JPS5965700A - Control method of lpg gasification facility - Google Patents

Abstract

PURPOSE:To have stable supply of gas by controlling the pressure in a main gas pipe, where propane gas and butane gas converge, which are sent from a propane gasification facility and butane gasification facility, respectively, in such a way as following up the change of load. CONSTITUTION:A requisite fuel rate signal FFD from a gas user is added as a Field Forward signal to the output of an adiustment meter 30 for the pressure in the main gas pipe so as to obtain a total gas requisite rate signal A. Setting rate-of-flow signal DP1, DP2 and DB1, DB2 for the gas rates to be borne by each carburettor in the gasification facilities are obtained by setting this signal A according to the command ratio signal alpha, which specifies the ratio of the rate of flow of propane gas to that of butane gas in the main gas pipe. These signals are added as a Field Forward signal to the liquid level control system and pressure control system, and now the pressure in the main gas pipe can be controlled at a high speed as well as the ratio of mixture gas in the main pipe controlled to a specified value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a gas main pipe connected to a debt source by combining the nolopane gas obtained from the Grono9 vaporization equipment that vaporizes propane liquid and the butane gas obtained from the butane vaporization equipment that vaporizes butane liquid. This invention relates to a control method for LPG vaporization equipment that leads to.

Conventionally, when controlling LPG vaporization equipment to keep the pressure in the main gas pipe constant against load fluctuations, the detection signal of the pressure in the main gas pipe was fed back ('c+' was the pressure reduction immediately before the main gas pipe). A feedback control system is configured to control the valve, and the pressure C in the evaporating drum of the vaporizer generated by the control of this pressure reducing valve is controlled by feedback control for each to compensate for force fluctuations and liquid level fluctuations. It formed a system. However, in such a control method, when pressure fluctuation occurs in the main gas pipe, the pressure reducing valve is controlled and then the
(The disadvantage of this is that it often takes a considerable amount of time before the control of 11 is carried out.Especially when the LPG vaporization equipment is close to the thermal power plant and there is one-on-one correspondence, the load can be reduced in the event of a power transmission line accident.) FCB (F
AST CUT BACK) and #, LRB (LO
Since there are severe load fluctuations such as AD RUN BACK), it is necessary to quickly follow the load fluctuations and perform control, and in such cases, conventional feedback control is rarely able to control the load. Therefore, the applicant has developed a control system that fully controls the pressure reducing valve immediately before the main gas tank, a pressure control system that controls the pressure inside the evaporation drum of the vaporizer, and a level control system that controls the liquid level inside the evaporation drum. We proposed the mll (iH+ method), which enables quick control by giving the fuel demand flow rate command signal from the engine as a feedforward signal (6). According to this control method, the Pressure fluctuations in the main pipe can be suppressed.When implementing this control method, if there is only one carburetor, the fuel demand flow command signal from the demand source can be directly transmitted to each control via a fan or a function generator. However, in reality, there are almost no vaporizers that consist of a single vaporizer, especially for LPG whose main components are zolopane and butane. In this case, it is necessary to not only control the pressure inside the main gas pipe at a constant level, but also to control the ratio of the flow rates of propane gas and butane gas flowing into the main gas line at a constant level. There is.

In such a case, even if the requested fuel flow rate command signal from the demand source is directly applied to the control system of each vaporization facility, it is not possible to perform the desired control.

Generally, the ratio of slag liquid and butane liquid that LPG vaporization equipment receives is not constant, so in order to properly consume the LPG received by the next receiving date, it is necessary to supply it to the demand source.
It is necessary to set the mixing ratio of the gas to be used appropriately depending on the ratio of the volume of the received Noropan liquid to the amount of the butane liquid. However, the mixing ratio of this gas cannot be set arbitrarily, but must be set appropriately within a range that allows each vaporizer to operate stably. In particular, when a thermosiphon type vaporizer is used as the vaporizer, if the gas flow 1 sent out from each vaporizer falls below a certain value +ik, stable operation will not be possible, so the mixing ratio should be set. When performing this, care must be taken to ensure that the load of each carburetor does not fall below the minimum stable load.In this case, the range of mixing ratios that are allowed for stable operation of each vaporizer is It will change depending on the required gas flow rate.

However, since the total gas required flow rate changes frequently, it is impossible to change the mixing ratio setting 111 using the setting device in response to changes in the total gas required flow rate.

When the set value of the mixing ratio is constant, if the mixing ratio of the gas in the main gas pipe is controlled using the set mixing ratio as the target value, if the total required gas flow rate fluctuates significantly, one of the vaporizers will The load may fall below the minimum stable load or exceed the maximum load, and when such a situation occurs, it becomes impossible to stably supply gas.

An object of the present invention is to provide an LPG vaporization facility that follows load fluctuations in an LPG vaporization facility in which sulfur gas and butane gas obtained from a professional gasification facility and a butane vaporization facility, respectively, are combined and guided to a main gas pipe. In addition to quickly controlling the pressure in the main gas pipe, it is possible to control the mixing ratio of noropan gas and butane gas in the main gas pipe to a predetermined value while always satisfying the conditions for stable operation of the vaporizers of each vaporization equipment. The purpose of this invention is to propose a control method for LPG vaporization equipment.

The control method of the present invention vaporizes the propane liquid discharged from the pro-mother liquid tank using a thermosiphon type vaporizer having an evaporator and a 9-ram tray, and supplies zolopane gas to the propane gas supply pipe. Zolopane vaporization equipment and butane vaporization equipment that vaporizes the butane liquid discharged from the butane liquid tank using a thermosiphon type vaporizer different from the thermosiphon type vaporizer (9) and supplies butane gas to the butane gas supply piping. 7R boil-off gas in the slag/mother solution tank and the mail-off gas in the butane liquid tank are supplied to the middle of the slag gas supply pipe and butane gas supply pipe, respectively. In an LPG vaporization facility equipped with a supply pipe and a gas main/vent which combines the nolopane gas and butane gas supplied through the propane gas supply pipe and the butane gas supply pipe, respectively, and supplies the gas to the demand source, the following (a) is carried out. By carrying out the above process, the pressure in the main gas pipe is controlled and the total mixing ratio of zolopane gas and butane gas in the main gas pipe is controlled to a predetermined value.

