Energy-water nexus at Argonne

By Dejan Ristic

Last year, Argonne saved about 29 million gallons of domestic, potable water by converting once-through cooling systems into closed-loop cooling systems at several buildings on the laboratory site. In a once-through system, potable water is run through heat exchangers only once before it is disposed of; whereas in a close-looped system, the water circulates perpetually through the system.

These retrofits annually save about $75,000 in water and $400 in electricity. Though four hundred dollars a year in electricity savings may not sound like much, it translates into the elimination of about 80,000 pounds of greenhouse gas (GHG) emissions per year.

So, how does electricity production result in GHG emissions? Electricity comes from a mix of power-generation sources. According to Commonwealth Edison’s June 2012 Environmental Disclosure Statement, almost all electricity is generated from coal (42 percent), nuclear sources (39 percent) and natural gas (14 percent). Biomass, hydropower, oil, wind and other sources each contribute one percent to the overall power-generation in the nation. This mix of power-generation sources emits about 1,043 pounds of GHG into the atmosphere per 1,000 kilowatt-hours (kWh) generated. Some energy sources — nuclear, hydropower and wind — are considered “clean” energy sources, meaning that they emit no GHGs, while other fossil fuel sources, like coal, oil and natural gas, emit pollutants and GHGs into the air when they’re burned.

So, what is the energy-water nexus and how are GHG emissions related to it? Power-generation companies use water in the form of steam to power turbines and generators. As coal or natural gas is burned, the heat converts water into steam, which powers the generators. An even greater quantity of water is used as a cooling agent. Cooling is needed at nuclear facilities and coal- and natural gas-burning facilities. Ultimately, it takes energy to pump and process water. Therefore, when power-generation facilities use less water – whether it be through steam production or cooling – it saves on GHG emissions.

Argonne is working to meet its energy and water intensity reduction goals, in line with U.S. Department of Energy sustainability efforts.

Dejan Ristic is a Pressure/Energy Systems Engineer and Group Leader at Argonne National Laboratory.

Posted August 7, 2012