Gas Turbine Handbook : Principles and Practices

276 Gas Turbine Handbook: Principles and Practices
that rotate at up to 96,000 RPM. The generator is cooled by airflow
into the gas turbine. Built-in relay protection (over/under voltage and
over/under frequency) automatically trips off the microturbines in
the event of a utility system outage or a power quality disturbance.
Excess electricity not used by ACHS is sold to Commonwealth Edison.
A 12-turbine system was selected to provide a system that will remain
functional as LFG production from HOD Landfill decreases. Based
on the initial LFG collection rates, up to 18 turbines could have been
installed. The final payback for this project, based on conservative
assumptions for future energy costs, is approximately 8 years. The
installed microturbines are shown on Figure 17-5.
Heat Generation
Each Capstone MicroTurbineTM produces exhaust energy of
around 290,000 Btu/hr at 550°F. The exhaust from the microturbines
is routed through heat exchangers that heat the liquid, which then
circulates through underground insulated steel pipes running beneath
a parking lot to the school’s boiler system. Because heat is being
transferred to the school through insulated 4-inch–diameter pipes,
locating the turbines next to the school was critical in preventing excess
heat loss. When waste heat recovery is not required by ACHS, the
microturbine exhaust is automatically diverted around the exchanger,
allowing continued electrical output. During extremely cold weather,
the school boiler system automatically uses natural gas to supplement
the heat output of the microturbines.
SUMMARY
This project serves as a model of how a landfill with relatively
small quantities of LFG can be used to produce clean efficient energy.
By using the electricity and heat created during power production,
microturbines become more practical for landfill gas utilization.
The main advantages of microturbine technology over other more
traditional internal combustion engines are the clean, quiet operation
and the ability to add and remove microturbines as gas flow increases
or decreases.
The project’s design and construction can be a model for other
communities that are interested in the beneficial reuse of nearby