Electric furnace flue gas waste heat recovery and catalytic purification integrated device and method

Abstract

The invention provides an electric furnace flue gas waste heat recovery and catalytic purification integrated device and method.The integrated device comprises a flue gas waste heat recovery unit and a flue gas purification unit, the flue gas waste heat recovery unit comprises a waste heat boiler and at least two stages of heat exchangers arranged in series, and the flue gas purification unit comprises an ammonia spraying mixer and a catalyst bed layer; the flue gas purification unit is arranged in front of the last stage of heat exchanger, the flue gas outlet of the last but one stage of heat exchanger is connected with the catalyst bed layer, and the ammonia spraying mixer is positioned on a pipeline between the two or externally connected between the two. The flue gas waste heat recovery unit and the catalytic purification unit are combined, and the heat utilization efficiency can be fully improved through the arrangement of the multi-stage heat exchanger; the catalytic purification unit is arranged in front of the last-stage heat exchanger, so that the flue gas is catalytically purified at a proper temperature, NOx and dioxin in the electric flue gas are removed at the same time, and the removal rate of pollutants is increased; the device is simple in structure and process, reasonable in equipment matching, capable of effectively reducing cost and wide in application range.

Description

Technical Field

[0001] The invention belongs to the technical field of flue gas waste heat recovery and treatment, and relates to an integrated device and method for electric furnace flue gas waste heat recovery and catalytic purification. Background Art

[0002] With the acceleration of industrialization, air pollution has become a global environmental problem, and the requirements of various countries for air quality are constantly increasing, leading to the tightening of industrial emission standards. As a common equipment in industrial production and scientific research, electric furnaces are widely used in metallurgy, chemical industry, electronics, medical treatment, building materials and other industries, but they have the characteristics of high energy consumption and high pollution, and the flue gas emitted needs to be effectively treated to reduce emissions, improve environmental quality, and improve energy efficiency.

[0003] According to the composition of the flue gas from the electric furnace, the NO x It is a major type of air pollutant. It is not only one of the main causes of acid rain and photochemical smog, but also damages the ozone layer and aggravates the greenhouse effect. In addition, electric furnace flue gas usually contains organic pollutants such as dioxins. Dioxins are semi-volatile. Once released into the environment, they will be photochemically oxidized or combined with particles for deposition. At the same time, dioxins will accumulate in the food chain and easily cause carcinogenicity and distortion. Based on this, it is necessary to purify the flue gas from the electric furnace, and according to the temperature characteristics of the flue gas from the electric furnace and the temperature requirements during purification, it is necessary to recover the waste heat of the high-temperature flue gas from the electric furnace to improve the utilization rate of the heat in the flue gas.

[0004] CN 104807341A discloses a system and process for purifying electric furnace flue gas and utilizing waste heat at the same time. The system includes an electric furnace, a scrap steel preheating device, a four-hole exhaust pipe, a quenching tower, a dust collector, an induced draft fan and a chimney connected in sequence; the end of the scrap steel preheating device connected to the electric furnace is provided with a mixing valve for mixing combustion-supporting gas to ensure that the combustible substances in the four-hole flue gas are fully burned, and the upper part of the scrap steel preheating device is provided with a burner for injecting fuel combustion to maintain the flue gas temperature in the device at 900-1000°C. The inner surface of the device is coated with a heat-insulating material for reducing the heat dissipation of the device, and a stepped feeding mechanism is provided inside. The device treats dust and dioxins in the flue gas of the electric furnace, but the treatment method of dioxins is high-temperature combustion rather than catalytic decomposition, and does not involve NO x The combustion treatment requires additional energy consumption, and the waste heat utilization is directly exchanged with scrap steel, which limits the scope of application.

[0005] CN 110793338A discloses a flue gas purification and waste heat utilization system and method, the system comprises a flue gas discharge unit, a primary waste heat utilization unit, a primary flue gas purification unit, a secondary waste heat utilization unit and a secondary flue gas purification unit connected in sequence along the flue gas flow direction, the primary flue gas purification unit is used to remove NO in the flue gas x , large particles and CO, the secondary flue gas purification unit is used to remove NO in the flue gas x The system has many structural units and operation steps, and each component in the flue gas is treated separately. x The treatment includes SNCR reaction and SCR reaction. The former requires a high temperature, resulting in higher energy consumption. When utilizing waste heat, two-stage heat exchange is also adopted, and the scrap steel preheating device used has higher requirements on the temperature of the flue gas.

