Steam Boiler
by International Energy Agency and Georges Liebecq
	A steam boiler transforms water into steam.  The necessary energy
is provided by combustion of a fuel of known composition.  Most often, the
flue gas resulting from the compustion process exchanges heat with the 
water through an economizer pre-heating the water, the evaporator and a 
steam superheater.
	Given a steam demand (i.e. mass flowrate, temperature and pressure)
and inlet conditions for the supply water, TYPE 57 computes the fuel
consumption, the flue gas stack temperature and the boiler efficiency, taking
into account:
-losses to flue gas;
-losses by radiation and convection to the environment;
-losses due to continous blowdown (water extraction to the purity of water);
-losses to the ashes extracted from the furnace at a temperature close to
 the combustion temperature.
	The model computes first a theoretical adiabatic combustion temperature
and the composition of the flue gas.  Then, it considers the boiler as a 
counterflow heat exchanger between flue gas and water.  Its UA-value (for 
nominal conditions) may be given by the user or can be computed if the stack
temperature is known.
Ref:A Simple Steam Boiler Model for TRNSYS; G. Liebecq June 1988
    (Type 57 File)