Part 43

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 classified according to their gravity as indicated by the Beaume hydrometer scale. Such a classification 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 passers, ash handlers, etc.

3rd. For equal heat value, oil occupies very much less space than coal. This storage space may be at a distance from the boiler without detriment.

4th. Higher efficiencies and capacities are obtainable with oil than with coal. The combustion is more perfect as the excess air is reduced to a minimum; the furnace temperature may be kept practically constant as the furnace doors need not be opened for cleaning or working fires; smoke may be eliminated with the consequent increased cleanliness of the heating surfaces.

5th. The intensity of the fire can be almost instantaneously regulated to meet load fluctuations.

6th. Oil when stored does not lose in calorific value as does coal, nor are there any difficulties arising from disintegration, such as may be found when coal is stored.

7th. Cleanliness and freedom from dust and ashes in the boiler room with a consequent saving in wear and tear on machinery; little or no damage to surrounding property due to such dust.

The disadvantages of oil are:

1st. The necessity that the oil have a reasonably high flash point to minimize the danger of explosions.

2nd. City or town ordinances may impose burdensome conditions relative to location and isolation of storage tanks, which in the case of a plant situated in a congested portion of the city, might make use of this fuel prohibitive.

3rd. Unless the boilers and furnaces are especially adapted for the use of this fuel, the boiler upkeep cost will be higher than if coal were used. This objection can be entirely obviated, however, if the installation is entrusted to those who have had experience in the work, and the operation of a properly designed plant is placed in the hands of intelligent labor.

TABLE 47

RELATIVE VALUE OF COAL AND OIL FUEL

+------+--------+-------+-----------------------------------------------+ |Gross | Net | Net | Water Evaporated from and at | |Boiler| Boiler |Evap- | 212 Degrees Fahrenheit per Pound of Coal | |Effic-|Effici- |oration+-----+-----+-----+-----+-----+-----+-----+-----+ | iency|ency| from | | | | | | | | | | with | with |and at | | | | | | | | | | Oil | Oil | 212 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | | Fuel | Fuel |Degrees| | | | | | | | | | | |Fahren-| | | | | | | | | | | | heit +-----+-----+-----+-----+-----+-----+-----+-----+ | | | per | | | | | Pound | Pounds of Oil Equal to One Pound of Coal | | | |of Oil | | +------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ | 73 | 71 | 13.54 |.3693|.4431|.5170|.5909|.6647|.7386|.8124|.8863| | 74 | 72 | 13.73 |.3642|.4370|.5099|.5827|.6556|.7283|.8011|.8740| | 75 | 73 | 13.92 |.3592|.4310|.5029|.5747|.6466|.7184|.7903|.8621| | 76 | 74 | 14.11 |.3544|.4253|.4961|.5670|.6378|.7087|.7796|.8505| | 77 | 75 | 14.30 |.3497|.4196|.4895|.5594|.6294|.6993|.7692|.8392| | 78 | 76 | 14.49 |.3451|.4141|.4831|.5521|.6211|.6901|.7591|.8281| | 79 | 77 | 14.68 |.3406|.4087|.4768|.5450|.6131|.6812|.7493|.8174| | 80 | 78 | 14.87 |.3363|.4035|.4708|.5380|.6053|.6725|.7398|.8070| | 81 | 79 | 15.06 |.3320|.3984|.4648|.5312|.5976|.6640|.7304|.7968| | 82 | 80 | 15.25 |.3279|.3934|.4590|.5246|.5902|.6557|.7213|.7869| | 83 | 81 | 15.44 |.3238|.3886|.4534|.5181|.5829|.6447|.7125|.7772| +------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ | | | Net | | | | |Evap- | | | | |oration| | | | | from | | | | |and at | | | | | 212 | Barrels of Oil Equal to One Ton of Coal | | | |Degrees| | | | |Fahren-| | | | | heit | | | | | per | | | | |Barrel | | | | |of Oil | | +------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ | 73 | 71 | 4549 |2.198|2.638|3.077|3.516|3.955|4.395|4.835|5.275| | 74 | 72 | 4613 |2.168|2.601|3.035|3.468|3.902|4.335|4.769|5.202| | 75 | 73 | 4677 |2.138|2.565|2.993|3.420|3.848|4.275|4.703|5.131| | 76 | 74 | 4741 |2.110|2.532|2.954|3.376|3.798|4.220|4.642|5.063| | 77 | 75 | 4807 |2.082|2.498|2.914|3.330|3.746|4.162|4.578|4.994| | 78 | 76 | 4869 |2.054|2.465|2.876|3.286|3.697|4.108|4.518|4.929| | 79 | 77 | 4932 |2.027|2.433|2.838|3.243|3.649|4.054|4.460|4.865| | 80 | 78 | 4996 |2.002|2.402|2.802|3.202|3.602|4.003|4.403|4.803| | 81 | 79 | 5060 |1.976|2.371|2.767|3.162|3.557|3.952|4.348|4.743| | 82 | 80 | 5124 |1.952|2.342|2.732|3.122|3.513|3.903|4.293|4.683| | 83 | 81 | 5187 |1.927|2.313|2.699|3.085|3.470|3.856|4.241|4.627| +------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+

Many tables have been published with a view to comparing the two fuels. Such of these as are based solely on the relative calorific values of oil and coal are of limited value, inasmuch as the efficiencies to be obtained with oil are higher than that obtainable with coal. Table 47 takes into consideration the variation in efficiency with the two fuels, but is based on a constant calorific value for oil and coal. This table, like others of a similar nature, while useful as a rough guide, cannot be considered as an accurate basis for comparison. This is due to the fact that there are numerous factors entering into the problem which affect the saving possible to a much greater extent than do the relative calorific values of two fuels. Some of the features to be considered in arriving at the true basis for comparison are the labor saving possible, the space available for fuel storage, the facilities for conveying the oil by pipe lines, the hours during which a plant is in operation, the load factor, the quantity of coal required for banking fires, etc., etc. The only exact method of estimating the relative advantages and costs of the two fuels is by considering the operating expenses of the plant with each in turn, including the costs of every item entering into the problem.

Burning Oil Fuel--The requirements for burning petroleum are as follows:

1st. Its atomization must be thorough.

2nd. When atomized it must be brought into contact with the requisite quantity of air for its combustion, and this quantity must be at the same time a minimum to obviate loss in stack gases.

3rd. The mixture must be burned in a furnace where a refractory material radiates heat to assist in the combustion, and the furnace must stand up under the high temperatures developed.

4th. The combustion must be completed before the gases come into contact with the heating surfaces or otherwise the flame will be extinguished, possibly to ignite later in the flue connection or in the stack.

5th. There must be no localization of the heat on certain portions of the heating surfaces or trouble will result from overheating and blistering.

The first requirement is met by the selection of a proper burner.

The second requirement is fulfilled by properly introducing the air into the furnace, either through checkerwork under the burners or through openings around them, and by controlling the quantity of air to meet variations in furnace conditions.

The third requirement is provided for by installing a furnace so designed as to give a sufficient area of heated brickwork to radiate the heat required to maintain a proper furnace temperature.

The fourth requirement is provided for by giving ample space for the combustion of the mixture of atomized oil and air, and a gas travel of sufficient length to insure that this combustion be completed before the gases strike the heating surfaces.