Device and method for reducing energy consumption of ionic liquid desulfurization system

Abstract

The invention discloses a device and a method for reducing energy consumption of an ionic liquid desulfurization system. The device comprises a desulfurization tower, a lean and rich amine heat exchanger, a desorption tower, a lean amine cooler, a lean amine storage tank, a desorbed gas condenser and a gas-liquid separator. Meanwhile, a flue gas flowmeter and an inlet flue gas SO2 concentration analyzer are arranged on a flue gas inlet pipeline of the desulfurization tower; and a lean amine flow meter and a rich amine flow meter are respectively arranged at the outlet of the lean amine spraying pump and the outlet of the rich amine conveying pump. According to the amount of flue gas entering the desulfurizing tower and the concentration of SO2 in the flue gas, the spraying amount of lean amine entering the desulfurizing tower is adjusted in real time; according to the invention, the moderate and reduced spraying of lean amine entering the desulfurization tower is realized, the total amount of lean amine consumed by spraying and the generation amount of rich amine in the desulfurization process are reduced, and the rich amine liquid with stable SO2 concentration is obtained. Meanwhile, the amount of rich amine entering the desorption tower is stabilized, and stable high-concentration SO2 desorbed gas is obtained. According to the invention, the steam consumption of the ionic liquid desulfurization system is reduced, and the energy conservation of the lean amine spray pump and the rich amine delivery pump is realized.

Description

Technical Field

[0001] The invention relates to the technical field of flue gas desulfurization, and in particular to a device and method for reducing energy consumption of an ion liquid desulfurization system. Background Art

[0002] In the field of flue gas desulfurization, ionic liquid desulfurization is the most efficient desulfurization method. However, it also has the following defects and shortcomings: 1. The traditional ionic liquid desulfurization system adopts a constant or relatively constant amount of lean amine spraying. When dealing with fluctuating sulfur-containing flue gas with changing sulfur content, the total amount of lean amine spray consumed in the desulfurization process is extremely large, and the pump operation energy consumption is high.

[0003] 2. When dealing with fluctuating sulfur-containing flue gas with changing sulfur content, the traditional ionic liquid desulfurization system produces a huge amount of rich amine during the desulfurization process, and the steam consumption during the desorption and regeneration of the rich amine is large, resulting in extremely high energy consumption.

[0004] 3. When dealing with fluctuating sulfur-containing flue gas with changing sulfur content, the traditional ion liquid desulfurization system has unstable SO2 concentration in the rich amine liquid, and the amount of high-concentration SO2 desorption gas generated during regeneration fluctuates greatly, which greatly affects the recovery and utilization of high-concentration SO2 desorption gas in subsequent processes.

[0005] The above defects of the traditional ionic liquid desulfurization system have seriously hindered the promotion and application of the ionic liquid desulfurization system. Summary of the invention

[0006] In order to solve the above technical problems, the present invention designs a device and method for reducing the energy consumption of an ionic liquid desulfurization system.

[0007] The present invention adopts the following technical solution: A device for reducing energy consumption of an ionic liquid desulfurization system, comprising a desulfurization tower, a lean-rich amine heat exchanger, a desorption tower, a lean amine cooler, a lean amine storage tank, a desorption gas condenser, and a gas-liquid separator; The lean amine liquid in the lean amine storage tank is transported to the desulfurization tower by a lean amine spray pump for spray desulfurization; the rich amine liquid produced after desulfurization is preheated by a rich amine delivery pump through a lean-rich amine heat exchanger and then sent to a desorption tower for desorption and regeneration; the high-concentration SO2 desorbed gas discharged from the top of the desorption tower is cooled and condensed by a desorbed gas condenser and separated by a gas-liquid separator, and then discharged from the exhaust port at the top of the gas-liquid separator to an external process for use; the desorbed lean amine liquid in the tower kettle of the desorption tower is cooled by a lean-rich amine heat exchanger and then sent to a lean amine cooler by a lean amine delivery pump for further cooling, and then sent to the lean amine storage tank for use in the desulfurization tower; A flue gas flow meter and an inlet flue gas SO2 concentration analyzer are provided on the flue gas inlet pipeline of the desulfurization tower.

