Pressure and temperature regulation system and control method

Abstract

The present invention discloses a pressure and temperature regulation system and control method. The present invention includes a medium pipeline, an inlet at the input end of the medium pipeline, a discharge port at the output end, a cooling mixing chamber, a buffer, and a muffler arranged on the medium pipeline in sequence, and a test piece arranged between the buffer and the muffler; the cooling mixing chamber is connected to a cooling water input pipeline system; it also includes a multi-position monitoring system for monitoring the flow, pressure, and temperature signals in the medium pipeline; a controller for adjusting the flow control valve, the temperature control valve, multiple pressure control valves, and multiple back pressure control valves according to the flow, pressure, and temperature signals in the medium pipeline. The system of the present invention increases the adjustment range of pressure and temperature, automatically and intelligently adjusts when the system is running with variable parameters, and automatically controls the process parameters and makes precise adjustments based on multi-contact information feedback without human intervention, so as to ensure the stability and accuracy of the system's variable parameter operation.

Description

Technical Field

[0001] The present invention belongs to the technical field of pressure vessel equipment for centralized or decentralized heating in industry or life, and specifically relates to a pressure and temperature regulating system and a control method. Background Art

[0002] When the existing temperature reduction and pressure reduction device is multi-stage regulated, the pressure is generally regulated by a single pressure control valve + multi-stage pressure reducing orifice plate structure; the temperature is regulated by a throttle valve / throttle device + flow control valve structure; the control system is a single-point control; and there are few system process parameter monitoring points. The existing temperature reduction and pressure reduction device has the following defects:

[0003] 1. When a single pressure control valve is used to adjust the pressure, the pressure adjustment range is limited and the adjustment accuracy is poor; the pressure reduction structure of the pressure control valve + multi-stage pressure reducing orifice is only suitable for systems with stable pressure parameters and small deviations in operating parameters. When the system parameters change greatly, the fixed pressure reducing effect of the pressure reducing orifice cannot be guaranteed, and the pressure adjustment relying solely on the pressure control valve cannot meet the operating requirements;

[0004] 2. Temperature regulation is only guaranteed by the regulation of a single flow control valve, which may result in low regulation accuracy and poor regulation effect;

[0005] 3. The control system is single-point control, the control process is incoherent, the degree of automation is low, and the adjustment effect is poor;

[0006] 4. There are few monitoring points for system process parameters, the feedback information is not accurate enough, and the feedback is delayed. Summary of the invention

[0007] The purpose of the present invention is to solve the deficiencies of the above-mentioned background technology and to provide a pressure and temperature regulation system and a control method.

[0008] The technical solution adopted by the present invention is: a pressure and temperature regulating system, comprising a medium pipeline, an inlet arranged at the input end of the medium pipeline, a discharge port at the output end, a temperature reduction mixing chamber, a buffer, and a muffler arranged on the medium pipeline in sequence, and a test piece arranged between the buffer and the muffler; the temperature reduction mixing chamber is connected to a temperature reduction water input pipeline system; and further comprising

[0009] Multi-position monitoring system, used to monitor the flow, pressure and temperature signals in the medium pipeline;

[0010] The controller is used to adjust the size of a flow control valve, a temperature control valve, multiple pressure control valves, and multiple back pressure control valves according to signals of flow, pressure, and temperature in a medium pipeline.

[0011] A first shut-off valve and a flow control valve are provided between the inlet and the cooling mixing chamber, and the plurality of pressure control valves are provided on the medium pipeline between the flow control valve and the cooling mixing chamber and on the cooling water input pipeline system.

[0012] The multiple pressure control valves include a first pressure control valve, a second pressure control valve and a third pressure control valve, wherein the first pressure control valve and the second pressure control valve are arranged on the medium pipeline between the flow control valve and the temperature reduction mixing chamber.

[0013] The desuperheating water input pipeline system includes a pump, and the desuperheating mixing chamber is connected to the pump via a desuperheating water medium pipeline; a second shut-off valve, a third pressure control valve and a temperature control valve are arranged on the desuperheating water medium pipeline.

[0014] Among them, the medium pipeline contains a mixture of water and water vapor; the cooling water medium pipeline contains liquid water.

[0015] The multiple back pressure control valves are arranged on the medium pipeline between the test piece and the muffler.

