IECM 12.0 beta User Manual > Modules Included with the IECM > Pulverized Coal (PC) Plant > SET PARAMETERS > Mercury >

Removal Efficiency

Inputs for the removal of the speciated mercury from the flue gas stream are entered on the Removal Efficiency parameter screen . The following parameters are available:

•Removal Efficiency of Mercury: The removal of mercury for each control technology configured is given as a percent of the total entering the control technology. The user is given the opportunity to specify the removal separately for each speciation type. Control technologies not currently configured are hidden.

•Furnace Removal (total): Mercury present in ash is removed from the furnace through the removal of bottom ash. The speciation is not known, so the removal is specified as a total removal. The mercury removed in bottom ash is not credited toward the required removal to meet the mercury emission constraint.

•Spray Dryer: (only shown when a spray dryer is configured)

•Spray Dryer (oxidized): Oxidized mercury is assumed to pass through the lime spray dryer. Although soluble in water, moisture injected into the spray dryer evaporates, resulting in the mercury remaining in the flue gas. The default value is zero.

•Spray Dryer (elemental): Elemental mercury is assumed to pass through the lime spray dryer. It is assumed that elemental mercury is present in the flue gas and is unreactive.

•Spray Dryer (particulate): This is the amount of particulate mercury removed by the spray dryer.

•Fabric Filter: (only shown if a fabric filter is configured)

•Fabric Filter (total w/o control): Mercury present in ash is removed from the fabric filter through the removal of captured fly ash. The speciation is not known, so the removal is specified as a total removal. The value shown is determined without regard to particular mercury control methods. It has a substantial effect on the amount of activated carbon needed to meet the required removal of mercury.

•Fabric Filter (oxidized): The fabric filter typically removes some mercury without adding a specific mercury control technology. This mercury is present in the ash and is removed with the collected ash. When a mercury control technology is added, the removal is enhanced. The default value is set to meet the overall removal efficiency constraint, with consideration given to the mercury removed by flue gas desulfurization and elemental mercury oxidized in a NOx control technology. The lower limit is set by the removal efficiency of ash alone as specified by "Fabric Filter (total w/o control)" specified above.

•Fabric Filter (elemental): Elemental mercury is assumed to be removed with the same efficiency as the removal of oxidized mercury specified above.

•Cold-Side ESP: (only shown if a cold-side ESP is configured)

•Cold-Side ESP (total w/o control): Mercury present in ash is removed from the cold-side ESP through the removal of captured fly ash. The speciation is not known, so the removal is specified as a total removal. The value shown is determined without regard to particular mercury control methods. It has a substantial effect on the amount of activated carbon needed to meet the required removal of mercury.

•Cold-Side ESP (oxidized): The cold-side ESP typically removes some mercury without adding a specific mercury control technology. This mercury is present in the ash and is removed with the collected ash. When a mercury control technology is added, the removal is enhanced. The default value is set to meet the overall removal efficiency constraint, with consideration given to the mercury removed by flue gas desulfurization and elemental mercury oxidized in a NOx control technology. The lower limit is set by the removal efficiency of ash alone as specified by "Cold-Side ESP (total w/o control)" specified above.

•Cold-Side ESP (elemental): Elemental mercury is assumed to be removed with the same efficiency as the removal of oxidized mercury specified above.

•Wet FGD: (only shown when a wet FGD is configured)

•Wet FGD (oxidized): The wet lime/limestone FGD typically removes all the oxidized mercury due to its high solubility in water.

•Wet FGD (elemental): Elemental mercury is assumed to pass through the wet lime/limestone FGD. It is assumed that elemental mercury is present in the flue gas and is unreactive.

•Wet FGD (particulate): This is the amount of particulate mercury removed by the Wet FGD.

•Percent Increase in Speciation: Although NOx control technologies do not remove mercury from the flue gas, they can change the mercury from one form to another. This is particularly true when catalysts are present. In this case, elemental mercury is converted to oxidized mercury. The parameters in this section define the percent increase in oxidized mercury across the control technology.

•In-furnace NOx (oxidized): Low NOx burners with or without overfire air and gas reburn can affect the amount of oxidized mercury. At present, there is insufficient information available to specify a default value. The default is set to zero.

•SNCR (oxidized): An SNCR does not affect the relative amounts of oxidized and elemental mercury. The default is set to zero.

•Hot-Side SCR (oxidized): Hot-side SCR as a control technology chances elemental mercury to oxidized mercury. It is believed that the catalyst is responsible for this shift in speciation. The default value is a function of the coal rank.