System and method for recycling carbide slag and waste gas in PVC (polyvinyl chloride) production process

Abstract

The invention belongs to carbide slag solid waste treatment and waste gas treatment in calcium carbide method PVC production, and belongs to the field of lime preparation. The method comprises the following steps: carrying out primary drying and carbonization on wet carbide slag discharged after filter pressing and impurity removal by using calcium carbide furnace tail gas (the main component is CO) to form semi-dry Ca (OH) 2 powder containing part of CaCO3, then carrying out secondary extrusion molding to form a bar with an inner hole, and finally carrying out secondary extrusion molding on the bar with the inner hole to form the calcium carbide slag and waste gas recycling system. The method comprises the following steps of: cutting into ring-shaped hollow pellets by a high-speed fly cutter, carbonizing the ring-shaped hollow pellets into pellets with certain strength by using shaft kiln tail gas (mainly comprising CO2) through a three-section plate chain carbonizing machine and a carbonizing storage tank, and calcining the pellets into calcium oxide pellets meeting the use requirements of a calcium carbide furnace in a shaft kiln. The calcium oxide pellets are prepared from the waste residues and the waste gas generated in the calcium carbide preparation process, cyclic utilization of the production waste residues and the waste gas is achieved, and good economic and social benefits are achieved.

Description

Technical Field

[0001] The present invention belongs to the fields of calcium carbide method PVC production, lime production, and solid waste treatment. It involves process methods such as preliminary carbonization drying of carbide slag, extrusion molding, pellet carbonization, and pellet calcination. Background Art

[0002] In the calcium carbide method PVC production process, 1 ton of lime is consumed for producing 1 ton of calcium carbide, that is, 1.78 tons of limestone, and about 140 - 180 kg of standard coal is consumed; about 0.6 tons of semi-coke is consumed for 1 ton of calcium carbide. During the production process of each ton of lime, about 2500 Nm 3 / t of calcium carbide of waste gas is generated by the lime kiln, with the main component being CO2, and about 400 Nm 3 / t of calcium carbide of combustible waste gas with the main component being CO is generated by the electric furnace, and about 1.12 tons of carbide slag (dry basis) is discharged. Therefore, during the calcium carbide method PVC production process, a large amount of limestone and coal are consumed, and a large amount of waste gas and waste residue are generated.

[0003] For the calcium carbide method PVC production process, the discharged carbide slag has a high water content, generally 35% - 40%, and the carbide slag has high viscosity and fine fineness. During the process of reducing it to lime, the evaporation intensity is low during drying, and a large amount of energy consumption is required to evaporate water. Moreover, when the powder is calcined into calcium oxide powder, the calcium oxide powder obtained from calcining a large amount of carbide slag has little use and can only be used as a desulfurizer, etc. Therefore, its treatment method has little practicality in industrial production.

[0004] The core part of the calcium carbide method PVC production process is that lumpy lime and semi-coke react at high temperature to produce calcium carbide. Currently, when treating carbide slag to make lumpy lime, roll extrusion molding is generally used for pelletizing. Since wet carbide slag is a very sticky material, the extrusion pelletizing requires low moisture content. Otherwise, not only the particle strength is low, but also the particle demolding is difficult. When extruding by this method, since there is air inside the particles, a high pressure of 80 - 200 MPa is required to ensure sufficient cold strength. If there are no measures during subsequent high-temperature calcination, the thermal expansion of air is likely to cause the phenomenon of ball explosion, and high-strength lumpy lime that meets the requirements of the electric furnace cannot be manufactured. Summary of the Invention

[0005] Object of the Invention: The object of the present invention is to propose a comprehensive utilization method. In the calcium carbide method PVC production process, the combustible waste gas (the main component is CO) generated thereby, and the waste gas (the main component is CO2) generated by the lime kiln during the lime preparation process are utilized to make carbide waste residue into lime pellets to replace the lumpy lime raw material, realizing the recycling of production waste residue and waste gas, and carbonizing the pellets with CO2 waste gas is beneficial to reducing greenhouse gas emissions.

[0006] Technical solution: To achieve the above object, the present invention provides a system for recycling carbide slag and waste gas in a calcium carbide method PVC production process, mainly including a preliminary drying and carbonization subsystem, an extrusion molding subsystem, a pellet three-stage carbonization subsystem, and a pellet calcination subsystem;

[0007] The preliminary drying and carbonization subsystem includes a double-screw extrusion granulator, a rotary flash carbonization dryer, a cyclone collector, a bag filter, and a plate chain conveyor; the double-screw extrusion granulator granulates carbide slag with a water content of 35-40% and sends it into the rotary flash carbonization dryer for drying and carbonization. The heat source of the rotary flash carbonization dryer is the hot flue gas generated after the carbide furnace tail gas is burned by a gas furnace; the cyclone collector is used to collect the powder in the rotary flash carbonization dryer, and the bag filter is used for secondary collection of the powder. The carbide slag with a water content of 8-18% after carbonization drying is sent to the extrusion molding subsystem through the plate chain conveyor;

