OIL BURNERS It is not the purpose of this publication to point out the good points or defects of any particular oil burner. It will be sufficient to say that there are a number of very good makes on the market, some of which are perhaps more suitable for a particular service than others, and it is largely a question of selecting the burner which will be the most econom ical in the service for which it is to be used.
In general it may be said that the distinguishing feature of oil burners is not so much the effectiveness of the atomization as the amount of steam required to properly atomize the oil. The variation in this respect among the different burners being from 1% to o % and more of the total evaporation of the boiler, although it should be stated that this depends largely upon the operation.
Oil burners are of two general classes: Internally Mixed Burners.
In this type of burner, the oil and atomizing agent (steam or air, as the case may be) come together inside the burner and issue from the burner tip in a more or less finely divided spray.
Externally Mixed Burners.
The mixture in this type takes place outside of the burner, the steam or air and oil discharge passages usually terminating at the burner tip in the same vertical plane, the oil being in the center and sur rounded by the atomizing agent.
When using oil of a fairly light body, the externally mixed burners possess the advantage of not requiring much oil pressure, as there is no back pressure of steam or air to be overcome. Elevating the oil storage tank about 15 feet above the burners will in most cases furnish a sufficient pressure of oil.
Some internally mixed burners are so designed as to secure a jet effect from the steam which draws the oil from the supply pipe, thus doing away with oil pressure pumps.
Mechanical Burners.
Oil burners depending upon either a comparatively high oil pressure or upon the rapid revolving of a circular disc to effect the atomization of the oil are termed mechanical burners. Such burners have not
come into general use at the present writing, but the field looks very promising for future develop ments along this line.
In either of the types of mechanical burners men tioned, the use of steam is indirectly necessary, since the high oil pressure maintained by the pump or the rotation of the circular disc will require the use of steam. The points to be considered are the effectiveness of the atomization, the simplicity and durability of the mechanism and the amount of steam used as compared with other types.
The U. S. Navy is using a system of this kind on some of its ships, maintaining oil pressures varying from 50 lbs. to 200 lbs., depending on the speed of the boat and operating as many as eleven burners under one boiler.
Burners depending upon pressure and the shape of the orifice to effect the atomization should have the oil well preheated and forced to the burners at a constant pressure. It is also considered essential to supply the air supporting combustion under a pressure sufficient to give it a velocity approximately equal to that of the oil as it leaves the burner, and in such a manner as to insure a speedy and intimate intermingling of the two. The best results are obtained when the air is preheated.
Number of Burners to be Used.
The tendency in most oil burning plants seems to be to use too few burners rather than too many.
While the majority of oil fuel burners are rated at 75 to ioo Boiler Horse Power, it is always desirable to use a sufficient number to insure a solid sheet of fire extending across the furnace to prevent air sup porting combustion from passing up the stack with out performing its function as explained on page 89 and also to prevent localizing the heat in the furnace.
Experiments have proven that a burner is less efficient, as regards the amount of steam used for atomizing, when being forced than it is when used at its normal rating.