System for producing sulfuric acid and co-producing lime and coupling calcium carbide through industrial by-product gypsum

Abstract

The utility model discloses a system for producing sulfuric acid and co-producing lime and coupling calcium carbide from industrial by-product gypsum, which relates to the technical field of production of sulfuric acid and co-producing lime and calcium carbide from industrial gypsum, and comprises a pretreatment drying system for removing impurities in ardealite and obtaining gypsum, and a gypsum decomposition system for decomposing the gypsum into solid CaO and SO2 flue gas, the sulfuric acid preparation system is used for treating SO2 flue gas; and the calcium carbide preparation system is used for preparing calcium carbide by taking solid CaO as a raw material. Compared with the traditional calcium carbide production system, the system provided by the utility model can directly reduce 80% of CO2 emission and save 100% of high-quality limestone resources.

Description

Technical Field

[0001] The utility model relates to the technical field of industrial gypsum sulfuric acid co-production lime and calcium carbide production, in particular to a system for industrial by-product gypsum sulfuric acid co-production lime coupled with calcium carbide production. Background Art

[0002] Phosphogypsum is a solid waste produced in the wet phosphoric acid production process. 90% of the phosphoric acid used in China is prepared by the wet process. The wet phosphoric acid process requires the use of concentrated sulfuric acid to decompose phosphate ore to produce phosphoric acid. For every 1t of phosphoric acid produced, 4.5-5.0t of phosphogypsum will be produced. The composition of phosphogypsum is relatively complex. In addition to calcium sulfate, there are also incompletely decomposed phosphate ore, residual phosphoric acid, fluoride, acid insoluble matter, organic matter, etc. Among them, the presence of fluorine and organic matter has the greatest impact on the resource utilization of phosphogypsum. The large-scale discharge and storage of phosphogypsum has seriously damaged the ecological environment, not only polluting groundwater resources, but also causing a waste of land resources. While my country produces a large amount of phosphogypsum as a by-product, sulfur resources are seriously insufficient. Every year, a large amount of sulfur needs to be imported from abroad to prepare concentrated sulfuric acid required for phosphoric acid production, which costs a huge amount of foreign exchange and causes the storage of phosphogypsum waste residue.

[0003] Desulfurized gypsum is an industrial byproduct obtained by desulfurizing and purifying the flue gas produced after the combustion of sulfur-containing fuels (coal, oil, etc.), and it mainly comes from thermal power plants. The vast majority of flue gas desulfurization devices in domestic thermal power plants use limestone flue gas desulfurization systems (i.e., coal-fired power plants use sulfur-containing coal to burn and produce tail gas containing sulfur dioxide, which is then washed with lime (stone) water to obtain desulfurized gypsum). Coal-fired power plants basically use this desulfurization technology. There is some calcium sulfite in the desulfurized gypsum that has not been completely converted into calcium sulfate. This compound is unstable and easily decomposed into calcium oxide, sulfur dioxide, etc.; most of the sulfides in the desulfurized gypsum are toxic substances, and they have great environmental risks after entering the groundwater system and the external environment.

[0004] Phosphogypsum and desulfurized gypsum are the types of industrial by-product gypsum with the largest production volume. Due to the high CaSO4·2H2O content, they are suitable for thermal decomposition to produce sulfuric acid and cement clinker (or lime) to achieve large-scale and high-value utilization. However, phosphogypsum contains many impurities and must be pretreated to remove the impurities in order to ensure that the solid product after decomposition can produce qualified cement clinker (or lime).

[0005] Sulfuric acid (H2SO4) is the most important oxygen-containing acid of sulfur. Sulfuric acid is an important industrial raw material that can be used to make fertilizers, medicines, explosives, pigments, detergents, batteries, etc. It is also widely used in industries such as petroleum purification, metal smelting, and dyes.

[0006] The main component of calcium carbide is calcium carbide (CaC2), a colorless crystal, known as the "mother of organic synthesis industry". It is an important organic chemical raw material that can synthesize many organic substances. With the continuous improvement of people's living standards, the market demand for products such as polyvinyl chloride, chloroprene rubber, and polyvinyl alcohol continues to increase. The calcium carbide industry still has a large room for development in the future.

