Automatic control system for multi-stage rectification of polycrystalline silicon

Abstract

The utility model discloses an automatic control system for multi-stage rectification of polycrystalline silicon, which comprises a three-stage rectification tower, a controller and a control component which are connected in sequence, the control assembly comprises a feeding flow control assembly, a steam flow control assembly, a tower top temperature control assembly, a tower kettle liquid level control assembly, a tower top pressure control assembly, a reflux tank liquid level control assembly, a reflux temperature control assembly and a tower feeding section pressure control assembly, and the control assembly is in signal connection with the controller. According to the polycrystalline silicon rectification control system, automatic control of polycrystalline silicon rectification is achieved through the control system host and the indication controller, the situation that manual control is not high in adjustment precision and prone to misoperation is avoided, and system safety is improved. Cascade association is carried out on manual control point positions through material balance and heat balance, the labor load of manual operation is greatly reduced, the labor cost is reduced, and the system stability is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of polysilicon multi-stage rectification, and particularly relates to an automatic control system for polysilicon multi-stage rectification. Background Art

[0002] Polysilicon multi-stage rectification uses energy cascade utilization technology for heat coupling of multi-stage rectification towers. By using component separation towers and light and heavy removal towers in series, it has the effects of low energy consumption and high product purity, and aims to meet the raw material quality requirements of electronic-grade polysilicon.

[0003] Currently, for polysilicon multi-stage rectification control, the feed flow rate of the component separation tower is adjusted. Through the change of the bottom temperature of the tower, the steam flow rate of the reboiler is manually controlled to meet the heat load. The changes in the feed load and heat load will affect the change of the temperature of the sensitive plate (sub-top temperature) below the top of the tower. Through the change of the sub-top temperature, the top reflux flow rate is manually controlled to ensure the purity of the light components at the top of the tower. The change in the feed rate will affect the liquid level of the top reflux drum and the bottom liquid level of the tower, and the automatic regulation of the extraction rate is realized through liquid level control.

[0004] After the top extraction of the component separation tower enters the light removal tower, due to the heat coupling effect at the top of the component separation tower, the bottom heat load changes with the change at the top of the component separation tower. The light removal tower has a fixed flow rate extraction at the top to remove light components and impurities. The liquid level of the reflux drum controls the reflux flow rate, and the liquid level of the bottom of the tower controls the extraction rate of the bottom of the tower.

[0005] After the bottom extraction of the light removal tower enters the heavy removal tower, through the change of the top pressure, the steam flow rate of the bottom reboiler is manually controlled. The heavy removal tower has a fixed flow rate extraction at the bottom of the tower, and the bottom of the tower removes heavy components and impurities. The reflux flow rate is manually controlled through the change of the liquid level at the bottom of the tower, and the change of the liquid level of the reflux drum controls the extraction flow rate at the top of the tower.

[0006] However, there are many manual control points, large operation load, lag in control adjustment, poor control accuracy, and poor system stability. It cannot meet the requirements for product purity of electronic-grade polysilicon.

[0007] Therefore, there is an urgent need to provide an automatic control system for polysilicon multi-stage rectification to solve the above problems. Summary of the Utility Model

[0008] The utility model aims to provide an automatic control system for polysilicon multi-stage rectification that is fast, efficient, and accurately controlled, and solves the problems of large product volatility and possible misoperations during the manual control and adjustment process of polysilicon multi-stage rectification due to many adjustment points and complex control processes. Through the control system host and the indicator controller, the automatic control of polysilicon rectification is realized, avoiding the problems of low accuracy and easy misoperation in manual control adjustment, and improving the system safety.

[0009] In order to achieve the above invention purpose, the technical solution of the utility model is as follows:

[0010] An automatic control system for multi-stage distillation of polysilicon, comprising three-stage distillation towers, a controller and a control component connected in sequence, wherein the top of the distillation tower is connected to a condenser, the tower kettle of the distillation tower is provided with a reboiler, the bottom of the condenser is connected to a reflux tank, the bottom of the reflux tank is connected to a reflux pump, the reflux pump is connected to the top of the distillation tower of this stage through a reflux pipeline, the reflux pump of the first-stage tower is connected to the feed inlet of the second-stage tower through a production pipeline, the reflux pump of the second-stage tower is connected to the light component production tank through the production pipeline, the reflux pump of the third-stage tower is connected to the trichlorosilane production tank through the production pipeline, the tower kettle of the second-stage tower is connected to the feed inlet of the third-stage tower through the production pipeline, and the third-stage tower The tower bottom is connected to the heavy component storage tank through the extraction pipeline, and the control component includes a feed flow control component, a steam flow control component, a tower top temperature control component, a tower bottom liquid level control component, a tower top pressure control component, a reflux tank liquid level control component, a reflux temperature control component, and a tower feed section pressure control component. The control component is connected to the controller signal; wherein the first-stage tower is a component separation tower, the second-stage tower is a light removal tower, and the third-stage tower is a weight removal tower. The control component collects data and transmits it to the controller, and the controller issues commands to the control components according to the measurement data fed back by each control component and the preset DCS control logic.

[0011] The reboiler heating medium pipelines of the 1st tower and the 3rd tower are connected to the steam pipeline, and the 1st tower and the 3rd tower are heated by steam; the top of the 1st tower is connected to the inlet of the reboiler heating medium pipeline of the 2nd tower, and the outlet of the reboiler heating medium pipeline of the 2nd tower is connected to the condenser of the 1st tower, and the 2nd tower is heated by the gas phase material temperature at the top of the 1st tower, and steam is not directly used, so as to achieve energy saving.

[0012] The feed flow control component includes a flow meter I, a feed regulating valve I and a feed flow indicating controller I arranged in the feed pipeline of the first-stage tower, and the flow meter I, the feed regulating valve I and the feed flow indicating controller I are respectively signal-connected; the feed flow indicating controller I monitors the feed flow of the first-stage tower in real time through the flow meter I, when the feed flow is higher than the set value, the feed flow indicating controller I controls the feed regulating valve I to reduce the opening, and when the feed flow is lower than the set value, the feed flow indicating controller I controls the feed regulating valve I to increase the opening.

