Engineering Bulletin No 1: Boiler and Furnace Testing | Page 7

form of arranging the results is as follows:
1. Date of test May 20, 1918 2. Duration of test hours 10 3. Weight of coal used pounds 5,000 4. Weight of water fed and evaporated do. 35,000 5. Average steam pressure, gauge do. 100 6. Average feed-water temperature ��F. 180 7. Factor of evaporation 1.0727 8. Equivalent evaporation from and at 212�� F. pounds 37,545
EFFICIENCY.
9. Efficiency of boiler and furnace per cent 54
CAPACITY.
10. Boiler horsepower developed 109 11. Builders' rated horsepower 150 12. Percentage of rated horsepower developed per cent 73
ECONOMIC RESULTS.
13. Actual evaporation per pound of coal pounds 7 14. Equivalent evaporation from and at 212�� F. per pound of coal as fired, pounds 7.5 15. Cost of coal per ton (2,000 pounds) $3.60 16. Cost of coal to evaporate 1,000 pounds from and at 212�� F. $0.24
HOW TO USE THE TEST RESULTS.
The object of working up a test is to obtain a clear idea as to the efficiency of operation of the boiler or its operating cost. Consequently, after the calculations have been made, they should be used as a basis for study with the idea of improving the boiler performance.
Take the matter of boiler efficiency, for example, as found from the test mentioned. Its value was 54 per cent. This is altogether too low and indicates wasteful operation. The efficiency of a hand-fired boiler ought not to be less than 65 per cent, and it can be increased to 70 per cent by careful management under good conditions.
The chart in figure 3 can be used to indicate the evaporation that should be obtained in order to reach a desired efficiency. Suppose, for example, that it is desired to know how much water per pound of coal must be evaporated to produce a boiler efficiency of 65 per cent with coal having a heating value of 13,500 B. t. u. per pound.
Locate 13,500 at the bottom of the chart, follow the vertical line until it meets the diagonal marked 65 per cent, and then from this point follow the horizontal line to the left-hand edge, where the figure 9 is found. This means that the equivalent evaporation from and by 212�� F. per pound of coal must be 9 pounds of water. If the steam pressure is 100 pounds gauge, and the feed-water temperature is 180�� F. the factor of evaporation is 1.0727, then the actual evaporation must be 9 �� 1.0727 = 8.36 pounds per pound of coal. In other words, to increase the efficiency from 54 per cent to 65 per cent under the same conditions of pressure and feed-water temperature, it would be necessary to increase the actual evaporation from 7 pounds to 8.36 pounds. This would mean practically 20 per cent more steam from the same weight of coal used.
[Illustration: Heating Value of Coal, in B. t. u. Per Pound
FIG. 3.]
How to do this will require some study and experimenting on the part of the fireman or engineer. The three most common reasons for low-boiler efficiency are (1) excess air, (2) dirty heating surfaces, and (3) loss of coal through the grates. The first of these items is the most important of the three. In most cases the greatest preventable waste of coal in a boiler plant is directly due to excess air. Excess air simply means the amount of air which gets into the furnace and boiler which is not needed for completing the combustion of the coal. Very often twice as much air is admitted to the boiler setting as is required. This extra or excess air is heated and carries heat out through the chimney instead of heating the water in the boiler to make steam. There are two ways in which this excess air gets into the furnace and boiler setting. First, by a combination of bad regulation of drafts and firing. The chances are your uptake damper is too wide open. Try closing it a little. Then, there may be holes in the fire. Keep these covered. The second way excess air occurs is by leakage through the boiler setting, through cracks in the brickwork, leaks around the frames and edges of cleaning doors, and holes around the blow-off pipes. There are also other places where such air can leak in.
Take a torch or candle and go over the entire surface of your boiler setting--front, back, sides, and top. Where the flame of the torch is drawn inward there is an air leak. Plaster up all air leaks and repair the brickwork around door frames where necessary. You should go over your boiler for air leaks once a month.
In regard to best methods of firing soft coal, see Technical Paper No. 80 of the Bureau of Mines, which may be obtained from your State Fuel Administrator.
Dirty heating surfaces cause low