2.1 Condenser surface area, turbine exhaust pressure and CW flow
In developing proposals for a new power station, necessary to optimise the design of the various component parts, and of the total system.
Traditionally, all the main component parts of the system are assessed separately, each being optimised according to its own set of design rules, using 'fixed' interface parameters based on a combination of previous experience and engineering judgement. However, some of these 'sub-optimisations' are in fact interdependent, for example, variations in the civil costs of the CW system may have a significant effect on the true optimum size of condenser. The problem is best approached by applying an iterative process, each sub-optimisation being repeated with revised values until the system design is fixed. This is very time consuming by hand calculation, but one which lends itself ideally to calculation by computer.
A computer program has been developed to assess lost economic condenser surface configuration, turbine exhaust pressure, and CW flow for any given site. It creates a mathematical model of the system, taking into account the cost and performance interrelationships between the different plant components, simultaneously. It can evaluate both direct-cooled systems and closed systems (cooling towers), and perform the repetitive calculations necessary to ultimately arrive at the lowest lifetime costs by balancing the capital costs and operating costs of each individual item of plant.
The paragraphs which follow, highlight the specific aims and objectives of a typical computer optimisation study for a seawater-cooled station, and describe the assessment procedure involved in achieving a realistic analysis.
The main parameters to be optimised are.
- Condenser surface area — hence the vacuum, assum-that an efficient tube layout is adopted.
- Cooling water flowrate.
- Number and size of condenser tubes — hence tube length and flow velocity in the tubes.
- Basement height.
- Seal pit weir height.
- Culvert flow velocity — hence culvert size.
- Culvert length — usually fixed by external considerations, e.g., avoiding recirculation between inlet and outlet.
From the culvert velocity and length, and other parameters, the CW pumping requirements can be determined. A typical assessment procedure is illustrated in Fig 4.3.