[0013] The steam flow control component includes a thermometer II and a temperature indicating controller II arranged at the middle and lower positions of the stripping section of the first-stage column, a flowmeter II, a steam regulating valve II, and a steam flow indicating controller II arranged on the heating medium pipeline of the reboiler of the first-stage column; the thermometer II, the temperature indicating controller II, the flowmeter II, the steam regulating valve II, and the steam flow indicating controller II are respectively connected by signals. The temperature indicating controller II monitors the temperature in the middle of the stripping section of the first-stage column in real time through the thermometer II. When the temperature is higher than the set value, the temperature indicating controller II controls the steam flow indicating controller II to decrease the flow set value. When the temperature is lower than the set value, the temperature indicating controller II controls the steam flow indicating controller II to increase the flow set value; the steam flow indicating controller II monitors the steam flow of the reboiler in real time through the flowmeter II. When the steam flow is higher than the set value, the steam flow indicating controller II controls the steam regulating valve II to decrease the opening degree. When the steam flow is lower than the set value, the steam flow indicating controller II controls the steam regulating valve II to increase the opening degree.

[0014] The top temperature control component includes a thermometer III and a temperature indicating controller III arranged at the top of the first-stage column and the second-stage column, a flowmeter III, a reflux regulating valve III, and a reflux flow indicating controller III arranged on the top reflux pipeline of the first-stage column and the second-stage column. The thermometer III, the temperature indicating controller III, the flowmeter III, the reflux regulating valve III, and the reflux flow indicating controller III are respectively connected by signals. The temperature indicating controller III of the first-stage column monitors the temperature of the sensitive plate at the lower part of the top of the column in real time through the thermometer III. When the temperature is higher than the set value, the temperature indicating controller III controls the reflux flow indicating controller III to increase the flow set value. When the temperature is lower than the set value, the temperature indicating controller III controls the reflux flow indicating controller III to decrease the flow set value; the reflux flow indicating controller III monitors the top reflux flow in real time through the flowmeter III. When the reflux flow is higher than the set value, the reflux flow indicating controller III controls the reflux regulating valve III to decrease the opening degree. When the reflux flow is lower than the set value, the reflux flow indicating controller III controls the reflux regulating valve III to increase the opening degree; the thermometer III of the first-stage column is arranged at the position of the sensitive plate at the lower part of the top of the column. The temperature indicating controller III of the first-stage column monitors the temperature of the sensitive plate at the lower part of the top of the column in real time through the thermometer III. The thermometer III of the second-stage column is arranged at the top of the column. The temperature indicating controller III of the second-stage column monitors the gas phase temperature at the top of the column in real time through the thermometer III.

[0015] The bottom liquid level control component includes the bottom liquid level control component I of the first-stage column, the bottom liquid level control component II of the second-stage column, and the bottom liquid level control component III of the third-stage column.

[0016] The bottom kettle liquid level control assembly I includes a liquid level gauge IV arranged at the bottom kettle of the 1st-stage tower, a kettle bottom extraction regulating valve IV arranged on the extraction pipeline of the 1st-stage tower bottom kettle, and a liquid level indicating controller IV. The liquid level gauge IV, the kettle bottom extraction regulating valve IV, and the liquid level indicating controller IV are respectively connected by signals. The bottom kettle liquid level indicating controller IV monitors the liquid level of the 1st-stage tower in real time through the liquid level gauge. When the liquid level is higher than the set value, the liquid level indicating controller IV controls the kettle bottom extraction regulating valve IV to increase the opening degree. When the liquid level is lower than the set value, the liquid level indicating controller IV controls the kettle bottom extraction regulating valve IV to decrease the opening degree.

[0017] The bottom kettle liquid level control assembly II includes a liquid level gauge V and a liquid level indicating controller V arranged at the bottom kettle of the 2nd-stage tower, a kettle bottom extraction flowmeter V, a kettle bottom extraction regulating valve V, and a kettle bottom extraction flow indicating controller V arranged on the extraction pipeline of the 2nd-stage tower bottom kettle. The liquid level gauge V, the liquid level indicating controller V, the kettle bottom extraction flowmeter V, the kettle bottom extraction regulating valve V, and the kettle bottom extraction flow indicating controller V are respectively connected by signals. The liquid level indicating controller V monitors the liquid level of the 2nd-stage tower bottom kettle in real time through the liquid level gauge V. When the liquid level is higher than the set value, the liquid level indicating controller V controls the kettle bottom extraction flow indicating controller V to increase the flow set value. When the liquid level is lower than the set value, the liquid level indicating controller V controls the kettle bottom extraction flow indicating controller V to decrease the flow set value. The kettle bottom extraction flow indicating controller V monitors the bottom kettle extraction flow in real time through the flowmeter V. When the kettle bottom extraction flow is higher than the set value, the kettle bottom extraction flow indicating controller V controls the kettle bottom extraction regulating valve V to decrease the opening degree. When the kettle bottom extraction flow is lower than the set value, the kettle bottom extraction flow indicating controller V controls the kettle bottom extraction regulating valve V to increase the opening degree.

[0018] The bottom kettle liquid level control assembly III includes a liquid level gauge VI and a liquid level indicating controller VI arranged at the bottom kettle of the 3rd-stage tower, a reflux flowmeter VI, a reflux regulating valve VI, and a reflux flow indicating controller VI arranged on the top reflux pipeline of the 3rd-stage tower. The liquid level gauge VI, the liquid level indicating controller VI, the reflux flowmeter VI, the reflux regulating valve VI, and the reflux flow indicating controller VI are respectively connected by signals. The liquid level indicating controller VI monitors the liquid level of the 3rd-stage tower bottom kettle in real time through the liquid level gauge. When the liquid level is higher than the set value, the liquid level indicating controller VI controls the reflux flow indicating controller VI to decrease the flow set value. When the liquid level is lower than the set value, the liquid level indicating controller VI controls the reflux flow indicating controller VI to increase the flow set value. The reflux flow indicating controller VI monitors the top reflux flow in real time through the flowmeter VI. When the reflux flow is higher than the set value, the reflux flow indicating controller VI controls the reflux regulating valve VI to decrease the opening degree. When the reflux flow is lower than the set value, the reflux flow indicating controller VI controls the reflux regulating valve VI to increase the opening degree.

