Inside Iowa State

Dec. 12, 2008

Coal-fired efficiency

by Diana Pounds

A lump of coal. Ultimately, that's what you're requesting when you boot up a computer, turn on a light or nudge the thermostat in your university workspace.

As we strive to "live green" at Iowa State, it's useful to know just how the university gets power and the very real role the campus community has in the efficiency of that power-producing process. Here is a quick look at the Iowa State power plant. (Information provided by Jeff Witt, assistant director of utilities, and other ISU utilities staff.)

How it works

• Six boilers at the power plant burn coal (154,000 tons per year) to create steam. Limestone (15,000 tons per year) is added to the combustion chamber to help remove sulfur from the coal.
• The steam spins turbines to generate electricity.
• Low-pressure steam that's already been used to produce electricity is extracted from turbine generators and used to heat buildings.
• Low-pressure extracted steam also is used to generate chilled water to cool buildings.

Cutting edge, since 1891

Most universities produce their own heating and cooling and buy their electricity elsewhere. Iowa State is among the few that heat, cool and generate electricity. This process, called "cogeneration," is more efficient because heat that normally would be discharged from a turbine is recovered and used. Public utility plants that don't cogenerate reach 35 to 42 percent thermal efficiency. The ISU power plant's efficiency is about 55 percent. Visionary Iowa State staff began the first cogenerating operation on campus in 1891.

Self-sufficient

Iowa State's power plant is capable of supplying all the heating, cooling and electricity needs of the university. However, when it's more economical to do so, ISU staff will purchase some electricity from other sources.

Environmental care

ISU power plant emissions are well below state and federal environmental limits. That's because the university buys Midwestern coal that's low in sulfur, and burns it in high-tech boilers that remove more than 90 percent of the sulfur. Emissions also are low because the cogeneration process doesn't use as much coal as traditional utility operations.

Each year, power plant operators must dispose of 30,000 tons of ash, the byproduct of burning coal. All of the ash is put to good use -- in reclaiming quarries, stabilizing soil, and manufacturing compost and cement.

Watt watch, in real time

An illuminating diagram on the utilities web site gives a real-time glimpse into what's going in and what's coming out of Iowa State's power plant at any given time of day. The web page shows how many tons of coal are in the boilers and how much steam is going to electricity, heating and cooling. Watch the campus steam figures as winter sets in. On a particularly cold winter day, steam used for heating might approach 300,000 pounds an hour. The "Real Time Utility Consumption" web page is at www.fpm.iastate.edu/utilities/plantdata.

Keeping the "co" in cogeneration

The host of electronics and appliances that have become staples of the modern work area have made things easier for most of us, but considerably harder for those trying to run an efficient power plant. In the past two decades, electricity and chilled water consumption at Iowa State have climbed and heating needs have declined. (All those electrical devices help to heat up the workspace.)

The bad news is that overall efficiency of Iowa State's power plant drops as the need for electricity overwhelms the cogenerating opportunities. Today, only 20 percent of the electricity used on campus can be cogenerated. The other 80 percent must be generated by the power plant like a conventional utility or bought from outside sources.

Have you saved your lump of coal today?

The good news is that Iowa State's energy consumption can be controlled by campus inhabitants. By shutting down equipment, appliances and lights not in use, individuals can have an immediate impact on the amount of electricity that must be generated in a given day. These green deeds will reduce coal use and emissions. And they may help the power plant regain some of its cogenerating capacity and efficiency.

Live Green!

More information on Iowa State's "Live Green!" initiative is online.