864
T H E JOCRLVdL O F I N D U S T R I A L A N D E N G I N E E R I N G C H E X I S T R Y
8. The width of the ditch a t the level of the pipe makes a great difference in the weight of filling resting on the pipe, this weight being greater the wider the ditch. Moreover, the narrower the ditch a t the midheight of the pipe, the more effective is the side support against the collapsing of cracked pipe. 9. Where the ditch filling over the pipe is rammed in layers during refilling, there is serious danger of cracking large drain tile and sewer pipe by using too heavy rammers 2nd too thin a layer just above the pipe. IO. While large amounts of cracked drain tile and sewer pipe are standing without collapsing in existing drains and sewers, the stability of cracked pipe must be considered precarious, as has been demonstrated by numerous collapses. 1 1 . Cracked pipe is especially dangerous in tile drains and storm sewers, for the reason that, in the best engineering practice, it is not found practicable to make the capacity of drains and sewers equal to the most exceptional floods. Hence they are certain eventually to be overcharged, and to run under pressure, and the collapse of cracked pipe is likely to result a t such times from the softening of the soil by water escaping through the joints and cracks. The general principles of the theory of loads on pipes in ditches, which were borne out by a long series of laboratory and field tests, may be in part summarized as follows: I . The weight of the filling in a drainage or sewerage ditch, a t the time of maximum load on the pipe, is carried partly by the pipe, and partly by friction against the sides of the ditch. Cohesion greatly reduces the loads carried by the pipe a t ordinary times, after the ditch is refilled and partly consolidated, except in the case of clean sand, or gravel filling, but does not appreciably affect the maximum loads. 2 . The maximum loads on pipes in ditches, due to the weight of ditch-filling materials, will usually occur a t the time of the first very thorough surface flooding of the ditch filling after construction, when there is a large settlement of the refill, but there is possibility of their occurring later. a t the time of extreme saturation of the ditch filling by surface flooding of the ditch and by overcharging of the drain or sewer. The maximum loads may even be postponed for many years in some cases, as is frequently shown by settlement of the filling in old ditches during paving construction. 3 . Safe values of the ordinarymaximumloadsonpipes in ditches, due to the weight of ditch-filling materials, can be computed by the formula W = CwBZ, using the values of C given where W = load on pipe in ditches, in pounds per linear foot; C = coefficient of loads on pipes in ditches; w = weight of ditch filling material, from 90 to I Z O lb. per cubic foot; B = breadth of ditch a t top of pipe, in feet; and H = height of fill, above top of pipe, in feet.
1701. j,
NO.10
the end thrust, and segmental brick of the proper radius, with thin points of fire clay. If thus constructed, i t will stand up under the high heat to which it is subjected.
The auxiliary air supply to the hollow bridge wall enters through the duct B B , controlled by the damper D ; to the transverse Passage c, which has a clean-out door; and then up and
FIG.2-HORIZONTAL
SECTION T H R O U G H
BOILERSETTIXC
out through l,'c-inch spaces between the fire brick in the crown of the bridge wall, The air is warmed by passage through the
-
A NEW DESIGN IN BOILER SETTINGS A modification of the usual horizontal tubular boiler setting is described in a recent bulletin issued by the Travelers' Indemnity Company, of Hartford, Conn. The two distinctive features of the settin: are the furnace arch A A , and the air duct B B , admitting secondary air through the bridge wall. I n the ordinary form of setting for horizontal tubular boilers, the fire sheet of the shell, relatively very much cooler than the burning gases in contact with it, acts as a check upon combustion by its chilling effect and is itself subject t o destructive strains. The deflecting arch, as shown by the sections, ends immediately back of the bridge wall, and the faces of fire brick are staggered to form projecting rings on its surface. This arch facilitates more staisfactory combustion of the furnace gases, and, in addition, distributes over the shell and tube surfaces the excess of work usually put upon the fire sheet. Both of these increase the efficiency of the boiler as well as add to t s life. The arch must be carefully laid, with good blocks for
..-..-.. GRATE
FIG. 3 - s E C T I O S
LEVEL
THROUGH I G N I T I O N A R C H
ducts, and is then introduced to the burning gases a t what has been experimentally determined to be the best point for its addition. - .._.. ~~~~
~
~
A SEPARATOR FOR DRY MATERIAL
F. 0. Stromberg, of Seattle, Wash., has devised an apparatus for the dry separation of ground ore, etc., which consists of a f a n or other means of introducing an air blast, which passes.
