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There are three basic configurations for power plants:
- Simple Cycle,
- Combined Cycle, and
- Cogeneration.
Simple Cycle
The Simple Cycle refers to a power plant with 1
(one) Prime Mover and 1 (one) Generator. Fuel is burned in the Prime
Mover which turns the Generator, and all of the remaining energy
is vented into the environment. This kind of system can convert
fuel energy into electrical energy with about a 30% efficiency.
Over the last 15 years, engineers have developed
methods to recover the remaining waste energy. When it's used to
create more electricity, we call it Combined Cycle. When the waste
energy is used to heat something, we call it Cogeneration.
Combined Cycle
So Combined Cycle refers to a power system that
re-uses waste energy to create even more power. You start with the
same basic equipment that's used in the Simple Cycle (1 Prime Mover,
1 Generator), but then you add a specially designed boiler (called
a Heat Recovery Steam Generator - HRSG) to collect the waste energy.
The HRSG converts the waste energy (hot exhaust gases) into steam,
which we feed into a Steam Turbine. The Steam Turbine is connected
to a second Generator. The steam makes the Steam Turbine spin, which
in turn spins the second Generator.
This kind of system can reach efficiencies between
50% and 60%. Using a Back-pressure Steam Turbine (a special Steam
Turbine that can recover even more energy), this kind of Combined
Cycle system can achieve efficiencies of over 85%!
With such high efficiencies, it's not surprising
that over half of the new electrical capacity added in North America
over the past 5 years, has used a Combined Cycle, natural gas turbine
system.
Cogeneration
Cogeneration refers to the simultaneous production
of two forms of energy from a single fuel. So in this case, we again
start with the equipment from the Simple Cycle (1 Prime Mover, 1
Generator) to generate electricity. And we add the HRSG to collect
the waste heat. But now, instead of using the steam we get from
the HRSG to create even more electricity, we use it 'as is' in some
part of our manufacturing process, for space heating or even to
cook food.
Let's take a closer
look at Cogeneration.
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