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Energy Department Examines Hydrogen-Production Benefits of Coal

Clean-burning coal may lead way to hydrogen economy

Researchers at the U.S. Department of Energy (DOE) Sandia National Laboratories in California are studying the burning characteristics of coal to prepare the way for a hydrogen economy.

There are many long-term options for providing hydrogen as a fuel of the future, but coal is the leading contender to provide a hydrogen source in the near term.

"While someday we may be able to produce hydrogen by breaking up water molecules in association with the high-temperature heat from nuclear power reactors, or through renewable energy technologies," said Chris Shaddix, principal investigator for clean coal combustion at Sandia, "right now the most cost-effective way to produce hydrogen is with coal."

Shaddix and colleagues are involved in experiments to optimize the combustion of coal to produce the most energy and the least possible pollution.

Traditional coal combustion produces harmful emissions, Shaddix said, but modern plants can meet environmental regulations for burning coal cleanly. As the cost of competing fuels - particularly natural gas - climbs, burning clean coal becomes cost competitive.

Add in the possible benefits of separating and storing carbon dioxide (CO2) emissions from the power plant stacks, and coal looks like a promising way to generate electricity and hydrogen to provide a bridge to the future technology.

"Utilities are starting to invest in coal," Shaddix said.

TWO APPROACHES

Two approaches to burning coal now are under study. The first, oxy-combustion, combines coal with pure oxygen. The second, gasification, burns coal only partially to create a fuel gas.

Oxy-combustion is driven by concern over emissions of CO2 and other pollutants. Burning coal in oxygen is a near-term solution that can produce exhaust streams that are close to pure CO2, Shaddix said. Harmful pollutants like nitrogen oxides, sulfur compounds and mercury are virtually eliminated.

Companies in Japan, Canada, Germany and elsewhere favor oxy-combustion and are building pilot plants.

U.S. companies tend to favor gasification technologies, which offer higher efficiency and low pollution formation.

One such technology, called steam reformation, combines the coal with steam in a hot environment to produce a syngas (synthetic gas) composed mostly of carbon monoxide (CO) and hydrogen.

Once the syngas is produced, it can be burned directly in a turbine to produce power, or further reacted with more steam to shift the remaining CO to CO2 and produce more hydrogen.

The CO2 can be stored in oil and gas fields and the hydrogen can be used in many potential applications - to power a car in an engine or a fuel cell, power a turbine to produce electricity or fly an airplane.

DOE already has demonstrated gasification technology in two pilot projects. Now, there are several commercial proposals in the United States for utilities to build plants without government support.

SANDIA'S COMBUSTION RESEARCH FACILITY

Working with the National Energy Technology Laboratory in West Virginia, the Sandia Combustion Research Facility (CRF) is working to understand the chemistry and physics of coal combustion using state-of-the-art diagnostic capabilities and modeling expertise.

"We apply computational models of reacting particles to the data," Shaddix said, "to understand why we see the results we see."

Shaddix and Alejandro Molina, a Sandia postdoctoral student, have been working in a small-scale laboratory to analyze coal combustion.

"It is very important to understand how fast [coal] burns and releases energy," Molina said.

Burning coal in pure oxygen rather than air eliminates some separation problems, leaving water and CO2, which can be stored, or sequestered, he added.

After two years of small-scale research, work is now under way to bring two other CRF facilities into the research.A gasification lab will help the researchers study the behavior of coal gas under pressure, and a two-story flow reactor will help them study the oxygen-coal combustion with recycled CO2.

Source: U.S. Department of State