Part 62

1st. It is sometimes found that the operating force is not fully acquainted with the boilers and apparatus. Probably the most general of such shortcomings is the fixed idea in the heads of the operatives that boilers run above their rated capacity are operating under a state of strain and that by operating at less than their rated capacity the most economical service is assured, whereas, by determining what a boiler will do, it may be found that the most economical rating under the conditions of the plant will be considerably in excess of the builder's rating. Such ideas can be dislodged only by demonstrating to the operatives what maximum load the boilers can carry, showing how the economy will vary with the load and the determining of the economical load for the individual plant in question.

2nd. Stokers. With stoker-fired boilers, it is essential that the operators know the limitations of their stokers as determined by their individual installation. A thorough understanding of the requirements of efficient handling must be insisted upon. The operatives must realize that smokeless stacks are not necessarily the indication of good combustion for, as has been pointed out, absolute smokelessness is oftentimes secured at an enormous loss in efficiency through excess air.

Another feature in stoker-fired plants is in the cleaning of fires. It must be impressed upon the operatives that before the fires are cleaned they should be put into condition for such cleaning. If this cleaning is done at a definite time, regardless of whether the fires are in the best condition for cleaning, there will be a great loss of good fuel with the ashes.

3rd. It is necessary that in each individual plant there be a basis on which to judge the cleanliness of a boiler. From the operative's standpoint, it is probably more necessary that there be a thorough understanding of the relation between scale and tube difficulties than between scale and efficiency. It is, of course, impossible to keep boilers absolutely free from scale at all times, but experience in each individual plant determines the limit to which scale can be allowed to form before tube difficulties will begin or a perceptible falling off in efficiency will take place. With such a limit of scale formation fixed, the operatives should be impressed with the danger of allowing it to be exceeded.

4th. The operatives should be instructed as to the losses resulting from excess air due to leaks in the setting and as to losses in efficiency and capacity due to the by-passing of gases through the setting, that is, not following the path of the baffles as originally installed. In replacing tubes and in cleaning the heating surfaces, care must be taken not to dislodge baffle brick or tile.

5th. That an increase in the temperature of the feed reduces the amount of work demanded from the boiler has been shown. The necessity of keeping the feed temperature as high as the quantity of exhaust steam will allow should be thoroughly understood. As an example of this, there was a case brought to our attention where a large amount of exhaust steam was wasted simply because the feed pump showed a tendency to leak if the temperature of feed water was increased above 140 degrees. The amount wasted was sufficient to increase the temperature to 180 degrees but was not utilized simply because of the slight expense necessary to overhaul the feed pump.

The highest return will be obtained when the speed of the feed pumps is maintained reasonably constant for should the pumps run very slowly at times, there may be a loss of the steam from other auxiliaries by blowing off from the heaters.

6th. With a view to checking steam losses through the useless blowing of safety valves, the operative should be made to realize the great amount of steam that it is possible to get through a pipe of a given size. Oftentimes the fireman feels a sense of security from objections to a drop in steam simply because of the blowing of safety valves, not considering the losses due to such a cause and makes no effort to check this flow either by manipulation of dampers or regulation of fires.

The few of the numerous shortcomings outlined above, which may be found in many plants, are almost entirely due to lack of knowledge on the part of the operating crew as to the conditions existing in their own plants and the better performances being secured in others. Such shortcomings can be overcome only by the education of the operatives, the showing of the defects of present methods, and instruction in better methods. Where such instruction is necessary, the value of records is obvious. There is fortunately a tendency toward the employment of a better class of labor in the boiler room, a tendency which is becoming more and more marked as the realization of the possible saving in this end of the plant increases.

The second aspect of boiler room management, dealing with specific recommendations as to the care and operation of the boilers, is dictated largely by the nature of the apparatus. Some of the features to be watched in considering this aspect follow.

Before placing a new boiler in service, a careful and thorough examination should be made of the pressure parts and the setting. The boiler as erected should correspond in its baffle openings, where baffles are adjustable, with the prints furnished for its erection, and such baffles should be tight. The setting should be so constructed that the boiler is free to expand without interfering with the brickwork. This ability to expand applies also to blow-off and other piping. After erection all mortar and chips of brick should be cleaned from the pressure parts. The tie rods should be set up snug and then slacked slightly until the setting has become thoroughly warm after the first firing. The boiler should be examined internally before starting to insure the absence of dirt, any foreign material such as waste, and tools. Oil and paint are sometimes found in the interior of a new boiler and where such is the case, a quantity of soda ash should be placed within it, the boiler filled with water to its normal level and a slow fire started. After twelve hours of slow simmering, the fire should be allowed to die out, the boiler cooled slowly and then opened and washed out thoroughly. Such a proceeding will remove all oil and grease from the interior and prevent the possibility of foaming and tube difficulties when the boiler is placed in service.

The water column piping should be examined and known to be free and clear. The water level, as indicated by the gauge glass, should be checked by opening the gauge cocks.

The method of drying out a brick setting before placing a boiler in operation is described later in the discussion of boiler settings.

