A 2011 survey by Black & Veatch identified command and control of the world’s water supply as the top environmental concern. This water sourcing concern also was expressed recently by the NETL (National Energy Technical Lab) during the 2011 ASME Power Conference. Indeed, similar water sourcing concerns/regulations proposed by the U.S. Environmental Protection Agency (EPA), Clean Water Act (CWA) Section(s) §316a & 316b, have raised water supply awareness to a higher level.
These regulations alone could impact more than 670 power plants in the U.S.
As a result, a demonstrable shift from the established and typical toward the unconventional has continued to evolve, foster and expand innovative and non-traditional cooling water alternatives for utilities and industrial users, posing new challenges for proper heat exchanger material selection.
Clearly, the expanded use of impaired, TSE or degraded water and its derivative namesakes – extracted and treated mine water, refrigerant and hydrocarbon process industry applications in the Middle
This paper will identify increasing efforts by impaired water generators, wastewater treatment plants and utilities to economically process, transport and utilize the numerous unknowns flowing from society to the ultimate user.
What do we have?
Three percent of the total worldwide water available to mankind is fresh water. Much of this is in the form of ice located in the polar regions of the planet and not directly accessible. Nearly 50 percent of U.S. freshwater withdrawals are consumed by thermoelectric power plants (Figure 1), and 92 percent of this is used for once-through cooling.
It also is estimated that there are more than 24,000 municipal wastewater treatment plants in the U.S. processing some 11.4 trillion gallons of product per year, and approximately 2,000 employ water reuse facilities. This percentage is even less when applied to power generation facilities. In 2006, a report by this author identified some 50 power plants in the U.S. that used reclaimed water for cooling. Today that number has increased to the hundreds, but it is pitifully low when compared to the ~10,000 power generating plants operating in the U.S.
Economic, legislative and logistical impediments to wholesale expansion of water reuse appear to be at the resistance forefront, followed closely by the high-cost medium processing and corrosion abatement activities.
Given the high thermoelectric power plant withdrawal percentage, the final water application or “Intensity Usage” is compared (Table 1) where plant type, cooling system, initial withdrawal and final consumption rates are represented. Note that when comparing various types of generation, nuclear might offer the best ratio of withdrawal to consumption.
Research is being conducted at the National Energy Technical Lab (NETL) to evaluate and develop cost-effective approaches to using non-traditional (aka impaired or alternative) sources of water to supplement or replace freshwater for cooling and other power plant needs. Opportunities exist for the utilization of lower-quality, non-traditional water sources. Examples of non-traditional waters include surface and underground mine pool water, coal-bed methane produced waters and industrial and/or municipal wastewater.
Research also is being performed in this program area to develop advanced technologies to reuse power plant cooling water and associated waste heat and to investigate methods to recover water from power plant flue gas. An additional component of the NETL investigation is focused on research to develop technologies that improve performance and reduce costs associated with wet cooling, dry cooling and hybrid cooling technologies.
Projections and costs
Pundits suggest water shortages will increase the amount of water reuse (Figure 2) in the U.S. from a current estimated 1.7 billion gallons to an estimated 12 billion gallons by the year 2015.
Figure 3 identifies the comparative raw cost of water worldwide. The U.S. enjoys a relatively low cost when compared to other locations. It has been suggested that this low, first cost poses economic roadblocks to the usage enlargement of impaired water.