Part 42

All experience with this class of fuel indicates that the best results are secured with high combustion rates. With a natural draft in the furnace of, say, three-tenths inch of water, a combustion rate of from 250 to 300 pounds per square foot of grate surface per hour may be obtained. With a blast of, say, five-tenths inch of water, this rate can be increased to 450 pounds per square foot of grate surface per hour. These rates apply to bagasse as fired containing approximately 50 per cent of moisture. It would appear that the most economical results are secured with a combustion rate of approximately 300 pounds per square foot per hour which, as stated, may be obtained with natural draft. Where a natural draft is available sufficient to give such a rate, it is in general to be preferred to a blast.

Fig. 27 shows a typical bagasse furnace with which very satisfactory results have been obtained. The design of this furnace may be altered to suit the boilers to which it is connected. It may be changed slightly in its proportions and in certain instances in its position relative to the boiler. The furnace as shown is essentially a bagasse furnace and may be modified somewhat to accommodate auxiliary fuel.

The fuel is ignited in a pit A on a hearth which is ordinarily elliptical in shape. Air for combustion is admitted through the tuyeres B connected to an annular space C through which the amount of air is controlled. Above the pit the furnace widens out to form a combustion space D which has a cylindrical or spherical roof with its top ordinarily from 11 to 13 feet above the floor. The gases pass from this space horizontally to a second combustion chamber E from which they are led through arches F to the boiler. The arrangement of such arches is modified to suit the boiler or boilers with which the furnace is operated. A furnace of such design embodies the essential features of ample combustion space and long gas travel.

The fuel should be fed to the furnace through an opening in the roof above the pit by some mechanical means which will insure a constant fuel feed and at the same time prevent the inrush of cold air into the furnace.

This class of fuel deposits a considerable quantity of dust, which if not removed promptly will fuse into a hard glass-like clinker. Ample provision should be made for the removal of such dust from the furnace, the gas ducts and the boiler setting, and these should be thoroughly cleaned once in 24 hours.

Table 45 gives the results of several tests on Babcock & Wilcox boilers using fuel of this character.

TABLE 45

TESTS OF BABCOCK & WILCOX BOILERS WITH GREEN BAGASSE ___________________________________________________________________ | Duration of Test | Hours | 12 | 10 | 10 | 10 | | Rated Capacity of Boiler |Horse Power| 319 | 319 | 319 | 319 | | Grate Surface |Square Feet| 33 | 33 | 16.5 | 16.5 | | Draft in Furnace | Inches | .30 | .28 | .29 | .27 | | Draft at Damper | Inches | .47 | .45 | .46 | .48 | | Blast under Grates | Inches | ... | ... | ... | .34 | | Temperature of Exit Gases | Degrees F.| 536 | 541 | 522 | 547 | | /CO{2} | Per Cent | 13.8 | 12.6 | 11.7 | 12.8 | | Flue Gas Analysis { O | Per Cent | 5.9 | 7.6 | 8.2 | 6.9 | | \CO | Per Cent | 0.0 | 0.0 | 0.0 | 0.0 | | Bagasse per Hour as Fired | Pounds | 4980 | 4479 | 5040 | 5586 | | Moisture in Bagasse | Per Cent |52.39 |52.93 |51.84 |51.71 | | Dry Bagasse per Hour | Pounds | 2371 | 2108 | 2427 | 2697 | | Dry Bagasse per Square Foot| | | | | | | of Grate Surface per Hour| Pounds | 71.9 | 63.9 |147.1 |163.4 | | Water per Hour from and at | | | | | | | 212 Degrees | Pounds |10141 | 9850 |10430 |11229 | | Per Cent of Rated Capacity | | | | | | | Developed | Per Cent | 92.1 | 89.2 | 94.7 |102.0 | |___________________________|_________|____|____|____|_____|

Tan Bark--Tan bark, or spent tan, is the fibrous portion of bark remaining after use in the tanning industry. It is usually very high in its moisture content, a number of samples giving an average of 65 per cent or about two-thirds of the total weight of the fuel. The weight of the spent tan is about 2.13 times as great as the weight of the bark ground. In calorific value an average of 10 samples gives 9500 B. t. u. per pound dry. The available heat per pound as fired, owing to the great percentage of moisture usually found, will be approximately 2700 B. t. u. Since the weight of the spent tan as fired is 2.13 as great as the weight of the bark as ground at the mill, one pound of ground bark produces an available heat of approximately 5700 B. t. u. Relative to bituminous coal, a ton of bark is equivalent to 0.4 ton of coal. An average chemical analysis of the bark is, carbon 51.8 per cent, hydrogen 6.04, oxygen 40.74, ash 1.42.