[0007] At present, the main method for industrial production of calcium carbide is the electrothermal method (the reaction device is an electric arc furnace, and the reaction temperature is 2000-2200℃). First, the lump lime and lump coke that meet the production requirements of calcium carbide (particle size and chemical composition) are mixed according to the specified ratio, and then the charge is sent to the top silo of the calcium carbide furnace by a bucket elevator, and the charge is added to the electric furnace through the material pipe. The charge is generated by the resistance heat reaction of the electrode arc pad and the charge in the electric furnace. The calcium carbide is taken out of the furnace at a fixed time and placed in the calcium carbide pot. After cooling, it is broken into a particle size required by a certain specification, and the finished calcium carbide is obtained. Because the electrothermal method uses block raw materials, the heat and mass transfer efficiency between the raw materials is low, and there are problems such as long chemical reaction time, high reaction temperature, high energy consumption and equipment investment cost, large dust emission, and serious pollution. At the same time, in order to ensure the smooth discharge of furnace gas, quicklime and coke have strict requirements on particle size. Therefore, in the current calcium carbide production process, the calcium carbide furnace cannot directly use powdered materials for production, resulting in a huge waste of resources and increased costs. It is impossible to get rid of the extreme dependence on high-quality limestone and high-quality coke, and carbon emissions remain high.

[0008] In order to free the production of cement clinker (lime) and calcium carbide products from dependence on high-quality limestone and significantly reduce carbon emissions, it is necessary to explore more uses for the solid products of thermal decomposition of industrial by-product gypsum and truly realize the large-scale and high-value utilization of industrial by-product gypsum.

[0009] The inventor of the utility model has designed a corresponding solution. The Chinese patent application with publication number CN116750984A discloses a method and system for treating byproduct gypsum of sulfuric acid co-production of cement clinker, and gives a detailed description of the method and process of industrial byproduct gypsum for sulfuric acid co-production of cement clinker. However, considering further optimizing process indicators, adapting to more different application scenarios, and allowing the byproducts after sulfuric acid production to derive more products, so as to utilize industrial byproduct gypsum on a larger scale, the utility model provides a system for industrial byproduct gypsum for sulfuric acid co-production of lime coupled with calcium carbide production. Utility Model Content

[0010] The purpose of the utility model is to overcome the shortcomings of the prior art and provide a system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and calcium carbide, thereby getting rid of the dependence on high-quality limestone in the production of cement clinker (lime) and calcium carbide products and realizing the large-scale and high-value utilization of industrial by-product gypsum.

[0011] In order to achieve the above purpose, the technical solution adopted by the utility model is as follows:

[0012] A system for producing sulfuric acid and co-producing lime from industrial by-product gypsum coupled with calcium carbide production, including a pretreatment drying system for removing impurities in phosphogypsum and obtaining gypsum, a gypsum decomposition system for decomposing gypsum into solid CaO and SO2 flue gas, a sulfuric acid production system for treating SO2 flue gas, and a calcium carbide production system for preparing calcium carbide using solid CaO as raw material.

[0013] Furthermore, the calcium carbide production system includes a mixing chamber for mixing solid CaO, carbon material and air, a pellet forming machine for extruding the material in the mixing chamber into pellets, a pyrolysis furnace for pyrolyzing the pellets, a closed calcium carbide furnace for smelting the pyrolyzed pellets into liquid calcium carbide, a liquid calcium carbide self-forming and cooling system for cooling the liquid calcium carbide, and a finished calcium carbide warehouse for storing calcium carbide.

[0014] Furthermore, the liquid calcium carbide self-forming and cooling system includes a molding unit that can process the liquid battery into granules, a cooling unit and a cooler for cooling the granular calcium carbide, and a closed conveyor for transporting the cooled calcium carbide to the finished product calcium carbide warehouse.

