For those units with Wet Flue Gas Desulfurization WFGD units, adding a precipitant to react with the aqueous mercury, removes the mercury from the aqueous phase, forming a solid particle which partitions to the solids. This allows the mercury MATS emission limit to be achieved.
Our precipitant is specially formulated to work in both oxidizing and reducing environments. We use precisely controlled peristaltic pumps to deliver the reliably and consistently. Avoid the messy and costly use of activated carbon injection into the fluework of the plant, and make use of your mass transfer capability waiting to be tapped in the WFGD system.
Selenium
In November 2015, the Federal EPA issued a final rule revising effluent limitation guidelines ELG for certain EGU’s. The rule establishes limits on As, Hg, NO2/NO3 and Se from FGD wastewater, fly ash and bottom ash transport water and flue gas mercury control wastewater. These limits were to be imposed as soon as possible after November 2018 and no later than December 2023. These requirements will be implemented through each facility’s wastewater discharge permit. Subsequently, the rule was challenged in the U.S. Court of Appeals for the Fifth Circuit. In March 2017, industry associations filed a petition for reconsideration of the rule with the Federal EPA. A revised final rule revising the compliance deadlines for FGD wastewater and bottom ash transport water to be no earlier than 2020 was issued in September 2017, effectively a two-year postponement of the earlier rule, with the added potential of revised limits.
Of these four entities; As, Hg, NO2/NO3, and Se, the most troublesome for many plants is the Se limit. Even with phys/chem systems installed, selenium can pose significant difficulties because of its ability to exist, in an oxidizing environment, as both selenite (a +4 oxidation state) and selenate (a +6 oxidation state). Selenate is more soluble than selenite and is harder to treat in downstream wastewater control systems
Much of the work currently being carried on selenium capture in those units that have WFGD systems, seeks to manipulate the slurry ORP such that the aqueous phase within the slurry liquid can preferentially form selenite over selenate. However, my approach is with the use of this unique additive, we can control the Hg within the slurry aqueous phase to meet the MATS limit requirements, while simultaneously partitioning the selenium to the solid phase of the slurry.
In August of 2017, a provisional patent on a new invention was filed titled “Chemically-coupled control for aqueous selenium and mercury”. With this new invention, it holds out the hope that we can simultaneously control the mercury in an effort to achieve the mercury MATS limit, while also partitioning a much greater fraction of the selenium to the solid gypsum phase of the slurry. We are not concerned with the selenium speciation manipulation, but the preferential phase partitioning of the selenium to the solid phase in lieu of the liquid phase.
We expect to complete field sample testing by the first quarter of 2019 to quantify the increase in selenium to the solid phase from the addition of the additive chemical. This will allow customers to determine the potential economic benefits of this additive.