As it was impossible to drive these piles across the old timber crib which formed the old dock front, the latter was cut through by a pneumatic caisson of wooden-stave construction, which formed part of one side of the cofferdam. At the river end of the cofferdam the rock was so deep that the concrete could not be carried down to its surface, and the tunnel section was built on a foundation of piles driven to the rock and cut off by a steam saw 19-1/2 feet below mean hightide. This section of the tunnel was built in a 65 x 48-foot floating caisson 24 feet deep. The concrete was rammed in it around the moulds and the sides were braced as it sunk. After the tunnel sections were completed, the caisson was sunk, by water ballast, to a bearing on the pile foundation.
Adjacent to the condensing water conduits is the 10 x 15-foot rectangular concrete tunnel, through which the underground coal conveyor is installed between the sh.o.r.e end of the pier and the power house.
[Sidenote: _Steel Work_]
The steel structure of the power house is independent of the walls, the latter being self-supporting and used as bearing walls only for a few of the beams in the first floor. Although structurally a single building, in arrangement it is essentially two, lying side by side and separated by a brick division wall.
There are 58 transverse and 9 longitudinal rows of main columns, the longitudinal s.p.a.cing being 18 feet and 36 feet for different rows, with special bracing in the boiler house to accommodate the arrangement of boilers. The columns are mainly of box section, made up of rolled or built channels and cover plates. They are supported by cast-iron bases, resting on the granite capstones of the concrete foundation piers.
Both the boiler house and the engine house have five tiers of floor framing below the flat portion of the roof, the three upper tiers of the engine house forming galleries on each side of the operating room, which is clear for the full height of the building.
The boiler house floors are, in general, framed with transverse plate girders and longitudinal rolled beams, arranged to suit the particular requirements of the imposed loads of the boilers, economizers, coal, etc., while the engine-room floors and pipe and switchboard galleries are in general framed with longitudinal plate girders and transverse beams.
There are seven coal bunkers in the boiler house, of which five are 77 feet and two 41 feet in length by 60 feet in width at the top, the combined maximum capacity being 18,000 tons. The bunkers are separated from each other by the six chimneys s.p.a.ced along the center line of the boiler house. The bottom of the bunkers are at the fifth floor, at an elevation of about 66 feet above the bas.e.m.e.nt. The bunkers are constructed with double, transverse, plate girder frames at each line of columns, combined with struts and ties, which balance the outward thrust of the coal against the sides. The frames form the outline of the bunkers with slides sloping at 45 degrees, and carry longitudinal I-beams, between which are built concrete arches, reinforced with expanded metal, the whole surface being filled with concrete over the tops of the beams and given a two-inch granolithic finish.
[Ill.u.s.tration: 58TH ST. POWER HOUSE--GENERAL PLAN OF COAL BUNKERS AND ECONOMIZERS.]
[Ill.u.s.tration: 58TH ST. POWER HOUSE--GENERAL PLAN OF MAIN OPERATING FLOOR.]
The six chimneys, s.p.a.ced 108 feet apart, and occupying the s.p.a.ce between the ends of the adjacent coal bunkers, are supported on plate-girder platforms in the fifth floor, leaving the s.p.a.ce below clear for a symmetrical arrangement of the boilers and economizers from end to end of the building. The platforms are framed of single-web girders 8 feet deep, thoroughly braced and carrying on their top f.l.a.n.g.es a grillage of 20-inch I-beam. A system of bracing for both the chimney platforms and coal bunkers is carried down to the foundations in traverse planes about 30 feet apart.
The sixth tier of beams const.i.tute a flat roof over a portion of the building at the center and sides. In the engine room, at this level, which is 64 feet above the engine-room floor, are provided the two longitudinal lines of crane runway girders upon which are operated the engine-room cranes. Runways for 10-ton hand cranes are also provided for the full length of the boiler room, and for nearly the full length of the north panel in the engine room.
Some of the loads carried by the steel structure are as follows: In the engine house, operating on the longitudinal runways as mentioned, are one 60-ton and one 25-ton electric traveling crane of 75 feet span. The imposed loads of the steam-pipe galleries on the south side and the switchboard galleries on the north side are somewhat irregularly distributed, but are equivalent to uniform loads of 250 to 400 pounds per square foot. In the boiler house the weight of coal carried is about 45 tons per longitudinal foot of the building; the weight of the brick chimneys is 1,200 tons each; economizers, with brick setting, about 4-1/2 tons per longitudinal foot; suspended weight of the boilers 96 tons each, and the weight of the boiler setting, carried on the first floor framing, 160 tons each. The weight of structural steel used in the completed building is about 11,000 tons.
