DFC by FuelCell Energy: Is Clean Coal on the Horizon?

November 16th, 2011 by David Gibbs* Leave a reply »

FuelCell Energy is a Danbury, Connecticut, manufacturer of ultra-clean fuel cell power plants. Their Direct Fuel Cell (DFC) systems are currently producing electricity at more than 50 locations worldwide and have generated over 850 million KWh of power.

FuelCell was recently named by the Department of Energy as the recipient of a $2,994,108 award to utilize its DFC power plant to capture carbon emitted from a conventional coal fueled power plant.

The DFC utilizes FuelCell’s patented hybrid fuel cell system.

FuelCell owns U.S. Patent No. 6,356,290, entitled “High-Efficiency Fuel Cell System” (‘290 Patent). The ‘290 Patent describes a carbonate fuel cell system that produces electricity through a series of chemical reactions.

Heat produced from the reactions can be used to drive an unfired turbine generator. Figure 1 of the ‘290 Patent depicts a heat engine (3), shown as a turbine generator, having a gas compressor (3A), and a gas decompression section (3B). By using the exhaust heat from the carbonate fuel cell reaction to drive a turbine, the plant is able to increase its overall energy output and efficiency.

Figure 1:

Fuel cell technology is efficient because it produces energy without going through the combustion process. Rather, fuel cells use an electro-chemical process to produce electricity and heat.

As a result, unlike conventional combustion based power plants, there are no harmful NOx’s or SOx’s produced. Learn more about fuel cells here and here.

The electro-chemical process used in the DFC fuel cell, based on the ‘290 Patent, involves three chemical reactions depicted below:

Reaction One (Internal Reforming):  CH4 + 2H2O –> 4H2 + CO2

Reaction Two (Anode Reaction):  4H2 + 4CO3 –> 4H2O + 4CO2 + 8e-

Reaction Three (Cathode Reaction):  2O2 + 4CO2 + 8e- –> 4CO3

The first reaction takes a fuel source such as methane and combines it with steam to produce hydrogen gas and CO2. The hydrogen gas produced in the first reaction is combined with a carbonate in the anode reaction to produce water, CO2 and electrons (electricity).

The third reaction (cathode reaction) uses oxygen, CO2 and electrons to produce a carbonate and heat. The carbonate is then used in the anode reaction. The heat produced in this reaction is used to drive a turbine generator.

FuelCell’s DFC technology may be able to utilize flue gases from a fossil fuel power plant, such as a coal power plant, for use in the above process. Flue gases can be concentrated so that the CO2 can be separated from the remaining air and NOx gases.

The air and CO2 can be used in the cathode reaction. The CO2 from both the flue gases and the fuel cell reactions can be collected, stored and sold in either gas or liquid form.

According to a recent FuelCell Press Release:

FuelCell Energy’s carbonate fuel cell technology separates and concentrates CO2 as a side reaction during the power generation process. DFC carbon capture research conducted by FuelCell Energy has demonstrated the DFC is a viable technology for the efficient separation of CO2 from a variety of industrial facility flue gases such as cement plants and refineries. In addition to the carbon capture, the research also verified that DFC technology is capable of destroying some of the nitrogen oxide (NOx) emissions in flue gas streams, thus, reducing the cost of NOx removal equipment. This award from the DOE will advance DFC carbon capture technology further by funding research to assess the capability of DFC technology to seperate the CO2 within the flue gas emitted by existing coal fired power plants in a cost-effective manner.

A Department of Energy Press Release states the Department’s goal for FuelCell’s award is to achieve at least 90 percent CO2 capture from flue gas of an existing plant with no more than a 35 percent increase in the cost of electricity produced.

FuelCell states, “Technology currently in use to capture CO2 from the emissions of coal fired power plants are energy-intensive with high operating costs. DFC power plants potentially represent an efficient and cost-effective approach to separating CO2 while generating ultra-clean power rather than consuming power, as required by current CO2 capture technologies.”

If FuelCell is able to caputure CO2 from a coal plant while producing excess electricity, it will represent a dramatic departure from current carbon capture systems, which require large amounts of energy and are net energy consumers. FuelCell’s DFC may make the illusive goal of efficient clean coal a reality.

David Gibbs is a contributor to Green Patent Blog.  David is currently in his third and final year at Thomas Jefferson School of Law in San Diego.  He received his undergraduate degree in Geology from the University of California, Berkeley.


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