CN108439411B - Device and method for reducing content of light component impurities in HCl absorption liquid in polycrystalline silicon dry recovery process - Google Patents
Device and method for reducing content of light component impurities in HCl absorption liquid in polycrystalline silicon dry recovery process Download PDFInfo
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- CN108439411B CN108439411B CN201810448943.9A CN201810448943A CN108439411B CN 108439411 B CN108439411 B CN 108439411B CN 201810448943 A CN201810448943 A CN 201810448943A CN 108439411 B CN108439411 B CN 108439411B
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- C01B33/00—Silicon; Compounds thereof
- C01B33/02—Silicon
- C01B33/021—Preparation
- C01B33/027—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material
- C01B33/03—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material by decomposition of silicon halides or halosilanes or reduction thereof with hydrogen as the only reducing agent
Abstract
The invention discloses a device and a method for reducing the content of light component impurities in HCl absorption liquid in a polysilicon dry recovery process, wherein the device comprises an absorption tower and a desorption tower, the bottom of the absorption tower is communicated with a tube side inlet of a heat exchanger, and a tube side outlet of the absorption tower is connected with a feed inlet of the desorption tower; a discharge port at the bottom of the desorption tower is connected with a shell pass inlet of the heat exchanger through a delivery pump, and a shell pass outlet of the desorption tower is connected with an absorption liquid inlet at the upper part of the absorption tower; a first branch pipeline is also arranged between the delivery pump and the heat exchanger, and the tail end of the first branch pipeline is provided with a high-purity silicon tetrachloride inlet. The absorption liquid enters the HCl absorption tower together with the pure STC pipeline on the pipeline entering the HCl absorption tower. Under the condition that the circulating amount and the liquid level of the desorption tower are constant, STC is increased, HCl absorption liquid can be discharged from the bottom of the HCl desorption tower continuously, and the effects of diluting absorption liquid impurities and purifying the HCl absorption liquid are achieved in a reciprocating mode, so that the influence of the impurities on hydrogen is reduced.
Description
Technical Field
The invention relates to the technical field of polycrystalline silicon production, in particular to a device and a method for reducing the content of light-component impurities in HCl absorption liquid in a polycrystalline silicon dry recovery process.
Background
In the polysilicon production technology, dry recovery technology is mostly adopted for tail gas recovery. The tail gas from a reduction furnace mixed with hydrogen, hydrogen chloride, dichlorosilane, trichlorosilane and silicon tetrachloride is subjected to multiple heat exchange, most of chlorosilane is condensed and separated, uncondensed gas is pressurized by a compressor and then enters an absorption tower, hydrogen chloride is sprayed and absorbed by relatively pure chlorosilane absorption liquid at the top of the absorption tower, unabsorbed hydrogen enters an absorption tower to be purified, chlorosilane liquid absorbing impurities such as hydrogen chloride enters a desorption tower and is heated and rectified by a reboiler, the hydrogen chloride and the chlorosilane are separated, relatively pure chlorosilane part is circulated to the absorption tower to be sprayed, and the residual HCl absorption liquid is sent to be rectified.
In the process flow of polysilicon dry recovery, although most of chlorosilane is removed after condensation, a small amount of chlorosilane enters an HCl absorption tower and is absorbed by absorption liquid, and the frequency and the flow of the absorption liquid discharged from the bottom of an HCl desorption tower are small, so that the absorption liquid can be enriched with impurities (mainly light-component impurities) brought by the chlorosilane from the front end along with the accumulation of time, and the impurities can enter a reduction furnace together with hydrogen in the HCl absorption tower, thereby increasing the impurity content of polysilicon and reducing the quality of the polysilicon.
Disclosure of Invention
The invention aims to provide a device and a method for reducing the content of light component impurities in HCl absorption liquid in a polysilicon dry recovery process.
