JPS6065211A - Operating method for lng coldness power generating plant - Google Patents

Abstract

PURPOSE:To prevent breakage of a medium circulation pump in a coldness power generating facility, when it is to be started, by overcooling an overcool coil installed inside the condensate liquid sump of a medium condenser by the use of LNG, and thereby preventing cabitation in the medium circulation pump. CONSTITUTION:An LNG coldness power generating facility of Rankin cycle system is composed chiefly of a medium condenser 1, medium circulation pump 7, medium evaporator 8 and medium turbine 10. When this facility is started, LNG4 is allowed to circulate in an overcool coil 3 installed inside a condensate liquid sump 2, which is furnished in the lower part of the drum of said medium condenser 1, so as to overcool the condensate liquid 6 in the condensate liquid 6 in the condensate liquid sump. Thus generation of cabitation in the medium circulation pump under the decompressive transient period can be prevented, so that breakage of medium circulation pump can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method of operating an LNG cryogenic power generation facility, and particularly relates to a method of operating a Rankine cycle type LNG cryogenic power generation facility.

[Background of the invention]

LNG cryogenic power generation equipment using the Rankine cycle system uses liquefied gases such as Freon 13 Bl, Freon 22, and propane as Rankine media.

These liquefied gases exchange heat with LNG in a medium condenser,
It vaporizes LNG and condenses it itself. The condensate is pressurized by a medium circulation pump, sent to a medium evaporator, where it is vaporized, rotates a medium turbine, returns to the medium condenser, and is recycled. Low-pressure operation is used to enable power recovery in the media turbine. For example, they are normally operated at near atmospheric pressure. The liquefied gas of the Rankine medium exhibits a saturation pressure at room temperature of 20° C. in a standby state before normal operation, and is about 7 to 13 to 9/cnG.

At startup, the pressure is reduced from this standby state to the normal operating state () to IKg/CIIQ, and the temperature is brought to a low temperature state. During depressurization operation, the medium condenser L N (
3 flow rate is set to 14 to 14 of the rated load, and cooling is performed while gradually closing the turbine bypass valve. In the transient state of vacuum cooling operation, although the pressure inside the medium condenser is low, the temperature of the medium sucked into the medium circulation pump has a time delay in the retention part of the medium condenser, and the pressure inside the medium condenser is saturated. Higher than temperature. Therefore, the effective NPS of the media circulation pump
H becomes smaller. Generally, the effective NPSH shown in equation (1) must be larger than the required $PSH of the medium circulation pump.

Effective N P S H = HpT + HHtoss - Hp
v＞Required NPSH・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・ (1) HPT: Container internal pressure (
Liquid column m) H: Water head of liquid (Liquid column m) H oss 'Pressure loss in flow path (Liquid column m) Hpv: Saturated vapor pressure of liquid at pump inlet (Liquid column m) can lead to damage to the media circulation pump. Also, if you try to increase the effective NFSH from the beginning, there will be a need to install the medium condenser at a high position.
The cost of construction and construction will be significant.

[Purpose of the invention]

An object of the present invention is to provide a method of operating an LNG cold-thermal power generation facility that can prevent cavitation from occurring in a medium circulation pump and prevent its damage by always maintaining effective NP8H greater than required NPSH.

[Summary of the invention]

The present invention provides a method for supplying LNG to a supercooling coil installed in a condensate reservoir installed in the lower body of a medium condenser at the time of startup of equipment.
This system is characterized by supercooling the condensate in the condensate reservoir by passing through the condensate, and the effective NPSH'5! : Always required NP
It is intended to be held larger than S H.

[Embodiments of the invention]

An embodiment of the present invention will be described with reference to the drawings.

) In the drawing, a supercooling coil 3 is installed in a superdilute I liquid storage section 2 provided at the lowest part of the body of the medium condenser 1.

The medium is condensed by the cold heat of LNG flowing through the heat transfer tube group of the medium condenser 1 and becomes a condensate 6, while the LNG 4 undergoes heat exchange in the medium condenser 1 and is vaporized to become NG gas 5, which is used as fuel. . The condensate 6 is pressurized by a medium circulation pump 7 and supplied to a medium evaporator 8 . In the medium evaporator 8 , the condensate 6 is vaporized by seawater 9 and is normally supplied to a medium turbine 10 . Electric power is recovered by the medium turbine 10, and the expanded and low-pressure medium is recycled again to the medium condenser 1. At startup, the internal pressure of the medium condenser 1 is approximately 100% because the condensate 6 is at room temperature. 7 to 13/cIIO is shown. The internal pressure of the medium condenser 1 is set to the normal operating pressure of 0-IK.
When the pressure is reduced to q/crlG, the flow is continued at a constant low load, and the turbine bypass valve 11 is gradually closed while the medium is circulated using the turbine bypass valve 11. The turbine bypass valve 11 is fully closed during normal operation, and 713 is a medium condenser 10) liquid level adjustment 3414, which has the function of the pressure regulator 12 as a protection control device for the medium turbine IO. The liquid level is controlled at a low level so that the condensate 6 does not enter the heat exchanger tube group of the condenser 1 and degrade heat exchange performance.

Reference numeral 14 denotes a bypass pipe for LNG 4, which allows LNG 4 to flow through the supercooling coil 3 to supercool the condensate 6 to prevent cavitation from occurring in the medium circulation pump 7 during depressurization operation when starting up the equipment. There is.

The operating method of this embodiment provides the following effects.

(1) When starting up the equipment, the medium sucked into the medium circulation pump is subcooled by LNG from the supercooling coil, and the medium is cooled to a temperature close to the saturation temperature of the pressure inside the medium condenser. Since the NPSH can be maintained larger than the required NPSH, cavitation in the medium circulation pump can be prevented, and damage to the medium circulation pump can be prevented.

(2) By providing the condensate reservoir at the bottom of the medium condenser,
By separating the condensation zone and the subcooling zone, the heat transfer area of the condensation zone can be fully utilized, reducing the depressurization operation time and the start-up time.

(3) Since the structure retains the condensate in the condensate reservoir, the space between the lower part of the heat transfer tube group in the body and the body is small, so the diameter of the body of the medium condenser is smaller than that of conventional ones. Can be made compact.

〔Effect of the invention〕

According to the present invention, when starting up a Rankine cycle type LNG cryothermal power generation facility, the condensate is supercooled with LNG in the condensate reservoir section of the medium condenser, and cavitation occurs in the medium circulation pump during the transition period of pressure reduction. This has the effect of preventing damage to the medium circulation pump.

[Brief explanation of the drawing]

The drawing is a system diagram showing an example of a Rankine cycle LNG cold-thermal power generation facility in which the present invention is implemented.

Claims (1)

[Claims] 1. A medium condenser, a medium circulation pump, a medium evaporator,
In a Rankine cycle type LNG cryogenic power generation facility mainly consisting of a medium turbine, when the facility is started up, LNG is supplied to a supercooling coil installed in a condensate reservoir provided at the bottom of the body of the medium condenser. A method for operating an LNG cryogenic power generation facility, which comprises supercooling condensate in a condensate reservoir by circulating it.