[0019] The top pressure control assembly includes a pressure gauge VII and a pressure indicating controller VII provided at the top of the distillation column, and a regulating valve VII provided in the overhead gas vent pipeline. The pressure gauge VII, the pressure indicating controller VII, and the regulating valve VII are respectively connected by signals. The pressure indicating controller VII monitors the top pressure of each column in real time through the pressure gauge LVII. When the pressure is higher than the set value, the pressure indicating controller VII controls the vent regulating valve VII to increase the opening degree. When the pressure is lower than the set value, the pressure indicating controller VII controls the vent regulating valve VII to decrease the opening degree.

[0020] The reflux drum liquid level control assembly includes a liquid level gauge VIII and a liquid level indicating controller VIII provided in the reflux drum, a top draw flowmeter VIII, a top draw regulating valve VIII, and a top draw flow indicating controller VIII provided in the reflux drum product pipeline. The liquid level gauge VIII, the liquid level indicating controller VIII, the top draw flowmeter VIII, the top draw regulating valve VIII, and the top draw flow indicating controller VIII are respectively connected by signals. The liquid level indicating controller VIII monitors the liquid levels of the reflux drums of the first-stage column, the second-stage column, and the third-stage column in real time through the liquid level gauge. When the liquid level is higher than the set value, the liquid level indicating controller VIII controls the top draw flow indicating controller VIII to increase the flow set value. When the liquid level is lower than the set value, the liquid level indicating controller VIII controls the top draw flow indicating controller VIII to decrease the flow set value; the top draw flow indicating controller VIII monitors the top draw flow rate in real time through the flowmeter VIII. When the top draw flow rate is higher than the set value, the feed flow indicating controller VIII controls the top draw regulating valve VIII to decrease the opening degree. When the top draw flow rate is lower than the set value, the top draw flow indicating controller VIII controls the top draw regulating valve VIII to increase the opening degree.

[0021] The reflux temperature control assembly includes a thermometer IX and a reflux temperature indicating controller IX provided in the condenser, and a circulating water return regulating valve IX is provided in the circulating water pipeline of the condenser. The thermometer IX, the reflux temperature indicating controller IX, and the circulating water return regulating valve IX are respectively connected by signals. The reflux temperature indicating controller IX monitors the temperature of the material at the outlet of the condenser in real time through the thermometer IX. When the temperature is higher than the set value, the reflux temperature indicating controller controls the circulating water return regulating valve IX to increase the opening degree. When the temperature is lower than the set value, the reflux temperature indicating controller IX controls the circulating water return regulating valve IX to decrease the opening degree.

[0022] The pressure control component of the tower feed section includes a pressure gauge X and a pressure indicating controller X arranged below the feed inlet of the third-stage tower, a flowmeter X, a steam regulating valve X, and a steam flow indicating controller X arranged on the steam pipeline of the third-stage tower reboiler; the pressure gauge X, the pressure indicating controller X, the flowmeter X, the steam regulating valve X, and the steam flow indicating controller X are respectively connected by signals. The pressure indicating controller X monitors the gas phase pressure below the feed inlet in real time through the pressure gauge X. When the pressure is higher than the set value, the pressure indicating controller X controls the steam flow indicating controller X to reduce the flow set value. When the pressure is lower than the set value, the pressure indicating controller X controls the steam flow indicating controller X to increase the flow set value; the steam flow indicating controller X monitors the steam flow of the reboiler in real time through the flowmeter X. When the steam flow is higher than the set value, the steam flow indicating controller X controls the steam regulating valve X to reduce the opening degree. When the steam flow is lower than the set value, the steam flow indicating controller X controls the steam regulating valve X to increase the opening degree.

[0023] Advantages of the present utility model:

[0024] 1. In the present utility model, the automatic control of polysilicon rectification is realized through the control system host and the indicating controller, avoiding inaccurate adjustment accuracy and easy misoperation due to manual control, and improving the system safety.

[0025] 2. In the present utility model, the manual control points are cascade-connected through material balance and heat balance, greatly reducing the manual operation labor load, reducing the labor cost, and improving the system stability.

[0026] 3. In the present utility model, the gas phase at the top of the heat source tower is used to heat the reboiler at the bottom of the coupled tower, enabling the cascade utilization of heat, reducing the usage amount of system steam and refrigerant, and reducing the energy consumption.

[0027] 4. In the present utility model, the reflux flow is cascade-controlled by the temperature of the sensitive plate at the top of the first stage tower, the steam flow is cascade-controlled by the bottom temperature, and the reflux flow is cascade-controlled by the temperature at the top of the second stage tower, making the temperatures at the top and bottom of the tower more stable and the components more stable, and improving the quality and output of the product.

[0028] 5. In the present utility model, the steam flow of the reboiler is cascade-controlled by the pressure at the third-stage feed section, so that the influence of the change in the feed flow on the feed section pressure acts on the regulation of the steam flow, realizing the automatic correlation of the heat load and the feed amount. Description of the drawings

[0029] Figure 1 It is a schematic structural diagram of the first-stage tower and the second-stage tower of the present utility model.

[0030] Figure 2 It is a schematic structural diagram of the third-stage tower of the present utility model.

[0031] Figure 3 This is a trend diagram of the bottom liquid level of a first-stage tower which has been in continuous operation for 3 months as an application example of the utility model.

[0032] Figure 4 This is a trend diagram of the bottom liquid level of the first-stage tower of the comparative example of the utility model which has been running continuously for 3 months.

[0033] Among them, 1, first-stage tower; 2, second-stage tower; 3, third-stage tower; 4, reflux tank; 5, reboiler; 6, condenser; 7, reflux pump. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with the embodiments, but the implementation manner of the present invention is not limited thereto.

[0035] Example 1

[0036] like Figure 1 and Figure 2 As shown, this embodiment provides an automatic control system for multi-stage distillation of polysilicon, including three-stage distillation towers, a controller and a control component connected in sequence, the top of the distillation tower is connected to a condenser 6, the tower kettle of the distillation tower is provided with a reboiler 5, the bottom of the condenser 6 is connected to a reflux tank 4, the bottom of the reflux tank 4 is connected to a reflux pump 7, the reflux pump 7 is connected to the top of the distillation tower of this stage through a reflux pipeline, the reflux pump 7 of the first-stage tower 1 is connected to the feed inlet of the second-stage tower 2 through a production pipeline, and the reflux pump 7 of the second-stage tower 2 is connected to the light component production line through a production pipeline. The reflux pump 7 of the 3-stage tower 3 is connected to the trichlorosilane extraction tank through the extraction pipeline, the tower kettle of the 2-stage tower 2 is connected to the feed port of the 3-stage tower 3 through the extraction pipeline, and the tower kettle of the 3-stage tower 3 is connected to the heavy component storage tank through the extraction pipeline. The control component includes a feed flow control component, a steam flow control component, a tower top temperature control component, a tower kettle liquid level control component, a tower top pressure control component, a reflux tank 4 liquid level control component, a reflux temperature control component, and a tower feed section pressure control component, and the control component is connected to the controller signal;

[0037] The heating medium pipelines of the reboiler 5 of the first-stage tower 1 and the third-stage tower 3 are connected to the steam pipeline; the top of the first-stage tower 1 is connected to the inlet of the heating medium pipeline of the reboiler 5 of the second-stage tower 2, and the outlet of the heating medium pipeline of the reboiler 5 of the second-stage tower 2 is connected to the condenser 6 of the first-stage tower 1.

