System and method for comprehensive utilization of magnesium reduction slag waste heat

Abstract

This application relates to the field of energy conservation and environmental protection technology, and in particular to a system and method for comprehensive utilization of waste heat from magnesium reduction slag. The system includes: a slag cooling unit, comprising a slag conveying section, a slag cooling furnace, a slag discharge device, and a reduction slag storage section; a flue gas purification unit, comprising a multi-tube cyclone dust collector, a settling chamber, a dust collection hopper, and a waste heat boiler; a flue gas utilization unit, comprising an ammonia production section, a denitrification reactor, and a desulfurization section; and a flue gas treatment unit, comprising a bag filter, an induced draft fan, and an exhaust chimney. Through air cooling, the waste heat from the magnesium reduction slag is countercurrently exchanged with the combustion flue gas from the reduction furnace, followed by two-stage dust removal treatment of the flue gas. The flue gas then exchanges heat with cooling water in the waste heat boiler to obtain high-heat steam. This steam is used to dissolve urea in the denitrification section and to produce ammonia through waste water hydrolysis, thereby removing NO from the flue gas. x Then, acidic substances in the flue gas are removed, and finally dust is removed, so that the waste heat of magnesium reduction slag can be recovered and the emitted flue gas can be treated at the same time.

Description

Technical Field

[0001] This application relates to the field of energy conservation and environmental protection technology, and in particular to a system and method for the comprehensive utilization of waste heat from magnesium reduction slag. Background Technology

[0002] In the Pidgeon process for magnesium production, the reduction process refers to the reduction of MgO in calcined white magnesium with ferrosilicon as a reducing agent at ~1473K and 10Pa to produce metallic magnesium. The main component of magnesium reduction slag is 2CaO·SiO2, which is an active cementitious admixture. Approximately 5.5 tons of reduction slag are produced to produce one ton of magnesium. The temperature of the slag exiting the furnace is approximately 1000℃. When the temperature of the reduction slag drops to 200℃ (below 200℃, it has virtually no recovery value), the theoretically calculated heat released by the reduction slag is 4.576 MJ, equivalent to the calorific value of 0.156 tons of standard coal. Currently, traditional magnesium enterprises handle the reduction slag by transporting the ash to a slag pit for dumping, water cooling, and natural cooling before loading it onto trucks. This process generates a large amount of dust and creates a harsh environment. Furthermore, this process not only fails to recover the waste heat from the reduction slag, but also reduces its activity when exposed to water, hindering its reuse.

[0003] With the increasing awareness of energy conservation, emission reduction and environmental protection among enterprises, the magnesium industry is also exploring technologies for recovering waste heat from reduction slag. Currently, there are two main solutions for waste heat recovery from reduction slag: slag cooler technology and waste heat boiler technology.

[0004] (1) The slag cooler technology involves passing high-temperature slag through a slag cooler equipped with a cooling water jacket, where it exchanges heat with softened cold water. The slag temperature is reduced to below 100°C and then sent to a slag silo for storage. The softened water temperature reaches 80-100°C and is then sent to a boiler to generate steam, used for heating, or cooled and reused in a closed cooling tower. For enterprises without boilers or during the non-heating season, the recovered high-temperature softened water has nowhere to be used and requires forced cooling, leading to increased operating costs. Therefore, its utilization value for waste heat recovery is relatively low.

[0005] (2) Waste heat boiler technology involves feeding high-temperature magnesia slag into the boiler through the top inlet. The slag descends slowly under its own weight, contacting the evaporator tubes on the boiler's heating surface. The medium inside the tubes is heated, generating steam. This steam is then recycled into the vacuum system of the reduction steam jet pump. The magnesia slag is discharged from the bottom after being cooled and released from heat. However, because magnesia slag is granular at high temperatures and easily pulverizes below 600℃, it causes ash accumulation on the heat exchanger walls. Fine dust particles adhere to the equipment surface, forming scale with even lower thermal conductivity, affecting heat exchange efficiency and ultimately impacting steam generation, thus adversely affecting the reduction vacuum system. Therefore, currently, the magnesium industry lacks ideal, mature, and reliable waste heat recovery technology and equipment for production. The recovery and utilization of magnesia slag waste heat remains a technical challenge for enterprises.

[0006] However, according to the "Emission Standard of Pollutants for Magnesium and Titanium Industry" (GB25468-2010), the pollutant emission indicators for the magnesium industry are required to meet the following standards: dust ≤ 10 mg / Nm³. 3 SO2 ≤ 100 mg / Nm 3 NOx ≤ 100 mg / Nm 3 However, the current emission concentration of flue gas from magnesium reduction systems exceeds the standard emission limits. Furthermore, the numerous and dispersed reduction furnaces result in a large total emission volume and low flue gas temperature (approximately 110℃), which is detrimental to denitrification and desulfurization reactions. Meanwhile, the reaction temperature for low-temperature denitrification should be controlled between 190-200℃; otherwise, the catalyst is prone to poisoning and inactivation, affecting denitrification efficiency and causing ammonia escape. The reaction temperature for dry desulfurization should be controlled between 120-150℃ for higher desulfurization efficiency. To meet environmental emission standards, hot air furnaces are currently used for secondary heating of the flue gas to increase its temperature. Additionally, electric or steam heating is required to produce ammonia, the denitrification agent, undoubtedly increasing the company's primary energy consumption and posing another challenge to energy conservation and emission reduction. Therefore, how to recover and utilize the waste heat from magnesium reduction slag while simultaneously treating the emitted flue gas is a pressing technical problem that needs to be solved. Summary of the Invention

[0007] This application provides a system and method for the comprehensive utilization of waste heat from magnesium reduction slag, in order to solve the technical problem in the prior art that it is difficult to simultaneously treat the emitted flue gas with the waste heat from magnesium reduction slag.

