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this cooling device the steam is again converted into water. The apparatus performing this function is known as a condenser, there being two general classes: surface condensers and jet condensers.
In the surface condenser the steam from the turbine and the cooling water from a nearby source of supply do not come into direct contact, but the cooling water is passed through inclosed tubes around which the steam from the turbine or power unit is made to pass. This type of condenser is used where large quantities of water are available for cooling purposes but not for steaming purposes. Thus the use of salt water, the only abundant supply available for ocean-going steamships and large power plants situated near the ocean, makes a condenser of the surface type imperative for such installation.
In the jet condenser the supply of cooling water is allowed to mingle with the steam as it drops from the turbine or power unit and thus the steam is at once condensed into water. The water from the jet, if the supply is pure, may be used in the hot-well for steam purposes.
Wet Vacuum Pumps.-The condensed steam, now in the form of water, is pumped from the condenser back again into the hotwell by means of what is known as the wet vacuum pump. This pump may be either a reciprocating or rotary pump, but in general the rotary type seems to have the preference. Thus the entire cycle for the water is traced from the make-up tank or hot-well through the boiler and power unit, and back again to the hot-well.
Dry Vacuum Pumps.-The condenser also has a dry vacuum pump in order to remove from the steam space within any air which may have been trapped from the steam generated in the boiler. This pump is nothing more nor less than an ordinary air compressor so designed that it will take air at a very low pressure and compress it up to atmospheric pressure, thus pumping, as it were, into the outer atmosphere such air as may have been entrapped in the condenser.
CIRCULATING WATER CYCLE
From the description of the working of the condenser it is seen that cooling water is necessary to convert the steam in the condenser back again into water. This cooling supply is known
as circulating water, which is usually taken through pipes from some large natural lake or river or even the ocean and forced by means of reciprocating or centrifugal pumps through the condenser back again into the open. The water in its journey is raised in temperature in the surface condenser system from 15 to 20°F. above its entering condition.
THE OIL CYCLE
Of general interest to boiler testing and operation is the cycle employed in the utilization of crude petroleum as a fuel. Let us then briefly trace the journey the oil makes through the modern power plant.
In the larger installations the oil is sidetracked from the main railway line in specially designed cars or barges for its easy conveyance and handling. An oil heater, consisting of a coil through which steam is passing, is lowered into the car in order to warm the oil as it is drawn, thus making its transfer considerably easier. By means of a pump this oil is then taken into a storage tank which may be of wood, steel, or concrete, depending upon the permanence of design thought necessary. From this storage tank the oil is pumped through oil heaters, the exhaust from the pumps in many cases being utilized in still further heating oil before it reaches the burner or atomizer.
An atomizer is a device used to vaporize or spray the oil into the furnace in fine globules or particles. This is accomplished by means of steam, air, or some mechanical contrivance. Immediately upon its being sprayed into the furnace carefully designed air regulating devices admit sufficient air from below to cause perfect combustion. The heat thus liberated from the oil due to its burning with the oxygen is caused to flow in and around
numerous tubes through which water is passing and thus this water is converted into steam. After passing these tubes the heated flue gases brought to life by the burning of the oil with the entering air are then conducted through the chimney out into the atmosphere.
An interesting detail in the boiler plant is the automatic system of firing employed to minimize labor and improve efficiency in burning the oil. The Moore patent fuel oil regulating system which, from one central point, controls the oil supply, the atomizing steam and the amount of air to each furnace, is an interesting example.
FIG. 9.-Moore steam to burner regulator.
This regulator is actuated by the pressure from the main steam header so that any variation in steam requirements will cause a corresponding change in the amount of oil fired, due to an increase or decrease in the steam supply to the oil pumps and atomizers. Any fluctuation in steam pressure operates a governor whose power arm controls a bleeder valve on the oil pump discharge line, thus cutting off the oil supply if the steam pressure is too high and increasing it if too low. Any change in pressure in the oil main, in turn, controls the amount of steam for atomizing and of air for burning the oil.
It is found that a simple straight line relationship exists between the amount of steam required for atomizing the oil and the
amount of oil burned. Two diaphragms are employed to balance the pressures in the oil main and in the steam main connected to the burners. Any difference in oil pressure operates a rotary chronometer valve in the steam main through the medium of a fulcrum, water motor and lever connecting rod. Likewise the variance in oil pressure actuates a counterweighted rock shaft which moves the dampers so as to vary the amount of air admitted for combustion.
Thus it is seen in this brief description that by using crude oil as fuel three main cycles of operation are synchronously carried on in the modern power plant. Briefly summarizing, these are as follows:
Water is taken through the boiler, converted into steam and passed through a driving mechanism, after which the steam is reconverted into water and this water again passed through the boiler. Simultaneously with this action water is being pumped through the circulating system to bring about the conversion of the steam from the power unit into water. Again oil in a finely atomized or gaseous state is being fed through pipes into the furnace, where it immediately combines with the proper quantity of oxygen from the entering air, and thus sufficient heat is liberated from the oil to evaporate the water supply of the boiler into steam for power generation.