[0038] In this embodiment, the first-stage tower 1 is a component separation tower, the second-stage tower 2 is a lightness removal tower, the third-stage tower 3 is a weight removal tower, and the controller is a DCS control host, and the specific model is DELL PowerEdge T640.

[0039] The first-stage tower 1 and the third-stage tower 3 are heated by steam, and the second-stage tower 2 is heated by the material temperature of the upper distillation tower instead of directly using steam, thereby achieving energy saving.

[0040] The control components collect data and transmit it to the host of the control system. The controller issues commands to the control components according to the measurement data fed back by each control component, and realizes the automatic control of polysilicon rectification through the host of the control system and the indicating controller, avoiding inaccurate adjustment accuracy and easy misoperation caused by manual control, and improving the system safety.

[0041] Embodiment 2

[0042] Compared with Embodiment 1, the difference in this embodiment is that in this embodiment, the feed flow control component includes a flowmeter I, a feed regulating valve I, and a feed flow indicating controller I provided on the feed pipeline of the first-stage tower 1; the flowmeter I, the feed regulating valve I, and the feed flow indicating controller I are respectively connected by signals. The remaining structures are the same as those in Embodiment 1.

[0043] In this embodiment, the flowmeter I is a mass flowmeter, the feed regulating valve I is a bellows regulating valve, and the feed flow indicating controller I uses a DELTAV MQ controller;

[0044] In this embodiment, the feed flow indicating controller I monitors the feed flow of the first-stage tower 1 in real time through the flowmeter I. When the feed flow is higher than the set value, the feed flow indicating controller I controls the feed regulating valve I to reduce the opening degree. When the feed flow is lower than the set value, the feed flow indicating controller I controls the feed regulating valve I to increase the opening degree. This embodiment realizes the automatic control of the feed flow of the first-stage tower 1 through the feed flow component, can reduce the interference of external material transportation, and improve the stability of the feed flow.

[0045] Embodiment 3

[0046] Compared with Embodiment 1, the difference in this embodiment is that in this embodiment, the steam flow control component includes a thermometer II and a temperature indicating controller II provided at the middle and lower part of the stripping section of the first-stage tower 1, a flowmeter II, a steam regulating valve II, and a steam flow indicating controller II provided on the heating medium pipeline of the reboiler 5 of the first-stage tower 1; the thermometer II, the temperature indicating controller II, the flowmeter II, the steam regulating valve II, and the steam flow indicating controller II are respectively connected by signals. The remaining structures are the same as those in Embodiment 1.

[0047] In this embodiment, the thermometer II is an integrated thermometer, the flowmeter II is an integrated averaging pitot tube flowmeter, the steam regulating valve II is a common butterfly valve regulating valve, and the steam flow indicating controller II and the temperature indicating controller II use DELTAV MQ controllers.

[0048] In this embodiment, the temperature indicating controller II monitors the temperature in the middle of the stripping section of the first-stage column 1 in real time through the thermometer II. When the temperature is higher than the set value, the temperature indicating controller II controls the steam flow rate indicating controller II to decrease the flow rate set value. When the temperature is lower than the set value, the temperature indicating controller II controls the steam flow rate indicating controller II to increase the flow rate set value; the steam flow rate indicating controller II monitors the steam flow rate of the reboiler 5 in real time through the flowmeter II. When the steam flow rate is higher than the set value, the steam flow rate indicating controller II controls the steam regulating valve II to decrease the opening degree. When the steam flow rate is lower than the set value, the steam flow rate indicating controller II controls the steam regulating valve II to increase the opening degree. In this embodiment, the automatic control of the temperature in the middle of the stripping section of the first-stage column 1 is realized through the steam flow control component, improving the stability of the bottom temperature and components.

[0049] Embodiment 4

[0050] Compared with Embodiment 1, the difference in this embodiment is that in this embodiment, the top temperature control component includes a thermometer III and a temperature indicating controller III provided at the top of the first-stage column 1 and the second-stage column 2, a flowmeter III, a reflux regulating valve III, and a reflux flow rate indicating controller III provided on the top reflux pipeline of the first-stage column 1 and the second-stage column 2; the thermometer III, the temperature indicating controller III, the flowmeter III, the reflux regulating valve III, and the reflux flow rate indicating controller III are respectively connected by signals, and the rest of the structure is the same as that in Embodiment 1.

[0051] In this embodiment, the thermometer III uses an integrated thermometer, the flowmeter III uses a vortex street flowmeter, the reflux regulating valve III uses a bellows regulating valve, and the temperature indicating controller III and the reflux flow rate indicating controller III use DELTAV MQ controllers.

[0052] In this embodiment, the temperature indicating controller III monitors the temperature at the top of the tower in real time through the thermometer III. When the temperature is higher than the set value, the temperature indicating controller III controls the reflux flow rate indicating controller III to increase the flow rate set value. When the temperature is lower than the set value, the temperature indicating controller III controls the reflux flow rate indicating controller III to decrease the flow rate set value. The reflux flow rate indicating controller III monitors the reflux flow rate at the top of the tower in real time through the flowmeter III. When the reflux flow rate is higher than the set value, the reflux flow rate indicating controller III controls the reflux regulating valve III to decrease the opening degree. When the reflux flow rate is lower than the set value, the reflux flow rate indicating controller III controls the reflux regulating valve III to increase the opening degree. The thermometer III of the first-stage tower 1 is arranged at the sensitive plate position below the top of the tower. The temperature indicating controller III of the first-stage tower 1 monitors the temperature of the sensitive plate below the top of the tower in real time through the thermometer III. The thermometer III of the second-stage tower 2 is arranged at the top of the tower. The temperature indicating controller III of the second-stage tower 2 monitors the gas-phase temperature at the top of the tower in real time through the thermometer III. In this embodiment, the automatic control of the temperature at the top of the tower is realized through the temperature control component at the top of the tower, which improves the purity and yield of the trichlorosilane product at the top of the tower.

