5.2.3  CEGB specifications

 

Specifications for plant include a requirement for the contractor to guarantee the thermal performance of the condenser. The contractor is expected to guarantee an absolute pressure at the turbine exhaust under the conditions of design steam flow, minimum cooling water quantity at the design cooling water inlet temperature and with the tubes in the brushed-clean condition. The temperature of condensate leaving the condenser and the air suction temperature, with the design air loading, are also guaranteed.

As a way of comparing how the design standards produced by the HEI and BEAMA reflect the level of performance which can be obtained from well designed condensers, Fig 4.18 shows the test results of a number of condensers of over 4600 m2, as presented by Steel [7]. Superimposed on these data are the values for the heat transfer coefficients, as recommended by the HEI and BEAMA standards.

Typical condenser test results of heat transfere coefficient plotted against water velocity in tubes

It can be seen that the Standard procedures closely represent the mean of test results obtained in practice. Furthermore, it should be recognised that these test results also incorporate the complexities of thermal and aerodynamic processes present in large condensers, and cover the diverse arrangement of tubenest geometry and differences in operating conditions.

Recognising the proven use of the BEAMA [6] and HEI [5] design codes to obtain well designed condensers, further development work has resulted in a single individual formulae being established for each design code which equates the total heat transfer coefficient based on the data and formulae of each code as shown in Fig 4.18. These equations are:

This not only simplifies the use of these design codes, but lends them ideal for use in computer analysis.

More recently, however, calculated values of heat transfer coefficient, based on laboratory measurements of steam and waterside coefficients, indicate that condenser performances better than those predicted by present design codes, i.e., HEI [5] or BEAMA [6], should be possible with careful attention to the tube-nest geometry.

 

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