Control of Mercury Emissions from Coal-Fired Power Plants

EPA Grant Number: R828170
Title: Control of Mercury Emissions from Coal-Fired Power Plants
Investigators: Helble, Joseph J. , Sarofim, Adel F.
Current Investigators: Helble, Joseph J. , Qiu, Joseph , Sarofim, Adel F. , Sterling, R.
Institution: University of Connecticut , University of Utah
EPA Project Officer: Shapiro, Paul
Project Period: July 1, 2000 through June 30, 2002 (Extended to September 30, 2003)
Project Amount: $224,642
RFA: Exploratory Research - Engineering, Chemistry, and Physics) (1999) RFA Text |  Recipients Lists
Research Category: Engineering and Environmental Chemistry , Water , Land and Waste Management , Air

Description:

Coal combustion remains one of the major anthropogenic sources of ambient mercury. Mercury capture in coal combustors is inhibited by incomplete mercury oxidation. This research project will explore methods for manipulating mercury chemistry in the post-combustion zone to increase the fraction of oxidized mercury and thus enhance mercury capture in existing pollution control devices.

Objectives/Hypothesis:

The objective of our proposed effort is to develop a novel, low-cost process for mercury emissions control. Small quantities of a hydrocarbon will be injected into post combustion gases to manipulate the radical pool and drive mercury toward the favored Hg(II) form. Our hypothesis, supported by preliminary calculations using kinetic models of chlorinated hydrocarbon combustion chemistry, is that this injection will increase the concentration of oxidizing chlorine radical species by 5-10 fold. Based upon recent studies of mercury oxidation kinetics, it is further hypothesized that this increase in chlorine radical species concentrations will increase the rate of mercury oxidation, thus driving mercury speciation toward the equilibrium-favored HgCl2 form.

Approach:

The approach for assessing the feasibility of this process is one of combining bench scale experiments with elementary reaction kinetics modeling. Specifically, a hydrocarbon will be injected into the 700 B 1200 K post combustion gases of an existing flat flame reactor system. Gases will be doped with mercury and HCl or Cl2 as a chlorine source in concentrations comparable to those obtained from fuel lean combustion of a typical U.S. eastern bituminous coal. Mercury and chlorine species will be measured using impinger trains and atomic absorption and ion chromatography. Chlorine radical species will also be measured indirectly by injecting trace quantities of vaporized benzene into the post combustion gases downstream of the methane injection point, and measuring benzene decay both with and without supplemental fuel injection. Benzene has been observed to effectively titrate reactive chlorine under similar conditions. Potential increases in the concentrations of other species (e.g. NOx, CO) will be closely monitored both experimentally and through gas phase homogeneous kinetic modeling.

Expected Results:

This project, if successful, will demonstrate the feasibility of changing mercury speciation in coal combustion gases through the injection of small quantities of a hydrocarbon such as natural gas. This is expected to lead to an improved and relatively inexpensive process for mercury emissions reductions in coal fired utility boilers.

Publications and Presentations:

Publications have been submitted on this project: View all 6 publications for this project

Supplemental Keywords:

heavy metals, toxics, particulate matter, air, waste reduction, RFA, Scientific Discipline, Air, Toxics, Waste, particulate matter, air toxics, Environmental Chemistry, HAPS, Environmental Monitoring, tropospheric ozone, Incineration/Combustion, Engineering, Chemistry, & Physics, 33/50, anthropogenic stresses, particulates, anthropogenic stress, combustion byproducts, mercury, stratospheric ozone, hydrocarbon, ion chromatography, ambient air, combustion emissions, air pollution, benzene, chemical composition, ambient emissions, methane, mercury speciation, combustion, hydrocarbons, mercury & mercury compounds, Mercury Compounds, flue gas emissions, Benzene (including benzene from gasoline), coal fired power plants, benzene emissions, coal combustion

Progress and Final Reports:

  • 2001 Progress Report
  • 2002
  • 2003
  • Final Report