Desulfurization system integrating ardealite drying dehydration and calcination decomposition

Abstract

The invention discloses an ardealite drying dehydration and calcination decomposition integrated desulfurization system which comprises a fluidized bed decomposition furnace, a cyclone separator and a return feeder, a flue gas outlet pipeline of the cyclone separator is connected with a first waste heat recovery unit used for heat exchange to generate water vapor, and part of the water vapor is input into the fluidized bed decomposition furnace; waste conveying pipelines of the fluidized bed decomposing furnace and the material returning device are connected with a second waste heat recovery unit for heat exchange to generate hot air; and the flue gas and the hot air which are subjected to heat exchange by the first waste heat recovery unit respectively supply heat for dehydration of phosphogypsum and coal before being input into the fluidized bed decomposition furnace. Waste heat can be effectively recovered and used for reactant pre-dehydration, and the energy utilization efficiency and the system stability are improved.

Description

Technical Field

[0001] The present invention relates to the desulfurization of phosphogypsum in the conversion of solid waste resources, and particularly to a desulfurization system integrating the drying and dehydration of phosphogypsum with its calcination and decomposition. Background Art

[0002] Phosphogypsum is a by-product of the phosphate fertilizer production industry, with the main component being CaSO4·2H2O. Exploring large-scale utilization ways of phosphogypsum, especially maximizing the recovery of calcium and sulfur resources in phosphogypsum, has important economic and environmental value.

[0003] In the past, the technical mode of decomposing phosphogypsum by means of a hollow rotary kiln to produce sulfuric acid and co-produce cement had problems such as high energy consumption costs, low waste heat utilization rate, and low target product yield. Due to the high gas-solid contact efficiency and excellent heat transfer performance of the circulating fluidized bed technology, it has become a preferred solution for phosphogypsum decomposition. However, the prior art fails to effectively integrate the drying and dehydration process with the calcination and decomposition process, and the self-heating capacity of the system is insufficient. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a desulfurization system integrating the drying and dehydration of phosphogypsum with its calcination and decomposition, which can effectively recover waste heat and use it for pre-dehydration of reactants.

[0005] Technical Solution: To achieve the above object, the desulfurization system integrating the drying and dehydration of phosphogypsum with its calcination and decomposition according to the present invention includes a fluidized bed decomposition furnace, a cyclone separator, and a return feeder. The flue gas outlet pipe of the cyclone separator is connected to a first waste heat recovery unit for generating water vapor through heat exchange, and part of the water vapor is input into the fluidized bed decomposition furnace; the waste material conveying pipes of the fluidized bed decomposition furnace and the return feeder are connected to a second waste heat recovery unit for generating hot air through heat exchange; the flue gas after heat exchange by the first waste heat recovery unit and the hot air preheated by the second waste heat recovery unit respectively supply heat for the dehydration of phosphogypsum and coal before they are input into the fluidized bed decomposition furnace.

[0006] Based on the above technical solution, by connecting the flue gas outlet pipe of the cyclone separator and the waste material conveying pipes of the fluidized bed decomposition furnace and the return feeder to two waste heat recovery units respectively, heat energy waste can be avoided, and the flue gas after heat exchange by the first waste heat recovery unit and the hot air generated by the second waste heat recovery unit are also respectively used for pre-dehydrating phosphogypsum and coal, avoiding the uncontrollable influence on the system heat and gas phase partial pressure caused by the gasification of crystal water during the reaction process, and improving the operation stability of the phosphogypsum thermal decomposition system; part of the water vapor generated by the first waste heat recovery unit is also input into the fluidized bed decomposition furnace to provide reaction, fluidization, and loosening atmospheres for the thermal decomposition of phosphogypsum, realizing the circular utilization of system heat energy.

[0007] Preferably, the second waste heat recovery unit is a combined air and water heat exchange device, with air and water for heat exchange flowing inside.

[0008] Water for heat exchange circulates inside the second waste heat recovery unit, enabling the recovered heat to provide hot water for other uses, thereby increasing the utilization rate of the recovered waste heat.

[0009] Preferably, the water vapor-containing air generated by coal dehydration is input into the fluidized bed decomposition furnace.

[0010] The water vapor-containing air generated by coal dehydration is also input into the fluidized bed decomposition furnace, and it can jointly provide a reaction, fluidization, and loosening atmosphere for the thermal decomposition of phosphogypsum with the water vapor generated by the first waste heat recovery unit. This not only avoids the waste of high-temperature water vapor generated by dehydration but also facilitates the thermal decomposition reaction in the fluidized bed decomposition furnace, improving the desulfurization effect.

[0011] Preferably, the flue gas after heating for phosphogypsum dehydration is input into the second waste heat recovery unit for heat exchange.

[0012] The flue gas after heating for phosphogypsum dehydration still contains a large amount of heat. Re-inputting it into the second waste heat recovery unit for heat exchange can not only achieve the condensation of water vapor therein for water removal but also effectively utilize the heat energy, further improving the energy utilization rate.

[0013] Preferably, the fluidized bed decomposition furnace performs thermal decomposition under normal pressure and within the range of [1050 °C, 1100 °C].