[0006] In summary, for the treatment device and method of electric furnace flue gas, it is necessary to select a suitable unit combination according to the composition and parameter characteristics of the flue gas, so as to realize the recovery and utilization of flue gas waste heat and remove NO in the flue gas. x It can remove pollutants and dioxins simultaneously to achieve full purification of flue gas and reduce costs and energy consumption. Summary of the invention

[0007] In view of the problems existing in the prior art, the present invention aims to provide an integrated device and method for waste heat recovery and catalytic purification of flue gas from an electric furnace. The device combines a flue gas waste heat recovery unit with a catalytic purification unit, uses a multi-stage heat exchanger to cool the flue gas, and generates steam to improve the utilization efficiency of heat, so that the flue gas can be catalytically purified within a suitable temperature, and dioxins and NO in the flue gas can be removed. x Removal is carried out at the same time to improve the removal rate of pollutants and reduce the equipment and energy consumption costs of flue gas treatment.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] On the one hand, the present invention provides an integrated device for waste heat recovery and catalytic purification of flue gas from an electric furnace, the integrated device comprising a waste heat recovery unit for flue gas and a flue gas purification unit, the waste heat recovery unit for flue gas comprising a waste heat boiler and at least two stages of heat exchangers arranged in series, the heat exchanger and the waste heat boiler perform heat exchange, the flue gas purification unit comprises an ammonia injection mixer and a catalyst bed, the flue gas purification unit is arranged before the last stage of the heat exchanger, the flue gas outlet of the penultimate stage of the heat exchanger is connected to the catalyst bed, the ammonia injection mixer is located on the pipeline between the penultimate stage of the heat exchanger and the catalyst bed or the outlet of the ammonia injection mixer is connected to the pipeline between the two, and the catalyst bed is used to remove NO in the flue gas from the electric furnace x and dioxins.

[0010] In the present invention, according to the source and composition of the flue gas from the electric furnace, it is necessary to cool down the gas before removing pollutants. By combining the flue gas waste heat recovery unit and the flue gas purification unit, especially by setting up a multi-stage heat exchanger, the flue gas and the feed water in the waste heat boiler are subjected to multiple heat exchanges, the utilization efficiency of heat is fully improved, and steam products are produced. In particular, the catalytic purification unit is set before the last stage of the heat exchanger, so that the flue gas is catalytically purified at a suitable temperature. By selecting the catalyst, NO in the flue gas from the electric furnace is reduced. x The flue gas pollutants can be removed simultaneously with dioxins, thereby improving the removal rate of flue gas pollutants; the device has a simple structure, reasonable equipment matching, simple process, can effectively reduce equipment and operating costs, and has a wide range of applications.

[0011] The following are preferred technical solutions of the present invention, but are not intended to be limitations of the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved and realized.

[0012] As a preferred technical solution of the present invention, the supporting structure of the waste heat boiler includes a deaerator and an economizer, and the boiler feed water of the waste heat boiler enters the waste heat boiler through the deaerator and the economizer in sequence.

[0013] Preferably, the flue gas from the electric furnace enters the heat exchanger after passing through the deaerator, and enters the economizer after passing through the last stage of heat exchanger.

[0014] Preferably, the structure in the waste heat boiler includes a steam drum, and steam is generated at the outlet of the steam drum.

[0015] In the present invention, the flue gas exchanges heat with water in the waste heat boiler to produce steam from the water. Before the flue gas enters the heat exchanger, it is first connected to the deaerator as a heat source for the deaerator to promote the discharge of dissolved oxygen in the water and avoid affecting the waste heat boiler.

[0016] As a preferred technical solution of the present invention, the number of stages of the heat exchanger is 3 to 6, such as 3, 4, 5 or 6, which is determined according to factors such as the amount of flue gas to be treated and its temperature, the size of a single heat exchanger, etc.

[0017] Preferably, the types of the heat exchanger include shell and tube heat exchangers and / or fin-tube heat exchangers.

[0018] Preferably, the penultimate heat exchanger is connected in series or in parallel with the ammonia spray mixer, and the ammonia sprayed from the ammonia spray mixer is mixed with the flue gas from the electric furnace and connected to the top of the catalyst bed, and the end of the catalyst bed is connected to the inlet of the last heat exchanger.

[0019] As a preferred technical solution of the present invention, the total height of the catalyst bed is 5.0 to 6.0 m, for example, 5.0 m, 5.2 m, 5.4 m, 5.5 m, 5.6 m, 5.8 m or 6.0 m, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] Preferably, the catalyst bed is a multi-bed structure, and the height of each bed is independently 1.0 to 2.0 m, for example, 1.0 m, 1.2 m, 1.4 m, 1.5 m, 1.6 m, 1.8 m or 2.0 m, etc., and the distance between two connected beds is 0.5 to 1.0 m, for example, 0.5 m, 0.6 m, 0.7 m, 0.8 m, 0.9 m or 1.0 m, etc.; but it is not limited to the listed values, and other unlisted values ​​within the respective numerical ranges are also applicable.

[0021] Preferably, the catalyst bed consists of a catalyst and a filler, and the catalyst is in a honeycomb shape and is laid in the filler.

[0022] Preferably, a metal plate is provided at the bottom of each catalyst bed as support.

[0023] In the present invention, the design of the catalyst bed should ensure sufficient contact between the flue gas and the catalyst, and should also avoid excessive accumulation of the bed layer, which would slow down the flue gas flow rate and affect the flue gas treatment efficiency.