(a) Using the detection signal of the pressure in the main gas pipe as a 74-dpak number, a gas required flow rate command signal that commands the flow rate of gas to be flowed into the main gas pipe in order to maintain the pressure in the main gas pipe at a set value. A single-element control system is configured to output a fuel demand flow rate command signal from the demand source as a feed (10) forward signal to the gas demand flow rate command signal to obtain a total gas demand flow rate command signal.

(b) The maximum gas flow rate obtained from each vaporizer of the Pro-Mon vaporization equipment and the butane vaporization equipment and the minimum gas flow rate that must be extracted from each vaporizer in order to operate each vaporizer of both vaporization equipment stably. The maximum value and minimum value of the mixing ratio are calculated from the above-mentioned recommended flow rate to obtain a maximum ratio signal and a minimum ratio signal.

(c) Compare the set ratio signal from the ratio setter for setting the mixing ratio with the maximum ratio signal and the minimum ratio signal, and if the set ratio signal is larger than the maximum ratio signal, set the maximum ratio signal. and when the set ratio signal is smaller than the maximum ratio signal and larger than the minimum ratio signal, select the set ratio signal, and when the set ratio signal is smaller than the minimum ratio signal, select the minimum ratio signal. This signal is used as a command ratio signal that determines the mixing ratio.

b) Allocate the total gas demand original sound command signal according to the command ratio signal to obtain the zero/mother gas a demand flow rate command No. 1H and the butane gas total demand flow sewing command No. I.

(e) Detect the flow rate of the boil-off gas supplied to the propane gas supply pipe and the butane gas supply pipe, respectively, to obtain a propane boil-off gas flow signal and a butane boil-off gas flow signal, and determine the total required flow rate of the pro-gun gas. By subtracting the nolopane gal off gas flow rate signal and the butane boil off gas flow rate signal from the command signal and the butane gas total required current command signal, respectively, a propane gas required flow rate command signal for the propane gas vaporization equipment and a butane gas required flow rate command for the butane vaporization equipment are obtained. Get a signal.

(f) Distribute the slag/'P gas demand flow rate command signal and the butane gas required flow rate command signal to each vaporizer of the solopane vaporization equipment and each vaporizer of the butane vaporization equipment, respectively, and generate a set flow rate command signal for each vaporizer. I ↓ Serve.

(g) Control the flow rate of gas flowing out from each vaporizer based on the detection signal of the flow rate of gas flowing out from each vaporizer of the 1itl vaporization equipment and the butane vaporization equipment and the set flow rate command signal for each vaporizer. do.

(e) The amount of inflow of professional liquid and butane liquid into the evaporating drums of both vaporizing equipment is controlled so that the liquid level in the evaporating drums of each vaporizer of the above-mentioned Noropane vaporizing equipment and butane vaporizing equipment is maintained at the set level. The set flow rate command signal for the corresponding vaporizer is added as a feedforward signal to each level control system to control the liquid level in the evaporation drum of each vaporizer.

(S) The set flow rate command signal for each vaporizer of the noropane vaporization equipment and the butane vaporization equipment is given to a function generator to obtain the set flow rate command signal of the heat medium for the corresponding vaporizer from the function generator, and the heat medium is Is the setting flow rate command signal applicable to the vaporizer glue? It is added as a feedforward signal to the control system that controls the flow rate of heat medium supplied to each vaporizer, and the flow rate of heat medium to each vaporizer is controlled to maintain the pressure in the evaporation drum of each vaporizer at a set value. do.

The control method of the present invention will be explained in detail below with reference to the drawings.

Figure 1 shows -(13
) This is a system flow diagram showing an example of Yang Cheng. In the figure, ■ is the Zoro Gun vaporization equipment, ■ is the butane vaporization equipment, and ■ is the main gas pipe connected to the demand light. The solopane vaporization equipment (2) is equipped with a zoropane liquid tank IP, and the propane liquid in this tank IP is supplied to two thermosiphon type vaporizers 3P1 and 3p2 through a dispensing pump 2P. vaporizer 3
P1 and 3p2 are evaporation drums 4P1 and 4P2, respectively.
and reboilers (heat exchangers) 5P1 and 5P2 forming a thermosiphon-type circulation system between the evaporation drum and these evaporation drums.
, and is supplied through the payout Inf2P.
The liquid is introduced into the evaporation drums 4P1 and 4P2 through flow control valves VL-P1 and VL-P2. In these vaporizers, a propane liquid is introduced into an evaporating drum from a proton liquid tank, is ssolled into the drum, heated by a regairer, and brought into direct contact with gas rising in the evaporating drum. As a result, a portion of the liquid introduced from the propane liquid tank into the evaporation drum is vaporized,
Unvaporized liquid collects at the bottom of the evaporation drum. The liquid at the bottom of the evaporating drum is sent to the finisher by the action of a thermosiphon (14), where it is indirectly heated by a heating medium. The heated Zoro-Gun liquid becomes a gas-liquid mixed phase state and is introduced into the evaporation drum again. In this way, the heat of the liquid and gas introduced into the evaporation drum from the grate is absorbed. It is used to vaporize and raise the temperature of Noropan liquid supplied from the liquid tank into the evaporation drum. Most of the vaporized gas is delivered from the top of the evaporator drum.

In the example shown in Figure 1? Hot water is used as a heat medium for heating, and hot water is supplied from the hot water tank 6P through the hot water ponnoa P through the flow control valves VW-PI and VW-P2.
It has been introduced into Rehydra 5P1 and 5P2 respectively through. The hot water discharged from the υNN shields P1 and 5P2 is returned to the hot water heater 8P and reheated.

The gas sent out from the upper part of the evaporation drums 4P1 and 4P2 passes through the superheaters 9P1 and 9P2, respectively, and is superheated to a predetermined knitting density, and then passes through the pressure reducing valves va-pi and Va-.
It is supplied to the propane gas supply pipe i 0P through p2. Hot water supplied through hot water pongua P is introduced into the heat exchangers of superheaters 9P1 and 9p2 via flow rate control valves Vs-P+ and VB-P2, respectively, and the hot water flowing out from these superheaters 'lpi and 9P2 is is returned to the hot water heater 8P.

