Water implications of low carbon energy production

The problem:
Climate change will likely have large impacts on the frequency and distribution of precipitation and on evapotranspiration. We address three key issues:

  1. water needs associated with existing and new energy technologies;
  2. changes in the statistics of drought in the U.S.; and
  3. impacts on electricity demand if technologies for water desalinization become common.

The research:
We will assess future water demand, its ecological and social consequences, and the potential impact of changing drought, on biomass fuel production, cooling for fossil plants (especially CCS); and water for natural gas extraction from deep shale.  Our work on drought will focus on the next two decades and will combine the impacts of climate change and natural multidecadal atmosphere-ocean variability on droughts. Iris Grossmann has recently completed an assessment of multidecadal patterns of Atlantic variability and will examine the impacts of large-scale Pacific and Atlantic patterns on droughts. Her work shows that on the timescales on which most water management decisions are made, the projected impacts of the investigated Pacific and Atlantic patterns on rainfall in some parts of the U.S. can be comparable in magnitude to changes projected due to global warming. In the new Center, we will continue this work to produce more detailed projections of the combined impacts of climate change and multidecadal variability, focusing in particular on robust decision options available to individual states or regions.

Most conventional fossil plants require water for cooling because more expensive dry cooling is rarely used. Many abatement technologies deployed to reduce GHG emissions will aggravate problems of water use. The addition of CCS at a conventional coal-burning plant would nearly double its consumptive water use. Carnegie Mellon researchers, led by Ed Rubin, have pioneered the development and dissemination of the IECM (Integrated Environmental Control Model) – a stochastic simulation model for estimating the performance, emissions, and cost of coal-based power plants with different environmental designs. The model is used world-wide to compare options for reducing emissions of both “conventional” pollutants and greenhouse gases. To study how consumptive water use might be reduced, we will extend the publicly available IECM power plant simulator to include a full accounting of water requirements and consumptive water use. This will allow model users to assess a broad range of options in the context of specific regional or local parameters.

The production of corn-based ethanol requires over a million gal/day of consumptive water use for a typical 100 million gal/yr plant for corn cleaning, preparation, fermentation and process steam. Similar amounts, 2-6 gal water/gal of ethanol, are predicted for cellulosic ethanol production. Land use change resulting from large-scale biomass production can impact stream and ground water recharge through changes in evapotranspiration processes and irrigation needs.  An acre of corn transpires 3 to 4 thousand gal/day per acre.  Grasses are thought to be slightly higher and trees can be as high as 40,000 gal per tree per year.  Michael Griffin and colleagues will incorporate water use for biofuels into a computer-based life cycle assessment (LCA) framework to allow decision makers to compare alternatives and explore ways to reduce or offset water use.

There is great interest in natural gas from the Marcellus Shale in the Appalachian region and similar “plays” in Texas, Arkansas and Louisiana.  Production of gas from these deposits has recently become feasible as a result of new capabilities in horizontal drilling and hydrofracing the shale to release the gas.  Chemicals are often added to the water used in this process to increase its viscosity so that it can efficiently carry small particles that will hold open the cracks that are formed. Most of this injected water must be removed before gas production begins.  In addition to the added chemicals this water contains significant amounts of dissolved solids from contact with the shale, yielding large volumes of contaminated water that must be treated if environmental contamination is to be avoided.  To date, such treatment has often been less than adequate resulting in elevated levels of dissolved solids in discharge waters. USGS notes: “While the technology…to extract gas resources from tight rock have improved over the past few decades, the knowledge of how this extraction might affect water resources has not kept pace. Agencies that manage and protect water resources could benefit from a better understanding of the impacts that drilling and stimulating Marcellus Shale wells might have on water supplies, and a clearer idea of the options for wastewater disposal.” Our research will aim to produce such an assessment in support of agency decision-making.

The decision makers:
BPA, EPRI, IRGC, NRDC, Westinghouse.