Joint production system and method for rodlike silicon and granular silicon

Abstract

The invention provides a joint production system and method for rodlike silicon and granular silicon, and belongs to the technical field of polycrystalline silicon production. The method comprises the following steps: preheating trichlorosilane and hydrogen by a raw material preheater, mixing, feeding into a reduction furnace, and carrying out chemical deposition reaction on the surface of an electrified high-temperature silicon rod to generate high-purity rod-like polycrystalline silicon; silane and hydrogen sequentially pass through a first-stage preheater and a second-stage preheater and then enter a fluidized bed, high-purity polycrystalline silicon fine particles are added into a fluidized bed reactor as seed crystals in the fluidized bed, the silane and the hydrogen are introduced from the bottom of the fluidized bed and react, the silane is rapidly decomposed and deposited on the surfaces of the silicon seed crystals, and the seed crystals grow into large-size silicon particles; the output end of reduction tail gas generated in the reduction furnace sequentially exchanges heat with gas in the second-stage preheater and gas in the raw material preheater, and tail gas generated by the fluidized bed exchanges heat with raw materials in the first-stage preheater. According to the combined process, the heat utilization rate of the reduction furnace can be greatly improved by utilizing energy coupling, the investment of a heat supply device required by a granular silicon production process is reduced, and the power consumption and the water consumption are further reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of polysilicon production, and relates to a system and method for the combined production of rod-shaped silicon and granular silicon. Background Art

[0002] Silicon material is the basic raw material of the photovoltaic industry and is the upstream link of photovoltaics. Silicon materials can be divided into two types according to their shape: rod-shaped silicon and granular silicon. At present, the production of polysilicon in China mainly adopts the modified Siemens method, which has become the most mature and widely used production technology for producing photovoltaic polysilicon. Reduction is the core reaction device of polysilicon. Its main steps are that high-purity trichlorosilane from the distillation section is preheated with hydrogen and then mixed in a certain proportion into the reduction furnace. A chemical deposition reaction occurs on the surface of the high-temperature silicon rod (reaction temperature is about 1050-1200°C) with electricity to generate high-purity rod-shaped polysilicon. This process realizes the closed-loop circulation of the polysilicon production process, but the rod-shaped silicon production process is intermittent operation, with high power consumption, and the waste heat utilization of the reduction furnace needs to be improved.

[0003] Compared with the modified Siemens method, the silane fluidized bed method for preparing granular silicon has good development prospects in the field of polysilicon. Its principle is to add high-purity polysilicon fine particles as seeds into the fluidized bed reactor, introduce silane and hydrogen from the bottom of the reactor and react at 500℃~700℃. Silane quickly decomposes and deposits on the surface of the silicon seed, making the seed grow into larger granular silicon. The process has a high reaction conversion rate, can achieve continuous production, and has relatively low reaction power consumption.

[0004] The main energy-consuming unit of the modified Siemens method is the reduction device, and its electricity consumption accounts for about 40-60% of the entire polysilicon process. In the prior art, in order to realize the comprehensive utilization of the heat energy of the reduction furnace, the high-temperature cooling water generated by the reduction furnace is usually sent to the flash evaporation system to produce by-product steam. However, in actual production, the by-product 0.4MpaG steam is in short supply, but the 0.2MpaG steam is still in large surplus, resulting in insufficient utilization of heat; at the same time, the high-temperature reduced tail gas needs to undergo a series of cooling treatments and is sent to the tail gas treatment unit to separate and purify chlorosilane, hydrogen and hydrogen chloride gas. This process consumes a large amount of refrigerant. How to efficiently utilize the heat energy of the reduction furnace to reduce the process production cost is still the key to the development of current polysilicon enterprises. Therefore, the two processes of the modified Siemens method and the silane fluidized bed method are thermally coupled to reduce the comprehensive energy consumption of the entire polysilicon production device and save costs. Summary of the invention

