LBL Researchers Make Clear Air Technology More Affordable

Sulfur-Dioxide Treatment Process Developed

May 6, 1994

Jeffery Kahn,

BERKELEY -- Stepping up the attack against acid rain and smog, researchers at Lawrence Berkeley Laboratory have developed a new technology to help eliminate sulfur dioxide air pollution from power plants, incinerators, chemical plants, and smelters. Part of a multistage treatment system, the LBL process treats concentrated sulfur dioxide, converting more than 95 percent of it to a valuable commodity. It generates elemental sulfur, a chemical feedstock that can be sold.

Cost is the overriding factor affecting the success of emissions treatment technology. A number of effective technologies have been developed to treat fossil fuel emissions prior to venting them into the atmosphere. However, due to the cost, most of the world's power plants do not significantly treat exhaust gases. Likewise, utilities often elect not to burn abundant fuels such as coal, which have a relatively high sulfur content, because of the expense of removing sulfur dioxide.

The LBL team -- it includes Shih-Ger Chang of LBL's Energy and Environment Division and visiting professors from Bejing University Yun Jin and Qiquan Yu -- say the primary advantages of their new technology are its affordability and simplicity.

The process relies on the team's invention, a new catalyst for which a patent is pending.

Said Chang, "The catalyst consists of an inexpensive mixture of iron-based metal oxides supported on alumina. We have tested it in the laboratory over a lifetime of 1080 hours and the catalytic activity is very stable. The yield of sulfur recovery over the course of our lifetime test was 96.5 percent."

Many countries including America and China have abundant coal reserves. However, in America the cost of desulfurization has been a major obstacle to the use of coal.

Dealing with sulfur has frustrated the emergence of one promising clean coal technology, the Integrated Gasification Combined-Cycle (IGCC) method. The method can convert 42 percent of the energy potential in coal into electricity, a seven percent improvement over the technologies now in common use.

IGCC combines coal, water, and heat to produce a synthetic gas that consists of carbon monoxide, hydrogen, and hydrogen sulfide. However, before this hot gas can be burned to produce electricity, the hydrogen sulfide must, in some way, be treated.

One emerging approach to this pollution problem starts by concentrating the hydrogen sulfide gas through a multistep treatment process that results in additional capital investment and energy loss. Ultimately, the concentrated hydrogen sulfide gas is fed through a Claus catalytic process that requires three or four stages of treatment to desulfurize the gas.

To make IGCC more energy-efficient, researchers have been looking for a way to remove hydrogen sulfide from the initial synthetic hot gas mix.

In a technique now under development, the hot gas is sprayed with metal salts such as zinc titanate or zinc ferrite, creating a metal sulfide product. The metal sulfides are then put through a regeneration process that yields metal salts for reuse and concentrated sulfur dioxide.

The new LBL process deals with this concentrated sulfur dioxide. Synthesis gas and concentrated sulfur dioxide are fed into a catalytic chamber, which in a single step, reduces more than 95 percent of the sulfur dioxide to elemental sulfur.

Whereas IGCC is an emerging technology, the current system that most existing power plants use to burn coal begins with the pulverization of the coal. This pulverized coal is then burned, creating electricity and an exhaust gas. Currently, more than 150 U.S. utility power plants use limestone scrubbers to strip sulfur dioxide from the smokestack emissions.

Because of their reliance on wet limestone or lime, existing scrubbers produce tons of sludge waste that must be trucked to landfills. A 500 megawatt plant burning coal with an average sulfur content of three percent will pump out 1,500 tons of sludge daily. New scrubber technology uses a variety of absorbent and adsorbent compounds to capture and concentrate sulfur dioxide. Again, the new LBL process is a natural complement, making these emerging technologies more efficient and thus more affordable.

Lawrence Berkeley Laboratory is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California.