[Sidenote: _Power House Superstructure_]
The design of the facework of the power house received the personal attention of the directors of the company, and its character and the cla.s.s of materials to be employed were carefully considered. The influence of the design on the future value of the property and the condition of the environment in general were studied, together with the factors relating to the future ownership of the plant by the city.
Several plans were taken up looking to the construction of a power house of ma.s.sive and simple design, but it was finally decided to adopt an ornate style of treatment by which the structure would be rendered architecturally attractive and in harmony with the recent tendencies of munic.i.p.al and city improvements from an architectural standpoint. At the initial stage of the power house design Mr.
Stanford White, of the firm of McKim, Mead & White, of New York, volunteered his services to the company as an adviser on the matter of the design of the facework, and, as his offer was accepted, his connection with the work has resulted in the development of the present exterior design and the selection of the materials used.
The Eleventh Avenue facade is the most elaborately treated, but the scheme of the main facade is carried along both the 58th and 59th Street fronts. The westerly end of the structure, facing the river, may ultimately be removed in case the power house is extended to the Twelfth Avenue building line for the reception of fourteen generating equipments; and for this reason this wall is designed plainly of less costly material.
The general style of the facework is what may be called French Renaissance, and the color scheme has, therefore, been made rather light in character. The base of the exterior walls has been finished with cut granite up to the water table, above which they have been laid up with a light colored buff pressed brick. This brick has been enriched by the use of similarly colored terra-cotta, which appears in the pilasters, about the windows, in the several entablatures, and in the cornice and parapet work. The Eleventh Avenue facade is further enriched by marble medallions, framed with terra-cotta, and by a t.i.tle panel directly over the front of the structure.
The main entrance to the structure is situated at its northeast corner, and, as the railroad track pa.s.ses along just inside the building, the entrance proper is the doorway immediately beyond the track, and opens into the entrance lobby. The doorway is trimmed with cut granite and the lobby is finished with a marble wainscoting.
The interior of the operating room is faced with a light, cream-colored pressed brick with an enameled brick wainscoting, eight feet high, extending around the entire operating area; the wainscoting is white except for a brown border and base. The offices, the toilets and locker rooms are finished and fitted with materials in harmony with the high-cla.s.s character of the building. The masonry-floor construction consists of concrete reinforced with expanded metal, and except where iron or other floor plates are used, or where tile or special flooring is laid, the floor is covered with a hard cement granolithic finish.
In the design of the interior arrangements, the value of a generous supply of stairways was appreciated, in order that all parts of the structure might be made readily accessible, especially in the boiler house section. In the boiler house and machinery portion of the plant the stairways, railings, and accessories are plainly but strongly constructed. The main stairways are, however, of somewhat ornate design, with marble and other trim work, and the railings of the main gallery construction are likewise of ornate treatment. All exterior doors and trim are of metal and all interior carpenter work is done with Kalomein iron protection, so that the building, in its strictest sense, will contain no combustible material.
[Sidenote: _Chimneys_]
The complete 12-unit power house will have six chimneys, s.p.a.ced 108 feet apart on the longitudinal center line of the boiler room, each chimney being 15 feet in inside diameter at the top, which is 225 feet above the grate bars. Each will serve the twelve boilers included in the section of which it is the center, these boilers having an aggregate of 72,000 square feet of heating surface. By these dimensions each chimney has a fair surplus capacity, and it is calculated that, with economizers in the path of the furnace gases, there will be sufficient draft to meet a demand slightly above the normal rating of the boilers. To provide for overload capacity, as may be demanded by future conditions, a forced draft system will be supplied, as described later.
As previously stated, the chimneys are all supported upon the steel structure of the building at an elevation of 76 feet above the bas.e.m.e.nt floor and 63 feet above the grates. The supporting platforms are, in each case, carried on six of the building columns (the three front columns of two groups of boilers on opposite sides of the center aisle of the boiler room), and each platform is composed of single-web plate girders, well braced and surmounted by a grillage of 20-inch I-beams. The grillage is filled solidly with concrete and flushed smooth on top to receive the brickwork of the chimney.
