ADVANTAGES AND DISADVANTAGES OF LIQUID FUEL From the foregoing it becomes evident that there are certain advantages which oil fuel has over coal when burned under boilers. These advantages may be summed up as follows : • (1) It is often found that it is desirable to push boilers far beyond their normal rating for a shorter or longer period of time. Tests that have been made by the United States Navy Depart ment with fuel oil show that the heat absorptive powers of boilers is very great, and that this pushing can be accomplished with only a small drop in efficiency. In their tests with fuel oil the evapora tion per square foot of heat surface has been increased from three pounds of water from and at 212 degrees F. to fifteen pounds of water. During this increase in rating, which is 500 per cent of the normal rating, there was a loss in efficiency of only two per cent. Boilers can be,pushed twice as rapidly with oil as they can with coal.
(2) The loss of heat up the stack is diminished owing to the smaller amount of air necessary for the complete combustion of oil over its equivalent in coal.
(3) A more equal heat distribution in the combustion cham ber is possible inasmuch as the fire box doors do not have to be open for firing and as a consequence there is higher efficiency.
(4) The cost of handling fuel is reduced because it is done mechanically by pumps when fuel oil is used and the reduction in the number of firemen is in the propOrtion of five or six to one.
(5) A large increase in steam capacity is possible. The grate area absolutely limits the amount of coal that can be burned efficiently, whereas the amount of oil that can be burned efficiently is not affected by the grate size. The output of boilers can be
augmented by 30 to 50 per cent by substituting oil for coal.
(6) Fires can be started and stopped instantly as required, avoiding standby losses, and this required head of steam can be rapidly obtained from a•cold boiler and can be maintained with the utmost regularity. No fuel is lost through banking.
(7) The storage tanks for fuel oil can be located where desired, while coal bins must be near the boilers.
(8) The life of the boilers is prolonged because ,in hand fired coal furnaces a combination of stresses on the furnace plates occurs when the furnace doors are frequently. opened.
(9) Fuel oil can be burned to smokeless combustion with out sparks.
While fuel oil will undoubtedly effect the economies claimed . for it, there are several disadvantages attendant on its use. These may be enumerated as follows : (1) Fire risk is increased and city ordinances, while becom ing less stringent, still look with disfavor on its use.
(2) Under certain conditions-the vapor from fuel oil forms an explosive mixture with air.
(3) Nearly all fuel oil burners make an objectionable roar ing sound.
(4) Auxiliary apparatus is necessary to start an oil fire or to maintain it, or both.
(5) Fuel oil has a tendency to leak through valves and joints in the system.