A process for obtaining granular magnesium sulfate monohydrate by spray drying flue gas desulfurization wastewater

Abstract

The invention discloses a process for obtaining granular magnesium sulfate monohydrate by spray drying flue gas desulfurization wastewater in the field of spray granulation drying technology. The process comprises a spray granulation dryer, a liquid supply system, an air supply system, an exhaust gas treatment system, a finished product screening system and a material return system; an air distribution plate is arranged in the spray granulation dryer, a dust collector is arranged below the air distribution plate, and the dust collector is used to collect dust passing through the air distribution plate to reduce the corrosion of the dust to the air supply system; the invention utilizes the pressure difference to make the gas flow into the air collection hood, and the interception net intercepts the dust, so that the dust is concentrated in the dust collector, which is convenient for cleaning the dust and reduces the damage of the dust to the heating pipeline.

Description

Technical Field

[0001] The invention relates to the technical field of spray granulation and drying, and in particular to a process for obtaining granular magnesium sulfate monohydrate by spray drying flue gas desulfurization wastewater. Background Art

[0002] Magnesium sulfate monohydrate is a chemical state of magnesium sulfate; magnesium sulfate monohydrate is a white fluid powder (granules) with a density of 2.66g / cm3, soluble in water, slightly soluble in alcohol, and insoluble in acetone; because magnesium is one of the main components of chlorophyll, people usually use magnesium sulfate monohydrate as an additive for fertilizers and mineral water. The advantage of magnesium sulfate over other fertilizers is its higher solubility.

[0003] The traditional magnesium sulfate industry produces magnesium sulfate monohydrate particles by reacting concentrated sulfuric acid with light-burned magnesium oxide to obtain magnesium sulfate heptahydrate crystals, which are then granulated and dried in a fluidized bed to increase the particle size and remove the remaining six crystal waters to obtain magnesium sulfate monohydrate particles with sufficient particle size.

[0004] Granulation requires higher temperature and greater wind force than drying. The higher temperature is to allow the water in the liquid mixture attached to the recycled particles to evaporate quickly, and the greater wind force is to keep the particles containing water fluidized to avoid flakes and agglomeration. However, greater wind force means that the air distribution plate needs a larger ventilation diameter. The larger the ventilation diameter, the greater the potential energy of the wind on the movement of the magnesium sulfate particles. It is inevitable that the undried magnesium sulfate dust will pass through the ventilation opening.

[0005] In addition, magnesium sulfate particles will adhere to the hot air duct. Since the air outlet duct is mostly made of metal material, the high temperature on the duct surface will cause the attached magnesium sulfate to generate toxic and corrosive smoke containing sulfur oxides, and the air outlet duct is easily corroded and damaged. In addition, when the magnesium sulfate particles attached to the pipeline are in a static state, they absorb moisture in the air, accelerate the hardening of magnesium sulfate, and increase the difficulty of cleaning the outer wall of the pipeline. At the same time, the magnesium sulfate that absorbs moisture may release sulfate ions, which may cause further corrosion to the pipeline. Summary of the invention

[0006] The technical problem of the present invention is to provide a process for obtaining granular magnesium sulfate monohydrate by spray drying flue gas desulfurization wastewater.

[0007] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: a process for obtaining granular magnesium sulfate monohydrate by spray drying of flue gas desulfurization wastewater, comprising a spray granulation dryer, a liquid supply system, an air supply system, an exhaust gas treatment system, a finished product screening system and a return system; an air distribution plate is arranged in the spray granulation dryer, a dust collector is arranged under the air distribution plate, and the dust collector is used to collect dust passing through the air distribution plate to reduce the corrosion of the dust to the air supply system;

[0008] The steps of the process for directly obtaining granular magnesium sulfate monohydrate from flue gas desulfurization wastewater are as follows:

[0009] S1: Extraction of stock solution: The desulfurization wastewater is pre-treated, and the wastewater is filtered by a filter press, aerated and oxidized, and finely filtered. The pure stock solution obtained after filtration is evaporated and concentrated by the MVR system, and the concentrated stock solution is sent to the temporary storage tank in the liquid supply system;

