Mercury mass balance

Total Mercury Mass Balance at a Coal-Fired Power Plant... 

A series of mercury mass balances was obtained at a coal-fired power plant by comparing the volatile and particulate mercury in the stack gas stream to the mercury initially in the coal, corrected for the mercury adsorbed and retained by the various ashes. These data were used to determine the fate of the mercury in the combustion process and to check the accuracy of the volatile mercury sampling procedure (gold amalgamation). The bottom ash had the lowest mercury concentration of the ash samples collected, and the mercury concentration increased as one proceeded through the ash collection system from the initial mechanical ash to the electrostatic ash. The mercury recovered in the various ashes represented about 10% of the total mercury introduced in the raw coal. 

Evaluating the quantitative effect of these factors on the volatile mercury concentration requires determining how much of the initial mercury found in the coal is 1. not volatilized from the coal during combustion, 2. recovered in the various ash collection mechanisms by some adsorption phenomena, and 3. released to the atmosphere. With this information, a mercury mass balance can be calculated in which the amount of mercury consumed during the combustion process is compared with the amount in the stack gas and the various ashes. During this study, this was accomplished by comparing the stack gas concentration with the amount of mercury initially in the coal, corrected for the amounts recovered in the ashes. Differences between these two values would represent adsorption and/or desorption onto and off the walls of the ducts and stack and any significant contribution from the ambient air used in the combustion process. 

The results of this study were divided into three areas stack gas analysis, solids sampling and analysis, and the mercury mass balance. 

Mercury Mass Balance. The mass balance consisted of comparing the amount of mercury in the stack gas stream with the amount in the coal minus that mercury recovered in the ash. In obtaining this balance it was assumed that the walls of the stack and the duct work did not affect the mercury concentration in the gas stream. The author felt that this was a correct assumption only if ... 

Kalb, G. W., Baldeck, C., The Determination of a Mercury Mass Balance... 

This chapter will review information relevant to the biogeochemical cycle of mercury, specifically (i) the speciation chemistry of mercury, (ii) the fate of mercury in air, water and sediment, and (iii) the effects of landscape changes on mercury fate. The chapter will end with a summary of a recent multidisciplinary mercury mass balance conducted in Kejimkujik Park (Nova Scotia, Canada). 

BIG DAM WEST LAKE MERCURY MASS BALANCE 6.1. Introduction... 

Henry EA, Dodge-Murphy LJ, Bigham GN, Klein SM, Gilmour CC. 1995. Total mercury and methylmercury mass balance in an alkaline, hypereutrophic urban lake (Onondaga Lake, N.Y.). Water Air Soil Pollut 80 489 98. 

Fitzgerald WF, Mason RP. 1996. The global mercury cycle oceanic and anthropogenic aspects. In Baeyens W, Ebinghaus R, Vasihev O, editors. Global and regional mercury cycles sources, fluxes and mass balances, Dordrecht, the Netherlands Kluwer Academic Publishers, p. 85-108. 

Griepink B eds.. Quality Assurance for Environmental Analysis, pp 89-110. Elsevier, Amsterdam. Horvat M (1996) Mercury speciation and analysis. In Global and Regional Mercury Cycles Sources. Fluxes and Mass Balances, Baeyens W, Ebinghaus R and Vasiliev O, eds. pp 1-31. Kluwer Academic Publishers, The Netherlands. 

Colwell, R.R., G.S. Sayler, J.D. Nelson, Jr., and A. Justice. 1976. Microbial mobilization of mercury in the aquatic environment. Pages 437-487 in J. 0. Nriagu (ed.). Environmental Biogeochemistry, Vol. 2. Metals Transfer and Ecological Mass Balances. Ann Arbor Sci. Publ., Ann Arbor, MI. 

This mass balance presents the possible links in the biogeochemical food web for various heavy metals. Some items may be neglected, like degassing of Pb, Cd, Cu and Zn metals. However, this process is of crucial importance for mercury (see Section 3.2). The output of the heavy metals with soil erosion may also be neglected. After elimination of these processes, the simplified following equation is workable. The sum of inputs by deposition, fertilizing, and waste and rubbish as fertilizer stands as the term Critical Load . 

Small catchment study of biogeochemical mass balance of mercury was carried out in southern Sweden in early 1990s. The fluxes of methyl Hg (Hgm) and total Hg (Hgt) were monitored (Figure 23). 

The model of a mercury cell described in this chapter represents an effective combination of empirical data accumulated over several years of operation and theoretical heat and mass balance equations. Modern software tools and fast desk-top computers make the task of implementing the model relatively straightforward and of low cost so that it can be exploited for plant optimisation. 

The mercury adsorption mechanism was equilibrium controlled Until these conditions have been achieved the rate of mercury adsorption on the walls will not equal the rate of desorption. The first two conditions were approximated in most of the tests reported. A second assumption in the mass balance was that the air utilized in the combustion process does not contribute a significant quantity of mercury to the system. 

The results of the mass balance are summarized in Table VI. The ratio of the mercury found in the gas stream to the amount of mercury released from the coal but not recovered in the ash is given in the third column. The average of this ratio is 1.19, with a standard deviation of 0.24. Within one standard deviation unit there is not a significant difference between the measured ratio and the expected ratio of 1.0. Therefore, based on 14 ratios at one plant, there is not a statistically significant difference between the total mercury found in the stack gas and the amount expected in the stack gas from the coal and ash determinations. Dual tests 13 and 14 showed close ratios of 0.88 and 0.95. 

Mass balance measurements for 41 elements have been made around the Thomas A. Allen Steam Plant in Memphis, Tenn. For one of the three independent cyclone boilers at the plant, the concentration and flow rates of each element were determined for coal, slag tank effluent, fly ash in the precipitator inlet and outlet (collected isokinetically), and fly ash in the stack gases (collected isokinetically). Measurements by neutron activation analysis, spark source mass spectroscopy (with isotope dilution for some elements), and atomic adsorption spectroscopy yielded an approximate balance (closure to within 30% or less) for many elements. Exceptions were those elements such as mercury, which form volatile compounds. For most elements in the fly ash, the newly installed electrostatic precipitator was extremely efficient. 

BOLTON ET AL. Trace Element Mass Balance Table V. Mercury Balance ... 

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