[0008] Preferably, the lean amine spray pump adopts a variable frequency pump, and the amount of lean amine sprayed into the desulfurization tower can be adjusted by frequency conversion. The outlet pipe of the lean amine spray pump is equipped with a lean amine flowmeter to display and measure the amount of lean amine sprayed into the desulfurization tower.

[0009] Optionally, a reflux pipe to the lean amine storage tank may be provided on the outlet pipe of the lean amine spray pump (before the lean amine flowmeter), and the reflux volume may be used to assist in regulating the lean amine spraying amount into the desulfurization tower.

[0010] Optionally, the flue gas flow meter and the inlet flue gas SO2 concentration analyzer can also be arranged in front of the inlet flue gas pipeline of the desulfurization tower, or on other equipment and pipelines that can accurately measure the amount of SO2 entering the desulfurization tower.

[0011] As a priority, when the flue gas flowmeter and the inlet flue gas SO2 concentration analyzer are set at a distance from the desulfurization tower inlet, the device and method set a delayed execution of the control and adjustment of the lean amine spray amount entering the desulfurization tower, and the delay time t = the internal volume of the system between the installation location of the flue gas flowmeter and the inlet flue gas SO2 concentration analyzer and the desulfurization tower inlet ÷ the flue gas operating flow rate.

[0012] Preferably, the desulfurization tower rich amine delivery pump adopts a variable frequency pump, and the delivery amount of the pump can be adjusted by frequency conversion. The outlet pipeline of the desulfurization tower rich amine delivery pump is equipped with a rich amine flowmeter to display and measure the rich amine delivery amount of the rich amine delivery pump. The rich amine delivery amount of the rich amine delivery pump is adjusted and delivered according to the average value of the lean amine spraying amount entering the desulfurization tower displayed by the lean amine flowmeter, ensuring the relative stability of the rich amine desorption amount delivered to the desorption tower by the rich amine delivery pump.

[0013] Preferably, the relative stability of the SO2 content of the rich amine and the relative stability of the rich amine delivery amount ensure the stability of the SO2 amount in the rich amine entering the desorption tower. Therefore, the amount of high-concentration SO2 gas desorbed by the desorption tower must be relatively stable, which greatly facilitates the treatment and reuse of this part of the high-concentration SO2 gas in subsequent processes.

[0014] Optionally, an amine liquid recovery section is provided at the upper portion of the desulfurization tower, and amine liquid entrained in the flue gas is recovered by circulating spraying through an external amine recovery tank and an amine recovery pump.

[0015] Preferably, an outlet flue gas SO2 concentration analyzer is provided on the outlet pipe of the desulfurization tower to detect and display the residual SO2 concentration in the outlet flue gas of the desulfurization tower in real time, thus realizing real-time monitoring of the desulfurization performance of the desulfurization tower and effectively ensuring the reliable operation of the desulfurization system.

[0016] Preferably, the lean amine delivery pump and the reflux liquid pump are both variable frequency pumps, and the delivery volume of the pump can be adjusted by frequency conversion.

[0017] A method for reducing energy consumption of an ionic liquid desulfurization system, the method comprising: adjusting the amount of lean amine spraying into the desulfurization tower according to the amount of flue gas Q entering the desulfurization tower measured by a flue gas flow meter at the inlet of the desulfurization tower and the SO2 concentration c in the flue gas entering the desulfurization tower measured by an inlet flue gas SO2 concentration analyzer, that is, adjusting the amount of lean amine spraying into the desulfurization tower in real time according to the fluctuation of the amount of SO2 in the sulfur-containing process flue gas entering the desulfurization tower, the lean amine spraying amount into the desulfurization tower V=Q×c×a, wherein V is the amount of lean amine spraying into the desulfurization tower, Q is the amount of flue gas entering the desulfurization tower, c is the SO2 concentration of the flue gas entering the desulfurization tower, and a is the amine liquid spray coefficient, which is determined by the properties of the amine liquid used. The SO2 content in the desulfurized rich amine obtained by spraying in this way is relatively stable.

[0018] Preferably, the desulfurization tower lean amine spraying volume V is adjusted according to the flue gas volume Q entering the desulfurization tower and the SO2 concentration c of the flue gas, and the adjustment method is automatic adjustment through instrument interlocking or manual tracking and adjustment based on the calculated value displayed by the control system.

