TESTS AND REPORTS.
An engineer should know whether or not he is getting the best possible results from the fuel that he is using, and also the percentage of capacity as compared with the builder's rating. He should know how to compare the value of the different fuels. By conducting tests he can determine the results, and by making alterations in furnace designs, air admis sion, pressure, etc., he can determine the effect of these changes.
As shown in the chapter on combustion, the neces sity of observing the conditions under which the fuel is being burned, we will now proceed to conduct a test in order to check up the results.
We must first prepare a record sheet showing the size and capacity of the holder, the analysis of the oil, with temperature, pressure, etc., as shown in com parative report. After having prepared the sheet, arrangements must be made to weigh the oil and water used during the tests.
Care should be taken to mark the height of of water in the boiler at the starting of the test, and to have exactly the same amount at the finish.
We are now ready to take the data regarding the pressures, temperatures, etc., as showli under items from 10 to 23 inclusive, ' pages 212 and 213. These are given for comparison and should be taken hourly and a general average made at the end of the test.. The total quantities are as shown in items 24 to 31 inclusive.
In order to determine the weight of dry oil con sumed, (item 25) we take the following figures : 100 — .07 X 6023 = 5956.7 100 The factors of evaporation being ascertained, we multiply it by the total weight of water evaporated (item 27) of item 28 X 27 or 1.0889 X 85,392 = 92,893. It being the total equivalent evaporation from and at 212° F.
It is important to know this item in order to ascertain the efficiency gained by heating the feed water.
The equivalent evaporation from and at 212° F.
can be held by the following W H —t equiva lent evaporation.
Where W = pounds of water per pound of fuel at the temperature of the feed water t.
H = total heat of steam at the temperature cor responding to the pressure, calculated from 32° F. (found by referring to table of properties of satur ated steam).
Items 30 and 31 can be ascertained by passing the exhaust steam through a steam trap and receiving it in a tank.
Items 32 to 36 can be ascertained by dividing the total quantities by the total time.
There are different rules for finding the heat value of fuels. When the analysis is known the fol lowing can be used : Divide the fraction of one pound which consists of oxygen by 8 and subtract the quotient from the fraction of a pound which consists of hydrogen. Mul
tiply the difference by 4.28 and add to the product the fraction of a pound which consists of carbon. Multiply the sum of 14,500 and the product will be the number of B.t.u.'s in a pound of fuel.
For oil, where the analysis is not known, B.t.u. per pound = 18650&40 (Beaume reading 10).
As will be seen by referring to item 37 the B.t.u.'s were obtained from a calorimeter.
A calorimeter, being an instrument for measuring the quantity of heat, a body parts with or absorbs when its temperature rises or lowers.
Item 39. The boiler horsepower developed is found by dividing the evaporation of water per hour from and at 212° F. by 34.5 (being the amount of water evaporated per one boiler horsepower from and at 212° F).
Item 40. The rated horsepower is found by divid ing the water heating surface by steam pressure.
Item 41. The percentage of horsepower devel oped is found by dividing the boiler horsepower rating by the boiler horsepower developed.
Items 43-47 are found as per computation chart. Item 48. The efficiency of the boiler is found by : 15.61X 970.4 divided by 18840 = 80.4.
Where 15.61 = equivalent evaporation per lb. of dry fuel from and at 212° F.
970.4 = B.t.u. of one pound of water at 212° F. 18840 = B.t.u. in one pound of oil used.
This chart was computed during the test (see Fig. 106, page 200).
Items 50 to 53 are obtained by instruments as described in chapter under combustion.
Item 54 being the theoretical amount of air re quired for combustion of one lb. of oil, can be found by knowing the analysis of oil, and referring to table on oxygen and air for combustion.
So, then, by referring to analysis we have : Carbon .856 X 11.52 = 9.861 lb. of air.
Hydrogen 1189 X .3456= 3.901 lb. of air.
Sulphur .0109 X 4.32 = .047 13,809 Or another more accurate formula is pounds of air required per pound of fuel The first method is the most simple and will do for ordinary practice, as we always require much more than the theoretical amount.
Oxygen and Air Required for Combustion.
1 lb. of carbon requires 11.52 lb. of air to burn from C to CO* 1 lb. of hydrogen requires 34.56 lb. of air to burn from H to H20 1 lb. of sulphur requires 4.25 lb. of air to burn from S to SO* Item 56. Heat absorbed by boilers, is Item 42X 970.4 = 14983 B.t.u. or 80.4 per cent.
By comparing Item 55, showing excess air for combustion as figured from curved and with the fol lowing formula, shows the closeness. Pounds of air N supplied per lb. of fuel =3.036