A method and system for treating byproducts in the process of preparing silane gas for granular silicon

Abstract

The invention discloses a method and system for treating byproducts of a silane gas preparation process for granular silicon. The silane vent gas is sent into a washing device and neutralized with a sodium hydroxide solution to produce sodium silicate. The sodium silicate produced in the step is reacted and concentrated with liquid caustic soda under steam heating. The product is dried and crystallized. Zero-water sodium metasilicate or pentahydrate sodium metasilicate is used as a crystal seed during the crystallization process to finally obtain zero-water sodium metasilicate or pentahydrate sodium metasilicate products. The invention neutralizes the waste liquid containing sodium silicate, precipitates it, dehydrates it, and then treats solid waste and wastewater. The waste liquid is processed into pentahydrate sodium metasilicate and zero-water sodium metasilicate for sale and generates economic benefits.

Description

Technical Field

[0001] The present invention belongs to the field of polysilicon production, and in particular relates to a method and system for processing byproducts of a silane gas preparation process for granular silicon. Background Art

[0002] In the current mainstream granular silicon production process, silane gas (SiH4) is introduced into a fluidized bed reactor with small granular silicon powder for continuous thermal decomposition reaction to generate granular polysilicon products. The silane gas preparation technology uses SiCl4, H2, HCl and industrial silicon as raw materials to produce SiHCl3 in a high-temperature and high-pressure fluidized bed (boiling bed). SiHCl3 is further disproportionated and hydrogenated to produce SiH2Cl2, and then silane gas is produced. Affected by the purity of the raw materials for silane gas production and the impurity content of the recovered hydrogen, the silane gas production process needs to be vented to remove impurities in the raw materials. The vent contains components such as SiH3Cl, SiH2Cl2, SiHCl3, SiCl4, Si2H6, etc. This vent is neutralized with sodium hydroxide at a concentration of 10%-35%. The specific reaction is as follows: SiH2Cl2+NaOH→Na2SiO3+2H2O+NaCl, SiCl4+6NaOH→Na2SiO3+4NaCl+3H2O…, and after the reaction, it contains 8%-15% Na2SiO3 (sodium hydroxide) and 3%-5% sodium hydroxide. In the past, the waste liquid was neutralized with acid and alkali and then treated harmlessly as wastewater and solid waste.

[0003] The sodium silicate content in silane washing wastewater (sodium silicate high alkaline wastewater) is 8%-12%, and the pH is greater than 14. It has high interference and scaling tendency when entering any system, which is not conducive to the zero emission of the system. The silane gas washing cannot be effectively replaced and discharged, which will lead to incomplete silane gas washing. The silane gas is entrained and discharged from the vent pipe. When it encounters air and suitable conditions, it is ignited, causing the vent pipeline to catch fire.

[0004] A large amount of silane gas tends to be saturated after being washed by liquid alkali solution, and needs to be effectively replaced after saturation. The high-alkali wastewater of sodium silicate after replacement cannot be absorbed by the current system, and environmental protection and safety issues need to be solved urgently. In the process of treating sodium silicate, acid-base neutralization and sedimentation are required, and additional production costs are required in the process of treating wastewater and solid waste. Summary of the invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for treating by-products of the silane gas preparation process for granular silicon in view of the shortcomings of the prior art, so as to utilize and process the waste liquid containing sodium silicate.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A method for treating byproducts of a silane gas preparation process for granular silicon comprises the following steps:

[0008] (1) The silane exhaust gas is sent into a washing device and neutralized with a sodium hydroxide solution to produce sodium silicate;

[0009] (2) reacting and concentrating the sodium carbonate produced in step (1) with liquid caustic soda under steam heating;

[0010] (3) drying and crystallizing the product of step (3), using zero-hydrate sodium metasilicate or pentahydrate sodium metasilicate as a seed crystal during the crystallization process, and finally obtaining zero-hydrate sodium metasilicate or pentahydrate sodium metasilicate product.

