In Wyoming’s Powder River Basin, efforts to access a major source of natural gas stalled when drilling for coal bed methane also produced millions of gallons of tainted groundwater. In order to release the methane gas, water trapped in the underground coal seams had to be pumped to the surface. The water was so laden with sodium (Na) that it could not be used for irrigation or released into nearby streams.
Typically, the water would be stored in huge pits, reinjected into the ground, or treated chemically. None of these solutions was satisfactory to the owner of the land’s surface rights where a gas exploration company was planning to drill. However, a partnership between EMIT Water Discharge Technology of Sheridan, Wyo., and Severn Trent Services produced a solution that has produced positive results.
EMIT employed Severn Trent’s Higgins Loop process, which incorporates a continuous countercurrent ion exchange contactor for liquid phase separations of ionic components using solid exchange (I-X) resins. The Higgins Loop contactor is a vertical cylindrical loop containing a packed bed of I-X resin that is separated into four operating zones by butterfly, or “loop” valves. These operating zones—adsorption, regeneration, backwashing and pulsing—function like four separate vessels.
Water containing high Na levels is fed to the adsorption zone within the Higgins Loop where it contacts strong acid cation resin that loads Na ions in exchange for hydrogen (H) ions. Treated water exits the loop containing less than 10 mg/L Na. The carbonate contained in the water, also harmful to the environment, is removed via carbon dioxide (CO2) evolution from the low pH treated water. The Higgins Loop’s features are ideally suited for the Powder River Basin application, where only cation exchange is required to purify the water of high levels of Na, CO3 and total dissolved solids.
Concurrent with adsorption and in the lower section of the Higgins Loop, Na-loaded resin is regenerated with either hydrochloric or sulfuric acid to produce a small, concentrated spent brine stream. Regenerated resin is rinsed with water prior to reentering the adsorption zone to remove acid from its pores.
As resin in the upper layer of the adsorption zone becomes loaded with Na, the flows to the Higgins Loop are momentarily interrupted to allow advancement of the resin bed (pulsing) through the loop in the opposite direction of liquid flow. Liquid flows are restarted after resin pulsing is complete.
Treated water is slightly acidic due to its increased H ion strength, and it is neutralized with limestone, which also increases its calcium concentration so that the water’s sodium adsorption ratio (SAR) is less than 1.0. Spent brine containing removed Na ions has a density high enough for use as a kill fluid—a dense solution used to seal old wells.
The Higgins Loop technology makes water with high levels of Na and CO3 safe for reintroduction to the environment. The byproduct water, which once was an environmental problem, now is being reused by ranchers for irrigation, watering cattle and as a source for drinking water—and no wastewater is generated in the process.
The machinery that cleans the water is portable and can be set up on a foundation of crushed gravel and wood, so site reclamation is minimal. It is an economically feasible solution to the basin’s problem of excessive discharge water, which could run as high as 1.6 million barrels a day. EMIT and Severn Trent currently are treating the water from 80 wells at a gas production field in Arvada, Wyo., producing 750 gpm to irrigate hundreds of acres of alfalfa and forage. In addition, water currently is being treated at five other gas fields in Wyoming and Montana.
The Higgins Loop technology has proven to be a more effective ion exchange technology than fixed bed and fluid bed systems. The Higgins Loop efficiently utilizes the resin capacity, uses less regenerant and fresh water, generates consistent product quality and minimizes wastewater volumes. The technology offers greatly expanded ranges for the use of ion exchange resins and adsorbents in commercial separations.