BOILER FURNACE ARRANGEMENT.
The construction of the furnace for oil varies with the type of boiler and the class of burner used. It is the most important part of the installation, but until recently has received the least attention by the engi neers. It is in the furnace that the proper combustion of the oil must take place. A slight difference in the amount of air admitted may mean a great loss of heat units. It is an easy matter to secure a smokeless fire, but efficiency can only be obtained by having a care fully designed furnace.
Fig. 12 shows the method of applying oil to a return tubular boiler employed by many engineers. It will be noticed that the air is supplied from the rear end of the boiler, and is compelled to travel the entire length of the furnace, under the grate, before entering the combustion chamber. Thus the air is pre heated before entering the fire box. Fig. 13 shows a patent furnace arrangement, with the burner placed at the back end of the furnace. This type of furnace has been successfully applied to water tube boilers of various designs. Fig. 14 illustrates the burner and furnace arrangements for the Coen system as applied to B. & W. marine boilers. It will be noticed that the regular coal firing doors have been moved from the furnace front, and special air regulating fronts sub stituted. The burners are located as shown, one in each doorway, and the main flow of air for combus tion is regulated by a sliding plate surrounding the burner. Auxiliary air is admitted through the ash pit doors.
An important feature of the interior furnace ar rangement is the provision for a current of insulating air to circulate from the back to the front end of the furnace, between the ash pan and the furnace deck. This is accomplished by cutting two air openings of sufficient area in the back of the furnace and con structing an air duct 2Y2 in. in height, running from front to back the full width of the furnace. When these rear doors are open, which is the case only when the fires are in operation, a current of air is admitted which travels rapidly forward through the ducts, en tering the combustion chamber through the arches in front of the burners. This circulating air
serves a double purpose; it affords perfect insulation between the ash pan and the furnace, and provides the furnace with preheated air, which is an important aid to rapid combustion.
Fig. 15 shows the furnace arrangement under the Parker boiler. The former grate bar level has not been changed ; a layer of fire brick properly spaced over the grate bars was all that was necessary to change to oil fuel.
Fig. 16 illustrates another furnace arrangement for a B. & W. boiler. The grate bars are lowered a few inches and then covered with a layer of fire brick. In spacing the fire brick, it is common practice to leave out one whole brick about five inches in front of the burner. The other bricks, for a distance of three feet from the front, are left about one inch apart, allowing the air for combustion to pass up and through the flame. The air is thus heated by coming into con tact with the hot bricks. The spread and length of the flame can be regulated by the spacing of the fire bricks.
Fig. 17, 18 and 19 show the general arrangement of the S. & P. burner as applied to the Scotch marine boiler. The grate bars are entirely removed, as are the bridge wall and front dead plate. A ring of fire brick is fitted in the throat of the furnace and a number of old grate bars are placed on an incline. On account of the round shape of the furnace they are cut off as shown in Fig. 18. A single layer of fire brick is placed over these bars and spaced as shown in Fig. 19. When forced draft is used the openings 1 and 2 are closed. The necessary air is regulated by the damper C. The burner is placed as shown, generally five inches above the fire brick. This type of furnace ar rangement has been used with great success by many of the large steamship companies operating on the Pacific Coast.