[0008] In a first aspect, this application provides a system for the comprehensive utilization of waste heat from magnesium reduction slag, the system comprising:

[0009] The cold slag unit includes a slag conveying section, a cold slag furnace, a slag discharge device, and a reducing slag storage section. The discharge port of the slag conveying section is connected to the feed port of the cold slag furnace, the discharge port of the cold slag furnace is connected to the feed port of the slag discharge device, and the discharge port of the slag discharge device is connected to the reducing slag storage section.

[0010] The flue gas purification unit includes a multi-tube cyclone dust collector, a settling chamber, a dust collection hopper, and a waste heat boiler. The outlet of the cold slag furnace is connected to the inlet of the multi-tube cyclone dust collector, the outlet of the multi-tube cyclone dust collector is connected to the inlet of the settling chamber, the outlet of the settling chamber is connected to the inlet of the waste heat boiler, and the dust collection hoppers are respectively located at the dust outlets of the multi-tube cyclone dust collector and the settling chamber. The outlet of the dust collection hopper is connected to the reduction slag storage section.

[0011] The flue gas utilization unit includes an ammonia production section, a denitrification reactor, and a desulfurization section. The outlet of the ammonia production section is connected to the denitrification reactor. The outlet of the settling chamber is located between the ammonia production section and the denitrification reactor. The outlet of the denitrification reactor is connected to the inlet of the desulfurization section.

[0012] The flue gas treatment unit includes a bag filter, an induced draft fan, and an exhaust chimney. The outlet of the desulfurization section is connected to the inlet of the bag filter, the outlet of the bag filter is connected to the inlet of the induced draft fan, and the outlet of the induced draft fan is connected to the inlet of the exhaust chimney to discharge compliant flue gas.

[0013] Optionally, the ammonia production unit includes a urea dry powder silo, a urea dissolving tank, a urea pump, a urea solution storage tank, a urea pressurizing pump, a urea hydrolysis reactor, NH3 and CO2 storage tanks, and an ammonia injection system. The inlet of the urea dry powder silo is connected to the inlet of the urea dissolving tank, the outlet of the urea dissolving tank is connected to the inlet of the urea pump, the inlet of the urea dissolving tank is connected to the outlet of the waste heat boiler, and the outlet of the urea pump is connected to the inlet of the urea solution storage tank. The outlet of the urea solution storage tank is connected to the inlet of the urea pressurizing pump. The inlet of the urea solution storage tank is connected to the outlet of the waste heat boiler. The outlet of the urea pressurizing pump is connected to the inlet of the urea hydrolysis reactor. The outlet of the urea hydrolysis reactor is connected to the inlet of the NH3 and CO2 storage tank. The outlet of the NH3 and CO2 storage tank is connected to the inlet of the ammonia injection system. The outlet of the ammonia injection system is connected to the SCR denitrification reactor.

[0014] Optionally, the ammonia production unit further includes a residual liquid recovery tank and a residual liquid recovery pump. The inlet of the residual liquid recovery tank is connected to the outlet of the urea hydrolysis reactor, the outlet of the residual liquid recovery tank is connected to the inlet of the residual liquid recovery pump, and the outlet of the residual liquid recovery pump is connected to the inlet of the urea dissolving tank.

[0015] Optionally, the flue gas utilization unit further includes a closed-loop cooling tower, a circulating water tank, a circulating water pump, a deaerator, and a boiler feed pump. The condensate outlets of the urea dissolving tank, the urea solution storage tank, and the urea hydrolysis reactor are respectively connected to the inlet of the closed-loop cooling tower. The outlet of the closed-loop cooling tower is connected to the inlet of the circulating water tank. The outlet of the circulating water tank is connected to the inlet of the deaerator. The outlet of the deaerator is connected to the inlet of the boiler feed pump. The outlet of the boiler feed pump is connected to the inlet of the waste heat boiler.

[0016] Optionally, the desulfurization unit includes a desulfurizing agent silo, a desulfurizing powder silo, a metering feed screw, a desulfurization reactor, and a desulfurization ash silo. The outlet of the desulfurizing agent silo is connected to the inlet of the desulfurizing powder silo. The outlet of the desulfurizing powder silo is connected to the inlet of the metering feed screw. The outlet of the metering feed screw is connected to the inlet of the desulfurization reactor. The inlet of the desulfurization reactor is also connected to the inlet of the denitrification reactor. The outlet of the desulfurization reactor is connected to the inlet of the bag filter. The dust removal port of the bag filter is connected to the inlet of the desulfurization ash silo. The residue port of the bag filter is connected to the inlet of the desulfurizing powder silo.

[0017] Optionally, the cold slag furnace has a circular or polyhedral structure, and is divided into a high-temperature slag pre-storage area, a feeding area and a cold slag area from top to bottom, with an umbrella-shaped air distribution plate arranged under the cold slag area.

