Among the main challenges to complete a cogeneration
combined heat and power project is having all the players work
A good way to have the cogeneration system follow the steam host's steam load is to duct
burn1 The amount of duct burning can be varied. This is
efficient because, with 15% oxygen in the gas turbine exhaust, no
additional air needs to be added(unless the duct burning is extremely
high). The additional air would have exited the stack at a temperature
higher than outdoor temperture- a waste.
- The Utility may not want to buy the power or may put large restrictions or costs to
connecting to the grid such as a standby charge when the cogenerator is shut down.
- The steam host may have fluctuating
heat or steam requirements which may be hard to follow.
With electricity more valuable, the tendancy is to generate a lot of electricity, leaving only a small proportion of the potential heat for the steam host and the rest lost at condenser cooling tower or heat exchanger to the river.