[0015] Furthermore, the molding unit includes a main body, a sealing cover arranged on the top of the main body, a liquid calcium carbide inlet opened on the sealing cover, a molding hole arranged inside the main body, and a rotating knife that can rotate below the molding hole; the molding unit is connected to the cooling unit through a disassembly flange.

[0016] Furthermore, a vertical cooler is provided on the pipeline from the mixing chamber to the pelletizing machine.

[0017] Furthermore, the pretreatment drying system includes a lime weighing bin for unloading lime, and a phosphogypsum pre-homogenization yard located below the lime weighing bin; the weighing bin, the wet material air-locking feeder, the gypsum drying crusher, and the first cyclone separator are sequentially arranged at the discharge port of the phosphogypsum pre-homogenization yard; the first cyclone separator is connected to a sulfuric acid delivery pipeline, and the discharge port of the first cyclone separator is sequentially connected to a bag dust collector and a semi-hydrated gypsum storage.

[0018] Furthermore, a first blower is provided in the gypsum decomposition system.

[0019] Furthermore, the system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and coupled with calcium carbide production is also equipped with a high-temperature fan connected to the gypsum decomposition system and used to discharge SO2 flue gas, and an SP boiler and an electrostatic precipitator are connected to the high-temperature fan in sequence; the sulfuric acid production system is connected to the electrostatic precipitator.

[0020] Furthermore, the system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and coupled with calcium carbide production is also provided with a first heat exchanger for cooling the products produced by the pyrolysis furnace; and is also provided with an exhaust gas waste heat boiler for cooling the exhaust gas produced in the closed calcium carbide furnace.

[0021] Furthermore, the system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and coupled calcium carbide production also includes a heat recovery system.

[0022] Compared with the prior art, the utility model has the following beneficial effects:

[0023] (1) Compared with the traditional calcium carbide production system, the system provided by the utility model can directly reduce CO2 emissions by 80% and save high-quality limestone resources by 100%.

[0024] (2) When calcium carbide is prepared using the system provided by the utility model, low-rank coal (lignite) can be used entirely as carbon material, saving more than 60% of the carbon material cost.

[0025] (3) In the utility model, hot pellets are prepared and then fed into the calcium carbide furnace. Since lime and lignite are mixed as powders, the heat and mass transfer efficiency between the raw materials is improved, the chemical reaction time is shortened, the reaction temperature is lowered (above 100°C), and the energy consumption is greatly reduced. The power consumption can be reduced by 1,000 degrees per ton of calcium carbide.

[0026] (4) The problem of sensible heat recovery from liquid calcium carbide has been successfully solved. The liquid calcium carbide self-forming and cooling system of the embodiment is adopted. The equipment has a unique design, is simple, mature and reliable, and can recover 30% of the heat consumption in calcium carbide production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The overall structural diagram of the system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and coupled calcium carbide production provided by the utility model;

[0028] Figure 2 A partial diagram of the system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and coupled calcium carbide production provided by the utility model;

[0029] Figure 3 Another partial diagram of the system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and coupled calcium carbide production provided by the utility model;

[0030] Figure 4 This is a structural diagram of the liquid calcium carbide self-forming and cooling system in the utility model;

[0031] Figure 5 This is a partial diagram of the liquid calcium carbide self-forming and cooling system in the utility model.

[0032] The names corresponding to the reference numerals are:

