Oct. 2, 2003 — A particulate agglomeration technology for coal-fired power plants, developed in Australia and brought to the U.S. by Southern Company and Indigo Technologies, Brisbane, Australia, is now being demonstrated on a Southern Company plant in Mississippi.
The technology now has the additional backing and cooperation of EPRI, Entergy, Cinergy, Ontario Power Generation, First Energy and Duke. Several more U.S. utilities are also considering participation.
The device – the Indigo Agglomerator – works by charging particulate matter both positively and negatively, causing the formation of larger particle clusters that can be removed from stack gases more easily than by electrostatic precipitators alone. “The fine negative particles are attracted to the large positive particles and vice-versa, creating particles of about 10 microns in size,” says Bob Crynack, president of Indigo Technologies LLC.
The first prototype Indigo Agglomerator was installed in December 2000 at Delta Electricity’s Vales Point Power Station in New South Wales, Australia. That installation verified the technology and provided data for the design of a full commercial installation. In March of this year, the first U.S. commercial installation was completed during a four-week outage at Mississippi Power Company’s Watson Plant in Gulfport, Miss.
The device was installed on Unit 4, a 250 MW opposed wall-fired boiler with two separate exhaust gas treatment and monitoring systems. The plant burns a variety of foreign and domestic coals.
Each of the plant’s gas treatment and monitoring systems has an air heater for waste heat recovery, an electrostatic precipitator (ESP) for dust removal and an induced draft fan to maintain a slightly negative furnace pressure and convey gas into a common exhaust chimney.
The monitoring system on each system measures gas flow, gas temperature and opacity (an optical measurement of dust emissions). The agglomerator was installed in the B exhaust gas treatment system between the air heater and the ESP.
Preliminary tests indicate up to 70% reduction in opacity levels, a 45% reduction in outlet dust load, and a reduction in PM 2.5 fine particulate emissions of more than 50%.
The agglomerator uses two key processes to reduce fine particle emissions. A bi-polar charger is used to charge half of the dust positively and half negatively. The bi-polar charger has a series of alternating positive and negative parallel passages that the gas and dust pass through to acquire a positive or negative charge.
The second key process is a specially designed mixing system that causes the fine positive particles to be carried by the gas and mixed with the large negative particles emitting from the adjacent negative passage. This mixing system also causes the fine negatively charged particles to mix with the large positive particles. This results in the oppositely charged particles attaching to each other and forming agglomerates.
The particle size distribution confirms that these results are due to a reduction in fine particle emissions, showing a greater than 350% reduction at 0.8 micron at the ESP outlet. Particles in the 1-micron size range have a large effect on the visibility of emissions, hence the large opacity reduction.
Source: This article is part of the Power Engineering October 2003 issue.