[0018] Secondly, this application provides a method for comprehensive utilization of waste heat from magnesium reduction slag, the method being adapted to the system described in the first aspect, the method comprising:

[0019] Magnesium reduction slag and combustion flue gas from the reduction furnace are subjected to countercurrent heat exchange to obtain heat-exchanged flue gas;

[0020] The waste heat of the heat exchange flue gas is recovered by using condensate water to obtain steam and reducing flue gas, respectively.

[0021] The steam is used to hydrolyze urea to obtain ammonia.

[0022] The reducing flue gas and the ammonia gas are mixed to carry out an SCR denitrification reaction to remove NOx from the reducing flue gas, thereby obtaining denitrified flue gas;

[0023] Dry powder desulfurizing agent is added to the denitrified flue gas to carry out a desulfurization reaction, followed by bag filter dust collection to obtain qualified flue gas.

[0024] Optionally, the temperature of the heat exchange flue gas is 400℃~500℃.

[0025] Optionally, the temperature of the steam is 150℃~250℃, and the pressure of the steam is 1.5MPa~3.0MPa.

[0026] Optionally, the temperature of the denitrification flue gas is 120℃~150℃.

[0027] The technical solutions provided in this application have the following advantages compared with the prior art:

[0028] This application provides a system for the comprehensive utilization of waste heat from magnesium reduction slag. Through air cooling, the waste heat from the magnesium reduction slag is counter-currently exchanged with the combustion flue gas from the reduction furnace. This heat is then transferred into the flue gas, which undergoes two-stage dust removal. The dust-removed flue gas is then exchanged with cooling water in a waste heat boiler to obtain high-temperature steam. This steam is used to dissolve urea in the denitrification section, and ammonia is produced through the hydrolysis of the waste water. The ammonia is then used to remove NO from the flue gas. x Then, acidic substances such as SO2 in the flue gas are removed by dry powder desulfurizing agent, and dust is removed by bag filter dust removal, so as to obtain standard emission flue gas. The above system can recover and utilize the waste heat of magnesium reduction slag while treating the emission flue gas. Attached Figure Description

[0029] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0030] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of a system for the comprehensive utilization of waste heat from magnesium reduction slag, provided in an embodiment of this application.

[0032] Figure 2 This is a system logic diagram of the comprehensive utilization of waste heat from magnesium reduction slag provided in an embodiment of this application.

[0033] Among them, 101-Slag hopper, 102-Traction locomotive, 103-Structure, 104-Feeding device, 105-Cold slag furnace, 106-Slag discharge device, 107-Cold slag conveyor chain bucket elevator, 108-Elevator, 109-Reduction slag bin, 110-Blower, 111-Multi-stage cyclone dust collector, 112-Cyclone dust collection conveyor, 113-Settling chamber, 114-Settling dust collection conveyor, 115-Waste heat boiler, 116-SCR reactor, 117-Bag filter dust collector, 118-Induced draft fan, 119-Chimney, 201-Urea dry powder bin 202-Urea dissolving tank, 203-Urea pump, 204-Urea liquid storage tank, 205-Urea pressurizing pump, 206-Urea hydrolysis reactor, 207-Residual liquid recovery tank, 208-Residual liquid recovery pump, 209-NH3 and CO2 storage tank, 210-Ammonia injection system, 301-Closed cooling tower, 302-Circulating water pool, 303-Circulating water pump, 304-Deaerator, 305-Boiler feed pump, 401-Desulfurizing agent silo, 402-Desulfurizing powder silo, 403-Metering feed screw, 404-Desulfurization reactor, 405-Desulfurization ash silo;

[0034] Figure 3 This is a schematic diagram of the method for comprehensive utilization of waste heat from magnesium reduction slag provided in an embodiment of this application. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0037] like Figure 1 As shown in the embodiment of this application, a system for comprehensive utilization of waste heat from magnesium reduction slag is provided, the system comprising:

[0038] The cold slag unit includes a slag conveying section, a cold slag furnace 105, a slag discharge device, and a reducing slag storage section. The discharge port of the slag conveying section is connected to the feed port of the cold slag furnace 105, the discharge port of the cold slag furnace 105 is connected to the feed port of the slag discharge device, and the discharge port of the slag discharge device is connected to the reducing slag storage section.

[0039] The flue gas purification unit includes a multi-tube cyclone dust collector, a settling chamber 113, a dust collection hopper, and a waste heat boiler 115. The outlet of the cold slag furnace 105 is connected to the inlet of the multi-tube cyclone dust collector, the outlet of the multi-tube cyclone dust collector is connected to the inlet of the settling chamber 113, and the outlet of the settling chamber 113 is connected to the inlet of the waste heat boiler 115. The dust collection hopper is located at the dust outlet of the multi-tube cyclone dust collector and the dust outlet of the settling chamber 113. The outlet of the dust collection hopper is connected to the reduction slag storage section.

[0040] The flue gas utilization unit includes an ammonia production section, a denitrification reactor, and a desulfurization section. The outlet of the ammonia production section is connected to the denitrification reactor. The outlet of the settling chamber 113 is located between the ammonia production section and the denitrification reactor. The outlet of the denitrification reactor is connected to the inlet of the desulfurization section.

