Cornerstone - Summer 2016 - 30 S T R AT E G I C A NALY S IS control is to operate the cleaning system to convert as much Hg0 as possible into HgP and Hg2+. Particulate Hg is desirable because essentially all Hg adsorbed onto suspended particles in the flue gas stream is readily captured in a particle collection device. Whether a plant uses an electrostatic precipitator (ESP), a fabric filter (FF), or a venturi wet scrubber, it collects all the HgP that enters it. An abundance of Hg2+ is preferable because the flue gas desulfurization (FGD) scrubbers that capture sulfur dioxide also collect all the Hg2+ entering with the flue gas, but none of the Hg0. Mercury captured this way ends up sequestered in the finest particles of gypsum, which is often a saleable byproduct in coal-fired electricity generation. So the keys to controlling Hg emissions are to (1) oxidize as much Hg0 into Hg2+ upstream of the FGD scrubber and (2) bind as much Hg0 and Hg2+ as possible into HgP upstream of the particle collector. "iPOG estimates the proportions of Hg0, Hg2+, and HgP at the inlets and outlets of every pollution control device in a gas-cleaning system." Controlling Hg emissions is a challenge for several reasons. Typical levels of coal-Hg are only about 100 ppb, and these levels are diluted by roughly a factor of 10 by the combustion process. To get a sense of how small such concentrations really are, imagine that a large football stadium was filled to the rafters with white ping pong balls. If a few handfuls of black balls were added to the stadium mix, they would be present at a concentration of 10 ppb or so, like the Hg0 concentration as it moves from the furnace into a gas-cleaning system. Mercury emissions control is like capturing only the black balls while the stadium is quickly evacuated through the gates. Another obstacle is the daunting number of furnace and cleaning conditions that determine how much of the coal-Hg is captured or emitted (as explained in detail elsewhere4). If the level of chlorine in coal is not sufficient to bind the mercury to the UBC particles before the stream reaches the particle collector, or the chlorine and UBC in the flue gas are not in the proper proportions to maximize the conversion to HgP, then an operator may consider spraying a bromine solution onto the coal before it is fed into the furnace. Activated carbon can also be injected into the flue gas upstream of the particle collector to compensate for deficient UBC. 30 The third obstacle is that several technical approaches could potentially meet an emissions target, but at markedly different cost. The pace and depth of current and impending emissions regulations usually dictate whether the units that control particulates, NOX, and SOX will be able to meet the regulations on Hg emissions with only minor adjustments and additives, or whether dedicated Hg control technologies will be needed. The first scenario takes advantage of so-called co-benefits for Hg emissions control, whereas the second uses dedicated or external Hg emissions controls. Both forms of control can be analyzed with iPOG. THE SCOPE OF IPOG CALCULATIONS iPOG estimates the proportions of Hg0, Hg2+, and HgP at the inlets and outlets of every pollution control device in a gascleaning system. Users start with calculations for their current gas-cleaning configuration, and the properties of their current fuels. Once the baseline Hg emissions have been estimated, users can quickly estimate the emissions reductions for a broad assortment of control strategies. They can evaluate coal pretreatments based on washing or float/sink separations, and consider different fuel-blending strategies, and fuel switching. Either chlorine or bromine compounds can be virtually added to the fuel stream as it enters the furnace. Furnaces are specified by their burner arrangements, megawatts of electricity output, and overall thermal efficiency, plus the amounts of excess air and the percentage of UBC in fly ash. The flue gas-cleaning configurations can have any arrangement of a selective catalytic reduction (SCR) reactor for NOX control, particle control units (ESP, FF), and a FGD scrubber. Units also can be added or omitted at will, to assess the co-benefits for Hg emissions control from better controls on particulates, NOX, and SOX. The dedicated Hg emissions controls cover injection of chlorine or bromine compounds, and conventional or brominated activated carbon at any point along the gas-cleaning system. The output screen in Figure 1 illustrates a typical calculation sequence. The flow diagram along the lower portion illustrates the user's entries for the cleaning configuration. This case shows coal being fed into a 750-MW wall-fired furnace without any additives. The flue gas leaves the furnace and passes through an SCR for NOX control, an air preheater, ESP to remove fly ash, and a wet FGD scrubber for SOX control, before it enters the stack. Along the bottom, the diagram gives the Hg withdrawal rates in ash from the bottom of the furnace, in fly ash captured by the ESP, and in the scrubber solution from the FGD. In this