[0053] Example 5

[0054] Compared with Example 1, the difference in this embodiment is that in this embodiment, the bottom liquid level control component includes the bottom liquid level control component I of the first-stage tower 1, the bottom liquid level control component II of the second-stage tower 2, and the bottom liquid level control component III of the third-stage tower 3.

[0055] The bottom liquid level control component I includes a liquid level gauge IV arranged at the bottom of the first-stage tower 1, a bottom product regulating valve IV arranged on the bottom product pipeline of the first-stage tower 1, and a liquid level indicating controller IV. The liquid level gauge IV, the bottom product regulating valve IV, and the liquid level indicating controller IV are respectively connected by signals.

[0056] The bottom liquid level control component II includes a liquid level gauge V and a liquid level indicating controller V arranged at the bottom of the second-stage tower 2, a bottom product flowmeter V, a bottom product regulating valve V, and a bottom product flow rate indicating controller V arranged on the bottom product pipeline of the second-stage tower 2. The liquid level gauge V, the liquid level indicating controller V, the bottom product flowmeter V, the bottom product regulating valve V, and the bottom product flow rate indicating controller V are respectively connected by signals.

[0057] The bottom liquid level control component III includes a liquid level gauge VI and a liquid level indicating controller VI arranged at the bottom of the third-stage tower 3, a reflux flowmeter VI, a reflux regulating valve VI, and a reflux flow rate indicating controller VI arranged on the top reflux pipeline of the third-stage tower 3. The liquid level gauge VI, the liquid level indicating controller VI, the reflux flowmeter VI, the reflux regulating valve VI, and the reflux flow rate indicating controller VI are respectively connected by signals.

[0058] The remaining structures are the same as those in Example 1.

[0059] In this embodiment, level gauges IV, V, and VI are differential pressure level gauges, kettle extraction control valves IV and V are bellows control valves, reflux control valve VI is a bellows control valve, reflux flowmeter VI is a vortex flowmeter, kettle extraction flowmeter V is a vortex flowmeter, and reflux flow indicating controller VI, level indicating controllers IV, V, and VI are DELTAV MQ controllers.

[0060] In this embodiment, level indicating controller IV of the tower kettle monitors the level of the first-stage tower 1 in real time through a level gauge. When the level is higher than the set value, level indicating controller IV controls kettle extraction control valve IV to increase the opening degree. When the level is lower than the set value, level indicating controller IV controls kettle extraction control valve IV to decrease the opening degree;

[0061] Level indicating controller V monitors the level of the kettle of the second-stage tower 2 in real time through level gauge V. When the level is higher than the set value, level indicating controller V controls kettle extraction flow indicating controller V to increase the flow set value. When the level is lower than the set value, level indicating controller V controls kettle extraction flow indicating controller V to decrease the flow set value; Kettle extraction flow indicating controller V monitors the kettle extraction flow in real time through flowmeter V. When the kettle extraction flow is higher than the set value, kettle extraction flow indicating controller V controls kettle extraction control valve V to decrease the opening degree. When the kettle extraction flow is lower than the set value, kettle extraction flow indicating controller V controls kettle extraction control valve V to increase the opening degree;

[0062] Level indicating controller VI monitors the level of the kettle of the third-stage tower 3 in real time through a level gauge. When the level is higher than the set value, level indicating controller VI controls reflux flow indicating controller VI to decrease the flow set value. When the level is lower than the set value, level indicating controller VI controls reflux flow indicating controller VI to increase the flow set value; Reflux flow indicating controller VI monitors the top reflux flow in real time through flowmeter VI. When the reflux flow is higher than the set value, reflux flow indicating controller VI controls reflux control valve VI to decrease the opening degree. When the reflux flow is lower than the set value, reflux flow indicating controller VI controls reflux control valve VI to increase the opening degree.

[0063] In this embodiment, the automatic control of the kettle levels of the first-stage tower 1, second-stage tower 2, and third-stage tower 3 is achieved through the tower kettle level control component, greatly reducing the frequency of manual adjustment, maintaining the stability of the kettle level, and improving the smoothness of heat exchange in the kettle.

[0064] Embodiment 6

[0065] Compared with Embodiment 1, this embodiment is different in that in this embodiment, the top pressure control assembly includes a pressure gauge VII and a pressure indicating controller VII provided at the top of the distillation column, and a regulating valve VII provided on the gas-phase vent pipeline at the top of the column; the pressure gauge VII, the pressure indicating controller VII, and the regulating valve VII are respectively connected by signals; the remaining structures are the same as those in Embodiment 1.

[0066] In this embodiment, the pressure gauge VII uses a diaphragm pressure transmitter, the regulating valve VII uses a bellows regulating valve, and the pressure indicating controller VII uses a DELTAV MQ controller.

[0067] In this embodiment, the pressure indicating controller VII monitors the pressure at the top of each column in real time through the pressure gauge LVII. When the pressure is higher than the set value, the pressure indicating controller VII controls the vent regulating valve VII to increase the opening degree. When the pressure is lower than the set value, the pressure indicating controller VII controls the vent regulating valve VII to decrease the opening degree. In this embodiment, the top pressure control assemblies are respectively provided in the first-stage column 1, the second-stage column 2, and the third-stage column 3, and the automatic control of the top pressure of the first-stage column 1, the second-stage column 2, and the third-stage column 3 is realized through the top pressure control assemblies, improving the stability of the top pressure.

[0068] Embodiment 7

[0069] Compared with Embodiment 1, this embodiment is different in that in this embodiment, the liquid level control assembly of the reflux drum 4 includes a liquid level gauge VIII and a liquid level indicating controller VIII provided in the reflux drum 4, a top draw flowmeter VIII, a top draw regulating valve VIII, and a top draw flow indicating controller VIII provided on the draw pipeline of the reflux drum 4; the liquid level gauge VIII, the liquid level indicating controller VIII, the top draw flowmeter VIII, the top draw regulating valve VIII, and the top draw flow indicating controller VIII are respectively connected by signals. The remaining structures are the same as those in Embodiment 1.

