During launch countdown, at approximately T-7 seconds, the Space Shuttle Main Engines (SSMEs) roar to life. When the controllers indicate normal operation, the solid rocket boosters ignite and the shuttle blasts off. Initially, the SSMEs throttle down to reduce stress during the period of maximum dynamic pressure, but soon after, they throttle up to propel the orbiter to 17,500 miles per hour. In just under 9 minutes, the three SSMEs burn over 1.6 million pounds of propellant, and temperatures inside the main combustion chamber reach 6,000 ˚F. To cool the engines, liquid hydrogen circulates through miles of tubing at -423 ˚F.
From 1981to 2011, the Space Shuttle fleet carried crew and cargo into orbit to perform a myriad of unprecedented tasks. After 30 years and 135 missions, the feat of engineering known as the SSME boasted a 100-percent flight success rate.
In the 1970s, the SSME was designed under contract to NASA by Rocketdyne, now part of Pratt & Whitney Rocketdyne (PWR), a United Technologies Company based in East Hartford, Connecticut. Working with Marshall Space Flight Center, PWR developed the most efficient rocket engines in existence, with ultra-high-pressure operation of the pumps and combustion chamber, which allowed expansion of all hot gasses through a higharea- ratio exhaust nozzle.
Soon after developing the highly efficient shuttle engines, PWR started creating highly efficient gasification systems. Gasification is a chemical process that converts carbon-containing materials such as coal, petcoke (a waste product from oil refineries), or biomass (organic material from plants or animals) into synthesis gas, or syngas. After the material is pulverized, it mixes with oxygen and steam at very high temperatures. The resulting syngas— comprised of carbon monoxide, hydrogen, carbon dioxide, and methane—can be burned as a fuel to create electricity, or further processed to make products such as substitute natural gas, chemicals, fertilizers, or liquid transportation fuels.
“We started looking at alternate forms of energy and alternate ways of using coal during the 1970s energy crisis,” says Don Stevenson, program area manager for Clean Fossil Fueled Energy Technologies at PWR. “By applying our rocket engine expertise, we are able to increase the temperatures and pressures in a gasifier, which resulted in a much higher efficiency system.”
In the 1980s, PWR built its proof-of-concept gasifier, but due to a lack of funding, the company temporarily shelved the technology. Years later, interest in the technology resurfaced, so PWR pursued new partnerships with the U.S. Department of Energy, ExxonMobil Research and Engineering, and Canada’s Alberta Innovates, to design, develop, and test the technology. By 2009, PWR had begun operating a pilot plant at the Gas Technology Institute in Des Plaines, Illinois, and in June 2011, test results established the gasifier’s successful performance and operation over a range of conditions.
PWR’s experience developing rocket technology was instrumental in improving gasification technology. Stevenson says, “The result is a much more compact, efficient, and lower-cost system.”
Several aspects of the compact gasification system have been influenced by the company’s experience with rocket engine design and development. The main component, however, is the rapid mix injector. “If it weren’t for the injector, which we think is the key secret ingredient, this wouldn’t be possible,” says Stevenson.
PWR’s rapid mix injector allows the gasifier to mix the carbon-based material, oxygen, and steam more efficiently at higher temperatures so the reaction can happen more quickly. PWR’s experience with rocket engines, which typically run at 5,000 ˚F or more, provided the expertise needed to build a gasifier system capable of withstanding extreme temperatures.