JPH0117037B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention comprises a steam drum and a reboiler.
The present invention relates to a method of controlling an LPG vaporizer, such as a vaporizer that supplies LPG gas to an LPG-fired boiler.

(Prior Art) The control mechanism of a conventional LPG vaporizer is shown in FIG. 3 by referring to the reference numerals of the embodiments of the present invention. , so that the drum pressure set value Pset and the drum pressure P are equal (for example, proportional
A correction signal (feedback signal) MVp is calculated by performing an integral operation.

The addition coefficient unit 31 receives a load command signal (feedback) indicating either the vaporization flow rate command signal _F A signal obtained by multiplying (signal) S _M by k (k is a proportionality constant) and the correction signal MVp are added to calculate the heat medium flow rate set value F _R ,set. Heat medium flow controller 34
is the operating signal for the heating medium flow rate control valve 35 so that the heating medium flow rate F _R (output of the converter 33) and F _R , set are equal.
_MR is calculated and the opening degree of the heat medium flow control valve 35 is operated.

The drum level controller 10 calculates a correction signal (feedback signal) MV _L so that the drum level set value Lset and the drum level L are equal.
The addition coefficient unit 24 adds the load command signal (feed forward signal) S _M and the correction signal MV _L ,
Calculate the supply liquid flow rate setting value F _F , set. The supply liquid flow rate controller 13 calculates the operation signal M _F of the supply liquid flow rate control valve 14 so that the supply liquid flow rate F _F (output of the converter 12) and F _F , set are equal, and the supply liquid flow rate control valve 14 Operate the opening degree of 14.

The vaporization flow rate controller 19 receives a vaporization flow rate command signal representing the vaporization flow rate required on the load plant side.
Calculate the operation signal M〓 of the control valve 20 so that F _D 21 and the vaporization flow rate F〓 (output of the converter 18) are equal,
The opening degree of the control valve 20 is operated.

That is, according to the conventional method, regarding drum pressure,
The feedforward signal, which is a signal corresponding to the amount of gas coming out of the drum, and the feedback signal, which detects the drum pressure and outputs a correction signal so that the value becomes a predetermined value, are combined, and the combined signal is used to control the reboiler. The flow rate of the heating medium supplied to the heating medium is controlled by changing the flow rate.

Regarding the drum level, a feedback signal that is a signal corresponding to the amount of gas emitted from the drum is combined with a feedback signal that detects the drum level and outputs a correction signal so that the value becomes a predetermined value. , the flow rate of the supply liquid supplied to the drum is changed based on the combined signal.

(Problem to be Solved by the Invention) According to the conventional control method described above, almost stable operation can be achieved in a range where the load change is gradual or the change width is small even if the load change speed is fast. It is difficult to say that stable operation is necessarily achieved in response to large and sudden load fluctuations that occur when a boiler auxiliary machine trips or when a power transmission line from a power plant is disconnected.

A phenomenon in which the carburetor becomes unstable is a situation in which the drum level and drum pressure fluctuate significantly, and in the worst case, the carburetor and boiler must be stopped.

The main reason for the loss of stability is that when the load suddenly changes, the dryness inside the reboiler tube changes rapidly, which causes the liquid volume in the mixed phase section inside the reboiler tube to change significantly. The amount of circulating fluid flowing into the reboiler will fluctuate significantly, and the drum level will fluctuate significantly.
Furthermore, in order to suppress fluctuations in the drum level, the amount of liquid supplied to the evaporation drum also fluctuates significantly. For example, in the case of an LPG vaporizer (a vaporizer that gasifies propane), the temperature of the feed liquid is around -42℃, and the temperature of the liquid inside the drum is around 19℃, so there is very cold material inside the drum. It is in a state where it is being supplied to. (The feed liquid is −42
It is at an extremely low temperature of ℃, and the drum is being cooled. ). If a large fluctuation in the amount of supplied liquid occurs under this condition, the thermal balance will be disrupted and the pressure in the steam drum will also fluctuate.

As a method to prevent the above-mentioned phenomenon, for example, when the load suddenly decreases, the drum level drops suddenly;
In order to reduce this effect, the flow rate of the supply liquid may be increased somewhat compared to the outlet gas amount.