The invention is realized by adopting the technical scheme that: a device for reducing the content of light component impurities in HCl absorption liquid in a polysilicon dry recovery process comprises an absorption tower and a desorption tower, wherein the bottom of the absorption tower is communicated with a tube side inlet of a heat exchanger, and a tube side outlet of the absorption tower is connected with a feed inlet of the desorption tower; a discharge port at the bottom of the desorption tower is connected with a shell pass inlet of the heat exchanger through a delivery pump, and a shell pass outlet of the desorption tower is connected with an absorption liquid inlet at the upper part of the absorption tower; a first branch pipeline is also arranged between the delivery pump and the heat exchanger, and the tail end of the first branch pipeline is provided with a high-purity silicon tetrachloride inlet.
Furthermore, a first liquid level regulating valve is arranged between the bottom of the absorption tower and a tube pass inlet of the heat exchanger, and a first flow regulating valve is arranged between the delivery pump and the first branch pipeline.
Furthermore, a high-purity silicon tetrachloride inlet of the first branch pipeline is connected with a high-purity silicon tetrachloride raw material tank, and a second flow regulating valve is arranged on the first branch pipeline.
Furthermore, a second branch pipeline is connected between the delivery pump and the first flow regulating valve, a surplus chlorosilane outlet is arranged at the tail end of the second branch pipeline, and a second liquid level regulating valve is further arranged on the second branch pipeline.
Furthermore, a Freon heat exchanger is arranged between the shell pass outlet of the heat exchanger and the absorption tower.
The invention also relates to a method for reducing the content of light component impurities in HCl absorption liquid in the polysilicon dry recovery process, which comprises the following steps:
compressing tail gas which is not condensed by polycrystalline silicon, then entering an absorption tower, adding absorption liquid from an absorption liquid inlet at the upper part of the absorption tower for spray absorption, discharging unabsorbed hydrogen from the top of the absorption tower, introducing the absorption liquid for absorbing HCl from a bottom discharge hole through a heat exchanger into a desorption tower for separation, and introducing the separated chlorosilane from a discharge hole at the bottom of the desorption tower through a delivery pump and the heat exchanger into the absorption liquid inlet at the upper part of the absorption tower for reuse; part of chlorosilane pumped out from a discharge hole at the bottom of the desorption tower is extracted, the other part of chlorosilane is recycled, and the recycled part of chlorosilane is mixed with high-purity silicon tetrachloride before entering a heat exchanger and then is sent into an absorption tower as absorption liquid.
Further, under the condition that the working conditions of the absorption tower and the desorption tower are stable, the circulating flow of chlorosilane is gradually increased to 35-50 m3After stabilization, the first flow regulating valve is put into automatic operation, the first liquid level regulating valve is set to be automatic, the set value is 60-80%, and the liquid level of the absorption tower is maintained to be constant; then the second level regulating valve was set to automatic with a set value of 50%, the liquid level was maintained constant, and finally the second flow rate regulating valve was set to automatic with a set value of 40m3/h。
Furthermore, the content of P in the high-purity silicon tetrachloride is less than or equal to 1.5ppbw, and the content of B in the high-purity silicon tetrachloride is less than or equal to 0.5 ppbw.
According to the invention, a pure STC pipeline is added on a pipeline entering the HCl absorption tower, and the pure STC pipeline and the absorption liquid enter the HCl absorption tower together. Under the condition that the circulating amount and the liquid level of the desorption tower are constant, STC is increased, HCl absorption liquid can be discharged from the bottom of the HCl desorption tower continuously, and the effects of diluting absorption liquid impurities and purifying the HCl absorption liquid are achieved by reciprocating. The purity of the HCl absorption liquid is improved, impurities in the hydrogen entering the adsorption tower to be recycled are reduced, the load of active carbon in the adsorption tower is reduced, and the service life of the active carbon is prolonged; and the influence of impurities on hydrogen is reduced to a great extent, and the method has an important effect on improving the quality of polycrystalline silicon.
Drawings
FIG. 1 is a schematic view of the structure of the apparatus of the present invention.
Detailed Description
The present invention will be described in more detail with reference to examples.
