Efficiency differences due to real constraints

It is reasonable to expect that there will be differences in efficiency between particular plants because of the

constraints within which they were constructed and operate. Considerations which can impact significantly

on efficiency include:

• fuel moisture content (influences latent and sensible heat losses);

• fuel ash content (impacts on heat transfer and auxiliary plant load);

• fuel sulphur content (sets design limits on boiler flue gas discharge temperature);

• use of closed-circuit, once-through or coastal cooling-water systems (determines cooling-water temperature);

• normal ambient air temperature and humidity;

use of flue gas cleaning technologies, e.g. selective catalytic reduction (SCR), fabric filtration, flue gas

desulphurisation (FGD) and CO2 capture (all increase on-site power demand); and

• use of low-NOx combustion systems (requires excess combustion air and increases unburned carbon).

A plant designed for high-moisture, high-ash coal, fitted with FGD and bag filters, and operating with a