[0014] Under the above conditions, the endothermic and exothermic reactions in the fluidized bed decomposition furnace can achieve balance, thereby realizing self-operation and hardly requiring heat supplementation from the outside.

[0015] Preferably, the temperature of the flue gas after heat exchange by the first waste heat recovery unit is controlled within the range of [450 °C, 580 °C].

[0016] Controlling the flue gas after heat exchange within the above temperature range can more effectively achieve phosphogypsum dehydration.

[0017] Preferably, the temperature of the hot air generated by the second waste heat recovery unit is controlled within the range of [130 °C, 180 °C].

[0018] Controlling the hot air within the above range can effectively dehydrate the coal. The remaining waste heat can be used to heat water for other purposes, more reasonably distributing the recovered waste heat and improving the energy utilization efficiency.

[0019] Beneficial effects: The present invention has the following advantages: By separately inputting the flue gas and waste generated by the thermal decomposition of phosphogypsum into two waste heat recovery units, and then using the flue gas after heat exchange and the hot air generated by heat exchange for the dehydration of phosphogypsum and coal, the energy utilization rate and the stability of system operation are improved; moreover, the water vapor generated by heat exchange can also be input into the fluidized bed decomposition furnace for use, realizing the cyclic use of the system's thermal energy. Brief Description of the Drawings

[0020] Figure 1 This is a schematic structural diagram of the system. Detailed Implementation Modes

[0021] The technical solutions of the present invention will be described in detail below in conjunction with the embodiments and the drawings.

[0022] As shown in the figure, the desulfurization system integrating phosphorus gypsum drying dehydration and calcination decomposition of the present invention includes a fluidized bed decomposition furnace 1, a cyclone separator 2, and a return feeder 3. The flue gas outlet pipe of the cyclone separator 2 is connected to a first waste heat recovery unit 4 for heat exchange to generate water vapor, and part of the water vapor is input into the fluidized bed decomposition furnace 1; the waste material conveying pipes of the fluidized bed decomposition furnace 1 and the return feeder 3 are connected to a second waste heat recovery unit 5 for heat exchange to generate hot air; the flue gas after heat exchange by the first waste heat recovery unit 4 and the hot air preheated by the second waste heat recovery unit are respectively used to supply heat for the dehydration of phosphorus gypsum and coal before being input into the fluidized bed decomposition furnace 1.

[0023] The cyclone separator 2 is a single-stage cyclone separator or a two-stage cyclone separator for separating the SO2-containing flue gas and CaO-containing slag generated by the thermal decomposition of phosphorus gypsum, and the return feeder 3 adopts a U-shaped structure to control the solid circulation flux returned to the fluidized bed decomposition furnace 1. In the first waste heat recovery unit 4, cold water and the high-temperature flue gas separated by the fluidized bed decomposition furnace 1 are input, and the two are heat-exchanged to output water vapor; the second waste heat recovery unit 5 is a combined air and water heat exchange device, which inputs the high-temperature solid waste, cold water, and cold air output by the fluidized bed decomposition furnace 1 and the return feeder 3. After the solid waste is heat-exchanged with the cold water and cold air, hot water and hot air are output.

[0024] The water vapor-containing air generated by the dehydration of coal and the water vapor generated by the first waste heat recovery unit 4 are jointly input into the fluidized bed decomposition furnace 1; part of the flue gas after heat exchange by the first waste heat recovery unit 4 is used to supply heat for the dehydration of phosphorus gypsum, and the flue gas containing water vapor generated after dehydration can be used to prepare sulfuric acid again, and the remaining flue gas not used for dehydration heating is directly used to prepare sulfuric acid.

[0025] The following is further illustrated by a specific example: The circulating fluidized bed phosphorus gypsum thermal decomposition furnace operates under normal pressure and at 1100 °C. When the annual treatment capacity of phosphorus gypsum in the device is close to 10,000 tons, the fluidized phosphorus gypsum thermal decomposition system can achieve continuous production and stable control in a self-heating state relying on the heat complementarity of endothermic and exothermic chemical reactions, and the net heat loss of the self-heating system does not exceed 110 kW.

[0026] Phosphogypsum is dried and dehydrated to remove crystal water by the flue gas 6-1 containing SO2 at a temperature of 580°C in the dehydration unit 8 of phosphogypsum to obtain dehydrated phosphogypsum 8-1. Coal is dried and dehydrated to remove moisture by hot air 5-1 at a temperature of 130°C in the dehydration unit 9 of coal to obtain dehydrated coal 9-1, and then enters the fluidized bed decomposer 1 together with the dehydrated phosphogypsum 8-1 to start the thermal decomposition desulfurization reaction of phosphogypsum.

[0027] After the reaction of coal reducing and decomposing phosphogypsum ends, the cyclone separator 2 separates the gas-solid products.