[0010] S2: Preparation: The blower in the air supply system atomizes the air through the heater and sprays it into the spray granulation dryer. The high-temperature gas dries and preheats the spray granulation dryer before being discharged. After the drying is completed, the blower is stopped and the small particles of magnesium sulfate are laid on the air distribution plate of the spray granulation dryer to form a material layer;

[0011] S3: Start working: After the material layer is laid, turn on the blower again, and the air flow ejected from the air supply system fluidizes the magnesium sulfate in the spray granulation dryer; when the air inlet temperature rises to 200-230°C and the exhaust temperature rises to 120-130°C, turn on the liquid pump of the temporary storage tank, spray the original liquid in the temporary storage tank into the spray granulation dryer, and turn on the discharge plug of the spray granulation dryer. At the same time, turn on the dust collector to collect the dust around the air supply system. The collected dust is used as the raw material for the next laying, and at the same time, the corrosion of the dust to the air supply system is reduced;

[0012] S4: Granulation and drying: The stock solution is dispersed into droplets after being sprayed out. The droplets contact and adhere to the magnesium sulfate in the fluidized material layer and are fully in contact with the hot air. The hot air and the magnesium sulfate undergo sufficient heat exchange, and the magnesium sulfate in the spray granulation dryer is dried. The dried magnesium sulfate is discharged into the tail gas treatment system from the outlet of the spray granulation dryer.

[0013] S5: Product screening: The screening machine in the finished product screening system screens out the discharged magnesium sulfate, and the qualified particles enter the cooler for cooling and then enter the packaging process for packaging; small particles of magnesium sulfate enter the return system and are returned to the spray granulation dryer by the return auger as crystal nuclei;

[0014] S6: Exhaust filtration: The exhaust gas after granulation and drying enters the exhaust gas treatment system, and is double filtered by the cyclone dust collector and the pulse bag dust collector. The air after dust removal is exhausted by the induced draft fan, and the dust returns to the spray granulation dryer as a crystal nucleus.

[0015] As a further solution of the present invention, the dust collector comprises:

[0016] The air collecting hood is sleeved on the air outlet end of the air supply system, and a cavity is arranged inside, and a one-way baffle is arranged on the inner wall of the bottom of the cavity in an inclined manner;

[0017] An interception net is arranged in the cavity to intercept dust;

[0018] A pressure regulating ring is slidably arranged on the side of the air outlet end of the air collecting cover close to the air supply system, and the pressure regulating ring is provided with a pressure regulating groove;

[0019] The control unit is arranged on the inner side of the top of the wind collecting hood. It can drive the pressure regulating ring to rise and fall according to the temperature of the gas ejected from the outlet end of the air supply system, change the distance between the pressure regulating groove and the outlet end of the air supply system, and adjust the pressure difference between the inside and outside of the pressure regulating groove.

[0020] As a further solution of the present invention, the control unit includes:

[0021] The sliding sleeve is fixedly arranged on the top of the inner side of the wind collecting cover, and the bottom is connected with the cavity;

[0022] A slide plate is slidably arranged in the sliding sleeve, and the sliding sleeve is divided into a yielding cavity and a fusion cavity by the slide plate, and the fusion cavity is communicated with the cavity body;

[0023] The yielding groove is arranged inside the wind collecting cover and is provided with a connecting piece inside. Two ends of the connecting piece are respectively fixed to the pressure regulating ring and the slide plate.

[0024] As a further solution of the present invention, a cleaning component is provided below the interception net, and the cleaning component comprises:

[0025] The scraper has a "7"-shaped cross section and is provided with a cleaning channel inside, and a cleaning baffle is rotatably provided on the vertical section of the cleaning channel;

[0026] A driving member is installed in the cavity, and a driving ring is provided between the driving member and the scraper, and the driving member drives the scraper to rotate along the axis of the wind collecting cover through the driving ring;

[0027] The base is fixedly arranged in the wind collecting cover and is fixedly connected with a dust guide pipe, and the end of the dust guide pipe passes through the wind collecting cover.

[0028] As a further solution of the present invention, an air nozzle is provided at the air outlet end of the air supply system, and the air nozzle includes: a pipe seat connected to the main air supply line, the pipe seat is threadedly connected to a pipe body, a conical head is installed on the top of the pipe body, and an exhaust hole is opened at the bottom of the side wall of the conical head.

