Date of Award

5-2000

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Abstract

Mercury is a toxic compound causing numerous health problems in humans. One of the ways that mercury is released into the atmosphere is through the burning of coal. The Environmental Protection Agency estimates that the United States consumes i billion tons of coal per year and coal-fired utilities emit 73 tons of mercury per year. Though there arc currently no regulations on mercury emissions, it will remain an environmental concern.

Activated carbon (AC) injection is a proposed technology for mercury control in coal-fired boilers. We are interested in determining whether the diffusion rate or the absorptive capacity of the sorbent particle limits mercury absorption. A mathematical model was developed to estimate mercury diffusion rates in flue gas. With the model, diffusion rates were studied for mono-sized particles, particle distributions, and temperature variations.

The diffusion rates appear to be the limiting factor except in the cases of small particle diameters (less than two microns at 95% mercury capture) and high temperatures. The results show that carbon requirements increase as the square of the particle diameter. Temperature has very little effect on mercury diffusion to the smaller particles but becomes increasingly important as the size increases. Particle distributions have a great impact on the carbon requirements. The mono-sized particle carbon requirements increased by factors of between 2.8 and 32 depending on the mean particle diameter and the geometric standard deviation.

There is ongoing research to improve sorbent technology. The Energy and Environmental Research Center has developed a promising new sorbent, indole- impregnated activated carbon. To estimate the production cost of the new sorbent, an economic analysis was performed for the production of 500 tons/yea

A high production cost of S7.83/lb. caused the project to be economically unattractive. The raw matenals made up 62% of the total product cost. The product cost was fairly insensitive to deviations of all factors except the costs of indole and base carbon. Significant reduction of the production cost must come through the lowering of raw material costs.

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