Waste acid recovery system for electronic-grade polycrystalline silicon

Abstract

The utility model relates to the technical field of waste acid recovery, in particular to a waste acid recovery system for electronic-grade polycrystalline silicon, which comprises a waste acid preheater and a primary stripping tower communicated with the waste acid preheater, a nitric acid jacket tank, a secondary rectifying tower, a secondary tower top condenser and an absorption tower are sequentially connected to the tower kettle of the primary stripping tower; wherein the tower top of the absorption tower is provided with a cavitation jet device, an inlet of the cavitation jet device is provided with a water inlet and an ozone inlet, and an outlet of the cavitation jet device is communicated with the tower top of the absorption tower through a pipeline. According to the device disclosed by the utility model, full-flow sealing is realized on the aspect of recycling of nitric acid, the reduction of nitric acid concentration caused by volatilization of nitric oxide is reduced, mixing of ozone and water is improved through the air jet device, OH <-> free radicals in water mist are favorably improved, and the absorption efficiency of nitric oxide in non-condensable gas is further improved.

Description

Technical Field

[0001] The utility model relates to the technical field of waste acid recovery, in particular to a waste acid recovery system for electronic grade polysilicon. Background Art

[0002] Electronic-grade polysilicon is mainly used in electronic chips, high-power rectifiers, and high-power transistors. Silicon is currently the main raw material for manufacturing integrated circuits. Its surface needs to go through etching, cleaning and other steps during the processing. In particular, the etching step requires a high-concentration hydrofluoric acid and nitric acid mixture for cleaning. After multiple pickling reactions using the etching solution, the metal ions and fluorosilicic acid in the pickling solution will increase to a certain concentration, which directly affects the cleaning effect. In addition, the increase in fluorosilicic acid hinders the further reaction of acid and silicon, resulting in a decrease in the etching rate. Therefore, the pickling waste liquid will be replaced.

[0003] The hydrofluoric acid in the pickling waste liquid is highly corrosive and toxic, and nitric acid is also highly corrosive. As important components of hazardous waste, both will cause great damage to the ecological environment if they are directly discharged without effective treatment. In the existing technology, chemical methods, evaporation methods, ion exchange methods and solvent extraction methods are often used for treatment and recycling. However, the conventional spraying generally has the problem of low absorption efficiency of non-condensable nitrogen oxides. Utility Model Content

[0004] The technical problem to be solved by the utility model is to provide a waste acid recovery system for electronic grade polysilicon to solve the problem of low absorption efficiency of non-condensable gas nitrogen oxides.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the utility model is: a waste acid recovery system for electronic grade polysilicon, comprising: a waste acid preheater, and a primary stripping tower connected to the waste acid preheater;

[0006] The bottom of the primary stripping tower is connected in sequence with a nitric acid jacketed tank, a secondary distillation tower, a secondary tower top condenser and an absorption tower;

[0007] Wherein, a cavitation jet device is arranged at the top of the absorption tower, a water inlet and an ozone inlet are arranged at the inlet of the cavitation jet device, and an outlet thereof is communicated with the top of the absorption tower through a pipeline.

[0008] Furthermore, an ozone decomposition device is provided at the top outlet of the absorption tower.

[0009] Furthermore, the bottom outlet of the absorption tower is connected to the nitric acid jacketed tank through a pipeline.

[0010] Furthermore, a filter is provided between the primary stripping tower and the nitric acid jacketed tank.

[0011] Furthermore, the secondary tower top condenser is connected to a secondary reflux tank.

[0012] Furthermore, the secondary reflux tank is connected to the secondary distillation tower.

[0013] Furthermore, the bottom of the secondary distillation tower is connected to a nitric acid storage tank.

[0014] Furthermore, a primary tower top condenser is connected to the top of the primary stripping tower.

[0015] Furthermore, the primary tower top condenser is connected to a hydrofluoric acid storage tank.

[0016] The beneficial effects of the utility model are as follows: the utility model realizes full-process closure in the recycling of nitric acid, reduces the reduction of nitric acid concentration caused by the volatilization of nitrogen oxides, and improves the mixing of ozone and water through the air jet device, which helps to increase the OH-free radicals in the water mist, thereby improving the absorption efficiency of nitrogen oxides in the non-condensable gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A structural schematic diagram of a system for recovering waste acid from electronic-grade polysilicon;

[0019] Figure 2 Another structural schematic diagram of an electronic grade polysilicon waste acid recovery system. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0021] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation method.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art in the technical field of the present invention. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0023] like Figure 1 The waste acid recovery system for electronic grade polysilicon shown in the figure comprises: a waste acid preheater 1, and a primary stripping tower 2 connected to the waste acid preheater 1; a nitric acid jacketed tank 3, a secondary distillation tower 4, a secondary tower top condenser 5 and an absorption tower 6 are sequentially connected to the bottom of the primary stripping tower 2; wherein, a cavitation jet device 7 is provided at the top of the absorption tower 6, and a water inlet and an ozone inlet are provided at the inlet of the cavitation jet device 7, and its outlet is connected to the top of the absorption tower 6 through a pipeline.