[0029] As a further solution of the present invention, a liquid supply pipe is provided at the liquid outlet end of the liquid supply system, and the liquid supply pipe includes a U-shaped tube with a nozzle installed, and both ends of the U-shaped tube are commonly connected to a transversely arranged cleaning pipe, and both ends of the cleaning pipe are provided with cleaning valves, and a three-way valve is provided in the middle of the cleaning pipe, and the main branch of the three-way valve is connected to the temporary storage tank.

[0030] As a further solution of the present invention, the air inlet end of the pulse bag dust collector described in S6 is provided with a temperature controller and a cooler.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] In the present invention, the air outlet end of the air supply system blows out a high-speed airflow, so that a pressure difference is formed inside and outside the air condensing hood. Under the action of the pressure difference, the gas in the air condensing hood moves from the cavity to between the air condensing hood and the air outlet end through the pressure regulating groove and flows with the high-temperature airflow, and then returns to the air condensing hood from the bottom side wall of the air condensing hood to form a cycle. The gas enters the air condensing hood carrying the dust dropped from the air distribution plate, and the dust is intercepted when passing through the interception net in the air condensing hood. The gas circulates back and forth and carries the dust on the outside of the air condensing hood into the inside of the air condensing hood and is adsorbed under the interception net. The dust can be collected centrally, thereby reducing the damage of the magnesium sulfate particles to the heating pipeline and affecting the transportation of the hot air of the spray granulation dryer.

[0033] In the present invention, the gas inside the yield cavity above the sliding sleeve expands and contracts due to heat and cold, causing the slide plate to move up and down. The slide plate drives the pressure regulating ring to move through the connecting piece. The pressure regulating ring changes the position of the pressure regulating groove, thereby changing the pressure difference between the inside and outside of the pressure regulating groove, changing the flow rate of the airflow passing through the wind collecting hood per unit time, and changing the dust collection speed, so that it can adjust the dust collection speed and reduce the obstruction of dust to the flow of hot air.

[0034] The method can directly produce magnesium sulfate monohydrate particles from desulfurization wastewater, turning waste into treasure, that is, realizing the comprehensive utilization of SO2 in flue gas, obtaining direct economic benefits of the product, and indirectly achieving zero wastewater discharge and zero environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0036] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0037] Figure 2 It is a schematic diagram of the overall cross-sectional structure of the present invention;

[0038] Figure 3 It is a schematic diagram of the structure of the gas supply system in the present invention;

[0039] Figure 4 It is a schematic diagram of the structure of the dust collector in the present invention;

[0040] Figure 5 For the present invention Figure 4 The enlarged structural diagram at A in the middle;

[0041] Figure 6 It is a schematic diagram of gas flow in the dust collector of the present invention;

[0042] Figure 7 This is a schematic diagram of the explosion structure of the dust collector in the present invention;

[0043] Figure 8 This is a schematic diagram of the cleaning component structure of the present invention;

[0044] Fig. 9 It is a schematic diagram of the dust collection state in the scraper of the present invention;

[0045] Fig.10 It is a schematic diagram of the structure of the liquid supply pipe in the present invention;

[0046] Fig.11 It is a schematic diagram of the process flow of the present invention;

[0047] The reference numerals in the accompanying drawings are as follows:

[0048] 1. Spray granulation dryer; 11. Air distribution plate; 13. Liquid supply system; 14. Air supply system; 15. Exhaust gas treatment system; 16. Finished product screening system; 17. Return system; 2. Dust collector; 21. Wind hood; 22. Cavity; 23. One-way baffle; 24. Intercepting net; 25. Pressure regulating ring; 26. Pressure regulating groove; 3. Control unit; 31. Sliding sleeve; 32. Slide plate; 33. Fusion cavity; 34. Position slot; 35, connecting piece; 36, give way cavity; 4, cleaning assembly; 41, scraper; 42, cleaning channel; 43, cleaning baffle; 44, driving piece; 45, driving ring; 46, base; 47, dust guide tube; 51, air nozzle; 52, tube seat; 53, tube body; 54, conical head; 55, exhaust hole; 61, liquid supply tube; 62, U-shaped tube; 63, cleaning tube; 64, cleaning valve; 65, three-way valve. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] See also Figure 1-Figure 11 The present invention provides a technical solution: a process for obtaining granular magnesium sulfate monohydrate by spray drying flue gas desulfurization wastewater, comprising a spray granulation dryer 1, wherein the spray granulation dryer 1 is provided with a pre-treatment system, a liquid supply system 13, an air supply system 14, an exhaust gas treatment system 15, a finished product screening system 16 and a return material system 17;