[0008] The extrusion molding subsystem includes a secondary extrusion molding machine, a belt conveyor, and a vibrating screen. The secondary extrusion molding machine extrudes the carbide slag into hollow rod strips and cuts them into annular hollow sections by a flying knife at the extrusion outlet. The finished products are sent into the vibrating screen through the belt conveyor, and the qualified products after screening by the vibrating screen are sent to the pellet three-stage carbonization subsystem;

[0009] The pellet three-stage carbonization subsystem includes a three-stage plate chain carbonization machine and a carbonization storage tank. The heat source for drying and carbonization comes from the lime kiln tail gas in the pellet calcination subsystem. After being adjusted by an electric control valve, it enters each stage of the carbonization machine respectively. Each stage of the carbonization machine is divided into multiple independent carbonization chambers. The air flow in each sub-chamber passes through the material from bottom to top, and part of the air flow is recycled by a circulating fan; the pellets after passing through the carbonization machine are transported to the carbonization storage tank by a belt conveyor, and the carbonized pellets in the carbonization storage tank are transported to the pellet calcination subsystem by a belt conveyor;

[0010] The pellet calcination subsystem includes a lime kiln and a high-temperature bag filter. The lime kiln is used to calcine the carbonized pellets into calcium oxide pellets. The heat source for calcination comes from the carbide furnace tail gas, and the waste gas is used as the carbonization heat source for the pellet three-stage carbonization subsystem after being dusted by the high-temperature bag filter.

[0011] Based on the above system, the present invention provides a process method for recycling carbide slag and waste gas in a calcium carbide method PVC production process, including the following steps:

[0012] Step S1: Preliminary drying and carbonization: The carbide slag with 35 - 40% water content discharged after pressure filtration and impurity removal is granulated by a double - screw extrusion granulator and then fed into a rotary flash carbonization dryer for drying and carbonization. The qualified powder enters the cyclone collector from the top for collection, and part of the fine powder enters the bag filter with the air flow for secondary collection. The separated tail gas is discharged into the atmosphere by a suction fan. The carbide slag with 8 - 18% water content after carbonization drying is sent to the next process by a slat conveyor. The heat source for carbonization drying comes from the carbide furnace tail gas (the main component is CO), which generates hot flue gas after combustion in a gas furnace. The temperature of the hot flue gas is adjusted to 250 - 300 °C by an electric cold air valve and enters the hot air inlet at the lower part of the rotary flash carbonization dryer in a tangential rotation mode as the heat source for drying and carbonization.

[0013] Step S2: Extrusion molding: The carbide slag processed in Step S1 is continuously fed into a secondary extrusion molding machine after passing through an on - line microwave moisture measuring instrument. It is made into a hollow rod with an outer diameter of Φ30 - 50 mm and an inner diameter of Φ15 - 25 mm by the secondary extrusion molding machine, and is cut into ring - shaped hollow segments with a length of 30 - 50 mm by a high - speed flying knife at the extrusion outlet (the finished product size and shape can be adjusted by replacing the extrusion outlet die). The finished product is fed into a vibrating screen for screening by a belt conveyor. The broken materials are returned to the molding machine by the belt conveyor, and the qualified products enter the next process.

[0014] Step S3: Pellet carbonization: The formed pellets enter a three - stage slat - type carbonization machine for further carbonization and drying. The heat source for drying and carbonization comes from the lime kiln tail gas, which is adjusted by an electric control valve and enters each section of the carbonization machine respectively. Each section of the carbonization machine is divided into multiple independent carbonization chambers. The air flow in each chamber passes through the material from bottom to top after being adjusted by an electric control valve. Part of the air flow is recycled by a circulating fan, and part of the air flow is discharged by an exhaust fan through an electric control valve. The pellets after passing through the carbonization machine are transported to a carbonization storage tank by a large - inclination belt conveyor. The tail gas from the lime kiln enters the carbonization storage tank after being adjusted by an electric control valve, and the waste gas is discharged after passing through a bag filter.

[0015] Step S4: Pellet calcination: The carbonized pellets are fed into a lime kiln by a large - inclination belt conveyor and calcined into calcium oxide pellets. The heat source for calcination comes from the carbide furnace tail gas, and the air for calcination is provided by a blower. The waste gas is discharged by a fan after being dust - removed by a high - temperature bag filter, and is used as the carbonization heat source for Step S3.

[0016] Preferably, in Step S1, the characteristic particle size of the particles extruded by the double - screw extrusion granulator is 5 - 10 mm, and the extrusion pressure is 0.4 - 1 MPa;

[0017] Hot air enters the hot air inlet at the lower part of the rotary flash carbonization dryer in a tangential rotation manner. Inside the cylinder of the rotary flash carbonization dryer, the rotation speed is 35 - 48 m / s, and the vertical upward speed is 3 - 7 m / s. The residence time of the carbide slag powder in the rotary flash carbonization dryer is 5 - 30 s, and the residence time in the cyclone collector and bag filter is 30 - 35 s;

[0018] The particle size value of the powder discharged from the rotary flash carbonization dryer is less than 160 μm. The carbonization degree of the carbide slag is 20 - 25%, and the moisture content is adjustable within the range of 8 - 18%.

