Freeze-Thaw

A Natural Process
Freeze–thaw/evaporation (FTE^®) provides the opportunity for cost-effective treatment of brackish or contaminated water. Bench-scale testing of FTE technology has proven it to be generally applicable to the treatment of ground and surface water, food-processing waste water, and oil and gas industry produced waters.

Advantages

Quality water for agricultural, industrial, and municipal purposes
Significant reductions in wastewater volume
Required refrigeration provided at no cost
No new wastes produced by the process

The Technology
When the ambient air temperature is below 32°F, the saline or contaminated water (feed water) is sprayed or dripped onto a freezing pad to create an ice pile. During subfreezing conditions, runoff from the ice pile will have elevated concentrations of chemical constituents compared to the feed water. This runoff can be diverted to a brine storage facility or back to the feed water storage facility for recycle. When temperatures promote melting or thawing, the runoff from the freezing pad will be highly purified water that can be diverted to a treated water storage facility for later beneficial uses of surface discharge. No new wastes are generated by the FTE process.

Personnel from the EERC and B.C. Technologies, Ltd. (BCT), began development of several freeze–thaw water purification processes in 1992. Laboratory-, bench-, and field-scale test research has been funded by the following sponsors:

U.S. Department of Energy
Gas Research Institute
Amoco Production Company
City of Grand Forks, North Dakota
U.S. Department of Agriculture
U.S. Bureau of Reclamation
McMurry Oil Company
A consortium made up of food-processing and agriculture-related plants in the North Dakota and Minnesota area
City of Devils Lake, North Dakota
North Dakota Department of Commerce Division of Community Services
North Dakota Department of Health
North Central Planning Council

The field-scale FTE testing that was started in 1995 has received national recognition for its successful treatment of coalbed methane produced water.

FTE Process
FTE couples conventional evaporation and freeze–thaw for treatment and disposal of wastewater. During warm months, the FTE system is operated as a conventional evaporation facility. However, during months with subfreezing (<32°F) temperatures, a large ice pile is created by spraying the water to be treated in a shallow pit, and the natural freeze–thaw process takes over. FTE has the potential to enhance the economic and environmental viability of oil and gas production by providing water for beneficial use and obtaining a substantial reduction in wastewater volume.

Meeting a Need
In every part of the world, water issues are increasingly important. Water supply and quality limit economic growth. FTE supports sustainable growth by:

Treatment of oil and gas produced water.
Reducing industrial wastewater volume.
Purifying waters for reuse or disposal from other industrial processes such as food processing.
Desalinizing natural water supplies for agricultural, municipal, and industrial use.

This simple, cost-effective technology can be used worldwide wherever natural weather patterns permit.

FTE Is Cost-Effective
Natural seasonal cycles are combined with inexpensive control equipment to automatically separate the process streams, offering industrial users reduced process water costs and reduced wastewater disposal costs.

FTE Is Ready for Commercialization
Field test results confirm both the process's economic viability and its potential to reduce wastewater volume and produce a usable, quality treated water.

Over 20 freeze–thaw bench-scale simulations have been done using oil and gas industry produced waters, food-processing plant wastewaters, other industrial wastewaters, or naturally occurring brackish waters. In all cases, the freeze–thaw process technology proved to be technically feasible as a water treatment process.

Between 1995 and 2001, three commercial-scale FTE plants were deployed to simultaneously remove salts, organics, and heavy metals from wastewaters generated in natural gas production fields in New Mexico and Wyoming. Industrial partners in these operations included Amoco Production Company, McMurry Oil Company, Crystal Solutions, and Gas Research Institute. The results of the field tests at these facilities confirm both the process's economic viability and its potential to produce a usable, quality treated water from oil and natural gas produced water. As of 2003, two FTE plants continued to operate commercially in Wyoming:one in the Jonah gas field south of Pinedale and the other in the Red Desert near Wamsutter. The treatment capacity of those plants is more than 40,000 gallons a day.

Clean Water for Our Future
The FTE process also offers opportunities to enhance water supplies for industrial and municipal uses. During the summer of 1996, an evaluation of the natural freeze–thaw process for the desalination of groundwater was conducted by the EERC in conjunction with BCT. The results confirmed the ability of the process to provide treated water of quality suitable for municipal and industrial water supplies from saline aquifers or other saline water sources. During 1998 and 1999, the EERC and BCT constructed and operated an FTE demonstration facility near Devils Lake, North Dakota. This project demonstrated the feasibility of FTE as a reliable alternative source of municipal water for the city of Devils Lake. Under suitable climatic conditions, FTE can be the solution to water supply and wastewater cleanup issues.