[0051] The pre-treatment system is used to treat desulfurization wastewater;

[0052] The liquid supply system 13 is used to supply magnesium sulfate liquid to the spray granulation dryer 1 and atomize it;

[0053] The gas system 14 is used to provide high-temperature gas to the spray granulation dryer 1;

[0054] The tail gas treatment system 15 is used to filter the tail gas discharged from the spray granulation dryer 1;

[0055] The finished product screening system 16 is used to screen the solid magnesium sulfate discharged from the spray granulation dryer 1;

[0056] The return system 17 is used to return the small-particle magnesium sulfate screened by the finished product screening system 16 to the spray granulation dryer 1;

[0057] An air distribution plate 11 is provided in the spray granulation dryer 1, and a dust collector 2 is provided below the air distribution plate 11. The dust collector 2 is used to collect dust passing through the air distribution plate 11 to reduce the corrosion of the dust on the air supply system 14; the dust collector 2 includes:

[0058] The air collecting cover 21 is sleeved on the air outlet end of the air supply system 14, and a cavity 22 is provided inside. A one-way baffle 23 is provided on the inner wall of the bottom of the cavity 22 in an inclined manner.

[0059] An interception net 24 is disposed in the cavity 22 and is used to intercept dust;

[0060] The pressure regulating ring 25 is slidably disposed on the air outlet side of the air collecting cover 21 close to the air supply system 14, and the pressure regulating ring 25 is provided with a pressure regulating groove 26;

[0061] The control unit 3 is arranged on the inner side of the top of the air collecting cover 21, and can drive the pressure regulating ring 25 to rise and fall according to the temperature of the gas ejected from the gas outlet of the gas supply system 14, change the distance between the pressure regulating groove 26 and the gas outlet of the gas supply system 14, and adjust the pressure difference between the inside and outside of the pressure regulating groove 26;

[0062] For details, please refer to Figure 2-Figure 4 , Figure 6 The air supply system 14 blows out the heated air at the air outlet, so that the air outlet blows out a high-speed hot air flow, so that a pressure difference is formed inside and outside the air collecting cover 21. Under the action of the pressure difference, the gas in the air collecting cover 21 flows from the cavity 22 to between the air collecting cover 21 and the air outlet through the pressure regulating groove 26 and flows with the high-temperature air flow, and then returns to the air collecting cover 21 from the bottom side wall of the air collecting cover 21 to form a cycle (such as Figure 6As shown), the gas enters the wind collecting hood 21 and carries the dust dropped from the air distribution plate 11. The dust is intercepted when passing through the interception net 24 in the wind collecting hood 21. The gas circulates back and forth and carries the dust outside the wind collecting hood 21 into the inside of the wind collecting hood 21 and is adsorbed under the interception net 24. The dust can be collected in a centralized manner, reducing the damage of the magnesium sulfate particles to the heating pipeline and affecting the use of the spray granulation dryer 1.

[0063] As a further solution of the present invention, the control unit 3 includes:

[0064] The sliding sleeve 31 is fixedly mounted on the top of the inner side of the wind collecting cover 21, and the bottom is connected to the cavity 22;

[0065] The slide plate 32 is slidably disposed in the sliding sleeve 31. The sliding sleeve 31 is divided into a yielding cavity 36 and a fusion cavity 33 by the slide plate 32. The fusion cavity 33 is communicated with the cavity 22.