[0019] Preferably, in step S2, for the secondary extrusion molding machine, the primary extrusion compression ratio is 2 - 3, the secondary extrusion compression ratio is 4 - 7, the extrusion pressure is 2 - 5 MPa, and the characteristic value of the compressive strength of the cross-section of the extruded finished pellet is 3 - 5 MPa; limestone powder is added at the feeding end of the extrusion molding machine. After being metered by a weighing scale, it is fed into the feeding port of the secondary extrusion molding machine; the incorporation amount of the limestone powder is 5 - 15%, and the particle size is 0 - 2 mm.

[0020] Preferably, in step S3, the total residence time of the pellets in the carbonization machine is 8 - 12 hours. After passing through the carbonization machine, the water content of the pellets is 3% - 5%, the carbonization degree is 80 - 88%, and the compressive strength is 420 - 490 N / pellet; after passing through the carbonization storage tank, the water content of the pellets is 1% - 2%, the carbonization degree is 88 - 96%, and the compressive strength is 800 - 820 N / pellet.

[0021] Preferably, in step S3, the tail gas from the lime kiln is adjusted by an electric control valve and then enters each section of the carbonization storage tank and the three-stage plate chain carbonization machine respectively. The temperature of the tail gas entering the carbonization machine is 180 °C, and the gas volume ratio of the tail gas entering the first, second, and third-stage carbonization machines is 20 - 30%, 20 - 30%, 40 - 60%; alternatively, the tail gas from the lime kiln first enters the carbonization storage tank and then enters the three-stage plate chain carbonization machine. The gas inlet mode is to first enter the third-stage carbonization machine, the tail gas discharged from the third-stage carbonization machine enters the second-stage carbonization machine, and the tail gas discharged from the second-stage carbonization machine enters the first-stage carbonization machine. The flue gas temperatures entering the third, second, and first-stage carbonization machines are 115 - 145 °C, 80 - 115 °C, and 50 - 80 °C respectively.

[0022] Beneficial effects: The present invention adopts the following process method: The wet calcium carbide slag discharged after impurity removal by pressure filtration is dried and carbonized preliminarily with the tail gas of the calcium carbide furnace to form a semi-dry Ca(OH)₂ powder containing partial CaCO₃, and then extruded and formed for the second time to become a rod with an inner hole. It is cut into ring-shaped hollow pellets by a high-speed flying knife, and then carbonized into pellets with a certain strength by the tail gas of the shaft kiln through a three-stage plate chain carbonizer and a carbonization storage tank, and calcined in a lime kiln to form calcium oxide pellets meeting the requirements for use in the calcium carbide furnace. Compared with the prior art, in the PVC production process by the calcium carbide method, the present invention utilizes the combustible tail gas (the main component is CO) generated therein and the tail gas (the main component is CO₂) generated in the lime kiln during the lime preparation process to make lime pellets from the calcium carbide waste residue to replace the lump lime raw material, realizing the recycling of production waste residue and waste gas. Moreover, carbonizing the pellets with CO₂ tail gas is beneficial to reducing greenhouse gas emissions, and has good economic and social benefits. Brief description of the drawings

[0023] Figure 1 It is a system flow chart of an embodiment of the present invention.

[0024] In the figure, 11 is a double-screw extrusion granulator; 12 is a rotary flash evaporation carbonization dryer; 13 is a cyclone collector; 14 is a bag filter; 15 is a fan; 16 is a gas furnace; 17 is an electric cold air valve; 18 is a plate chain conveyor; 21 is an on-line microwave moisture measuring instrument; 22 is a secondary extrusion molding machine; 23 is a belt conveyor; 24 is a vibrating screen; 25 is a belt conveyor; 26 is a belt weighing scale; 31 is a three-stage plate chain carbonizer; 32 is an electric control valve; 33 is a fan; 34 is an electric control valve; 35 is an electric control valve; 36 is a large-inclination belt conveyor; 37 is a carbonization storage tank; 38 is a bag filter; 39 is an electric control valve; 41 is a large-inclination belt conveyor; 42 is a lime kiln (shaft kiln); 43 is a high-temperature bag filter; 44 is a fan; 45 is a blower.

[0025] Figure 2 It is a process flow diagram of an embodiment of the present invention. Detailed implementation manners

[0026] Next, the technical solutions of the present invention will be described clearly and completely in conjunction with the drawings and specific embodiments.

