Teresa Hansen, Section Editor
Brooklyn Navy Yard Cogeneration Partners L.P. (BNYCP) is a 286 MW plant located in Brooklyn, N.Y. that continuously produces 220 MW of electricity and up to 1 million pounds of steam each hour.
BNYCP has a waste stream (which includes oily water) that travels to a sump and is then processed via an oil-water separator. The processed mixture empties into the city sewer system and is treated in the nearby wastewater treatment plant.
Due to the specific gravity and surface tension of the oily water waste, oil entering the sump separates to the liquid surface. This oil remains on the surface and is not pumped to the oil-water separators because a low sump level is maintained by a series of floats that turn the pumps on and off. Over time, dirt and particles can combine with the oil. This turns it into sediment/sludge that is heavier than water, meaning it falls to the bottom of the sump where it is pumped through oil-water separators.
The oil-water separators are designed to remove clean floating hydrocarbons. However, because the sludge-laden hydrocarbons are heavier than water, they become trapped inside the piping, oil-water separator and auxiliary controls. This interrupts the facility’s monitoring equipment and causes increased operating and maintenance costs.
Brooklyn Navy Yard used in-plant personnel and outside contractors to clean the separator and the sump to keep them performing under the New York State Department of Environmental Protection’s required hydrocarbon level of 50 parts per million. These protocols were not only costly but also time consuming.
 The Model 6V oil skimmer, which can skim up to 100 gallons an hour, transports the recovered oil to a collection container. |
“In an effort to reduce the operation and maintenance costs, we began researching alternative maintenance solutions,” said Andrew Scano, former environmental safety and health coordinator for Palmark at BNYCP. Scano was responsible for regulatory reporting to federal, state and local environmental agencies, and managing operational permits. Now the plant’s operations manager, Scano arranged for a meeting with an Oil Skimmers sales representative to see the Model 6V oil skimmer in operation at a nearby Consolidated Edison facility.
The Model 6V oil skimmer removes floating hydrocarbons on the surface of water via a collector tube. Oil adheres to the outside of the closed-loop tube, which is slowly drawn across the surface of the water and into the oil skimmer. The tube then is drawn into the oil skimmer and through scrapers that remove the oil. The clean tube then returns to the water to skim more oil.
The Model 6V, which can skim up to 100 gallons an hour, transports the recovered oil to a collection container. The tube automatically adjusts to varying water levels and is flexible enough to wind over and around floating debris. The skimmer is designed to recover oil 24 hours a day, seven days a week, without an operator.
BNYCP plant personnel installed the skimmer and the hydrocarbon concentration in the wastewater stream leaving the plant fell from a continuous 15 to 25 parts per million to zero.
“The hydrocarbons are now virtually undetectable,” said Scano. “We also saw the scum layer disappear and the water become clearer.”
Scano took samples of the wastewater stream and sent them to a New York certified lab, which confirmed a low level of hydrocarbon. Findings from the facility’s online continuous hydrocarbon analyzer and the lab results confirmed that the oil skimmer is improving the wastewater.
The skimmer has been in place for almost two years and the plant has saved about $30,000 to $40,000 annually between in-house and contractor labor, and replacement parts for monitoring equipment.
“We used to spend about $4,000 to $6,000 every four months to have the sump pumped and skimmed, and another few thousand dollars to have the separator cleaned by contractors,” said Scano. “We also used to have a maintenance technician spend several hours per week cleaning and monitoring the equipment to maintain accuracy.”
Now, Brooklyn Navy Yard has significantly reduced its annual operation and maintenance cost to about $10,000, which consists of routine cleaning of the skimmer, monitoring equipment and oil-water separators.
“Conventional methods of pumping oil-water mixtures are much less efficient than using an oil skimmer,” said Scano. “It’s an established technology that works effectively with minimum maintenance.”
According to Scano, the plant’s owner (Delta Power) is pleased with the efforts made by plant personnel. The New York DEP is equally pleased with the reduction of hydrocarbons in the wastewater stream and the plant’s proactive efforts in making a difference.
“I think people in the industry need to be aware of different alternatives for reducing hydrocarbons,” said Scano. “We took an idea from the wastewater industry and applied it to the power industry. This technology goes across industry boundaries. It’s about being open to new technologies and learning how to apply them.”