure). Specifically, the first catalyst layer and / or the third catalyst layer adopts a fixed bed catalyst, the first catalyst layer and / or the third catalyst layer adopts a inclined plate arrangement, a catalyst loading port is arranged at the uppermost end of the inclined direction of the first catalyst layer and / or the third catalyst layer, a catalyst discharge port is arranged at the lowermost end of the inclined direction of the first catalyst layer and / or the third catalyst layer, and the catalyst particles in the first catalyst layer and / or the third catalyst layer can be completely discharged through the catalyst discharge port under the action of gravity, so as to realize the online replacement of the first catalyst layer and / or the third catalyst layer.

[0046] The flue gas denitration method of the present application adopts coke oven gas or natural gas as the denitration agent, which is introduced from the denitration agent uniform distribution device 3. After the denitration agent is mixed with the flue gas to be treated in the inlet flue 2, the mixed gas enters the tower body through the flue gas rectifying device 4. The mixed gas passes through the first catalyst layer 6, the second catalyst layer 7, and the third catalyst layer 10, and is finally discharged through the outlet flue 11.

[0047] Further, the outlet flue 11 is also provided with an online detection device interface. The online detection device probe is arranged in the outlet flue 11 to simultaneously detect the NOx concentration in the discharged gas, and the composition ratio of the denitration agent is adjusted according to the detection data to ensure that the denitration system finally reaches the designed denitration efficiency and meets the emission indicators required by national environmental protection requirements.

[0048] Further, temperature detection devices can be optionally arranged in each layer of the catalyst layer of the tower body to detect the temperature of each region in the tower body and transmit the temperature signal to the main control room. The control system is provided with low-temperature alarm and high-temperature alarm functions to remind the operator to reasonably adjust the operating conditions of the denitration system according to the temperature change, so that the denitration system is always in a reasonable and controllable temperature range, and the designed denitration efficiency is realized with low energy consumption.

[0049] Test example:

[0050] Example 1

[0051] Raw gas composition: oxygen 16.2%, nitrogen 68.39%, water 10.2%, carbon dioxide 5.2%, sulfur dioxide 800㎎ / Nm 3 , nitrogen oxide 280㎎ / Nm 3 , smoke content 100㎎ / Nm 3 .

[0052] Denitration agent composition: hydrogen 60.15%, oxygen 0.07%, carbon monoxide 6.45%, methane 21.24%, carbon dioxide 1.82%, CnHm 2.44%, nitrogen 7.83%, and heat value 3916 Kcal / Nm 3

[0053] The inlet flue gas temperature of the denitration system is 150℃, and the gas flow rate is 60000m 3 / h. The online detection device arranged at the outlet of the denitration tower detects and analyzes that the main components of the outlet gas are as follows: oxygen: 16.36% sulfur dioxide: 760㎎ / Nm 3 nitrogen oxide: 22㎎ / Nm 3 smoke content: 20㎎ / Nm 3 .

[0054] Example 2-4

[0055] The process flow and steps are the same as those of Example 1, the flue gas flow and main flue gas components of each example are unchanged, the temperature and pressure conditions of the system control are unchanged, the denitration agent composition concentration at the inlet of the denitration tower and the bed temperature in the denitration tower are adjusted respectively, and the reaction results are shown in Table 1.

[0056] Table 1: Raw material composition and test results of each example

[0057]

[0058]

[0059] From the test examples of the above denitration method, it can be seen that the sintering flue gas denitration process involved in the present application can process flue gas with an inlet sulfur content of 800㎎ / Nm 3 , dust content of 100㎎ / Nm 3 , and the NO X emission concentration is ≤50㎎ / Nm 3 , and the denitration efficiency is more than 90%.

[0060] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A denitration system for removing nitrogen oxides from sintering flue gas, characterized by, The denitration system comprises a tower body, an inlet flue and an outlet flue; wherein the tower body comprises, from bottom to top, a dust hopper, a first catalyst layer dust cleaning device, a first catalyst layer, a second catalyst layer, a second catalyst layer soot blower, a third catalyst layer dust cleaning device and a third catalyst layer; The dust hopper is used for receiving flue gas dust peeled off from the surface of the first catalyst layer by the first catalyst layer dust cleaning device; The second catalyst layer soot blower is used for cleaning dust deposited on the surface of the second catalyst layer; The third catalyst layer serves as a standby catalyst layer; The inlet flue is arranged at the upper part of the dust hopper and is in contact with the side surface of the tower body, and the interior of the inlet flue further comprises a denitration agent uniform distribution device and a flue gas rectifier, and the flue gas rectifier is installed at the connection between the inlet flue and the tower body; The dust hopper is arranged at the bottom of the tower body, the flue gas rectifier is arranged at the connection between the inlet flue and the tower body, and the denitration agent uniform distribution device is arranged in the inlet flue; The treated flue gas enters the tower body from the inlet flue through the denitration agent uniform distribution device and the flue gas rectifier in sequence, and the treated flue gas is fully mixed with the denitration agent before entering the tower body, and then passes through the first catalyst layer, the second catalyst layer and the third catalyst layer, and finally is discharged from the outlet flue; The denitration agent is in the form of gas, is introduced into the denitration system through a pipeline from the denitration agent uniform distribution device; and The denitration agent is coke oven gas or natural gas; The first catalyst layer and / or the third catalyst layer can be replaced on line; The first catalyst layer and / or the third catalyst layer adopts fixed bed catalyst, and the first catalyst layer and / or the third catalyst layer adopts inclined plate arrangement, a catalyst loading port is arranged at the uppermost end in the inclined direction of the first catalyst layer and / or the third catalyst layer, a catalyst unloading port is arranged at the lowermost end in the inclined direction of the first catalyst layer and / or the third catalyst layer, and the catalyst particles in the first catalyst layer and / or the third catalyst layer can be completely discharged through the catalyst unloading port under the action of gravity, so that the first catalyst layer and / or the third catalyst layer can be replaced on line; The denitration agent first completes the temperature rising of flue gas through catalytic oxidation in the denitration tower, so as to reach the temperature interval required by the reduction reaction, and under this temperature condition, part of the denitration agent components in the denitration agent which are not catalytically oxidized by oxygen in the flue gas have strong reaction activity, and forcibly reduce NOX in the flue gas into harmless N2 on the surface of the second and third catalyst layers; During the denitration process, the temperature of the first catalyst layer is controlled to be 60-600℃; the second catalyst layer is heated by the heat released in the oxidation-reduction reaction process, and the temperature is controlled to be 100-550℃; and the temperature of the third catalyst layer is controlled to be 100-550℃.

2. The de-NOx system according to claim 1, characterized by, The denitration agent uniform distribution device is a gas distributor.

3. The de-NOx system according to claim 1 or 2, characterized by, The second catalyst layer soot blower is an ultrasonic soot blower.

4. The de-NOx system according to claim 3, characterized by, The device is provided with an inlet on-line detection equipment connecting hole between the denitration agent uniform distribution device and the flue gas rectifying device, which is used for installing an inlet on-line detection equipment probe.

5. The de-NOx system according to claim 4, characterized by The second catalyst layer adopts a corrugated plate type or a honeycomb type catalyst layer.

6. The de-NOx system according to claim 5, characterized by The denitration system adopts a lower inlet and upper outlet mode or an upper inlet and lower outlet mode.

7. A method for flue gas denitration using the denitration system according to any one of claims 1 to 6, characterized by, Coke oven gas or natural gas is used as the denitration agent.

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