Flow rate transmitters 11P1 and 11P2 are provided in the pipes on the inlet side of the flow rate control valves VL-PI and vL-P2, respectively.
Pro 4 liquid flow rate detection signals FL-P1 and F"L-P2 indicating the flow rate of the pro/mother liquid introduced into p2 are obtained.Furthermore, the inlet 1 of the flow rate regulating valves Vw-p1 and vw-P2 are obtained.
Flow rate transmitters 12P1 and 12P2 are provided in the 1111 pipe, and hot water flow detection signals F are sent from these transmitters, respectively.
W-P1 and FW-P2 are obtained. Furthermore, the pressure reducing valve va-
Flow rate transmitter 13P1 is installed on the outlet side passage of p+ and VO-P2.
and 13P2 are provided, and flow rate detection signals FG-P1 and FG-P2 are obtained from these transmitters, respectively.

The evaporation drums 4p+ and 4P2 are provided with pressure detectors 14P1 and 14P2 and liquid level V-pel detectors 15P1 and 15P2, and these detectors output drum internal pressure detection signals PD-Pi and PD-P2 and liquid level, respectively. Detection signals LD-1 and LD-P2 are obtained. Also superheater 9
Temperature detector 16P on the gas piping on the outlet side of P1 and 9p2
1 and 16P2 are provided, and gas temperature detection signals TIIG-P1 and TIIG-P2 are obtained from these detectors.

A pipe 17P for taking out the gale-off gas (hereinafter referred to as BOG) is connected to the upper part of the Noropan liquid tank IP, and this pipe is connected to the BOG compressor 1sp. Compressor 18
It is supplied to the middle of the Zoro Gun gas supply pipe 10p through the Noropane liquid tank compressed by P and the Pro-Sen7 BOG supply pipe 19p. Professional mother Boa child 1m size '1
A flow rate transmitter 20P is provided at 19p, and a BOG flow rate detection signal FIIOG-P is obtained from this transmitter.

Butane vaporization equipment ■ pays out 11% of the butane liquid tank? hmm! 2
B. Vaporizers 3B1 and 3B2 consisting of evaporation drums 4B1 and 4B2 and repoiler Sat and 5B2, hot water tank 6B% hot water tank 7' 7B% hot water heater 8Bs superheater 9n+ + 982, and the above-mentioned professional and mother vaporization equipment. are configured similarly. Each part and each detection signal of this butane vaporization equipment are given the same reference numerals by replacing the suffixes P1 and P2 of the code indicating the equivalent (17) part and detection signal of the zolopane vaporization equipment with B1 and B2, respectively. The explanation will be omitted.

Did it occur in the butane liquid tank IB? Illoff gas is tube 1
7B, BOG compressor 18B and Zotan BOG supply distribution v1
The butane gas is supplied to the middle of the butane gas supply pipe 10B through 9B.

Grono-4 gas and butane gas supplied through the solopane and butane gas supply pipes 10p and 10n of the slag vaporization equipment I and the butane vaporization equipment ■ are combined and introduced into the gas main pipe ■, to meet the demand for LPG gas. Supplied. A pressure detector 21 is provided in the gas main pipe (2), and a gas main pipe pressure detection signal PM is obtained from this detector.

In the LPG vaporization equipment shown in FIG.
1 and 3P2 into evaporation drums 4Pi and 4p2. Zoronof introduced into evaporation drums 4P1 and 4P2
The liquid is vaporized by the above-mentioned action, and the vaporized Pro/IP
After being superheated through superheaters 911 and 9P2, the gas is led to the solopane gas supply pipe 10p.

Also, what about Noropan that occurred in the Noropan liquid tank IP?
The oil-off gas BOG is pressurized by the compressor 18p and supplied to the middle of the propane gas supply distribution 110P.

Similarly, the butane liquid in the butane liquid tank IB is pumped to the evaporating drums 4B1 and 4 of the vaporizers 3B1 and 382 by the pump 2B.
It is introduced into B2 and vaporized, superheated by superheaters 981 and 9B2, and then led to butane gas supply pipe 10B. Further, the butane boil-off gas BOG generated in the butane liquid tank IB is pressurized through the compressor 18B and supplied to the middle of the butane gas supply pipe 10B.

Propane gas supply piping 10p and butane gas supply amount'#
Propane gas in 10a and! The tank gas joins and flows into the main gas pipe m, and is supplied to the gas demand of thermal power plants and the like.

Referring to FIG. 2, there is shown an example of the configuration of a control system when the LPG vaporization equipment of FIG. 1 is controlled by the method of the present invention.
In FIG. 2, PI means a proportional integrator, and f(x) means a function generator. In FIG. 2, numeral 30 is a controller constituting a single element control system for controlling the pressure inside the main gas pipe. Feedback has been provided.

The subtractor 31 calculates the deviation between the gas main bone pressure pM and the set value PM8, and supplies it to the proportional integrator 32.
is a gas request 1#, M that commands the gas flow rate in the gas main pipe necessary to make the deviation between the gas main bone pressure and the set value zero.
:Outputs a command signal. 33 is an adder, which adds the fuel request #t from the gas demand light and the amount command signal FFD to the gas request juxtaposition command signal obtained from the controller 30 as a feedforward signal to obtain a total gas request flow rate command signal. Output A.

The total gas ammonium water flow rate command signal A is input to a multiplier 34 whose multiplier is a command ratio signal α that commands the ratio between the nolopane gas flow rate and the butane gas flow rate in the gas master, and is input to the output side of the multiplier 34. A total required flow rate command signal AP=αA of slag and mother gas is obtained. This signal AP is input as a subtracted number to a subtracter 35 which uses the signal A as its subtracted number. The subtractor 35 subtracts the nolopane gas a required flow rate command signal Ap from the total gas required flow rate command signal A to obtain the butane gas total required flow rate command signal AB.
-(1-α)A is output.

The total required flow rate command signal AP for slag gas is a subtracter 3 that uses the propane boil-off gas flow rate signal FIIOG as a subtractor.
6 is input as the minuend, and the butane gas total required flow rate command signal AB is input as the butane gas flow rate signal Fmoa-
It is input as the minuend to a subtracter 37 which uses tt as the subtrahend. The subtractor 36 receives the Zoropan gas total demand flow command signal A.
From P to Noro/Sendail off gas flow rate detector F'ao
The subtractor 37 subtracts OP and outputs the required gas flow rate command signal Cp for the gasification equipment.
Tongue gas total required flow rate command signal AB color! A butane gas required flow rate command signal CB for the butane vaporization equipment is output by subtracting the tangoil off gas flow detection signal FBOG-B.

