Document XzJ9RvXqqJ4N9Q0wQN8mroyeG

CHAPTER 15 . 1954 Guide 3o7f0excess air. This will result in less heat, reduced economy;and possibly, a cTohmeplfeotleloiwnitnegrrufapctitoonrsomf saeyrvicnefl.uence the air supply: (1) changes in combustion draft due to a variety of causes (i.e., changes in chimney draft because of weather changes, seasonal changes, back drafts, failure or inadequacy of automatic draft regulator, use of chimney for other' purposes, possible stoppage of the chimney, and changes in draft resistance! of boiler due to partial stoppage of the flues); and (2) changes in air inlet adAjuisrtmleeanktasgaetitnhteofathne. boiler or furnace setting should be reduced to a minimum. The amount of air leakage will be determined by the draft in the combustion chamber. It is important that this draft should be reduced as low as is consistent with the proper disposal of the gases of; combustion. When using mechanical draft burners with average' condi-> tions, the combustion chamber draft should not be allowed to .-- 0.02-0.05 in. water. An automatic draft regulator is necessary in order# maintain constant draft conditions which, in turn, improve efficiency?;'; operation. The draft regulator should be adjusted in accordance witKltfigJ maEnvuefanctthuoreurg'shinastfraunctiisongse.nerally used to supply the air for combustion) in most oil burners, the importance of a proper chimney should ; overlooked. The chimney should have sufficient height and size toiasurtt that the draft will be uniform within the limits given, if maximum efficieopi throughout the heating season is to be maintained. MeSainscuereemffeicniteonft dcioemEbffuicsiteionncyisofbCasoemdbuusptoionn a clean flame and drf|jj?y proportions of oil and air employed, it is possible to determine the by analyzing the combustion gases. Tt is usually sufficient to anwEi. only for carbon dioxide (CO2) and to obtain the temperature of the:stg-. altgflaasm. e Ais schleoawn.ingMoof s1t0otfoth1e2 gpoeorcdeinntsitnadlliacatiotenssthsheobwesfrtoamdj8usttome1n0t,PerCfi{;' 1 Automatic Fuel Burning Equipment 371 COj. Taking into account the potential hazard of low excess air (high COt), a setting to give 10 percent CO2 constitutes a reasonable standard for most oil burners. Commercial Standard CS-75 requires that oil burners labeled as complying with the standard shall obtain smoke-free combustion at 10 percent C02. In all cases smokeless combustion is a requirement for oil burners. Combustion Chamber Design With burners requiring a refractory combustion chamber, the size and shape should be in accordance with the manufacturer's instructions. It is important that the chamber be as nearly air tight as is possible, except when the particular burner requires a secondary supply of air for combustion. The atomizing burner is dependent upon the surrounding heated com bustion chamber surfaces to vaporize the oil and' support combustion. Unsatisfactory combustion may be due to inadequate atomization and mixing. A combustion chamber can only compensate for these things to a limited extent. If liquid fuel continually reaches some part of the fire brick surface, a carbon deposit will result. The combustion chamber should enclose a space having a shape similar to the flame, but large enough to avoid flame contact. The nearest approach in practice is to have the bottom of the combustion chamber flat, but far enough below the nozzle to avoid flame contact, the sides tapering from the air tube at the same angle as the nozzle spray, and the back wall rounded. A plan view of the combustion chamber resembles in shape the outline of the flame. This insures quick vaporization, rapid combustion and better mixing by elimi nating dead spaces in the combustion chamber. An overhanging arch at the back of the fire pot is sometimes used to increase the flame travel and give more time for mixing and burning, and sometimes to prevent the gases from going too directly into the boiler flues. When good atomization and vigorous mixing are achieved by the burner, combustion chamber design becomes a less critical matter. Where secondary air is used, combustion chamber design is quite important. When installing some of the vertical rotary burners, the manufacturer's instructions must be followed carefully when installing the hearth, as in this class successful performance depends upon this factor. Boiler Settings . As the volume of space available for combustion is a determining factor >n oil comsumption, it is general practice to remove grates and extend the combustion chamber downward to include or even exceed the ash pit volume; in new installations the boiler may be raised to make, added volume available. Approximately 1 cu ft of combustion volume should be Provided for every developed boiler horsepower, and in this volume from 0 to 2.5 lb of oil per hour can properly be burned. This corresponds to an Jrer?Se liberation of about 38,000 Btu per cubic foot per hour. At times uch higher fuel rates may be satisfactory. For best results, care should be is e^ ^eeP the S48 velocity below 40 fps. Where checkerwork of brick onp Provide secondary air, good practice calls for about 1 sq in. of pening for each pound of oil fired per hour. Such checkerwork is best to flat flames, or to conical flames that can be spread over the f. * the combustion chamber. The proper bricking of a large or even to cn01 s'ze<^ boiler for oil firing is important, and frequently it is advisable consult an authority on this subject. The essential in combustion