JPH0574759B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention provides a pressure control method for adjusting the calorific value when natural gas from a liquefied natural gas storage facility is supplied as city gas after being adjusted to a constant calorific value. Regarding BOG (evaporative gas) from LNG storage tanks, etc.
Even if the mixing pressure suddenly changes, the adjustment can be controlled within the normal control range of heat amount adjustment.

[Prior Art] When supplying liquefied natural gas (LNG) as city gas, it is necessary to adjust and supply a certain amount of heat.

For this reason, a conventional method for adjusting the calorific value is to mix liquefied petroleum gas (LPG), such as butane or propane, with LNG vaporized gas as a calorific value adjusting gas.

Therefore, conventionally, LNG, which is stored in a liquid state in LNG storage equipment, is vaporized using seawater as a heat source to create LNG vaporized gas.
For example, butane, propane, or the like is mixed as a heat value adjusting gas.

The heat amount adjusting device for this purpose is as shown in the schematic configuration in Figure 3.
The flow rate of LNG vaporized gas is detected by the flow rate detector 2 and sent to the ratio control controller 3, and the control signal of this ratio control controller 3 is detected by the flow rate detector 5 which detects the flow rate of the calorific value adjustment gas from the LPG vaporizer 4. The LNG vaporized gas whose calorific value has been adjusted is mixed with the calorific value adjustment gas by outputting the signal together with the controller of the flow control valve 6 for flow rate adjustment to adjust the calorific value, and further,
The calorific value of the mixed city gas is measured by a calorimeter 9, and a calorific value correction signal is fed back to the ratio control controller 3 based on the detected value.

On the other hand, in LNG storage facilities, liquefied natural gas evaporates due to heat entering from the outside.
BOG (evaporated gas) is generated, and if it is not treated in some way, the pressure in the storage equipment will increase, so a reliquefaction device is installed to liquefy it and return it to the storage equipment.
As shown in FIG. 3, after pressurizing with the BOG compressor 10, if a thermal power plant etc. is adjacent,
They are treating it by supplying it as fuel.

[Problems to be solved by the invention] However, in LNG terminals where there is no adjacent equipment that consumes large amounts of BOG (evaporative gas),
Emitting (evaporative gas) into the atmosphere is dangerous and wastes energy resources, so
This BOG (evaporative gas) will also be used as a raw material for city gas, and this BOG (evaporative gas) will be used as a raw material for LNG.
It is conceivable to adjust the amount of heat by mixing the amount of heat adjusting gas after mixing with the vaporized gas.

However, the amount of BOG (evaporated gas) generated varies greatly, and a large amount is generated when LNG is received, and the amount decreases during the winter, but the amount of BOG mixed in Attempting to control the BOG compressor to a predetermined amount may lead to an increase in the pressure in the LNG storage equipment, so the capacity of the BOG compressor must be controlled based on the pressure in the LNG storage equipment.

Fluctuations in the amount of BOG (evaporated gas) caused by adjusting the capacity of the BOG compressor become a disturbance to the control system that adjusts the amount of heat.

For this reason, when attempting to adjust the amount of heat by mixing BOG (evaporated gas) with LNG vaporized gas and then mixing the amount of heat adjustment gas, the control range of the ratio control controller must be widened to accommodate disturbances with large fluctuations. However, there are problems such as the equipment becomes large-scale and controllability deteriorates.

This invention was made in view of the problems of the prior art, and when BOG (evaporated gas) is used as a raw material for city gas, the amount generated fluctuates greatly.
Even if the pressure fluctuates greatly, the amount of heat can be easily and efficiently adjusted and controlled without increasing the control range.
This paper attempts to provide a pressure control method for adjusting the amount of heat that takes into account BOG flow rate fluctuations.

[Means for Solving the Problems] In order to solve the above problems, the heat amount adjustment control method of the present invention that takes into account BOG flow rate fluctuations is based on the LNG vaporized gas obtained by vaporizing liquefied natural gas and the BOG (evaporated gas) from the storage tank. BOG (evaporated gas) is mixed into the LNG vaporized gas when adjusting the calorific value by mixing the calorific value adjustment gas made by evaporating liquefied petroleum gas with the LNG gas.
A flow rate adjustment valve is provided in the piping system on the discharge side of the BOG compressor that compresses BOG, and this flow rate adjustment valve allows the BOG pressure to accumulate in the piping system, and also adjusts the BOG pressure when the load by the BOG compressor is within a steady range. The pressure controller for controlling the BOG compressor and the pressure controller for when the load fluctuates are switched, and when the load on the BOG compressor increases, the pressure of the mixture into the LNG vaporized gas increases rapidly while maintaining the flow rate increase rate at a predetermined value. A method of controlling the flow rate control valve to gradually reduce the pressure while preventing the flow rate, and when the load on the BOG compressor decreases, the flow rate decrease rate is maintained at a predetermined value while gradually increasing the BOG (evaporated gas) to the LNG vaporized gas.
The present invention is characterized in that the flow control valve is controlled so as to increase the mixing pressure.