That is, it is sufficient to avoid a sudden decrease in the amount of supplied liquid. For this purpose, it is recommended to add a delay element such as a first-order delay element (in addition, it is possible to install a second-order delay element, a dead time element, a speed-of-change limiter, etc.) to the feedforward signal system of the drum level control system. In addition to being effective in stabilizing the drum level, the heat balance does not fluctuate significantly (for example, when the amount of gas at the exit of the vaporizer is throttled, there is a delay in the process even if the flow rate of the heat medium is simultaneously throttled). The drum pressure cannot be kept constant and the drum pressure tries to rise, but the decrease in the amount of supplied liquid is less than the decrease in the amount of gas in the vaporizer, so the drum is cooled with the amount of supplied liquid commensurate with the decrease in the amount of gas in the vaporizer. It was found that this method is effective in stabilizing drum pressure.

(Means for Solving the Problems) The present invention is a drum level control method for an LPG vaporizer developed to address the above-mentioned problems, and includes a steam drum and a reboiler.
A feedback signal, which is a signal corresponding to the amount of gas coming out of the steam drum in the LPG vaporizer, is synthesized with a feedback signal that detects the steam drum level and outputs a correction signal so that the value becomes a predetermined value. In a steam drum level control method in which the flow rate of liquid supplied to the steam drum is controlled by the composite signal, a delay element interposed in the feedforward signal line is used to control the amount of gas flowing out from the steam drum. It is characterized by a structure that gently changes the flow rate of liquid supplied to the steam drum, and its purpose is to maintain a stable operating state of the vaporizer even during sudden and large load fluctuations. To provide a drum level control method.

(Function) Since the present invention is configured as described above, when the load suddenly changes, that is, when the amount of gas at the exit of the LPG vaporizer suddenly changes, the amount of gas flowing out from the steam drum of the LPG vaporizer is transferred to the steam drum rather than the amount of gas flowing out from the steam drum of the LPG vaporizer. The supplied liquid flow rate is changed slowly to stabilize the pressure and level in the evaporator drum. Therefore, vapor is stably supplied to a load-side plant such as a boiler.

(Example) Figures 1 and 2 show an example of the present invention, which shows a reboiler that gasifies low-temperature LPG with a heating medium and supplies LPG as fuel to an LPG-fired boiler. This is applied to an LPG vaporizer consisting of an evaporating drum and an evaporating drum.

In Fig. 1, reference numeral 1 denotes an evaporation drum that stores LPG liquid 2.
LPG liquid (hereinafter referred to as liquid) is supplied in a spray form through a supply pipe 3, exchanges heat with vaporized vapor in a reboiler 4, is heated, and is stored at the bottom of the tower.

The bottom of the evaporation drum 1 and the bottom of the tube side of the reboiler 4 are connected by a pipe 5, and the middle part of the evaporation drum 1 and the top of the tube side of the reboiler 4 are connected by a pipe 6. The liquid is heated by the heating medium supplied to the shell side of the reboiler 4, and a density difference occurs between the liquid portion at the bottom of the tower, the pipe 5, and the reboiler 4 side, and the gas-liquid mixed phase portion on the tube side of the reboiler 4. , and the liquid is circulated through piping 5.
→ Reboiler 4 → Piping 6 route.

A demister 7 is disposed in the upper part of the evaporation drum 1, and a pipe 8 is connected to the top of the drum 1. The gas-liquid mixture heated and partially vaporized in the reboiler 4 is transferred from the pipe 6 to the evaporation drum 1. Although it is returned to
The liquid returns to the bottom of the tower, and the vapor rises inside the evaporation drum 1, exchanging heat with the LPG liquid supplied in the form of a spray, and a part of it condenses and is removed together with the entrained droplets in the demister 7, and then goes into the piping. 8 and then supplied to load plants such as LPG-fired boilers.

A level detector 9 is provided at the bottom of the evaporation drum 1, and the output end of the level detector 9 is connected to the level controller 1.
It is connected to the input terminal of 0. Level controller 10
The output is connected to the input end of the addition coefficient unit 24 as a feedback signal for the drum level control system.

On the other hand, a vaporization flow rate detector 17 is attached to the piping 8 to detect the vaporization flow rate going out to the load plant, and the flow rate detection signal detected by the flow rate detector 17 is transmitted via a converter 18 to the vaporization flow rate. Controller 19
The controller 19 calculates an operation signal so as to match the vaporization flow rate command signal 21 requested from the load plant and gives it to the control valve 20.
The control valve 20 operates according to the aforementioned operation signal.