[0016] The plurality of back pressure control valves include a first back pressure control valve, a second back pressure control valve, and a third back pressure control valve.

[0017] The multi-position monitoring system comprises:

[0018] A first pressure sensor is arranged on the medium pipeline at the rear end of the first pressure control valve and is used to collect pressure signals;

[0019] A second pressure sensor is arranged on the medium pipeline at the rear end of the second pressure control valve and is used to collect pressure signals;

[0020] A third pressure sensor is provided on the medium pipeline at the front end of the buffer and is used to collect pressure signals;

[0021] A fourth pressure sensor is provided on the test piece and is used to collect pressure signals;

[0022] A first temperature sensor is arranged on the medium pipeline at the front end of the buffer and is used to collect temperature signals;

[0023] A second temperature sensor is provided on the test piece and is used to collect temperature signals;

[0024] A first flow monitoring meter is provided on the test piece and is used to collect flow signals;

[0025] The second flow monitor is arranged on the medium pipeline at the rear end of the flow control valve and is used for collecting flow signals.

[0026] The controller is used to adjust the sizes of the first pressure control valve, the second pressure control valve, the third pressure control valve, the first back pressure control valve, the second back pressure control valve, and the third back pressure control valve according to the pressure signals collected by the first pressure sensor, the second pressure sensor, the third pressure sensor, and the fourth pressure sensor;

[0027] The controller is used to adjust the size of the temperature control valve according to the temperature signals collected by the first temperature sensor and the second temperature sensor;

[0028] The controller is used to adjust the size of the flow control valve according to the flow signals collected by the first flow monitor and the second flow monitor.

[0029] The pressure control valves at the inlet of the medium pipeline input end and the outlet of the medium pipeline output end distribute the pressure according to the pressure reduction ratio ρ=0.546.

[0030] A control method for a pressure and temperature regulating system, comprising controlling the opening and closing of a first shut-off valve and a second shut-off valve according to set conditions; adjusting the sizes of a first pressure control valve, a second pressure control valve, a third pressure control valve, a first back pressure control valve, a second back pressure control valve, and a third back pressure control valve according to pressure signals collected by a first pressure sensor, a second pressure sensor, a third pressure sensor, and a fourth pressure sensor; adjusting the size of a temperature control valve according to temperature signals collected by a first temperature sensor and a second temperature sensor; and adjusting the size of a flow control valve according to flow signals collected by a first flow monitor and a second flow monitor.

[0031] The invention is composed of a shut-off valve, a flow control valve, a pressure control valve, a temperature reducing mixing chamber, a back pressure control valve, a pressure and temperature sensor, a flow monitoring meter and a control system.

[0032] The shut-off valve controls the opening and closing of the system. Suitable stop valves and gate valves are selected to realize the switching function. The signal input point is connected to the central control room or the system operation program, and the system switching operation is automatically controlled according to the set conditions.

[0033] The flow control valve controls the flow of media entering the system. Regulating valves with different structures and pressure levels can be selected as needed to control the flow of media.

[0034] The pressure control valve adjusts the system pressure in stages, and the pressure reduction stage is determined by the difference between the system inlet medium pressure and the system required outlet pressure.

[0035] The cooling mixing chamber consists of a cooling nozzle, cooling water, a flow control valve, a pressure control valve, a switch valve, etc., which are combined to distribute the pressure and flow of the cooling water, and work together to ultimately achieve a cooling effect.

[0036] Multiple back pressure control valves are set according to the pressure level required by the system. Pressure control valves of different levels are used to adjust the system back pressure to ensure the stability and accuracy of the operating parameters.

[0037] A group of pressure sensors is set behind each stage of pressure control valve to accurately monitor the pressure change process; a group of temperature sensors is set at the inlet and outlet of the main pipeline to monitor the temperature changes of the system inlet and outlet; a flow monitoring meter is set at the system inlet to monitor the changes of the medium flow at the system inlet in real time.

