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COGENERATION AT THE CENTRAL POWER PLANT
Summary:
The University of Michigan (U-M) Central Power Plant (CPP) is a major contributor to energy efficiency and reduced air pollution due to the implementation of a process called cogeneration. Cogeneration refers to the simultaneous production of both useful steam and electricity. By combining these processes into one power plant, the overall fuel efficiency is more than doubled, when compared to a conventional thermal-electric power plant.

 

Applicable Regulations
None.

 

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.

 

Waste Minimization Procedure
Not applicable.

 

Known Limitations
None known.

 

Safety & Health Precautions/Personal Protective Equipment
Follow all applicable safety and health protocols and regulations as established by your institution.

 

Benefits
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 chart below).

 

Disadvantages
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)

  CPP MDEQ Standard Coal-Fired Plant
CO 51.7 96.7 336.5
NOx 415.0 720.8 1,019.7
SO2 7.2 7.2 2,039.3
Total 473.9 824.7 3,395.5
*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.

 

Project Related Costs
One recent estimate determined that cogeneration saves the U-M about $4 million each year in reduced energy charges.

 

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