Feed Water System

Tang Sae Yiang Green Power Co, Ltd Technical RequirementContract Document

Volume 2,Section 6:Feed water System

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A Engineering Consultant Co. Ltd; 27-Mar-11

VOLUME 2

SECTION 6: FEEDWATER SYSTEM



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VOLUME 2

SECTION 6 FEEDWATER SYSTEM

TABLE OF CONTENTS

6 FEEDWATER SYSTEM......................................................................................................3

6.1 GENERAL...................................................................................................................3

6.2 BOILER FEED SYSTEM...........................................................................................3

6.3 CONDENSATE SYSTEM...........................................................................................4

6.4 CYCLE MAKEUP AND STORAGE SYSTEM.........................................................5




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6 FEEDWATER SYSTEM

6.1 GENERAL

As shown schematically in Appendix 1, the feedwater system shall consist of the following systems for flow of feedwater from the condenser hot well to the boiler inlet:

- Boiler feed system

- Condensate system

- Cycle makeup and storage system

6.2 BOILER FEED SYSTEM

The boiler feed system provides flow of feedwater from the deaerator storage tank to the boiler inlet. It also provides for desuperheating spray to the boiler attemperator.

The boiler feed system comprises of two (2) 100% capacity electric motor driven boiler feed pumps. The boiler feed pump will be multi-stage centrifugal feed water pumps driven by electric motor. The design duty of feedwater pump shall be based on the ability to deliver a water flow corresponding to design capacity of 54m3/hr when in operation at 130C feed water temperature. The design head of the pump equals to about 870 MLC (Meter Liquid Column) & shall be finalized during detailed engineering

NPSHR Characteristics

At rated capacity, margins between required and available NPSH shall be selected under strainer 50% clogged conditions.

NPSHR curve should be a continuously rising one in the range of operation, from the minimum flow in the range to the maximum flow in the range. Required NPSH values shall not exceed available values over the entire range from minimum to rated flow.

Each pump shall be provided with a suction and discharge isolating valve of gate type and a separate discharge non-return valve.

The pumps shall be designed to provide the feedwater requirements consistent with the boiler design. For normal operating conditions for the boiler feed system will be dependent upon the heat balance supplied by the turbine manufacturer.

The de-superheating spray water requirement will depend on the boiler manufacturer’s design as well as the boiler rate.

Feedwater from the de-aerator storage tank will flow to the boiler feed pumps suction. The pumps will supply the pressure head necessary to overcome the friction losses in the piping,




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and provide the pressure required at the boiler inlet. The branch line supplying spray water to the boiler attemperator contains a pneumatically operated control valve and gate valves both at its upstream and at the downstream. The control valve modulates the spray water flow to control the steam temperature downstream of the attemperator.

6.3 CONDENSATE SYSTEM

The condensate system condenses main cycle exhaust steam and provides a flow path to the deaerator.

The condensate system typically contains the following major components, but as the contractor has overall responsibility for the design, the listed items should be considered as a suggestion:

- Two (2) x 100% capacity condensate pumps from condenser hot well.

- One direct-contact spray and tray type de-aerator with a horizontal cylindrical shell storage tank.

The condensate system shall be designed to provide condensate de-aeration consistent with the turbine generator design conditions.

During normal operation, condensate shall be supplied to de-aerator by one condensate pump (One pump for standby) from the condenser hot well into the de-aerator.

The steady state NPSH available shall be as per pump manufacturer’s standard

Mechanical seal flush lines and vent lines of the condensate pumps shall be provided for prevent air in-leakage into the system.

The P&ID for the plant feedwater & condensate system will be provided during detailed engineering for review & approval, which shall detail the complete system.

The deaerator shall be located near the boiler depending on the detail engineering & the plant layout, to provide sufficient NPSH margin for the boiler feed pumps and shall guarantee reduction of the oxygen content in the feedwater to not greater than 0.007 ppm as measured by the HEI method at the storage tank outlet. The de-aerator unit shall consist of a de-aerator heater, water storage tank, de-aerating spray nozzles and tray nests, and all necessary pipes, valves and auxiliaries. Equipment shall be provided to maintain the de-aerator pressure even when the steam turbine is operating at low load.

The de-aerated water storage tank shall have a capacity, at normal water level, sufficient to provide 20m3 storage capacity.

Equipment shall be provided to supply the de-aerator with steam from the main steam line during start-up, and low load operation.

The de-aerator shall be designed for system pressure and full vacuum.




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6.4 CYCLE MAKEUP AND STORAGE SYSTEM

The cycle makeup and storage system provides demineralized water storage and pumping capacities for makeup to the steam cycle to compensate for the boiler blow down, vents and drains.

The cycle makeup and storage system typically consists of the following major components.

- Four (4) de-mineralized FRP water storage tank of 30 m3 capacity each.

- Two (2) x 100% capacity, cycle makeup water pumps for normal make-up

The cycle makeup and storage system shall be capable of providing the required makeup water to the steam cycle under all startup and operating conditions, including chemical cleaning, steam blowing, flushing and hydrostatic testing.

Each pump shall be provided with a suction and discharge isolating valve of gate type and a separate discharge non-return valve.

Alarms are provided for low-low and high-high water levels in both the demineralized water storage tanks. The water level in the tank shall be displayed in the control room

The cycle makeup and storage system receives demineralized water through pipe from the demineralization WTP system. All the water storage tanks are located semi-outdoor. The cycle makeup pumps take suction from the condensate/DM water storage tank. The cycle makeup water pumps discharge into a pipe that connects to the condensate system

The demineralized water storage tank shall be a vertical, cylindrical, atmospheric, field erected water tank of FRP construction.

The cycle makeup water pumps shall be a constant speed, centrifugal type driven by electric motor. The shaft and sleeve of pump shall be stainless steel.


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Feed Water System