Tan bark is burned in isolated cases and in general the remarks on burning wet wood fuel apply to its combustion. The essential features are a large combustion space, large areas of heated brickwork radiating to the fuel bed, and draft sufficient for high combustion rates. The ratings obtainable with this class of fuel will not be as high as with wet wood fuel, because of the heat value and the excessive moisture content. Mr. D. M. Meyers found in a series of experiments that an average of from 1.5 to 2.08 horse power could be developed per square foot of grate surface with horizontal return tubular boilers. This horse power would vary considerably with the method in which the spent tan was fired.

LIQUID FUELS AND THEIR COMBUSTION

Petroleum is practically the only liquid fuel sufficiently abundant and cheap to be used for the generation of steam. It possesses many advantages over coal and is extensively used in many localities.

There are three kinds of petroleum in use, namely those yielding on distillation: 1st, paraffin; 2nd, asphalt; 3rd, olefine. To the first group belong the oils of the Appalachian Range and the Middle West of the United States. These are a dark brown in color with a greenish tinge. Upon their distillation such a variety of valuable light oils are obtained that their use as fuel is prohibitive because of price.

To the second group belong the oils found in Texas and California. These vary in color from a reddish brown to a jet black and are used very largely as fuel.

The third group comprises the oils from Russia, which, like the second, are used largely for fuel purposes.

The light and easily ignited constituents of petroleum, such as naphtha, gasolene and kerosene, are oftentimes driven off by a partial distillation, these products being of greater value for other purposes than for use as fuel. This partial distillation does not decrease the value of petroleum as a fuel; in fact, the residuum known in trade as "fuel oil" has a slightly higher calorific value than petroleum and because of its higher flash point, it may be more safely handled. Statements made with reference to petroleum apply as well to fuel oil.

In general crude oil consists of carbon and hydrogen, though it also contains varying quantities of moisture, sulphur, nitrogen, arsenic, phosphorus and silt. The moisture contained may vary from less than 1 to over 30 per cent, depending upon the care taken to separate the water from the oil in pumping from the well. As in any fuel, this moisture affects the available heat of the oil, and in contracting for the purchase of fuel of this nature it is well to limit the per cent of moisture it may contain. A large portion of any contained moisture can be separated by settling and for this reason sufficient storage capacity should be supplied to provide time for such action.

A method of obtaining approximately the percentage of moisture in crude oil which may be used successfully, particularly with lighter oils, is as follows. A burette graduated into 200 divisions is filled to the 100 mark with gasolene, and the remaining 100 divisions with the oil, which should be slightly warmed before mixing. The two are then shaken together and any shrinkage below the 200 mark filled up with oil. The mixture should then be allowed to stand in a warm place for 24 hours, during which the water and silt will settle to the bottom. Their percentage by volume can then be correctly read on the burette divisions, and the percentage by weight calculated from the specific gravities. This method is exceedingly approximate and where accurate results are required it should not be used. For such work, the distillation method should be used as follows:

Gradually heat 100 cubic centimeters of the oil in a distillation flask to a temperature of 150 degrees centigrade; collect the distillate in a graduated tube and measure the resulting water. Such a method insures complete removal of water and reduces the error arising from the slight solubility of the water in gasolene. Two samples checked by the two methods for the amount of moisture present gave,

