Waste Heat Recovery & Economisers

• By capturing the waste heat in the flue gas with an economiser and diverting it to pre-heat the steam boiler
  feed water, the boiler thermal efficiency can be increased to as much as 95%.
• Improving thermal efficiency cuts fuel consumption resulting in significant cost savings often in the region of 4-6% p.a.
• Payback can often be as little as 12 months.
• Using less fuel cuts carbon emissions.

The operational efficiency of a boiler is measured by the percentage of the fuel input energy that is eventually delivered as useful heat output. Not all of the heat released when the fuel is combusted can be used.

Major sources of heat loss from steam boilers are through the flue gas, blowdown and radiation to the boiler’s surroundings. For a shell type steam boiler the losses are:

• Flue losses ~18%
• Heat transfer gas and water side losses ~2%
• Insulated chamber radiation losses ~2%
• Water outlet blowdown losses ~3%

1. An extended-surface finned tube heat exchanger is fitted inside an exhaust flue.
2. Through the fins of the heat exchanger the heat from exhaust gases is transferred to water within the tubes to which the fins are attached.
3. This water is heated and transported via water pipe system to feed the boiler.
4. With preheated feed-water less energy is required by the boiler to create the steam.

Heat energy is critical to the chemical processing industry and heat recovery and reuse are central to the energy management process. Turnbull and Scott design engineers work closely with process engineers from the industry to support this.

Click here to view our case study on this topic.