Enginuity 2011

Air-quality research

Getting flared up over flares

Factory flareFlying over Southeast Texas at night, the area looks like a huge birthday cake with hundreds of candles aglow. The flames come from flare stacks at the refineries, chemical plants and oil and gas wells. They burn off waste gas and act as a safety measure to release pressure in the system when needed. They can also help burn off gas reserves in an emergency situation. The problem? The flares are a likely source of under-reported or non-reported air pollution.

Daniel Chen, a professor in the Dan F. Smith Department of Chemical Engineering, is working with the Air Quality Research Program on a project dealing with flares. The University of Texas administers the program, which the Texas Commission on Environmental Quality (TCEQ) oversees. The commission is in charge of the Texas State Implementation Plan, the state’s overall plan to clean the air and meet federal air-quality standards.

Air quality studies tipped off researchers to the potential problem. The Texas Air Quality Study 2000 and Texas Air Quality Study II found that air quality models often significantly under-predict observed peak ozone. That discovery led to the theory that some volatile-organic-compound (VOC) sources might not be recognized as sources or, if they are, then they are significantly under-reported.

The plan for Chen and his team is to model controlled-flare tests that were conducted in Tulsa, Okla., last September. The computational fluid dynamics (CFD) model will estimate flare efficiencies and flare emissions.

Photochemical models are currently being used. These models predict photochemical ozone production in urban areas using chemistry, emission inventories and meteorological data. Volatile organic compounds react with nitrogen oxides under sunlight to produce urban ozone. High ozone occurs in summer when sunlight intensity is high and wind conditions make the dissipation of ozone difficult.

Current emission inventory from flaring is simply a 98 percent mass reduction without any consideration of by-products formation. In other words, 98 percent of the gas is burned off, which is good, but the 98 percent destruction efficiency is only under rather “normal” or ideal conditions. If the operations are outside the “norm,” the flaring can fare very poorly, and the destruction efficiency can go much lower than the assumed 98 percent. Further, the process creates hazardous byproducts, including volatile organic compounds and highly reactive volatile organic compounds. The basic premise is that the flares are not burning off all the gas and chemicals being vented.

This incomplete combustion releases contaminants into the air including ethylene, propylene and formaldehyde. This is especially bad when there are high cross winds, plant upsets and start-ups with the ensuing high-volume release of chemicals or when flaring very low-heating-value gases. “We anticipate these VOC emissions,” Chen said. “But we will have to compare our model values with the flare-test measurements.”

The goal of Chen’s flare research is to help industries find good flare-operating conditions to minimize air emissions based on validated simulation results, given a set of ambient conditions including cross-winds and operating conditions including the type of waste gas, the type of flare design and the exit velocity. “The developed know-how will be shared with industries and regulatory agencies,” he said. “TCEQ can use this piece of information to help revise the State Implementation Plan. Eventually, both industries and the public will benefit from our efforts.”

Daniel ChenChen’s research interests include catalysis and photo-catalysis for air-pollution and water-pollution abatement. “In air pollution, we apply photo-catalysts in VOC oxidation to water and carbon dioxide, much like ambient-condition incineration,” he said. “Another interesting application in air-pollution control is to apply photo-catalysts in concrete pavements where nitric oxide is further oxidized to nitric acid, then neutralized by the cement ingredients to become soluble nitrates that can be washed off by rainfalls. We also apply photo-catalysis to herbicide treatments to break them down to less harmful products or completely mineralize them into water and carbon dioxide.”

When it’s time for the professor to take on a new research challenge, he assembles a multi-disciplinary team. “Many times, we need facilities and faculty expertise from other departments or other institutions to complete a given project,” Chen said. “This is a very common practice in today’s research. We are very fortunate to get Dr. Xian Chang Li, assistant professor of mechanical engineering, who is the expert in computational fluid dynamics, and Dr. Christopher Martin, associate professor of chemistry, who is an expert in reaction mechanisms, to come on board this project. Within our department, Dr. Kuyen Li, professor of chemical engineering, and Dr. Helen Lou, professor of chemical engineering are both very talented and experienced researchers in industrial flares, process modeling and parallel-computing areas.”

This University Scholar for 2010-2011 has guided nine doctoral students and 30 master’s students, but he is modest about this teaching accomplishment. “I would not call myself a great teacher or mentor,” Chen said. “I think we all improve over time.” He is pleased with the many talented and dedicated students who help make all the research results possible.

“Some students already have very good industrial experience when they join our research team, and that has been a great asset for Lamar and for me personally,” he said.