[0024] On the other hand, the present invention provides a method for recovering waste heat and catalytically purifying flue gas from an electric furnace using the above-mentioned integrated device, the method comprising:

[0025] The flue gas from the electric furnace is passed through the heat exchanger to conduct multi-stage heat exchange with the feed water in the waste heat boiler. After cooling, it is mixed with ammonia for catalytic purification. x After the removal of dioxins, the flue gas is heated and cooled again to obtain purified flue gas.

[0026] As a preferred technical solution of the present invention, the temperature of the electric furnace flue gas is 450-500°C, for example, 450°C, 460°C, 480°C, 500°C, 520°C, 540°C or 550°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] In the present invention, the source of the electric furnace flue gas includes the flue gas generated during the electric furnace steelmaking process, the flue gas generated during the smelting process, or the flue gas generated during the steel tapping process.

[0028] Preferably, the flow rate of the electric furnace flue gas is 100000~300000Nm 3 / h, for example 100000Nm 3 / h、120000Nm3 / h、150000Nm 3 / h、180000Nm 3 / h、200000Nm 3 / h、240000Nm 3 / h、270000Nm 3 / h or 300000Nm 3 / h, etc., but are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] Preferably, the NO in the electric furnace flue gas x The concentration is 300~400mg / Nm 3 , for example 300mg / Nm 3 、320mg / Nm 3 、340mg / Nm 3 、360mg / Nm 3 、380mg / Nm 3 or 400mg / Nm 3 etc., but are not limited to the listed values. Other values ​​not listed in this range are also applicable; the concentration of dioxin is 5-10ng TEQ / Nm 3 , for example 5ng TEQ / Nm 3 、6ng TEQ / Nm 3 、7ng TEQ / Nm 3 、8ng TEQ / Nm 3 、9ng TEQ / Nm 3 or 10ng TEQ / Nm 3 The above range is not limited to the listed values, and other values ​​not listed within the above range are also applicable.

[0030] Preferably, the inlet flow rate of the electric furnace flue gas is 7.0-9.0 m / s, for example, 7.0 m / s, 7.2 m / s, 7.5 m / s, 7.8 m / s, 8.0 m / s, 8.2 m / s, 8.5 m / s, 8.8 m / s or 9.0 m / s, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] As a preferred technical solution of the present invention, the heat exchange medium of the heat exchanger is boiler feed water, and the feed water enters the waste heat boiler after being preheated by a deaerator and an economizer.

[0032] Preferably, the electric furnace flue gas undergoes 2 to 5 heat exchanges, for example 2, 3, 4 or 5 times, before catalytic purification, and is cooled to 210 to 220°C, for example 210°C, 212°C, 214°C, 215°C, 216°C, 218°C or 220°C, etc., but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0033] Preferably, the steam output of the waste heat boiler is 30.0-34.0 t / h, for example, 30.0 t / h, 30.5 t / h, 31.0 t / h, 31.5 t / h, 32.0 t / h, 32.5 t / h, 33.0 t / h, 33.5 t / h or 34.0 t / h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] In the present invention, as the steam output increases, the heat exchange efficiency will also increase accordingly.

[0035] Preferably, the steam-water ratio of the waste heat boiler refers to the mass ratio of the steam produced by the boiler to the feed water, and the ratio is (10-12):1, for example, 10:1, 10.5:1, 11:1, 11.5:1 or 12:1, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] In the present invention, the steam-to-water ratio in the waste heat boiler is selected to be within a suitable range, so that the steam can effectively take away heat and improve the heat exchange efficiency; if the steam-to-water ratio is too high, it may cause steam supersaturation, reduce the effective transfer of heat energy, and thus reduce the thermal efficiency; if the steam-to-water ratio is too low, the water content increases, which may increase the heat loss of the boiler, because the specific heat capacity of water is lower than that of steam, absorbs heat more slowly, and has a lower heat exchange efficiency, and more water is needed to absorb heat.

[0037] As a preferred technical solution of the present invention, ammonia is sprayed into the electric furnace flue gas before catalytic purification. The source of the ammonia includes any one of aqueous ammonia, urea or liquid ammonia, or a combination of at least two of them. Typical but non-limiting examples of the combination include: a combination of aqueous ammonia and urea, a combination of urea and liquid ammonia, a combination of aqueous ammonia, urea and liquid ammonia, etc.

[0038] Preferably, the ammonia gas and NO in the electric furnace flue gas x The molar ratio is (0.5-1):1, for example 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1 or 1:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] As a preferred technical solution of the present invention, the catalyst used for catalytic purification includes a vanadium-titanium catalyst, which is composed of an active component and a carrier, wherein the mass ratio of the active component to the carrier is (0.4-0.8):1, for example 0.4:1, 0.45:1, 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1, 0.75:1 or 0.8:1, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] Preferably, the vanadium-titanium series catalyst includes a vanadium-tungsten-titanium series catalyst or a vanadium-cerium-titanium series catalyst.

[0041] Preferably, the active component in the vanadium-titanium catalyst is vanadium-tungsten oxide (V2O5-WO3) or vanadium-cerium oxide (V2O5-CeO2), and the carrier is titanium oxide TiO2.