[0027] As Figure 1As shown in the figure, a carbide slag and waste gas recycling system in a calcium carbide method PVC production process disclosed in an embodiment of the present invention mainly includes a preliminary drying and carbonization subsystem, an extrusion molding subsystem, a pellet three-stage carbonization subsystem, and a pellet calcination subsystem; among them, the preliminary drying and carbonization subsystem mainly includes a double-screw extrusion granulator 11, a rotary flash carbonization dryer 12, a cyclone collector 13, a bag filter 14, and a plate chain conveyor 18; the double-screw extrusion granulator 11 granulates carbide slag with a water content of 35-40% and sends it to the rotary flash carbonization dryer 12 for drying and carbonization. The heat source of the rotary flash carbonization dryer 12 is the hot flue gas generated after the tail gas of the calcium carbide furnace is burned by the gas furnace 16; the cyclone collector 13 is used to collect the powder in the rotary flash carbonization dryer 12, and the bag filter 14 is used for secondary collection of the powder. The carbide slag with a water content of 8-18% after carbonization drying is sent to the extrusion molding subsystem through the plate chain conveyor 18; the extrusion molding subsystem mainly includes a secondary extrusion molding machine 22, belt conveyors 23, 25, and a vibrating screen 24. The secondary extrusion molding machine 22 extrudes the carbide slag into hollow rod strips and cuts them into annular hollow sections by the flying knife at the extrusion outlet. The finished product is sent into the vibrating screen 24 through the belt conveyor 25, and the qualified products after screening by the vibrating screen 24 are sent to the pellet three-stage carbonization subsystem; the pellet three-stage carbonization subsystem mainly includes a three-stage plate chain carbonization machine 31 and a carbonization storage tank 37. The heat source for drying and carbonization comes from the tail gas of the lime kiln 42 in the pellet calcination subsystem. After being adjusted by the electric control valve 35, it enters each stage of the carbonization machine respectively. Each stage of the carbonization machine is divided into multiple independent carbonization chambers, and the air flow in each chamber passes through the material from bottom to top, and part of the air flow is recycled by the circulation fan; the pellets after passing through the carbonization machine 31 are transported to the carbonization storage tank 37 by the belt conveyor 36, and the carbonized pellets in the carbonization storage tank 37 are transported to the pellet calcination subsystem by the belt conveyor 41; the pellet calcination subsystem mainly includes a lime kiln 42 and a high-temperature bag filter 43. The lime kiln 42 is used to calcine the carbonized pellets into calcium oxide pellets. The heat source for calcination comes from the tail gas of the calcium carbide furnace, and the waste gas is used as the carbonization heat source for the pellet three-stage carbonization subsystem after being dusted by the high-temperature bag filter 43.

[0028] Based on the above system, a process method for recycling carbide slag and waste gas in a calcium carbide method PVC production process disclosed in an embodiment of the present invention includes the following steps:

[0029] Step S1: Preliminary drying and carbonization: The carbide slag with 35 - 40% water content discharged after filtration and impurity removal is granulated by a double - screw extrusion granulator 11 and then fed into a rotary flash carbonization dryer 12 for drying and carbonization. Qualified powder enters a cyclone collector 13 from the top for collection, and part of the fine powder enters a bag filter 14 with the air flow for secondary collection. The separated tail gas is discharged into the atmosphere by an induced draft fan 15. The carbide slag with 8 - 18% water content after carbonization and drying is sent to the next process by a slat conveyor 18. The heat source for carbonization and drying comes from the carbide furnace tail gas (the main component is CO), which is burned by a gas furnace 16 to generate hot flue gas. The temperature of the hot flue gas is adjusted to 250 - 300 °C by an electric cold air valve 17 and enters the hot air inlet at the lower part of the rotary flash carbonization dryer 12 in a tangential rotation mode as the heat source for drying and carbonization.

[0030] Step S2: Extrusion molding: The carbide slag processed in Step S1 is continuously fed into a secondary extrusion molding machine 22 after passing through an on - line microwave moisture measuring instrument 21. Hollow rods with an outer diameter of Φ30 - 50 mm and an inner diameter of Φ15 - 25 mm are formed by the secondary extrusion molding machine 22 and are cut into ring - shaped hollow segments with a length of 30 - 50 mm by high - speed flying knives at the extrusion outlet (the finished product size and shape can be adjusted by replacing the extrusion outlet die). The finished product is fed into a vibrating screen 24 for screening by a belt conveyor 23. The broken materials are returned to the molding machine by a belt conveyor 25, and the qualified products enter the next process.

[0031] Step S3: Pellet carbonization: The formed pellets enter a three - stage slat - type carbonization machine for further carbonization and drying. The heat source for drying and carbonization comes from the tail gas of a lime kiln 42. After being adjusted by an electric control valve 35, it enters each section of the carbonization machine respectively. Each section of the carbonization machine is divided into multiple independent carbonization chambers. The air flow in each chamber passes through the material from bottom to top after being adjusted by an electric control valve 34. Part of the air flow is recycled by a circulation fan, and part of the air flow is discharged by an induced draft fan through an electric control valve 32. The pellets after passing through the carbonization machine are transported to a carbonization storage tank 37 by a large - angle belt conveyor 36. The tail gas from the lime kiln 42 enters the carbonization storage tank 37 after being adjusted by an electric control valve 39, and the waste gas is discharged into the air after passing through a bag filter 38.

[0032] Step S4: Pellet calcination: The carbonized pellets are fed into a lime kiln 42 by a large - angle belt conveyor 41 and calcined into calcium oxide pellets. The heat source for calcination comes from the carbide furnace tail gas, and the air for calcination is provided by a blower 45. The waste gas is discharged by a fan 44 after being dust - removed by a high - temperature bag filter 43, and is used as the carbonization heat source for Step S3.

[0033] The double - screw extrusion granulator 11 adopts a front - extrusion method, and the discharge port is hermetically connected to the feed port of the rotary flash carbonization dryer 12. The characteristic particle size of the extruded particles is 5 - 10 mm, and the extrusion pressure is 0.4 - 1 MPa.

