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Metro Plant incinerators cut emissions, utility costs

New facility is projected to save the Council $4 million on energy annually

New wastewater solids incinerators at the Metropolitan Council’s Metro Wastewater Treatment Plant in St. Paul have dramatically reduced both air emissions and energy costs at the plant.

The three “fluidized bed” incinerators began full operation in January 2005, and in the first year reduced air emissions of many pollutants, including particulates and mercury, by more than 95 percent (see chart). The discharge of pollutants is expected to be the lowest of any operating sludge incinerator facility in the U.S.

Energy savings are dramatic

The equipment uses about 80 percent less natural gas, cutting plant costs by $3.4 million annually. It recovers more heat, helping to heat the plant and generate electricity, saving up to $600,000 annually in avoided electricity costs. The Council also received a one-time rebate of $958,000 from Xcel Energy for installing the energy-saving equipment.

“The new incinerators, along with new processes and equipment for dewatering the solids removed from the wastewater, are reducing fuel cost, air emissions and odors,” said Bill Moore, general manager of the Council’s environmental services division. “We couldn’t be more pleased with the results in the first year.”

For six decades, the Metro Plant had been using multiple hearth incineration technology developed more than a century ago. The aging system was creating increasing operations and maintenance costs.

Process generates electricity for plant

The new $159 million solids processing facility uses state-of-the-art incineration and air pollution control equipment. It also reduces dependence on nonrenewable energy by utilizing the fuel value of the wastewater solids, which enable the incinerators to operate without external fuel. Hot exhaust gases are used to generate steam for plant heating and cooling, and up to five megawatts of electricity is produced in the steam-driven turbine generator.

Planning, design and construction of the new facility took place over the course of a decade. Construction began in October 2001 and in January 2005 the new facility began processing all wastewater solids produced at the plant, enabling shutdown of the old system. The Metro Plant currently processes 210 tons of dry solids daily. The new facility has capacity to process 315 tons daily.

The Metro Plant treats an average of 190 million gallons of wastewater each day. It is by far the largest of the Council’s eight regional wastewater treatment plants, serving a population of about 1.7 million people and 800 industries.