Series heat exchanger coupling process control device

Abstract

The utility model discloses a series heat exchanger coupling process control device, and particularly relates to a control circuit, which comprises a liquid oxygen evaporation heat exchanger, a main heat exchanger and a liquid air subcooler, wherein a first temperature sensor is communicated with a pipeline between a first input end at the bottom of the liquid oxygen evaporation heat exchanger and a first output end of the liquid air subcooler in series; a second temperature sensor and a liquid air regulating valve are sequentially communicated with a pipeline at the second output end of the liquid air subcooler in series; and a first pressure sensor is communicated with a pipeline between the first input end of the main heat exchanger and the first output end of the top of the liquid oxygen evaporation heat exchanger in series. By selecting rapid and reliable process detection points and operation control variables, through rapid response of an auxiliary process control loop in a cascade control mode and based on the basic principle of process design, the state of each heat exchange material of the heat exchanger is effectively controlled to be kept in a design range, and the process safety of liquid oxygen in the heat exchange process is ensured.

Description

Technical Field

[0001] The utility model relates to a control circuit, in particular to a series heat exchanger coupling process control device. Background Art

[0002] Most of the heat exchangers used in the low-temperature cold end unit of the air separation plant are aluminum plate-fin heat exchangers. If there is a condition of liquid oxygen evaporation heat transfer in the aluminum plate-fin heat exchanger, there are clear safety requirements for the oxygen evaporation pressure. As the oxygen evaporation pressure decreases, in the channels of the aluminum plate-fin heat exchanger, during the oxygen evaporation process, some harmful substances, mainly hydrocarbons, will show a decrease in solubility, and even these harmful substances will precipitate. Therefore, during the oxygen evaporation process, they will accumulate on the surface of the heat transfer fins. As the liquid oxygen evaporation process continues, the gas-liquid mixture during the evaporation process will scour the harmful substances on the fins, which may cause combustion and explosion accidents. Therefore, during the low liquid oxygen evaporation process, a bath-type heat exchanger is used, that is, the aluminum plate-fin heat exchanger is immersed below the liquid oxygen level, so that during the low-pressure liquid oxygen evaporation process, the oxygen heat transfer channels are always in a state of being immersed in liquid oxygen, which can effectively avoid the precipitation of harmful substances and the resulting safety risks under low-pressure liquid oxygen evaporation conditions. If a non-bath-type heat exchanger is used during the liquid oxygen heat transfer process, only by ensuring that the liquid oxygen has not undergone a phase change in the channels of the aluminum plate heat exchanger of the oxygen heat exchanger and maintaining a uniform liquid oxygen state can the safe operation of the oxygen heat exchanger during the heat transfer process be ensured.

[0003] Due to different pressure requirements for oxygen products at the downstream product demand end of the air separation plant, taking the non-ferrous smelting industry as an example, the pressure of the oxygen product required by customers is lower than 3 bar(a). In order to ensure the safety of the aluminum plate heat exchanger in the second stage during the oxygen evaporation process, a bath-type liquid oxygen evaporator is used. However, the process liquid oxygen coming from the front end is in a state of relatively large subcooling degree. In order to recover the cold energy and improve the operation efficiency of the device, a heat exchanger connected in series with the liquid oxygen evaporator is set up. The saturated liquid air after heat exchange with the heat source of the liquid oxygen evaporator is used to reheat the relatively low-temperature subcooled liquid oxygen and enter the liquid oxygen evaporator. At the same time, the liquid air in a saturated state at the outlet of the liquid oxygen evaporator is heat-exchanged with the subcooled liquid oxygen, and the liquid air is gradually cooled to a subcooled state and sent to downstream process equipment to achieve energy conservation. The liquid oxygen and liquid air in the liquid oxygen evaporator are both in a saturated state, and the liquid air at the outlet of the liquid air subcooler is in a subcooled state. The liquid oxygen entering the liquid oxygen evaporator is close to the saturated state, but must not reach the saturated state to avoid any evaporation of the liquid oxygen in the aluminum fins of the heat transfer channels of the liquid air subcooler. The liquid oxygen will be controlled to enter the liquid oxygen evaporator in a pure liquid state, and at the same time, the cold energy of the liquid oxygen is recovered as much as possible. Summary of the Utility Model

[0004] The purpose of the utility model is to provide a series heat exchanger coupling process control device to solve the above problems.