[0011] Specifically, in step (2), the liquid alkali is a sodium hydroxide aqueous solution; the material ratio of the two is calculated as follows:

[0012] nNa2O·mSiO2+2(m-n)NaOH→mNa2SiO3

[0013] Among them, m and n are both sodium silicate modulus, which refers to the molar ratio of silicon dioxide to sodium oxide in sodium silicate; m is the modulus measured by sodium silicate after testing; n is the target modulus of sodium silicate solution after modulus adjustment; the value range of n target adjustment modulus is 0.93-1.05, and n=1 is preferred. Sodium silicate modulus is an important indicator for measuring the hydrate content in the hydrolysis product of sodium silicate. The molar ratio of silicon dioxide to sodium oxide in sodium silicate is called modulus. It is mainly used to measure product quality in sodium silicate production, generally between 1.5 and 3.5. It is of great significance to ensure the quality of sodium silicate.

[0014] By testing and calculating the material ratio, the sodium carbonate and liquid caustic soda are pumped from the storage tank into the mold adjustment tank according to the ratio. The liquid caustic soda is pumped first and then the sodium carbonate.

[0015] Specifically, in step (2), the temperature of the reaction under steam heating is 100°C-150°C, the reaction is carried out under stirring, and the stirring speed is 1-4r / min; the reaction time is 2-3 hours, and detection is carried out every half hour to determine whether alkali solution or sodium carbonate is added.

[0016] Specifically, in step (3), the seed crystals are first put into the drying crystallization equipment, and then the product of step (2) is sent in by spraying, maintaining the inlet temperature at 300-400° C.; hot air is introduced into the drying crystallization equipment for drying and maintaining the temperature of the material inlet.

[0017] Furthermore, the present invention also provides a byproduct treatment system for the silane gas preparation process for granular silicon, comprising a silane gas venting washing tower, a sodium carbonate storage tank, a liquid caustic soda storage tank, a film adjustment and concentration reaction tank, and a crystallization and drying device;

[0018] The tower side of the silane gas venting washing tower is connected to the silane venting air guide pipe, and the bottom of the tower kettle is connected to the sodium carbonate storage tank through a discharge pipe; the bottoms of the sodium carbonate storage tank and the liquid caustic soda storage tank are respectively connected to the film adjustment and concentration reaction tank through pipelines; the bottom of the film adjustment and concentration reaction tank is connected to the feed inlet at the top of the crystallization drying device through a feed discharge pipe; a group of nozzles are arranged at the top feed inlet of the crystallization drying device, and the two ends of the crystallization drying device are arranged as air inlets and air outlets, and the air inlet and air outlet are connected to the hot air blower through air ducts.

[0019] Specifically, the bottom discharge pipe of the silane gas venting washing tower is also provided with a reflux pipe connected to the top of the tower; the bottom discharge pipe of the silane gas venting washing tower is equipped with a washing liquid discharge pump.

[0020] Specifically, a sodium carbonate discharge pump and a liquid caustic soda discharge pump are respectively provided on the discharge pipes at the bottom of the sodium carbonate storage tank and the liquid caustic soda storage tank.

[0021] Specifically, the membrane adjustment and concentration reaction tank is provided with a stirring device inside and a steam heating jacket outside; and a concentrated liquid discharge pump is provided on the bottom discharge pipe.

[0022] Specifically, the crystallization and drying device includes a rotating drum and a driving assembly; one end of the rotating drum is higher than the other end, and both ends are rotatably mounted on a bearing seat through bearings, and the rotating drum is driven to rotate by the driving assembly; the bottom of the film adjustment and concentration reaction tank is detachably connected to a feed port opened on the side of the higher end of the rotating drum through a feed pipe, and is connected to a group of nozzles located in the rotating drum, and the concentrated liquid is sprayed into the rotating drum through the nozzles; a seed feeding port is provided on the bearing seat at the higher end of the crystallization and drying device, and the seed feeding port feeds the added seeds into the rotating drum through the chute below; an air inlet is provided at the lower end of the rotating drum, an air outlet is provided at the higher end, and a discharge port is provided on the side of the rotating drum at the lower end.

[0023] Specifically, an electric heater is provided on the air duct between the hot air blower and the air inlet of the crystallization drying device.

