part 1: overview of cogeneration and its status in asia - Fire

28 Part I: Overview of cogeneration and its status in Asia
- heat-to-power ratio;
- quality of thermal energy needed;
- electrical and thermal energy demand patterns;
- fuel availability;
- Required system reliability;
- Local environmental regulations;
- dependency on the local power grid;
- option for exporting excess electricity to the grid or a third party, etc.
Some of these concerns are further elaborated below.
1-Technical Analysis 2-Economic Study
4-Financial Arrangement
6-Execution
3-Selection of Best Solution
7-Starting off
5-DECISION
8-Technical &Financial
Result
Figure 3.1 Typical steps for cogeneration project development
A cogeneration system may be sized to meet either the electricity or the heat demand of the
site. When the local power utility allows selling excess electricity generated at the site, one
should make sure that the buy-back rate is attractive enough before over-sizing the
cogeneration plant.
As the electrical and thermal loads of the site tend to vary with time, the cogeneration system
may require that any shortfall in the electricity supply be met by the purchase of electricity
from the grid. Likewise, any shortfall of thermal energy should be met by either postcombustion
of exhaust gases in the case of gas turbines or reciprocating engines, or from an
auxiliary source such as a stand-by boiler. These solutions will certainly have consequences
on the annual average efficiency and the economics of the project. The ideal operation would
thus consist of the use of the maximum electricity on site, while assuring continuous
operation of the processes at nominal conditions and avoiding the generation of excess
thermal energy.
If the thermal load is negligible or if it is required to produce only low-pressure steam or to
heat a fluid at low temperature, gas engine may be preferred because of its higher efficiency.