[0005] In order to achieve the above purpose, the utility model provides the following technical solutions:

[0006] A series of heat exchanger coupling process control device, including liquid oxygen evaporation heat exchanger, main heat exchanger and liquid air subcooler, where:

[0007] A first temperature sensor is connected in series on the pipeline communicating between the first input end at the bottom of the liquid oxygen evaporation heat exchanger and the first output end of the liquid air subcooler;

[0008] A second temperature sensor and a liquid air regulating valve are connected in series in sequence on the pipeline of the second output end of the liquid air subcooler;

[0009] A first pressure sensor is connected in series on the pipeline communicating between the first input end of the main heat exchanger and the first output end at the top of the liquid oxygen evaporation heat exchanger;

[0010] A flow meter is fixedly installed on the first output end of the main heat exchanger, and an electromagnetic flow meter is fixedly installed on the second input end.

[0011] Preferably, the second output end of the main heat exchanger communicates with the second input end of the liquid oxygen evaporation heat exchanger.

[0012] Preferably, the second output end of the liquid oxygen evaporation heat exchanger communicates with the first input end of the liquid air subcooler.

[0013] Preferably, the data output ends of the flow meter and the first temperature sensor are connected to the input end of the PID control loop on the electromagnetic flow meter.

[0014] Preferably, the data output end of the second temperature sensor is connected to the input end of the PID control loop on the liquid air regulating valve.

[0015] In the above technical solution, a series of heat exchanger coupling process control device provided by the present utility model has the following beneficial effects:

[0016] 1. By designing a process cascade control loop, the liquid oxygen temperature at the outlet of the liquid air subcooler is effectively controlled so that it is not higher than the saturation temperature under the oxygen evaporation pressure in the liquid oxygen bath type evaporation heat exchanger, ensuring that the liquid oxygen remains in a pure liquid state during the heat exchange process of the liquid air subcooler and avoiding the phenomenon of oxygen evaporation in the liquid oxygen heat exchange channel of the liquid air subcooler.

[0017] 2. The detection variable of the main loop of this process control is the temperature of the liquid oxygen leaving the subcooler. Through this PID control loop of the temperature at the outlet of the liquid oxygen subcooler, the output is used as the set compensation for the pressurized air flow of the system heat exchange heat source. This compensation is set within a certain control range to avoid overshoot.

[0018] 3. According to the change of the gas consumption load of the actual product, the temperature at the outlet of the liquid oxygen subcooler can be effectively controlled. At the same time, the heat exchange material heat source is used to increase the air flow rate, which is automatically controlled according to the heat exchange of the product oxygen with which it exchanges heat. Based on the ratio of the two fluid streams for heat exchange, the DCS system automatically controls according to the ratio of the heat exchange materials. Then, the main process control loop output of the temperature at the outlet of the liquid oxygen subcooler compensates for the setting of the increased air flow rate for heat exchange to achieve precise automatic control. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present utility model. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings.

[0020] Figure 1 Control schematic diagram provided by an embodiment of the present utility model

[0021] Figure 2 Process control loop diagram provided by an embodiment of the present utility model.

[0022] Description of the reference numerals in the drawings:

[0023] E01, main heat exchanger; E07, liquid oxygen evaporation heat exchanger; E17, liquid air subcooler; TIC1563, first temperature sensor; TI1564, second temperature sensor; FV1563, liquid air regulating valve; PI1563, first pressure sensor; FI1511, flow meter; FIC1563, electromagnetic flow meter. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] In order to enable those skilled in the art to better understand the technical solutions of the present utility model, the following will further introduce the present utility model in detail in conjunction with the drawings.

[0025] As Figure 1 shown, a series heat exchanger coupling process control device includes a liquid oxygen evaporation heat exchanger E07, a main heat exchanger E01, and a liquid air subcooler E17, wherein:

[0026] A first temperature sensor TIC1563 is connected in series on the pipeline communicating between the first input end at the bottom of the liquid oxygen evaporation heat exchanger E07 and the first output end of the liquid air subcooler E17;

[0027] A second temperature sensor TI1564 and a liquid air regulating valve FV1563 are connected in series on the pipeline at the second output end of the liquid air subcooler E17;

[0028] A first pressure sensor PI1563 is connected in series on the pipeline communicating between the first input end of the main heat exchanger E01 and the first output end at the top of the liquid oxygen evaporation heat exchanger E07.

[0029] A flowmeter FI1511 is fixedly installed on the first output end of the main heat exchanger E01, and an electromagnetic flowmeter FIC1563 is fixedly installed on the second input end.

[0030] The second output end of the main heat exchanger E01 is communicated with the second input end of the liquid oxygen evaporation heat exchanger E07.

[0031] The second output end of the liquid oxygen evaporation heat exchanger E07 is communicated with the first input end of the liquid air subcooler E17.

[0032] The data output ends of the flowmeter FI1511 and the first temperature sensor TIC1563 are connected to the input end of the PID control loop on the electromagnetic flowmeter FIC1563.

