Techno-economic analysis of extraction, treatment, and distribution of brines as a part of pressure management operations for CO2 storage in saline aquifers

Large-scale storage of CO₂ in saline aquifers may be required to permit carbon capture and storage (CCS) technology to be widely deployed on fossil-fired electricity generators. The quantity of CO₂ that must be handled is a key technical issue. A large coal-fired power plant could emit 6 to 8 million metric tons of CO₂ per year at full capacity. Injecting even a fraction of such quantities of CO₂ will tend to increase pressures and stresses in the subsurface, and proper management of the pressure will be required to ensure secure long-term storage. This pressure management may involve extracting and handling large quantities of brine from the target formation

In this Brine Extraction Storage Test (BEST) project, we set out to estimate the cost of extracting brine from a saline aquifer, the treatment of that brine to produce clean water and concentration, and transmission of the cleaned water to a theoretical customer. Our analysis was based on the conditions at a power plant in the southeastern U.S. We investigated multiple brine compositions covering total dissolved solids (TDS) contents from 30,000 to 165,000 mg/L, including some that included high levels of calcium or sulfate.

The water treatment processes considered comprised either one desalination process or two separate processes in series. These processes included both permeation-based (reverse osmosis, forward osmosis, and stacked membrane systems) and evaporation-based processes (vapor compression evaporation, hybrid evaporation/crystallization, and adiabatic evaporation/crystallization processes). Our analysis also included any pre-treatment steps required by a specific process and, if necessary, a final crystallization step.

We estimated the capital and operating costs for different scenarios that each considered a different combination of brine extraction rate, brine composition, and water treatment process. These costs were used to estimate the cost to deliver a unit of desalinated water and the cost that the whole process would impose on each unit of CO₂ stored. The unit costs of water ranged from $0.023 to $0.327 per gallon and the additional costs to CO₂ storage ranged between $2.65 to $70.79 per metric ton CO₂, depending on the brine, extraction rate, and assumed energy prices. In all cases, the cost of the water treatment process made up most of the both the total capital and operating costs. For some brines, the high hardness lead to high pre-treatment costs. Because of the potential for brine treatment to add to the cost of CCS, the potential need for extracting brine and the challenge of treating that brine should be considered in any CO₂ storage project in a saline aquifer.