[0024] The waste acid components after cleaning the silicon material are H2SIF6, HF, HNO3 and nitrogen oxides, etc. After the waste acid is heated by the waste acid preheater 1, it enters the primary stripping tower 2. The primary stripping tower 2 is operated by decompression. The bottom of the primary stripping tower 2 contains nitric acid solution and fluorosilicic acid solution. After being heated by the preheater, the temperature of the bottom of the tower rises, and the fluorosilicic acid directly undergoes hydrolysis reaction in the hot solution to form silicate precipitation, nitric acid solution and some undissolved nitrogen oxides, which enter the nitric acid jacket tank 3; steam is introduced into the nitric acid jacket tank 3. Under heating, the nitrogen oxides in the nitric acid solution continue to volatilize. When the volatilization reaches a certain amount, that is, the mass of the nitric acid aqueous solution is When the mass fraction reaches 68%, an azeotropic system will be formed. At this time, the nitric acid solution exists in the form of HNO3 vapor, decomposed NO2, and H2O vapor at the top of the storage tank. The vapor at the top of the tank is introduced into the secondary distillation tower 4; the gas phase of the secondary distillation tower 4 is condensed, and non-condensable nitrogen oxides exist. The non-condensable gas is then introduced into an absorption tower 6. The absorption tower 6 uses water as an absorbent and is mixed with ozone before entering the tower. The water is cavitated by the cavitation jet device 7 to form fine droplets, which not only improves the mixing of ozone and water, but also helps to increase the OH-free radicals in the water mist, thereby improving the absorption efficiency of nitrogen oxides in the non-condensable gas. In addition, this method can also reduce the amount of water used.

[0025] like Figure 2 As shown, the top outlet of the absorption tower 6 is provided with an ozone decomposition device 8, which can decompose the remaining ozone to ensure that its concentration drops below a safe level, thereby protecting the environment and the health of users.

[0026] In the preferred embodiment of the utility model, the outlet of the tower kettle of the absorption tower 6 is connected to the nitric acid jacket tank 3 through a pipeline. After the absorption operation, a nitric acid aqueous solution with a relatively high concentration is obtained, which is added to the nitric acid jacket tank 3, so that a large amount of waste acid generated in the production process of polysilicon is formed into a recovery mechanism, thereby improving the utilization rate of nitric acid.

[0027] In order to prevent the silica precipitate formed by hydrolysis from affecting the nitric acid jacket tank 3, a filter 9 is provided between the primary stripping tower 2 and the nitric acid jacket tank 3. The silica precipitate is filtered through the filter 9 to precipitate out, and only the nitric acid solution containing part of the nitrogen oxides enters the nitric acid jacket tank 3.

[0028] In addition, in the preferred embodiment, the secondary tower top condenser 5 is connected to a secondary reflux tank 10, and the secondary reflux tank 10 is connected to the secondary distillation tower 4. The condensed liquid enters the secondary reflux tank 10 and is then sent to the secondary distillation tower 4 for further distillation treatment to maximize the recovery and reuse of the condensed liquid.

[0029] In the preferred embodiment of the utility model, the bottom of the secondary distillation tower 4 is connected to a nitric acid storage tank (not shown in the figure). By connecting the bottom of the secondary distillation tower 4 with the nitric acid storage tank, the nitric acid solution after distillation can be effectively collected and stored, achieving efficient recovery of nitric acid and avoiding waste and potential safety risks.

[0030] In the preferred embodiment of the present invention, the top of the primary stripping tower 2 is connected to a primary tower top condenser 11, and the primary tower top condenser 11 is connected to a hydrofluoric acid storage tank 12. The primary stripping tower 2 separates HF (hydrofluoric acid) gas from the top of the tower by decompression operation, and the separated HF (hydrofluoric acid) gas is condensed by the primary tower top condenser 11. Since the feed composition is an aqueous solution, some water vapor is still carried out from the top of the tower, and the condensed product is a high-concentration hydrofluoric acid solution. The condensed high-concentration hydrofluoric acid solution will enter the hydrofluoric acid storage tank 12, realizing efficient separation and recovery of HF gas and ensuring safe storage and management of the product.

[0031] Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the description are only for explaining the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which are within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A system for recovering waste acid from electronic grade polysilicon, characterized in that: include: A waste acid preheater, and a primary stripping tower connected to the waste acid preheater; The bottom of the primary stripping tower is connected in sequence with a nitric acid jacketed tank, a secondary distillation tower, a secondary tower top condenser and an absorption tower; Wherein, a cavitation jet device is arranged at the top of the absorption tower, a water inlet and an ozone inlet are arranged at the inlet of the cavitation jet device, and an outlet thereof is communicated with the top of the absorption tower through a pipeline.

2. The electronic grade polysilicon waste acid recovery system according to claim 1, characterized in that: An ozone decomposition device is arranged at the top outlet of the absorption tower.

3. The electronic grade polysilicon waste acid recovery system according to claim 1, characterized in that: The tower kettle outlet of the absorption tower is connected with the nitric acid jacketed tank through a pipeline.

4. The electronic grade polysilicon waste acid recovery system according to claim 1, characterized in that: A filter is provided between the primary stripping tower and the nitric acid jacketed tank.

5. The electronic grade polysilicon waste acid recovery system according to claim 1, characterized in that: The secondary tower top condenser is connected to a secondary reflux tank.

6. The electronic grade polysilicon waste acid recovery system according to claim 5, characterized in that: The secondary reflux tank is communicated with the secondary distillation tower.

7. The electronic grade polysilicon waste acid recovery system according to claim 1, characterized in that: The bottom of the secondary distillation tower is connected to a nitric acid storage tank.

8. The electronic grade polysilicon waste acid recovery system according to claim 1, characterized in that: The top of the primary stripping tower is connected to a primary top condenser.

9. The electronic grade polysilicon waste acid recovery system according to claim 8, characterized in that: The primary tower top condenser is connected to a hydrofluoric acid storage tank.

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