Friday, September 28, 2012

Underground Coal Gasification and How It Could Compete With Biogas

Underground Coal Gasification is a process for exploiting coal that cannot be mined because the seam is too deep, thin or fractured. The process involves using the drilling technology usually used for fracking to get oxygen into the coal seam and then setting the seam on fire. By controlling the amount of oxygen injected it is then possible to only partially burn the coal and bring the gases produced to the surface where they can be burn to produce energy. The process is associated with serious groundwater contamination and massive carbon emissions.

When coal is gasified, rather than burned as at conventional coal plants, impurities such as sulfur and mercury can be stripped out of the gas stream, instead of otherwise being emitted into the air. The resulting fuels burn virtually free of these pollutants. Sulfur-free fuel means less smog and acid rain, among many other benefits.

No Smokestack!

Unlike conventional coal burning plants that ignite the coal and send pollutants up a smokestack and into the air, synfuel plants gasify coal and there is no direct smoke emission. This thermo-chemical conversion takes place in a contained reaction and creates only syngas, a mixture of gases which then can be made into liquid fuel. Just like biogas, syngas can be used for liquid fuel production, and syngas can also be upgraded to natural gas just as biogas can be upgraded into biomethane to be sold on the market or can be used directly as fuel for a power plant.

Now you will say that this is surely environmentally damaging due to the fossil fuel based carbon dioxide emissions, but the coal gasification industry has an answer to that. Plants using syngas could invest in what is known as Integrated Gasification Combined Cycle (IGCC) plants, and although these are currently rare and still in development, they are among the cleanest types of electricity generators.

So, rather than burning coal directly, gasification breaks down coal, or virtually any carbon-based feedstock, into its basic chemical constituents. In a modern gasifier, coal is typically exposed to steam and carefully controlled amounts of air or oxygen under high temperatures and pressures. Under these conditions, molecules in coal break apart, initiating chemical reactions that typically produce a mixture of carbon monoxide, hydrogen and other gaseous compounds.

Gasification is, as we said already  a thermo-chemical process which investors will like as there is no start up time of several weeks of the sort that anaerobic digestion plants need before they produce biogas.

Who Said That Underground Coal Gasification Was Not Environmentally Sound?

The environmental benefits of gasification in combination with the IGCC process during which the syngas is converted to energy by combustion. Its great advantages stem from the capability to achieve extremely low SOx, NOx and particulate emissions from burning coal-derived gases. Sulfur in coal, for example, is converted to hydrogen sulfide and can be captured by processes presently used in the chemical industry. In some methods, the sulfur can be extracted in either a liquid or solid form that can be sold commercially. In an Integrated Gasification Combined-Cycle (IGCC) plant, the syngas produced is to all purposes free of fuel-bound nitrogen.

NOx from the gas turbine is limited to thermal NOx. It is reported that diluting the syngas allows for NOx emissions as low as 15 parts per million. Selective Catalytic Reduction (SCR) can even be used to reach levels comparable to firing with natural gas if required to meet more stringent emission levels. Other advanced emission control processes are stated as being developed that could reduce NOx from hydrogen fired turbines to as low as 2 parts per million.

Carbon Capture is the Trump Card?

These benefits could be combined with carbon capture to prevent the climate changing effects of carbon dioxide emissions once carbon capture and long-term underground storage of the CO2 has been demonstrated to be effective. In which case investors may prefer to put their cash into these power plants, which can be built on a huge scale to allow underground coal gasification to rival the output of traditional coal power plants, so watch out anaerobic digestion for renewable energy!

The US Department of Energy is reported to be working with industry to keep the United States at the forefront of carbon capture, utilization, and storage technologies. An innovative clean coal demonstration project in Texas, supported by the Department’s Office of Fossil Energy, is underway.

The United Kingdom is well placed within Europe to develop underground coal gasification by having large reserves of indigenous coal both onshore and offshore in the southern North Sea. These reserves have the potential to provide security of future energy supplies long after oil and natural gas are exhausted. The UK is already building a part UK government and EU funded power station "retrofit" to demonstrate carbon capture and storage in old natural gas fields under the North Sea.

Furthermore, syngas or what is termed as hydrogen oriented Underground Coal Gasification (UGC) for Europe and its Environmental and Safety Aspects are being studied, HUGE2 is a R&D project (2011-2014) co-financed by the EU within the Research Fund for Coal and Steel. It is a follow-up of the project Hydrogen Oriented Underground Coal Gasification for Europe known as HUGE, which was completed in 2010. The EU has funds (although not a much cash as expected due to carbon offsets trading price drops) to fund more projects in carbon capture and IGCC.

Traditional mining methods however are not suited to working many of the UK's on land and offshore reserves, and development and infrastructure costs of new mines so without new technology like underground coal gasification, also known as fracking, many UK and indeed, worldwide reserves would be likely to remain unused, giving anaerobic digestion the best chance to thrive.

Watch Out Biogas? Another Competitor?

But, the concept of gasifying coal underground and bringing the energy to the surface as a gas for subsequent use in heating or power generation has considerable attraction, with spin-offs as a chemical production refinery feedstock instead of oil. So, watch out anaerobic digestion and biogas production devotees, because underground coal gasification (UCG) has the potential to provide a clean and convenient source of energy from coal seams where traditional mining methods are either impossible or uneconomical, and its development is gathering pace.

1 comment:

SteveK said...

Remember Centralia! Underground coal fires are largely impossible to extinguish. This is rank folly!