“SO₃ Measurement and Control” - Hot Topic Hour on March 8, 2012

SO₃ in the flue gas stream from a fossil-fueled boiler has long been a concern for plant operators because of the potential for fouling and corrosion in the air heater and corrosion in ducts and equipment downstream caused by the sulfuric acid formed from the SO₃.  Excessive SO₃ in emissions from the stack can also cause opacity (blue plume) and acid mist deposition problems. In addition, the presence of SO₃ adversely affects the removal of mercury from the flue gas with ACI. The affect of SO₃ aerosols on particulate emissions has also been a concern - more so in some plants than others.

But SO₃ in flue gas will soon be a much bigger concern for all. Because SO₃ contributes to the formation of condensable or fine particle emissions, the recent changes in the National Ambient Air Quality Standards (NAAQS) for particulates and ozone may force even greater control of SO₃ under local standards or under regulations dealing with particulates. And the utility MATS with lower limits on mercury and SO₂ will further complicate the issue.

Control of SO₃ is a complex problem that can be highly dependent on the control technology utilized for NO_x, SO₂, mercury and particulates. In addition, measurement of SO₃ can be difficult which further complicates the control problem. Yesterday, five very knowledgeable speakers presented the current “state of the art” for SO₃ measurement and control.

James (Jim) C. Dickerman, Director of Flue Gas Treatment Applications at Lhoist North America (formerly Chemical Lime Company), presented an overview of SO₃ emission control with hydrated lime. He discussed the development history of the technology as well as the key design parameters that need to be considered for successful operations. Initial problems (primarily plugging of lances) were resolved and the technology is fully commercialized now with installations at over 30 utility boilers. Future development is focused on the control of other acid gases such as HCl and SO_2.  He said they have demonstrated that hydrated lime can be injected downstream of the ESP (upstream of a scrubber) and not increase particulate emissions. Also injecting hydrated lime at two locations is more effective than one location. Injection upstream of the air heater can reduce ABS formation with no downstream impacts.

James (Jim) B. Jarvis, Project Manager at URS Corporation, stood in for Sterling Gray, Manager of SBS Injection Technology. He described the application of a liquid sodium based reagent (SBS) to reduce SO₃ and mercury emissions at power plants. He stated that since 2005 they have learned that injection of SBS upstream of the air preheater provides maximum benefits. Since 2005, they have had 24 boilers operating with upstream injection, some of which had downstream injectors relocated. They also have four installations ahead of the SCR that have been operating for three years. He stated that SBS injection can significantly reduce SO₃ levels prior to the air heater and reduce stack emissions of SO₃ to less than 1ppm and 0.003 lbs/MMBtu SAM. He presented a number of graphs showing that mercury capture rates of 50 to 90 percent can be achieved with high-efficiency SO₃ control and with little to no carbon injection.

Curtis (Curt) Laush, Ph.D., Senior Scientist at Industrial Monitor and Control Corp. (IMACC), described the capabilities, operation and field-testing of a CEM-type analyzer based on a quantum cascade laser (QCL) absorption spectrometer for real time continuous monitoring of SO₃ and SO₂ across flue gas ducts. The in-situ design eliminates sample extraction issues allowing a truly representative measurement of SO₂, SO₃ and water vapor with fast response (less than 1 minute) and high resolution (500 ppb in a 5 meter duct).  In May IMACC will begin field-testing a second-generation instrument and expects to have it commercialized by the end of the year. Potential applications include tracking SO₂ oxidation in real time across catalysts and downstream, tracking potential SO₃ dew points when optimizing air heater operation and optimizing sorbent usage for SO₃ mitigation.

Dr. Yougen Kong, P.E., Technical Development Manager at Solvay Chemicals, Inc., discussed the interactions between SO₃, HCl, HBr, PM and Trona in flue gas. Trona injected before and after the air heater can be very effective at controlling acid gases as well as enhancing mercury removal. However, he emphasized that flue gas treatment at a coal-fired power plant has become a chemical processing plant and a solution for one plant may not fit another plant. Treating one component in the gas can affect the other components. Therefore to be successful, you must understand the chemistry of the gas, apply a systems approach and all suppliers of APC equipment and the design engineers must work closely together.

Jeff Socha, R & D Project Leader for the SO₃ CEMS at Thermo Fisher Scientific Air Quality Instruments described capabilities of and initial field test results for a dilution extractive SO₃ monitor being developed for real time monitoring of SO₃ in flue gas. The instrument uses a cascade laser and has an integrated SO₃ gas generator for daily calibrations and dynamic spiking to detect bias. The detection limit is 0.4 ppm. Two systems are currently undergoing beta evaluations at two power plants – one downstream of an FGD and one downstream of an ESP. An instrument with a 100-foot sample line has a response time of 19 minutes.

The Bio and Abstract information is linked below.

BIOS, ABSTRACTS, PHOTOS - MARCH 8, 2012.htm