Consumers Energy, besides the seven older coal units that it plans to retire in April 2016, is retrofitting the surviving coal units for compliance with the federal Mercury and Air Toxics Standards (MATS) and other clean-air needs.
Linda M. Hilbert, employed by Consumers Energy as the Manager of Environmental Services, provided details on the CMS Energy (NYSE: CMS) subsidiary’s clean-air work as part of a rate case application filed Dec. 5 with the Michigan Public Service Commission.
Hilbert noted that some form of FGD scrubber, which also needs to be paired with a particulate matter collection device, is required in order to achieve the reduction of acid gases required by MATS. Campbell Units 1 and 2 will be equipped with dry sorbent injection (DSI) and Campbell Unit 3 will be equipped and Karn Units 1 and 2 are currently equipped with spray dry absorbers (SDAs). All five these surviving units will also be equipped with pulse jet fabric filters (PJFFs).
PJFFs were installed at Karn Units 1 and 2 in 2011 and 2010, respectively, and the PJFF at Campbell Unit 2 was completed in the spring of 2013. The PJFF at Campbell Unit 1 is currently in the construction phase and the PJFF at Campbell Unit 3 is also in the construction phase. The long procurement, delivery constraints, other emission control projects, and long construction times required that some of the PJFF projects begin well in advance of the MATS compliance deadline. The ACI systems are much smaller in scale and will be fit into the PJFF construction schedule optimally, Hilbert noted.
The SDA at Campbell Unit 3 is in the construction phase. Much like the PJFF projects, the long procurement, delivery constraints, and construction times required that the SDA projects begin well in advance of the compliance deadline for MATS due to the size of the projects and congestion at the sites. Campbell Units 1 and 2 will get DSI systems and those projects are currently in the design phase.
ESPs didn’t make the cut on particulate compliance
Another approach to mercury removal utilizes the electrostatic precipitator (ESP) for particulate matter collection following the ACI system in lieu of PJFFs. The Electric Power Research Institute (EPRI) data indicated that significant ACI injection rates (>4 lb/million actual cubic feet) are required to achieve high levels of mercury removal with ESP operation. Consequently, the high solids loading can result in an increase in particulate matter emissions above the limits.
Consumers Energy has evaluated the impact of ACI on its ESPs and determined that injection rates of this magnitude resulted in an increase in particulate matter emissions above the significance level that would require installation of best available control technology (BACT). This study was performed by Air Consulting Associates, an expert in ESP modeling. PJFF systems are currently defined by the EPA as BACT. This led Consumers Energy to pursue PJFF coupled with ACI as the technology of choice for removal of mercury.
The industry has the most experience with carbon based sorbents such as activated carbon; however, there are non-carbon sorbents available in the market today. Once an injection system is installed, sorbent testing can identify the optimum sorbent (carbon or non-carbon) for the individual unit that results in the most cost-effective compliance option. Based on this information, Consumers Energy has chosen PJFF and ACI as the mercury removal technology of choice.
Consumers Energy only considered SDA and DSI because wet scrubbers are best suited for units that burn higher sulfur coals and the company transitioned away from the use of higher sulfur coals in the 1990s.
DSI is utilized on smaller (<250 MW) units to avoid high sorbent injection rates associated with larger units. From a unit compatibility perspective, DSI is considered compatible on all units except Campbell Unit 3 (830 MW) due to its size. Utilization of DSI on large units is problematic due to the high injection rates of the sorbent. The high injection rates can result in stack plumes and opacity increases, as well as duct deposition that increases equipment fouling. Efficient mixing and chemical reactions in larger ducts associated with larger units is also problematic.
The SDA can provide sufficient reductions of both acid gases and SO2 expected to meet current and future regulations. For Consumers Energy’s units that consistently burn blended coal, at least a 90% reduction in acid gases is needed for MATS compliance. For those units (Karn Units 1and 2), DSI cannot provide the required reductions and assure reliable operations. As a result, DSI was eliminated as an option for Karn Units 1 and 2.
DSI testing conducted in late 2012 on Campbell Unit 1 indicated that DSI could be a feasible alternative compliance approach due to the emission reductions that were recognized during the trial. This resulted in an opportunity for the company to reevaluate the potential of reducing operating and compliance costs by utilizing DSI,nwhich is much less capital intensive than SDA. The success of the DSI testing at Campbell Unit 1 prompted a reevaluation of the Campbell Unit 2 compliance options. In the summer of 2013, the company performed DSI testing at Campbell Unit 2. The DSI test was successful and showed that MATS compliance could be achieved. Ultimately, the company decided to move forward with utilizing DSI as a compliance option at both Campbell Units 1 and 2. At the SO2 and acid gas removal rates needed for Campbell Units 1 and 2, DSI is the more cost-effective choice.
“Based on the three evaluation criteria, Consumers Energy believes that the installation of three SDAs (Karn Units 1 and 2 and Campbell Unit 3) and two DSI systems (Campbell Units 1 and 2) is the most appropriate and cost-effective means to provide both acid gas and SO2 reductions required by MATS and [the Clean Air Interstate Rule (CAIR)]” Hilbert wrote.
Consumers has gotten to the end of coal switching benefits
“Our strategic approach to compliance, which has included switching to lower cost and lower sulfur western coal and allowance purchases, has allowed us to defer significant capital investments. These actions have been in the customers’ best interest. At this juncture, moving ahead with the investment in control equipment for Karn and Campbell is essential. Our technology decisions have been based on specific unit designs, consideration of new and leading edge technologies and economic evaluations that consider both the capital and O&M expenditures. In the case of Campbell Units 1 and 2, our reconsideration of DSI in lieu of SDA resulted in approximately $200 million in reduced capital expenditures. Furthermore, bidding strategies, application of best in class project management principles, project costs benchmarking, and advanced contract strategies have resulted in cost-effective implementation of these major projects.”
Said Hilbert about the company’s whole environmental program for the five surviving coal units: “When complete, these major investments in emission control technology will provide significant environmental benefits through the significant reduction of SO2, NOx, particulate matter, mercury, metals, acid gases, and other pollutants as well as an enhancement in CCR management, water management, and fish protection. These efforts will improve the quality of life we enjoy in Michigan. These investments also allow the continued operation of 1,250 MW of Michigan-based, coal-fired generation thus preserving the fuel diversity that is necessary to protect customers from significant fuel price fluctuations.”
The company’s coal units are:
- JH Campbell 1&2, 611 MW, West Olive, MI
- JH Campbell 3, 751 MW (93% owned share), West Olive, MI
- DE Karn 1&2, 510 MW, Essexville, MI
- BC Cobb 4&5, 307 MW, Muskegon, MI
- JR Whiting 1-3, 317 MW, Erie, MI
- JC Weadock 7&8, 309 MW, Essexville, MI
The seven units to be shut in 2016 are: Cobb Units 4 and 5, Weadock Units 7 and 8, and Whiting Units 1, 2, and 3.