Combitherm Boiler is a unique membrane design water wall type boiler which combines the advantages of both water tube & smoke tube steam boilers. The radiation zone of the furnace is covered on three sides by wall of water tubes forming the first pass and the conventional smoke tube shell has tubes lined up forming the second and third pass of flue gases. Thus, the water wall furnace recovers the radiation heat of the furnace and the smoke tube shell provides large water & steam holding capacities to give the maximum advantage.
Water is fed to the boiler from a feed pipe connection. Firstly the water fills in the shell and then gets transported to the Bottom Header of water wall from the Down-comers welded to the Boiler Shell. From here the water rises up in the tubes of water wall and gets thrown back to the boiler shell from the top header. As firing is done in the furnace, because of radiation the surface temperature of water wall membrane rises and the water present in the tubes gets heated up and starts getting converted to steam. Now this steam, being lesser dense (creating natural circulation of steam-water in the system), rises up to the top header and gets to the Boiler Shell. The flue gas from the furnace (1st pass), travelling in the membrane, then enters the tube of Boiler Shell (2nd pass) and again after reversal (3rd Pass), now its smoke tube