One of the largest power stations in the world, in which electricity is produced by steam turbines, has been built on land reclaimed from the waters of Lake Michigan, North America
STATE LINE POWER STATION is so called because it lies across the boundary between the States of Indiana and Illinois, at Hammond, near Chicago. Lake Michigan is the source of the water which is turned into steam to drive the turbines. About 73 acres of land were reclaimed from the lake to form the site of the power station.
WITH the growth of Chicago along the shores of Lake Michigan, the demand for electricity has constantly increased, and power stations have been built, one after another, to meet the Requirements of a vast and steadily increasing population. One of Nature’s gifts is the mighty force of steam that can split the earth’s crust and blast to the skies vast masses of molten rock from the depths of a giant volcano. The power of steam can be controlled, and at Chicago’s great State Line Power Station - one of the largest in the world - a man-made volcano of steam roars through a series of giant turbines, generating light and power for hundreds of thousands of people.
The men who planned this great steam-driven power house made provision for its ultimate expansion to a capacity of one million kilowatts - equivalent in mechanical energy to over 1,330,000 horse-power.
The site chosen for the vast undertaking was at Hammond, on Lake Michigan, on the boundary between the States of Indiana and Illinois. The great power station, with its coal dumps and sidings, was planned to be built out over Lake Michigan. The first task was the reclamation from the lake of a great rectangle of land, nearly 3,000 feet long and 73 acres in area. The station buildings and equipment were built on concrete foundations laid upon timber piling - great baulks of wood driven deep into the ground. The heaviest machinery, however, was carried on steel caissons sunk to the solid rock of the lake bed.
On the land side of this huge artificial island are sidings running parallel with the railroads that skirt the shores of the lake. Transfer of the great coal cars from the railroads to the station sidings is a comparatively simple matter, despite the size of the loads - a twelve-wheeled “gondola” on United States railways holds 120 tons of coal. Most of the marshalling of cars in the power station sidings is done by an electric locomotive weighing 120 tons. The supply of coal from the sidings to the power house is a more complex matter and the equipment is amazingly efficient. A loaded gondola is placed ready for its final journey to the unloading machinery. In front of the car stretches an incline or ramp about a hundred yards long, leading up to a “dumper”. Between the track rails on the ramp is an inner set of rails, of narrower gauge, on which runs a massive four-wheeled truck or bogie, known as a “mule”. The mule is hauled by a cable, which is operated by an electric motor placed below ground about half-way up the ramp.
The mule emerges from the bottom end of a long pit between the rails. Part of the roof of this pit is hinged to form a gate or short ramp leading to the main incline. When in position behind the gondola, the mule is set in motion by the hauling engine and the coal begins its journey up the incline to the dumper. When the mule and coal car have reached the top of the ramp, the coal car already there from the previous haul is pushed off to the dumper and the mule is hauled down through an upper gate, along the pit between the outer rails, and so under the next car that has already been placed in position by the electric locomotives. By this means a constant stream of coal cars - about twenty an hour - runs up from the sidings to the dumper.
ROTARY CAR DUMPER, or tippler, at State Line Power Station, Chicago. Large trucks or gondolas of coal are pushed up an incline on to the platform of the dumper. The dumper is then rotated so that the contents of the truck are emptied into a hopper below.
This machine resembles a huge steel drum and is 62 feet long. The drum portion is more than 25 feet in diameter, and its function is to receive a gondola containing 120 tons of coal and to turn it upside down. The drum or cradle, in common with the mule, is operated electrically, and its action, once set in motion, is entirely automatic. When emptied and turned right side up, the coal car is pushed off down a slope to sidings. Its progress is controlled by track retarders, worked by compressed air, that grip the car wheels.
The coal falls into a large hopper that feeds it on to a conveyer belt, 42 in. wide, which carries it at a speed of 360 feet a minute to the breaker house. Here the coal is broken up by a battery of rotating drums, each of which is capable of breaking 250 tons of coal an hour. When it is broken the coal travels on another conveyer to the top of a tower, about 100 feet high, from which other conveyers carry it, high overhead, to the boiler house. Not all of the broken coal is taken direct to the boiler house; some of it is stored. One storage ground accommodates 125,000 tons of coal.
An interesting feature of the equipment that reclaims coal from storage is the “weightometer”, which records automatically the weight of the coal and the speed at which it is travelling, on the conveyer, in tons per hour.
Coal is the life-blood of the whole vast enterprise - it must be visualized as a great black torrent rushing headlong to a series of enormous furnaces.