[0005] The purpose of the present invention is to provide a combined production process of rod-shaped silicon and granular silicon, which combines the two process devices of the improved Siemens method and the silane fluidized bed method, can comprehensively utilize the waste heat of the reduction furnace reaction, improve the utilization rate of electric energy, effectively reduce electricity consumption and water consumption, and save production costs.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for the combined production of rod-shaped silicon and granular silicon, wherein trichlorosilane and hydrogen are preheated in a raw material preheater and then mixed into a reduction furnace, and then a chemical deposition reaction occurs on the surface of a high-temperature silicon rod that is powered to generate high-purity rod-shaped polycrystalline silicon;

[0008] Silane and hydrogen are sequentially passed through the primary preheater and the secondary preheater before being fluidized in a fluidized bed. In the fluidized bed, high-purity polysilicon fine particles are added as seeds into the fluidized bed reactor. Silane and hydrogen are introduced from the bottom of the fluidized bed and reacted. Silane is rapidly decomposed and deposited on the surface of the silicon seed crystal, causing the seed crystal to grow into larger granular silicon.

[0009] The output end of the reduction tail gas generated in the reduction furnace exchanges heat with the gas in the secondary preheater and the raw material preheater in turn, and the tail gas generated by the fluidized bed exchanges heat with the raw material in the primary preheater.

[0010] In the above-mentioned combined production method, the raw material preheater is heated to 140-160°C.

[0011] In the above-mentioned combined production method, the reaction temperature of the reduction furnace is 1050-1200° C., and the reaction pressure is 0.5-0.7 MPaG.

[0012] In the above-mentioned combined production method, the reaction temperature of the fluidized bed is 500°C to 700°C.

[0013] In the above-mentioned joint production method, the method comprises the following steps:

[0014] (1) Trichlorosilane and hydrogen are heated to 140-160°C by a raw material preheater and enter the furnace from the bottom of the reduction furnace. On the surface of the high-temperature silicon core silicon rods powered by electricity in the furnace, trichlorosilane is reduced by hydrogen to crystalline silicon and deposited on the surface of the silicon core silicon rods, causing the diameter of the silicon rods to grow continuously until the specified size is reached;

[0015] Since the reduction furnace performs chemical vapor deposition reaction at the operating conditions of 1050℃~1200℃ and 0.6MpaG, the high-temperature reduction tail gas generated by the reaction is used as a heat source to heat the secondary preheater of silane. After cooling, the tail gas exchanges heat with the raw material preheater to achieve cascade utilization of energy, and finally enters the tail gas recovery device to separate and recycle the unreacted chlorosilane, hydrogen and hydrogen chloride.

[0016] (2) High-purity silane and carrier gas hydrogen are used as raw materials and are continuously heated in the primary preheater and the secondary preheater before entering from the bottom of the fluidized bed. The reaction temperature of the fluidized bed method is 500°C to 700°C. At the same time, prefabricated silicon seed crystals are added to the top of the fluidized bed reactor. Silane and hydrogen silane react on the silicon seed crystals by vapor deposition to produce granular polysilicon products. The tail gas that does not participate in the reaction in the raw material fluidized bed is cooled in the primary preheater and then enters the tail gas recovery device to recover a small amount of unreacted silane gas and most of the hydrogen. The recovered hydrogen can be returned to the cold hydrogenation device as a raw material to continue to participate in the reaction.

[0017] In the technical solution of the present invention, the high-temperature waste heat of the reduction furnace is used to heat the fluidized bed, saving power consumption and further optimizing the heat exchange network of the process flow. When producing granular silicon alone, the reaction temperature of the fluidized bed needs to be heated to 500°C to 700°C by a secondary preheater (not heated by the fluidized bed itself) to directly enter the fluidized bed to participate in the reaction. However, after the rod-shaped silicon is combined with the granular silicon, the high-temperature tail gas waste heat of the rod-shaped silicon reduction furnace is used to directly heat the secondary preheater, saving the heat source supply for heating the secondary preheater alone.

