Dakota Gas is investing in improvements to their water balance system, a system that balances the current inventory of water and the space to store it. These improvements will improve efficiency while limiting any waste put back into the environment.
During the gasification process, approximately 3000 gallons of water is created per minute and is introduced to the plant cooling water system. Ultimately, all of the water that is created evaporates at the cooling tower and the heat for evaporation comes from cooling the equipment throughout the plant; however, depending on the temperatures outside, water may not evaporate as quickly which requires Dakota Gas to store it in their two storage ponds with a capacity of 87 million gallons.
“During warm weather we can evaporate far more water than we produce,” said Troy Johnson, shift superintendent at Dakota Gas. “During the winter months, we are not able to evaporate as much water as we produce so the excess water is pumped to the storage ponds. When summer arrives, we pump the water from the storage ponds back into the cooling tower system as makeup water lost from evaporation.”
Dakota Gas also stores storm water collected from the plant in three storage ponds. Once the water has been sampled and, if necessary, treated, to meet environmental requirements, the water is discharged to the creek leaving the plant site. If the water doesn’t meet environmental requirements, it’s either run through the process of evaporation in the cooling tower or transferred to the deepwell injection system for underground injection.
“We need to be able to balance how much water we store through the winter with the storage space available and the amount of water we will be able to evaporate the following summer," Johnson said. "In some years it can be very challenging to ensure that the ponds do not overflow in the winter particularly if the ponds are not completely emptied by the end of the summer, or if the plant performance is abnormal for extended periods of time.” For example, the outage in the fall of 2023 caused the pond inventory to increase in a time when the pond levels are normally depleted.
The team has completed several improvements including repairs to piping, replacement of a seal flush, installation of a larger cooling tower surge pond pump, redirecting collected storm water, rental of temporary storage tanks, and installation of an aeration system in the storm ponds.
Improvements in process include completing ongoing work on a cooling tower, which will help to evaporate more water from the water balance system, and repairing the system that restores water balance.
The team is also considering the implementation of future improvements. These include studying how to use storm pond water as a raw water source for the water treatment system. “A treatment system like this would allow us to treat the storm water and reuse the water in the plant rather than bringing in more fresh water,” Johnson said.
Basin Electric senior vice president and plant manager at Dakota Gas Dale Johnson said the improvements to the water balance system are necessary to ensure plant operations are in compliance with or exceed state and federal environmental regulations. “As a cooperative we are committed to environmental stewardship and responsible management of resources. These improvements are one of the many ways we operate in an environmentally responsible manner,” he said.
