Steam, Its Generation and Use Part 27

VALUE OF ONE POUND OF MILL BAGa.s.sE AT DIFFERENT EXTRACTIONS

1: Per Cent Extraction of Weight of Cane 2: Per Cent Moisture in Baga.s.se 3: Per Cent in Baga.s.se 4: Fuel Value, B. t. u.

5: Per Cent in Baga.s.se 6: Fuel Value, B. t. u.

7: Per Cent in Baga.s.se 8: Fuel Value, B. t. u.

9: Total Heat Developed per Pound of Baga.s.se 10: Heat Required to Evaporate Moisture[42]

11: Heat Available for Steam Generation 12: Pounds of Baga.s.se Equivalent to one Pound of Coal of 14,000 B. t. u.

+----------------------------------------------------------------+ |+---+-----+----------+---------+---------+----------------+----+| || | | | | |B.t.u. Value per| || || | | Fiber | Sugar |Mola.s.ses |Pound of Baga.s.se| || || | +-----+----+----+----+----+----+-----+----+-----+ || || | | | | | | | | | | | || || 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 || |+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| || BASED UPON CANE OF 12 PER CENT FIBER AND JUICE CONTAINING || ||18 PER CENT OF SOLID MATTER. REPRESENTING TROPICAL CONDITIONS || |+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| ||75 |42.64|48.00|3996|6.24|451 |3.12|217 |4664 |525 |4139 |3.38|| ||77 |39.22|52.17|4343|5.74|414 |2.87|200 |4958 |483 |4475 |3.13|| ||79 |35.15|57.14|4757|5.14|371 |2.57|179 |5307 |433 |4874 |2.87|| ||81 |30.21|63.16|5258|4.42|319 |2.21|154 |5731 |372 |5359 |2.61|| ||83 |24.12|70.59|5877|3.53|256 |1.76|122 |6255 |297 |5958 |2.35|| ||85 |16.20|80.00|6660|2.40|173 |1.20| 83 |6916 |200 |6716 |2.08|| |+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| || BASED UPON CANE OF 10 PER CENT FIBER AND JUICE CONTAINING || ||15 PER CENT OF SOLID MATTER. REPRESENTING LOUISIANA CONDITIONS|| |+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| ||75 |51.00|40.00|3330|6.00|433 |3.00|209 |3972 |678 |3294 |4.25|| ||77 |48.07|43.45|3617|5.66|409 |2.82|196 |4222 |592 |3630 |3.86|| ||79 |44.52|47.62|3964|5.24|378 |2.62|182 |4524 |548 |3976 |3.52|| ||81 |40.18|52.63|4381|4.73|342 |2.36|164 |4887 |495 |4392 |3.19|| ||83 |35.00|58.82|4897|4.12|298 |2.06|143 |5436 |431 |5005 |2.80|| ||85 |28.33|66.67|5550|3.33|241 |1.67|116 |5907 |349 |5558 |2.52|| |+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| +----------------------------------------------------------------+

Furnace Design and the Combustion of Baga.s.se--With the advance in sugar manufacture there came, as described, a decrease in the amount of baga.s.se available for fuel. As the general efficiency of a plant of this description is measured by the amount of auxiliary fuel required per ton of cane, the relative importance of the furnace design for the burning of this fuel is apparent.

In modern practice, under certain conditions of mill operation, and with baga.s.se of certain physical properties, the baga.s.se available from the cane ground will meet the total steam requirements of the plant as a whole; such conditions prevail, as described, in Java. In the United States, Cuba, Porto Rico and like countries, however, auxiliary fuel is almost universally a necessity. The amount will vary, depending to a great extent upon the proportion of fiber in the cane, which varies widely with the locality and with the age at which it is cut, and to a lesser extent upon the degree of purity of the manufactured sugar, the use of the maceration water and the efficiency of the mill apparatus as a whole.

[Ill.u.s.tration: Fig. 27. Babc.o.c.k & Wilc.o.x Boiler Set with Green Baga.s.se Furnace]

Experience has shown that this fuel may be burned with the best results in large quant.i.ties. A given amount of baga.s.se burned in one furnace between two boilers will give better results than the same quant.i.ty burned in a number of smaller furnaces. An objection has been raised against such practice on the grounds that the necessity of shutting down two boiler units when it is necessary for any reason to take off a furnace, requires a larger combined boiler capacity to insure continuity of service. As a matter of fact, several small furnaces will cost considerably more than one large furnace, and the saving in original furnace cost by such an installation, taken in conjunction with the added efficiency of the larger furnace over the small, will probably more than offset the cost of additional boiler units for spares.

The essential features in furnace design for this cla.s.s of fuel are ample combustion s.p.a.ce and a length of gas travel sufficient to enable the gases to be completely burned before the boiler heating surfaces are encountered. Experience has shown that better results are secured where the fuel is burned on a hearth rather than on grates, the objection to the latter method being that the air for combustion enters largely around the edges, where the fuel pile is thinnest. When burned on a hearth the air for combustion is introduced into the furnace through several rows of tuyeres placed above and symmetrically around the hearth. An arrangement of such tuyeres over a grate, and a proper manipulation of the ashpit doors, will overcome largely the objection to grates and at the same time enable other fuel to be burned in the furnace when necessary. This arrangement of grates and tuyeres is probably the better from a commercially efficient standpoint. Where the air is admitted through tuyeres over the grate or hearth line, it impinges on the fuel pile as a whole and causes a uniform combustion.

