WTUI – Pueblo Airport Generation Station

3. Most advanced LMS100s, LM6000s in service power year’s first GT

(Scroll to the bottom for graphics.)

Black Hills Corp’s world-class Pueblo Airport Generation Station became the first gas-turbine-powered generating facility to begin commercial service in 2012. The 380-MW combination simple-cycle/combined-cycle plant, began serving load on January 1. It is managed by WTUI Board Member Don Stahl and is located just over the fence from the Pueblo (Colo) airport.

   The plant is unique. It features two LMS100 peakers owned by Black Hills Energy, a regulated electric utility serving 94,000 customers in southeastern Colorado (Fig 1) and two LM6000PF-powered 2 x 1 combined cycles owned by Black Hills Colorado IPP, an independent power producer (Fig 2). Both of these owners are, in turn, subsidiaries of Black Hills Corp. All generating units are located on the same site and operated by a common staff from a common control room.

   Here’s how this came to be. In July 2008, Black Hills Corp acquired five Aquila Inc utilities in four states, including its electric and gas utility operations in Colorado, where the company does business in as Black Hills Energy. At the time of the acquisition, Xcel Energy had already notified Aquila that its agreement to supply about 75% of the Colorado utility’s electricity needs would not be renewed when the contract expired at the end of 2011.

   In August 2008, Black Hills Energy filed its Electric Resource Plan with the Colorado Public Utilities Commission (CPUC) and offered an analysis of the best and least-cost option for serving customer needs when the Xcel agreement expired at the end of 2011.   

   Director of Operations George Tatar,  in Pasadena for the Western Turbine meeting along with Stahl, recalled that the resource plan “looked at every available option.” System peak was slightly less than 400 MW at the time but was expected to be 406 MW in 2012 with an additional 61 MW needed for reserve capacity. The installation of fuel-efficient generation assets was a priority. Only natural-gas-fired facilities could be permitted and installed on time and the need to have the capability to back up intermittent renewable energy resources required quick start natural-gas-fired facilities. 

  The two engine models installed on the Pueblo site were the only two gas turbines in GE’s ecomagination™ product portfolio when they were ordered. To earn ecomagination approval, a product is evaluated for its ability to significantly and measurably improve the owner’s environmental and operating performance. The LMS100 offers a simple-cycle efficiency of 46% and is said to offer the highest level of performance of any aero on the market. The LM6000PF offers fast-start capability and low emissions (15 ppm NOx).

   In March 2009, the CPUC approved the construction of the two LMS100s by Black Hills Energy but decided that the company should conduct a competitive solicitation for the remaining capacity needed. An independent evaluator was hired to oversee the competitive solicitation.  Black Hills Corp formed Black Hills Colorado IPP to participate in that bidding process. The unregulated subsidiary was selected as the winning bidder and received a 20-yr PPA (power purchase agreement) to provide the remaining energy needed to serve customers when the Xcel contract expired Dec 31, 2011.

   The LMS100 peakers are equipped with chillers (Stellar Energy Americas) in their respective Altair® air-inlet filter houses. The exhaust system, which includes catalyst and support equipment for NOx and CO emissions reduction, was supplied by Braden Manufacturing LLC.

   Recall that he LMS100 is a three-shaft gas turbine that uses intercooling technology to increase power and efficiency. It incorporates elements of on-wing and industrial gas turbines and is said to represent the most extensive collaboration of design and manufacturing expertise in the history of GE.

   The six-stage LP compressor was derived from the MS6001FA; the so-called “supercore,” which includes the 14-stage HP compressor, combustor, and HP turbine, is derived from the CF6-80C2 and CF6-80E aircraft engines that power many Boeing 747s and 767s (Figs 3, 4). Pressure ratio is 42:1. The HP turbine consists of two air-cooled stages; the IP turbine has two stages and the power turbine five. The generator is air-cooled.