[0041] The flue gas treatment unit includes a bag filter 117, an induced draft fan 118, and an exhaust chimney 119. The outlet of the desulfurization section is connected to the inlet of the bag filter 117, the outlet of the bag filter 117 is connected to the inlet of the induced draft fan 118, and the outlet of the induced draft fan 118 is connected to the inlet of the exhaust chimney 119, so as to discharge compliant flue gas.

[0042] In this embodiment, the slag transport unit consists of a reduction slag hopper 101, a traction locomotive 102, an APS positioning device, a hoisting mechanism 103, a loading device, and other equipment, and mainly completes the work of receiving slag, transporting slag, and loading slag.

[0043] After cooling, the reducing slag in the reducing slag storage section is discharged quantitatively, continuously, and in a sealed manner to the slag conveying equipment by equipment such as plate gate valves and sealed feeders. It is then sent to the reducing slag silo 109 by elevator 108 and periodically transported by truck to the cement plant for comprehensive utilization.

[0044] In some optional embodiments, the ammonia production unit includes a urea dry powder silo 201, a urea dissolving tank 202, a urea pump 203, a urea liquid storage tank 204, a urea pressurizing pump 205, a urea hydrolysis reactor 206, NH3 and CO2 storage tanks 209, and an ammonia injection system 210. The inlet of the urea dry powder silo 201 is connected to the inlet of the urea dissolving tank 202, the outlet of the urea dissolving tank 202 is connected to the inlet of the urea pump 203, the liquid inlet of the urea dissolving tank 202 is connected to the liquid outlet of the waste heat boiler 115, and the outlet of the urea pump 203 is connected to the urea... The inlet of the urea liquid storage tank 204 is connected to the outlet of the urea liquid storage tank 204, which is connected to the inlet of the urea pressurizing pump 205. The inlet of the urea liquid storage tank 204 is connected to the outlet of the waste heat boiler 115. The outlet of the urea pressurizing pump 205 is connected to the inlet of the urea hydrolysis reactor 206. The outlet of the urea hydrolysis reactor 206 is connected to the inlet of the NH3 and CO2 storage tank 209. The outlet of the NH3 and CO2 storage tank 209 is connected to the inlet of the ammonia injection system 210. The outlet of the ammonia injection system 210 is connected to the SCR denitrification reactor.

[0045] In this embodiment, by refining the specific composition of the ammonia production unit, the steam after heat exchange in the waste heat boiler 115 accelerates the dissolution of urea in the urea dissolution tank 202 to form a urea solution. The steam after heat exchange in the waste heat boiler 115 then heats the urea solution in the urea solution storage tank 204. The urea solution is then decomposed into ammonia gas through the urea hydrolysis reactor 206. The ammonia gas then enters the denitrification reactor through the ammonia injection system 210 to remove NO from the flue gas. x Impurities.

[0046] In some optional embodiments, the ammonia production unit further includes a residual liquid recovery tank 207 and a residual liquid recovery pump 208. The inlet of the residual liquid recovery tank 207 is connected to the outlet of the urea hydrolysis reactor 206, the outlet of the residual liquid recovery tank 207 is connected to the inlet of the residual liquid recovery pump 208, and the outlet of the residual liquid recovery pump 208 is connected to the inlet of the urea dissolving tank 202.

[0047] In this embodiment, by introducing a residual liquid recovery tank 207 and a residual liquid recovery pump 208 into the ammonia production section, the residual liquid recovery tank 207 recovers the hydrolysis residual liquid from the urea hydrolysis reactor 206, and the residual liquid recovery pump 208 recovers the hydrolysis residual liquid into the urea dissolving tank 202, thereby achieving repeated decomposition of the urea solution to obtain sufficient ammonia gas. Therefore, NO in the flue gas can be removed more effectively. x Impurities.

[0048] In some optional embodiments, the flue gas utilization unit further includes a closed cooling tower 301, a circulating water tank 302, a circulating water pump 303, a deaerator 304, and a boiler feed pump 305. The condensate outlets of the urea dissolving tank 202, the urea solution storage tank 204, and the urea hydrolysis reactor 206 are respectively connected to the inlet of the closed cooling tower 301. The outlet of the closed cooling tower 301 is connected to the inlet of the circulating water tank 302. The outlet of the circulating water tank 302 is connected to the inlet of the deaerator 304. The outlet of the deaerator 304 is connected to the inlet of the boiler feed pump 305. The outlet of the boiler feed pump 305 is connected to the inlet of the waste heat boiler 115.

[0049] In this embodiment of the application, by refining the specific flue gas utilization unit, the condensate in the system can be cooled by the closed cooling tower 301, the circulating water pool 302, and the circulating water pump 303. The oxygen is then removed by the deaerator 304, and the qualified water is introduced into the waste heat boiler 115 by the boiler feed water pump 305 for use as heat exchange cold water, thereby realizing the recycling of resources.

