Transactions of the American Society of Civil Engineers Part 12

The entire building is ventilated by a force or blower fan in the bas.e.m.e.nt, and by an exhaust fan in the attic with sufficient capacity to insure complete renewal of air in each laboratory once in 20 min.

The blower fan is placed in the center of the building, on the ground floor, and is 100 in. in diameter. Its capacity is about 30,000 cu. ft.

of air per min., and it forces the air, through a series of pipes, into registers placed in each of the laboratories.

The exhaust fan, in the center of the attic, is run at 550 rev. per min., and has a capacity of 22,600 cu. ft. of air per min. It draws the air from each of the rooms below, as well as from the hoods, through a main pipe, 48 in. in diameter.

_Steaming and Combustion Tests._--The investigations included under the term, fuel efficiency, relate to the utilization of the various types of fuels found in the coal and oil fields, and deal primarily with the combustion of such fuels in gas producers, in the furnaces of steam boilers, in locomotives, etc., and with the efficiency and utilization of petroleum, kerosene, gasoline, etc., in internal-combustion engines.

This work is under the general direction of Mr. R. L. Fernald, and is conducted princ.i.p.ally in Buildings Nos. 13 (Plate XVII) and 21.

For tests of combustion of fuels purchased by the Government, the equipment consists of two Heine, water-tube boilers, each of 210 h.p., set in Building No. 13. One of these boilers is equipped with a Jones underfeed stoker, and is baffled in the regular way. At four points in the setting, large pipes have been built into the brick wall, to permit making observations on the temperature of the gas, and to take samples of the gas for chemical a.n.a.lysis.

The other boiler is set with a plain hand-fired grate. It is baffled to give an extra pa.s.sage for the gases (Fig. 15). Through the side of this boiler, at the rear end, the gases from the long combustion chamber (Plate XVIII) enter and take the same course as those from the hand-fired grate. Both the hand-fired grate and the long combustion chamber may be operated at the same time, but it is expected that usually only one will be in operation. A forced-draft fan has been installed at one side of the hand-fired boiler, to provide air pressure when coal is being burned at high capacity. This fan is also connected in such a way as to furnish air for the long combustion chamber when desired. A more complete description of the boilers may be found in Professional Paper No. 48, and Bulletin No. 325 of the U.S. Geological Survey, in which the water-measuring apparatus is also described.[13]

On account of the distance from Building No. 21 to the main group of buildings, it was considered inadvisable to attempt to furnish steam from Building No. 13 to Building No. 21, either for heating or power purposes. In view, moreover, of the necessity of installing various types and sizes of house-heating boilers, on account of tests to be made thereon in connection with these investigations, it was decided to install these boilers in the lower floor of Building No. 21, where they could be utilized, not only in making the necessary tests, but in furnishing heat and steam for the building and the chemical laboratories therein.

[Ill.u.s.tration: Fig. 15.

SETTING FOR 210-HORSE POWER, HAND-FIRED BOILERS]

In addition to the physical laboratory on the lower floor of Building No. 21, and the house-heating boiler plant with the necessary coal storage, there are rooms devoted to the storage of heavy supplies, samples of fuels and oils, and miscellaneous commercial apparatus. One room is occupied by the ventilating fan and one is used for the necessary crushers, rolls, sizing screens, etc., required in connection with the sampling of coal prior to a.n.a.lysis.

The Quartermaster's Department having expressed a wish that tests be made of the heating value and efficiency of the various fuels offered that Department, in connection with the heating of military posts throughout the country, three house-heating boilers were procured which represent, in a general way, the types and sizes used in a medium-sized hospital or other similar building, and in smaller residences (Fig. 2, Plate XVI). The larger apparatus is a horizontal return-tubular boiler, 60 in. in diameter, 16 ft. long, and having fifty-four 4-in. tubes.[14]

In order to determine whether such a boiler may be operated under heating conditions without making smoke, when burning various kinds of coal, it has been installed in accordance with accepted ideas regarding the prevention of smoke. A fire-brick arch extends over the entire grate surface and past the bridge wall. A baffle wall has been built in the combustion chamber, which compels the gases to pa.s.s downward and to divide through two openings before they reach the boiler sh.e.l.l.