The required gas flow rate command number CP for the NORO/9N vaporization equipment is input to a multiplier 40 that uses the distribution ratio β as a multiplier, and from the multiplier 40 the setting for the first vaporizer 3P+ of the PRO/Mother vaporization equipment is input. Flow rate command signal (21) DPI-βCP is obtained. Further, this No. 16 DPI is input as a subtractor to a subtracter 41 having the signal CP as a subtractive, and a set flow rate command signal DP2-(1-β)Cp for the second carburetor 3P2 is obtained from the subtracter 41.

On the other hand, against butane vaporization equipment! The tonne gas demand command signal CB is input to a multiplier 42 with the distribution ratio γ as a multiplier, and from the multiplier 42 the first vaporization 53n of the butane vaporization equipment is inputted.
Set flow rate command signal DB1 for +: rCB is obtained. Further, this signal I) a+ is input to a subtracter 43 whose subtractive is the above-mentioned number H CB, and from the subtracter 43, a set flow rate command signal DB2-(1-γ)CB for the second vaporizer 382 of the butane vaporization equipment is input. is obtained.

The above distribution ratios β and γ are the proportions of gas dispersion to be borne by the two vaporizers, the sulfuric acid vaporization equipment (1) and the butane vaporization equipment (2), respectively. When the lid is equally distributed between two vaporizers, β=γ;0.5.

(22
) The set flow rate command signal DPT is the gas flow 1?1i111111j system 51P that controls the flow rate of gas sent out from the first vaporizer through the signal limiter 50P1 that limits the upper limit of the signal.
1 as a setting signal, and a liquid flow rate control system 52P1 that controls the flow rate of the propane liquid flowing into the evaporating drum 4P1 so as to maintain the liquid level in the evaporating drum 4P1 of the first vaporizer at the set value. , a pressure control system 5 that controls the flow rate of hot water supplied to the IJ g-in 5P1 of the first vaporizer so as to maintain the pressure inside the evaporation drum 4111 at a set value.
3P1 as a feedforward signal.

The gas flow rate control system 51P1 includes a subtractor 51a, a proportional integrator 51b, and a function generator 51e, and operates a pressure reducing valve VG to zero the deviation between the set flow rate command signal DPI and the propane gas flow rate detection signal FCi-P1. - Control P1.

The liquid flow rate control system 52P1 includes a subtractor 52a and a proportional integrator 52.
b, an adder/subtractor 52c, a proportional integrator 52d1, and a function generator 52e. 1-Liquid level detection signal T from P1
Subtract JD-P1 and output a deviation signal.

In order to account for this deviation, the proportional integrator 52b outputs a zero/yan liquid flow rate command signal that commands the necessary professional/yan liquid flow rate, and inputs this command signal to the adder/subtractor 52c. The power (1 subtractor 52c) adds the set flow rate command signal I) p+ to the command signal to calculate the desired flow rate of the pro-gun liquid to be supplied into the evaporating drum JPi, and also calculates the required flow rate of the pro-gun liquid to be supplied into the evaporating drum JPi. The difference between the required flow rate of Noronone liquid and the actual flow rate is output by subtracting the Grono-4 liquid flow rate detection signal FL-PI, which indicates the actual flow rate of Pro-Mother liquid, from the signal. The proportional integrator 52d determines the amount of slag and slag liquid required to maintain the slag and slag liquid surrounding level in the evaporating drum 4m'1 at the set value based on the deviation No. 1 inputted from the adder/subtractor 52c. A liquid flow rate correction signal indicating the amount of correction is given to the function generator 52e. The function generator 52e outputs a valve operation signal indicating the amount of operation of the flow control valve VL-Pi based on the correction signal obtained from the proportional integrator 52d. By this operation signal, the flow acid adjustment 3PVL
-p+ is operated to maintain the liquid level in the evaporation drum 4P1 at the set value.

The pressure control system 53P1 includes a subtracter 53a and a proportional axis divider 53.
b, consists of an adder/subtractor 53C1, a proportional divider 53d1, and function generators 53e, 53f, and the subtracter 53a receives the detection signal PD-PI of the pressure in the evaporating drum 4P1 and its setting signal p.
,, 8-Proportional integrator 5 that accounts for the deviation from P1
3b is the evaporating drum 4P based on the output of this subtracter 53m.
5 points of VZ error required to maintain the pressure inside the i at the set value
Outputs a hot water flow rate command signal that commands the hot water flow rate. The function generator 53f calculates a hot water flow rate setting signal indicating the flow rate of hot water to the reboiler 5p+ based on the set flow rate signal DPI, and inputs the output signal from the function generator 53f to the adder/subtractor 53c. Adder/subtractor 53e is proportional integrator 53
Adding the hot water flow rate setting signal obtained from the function generator 53f to the hot water flow rate command signal obtained from b, calculates the flow rate of hot water to be supplied to the reboiler 5P1, and calculates the actual flow rate of hot water from the signal of the required flow rate. The hot water flow rate detection signal F'
By subtracting w-p+, the deviation between the required flow rate of hot water and the actual flow rate is output. Proportional integral (25) gi>53d is a function of the hot water flow rate command signal indicating the amount of correction of the hot water flow rate necessary to maintain the pressure in the evaporating drum 4P1 at the set value based on the deviation signal given from the adder/subtractor 53c. It is given to the generator 53e. The function generator 53s outputs a valve operation signal indicating the operation amount of the flow rate restriction valve V, -, i based on the correction signal.

The control valve Vw-p+ is operated by this operation signal, and the pressure within the evaporating drum 'lp+ is maintained at a set value.

For the first vaporizer 3P1 of the propane vaporization equipment, gas temperature control is further performed to control the flow rate of hot water supplied to the superheater 9P1 so as to maintain the gas temperature i at the outlet of the superheater 9P1 at a set value. A system 54P1 is provided. This control system consists of a subtracter 54a, a proportional integrator 54b, and a function generator 54c.
Setting signal TIIGII indicating the setting value of the outlet gas temperature of j
-P1 is input. The subtracter 54m is a setting signal'
The gas temperature detection signal T8Q-P1 is subtracted from rscs-p+ to output a deviation signal, and the proportional integrator 54b calculates the amount of gas temperature correction required to make this deviation signal zero. The degree correction signal is manually input to the function generator 54c. The function generator 54c is a control valve V8-Pj necessary to change the gas temperature by a correction amount.
Outputs a valve operation signal indicating the amount of operation. The control valve VS-PI is operated by this valve operation signal, and the gas temperature at the outlet of the superheater 9P1 is maintained at the set value.