[0042] Preferably, the mass ratio of vanadium oxide to carrier titanium oxide in the active component is (0.1-0.3):1, such as 0.1:1, 0.15:1, 0.2:1, 0.25:1 or 0.3:1, and the mass ratio of tungsten oxide or cerium oxide to carrier titanium oxide is (0.3-0.5):1, such as 0.3:1, 0.35:1, 0.4:1, 0.45:1 or 0.5:1, etc.; but it is not limited to the listed values, and other unlisted values ​​within the respective numerical ranges are also applicable.

[0043] In the present invention, the selection of the catalyst type can simultaneously remove NO x Vanadium-titanium catalysts are usually used for SCR reactions, and their catalytic performance is excellent. The catalytic temperature can be significantly reduced, and basically complete conversion can be achieved at 200-220°C. The mechanism by which vanadium-titanium catalysts can catalytically decompose dioxins is that the catalysts adsorb dioxin molecules through the active sites on their surfaces and catalyze oxidation reactions under heating conditions to decompose them into harmless small molecules such as carbon dioxide, water and hydrogen chloride.

[0044] As a preferred technical solution of the present invention, the temperature of the catalytic purification is 200-220°C, for example, 200°C, 203°C, 205°C, 208°C, 210°C, 212°C, 215°C, 218°C or 220°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] Preferably, during the catalytic purification process, NO x It is reduced to N2 and dioxins are decomposed into HCl, CO2 and H2O.

[0046] Preferably, the electric furnace flue gas after catalytic purification is 200-210°C, for example, 200°C, 202°C, 204°C, 205°C, 206°C, 208°C or 210°C, etc., enters the last stage heat exchanger for heat exchange, and is discharged after heat exchange in the economizer.

[0047] Preferably, the temperature of the purified flue gas is 150-160°C, for example, 150°C, 152°C, 154°C, 155°C, 156°C, 158°C or 160°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0048] In the present invention, the temperature of the purified flue gas is not high after leaving the economizer, and no further processing is required, and the flue gas can be basically discharged directly.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] (1) The device of the present invention combines a flue gas waste heat recovery unit with a catalytic purification unit, and in particular, provides a multi-stage heat exchanger to perform multiple heat exchanges between the flue gas and the feed water in the waste heat boiler, thereby fully improving the utilization efficiency of heat and producing steam products;

[0051] (2) The device of the present invention arranges the catalytic purification unit before the last stage heat exchanger, so that the flue gas is catalytically purified at a suitable temperature. By selecting the catalyst, NO in the flue gas of the electric furnace is reduced to x Simultaneous removal of flue gas pollutants and dioxins can increase the removal rate to more than 98%;

[0052] (3) The device of the present invention has a simple structure, reasonable equipment matching, and simple process, which can effectively reduce equipment and operating costs and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 1 is a schematic diagram of the structure of an integrated device for recovering waste heat from flue gas from an electric furnace and for catalytic purification provided in Example 1 of the present invention;

[0054] Among them, 1-waste heat boiler, 21-primary heat exchanger, 22-secondary heat exchanger, 23-third-stage heat exchanger, 24-fourth-stage heat exchanger, 25-fifth-stage heat exchanger, 3-ammonia injection mixer, 4-catalyst bed, 5-deaerator, 6-economizer, 7-steam drum. DETAILED DESCRIPTION

[0055] In order to better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the present invention is further described in detail below. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0056] The following are typical but non-limiting embodiments of the present invention:

[0057] Embodiment 1:

[0058] This embodiment provides an integrated device for recovering waste heat from flue gas from an electric furnace and catalytically purifying the flue gas. The structural schematic diagram of the integrated device is shown in FIG. Figure 1 As shown, it includes a flue gas waste heat recovery unit and a flue gas purification unit, the flue gas waste heat recovery unit includes a waste heat boiler 1 and a five-stage series heat exchanger, the heat exchanger and the waste heat boiler 1 perform heat exchange, the flue gas purification unit includes an ammonia injection mixer 3 and a catalyst bed 4, the flue gas purification unit is arranged before the last stage of the heat exchanger, the flue gas outlet of the penultimate stage of the heat exchanger is connected to the catalyst bed 4, the ammonia injection mixer 3 is located on the pipeline between the penultimate stage of the heat exchanger and the catalyst bed 4, the catalyst bed 4 is used to remove NO in the flue gas of the electric furnace x and dioxins.

[0059] The supporting structure of the waste heat boiler 1 includes a deaerator 5 and an economizer 6. The boiler feed water of the waste heat boiler 1 enters the waste heat boiler 1 through the deaerator 5 and the economizer 6 in sequence.

[0060] The electric furnace flue gas passes through the deaerator 5 and enters the heat exchanger, and then passes through the last stage of the heat exchanger and enters the economizer 6.

[0061] The structure in the waste heat boiler 1 includes a steam drum 7, and the outlet of the steam drum 7 generates steam.

