This section is from the "Modern Machine Shop Construction, Equipment, And Management" book, by Oscar E. Perrigo. Also see Amazon: Modern Machine Shop Construction, Equipment, And Management.
The styles and types of boilers in the market are many and various, and most of them have good and practical claims to consideration in one way or another. But it is somewhat doubtful if any type will be devised that will become as popular for general use - or in the long run any more efficient and economical for hard,.every-day service - as the return tubular type.
Ofttimes the space in which the boilers must be located will determine the type, whether they shall be upright or horizontal; and the method of firing them, as well as the kind of fuel to be used, must also be taken into consideration.
Mechanical stoking is used with success in some instances, but as yet has not come into general use. Both oil and natural gas as a fuel are much -used in such localities as render them more economical than coal.
Our boilers will therefore be of the return tubular type, fired by hand, with the usual kind of soft or bituminous coal. They will be 66 inches diameter and 16 feet long, exclusive of the curtain sheet under the space occupied by the "up-take," or smoke connection.
The arrangement for setting the boilers is shown in vertical, longitudinal section in Fig. 75; in a half vertical cross-section, and half front elevation in Fig. 76, and in a horizontal section above the grate line in Fig. 77.
There are several matters in connection with the setting of boilers which should be strictly attended to. Among these are the following: Two courses of bricks should be laid above the floor line of the boiler room for the boiler fronts to rest upon; the top course at least should be headers, and carefully leveled up. They should be so located that at least two inches will project in front of the boiler fronts. The ashpits should be cemented so as to allow of the introduction of a few inches of water.
The front supporting brackets should rest fairly upon iron plates in the side walls, while the rear brackets rest on rollers, which in turn rest on the iron plates set in the walls, by which arrangement all expansion of the boiler is toward the rear. The brickwork around the brackets should be entirely clear of them so as to leave the boilers opportunity to expand and contract without injury to the walls.
The grates should incline from front to back from ¬ to ¾ inch per foot.
Fig. 75. Longitudinal Section of Boiler-Selling.
The bridge wall should come up to within 12 or 14 inches of the bottom of the boiler, and be curved to suit its form, although this is not absolutely necessary. The width of grate surface should be equal to the diameter of the boiler.
The side walls of the furnace are to incline outwards, so as to be two inches from the sides of the boiler, at a point one course of bricks below the bottom of the brackets. The fire bricks should be laid with a header course every five courses, so that burned-out bricks may be conveniently replaced.
At each side of the fire doors cast iron "cheek-pieces" should be put in, the cast iron arch plate over the door resting on them. These "cheek-pieces" should be about 1¬ inches thick, of the form shown in Fig. 77, and have as many half-inch holes cored in them as possible, the holes spaced two inches from center to center, for an air supply to prevent them from burning out. Their height is equal to the height of the fire door at the side. They will be found to be very durable and to save much expense in fire brick repairs.
They may be removed and replaced whenever the furnace is cool, by jacking up the arch plate a trifle and letting it down on the new "cheek-piece" introduced. Their inclined form renders the cleaning of the fire much more convenient and the extreme front corner which they cut off is of little benefit in making steam.
Fig. 76. Vertical Half Cross Section and Elevation of Boiler Setting.
Both outside and division walls should have a two-inch air space, as shown. The top of the boiler should be covered with asbestos, or with a brick arch. If the latter, there should be a two-inch air space left between it and the boiler. The boilers must rest only on the supporting brackets and in no case on the boiler fronts.
Fig. 77. Horizontal Section of Boiler Setting.
The fronts are held in place by anchor bolts ¾ inch in diameter and 4 feet long, with the inner ends bent to a right angle 10 or 12 inches long. Their front ends are threaded for nuts coming outside of the boiler fronts, so that a defective or cracked portion of the front may be readily removed and replaced without disturbing the brickwork.
The smoke connections from the boilers to the stack may be the same width all the way through, in which case its height is to be increased from the first to the sixth boiler to include the additional area necessary for each boiler as it progresses toward the stack. Thus it may be 36 inches wide and 20 inches high at the first boiler, and increasing to 78 inches high at the sixth boiler. It will perhaps be more convenient to increase also the width, in order that the area at the large end may equal that of the stack without increasing the height to such an extent.
By this method we may make the larger end 48 inches wide and 60 inches high. There should be a cleaning door in the end of the smoke connection at the first boiler, and a pivoted damper properly balanced between the sixth boiler and the stack. It will be convenient also to have dampers in the "uptake" from each boiler to the main smoke connection, so as to shut these off whenever a boiler is laid off for cleaning or repairs.