case, hardly any Hg was withdrawn from the furnace, whereas almost 16% was collected with the fly ash, and 88% of the Hg coming into the FGD was retained in the wastewater. Table of Contents for the Digital Edition of Cornerstone - Summer 2016 From the Editor: The World is Changing with Smart Technologies CoverStory: Digital, Interconnected Power Plants to Improve Efficiency and Reduce Emissions Developing Conventional and Alternative Energy in China The Essential Role of Coal in Past and Future Economic Growth Juggling Development Objectives and the Role for Coal After the Paris Agreement Policy Parity for CCS Would Move the U.S. Closer to Its Ultimate Goals A New Platform to Estimate Mercury Emissions India's Dash for Coal Loses Pace Coal and Clean Coal Technologies in Turkey Powers of Perception: The State of the Art and Future of Sensors in Coal Power Plants Using Automation to Increase Mining Safety and Productivity Advances in Pressurized Oxy-Combustion for Carbon Capture Doing the Right Work at the Right Time in the Power Plant of Tomorrow Global News Cornerstone - Summer 2016 - Cover1 Cornerstone - Summer 2016 - Cover2 Cornerstone - Summer 2016 - From the Editor: The World is Changing with Smart Technologies Cornerstone - Summer 2016 - 2 Cornerstone - Summer 2016 - 3 Cornerstone - Summer 2016 - CoverStory: Digital, Interconnected Power Plants to Improve Efficiency and Reduce Emissions Cornerstone - Summer 2016 - 5 Cornerstone - Summer 2016 - 6 Cornerstone - Summer 2016 - 7 Cornerstone - Summer 2016 - 8 Cornerstone - Summer 2016 - 9 Cornerstone - Summer 2016 - Developing Conventional and Alternative Energy in China Cornerstone - Summer 2016 - 11 Cornerstone - Summer 2016 - 12 Cornerstone - Summer 2016 - 13 Cornerstone - Summer 2016 - The Essential Role of Coal in Past and Future Economic Growth Cornerstone - Summer 2016 - 15 Cornerstone - Summer 2016 - 16 Cornerstone - Summer 2016 - 17 Cornerstone - Summer 2016 - 18 Cornerstone - Summer 2016 - Juggling Development Objectives and the Role for Coal After the Paris Agreement Cornerstone - Summer 2016 - 20 Cornerstone - Summer 2016 - 21 Cornerstone - Summer 2016 - 22 Cornerstone - Summer 2016 - 23 Cornerstone - Summer 2016 - Policy Parity for CCS Would Move the U.S. Closer to Its Ultimate Goals Cornerstone - Summer 2016 - 25 Cornerstone - Summer 2016 - 26 Cornerstone - Summer 2016 - 27 Cornerstone - Summer 2016 - 28 Cornerstone - Summer 2016 - A New Platform to Estimate Mercury Emissions Cornerstone - Summer 2016 - 30 Cornerstone - Summer 2016 - 31 Cornerstone - Summer 2016 - 32 Cornerstone - Summer 2016 - India's Dash for Coal Loses Pace Cornerstone - Summer 2016 - 34 Cornerstone - Summer 2016 - 35 Cornerstone - Summer 2016 - 36 Cornerstone - Summer 2016 - 37 Cornerstone - Summer 2016 - Coal and Clean Coal Technologies in Turkey Cornerstone - Summer 2016 - 39 Cornerstone - Summer 2016 - 40 Cornerstone - Summer 2016 - 41 Cornerstone - Summer 2016 - 42 Cornerstone - Summer 2016 - 43 Cornerstone - Summer 2016 - Powers of Perception: The State of the Art and Future of Sensors in Coal Power Plants Cornerstone - Summer 2016 - 45 Cornerstone - Summer 2016 - 46 Cornerstone - Summer 2016 - 47 Cornerstone - Summer 2016 - Using Automation to Increase Mining Safety and Productivity Cornerstone - Summer 2016 - 49 Cornerstone - Summer 2016 - 50 Cornerstone - Summer 2016 - 51 Cornerstone - Summer 2016 - Advances in Pressurized Oxy-Combustion for Carbon Capture Cornerstone - Summer 2016 - 53 Cornerstone - Summer 2016 - 54 Cornerstone - Summer 2016 - 55 Cornerstone - Summer 2016 - 56 Cornerstone - Summer 2016 - Doing the Right Work at the Right Time in the Power Plant of Tomorrow Cornerstone - Summer 2016 - 58 Cornerstone - Summer 2016 - 59 Cornerstone - Summer 2016 - 60 Cornerstone - Summer 2016 - 61 Cornerstone - Summer 2016 - 62 Cornerstone - Summer 2016 - Global News Cornerstone - Summer 2016 - 64 Cornerstone - Summer 2016 - Cover3 Cornerstone - Summer 2016 - Cover4 http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2016winter http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2016autumn http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2016summer http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2016spring http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2015winter http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2015autumn http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2015summer http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2015spring http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2014winter http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2014autumn http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2014summer http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2014spring http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2013winter http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2013autumn http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2013summer http://www.nxtbook.com/nxtbooks/wiley/cornerstone_2013spring http://www.nxtbookMEDIA.com
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