[0018] A system for implementing the above method, the system comprises a raw material preheater, the output ends of the trichlorosilane and hydrogen are connected to the raw material preheater and the reduction furnace in sequence;

[0019] The output ends of the silane and hydrogen are connected to the primary preheater, the secondary preheater and the fluidized bed in sequence;

[0020] The reduction tail gas output end of the reduction furnace is connected to the raw material preheater through the secondary preheater, and the reaction tail gas output end of the fluidized bed is connected to the primary preheater.

[0021] This method is a joint production process of rod-shaped silicon and granular silicon. The production of rod-shaped silicon adopts the modified Siemens method, which is a mature and stable technology and is the mainstream processing route in the industry; the production of granular silicon adopts the silane fluidized bed method, which is the second largest polycrystalline silicon preparation process and mainly uses silane as a raw material to participate in the pyrolysis reaction.

[0022] Beneficial effects of the present invention:

[0023] (1) The combined process utilizes energy coupling to significantly improve the heat utilization rate of the reduction furnace, reduce the investment in heating equipment required for the granular silicon production process, and further reduce electricity and water consumption.

[0024] (2) Improve the utilization of the heat energy of the high-temperature cooling water of the existing reduction furnace system, produce high-grade steam as a by-product, and achieve efficient recovery of the heat energy of the high-temperature cooling water of the reduction furnace, thereby achieving the goal of reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the method of the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with embodiments, but the protection scope of the present invention is not limited thereto:

[0027] like Figure 1 A method for realizing the combined production of rod-shaped silicon and granular silicon, the system comprises a raw material preheater, the output ends of trichlorosilane and hydrogen are connected to the raw material preheater and the reduction furnace in sequence; the output ends of silane and hydrogen are connected to the primary preheater, the secondary preheater and the fluidized bed in sequence; the reduction tail gas output end of the reduction furnace is connected to the raw material preheater through the secondary preheater, and the reaction tail gas output end of the fluidized bed is connected to the primary preheater.

[0028] Example 1

[0029] In the improved Siemens process, high-purity trichlorosilane produced by the distillation device and hydrogen from the tail gas recovery device are used as raw materials. They are heated to about 150°C by the raw material preheater and enter the furnace from the bottom of the reduction furnace. On the surface of the high-temperature silicon core (silicon rod) powered by electricity in the furnace, trichlorosilane is reduced by hydrogen into crystalline silicon and deposited on the surface of the silicon core (silicon rod), causing the diameter of the silicon rod to continue to grow until it reaches the specified size. Since the reduction furnace carries out chemical vapor deposition reaction under the operating conditions of 1050℃~1200℃ and 0.6MpaG, the reaction temperature is relatively high and the reaction tail gas needs to be continuously cooled down and sent to the tail gas recovery treatment. In order to realize the comprehensive utilization of the heat energy of the reduction furnace, the high-temperature reduction tail gas is used as a heat source to heat the secondary preheater of silane. On the one hand, the amount of high-temperature cooling water of the reduction furnace is saved, and on the other hand, the consumption of electric energy of the silane fluidized bed is saved. The tail gas is cooled and then heat-exchanged with the raw material preheater to realize the cascade utilization of energy, and finally enters the tail gas recovery device to separate and recycle the unreacted chlorosilane, hydrogen and hydrogen chloride; secondly, the high-purity silane after disproportionation and distillation and the carrier gas hydrogen are used as raw materials and continuously heated in the primary preheater and the secondary preheater and then sent to the fluidized bed to participate in the reaction. Compared with the improved Siemens method, the reaction temperature of the silane fluidized bed method is 500℃~700℃. The raw materials silane and hydrogen enter from the bottom of the fluidized bed, and prefabricated silicon seed crystals are added to the top of the fluidized bed reactor. Silane undergoes a vapor deposition reaction on the silicon seed crystals to produce granular polysilicon products. The tail gas that does not participate in the reaction in the fluidized bed is cooled by the primary preheater and enters the tail gas recovery device to recover a small amount of unreacted silane gas and most of the hydrogen. The recovered hydrogen can be returned to the cold hydrogenation device as a raw material to continue to participate in the reaction.