In addition, the vaporization flow rate command signal 21 and the converter 18
The output of is connected to the relay 22, and one of the signals is sent to the delay element 23 via the relay 22, and the delay element 23 outputs one of the above-mentioned signals, that is, the load amount fluctuation according to the load amount. A slower signal is calculated and connected to the other input end of the addition coefficient unit 24 as a feed forward signal for the evaporator drum level control system. Addition coefficient unit 2
4 uses the feedback signal that is the output of the drum level controller 10 and the feedback signal that is the output of the delay element 23 to output a correction signal to keep the drum level at a predetermined value. The controller 13 outputs the output signal (correction signal) of the addition coefficient 24 and the supply liquid flow rate detection signal obtained from the supply liquid flow rate detector 11 via the converter 12. The operation signal is calculated so that the supply liquid flow rate control valve 1
4, and the control valve 14 is operated in accordance with the aforementioned operation signal.

Further, a pressure detector 30 detects the evaporating drum pressure, and the detection signal is given as an input to a drum pressure regulator 36. The output of the drum pressure regulator 36 is input to the addition coefficient unit 31 as a feedback signal for the drum pressure control system. On the other hand, the output signal of the relay 22 (a signal according to the load) is input to the addition coefficient unit 31. The addition coefficient unit 31 uses the output of the drum pressure controller 36 and the output signal of the relay 22 to calculate a correction signal for keeping the drum pressure at a predetermined value, and this correction signal is sent to the heat medium flow controller 34. The controller 34 calculates an operation signal so that the output signal of the addition coefficient unit 31 and the heating medium flow rate detection signal obtained from the heating medium flow rate detector 32 via the exchanger 33 match, and The control valve 35 is supplied to the flow control valve 35, which is operated in accordance with the operation signal.

Therefore, the flow rate of the heat medium passing through the pipe 15 and the tube side of the reboiler 4 from the pipe 16 to the outside of the reboiler 4 is changed so that the evaporating drum pressure becomes a predetermined value.

If the load suddenly and significantly decreases while the load is stable, the output of the delay element 23 and relay 22, which are feedforward signals, will decrease significantly, and the inlet supply fluid The set values of the flow rate regulator 13 and the heat medium flow rate regulator 34 will also decrease in accordance with the load reduction, and the opening degrees of the inlet supply liquid flow rate control valve 14 and the heat medium flow rate control valve 35 will decrease. Therefore, both the inlet supply liquid flow rate and the heat medium flow rate are significantly reduced.

Therefore, the drum pressure is prevented from increasing when the load suddenly increases.

The drum level is likely to drop rapidly due to changes in the dryness inside the reboiler tube, but
By providing the delay element 23, the output signal of the delay element 23 is larger than the vaporization flow rate command 21 in a transient state when the load suddenly decreases, so that the inlet supply liquid flow rate is greater than the outlet gas flow rate.
This decrease (decrease in drum level) will be suppressed.

Of course, the drum level controller 10 and drum pressure controller 36 are always operating, and the controller output is changed to match their respective target values.
Therefore, both the drum level and drum pressure gradually converge to their respective target values after a sudden change in load.

As an example, LPG (in the case of propane) vapor generation amount is 50T/H, drum pressure (operating value) is 6.5Kg/
In the case of a cm ² G vaporizer, when a first-order delay element is used as the delay element 23, an appropriate first-order delay time constant is 0.5 to 1 minute.

Contrary to the above explanation, when the load increases while the load is stable, the opening degrees of the supply liquid flow rate control valve 14 and the hot water flow rate control valve 35 are increased by the same effect, and the drum The drop in pressure and the sudden increase in drum level will be suppressed. (In this case, in a transient state when the load suddenly increases, the inlet supply liquid flow rate is smaller than the outlet gas amount.) The method for controlling the drum level of the LPG vaporizer is shown in the control mechanism diagram in Fig. 2. To explain the operation of the control mechanism as shown in the figure, the drum pressure regulator 3
6 calculates a correction signal (feedback signal) MVp so that the drum pressure set value Pset and the drum pressure P become equal (for example, by performing proportional/integral calculations). The addition coefficient unit 31 receives a load command signal (feedback) indicating either the vaporization flow rate command signal _F A signal obtained by multiplying (signal) S _M by k (k is a proportionality constant) and the correction signal MVp are added to calculate the heat medium flow rate set value F _R ,set. The heat medium flow rate controller 34 has a heat medium flow rate F R (output of the converter 33) and a heat medium flow rate F _R (output of the converter 33).
Heat medium flow control valve 35 so that F _R and set are equal.
The operating signal M _R is calculated, and the opening degree of the heat medium flow control valve 35 is controlled.

