Energy-saving method and system for multiple utilization of energy of polycrystalline silicon rectification high-pressure steam condensate

Abstract

The invention relates to an energy-saving method for multi-utilization of energy of polycrystalline silicon rectification high-pressure steam condensate. The method is suitable for heating and separating chlorosilane liquid in a rectifying tower by using steam in a polycrystalline silicon production process, the rectifying tower comprises a first rectifying tower and a second rectifying tower, and the method comprises the following steps: performing heat exchange on the chlorosilane liquid in the first rectifying tower and the second rectifying tower by using low-pressure steam and high-pressure steam respectively to generate condensate, the high-pressure steam condensate is collected in a condensate flash tank, and low-pressure steam is generated through a flash process and merged into a first rectifying tower for heat exchange. And the flash residual liquid can be used for carrying out heat exchange on the low-pressure steam condensate to regenerate low-pressure steam. By optimizing the technological process, flash evaporation of 0.4 MPa.G steam condensate and recycling of heat energy are achieved, and therefore the energy utilization efficiency is improved, the production cost is reduced, and the influence on the environment is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of polysilicon generation, and in particular to an energy-saving method and system for multiple utilization of polysilicon rectification high-pressure steam condensate energy. Background Art

[0002] In the production process of polysilicon, the separation and purification of chlorosilane (such as trichlorosilane, silicon tetrachloride, etc.) liquid is a key step. This separation and purification is usually achieved through a distillation tower. The distillation tower uses steam to heat the chlorosilane liquid to vaporize it and separate it into different components through a cyclic process of condensation and re-evaporation.

[0003] At present, 0.2MPa.G and 0.4MPa.G steam are commonly used according to demand. Taking 0.4MPa.G steam as an example, after the steam is condensed, the condensate is directly collected in the corresponding steam condensate tank, and the condensate is usually sent back to the reduction workshop 804 storage tank for reuse. However, the excess gas in the condensate is often directly vented, resulting in a large amount of energy waste. Summary of the invention

[0004] In order to overcome the above problems, the present invention proposes an energy-saving method and system for flash evaporation of high-pressure steam condensate from polysilicon distillation into low-pressure steam. By optimizing the process flow, flash evaporation of 0.4MPa.G steam condensate and repeated use of heat energy are achieved, thereby improving energy utilization efficiency, reducing production costs, and reducing environmental impact. The following technical solutions are adopted:

[0005] An energy-saving method for multiple utilization of polysilicon distillation high-pressure steam condensate energy, the method is applicable to the distillation tower using steam to heat and separate chlorosilane liquid in the polysilicon production process, the distillation tower includes a first distillation tower and a second distillation tower, and includes the following steps:

[0006] In the first step, low-pressure steam is used to perform heat exchange on the chlorosilane liquid in the first distillation tower to produce low-pressure steam condensate, and high-pressure steam is used to perform heat exchange on the chlorosilane liquid in the second distillation tower to produce high-pressure steam condensate;

[0007] In the second step, the high-pressure steam condensate is collected in a condensate flash tank;

[0008] In the third step, the high-pressure steam condensate is depressurized by a flash evaporation process to generate the low-pressure steam required in the first step, while the remaining flash evaporation residue;

[0009] In the fourth step, the generated low-pressure steam is merged into the low-pressure steam of the first distillation tower for heat exchange with the chlorosilane liquid in the first distillation tower, thereby realizing energy reuse.

[0010] Furthermore, the flash residual liquid can be used to perform heat exchange on the low-pressure steam condensate to generate the low-pressure steam required for the first step again and merge it into the low-pressure steam of the first distillation tower.

[0011] Furthermore, the high-pressure steam is 0.4 MPa.G steam, and the low-pressure steam is 0.2 MPa.G steam.

[0012] The present invention also protects a system for using the above method, specifically comprising:

[0013] 1# distillation tower, the 1# distillation tower is connected to the 1# distillation tower heat exchanger, the 1# distillation tower heat exchanger is connected to the 0.2MPa.G steam main pipe, the 0.2MPa.G steam main pipe is used to provide 0.2MPa.G steam to the 1# distillation tower heat exchanger, and perform heat exchange on the chlorosilane liquid of the 1# distillation tower;

[0014] 2# distillation tower, the 2# distillation tower is connected to the 2# distillation tower heat exchanger, the 2# distillation tower heat exchanger is connected to the 0.4MPa.G steam main pipe, the 0.4MPa.G steam main pipe is used to provide 0.4MPa.G steam to the 2# distillation tower heat exchanger, and perform heat exchange on the chlorosilane liquid of the 2# distillation tower;

[0015] The condensate flash tank is connected to the 2# distillation tower heat exchanger, and is used to collect high-temperature condensate from the 2# distillation tower heat exchanger and perform flash treatment to generate 0.2MPa.G for the 1# distillation tower. The condensate flash tank is connected to the 0.2MPa.G steam main pipe, and the generated 0.2MPa steam is merged into the 0.2MPa.G steam main pipe.