[0038] The control system consists of detection elements, transmitters, controllers, actuators and controlled objects. Detection elements and transmitters are used to detect controlled variables and convert detection signals into standard signals. The controller compares the standard signal output by the detection and transmission link with the set value to obtain a deviation signal, calculates the deviation signal according to a certain control law, and sends the calculated output to the actuator. The controller can be implemented with an analog instrument or a digital controller composed of a microprocessor, such as the PID control function module used in DCS and FCS. The actuator is in the final position of the control loop, that is, the final element. The actuator is used to receive the output signal of the controller and control the changes of various technical parameters in the system. When the load of the production process changes or the operating conditions change, the controlled variable of the process is sent to the controller through the detection and transmission of the detection element and the transmitter. After the regular operation of the controller, it is output to the actuator of the regulating valve to change the corresponding technical parameters in the process so that the controlled variable is consistent with the set value.

[0039] The present invention is mainly aimed at the pressure and temperature control system with variable parameter operation, which increases the adjustment range of pressure and temperature, and automatically and intelligently adjusts the system with variable parameters. Without human intervention, it automatically controls the process parameters and makes precise adjustments based on multi-contact information feedback, thereby ensuring the stability and accuracy of the system with variable parameters.

[0040] The present invention sets up intelligent linkage processing of the control system in the system, upgrading the existing single-point independent control to linear continuous control; at the same time, an intelligent calculation module is added to the control system, and human intervention is no longer required when the system changes parameters during operation. The system can automatically control the valve action according to the preset operating curve, adjust the operating parameters by itself, and improve the stability and accuracy of the system operation.

[0041] The present invention adds a multi-bit monitoring system, namely, a pressure sensor, a temperature sensor, and a flow monitor, to the system, which can accurately monitor the change process of variable parameters in the system online in real time, and promptly feed back to the control system, providing accurate data for system operations, while providing data support for precise control of the system, thereby improving the precision of system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic diagram of the system of the present invention.

[0043] Among them, 1-first shut-off valve, 2-second shut-off valve, 3-flow control valve, 4-first pressure control valve, 5-second pressure control valve, 6-third pressure control valve, 7-temperature control valve, 8-first back pressure control valve, 9-second back pressure control valve, 10-third back pressure control valve, 11-pump, 12-cooling mixing chamber, 13-buffer, 14-test piece, 15-muffler, 16-controller, 17-first pressure sensor, 18-second pressure sensor, 19-third pressure sensor, 20-fourth pressure sensor, 21-first temperature sensor, 22-second temperature sensor, 23-first flow monitor, 24-second flow monitor, A-inlet, B-discharge port. DETAILED DESCRIPTION

[0044] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments to facilitate a clear understanding of the present invention, but they do not constitute a limitation on the present invention.

[0045] like Figure 1 As shown, the present invention is a pressure and temperature regulating system, comprising a medium pipeline, an inlet A arranged at the input end of the medium pipeline, a discharge port B at the output end, a temperature reduction mixing chamber 12, a buffer 13, and a muffler 15 arranged in sequence on the medium pipeline, and a test piece 14 arranged between the buffer 13 and the muffler 15; the temperature reduction mixing chamber 12 is connected to a temperature reduction water input pipeline system; and further comprising

[0046] Multi-position monitoring system, used to monitor the flow, pressure and temperature signals in the medium pipeline;

[0047] The controller 16 is used to adjust the flow control valve 3, the temperature control valve 7, multiple pressure control valves, and multiple back pressure control valves according to the signals of the flow, pressure, and temperature in the medium pipeline.

[0048] A first shut-off valve 1 and a flow control valve 3 are provided between the inlet A and the cooling mixing chamber 12, and the plurality of pressure control valves are provided on the medium pipeline between the flow control valve 3 and the cooling mixing chamber 12 and on the cooling water input pipeline system.

[0049] The multiple pressure control valves include a first pressure control valve 4 , a second pressure control valve 5 and a third pressure control valve 6 , wherein the first pressure control valve 4 and the second pressure control valve 5 are arranged on the medium pipeline between the flow control valve 3 and the cooling mixing chamber 12 .

[0050] The desuperheating water input pipeline system includes a pump 11, and the desuperheating mixing chamber 12 is connected to the pump 11 through a desuperheating water medium pipeline; the desuperheating water medium pipeline is provided with a second shut-off valve 2, a third pressure control valve 6 and a temperature control valve 7.

[0051] The multiple back pressure control valves are arranged on the medium pipeline between the test piece 14 and the muffler 15 .