[Function] According to this pressure control method for adjusting the amount of heat that takes into account BOG flow rate fluctuations, BOG (evaporated gas), which has large pressure fluctuations due to fluctuations in the amount generated, is
The piping system on the discharge side of the compressor is used to accumulate pressure, and control is switched between using separate pressure controllers such as a PID controller with a gap and a PID controller depending on whether the pressure fluctuation is large or normal. Therefore, the rate of pressure fluctuation is kept at a predetermined value using an output change rate limiter, etc., despite fluctuations in the load of the BOG compressor, and the range of fluctuation in the pressure of BOG (evaporated gas) mixed into LNG vaporized gas is increased. In this way, the BOG pressure necessary for adjusting the amount of heat can be controlled with good controllability within a small control range.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail based on the drawings.

FIG. 1 is a schematic diagram of an embodiment of a pressure control method in adjusting the amount of heat in consideration of BOG flow rate fluctuations according to the present invention.

In pressure control method 20 for adjusting the amount of heat in consideration of BOG flow rate fluctuation, BOG (evaporated gas)
(BOG) flow rate control system 30 that controls the flow rate fluctuation of LNG vaporized gas and this BOG (evaporated gas)
and a heat amount control system 50 that adjusts the amount of heat and produces city gas after mixing the two gases.

Pressure control method 20 in this heat amount adjustment
The BOG flow rate control system 30, as shown in the schematic configuration in FIG.
(evaporated gas) is pressurized by the BOG compressor 32.
The LNG vaporized gas is mixed through the BOG pipe 33 in the middle of the LNG pipe 35 for LNG vaporized gas vaporized in the LNG vaporizer 34 . This BOG piping 33
A BOG pressure detector 36, a BOG flow rate detector 37, and a BOG flow rate control valve 38 are interposed in the middle.

Then, the detection signal of the BOG pressure detector 36 is 2.
BOG flow rate detector 37
The detection signal is input to the controller 41 of the BOG flow control valve 38. These 2
One of the two pressure controllers 39 and 40 is a PID with a gap that prevents the controller from functioning within a certain gap range.
The other pressure controller 40 is a pressure controller for controlling a normal constant pressure, and is adapted to be switched and used by a changeover switch 42 according to preset conditions.

In the BOG flow rate control system 30 configured in this way, for example, the pressure controller 39 is composed of a portion 39a that generates a gap gain, a PID calculator 39b, and an output change rate limiter 39c, and the pressure
In the range of 11~12Kg/ ^cm2G , set the gap gain to 0.
At the same time, the rate of change in BOG flow rate per minute is set not to exceed 1t/H, and the pressure controller 40 controls the BOG pressure to 12Kg/cm ² G.
I'm learning to keep it that way.

When the flow rate of BOG (evaporated gas) decreases (BOG compressor load down), in this case, as shown in Figure 2a, BOG
The changeover switch 42 is switched in response to the load down signal of the compressor 32, and the pressure controller 4
Switch from the 0 side to the pressure controller 39 side.

Then, this pressure controller 39 is provided with a gap gain generating section 39a, and when the BOG pressure is in the range of 10 to 12 Kg/cm ² G, the output of the pressure controller 39 is maintained as it is by setting the gap gain to 0. , is output to the controller 41 of the BOG flow rate control valve 38 to maintain the current opening degree of the BOG flow rate control valve 38 (portion A in the figure).

Then, when the BOG pressure becomes 11Kg/cm ² G or less, the PID calculation section 39b of the pressure controller 39
A signal to throttle the flow rate is output from the controller 41 to the BOG flow rate control valve 38.

In this case, rapidly restricting the BOG flow rate control valve 38 in order to increase the pressure will cause a disturbance in the calorific value control system 50, so the output change rate limiter 39c of the pressure controller 39 will reduce the flow rate to 1 t/H per minute.
(Part B in the figure).

As a result of increasing the pressure while reducing the flow rate at a constant rate, the BOG pressure was 11Kg/
When it returns to cm ² G, turn the changeover switch 4.
2 and return from the pressure controller 39 side to the pressure controller 40 side again, and after increasing the BOG pressure to 12 kg/cm ² G, steady operation begins (section C in the figure).

Note that if the decrease in pressure due to load down of the BOG compressor 32 is small and the BOG pressure does not fall below 11 kg/cm ² G, the changeover switch 42 is switched by a timer (not shown), and the pressure is returned to the pressure controller 40. All you have to do is to do this.

When the flow rate of BOG (evaporative gas) increases (BOG compressor load-up), as shown in Figure 2b, the BOG
In response to the load-up signal of the compressor 32, the selector switch 42 is switched, and the pressure controller 4
Switch from the 0 side to the pressure controller 39 side.