[0050] In some optional embodiments, the desulfurization unit includes a desulfurizing agent silo 401, a desulfurizing powder silo 402, a metering feed screw 403, a desulfurization reactor 404, and a desulfurization ash silo 405. The outlet of the desulfurizing agent silo 401 is connected to the inlet of the desulfurizing powder silo 402. The outlet of the desulfurizing powder silo 402 is connected to the inlet of the metering feed screw 403. The outlet of the metering feed screw 403 is connected to the inlet of the desulfurization reactor 404. The inlet of the desulfurization reactor 404 is also connected to the inlet of the denitrification reactor. The outlet of the desulfurization reactor 404 is connected to the inlet of the bag filter 117. The dust removal port of the bag filter 117 is connected to the inlet of the desulfurization ash silo 405. The residue port of the bag filter 117 is connected to the inlet of the desulfurizing powder silo 402.

[0051] In this embodiment of the application, by refining the specific desulfurization section, the desulfurizing agent can react with the acidic gas in the flue gas to obtain desulfurization ash, which is then removed by the bag filter 117 to obtain qualified flue gas. At the same time, the bag filter 117 can also return the excess desulfurizing agent to the desulfurization powder silo 402 for further desulfurization.

[0052] In some optional embodiments, the cold slag furnace 105 has a circular or polyhedral structure, and the cold slag furnace 105 is divided into a high-temperature slag pre-storage area, a feeding area and a cold slag area from top to bottom, with an umbrella-shaped air distribution plate arranged under the cold slag area.

[0053] In this embodiment of the application, by controlling the specific shape and specific partitions of the cold slag furnace 105, the umbrella-shaped air distribution plate set in the cold slag zone can be used to make the combustion exhaust gas of the reduction furnace introduced by the blower evenly distributed, so that the waste heat of magnesium reduction slag can be evenly mixed with the combustion exhaust gas of the reduction furnace, so that the heat exchange is sufficient.

[0054] The lining of the cold slag furnace 105 can be made of refractory materials.

[0055] like Figure 3 As shown, based on a general inventive concept, this application provides a method for comprehensive utilization of waste heat from magnesium reduction slag. The method is adapted to the system described above and includes:

[0056] S1. The magnesium reducing slag and the combustion flue gas from the reducing furnace are subjected to countercurrent heat exchange to obtain heat-exchanged flue gas;

[0057] S2. Waste heat is recovered from the heat exchange flue gas using condensate to obtain steam and reducing flue gas, respectively;

[0058] S3. Use the steam to hydrolyze urea to obtain ammonia;

[0059] S4. Mix the reducing flue gas and the ammonia gas to carry out an SCR denitrification reaction to remove NO from the reducing flue gas. x The denitrified flue gas is obtained;

[0060] S5. Add dry powder desulfurizing agent to the denitrified flue gas to carry out desulfurization reaction, and then perform bag filter dust removal to obtain qualified flue gas.

[0061] In this embodiment, by employing an adaptive system, the heat from the magnesium reduction slag is transferred to the combustion flue gas in the reduction furnace via countercurrent heat exchange. Heat exchange is then conducted between the condensate and the flue gas to produce steam and reducing flue gas. The steam is then used to hydrolyze the urea solution to generate ammonia, which is then used to perform SCR denitrification treatment on the reducing flue gas. Finally, a dry powder desulfurizing agent is added to carry out a desulfurization reaction, resulting in qualified flue gas. This process transfers the heat from the magnesium reduction slag to the combustion flue gas in the reduction furnace for use in subsequent flue gas treatment, achieving a dual-cycle utilization of energy and resources.

[0062] This method is based on the system described above. The specific structure of the system can be referred to in the above embodiments. Since this method adopts some or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated here.

[0063] In some alternative embodiments, the temperature of the heat exchange flue gas is 400°C to 500°C.

[0064] In this embodiment, controlling the specific temperature of the heat exchange flue gas can, on the one hand, indicate that the heat exchange between the magnesium reduction slag and the combustion flue gas in the reduction furnace is complete, and on the other hand, facilitate the subsequent heat exchange between the heat exchange flue gas and the condensate in the waste heat boiler, thereby realizing the conversion of the heat source and obtaining high-heat water vapor.

[0065] In some alternative embodiments, the temperature of the steam is 150°C to 250°C, and the pressure of the steam is 1.5 MPa to 3.0 MPa.

[0066] In this embodiment, controlling the specific temperature and pressure of the steam allows the steam to act as a heat source, promoting urea dissolution and simultaneously accelerating the hydrolysis of the urea solution. This rapid hydrolysis releases a large amount of ammonia, enabling effective removal of NO from the flue gas. x Impurities.

[0067] In some optional embodiments, the temperature of the denitrified flue gas is 120°C to 150°C.

[0068] In this embodiment of the application, controlling the specific temperature of the denitrification flue gas can ensure the smooth progress of the desulfurization reaction, thereby achieving effective treatment of the flue gas.

