Research under way at Associated Electric (AECI) Cooperative’s New Madrid Power Plant could save members hundreds of millions of dollars on environmental controls, and the key ingredient is found in most households. It’s baking soda, or sodium bicarbonate. While it’s not as simple as mixing up a batch of pancakes, injecting baking soda into the flue gas stream of power plant emissions captures sulfur dioxide. Current tests are achieving 60 percent to 80 percent reductions in SO2 consistently, making dry sorbent injection (DSI) technology an effective tool to meet pending environmental regulations. It also costs less – a lot less: $20 million in capital costs per coal unit compared to $300 million per unit to build scrubbers. “We believe this will be the lowest-cost alternative to having to install scrubbers on our assets,” said Ken Wilmot, director of Power Production.
AECI conducted short-term DSI testing in 2010 and 2011. Current research on New Madrid Unit 2 will run about 90 days at a cost of $3.3 million, which includes mobile silos and equipment to inject the baking soda. The objective: achieve SO2 reductions with no adverse impacts on the operation and efficiency of the unit or existing environmental controls, said Todd Tolbert, senior environmental analyst.
DSI research builds on AECI’s environmental investments, particularly its conversion to low-sulfur coal in 1995 that reduced its SO2 emissions 90 percent. Because its SO2 emissions already are very low, Associated is in good position to meet the Environmental Protection Agency’s pending Cross-State Air Pollution Rule (CSAPR), as well as other EPA air quality mandates, using DSI technologies versus scrubbers.
While DSI’s annual operating and maintenance costs are higher – about $12 million a year compared to $8 million a year for scrubbers, DSI technology provides AECI more operational and financial flexibility. The technology is easy to set up and remove, versus the large capital cost and footprint of scrubbers.
Here’s how it works
Baking soda is produced in Wyoming. Because it’s very reactive with the environment, it’s transported in dry, air conditioned rail cars and then put in two 100-ton silos on site. From there, it’s finely ground and injected into the ductwork carrying exhaust flue gas. There, it mixes and reacts to form sodium bisulfate, which is captured in the ash particles by the electrostatic precipitators (ESPs), Todd said.
Research has shown so far the baking soda has no impact on the ESP equipment, and may even improve its performance. Staff also has discovered existing environmental controls that capture nitrogen oxides (the SCRs) improve DSI capture of SO2. While the 90-day testing will help discover any downsides to DSI, staff anticipates it will increase the amount of ash going through the ash-handling equipment and to the utility landfill.