[0066] The clearance groove 34 is provided inside the wind collecting cover 21, and a connecting member 35 is provided inside. The two ends of the connecting member 35 are respectively fixed to the pressure regulating ring 25 and the slide plate 32;

[0067] The high temperature at the air outlet will increase the internal temperature of the spray granulation dryer, accelerate the evaporation rate of the water in the magnesium sulfate liquid droplets, and the droplets will not attach to the crystal nuclei in time, thus forming fine dust, which will increase the amount of dust in the spray granulation dryer 1; in addition, as the temperature rises, the water content of the dust decreases, making it lighter, and at the same flow rate, the floating speed of the dust increases, which will further increase the amount of dust under the air distribution plate 11;

[0068] For details, see Figure 4 , Figure 5 and Figure 6 When the temperature at the air outlet increases, the gas inside the give way chamber 36 above the sliding sleeve 31 expands due to the heat and pushes the slide plate 32 down to close the give way chamber 36, while the fusion chamber 33 is connected with the cavity 22 and indirectly connected with the inside of the spray granulation dryer 1. Therefore, the expansion of the gas volume in the fusion chamber 33 has little effect on the movement of the slide plate 32. The slide plate 32 drives the pressure regulating ring 25 to descend through the connecting piece 35, and the pressure regulating ring 25 approaches the air outlet, so that the pressure difference between the inside and outside of the pressure regulating groove 26 increases, and the flow rate of the airflow passing through the wind collecting hood 21 per unit time increases, so that the dust collection speed increases.

[0069] As a further solution of the present invention, a cleaning component 4 is provided below the interception net 24, and the cleaning component 4 includes:

[0070] The scraper 41 has a "7"-shaped cross section and is provided with a cleaning channel 42 inside. A cleaning baffle 43 is rotatably provided in the vertical section of the cleaning channel 42;

[0071] The driving member 44 is installed in the cavity 22, and a driving ring 45 is provided between the driving member 44 and the scraper 41. The driving member 44 drives the scraper 41 to rotate along the axis of the wind collecting cover 21 through the driving ring 45.

[0072] The base 46 is fixedly arranged in the wind collecting cover 21 and is fixedly connected with a dust guide pipe 47, and the end of the dust guide pipe 47 passes through the wind collecting cover 21;

[0073] The spray granulation dryer 1 can perform granulation work for a long time. When the dust intercepted by the interception net 24 reaches a certain thickness, the mesh of the interception net 24 is gradually blocked, so that the air collecting hood 21 is blocked and the gas cannot pass through, and the dust cannot be collected.

[0074] For details, see Figure 4 and Figure 8 The driving member 44 drives the scraper 41 to rotate along the axis of the wind collecting hood 21 through the driving ring 45. The scraper 41 cleans the bottom of the intercepting net 24, so that the dust adsorbed on the bottom of the intercepting net 24 enters the scraper 41. When the dust is piled up above the cleaning baffle 43, the horizontal section of the scraper 41 is filled tightly. As the dust entering the scraper 41 increases, the cleaning baffle 43 gradually opens, and the dust close to the cleaning baffle 43 falls from the gap between the cleaning baffle 43 and the scraper 41. Since the horizontal section of the scraper 41 is filled tightly, the dust falling at the cleaning baffle 43 is not affected. Similarly, the scraper 41 will not affect the airflow passing through the intercepting net 24. When the bottom of the scraper 41 rotates to above the dust guide pipe 47, the collected dust falls into the dust guide pipe 47 for centralized collection, so that the intercepting net 24 can intercept dust for a long time.

[0075] As a further solution of the present invention, an air nozzle 51 is provided at the air outlet of the air supply system 14, and the air nozzle 51 includes: a pipe seat 52 connected to the main air supply line, a pipe body 53 is threadedly connected to the pipe seat 52, a conical head 54 is installed on the top of the pipe body 53, and an exhaust hole 55 is opened at the bottom of the side wall of the conical head 54;

[0076] For details, see Figure 6 The tube body 53 can connect the air nozzle 51 to the air supply system through the tube seat 52. In addition, the conical head 54 can change the flow path of the hot air after it is discharged from the exhaust hole 55 to gradually increase. In conjunction with the wind gathering hood 21, the conical head 54 of different shapes can be replaced according to the required pressure, so that the internal and external pressure difference variables changed during the lifting and lowering of the pressure regulating tank 26 can be controlled.