[0019] The beneficial effects of the present invention are as follows: (1) by arranging a flue gas flow meter and a flue gas SO2 concentration analyzer on the flue gas inlet pipe of the desulfurization tower, the real-time measurement of the flue gas volume and the flue gas SO2 concentration of the desulfurization tower is realized. Furthermore, the real-time fluctuation of the SO2 amount in the sulfur-containing process flue gas entering the desulfurization tower can be tracked in real time; (2) by linking the lean amine spraying amount entering the desulfurization tower with the flue gas flow entering the desulfurization tower and the flue gas SO2 concentration, the lean amine spraying amount entering the desulfurization tower is adjusted in real time according to the fluctuation of the SO2 amount in the flue gas entering the desulfurization tower. The lean amine liquid is sprayed appropriately on the SO2 amount in the flue gas entering the desulfurization tower, which greatly reduces the total amount of lean amine spray consumed during the desulfurization process, reduces the operating power consumption of the lean amine spray pump, and ensures the relative stability of the rich amine sulfur concentration after desulfurization. At the same time, the amount of rich amine produced during the desulfurization process is reduced, the total amount of rich amine required for desorption by the system is reduced, and the steam consumption of the desorption tower is greatly reduced; (3) By controlling the rich amine delivery amount according to the average value of the lean amine spraying amount entering the desulfurization tower displayed by the lean amine flowmeter, the rich amine desorption amount delivered to the desorption tower by the rich amine delivery pump is relatively stable. (4) The relative stability of the sulfur content of the rich amine after desulfurization and the relative stability of the rich amine desorption amount entering the desorption tower jointly achieve the relative stability of the SO2 content in the rich amine liquid entering the desorption tower. Therefore, the amount of high-concentration SO2 gas desorbed from the desorption tower is also relatively stable. It is beneficial to the subsequent process to recycle the high-concentration SO2 desorption gas; (5) The relative stability of the sulfur content of the rich amine after desulfurization and the relative stability of the rich amine desorption amount entering the desorption tower jointly achieve the stability of the steam consumption of the desorption tower, which is beneficial to the stable and efficient operation of the external steam supply pipeline network, and greatly reduces the operating energy consumption of the ionic liquid desulfurization system with flue gas sulfur content changing in the desulfurization tower. The extent of reducing the energy consumption of the ionic liquid desulfurization system varies according to the fluctuation of the sulfur content of the flue gas entering the desulfurization tower. For a fluctuating sulfur-containing process flue gas ionic liquid desulfurization system with a maximum instantaneous SO2 amount entering the desulfurization tower ÷ average SO2 amount = 10, the steam consumption, power consumption of the rich amine delivery pump and the lean amine spray pump of the present invention are about 1 / 10 of those of the traditional ionic liquid desulfurization system, which greatly reduces the operating energy consumption of the ionic liquid desulfurization system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the present invention; Figure 2 is a flue gas volume fluctuation curve diagram in the flue gas containing sulfur in this embodiment; Figure 3 is a graph of SO2 concentration in fluctuating sulfur-containing process flue gas in this embodiment; Figure 4 is a graph showing the SO2 content in the fluctuating sulfur-containing process flue gas in this embodiment; In the figure: 1. desulfurization tower, 2. lean and rich amine heat exchanger, 3. desorption tower, 4. lean amine cooler, 5. lean amine storage tank, 6. desorption gas condenser, 7. gas-liquid separator, 8. reboiler, 9. amine recovery tank, 10. rich amine delivery pump, 11. lean amine delivery pump, 12. lean amine spray pump, 13. amine recovery pump, 14. reflux liquid pump, 15. flue gas flow meter, 16. inlet flue gas SO2 concentration analyzer, 17. lean amine flow meter, 18. rich amine flow meter, 19. outlet flue gas SO2 concentration analyzer. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described in detail below through specific embodiments and in conjunction with the accompanying drawings: like Figure 1 As shown, a device for reducing energy consumption of an ionic liquid desulfurization system comprises a desulfurization tower 1, a lean-rich amine heat exchanger 2, a desorption tower 3, a lean amine cooler 4, a lean amine storage tank 5, a desorption gas condenser 6, a gas-liquid separator 7, a reboiler 8, and an amine recovery tank 9; The lean amine liquid in the lean amine storage tank 5 is transported to the desulfurization tower 1 for spray desulfurization by the lean amine spray pump 12; the rich amine liquid produced after desulfurization is sent to the desorption tower 3 for desorption and regeneration after being preheated by the lean-rich amine heat exchanger 2 by the rich amine delivery pump 10; the high-concentration SO2 desorbed gas discharged from the top of the desorption tower 3 is cooled and condensed by the desorbed gas condenser 6 and separated by the gas-liquid separator 7, and then discharged from the exhaust port at the top of the gas-liquid separator 7 to the external process for use; the desorbed lean amine liquid in the tower kettle of the desorption tower 3 is first cooled by the lean-rich amine heat exchanger 2, and then sent to the lean amine cooler 4 by the lean amine delivery pump 11 for further cooling, and then sent to the lean amine storage tank 5 for use by the desulfurization tower 1; The flue gas inlet pipe of the desulfurization tower 1 is provided with a flue gas flow meter 15 and an inlet flue gas SO2 concentration analyzer 16 .

