OCR Text |
Show Sedimentation and aggregation have been investigated and several techniques are available which appear to provide COM stability for periods of about 12 months. Viscosity has been shown by Savage (6) and others to be controllable by temperature. Consequently, COM can be handled in much the same manner as heavy fuel oil. Firetube Boiler Description Firetube packaged boilers are typically two, three or four pass with either a wet or dry back arrangement. In a firetube boiler, water surrounds the tubes and the hot gases flow through the tubes. The first pass is the furnace tube or combustion chamber. The furnace tube is designed to achieve complete combustion of the fuel oil. Its length is, therefore, determined by the burner characteristics as well as the fuel characteristics. The primary mode of heat transfer in the furnace tube is predominantly by radiation. Generally, 45 to 50 percent of the total heat transferred to the water occurs in the furnace tube. Subsequently, combustion gases pass through tubes and exhaust at the stack outlet. Heat transfer in the flue tubes is by convection. The flue gas velocity in each pass is usually controlled to ensure good heat transfer. Heat transfer surfaces, which are free of contamination (soot, etc.), assure good boiler performance. A wet back boiler has a rear wall or door which is water cooled while a dry back boiler has a refractory lined rear wall or door. The fire side surface of a dry back boiler is clearly at a higher temperature than that of a wet back boiler. The burner assembly is attached to the boiler front head. Combustion air enters through the air inlet and is forced through the rotary air damper and the diffuser into the combustion chamber by a forced air fan. Fuel is pumped 15-3 |