[0077] A process for obtaining granular magnesium sulfate monohydrate by spray drying flue gas desulfurization wastewater, the specific steps of which are as follows:

[0078] S1: Extraction of stock solution: The desulfurization wastewater is pre-treated, and the wastewater is filtered by a filter press, aerated and oxidized, and finely filtered. The pure stock solution obtained after filtration is evaporated and concentrated by the MVR system, and the concentrated stock solution is sent to the temporary storage tank in the liquid supply system 13;

[0079] S2: Preparation: The blower in the air supply system 14 atomizes the air through the heater and sprays it into the spray granulation dryer 1. The high-temperature gas dries and preheats the spray granulation dryer 1 before being discharged. After the drying is completed, the blowing of the blower is stopped, and the small particles of magnesium sulfate are laid on the air distribution plate 11 of the spray granulation dryer 1 to form a material layer;

[0080] S3: Start working: After the material layer is laid, turn on the blower again, and the air supply system 14 ejects airflow to fluidize the magnesium sulfate in the spray granulation dryer 1; when the air inlet temperature rises to 200-230°C and the exhaust air temperature rises to 120-130°C, turn on the liquid pump of the temporary storage tank, spray the stock liquid in the temporary storage tank into the spray granulation dryer 1, and turn on the discharge plug of the spray granulation dryer 1. At the same time, the dust collector 2 is turned on to collect the dust around the air supply system 14. The collected dust is used as the raw material for the next laying, and at the same time, the corrosion of the dust to the air supply system 14 is reduced;

[0081] S4: Granulation and drying: The stock solution is dispersed into droplets after being sprayed out, and the droplets contact and adhere to the magnesium sulfate in the fluidized material layer, and are fully in contact with the hot air. The hot air and the magnesium sulfate are fully heat exchanged, and the magnesium sulfate in the spray granulation dryer 1 is dried. The dried magnesium sulfate is discharged from the outlet of the spray granulation dryer 1 into the exhaust gas treatment system 15;

[0082] S5: Product screening: The screening machine in the finished product screening system 16 screens out the discharged magnesium sulfate, and the magnesium sulfate with qualified particle size enters the cooler for cooling and then enters the packaging process for packaging; the small-particle magnesium sulfate enters the return system 17 and is returned to the spray granulation dryer 1 by the return auger as a crystal nucleus;

[0083] S6: Exhaust filtration: The exhaust gas after granulation and drying enters the exhaust gas treatment system 15, and is double-filtered by the cyclone dust collector and the pulse bag dust collector. The air after dust removal is exhausted by the induced draft fan, and the dust returns to the spray granulation dryer 1 as a crystal nucleus;

[0084] The direct production of magnesium sulfate monohydrate particles from desulfurization wastewater has been achieved, turning waste into treasure, that is, the comprehensive utilization of SO2 in flue gas has been achieved, the direct economic benefits of the product have been obtained, and indirectly zero wastewater discharge and zero environmental pollution can be achieved.

[0085] When the hot air temperature rises to 100°C and the exhaust air temperature is about 60°C, check whether the air distribution plate 11 of the spray granulation dryer 1 is dried, then open the manhole door of the spray granulation dryer 1, start to manually add materials to establish a material layer, and stop adding materials after about 500mm of fluidized material layer is manually added to allow magnesium sulfate to fluidize normally in the spray granulation dryer 1. When the inlet air temperature rises to 200-230°C and the exhaust air temperature rises to 125°C, the liquid supply system 13 is turned on. The nozzles in the liquid supply system 13 are arranged in a linear array. The nozzles are opened from the middle to both sides, and the opening interval is eight to twelve minutes. After the nozzles are turned on, the discharge plug of the spray granulation dryer 1 is opened in time to ensure that there is crystal nucleus return. In the initial stage, the amount of crystal nucleus return is small, and it is necessary to pay attention to the changes in hot air and exhaust air temperature. The exhaust air temperature is maintained between 120°C and 130°C to avoid high temperature burning of the bags in the pulse bag dust collector. When the exhaust air temperature exceeds 130°C, the exhaust air must be cooled in time to prevent burning of the bags.