Then, since this pressure controller 39 is provided with an output change rate limiter 39c,
Without suddenly opening the BOG flow control valve 38,
Flow rate is increased to 1t/H per minute for increasing BOG pressure.
(Part D in the figure).

As a result of increasing the flow rate and decreasing the pressure at a constant rate, the BOG pressure was 12
When the pressure has decreased to Kg/cm ² G, switch the changeover switch 42 and return from the pressure controller 39 side to the LNG controller 40 side again.
After that, steady operation begins (section E in the figure).

Next, a calorific value control system 50 that adjusts the calorific value of the mixed gas of BOG (evaporated gas) sent from the BOG flow rate control system 30 and LNG vaporized gas vaporized by the LNG vaporizer 34 is shown in FIG. Since the configuration is the same as that explained in , the same parts will be numbered in the 50s and the explanation will be omitted.

In this way, BOG (evaporated gas) whose flow rate fluctuates widely is stored by the BOG flow rate control system 30 using the BOG piping 33 on the discharge side of the BOG compressor 32, and the two pressure controllers 39, 40
BOG gas is connected to LNG pipe 3 by switching
Since the heat quantity control system 50 is designed to prevent the mixed gas from flowing into the mixed gas with a sudden change in flow rate, the heat quantity control system 50 can adjust and control the quantity of heat of the mixed gas without enlarging the control range.

Therefore, there is no need to install a large-capacity heat control system, and it is easy to use BOG (evaporative gas) as city gas, and there is no need to install a large-capacity calorific value control system, and it is easy to use BOG (evaporative gas) as a city gas if there is a large amount of BOG (evaporative gas) consuming equipment such as a power plant nearby. Not done
Effective for LNG terminals, etc.

[Effects of the Invention] As described above in detail with one embodiment, according to the pressure control method for adjusting the amount of heat that takes into account BOG flow rate fluctuations of the present invention, BOG (evaporated gas), which has a large fluctuation in the amount of generated gas, is The piping system on the discharge side of the compressor is used to accumulate pressure, and the flow rate fluctuation rate is maintained at a predetermined value regardless of changes in the BOG compressor load. Pressure fluctuations are controlled by switching the pressure controller, etc. By controlling this, the range of fluctuation in the pressure of BOG (evaporated gas) mixed into LNG vaporized gas is reduced, so the control range of the mixed gas calorific value control system can be reduced, and the calorific value can be adjusted with high precision. .

Therefore, there is no need to install a large-capacity heat control system, and it is easy to use BOG (evaporative gas) as city gas, and there is no need to install a large-capacity calorific value control system, and it is easy to use BOG (evaporative gas) as a city gas if there is a large amount of BOG (evaporative gas) consuming equipment such as a power plant nearby. Not done
Effective for LNG terminals, etc.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of an embodiment of the pressure control method for adjusting the amount of heat in consideration of fluctuations in BOG flow rate according to the present invention, and Fig. 2 shows the pressure control method for adjusting the amount of heat in consideration of fluctuations in BOG flow rate according to the present invention. FIG. 3, which is an explanatory diagram of the operation of one embodiment, is a schematic configuration diagram of a conventional heat amount adjusting device. 20: Pressure control method in heat adjustment considering BOG flow rate fluctuation, 30: BOG flow rate control system, 5
0: Calorific value control system, 31: LNG tank, 32:
BOG compressor, 33: BOG piping, 34: LNG vaporizer, 35: LNG piping, LPG flow rate detector, 36:
BOG pressure detector, 37: BOG flow rate detector, ratio control controller, 38: BOG flow rate control valve, 3
9, 40: Pressure controller, 41... Controller, 42: Changeover switch, 52: Flow rate detector,
53: ratio control controller, 54: LPG vaporizer, 55: LPG flow rate detector, 56: flow rate control valve,
57: Controller, 58: Mixer, 59: Calorimeter.

Claims (1)

[Claims] 1. When adjusting the calorific value by mixing LNG vaporized gas obtained by vaporizing liquefied natural gas and BOG (evaporated gas) from a storage tank with calorific value adjustment gas obtained by vaporizing liquefied petroleum gas, it is mixed into LNG vaporized gas.
A flow control valve is installed in the piping system on the discharge side of the BOG compressor that compresses BOG (evaporated gas), and this flow control valve allows the BOG pressure to accumulate in the piping system, and the load by the BOG compressor is within a steady range. When the BOG compressor load increases, the pressure controller for controlling the BOG pressure in the case of The flow control valve is controlled to gradually reduce the pressure while preventing a sudden increase in pressure.When the load on the BOG compressor decreases, the flow rate decrease is maintained at a predetermined value and the BOG (evaporated gas ) is characterized in that the flow control valve is controlled so as to increase the mixing pressure of
Pressure control method for adjusting heat amount considering BOG flow rate fluctuation.