[0024] Beneficial effects:

[0025] The present invention neutralizes the waste liquid containing sodium silicate, and then treats solid waste and wastewater after precipitation and dehydration, and processes it into pentahydrate sodium metasilicate and zero-water sodium metasilicate for sale and economic benefits. It is calculated that the cost of solid waste treatment, including material consumption, labor, equipment, solid waste, and wastewater treatment, is about 500 yuan / ton. The production of one ton of sodium metasilicate product is 50,000 yuan / ton, and after deducting the production cost, each ton can generate 30,500 yuan / ton of benefits. After the sodium silicate is concentrated by liquid alkali mold adjustment, it is enriched and crystallized on the seed in the crystallization drying equipment, and the corresponding grade of product is obtained after drying. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0027] Figure 1 It is a schematic diagram of the structure of the by-product processing system of the silane gas preparation process of granular silicon.

[0028] Wherein, each reference numeral represents:

[0029] 1-1 silane gas venting washing tower; 1-2 washing liquid discharge pump; 2-1 sodium carbonate storage tank; 2-2 liquid caustic soda storage tank; 2-3 sodium carbonate discharge pump; 2-4 liquid caustic soda discharge pump; 3-1 film adjustment and concentration reaction tank; 3-2 concentrated liquid discharge pump; 4-1 crystallization drying device; 4-2 seed crystal feeding port; 4-3 nozzle; 4-4 discharge port; 4-5 rotating drum; 5-1 hot air blower; 6-1 electric heater. DETAILED DESCRIPTION

[0030] The present invention can be better understood with reference to the following examples.

[0031] Combination Figure 1 The byproduct processing system of the silane gas preparation process for granular silicon of the present invention comprises a silane gas venting washing tower 1-1, a sodium carbonate storage tank 2-1, a liquid caustic soda storage tank 2-2, a film adjustment and concentration reaction tank 3-1 and a crystallization drying device 4-1.

[0032] Among them, the tower side of the silane gas venting washing tower 1-1 is connected to the silane venting air guide pipe, and the bottom of the tower kettle is connected to the sodium carbonate storage tank 2-1 through a discharge pipe; the bottoms of the sodium carbonate storage tank 2-1 and the liquid alkali storage tank 2-2 are respectively connected to the film adjustment and concentration reaction tank 3-1 through pipelines; the bottom of the film adjustment and concentration reaction tank 3-1 is connected to the feed port at the top of the crystallization drying device 4-1 through a feed pipe; a group of nozzles are arranged at the top feed port of the crystallization drying device 4-1, and the two ends of the crystallization drying device 4-1 are arranged as air inlet and air outlet, and the air inlet and air outlet are connected to the hot air blower 5-1 through air ducts.

[0033] The bottom discharge pipe of the silane gas venting washing tower 1-1 is also provided with a reflux pipe connected to the top of the tower; the bottom discharge pipe of the silane gas venting washing tower 1-1 is equipped with a washing liquid discharge pump 1-2.

[0034] A sodium carbonate discharge pump 2-3 and a liquid caustic soda discharge pump 2-4 are respectively provided on the discharge pipes at the bottom of the sodium carbonate storage tank 2-1 and the liquid caustic soda storage tank 2-2.

[0035] The membrane adjustment and concentration reaction tank 3-1 is provided with a stirring device inside and a steam heating jacket outside; a concentrated liquid discharge pump 3-2 is provided on the bottom discharge pipe.

[0036] The crystallization drying device 4-1 includes a drum 4-5 and a driving assembly; the drum 4-5 is higher at one end and lower at the other end, and both ends are rotatably mounted on a bearing seat through bearings, and the drum 4-5 is driven to rotate by the driving assembly; the bottom of the membrane adjustment and concentration reaction tank 3-1 is detachably connected to a feed port opened on the side of the higher end of the drum 4-5 through a feed pipe, and is connected to a group of nozzles 4-3 located in the drum 4-5, and the concentrated liquid is sprayed into the drum 4-5 through the nozzles 4-3; a seed feeding port 4-2 is provided on the bearing seat at the higher end of the crystallization drying device 4-1, and the seed feeding port 4-2 feeds the added seeds into the drum 4-5 through the inclined slot below; an air inlet is provided at the lower end of the drum 4-5, and an air outlet is provided at the higher end, and a discharge port 4-4 is provided on the side of the lower end of the drum 4-5.

