System for treating and recycling surplus hydrogen in tail gas of cold hydrogenation process

Abstract

A system for treating and recycling surplus hydrogen in tail gas of a cold hydrogenation process comprises an intermediate tank, the top of the intermediate tank is connected with the bottom of a cooler through a first pipeline and connected with the middle of the cooler through a second pipeline, the top of the cooler is connected with a hydrogen supplementing buffer tank through a third pipeline, and the hydrogen supplementing buffer tank is connected with a circulating hydrogen buffer tank. According to the system, surplus cold energy of the low-temperature silicone oil unit is fully utilized, surplus hydrogen is recycled, and the maximum economic benefit is achieved in the aspects of energy utilization and raw material recycling. High-pressure and low-pressure tail gas in the system is treated separately, the stability of the system is improved, and meanwhile damage to instruments and equipment is avoided.

Description

Technical Field

[0001] This utility model belongs to the photovoltaic industry and specifically relates to a system for treating and recovering excess hydrogen in the tail gas of a cold hydrogenation process. Background Technology

[0002] Trichlorosilane is required as a raw material in the production of polysilicon and silane gas. Currently, the vast majority of photovoltaic products use a cold hydrogenation process to produce trichlorosilane. This process uses silicon tetrachloride, hydrogen, and silicon powder as raw materials to react in a fluidized bed to produce trichlorosilane. Hydrogen has become an essential raw material in this process, and its consumption is increasing. However, due to the low conversion rate of trichlorosilane and uneven material ratios, not all the hydrogen in the system participates in the reaction, resulting in a large amount of exhaust gas formed by reacting with other gases in the production process.

[0003] Analysis of the economic and environmental benefits of tail gas treatment reveals the following advantages in recovering and reusing hydrogen from tail gas: First, if hydrogen in tail gas is not recovered and reused, the system needs to replenish it significantly during production, increasing production costs. Hydrogen recovery can reduce the amount of hydrogen purchased. Second, hydrogen is a renewable and clean energy source, and its resource value is increasingly prominent. Recovering hydrogen from the tail gas of the cold hydrogenation process can achieve effective utilization of hydrogen resources and reduce waste. Third, recovering hydrogen from tail gas and reusing it in the cold hydrogenation reaction can improve hydrogen utilization efficiency. Fourth, in the cold hydrogenation process, directly discharging or sending hydrogen-containing tail gas to the waste gas treatment process not only wastes hydrogen resources but also increases the load and cost of waste gas treatment. By recovering hydrogen, the hydrogen content in the tail gas can be reduced, lowering the difficulty and cost of waste gas treatment, making the entire process more efficient and economical. Therefore, maximizing the recovery of surplus hydrogen is a topic that the industry has been researching.

[0004] The intermediate tank is used to receive condensed chlorosilanes, which contain some non-condensable gases. Analysis of the tail gas samples revealed that silicon tetrachloride (SiCl4) accounted for 40.41%, trichlorosilane (SiHCl3) for 32.51%, dichlorosilane (SiH2Cl2) for 1.29%, hydrogen chloride (HCl) for 0.22%, hydrogen (H2) for 11.57%, and other light impurities for 13.91%. The complex composition and excessively high concentration of these tail gases, when entering the tail gas treatment system through the intermediate tank, would place a severe workload on equipment such as the tail gas cooler and tail gas heater. Furthermore, the frequent reception of chlorosilanes from the tail gas cooler by the tail gas recovery tank increases the start-up and shutdown frequency of the tail gas recovery pump, potentially leading to equipment malfunction or damage. Summary of the Invention

[0005] The technical problem to be solved by this utility model is to provide a system for treating and recovering excess hydrogen in the tail gas of a cold hydrogenation process, so as to recover the hydrogen and return it to the system to participate in the reaction, thereby effectively reducing the waste of raw materials.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is as follows:

[0007] A system for treating and recovering excess hydrogen in the tail gas of a cold hydrogenation process includes an intermediate tank. The top of the intermediate tank is connected to the bottom of a cooler via a first pipe. The top of the intermediate tank is connected to the middle of the cooler via a second pipe. The top of the cooler is connected to a supplementary hydrogen buffer tank via a third pipe. The supplementary hydrogen buffer tank is connected to a circulating hydrogen buffer tank.