There is, however, another stage through which the hard black coal must pass before its transformation into a, sea of white hot flame. The coal is ground into a fine powder. The machinery that performs this task and the bunkers that feed the pulverizing mills are housed within the power station.
The coal bunkers and pulverizing mills are housed in the boiler room, which is 211 feet long, 198 feet wide and 104 feet high to the roof. There are six boilers serving the group of machines known as Unit No. 1. Each boiler is about 70 feet high, 44 feet wide and 23 feet from back to front. The two chimneys are of steel, lined with fireproof material, and are 250 feet high.
The adjoining turbine room measures 213 feet by 134 feet and is 94 feet high. Alongside are the operating and battery rooms and the switch house. The turbine room is on the land side of the boiler room. On the opposite side of the boiler room is the ash sluice house, the function of which is the disposal of ashes from the boiler room. Some distance on the farther side of the ash house is a building known as the crib house, where the circulating pumps are accommodated. These pumps take water from a forebay on Lake Michigan for cooling the condensers in the turbine room.
High above the roof of the boiler room runs the covered gantry which houses the coal conveyer, and immediately below this are the bunkers, two for each boiler, with a total coal capacity of over 4,000 tons. The bottom of each bunker is divided into two compartments, with chain operated gates, and pipes leading down to a coal scale or measuring device. Below the coal scale are the electrically operated pulverizing mills that reduce the coal to the consistency of fine flour.
COAL-HANDLING PLANT at State Line Power Station is ingenious in design and expeditious in action. Coal emptied from the dumper (left) is fed from a hopper on to a 42-in. belt conveyer which carries it up to the breaker house at a speed of 360 feet a minute. Here the coal is broken up by a battery of rotating drums, each with a capacity of 250 tons an hour. The broken coal is then carried up to a tower, about 100 feet high, by another conveyer. Thence it is carried to the boiler house or to the storage grounds.
The pulverized coal is then pumped from the mills and fed into the furnaces by a blast of air. There are two coal pumps or exhausters to each boiler; they supply eight burners. The forced draught is supplied to the furnaces by batteries of electric fans arranged on the floor above the boilers, 85 ft. 6 in. above ground level.
The pulverized coal burns with an intensely hot white flame - a veritable whirlpool of fire, for it is spun round as it burns.
The boilers are designed for a pressure of 800 lb. and operated at 650 lb. per square inch at the turbines. Each boiler has a total heating surface of 10,294 square feet. The fifty-two vertical sections of each boiler comprise nests of inclined tubes. Enclosed by the tubes is a combustion chamber 34 ft. 7 in. long, 19 ft. 9 in. wide and 29 feet high. Inside that great cavern the blast of white hot fire surges and eddies, imparting its fierce heat to the water in the tubes and generating the vast volumes of steam demanded by the turbines.
Over the tubes in each boiler is arranged a superheater which raises the temperature of the steam to 750° Fahrenheit.
Adjacent to each boiler is an economizer, comprising nests of tubes with a heating surface of nearly 20,000 square feet, and in these the feed water for the boiler is brought to a high temperature. The hot gases then pass through special heaters that raise the temperature of the air supplied direct to the furnace and to the pulverizers by the forced draught fans. The air is heated to a temperature of 520° Fahr. and now another set of fans - induced draught fans - draws the gases on their way through the heaters. Every boiler is provided with two induced draught fans, each driven by an electric motor of 350 horse-power.
When the furnace gases have yielded up as much heat as might reasonably be expected, they have one more duty to perform before passing into the long rectangular flue that connects up with the two great chimneys. The furnace gases have to give up the particles of unburnt dust and grit that would otherwise be flung in vast clouds from the chimney tops to contaminate the lake and the city along its shores.
The dust collectors are large, interesting and of several different types - even in this one power unit. The first three boilers are equipped with dust collectors known as electric precipitators, in which the particles of dust are removed by electricity at 55,000 to 75,000 volts. A special substation supplies current to the precipitators.
Boiler No. 4 is provided with dust collectors that depend for their action on centrifugal force. The gases are whirled round at high speed in a tapering casing and as the particles of solid matter are flung outwards they fall to the bottom of the container, from which they are later removed. The fifth boiler has two dust collectors that break up the gas stream by baffles. These form vortices and so cause the dust to be deposited for removal by a screw conveyer.
The remaining boiler has two dust removers of particularly interesting design. The gases pass through perforations in a large number of corrugated plates, hung vertically about ⅜-in. apart. Dust collects on the plates and to remove the deposit, sections of the plates are lifted periodically and dropped suddenly for a distance of half an inch. The jarring shakes off the grit and dust, which is removed by a screw conveyer, resembling a domestic mincing machine on a large scale.
