ATTENTION REPORTERS/EDITORS: Black-and-white photographs of the researcher and the shock wave reactor facility are available upon request.
A radical new technique for processing natural gas that could save the petrochemical industry billions of dollars in energy and maintenance costs has been developed by University of Washington researchers. Experiments using supersonic steam and shock waves, instead of a conventional furnace, to break down natural gas compounds recently produced yields of ethylene that are 20-25 percent higher than the industry average.
“These higher yields are dramatic when you’re talking about a multi-billion dollar industry that gets excited about 1 or 2 percent increases in production,” said Tom Mattick, an associate professor in the UW College of Engineering’s Aerospace and Energetics Research Program and lead investigator of the shock wave reactor project. “This is a radical new idea. People in the petrochemical industry aren’t used to talking about shock waves and supersonic flows, but they’re very interested in the promise our technique has for boosting yields.”
The shock-wave reactor has been patented, and Mattick is working with the university’s Office of Technology Transfer to license the process to major petrochemical and refinery construction companies which have been following the research.
For the past 40 years, conventional chemical reactors have used high-temperature furnaces to “crack,” or break down, natural gas feedstocks such as ethane and propane into molecular fragments. After passing through the cracking furnaces, the fragments re-form into new compounds, including olefins, which are the building blocks of a huge variety of consumer products ranging from rubber tires and plastics to pharmaceuticals and antifreeze. Production of ethylene, the most versatile of the olefins, is a $30 billion-a- year business worldwide, according to industry reports.
One of the largest single costs in producing olefins is the energy required to heat the furnaces to 900-1,100 degrees Celsius to crack the feedstocks. Even at those temperatures, Mattick said, only about 60 percent of the feedstock is converted into new compounds. And just over half of the converted materials re-form into the desired end product such as ethylene. For years, scientists and industry engineers have known they can increase yields of ethylene by raising furnace temperatures and reducing reaction times. This has been done with liquid feedstocks but isn’t possible with gases due to the higher temperatures required.
“With current materials, it’s impossible to apply enough heat to the gases fast enough without damaging the processing equipment,” Mattick explained. “They’ve hit a brick wall.”
Shock waves, which can instantaneously heat feedstocks to optimum temperatures, may break through that wall and yield several other benefits for petrochemical processing. A shock wave is a disturbance in a flow of gas that forms when the flow suddenly changes from supersonic to subsonic speeds, as in supersonic flow about an airplane wing. Mattick along with UW professors of aeronautics and astronautics David Russell and Abe Hertzberg began work on the shock wave reactor project in 1990. They received a $1 million grant from the U.S. Department of Energy in 1993 to build an experimental reactor.
Using the UW’s Kirsten Wind Tunnel, the researchers conducted studies to design and test supersonic flow control devices, measurement and diagnostic instruments and optimum flow channel dimensions for the shock wave reactor. The facility (see attached diagram) has a large boiler that heats steam to about 1,250 degrees Celsius. The steam is fed into the reactor channel through specialized nozzles that force it to supersonic speeds. In a separate reservoir, ethane also is heated and injected into the channel at supersonic speeds. The supersonic flow lowers the temperature of the steam and ethane to prevent it from reacting prematurely. A shock wave is formed in the channel as the mixture slows to subsonic speeds. The shock wave heats the flow in microseconds to roughly 1,150 degrees Celsius, the optimum temperature for cracking ethane. After passing through the shock wave and reacting for a brief period, the mixture goes into a quencher that cools the gas and preserves the chemical products.
Over the past year, Mattick, Russell and a team of graduate students have been working to refine the process and achieve the higher yields predicted by computer models and flow studies. In experiments completed this summer, the researchers successfully converted, or cracked, about 80 percent of the ethane feedstock. And 80-90 percent of the converted material turned into ethylene. That represents a 20 percent improvement in yield over the industry average using the conventional process.
An added benefit of the new process is that the quick reaction time and the use of steam greatly reduce coking and fouling of the channel tubes. Conventional reactors must be shut down every six to eight weeks for cleaning at a cost of up to $1 million a day in lost revenue, Mattick said. Another plus is the potential of the new process to crack methane. It is a far more abundant component of natural gas than ethane but requires a temperature of 1,800 degrees Celsius to crack and produce usable amounts of ethylene. The high temperature makes it impossible to process methane using conventional methods.
One reason the petrochemical industry is so interested in the UW process, according to Mattick, is that it can be utilized with only minimal retrofitting of existing plants: replace the furnace element with UW technology and the rest of the plant can remain the same.
“Only about 15 percent of the cost of the plant is the furnace; most of the investment is in the separation process downstream,” Mattick said. “Despite the fact that the cracking mechanism is the least expensive part of the plant, it’s the most critical in terms of getting high yield to begin with. That makes our process relatively easy to implement and extremely attractive to industry.”
For more information, contact Mattick at (206) 543-6181, or Russell at (206) 543-6224, .