Each chimney is 162 feet in total height of brickwork above the top of the supporting platform, and each chimney is 23 feet square in the outside dimension at the base, changing to an octagonal form at a point 14 feet 3 inches above the base. This octagonal form is carried to a height of 32 feet 6 inches above the base, at which point the circular section of radial brick begins.
The octagonal base of the chimney is of hard-burned red brick three feet in thickness between the side of the octagon and the interior circular section. The brick work is started from the top of the grillage platform with a steel channel curb, three feet in depth, through which two lines of steel rods are run in each direction, thus binding together the first three feet of brickwork, and designed to prevent any flaking at the outside. At a level of three feet above the bottom of the brickwork, a layer of water-proofing is placed over the interior area and covered with two courses of brick, upon which are built diagonal brick walls, 4 inches thick, 12 inches apart, and about 18 inches in height. These walls are themselves perforated at intervals, and the whole is covered with hand-burned terra-cotta blocks, thus forming a cellular air s.p.a.ce, which communicates with the exterior air and serves as an insulation against heat for the steelwork beneath. A single layer of firebrick completes the flooring of the interior area, which is also flush with the bottom of the flue openings.
There are two flue openings, diametrically opposite, and 6 feet wide by 17 feet high to the crown of the arched top. They are lined with fire brick, which joins the fire-brick lining of the interior of the shaft, this latter being bonded to the red-brick walls to a point 6 feet below the top of the octagon, and extended above for a height of 14 feet within the circular shaft, as an inner sh.e.l.l. The usual baffle wall is provided of fire brick, 13 inches thick, extending diagonally across the chimney, and 4 feet above the tops of the flue openings.
Where the chimney pa.s.ses through the roof of the boiler house, a steel plate and angle curb, which clears the chimney by 6 inches at all points, is provided in connection with the roof framing. This is covered by a hood flashed into the brickwork, so that the roof has no connection with or bearing upon the chimney.
At a point 4 feet 6 inches below the cap of the chimney the brickwork is corbeled out for several courses, forming a ledge, around the outside of which is placed a wrought-iron railing, thus forming a walkway around the circ.u.mference of the chimney top. The cap is of cast iron, surmounted by eight 3 x 1-inch wrought-iron ribs, bent over the outlet and with pointed ends gathered together at the center. The lightning conductors are carried down the outside of the shaft to the roof and thence to the ground outside of the building. Galvanized iron ladder rungs were built in the brickwork, for ladders both inside and outside the shaft.
The chimneys, except for the octagonal red-brick base, are constructed of the radial perforated bricks. The lightning rods are tipped with pointed platinum points about 18 inches long.
[Sidenote: _North River Pier_]
Exceptional facilities have been provided for the unloading of coal from vessels, or barges, which can be brought to the northerly side of the recently constructed pier at the foot of West 58th Street. The pier was specially built by the Department of Docks and Ferries and is 700 feet long and 60 feet wide.
The pier construction includes a special river wall across 58th Street at the bulkhead line through which the condensing water will be taken from and returned to the river. Immediately outside the river wall and beneath the deck of the pier, there is a system of screens through which the intake water is pa.s.sed. On each side where the water enters the screen chamber, is a heavy steel grillage; inside this is a system of fine screens arranged so that the several screens can be raised, by a special machine, for the purpose of cleaning. The advantages of a well-designed screening outfit has been appreciated, and considerable care has been exercised to make it as reliable and effective as possible.
At each side of the center of the pier, just below the deck, there are two discharge water conduits constructed of heavy timber, to conduct the warm water from the condensers away from the cold water intakes at the screens. Two water conduits are employed, in order that one may be repaired or renewed while using the other; in fact, the entire pier is constructed with the view of renewal without interference in the operation for which it was provided.
CHAPTER IV
POWER PLANT FROM COAL PILE TO SHAFTS OF ENGINES AND TURBINES
From the minute and specific description in Chapter III, a clear idea will have been obtained of the power house building and its adjuncts, as well as of the features which not only go to make it an architectural landmark, but which adapt it specifically for the vital function that it is called upon to perform. We now come to a review and detailed description of the power plant equipment in its general relation to the building, and "follow the power through" from the coal pile to the shafts of the engines or steam turbines attached to the dynamos which generate current for power and for light.