OCt.,
1913
T H E J O C R A Y A 4 LO F 1 , V D U S T R I A L A N D E - V G I N E E R I S G C H E M I S T R I ‘
through a conical-shaped connection into a box, the bottcm of which is divided into separate cone-bottomed receptacles. A screen is placed a t the entrance of the box, shown a t A in the drawing, for the purpose of creating eddies which will permit the greater part of the material to pass through the central slot formed by the movable partitions B . These partitions are adjustable and removable, and both the front and rear edges of each partition may be vertically independently adjusted. The arrows in the sketch show that the wind delivered from the fan passes into the inlet of the box and then expands slightly into strata or currents, the central one of which will pass along into a n d through the inlet without obstruction. Those currents which flow,along the top and bottom of the box will set up eddies, as indicated by the fine arrows, and it is the purpose of these partitions to check the tendency to the formation of eddies
a n d to deliver the blasts of air into the box in several strata moving horizontally, and a t equal speed. If these screenpanels are used with different meshes, an important bearing will be had upon the amount of air admitted through the slot or opening covered by t h a t particular screen. Power is applied t o the fan which sets up a blast of air through the trunk and screen partition and throughout the length of the box to its outlet end. The material fed into the air-current encounters various strata of air which move a t different velocities, according as the partitions have been set, and according to the mesh of the screen a t the various openings; the larger pieces naturally offer more resistance to blasts of air than the smaller ones, and, therefore, the larger pieces will fall into the hopper nearest to the entrance of the long box, while the finer particles will fall into successive hoppers further along until the finest are discharged a t the end of the box in the form of dust.
ABSORPTION AND REACTION TOWERS FOR CHEMICAL WORKS Rudolf Heinz,’ after reminding the reader t h a t the main requirements for good absorption are greatest possible surface per cubic foot of filling, good mixing of gas, and the correct proportioning of the ratio between the section of the tower and the net section free for the passage of the gases, points out that the intending purchaser has a large variety of tower packings t o select from. The days of coke as a filling material, except in certain very special cases, are numbered, and it has long been established that a small tower with good packing will accomplish the same amount of work as a large coke tower. Plain acid-proof bricks, prism-shaped bricks, triangular, rhombohedral, and trough-shaped bricks, and rings of various kinds, have all been tried in practice, and all have been found to have a common defect, namely, that they occupy a large percentage of the volume of the tower and leave insufficient “absorption space” for the gases. Heinz states t h a t the most successful tower packing of recent years were the “ G u t t m a n n ” hollow balls; the success of these was due to their very high “free space” ithe percentage of the cubic capacity of a tower which remains free for gases). Millions of these balls were sold, but they could not come into general use on account of their high cost and because they were unsuitable for large towers and gases containing dust. 12.
angew. Chem., 26, X o . S i , 419; see also Chem. Trade J., 63, 75.
86 j
The latest type of filling material, “ G u t t m a n n ” cells, are stated t o be superior to even hollow balls, not only in regard to efficiency, but also because the cells are cheaper and possess a very high “free space.” As shown in the illustrations (Figs. I and 2 ) , these cells, when built up in a tower, form in section a regular honeycomb structure, each four cells enclosing a reaction space corresponding t o a n additional cell. The whole of the tower is thus symmetrically divided up into a number of equal reaction spaces, and in such a manner t h a t both the outer and inner surfaces of the cells are wetted, and must be traversed by the gases which are ascending and diffusing through the tower filling. The formation of separate streams of liquids or gases cannot occur when these cells are used. Fig. I shows diagrammatica ly four cells arranged in the same manner as if they were stacked in a tower, the path of the liquid being
1:XG
1
FlG
2
indicated by plain arrows and the probable course of the gases by means of circled arrows. Slots ( a ) are made in the top and bottom walls of the cells; the gases entering from below expand in the interior of the cell, and pass out through the slots a t the top. Each cell is provided a t the sides with a number of projections ( b ) , which rest against corresponding projections on the neighboring cells, and, a t the same time, form the slots for the reaction space formed by four adjacent cells. The side walls of the cells being very steep, render it practically impossible, Heinz claims, for solid matter to collect on them, while, if necessary, the cells may be readily and quickly flushed down and cleaned. For extremely dusty gases-such, for example, as pass through a Glover tower-the lower third of the tower may be filled with large slabs or bricks in the usual way. The “active surface” of the large cells is 15 square feet per cubic foot, and of the small cells 3 0 square feet per cubic foot, and they are said t o be designed and proportioned in every way t o give the best results.
THE ROTAMETER The “Rotameter” is a new instrument which indicates the volume of gas or liquid consumed per hour. It does not, however, measure absolute quantities like an ordinary gas meter or voltmeter, but gives the force of the gas current. It is based upon the following principle: The gas current which is to be measured flows through a vertical glass tube, the inside diameter of which increases continuously from the bottom to the top. Inside the glass tube is a conical float which rises to a certain height when gas is flowing through the former. The lift of the float depends upon the velocity of the gas or upon the volume of gas going through the tube in a n hour, minute or second. On the float is a notched cylindrical rim. The gas, shooting through these notches, rotates the float like a Segner waterwheel, and