[0022] The liquid separated by the gas-liquid separator 7 is transported back to the desorption tower for spraying by the reflux pump 14. The upper part of the desulfurization tower is provided with an amine liquid recovery section, which is circulated and sprayed by an external amine recovery tank 9 and an amine recovery pump 13 to recover the amine liquid entrained in the flue gas.

[0023] A reboiling section is arranged at the lower part of the kettle of the desorption tower 3, and the lean amine liquid after desorption is reboiled through the reboiler 8 and then returned to the desorption tower 3 for sufficient desorption.

[0024] The lean amine spray pump 12 adopts a variable frequency pump, and the outlet pipe of the lean amine spray pump 12 is equipped with a lean amine flow meter 17.

[0025] The rich amine delivery pump 10 adopts a variable frequency pump, and the outlet pipeline of the rich amine delivery pump 10 is equipped with a rich amine flowmeter 18.

[0026] An outlet flue gas SO2 concentration analyzer 19 is provided on the outlet flue gas pipeline of the desulfurization tower 1. The lean amine delivery pump 11 and the reflux liquid pump 14 use variable frequency pumps.

[0027] A method for reducing energy consumption of an ion liquid desulfurization system, the method comprising: adjusting the lean amine spraying amount entering the desulfurization tower according to the flue gas volume Q entering the desulfurization tower measured by a flue gas flow meter at the inlet of the desulfurization tower and the SO2 concentration c in the flue gas entering the desulfurization tower measured by an inlet flue gas SO2 concentration analyzer, that is, adjusting the lean amine spraying amount entering the desulfurization tower in real time according to the fluctuation of the SO2 amount in the sulfur-containing process flue gas entering the desulfurization tower, the lean amine spraying amount entering the desulfurization tower V=Q×c×a, wherein V is the lean amine spraying amount of the desulfurization tower, Q is the flue gas volume entering the desulfurization tower, c is the SO2 concentration of the flue gas entering the desulfurization tower, and a is the amine liquid spraying coefficient, which is determined by the properties of the amine liquid used.

[0028] Example: For a fluctuation period of 10 hours, the maximum peak SO2 content is 3000Nm 3 / h, average SO2 content is 500Nm 3 / h fluctuating sulfur-containing process flue gas. The flue gas volume fluctuation curve, flue gas SO2 concentration curve, and flue gas SO2 content curve are as follows: Figure 2-4 shown.

[0029] Using the traditional ionic liquid desulfurization method, the desulfurization tower lean amine spraying volume is 3000×am 3 / h (where a is the amine liquid spray coefficient, which is determined by the properties of the amine liquid used in the ionic liquid desulfurization system). The total lean amine spray volume in one cycle is 3000a×10=30000a m 3 , the amount of rich amine produced after desulfurization is 30000a m 3 The SO2 concentration in the rich amine fluctuates dramatically with the change of the SO2 content in the sulfur-containing process flue gas. The amount of high-concentration SO2 gas obtained after desorption in the desorption tower also fluctuates dramatically with the SO2 content curve in the sulfur-containing process flue gas.