[0037] An electric heater 6-1 is provided on the air duct between the hot air blower 5-1 and the air inlet of the crystallization drying device 4-1.

[0038] The method for treating byproducts of the silane gas preparation process of granular silicon using the system comprises the following steps:

[0039] (1) The silane exhaust gas is sent into a washing device and neutralized with a sodium hydroxide solution to produce sodium silicate;

[0040] (2) reacting and concentrating the sodium carbonate produced in step (1) with liquid caustic soda under steam heating;

[0041] (3) drying and crystallizing the product of step (3), using zero-hydrate sodium metasilicate or pentahydrate sodium metasilicate as a seed crystal during the crystallization process, and finally obtaining zero-hydrate sodium metasilicate or pentahydrate sodium metasilicate product.

[0042] Specifically, in step (2), the liquid alkali is a sodium hydroxide aqueous solution; the material ratio of the two is calculated as follows:

[0043] nNa2O·mSiO2+2(m-n)NaOH→mNa2SiO3

[0044] Among them, m and n are both the modulus of sodium silicate, which refers to the molar ratio of silicon dioxide to sodium oxide in sodium silicate; m is the modulus measured by the detection of sodium silicate; n is the target modulus of the sodium silicate solution after mold adjustment; n is the target adjustment modulus, and its value is 1. By testing and calculating the material ratio, sodium silicate and liquid caustic soda are pumped from the storage tank to the mold adjustment tank according to the ratio. First pump the liquid caustic soda and then the sodium silicate.

[0045] Specifically, in step (2), the temperature of the reaction under steam heating is 100°C-150°C, the reaction is carried out under stirring, and the stirring speed is 1-4r / min; the reaction time is 2-3 hours, and detection is performed every half an hour during the operation to determine whether to add alkali liquid or sodium carbonate. After the materials are prepared, steam can be passed to heat the reaction and concentrate, and stirring can be started. After passing steam for half an hour, the modulus in the tank can be sampled and tested, and whether to add liquid alkali or sodium carbonate, and the amount of addition can be determined based on the sampling results.

[0046] The relationship between crystallization solutions with different n(Na2O) / mSiO2 ratios and crystallization time is shown in Table 1.

[0047] Table 1

[0048]

[0049] In step (3), the seed crystal is first put into the drying crystallization equipment, and then the product of step (2) is sent in by spraying, and the inlet temperature is maintained at 300-400°C; hot air is introduced into the drying crystallization equipment for drying and maintaining the temperature of the material inlet. Liquid sodium metasilicate is enriched and grown on the seed crystal, and the drying temperature is normally produced by controlling the drying air: the obtained product is packaged from the feed port after drying and then sold out. The main technical indicators of the sodium metasilicate prepared by the present invention are shown in Table 2.

[0050] Table 2

[0051]

[0052] The present invention provides a method and system for treating byproducts of the silane gas preparation process for granular silicon. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A system for processing byproducts of a silane gas preparation process for granular silicon, characterized in that: It includes a silane gas venting washing tower (1-1), a sodium carbonate storage tank (2-1), a liquid caustic soda storage tank (2-2), a film adjustment and concentration reaction tank (3-1), and a crystallization drying device (4-1); The tower side of the silane gas venting washing tower (1-1) is connected to the silane venting air guide pipe, and the bottom of the tower kettle is connected to the sodium carbonate storage tank (2-1) through a discharge pipe; the bottoms of the sodium carbonate storage tank (2-1) and the liquid caustic soda storage tank (2-2) are respectively connected to the film adjustment and concentration reaction tank (3-1) through pipelines; the bottom of the film adjustment and concentration reaction tank (3-1) is connected to the feed inlet at the top of the crystallization drying device (4-1) through a feed pipe; a group of nozzles are arranged at the feed inlet at the top of the crystallization drying device (4-1), and the two ends of the crystallization drying device (4-1) are arranged as an air inlet and an air outlet, and the air inlet and the air outlet are connected to the hot air blower (5-1) through an air duct.