[0016] Furthermore, the system also includes a 0.2MPa.G condensate heater, which is respectively connected to the 2# distillation tower heat exchanger and the condensate flash tank, for collecting low-pressure steam condensate, and performing heat exchange on the low-pressure steam condensate through the flash residual liquid of the condensate flash tank to generate 0.2MPa.G steam.

[0017] Furthermore, the 0.2 MPa.G condensate heater is connected to the 0.2 MPa.G steam main pipe, so that the generated 0.2 MPa.G steam is merged into the 0.2 MPa.G steam main pipe.

[0018] The beneficial effects of the present invention include at least one of the following:

[0019] The present invention realizes multiple utilization of high-pressure steam condensate through flash evaporation and heat exchange processes, thereby significantly improving the energy utilization efficiency of the system.

[0020] The present invention saves the use of a 0.4MPa.G steam condenser by reducing the demand for external steam, and at the same time saves 0.2MPa.G steam, thereby reducing production costs.

[0021] The present invention reduces the impact on the environment and improves the environmental protection benefits of the system by reducing the direct discharge of steam. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The figure is a process system flow chart of an embodiment of the present invention.

[0023] In the figure: 1. 1# distillation tower; 2. 2# distillation tower; 3. 1# distillation tower heat exchanger; 4. 2# distillation tower heat exchanger; 5. steam condensate water heat exchanger; 6. steam condensate flash tank. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The present invention provides an energy-saving method for multiple utilization of polysilicon rectification high-pressure steam condensate energy, and the specific steps include:

[0026] The method is applicable to the distillation tower in the polysilicon production process, where steam is used to heat and separate the chlorosilane liquid. The distillation tower includes a first distillation tower and a second distillation tower, and includes the following steps:

[0027] In the first step, low-pressure steam is used to perform heat exchange on the chlorosilane liquid in the first distillation tower to produce low-pressure steam condensate, and high-pressure steam is used to perform heat exchange on the chlorosilane liquid in the second distillation tower to produce high-pressure steam condensate;

[0028] In the second step, the high-pressure steam condensate is collected in a condensate flash tank;

[0029] In the third step, the high-pressure steam condensate is depressurized by a flash evaporation process to generate the low-pressure steam required in the first step, while the remaining flash evaporation residue;

[0030] In the fourth step, the generated low-pressure steam is merged into the low-pressure steam of the first distillation tower for heat exchange with the chlorosilane liquid in the first distillation tower, thereby realizing energy reuse.

[0031] Preferably, the flash residual liquid can be used to perform heat exchange on the low-pressure steam condensate to generate the low-pressure steam required for the first step again and merge it into the low-pressure steam of the first distillation tower.

[0032] Preferably, the high-pressure steam is 0.4 MPa.G steam, and the low-pressure steam is 0.2 MPa.G steam.

[0033] Embodiment 1:

[0034] This embodiment is described below in conjunction with an application system of the method adopted by the present invention.

[0035] Reference Figure 1 , the system provided in this embodiment includes:

[0036] The 1# distillation tower heat exchanger 3 is connected to the 0.2MPa.G steam main pipe and uses 0.2MPa.G steam to perform heat exchange on the chlorosilane liquid in the 1# distillation tower 1 to produce low-pressure steam condensate with a temperature of about 90°C.

[0037] The 2# distillation tower heat exchanger 4 is connected to the 0.4MPa.G steam main pipe and uses 0.4MPa.G high-pressure steam to perform heat exchange on the chlorosilane liquid in the 2# distillation tower 2 to generate high-pressure steam condensate with a temperature of about 145°C.

[0038] The high-pressure steam condensate is collected in the condensate flash tank 6 and its pressure is reduced by a flash process to generate 0.2 MPa.G steam.

[0039] Through calculation, the high-pressure steam condensate flashes to generate low-pressure steam, and the flow rate is about 1.79t / h. The calculation formula is as follows:

[0040]

[0041] Among them, m fs is the flash steam flow rate (about 34t / h);

[0042] m c is the condensed water load (about 610 kJ / kg);

[0043] h c is the enthalpy of condensed water (about 504 kJ / kg);

[0044] h fc is the saturated water enthalpy (about 610 kJ / kg);

[0045] hfg is the latent heat of flash steam (about 2014 kJ / kg);

[0046] Substituting into the formula, mf s =1.79t / h.

[0047] The temperature of the residual liquid after flash evaporation is about 139° C., and it is transported to the steam condensate heat exchanger 5 through a pipeline.

[0048] The generated 0.2MPa.G is incorporated into the 0.2MPa.G steam main and used for the 1# distillation tower heat exchanger 3 to heat the 1# distillation tower 1, thereby realizing the reuse of energy.

