“… the cost to bring the plant into compliance could be millions of dollars. I believed otherwise. This is my story of what happened on Dec. 7, 1990, to rescue the university from that dire situation.”
By Joseph Landwehr, BS AgE 1969, MS 1971
On Dec. 6, 1990, a front-page article in the Columbia Missourian described student protests at the MU campus power plant. Since that October, the University of Missouri had been issued five violations for stack opacity — or visible emissions — exceeding 20 percent at the campus power plant. According to that article, the cost to bring the plant into compliance could be millions of dollars. I believed otherwise. This is my story of what happened on Dec. 7, 1990, to rescue the university from that dire situation.
Prior to 1990, if you drove down Interstate 70 and looked south toward the City of Columbia Power Plant, you would likely see a smoke plume discharging from the plant chimney. Even after 1979, when the city had added a baghouse to collect the fly ash, the plume opacity still was not clear. In 1990, the city converted the plant to low sulfur coal, resulting in a clear plume and solving its air quality compliance problem.
A decade earlier, in 1980 and 1981, MU installed two baghouses and two brick-lined concrete chimneys at campus power plant. At the time of the baghouse construction, I made several trips to the MU campus to visit friends, and while there, I always drove down Stewart Road to view the construction progress. Unfortunately, the project did not result in a clear plume because MU was still burning high sulfur coal, same as what the City of Columbia had been burning prior to 1990.
Although the engineering company where I was working at the time was not involved in the baghouse project, I was disappointed when the baghouse retrofits did not fix the opacity problem. By then, I had 17 years of design experience in air pollution systems for coal fired plants, and I knew that any sulfur reduction alternatives, such as switching to low sulfur coal or installing flue gas desulfurization, would be expensive.
In 1985, my company was invited to submit a proposal to inspect the baghouses and related induced draft booster fans and to recommend improvements to mitigate corrosion of carbon steel components deteriorated by the flue gases. Our company was awarded that engineering project, and I was in charge of the inspections and the report of the findings and recommendations. Alloy sleeves were added to protect the fan shafts, and other improvements were made to reduce air in-leakage causing cold spots at various locations in the baghouse structure. A common problem with plants burning high sulfur coal, cold spots allowed sulfuric acid to condense on metal surfaces, leading to corrosion.
In spring of 1990, my company was awarded another contract to perform another inspection and make recommendations. One of my recommendations was to perform a proof-of-concept demonstration consisting of injecting an alkali powder into the flues upstream of the South Baghouse. I predicted that this would neutralize the sulfur trioxide that was causing the corrosion and thereby reduce the sulfuric acid mist that resulted in the visible smoke plume.
I knew that injecting any foreign material into a baghouse would be risky since there was a possibility that a reaction might occur that would “blind” the bags with some sticky compound. This could reduce the fabric permeability and render the bags useless. However, the plant had a source of high alkali flyash, approximately 40 percent Calcium oxide (CaO), from a circulating fluid bed boiler that discharged to the North Baghouse. My recommendation was to inject fly ash collected from that baghouse since it was not likely to “blind” the bags.
On Friday morning, Dec. 7, I showed up at the plant at the invitation of the plant manager. After plant maintenance personnel followed a few simple instructions, and using the induced draft from the boiler ID Fan, sucked the high alkali flyash into the flues leading into the South Baghouse. In one hour, the plume from the south chimney went from an opacity violation to perfectly clear. In addition plant maintenance measured the acid dew point using a Land Dew Point meter, and the results showed that the sulfur trioxide concentration had been reduced by 90 percent. This confirmed to everyone that the sulfuric acid mist had caused the opacity violations.
The university subsequently installed a permanent lime injection system, as this was more economical than collecting, storing and injecting fly ash. This process is now commonly used at coal-fired utility plants to meet today’s stringent regulations. But 25 years ago, it was unheard of.
That I figured out an inexpensive way to reduce the sulfur trioxide concentration is certainly a tribute to the mentoring by the MU engineering professors who not only taught us the range of subjects, but also fostered our creative approach and confidence in solving engineering problems. Many thanks to those professors who taught me at MU.
Joe Landwehr lives in Kansas City, Mo.