Heating using waste heat gas

The heat from hot flue gases generated by upstream processes – such as combined heat and power from CHP units or gas turbines, industrial manufacturing and production processes in the metal industry, or the thermal recovery of waste materials – is suitable for generating process heat in shell boilers.

The potential output from the flue gases depends primarily on three criteria:

• Temperature level at which the flue gases are available
  The higher the temperature level of the flue gases, the greater the heat output that can be achieved. The temperature level can range from around 360 – 550 °C in motor flue gases to as high as 1,000 °C in industrial processes such as the melting or forging of workpieces, or in thermal recovery processes.
• Flue gas volume and the duration for which the flue gases are available
  It is important to note whether flue gas is available continuously or only during specific operating times. In addition, the volume of flue gases must be taken into account. In combined heat and power generation using a gas turbine, for example, the high excess air during combustion means that up to five times more flue gas is produced than in an internal combustion engine of the same electrical output.
• Temperature level at which the process heat is to be provided
  The higher the flow temperature is set, the smaller the temperature difference between the flue gas and the hot water that is available for heat transfer. At higher flue gas temperatures, a correspondingly higher temperature level can also be achieved.

Other framework parameters to consider when selecting a suitable boiler include the sulphur content, the solids content and any other corrosive substances, such as the chlorine content in the flue gas.

Due to the wide range of possible variations in waste heat gas, it is always advisable to carry out comprehensive planning well in advance of installing a waste heat boiler system in order to ensure optimum heat utilisation.