Tuesday, June 30, 2015

Water Use Declining as Natural Gas Grows

As the U.S. has undergone a rapid and massive shift to natural gas from coal, one benefit has gone almost entirely overlooked:  the amount of water needed to cool the nation’s power plants has dropped substantially.

The widespread adoption of hydraulic fracturing (fracking) technology has led to dramatically higher natural gas production in the U.S. since 2005.  The resulting drop in natural gas prices, coinciding with new EPA air quality regulations for coal-fired power plants, has led to a surge in natural gas-fired electricity generation nationwide.

Between 2005 and 2012, coal’s share of electricity generation fell to 37 percent from 50 percent.  Natural gas rose to 30 percent from 19 percent. Total electricity generation stayed roughly constant.

That shift has translated into big changes in the amount of water being withdrawn from lakes and rivers to cool power plants.  And it’s an important shift as nationally, 38 percent of all water withdrawn is for power plants.

During the most recent 7-year period with reliable data, water use fell dramatically to 33 trillion gallons in 2012 from 52 trillion gallons in 2005.  On average, the current natural gas power plants use four times less water per megawatt-hour generated than their coal-fired counterparts.

Water withdrawals for power generation dropped by more than 1.5 trillion gallons per year in Ohio, New York, and Illinois; 10 states had decreases of 1 trillion gallons or more.  Electricity generated from natural gas increased 370 percent on average in those 10 states, with the largest absolute increases coming in Alabama and New York.

Some power plants are designed to be cooled by water withdrawn from a river, lake, or ocean and then returned to those waters.  To protect fish and other wildlife from dramatic increases in water temperatures from the discharges, regulations limit how much the water can be warmed at the power plant before it is discharged.  In hot and/or dry periods some power plants have been forced to reduce output, shut down completely, or seek exemptions from the regulations.

Water consumption in power generation refers to water withdrawn from a river, lake, or ocean but not returned to the water body from which it came.  Evaporation from a cooling tower is one example.  Nationally, freshwater consumed to cool power plants was about 1 trillion gallons in 2012.  In contrast, freshwater withdrawals were 33 trillion gallons.  Power plants without cooling towers account for most of the withdrawals.  These plants use “once-through” cooling systems in which water withdrawn from a river, lake, or the sea absorbs heat as it cools the plant and is discharged back to its source before its temperature exceeds the regulated limit. Most new natural gas power plants use cooling towers and many recently retired coal plants used once-through cooling, which helps explain the drop in water withdrawals for power generation nationally.

Read more at Water Use Declining as Natural Gas Grows

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