[0052] The plurality of back pressure control valves include a first back pressure control valve 8 , a second back pressure control valve 9 and a third back pressure control valve 10 .

[0053] The multi-position monitoring system comprises:

[0054] The first pressure sensor 17 is arranged on the medium pipeline at the rear end of the first pressure control valve 4 and is used to collect pressure signals;

[0055] The second pressure sensor 18 is arranged on the medium pipeline at the rear end of the second pressure control valve 5 and is used to collect pressure signals;

[0056] The third pressure sensor 19 is arranged on the medium pipeline at the front end of the buffer 13 and is used to collect pressure signals;

[0057] A fourth pressure sensor 20 is provided on the test piece 14 and is used to collect pressure signals;

[0058] A first temperature sensor 21 is provided on the medium pipeline at the front end of the buffer 13 and is used to collect temperature signals;

[0059] A second temperature sensor 22 is provided on the test piece 14 and is used to collect temperature signals;

[0060] A first flow monitor 23, provided on the test piece 14, for collecting flow signals;

[0061] The second flow monitor 24 is arranged on the medium pipeline at the rear end of the flow control valve 3 and is used to collect flow signals.

[0062] The controller 16 is used to adjust the sizes of the first pressure control valve 4, the second pressure control valve 5, the third pressure control valve 6, the first back pressure control valve 8, the second back pressure control valve 9, and the third back pressure control valve 10 according to the pressure signals collected by the first pressure sensor 17, the second pressure sensor 18, the third pressure sensor 19, and the fourth pressure sensor 20;

[0063] The controller 16 is used to adjust the size of the temperature control valve 7 according to the temperature signals collected by the first temperature sensor 21 and the second temperature sensor 22;

[0064] The controller 16 is used to adjust the size of the flow control valve 3 according to the flow signals collected by the first flow monitor 23 and the second flow monitor 24 .

[0065] The pressure control valves at the inlet A at the input end of the medium pipeline and the outlet B at the output end of the medium pipeline distribute the pressure according to a pressure reduction ratio ρ=0.546.

[0066] A control method for a pressure and temperature regulating system, comprising controlling the opening and closing of a first shut-off valve 1 and a second shut-off valve 2 according to set conditions; adjusting the sizes of a first pressure control valve 4, a second pressure control valve 5, a third pressure control valve 6, a first back pressure control valve 8, a second back pressure control valve 9, and a third back pressure control valve 10 according to pressure signals collected by a first pressure sensor 17, a second pressure sensor 18, a third pressure sensor 19, and a fourth pressure sensor 20; adjusting the size of a temperature control valve 7 according to temperature signals collected by a first temperature sensor 21 and a second temperature sensor 22; and adjusting the size of a flow control valve 3 according to flow signals collected by a first flow monitor 23 and a second flow monitor 24.

[0067] Control system operation principle:

[0068] 1. Design and input the required flow, pressure and temperature values;

[0069] 2. Line ①: Compare the actual value Q measured at the flow monitoring point with the designed flow value QF, then

[0070] a: Q = QF ± 1.2t / h, flow control valve 3 does not act and maintains the initial state;

[0071] b: Q>QF+1.2t / h, flow control valve 3 automatically adjusts to reduce the flow area and is fixed at the adjustment position after meeting the flow requirement;

[0072] c: Q<QF-1.2t / h, flow control valve 3 automatically adjusts to increase the flow area and is fixed at the adjustment position after meeting the flow requirement;

[0073] 3. Line ②: Compare the actual value P measured at the pressure signal sampling point with the design input pressure value PF, then

[0074] (1) When the second pressure level ≤ PF < the first pressure level:

[0075] a: P = PF ± 0.15 MPa, the first pressure control valve 4 and the second pressure control valve 5 do not operate and maintain the initial state;

[0076] b: P>PF+0.15MPa, the first pressure control valve 4 is automatically adjusted to reduce the flow area and increase the pressure loss. After the pressure requirement is met, it is fixed in the adjustment position, and the second pressure control valve 5 remains in the fully open state;

[0077] c: P<PF-0.15MPa, the first pressure control valve 4 automatically adjusts to increase the flow area and reduce the pressure loss. After the pressure requirement is met, it is fixed in the adjustment position, and the second pressure control valve 5 remains in the fully open state;

