by the use of a prewarming coil placed in the flue. A reduction of 200° F. in the temperature of flue gases under average conditions corresponds to a 10 to 15 per cent saving in fuel.

Although perfect combustion practically can not be obtained when only the amount of air theoretically required is used, the excess quantity should not exceed 50 per cent with an oil fuel and a correctly designed furnace.

These batteries are constructed to permit preheating the air used for combustion, though no advantage is taken of this feature. If the air used were heated 100° F. by heat otherwise wasted in its travel around the air space of the batteries, the saving in fuel would be more than 5 per cent.

Briefly, the figures given show some of the more important fuel losses that might be corrected but are overlooked in the operation of many plants. Attending to these losses would materially increase the over-all efficiency.

The importance of frequent analysis of flue gases in oil-burning apparatus can not be too strongly emphasized.

POSSIBLE CHANGES AND IMPROVEMENTS.

With the method used of heating in fractions, it would seem that the fractions thus obtained should be fractionally cooled by the installation of dephlegmators on each vapor line, and the heavier distillates separated in the first running. The vapors coming from each dephlegmator could then each constitute a distinct product requiring only slight treatment in the steam stills. The result would be a saving in fuel and a reduction in plant area, as the steam-still capacity could be reduced. The capacity of the crude batteries would not be affected.

The crude settings should incorporate some type of prewarmer to utilize the waste flue gases and reduce the stack temperature. It would be possible to pass these gases on their way to the stack through a tubular boiler containing the entering oil from the heat exchangers, thus materially reducing the temperature of the flue gases. The heat recovered by the oil would probably obviate the necessity of firing the first still, which could then be used as a separating chamber only for the vapors evolved.

The rate of heat transfer in the exchangers is unusually high and justifies the effort to embody correct engineering principles. The velocities of the fluid are high, and the cross-sectional areas of the oil spaces small, both conditions being necessary for rapid heat exchange. By causing the entering oil to flow through the 2-inch pipes, all heat acquired by it is retained for useful duty, whereas the heat radiated to the air by the residuum probably does not lessen appreciably the amount transferred to the oil, and does assist in cooling the residue before it passes to storage.

MISCELLANEOUS TOPPING PLANTS.

PLANT CONSTRUCTED AFTER DESIGN OF A. F. L. BELL. GENERAL DESCRIPTION.

A topping plant of the Bell design has been running successfully for several years at Gaviota, Cal. In 1911-12 two batteries of such plants were constructed for the large refinery at Avon, Cal., already mentioned. They are the most recent installations of this type, and therefore description of the type is confined to the Avon plant.

The refinery handles about 20,000 barrels of 26° B. oil (specific gravity, 0.8974) daily, which is supplied by two 8-inch oil lines from the Fresno and Kern County fields. The toppers normally handle 3,500 barrels each, the remainder being topped in two batteries of conventional stills, described elsewhere.

The topping plant in general consists of two batteries of retorts each containing several banks of 4-inch pipes arranged as a continuous coil for the flow of the oil under fire. Each battery feeds a separating tower, the vapors from each tower in turn being led to two box condensers connected in parallel. In addition, each battery is provided with a heat exchanger for the exchange of heat between ingoing oil and outgoing residuum.

The first-run distillates are rerun through four combination steam and fire stills and two steam stills, each of which is provided with condensers of the same type and size as those used on the crude set.

Each still is equipped with a vapor-separating tower similar to those of the topping set. The interior construction, however, differs, and is described in the text following.

DETAILED DESCRIPTION OF APPARATUS.

RETORTS.

Plates IV, V, VI, and VII show the construction of these retorts. Data on apparatus shown in Plate IV.

Each retort battery consists of three parallel adjacent furnaces 5 feet wide by 28 feet long, constructed of 13-inch red-brick walls 5 feet high. These walls are faced with fire brick for 10 feet from the front end of the furnaces. The front wall of the battery is 7 feet 7 inches high and 17 inches thick, of red brick faced with fire brick to the top of the division walls between the furnaces. The rear wall is 8 feet 9 inches high and 13 inches thick, of red brick. Three rows