Electricity From Plant’s Sewage Gas Misfires for City

After almost 11 months of operation, a generator that burns gas produced at the Point Loma Waste Treatment Plant is producing electricity but remains far from flawless, the City Council learned this week.

The generator, which recycles 1 million cubic feet of gases per day (67% methane and assorted others) as a byproduct of the digester in the waste treatment plant, producing 70,000 kilowatt hours of electricity each month, has been plagued with difficulties ever since it was approved by the City Council in 1977. Structural problems, pollution regulations and other difficulties resulted in years of delay and swelled the cost of the project to about $12 million, with 60% covered by local government and some costs still under dispute with the federal government.

It had appeared that the innovative project would finally begin to pay off for the city this August, eliminating all the power needs of the Point Loma plant and generating revenue through the sale of excess electricity.

But problems with the valves in the two eight-cylinder generator engines have reduced production of electricity to 85% of capacity, and the plummeting price of oil has shaved the price that the plant receives from San Diego Gas & Electric for the electricity it sells.

“We originally projected that it would take five to six years for the project to pay back the capital costs; now it appears like that may be 10 years or more,” said Roger Graff, deputy director of the Water Utilities Department.

Plant operators have been forced to replace the valves for the two engines at a rate of once a month, forcing repeated shutdowns of the engines and causing a loss of compression in the cylinders, Graff said. The water department believes that the problem is caused by a catalytic converter needed to gain the Air Pollution Control District’s approval of the plan.

“The company that sold us the generators keeps suggesting improvements . . . but it hasn’t done any good,” Graff said.

Now, the plant is planning to install a gas scrubber, which would remove some of the acid and sulfides from the sewage gas before it can corrode the valves, Graff said. The $80,000 proposal will go before the council sometime in the next two months, but even with the scrubber there is no guarantee that the problem will be fixed, Graff admitted.

A decline in the price that the plant is paid for its electricity has also reduced the project’s profitability, Graff said. Now the water department is considering hooking up the generator to a pumping station near the airport, 15 miles away. Although the pumping station would consume all the electricity that the plant produces, the hookup alone would cost about $10 million, Graff said.