[0078] (2) When the third pressure level ≤ PF < the second pressure level, the first pressure control valve 4 is set to the second pressure level value when the pressure P1 at the first pressure sensor 17 is:

[0079] a: P = PF ± 0.15 MPa, the first pressure control valve 4 and the second pressure control valve 5 do not operate and maintain the initial state;

[0080] b: P>PF+0.15MPa, the second pressure control valve 5 automatically adjusts to reduce the flow area and increase the pressure loss. After the pressure requirement is met, it is fixed at the adjustment position, and the first pressure control valve 4 is fine-tuned for compensation;

[0081] c: P<PF-0.15MPa, the second pressure control valve 5 automatically adjusts to increase the flow area and reduce the pressure loss. After the pressure requirement is met, it is fixed at the adjustment position, and the first pressure control valve 4 is fine-tuned for compensation;

[0082] 4. Line ③: Compare the actual value T measured at the temperature signal sampling point with the designed input temperature value TF, then

[0083] a: T = TF ± 3 °C, the temperature control valve 7 does not move and maintains the initial state;

[0084] b: T>TF+3℃, the temperature control valve 7 automatically adjusts to increase the flow area and the cooling water volume, and is fixed at the adjustment position after the temperature requirement is met;

[0085] c: T<TF-3℃, the temperature control valve 7 automatically adjusts to reduce the flow area and the amount of cooling water, and is fixed at the adjustment position after the temperature requirement is met;

[0086] 5. During the operation of the system, the first back pressure control valve 8, the second back pressure control valve 9 and the third back pressure control valve 10 are always in a continuous automatic adjustment state.

[0087] The working principle of the system of the present invention:

[0088] The control of system pressure, temperature and flow is regulated by the corresponding control valves, and the control area of ​​each valve is set according to the changes in the system operating parameters. When the system operating parameters meet the operating setting parameter range of a certain valve, the system automatically sends instructions to the valve actuator to drive the valve to move up and down, changing the medium flow through the valve, thereby changing the flow, pressure and temperature of the medium passing through the valve.

[0089] Working principle of control system:

[0090] The control system receives and converts the monitoring signals sent back by each monitoring unit in the monitoring system, compares them with the initial setting values ​​in the system, calculates the deviation signals according to certain control rules, and then issues adjustment instructions suitable for the system operation. The instructions are transmitted to each execution unit to guide the execution unit to take action, thereby changing the operating parameters of each adjustment system to ensure the normal and stable operation of the system.

[0091] Because the adjustment units of the system are connected in series, the action of one unit will affect the action of other control units. Therefore, the control process is a linear continuous change process until the final parameters are determined and the system starts to operate stably. The adjustment process is an intelligent automatic adjustment process.

[0092] The present invention changes the single, small-range adjustable pressure and temperature control system in the existing system into a composite, large-range adjustable pressure and temperature control system, thereby increasing the operating range of system parameters and improving the adjustment capability of the system; meeting the customer's multi-parameter, large-range adjustable operation requirements, improving product utilization, reducing repeated equipment purchases, and reducing corporate procurement costs.

[0093] The present invention sets up intelligent linkage processing of the control system in the system design, and upgrades the original single-point independent control to linear continuous control; at the same time, an intelligent calculation module is added to the control system, and human intervention is no longer required when the system variable parameters are running, thereby improving the stability and accuracy of the system operation; at the same time, the efficiency of the system variable parameter debugging is also improved, avoiding the possibility of errors during manual debugging and saving manual debugging costs.

[0094] The present invention adds a multi-bit monitoring system, namely, a pressure sensor, a temperature sensor, and a flow monitor, to the system, which can accurately monitor the change process of variable parameters in the system online in real time and in a timely manner, and provide timely feedback to the control system, so that technical personnel can understand the operation status of the system in a timely and accurate manner; at the same time, it also provides strong data support for the real-time calculation and precise control of the system, thereby improving the precision of the system operation.

