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Welcome to the Energy & Environment (E&E) Exchange, a blog dedicated to science and engineering topics that are (generally) related to energy and the environment. This blog is meant to encourage discussion about the challenges and possibilities surrounding sustainability through science and technology. The blog's owner, cheme_wordsmithy, is a former technical writer and engineering editor at IHS GlobalSpec, the company that powers CR4.

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Cleaner, Cheaper “Liquid Coal”

Posted January 18, 2012 9:30 AM by cheme_wordsmithy

Okay, so "liquid coal" isn't technically correct, nor is it magic (see image right) but it does sound cool.

CTLF (coal-to-liquid-fuel) technology has been gaining increased attention in recent years, and researchers are hoping to bring it to market.

SRI International, an independent, nonprofit research institute, promises that a

new process for coal to liquid fuel (CTLF) production will be cleaner and cheaper. But what does this mean for a technology sector that has had little success over the last half-century?

Conventional CTLF Processes

The CTLF process is the conversion of coal to liquid synthetic fuels. CTLF technology dates back to the 1920s and was used most prominently in Germany during World War II: a whopping 90% of their fuel needs came from coal. But with the exception of South Africa, the technology has had little use since then because of its cheaper competitor, crude oil.

Most CTLF plants in the U.S. utilize indirect liquefaction, a process which involves gasifying coal and then converting the resulting syngas into synthetic fuels. The syngas is produced by blending pure oxygen, steam, and coal at high temperatures and pressures.

But the process is neither clean nor cheap. Because of the water used, the gasification process results in a large amount of heat absorption, requiring high (and thus costly) temperatures to operate. The blending process also creates carbon dioxide through some coal combustion and undesirable reactions between the water and carbon.

The New Process

SRI's CTLF method involves replacing the steam with preheated methane. The

gas reduces the amount of water required, which in turn lowers the heat absorbed by the process (meaning lower required operating temperatures). These lower requirements allow the liquefaction process to implement (non-combustion / zero-emissions) alternatives like nuclear or renewables to power the reaction.

Eliminating the need for pure oxygen not only removes carbon dioxide from the equation, but also means there is no need for an oxygen plant, further lowering costs.

This device (pictured left) injects methane and coal into the gasification reactor as part of SRI International's new process.

SRI's predicted cost to generate jet fuel is said to be $2.82 per gallon in a 100,000 barrel/day plant costing $3.2 billion to build (current CTLF plants cost ~$6 billion). These estimates come only from a bench scale analysis, and a pilot plant will need to be developed in order to further prove its viability.

The Future for Coal Liquefaction

While the research was funded and intended for producing jet fuel, the process could have wholesale implications for coal-derived fuels. One primary advantage of coal is that there is such an abundant amount available in the U.S. (some 270 billion tons or 250 years-worth at current usage rates). The volatility of oil prices and the ever-present desire for greater energy independence are additional incentives.

But even if this new CTL process leads to the economic viability of coal-derived fuel, it doesn't compute with current initiatives driving the focus away from fossil fuels. Even if the process is driven by zero-emission sources, the carbon dioxide generated from burning the fuel makes no improvements over oil. As Eric Larson, research engineer at Princeton University, points out, "on a life-cycle basis, the fuel is no better than petroleum fuel on greenhouse-gas emissions."

Personally, I think liquid coal will inevitably begin fueling a large part of the transportation industry because of depleting oil reserves, estimated to last only another 40-45 years. Progress on other alternatives (EVs, hydrogen, or biofuels) leads me to believe they will still only be a supplement of the market by that point, leaving a large gap for CTLF to fill. Because of this, I am hoping to see major advancements in CTLF processes in future years to help make its production more economical and curb its environmental impact.

Currently, environmental policies would likely not accept such a large scale of coal-derived fuel production using methods that emit more CO2 than in refining crude oil. To create a zero-emissions production step, CTLF processes must utilize either CO2 sequestration (costly) or zero-emission power sources (SRI's new process). But from an environmental standpoint, taking "clean" power generation off the grid to create fossil fuels seems somewhat backwards…

Sources:

Cleaner, Cheaper Liquid Fuel from Coal - Technology Review

Coal-to-liquid fuels poised for a comeback - MIT News

AAAS Policy Brief: Coal-to-Liquid Technology

Image Sources:

Wired.com

SRI International

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#1

Re: Cleaner, Cheaper “Liquid Coal”

01/22/2012 12:14 AM

The more process you put on to your product the more ineffecient that is, much worse if you are adding H2O on it to have it liquify. Heat value will be less, as consumed by the latent heat of water converting it from liquid to vapor at combustion.

This is not a good idea, an I wont be supporting it.

I'd rather be promoting the idea of having war using sticks.

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