[0049] Preferably, the temperature of the residual liquid after flash evaporation is about 139°C, and it is transported to the steam condensate heat exchanger 5 through a pipeline. The residual liquid (139°C) after flash evaporation of the high-pressure steam condensate is used to exchange heat with the low-pressure steam condensate (90°C) to generate more low-pressure steam, which is then added to the 0.2MPa.G steam main. In the heat exchanger, the 0.4MPa(G) steam condensate (139°C) is used to heat the 0.2MPa(G) steam condensate (90°C), and the heat load calculation formula of the heat exchanger is used:

[0050]

[0051] Q=M×Cp×4t

[0052] Where Q is the heat load of the heat exchanger (kJ / h or kW);

[0053] M is the mass flow rate of the fluid (kg / h);

[0054] Δt is the temperature difference (°C);

[0055] Cp is the specific heat capacity of steam (kJ / kg·℃);

[0056] T1 and T2 are the temperatures of high-pressure steam condensate and low-pressure steam condensate;

[0057] t1 and t2 are the inlet and outlet temperatures.

[0058] According to the heat exchange calculation results, this embodiment can generate about 1.41 t / h of 0.2 MPa (G) steam through the heat exchanger.

[0059] The energy-saving effect of the present invention has been verified through the application of the system of this embodiment. The results show that the present invention realizes the multiple utilization of high-pressure steam condensate through flash evaporation and heat exchange processes, and significantly improves the energy utilization efficiency of the system. The verification results show that 1.79 tons of 0.2MPa(G) steam are generated per hour through the flash evaporation process, and an additional 1.41 tons of 0.2MPa(G) steam are generated per hour through heat exchange in the heat exchanger, saving a total of 3.2 tons of 0.2MPa(G) steam per hour, reducing the demand for external steam and significantly reducing production costs. In addition, the present invention reduces the impact on the environment and improves the environmental benefits of the system by reducing the direct venting of steam. By utilizing the combined process of flash evaporation of high-pressure steam condensate and waste heat recovery, the present invention fully realizes the multiple utilization of thermal energy and further optimizes the energy configuration of the distillation tower in the polysilicon production process.

[0060] This embodiment verifies that the present invention achieves efficient thermal energy utilization and significant energy-saving effects in the distillation process of polysilicon production, which not only effectively improves production efficiency and economic benefits, but also significantly reduces carbon emissions, and has significant environmental benefits and sustainable development significance.

Claims

1. An energy-saving method for multiple utilization of the energy of high-pressure steam condensation in polysilicon distillation, which is applicable to the distillation tower using steam to heat and separate chlorosilane liquid in the polysilicon production process, characterized in that: The distillation tower comprises a first distillation tower and a second distillation tower, and comprises the following steps: S1, using low-pressure steam to perform heat exchange on the chlorosilane liquid in the first distillation tower and produce low-pressure steam condensate, and simultaneously using high-pressure steam to perform heat exchange on the chlorosilane liquid in the second distillation tower and produce high-pressure steam condensate; S2, collects the high-pressure steam condensate produced in S1 in a condensate flash tank; S3, reducing the pressure of the high-pressure steam condensate by flash evaporation to produce low-pressure steam, while remaining flash evaporation residue; S4, the generated low-pressure steam is merged into the low-pressure steam of the first distillation tower for heat exchange of the chlorosilane liquid in the first distillation tower, thereby realizing energy reuse.

2. The energy-saving method for multiple utilization of polysilicon rectification high-pressure steam condensate energy according to claim 1, characterized in that: The flash residual liquid described in S3 is used to perform heat exchange on the low-pressure steam condensate described in S1 to generate low-pressure steam again, which is then incorporated into the low-pressure steam of the first distillation tower.

3. The energy-saving method for multiple utilization of polysilicon rectification high-pressure steam condensate energy according to claim 1, characterized in that: The high-pressure steam is 0.4 MPa.G steam, and the low-pressure steam is 0.2 MPa.G steam.

4. An energy-saving system for multiple utilization of polysilicon distillation high-pressure steam condensate energy, characterized in that: The system is used for the energy-saving method for multiple utilization of polysilicon rectification high-pressure steam condensate energy as claimed in any one of claims 1 to 3, specifically comprising: 1# distillation tower, the 1# distillation tower is connected to the 1# distillation tower heat exchanger, and the 1# distillation tower heat exchanger is connected to the 0.2MPa.G steam main; 2# distillation tower, the 2# distillation tower is connected to the 2# distillation tower heat exchanger, and the 2# distillation tower heat exchanger is connected to the 0.4MPa.G steam main; A condensate flash tank, wherein the condensate flash tank is connected to a 2# distillation tower heat exchanger; The condensate flash tank is connected to the 0.2MPa.G steam main.

5. The system according to claim 4, characterized in that The system further comprises a condensate heater, which is respectively connected to the 2# distillation tower heat exchanger and the condensate flash tank.

6. The system according to claim 5, characterized in that The 0.2MPa.G condensate heater is connected to the 0.2MPa.G steam main.

Images