Gas Turbine Cooling Water System

General

The cooling water system is a pressurized, closed system, designed to accommodate the heat dissipation requirements of the turbine, the lubrication system, the turbine support legs and the flame detector mounts. An aqueous solution of ethylene glycol is used in the system; therefore, it is capable of performing its function throughout the year if the ambient temperatures are not too high. During frost the cooling system must be filled with an aqueous solution of ethylene glycol. During high temperatures it is necessary to fill the system with a solution whose quality is specified in the "Gas turbine subcontractor’s literature chapter". In the text that follows, this solution is referred to as the cooling water.

Included in the cooling water system are the cooling cells, the pumps, miscellaneous valves and certain control and protection devices. The cooling system is connected to the customer's cooling water system.


Functional Description

The cooling water system circulates water as a cooling medium to maintain the lubricating oil at acceptable lubrication system temperature levels and to cool several turbine components. The system normally operates at a slightly positive pressure which results when the fuel in the system expands with the increase in temperature during operation.

During operation the coolant is supplied by the owner's cooling system and circulates through the chosen lube oil, the turbine support legs (in parallel with the system of heat exchanger) and the flame detector mounts. After absorbing the heat rejected by these items, the coolant flows through the owner's water cooling system where it is cooled.

The flame detector mounts are cooled to extend the life of the flame detectors. The coolant jackets on the flame detector mounts provide a thermal break in the heat conduction from the combustor can housing to the flame detector instrument.



Flow regulating valves

The coolant circuit for the lube oil has a temperature actuated 3-way valve (VTR-1) installed in the coolant inlet line to the heat exchanger.

This type of valve, which controls coolant flow to the heat exchanger, has a manually operated device which can override the thermal element. The manual override device should be used only when the valve's thermal element is inoperative but machine operation is required. Lube Oil feed header temperature is sensed by the bulb associated with the valve which controls the flow of coolant through the heat exchanger and maintains the lube oil temperatures at predetermined values. The valve automatically controls flow of the medium passing through it (coolant) to the heat exchanger by responding to temperature changes affecting the bulb.

The bulb contains a thermal-sensitive liquid which vaporizes when heated. Pressure thus generated in the bulb is transmitted through the capillary tube to the bellows, which positions the valve disc to control the flow of coolant through the heat exchanger. The valve is closed during turbine startup, and will start to open as the sensed fluid temperature approaches the control setting.

At the inlet of each cooling water circuit (lube oil heat exchanger circuit and turbine support legs circuit), an orifice allows water flow rate calibration to the circuit concerned.


Shut-off valves

Shut-off valves are provided in the piping so that the tube side of the lube oil heat exchanger may be isolated from the water system for maintenance.

Temperature, pressure measuring and/or protective devices Thermocouples, WT_TL-1,-2 at turbine support legs outlet located at GT cooling system outlet, give a GT cooling water temperature indication.

NOTE: For the recommendations about the various components of the circuits, refer to The "Gas turbine subcontractor’s literature chapter".