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Industrial waters 77

protection goals, particularly in environmentally sensitive locations (Crook et
al., 1994; Puckorius, 1997). It is thus important to develop more efficient
approaches to management of water in the thermoelectric power industry.
Over the past decade, recurring water shortages coupled with more
rigorous water quality requirements have prompted a re-examination of current
cooling water practices. Water availability poses challenges to the siting of new
power production facilities. In addition, a growing water resource management
trend worldwide is to prioritise the use of water based on water quality and
availability. Where appropriate, the emphasis is on preserving the highest
quality water sources for potable water applications by using secondary sources
for applications that have less stringent water quality requirements. As is
evident from Fig. 3.1, efforts to reduce the quantity of water used for
thermoelectric power generation can have a direct impact on balancing the
distribution of water resources. This section aims to discuss the potential for
using reclaimed water as a water source for cooling operations. A description of
cooling water applications is given, water quality requirements are discussed
and treatment alternatives presented. Some existing examples of cooling
operations using reclaimed water are also given.

3.7.2 Overview of cooling water systems
Thermoelectric power plants typically derive energy from heat-generating fuels,
such as nuclear fuel, coal, oil, natural gas, municipal solid waste, or refuse-
derived fuel. The heat is used to produce steam in a boiler. The steam passes
through a turbine and is then condensed back to water and pumped back to the
boiler to repeat the cycle. The turbine drives a generator that produces
electricity. Steam turbines extract power from steam as it passes from high-
pressure and high-temperature conditions at the inlet to low-pressure and
low-temperature conditions at the outlet. The outlet pressure is a function of
the temperature of the cooling water used to absorb heat and reject it from the
condenser (Asanoetal., 1988; Burger, 1979; Kemmer, 1988).
The water requirements for power plants are based on providing water for
cooling and water as a source of steam in boilers. Typically, higher quality water
is needed for boiler feed water as compared to cooling water. In general, cooling
systems function to remove excess heat from heat sources. A cooling tower acts
as a heat exchanger by driving ambient air through falling water, causing
some of the warmed water to evaporate, thereby dissipating heat and
providing cooling. The cooler water is then circulated back to the equipment
that needs cooling. In thermoelectric power plants, cooling water is used to
remove heat from the turbine exhaust and condense it back to liquid prior to its
return to the steam generator.
Cooling tower operations consist of evaporative condensation and exchange of
heat. Latent heat of vapourisation is released from the air and water mixture,
resulting in evaporation of water at a rate dependent on the temperature and
pressure. The amount of heat consumed is about 2.3 kJ 8-l of water evaporated.
For each 5.5"C of cooling, about 1.2% of the water is released from the cooling