[0070] In this embodiment, the liquid level gauge VIII uses a differential pressure liquid level gauge, the flowmeter VIII uses a vortex flowmeter, the regulating valve VIII uses a bellows regulating valve, and the liquid level indicating controller VIII and the flow indicating controller VIII use DELTAV MQ controllers.

[0071] In this embodiment, the liquid level indicating controller VIII monitors the liquid levels of the reflux drums 4 of the first-stage tower 1, the second-stage tower 2, and the third-stage tower 3 in real time through liquid level gauges. When the liquid level is higher than the set value, the liquid level indicating controller VIII controls the top draw flow indicating controller VIII to increase the flow set value. When the liquid level is lower than the set value, the liquid level indicating controller VIII controls the top draw flow indicating controller VIII to decrease the flow set value. The top draw flow indicating controller VIII monitors the top draw flow rate in real time through the flowmeter VIII. When the top draw flow rate is higher than the set value, the feed flow indicating controller VIII controls the top draw regulating valve VIII to reduce the opening degree. When the top draw flow rate is lower than the set value, the top draw flow indicating controller VIII controls the top draw regulating valve VIII to increase the opening degree. In this embodiment, liquid level control components are respectively arranged in the first-stage tower 1, the second-stage tower 2, and the third-stage tower 3 to realize the automatic control of the liquid levels of the reflux drums 4 of the first-stage tower 1, the second-stage tower 2, and the third-stage tower 3 through the liquid level control components of the reflux drums 4, thereby improving the liquid level stability of the reflux drums 4.

[0072] Embodiment 8

[0073] Compared with Embodiment 1, the difference in this embodiment is that in this embodiment, the reflux temperature control component includes a thermometer IX and a reflux temperature indicating controller IX arranged on the condenser 6, and a circulating water return regulating valve IX is arranged on the circulating water pipeline of the condenser 6. The thermometer IX, the reflux temperature indicating controller IX, and the circulating water return regulating valve IX are respectively connected by signals. The rest of the structure is the same as that of Embodiment 1.

[0074] In this embodiment, the thermometer IX uses an integrated thermometer, the regulating valve IX uses an ordinary butterfly valve regulating valve, and the temperature indicating controller IX uses a DELTAV MQ controller.

[0075] In this embodiment, the reflux temperature indicating controller IX monitors the temperature of the material at the outlet of the condenser 6 in real time through the thermometer IX. When the temperature is higher than the set value, the reflux temperature indicating controller controls the circulating water return regulating valve IX to increase the opening degree. When the temperature is lower than the set value, the reflux temperature indicating controller IX controls the circulating water return regulating valve IX to decrease the opening degree. In this embodiment, reflux temperature control components are respectively arranged in the first-stage tower 1, the second-stage tower 2, and the third-stage tower 3 to realize the automatic control of the reflux temperatures of the first-stage tower 1, the second-stage tower 2, and the third-stage tower 3 through the reflux temperature control components, ensuring the stability of the reflux temperature and the smoothness of the gas-liquid in the distillation column.

[0076] Embodiment 9

[0077] Compared with Example 1, the present embodiment is different in that, in the present embodiment, the tower feed section pressure control assembly includes a pressure gauge X and a pressure indicating controller X arranged below the feed port of the 3-stage tower 3, a flow meter X, a steam regulating valve X and a steam flow indicating controller X arranged in the steam pipeline of the reboiler 5 of the 3-stage tower 3; the pressure gauge X, the pressure indicating controller X, the flow meter X, the steam regulating valve X and the steam flow indicating controller X are respectively signal-connected. The rest of the structure is the same as that of Example 1.

[0078] In this embodiment, the pressure gauge X adopts a diaphragm pressure transmitter, the flow meter X adopts a vortex flow meter, the regulating valve X adopts a bellows regulating valve, and the pressure indicating controller X and the flow indicating controller X adopt DELTAV MQ controllers.

[0079] In this embodiment, the pressure indicating controller X monitors the gas phase pressure below the feed port in real time through the pressure gauge X. When the pressure is higher than the set value, the pressure indicating controller X controls the steam flow indicating controller X to reduce the flow setting value. When the pressure is lower than the set value, the pressure indicating controller X controls the steam flow indicating controller X to increase the flow setting value. The steam flow indicating controller X monitors the steam flow of the reboiler 5 in real time through the flow meter X. When the steam flow is higher than the set value, the steam flow indicating controller X controls the steam regulating valve X to reduce the opening. When the steam flow is lower than the set value, the steam flow indicating controller X controls the steam regulating valve X to increase the opening. In this embodiment, the feed pressure of the three-stage tower 3 is automatically controlled through the tower feed section pressure control component, so that the tower heat load automatically matches the feed flow.

[0080] Application Examples

[0081] This application example provides an automatic control system for multi-stage distillation of polysilicon, including three-stage distillation towers, a controller and a control component connected in sequence, the top of the distillation tower is connected to a condenser 6, the bottom of the distillation tower is provided with a reboiler 5, the bottom of the condenser 6 is connected to a reflux tank 4, the bottom of the reflux tank 4 is connected to a reflux pump 7, the reflux pump 7 is connected to the top of the distillation tower of this stage through a reflux pipeline, the reflux pump 7 of the first-stage tower 1 is connected to the feed inlet of the second-stage tower 2 through a production pipeline, and the reflux pump 7 of the second-stage tower 2 is connected to the light component production line through the production pipeline. The reflux pump 7 of the 3-stage tower 3 is connected to the trichlorosilane extraction tank through the extraction pipeline, the tower bottom of the 2-stage tower 2 is connected to the feed port of the 3-stage tower 3 through the extraction pipeline, and the tower bottom of the 3-stage tower 3 is connected to the heavy component storage tank through the extraction pipeline. The control component includes a feed flow control component, a steam flow control component, a tower top temperature control component, a tower bottom liquid level control component, a tower top pressure control component, a reflux tank 4 liquid level control component, a reflux temperature control component, and a tower feed section pressure control component, and the control component is connected to the controller signal.

[0082] The reboiler 5 heating medium pipelines of the first-stage tower 1 and the third-stage tower 3 are connected to the steam pipeline; the top of the first-stage tower 1 is connected to the inlet of the reboiler 5 heating medium pipeline of the second-stage tower 2, and the outlet of the reboiler 5 heating medium pipeline of the second-stage tower 2 is connected to the condenser 6 of the first-stage tower 1.