[0033] 1-phosphogypsum pre-homogenization yard, 2-first cyclone separator, 3-low calorific value coal gangue pre-combustion hot air furnace system, 4-first multi-cyclone preheater, 5-second multi-cyclone preheater, 6-dual atmosphere circulation material gypsum decomposition furnace, 7-first blower, 8-electromagnetic heating device, 9-second cyclone separator, 10-feeding port, 11-SP boiler, 12-electric dust collector, 13-sulfuric acid system, 14-carbon raw material powder silo, 15-adhesive storage silo, 16-mixing chamber, 17-vertical cooler, 18-pellet forming machine, 1901-first lifting device, 1902-second lifting motor, 20-pyrolysis furnace, 21-feeding device, 22-closed calcium carbide furnace, 23-liquid Calcium carbide self-forming and cooling system, 2301-forming unit, 2302-cooling unit, 2303-elevator, 2304-cooler, 2305-closed conveyor, 2306-third cyclone separator, 2307-second heat exchanger, 2308-inert gas circulation fan, 2309-second blower, 24-exhaust waste heat boiler, 25-first heat exchanger, 26-lime weighing bin, 27-weighing bin, 28-wet material lock air feeder, 29-gypsum drying and crushing machine, 30-sulfuric acid conveying pipeline, 31-bag dust collector, 32-semi-hydrated gypsum warehouse, 33-high temperature fan, 34-sealing cover, 35-liquid calcium carbide inlet, 36-forming hole, 37-rotating knife. DETAILED DESCRIPTION

[0034] The present invention is further described below in conjunction with the accompanying drawings and embodiments. The present invention includes but is not limited to the following embodiments.

[0035] A method and system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and coupled calcium carbide production, comprising:

[0036] (1) Pre-treating the phosphogypsum by lime neutralization and sulfuric acid pickling to remove impurities such as organic phosphorus and eutectic phosphorus, and storing it for future use;

[0037] (2) A blower is added at the bottom of the inlet of the dual atmosphere circulating material gypsum decomposition furnace to force the combustion air of the decomposition furnace, and an air distribution plate and a wind cap are also provided;

[0038] (3) A set of electromagnetic heating devices is added to the furnace wall of the weak reduction zone and weak oxidation zone of the dual atmosphere circulating material gypsum decomposition furnace to generate a temperature field above 900°C, so as to reduce the amount of coal used in the decomposition furnace, thereby reducing the amount of air and further increasing the SO2 concentration. The sulfuric acid production system can achieve three-turn and three-absorption, so as to reduce the investment and operation cost of the sulfuric acid system;

[0039] (4) The furnace series multi-stage preheater adopts a circulating fluidized bed hot air furnace to use low calorific value coal or coal gangue to reduce costs;

[0040] (5) The solid product calcium oxide (lime) obtained by decomposition is in powder form, and the carbon material (pulverized coal) used to produce calcium carbide is mixed in the mixing chamber. The carbon material uses low-rank coal such as lignite;

[0041] (6) The fuel used in the decomposition furnace is all the furnace gas from the closed calcium carbide and low-rank coal pyrolysis furnace, which is no longer consumed separately and is recycled;

[0042] (7) After the powdered lime and carbon material (pulverized coal) leave the mixing chamber, they are made into pellets by a pelletizer and then sent to an internal combustion pyrolysis furnace for pyrolysis at a temperature above 850°C;

[0043] (8) The hot pellets discharged from the pyrolysis furnace are fed into a closed calcium carbide furnace through a lifting device and a pellet feeder for smelting at a temperature of 1900 to 2000°C;

[0044] (9) The molten calcium carbide is discharged from the bottom of the furnace, cooled by the liquid calcium carbide self-forming and cooling system, and then transported to the calcium carbide finished product warehouse by a closed conveyor;

[0045] (10) The gas from the closed calcium carbide furnace is cooled by the waste heat boiler and then mixed with the gas from the pyrolysis furnace (cooled by the heat exchanger) to serve as fuel for the decomposition furnace.

[0046] The following is a further detailed description with reference to the accompanying drawings. Figures 1 to 3 As shown, the system for producing sulfuric acid from industrial by-product gypsum and co-producing lime coupled with calcium carbide production provided in this embodiment includes the following five modules:

[0047] (I) Pretreatment and drying system of phosphogypsum

[0048] The pretreatment and drying system includes a phosphogypsum pre-homogenization yard 1 for neutralizing phosphogypsum with lime, and a first cyclone separator 2 for pickling phosphogypsum with sulfuric acid. A lime weighing bin 26 is provided at the upper end of the phosphogypsum pre-homogenization yard 1. The material treated by the phosphogypsum pre-homogenization yard 1 enters the wet material air-locking feeder 28 through the weighing bin 27, and then enters the first cyclone separator 2 through the action of the gypsum drying crusher 29. A sulfuric acid delivery pipeline 30 is connected to the first cyclone separator 2. The material treated by the first cyclone separator 2 enters the semi-hydrated gypsum warehouse 32 after being treated by the bag dust collector 31.