Distillation Dilution Per Cent Per Cent 8.71 6.25 8.82 6.26

TABLE 46

COMPOSITION AND CALORIFIC VALUE OF VARIOUS OILS

+-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+ | Kind of Oil | %C | %H | %S | %O |S.G.|FP | %H2O |Btu |Authority | +-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+ |California, Coaling | | | | |.927|134| |17117|Babcock & Wilcox Co. | |California, Bakersfield | | | | |.975| | |17600|Wade | |California, Bakersfield | | |1.30| |.992| | |18257|Wade | |California, Kern River | | | | |.950|140| |18845|Babcock & Wilcox Co. | |California, Los Angeles | | |2.56| | | | |18328|Babcock & Wilcox Co. | |California, Los Angeles | | | | |.957|196| |18855|Babcock & Wilcox Co. | |California, Los Angeles | | | | |.977| | .40 |18280|Babcock & Wilcox Co. | |California, Monte Christo| | | | |.966|205| |18878|Babcock & Wilcox Co. | |California, Whittier | | | .98| |.944| |1.06 |18507|Wade | |California, Whittier | | | .72| |.936| |1.06 |18240|Wade | |California |85.04|11.52|2.45| .99| | |1.40 |17871|Babcock & Wilcox Co. | |California |81.52|11.51| .55|6.92| |230| |18667|U.S.N. Liquid Fuel Board| |California | | | .87| | | | .95 |18533|Blasdale | |California | | | | |.891|257| |18655|Babcock & Wilcox Co. | |California | | |2.45| |.973| |1.50|17976|O'Neill | |California | | |2.46| |.975| |1.32 |18104|Shepherd | |Texas, Beaumont |84.6 |10.9 |1.63|2.87 |.924|180| |19060|U.S.N. Liquid Fuel Board| |Texas, Beaumont |83.3 |12.4 | .50|3.83 |.926|216| |19481|U.S.N. Liquid Fuel Board| |Texas, Beaumont |85.0 |12.3 |1.75| .92| | | |19060|Denton | |Texas, Beaumont |86.1 |12.3 |1.60| |.942| | |20152|Sparkes | |Texas, Beaumont | | | | |.903|222| |19349|Babcock & Wilcox Co. | |Texas, Sabine | | | | |.937|143| |18662|Babcock & Wilcox Co. | |Texas |87.15|12.33|0.32| |.908|370| |19338|U. S. N. | |Texas |87.29|12.32|0.43| |.910|375| |19659|U. S. N. | |Ohio |83.4 |14.7 |0.6 |1.3 | | | |19580| | |Pennsylvania |84.9 |13.7 | |1.4 |.886| | |19210|Booth | |West Virginia |84.3 |14.1 | |1.6 |.841| | |21240| | |Mexico | | | | |.921|162| |18840|Babcock & Wilcox Co. | |Russia, Baku |86.7 |12.9 | | |.884| | |20691|Booth | |Russia, Novorossick |84.9 |11.6 | |3.46 | | | |19452|Booth | |Russia, Caucasus |86.6 |12.3 | |1.10 |.938| | |20138| | |Java |87.1 |12.0 | | .9 |.923| | |21163| | |Austria, Galicia |82.2 |12.1 |5.7 | |.870| | |18416| | |Italy, Parma |84.0 |13.4 |1.8 | |.786| | | | | |Borneo |85.7 |11.0 | |3.31 | | | |19240|Orde | +-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+

%C = Per Cent Carbon %H = Per Cent Hydrogen %S = Per Cent Sulphur %O = Per Cent Oxygen S.G. = Specific Gravity FP = Degrees Flash Point %H_{2}O = Per Cent Moisture Btu = B. t. u. Per Pound

Calorific Value--A pound of petroleum usually has a calorific value of from 18,000 to 22,000 B. t. u. If an ultimate analysis of an average sample be, carbon 84 per cent, hydrogen 14 per cent, oxygen 2 per cent, and assuming that the oxygen is combined with its equivalent of hydrogen as water, the analysis would become, carbon 84 per cent, hydrogen 13.75 per cent, water 2.25 per cent, and the heat value per pound including its contained water would be,

Carbon .8400 × 14,600 = 12,264 B. t. u. Hydrogen .1375 × 62,100 = 8,625 B. t. u. ------[**Should be .1375 x 62,000 = 8,525] Total 20,889 B. t. u.[**Would be Total = 20,789]

The nitrogen in petroleum varies from 0.008 to 1.0 per cent, while the sulphur varies from 0.07 to 3.0 per cent.

Table 46, compiled from various sources, gives the composition, calorific value and other data relative to oil from different localities.