[0069] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national standards. If there is no corresponding national standard, then general international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0070] Example 1

[0071] like Figure 1 and Figure 2As shown, a system for comprehensive utilization of waste heat from magnesium reduction slag first collects the 1000℃ high-temperature slag discharged from the reduction furnace into a slag hopper 101, and then transports it to the top of the cold slag furnace 105 via a traction locomotive 102 and a hoisting mechanism 103. The slag is then added to the cold slag furnace via a reducing slag feeding device 104. The high-temperature slag descends by gravity and exchanges heat with the counter-current combustion flue gas from the reduction furnace. The cooled reducing slag is discharged through a slag discharge device 106 and then sent to a reducing slag silo 109 for storage via a cold slag conveying chain bucket elevator 107 and an elevator 108. The slag is then transported out by truck periodically. The combustion flue gas from the reduction furnace is blown into the lower air distribution plate of the cold slag furnace 105 by blower 110. After heat exchange with the reduction slag, the flue gas temperature reaches 400℃~500℃ and is discharged from the annular flue at the top of the cold slag furnace 105. It undergoes primary dust removal by a multi-tube cyclone dust collector 111, and the collected dust is returned to the cold slag conveyor chain bucket elevator 107 via cyclone dust collector conveyor 112. The flue gas then undergoes secondary dust removal and purification in the settling chamber 113 before entering the waste heat boiler 115. The collected dust in the settling chamber 113 is returned to the cold slag conveyor chain bucket elevator 107 via settling dust collector conveyor 114. The steam generated by the waste heat boiler 115 has a temperature of 150℃~250℃ and a pressure of 1.5MPa~3.0MPa, which is used for urea hydrolysis to produce ammonia. The flue gas temperature from the waste heat boiler 115 is about 200℃. It mixes with the ammonia gas generated by the ammonia production system and enters the SCR denitrification reactor 116 to remove NO from the flue gas. x After ammonia removal, the flue gas temperature is 120℃~150℃. It then undergoes a desulfurization reaction with dry powder desulfurizing agent in desulfurization reactor 404 to remove acidic substances such as SO2 from the flue gas. Finally, the dust in the flue gas is recovered by bag filter 117. The flue gas that meets the emission requirements is discharged through induced draft fan 118 and chimney 119.

[0072] Furthermore, the system also includes an ammonia production section. Purchased urea powder is added to the urea dry powder silo 201, and after metering, it is added to the urea dissolving tank 202. Simultaneously, deionized water is added to the urea dissolving tank 202 to stir the solution. Steam from the waste heat boiler 115 is connected to the steam indirect heating coil in the urea dissolving tank 202 to heat the dissolving solution. The qualified urea solution, after stirring and dissolving, is pumped by the urea pump 203 into the urea solution storage tank 204 for storage. Steam from the waste heat boiler 115 is connected to the steam chamber in the storage tank 204. The urea storage solution is heated by a heating coil, and then pressurized to a gauge pressure of 2.6 MPa by a urea pressurization pump 205 before being sent to the urea hydrolysis reactor 206 for decomposition. Saturated steam from the waste heat boiler 115 enters the urea hydrolysis reactor 206 indirectly to heat the urea solution for hydrolysis via a coil. A mixture of NH3, CO2, and water vapor exiting from the top outlet of the urea hydrolysis reactor 206 enters the NH3 and CO2 storage tank 209, and after depressurization, enters the ammonia injection system 210 as a denitrification reducing agent. The hydrolysis residue exiting from the bottom of the urea hydrolysis reactor 206 enters the residue recovery tank 207, and is then returned to the urea dissolving tank 202 via the residue recovery pump 208 as urea dissolving solution.

[0073] Furthermore, it also includes a flue gas utilization unit. The steam condensate from the steam indirect heating coil in the urea dissolving tank 202, urea liquid storage tank 204, and urea hydrolysis reactor 206 enters the closed cooling tower 301 for cooling. The cooling water enters the circulating water pool 302, and then enters the deaerator 304 for deoxygenation via the circulating water pump 303. The qualified water enters the waste heat boiler 115 for reuse via the boiler feed water pump 305.

[0074] Furthermore, it also includes a desulfurization section. Purchased desulfurizing agent is added to the desulfurizing agent silo 401, and after being pulverized, it enters the desulfurization powder silo 402. The desulfurization powder enters the desulfurization reactor 404 through the metering feed screw 403. At the same time, compressed air is introduced into the reactor 404. After the flue gas and desulfurization powder are fully mixed and reacted, they enter the bag filter dust collector 117 to remove dust. The dust is desulfurization ash. The desulfurization powder that has not fully reacted is returned to the desulfurization powder silo 402 for reuse. The desulfurization ash that has fully reacted is stored in the desulfurization ash silo 405 and is periodically transported by truck for reuse.

[0075] Example 2

[0076] Comparing Example 2 with Example 1, the difference between Example 2 and Example 1 is as follows:

[0077] like Figure 3 As shown, a method for comprehensive utilization of waste heat from magnesium reduction slag includes:

[0078] Magnesium reduction slag and combustion flue gas from the reduction furnace are subjected to countercurrent heat exchange to obtain heat-exchanged flue gas;

[0079] Waste heat is recovered from the heat exchange flue gas by using condensate water to obtain steam and reducing flue gas, respectively.

[0080] Urea is hydrolyzed using steam to obtain ammonia.

[0081] SCR denitrification reaction is carried out by mixing reducing flue gas and ammonia to remove NOx from the reducing flue gas and obtain denitrified flue gas;

[0082] Dry powder desulfurizing agent is added to the denitrification flue gas to carry out the desulfurization reaction, followed by bag filter dust collection to obtain qualified flue gas.

[0083] The temperature of the heat exchange flue gas is 400℃~500℃.

[0084] The steam temperature is 150℃~250℃, and the steam pressure is 1.5MPa~3.0MPa.

[0085] The temperature of the denitrification flue gas is 120℃~150℃.