[0083] The feed flow control assembly includes a flowmeter I, a feed regulating valve I, and a feed flow indicating controller I provided in the feed pipeline of the first-stage tower 1. The flowmeter I, the feed regulating valve I, and the feed flow indicating controller I are respectively connected by signals

[0084] The steam flow control assembly includes a thermometer II and a temperature indicating controller II provided at the middle and lower part of the stripping section of the first-stage tower 1, a flowmeter II, a steam regulating valve II, and a steam flow indicating controller II provided in the reboiler 5 heating medium pipeline of the first-stage tower 1.

[0085] The steam flow control assembly includes a thermometer II and a temperature indicating controller II provided at the middle and lower part of the stripping section of the first-stage tower 1, a flowmeter II, a steam regulating valve II, and a steam flow indicating controller II provided in the reboiler 5 heating medium pipeline of the first-stage tower 1. The thermometer II, the temperature indicating controller II, the flowmeter II, the steam regulating valve II, and the steam flow indicating controller II are respectively connected by signals.

[0086] The top temperature control assembly includes a thermometer III and a temperature indicating controller III provided at the tops of the first-stage tower 1 and the second-stage tower 2, a flowmeter III, a reflux regulating valve III, and a reflux flow indicating controller III provided on the top reflux pipelines of the first-stage tower 1 and the second-stage tower 2. The thermometer III, the temperature indicating controller III, the flowmeter III, the reflux regulating valve III, and the reflux flow indicating controller III are respectively connected by signals.

[0087] The bottom liquid level control assembly includes the bottom liquid level control assembly I of the first-stage tower 1, the bottom liquid level control assembly II of the second-stage tower 2, and the bottom liquid level control assembly III of the third-stage tower 3.

[0088] The bottom liquid level control assembly I includes a liquid level gauge IV provided at the bottom of the first-stage tower 1, a bottom product regulating valve IV and a liquid level indicating controller IV provided on the bottom product pipeline of the first-stage tower 1. The liquid level gauge IV, the bottom product regulating valve IV, and the liquid level indicating controller IV are respectively connected by signals.

[0089] The bottom liquid level control assembly II includes a liquid level gauge V and a liquid level indicating controller V provided at the bottom of the second-stage tower 2, a bottom product flowmeter V, a bottom product regulating valve V, and a bottom product flow indicating controller V provided on the bottom product pipeline of the second-stage tower 2. The liquid level gauge V, the liquid level indicating controller V, the bottom product flowmeter V, the bottom product regulating valve V, and the bottom product flow indicating controller V are respectively connected by signals.

[0090] The bottom tower liquid level control component III includes a liquid level gauge VI and a liquid level indicating controller VI provided at the bottom of the third-stage tower 3, a reflux flowmeter VI, a reflux regulating valve VI and a reflux flow indicating controller VI provided on the reflux pipeline at the top of the third-stage tower 3. The liquid level gauge VI, the liquid level indicating controller VI, the reflux flowmeter VI, the reflux regulating valve VI and the reflux flow indicating controller VI are respectively connected by signals.

[0091] The top tower pressure control component includes a pressure gauge VII and a pressure indicating controller VII provided at the top of the distillation column, and a regulating valve VII provided on the gas-phase vent pipeline at the top. The pressure gauge VII, the pressure indicating controller VII and the regulating valve VII are respectively connected by signals.

[0092] The reflux drum 4 liquid level control component includes a liquid level gauge VIII and a liquid level indicating controller VIII provided in the reflux drum 4, a top draw flowmeter VIII, a top draw regulating valve VIII and a top draw flow indicating controller VIII provided on the draw pipeline of the reflux drum 4. The liquid level gauge VIII, the liquid level indicating controller VIII, the top draw flowmeter VIII, the top draw regulating valve VIII and the top draw flow indicating controller VIII are respectively connected by signals.

[0093] The reflux temperature control component includes a thermometer IX and a reflux temperature indicating controller IX provided in the condenser 6, and a circulating water return regulating valve IX is provided on the circulating water pipeline of the condenser 6. The thermometer IX, the reflux temperature indicating controller IX and the circulating water return regulating valve IX are respectively connected by signals.

[0094] The tower feed section pressure control component includes a pressure gauge X and a pressure indicating controller X provided below the feed port of the third-stage tower 3, a flowmeter X, a steam regulating valve X and a steam flow indicating controller X provided on the steam pipeline of the reboiler 5 of the third-stage tower 3. The pressure gauge X, the pressure indicating controller X, the flowmeter X, the steam regulating valve X and the steam flow indicating controller X are respectively connected by signals.

[0095] The trend chart of the bottom tower liquid level of the first-stage tower 1 continuously operating for 3 months in this application example is as Figure 3 shown.

[0096] Comparative example

[0097] The difference between this comparative example and the application example is that in this application example, an automatic control system is not used in this comparative example, and manual control and adjustment are performed on each point.

[0098] The trend chart of the bottom tower liquid level of the first-stage tower 1 continuously operating for 3 months in this comparative example is as Figure 4 shown.

[0099] The above application examples and comparative examples were judged and evaluated according to the trichlorosilane product output, trichlorosilane product impurities, and the amplitude of tower liquid level fluctuation of the tower under the same feed load. The evaluation results are shown in Table 1.

[0100] Table 1 Stability evaluation results of application example and comparative example 1

[0101]

[0102] From Table 1, Figure 3 and Figure 4 it can be seen that: through the optimization of the automatic control logic of Example 1, the output and quality of the products of the multi-stage distillation tower have been greatly improved, and the stability of the system has been improved.

[0103] It can be understood that the present utility model is described through some embodiments. Those skilled in the art know that without departing from the spirit and scope of the present utility model, various changes or equivalent substitutions can be made to these features and embodiments. In addition, under the teaching of the present utility model, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present utility model. Therefore, the present utility model is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present application belong to the scope protected by the present utility model.

