Emission controls

Modern biofilters and scrubbers have capabilities and cost efficiencies that exceed their recent predecessors. Integrated tools slash emissions by reducing plant start-up times. Portable diesel engine filters and green fuel emission controls are satisfying unique application requirements. Meanwhile, researchers are developing new approaches to managing hazardous releases from coal-fired power plants.

Advanced biotreatment: When released in excessive quantities, volatile organic compounds pose a threat to human health and the environment. New VOC control technologies improve upon the capabilities of regenerative thermal oxidizers and conventional biotreatment alternatives. An example is Tri-mer’s MultiPhase BioSystem, a combined biofilter and bioscrubber constructed of proprietary synthetic ceramic biomedia that tolerates higher gas temperatures and doesn’t degrade.

The MultiPhase BioSystem’s bioremediation techniques treat multiple VOC emission types in liquid and gas phases with as much as 98% efficiency, producing only clean, non-hazardous solids for disposal or burning, while treated air exits the stacks. The system doesn’t generate NOx byproducts typical of older combustion approaches. Much less carbon dioxide is released because natural gas isn’t burned. The self-cleaning, clog-free system also is more compact and less expensive to install and operate.

Fast start: One way for power plants to reduce emissions is to achieve faster start-ups. The Siemens Flex-Plant 30 power island recently ordered by its first U.S. customer is designed to start up within 30 minutes and reduce carbon monoxide release by more than 200 tons per year compared to standard F-class combined-cycle plants.

The Flex-Plant 30’s fast-start features include a three-pressure heat recovery steam generator (HRSG) with Benson once-through technology; high-capacity steam attemperation and full capacity steam bypass systems; piping warm-up capabilities; Siemens’ steam turbine stress controller; modern water treatment system; and optimized plant stand-by using auxiliary steam to maintain vacuum. These integrated technologies result in 50% shorter plant start-up times.

Mobile control: Diesel engine soot is carcinogenic and subject to strict emissions regulations. Mobile diesel power users who require portable filtering technology have an alternative from Rypos. The company’s Mobile Power Emissions Control System, which is trailer-mounted and quickly connects to mobile diesel power generators ranging from 100 kW to 500 kW, reduces particulate matter by as much as 95%.

While passive diesel particulate filters depend on high exhaust temperatures and are prone to soot accumulation and clogging, Rypos’ proprietary active diesel particulate filters are engineered for controlled, active regeneration and operation that is essentially maintenance-free. Because the system uses no more than 1% of the energy output to regenerate, there is virtually no increase in fuel consumption.

Green cleaning: Alternative fuel projects produce unique emission control needs. For instance, a company that burns discarded carpet flooring instead of fossil fuel needed a central particulate control system to manage the steam boiler’s hazardous emissions. Griffin Filters, a subsidiary of Cemtrex Inc., provided air filtration equipment to control the emissions from burning alternative fuels. The boiler flue gas is treated to remove harmful components and the residual ash is captured in a baghouse.

Mercury management: Coal-fired power plants represent the greatest share of human-generated atmospheric mercury emissions. National Energy Technology Laboratory (NETL) researchers developed a TOXECON process for coal-based power generators to reduce mercury emissions significantly, increase particulate matter collection efficiency and maximize the use of coal combustion by-products. The process injects sorbents between existing particulate control devices and captures pollutants in a pulsed-jet baghouse.

A recently-completed three-year TOXECON demonstration project in Michigan resulted in removing more than 90% of the mercury in the flue gas. NETL estimates approximately 97 lbs. of mercury and 250 tons of particulate matter will be captured at the plant annually.

Gas scrubber: Sulfur dioxide and carbon dioxide also are hazardous byproducts of coal-fired power plants. Pacific Northwest National Laboratory (PNNL) researchers working to capture sulfur dioxide and other acid gases developed a Reversible Acid Gas Capture process that binds oil-like organic liquids with acid gases in power plant emissions. The liquid is then heated to recover the gases for disposal.

This technique reportedly captures twice as much pollutants as water-based scrubbers and is more energy efficient because water requires more energy to pump and heat. The PNNL technology is anticipated to be an easy retrofit for existing coal-fired plants.

E-mail Contributing Editor Sheila Kennedy, managing director of Additive Communications, at [email protected].