[0030] This process can make full use of the waste heat from the high-temperature exhaust gas of the reduction furnace, provide a heat source for the fluidized bed through multi-stage heat exchange, and reduce the investment in heating equipment required for the granular silicon production process. Compared with the separate modified Siemens method and the separate silane fluidized bed method for simultaneously producing two types of silicon materials, it can save about 5kw·h / kg·Si in electricity consumption.

Claims

1. A method for the combined production of rod-shaped silicon and granular silicon, characterized in that: The method is that trichlorosilane and hydrogen are preheated in a raw material preheater and then mixed into a reduction furnace, and then a chemical deposition reaction occurs on the surface of a high-temperature silicon rod that is powered to generate high-purity rod-shaped polycrystalline silicon; Silane and hydrogen are sequentially passed through the primary preheater and the secondary preheater before being fluidized in a fluidized bed. In the fluidized bed, high-purity polysilicon fine particles are added as seeds into the fluidized bed reactor. Silane and hydrogen are introduced from the bottom of the fluidized bed and reacted. Silane is rapidly decomposed and deposited on the surface of the silicon seed crystal, causing the seed crystal to grow into larger granular silicon. The output end of the reduction tail gas generated in the reduction furnace exchanges heat with the gas in the secondary preheater and the raw material preheater in turn, and the tail gas generated by the fluidized bed exchanges heat with the raw material in the primary preheater.

2. The method for co-producing rod-shaped silicon and granular silicon according to claim 1, characterized in that: The raw material preheater is heated to 140-160°C.

3. The method for co-producing rod-shaped silicon and granular silicon according to claim 1, characterized in that: The reaction temperature of the reduction furnace is 1050-1200°C, and the reaction pressure is 0.5-0.7MpaG.

4. The method for co-producing rod-shaped silicon and granular silicon according to claim 1, characterized in that: The reaction temperature of the fluidized bed is 500°C to 700°C.

5. The method for co-producing rod-shaped silicon and granular silicon according to claim 1, characterized in that: The method comprises the following steps: (1) Trichlorosilane and hydrogen are heated to 140-160°C by a raw material preheater and enter the furnace from the bottom of the reduction furnace. On the surface of the high-temperature silicon core silicon rods powered by electricity in the furnace, trichlorosilane is reduced by hydrogen to crystalline silicon and deposited on the surface of the silicon core silicon rods, causing the diameter of the silicon rods to grow continuously until the specified size is reached; Since the reduction furnace performs chemical vapor deposition reaction at the operating conditions of 1050℃~1200℃ and 0.6MpaG, the high-temperature reduction tail gas generated by the reaction is used as a heat source to heat the secondary preheater of silane. After cooling, the tail gas exchanges heat with the raw material preheater to achieve cascade utilization of energy, and finally enters the tail gas recovery device to separate and recycle the unreacted chlorosilane, hydrogen and hydrogen chloride. (2) High-purity silane and carrier gas hydrogen are used as raw materials and are continuously heated in the primary preheater and the secondary preheater before entering from the bottom of the fluidized bed. The reaction temperature of the fluidized bed method is 500°C to 700°C. At the same time, prefabricated silicon seed crystals are added to the top of the fluidized bed reactor. Silane and hydrogen silane react on the silicon seed crystals by vapor deposition to produce granular polysilicon products. The tail gas that does not participate in the reaction in the raw material fluidized bed is cooled in the primary preheater and then enters the tail gas recovery device to recover a small amount of unreacted silane gas and most of the hydrogen. The recovered hydrogen can be returned to the cold hydrogenation device as a raw material to continue to participate in the reaction.

6. A system for implementing the method of claim 1, characterized in that: The system comprises a raw material preheater, and the output ends of trichlorosilane and hydrogen are connected to the raw material preheater and the reduction furnace in sequence; The output ends of the silane and hydrogen are connected to the primary preheater, the secondary preheater and the fluidized bed in sequence; The reduction tail gas output end of the reduction furnace is connected to the raw material preheater through the secondary preheater, and the reaction tail gas output end of the fluidized bed is connected to the primary preheater.

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