Claims

1. An automatic control system for multi-stage rectification of polysilicon, characterized in that: The invention comprises three-stage distillation towers, a controller and a control component connected in sequence, wherein the top of the distillation tower is connected to a condenser (6), the bottom of the distillation tower is provided with a reboiler (5), the bottom of the condenser (6) is connected to a reflux tank (4), the bottom of the reflux tank (4) is connected to a reflux pump (7), the reflux pump (7) is connected to the top of the distillation tower of the same stage through a reflux pipeline, the reflux pump (7) of the first-stage tower (1) is connected to the feed inlet of the second-stage tower (2) through a production pipeline, the reflux pump (7) of the second-stage tower (2) is connected to the light component production tank through the production pipeline, and the third-stage tower ( The reflux pump (7) of the second-stage tower (2) is connected to the trichlorosilane extraction tank through an extraction pipeline, the bottom of the second-stage tower (2) is connected to the feed port of the third-stage tower (3) through an extraction pipeline, and the bottom of the third-stage tower (3) is connected to the heavy component storage tank through an extraction pipeline. The control components include a feed flow control component, a steam flow control component, a tower top temperature control component, a tower bottom liquid level control component, a tower top pressure control component, a reflux tank (4) liquid level control component, a reflux temperature control component, and a tower feed section pressure control component. The control components are connected to the controller signal.

2. The automatic control system according to claim 1, wherein: The heating medium pipelines of the reboilers (5) of the first-stage tower (1) and the third-stage tower (3) are connected to the steam pipeline; the top of the first-stage tower (1) is connected to the inlet of the heating medium pipeline of the reboiler (5) of the second-stage tower (2), and the outlet of the heating medium pipeline of the reboiler (5) of the second-stage tower (2) is connected to the condenser (6) of the first-stage tower (1).

3. The automatic control system according to claim 2, characterized in that: The feed flow control component comprises a flow meter I, a feed regulating valve I and a feed flow indicating controller I arranged in a feed pipeline of a first-stage tower (1), wherein the flow meter I, the feed regulating valve I and the feed flow indicating controller I are respectively signal-connected.

4. The automatic control system according to claim 2, characterized in that: The steam flow control assembly comprises a thermometer II and a temperature indicating controller II arranged at a lower position of the stripping section of the first-stage tower (1), a flow meter II, a steam regulating valve II and a steam flow indicating controller II arranged in a heating medium pipeline of a reboiler (5) of the first-stage tower (1), wherein the thermometer II, the temperature indicating controller II, the flow meter II, the steam regulating valve II and the steam flow indicating controller II are respectively signal-connected.

5. The automatic control system according to claim 2, characterized in that: The tower top temperature control assembly comprises a thermometer III and a temperature indicating controller III arranged at the tower tops of the first-stage tower (1) and the second-stage tower (2), and a flowmeter III, a reflux regulating valve III and a reflux flow indicating controller III arranged on the tower top reflux pipelines of the first-stage tower (1) and the second-stage tower (2), wherein the thermometer III, the temperature indicating controller III, the flowmeter III, the reflux regulating valve III and the reflux flow indicating controller III are respectively signal-connected.

6. The automatic control system according to claim 2, characterized in that: The tower bottom liquid level control component comprises a tower bottom liquid level control component I of a first-stage tower (1), a tower bottom liquid level control component II of a second-stage tower (2), and a tower bottom liquid level control component III of a third-stage tower (3).

7. The automatic control system according to claim 6, wherein: The bottom kettle liquid level control component I includes a liquid level gauge IV arranged at the bottom kettle of the first-stage tower (1), a kettle bottom extraction regulating valve IV and a liquid level indicating controller IV arranged on the bottom kettle extraction pipeline of the first-stage tower (1), and the liquid level gauge IV, the kettle bottom extraction regulating valve IV and the liquid level indicating controller IV are respectively connected by signals.

8. The automatic control system according to claim 6, wherein: The bottom kettle liquid level control component II includes a liquid level gauge V and a liquid level indicating controller V arranged at the bottom kettle of the second-stage tower (2), a kettle bottom extraction flowmeter V, a kettle bottom extraction regulating valve V and a kettle bottom extraction flow indicating controller V arranged on the bottom kettle extraction pipeline of the second-stage tower (2), and the liquid level gauge V, the liquid level indicating controller V, the kettle bottom extraction flowmeter V, the kettle bottom extraction regulating valve V and the kettle bottom extraction flow indicating controller V are respectively connected by signals.

9. The automatic control system according to claim 6, wherein: The bottom kettle liquid level control component III includes a liquid level gauge VI and a liquid level indicating controller VI arranged at the bottom kettle of the third-stage tower (3), a reflux flowmeter VI, a reflux regulating valve VI and a reflux flow indicating controller VI arranged on the top reflux pipeline of the third-stage tower (3), and the liquid level gauge VI, the liquid level indicating controller VI, the reflux flowmeter VI, the reflux regulating valve VI and the reflux flow indicating controller VI are respectively connected by signals.

10. The automatic control system according to claim 2, characterized in that: The top pressure control component includes a pressure gauge VII and a pressure indicating controller VII arranged at the top of the distillation column, and a regulating valve VII arranged on the top gas phase vent pipeline, and the pressure gauge VII, the pressure indicating controller VII and the regulating valve VII are respectively connected by signals.

11. The automatic control system according to claim 2, wherein: The reflux drum (4) liquid level control component includes a liquid level gauge VIII and a liquid level indicating controller VIII arranged in the reflux drum (4), a top extraction flowmeter VIII, a top extraction regulating valve VIII and a top extraction flow indicating controller VIII arranged on the extraction pipeline of the reflux drum (4), and the liquid level gauge VIII, the liquid level indicating controller VIII, the top extraction flowmeter VIII, the top extraction regulating valve VIII and the top extraction flow indicating controller VIII are respectively connected by signals.

12. The automatic control system according to claim 2, wherein: The reflux temperature control component includes a thermometer IX and a reflux temperature indicating controller IX arranged in the condenser (6), and a circulating water return regulating valve IX is arranged on the circulating water pipeline of the condenser (6), and the thermometer IX, the reflux temperature indicating controller IX and the circulating water return regulating valve IX are respectively connected by signals.

13. The automatic control system according to claim 2, wherein: The tower feed section pressure control component includes a pressure gauge X and a pressure indicating controller X arranged below the feed port of the third-stage tower (3), a flowmeter X, a steam regulating valve X and a steam flow indicating controller X arranged on the steam pipeline of the reboiler (5) of the third-stage tower (3), and the pressure gauge X, the pressure indicating controller X, the flowmeter X, the steam regulating valve X and the steam flow indicating controller X are respectively connected by signals.

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