ince the early 1990’s, when a preheating system has been replaced, BHs have been installed on sites. To date BHs have been the preferred method for preheating. Sites with BHs around 5 years old and older have floor mounted gas fired boilers. Newer installations are usually provided with more efficient multiple (modular) wall mounted condensing gas fired boilers. Each gas stream requires one Heat Exchanger (HX). Pipework from the BH can serve more than one HX as required. The total energy able to be produced by the BH is sized to serve the peak demand of the gas stream with some redundancy to allow for plant failures or planned maintenance.
The system efficiency of this method of preheating should not be assessed by looking at the efficiency of the boilers in isolation. To date, no study has been published to demonstrate the system efficiency of BH’s used in preheating gas. As such, losses of heat to atmosphere through pipework and HXs, and losses due to the system providing heat to the gas stream unnecessarily must be assumed. No study has been provided into the excess energy used when overheating the gas stream. Additionally, the total electrical load, is not considered when calculating the boiler efficiency.