[0028] The flue gas 2-1 containing SO2 at a temperature of 1100°C enters the first waste heat recovery unit 4 to conduct heat transfer and exchange with the cooling water at a temperature of 20°C supplied externally. The flue gas containing SO2 is cooled to 580°C to obtain the cooled flue gas 4-1, and the cooling water is heated and vaporized to form steam 4-2 at a temperature of 500°C. The steam is generated in a closed pipeline, and because the space is closed, pressurization will be achieved, and then high-temperature steam will be generated.

[0029] A part of the slag containing CaO at a temperature of 1100°C falls into the return feeder 3 and circulates back to the fluidized bed decomposer 1 according to the provided reaction residence time. Another part enters the second waste heat recovery unit 5 through the slag discharge pipe at the bottom of the fluidized bed decomposer 1 or the return feeder 3, and exchanges heat with the cold air at a temperature of 30°C and the cooling water at a temperature of 20°C supplied externally respectively. The slag containing CaO is cooled to 60°C, the cold air is preheated to hot air 5-1 at a temperature of 130°C, and the cooling water is heated into boiling water at 100°C.

[0030] After the waste heat recovery of the gas-solid products is completed, more than half of the separated flue gas 6-1 of the cooled flue gas 4-1 containing SO2 at a temperature of 580°C is separated by the flue gas splitting unit 6 and enters the dehydration unit 8 of phosphogypsum; the hot air 5-1 at a temperature of 130°C enters the dehydration unit 9 of coal, and so on in a cycle.

[0031] Phosphogypsum is made into pellets by the granulation method of extrusion and rolling of phosphogypsum powder raw materials and attapulgite clay. The fluidized bed decomposer 1 is a fast circulating fluidized bed reactor. The cyclone separator 2 is a single-stage cyclone separator or a double-stage cyclone separator with high temperature resistance and corrosion resistance. The return feeder 3 is a U-shaped return feeder with high stability and safety. The second waste heat recovery unit 5 is a combined air and water type slag cooler. At the same time, a slag discharge port is reserved at the bottom of each of the fluidized bed decomposer 1 and the return feeder 3.

[0032] The steam 4-2 at a temperature of 500°C is separated by the steam splitting unit 7 to obtain a certain flow rate of steam 7-1 as the reaction steam, which enters the fluidized bed decomposer 1 together with the air 9-2 containing the steam formed by the gasification of the moisture in the coal leaving the dehydration unit 9 of coal to provide a reaction, fluidization and loosening atmosphere for the thermal decomposition desulfurization of phosphogypsum.

[0033] The flue gas that has not entered the dehydration unit 8 of phosphogypsum and the post-heating flue gas 8-2 that enters it, completes heating, and then leaves are both rich in waste heat. Moreover, the latter contains water vapor formed by the gasification of the crystal water in phosphogypsum. Therefore, it is necessary to further recover the waste heat of the flue gas using cooling water, or introduce them into the second waste heat recovery unit 5 to further increase the temperature of the hot air 5-1, so as to remove the moisture in the coal to the greatest extent while obtaining steam or hot water.

Claims

1. A desulfurization system integrating phosphorus gypsum drying, dehydration and calcination decomposition, comprising a fluidized bed decomposition furnace (1), a cyclone separator (2) and a return feeder (3), characterized in that: The flue gas outlet pipe of the cyclone separator (2) is connected to a first waste heat recovery unit (4) for heat exchange to generate steam, and part of the steam is input into the fluidized bed decomposer (1); the waste material conveying pipes of the fluidized bed decomposer (1) and the return feeder (3) are connected to a second waste heat recovery unit (5) for heat exchange to generate hot air; the flue gas and the hot air after heat exchange by the first waste heat recovery unit (4) are respectively used to heat the dehydration of phosphogypsum and coal before being input into the fluidized bed decomposer (1).

2. The desulfurization system according to claim 1, characterized in that: The second waste heat recovery unit (5) is a combined air and water heat exchange device, and air and water for heat exchange flow inside it.

3. The desulfurization system according to claim 1, characterized in that: The steam-containing air generated by coal dehydration is input into the fluidized bed decomposer (1).

4. The desulfurization system according to claim 1, wherein: The flue gas after heating the dehydration of phosphogypsum is input into the second waste heat recovery unit (5) for heat exchange.

5. The desulfurization system according to claim 1, wherein: The cyclone separator (2) is a single-stage cyclone separator or a two-stage cyclone separator.

6. The desulfurization system according to claim 1, wherein: The return feeder (3) adopts a U-shaped structure.

7. The desulfurization system according to claim 1, wherein: The fluidized bed decomposer (1) performs thermal decomposition under normal pressure and within the range of [1050°C, 1100°C].

8. The desulfurization system according to claim 1, wherein: Part of the flue gas after heat exchange by the first waste heat recovery unit (4) is used to heat the dehydration of phosphogypsum, and the rest is directly used to prepare sulfuric acid.

9. The desulfurization system according to claim 1, wherein: The temperature of the flue gas after heat exchange by the first waste heat recovery unit (4) is controlled within the range of [450°C, 580°C].

10. The desulfurization system according to claim 1, characterized in that: The temperature of the hot air generated by the second waste heat recovery unit (5) is controlled within the range of [130°C, 180°C].

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