[0062] The heat exchanger has five stages, namely, a first-stage heat exchanger 21 , a second-stage heat exchanger 22 , a third-stage heat exchanger 23 , a fourth-stage heat exchanger 24 , and a fifth-stage heat exchanger 25 .

[0063] The type of heat exchanger is a shell and tube heat exchanger.

[0064] The penultimate heat exchanger is connected in series with the ammonia spray mixer 3. The ammonia sprayed from the ammonia spray mixer 3 is mixed with the flue gas of the electric furnace and connected to the top of the catalyst bed 4. The end of the catalyst bed 4 is connected to the inlet of the last heat exchanger.

[0065] The total height of the catalyst bed 4 is 5.0 m.

[0066] The catalyst bed 4 is a multi-bed structure, the height of each bed is 2.0 m, and the distance between two connected beds is 1.0 m.

[0067] The catalyst bed 4 is composed of a catalyst and a filler. The catalyst is in a honeycomb shape and is laid in the filler.

[0068] An iron plate is provided at the bottom of each catalyst bed 4 as support.

[0069] Embodiment 2:

[0070] The present embodiment provides an integrated device for waste heat recovery and catalytic purification of flue gas from an electric furnace, the integrated device comprising a waste heat recovery unit for flue gas and a flue gas purification unit, the waste heat recovery unit for flue gas comprising a waste heat boiler 1 and a three-stage series-arranged heat exchanger, the heat exchanger and the waste heat boiler 1 perform heat exchange, the flue gas purification unit comprises an ammonia injection mixer 3 and a catalyst bed 4, the flue gas purification unit is arranged before the last stage of the heat exchanger, the flue gas outlet of the penultimate stage of the heat exchanger is connected to the catalyst bed 4, the outlet of the ammonia injection mixer 3 is connected to the pipeline between the penultimate stage of the heat exchanger and the catalyst bed 4, the catalyst bed 4 is used to remove NO in the flue gas from the electric furnace x and dioxins.

[0071] The supporting structure of the waste heat boiler 1 includes a deaerator 5 and an economizer 6. The boiler feed water of the waste heat boiler 1 enters the waste heat boiler 1 through the deaerator 5 and the economizer 6 in sequence.

[0072] The electric furnace flue gas passes through the deaerator 5 and enters the heat exchanger, and then passes through the last stage of the heat exchanger and enters the economizer 6.

[0073] The structure in the waste heat boiler 1 includes a steam drum 7, and the outlet of the steam drum 7 generates steam.

[0074] The heat exchanger has three stages, namely, a primary heat exchanger 21 , a secondary heat exchanger 22 and a tertiary heat exchanger 23 .

[0075] The type of heat exchanger is a fin-tube heat exchanger.

[0076] The penultimate heat exchanger is connected in parallel with the ammonia spray mixer 3. The ammonia sprayed from the ammonia spray mixer 3 is mixed with the flue gas of the electric furnace and connected to the top of the catalyst bed 4. The end of the catalyst bed 4 is connected to the inlet of the last heat exchanger.

[0077] The total height of the catalyst bed 4 is 6.0 m.

[0078] The catalyst bed 4 is a multi-bed structure, the height of each bed is 1.5m, and the distance between two connected beds is 0.75m.

[0079] The catalyst bed 4 is composed of a catalyst and a filler. The catalyst is in a honeycomb shape and is laid in the filler.

[0080] An iron plate is provided at the bottom of each catalyst bed 4 as support.

[0081] Embodiment 3:

[0082] The present embodiment provides an integrated device for waste heat recovery and catalytic purification of flue gas from an electric furnace, the integrated device comprising a waste heat recovery unit for flue gas and a flue gas purification unit, the waste heat recovery unit for flue gas comprising a waste heat boiler 1 and a heat exchanger arranged in series in four stages, the heat exchanger and the waste heat boiler 1 perform heat exchange, the flue gas purification unit comprises an ammonia injection mixer 3 and a catalyst bed 4, the flue gas purification unit is arranged before the last stage of the heat exchanger, the flue gas outlet of the penultimate stage of the heat exchanger is connected to the catalyst bed 4, the outlet of the ammonia injection mixer 3 is connected to the pipeline between the penultimate stage of the heat exchanger and the catalyst bed 4, the catalyst bed 4 is used to remove NO in the flue gas from the electric furnace x and dioxins.

[0083] The supporting structure of the waste heat boiler 1 includes a deaerator 5 and an economizer 6. The boiler feed water of the waste heat boiler 1 enters the waste heat boiler 1 through the deaerator 5 and the economizer 6 in sequence.

[0084] The electric furnace flue gas passes through the deaerator 5 and enters the heat exchanger, and then passes through the last stage of the heat exchanger and enters the economizer 6.

[0085] The structure in the waste heat boiler 1 includes a steam drum 7, and the outlet of the steam drum 7 generates steam.

[0086] The heat exchanger has four stages, namely, a primary heat exchanger 21 , a secondary heat exchanger 22 , a tertiary heat exchanger 23 and a quaternary heat exchanger 24 .