[0030] According to an embodiment of the present invention, Figure 1 As shown: Before the sulfur-containing process flue gas enters the desulfurization tower 1, the flue gas flow rate Q and the SO2 concentration c in the flue gas that will enter the desulfurization tower 1 are measured in real time in advance by the flue gas flow meter 15 and the inlet flue gas SO2 concentration analyzer 16 installed in front of the desulfurization tower. Therefore, the amount of SO2 that will enter the desulfurization tower can be calculated in advance by the control system (SO2 amount = Q×c).

[0031] The control system adjusts the operating frequency of the lean amine spray pump 12 according to the received flue gas flow Q and flue gas SO2 concentration c entering the desulfurization tower 1, and controls the lean amine spray amount entering the desulfurization tower 1 according to the formula: lean amine spray amount entering the desulfurization tower V=Q×c×a (where V is the lean amine spray amount of the desulfurization tower, Q is the flue gas volume entering the desulfurization tower, c is the SO2 concentration of the flue gas entering the desulfurization tower, and a is the amine liquid spray coefficient determined by the properties of the amine liquid used). After spray desulfurization, rich amine with a relatively stable SO2 concentration is obtained.

[0032] Since the fluctuation period of the sulfur-containing process flue gas is 10 hours, the average SO2 content is 500Nm 3 / h, so the total amount of SO2 entering the desulfurization tower in one cycle is 500*10=5000Nm 3 / h. During the whole desulfurization process of this device, the lean amine liquid is sprayed in appropriate amount according to the amount of SO2 entering the desulfurization tower 1 for desulfurization. Therefore, the total amount of lean amine sprayed into the desulfurization tower 1 in a 10-hour fluctuation cycle is 5000a m 3 . At the same time, 5000a m 3 of rich amine solution.

[0033] The desulfurized rich amine liquid produced after the lean amine liquid is sprayed and desulfurized in the desulfurization tower 1 is delivered by the rich amine delivery pump 10 according to the average value of the lean amine spraying amount into the desulfurization tower shown by the lean amine flowmeter 17 (5000a÷10=500a m 3 / h), the rich amine liquid is heated by the poor-rich amine heat exchanger 2 and then sent to the desorption tower 3 for desorption at a constant flow rate. The rich amine flow meter 18 displays the flow rate. An approximately stable high-concentration SO2 desorption gas (5000÷10=500 Nm 3 / h).

[0034] The lean amine solution (500 a m 3 / h), first cooled by the lean-rich amine heat exchanger 2, then sent to the lean amine cooler 4 by the lean amine delivery pump 11 for further cooling, and then sent to the lean amine storage tank 5 for continued use.

[0035] The sulfur-containing process flue gas is discharged from the top of desulfurization tower 1 after being desulfurized by lean amine spraying in desulfurization tower 1 and amine recovery in the upper part of the desulfurization tower.

[0036] The outlet flue gas SO2 concentration analyzer 19 arranged on the outlet flue gas duct of the desulfurization tower 1 detects the residual SO2 concentration in the flue gas after desulfurization in real time, thereby realizing the monitoring and tracking of the desulfurization effect of the desulfurization tower.

[0037] Through the above process, the total amount of lean amine spray consumed in one flue gas cycle (10h) is 5000am. 3 , while generating 5000a m 3 Compared with the 30000a m3 The total amount of lean amine spraying and 30000a m 3 Compared with the rich amine desorption capacity, the power consumption of the lean amine spray pump and the rich amine delivery pump of the present invention, as well as the steam consumption consumed in the rich amine desorption process, are both about 16.7% of that of the traditional ionic liquid desulfurization system, which greatly reduces the operating energy consumption of the ionic liquid desulfurization system.

[0038] At the same time, since the sulfur content of the rich amine and the amount of rich amine desorbed into the desorption tower are relatively constant, a stable high-concentration SO2 desorbed gas (wherein the amount of SO2 is 500 Nm 3 / h).

[0039] The above-described embodiment is only a preferred solution of the present invention and does not limit the present invention in any form. There are other variations and modifications without exceeding the technical solution described in the claims.

