All boilers operate under the same fundamental thermodynamic principles and therefore, just like any other piece of thermal transfer equipment, knowing the log mean temperature difference (LMTD), in this case, between the furnace temperature and the flue gas outlet then the theoretical efficiency can be calculated.
To borrow a phrase from Xylem Corp., ‘Let’s Solve Water’ in this case the supply, storage, heating and delivery to the boiler of the feedwater.
Steam production is part of a dynamic system where freshwater is chemically treated stored in a feedtank heated and pumped into a boiler where the combustion process converts the energy contained in the fuel into heat energy, which is then transferred into the water and steam generated. Within this steam cycle there is a natural time delay between the distribution of steam from the boiler house and the return of condensate, during which time the boiler requires additional water. To ensure a constant supply of water is available a storage tank is provided.
We are constantly encouraged to replace old equipment with new energy efficient units. Whether at home with fridges and washing machines or at work with the latest efficient electrical motors and compressors. All in the name of reducing our energy consumption.
Yet when it comes to steam boiler control, providing we, in the UK, conform to the HSE or CEA guidelines we appear to be content with wasting energy every time the boiler blows down or a weekly evaporative test is carried out.
‘Combustion’, automatic balancing of the air/fuel mixture and matching heat input to the varying steam load, referred to as turndown’ is a subject in its own right and best left to the experts, the Dunphy’s and Saacke’s of this world.