[0087] The type of heat exchanger is a shell and tube heat exchanger.

[0088] The penultimate heat exchanger is connected in parallel with the ammonia spray mixer 3. The ammonia sprayed from the ammonia spray mixer 3 is mixed with the flue gas of the electric furnace and connected to the top of the catalyst bed 4. The end of the catalyst bed 4 is connected to the inlet of the last heat exchanger.

[0089] The total height of the catalyst bed 4 is 5.5 m.

[0090] The catalyst bed 4 is a multi-bed structure, the height of each bed is 1.0 m, and the distance between two connected beds is 0.5 m.

[0091] The catalyst bed 4 is composed of a catalyst and a filler. The catalyst is in a honeycomb shape and is laid in the filler.

[0092] A stainless steel plate is provided at the bottom of each catalyst bed 4 as support.

[0093] Embodiment 4:

[0094] This embodiment provides an integrated treatment method for waste heat recovery and catalytic purification of flue gas from an electric furnace. The method uses the device in Embodiment 1 and includes the following steps:

[0095] (1) The flue gas from the electric furnace is passed through a heat exchanger to perform multi-stage heat exchange with the feed water in the waste heat boiler. The temperature of the flue gas from the electric furnace is 500°C and the flow rate of the flue gas from the electric furnace is 200,000 Nm 3 / h, NO in the flue gas of electric furnace x The concentration is 350mg / Nm 3 , the concentration of dioxins is 8ng TEQ / Nm 3 The flow rate of the electric furnace flue gas is 8.0 m / s. The feed water enters the waste heat boiler after passing through the deaerator and economizer, and is cooled to 215°C after 4 heat exchanges. The steam output of the waste heat boiler is 32.0 t / h, and the steam-water mass ratio of the waste heat boiler is 10:1;

[0096] (2) The furnace flue gas after cooling in step (1) is mixed with ammonia gas for catalytic purification, wherein the source of the ammonia gas is ammonia water, and the ammonia gas is mixed with NO in the furnace flue gas for catalytic purification. x The molar ratio of is 0.8:1, the catalyst used in the catalytic purification includes a vanadium-tungsten-titanium catalyst, wherein the active component is V2O5-WO3, the carrier is TiO2, the mass ratio of V2O5 to TiO2 is 0.2:1, and the mass ratio of WO3 to TiO2 is 0.4:1. The temperature of the catalytic purification is 215°C. During the catalytic purification process, NO x is reduced to N2, dioxins are decomposed into HCl, CO2 and H2O, and the NO in the flue gas of the electric furnace is x After the removal of dioxins, the flue gas enters the last stage heat exchanger for heat exchange again, and then passes through the economizer for heat exchange before being discharged to obtain purified flue gas, the temperature of which is 155°C.

[0097] In this embodiment, the above method is used to recover the waste heat and catalytically purify the flue gas from the electric furnace, and the dioxins and NO x The removal rate reaches 98.5%, and the flue gas heat utilization efficiency is high and the treatment cost is low.

[0098] Embodiment 5:

[0099] This embodiment provides an integrated treatment method for waste heat recovery and catalytic purification of flue gas from an electric furnace. The method uses the device in Example 2 and includes the following steps:

[0100] (1) The flue gas from the electric furnace is passed through a heat exchanger to perform multi-stage heat exchange with the feed water in the waste heat boiler. The temperature of the flue gas from the electric furnace is 450°C and the flow rate of the flue gas from the electric furnace is 150,000 Nm 3 / h, NO in flue gas from electric furnace x The concentration is 300mg / Nm 3 , the concentration of dioxins is 5ng TEQ / Nm 3The flow rate of the electric furnace flue gas is 9.0 m / s. The feed water enters the waste heat boiler after passing through the deaerator and economizer, and is cooled to 220°C after two heat exchanges. The steam output of the waste heat boiler is 30.0 t / h, and the steam-water mass ratio of the waste heat boiler is 11:1;

[0101] (2) The furnace flue gas after cooling in step (1) is mixed with ammonia for catalytic purification, wherein the source of the ammonia is urea, and the ammonia and NO in the furnace flue gas are x The molar ratio of is 0.5:1, the catalyst used in the catalytic purification includes a vanadium-cerium-titanium catalyst, wherein the active component is V2O5-CeO2, the carrier is TiO2, the mass ratio of V2O5 to TiO2 is 0.3:1, the mass ratio of CeO2 to TiO2 is 0.3:1, the temperature of the catalytic purification is 220°C, and during the catalytic purification process, NO x is reduced to N2, dioxins are decomposed into HCl, CO2 and H2O, and the NO in the flue gas of the electric furnace is x After the removal of dioxins and flue gases, the flue gas enters the last stage heat exchanger for heat exchange again, and then passes through the economizer for heat exchange before being discharged to obtain purified flue gas, the temperature of which is 160°C.