Similarly, a signal limiter 50P2, a gas flow rate control system 51P2, a liquid flow rate control system 52P2, a pressure control system 53P2, and a gas temperature control system 54P2 are provided for the second vaporizer 3p2 of the Noro Gun vaporization equipment. The control system of valve vo
-p21 VL-P2+ VW-P2 and VB-P2 are each operated to determine the gas flow rate flowing out from the second vaporizer 3P2, the liquid level in the evaporating drum 4Pj, the pressure in the evaporating drum 4P2, and the superheater 9p2. The temperature of the gas at the outlet is controlled. The configurations of these control systems are completely the same as the configurations of the control systems 51P1 to 54P1 for the first carburetor, so the same parts are given the same reference numerals and the explanation thereof will be omitted.

In exactly the same way, the first and second vaporizers 31 of the butane vaporization equipment
11 and 382, signal limiters 50B1 and 5
0B2, gas flow rate control systems 51B1 and 51B2, liquid flow current control@1 systems 52B1 and 52B2, and pressure control σM system 5
3B1 and 53B2 and gas temperature control system 54B1 and 5
4B2 are provided, and the set flow and quantity command signals DBI and DB2 are supplied as setting signals to the gas flow rate control systems 51B1 and 51B2 through the signal limiters 50B1 and 5082, and the liquid flow rate control systems 52B1 and 52B2.
and pressure control systems 53R1 and 53B2 as feedforward signals. The configuration of these control systems is exactly the same as the control system for slag/yarn vaporization equipment, and includes a gas flow rate control valve 51m++ 5182, a liquid flow control system 52B1r 52a2, a pressure control system 53g+,
5382 and gas temperature control system 54a1.54B2 respectively, valves vG-a j and VG-82rVL-B++
VL-121VW-1111vw-n2 and Vs-s
11vs-82 is operated and the carburetor 3n1+ 3B2
The flow rate of gas flowing out from the evaporator drum 4at+ 412, the pressure in the evaporator drum 4B1+482, and the gas knitting on the outlet side of the superheater 9a1+ 9B2 are controlled.

Pro A in gas main GTU? With Ngas! The mixing ratio of tonne gas is set appropriately by a ratio setting device mainly depending on the received pans of Noropane liquid and butane liquid, but the setting ratio signal obtained from this ratio setting device is directly used as the command ratio signal α. As a propane gas a demand flow command signal AP for propane vaporization equipment and for butane vaporization equipment! Upon obtaining the tongue gas total required flow rate command signal AB,
Depending on the total gas demand flow rate and the value of the set ratio signal, the load on one of the vaporizers may become smaller than the minimum stable load, and the gas flow rate from that vaporizer will be the minimum gas required to operate the vaporizer stably. The flow rate may be less than °. Of course, it is necessary to avoid setting ratios that would load each vaporizer more than its maximum gas outflow. In the present invention, no matter what ratio is set by the setting device, the load of each carburetor does not fall below the minimum stable load, and the load of each carburetor does not exceed its maximum load. First of all, the maximum gas flow needle obtained from each vaporizer of the nitrogen vaporization equipment and the butane vaporization equipment (29) and the maximum gas flow needle that must be taken out from each vaporizer in order to stably transmit the gas to each vaporizer of both vaporization equipment. The maximum and minimum allowable mixing ratios are calculated from the minimum gas flow rate and the total gas demand flow command to obtain a maximum ratio signal and a minimum ratio signal. Next, the set ratio signal from the ratio setter for setting the mixing ratio of professional gas and butane gas in the main gas pipe is compared with the maximum ratio signal and the minimum ratio signal, and the set ratio signal is determined as the maximum ratio signal. If the set ratio signal is between the maximum ratio signal and the minimum ratio signal, the set ratio signal is used. If the set ratio signal is smaller than the minimum ratio signal, the minimum ratio signal is used. The selected signal is selected as the command ratio signal α that determines the target +jW of the mixing ratio. In order to automatically perform these operations, a command ratio signal generation circuit 60 is provided in the example shown in FIG. In the same circuit, 61a to 61d are adders, and the adder 61
In a, the operation of the vaporizer of the butane vaporization equipment (
30) The butane vaporization equipment maximum gas flow rate signal FMAx-B×N, which corresponds to the value multiplied by the base number N, and the butane gale off gas flow rate detection signal FBOQ-1+ are manually generated. force n
The calculator 61b is equivalent to the minimum gas flow rate FMIN-P that must be taken out from each vaporizer in order to stably operate each vaporizer in the nolopane vaporization equipment multiplied by the operating number N of the vaporizers in the propane vaporization equipment. The propane vaporization equipment minimum gas flow signal F old N-PXIIJ and propane BOG flow tm output signal F'noa-p are manually input.

The adder 61c also contains a pro-gin vaporizer maximum gas flow rate signal FMAX-, which corresponds to the product of the maximum gas flow rate FMAX-P of each vaporizer in the Noropane vaporizer equipment and the operating number N of the vaporizers in the propane vaporizer equipment. P XN and \pu7i+nB
The OG flow rate detection signal FBOG-P is input manually, and the adder 6
1d is the minimum gas flow tFM of each vaporizer of the butane vaporization equipment.
The butane vaporization equipment minimum gas flow rate signal FMIN-slN corresponding to rN-n multiplied by the operating number N of the vaporizer and the butane BOG a, it detection signal FBOG-B are input. The outputs of additions 561a to 61d are divided into dividers 62a to 62a, each using the total gas required flow rate command signal A as a divisor.
62d is entered manually as the dividend. The output of the divider 62a and the output of the divider 62d are respectively calculated manually by "1".
'', inverts the sign of the result, and outputs the result. Here, the computing unit 63
a, the signals output from the dividers 62b, 62c, and the arithmetic unit 63b, respectively, are expressed as pro-population ratios R1, R2, and R.

and R4, these signals are expressed by the following equations (1) to (4).

R1=1 ((FMAM-BXN+FIIOG-8)/
A)...(1) R2=(FMIN-PXN+F'1
lo()-p)/A +++ (2) R4=(
FMAx-i+×N+Fnoo-p)/A-(
3) R4= 1-((FMrN-n XN+FBOG-
B)/A)...(4) The above signals R7 and R2 are sent to the I/H selector 6 which selects the larger one of the input signals and sends it to the next stage.
4a, and the larger one of R4 and R2 is input to the arithmetic unit 6.
given to 5.

