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Process Heating Has Major Potential for Energy Savings

Key Points
  • Process heating accounts for up to 15 percent of total production costs.
  • Industrial process heating systems offer opportunities to save significant amounts of energy. 
  • Using best practices can reduce energy consumption by 25 percent.
Source: www.energy.gov
process heating

Most finished products require a process heating step that includes one or more of the following: heating of fluids, calcining raw materials, extracting metals from ores (smelting), melting materials, drying a material or product to remove moisture, densifying a compacted mixture in a kiln or furnace and curing or heat treating a material to improve its properties. According to the U.S. Department of Energy (DOE), these heating processes (not including steam generation) consume about 5.2 quads (quadrillion Btu) annually, which is nearly 17 percent of all energy used by industry. Heat derived from the combustion of fossil fuels accounts for 92 percent of this energy and electricity use accounts for the remaining 8 percent.

For many industrial applications, process heating requires high temperatures and thus energy costs for process heating represent 2 percent to 15 percent of a product’s total cost. Many factors determine the energy efficiency of a process heating system, including process temperature, equipment design and operation and the type of heat recovery systems used. Hence, industrial process heating systems offer opportunities to save significant amounts of energy.

With such a large amount of energy being consumed by these systems, efforts to improve their efficiency are in the best interests of all manufacturers. The following short-term steps can offer early paybacks; usually within six months:

  • Check and adjust air-fuel ratios regularly in process heating burners for savings of up to 25 percent
  • Preheat combustion air and preheat and/or dry the charge load for up to 25 percent savings
  • Keep all heat transfer surfaces of indirectly heated systems clean or employ direct heating methods for up to 15 percent savings
  • Use refractory fiber liners or other optimum level insulation for heat containment components for up to 15 percent savings
  • Recovering the waste heat from ovens, furnaces and kilns for preheating combustion air or other uses can contribute to energy-use reductions and savings of up to 25 percent
  • Develop procedures for regular operation, calibration and maintenance of process and process management sensors, such as pressure, temperature and flow; and controllers for up to 10 percent savings
  • Use process models and design simulation to optimize equipment design operations for up to 10 percent savings

Tools you can use

The DOE has developed the Process Heating Assessment and Survey Tool (PHAST), which can be used to assess the energy consumption of your process heating equipment and make preliminary evaluations of the benefits of various equipment and operating upgrades. A detailed heat balance is calculated based on data collected on any oven or furnace in your plant, including the energy consumption of electric motors on accessories like fans, conveyor drives and so on.

For instance, at one steel mill, PHAST identified total potential savings in a steel reheating furnace of 37 MMBtu per hour (or 22 percent of all energy used by the furnace). The furnace’s fuel use could be reduced by approximately 30 MMBtu per hour for the heating zone and 5 MMBtu per hour for the soak zone. Another 2 MMBtu per hour could be saved by reducing heat loss.

PHAST also lets you plug in your energy costs and run what if? comparisons between your heating equipment as it operates now and after some specified change. PHAST 3.0, introduced in 2010, includes a major update with the addition of a new electrotechnology section that allows users to choose between electrotechnology and fuel-fired systems. There is also a section that allows the use of International units. Another update was planned for 2012.

References

Improving Process Heating System Performance: A Sourcebook for Industry, Second Edition. U.S. Department of Energy. 2007. Last accessed on February 6, 2013.

Process Heating: The Big Picture on Process Heating. U.S. Department of Energy. Last accessed on February 6, 2013.

Save Energy Now in Your Process Heating Systems. U.S. Department of Energy. January 2006. Last accessed on February 6, 2013.

Thekdi, Arvind. Seven Ways to Optimize Your Process Heat System. U.S. Department of Energy. Last accessed on February 6, 2013.

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