Claims

1. A device for reducing energy consumption of an ionic liquid desulfurization system, Its characteristics are: It comprises a desulfurization tower (1), a lean-rich amine heat exchanger (2), a desorption tower (3), a lean amine cooler (4), a lean amine storage tank (5), a desorption gas condenser (6), and a gas-liquid separator (7); The lean amine liquid in the lean amine storage tank (5) is transported to the desulfurization tower (1) by a lean amine spray pump (12) for spray desulfurization; the rich amine liquid generated after desulfurization is preheated by the rich amine delivery pump (10) through the lean and rich amine heat exchanger (2) and then transported to the desorption tower (3) for desorption and regeneration; the high-concentration SO 2 The desorbed gas is cooled and condensed by the desorbed gas condenser (6) and separated into gas and liquid by the gas-liquid separator (7), and then discharged from the top exhaust port of the gas-liquid separator (7) to be used in an external process. The desorbed lean amine liquid in the tower kettle of the desorber (3) is cooled by the lean-rich amine heat exchanger (2) and then sent to the lean amine cooler (4) by the lean amine delivery pump (11) for further cooling, and then sent to the lean amine storage tank (5) for use in the desulfurization tower. The flue gas inlet pipe of the desulfurization tower (1) is provided with a flue gas flow meter (15) and an inlet flue gas SO 2 Concentration Analyzer (16).

2. A device for reducing energy consumption of an ionic liquid desulfurization system according to claim 1, Its characteristics are: The liquid after gas-liquid separation in the gas-liquid separator (7) is transported back to the desorption tower (3) by a reflux liquid pump (14) for spraying.

3. A device for reducing energy consumption of an ionic liquid desulfurization system according to claim 1, Its characteristics are: An amine liquid recovery section is provided at the top of the desulfurization tower, and amine liquid entrained in the flue gas is recovered by circulating spraying through an external amine recovery tank (9) and an amine recovery pump (13).

4. A device for reducing energy consumption of an ionic liquid desulfurization system according to claim 1, Its characteristics are: A reboiling section is arranged at the lower part of the kettle of the desorption tower (3), and the desorbed lean amine liquid is reboiled through a reboiler (8) and then returned to the desorption tower (3) for full desorption.

5. A device for reducing energy consumption of an ionic liquid desulfurization system according to claim 1, Its characteristics are: The lean amine spray pump (12) adopts a variable frequency pump, and the outlet pipe of the lean amine spray pump (12) is equipped with a lean amine flow meter (17).

6. A device for reducing energy consumption of an ionic liquid desulfurization system according to claim 5, Its characteristics are: The rich amine delivery pump (10) is a variable frequency pump. The outlet pipe of the rich amine delivery pump (10) is equipped with a rich amine flow meter (18). The rich amine delivery pump (10) delivers rich amine liquid according to the average value of the lean amine spraying amount measured by the lean amine flow meter (17).

7. A device for reducing energy consumption of an ionic liquid desulfurization system according to claim 1, Its characteristics are: The outlet flue gas pipeline of the desulfurization tower (1) is provided with an outlet flue gas SO 2 Concentration Analyzer (19).

8. A device for reducing energy consumption of an ionic liquid desulfurization system according to claim 2, Its characteristics are: The lean amine delivery pump (11) and the reflux liquid pump (14) are variable frequency pumps.

9. A method for reducing energy consumption of an ionic liquid desulfurization system according to any one of claims 1 to 8, Its characteristics are: The method is as follows: according to the flue gas flow rate Q of the desulfurization tower and the inlet flue gas SO measured by the flue gas flow meter (15) at the inlet of the desulfurization tower, 2 The concentration analyzer (16) measures the SO in the flue gas entering the desulfurization tower. 2 concentration c, and adjust the lean amine spraying amount entering the desulfurization tower (1), that is, according to the SO 2 The amount of lean amine spraying into the desulfurization tower (1) is adjusted in real time to prevent fluctuations in the amount of lean amine. The amount of lean amine spraying into the desulfurization tower V = Q × c × a, where V is the amount of lean amine spraying into the desulfurization tower, Q is the amount of flue gas into the desulfurization tower, and c is the amount of SO in the flue gas into the desulfurization tower. 2 concentration, a is the amine solution spray coefficient, which is determined by the properties of the amine solution used.

10. A method for reducing energy consumption of an ionic liquid desulfurization system according to claim 9, Its characteristics are: The desulfurization tower lean amine spraying volume V is adjusted according to the flue gas volume Q entering the desulfurization tower and the SO2 concentration c of the flue gas. The adjustment method adopts automatic adjustment through instrument interlocking or manual tracking and adjustment based on the calculated value displayed by the control system.

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