[0008] Preferably, the intermediate tank is used to store exhaust gas, a third valve is installed on the first pipeline, a second valve is installed on the second pipeline, a first branch pipe is installed on the first pipeline, and a fourth valve is installed on the first branch pipe.

[0009] Preferably, the second pipeline is provided with a second branch pipe, and the second branch pipe is provided with a first valve.

[0010] Preferably, the third pipeline is equipped with a fifth valve, a sixth valve, a seventh valve and a tenth valve, and a third branch pipe is provided on the third pipeline. The third branch pipe is equipped with a ninth valve, and the third pipeline is located between the fifth valve and the sixth valve.

[0011] Preferably, the input end of the fifth valve and the input end of the seventh valve are connected in parallel to a fourth pipe, and an eighth valve is provided on the fourth pipe.

[0012] Preferably, a flow meter is provided between the seventh valve and the tenth valve.

[0013] The present invention can achieve the following beneficial effects:

[0014] 1. By optimizing the pipeline layout and changing the connection method, the excess cooling capacity of the low-temperature silicone oil unit was fully utilized and the excess hydrogen was recovered, achieving maximum economic benefits in terms of energy utilization and raw material recovery.

[0015] 2. By improving the exhaust gas recovery system, the workload of the exhaust gas heat exchanger in the subsequent exhaust gas treatment section was reduced, effectively avoiding safety and production problems caused by equipment overload operation.

[0016] 3. Effectively reduces the number of times the exhaust gas recovery pump starts and stops, avoiding damage to the recovery pump due to overload operation and energy waste caused by frequent start-stop.

[0017] 4. It separates the high and low pressure exhaust gases in the system for treatment, thus improving the system's stability. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0019] Figure 1 This is a system structure diagram of the present invention;

[0020] Figure 2 This is a process flow diagram of the present invention.

[0021] In the diagram: 1# represents the first valve; 2# represents the second valve; 3# represents the third valve; 4# represents the fourth valve; 5# represents the fifth valve; 6# represents the sixth valve; 7# represents the seventh valve; 8# represents the eighth valve; 9# represents the ninth valve; and 10# represents the tenth valve. Detailed Implementation

[0022] Preferred solutions include Figures 1 to 2 As shown, a system for treating and recovering excess hydrogen in the tail gas of a cold hydrogenation process includes an intermediate tank. The top of the intermediate tank is connected to the bottom of a cooler via a first pipe, and the top of the intermediate tank is connected to the middle of the cooler via a second pipe. The top of the cooler is connected to a supplementary hydrogen buffer tank via a third pipe, and the supplementary hydrogen buffer tank is connected to a circulating hydrogen buffer tank.

[0023] The intermediate tank is used to store exhaust gas. A third valve is installed on the first pipeline, a second valve is installed on the second pipeline, and a first branch pipe is installed on the first branch pipe, with a fourth valve installed on the first branch pipe. This ensures the effective recovery and reuse of hydrogen while guaranteeing operational safety and efficiency.

[0024] The second pipeline has a second branch pipe, and the second branch pipe has a first valve. When necessary, gas flow can be guided through the second branch pipe, while the first valve can control the gas flow rate in this path or completely block the gas flow, thus providing the system with additional operational flexibility and safety.

[0025] The third pipeline is equipped with valves five, six, seven, and ten, allowing the operator to precisely control the flow of hydrogen within the pipeline, ensuring safe system operation and optimizing the hydrogen recovery process. A third branch pipe is also located on the third pipeline, with valves five, six, seven, and ten installed on it. A ninth valve is also installed on the third branch pipe, which is situated between valves five and six.

[0026] The input end of the fifth valve and the input end of the seventh valve are connected in parallel to the fourth pipe, and the eighth valve is installed on the fourth pipe.

[0027] A flow meter is installed between the seventh and tenth valves. The flow meter monitors the hydrogen flow rate through this section of the pipeline in real time, ensuring the accuracy and stability of hydrogen recovery.

[0028] The operating principles of each device in this system are as follows:

[0029] 1) Silicone Oil Cooler: The chlorosilanes in the exhaust gas are condensed into liquid and returned to the intermediate tank using the cooling capacity provided by the low-temperature cooling unit. The temperature of the silicone oil cooler is -60 to -70℃. The cooling temperatures for chlorosilanes are: silicon tetrachloride 50 to 60℃, trichlorosilane 30 to 35℃, and dichlorosilane -30 to -40℃.