Provision has been made for the admission of air at the front of the furnace, underneath the arch, and at the rear end of the bridge wall, thus furnishing air both above and below the fire. It is not expected that all coals can be burned without smoke in this furnace, but it is desirable to determine under what conditions some kinds of coals may be burned without objectionable smoke.[15]

For sampling the gases in the smokebox of the horizontal return-tubular boiler, a special flue-gas sampler was designed, in order to obtain a composite sample of the gases escaping from the boiler.

The other heaters are two cast-iron house-heating boilers. One can supply 400 sq. ft. of radiation and the other about 4,000 sq. ft. They were installed primarily for the purpose of testing coals to determine their relative value when burned for heating purposes. They are piped to a specially designed separator, and from this to a pressure-reducing valve. Beyond this valve an orifice allows the steam to escape into the regular heating mains. This arrangement makes it possible to maintain a practically constant load on the boilers.

[Ill.u.s.tration: PLATE XVIII.

Fig. 1.--Long Combustion Chamber.

Fig. 2.--Gas Sampling Apparatus, Long Combustion Chamber.]

There is a fourth boiler, designed and built for testing purposes by the Quartermaster's Department. This is a tubular boiler designed on the lines of a house-heating boiler, but for use as a calorimeter to determine the relative heat value of different fuels reduced to the basis of a standard cord of oak wood.

A series of research tests on the processes of combustion is being conducted in Building No. 13, by Mr. Henry Kreisinger. These tests are being made chiefly in a long combustion chamber (Figs. 16 and 17, and Figs. 1 and 2, Plate XVIII), which is fed with coal from a Murphy mechanical stoker, and discharges the hot gases at the rear end of the combustion chamber, into the hand-fired Heine boiler. The walls and roof of this chamber are double; the inner wall is 9 in. thick, of fire-brick; the outer one is 8 in. thick, and is faced with red pressed brick. Between the walls of the sides there is a 2-in. air s.p.a.ce, and between them on the roof a 1-in. layer of asbestos paste is placed. The inner walls and roof have three special slip-joints, to allow for expansion. The floor is of concrete, protected by a 1-in. layer of asbestos board, which in turn is covered by a 3-in. layer of earth; on top of this earth there is a 4-in. layer of fire-brick (not shown in the drawings).

[Ill.u.s.tration: Fig. 16.

CROSS-SECTIONS OF CHAMBER AND OF FURNACE, LONG COMBUSTION CHAMBER]

Inasmuch as one of the first problems to be attacked will be the determination of the length of travel and the time required to complete combustion in a flame in which the lines of stream flow are nearly parallel, great care was taken to make the inner surfaces of the tunnel smooth, and all corners and hollows are rounded out in the direction of travel of the gases.

Provision is made, by large peep-holes in the sides, and by smaller sampling holes in the top, for observing the fuel bed at several points and also the flame at 5-ft. intervals along the tunnel. Temperatures and gas samples are taken simultaneously at a number of points through these holes, so as to determine, if possible, the progress of combustion (Fig. 1, Plate XVIII).

About twenty thermo-couples are embedded in the walls, roof, and floor, some within 1 in. of the inside edge of the tunnel walls, and some in the red pressed brick near the outer surface, the object of which is to procure data on heat conduction through well-built brick walls[16] (Fig.

2, Plate XVIII).

In order to minimize the leakage of air through the brickwork, the furnace and tunnel are kept as nearly as possible at atmospheric pressure by the combined use of pressure and exhausting fans.

Nevertheless, the leakage is determined periodically as accurately as possible.

At first a number of tests were run to calibrate the apparatus as a whole, all these preliminary tests being made on cheap, carefully inspected, uniform screenings from the same seam of the same mine near Pittsburg. Later tests will be run with other coals of various volatile contents and various distillation properties.