[0049] Phosphogypsum pretreatment (lime neutralization + sulfuric acid pickling) to remove impurities: Phosphorus in phosphogypsum mainly exists in the form of soluble phosphorus, insoluble phosphorus and eutectic phosphorus, collectively known as total phosphorus. Soluble phosphorus mainly exists in the form of H3PO4, H2PO4 - and HPO4 2- There are two forms: Ca3(PO4)2 is the main form of insoluble phosphorus, HPO4 2- Some SO42- It enters the sulfuric acid lattice by isomorphous substitution to form eutectic phosphorus CaHPO4·2H2O.

[0050] Lime neutralization: mainly for soluble phosphorus and soluble fluorine, add about 0.5% lime to phosphogypsum, mechanically mix and homogenize, pile and age for 24 hours, the reaction equation is as follows:

[0051] P2O5+3H2O+3CaO=Ca3(PO4)2↓+3H2O

[0052] 2F - +CaO+H2O=CaF2↓+2OH -

[0053] This measure can achieve a removal rate of 93.27% and 29.07% of soluble phosphorus and soluble fluorine in phosphogypsum respectively. The process is carried out in the phosphogypsum pre-homogenization yard.

[0054] Sulfuric acid pickling: mainly for insoluble phosphorus Ca3(PO4)2 eutectic phosphorus CaHPO4 and insoluble fluorine CaF2, using the molecular channels of phosphogypsum after drying and dehydration from dihydrate gypsum to semi-hydrated (anhydrous) gypsum, using concentrated sulfuric acid spray to make sulfuric acid and phosphogypsum contact with sulfuric acid in a suspended state, the reaction equation is as follows:

[0055] Ca3(PO4)2+H2SO4→2CaHPO4+CaSO4

[0056] CaHPO4·2H2O+H2SO4→CaSO4+H3PO4+2H2O

[0057] CaF2+H2SO4→CaSO4+2HF

[0058] After acid washing, the phosphogypsum crystals change from rhombus blocks to flakes, and the eutectic phosphorus in the phosphogypsum is removed. This process is carried out in the first cyclone separator at the outlet of the phosphogypsum drying and crushing machine.

[0059] The above two comprehensive measures can completely eliminate the influence of harmful components in phosphogypsum and ensure that the strength of cement clinker and the activity indicators of active lime reach normal values.

[0060] There is no water washing process for the sulfuric acid after pickling, because the excessive sulfuric acid will be cracked at 1000℃ as the temperature continues to rise in the subsequent process. The reaction equation is as follows:

[0061] H2SO4→H2O+SO2+1 / 2O2

[0062] The cracking (thermal decomposition) of sulfuric acid is an endothermic process with an endothermic value of 275 kJ / mol. However, since the proportion of excess sulfuric acid added is very small, the impact on the system is very small. The SO2 gas produced by cracking is recycled and produced into sulfuric acid through the acid production system.

[0063] (II) Gypsum decomposition system

[0064] The decomposition process and system elements of gypsum are consistent with those described in the patent application with publication number CN116750984A, including a first multi-cyclone preheater 4, a second multi-cyclone preheater 5, a dual-atmosphere circulating material gypsum decomposition furnace 6, a low calorific value coal gangue pre-combustion hot air furnace system 3 and a second cyclone separator 9. A first blower 7 is added at the bottom of the inlet of the dual-atmosphere circulating material gypsum decomposition furnace 6 to force the decomposition furnace to use combustion air. In addition, an air distribution plate and a hood are provided.

[0065] All fuels used are gaseous fuels, which are furnace gases from closed calcium carbide and low-rank coal pyrolysis furnaces. They are no longer consumed separately and are recycled.

