Distributed Generation

Distributed generation (DG) allows you to create your own electricity at a business facility, using small power-generating units that produce between 5 kilowatts to 25 megawatts. Creating energy right where it will be used is highly efficient. You can use DG to save money on power bills, to supplement the electricity you buy through the electric grid, to manage energy service needs or to help meet increasingly rigorous requirements for power quality and reliability.

Distributed generation technologies that use natural gas include industrial gas turbines, reciprocating engines and microturbines.

There is more information about each of these technologies below. If you’re interested in talking to Elizabethtown Gas about distributed generation options, e-mail us at gasadvantage@aglresources.com. Or just call us at 1-800-242-5830 .

Industrial Gas Turbines

Natural gas-fueled turbines can save industrial customers money on electricity. The popularity of gas turbines is growing among industrial plant operators, as well as large commercial energy users and institutions, such as hospitals and universities). When heat from the gas turbine's exhaust is recovered to produce high-pressure steam or other useful thermal energy, the system is called combined heat and power (CHP), or cogeneration.

Major process industries — primarily chemicals, paper, and oil and gas — have been using large turbine CHP systems (over 25 MW) for some time. But the economics of smaller turbine systems (1 to 10 MW) have recently become more attractive. Improvements to existing gas turbines include higher power ratings and efficiencies, advanced controls, lower emissions of nitrogen oxides (NOx) and lower lifecycle costs.

Gas turbines can be operated in three ways:

• Simple cycle turbines use an air-compression section, a burner and a power turbine driving a load, such as a generator for producing electricity. The turbine's high temperature exhaust heat can be used to produce process steam.
• Recuperated turbines incorporate a heat exchanger, which recovers heat from the turbine exhaust to preheat the compressed air before it enters the burner.
• Combined-cycle turbine systems use exhaust heat to produce steam to drive a second turbine, which produces additional electricity. Most combined-cycle systems are larger than industrial-scale plants.

Today's turbines reach efficiencies of 30 to 40 percent or greater; in systems with heat recovery, overall thermal efficiencies of 70 to 80 percent are common, and 90 percent is achievable.

Air emissions from gas turbines have decreased substantially. Early systems used water or steam injection to reduce flame temperature and control NOx emissions. Recently, manufacturers introduced "dry" (no water or steam) low-NOx combustors, which reduce NOx emissions to 25 parts per milllion or lower.

Reciprocating Engines

Reciprocating engines are the fastest-selling, lowest-cost form of DG. They can be used in a variety of applications due to their small size, low unit cost and useful thermal output. Reciprocating engines are available commercially in sizes from .5 kW to 6.5 MW, making them suitable for a wide range of commercial, industrial and institutional applications. These applications include continuous power generation, peak shaving, back-up power, standby power and mechanical drive use.

Reciprocating engines also offer heat recovery potential. They make up a large portion of the cogeneration market in the United States.

Microturbines

Microturbines are essentially miniature jet engines that are connected to small electric generators. They have very sophisticated electronic systems, which allow them to provide safe and efficient operation by consistently monitoring themselves.

Microturbines are easy to install and have low emissions. In areas where natural gas rates are low in comparison to electric rates, it may be more economical to use a microturbine instead of relying on electricity from the grid. For the most part, however, microturbines are used for avoiding the high demand charges associated with using electricity during peak time periods. Microturbines are particularly cost effective when the waste heat from the exhaust is captured and used to offset the energy needed to heat or cool a building or preheat a boiler.

To create electricity, microturbines burn natural gas. As the gas flame heats the incoming air, the air expands and flows over a turbine with blades, forcing the blades to spin. The spinning action (torque) spins the shaft of a generator, which converts the mechanical torque to an electrical output. This electrical output is converted to a usable voltage and frequency. The exhaust heat, which is about 600 degrees Fahrenheit, is captured and used for heating, cooling, water heating, or preheat boiler applications. Like larger turbines that burn natural gas, microturbines are environmentally friendly and produce very low emissions.

Distributed Generation Fallacies If you’ve heard arguments against distributed generation, we recommend reading this article by Jerry Jackson, president of Jackson Associates, a firm that does research and analysis on energy usage.