It is antic.i.p.ated that the progress of the tests may suggest changes in the construction or operation of this chamber. It is especially contemplated that the section of the chamber may be narrowed down by laying sand in the bottom and fire-brick thereon; also that baffle walls may be built into various portions of it, and that cooling surfaces with baffling may be introduced. In addition to variations in the tests, due to changes in construction in the combustion chamber, there will be variations in the fuels tested. Especial effort will be made to procure fuels ranging in volatile content from 15 to 27 and to 40%, and those high in tar and heavy hydro-carbons. It is also proposed to vary the conditions of testing by burning at high rates, such as at 15, 20, and 30 lb. per ft. of grate surface, and even higher. Records will be kept of the weight of coal fired and of each firing, of the weight of ash, etc.; samples of coal and of ash will be taken for chemical and physical a.n.a.lysis, as well as samples of the gas, and other essential data. These records will be studied in detail.

[Ill.u.s.tration: Fig. 17.

LONGITUDINAL SECTIONS OF LONG COMBUSTION CHAMBER]

A series of heat-transmission tests undertaken two years ago, is being continued on the ground floor of Building No. 21, on modified apparatus reconstructed in the light of the earlier experiments by Mr. W. T. Ray.

The purpose of the tests on this apparatus has been to determine some of the laws controlling the rate of transmission of heat from a hot gas to a liquid and _vice versa_, the two being on the opposite sides of a metal tube.

It appears that four factors determine the rate of heat impartation from the gas to any small area of the metal[17]:

[Footnote 17: The a.s.sumption is made that a metal tube free from scale will remain almost as cool as the water; actual measurements with thermo-couples have indicated the correctness of this a.s.sumption in the majority of cases.]

(1).--The temperature difference between the body of the gas and the metal;

(2).--The weight of the gas per cubic foot, which is proportional to the number of molecules in any unit of volume;

(3).--The bodily velocity of the motion of the gas parallel to any small area under consideration; and (probably),

(4).--The specific heat of the gas at constant pressure.

The apparatus consists of an electric resistance furnace containing coils of nickel wire, a small (interchangeable) multi-tubular boiler, and a steam-jet apparatus for reducing the air pressure at the exit end, so as to cause a flow of air through the boiler. A surface condenser was attached to the boiler's steam outlet, the condensed steam being weighed as a check on the feed-water measurements. A number of thermometers and thermo-couples were used to obtain atmospheric-air temperature, temperatures of the air entering and leaving the boilers, and feed-water temperature.

The apparatus is now being reconstructed with appliances for measuring the quant.i.ty of air entering the furnace, and an automatic electric-furnace temperature regulator.

[Ill.u.s.tration: PLATE XIX.

Fig. 1.--Gas Producer, Economizer, and Wet Scrubber.

Fig. 2.--Producer Gas: Dry Scrubber and Gas Holder.]

Three sizes of boiler have been tested thus far, the dimensions being as given in Table 4.

Each of the three boilers was tested at several temperatures of entering air, up to 1,500 Fahr., about ten tests being made at each temperature.

It is also the intention to run, on these three boilers, about eight tests at temperatures of 1,800, 2,100 and 2,400 Fahr., respectively.

A bulletin on the work already done, together with much incidental matter, is in course of preparation.[18]

TABLE 4.--Dimensions of Boilers Nos. 1, 2, and 3.

------------------------------------+--------+--------+-------- Items. | Boiler | Boiler | Boiler | No. 1. | No. 2. | No. 3.

------------------------------------+--------+--------+-------- Distance, outside to outside of | | | boiler heads, in inches | 8.28 | 8.28 | 16.125 Actual outside diameter of flues, | 0.252 | 0.313 | 0.252 in inches | | | Actual inside diameter of flues, | 0.175 | 0.230 | 0.175 in inches | | | Number of flues (tubes) | 10 | 10 | 10 ------------------------------------+--------+--------+--------