[0034] The rotational speed of the hot air flow inside the cylinder of the rotary flash carbonization dryer 12 is 35 - 48 m / s, and the vertical upward speed is 3 - 7 m / s. The residence time of the carbide slag powder in the rotary flash carbonization dryer 12 is 5 - 30 s, and the residence time in the cyclone collector 13 and the bag filter 14 is 30 - 35 s. The particle size value of the powder discharged from the dryer is less than 160 μm, and the moisture content is adjustable within 8 - 18%.

[0035] In the preliminary drying and carbonization system, the volume content of CO in the hot flue gas entering the rotary flash carbonization dryer 12 is approximately 65 - 85%, the carbonization degree of the treated carbide slag is 20 - 25%, and the flue gas discharge temperature is 90 - 115 °C.

[0036] In the secondary extrusion molding machine 22, the primary extrusion screw adopts a double - screw front - end extrusion structure. The extrusion end is hermetically connected to the upper end of the vacuum chamber. The material is transported to the extrusion cylinder at the end, and its compression ratio is 2 - 3. The material is extruded once and fed into the vacuum chamber to remove the air in the material. The vacuum chamber is externally connected to a vacuum compressor to extract the air in the material box to make it in a vacuum state. A pressure plate is arranged in the middle of the vacuum chamber to densely press the material into the secondary extrusion section. The lower end of the vacuum chamber is hermetically connected to the secondary extrusion screw. The secondary extrusion screw adopts a single - screw or double - screw front - end extrusion method, and the compression ratio is 4 - 7. Then it is formed through the outlet die and cut into finished pellets by a high - speed flying knife. The extrusion pressure of this extrusion molding machine is 2 - 5 MPa, and the characteristic value of the compressive strength of the cross - section of the extruded finished pellets is 3 - 5 MPa. The finished products extruded by the secondary extrusion molding machine 22 can be any honeycomb - shaped inner - hole structure for increasing the surface area and outer structures such as rectangular and diamond - shaped.

[0037] The pellets in the three - stage plate - chain carbonization machine 31 are in a static stacked state and are continuously and slowly dragged by the plate chain. The temperature of the tail gas of the lime kiln 42 introduced is 180 - 250 °C, and the CO2 content is 22% - 25%. The carbonization time of the pellets is 8 - 12 hours. The water content of the dried pellets is 3% - 5%, the carbonization degree is 80 - 88% (including the carbonization degree of step S1), and the compressive strength is 420 - 490 N / pellet.

[0038] After passing through the carbonization storage tank 37, the water content of the pellets is 1% - 2%, the carbonization degree is 88 - 96% (including the carbonization degree of step S1), and the compressive strength is 800 - 820 N / pellet.

[0039] Limestone powder is added at the feeding end of the extrusion molding machine. After being metered by the belt weighing scale 26, it is fed into the feeding port of the secondary extrusion molding machine 22. The incorporation amount of the limestone powder is 5 - 15%, and the particle size is 0 - 2 mm.

[0040] The tail gas of the lime kiln 42 can be used in the following ways: First, after being adjusted by the electric control valves 39 and 35, it enters the carbonization storage tank 37 and each section of the three-stage plate chain carbonization machine 31 respectively. The temperature of the tail gas entering the carbonization machine is 180 °C. The ratio of the tail gas volume entering the first, second, and third-stage carbonization machines in the three-stage plate chain carbonization machine 31 is 20 - 30%, 20 - 30%, and 40 - 60%; the distribution of the tail gas volume is that the third-stage carbonization machine > the first-stage carbonization machine > the second-stage carbonization machine.

[0041] Second, the tail gas of the lime kiln 42 first enters the carbonization storage tank 37, and then enters the plate chain carbonization machine. The air intake method is to first enter the three-stage plate chain carbonization machine 31. The tail gas discharged from the third-stage carbonization machine enters the second-stage carbonization machine, and the tail gas discharged from the second-stage carbonization machine enters the first-stage carbonization machine. The flue gas temperatures entering the third, second, and first-stage carbonization machines are 115 - 145 °C, 80 - 115 °C, and 50 - 80 °C respectively.

[0042] The following combines two examples to illustrate the specific effects of the embodiments of the present invention.

[0043] Example 1:

[0044] Step S1: Preliminary drying and carbonization: The calcium carbide slag containing 40% water discharged after filtration and impurity removal is granulated by the double-screw extrusion granulator 11 and then fed into the rotary flash carbonization dryer 12 for drying and carbonization. The qualified powder is collected from the top by the cyclone collector 13. Part of the fine powder enters the bag filter 14 with the air flow for secondary collection. The separated tail gas is discharged into the atmosphere by the induced draft fan. The calcium carbide slag with 13% water after carbonization and drying is sent to the next process by the plate chain conveyor 18. The drying heat source comes from the tail gas of the calcium carbide furnace (the main component is CO), with a calorific value of 3000 Kcal / m 3 , which generates hot flue gas at 600 - 650 °C after being burned by the gas furnace 16. The temperature of the hot flue gas is adjusted to about 300 °C by the electric cold air valve 17 and enters the hot air inlet at the lower part of the rotary flash carbonization dryer 12 in a tangential rotation manner as the heat source for drying and carbonization. The calcium carbide slag containing 40% water is in a paste state. After being granulated by the double-screw extrusion granulator 11, the contact area with the flue gas is increased, which is beneficial to carbonization and drying; the gas temperature at the outlet of the tail exhaust fan is maintained above 100 °C. The humidity of the gas is relatively high after the material evaporates water, which makes the carbonization reaction proceed rapidly. The material stays in the rotary flash carbonization dryer 12 until it is separated from the gas in the bag filter 14, and the residence time is about 60 - 90 s, which can carbonize about 30% of the Ca(OH)2 in the calcium carbide slag into CaCO3.