Further, the signals R3 and R4 are inputted to a signal selector 64b which selects the smaller one of the input signals and sends it to the next stage, and the smaller one of R3 and R4 is given to the arithmetic unit 65. The arithmetic unit 65 adds the two human power signals and divides by 2 to output the average value αm of both human power signals. A signal selector 64e selects the smaller of the input signals together with the output of the arithmetic unit 65 αml'i signal selector 64a and sends it to the next stage.
is man-powered. The output αm of the arithmetic unit 65 is also input to a signal selector 64d which selects the larger one of the input signals together with the output of the signal selector 64b and sends it to the next stage.

The signal selector 64c outputs a minimum ratio signal αMIN that allows each vaporizer in the vaporization equipment to operate stably, and the signal selector 64d outputs a maximum ratio signal αMAX that allows each vaporizer in the vaporization equipment to operate stably. do. Maximum ratio signal αMA
X is the smaller of the input signals, together with the setting ratio signal α obtained from the setting device that sets the mixing ratio of slag/l gas and butane gas in the main gas pipe as the ratio of the slag gas flow value to the total gas flow rate. Signal selector 6 to select
The output of the signal selector 64e is input to a signal selector 64f which selects the larger one of the input signals together with the minimum ratio signal αWIN. Signal selector 6
4f(33) outputs a command ratio signal α and supplies it to the multiplier 34.

The contents of this command ratio signal α are α8, αMAX, and αA(
It changes as follows depending on the size relationship between I and N.

(,) When α,〉αMAX, α2αMAX (b) When αold N≦αwork≦αMAX, α=αwork (c) When αwork〈αMIN, α0αMIN In the command ratio signal generation circuit 60, the signal R4 is a signal indicating the minimum value of the ratio of the gas flow rate to the total gas flow rate that must be borne by the propane vaporization equipment in order to prevent the load of each vaporizer in the butane vaporization equipment from exceeding its maximum load. Further, the signal R2 is a signal indicating the ratio of the minimum gas flow rate to the total gas flow rate that must be borne by the propane vaporization equipment in order to stably operate each vaporizer in the propane vaporization equipment. Furthermore, signal R3 represents the ratio of the gas flow rate to the total gas flow rate that must be loaded on the butane vaporization equipment in order to prevent the load of each vaporizer in the pro-butane vaporization equipment from exceeding the maximum load, expressed as a propane ratio. It is a signal indicating the maximum value of the ratio, and the signal R
4 is the ratio of the minimum gas flow rate to the gas flow rate that must be loaded on the butane vaporization equipment in order to stably operate each vaporizer in the butane vaporization equipment, expressed as the zolopane ratio, and the maximum value of that ratio. This is a signal indicating. - As an example, BOG a t of nolopane and butane are both O(
Fnoa-p = Fsoa-B = 0), and the maximum gas flow rate that can be extracted from each vaporizer of the Pro-Sen vaporization equipment and the butane vaporization equipment is 50 t/hour (FMAX-P
= FMAX-B-50t/Ij). In addition, in order to operate each vaporizer stably, the amount of gas flowing out from each vaporizer must not be less than 15 times the maximum gas flow rate. That is, the stable minimum gas outflow amount of each vaporizer is set to 7.5 t/hour (=50 x 15/100).

Under these conditions, R1-R4 when N=1 (when one vaporizer in each vaporizer is in operation) is as follows.

R, = 1-(50/A) ... (1)'R
2=7.5/A... (2)'R3
=50/A... (3)'R4=
1- (7,5/A, ) ... (4)' If the larger one of the above R1 and R2 is taken, the minimum ratio signal αM
IN is obtained, and if the smaller of R3 and R4 is taken, the maximum ratio signal αMAX is obtained.If 0αMIN and αMAX are illustrated for the total gas command flow M:command signal A, the third
The curve shown in the figure is a solid line, with the lower half of the curve representing αMIN and the upper half of the curve representing αMAX k. In FIG. 3, the curved portions labeled R1 to R4 are curves expressed by the above equations (1)' to (4)', respectively. In FIG. 3, the area surrounded by the curve shows the range of values that the command ratio signal α can take. In the present invention, the signal α is set by a setting device. When is smaller than αoldN, αMIN is set as the command ratio signal α,
When α work is larger than α MAX, the α MAX gold command ratio signal α is set. Further, when α engineering is within the range of αMIN to αIIIAX, αX itself is set as the command ratio signal α.

In Figure 3, the straight line that connects to the left end of the curve is R2
This shows the average value α□ of
This means that the command ratio signal α is set as the command ratio signal α. In the region to the left of the left end of the curve in Figure 3, the load of each carburetor becomes smaller than the stable minimum load, and the operation of each carburetor becomes unstable; Since gas can be supplied up to this range, in this embodiment, the operation is continued with α=α□ in this range.

In the above explanation, the BOG of Zorone and butane was assumed to be O, but when there is BOG, the curve showing the range of the command ratio signal is a curve that is parallelly shifted to the right from the curve when BOG is 0. . For example, in the above example, when the BOG of zolopane and butane is 5 tons per hour, the curve showing the range of the command ratio signal α is the curve shown by the broken line in FIG.

For reference, FIG. 4 shows a curve showing the range of the command ratio signal t97) when two vaporizers are operated in each vaporization facility (in the case of N-2). In Figure 4, the solid line indicates the flow rate of propane and butane BOG is 0.
The curve shown by the broken line shows the case where the flow rate of grono-4 and butane BOG is 5 t/H.

As in the above example, the fuel demand flow command signal FFD from the gas demand source is added as a feedforward signal to the output of the single element control system (controller 30) for the gas main residual pressure to determine the total gas demand flow rate. A command signal A is obtained, and this command signal A is used to generate a total required flow rate command signal C of 1,000 liters of gas in accordance with a command ratio signal α that commands the ratio between the flow rate of noropan gas and the flow rate of butane gas in the main gas pipe.

and a butane gas total required flow rate command signal CB, and from these gas total required flow rate command signals CP and CB, a set flow rate command signal DPI+ DP2 + DBj which is a setting signal for the gas flow rate to be borne by each vaporizer of the relevant vaporization equipment. +
DB2 is obtained and these set flow rate command signals are used as setting signals for the gas current control system of the corresponding vaporizer, and are also applied as feedforward signals to the liquid level flJ control system and pressure control system. ) Even when the load fluctuates rapidly, the pressure in the main gas pipe can be quickly controlled and the mixing ratio of the gases in the main pipe can be controlled to a predetermined value.

