Consumers Energy permits gas plant for up to 1,400 MW of capacity

The Thetford gas-fired power project of Consumers Energy (CECo) will be designed to produce up to a nominal 1,400 MWe of electricity for distribution into the transmission grid, said the project air permit application filed at the Michigan Department of Environmental Quality.

The application, for a permit-to-install, was filed in December 2012 and recently obtained by GenerationHub. The DEQ is still working on the application and has not put out a draft permit yet. Consumers Energy, a unit of CMS Energy (NYSE: CMS), has indicated this plant is needed in part to replace some of its older coal-fired capacity, which is due for shutdown in the face of new air emissions constraints.

Currently, there are several smaller, natural gas-fired simple-cycle combustion turbines (CTs) located at the Thetford facility that will be retired after the new generating station is commissioned, said the application, written by consultant Fishbeck, Thompson, Carr & Huber Inc.

“The proposed electric generating station will be designed to produce up to a nominal 1,400 MWe of electricity for distribution into the transmission grid system,” the application said. “The new generating station will be located directly east of the existing CTs and southeast of the existing Thetford substation in Section 27, Thetford Township, Genesee County, Michigan.”

Notable is that Consumers Energy has talked about Thetford as a 700-MW project in its initial stages, with the possibility of adding another 700-MW of capacity later on. The utility wants the $750m first stage in operation in 2017.

The project will include:

  • A total of four natural gas-fired F-class combined-cycle CTs each coupled to a heat recovery steam generator (HRSG) equipped with natural gas-fired duct burner, configured in two CT/HRSG trains per block (for a total of two 2×1 blocks);
  • Two natural gas-fired simple-cycle Black Start/Peaking CTGs;
  • Two Air Cooled Condensers (one per 2×1 block);
  • One small, common diesel engine-powered Emergency Fire Pump;
  • Two natural gas-fired Auxiliary Boilers (one per 2×1 block); and
  • Two Fuel Gas Heaters (one per 2×1 block).

There is adequate natural gas supply to the site, the transmission interconnect is directly adjacent to the proposed site, and the facility is located in the middle of a very rural setting on about 272 acres of land, the application noted. The nearby terrain is relatively flat and this site is located more than 300 kilometers from the nearest Class I protected area (Seney National Wildlife Refuge in Michigan’s Upper Peninsula).

Equipment supplier decisions yet to be made

More details of the project components include:

Four identical natural gas-fired combined-cycle CTGs – These units will be divided into two 2×1 power blocks. Each CTG is nominally rated at 211-230 MW of gross power output at ISO conditions. To provide flexibility in meeting future load demands, each CTG unit will be coupled to an HRSG that is capable of un-fired and fired operating modes. There are two most likely potential equipment suppliers for the primary CTGs. The preliminary performance specifications for each of the most likely equipment suppliers will vary slightly. Once the permit application has been approved by the MDEQ, the bidding process will determine which equipment supplier will be used, the application said. The CTs will be fired by pipeline quality natural gas and annual operation of each combined-cycle CT will be up to 8,760 hr/yr. Each combined-cycle turbine and HRSG train will be equipped with selective catalytic reduction (SCR) to cut NOX emissions and an oxidation catalyst to minimize carbon monoxide (CO). Each CT will include an advanced air compressor section, gas combustion system (utilizing dry, low NOX combustors), power turbine, and a generator.

Two natural gas-fired simple-cycle Black Start/Peaking CTGs – Each Black Start/Peaking CTG will be limited to 2,000 hr/yr of operation. The units will provide both black starting capabilities for system restoration after a transmission outage, as well as fast-starting peaking capacity when the Midwest ISO system requires it.

Two new Air Cooled Condensers – Each condenser will be used for condensing steam exhausted from the steam turbine generator associated with each 2×1 block, to enable re-use of the collected condensate water.

A common RICE-powered Emergency Fire Pump – The pump will be rated at approximately 315 HP output as a back-up fire pump. The non-emergency operation will be limited to 100 hr/yr, principally during periodic tests required to confirm starting reliability.

Two natural gas-fired Auxiliary Boilers – The boilers will provide auxiliary steam to preheat the HRSG and STG equipment during periods when the two 2×1 power blocks are not operating.

Two Fuel Gas Heaters – The heaters (equipped with gas-fired combustors) will be used to remove moisture from the natural gas when the CTs are operating.

In addition to meeting power generation needs projected by CECo’s integrated resource planning, the new station and equipment must be capable of “black starting” and providing power to the utility’s Karn Station for system restoration. This will be accommodated by first starting a black start/peaking CTG and then one of the four CT/HRSG trains. It is imperative that the generating equipment purchased for this project has proven reliability with minimal outages for maintenance, the application added.

“Given its location in the State of Michigan, the Thetford Substation currently provides an important point of generating capacity for ensuring that the transmission grid remains stable,” said the application. “The current configuration calls for the existing Thetford Peaking CTGs to provide black start power for CECo’s Karn Station which, upon start, initiates system restoration efforts. As the existing CTGs will be retired upon commencement of normal operation for the proposed station, the new Thetford Generating Station will be equipped with the ability to start a single F-Class CTG and HRSG train when the transmission grid is unavailable (e.g., ‘black start’), to provide sufficient electric power to restart the Karn Station. Operation of a single 13 MW CTG should be adequate to start, ramp, and produce sufficient electricity within the Thetford Station boundary (e.g., ‘island’) to facilitate an F-Class CTG static start, and the second 13 MW CTG is being installed as a fully redundant back-up to ensure reliable black start capability. A black start requirement for the transmission system is rare and has only occurred once in the past 10 years. To better utilize these two assets, CECo also intends to operate the CTGs during periods when the MISO controlled grid has a demand for peaking power and has estimated the annual operating hours to be less than 2,000 hours.”

About Barry Cassell 20414 Articles
Barry Cassell is Chief Analyst for GenerationHub covering coal and emission controls issues, projects and policy. He has covered the coal and power generation industry for more than 24 years, beginning in November 2011 at GenerationHub and prior to that as editor of SNL Energy’s Coal Report. He was formerly with Coal Outlook for 15 years as the publication’s editor and contributing writer, and prior to that he was editor of Coal & Synfuels Technology and associate editor of The Energy Report. He has a bachelor’s degree from Central Michigan University.