A device for reducing the content of light component impurities in HCl absorption liquid in a polysilicon dry recovery process is shown in figure 1 and comprises an absorption tower 1 and a desorption tower 2, wherein the bottom of the absorption tower 1 is communicated with a tube side inlet of a heat exchanger 3, and a tube side outlet of the absorption tower is connected with a feed inlet of the desorption tower; a discharge port at the bottom of the desorption tower is connected with a shell pass inlet of the heat exchanger 3 through a delivery pump 6, and a shell pass outlet of the desorption tower is connected with an absorption liquid inlet at the upper part of the absorption tower 1; a first branch pipeline is also arranged between the delivery pump 6 and the heat exchanger, and the tail end of the first branch pipeline is a high-purity silicon tetrachloride inlet.
Further, a first liquid level regulating valve 4 is arranged between the bottom of the absorption tower 1 and a tube pass inlet of the heat exchanger 3 and used for controlling the liquid level of the absorption tower; and a first flow regulating valve 5 is arranged between the delivery pump and the first branch pipeline and is used for controlling the flow of the chlorosilane poor solution in the desorption tower into the absorption tower. The heat exchanger 3 is a multistage heat exchanger.
Furthermore, a high-purity silicon tetrachloride inlet of the first branch pipeline is connected with a high-purity silicon tetrachloride raw material tank, and a second flow regulating valve 7 is arranged on the first branch pipeline to play a role in regulating the flow of the high-purity silicon tetrachloride.
Furthermore, a second branch pipeline is connected between the delivery pump 6 and the first flow regulating valve 5, a surplus chlorosilane outlet is arranged at the tail end of the second branch pipeline, and a second liquid level regulating valve 8 is further arranged on the second branch pipeline and used for controlling the liquid level of the desorption tower.
Under the condition of stable working conditions of the absorption tower and the desorption tower, the circulating flow of chlorosilane can be gradually increased to 35-50 m3After the first flow regulating valve is stabilized, the first flow regulating valve is put into automatic operation; the first liquid level regulating valve is put into operation automatically, and a set value is given by 60 percent to 80 percent,maintaining a high liquid level can be an extended dwell time under abnormal conditions; the second level regulating valve is automatically switched on, and a set value is given 50%, so that the liquid level is maintained, on one hand, the HCl can be fully desorbed, and on the other hand, the whole system is stabilized.
After the system is stabilized, the second flow regulating valve is gradually opened in a manual state, high-purity silicon tetrachloride and HCl absorption liquid are introduced to enter the absorption tower together, the hydrogen mixture entering the absorption tower is sprayed and absorbed, the opening degree of the second flow regulating valve is increased to be a slow process, and the second flow regulating valve is greatly regulated to cause the fluctuation of the flow of the HCl absorption liquid, so that the system is abnormal. When high-purity silicon tetrachloride is introduced to reach 40m3And h, the second flow regulating valve is automatically switched, and the opening degrees of the first flow regulating valve and the second liquid level regulating valve are closely concerned, and the whole system is stable.
The HCl absorption liquid flow that gets into the absorption tower is unchangeable, and the absorption tower can incessantly discharge the absorption liquid with the invariable condition of liquid level of desorption tower bottom, so reciprocal just reaching the effect of diluting absorption liquid impurity, purifying the absorption liquid to reduce the influence of impurity to hydrogen, had the great effect to promoting the polycrystalline silicon quality.
Example (b):
at a rate of 40m per hour3High-purity silicon tetrachloride with the purity of more than 99 percent (the P content is less than or equal to 1.5ppbw, the B content is less than or equal to 0.5ppbw) and chlorosilane poor solution from a desorption tower are converged and then enter the top of an absorption tower for spraying, the constant liquid level of the absorption tower and the desorption tower is controlled, and redundant chlorosilane is discharged from the bottom of the desorption tower, so that the effect of diluting HCl absorption solution is achieved. The ratio of main components and the content of impurities in the HCl absorption solution before and after the implementation are shown in the following table 1:
TABLE 1 comparison table of the ratio of each main component and the content of impurities in HCl absorbent solution before and after the implementation
| Names of impurities of the respective components | DCS | TCS | STC | B/ppbw | P/ppbw |
| Before implementation | 16.45％ | 70.03％ | 12.94％ | 8.48 | 15.78 |
| After being implemented | 4.08％ | 52.60％ | 43.18％ | 1.22 | 3.4 |
Before and after implementation, under the condition that other processes are not changed, the quality of the polycrystalline silicon is improved from the first grade of solar energy to the second grade of electrons, and the comparison table is shown in the following table 2:
table 2 polysilicon quality comparison table before and after implementation
| Item | Donor impurity concentration/ppba | Acceptor impurity concentration/ppba | Minority carrier lifetime |
| Before implementation | 0.46 | 0.21 | 480 |
| After being implemented | 0.19 | 0.08 | 1230 |
The above-described embodiments are merely preferred embodiments of the present invention, and should not be construed as limiting the present invention, and the scope of the present invention is defined by the claims, and equivalents including technical features described in the claims. I.e., equivalent alterations and modifications within the scope hereof, are also intended to be within the scope of the invention.
