reduce boiler fuel costs

Upload: joepulaski

Post on 03-Apr-2018

222 views

Category:

Documents


0 download

TRANSCRIPT

  • 7/28/2019 Reduce Boiler Fuel Costs

    1/2

    Reduce boiler fuel costs: use the proper air-to-fuel ratio

    2/10/2003 7:04:00 AM

    Do you know what the most common energy and cost saving opportunity in steam systems

    is? According to the results of 41 steam plant audits performed by Enbridge Consumers Gasof Toronto, Canada, the answer is combustion improvement.

    The audits, which frequently involved multiple boilers in one plant, revealed a total of 45opportunities for combustion improvement projects including: boiler tune-ups, combustioncontrol repair, burner repair, and repairs to existing oxygen trim systems.

    With an average payback period of less than half a year, optimizing steam systemcombustion is a proven and effective way to reduce operating costs.

    A simple, low-cost way of optimizing combustion is to maintain the proper air-to-fuel ratio inboiler operations. To completely combust the fuel, there must be a slight excess of oxygen,

    since real-life combustion conditions are never capable of achieving the perfectstoichiometric air-to-fuel ratio.

    Too little air causes incomplete combustion, resulting in excessive soot and fireside fouling,as well as an explosion hazard. Excess air creates fireside fouling and sends thermalresources up the stack. Extremes in either direction create air pollution and costlyinefficiency by wasting fuel.

    A general rule of thumb is that boiler efficiency can be increased by 1% for each 15%reduction in excess air or 40F reduction in stack gas temperature.

    The appropriate amount of excess air for optimal combustion varies with the type of fuel and

    burner in a system. The U.S. Department of Energys BestPractices Steam program assertsthat for well-designed natural gas fired systems, an excess air level of 10% is attainable.

    The first step in determining the proper amount of excess air is to measure the currentamount of oxygen in the flue gas. This can be done with a gas absorbing test kit or anelectronic flue gas analyzer.

    Two additional measurements required are the temperature of the flue gas and thetemperature of the air going into the boiler. Unless an electronic tester is used that calculatesthe combustion efficiency based on these measurements, an efficiency table or graph for thespecific fuel being combusted must be referenced.

    Combustion efficiency tables or graphs come with test equipment, are available in referencebooks, and are included in the BestPractices Steam System Survey Guide, found online athttp://www.oit.doe.gov/bestpractices/steam/pdfs/steam_survey_guide.pdf.

    Calculating operating cost savings

    The amount of money a facility will save can be demonstrated by instituting a regular air-to-fuel ratio measurement and adjustment practice for the boiler. The formula for showingsavings associated with optimized boiler combustion efficiency is:

  • 7/28/2019 Reduce Boiler Fuel Costs

    2/2

    Cost Savings = Fuel Consumption x (1- E1/E2) x Steam Cost

    E1 = existing combustion efficiency, %

    E2 = optimized combustion efficiency, %

    A sample calculation can be found on the BestPractices Steam Tip Sheet entitled ImproveYour Boilers Combustion Efficiency.

    Information supplied by Tony Tubiolo and Christopher Russell of the Alliance to SaveEnergy. They can be reached at 202-530-2225.

    BestPractices Steam, a U.S. DOE initiative, generates references, diagnostic software, casestudies, and industry outreach events for the benefit of the industrial steam community.Download tip sheets and other resources from oit.doe.gov/BestPractices andsteamingahead.org/resources.htm.

    Details of the Enbridge Consumers steam audit is included in Steam Digest 2001, available

    free by contacting the BestPractices Clearinghouse, 800-862-2086 or downloading thearticle from ase.org/steamingahead/digest2001/sd01art6.pdf.