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Process Heating: Making the Switch

Key Points
  • Manufacturers using process heating may want to switch to natural gas.
  • Additional benefits may include improved productivity and less maintenance.
  • Switching to natural gas requires additional safety features to meet fire codes.
Source: www.energy.gov
melting metal

With energy costs rising, manufacturers are constantly looking for ways to compensate. For those who use process heating, switching from electricity to natural gas as a fuel source is one option. This depends on how electric rates compare to natural gas prices on an average kilowatt-hour cost basis, and peak demand (kW) charges. In addition, not all processes are suitable, such as specialized induction heating and metal melting operations.

Smaller electric furnaces may be appropriate for replacement or retrofitting with natural gas equipment. In addition to lower energy costs, other potential benefits include increased productivity or lower maintenance costs. Electric resistance heating elements usually require annual replacement compared to direct gas-fired burners, which can last up to 20 years. In general, direct-fired gas furnaces heat up faster than electric.

Possible candidates include the following:

  • Aluminum melting furnaces (crucible or reverberatory type)
  • Aluminum or steel heat treating furnaces (atmosphere or non-atmosphere)
  • Drying or curing ovens using infrared heat (powder coatings)
  • Localized heating of parts for forging (electric induction to gas-fired rapid heating)

Catalytic gas-fired infrared ovens are a potential alternative to electric infrared units, especially for powder coatings, because they offer better efficiency (an effective heat conversion ratio of 85 percent) and lower operating costs. Some gas catalytic systems also are flameless, which eliminates nitric oxide or nitrogen dioxide emissions.

For retrofitting a batch furnace, the heating elements are removed and replaced with a direct-fired or indirect-fired burner system. A source of combustion air is required and additional controls must be integrated with process controllers for the air and gas feeds. Direct-fired furnaces require exhaust ductwork. For a continuous furnace with multiple zones, the front zones should be converted first because they require the most heat. Back zones can remain electric.

A retrofit must also consider National Fire Protection Association codes, such as NFPA 86, which minimizes fire and explosion hazards of ovens and furnaces. For direct gas-fired ovens, required safety features include:

  • Powered exhaust fan
  • Airflow safety switches
  • Internal pressure relief
  • High-low gas pressure switch
  • Flame safety/spark ignition

Class C type furnaces and ovens, which include integral quench furnaces and molten salt bath furnaces, have special requirements (such as casing thicknesses) because they require a flammable or other special atmosphere.

Safety features add to the capital costs of a gas furnace. Before switching:

  • Consider both capital and operating expenses
  • Set a realistic payback time and consider future gas price predictions
  • Check if a comprehensive engineering evaluation is available

Remember that the variation in fuel prices will affect payback.

75 percent energy cost reduction

In 2010, a company providing heat treating of steel mill rolls converted its tilt-style electric heat furnace (operating at 1600°F) to indirect gas firing. The conversion required installation of a radiant tube/recuperative burner system and an exhaust system. The furnace structure was also upgraded to handle the additional weight of the combustion system.

The retrofitted furnace had a faster heat-up time and reduced energy costs:

  • For a 100-kW load, the energy cost per hour was reduced by about three fourths, saving more than $17,000 per shift per year.
  • For a load of 750 kW, savings jumped to about $131,000 per shift per year.

The fuel cost savings paid for the conversion in less than one year.

Upgrade and Save!

By improving your facility with high-efficiency natural gas equipment, your business can be more energy efficient and environmentally responsible while maximizing your business potential. Visit the Southwest Gas website or call 800-654-2765 for more information on how to make your business more efficient.