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Case Studies: Gas Turbines - Microturbines - Walgreen's Drugstore

Microturbine Powers Store's Total Energy System
Published: 3/12/01

At a Glance: Gas Microturbine Cogeneration

  • Supplies electricity reliably around the clock
  • Heat recovery system can provide air conditioning, dehumidification, building heat, and hot water
  • Operates at high overall energy efficiency, reducing costs
  • Enhances reliability and power quality
  • Produces very low emissions of nitrogen oxides and other pollutants

As deregulation of the electric industry progresses, not only in North America but internationally as well, energy consumers will have more choices than ever before. Where electric rates and demand charges are high, natural gas-fueled microturbines can reduce operating costs for many of these customers while providing enhanced reliability and power quality benefits.

Gas microturbines are ideally suited for distributed generation, which supplies electricity at the customer's facility or nearby. But the economic benefits of microturbine power generation are increased substantially by recovering heat from the turbine exhaust for a variety of purposes including air-conditioning, dehumidification, building heat, and hot water. This energy technology is called cogeneration, or combined heat and power (CHP).

Total Energy Approach Taken by Walgreen's Drugstore
As the nation's leading drugstore chain, Walgreen Company is also taking the lead in energy technology by operating a first-of-its-kind microturbine-based total energy system. The cogeneration system has been operating since August 1999 at a Walgreen's drugstore in Chesterton, Indiana. Yvette Venable, a Chesterton store representative, says, "We have not experienced any problems with the system. It has been reliable, and we have been very satisfied with its performance." Walgreen's operates 2,776 drugstores in 38 states and Puerto Rico.

The heart of this innovative total energy system is the 30-kW Model 330 MicroTurbine™ manufactured by Capstone Turbine Corporation, Chatsworth, CA. Capstone is the developer and manufacturer of the first commercial microturbine power generator for the distributed energy market (see Gas Technology, Volume 12, Issue1). The microturbine generator operates on the same principle as the jet engine, but with the cost efficiencies of an automotive turbocharger. The microturbine's clean, 500ºF exhaust heat is captured and used to power the building's heating and air conditioning system. The other key components of the Walgreen's total energy system include a 10-ton absorption chiller (Yazaki Model WFC-10) and a heat recovery unit, which was developed and manufactured by Modine Manufacturing Co. (Racine, WI).

Due to the use of recovered heat, the energy efficiency of cogeneration systems like Walgreen's is about twice that of conventional power generation, which translates to bottom-line savings on energy bills. Also, emissions are low because the turbine uses clean natural gas. Nitrogen oxide emissions from the Capstone microturbine are only 9 parts per million (ppm). The total energy system was developed and supplied by NiSource, Inc. (Merrillville, IN), parent of the local utility at the Walgreen's store.

Next-Generation Systems
Walgreen's has been so happy with the microturbine total energy system's performance that the drugstore chain installed another, more advanced system at the initial location in November 2000 and is planning another installation at a second store during the first quarter of 2001. The next-generation unit has been enhanced to further improve the efficiencies of the system. Also, the footprint of the microturbine has been reduced, and additional development has made its operation even quieter than the original version. The new system will be capable of operating entirely independent of the electric utility grid.

In a related effort, Capstone has developed a microturbine that generates twice the electricity as its current model, yet is almost as small - about the same height and width and only about 2 feet more in depth. The company shipped its first 60-kW gas-powered microturbine in September 2000 to Midwest distributor Interstate Power Systems (Minneapolis), destined for installation at a propane and liquefied natural gas storage facility operated by Reliant Energy Minnegasco. The unit's power will be used as a supplement and backup to the local utility grid to assure proper temperature maintenance of the stored fuels.

In addition, the exhaust heat from the Capstone 60 unit will be ported through an absorption chiller that will deliver refrigerated air for cooling. Reliant Energy Minnegasco currently uses one of Capstone's 30-kW model 330 systems to provide load-following and standby energy to the facility's control center. The exhaust from the current system will pass through a Unifin heat exchanger for space heating at the facility.

NiSource is also testing one of the new 60-kW microturbines and plans to include it as an option in future micro-cogeneration system designs.