[0086] In summary, the system for comprehensive utilization of waste heat from magnesium reduction slag provided in this application embodiment can effectively recover the waste heat from the reduction slag. The recovered heat is used for the desulfurization, denitrification, and dust purification system of the reduction flue gas. At the same time, it solves the problems of waste heat recovery and reuse of reduction slag and environmental compliance of combustion exhaust gas from the reduction furnace, reduces primary energy consumption, and achieves the goals of waste heat recovery, resource recycling, environmental protection, energy conservation, and emission reduction in the magnesium smelting reduction system.

[0087] One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0088] (1) The system for comprehensive utilization of waste heat of magnesium reduction slag provided in this application embodiment is as follows: the cold slag furnace 105 adopts air cooling method, the cooling air is low temperature flue gas of the reduction furnace, the reduction slag is cooled by air cooling and then stored in the warehouse by the conveying equipment, and transported in sealed tank trucks regularly, which ensures the activity of the reduction slag and is conducive to the secondary utilization of the reduction slag.

[0089] (2) The system for comprehensive utilization of waste heat of magnesium reduction slag provided in this application embodiment is that the flue gas after heat exchange with the reduction slag enters the waste heat boiler 115 after passing through multi-stage cyclone dust removal and sedimentation dust removal. After the dust is collected, it is periodically returned to the reduction slag silo 109 through the conveying equipment. The reduction slag is transported in a closed manner, which reduces the pollution of the environment caused by dust escape.

[0090] (3) The embodiment of this application provides a system for comprehensive utilization of waste heat from magnesium reduction slag. After two-stage dust removal, the flue gas enters the waste heat boiler 115, which reduces the impact of dust on the waste heat boiler 115 and improves the boiler's thermal efficiency. At the same time, the dust removal resistance is small, which reduces the load on the induced draft fan 118.

[0091] (4) The embodiment of this application provides a system for comprehensive utilization of waste heat from magnesium reduction slag. The steam generated by the waste heat boiler 115 is used for urea dissolution and hydrolysis to produce ammonia in the denitrification system, thereby reducing the primary energy consumption of the denitrification system. The steam is heated indirectly, and the steam condensate is cooled and deoxygenated before being recycled back to the waste heat boiler 115, thus saving water consumption.

[0092] (5) The method for comprehensive utilization of waste heat from magnesium reduction slag provided in this application embodiment is that the flue gas temperature from the waste heat boiler 115 is 190℃~200℃, and there is no need for auxiliary heat sources such as hot air furnaces to heat it, which is conducive to the SCR denitrification reaction, extends the service life of the catalyst, and reduces the operating cost of the catalyst.

[0093] (6) The method for comprehensive utilization of waste heat of magnesium reduction slag provided in this application embodiment is that the flue gas temperature from the SCR denitrification tower is 120℃~150℃, which can react with dry powder desulfurizing agent and is higher than the flue gas dew point temperature, thus avoiding the blockage of bag filter 117 and increasing system resistance. The dust collected by the bag filter can be returned to the desulfurization system for secondary use, or it can be stored in the ash silo and transported out for secondary use on a regular basis.

[0094] (7) The method for comprehensive utilization of waste heat from magnesium reduction slag provided in this application follows the principle of energy cascade utilization, focuses on the recycling of materials, has no wastewater or waste residue discharge, reduces primary energy consumption, and truly achieves the purpose of waste heat recovery, resource recycling, energy conservation and emission reduction, and environmental protection compliance.

[0095] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0096] In this application, unless otherwise stated, directional terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Furthermore, in the description of this application, terms such as "comprising" and "including" mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0097] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A system for comprehensive utilization of waste heat from magnesium reduction slag, characterized in that, The system includes: The cold slag unit includes a slag conveying section, a cold slag furnace (105), a slag discharge device, and a reducing slag storage section. The discharge port of the slag conveying section is connected to the feed port of the cold slag furnace (105), the discharge port of the cold slag furnace (105) is connected to the feed port of the slag discharge device, and the discharge port of the slag discharge device is connected to the reducing slag storage section. The cold slag furnace is used to cool magnesium reducing slag by air cooling. The cooling medium is the combustion flue gas of the reducing furnace. The magnesium reducing slag and the combustion flue gas of the reducing furnace exchange heat countercurrently in the cold slag furnace. The cold slag furnace (105) has a circular or polyhedral structure. The cold slag furnace (105) is divided into a high-temperature slag pre-storage area, a feeding area, and a cold slag area from top to bottom. An umbrella-shaped air distribution plate is arranged under the cold slag area. The flue gas purification unit includes a multi-tube cyclone dust collector, a settling chamber (113), a dust collection hopper, and a waste heat boiler (115). The outlet of the cold slag furnace (105) is connected to the inlet of the multi-tube cyclone dust collector, the outlet of the multi-tube cyclone dust collector is connected to the inlet of the settling chamber (113), the outlet of the settling chamber (113) is connected to the inlet of the waste heat boiler (115), and the dust collection hopper is respectively located at the dust outlet of the multi-tube cyclone dust collector and the dust outlet of the settling chamber (113); the discharge port of the dust collection hopper is connected to the reduction slag storage section. The flue gas utilization unit includes an ammonia production section, a denitrification reactor, and a desulfurization section. The ammonia production section uses steam generated by the waste heat boiler to hydrolyze urea to produce ammonia. The outlet of the ammonia production section is connected to the denitrification reactor. The outlet of the settling chamber (113) is located between the ammonia production section and the denitrification reactor. The outlet of the denitrification reactor is connected to the inlet of the desulfurization section. The flue gas treatment unit includes a bag filter (117), an induced draft fan (118), and an exhaust chimney (119). The outlet of the desulfurization section is connected to the inlet of the bag filter (117), the outlet of the bag filter (117) is connected to the inlet of the induced draft fan (118), and the outlet of the induced draft fan (118) is connected to the inlet of the exhaust chimney (119) to discharge compliant flue gas.