Such tuyeres connect with an annular s.p.a.ce in which, where a blast is used, the air pressure is controlled by a blower.

All experience with this cla.s.s 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 baga.s.se 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 baga.s.se 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 baga.s.se 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 s.p.a.ce C through which the amount of air is controlled. Above the pit the furnace widens out to form a combustion s.p.a.ce D which has a cylindrical or spherical roof with its top ordinarily from 11 to 13 feet above the floor. The gases pa.s.s from this s.p.a.ce 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 s.p.a.ce 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 cla.s.s of fuel deposits a considerable quant.i.ty of dust, which if not removed promptly will fuse into a hard gla.s.s-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 Babc.o.c.k & Wilc.o.x boilers using fuel of this character.

TABLE 45

TESTS OF BABc.o.c.k & WILc.o.x BOILERS WITH GREEN BAGa.s.sE ____________________________________________________________________ | 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 a.n.a.lysis { O | Per Cent | 5.9 | 7.6 | 8.2 | 6.9 | | CO | Per Cent | 0.0 | 0.0 | 0.0 | 0.0 | | Baga.s.se per Hour as Fired | Pounds | 4980 | 4479 | 5040 | 5586 | | Moisture in Baga.s.se | Per Cent |52.39 |52.93 |51.84 |51.71 | | Dry Baga.s.se per Hour | Pounds | 2371 | 2108 | 2427 | 2697 | | Dry Baga.s.se 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.[43] 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 a.n.a.lysis 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 s.p.a.ce, large areas of heated brickwork radiating to the fuel bed, and draft sufficient for high combustion rates. The ratings obtainable with this cla.s.s 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.

[Ill.u.s.tration: 686 Horse-power Babc.o.c.k & Wilc.o.x Boiler and Superheater in Course of Erection at the Quincy, Ma.s.s., Station of the Bay State Street Railway Co.]

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 const.i.tuents 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 quant.i.ties of moisture, sulphur, nitrogen, a.r.s.enic, 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|Babc.o.c.k & Wilc.o.x Co. | |California, Bakersfield | | | | |.975| | |17600|Wade | |California, Bakersfield | | |1.30| |.992| | |18257|Wade | |California, Kern River | | | | |.950|140| |18845|Babc.o.c.k & Wilc.o.x Co. | |California, Los Angeles | | |2.56| | | | |18328|Babc.o.c.k & Wilc.o.x Co. | |California, Los Angeles | | | | |.957|196| |18855|Babc.o.c.k & Wilc.o.x Co. | |California, Los Angeles | | | | |.977| | .40 |18280|Babc.o.c.k & Wilc.o.x Co. | |California, Monte Christo| | | | |.966|205| |18878|Babc.o.c.k & Wilc.o.x 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[44]| | |1.40 |17871|Babc.o.c.k & Wilc.o.x Co. | |California |81.52|11.51| .55|6.92[44]| |230| |18667|U.S.N. Liquid Fuel Board| |California | | | .87| | | | .95 |18533|Blasdale | |California | | | | |.891|257| |18655|Babc.o.c.k & Wilc.o.x Co. | |California | | |2.45| |.973| |1.50[45]|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[44]| | | |19060|Denton | |Texas, Beaumont |86.1 |12.3 |1.60| |.942| | |20152|Sparkes | |Texas, Beaumont | | | | |.903|222| |19349|Babc.o.c.k & Wilc.o.x Co. | |Texas, Sabine | | | | |.937|143| |18662|Babc.o.c.k & Wilc.o.x 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|Babc.o.c.k & Wilc.o.x 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 a.n.a.lysis of an average sample be, carbon 84 per cent, hydrogen 14 per cent, oxygen 2 per cent, and a.s.suming that the oxygen is combined with its equivalent of hydrogen as water, the a.n.a.lysis 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.

The flash point of crude oil is the temperature at which it gives off inflammable gases. While information on the actual flash points of the various oils is meager, it is, nevertheless, a question of importance in determining their availability as fuels. In general it may be stated that the light oils have a low, and the heavy oils a much higher flash point. A division is sometimes made at oils having a specific gravity of 0.85, with a statement that where the specific gravity is below this point the flash point is below 60 degrees Fahrenheit, and where it is above, the flash point is above 60 degrees Fahrenheit. There are, however, many exceptions to this rule. As the flash point is lower the danger of ignition or explosion becomes greater, and the utmost care should be taken in handling the oils with a low flash point to avoid this danger. On the other hand, because the flash point is high is no justification for carelessness in handling those fuels. With proper precautions taken, in general, the use of oil as fuel is practically as safe as the use of coal.

Gravity of Oils--Oils are frequently cla.s.sified according to their gravity as indicated by the Beaume hydrometer scale. Such a cla.s.sification is by no means an accurate measure of their relative calorific values.

Petroleum as Compared with Coal--The advantages of the use of oil fuel over coal may be summarized as follows:

1st. The cost of handling is much lower, the oil being fed by simple mechanical means, resulting in,

2nd. A general labor saving throughout the plant in the elimination of stokers, coal pa.s.sers, ash handlers, etc.