The drum level controller 10 calculates a correction signal (feedback signal) MV _L so that the drum level set value Lset and the drum level L are equal.

The addition coefficient unit 24 adds the correction signal MV _L to the output S _M ′ (feed forward signal) of the delay element 23 obtained by performing calculations such as first-order lag on the load command signal S _M , and determines the supply liquid flow rate setting value. Calculate F _F , set.

That is, F _F and set are given as feedforward signals that are gentler than S _M according to the load amount. The supply liquid flow rate controller 13 controls the operation signal M _F of the supply liquid flow rate control valve 14 so that the supply liquid flow rate F _F (output of the converter 12) and F _F , set are equal.
is calculated, and the opening degree of the supply liquid flow rate control valve 14 is operated.

The vaporization flow rate controller 19 receives a vaporization flow rate command signal representing the vaporization flow rate required on the load plant side.
Calculate the operation signal M〓 of the control valve 20 so that F _D 21 and the vaporization flow rate F〓 (output of the converter 18) are equal,
The opening degree of the control valve 20 will be controlled.

A feedforward signal, which is a signal corresponding to the amount of gas emitted from the evaporating drum in an LPG vaporizer consisting of an evaporating drum and a reboiler, and a correction signal that detects the evaporating drum level and makes the value a predetermined value. In the evaporating drum level control method, the flow rate of the liquid supplied to the evaporating drum is controlled by combining the feedback signals to be outputted, and the flow rate of the liquid supplied to the evaporating drum is controlled by the combined signal. The flow rate of liquid supplied to the evaporation drum is changed more slowly than the fluctuation in the amount of gas released.

(Effects of the Invention) As described above, according to the present invention, not only the drum level, which is the most important for an LPG vaporizer, but also the internal pressure can be extremely effectively stabilized even during sudden and large load changes. , stable operation of LPG vaporizer can be achieved. Therefore, in the case of a vaporizer consisting of a boiler that supplies LPG as fuel to an LPG-fired boiler and an evaporation drama, there is a possibility that the vaporizer may trip when there is a large and rapid load change that occurs when the boiler auxiliary equipment trips or when the power transmission line is disconnected. As a result, the boiler can be operated stably.

Although the present invention has been described above with reference to embodiments, it goes without saying that the present invention is not limited to such embodiments, and that various design modifications can be made without departing from the spirit of the present invention. .

[Brief explanation of drawings]

Fig. 1 is a mechanical diagram of an LPG vaporizer showing an embodiment of the present invention, Fig. 2 is a diagram of the drum level control mechanism of the embodiment of the present invention shown in Fig. 1, and Fig. 3 is a drum level control mechanism of a conventional example. It is a diagram. 1: Evaporation drum, 4: Reboiler, 5, 6, 8:
Piping, 7: Demister, 9: Level detector, 10:
Level controller, 11: Supply liquid flow rate detector, 12:
Converter, 13: Supply liquid flow rate controller, 14: Supply liquid flow rate control valve, 17: Vaporization amount detector, 18: Converter, 19: Vaporization flow rate controller, 20: Control valve, 2
1: Vaporization flow rate command signal, 22: Relay, 23: Delay element, 24: Addition coefficient unit, 31: Addition coefficient unit,
32: heat medium flow rate detector, 33: converter, 34: heat medium flow rate regulator, 35: heat medium flow rate control valve, 36: drum pressure regulator.

Claims (1)

[Claims] 1. A feed forward signal which is a signal corresponding to the amount of gas coming out of the steam drum in an LPG vaporizer consisting of a steam drum and a reboiler, and a correction signal that detects the steam drum level and adjusts the value to a predetermined value. In the steam drum level control method, the flow rate of liquid supplied to the steam drum is controlled by the synthesized signal, and the flow rate of the liquid supplied to the steam drum is controlled by a delay element interposed in the feedback signal line. A drum level control method for an LPG vaporizer, characterized in that the flow rate of liquid supplied to the steam drum is changed more gradually than the fluctuation in the amount of gas emitted from the drum.