Further, no matter how the mixing ratio is set, the vaporizers of each vaporization equipment are maintained in a stable operating state, so that a stable supply of gas to the demand source can be achieved.

In the present invention, when the set value of the gas mixture ratio in the gas main pipe is p larger than the maximum ratio or smaller than the minimum ratio, the maximum ratio signal or the minimum ratio signal is used as the command ratio signal. This is because the first premise is to provide a stable supply of gas to the demand source, and it is absolutely not possible to operate in a way that causes unstable operation of the vaporizer by forcibly bringing the gas mixture ratio close to the set value. This is because it must be avoided. In the above example, PronoJ in the gas main pipe?
The mixing ratio of butane gas and butane gas is set by setting the ratio to the total gas flow rate of 1,000 liters of gas, but conversely, the mixing ratio can be set by setting the ratio of the butane gas flow rate to the total gas flow rate. May be set.

In the above example, the Noro Gun vaporization equipment and the butane vaporizer (RI
Although the same number of vaporizers are provided in each vaporizer, the present invention can be applied in the same manner even if the number of vaporizers in both vaporizers is different, and the number of vaporizers provided in each vaporizer is arbitrary.

In the embodiment shown in FIG. 2, the signal limiter (upper limit limiter) 50p++ 50p2+ 50B+ and 50B
2 is a situation in which when a vaporizer in each vaporizer equipment trips (emergency shutoff), a load higher than the maximum load is applied to the other vaporizers, causing the vaporizers in each vaporizer equipment to repeatedly trip. The signal limiters 50p1+50p2.50a1 and 50I+2 are set flow rate command signals DP I + DP2 + DB 1 for the vaporizers 3P113F21381 and 382, respectively.
and DB2 are limited so that they do not exceed the capacity of each vaporizer.

In the above embodiment, the set flow rate command signal DP++DP
2 + DB 1+ DB 2 instead of adding it as a feedforward signal to the corresponding liquid level control system and pressure control system, the pressure reducing valve vG-P1+ VG-P21 VG
-8,l VG-82 outlet side gas flow rate detection signal FG
It is also possible to add -P1+ FO-P2 +FG-BiPG-112 to the corresponding liquid level control system and pressure control system as a feedforward signal, but in this case, the detection signal F'c-p+ FG-P'2
- Since the fluctuations in Pa-B1 and FG-82 are quite large, it is difficult to perform stable control. On the other hand, as in the present invention, the set flow rate command signal Dp 1 + DP
2 + DB 1 + DR2 is added to the corresponding liquid level control system and pressure control system as a feedforward signal, and since the fluctuation range of these command signals is small, stable control can be performed.

In the above embodiment, the gas temperature control system 54P1+54
P2154p+++ The set flow rate command signal is not added to 5412 as a feedforward signal, but generally L
The outlet temperature of the superheater of the PG vaporization equipment may be about vaporization temperature (saturation temperature) + 10C, and the temperature range of the re-JO heat by the superheater may be less than 100%. Steam trace (thermal insulation measures using steam 17)
1), the system that changes the temperature of the gas on the side of the superheater t+'r as the LPG vaporization temperature changes becomes a system with a very large time constant. Therefore, if the set flow rate command signal is applied to the gas temperature control system as a feedforward signal, it will not only disturb the control system but also disturb other hot water flow rate controls. It is possible to perform more stable control by using a single element control system. However, when the load is combined cycle power generation, where it is necessary to suppress the temperature of the gas supplied to the demand source within a very narrow range of fluctuation, the gas temperature control system also has a set flow rate. By adding the command signal as a feedforward signal, rapid control can be performed.

As described above, according to the present invention, Norono! In LPG vaporization equipment, the LPG gas and butane gas obtained from the LPG vaporization equipment and the butane vaporization equipment, respectively, are combined and fed into the main gas pipe. In addition, it is possible to control the mixing ratio of proton and butane within the main gas charge to a predetermined value, and the load on each vaporizer can be controlled regardless of the setting value of the mixing ratio. Since it can be maintained within a range that allows stable operation, stable gas supply can be guaranteed.

[Brief explanation of drawings]

