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2020 / 2021 Edition

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Improving energy efficiency

NA-Stordy say that in the UK there are more than 30 sites currently operating conical-flame burners. The design and flame shape of this type of burner promotes a high transfer of energy into the aggregate within the batch heater drum configuration.

Both batch times and burner settings are critical as any increase in batch time due to increased oil viscosity, insufficient fuel supply pressure or poor maintenance can have a significant effect on costs. A 25% increase in batch time equates to a 20% drop in production coupled with a 25% increase in fuel usage; this could equate to more than £30,000 in added production costs if using gas oil.

Although the basic principle and burner head design have not changed in 40 years, the ancillary/support and operational equipment have improved. New features include:

  • high fire output modulation via a pneumatic positioner for matching burner output to the production requirement
  • electro-magnetic fire-valve system
  • fuel usage metering system with pulsed outputs for data-logging
  • high-efficiency motors (EFF1)
  • RAP system modifications.

With the impending Waste Incineration Directive, operators are looking at alternative fuels. The conical-flame burner can accept fuels with viscosities up to 400s Redwood no.1 (15 centistokes), such as: natural gas, LPG/propane, gas oil, waste/reclaimed fuel oil, and medium/heavy fuel oil.

Many users are looking at natural gas and heavier (virgin) fuel oils, but there are a number of important factors to consider. Over the years the demand for fuel oils has forced refineries to find new and better ways to refine crude oil. In the 1930s the process converted only 10% of each barrel of crude into distillate fuel oils. The heavy residual that remained (27% of each barrel) posed a disposal problem and was offered as low-cost fuel oil. By 1966 additional crude oil refining processes meant that up to 89% of each barrel was taken as petrol, distillate oils and other saleable products. Only 11% remained as heavy fuel oil or as a blending base for heavy fuel oil. Today’s fuel oils are made from blending distillates with these heavy residuals.

Oil blending is not new, but the components obtained from the cracking and reforming processes used in today’s blends may have a higher carbon/ hydrogen ratio, which can lead to chemical instability.

The decision whether to have a heavy oil system depends on a number of factors: financial, operational/burning cleanliness, ease of handling, and compatibility with existing processes. It is important that compromises are not made with the supply and conditioning equipment if operational problems are to be avoided. The possible chemical/physical instability of the fuel oils make it necessary to consider storage tank conditions. Unless the tank is heated and/or stirred, the oil may stratify. Low temperatures accelerate the rate at which heavier oils separate out. Another option is to have oil circulated at the burning/ atomization temperature with an amount returned directly to the tank, providing circulation and agitation in the tank.

While heavy fuel oils are an option, storage and system engineering needs to be considered carefully. Factors to consider include:

  • viscosity and temperatures required to atomize efficiently
  • tank heating and/or stirring
  • lagging and trace heating of pipework
  • energy cost associated with the daily use of the system
  • maintenance requirements
  • adequate filtration.

NA-Stordy Combustion Ltd, Heathmill Road, Wombourne, Wolverhampton WV5 8BD; tel: (01902) 891200; fax: (01902) 895552.

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