AU2002100542B4 - Improved steam turbine cooling system - Google Patents

Description

P/00/012 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION INNOVATION PATENT Invention Title: "IMPROVED STEAM TURBINE COOLING SYSTEM" The following statement is a full description of this invention, including the best method of performing it known to us: 2 IMPROVED STEAM TURBINE COOLING SYSTEM The invention relates to steam turbine cooling systems and in particular to a modified cooling system that provides improved cooling.

BACKGROUND TO THE INVENTION Known power generator stations employ water as the primary coolant. The plant cooling system provides parallel cooling water flow through the steam turbine condenser and the unit coolers. The unit coolers provide cooling to plant elements such as pumps, alternator windings and oil cooling plant. Cooled water is normally provided from a cooling tower somewhat removed from the turbines and cooling units.

The cooling load from the turbine condenser is generally quite different from the unit coolers. Yet, the cooling water is provided through a single supply pipe and delivered in parallel to both loads.

The water from each load is returned to the cooling tower through the same pipe. The temperature rise in the cooling water is generally much less from the unit coolers than from the turbine condenser.

The inventor has realized that the existing arrangement is inefficient. A better cooling system is required that takes into account the different heat loads from the turbine plant and the unit coolers and the different temperature rises in the cooling water.

OBJECT OF THE INVENTION It is an object of the invention to provide an improved cooling system for turbine power generating plants.

DISCLOSURE OF THE INVENTION In one form, although it need not be the only or indeed the broadest form, the invention resides in an improved cooling system for a turbine power plant of the type having a source of coolant and at least two heat sources with different loads, said improved cooling system comprising: a first supply line carrying coolant from said source of coolant to said at least two heat sources in parallel; a second supply line carrying coolant from one of said at least two heat sources having a lower load to at least one of said at least two heat sources having a higher load; and a return line carrying heated coolant from said at least two heat sources to said source of coolant.

The inventor has found that the proposed arrangement makes significantly more efficient use of the heat capacity of the coolant by using remaining heat capacity of the coolant after cooling the lower load to provide additional cooling of the higher load.

The invention may suitably include a booster pump in the second supply line between the lower load heat source(s) and the higher load heat source(s).

The invention may suitably include a non-return valve in the second supply line between the lower load heat source(s) and the higher load heat source(s).

The invention may suitably include an isolation valve in the return line to activate and deactivate the improved cooling system.

In preference, the invention is installed as a modification to an existing cooling system with the existing cooling system remaining as a back-up system.

BRIEF DETAILS OF THE DRAWINGS To assist in understanding the invention, preferred embodiments will now be described with reference to the following figures in which: FIG 1 is a schematic of a prior art cooling system; FIG 2 is a schematic of a first embodiment of an improved cooling system; and FIG 3 is a schematic of a second embodiment of an improved cooling system.

DETAILED DESCRIPTION OF THE DRAWINGS In the drawings, like reference numerals refer to like parts. A prior art cooling scheme is depicted in FIG 1. The heart of the power plant is a steam turbine 1 that produces steam to be cooled in condenser 2. A cooling tower 3 is a source of cooled water for cooling the steam condenser 2. The cooled water is also used in unit coolers 4.

Cooled water from the cooling tower 3 is supplied in supply line 5. Pumps 6 provide the pressure to move the cooled water through the lines. The line is split into parallel supply lines 5a and to the condenser 2 and the coolers 4 respectively. After passing through the condenser 2 and the coolers 4 the warmed water is returned through return lines 7a and 7b until the parallel systems are recombined and the warmed water is returned to the cooling tower in return line 7.

The inventor has realized that the heat loads and temperature rises of the unit coolers 4 and condenser 2 are usually different, often significantly so. Thus there is a considerable difference in the temperature of the water in return line 7a compared to return line 7b.

An improved cooling system is shown in FIG 2. The improved system is fitted as a modification to the existing cooling system and leaves the existing cooing system in place as a back-up system.

A junction 8 is placed in the return line 7b of the lower load heat source, which is normally the unit coolers 4. A feed line 9 carries warmed water from unit coolers 4 to the condenser 2. A booster pump 10 will normally be required to provide pressure to move the water to the condenser. It may also be convenient to provide a nonreturn valve 11 to account for pressure differences between the cooling sub-systems of the unit coolers and the turbine condenser.