[Sidenote: _Coal and Ash Handling Equipment_]
The elements of the coal handling equipment comprise a movable electric hoisting tower with crushing and weighing apparatus--a system of horizontal belt conveyors, with 30-inch belts, to carry the crushed and weighed coal along the dock and thence by tunnel underground to the southwest corner of the power house; a system of 30-inch belt conveyors to elevate the coal a distance of 110 feet to the top of the boiler house, at the rate of 250 tons per hour or more, if so desired, and a system of 20-inch belt conveyors to distribute it horizontally over the coal bunkers. These conveyors have automatic self reversing trippers, which distribute the coal evenly in the bunkers. For handling different grades of coal, distributing conveyors are arranged underneath the bunkers for delivering the coal from a particular bunker through gates to the downtake hoppers in front of the boilers, as hereafter described.
The equipment for removing ashes from the boiler room bas.e.m.e.nt and for storing and delivering the ashes to barges, comprises the following elements: A system of tracks, 24 inches gauge, extending under the ash-hopper gates in the boiler-house cellar and extending to an elevated storage bunker at the water front. The rolling stock consists of 24 steel cars of 2 tons capacity, having gable bottoms and side dumping doors. Each car has two four-wheel pivoted trucks with springs. Motive power is supplied by an electric storage battery locomotive. The cars deliver the ashes to an elevating belt conveyor, which fills the ash bunker. This will contain 1,000 tons, and is built of steel with a suspension bottom lined with concrete. For delivering stored ashes to barges, a collecting belt extends longitudinally under the pocket, being fed by eight gates. It delivers ashes to a loading belt conveyor, the outboard end of which is hinged so as to vary the height of delivery and to fold up inside the wharf line when not in use.
The coal handling system in question was adopted because any serious interruption of service would be of short duration, as any belt, or part of the belt mechanism, could quickly be repaired or replaced. The system also possessed advantages with respect to the automatic even distribution of coal in the bunkers, by means of the self reversing trippers. These derive their power from the conveying belts. Each conveyor has a rotary cleaning brush to cleanse the belt before it reaches the driving pulley and they are all driven by induction motors.
The tower frame and boom are steel. The tower rolls on two rails along the dock and is self-propelling. The lift is unusually short; for the reason that the weighing apparatus is removed horizontally to one side in a separate house, instead of lying vertically below the crusher.
This arrangement reduces by 40 per cent. the lift of the bucket, which is of the clam-sh.e.l.l type of forty-four cubic feet capacity. The motive power for operating the bucket is perhaps the most ma.s.sive and powerful ever installed for such service. The main hoist is directly connected to a 200 horse-power motor with a special system of control.
The trolley engine for hauling the bucket along the boom is also direct coupled to a multipolar motor.
The receiving hopper has a large throat, and a steel grizzly in it which sorts out coal small enough for the stokers and bypa.s.ses it around the crusher. The crusher is of the two-roll type, with relieving springs, and is operated by a motor, which is also used for propelling the tower. The coal is weighed in duplex two-ton hoppers.
Special attention has been given to providing for the comfort and safety of the operators. The cabs have baywindow fronts, to enable the men to have an un.o.bstructed view of the bucket at all times without peering through slots in the floor. Walks and hand lines are provided on both sides of the boom for safe inspection. The running ropes pa.s.s through hardwood slides, which cover the slots in the engine house roof to exclude rain and snow.
This type of motive power was selected in preference to trolley locomotives for moving the ash cars, owing to the rapid destruction of overhead lines and rail bonds by the action of ashes and water. The locomotive consists of two units, each of which has four driving wheels, and carries its own motor and battery. The use of two units allows the locomotive to round curves with very small overhangs, as compared with a single-body locomotive. Curves of 12 feet radius can be turned with ease. The gross weight of the locomotive is about five tons, all of which is available for traction.
[Sidenote: _Coal Downtakes_]
The coal from the coal bunkers is allowed to flow down into the boiler room through two rows of downtakes, one on each side of the central gangway or firing place. Each bunker has eight cast-iron outlets, four on each side, and to these outlets are bolted gate valves for shutting off the coal from the corresponding downtakes. From these gates the downtakes lead to hoppers which are on the economizer floor, and from these hoppers the lower sets of downtakes extend down to the boilers.