If the rotating equipment and boiler are a plant’s brawn, then a control system that efficiently integrates myriad plant functions is its brains. Luckily, in a power plant, we can perform a brain transplant when the control system becomes unreliable or too costly to maintain. But first, you have to justify that surgery.
The New Harquahala Generating Project (HGP), owned by MACH Gen LLC, is a 1,080-MW combined-cycle plant located in Maricopa County, Arizona, about 60 miles west of Phoenix. HGP entered commercial service late in 2004 and sells into the merchant power market in the southwestern U.S., primarily to Arizona utilities, especially during the July to November time frame, when the plant runs almost continuously. MACH Gen retained Competitive Power Ventures Inc. (CPV) a couple of years ago to serve as the plant’s asset manager, and NAES Corp. was selected as the operations and maintenance (O&M) provider. The plant reports an annual capacity factor around 30%, not unlike many merchant gas-fired combined-cycle plants across the nation.
Each of the plant’s three units is configured in a unique 1 x 1 configuration based on the Siemens SGT6-6000G (formerly W501G) gas combustion turbines. To give you some idea of the scale of this project, HGP is essentially the PGE Port Westward 1 x 1 project (profiled as a 2007 Top Plant in our September 2007 issue) times three (Figure 1). Each of the three Siemens 120-MW SST6-PAC 3000 steam turbines includes a high-pressure and combined intermediate-pressure/low-pressure section. NEM supplied the three-pressure heat-recovery steam generators (HRSGs) that have been remarkably trouble-free in spite of the plant’s routine cycling.
1. Desert dweller. The New Harquahala Generating Project, located west of Phoenix, Arizona, is a 1,080-MW plant with three 1 X 1 combined-cycle units. The gas turbine is a Siemens SGT6-6000G outfitted with steam injection for power peaking. Courtesy: Harquahala Generating Corp.
Net plant heat rate is on the order of 7,100 Btu/kWh, which places the plant at the top of the food chain as far as plant efficiency is concerned. Power reaches the Palo Verde 500-kV grid through an HGP-owned 23-mile transmission line that connects to the Salt River Project Hassayampa switchyard and ultimately to the Palo Verde grid. Uniquely, the plant’s switchyard and transmission line, operated under contract by Constellation Energy, are considered a separate control area under North American Electric Reliability Corp. (NERC) rules.
Another unique feature of this gas turbine is its capability to peak its power output by injecting 400 psig and 650F cold reheat steam into the combustion shell through four spray nozzles up to a maximum 1:1 steam/fuel mass flow ratio. Up to an additional 15 MW per turbine can be brought on within 10 minutes and on occasion is helpful in meeting Western Electricity Coordinating Council spinning reserve requirements.
Siemens has fielded a total of six G-class turbines with this technology; three are located at HGP. The system is reported by Plant Manager Malcolm Hubbard as working extremely well after his team commissioned the system and it overcame a few growing pains. Hubbard manages HGP’s razor-thin O&M staff of 31.
A Weak-Brained System
Perhaps the biggest challenge encountered by plant operators during the first few years of operation was the inflexible Teleperm XP (TXP) control system installed as part of the original turnkey project contract. Merchant plants make money with a low heat rate, high availability, and nimble response to load control signals. Unfortunately, the TXP wasn’t up to those tasks. Instead, it led to excessive control system – caused trips, featured a difficult-to-use interface, and had antiquated debugging tools. If you are operating and maintaining a plant with a dinosaur of a control system, every function seems slow and unwieldy. In addition, the TXP couldn’t be configured to meet new NERC cyber security rules.
The challenge for the HGP staff in late 2007 was to convince MACH Gen and CPV that an investment in an upgraded controls system would yield an acceptable payback based on increased plant reliability and availability. That justification was not unlike asking your boss for a new computer at work — the problem is justifying the expenditure for reasons beyond the computer’s age. To the untrained eye, the HGP upgrades would be virtually invisible when walking through the plant, yet they’d be obvious to the experienced plant operator in the control room (Figure 2). They would also give a boost to the plant’s operating stats and, hence, owners could be more aggressive in bidding the plant into the power market.
2. Efficient layout. As part of the T3000 control system upgrade, the human-machine interface layout of the control panels, monitors, and room were rearranged. The footprint of the control panel was reduced considerably, yet system capability increased significantly. Lead O&M Technician Lamont Packer demonstrated many of the advanced features of the T3000. Source: POWER
Email
Comments
Print
Reuse
Comments (1)