[0066] On the furnace wall of the weak reduction zone and weak oxidation zone of the dual atmosphere circulating material gypsum decomposition furnace, a group of electromagnetic heating devices 8 are added respectively. After power is turned on, a temperature field above 900°C is generated to reduce the coal consumption of the decomposition furnace, thereby reducing the air volume and further increasing the SO2 concentration. The sulfuric acid production system can achieve three-turn and three-absorption to reduce the investment and operation cost of the sulfuric acid system.

[0067] (III) Sulfuric acid production system

[0068] The SO2-rich flue gas obtained by gypsum decomposition is discharged from the high-temperature fan 33 at the upper end of the second multi-cyclone preheater 5, cooled by the SP boiler 11 and purified by the electrostatic precipitator 12, and then enters the sulfuric acid production system 13. Since the SO2 concentration of the flue gas obtained by the gypsum decomposition system is close to 30%, the three-transformation and three-absorption process can be fully realized, the investment in the acid production system can be reduced by nearly 50%, and the operating cost can be reduced by 30%, which is quite impressive.

[0069] (IV) Calcium carbide system

[0070] The solid product CaO (lime) obtained by decomposing gypsum is separated by the second cyclone separator 9 and enters the mixing chamber 16 from the discharge port 10 at the bottom of the second cyclone separator 9, and is fully mixed with carbon materials (from the carbon raw material powder bin 14, which is low-grade coal powder such as lignite, accounting for 1.2-1.5 times the lime output) and natural air for cooling (the material temperature here is about 400°C). The mixed materials are then mixed with adhesives (from the adhesive storage bin 15) and enter the pellet forming machine 18 for extrusion into pellets. It is transported to the pyrolysis furnace 20 through the first lifting device 1901 to pyrolyze the lignite (the material temperature is 850-1000°C). The hot pellets after pyrolysis are then transported to the feeding device 21 on the top of the calcium carbide furnace through the second lifting device 1902, and enter the closed calcium carbide furnace 22 for smelting calcium carbide (the calcium carbide furnace can be one of an electric arc furnace or an electromagnetic furnace, and the material temperature is 1700-2100°C). Qualified liquid calcium carbide is cooled to 80°C by the liquid calcium carbide self-forming and cooling system 23, and then enters the finished calcium carbide warehouse through the closed conveyor 2305. Taking into account the intermittent discharge of liquid calcium carbide from the calcium carbide furnace, this embodiment is designed as a single liquid calcium carbide self-forming and cooling system (generating hot inert gas), and then the granular finished calcium carbide cooled by multiple calcium carbide furnaces uses a set of closed transportation system to enter the finished calcium carbide warehouse. The heat generated by multiple liquid calcium carbide self-forming and cooling systems (generating hot air and inert gas) is merged into the factory's pipeline network (to ensure the stability of the system operation), and finally merged into the waste heat boiler to generate superheated steam. The steam can be used for power generation or external sales.

[0071] like Figure 4 and 5 As shown, the liquid calcium carbide self-forming and cooling system 23 is composed of a molding unit 2301 and a cooling unit 2302, an elevator 2303, a cooler 2304, a third cyclone separator 2306, a second heat exchanger 2307, an inert gas circulation fan 2308 and a second blower 2309; the molding unit 2301 includes a main body, a sealing cover 34 arranged on the top of the main body, a liquid calcium carbide inlet 35 opened on the sealing cover 34, a molding hole 36 arranged inside the main body, and a rotating knife 37 that can rotate below the molding hole 36; the molding unit 2301 is connected to the cooling unit 2302 through a disassembly flange.