   Service intervals at this stage of engine experience are the following:

  • Every 4000 hours, conduct borescope inspection. Planned outage duration is 12 hours including the cool-down time.
  • Every 25,000 hours, hot-gas-path (HGP) inspection. Spare module—combustor and HP and IP turbines—is installed and the unit restarted within four days; owner’s engine is sent to the shop for overhaul.
  • Every 50,000 hours, major inspection. Same as HGP, plus power-turbine overhaul, LP compressor and shaft inspection/maintenance, and inspection of the following major components: booster, intercooler, scroll frames, HP compressor, aft shaft, and hydrodynamic bearings. Roller and ball bearings are replaced. There is a 60-day turn on all this work which can be reduced to four days if rotating spares are installed while shop work is done.

   Fleet operating history. Fleet RAM (reliability, availability, maintainability) stats are presented below. They were compiled by Strategic Power Systems, Charlotte, based on the 16 LMS100s reporting data through the company’s ORAP® system for the period January 2008 through December 2010.

  • Availability, engine only (including the intercooler). 94.7%.
  • Availability, simple-cycle plant (including engine, generator, and station equipment), 87.7%.
  • Reliability, engine only, 97.8%.
  • Availability, simple-cycle plant, 94.6%.

   Starting reliability as reported by the OEM was 97.8% based on a 12-month rolling average through December 2010. The OEM’s expected goals for a mature product—defined as 100,000 total service hours—is 99.2% reliability, 97.1% availability.

   Exhaust section. Braden had total responsibility for the exhaust sections of both LMS100s. The project included supply of the NOx and CO reduction systems (catalysts by Haldor Topsoe Inc and BASF’s Catalysts Div, respectively), ammonia injection skids for the SCRs (provided by Braden subsidiary Consolidated Fabricators LLC), tempering air systems, exhaust stacks, and PLC connections to the plant DCS (Figs 5, 6).

   The air permit for the LMS100s establishes limits sufficient to allow operation of all units 100% of the time.  The limits for the two LMS100s are as follows:

  • NOx, 5 ppmvd at 15% O2.
  • CO, 10 ppmvd at 15% O2.
  • VOC, 2.5 ppmvd at 15% O2.
  • Acoustic, 60 dB(A) at the fence line.

   In designing the exhaust section, Braden was able to meet a tight schedule requirement by employing in-house engineering for all major disciplines—mechanical, electrical, structural. In addition, gas flow modeling was performed by Braden engineers along with acoustic modeling for stringent noise abatement. Pressure drop was a key concern to meet efficiency goals. Braden brought its years of experience in the design of ductwork and exhaust and silencing systems to bear to hold backpressure under 10 in. H2O (Fig 7).

   The ammonia injection skids were fabricated, insulated, and wired in Consolidated’s shop to assure fast installation at the jobsite (Fig 8). And, to minimize fit-up errors onsite, Braden fabricated very large subassemblies offsite and trucked them to Pueblo (Fig 9). An additional benefit of pre-fab was a reduction in site labor requirements. High reliability of the exhaust sections is assured by use of redundant PLCs, fans, and ammonia heaters.

   The insulated stacks (71 ft tall x 13.5 ft diam) have a floating liner system to accommodate the thermal cycles. The stacks were trucked to the site in two pieces for rapid erection on a foundation provided by Black Hills (Fig 10). Teamwork among personnel from Braden, Black Hills, the construction contractor, and the turbine manufacturer minimized the amount of time required for commissioning and verification of emissions permit requirements.

   One cooling tower serves both LMS100s to release heat absorbed by water flowing through the engine intercoolers.  

  LM6000PF combined cycles. The two chiller-equipped LM6000PF gas turbines in both combined cycles are connected through dual-pressure Nooter/Eriksen Inc heat-recovery steam generators to a steamer made by Siemens Energy Inc in the Czech Republic. The 40-MW gas turbines have air-cooled generators, the 20-MW steamer water-cooled. Boiler blowdown is routed to the cooling tower provided for each combined cycle.  

   Interestingly, one of the four LM6000s installed at Pueblo was the 1000th of that model series shipped by GE (Fig 11).   The LM6000 has a five-stage LP compressor and 14-stage HP compressor. Pressure ratio is 28.5:1. On the turbine end, the HP unit has two stages, the LP turbine has six (Fig 12).  CCJ

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