The Wisconsin Department of Natural Resources is taking comment until Aug. 20 on its preliminary decision to grant air permitting to Wisconsin Power and Light for refined coal usage at the Columbia Energy Center (CEC) in Pardeeville, Wisconsin.
WPL submitted a construction permit application for the construction and operation of Refined Coal (RC) production equipment at CEC. On July 2, 2015, the Department issued a construction permit allowing WPL to construct and initially operate a RC preparation facility at CEC. This approval was for using a refined coal preparation process in partnership with Clean Coal Solutions. WPL has yet to construct any of the allowed emission units approved for construction and initial operation under that permit.
Since issuance of that permit, WPL has applied for and received a research and testing exemption to evaluate the use of RC additives MerSorb and S-Sorb in partnership with DTE Energy Services (DTE). This approval, received on March 11, 2016, did not allow for the construction or operation of any permanent equipment or functions that would enable long-term use of these products.
The purpose of this latest application is to obtain authorization to commence construction on the equipment to be utilized in the process of preparing RC using these additives for the CEC over the long term. Additionally, WPL is not proposing to conduct any of the RC testing allowed under the permit exemption.
The use of RC in place of unprocessed coal results in lower mercury and NOx emissions. DTE utilizes the Chem-Mod process to produce RC. The Chem-Mod process involves the application and mixing of two reagents to the coal prior to combustion – a dry bulk solid called S-Sorb for the control of NOx, and a liquid aqueous solution called MerSorb for the control of mercury emissions.
This new project is considered as a continuation of a project previously permitted, which authorized the construction of a spray dryer absorber and baghouse for the control of acid gas emissions, and also activated carbon injection for the control of mercury emissions.
The CEC site includes 2,726 acres south of Portage, Wisconsin. Key production equipment includes S-Sorb storage silos, an S-Sorb day bin, a MerSorb storage tank, a mixer (in line with a conveyor belt for blending the reagents with coal), new conveyors and various chute work. This equipment will be located within the existing CEC crusher house.
- MerSorb is an aqueous solution of approximately 51% by weight calcium bromide (CaBr2), with small amounts of iron oxide (Fe2O3), magnesium oxide (MgO), and sodium oxide (Na2O). MerSorb will be added at a maximum rate of 0.0035% by weight of coal (0.0035 pounds per 100 pounds of coal). At the maximum coal flow rate of 2,000 tons per hour through the coal reclaim system, the maximum MerSorb addition rate will be 140 pounds per hour.
- S-Sorb is a solid additive derived from cement kiln by-products consisting primarily of calcium carbonate (CaC03) and calcium oxide (CaO), with smaller concentrations of calcium sulfate (CaSO4), aluminum oxide (Al2O3), iron oxide (Fe2O3), magnesium oxide (MgO), and crystalline silica (SiO2). S-Sorb is an alkaline additive formulated primarily from cement kiln dust. S-Sorb will be added at a maximum rate of 0.50% by weight of coal (0.005 pounds per 100 pounds coal). At the maximum coal flow rate of 2,000 tons per hour through the coal reclaim system, the maximum S-Sorb addition rate will be 10 tons per hour (20,000 pounds per hour).
One of the major factors influencing the native capture and control of mercury in existing air quality control systems is the chlorine content of the coal. Chlorine assists in the oxidation of elemental mercury (HgO) to oxidized mercury (Hg2+). Mercury capture in PM and SO2 control systems is more effective if the mercury is oxidized. Unfortunately in this context, subbituminous coals such as those burned at CEC have low chlorine levels, and, thus, lower levels of native mercury capture and control. Chlorine and bromine are one of a class of elements with high electronegativity (i.e. tends to attract electrons in chemical reactions) called halides. Thus, the high bromine content of the MerSorb assists in controlling mercury emissions in a similar manner to chlorine in higher chlorine content coals. The bromine in the MerSorb also reacts with the alkaline ash of subbituminous coals to form salts. These salts are then collected in the ESP and baghouse, effectively eliminating almost all of these potential emissions.
While the Columbia Energy Center currently applies Calcium Bromide to its inlet coal supply, the use of MerSorb would provide a more cost-effective manner in which to apply the chemical, potentially taking the place of the current application method. The primary sorbent substance in S-Sorb is CaO which may react with SO2 in the furnace and in the flue gas to form calcium sulfate. S-Sorb may also react with other acid gases such as hydrogen chloride (HCl), hydrogen fluoride (HF), sulfur trioxide (SO3), and nitrogen dioxide (NO2) to form solid salts which can be collected in the existing PM control systems.
The Columbia Energy Center consists of two coal-fired units. These units began operation in 1975 and 1978, and have nameplate generation capacities of 512 MW and 511 MW. WPL operates both units.