Claims (6)
1. The device for reducing the content of light component impurities in HCl absorption liquid in the polysilicon dry recovery process is characterized by comprising an absorption tower (1) and a desorption tower (2), wherein the bottom of the absorption tower (1) is communicated with a tube side inlet of a heat exchanger (3), and a tube side outlet of the absorption tower is connected with a feed inlet of the desorption tower; a discharge port at the bottom of the desorption tower is connected with a shell pass inlet of the heat exchanger (3) through a delivery pump (6), and a shell pass outlet of the desorption tower is connected with an absorption liquid inlet at the upper part of the absorption tower (1); a first branch pipeline is also arranged between the delivery pump (6) and the heat exchanger, and the tail end of the first branch pipeline is provided with a high-purity silicon tetrachloride inlet; the purity of the high-purity silicon tetrachloride is more than or equal to 99 percent, the P content is less than or equal to 1.5ppbw, and the B content is less than or equal to 0.5 ppbw;
the method comprises the following specific operation steps:
compressing tail gas which is not condensed by polycrystalline silicon, then entering an absorption tower, adding absorption liquid from an absorption liquid inlet at the upper part of the absorption tower for spray absorption, discharging unabsorbed hydrogen from the top of the absorption tower, introducing the absorption liquid for absorbing HCl from a bottom discharge hole through a heat exchanger into a desorption tower for separation, and introducing the separated chlorosilane from a discharge hole at the bottom of the desorption tower through a delivery pump and the heat exchanger into the absorption liquid inlet at the upper part of the absorption tower for reuse; part of chlorosilane pumped out from a discharge hole at the bottom of the desorption tower is extracted, the other part of chlorosilane is recycled, and the recycled part of chlorosilane is mixed with high-purity silicon tetrachloride before entering a heat exchanger and then is sent into an absorption tower as absorption liquid.
2. The apparatus of claim 1, wherein: a first liquid level regulating valve (4) is arranged between the bottom of the absorption tower (1) and a tube side inlet of the heat exchanger (3), and a first flow regulating valve (5) is arranged between the delivery pump and the first branch pipeline.
3. The apparatus of claim 2, wherein: and a high-purity silicon tetrachloride inlet of the first branch pipeline is connected with a high-purity silicon tetrachloride raw material tank, and a second flow regulating valve (7) is arranged on the first branch pipeline.
4. The apparatus of claim 3, wherein: and a second branch pipeline is connected between the delivery pump (6) and the first flow regulating valve (5), the tail end of the second branch pipeline is a surplus chlorosilane outlet, and a second liquid level regulating valve (8) is further arranged on the second branch pipeline.
5. The apparatus of claim 3, wherein: and a Freon heat exchanger is also arranged between the shell pass outlet of the heat exchanger (3) and the absorption tower (1).
6. The apparatus of claim 3, wherein: under the condition that the working conditions of the absorption tower and the desorption tower are stable, the circulating flow of chlorosilane is gradually increased to 35-50 m3After stabilization, the first flow regulating valve is put into automatic operation, the first liquid level regulating valve is set to be automatic, the set value is 60-80%, and the liquid level of the absorption tower is maintained to be constant; then the second level regulating valve was set to automatic with a set value of 50%, the liquid level was maintained constant, and finally the second flow rate regulating valve was set to automatic with a set value of 40m3/h。
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