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Fri February 10, 2012
The science of Syngas
DKRW Advanced Fuels has licensed technology from GE and Exxon-Mobil to transform coal into gasoline at a proposed plant in Medicine Bow. But theirs is just one system of creating liquid fuel. Wyoming Public Radio’s Rebecca Martinez spoke with some experts about how synthetic gas, or syngas, is made.
REBECCA MARTINEZ: Fuels like oil, butane and gasoline are made from hydrocarbons, a combustible fuel-source composed of carbon and hydrogen. Hydrocarbons occur naturally in crude oil, but they can be made synthetically from other kinds of feedstock, like natural gas, oil shale, or coal… which is solid carbon.
VIJAY SETHI: Coal is solid because it’s missing hydrogen. If you can add hydrogen to it, we can make liquid fuel.
MARTINEZ: VijaySethi is the Senior V-P at the Western Research Institute, where they’re working on different ways to turn gas, coal and woodchips into replacements for ethanol. He says there are many ways to turn coal into liquid, but they follow similar steps at the start.
SETHI: And a source of hydrogen is water. So if we can do a reaction of coal, with steam for example, coal is converted into a mixture of carbon monoxide and hydrogen. That mixture is now the building blocks from which we can make any other fuel or chemical.
MARTINEZ: In other words, if you add hydrogen to the coal, it can become liquid fuel. This is nothing new. Chemical plants in South Africa have been using the Fischer-Tropsch Process to create diesel fuel for decades. The process allows companies to use natural gas or coal to create a variety of synthetic petroleum products.
Bob Kelly, a co-founder of DKRW said his company knew it would be using just goal and trying to make just gasoline… so their process could be simpler.
BOB KELLY: The alternative way, this process, technically, is called MTG or Methanol-to-Gasoline.
MARTINEZ: It’s a process DKRW licensed from Exxon-Mobil. Plants in New Zealand and China have been using the M-T-G process for years. But it’s really only the final part of DKRW’s system that will turn a lump of coal into the stuff Denver motorists will pump into their cars… So, first, the plant will take coal from the mine, crush it, and add water to make a slurry. That mixture is fed into a gasifier DKRW licensed from GE. It applies heat and pressure.
KELLY: So the first step is, you put the goal in a gasifier. It changes state to a gas.
MARTINEZ: What comes out is a gaseous mixture of hydrogen, carbon monoxide and carbon dioxide, or CO2. There are also traces of sulfur and other particulates, which will get removed and discarded. Then the gas moves on to another patented process called Selexol.
Kelly: So it separates the CO2 from the CO and hydrogen. That CO2 will get compressed, which turns it from a gas to a liquid.
MARTINEZ: From there, most of the CO2 will be sent through a pipeline to another company that’s buying it to use in enhanced oil recovery. So, that leaves behind a relatively pure syngas mixture of hydrogen and carbon monoxide. They add some more hydrogen, and then the mixture goes into a reactor where it’s compressed and catalyzed to become a liquid called methyl alcohol, or methanol.
KELLY: Methanol’s like a clear liquid. You can actually use it as a fuel in and of itself.
MARTINEZ: Monster trucks run on pure methanol. But it’s not gasoline, yet. The methanol is pulled from one tank to another, which contains a catalyst that reacts with the methanol. This portion of the process was brought to you by Exxon-Mobil.
KELLY: What methanol is… Methanol’s just… the chemists will cringe when I say this, but it’s like a gasoline molecule with water molecules around it. And what the Exxon-Mobil process does is it strips the water off.
MARTINEZ: So the water gets removed and recycled for the next go-round. What remains in synthetic gasoline that will be shipped down to Denver and pumped into the average car, pickup truck or SUV… So that’s the plan. David Bell, a chemical and petroleum engineer at the University of Wyoming, reviewed it in collaboration with Idaho National Laboratory.
DAVID BELL: The project is intended to make 10,000 barrels of gasoline a day. In terms of an oil refinery, that would be a fair small oil refinery. It’s about four times the size of the coal-to-gasoline project in China.
MARTINEZ: Bell says other MTG facilities have used lots of water in process and to cool the machinery, but DKRW plans to recycle the water from its closed-system process, and it’ll cool machinery using air. Idaho National Lab found that the coal-to-gasoline process has a slightly higher carbon footprint than conventional gasoline production, but Bell doesn’t think that’s a fair comparison.
BELL: If you had plenty of conventional crude oil available at a reasonable price, then that would be the environmentally-preferred option. But supplies of conventional crude oil are getting more expensive, more difficult to obtain, and we have to look at our options moving forward.
MARTINEZ: For Wyoming Public Radio, I’m Rebecca Martinez.