Fig. 1 is a system flow diagram showing an example of LPG vaporization equipment to which the control method of the present invention is applied, and Fig. 2 is a control system flow diagram showing an example of the configuration of a control system when the present invention is applied to the vaporization equipment of Fig. 1. The logic diagram, FIG. 3, and FIG. 4 are diagrams showing different examples of the relationship between the command ratio signal and the total gas required flow rate command signal, respectively. ■...Vaporization equipment for Pro/Sen, ■...Vaporization equipment for butane, In...Gas main pipe, IP...Propane liquid tank, 2P...Propane liquid dispensing pump, 3p1+ 3p
2... Vaporizer for Noropan, 4P++ 4p2... Evaporation drum of vaporizer for Noropan, 5P1+ 5p2...
I don't like the glue for the vaporizer for Grono's armpits, 9P1+ 9P2...
・Propane superheater, 10P...Grono 4 gas supply piping, 19P...Pro? Illoff gas supply control, IB...butane liquid tank, 2B...butane dispensing pump, 3n++ 3a2...butane vaporizer, 4n++
4a2...Evaporation drum of butane vaporizer, 5n1+
5n2...Repoiler for butane vaporizer, 9B+,
9B2... Butane superheater, 10B... Butane gas supply piping, 19B... Butane boil-off gas supply piping, 60... Command ratio signal generation circuit, 61 a ・-6
1d... Adder, 62a-62d... Divider, 6
4a to 64f...Signal selector, PM...Gas main pipe pressure detection signal, PMS...Gas main pipe pressure setting signal, FF
D...Fuel required flow rate command 4 words from gas demand source, F
BOG-P...propane? Air off gas flow rate detection signal, FBQQ-8... Butane is air off gas flow detection signal, Fa-p+* FG-P2... Pro-sen gas current detection signal, "G-air F'G-B2... Butane gas Flow rate detection newsletter, "D-PllLo-p2... Propane liquid level detection signal, IjDS-PllLDII
-P2... #Zorono4 liquid level setting signal in the older drum, TJD-B 1 + LD-82... Butane liquid level detection signal in the evaporating drum, LDIII-B1+ T
JD8-B2... Butane liquid level setting signal in the evaporating drum, PD-11+ PD-P2... Propane gas pressure detection signal in the evaporating drum, PDS-Pll PDS-P
2...Pro-9 gas pressure setting signal in the evaporation tram, P
D-BllPD-82... Butane gas pressure detection signal inside the evaporating drum, PDS-Bl, PD8-B2... Inside the evaporating drum! Tongue gas pressure setting signal, TSG-Pll T
so-p2...Ro side professional A temperature detection signal for superheater, 'rsos-p 1 + TSG8-P2 "'Lo side zolopane gas temperature setting signal for superheater, Tsa-a1+
TSG-12...Superheater side gas temperature detection signal, T8QB-81゜TaH2-12...Superheater outlet side butane gas temperature setting signal, Fj-p++ FL-P
2”°°Pronogun liquid flow rate detection signal XFL-B1+FL
-B2... Butane liquid flow rate detection signal, F'w-p 1
+ FW-P2...propane vaporizer glue, yira hot water flow rate detection signal, FW-111FW-112...reboiler hot water flow rate detection signal for butane vaporizer, PI...proportional integrator, f(x )...Function generator, vG-P 1+
VG-P2 ... Noro z47 gas vacuum box -VG-B
11VG-B2 ``'! Methane pressure reducing valve, VL-p+
*VL-p2-propane liquid flow control valve, VL-B1+
vL-B2... Butane liquid flow rate control machine, vw-Pin
"W-P2...Grono 4-heater glue width water flow rate adjustment valve, VW-111+ vW-B2...Butane vaporizer glue zira hot water flow rate control valve, Vs-p++ (45
) Vs-p2...Superheater hot water flow rate control valve for Noron/4'-on, VB-B1+ VB-12...Superheater hot water flow rate control valve for butane, A...Total gas required flow rate command signal, AP・
・Propane gas total required flow rate command information, AB... Butane gas total narrowed flow rate command signal, CP... Propane gas required flow rate command signal for the nolopane vaporization equipment, CB... For the butane vaporization equipment! Tongue gas required flow rate command signal, D
pj, Dp2... Set flow rate command signal for each vaporizer of the Noropane vaporization equipment, DB 1 + DB 2... Set flow rate command signal for each vaporizer of the butane vaporization equipment, α
X...setting ratio signal, αWAX...maximum ratio signal,
αMIN: Minimum ratio signal, α: Command ratio signal. (46)

Claims (1)

[Claims] Propane vaporization equipment that vaporizes the propane liquid discharged from the propane liquid tank using a thermosiphon type vaporizer having an evaporating drum and a redeira, and supplies propane gas to the propane gas supply piping. and a butane vaporization equipment that vaporizes the butane liquid discharged from the butane liquid tank using a thermosiphon type vaporizer different from the thermosiphon type vaporizer and supplies butane gas to the butane gas supply distribution; Ill-off gas and U in the e-liquid tank
7" The boil-off gas in the tying liquid tank is supplied to the front six zolopan gas supply piping and the butane and boil-off gas supply piping, and the butane and boil-off gas supply piping, respectively, which supply the boil-off gas in the middle of the ! In an LPG vaporization facility equipped with a gas supply pipe U and a main gas pipe that combines proton gas and butane gas supplied through the butane gas supply pipe and supplies them to the demand source, the following steps (a) to (1) are carried out. (1) A method for controlling LPG vaporization equipment, characterized in that by performing (1), the pressure in the main gas pipe is kept constant and the mixing ratio of proton gas and butane gas is controlled to a predetermined value. ( b) Using the detection signal of the pressure in the gas main pipe as a feedback signal, output a gas Yasugi flow rate command signal that instructs the f flow to flow into the gas main pipe in order to maintain the pressure in the gas main pipe at the set value. A monoanium element control system is configured to include a fuel demand t from the gas demand source in the gas demand flowmeter command signal.
The W1 command signal is added as a feedforward signal to obtain the required gas flow rate command signal. (b) The maximum gas flow needle obtained from each vaporizer of the slag vaporization equipment and the butane vaporization equipment, and the maximum ratio signal and minimum ratio of each vaporizer in order to stably operate each vaporizer of the internal vaporization equipment. Get a signal. ? -) Comparing the set ratio signal from the ratio setter for setting the mixing ratio with the maximum ratio signal and the minimum ratio signal, and when the set ratio signal is larger than the maximum ratio signal, select the maximum ratio signal. When the set ratio signal is smaller than the maximum ratio signal and larger than the minimum ratio signal, the set ratio signal is selected, and when the set ratio signal is smaller than the minimum ratio signal, K selects the minimum ratio signal. The selected signal is used as a command ratio signal for determining the mixing ratio. B) Allocating the total required gas flow rate command signal according to the command ratio signal to obtain a total required gas flow rate command signal and a total required flow rate command signal for butane gas. (e) Detecting the flow rate of the dill-off gas supplied to the middle of the f o zf gas supply piping and the butane gas supply piping, respectively, to obtain a propane boil-off gas flow rate detection signal and a butane gas flow detection signal; Professional Yangas total required flow rate command signal and! The propane number (il-off gas current detection signal and butane boil-off gas adhesion detection signal) are subtracted from the tan gas total demand flow leaf command signal to obtain the propane gas low flow command signal for the propane vaporization equipment and the butane gas demand flow information for the butane vaporization equipment: Obtain the command signal. (f) The Noropan distributes the steam flow rate command signal and the butane gas demand flow meter command signal to each vaporizer of the Zoro/Yan vaporization equipment and each vaporizer of the butane vaporization equipment, respectively, and performs valley vaporization. Obtain a set flow rate 1 command signal for each vaporizer. Control the flow value of the gas flowing out from each vaporizer. (a) The internal vaporization equipment maintains the liquid level in the evaporation drum of each vaporizer of the slag and butane vaporization equipment and the butane vaporization equipment at all set levels. Inflow of pan liquid and butane liquid into the evaporation drum of Control the liquid level in the drum. (S) The settings #i, M for each vaporizer of the propane vaporization equipment and the butane vaporization equipment: Give a command signal to the function generator to control the corresponding vaporizer from the function generator. The set flow rate command signal of the heat medium is obtained as a feedforward signal to the control system that controls the flow rate of the heat medium supplied to the evaporator drum of each vaporizer. Controls the flow of heat medium into each air vessel so as to maintain the pressure within the air at a set value.