A boiler should not be cut into the line with other boilers until the pressure within it is approximately that in the steam main. The boiler stop valve should be opened very slowly until it is fully opened. The arrangement of piping should be such that there can be no possibility of water collecting in a pocket between the boiler and the main, from which it can be carried over into the steam line when a boiler is cut in.

In regular operation the safety valve and steam gauge should be checked daily. In small plants the steam pressure should be raised sufficiently to cause the safety valves to blow, at which time the steam gauge should indicate the pressure at which the valve is known to be set. If it does not, one is in error and the gauge should be compared with one of known accuracy and any error at once rectified.

In large plants such a method of checking would result in losses too great to be allowed. Here the gauges and valves are ordinarily checked at the time a boiler is cut out, the valves being assured of not sticking by daily instantaneous opening through manipulation by hand of the valve lever. The daily blowing of the safety valve acts not only as a check on the gauge but insures the valve against sticking.

The water column should be blown down thoroughly at least once on every shift and the height of water indicated by the glass checked by the gauge cocks. The bottom blow-offs should be kept tight. These should be opened at least once daily to blow from the mud drum any sediment that may have collected and to reduce the concentration. The amount of blowing down and the frequency is, of course, determined by the nature of the feed water used.

In case of low water, resulting either from carelessness or from some unforeseen condition of operation, the essential object to be obtained is the extinguishing of the fire in the quickest possible manner. Where practicable, this is best accomplished by the playing of a heavy stream of water from a hose on the fire. Another method, perhaps not so efficient, but more generally recommended, is the covering of the fire with wet ashes or fresh fuel. A boiler so treated should be cut out of line after such an occurrence and a thorough inspection made to ascertain what damage, if any, has been done before it is again placed in service.

The efficiency and capacity depend to an extent very much greater than is ordinarily realized upon the cleanliness of the heating surfaces, both externally and internally, and too much stress cannot be put upon the necessity for systematic cleaning as a regular feature in the plant operation.

The outer surfaces of the tubes should be blown free from soot at regular intervals, the frequency of such cleaning periods being dependent upon the class of fuel used. The most efficient way of blowing soot from the tubes is by means of a steam lance with which all parts of the surfaces are reached and swept clean. There are numerous soot blowing devices on the market which are designed to be permanently fixed within the boiler setting. Where such devices are installed, there are certain features that must be watched to avoid trouble. If there is any leakage of water of condensation within the setting coming into contact with the boiler tubes, it will tend toward corrosion, or if in contact with the heated brickwork will cause rapid disintegration of the setting. If the steam jets are so placed that they impinge directly against the tubes, erosion may take place. Where such permanent soot blowers are installed, too much care cannot be taken to guard against these possibilities.

Internally, the tubes must be kept free from scale, the ingredients of which a study of the chapter on the impurities of water indicates are present in varying quantities in all feed waters. Not only has the presence of scale a direct bearing on the efficiency and capacity to be obtained from a boiler but its absence is an assurance against the burning out of tubes.

In the absence of a blow-pipe action of the flames, it is impossible to burn a metal surface where water is in intimate contact with that surface.

In stoker-fired plants where a blast is used, and the furnace is not properly designed, there is a danger of a blow-pipe action if the fires are allowed to get too thin. The rapid formation of steam at such points of localized heat may lead to the burning of the metal of the tubes.

Any formation of scale on the interior surface of a boiler keeps the water from such a surface and increases its tendency to burn. Particles of loose scale that may become detached will lodge at certain points in the tubes and localize this tendency at such points. It is because of the danger of detaching scale and causing loose flakes to be present that the use of a boiler compound is not recommended for the removal of scale that has already formed in a boiler. This question is covered in the treatment of feed waters. If oil is allowed to enter a boiler, its action is the same as that of scale in keeping the water away from the metal surfaces.

It has been proven beyond a doubt that a very large percentage of tube losses is due directly to the presence of scale which, in many instances, has been so thin as to be considered of no moment, and the importance of maintaining the boiler heating surfaces in a clean condition cannot be emphasized too strongly.

The internal cleaning can best be accomplished by means of an air or water-driven turbine, the cutter heads of which may be changed to handle various thicknesses of scale. Fig. 41 shows a turbine cleaner with various cutting heads, which has been found to give satisfactory service.

Where a water-driven turbine is used, it should be connected to a pump which will deliver at least 120 gallons per minute per cleaner at 150 pounds pressure. This pressure should never be less than 90 pounds if satisfactory results are desired. Where an air-driven turbine is used, the pressure should be at least 100 pounds, though 150 pounds is preferable, and sufficient water should be introduced into the tube to keep the cutting head cool and assist in washing down the scale as it is chipped off.

Where scale has been allowed to accumulate to an excessive thickness, the work of removal is difficult and tedious. Where such a heavy scale is of sulphate formation, its removal may be assisted by filling the boiler with water to which there has been added a quantity of soda ash, a bucketful to each drum, starting a low fire and allowing the water to boil for twenty-four hours with no pressure on the boiler. It should be cooled slowly, drained, and the turbine cleaner used immediately, as the scale will tend to harden rapidly under the action of the air.