[0045] Step S2: Extrusion Molding: The carbide slag processed in Step S1 is continuously fed into the secondary extrusion molding machine 22 after passing through the on-line microwave moisture measuring instrument 21, and is made into a hollow rod with an outer diameter of Φ50mm and an inner diameter of Φ20mm under an extrusion pressure of 2.8 - 3 Mpa by the secondary extrusion molding machine 22. It is cut into ring-shaped hollow segments with a length of 50mm by a high-speed flying knife at the extrusion outlet. The finished product is fed into the vibrating screen 24 by the belt conveyor 23 for screening. The crushed materials are returned to the molding machine by the belt conveyor 25, and the qualified products enter the next process. If the feeding moisture is too high, the incorporation amount of limestone powder is adjusted through the control system to maintain the consistency of the moisture of the materials in the extruder. The cross-sectional compressive strength of the extruded strip is stably maintained at 3.4 - 3.8 Mpa. Extrusion molding in a vacuum removes the air in the materials, making the formed pellets denser, and the subsequent carbonization speed faster. The closely connected particles make the carbonized pellets have higher strength, and higher cold-state strength can be obtained with a lower pressure.

[0046] Step S3: Pellet Carbonization: The formed pellets enter the three-section plate chain carbonization machine for further carbonization and drying. The heat source for drying and carbonization comes from the tail gas of the lime kiln 42. After being adjusted by the electric control valves 39 and 35, it enters the carbonization storage tank 37 and each section of the carbonization machine respectively. The temperature of the tail gas entering the carbonization machine is 180°C, and the amounts of tail gas entering the first, second, and third sections are 30%, 20%, and 50% respectively. Each section of the carbonization machine is divided into 4 independent carbonization chambers. The air flow in each chamber passes through the materials from bottom to top after being adjusted by the electric control valve 34. 70% of the air flow is recycled by the circulation fan, and 30% of the air flow is discharged by the exhaust fan 33 through the electric control valve 32. The residence time of the materials in the carbonization machine is 10h, the carbonization degree is 82%, and the compressive strength is 424 N / pellet. The pellets after passing through the carbonization machine are transported to the carbonization storage tank 37 by the large-inclination belt conveyor 36. The tail gas from the lime kiln 42 at 180°C enters the carbonization storage tank 37 after being adjusted by the electric control valve 39, and the waste gas is discharged into the air after passing through the bag filter 38. The total residence time of the materials in the carbonization storage tank 37 is 24h, the carbonization degree is 95%, and the compressive strength is 800 N / pellet. Practice shows that the carbonization of carbide slag requires the presence of moisture or water vapor. The wet tail gas is recycled in the carbonization machine, which can make its carbonization faster and obtain a higher carbonization degree and pellet strength.

[0047] Step S4: Pellet Calcination: The carbonized pellets are fed into the vertical kiln by the large-inclination belt conveyor 41 and calcined into calcium oxide pellets. The heat source for calcination comes from the tail gas of the electric furnace. The air volume opening of the blower 45 for calcination is about 80%. The temperature of the high-temperature calcination zone is about 1020°C. The residence time of the materials is about 12h, and the waste gas temperature is 220°C. After being dusted by the high-temperature bag filter 43, it is discharged by the fan 44 at a temperature of 180°C, which is used as the carbonization heat source for Step S3. The total calcium content of the calcined calcium oxide pellets is 92%, and the effective calcium oxide content is 89%.

[0048] Example Two:

[0049] The carbide slag with 35% water content, after preliminary drying and carbonization, has 8% water content and a carbonization degree of 25%. It is fed into the secondary extrusion molding machine 22, and the secondary extrusion molding machine 22 is adjusted to produce a hollow rod with an outer diameter of Φ40mm and an inner diameter of Φ15mm under an extrusion pressure of 4.2 - 4.5 Mpa. It is cut into ring-shaped hollow segments with a length of 40mm by a high-speed flying knife at the extrusion outlet, and the compressive strength of the strip cross-section is 4.2 - 4.5 MPa.

[0050] The temperature of the vertical kiln tail gas is 180°C. It first enters the carbonization storage tank 37, and then enters the plate chain carbonization machine. The inlet gas temperature is 140°C. It first enters the three-stage plate chain carbonization machine 31. In each stage of the carbonization machine, 50% of the gas flow is recycled, and 50% of the gas flow enters the next stage. The gas temperature entering the secondary carbonization machine is 90°C. The tail gas discharged from the secondary carbonization machine enters the primary carbonization machine, and the gas temperature is 50°C. The total residence time of the material in the carbonization storage tank 37 and the carbonization machine is 24h and 12h respectively, the carbonization degree is 96%, and the compressive strength is 820 N / ball.