[0033] The data output end of the second temperature sensor TI1564 is connected to the input end of the PID control loop on the liquid air regulating valve FV1563.

[0034] Combined Figure 2 As shown, by designing the main process control loop of the first temperature sensor TIC1563, that is, through the accurate PID control calculation of the DCS, the working pressure detected in real time by the liquid oxygen evaporation heat exchanger E07 is used. Through this real-time detected pressure data, through process calculation, this calculation is also carried out inside the DCS through the calculation model formula. The temperature at which the liquid air subcooler E17 enters the liquid oxygen evaporation heat exchanger E07 that should be controlled in real time is firmly and accurately controlled. The change in the pressure of the liquid oxygen evaporation heat exchanger E07 under the interference of oxygen evaporation is monitored by the first pressure sensor PI1563, and calculations are carried out in real time. The calculated oxygen evaporation temperature control index is used as the set value of the first temperature sensor TIC1563 for automatic setting.

[0035] The core process control is the liquid oxygen temperature at the outlet of the liquid air subcooler E17. Since it takes a certain amount of time for the heat exchange process conditions to change, unlike indicators such as flow rate and pressure that are sensitive, the output calculated by the PID control loop of the first temperature sensor TIC1563 is used as the compensation for the given value of the forward-flow pressurized air flow rate in the heat exchanger. Through the change of this core process index, the flow rate compensation after PID operation is given to the calculated given value of the forward-flow air flow rate, enabling completely accurate control of the first temperature sensor TIC1563. A range needs to be set for the compensation amount of the control output of the first temperature sensor TIC1563 cascaded to the electromagnetic flowmeter FIC1563 to avoid overshoot, which is also a basic principle of cascade control design. Based on the adjustment range of the forward-flow pressurized air flow rate, the corresponding output range of the first temperature sensor TIC1563 is ((-5000 to 5000 Nm3 / h)). At the same time, the PID operation tuning parameters of the first temperature sensor TIC1563 are optimized. For the temperature automatic control with a large lag in the process, the integral time adopts the process response time. In this process, the integral time is 250 s, and the derivative setting is appropriately increased. Through the lead feedforward control based on the basic principle of heat balance of the heat exchange unit and the optimization of the main process PID control loop parameters, combined with the setting of the output control range, the control deviation caused by pure lag in the process is completely avoided. Based on the heat balance principle, the synchronous setting of the pressurized air flow rate after the product load changes basically achieves the matching of the heat exchange materials, ensuring that the temperature of the liquid oxygen leaving the subcooler is basically within the control range. Through the PID main process control loop of the temperature, accurate compensation is achieved, and the set temperature is completely controlled at the optimal process value, which not only ensures process safety but also ensures that the liquid air subcooler recovers the cold energy of the liquid oxygen as much as possible, achieving the purpose of energy conservation.

[0036] Only some exemplary embodiments of the present invention have been described by way of illustration above. Undoubtedly, for those of ordinary skill in the art, the described embodiments can be modified in various different ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and description are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A tandem heat exchanger coupling process control device, characterized in that It includes a liquid oxygen evaporation heat exchanger (E07), a main heat exchanger (E01), and a liquid air subcooler (E17), where: A first temperature sensor (TIC1563) is connected in series on the pipeline communicating between the first input end at the bottom of the liquid oxygen evaporation heat exchanger (E07) and the first output end of the liquid air subcooler (E17); A second temperature sensor (TI1564) and a liquid air regulating valve (FV1563) are successively connected in series on the pipeline of the second output end of the liquid air subcooler (E17); A first pressure sensor (PI1563) is connected in series on the pipeline communicating between the first input end of the main heat exchanger (E01) and the first output end at the top of the liquid oxygen evaporation heat exchanger (E07); A flow meter (FI1511) is fixedly installed on the first output end of the main heat exchanger (E01), and an electromagnetic flow meter (FIC1563) is fixedly installed on the second input end; 2. The series heat exchanger coupling process control device according to claim 1, wherein The second output end of the main heat exchanger (E01) communicates with the second input end of the liquid oxygen evaporation heat exchanger (E07); 3. The serial heat exchanger coupling process control device according to claim 1, characterized in that, The second output end of the liquid oxygen evaporation heat exchanger (E07) communicates with the first input end of the liquid air subcooler (E17); 4. A series heat exchanger coupling process control device according to claim 1, characterized in that, The data output ends of the flow meter (FI1511) and the first temperature sensor (TIC1563) are connected to the input end of the PID control loop on the electromagnetic flow meter (FIC1563); 5. The tandem heat exchanger coupling process control device according to claim 1, characterized in that, The data output end of the second temperature sensor (TI1564) is connected to the input end of the PID control loop on the liquid air regulating valve (FV1563).

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