[0072] The process flow of the liquid calcium carbide self-forming and cooling system is as follows: the liquid calcium carbide inlet on the liquid calcium carbide forming unit enters the forming pot, and the bottom of the pot is provided with a round hole of suitable size. The liquid calcium carbide enters the forming pot and passes through the round hole to form a long filament like vermicelli, which is cut by the rotating knife below to form particles and enter the cooling unit 2302. The inert gas cooled by the second heat exchanger (waste heat boiler) 2307, the circulating inert gas after cooling enters the wind chamber by the circulating fan 2308, is evenly distributed in the cooling unit 2302, is cooled to below 200°C, and is transported to the cooler 2304 by the elevator 2303 to continue cooling to about 60°C, and enters the finished calcium carbide warehouse through the closed conveyor 2305. The air supply of the cooler 2304 is supplied by the second blower 2309. The high-temperature inert gas from the molding unit and the cooling unit is collected in the third cyclone separator 2306 for separation and purification, and finally enters the second heat exchanger 2307 to generate superheated steam, thereby cooling the inert gas to achieve the purpose of heat recovery and gas recycling.

[0073] Since the system can store the output of the calcium carbide furnace for more than one hour, the instability of intermittent discharge of a single calcium carbide furnace can be eliminated, forming a continuous cooling operation. If the cooling systems of multiple calcium carbide furnaces share one boiler, the stability will be better.

[0074] A detachable flange is designed on the outer wall of the molding unit of the system, which can be lifted out at any time for offline maintenance without affecting the production of the calcium carbide furnace.

[0075] Another channel is provided on the lime pipeline from the mixing chamber 16 to the pelletizing machine 18, and a vertical cooler 17 may be provided to further cool the lime and enter the commercial lime warehouse. The lime can be sold as commercial lime.

[0076] (V) Heat recovery system

[0077] The combustible products produced by the pyrolysis furnace 20 are cooled by the first heat exchanger 25 and then stored in a dedicated device. They are combined with the tail gas of the closed calcium carbide furnace and sent to the gypsum decomposition furnace for recycling as fuel.

[0078] The exhaust gas (CO reaches 85-90%) generated in the closed calcium carbide furnace 22 is cooled by the exhaust gas waste heat boiler 24 (the patent application "A method for producing sulfuric acid and calcium carbide from phosphogypsum" with publication number CN102442650A does not have a waste heat boiler as an exhaust gas cooling device, and the exhaust gas is directly led to the gypsum decomposition furnace. The high-temperature furnace gas of 500-1000°C generated during the operation of the closed calcium carbide furnace cannot be withstood by the fan material if it is not cooled), and then sent to the gypsum decomposition furnace for reuse as fuel.

[0079] The large amount of superheated steam generated by the sulfuric acid production system is combined with the steam from the calcium carbide furnace tail gas boiler and used for power generation or external sales.

[0080] Liquid calcium carbide self-forming and cooling system (liquid calcium carbide sensible heat recovery system) 23, the hot air (inert gas circulation) recovered by the system, the second heat exchanger (or waste heat boiler) 2307 for heat exchange and cooling, the cooled inert gas returns to the system for recycling. The large amount of superheated steam generated by the second heat exchanger (or waste heat boiler) 2307 enters the steam network of the factory.

[0081] Calcium carbide purification ash is recycled. Each ton of calcium carbide can recycle 10-14kg of standard coal. After being processed by the recycling system, it is added to the by-product gypsum for recycling.

[0082] The patent application "A method for producing sulfuric acid and calcium carbide from phosphogypsum" with publication number CN102442650A has a slag cooler as a cooling device for lime. In this embodiment, the cooling system of lime is cancelled, which directly increases the initial temperature of lignite, and the energy saving effect is significant. The traditional process is that quicklime (particle size 10-100mm) and carbon materials (coke, blue charcoal, etc. with particle size 5-40mm) react at a high temperature of 1800℃ to 2100℃ to generate calcium carbide (CaC2) by relying on the electric arc and resistance heat of the calcium carbide furnace, and at the same time produce calcium carbide furnace tail gas (main component CO); this embodiment uses powdered lime and powdered lignite, which expands the material source of calcium carbide and the utilization of by-product gypsum, and at the same time harvests the combustible components such as H2 and tar produced by pyrolysis for the gypsum decomposition system, reducing production costs.