2. The byproduct processing system of the silane gas preparation process for granular silicon according to claim 1, characterized in that: The bottom discharge pipe of the silane gas venting washing tower (1-1) is also provided with a reflux pipe connected to the top of the tower; the bottom discharge pipe of the silane gas venting washing tower (1-1) is equipped with a washing liquid discharge pump (1-2).

3. The byproduct processing system of the silane gas preparation process for granular silicon according to claim 1, characterized in that: A sodium carbonate discharge pump (2-3) and a liquid caustic soda discharge pump (2-4) are respectively provided on discharge pipes at the bottom of the sodium carbonate storage tank (2-1) and the liquid caustic soda storage tank (2-2).

4. The byproduct processing system of the silane gas preparation process for granular silicon according to claim 1, characterized in that: The membrane adjustment and concentration reaction tank (3-1) is provided with a stirring device inside and a steam heating jacket outside; a concentrated liquid discharge pump (3-2) is provided on the bottom discharge pipe.

5. The byproduct processing system of the silane gas preparation process for granular silicon according to claim 1, characterized in that: The crystallization drying device (4-1) comprises a rotating drum (4-5) and a driving assembly; one end of the rotating drum (4-5) is higher than the other end, and both ends are rotatably mounted on a bearing seat through bearings, and the rotating drum (4-5) is driven to rotate by the driving assembly; the bottom of the film adjustment concentration reaction tank (3-1) is detachably connected to a feed port opened on the side of the higher end of the rotating drum (4-5) through a feed pipe, and is connected to a group of nozzles (4-3) located in the rotating drum (4-5), and the concentrated liquid is sprayed into the rotating drum (4-5) through the nozzles (4-3); a seed feeding port (4-2) is provided on the bearing seat at the higher end of the crystallization drying device (4-1), and the seed feeding port (4-2) feeds the added seed into the rotating drum (4-5) through the inclined groove below; an air inlet is provided at the lower end of the rotating drum (4-5), and an air outlet is provided at the higher end, and a discharge port (4-4) is provided on the side of the lower end of the rotating drum (4-5).

6. The byproduct processing system of the silane gas preparation process for granular silicon according to claim 1, characterized in that: An electric heater (6-1) is provided on the air duct between the hot air blower (5-1) and the air inlet of the crystallization drying device (4-1).

7. The system for treating byproducts of the silane gas preparation process for granular silicon according to claim 1, wherein the steps for treating byproducts of the silane gas preparation process for granular silicon using the system are as follows: (1) The silane exhaust gas is sent into a washing device and neutralized with a sodium hydroxide solution to produce sodium silicate; (2) reacting and concentrating the sodium carbonate produced in step (1) with liquid caustic soda under steam heating; (3) Drying and crystallizing the product of step (3), using zero-hydrate sodium metasilicate or pentahydrate sodium metasilicate as a seed crystal during the crystallization process, and finally obtaining zero-hydrate sodium metasilicate or pentahydrate sodium metasilicate product.

8. The system for treating byproducts of the silane gas preparation process for granular silicon according to claim 7, wherein in step (2), the liquid alkali is a sodium hydroxide aqueous solution; and the material ratio of the two is calculated as follows: nNa2O·mSiO2+2(m-n)NaOH→mNa2SiO3 in, m and n are both sodium silicate modulus, which refers to the molar ratio of silicon dioxide to sodium oxide in sodium silicate; m is the modulus of sodium silicate measured by testing; n is the target modulus; the value range of n target modulus is 0.93-1.

05.

9. The by-product treatment system of the silane gas preparation process for granular silicon according to claim 7 is characterized in that, in step (2), the temperature of the reaction under steam heating is 100°C-150°C, the reaction is carried out under stirring, and the stirring speed is 1-4r / min; the reaction time is 2-3 hours, and detection is carried out every half hour during the operation to determine whether alkali solution or sodium carbonate is added.

10. The by-product processing system of the silane gas preparation process for granular silicon according to claim 7, wherein in step (3), the seed crystal is first put into the drying crystallization equipment, and then the product of step (2) is sent in by spraying, maintaining the inlet temperature at 300-400°C; hot air is introduced into the drying crystallization equipment for drying and maintaining the temperature of the material inlet.

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