[0051] The carbonized pellets are fed into the vertical kiln by the large-inclination belt conveyor 41 and calcined into calcium oxide pellets. The air volume opening of the blower 45 for calcination is about 80%. The temperature in the high-temperature calcination zone is about 950 - 980°C. The residence time of the material is about 12h, and the waste gas temperature is 180°C. After being dusted by the high-temperature bag filter 43, it is discharged by the fan 44 and used as the carbonization heat source in step S3. The total calcium content of the calcined calcium oxide pellets is 90%, and the effective calcium oxide content is 86%.

Claims

1. A carbide slag and waste gas recycling system in the calcium carbide method PVC production process, characterized in that, It includes a preliminary drying and carbonization subsystem, an extrusion molding subsystem, a pellet three-stage carbonization subsystem, and a pellet calcination subsystem; The preliminary drying and carbonization subsystem includes a double-screw extrusion granulator, a rotary flash carbonization dryer, a cyclone collector, a bag filter, and a plate chain conveyor; the double-screw extrusion granulator granulates carbide slag with 35-40% water content and sends it into the rotary flash carbonization dryer for drying and carbonization. The heat source of the rotary flash carbonization dryer is the hot flue gas generated after the carbide furnace tail gas is burned by a gas furnace; the cyclone collector is used to collect the powder in the rotary flash carbonization dryer, and the bag filter is used for secondary collection of the powder. The carbide slag with 8-18% water content after carbonization and drying is sent to the extrusion molding subsystem through the plate chain conveyor; The extrusion molding subsystem includes a secondary extrusion molding machine, a belt conveyor, and a vibrating screen. The secondary extrusion molding machine extrudes the carbide slag into hollow rod-shaped strips and cuts them into annular hollow sections by a flying knife at the extrusion outlet. The finished product is sent into the vibrating screen through the belt conveyor, and the qualified products after screening by the vibrating screen are sent to the pellet three-stage carbonization subsystem; The pellet three-stage carbonization subsystem includes a three-stage plate chain carbonization machine and a carbonization storage tank. The heat source for drying and carbonization comes from the lime kiln tail gas in the pellet calcination subsystem. After being adjusted by an electric control valve, it enters each stage of the carbonization machine respectively. Each stage of the carbonization machine is divided into multiple independent carbonization chambers. The air flow in each sub-chamber passes through the material from bottom to top, and part of the air flow is recycled by a circulating fan; the pellets after passing through the carbonization machine are transported to the carbonization storage tank by a belt conveyor, and the carbonized pellets in the carbonization storage tank are transported to the pellet calcination subsystem by a belt conveyor; The pellet calcination subsystem includes a lime kiln and a high-temperature bag filter. The lime kiln is used to calcine the carbonized pellets into calcium oxide pellets. The calcination heat source comes from the carbide furnace tail gas, and the waste gas is used as the carbonization heat source of the pellet three-stage carbonization subsystem after being dusted by the high-temperature bag filter.

2. The carbide slag and waste gas recycling system in a calcium carbide method PVC production process according to claim 1, wherein In the preliminary drying and carbonization subsystem, the characteristic particle size of the particles extruded by the double-screw extrusion granulator is 5-10 mm, and the extrusion pressure is 0.4-1 MPa; the hot flue gas enters the hot air inlet at the lower part of the rotary flash carbonization dryer in a tangential rotation manner, with a rotation speed of 35-48 m / s and a vertical upward speed of 3-7 m / s. The particle size value of the powder leaving the rotary flash carbonization dryer is less than 160 μm, and the carbonization degree of the carbide slag is 20-25%.

3. The carbide slag and waste gas recycling system in the calcium carbide method PVC production process according to claim 1, wherein, In the extrusion molding subsystem, the primary extrusion compression ratio of the secondary extrusion molding machine is 2-3, the secondary extrusion compression ratio is 4-7, the extrusion pressure is 2-5 MPa, and the characteristic value of the compressive strength of the cross-section of the extruded finished product pellets is 3-5 MPa.

4. The carbide slag and waste gas recycling system in a calcium carbide method PVC production process according to claim 1, characterized in that, In the extrusion molding subsystem, limestone powder is added at the feeding end of the secondary extrusion molding machine. After being metered by a weighing scale, it is fed into the feeding port of the secondary extrusion molding machine; the incorporation amount of the limestone powder is 5-15%, and the particle size is 0-2 mm.

5. A carbide slag and waste gas recycling system in a calcium carbide method PVC production process according to claim 1, characterized in that, In the pellet three-stage carbonization subsystem, the tail gas from the lime kiln is regulated by an electric control valve and then enters the carbonization storage tank and each section of the three-stage plate chain carbonization machine respectively. The ratio of the tail gas volume entering the first, second, and third-stage carbonization machines is 20 - 30%, 20 - 30%, and 40 - 60%; alternatively, the tail gas from the lime kiln first enters the carbonization storage tank and then enters the three-stage plate chain carbonization machine. The gas inlet mode is to first enter the third-stage carbonization machine, and the tail gas discharged from the third-stage carbonization machine enters the second-stage carbonization machine, and the tail gas discharged from the second-stage carbonization machine enters the first-stage carbonization machine.