[0086] As a further solution of the present invention, a liquid supply pipe 61 is provided at the liquid outlet of the liquid supply system 13, and the liquid supply pipe 61 includes a U-shaped pipe 62 with a nozzle installed, and both ends of the U-shaped pipe 62 are commonly connected to a transversely arranged cleaning pipe 63, and both ends of the cleaning pipe 63 are provided with a cleaning valve 64, and a three-way valve 65 is provided in the middle of the cleaning pipe 63, and the main branch of the three-way valve 65 is connected to the temporary storage tank;

[0087] For details, see Fig.10 When cleaning the pipeline, close the three-way valve 65, connect the cleaning liquid to the cleaning pipe 63 on one side, and the cleaning liquid flows from one end of the U-shaped tube 62 to the other end. The cleaning liquid flushes the impurities remaining in the U-shaped tube 62 and is discharged from the cleaning pipe 63 on the other side.

[0088] As a further solution of the present invention, a temperature controller and a cooler are provided at the air inlet end of the S6 pulse bag dust collector; when the exhaust air temperature approaches 130°C, the cooler is turned on to cool the exhaust air; when the exhaust air temperature approaches 120°C, the cooler is turned off to control the exhaust air temperature between 120°C and 130°C to prevent over-temperature from burning the bags.

Claims

1. A process for obtaining granular magnesium sulfate monohydrate by spray drying flue gas desulfurization wastewater, comprising a spray granulation dryer (1), a liquid supply system (13), an air supply system (14), an exhaust gas treatment system (15), a finished product screening system (16) and a return system (17); the spray granulation dryer (1) is provided with an air distribution plate (11), characterized in that: A dust collector (2) is provided below the air distribution plate (11), and the dust collector (2) is used to collect dust that passes through the air distribution plate (11) to reduce dust corrosion on the air supply system (14); the dust collector (2) comprises: An air collecting hood (21) is sleeved on the air outlet end of the air supply system (14), and a cavity (22) is provided inside the hood. A one-way baffle (23) is provided on the inner wall of the bottom of the cavity (22) in an inclined manner. An interception net (24) is arranged in the cavity (22) and is used to intercept dust; A pressure regulating ring (25) is slidably disposed on a side of the air collecting cover (21) close to the air outlet end of the air supply system (14), and the pressure regulating ring (25) is provided with a pressure regulating groove (26); The control unit (3) is arranged on the inner side of the top of the air collecting cover (21), and can drive the pressure regulating ring (25) to rise and fall according to the temperature of the gas ejected from the gas outlet of the gas supply system (14), thereby changing the distance between the pressure regulating groove (26) and the gas outlet of the gas supply system (14), and adjusting the pressure difference between the inside and outside of the pressure regulating groove (26); The steps of the process for directly obtaining granular magnesium sulfate monohydrate from flue gas desulfurization wastewater are as follows: S1: Extraction of raw liquid: The desulfurization wastewater is pre-treated, and the wastewater is filtered by a filter press, aerated and oxidized, and finely filtered. The pure raw liquid obtained after filtration is evaporated and concentrated by the MVR system, and the concentrated raw liquid is sent to the temporary storage tank in the liquid supply system (13); S2: Preparation: The blower in the air supply system (14) atomizes the air after passing through the heater and sprays it into the spray granulation dryer (1). The high-temperature gas dries and preheats the spray granulation dryer (1) and is then discharged. After the drying is completed, the blower is stopped and the small particles of magnesium sulfate are laid on the air distribution plate (11) of the spray granulation dryer (1) to form a material layer. S3: Start working: After the material layer is laid, the blower is turned on again, and the air supply system (14) sprays air to fluidize the magnesium sulfate in the spray granulation dryer (1); when the air inlet temperature rises to 200-230°C and the exhaust air temperature rises to 120-130°C, the liquid pump of the temporary storage tank is turned on to spray the original liquid in the temporary storage tank into the spray granulation dryer (1), and the discharge plug of the spray granulation dryer (1) is turned on. At the same time, the dust collector (2) is turned on to collect dust around the air supply system (14). The collected dust is used as the raw material for the next laying of materials, and at the same time, the corrosion of the dust to the air supply system (14) is reduced; S4: Granulation and drying: The stock solution is dispersed into droplets after being sprayed out. The droplets contact and adhere to the magnesium sulfate in the fluidized material layer and are fully in contact with the hot air. The hot air and the magnesium sulfate are fully heat-exchanged. The magnesium sulfate in the spray granulation dryer (1) is dried. The dried magnesium sulfate is discharged from the outlet of the spray granulation dryer (1) into the exhaust gas treatment system (15); S5: Product screening: The screening machine in the finished product screening system (16) screens out the discharged magnesium sulfate, and the magnesium sulfate with qualified particle size enters the cooling machine for cooling and then enters the packaging process for packaging; the small magnesium sulfate particles enter the return system (17) and are returned to the spray granulation dryer (1) by the return auger as crystal nuclei; S6: Exhaust filtration: After the granulation and drying process, the exhaust gas enters the exhaust gas treatment system (15), where it is double filtered by the cyclone dust collector and the pulse bag dust collector. The air after dust removal is exhausted by the induced draft fan, and the dust returns to the spray granulation dryer (1) as a crystal nucleus.

