By Juzer Jangbarwala
Wyoming’s Rocky Mountain Powder River Basin receives precious little rainfall but is home to some of the world’s largest sources of coal bed methane (CBM). CBM is an unconventional fuel harvested by removing water covering underground coal beds to release methane from coal seams. CBM production offers a dual solution to the challenges of limited water supply and need for low-cost, clean domestic energy.
While releasing and capturing the methane is relatively inexpensive, resulting “produced” water usually contains excessive levels of sodium bicarbonate, making it unsuitable for irrigation, consumption or discharge into bodies of water. The water also may have high levels of sulfur compounds, other unwanted minerals and up to 5,000 ppm total dissolved solids (TDS). Appropriately treated, this wastewater can become a much needed resource for irrigation, livestock consumption or even human consumption.
Numerous methods have been developed to treat CBM produced water to make it usable for agricultural purposes or environmental discharge, yet these traditional methods, such as use of evaporative ponds, can result in a harmful long-term rise in TDS. Ion exchange and reverse osmosis (RO) are the only technologies deployed to date that remove the sodium. Of these, ion exchange has proven most cost effective and environmentally sound. The salinity of discharged water must match that of existing water bodies, or the local ecosystem would be harmed by the change.
Recently, a new fixed bed dynamic flow ion exchange system specifically designed for signature characteristics of CBM water was deployed in Wyoming’s Powder River Basin. It has dramatically reduced the waste stream to less than 1% of treated water volume and has proven its economic viability.
Figure 2. Process Flow Diagram
Alkalinity associated cations (such as sodium associated with bicarbonates) can be removed from water using weakly acidic cation resins. The fixed bed dynamic ion exchange system uses a weak acid cation (WAC) ion exchange resin, which has a very high capacity to remove sodium bicarbonate and other alkalinity associated cations. This resin’s carboxylic acid functionality solely targets the alkalinity-associated sodium and neutralizes it. Most other ion exchange systems use strong acid cation (SAC) resins, which have lower operating capacities and require 100-200% stoichiometric excess of acid to regenerate. WAC resins outperform SAC resins for this application due to their high capacity, virtually 100% acid utilization (no acid wasted) and effluent pH within discharge limits.
RG Global’s Catalyx Fluid Solutions (CFS) division’s fixed bed dynamic flow ion exchange system is designed to cost effectively treat water produced from CBM wells and resolve challenges that have kept CBM from being an economically viable source of domestic energy. The patent pending system is currently in use by Yates Petroleum in the Powder River Basin near Gillette, WY. The 30,000 bpd-capacity plant is the first of a three-phase contract, which will eventually have a 90,000 bpd capacity. It removes excessive sodium bicarbonate (NaHCO3) and other undesirable minerals from the water, making it suitable for irrigation or discharge into the Powder River at a low total cost and less than 1% waste byproduct.
The following design steps enable the system to produce such a small waste stream, minimizing cost:
- System utilizes aluminosilicate (zeolite) filtration media to remove dissolved iron.
- The two-stage ion exchange unit uses in each stage a weak acid cation as a catalyst (proton source) pumped through a resin bed in a counter current manner to convert the bicarbonate to CO2. Once exhausted, the resin bed is regenerated with dilute sulfuric acid. The acid is completely utilized producing a stream of sodium sulphate and neutralized water. CO2 generated at each stage is removed by a degasification step.
Rinse water from each stage is saved and reused for the next regeneration cycle or for rinsing, thereby minimizing the waste stream.
- Rinse 1 – Rinse water from a second tank is pumped into the first tank after rinsing the resin. This first rinse saved in the tank is used for pre-mixing acid for the next regeneration cycle.
- Rinse 2 – Rinse water from a third tank rinses the resin for the second time. This rinse is saved and becomes the first rinse for the next full regeneration cycle.
- Rinse 3 – Treated water is pumped into the tank for the third and final resin rinse. It’s saved and becomes the second rinse for the next full regeneration cycle.
Valuable waste byproduct
The waste byproduct is a rich stream of sodium sulfate amounting to slightly less than one bed volume of resin. An additional system (under deployment) varies the temperature of the sodium sulfate-laden waste stream, crystallizing it into sodium sulfate decahydrate or anhydrous sodium sulfate. The resulting products can be harvested and reused, i.e., sold, as industrial grade raw materials with multiple applications, thereby completely eliminating liquid-waste discharge from the plant.
Testing the water at the outflow.
Ag/green Energy Uses
Currently, RG Global’s CFS custom designed solution treats the CBM produced water to conform to pH and salinity levels of existing water bodies or for irrigation. With additional processing, the water could be suitable for livestock consumption and even meet human drinking water requirements.
In the semi-arid Powder River Basin, this valuable resource of treated CBM produced water also could enable cultivation of vast areas of land for crops, including energy crops that could be biodegraded in anaerobic plants to produce additional methane. The resulting methane could be deposited into the existing CBM processing and transport infrastructure, increasing revenue and domestic energy supply.
Conclusion
With appropriate customized treatment, the produced water – a limiting factor in coal bed methane capture as an energy source – becomes a valuable, environmentally friendly resource. With the waste stream minimized into a reusable form, disposal costs are eliminated and the byproduct becomes a source of revenue. Overall, the net cost reduction makes CBM production a viable form of domestic energy, and yields a much needed source of safe, usable water.
About the Author: Juzer Jangbarwala is the former chief technology officer and chairman of RG Global Lifestyles Inc., of Anaheim, CA. In 1989, he was founder and CEO of Hydromatix Inc., acquired by BOC Edwards in 2002. In 2002, he founded and became CEO of Catalyx Inc., a technology incubator. In 2004, he became CEO of Energix Research Inc., a subsidiary of Catalyx Inc., as a developer of low-cost hydrogen generators. In 2006, Catalyx spun off Catalyx Fluid Solutions (CFS) to RG Global. Contact: 949-888-9500, [email protected] or www.rgglife.com
