... &oil-fired boiler Sigle&Dou. Drum, Horizontal, three-pass Wet back shell boiler High efficiency WNS series automatic Oil&Gas-fired boiler is ... horizontal, three-pass, wet back shell boiler. The main structure includes: Boiler shell, Bellows furnace, ... . The shell and the furnace are made by 20g boiler special steel. Furnace & Returns burns room, Tube plate ...