[0102] In this embodiment, the above method is used to recover the waste heat and catalytically purify the flue gas from the electric furnace, and the dioxins and NO x The removal rate reaches 98.3%, and the flue gas heat utilization efficiency is high and the treatment cost is low.

[0103] Embodiment 6:

[0104] This embodiment provides an integrated treatment method for waste heat recovery and catalytic purification of flue gas from an electric furnace. The method uses the device in Embodiment 3 and includes the following steps:

[0105] (1) The flue gas from the electric furnace is passed through a heat exchanger to perform multi-stage heat exchange with the feed water in the waste heat boiler. The temperature of the flue gas from the electric furnace is 480°C and the flow rate of the flue gas from the electric furnace is 250,000 Nm 3 / h, NO in flue gas from electric furnace x The concentration is 400mg / Nm 3 , the concentration of dioxin is 10ng TEQ / Nm 3 The flow rate of the flue gas from the electric furnace is 7.0 m / s. The feed water enters the waste heat boiler after passing through the deaerator and the economizer. After three heat exchanges, the temperature is reduced to 210°C. The steam output of the waste heat boiler is 34.0 t / h, and the steam-water mass ratio of the waste heat boiler is 12:1.

[0106] (2) The furnace flue gas after cooling in step (1) is mixed with ammonia gas for catalytic purification, wherein the source of the ammonia gas is liquid ammonia, and the ammonia gas is mixed with NO in the furnace flue gas for catalytic purification. xThe molar ratio of 1:1, the catalyst used in the catalytic purification includes a vanadium-tungsten-titanium catalyst, wherein the active component is V2O5-WO3, the carrier is TiO2, the mass ratio of V2O5 to TiO2 is 0.1:1, and the mass ratio of WO3 to TiO2 is 0.5:1. The temperature of the catalytic purification is 210°C. During the catalytic purification process, NO x is reduced to N2, dioxins are decomposed into HCl, CO2 and H2O, and the NO in the flue gas of the electric furnace is x After the removal of dioxins and flue gases, the flue gas enters the last stage heat exchanger for heat exchange again, and then passes through the economizer for heat exchange before being discharged to obtain purified flue gas, the temperature of which is 150°C.

[0107] In this embodiment, the above method is used to recover the waste heat and catalytically purify the flue gas from the electric furnace, and the dioxins and NO x The removal rate reaches 98.0%, and the flue gas heat utilization efficiency is high and the treatment cost is low.

[0108] Embodiment 7:

[0109] This embodiment provides an integrated treatment method for waste heat recovery and catalytic purification of electric furnace flue gas. The method refers to the method in Example 4, with the only difference being that the introduction rate of the electric furnace flue gas in step (1) is 10.0 m / s.

[0110] In this embodiment, since the introduction rate of the electric furnace flue gas is relatively high, it is easy for the flue gas to stay in the heat exchanger and the catalyst bed for a period of time, resulting in insufficient heat exchange and inappropriate temperature during catalytic purification, resulting in a lower pollutant removal rate. The removal rate at this time is 81%.

[0111] Embodiment 8:

[0112] This embodiment provides an integrated treatment method for waste heat recovery and catalytic purification of electric furnace flue gas. The method refers to the method in Example 4, with the only difference being that the steam output of the waste heat boiler in step (1) is 35.0 t / h.

[0113] In this embodiment, since the steam output of the waste heat boiler is relatively high, that is, the heat exchange efficiency of the heat exchanger is relatively high, the flue gas temperature drops too much, making it unable to meet the temperature of the catalyst for catalytic purification, and the pollutant removal rate is reduced to only 86%.

[0114] Based on the above embodiments, it can be seen that the device of the present invention combines the flue gas waste heat recovery unit and the catalytic purification unit, especially arranges a multi-stage heat exchanger, exchanges heat between the flue gas and the feed water in the waste heat boiler for multiple times, fully improves the heat utilization efficiency, and produces steam products; the device arranges the catalytic purification unit before the last stage of the heat exchanger, so that the flue gas is catalytically purified at a suitable temperature, and NO in the flue gas of the electric furnace is reduced by selecting the catalyst. xThe removal rate of flue gas pollutants can be increased to more than 98% by removing dioxins and flue gas pollutants at the same time; the device has a simple structure, reasonable equipment matching, simple process, can effectively reduce equipment and operation costs, and has a wide range of applications.

[0115] The applicant declares that the present invention uses the above embodiments to illustrate the detailed devices and methods of the present invention, but the present invention is not limited to the above detailed devices and methods, that is, it does not mean that the present invention must rely on the above detailed devices and methods to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the device of the present invention, addition of auxiliary devices, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. An integrated device for waste heat recovery and catalytic purification of electric furnace flue gas, characterized in that: The integrated device comprises a flue gas waste heat recovery unit and a flue gas purification unit. The flue gas waste heat recovery unit comprises a waste heat boiler and at least two stages of heat exchangers arranged in series. The heat exchanger and the waste heat boiler perform heat exchange. The flue gas purification unit comprises an ammonia spray mixer and a catalyst bed. The flue gas purification unit is arranged before the last stage of the heat exchanger. The flue gas outlet of the penultimate stage of the heat exchanger is connected to the catalyst bed. The ammonia spray mixer is located on the pipeline between the penultimate stage of the heat exchanger and the catalyst bed or the outlet of the ammonia spray mixer is connected to the pipeline between the two. The catalyst bed is used to remove NO in the flue gas of the electric furnace. x and dioxins.

