Document NGX1D6roVZxLmOMzryvgv2d8b

American Society of Heating and Ventilating' Engineers Guide, 1930 through the boiler passages and up the stack. With other burners there is an air register, designed as part of the burner, which admits the air by natural draft through adjustable vanes, giving a. rotating motion to the air as it enters the combustion chamber about the atomizer. Some installations are provided with forced draft by connecting the air register to a.duct from a fan blower. There are many factors that should be taken into consideration when selecting burners for application to a particular installation. A good burner should be flexible in its adjustments; it should be adjusted easily over a considerable capacity range; it should be suitable for the lowest grade of oil that will be used, and its design should permit the shaping of the resulting flame from the burner so that the flame will fit the com bustion chamber closely. A flame that does not fit properly the shape of the combustion chamber permits air to escape around the flame with out mixing, with the fuel and is, therefore, responsible for inefficient com bustion results. If possible, it is best to use a single burner, rather than burners in multiple, wherever the shape of the flame can be adjusted to meet the combustion chamber requirements and whenever the burner has sufficient capacity and flexibility to meet the variable loads imposed on the boiler. Single burners ordinarily meet the requirements of buildings such as schools, theaters, churches and apartments. For large office and commercial buildings the boilers usually are of such size as to require two or more burners per boiler in order to obtain the required flame application and flexibility of control. . Draft for Industrial Burners There are several reasons why less draft may be required with oil burning equipment than is necessary where coal is used as a fuel: The _ principal reasons are that the draft loss through the fuel bed and grate ; is eliminated, and as a general rule the stack temperatures are lower and . the volume of gas less than with coal. For this reason the cross-sectional area of the stack may be smaller. Some authorities say that it may be safely assumed as 60 per cent of the area that would be furnished for an equivalent coal-fired boiler. In determining the height of the stack, care ! should be taken to secure sufficient draft for the maximum requirements of the boiler and no more. It is advisable, therefore, to follow the recom- : mendations of the heater manufacturer, and if possible the burner manu- . facturer should also be consulted, so that the air-ways shall be designed correctly for the available draft, and provide for sufficient air to develop the. rating of the boiler in the combustion volume available. Furnace Under average conditions the combustion volume should be such that' a release of 40,000 B.t.u. pier cubic foot per hour shall not be exceeded at: 100 per cent of the boiler rating. This is not the maximum heat release possible, but it is representative of good practice. . - Where oil-burning equipment is applied to existing coal-burning boilers excess draft can be corrected by using a damper. It also is advisable in many cases to use baffles to provide for a longer flue travel. In fire-tube boilers it is good practice to insert retarders in the tubes of a type which 244 Chapter 12--Heating by Oil will give the flue gases a spiral motion and which will keep the gases in contact with the surface of the tube. Auxiliary Apparatus Regardless of the type of burner used, the installation of the oil system, which includes the tank, heaters, strainers, pumps and piping, is im portant. Tanks should be installed in accordance with the local rules for the storage of oil fuel, but in the absence of local regulations, it is suggested that the rules and regulations of the National Board of Fire Underwriters be followed. The size of the storage tank is often governed by the amount of space available but it is a question that should be given due considera tion, taking into account the time required for delivery, the daily fuel requirements, and the price in various quantities. Where purchases are to be made by carloads it is advisable to have at least a 15,000 gal. tank. 1 While oil consumption can be fairly accurately checked by gaging the tank with a stick gage through the measuring well, the use of an oil meter is the most logical method of determining fuel costs and for gaging the relation between fuel consumption and work performed. It is recom mended that each tank be equipped with a direct reading gage so that a constant check may be kept of the fuel on hand. A small heater usually is installed in the storage tank around the suction inlet. This heater is used to reduce the viscosity of the oil so that it can be pumped readily. The oil heaters are usually steam coils, but some local regulations require that this heating be done by hot water only. The oil is delivered from the pump to the supply line for the burners and is passed through larger heaters where the temperature is raised to a point that insures the viscosity being low enough for atomiza tion. This temperature is variable for different oils but will usually be between 150 and 200 deg. fahr. It is important that oil be kept at a uniform temperature for satisfactory atomization. This is done by means of automatic temperature regulators which open and close the steam supply valve to the heater coils. From the heaters the oil is delivered as directly as possible to the burners for atomization. As all fuel oils contain a certain amount of foreign matter in suspension, it is important that the oil line have large strainers with sufficient screen area to permit their being used for some period of time without the screens becoming clogged and preventing the flow of oil. The best practice calls for strainers in duplicate on the suction side of the pump, and additional strainers, known as discharge oil strainers, on the delivery side of the pump. It is important that strainers be located where they are readily accessible for cleaning. For small commercial installations, the oil pumps are usually of the rotary type driven by electric motors and are sometimes incorporated into the design of the burners. For large installations, steam operated piston type pumps are commonly used. It is recommended that pumps and heaters be installed in duplicate. This also is required by some local regulations where the boiler service is used in connection with the fire protection apparatus. With the various types of burners which are being used, there have been developed oil-handling systems which differ in their construction 245