Past due for maintenance, two turbines that burn waste gas to produce electricity and steam at Fresno’s sewage treatment plant have stopped working, resulting in a $1.3 million repair bill that the City Council will review for a second time Thursday.
One of the turbines broke down more than a year ago, and the other failed about three weeks ago, said Stephen Hogg, assistant public utilities director and manager of the plant on Jensen Avenue southwest of the city.
Since the second failure, the plant has been burning waste gas in a flare and buying electricity to replace what the turbines would have generated, Hogg said.
By the time they failed, both units had run longer without an overhaul than their manufacturer recommends — about twice as long in the case of the second unit. Hogg said the reason maintenance was delayed comes down to the cost of an overhaul.
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“We don’t want to spend money we don’t have to,” he said. “Having said that, we probably should have taken them down a little sooner.”
Having both turbines offline is costing the city thousands of dollars in electricity.
When running, the turbines and related equipment save the city $80,000 to $100,000 per month in electricity and provide about 90% of the power needed by the plant, which also serves much of Clovis.
When one turbine is down, the other can produce 60-70% of the need. With both of them out, none of the need is covered, Hogg said.
The turbine failures and burning of waste gas don’t violate any air pollution regulations or permit conditions, partly because the increase in emissions is “not particularly significant,” said John Copp, an inspector for the San Joaquin Valley Air Pollution Control District. Still, he said, “It’s always a crying shame to see people not using their fuel.”
The gas burned in the turbines is produced in sewage treatment and is slightly more than half methane, with carbon dioxide making up most of the remainder, Hogg said. Before burning, it is mixed with commercial natural gas, which has a higher methane content and burns hotter to help keep pollution levels down.
Each of the treatment plant’s turbines can produce 3.37 megawatts of electricity, enough to meet the needs of 2,500 to 3,400 area homes.
The City Council had approved repairs in February, before the second turbine failed. It took almost a year to get to that point, Hogg said, because of the time required to investigate the first turbine’s failure as well as prepare specifications for the repairs and take bids from repair contractors.
After February, moreover, a subsequent review by the city attorney’s office raised several concerns about late changes in the bid documents, according to a staff report prepared for the council. As a result, the council will be asked to reaffirm its approval.
If the council says no, the city could face an estimated $600,000 in additional costs because the time needed for a new round of bidding would trigger new pollution controls, Hogg said. Tighter air pollution regulations go into effect in 2011 for existing turbines, but immediately for any major overhaul completed after July 1.
As a result, if the repairs are not done in time, the city could be forced to spend that money on new pollution controls this year instead of 2011.