2. The integrated device according to claim 1, characterized in that: The supporting structure of the waste heat boiler includes a deaerator and an economizer, and the boiler feed water of the waste heat boiler enters the waste heat boiler through the deaerator and the economizer in sequence; Preferably, the electric furnace flue gas enters the heat exchanger after passing through the deaerator, and enters the economizer after passing through the last stage of heat exchanger; Preferably, the structure in the waste heat boiler includes a steam drum, and steam is generated at the outlet of the steam drum.

3. The integrated device according to claim 1 or 2, characterized in that: The number of stages of the heat exchanger is 3 to 6; Preferably, the type of the heat exchanger includes a shell and tube heat exchanger and / or a fin-tube heat exchanger; Preferably, the penultimate heat exchanger is connected in series or in parallel with the ammonia spray mixer, and the ammonia sprayed from the ammonia spray mixer is mixed with the electric furnace flue gas and connected to the top of the catalyst bed, and the end of the catalyst bed is connected to the inlet of the last heat exchanger.

4. The integrated device according to any one of claims 1 to 3, characterized in that: The total height of the catalyst bed is 5.0 to 6.0 m; Preferably, the catalyst bed is a multi-bed structure, the height of each bed is independently 1.0 to 2.0 m, and the distance between two connected beds is 0.5 to 1.0 m; Preferably, the catalyst bed is composed of a catalyst and a filler, and the catalyst is in a honeycomb shape and is laid in the filler; Preferably, a metal plate is provided at the bottom of each catalyst bed as support.

5. A method for recovering waste heat and catalytically purifying flue gas from an electric furnace using the integrated device according to any one of claims 1 to 4, characterized in that: The method comprises: The flue gas from the electric furnace is passed through the heat exchanger to conduct multi-stage heat exchange with the feed water in the waste heat boiler. After cooling, it is mixed with ammonia for catalytic purification. x After the removal of dioxins, the flue gas is heated and cooled again to obtain purified flue gas.

6. The method according to claim 5, characterized in that The temperature of the electric furnace flue gas is 450-500°C; Preferably, the flow rate of the electric furnace flue gas is 100000~300000Nm 3 / h; Preferably, the NO in the electric furnace flue gas x The concentration is 300~400mg / Nm 3 The concentration of dioxins is 5-10 ng TEQ / Nm 3 ; Preferably, the inlet flow rate of the electric furnace flue gas is 7.0-9.0 m / s.

7. The method according to claim 5 or 6, characterized in that: The heat exchange medium of the heat exchanger is boiler feed water, which enters the waste heat boiler after being preheated by the deaerator and economizer; Preferably, the electric furnace flue gas undergoes 2 to 5 heat exchanges before catalytic purification, and is cooled to 210 to 220°C; Preferably, the steam output of the waste heat boiler is 30.0-34.0 t / h; Preferably, the steam-water ratio of the waste heat boiler refers to the mass ratio of the steam produced by the boiler to the feed water, and the ratio is (10-12):

1.

8. The method according to any one of claims 5 to 7, characterized in that: Before the electric furnace flue gas is catalytically purified, ammonia is sprayed into the flue gas, and the source of the ammonia includes any one of ammonia water, urea or liquid ammonia, or a combination of at least two of them; Preferably, the ammonia gas and NO in the electric furnace flue gas x The molar ratio is (0.5~1):

1.

9. The method according to any one of claims 5 to 8, characterized in that: The catalyst used in the catalytic purification includes a vanadium-titanium catalyst, which is composed of an active component and a carrier, wherein the mass ratio of the active component to the carrier is (0.4-0.8):1; Preferably, the vanadium-titanium catalyst comprises a vanadium-tungsten-titanium catalyst or a vanadium-cerium-titanium catalyst; Preferably, the active component in the vanadium-titanium catalyst is vanadium-tungsten oxide or vanadium-cerium oxide, and the carrier is titanium oxide; Preferably, the mass ratio of vanadium oxide to carrier titanium oxide in the active component is (0.1-0.3):1, and the mass ratio of tungsten oxide or cerium oxide to carrier titanium oxide is (0.3-0.5):

1.

10. The method according to any one of claims 5 to 9, characterized in that: The temperature of the catalytic purification is 200-220°C; Preferably, during the catalytic purification process, NO x is reduced to N2, and dioxins are decomposed into HCl, CO2, and H2O; Preferably, the electric furnace flue gas after catalytic purification is 200-210°C, enters the last stage heat exchanger for heat exchange, and then passes through the economizer for heat exchange before being discharged; Preferably, the temperature of the purified flue gas is 150-160°C.

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