[0030] 2) Intermediate tank: Receives liquid chlorosilane and tail gas from the crude tower recovery tank. The pressure of the intermediate tank is 0.7-1.0 MPa.

[0031] 3) Supplemental hydrogen buffer tank: Receives non-condensable gas (hydrogen) from the silicone oil cooler and hydrogen supplied by the gas station, and then supplies it to the circulating hydrogen buffer tank via a compressor. It is a protective container, and the pressure of the supplemental hydrogen buffer tank is 0.5–1.0 MPa.

[0032] This system fully utilizes the excess cooling capacity of the low-temperature silicone oil chiller and recovers excess hydrogen, achieving maximum economic benefits in energy utilization and raw material recovery. The system separates high- and low-pressure exhaust gases, improving system stability and preventing damage to equipment.

[0033] Example 1:

[0034] 1. The top of the intermediate tank is connected to the upper part of the cooler, and the bottom of the cooler is connected to the upper part of the intermediate tank. Because of the pressure difference between the intermediate tank and the cooler, the exhaust gas from the top of the intermediate tank enters the silicone oil cooler, while the condensed liquid in the silicone oil cooler returns to the intermediate tank, achieving the purpose of hydrogen separation. The non-condensable gas (hydrogen) is transported through pipeline to the replenished hydrogen buffer tank, and then compressed by a compressor for recycling.

[0035] 2. After normal production begins, the tail gas from the crude oil recovery tank enters the intermediate tank. Open valve #2 and close valve #1 to allow the tail gas to enter the silicone oil cooler. If the cooler malfunctions, close valve #2 and open valve #1, allowing the tail gas to directly access the tail gas recovery treatment system. The gaseous chlorosilane in the tail gas is condensed into liquid chlorosilane at low temperature. Open valve #3 and close valve #4, allowing the liquid chlorosilane to return to the intermediate tank through the lower pipeline. Open valves #5, #6, #7, and #10, and close valves #8 and #9 to allow the non-condensable gas (hydrogen) in the silicone oil cooler to enter the supplementary hydrogen buffer tank. If valve #6 malfunctions, close valves #5 and #7 and open valve #8, allowing the gas to enter the supplementary hydrogen buffer tank through the backup pipeline.

[0036] The above embodiments are merely preferred technical solutions of this utility model and should not be considered as limitations on this utility model. The protection scope of this utility model should be the technical solution described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the protection scope of this utility model.

Claims

1. A system for treating and recovering excess hydrogen from a cold hydrogenation process off-gas, comprising an intermediate tank, characterized in that: The top of the intermediate tank is connected with the bottom of the cooler through a first pipeline, the top of the intermediate tank is connected with the middle of the cooler through a second pipeline, and the top of the cooler is connected with a supplementary hydrogen buffer tank through a third pipeline.

2. The system for treating and recovering excess hydrogen from a cold hydrogenation process off-gas of claim 1, wherein: The intermediate tank is used for storing tail gas, a third valve is arranged on the first pipeline, a second valve is arranged on the second pipeline, a first branch pipe is arranged on the first pipeline, and a fourth valve is arranged on the first branch pipe.

3. The system for treating and recovering excess hydrogen from a cold hydrogenation process off-gas of claim 1, wherein: A second branch pipe is arranged on the second pipeline, and a first valve is arranged on the second branch pipe.

4. The system for treating and recovering excess hydrogen from a cold hydrogenation process off-gas of claim 1, wherein: A fifth valve, a sixth valve, a seventh valve and a tenth valve are arranged on the third pipeline, a third branch pipe is arranged on the third pipeline, a ninth valve is arranged on the third branch pipe, and the third pipeline is located between the fifth valve and the sixth valve.

5. The system for treating and recovering excess hydrogen from a cold hydrogenation process off-gas of claim 4, wherein: A fourth pipeline is connected in parallel between the input end of the fifth valve and the input end of the seventh valve, and an eighth valve is arranged on the fourth pipeline.

6. The system for treating and recovering excess hydrogen from a cold hydrogenation process off-gas of claim 4, wherein: A flow meter is arranged between the seventh valve and the tenth valve.

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