[0083] Directly using lignite to replace semi-coke, if used in thermal power plants to treat desulfurized gypsum, can save the phosphogypsum pretreatment system, coupled with the electricity price advantage, the cost of calcium carbide can be reduced to a greater extent, and calcium carbide products have a stronger cost advantage. The calcium oxide required for calcium carbide production comes from the decomposition of gypsum, there is no CO2 emission, and it is a low-carbon calcium carbide.

[0084] The above embodiment is only one of the preferred implementation modes of the present utility model and should not be used to limit the protection scope of the present utility model. Any changes or modifications that are made to the main design concept and spirit of the present utility model without any substantive significance, as long as the technical problems solved are still consistent with the present utility model, should be included in the protection scope of the present utility model.

Claims

1. A system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and calcium carbide, characterized in that: It includes a pretreatment drying system for removing impurities from phosphogypsum and obtaining gypsum, a gypsum decomposition system for decomposing gypsum into solid CaO and SO2 flue gas, a sulfuric acid production system for treating SO2 flue gas, and a calcium carbide production system for preparing calcium carbide using solid CaO as raw material.

2. The system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and calcium carbide according to claim 1 is characterized in that: The calcium carbide production system comprises a mixing chamber (16) for mixing solid CaO, carbon material and air, a pellet forming machine (18) for extruding the material in the mixing chamber (16) into pellets, a pyrolysis furnace (20) for pyrolyzing the pellets, a closed calcium carbide furnace (22) for smelting the pyrolyzed pellets into liquid calcium carbide, a liquid calcium carbide self-forming and cooling system (23) for cooling the liquid calcium carbide, and a finished calcium carbide warehouse for storing calcium carbide.

3. The system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and calcium carbide according to claim 2 is characterized in that: The liquid calcium carbide self-forming and cooling system (23) includes a forming unit (2301) capable of processing the liquid battery into granules, a cooling unit (2302) and a cooler (2304) for cooling the granular calcium carbide, and a closed conveyor (2305) for conveying the cooled calcium carbide to a finished product calcium carbide warehouse.

4. The system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and calcium carbide according to claim 3 is characterized in that: The molding unit (2301) includes a main body, a sealing cover (34) arranged on the top of the main body, a liquid calcium carbide inlet (35) opened on the sealing cover (34), a molding hole (36) arranged inside the main body, and a rotating knife (37) that can rotate below the molding hole (36); the molding unit (2301) is connected to the cooling unit (2302) through a disassembly flange.

5. The system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and calcium carbide according to claim 2 is characterized in that: A vertical cooler (17) is provided on the pipeline from the mixing chamber (16) to the pelletizing machine (18).

6. The system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and calcium carbide according to claim 2, characterized in that: The pretreatment drying system comprises a lime weighing bin (26) for unloading lime, and a phosphogypsum pre-homogenization yard (1) located below the lime weighing bin (26); a weighing bin (27), a wet material air-locking feeder (28), a gypsum drying crusher (29), and a first cyclone separator (2) are sequentially arranged at the discharge port of the phosphogypsum pre-homogenization yard (1); a sulfuric acid delivery pipeline (30) is connected to the first cyclone separator (2), and the discharge port of the first cyclone separator (2) is sequentially connected to a bag dust collector (31) and a semi-hydrated gypsum storage (32).

7. The system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and calcium carbide according to claim 2, characterized in that: A first blower (7) is provided in the gypsum decomposition system.

8. The system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and calcium carbide according to claim 2, characterized in that: A high-temperature fan (33) connected to the gypsum decomposition system and used for discharging SO2 flue gas is also provided, and an SP boiler (11) and an electrostatic precipitator (12) are sequentially connected to the high-temperature fan (33); the sulfuric acid production system (13) is connected to the electrostatic precipitator (12).

9. The system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and calcium carbide according to claim 2, characterized in that: A first heat exchanger (25) is also provided for cooling the product generated by the pyrolysis furnace (20); and a tail gas waste heat boiler (24) is also provided for cooling the tail gas generated in the closed calcium carbide furnace (22).

10. A system for producing sulfuric acid from industrial by-product gypsum and co-producing lime and calcium carbide according to any one of claims 1 to 9, characterized in that: Also includes a heat recovery system.

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