Ash is another waste product of the furnaces and must be disposed of. Beneath each furnace is an ash pit fitted with water sprays for quenching purposes. The quenched ashes drop through doors on to a sloping surface, during which process they are again sprayed with water. The ashes then fall into a sluicing trough and are Washed down to a deep concrete pit in the ash house. Surplus water drains off this pit, over a weir, into the lake and the wet ashes are loaded into cars by a grab and overhead crane in the ash house.
ON THE INCLINE leading up to the dumper the 120-tons coal trucks are pushed by a four-wheeled truck or bogie known as a mule. The mule is hauled by a cable operated by an electric motor placed below ground, about half-way up the ramp.
Elaborate electrical and mechanical devices control the operations of the huge boilers. The output of the boilers is governed by regulating the supply of fuel and air to the furnaces, and the whole process is entirely automatic. A master controlling device in the boiler room is connected with the main steam pipe, and changes of pressure due to variations in load on the machinery operate an electric circuit that effects the necessary adjustments.
It is in this way that coal is turned first into black dust, then into white flame giving its heat to water and so producing steam. The steam from the State Line boilers, at a pressure of 650 lb. per sq. in., and at a temperature of 750° Fahr., is a gas which might be called a man-made volcano.
In the turbine room, housing Unit No. 1, at the State Line Station man uses the wonderful power of steam that has been placed at his disposal.
There are three turbines, one high-and two low-pressure. The high-pressure turbine occupies a central position in the turbine room, and is over twenty-four feet long. It comprises an enormous steel casing, on the inside of which are rows of steel blades, of curved section, pointing inwards towards a central drum or rotor. The rotor is fitted with corresponding blades, arranged in spoke fashion, and these revolve between the fixed blades in the casing. The shape of these blades is of great importance and their design was the work of the famous British engineer Sir Charles Parsons.
There are thousands of blades in the high-pressure turbine and they increase in size from the steam inlet end of the machine. This increase allows for the expansion of the steam as it passes through the turbine, in which there are seventeen stages of expansion.
Elaborate Governing Gear
The blast of hot steam enters the turbine casing and is directed by special nozzles against the first row of moving blades. It then impinges on the first row of fixed blades, which causes it to pass to the second row of moving blades. This action is repeated throughout the length of the turbine, and the rotor is spun at enormous speed, driving with it the 76,000-kilowatts generator to which it is coupled. An elaborate governing gear controls the speed of the turbine, and an array of ingenious mechanical devices is used to ensure efficiency and safety in the turbine’s operation.
When the steam leaves the high-pressure turbine it has given up a large proportion of its energy and the pressure has dropped to 100 lb. per sq. in. The steam is therefore reheated to 500° Fahr. and is ready for the next stage of its journey—to the two low-pressure turbines that flank the high-pressure unit.
With the decrease in the steam’s pressure, provision must be made for a great increase in its volume, and the two low-pressure units are of enormous dimensions - the floor space occupied by either measures over 70 feet by 50 feet.
The low-pressure turbines are similar in general construction to the high-pressure machine; but the steam, instead of entering at one end of the casing, is admitted at the centre and rushes along to the ends. On either side of the steam inlet there are eleven stages of expansion. At either end of each low-pressure turbine is a huge “breeches pipe” that takes the exhaust steam to the condenser. There are four condensers to each low-pressure unit. The condensers are over 25 feet high and 12 feet in diameter, and about half of their height is below the level of the turbine room floor. Each condenser is provided with nests of tubes, over 20 feet long, giving a cooling surface of 22,000 square feet. Cooling water is supplied to the condensers through concrete tunnels that lead under the boiler room to the crib house.
The speed of the three turbines is 1,800 revolutions a minute and the main generators supply current at a pressure of 22,000 volts. This voltage is “stepped up” by transformers to the high pressures - 33,000, 66,000 and 132,000 volts - required for economical transmission to the outlying districts of Chicago and to the States of Indiana and Illinois.
THE 208,000-KILOWATTS TURBINE SET in the turbine room of the State Line Power Station. The set comprises one high-pressure and two low-pressure turbo-alternators. The high-pressure machine has a rating of 76,000 kilowatts and generates at 22,000 volts. The low-pressure units generate at the same voltage and each has a capacity of 62,000 kilowatts. On the shaft of each low-pressure machine are an exciter and a 4,000-kilowatts machine generating at 2,300 volts.