[0095] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A pressure and temperature regulating system, comprising a medium pipeline, characterized in that: An inlet (A) provided at the input end of the medium pipeline, a discharge port (B) provided at the output end, a cooling mixing chamber (12), a buffer (13), and a muffler (15) provided in sequence on the medium pipeline, and a test piece (14) provided between the buffer (13) and the muffler (15); the cooling mixing chamber (12) is connected to a cooling water input pipeline system; and further includes Multi-position monitoring system, used to monitor the flow, pressure and temperature signals in the medium pipeline; A controller (16) is used to adjust the flow control valve (3), the temperature control valve (7), a plurality of pressure control valves, and a plurality of back pressure control valves according to signals of flow, pressure, and temperature in the medium pipeline; A first shut-off valve (1) and a flow control valve (3) are provided between the inlet (A) and the cooling mixing chamber (12); the plurality of pressure control valves are provided on the medium pipeline between the flow control valve (3) and the cooling mixing chamber (12) and on the cooling water input pipeline system; The multiple pressure control valves include a first pressure control valve (4), a second pressure control valve (5) and a third pressure control valve (6), wherein the first pressure control valve (4) and the second pressure control valve (5) are arranged on the medium pipeline between the flow control valve (3) and the temperature reduction mixing chamber (12); the multiple back pressure control valves are arranged on the medium pipeline between the test piece (14) and the muffler (15); The multi-position monitoring system comprises: A first pressure sensor (17) is arranged on the medium pipeline at the rear end of the first pressure control valve (4) and is used to collect pressure signals; A second pressure sensor (18) is arranged on the medium pipeline at the rear end of the second pressure control valve (5) and is used to collect pressure signals; A third pressure sensor (19) is arranged on the medium pipeline at the front end of the buffer (13) and is used to collect pressure signals; a fourth pressure sensor (20), disposed on the test piece (14) and used for collecting pressure signals; A first temperature sensor (21) is arranged on the medium pipeline at the front end of the buffer (13) and is used to collect temperature signals; A second temperature sensor (22) is disposed on the test piece (14) and is used to collect a temperature signal; A first flow monitor (23), disposed on the test piece (14) and used for collecting flow signals; The second flow monitor (24) is arranged on the medium pipeline at the rear end of the flow control valve (3) and is used to collect flow signals.

2. The pressure and temperature regulating system according to claim 1, characterized in that: The desuperheating water input pipeline system comprises a pump (11); the desuperheating mixing chamber (12) is connected to the pump (11) via a desuperheating water medium pipeline; the desuperheating water medium pipeline is provided with a second shut-off valve (2), a third pressure control valve (6) and a temperature control valve (7).

3. The pressure and temperature regulating system according to claim 1, characterized in that: The plurality of back pressure control valves include a first back pressure control valve (8), a second back pressure control valve (9) and a third back pressure control valve (10).

4. The pressure and temperature regulating system according to claim 1, characterized in that: The controller (16) is used to adjust the sizes of the first pressure control valve (4), the second pressure control valve (5), the third pressure control valve (6), the first back pressure control valve (8), the second back pressure control valve (9), and the third back pressure control valve (10) according to the pressure signals collected by the first pressure sensor (17), the second pressure sensor (18), the third pressure sensor (19), and the fourth pressure sensor (20); The controller (16) is used to adjust the size of the temperature control valve (7) according to the temperature signals collected by the first temperature sensor (21) and the second temperature sensor (22); The controller (16) is used to adjust the size of the flow control valve (3) according to the flow signals collected by the first flow monitor (23) and the second flow monitor (24).

5. The pressure and temperature regulating system according to claim 1, characterized in that: The pressure control valves at the inlet (A) of the medium pipeline input end and the outlet (B) of the medium pipeline output end distribute the pressure according to the pressure reduction ratio ρ=0.

546.

6. The control method of the pressure and temperature regulating system according to claim 3, characterized in that: The method comprises controlling the opening and closing of a first shutoff valve (1) and a second shutoff valve (2) according to set conditions; adjusting the sizes of a first pressure control valve (4), a second pressure control valve (5), a third pressure control valve (6), a first back pressure control valve (8), a second back pressure control valve (9), and a third back pressure control valve (10) according to pressure signals collected by a first pressure sensor (17), a second pressure sensor (18), a third pressure sensor (19), and a fourth pressure sensor (20); The size of the temperature control valve (7) is adjusted according to the temperature signals collected by the first temperature sensor (21) and the second temperature sensor (22); the size of the flow control valve (3) is adjusted according to the flow signals collected by the first flow monitor (23) and the second flow monitor (24).

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