6. A process method for recycling carbide slag and waste gas in a calcium carbide method PVC production process, characterized in that, It includes the following steps: Step S1: Preliminary drying and carbonization: The carbide slag with a water content of 35 - 40% is granulated by a double-screw extrusion granulator and then fed into a rotary flash carbonization dryer for drying and carbonization. The qualified powder enters the cyclone collector for collection from the top, and part of the fine powder enters the bag filter for secondary collection along with the air flow. The carbide slag with a water content of 8 - 18% after carbonization drying is sent to the next process by a plate chain conveyor; the drying heat source comes from the hot flue gas generated after the tail gas from the electric furnace is burned by a gas furnace. Step S2: Extrusion molding: The carbide slag processed in Step S1 is fed into a secondary extrusion molding machine, and hollow rod bars are formed by the secondary extrusion molding machine. They are cut into annular hollow sections by high-speed flying knives at the extrusion outlet. The finished products are fed into a vibrating screen for screening by a belt conveyor, and the qualified products enter the next process. Step S3: Pellet carbonization: The formed pellets enter the three-stage plate chain carbonization machine for further carbonization and drying; the drying and carbonization heat source comes from the tail gas of the lime kiln, which is regulated by an electric control valve and then enters each section of the carbonization machine respectively. Each section of the carbonization machine is divided into multiple independent carbonization chambers, and the air flow in each sub-chamber passes through the material from bottom to top, and part of the air flow is recycled by a circulation fan; the pellets after passing through the carbonization machine are transported to the carbonization storage tank by a belt conveyor. Step S4: Pellet calcination: The carbonized pellets are fed into a lime kiln by a belt conveyor to be calcined into calcium oxide pellets. The calcination heat source comes from the tail gas of the electric furnace, and the waste gas is dusted by a high-temperature bag filter and used as the carbonization heat source in Step S3.

7. According to the process method for recycling carbide slag and waste gas in a calcium carbide method PVC production process as described in claim 6, it is characterized in that: In Step S1, the characteristic particle size of the particles extruded by the double-screw extrusion granulator is 5 - 10 mm, and the extrusion pressure is 0.4 - 1 MPa. The hot air flow enters the hot air inlet at the lower part of the rotary flash carbonization dryer in a tangential rotation mode, with a rotation speed of 35 - 48 m / s and a vertical upward speed of 3 - 7 m / s in the rotary flash carbonization dryer cylinder. The residence time of the carbide slag powder in the rotary flash carbonization dryer is 5 - 30 s, and the residence time in the cyclone collector and the bag filter is 30 - 35 s. The particle size value of the powder discharged from the rotary flash carbonization dryer is less than 160 μm, the carbonization degree of the carbide slag is 20 - 25%, and the water content is adjustable within 8 - 18%.

8. According to the process method for recycling carbide slag and waste gas in a calcium carbide method PVC production process as described in claim 7, it is characterized in that: In the secondary extrusion molding machine in step S2, the primary extrusion compression ratio is 2 to 3, the secondary extrusion compression ratio is 4 to 7, the extrusion pressure is 2 to 5 MPa, and the characteristic value of the compressive strength of the cross-section of the extruded finished pellet is 3 to 5 MPa; limestone powder is added at the feeding end of the extrusion molding machine, and after being metered by a weighing scale, it is fed into the feeding port of the secondary extrusion molding machine; the incorporation amount of limestone powder is 5-15%, and the particle size is 0-2 mm.

9. The process method for recycling carbide slag and waste gas in a calcium carbide method PVC production process according to claim 7, characterized in that: In step S3, the total residence time of the pellets in the carbonization machine is 8-12 hours. After passing through the carbonization machine, the pellets contain 3% to 5% water, the carbonization degree is 80 to 88%, and the compressive strength is 420 to 490 N / pellet; after passing through the carbonization storage tank, the pellets contain 1% to 2% water, the carbonization degree is 88 to 96%, and the compressive strength is 800 to 820 N / pellet.

10. A process method for recycling carbide slag and waste gas in a calcium carbide method PVC production process according to claim 7, characterized in that: In step S3, the tail gas from the lime kiln is adjusted by an electric control valve and then enters each section of the carbonization storage tank and the three-stage plate chain carbonization machine respectively. The temperature of the tail gas entering the carbonization machine is 180°C, and the ratio of the tail gas volume entering the first, second, and third-stage carbonization machines is 20 to 30%, 20 to 30%, and 40 to 60%; Alternatively, the tail gas from the lime kiln first enters the carbonization storage tank and then enters the three-stage plate chain carbonization machine. The gas inlet mode is to first enter the third-stage carbonization machine. The tail gas discharged from the third-stage carbonization machine enters the second-stage carbonization machine, and the tail gas discharged from the second-stage carbonization machine enters the first-stage carbonization machine. The flue gas temperatures entering the third, second, and first-stage carbonization machines are 115-145°C, 80-115°C, and 50-80°C respectively.

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