Pollution down at Monroe’s DTE power plant
MONROE – When DTE Energy’s Monroe Power Plant demolishes its last 800-foot concrete stack in June, it will remove its last testament to its pollution-filled past.
The stack, which used to be one of two billowing out plumes of smoke in its heyday, has been replaced by two 580-foot stacks that now release water vapor instead of large amounts of toxins like their predecessors, according to the Monroe News.
With the power plant’s fourth and final selective catalytic reduction unit online as of mid- October, it marks the completion of a 14- year process to reduce sulfur dioxide, nitrogen oxides and mercury emissions by at least 80 percent across the board, making it among the cleanest coal-fired plants in the country, officials say.
“We’re very proud of what we’ve done here at the power plant,” said Bill Rogers, manager of environmental strategy and emission quality for DTE Energy. “This is a huge milestone for us.”
The plant now has four selective catalytic reduction units working to remove 90 percent of nitrogen oxide emissions and four flue gas desulfurization units to remove 97 percent of sulfur dioxide emissions and other acid gasses. Together they remove 80 percent of mercury emissions.
This $2 billion project doubled the footprint of the power plant, adding an entire complex to house the FGD units and building 14-story-high SCR units, ensuring that each step of the process contributed to removing toxins or recycling byproducts.
“When the plant was made in the 1970s, it was not designed for (these facilities),” Rogers said. “We had to retrofit all this onto existing equipment.”
When the coal is first burned in the boiler, the flue gas travels to the SCR units, which add ammonia gas to the mix, splitting the nitrogen oxides into nitrogen and water.
It then travels down the unit through a series of catalysts, which can be layers of ceramic or metal modules containing materials such as tungsten to draw out more nitrous oxides while gas continues to pass through holes in the modules like a giant sieve, Rogers said.
After the gas passes through the SCR units, it goes into an air preheater, which transfers some of the heat back into the boiler to conserve energy before the gas moves on to the electrostatic precipitator.
The ESP removes particles from the gas such as fly ash and bottom ash by creating an electrical charge to attract them onto wires, which removes 99.9 percent of particles, Rogers said.
The power plant recycles 45 percent of the ash for use as a concrete additive while the rest goes into the fly ash basin, he said.
The final process the gas goes through is flue gas desulfurization. The gas runs through an absorption chamber that sprays a limestone powder and water mix downward at the gas.
When the sulfur dioxide mixes with the limestone slurry, the chemical reaction creates gypsum, which falls to the bottom as the rest of the gas escapes through the stacks as water vapor.
The gypsum later is collected and recycled for wall board. The first shipment was exported to USG in Canada in August.
Combined, the SCR and FGD processes also remove mercury, Rogers said. When the gas runs through the SCR units, it becomes oxidized and water soluble, allowing it to be caught in the limestone slurry in the FGD unit.
“Looking back at all the work we’ve done, we’ve made significant strides in our mission,” he said.
With this project complete, DTE will focus on reducing emissions in its other plants, said Randi Berris, senior media relations specialist.
Installation of activated carbon injection and dry sorbent injection systems has begun in the Belle River Power Plant while plans are being finalized for the Trenton Channel Power Plant, River Rouge Power Plant and the St. Clair Power Plant.
The activated carbon systems are similar to those used in water treatment plants and can draw out toxins from the exhaust, Berris said.
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Information from: Monroe News, http://www.monroenews.com
This is an AP Member Exchange shared by the Monroe News.