2. The process for obtaining granular magnesium sulfate monohydrate by spray drying flue gas desulfurization wastewater according to claim 1, characterized in that: The control unit (3) comprises: The sliding sleeve (31) is fixedly mounted on the top of the inner side of the wind collecting cover (21), and the bottom of the sliding sleeve is in communication with the cavity (22); A slide plate (32) is slidably disposed in the sliding sleeve (31), and the sliding sleeve (31) is divided into a clearance cavity (36) and a fusion cavity (33) by the slide plate (32), wherein the fusion cavity (33) is communicated with the cavity (22); The clearance groove (34) is formed inside the wind collecting cover (21) and is provided with a connecting piece (35) inside. The two ends of the connecting piece (35) are respectively fixed to the pressure regulating ring (25) and the slide plate (32).

3. The process for obtaining granular magnesium sulfate monohydrate by spray drying flue gas desulfurization wastewater according to claim 2, characterized in that: A cleaning component (4) is provided below the interception net (24), and the cleaning component (4) comprises: The scraper (41) has a "7"-shaped cross section and is provided with a cleaning channel (42) therein, wherein a cleaning baffle (43) is rotatably provided in a vertical section of the cleaning channel (42); A driving member (44) is installed in the cavity (22), and a driving ring (45) is provided between the driving member (44) and the scraper (41), wherein the driving member (44) drives the scraper (41) to rotate along the axis of the wind collecting cover (21) via the driving ring (45); The base (46) is fixedly disposed in the wind collecting cover (21) and is fixedly connected to a dust guide pipe (47), wherein the end of the dust guide pipe (47) passes through the wind collecting cover (21).

4. A process for obtaining granular magnesium sulfate monohydrate by spray drying flue gas desulfurization wastewater according to any one of claims 1 to 3, characterized in that: The air outlet end of the air supply system (14) is provided with an air nozzle (51), the air nozzle (51) comprising: a pipe seat (52) connected to the main air supply line, a pipe body (53) being threadedly connected to the pipe seat (52), a conical head (54) being mounted on the top of the pipe body (53), and an air exhaust hole (55) being provided at the bottom of the side wall of the conical head (54).

5. The process for obtaining granular magnesium sulfate monohydrate by spray drying flue gas desulfurization wastewater according to claim 4, characterized in that: A liquid supply pipe (61) is provided at the liquid outlet end of the liquid supply system. The liquid supply pipe (61) comprises a U-shaped pipe (62) equipped with a nozzle. Both ends of the U-shaped pipe (62) are connected to a transversely arranged cleaning pipe (63). Both ends of the cleaning pipe (63) are provided with cleaning valves (64). A three-way valve (65) is provided in the middle of the cleaning pipe (63). The main branch of the three-way valve (65) is connected to a temporary storage tank.

6. The process for obtaining granular magnesium sulfate monohydrate by spray drying flue gas desulfurization wastewater according to claim 5, characterized in that: The pulse bag dust collector described in S6 is provided with a temperature controller and a cooler at the air inlet end.

Images