2. The system according to claim 1, characterized in that, The ammonia production unit includes a urea dry powder silo (201), a urea dissolving tank (202), a urea pump (203), a urea liquid storage tank (204), a urea pressurizing pump (205), a urea hydrolysis reactor (206), NH3 and CO2 storage tanks (209), and an ammonia injection system (210). The inlet of the urea dry powder silo (201) is connected to the inlet of the urea dissolving tank (202), the outlet of the urea dissolving tank (202) is connected to the inlet of the urea pump (203), the liquid inlet of the urea dissolving tank (202) is connected to the liquid outlet of the waste heat boiler (115), and the outlet of the urea pump (203) is connected to the urea liquid storage tank. The inlet of (204) is connected to the urea solution storage tank (204), the outlet of the urea solution storage tank (204) is connected to the inlet of the urea pressurizing pump (205), the inlet of the urea solution storage tank (204) is connected to the outlet of the waste heat boiler (115), the outlet of the urea pressurizing pump (205) is connected to the inlet of the urea hydrolysis reactor (206), the outlet of the urea hydrolysis reactor (206) is connected to the inlet of the NH3 and CO2 storage tank (209), the outlet of the NH3 and CO2 storage tank (209) is connected to the inlet of the ammonia injection system (210), and the outlet of the ammonia injection system (210) is connected to the SCR denitrification reactor.

3. The system according to claim 2, characterized in that, The ammonia production unit also includes a residual liquid recovery tank (207) and a residual liquid recovery pump (208). The inlet of the residual liquid recovery tank (207) is connected to the outlet of the urea hydrolysis reactor (206), the outlet of the residual liquid recovery tank (207) is connected to the inlet of the residual liquid recovery pump (208), and the outlet of the residual liquid recovery pump (208) is connected to the inlet of the urea dissolving tank (202).

4. The system according to claim 2, characterized in that, The flue gas utilization unit also includes a closed cooling tower (301), a circulating water tank (302), a circulating water pump (303), a deaerator (304), and a boiler feed pump (305). The condensate outlets of the urea dissolving tank (202), the urea liquid storage tank (204), and the urea hydrolysis reactor (206) are respectively connected to the inlet of the closed cooling tower (301). The outlet of the closed cooling tower (301) is connected to the inlet of the circulating water tank (302). The outlet of the circulating water tank (302) is connected to the inlet of the deaerator (304). The outlet of the deaerator (304) is connected to the inlet of the boiler feed pump (305). The outlet of the boiler feed pump (305) is connected to the inlet of the waste heat boiler (115).

5. The system according to claim 1, characterized in that, The desulfurization unit includes a desulfurizing agent silo (401), a desulfurizing powder silo (402), a metering feed screw (403), a desulfurization reactor (404), and a desulfurization ash silo (405). The outlet of the desulfurizing agent silo (401) is connected to the inlet of the desulfurizing powder silo (402), the outlet of the desulfurizing powder silo (402) is connected to the inlet of the metering feed screw (403), and the outlet of the metering feed screw (403) is connected to the... The feed inlet of the desulfurization reactor (404) is also connected to the feed inlet of the denitrification reactor. The discharge outlet of the desulfurization reactor (404) is connected to the feed inlet of the bag filter (117). The dust removal port of the bag filter (117) is connected to the feed inlet of the desulfurization ash silo (405). The residual material port of the bag filter (117) is connected to the feed inlet of the desulfurization powder silo (402).

6. A method for comprehensive utilization of waste heat from magnesium reduction slag, characterized in that, The method is adapted to the system as described in any one of claims 1-5, and the method includes: Magnesium reduction slag and combustion flue gas from the reduction furnace are subjected to countercurrent heat exchange to obtain heat-exchanged flue gas; The waste heat of the heat exchange flue gas is recovered by using condensate water to obtain steam and reducing flue gas, respectively. The steam is used to hydrolyze urea to obtain ammonia. The reducing flue gas and the ammonia gas are mixed to carry out an SCR denitrification reaction to remove NOx from the reducing flue gas, thereby obtaining denitrified flue gas; Dry powder desulfurizing agent is added to the denitrified flue gas to carry out a desulfurization reaction, followed by bag filter dust collection to obtain qualified flue gas.

7. The method according to claim 6, characterized in that, The temperature of the heat exchange flue gas is 400℃~500℃.

8. The method according to claim 6, characterized in that, The temperature of the steam is 150℃~250℃, and the pressure of the steam is 1.5MPa~3.0MPa.

9. The method according to claim 6, characterized in that, The temperature of the denitrification flue gas is 120℃~150℃.

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