An isolation valve 12 is placed in the return line 7b to isolate the existing cooling system and activate the modified cooling system.

If necessary, for example due to failure of the booster pump 10, the original cooling system can be reactivated by opening the isolation valve.

Introduction of the partly heated water from the feed line 9 to the higher load heat source, which is normally the condenser 2, can be achieved in a variety of ways. One preferred solution is depicted in FIG 2. Most condensers have a two pass cooling action. Cool water from the cooling tower 3 passes through tubes 13 to a return water box 14. The partly warmed water passes from the return water box 14 through further tubes 15 to the return line 7a and hence to the cooling tower 3. Steam from the turbine 1 passes over the tubes 13, and is cooled through heat exchange with the cooler water in the tubes. Partly heated water from the unit coolers 4 is added to the return water box 14 thus lowering the temperature of the water in the return water box before flowing through the tubes 15. The cooling capacity of the condenser 2 is improved by using the untapped heat capacity of the partly heated water from the unit coolers. A manifold 16 may be used to deliver the water from the feed line 9 to the return water box 14 to improve mixing.

Another option for supplying the partly heated water from the cooling units 4 to the condenser 2 is shown in FIG 3. In this case the feed line 9 is connected to an inlet water box 17 in the condenser 2.

In other respects the modified cooling system is identical.

For most practical applications the option depicted in FIG 2 is preferred since the feed pipe 9 can be split into manifold 16 for delivery of partly heated water into the return water box 14. The physical arrangement of the condenser in most known cooling systems makes it impractical to fit a manifold to the inlet water box.

By way of example the inventor has considered the benefit of the modified cooling system to a known power station in Australia.

The power station is a 350MW coal burning station. Unit coolers take approximately 12% of the supplied cooling water but only cause a 2.50C temperature rise. The condenser causes a 6.20C temperature rise in each pass for a total temperature rise of 12.4°C.

If the partly heated water from the unit coolers is supplied to the return water box of the condenser, the temperature of the water in the header tank is reduced by 0.460C. The increased flow through the condenser return section 15 also improves the cooling efficiency for a total reduction in water temperature immediately after the condenser of 1.10C.

Other advantages also accrue through the modifications. The condenser vacuum is reduced by the combined effects of lower water temperature and increased water flow. Turbine efficiency and output increases with reduced vacuum. The inventor estimates the vacuum increase to be between 0.5kPa and 1.0kPa which equates to an efficiency gain of between 0.25% and 0.5% of output, or about 1MW for a 350MW station. These figures take into account the additional power of the booster pump.

The inventor has surprisingly found that a significant improvement to power plant efficiency can be achieved with a modification that is relatively easy and cheap to implement.

Although the discussion of the preferred embodiments has been in terms of water as a coolant, the inventor envisages that the improvement is also applicable to cooling systems that may use other coolants.

Throughout the specification the aim has been to describe the preferred embodiments of the invention without limiting the invention to any one embodiment or specific collection of features.

Claims (4)

1. An improved cooling system for a turbine power plant of the type having a source of coolant and at least two heat sources with different loads, said improved cooling system comprising: a first supply line carrying coolant from said source of coolant to said at least two heat sources in parallel; a second supply line carrying coolant from one of said at least two heat sources having a lower load to at least one of said at least two heat sources having a higher load; and a return line carrying heated coolant from said at least two heat sources to said source of coolant.

2. The improved cooling system of claim 1, further comprising a booster pump in the second supply line between the lower load heat source(s) and the higher load heat source(s).

3. The improved cooling system of claim 1, further comprising a non-return valve in the second supply line between the lower load heat source(s) and the higher load heat source(s).

4. The improved cooling system of claim 1, further comprising an isolation valve in the return line to activate and deactivate the improved cooling system. 8 An improved cooling system substantially as hereinbefore described with reference to accompanying Figures 2 and 3. DATED this First day of July 2002 SIGMA PROCESS SOLUTIONS PTY LTD By their Patent Attorneys FISHER ADAMS KELLY