Overview of Procedure
Briefly, the process of
cogeneration is as follows: natural gas is burned in boilers to produce steam at a
pressure of 400 pounds per square inch (psi). The steam is fed into turbines that generate
electricity. The steam leaving the turbines is at a much lower pressure, about 9 psi. This
low pressure "discharge" steam is fed into the steam pipes for distribution to
buildings throughout the central campus.
The process of cogeneration contrasts
dramatically to the practice of most thermal-electric power plants, which essentially
"throw away" the exhaust steam from the electric turbines. By using this exhaust
steam, the fuel efficiency of the CPP is approximately 78 percent, compared to a fuel
efficiency of approximately 40 percent for most private utility plants.
& Health Precautions/Personal Protective Equipment
Follow all applicable
safety and health protocols and regulations as established by your institution.
The CPP is not only
energy-efficient, but also emits lower quantities of pollutants, compared to other energy
processes. The visible emission coming out of the smokestacks is often mistaken for smoke;
however, it is actually excess water vapor from steam production. The burning of natural
gas does produce some chemical by-products. However, the amounts of these chemicals are 42
percent less than the emissions standards set by the Michigan Department of Environmental
Quality (MDEQ), and far below the emission levels of a typical coal-fired power plant (see
The main disadvantage to
using cogeneration is that the demand for steam and electricity must occur simultaneously
in order for the process to work. This is not a problem during the winter months, when
both steam and electricity are required on a relatively high and constant level. In the
summer, however, there is little demand for steam heating. To ensure there is a steam
demand during the summer months, the University uses steam-powered air conditioning
systems in many buildings. Although these systems are commonly more expensive than their
electric counterparts, the long term savings more than make up for it.
Emissions Per Year (Tons)
|*Based on 1995 CPP data and MDEQ
report. MDEQ standards from MDEQ published Revolving Energy Account Fund figures.
Coal-fired figures from published emission factors for coal combustion. MDEQ and
Coal-fired based on equivalent BTU input.
One recent estimate
determined that cogeneration saves the U-M about $4 million each year in reduced energy