THE BURNING OF TOWN REFUSE AT LEEDS.
[Footnote: From selected papers of the Institution of Civil Engineers, London, by Charles Slagg, Assoc. Memb. Inst. C.E.]
In large towns it is necessary to adopt some regular system of removal and disposal of the cinders and ashes of house fires, and of the animal and vegetable refuse of the houses, and, in short, of everything thrown away which cannot be admitted into the sewers. In towns where the excreta are separated by means of water closets, the disposal of the other refuse presents less difficulty, but still a considerable one, because the animal and vegetable refuse is not kept separate from the cinders and ashes, all being thrown together into the ash pit or dust bin. The contents, therefore, cannot be deposited upon ground which may afterward be built upon, although that custom obtained generally in former times. Hence the refuse has been removed to a depot where that wretched industry is created of picking out the other parts from the cinders and ashes.
FIG. 1.--DESTRUCTOR.
Elevation.
Section through feeding-holes of cells.
Section through air-passages of cells.
But in towns unprovided with water closets, or so far as they are not adopted in any town, where the privies are connected with the ash pits, and where, consequently, the excreta of the population are added to the other contents of ash pits, the difficulties of removal and disposal of the refuse are much increased.
Where the privy-ashpit system is in use--as it still is to a large extent--as much of the contents of the ash pits as can be sold at any price, however small, are collected separately from the drier portions, and sent out of town as manure; but what remains is still too offensive to be deposited on ground near the town; and when it is attempted to collect the excreta separately by the pail system, the process is no less unsatisfactory. These difficulties led to the adoption, under the advice of the late Mr. A.W. Morant, M. Inst. C.E., the Borough Engineer at Leeds, of Fryer's method of destruction by burning--that is, of the dry ashes and cinders and the animal and vegetable refuse. The author was Mr. Morant's assistant. The first kiln was constructed at Burmantofts, 1½ miles from the center of the town in a northeasterly direction, and has been in use since the beginning of the year 1878. In 1879 another kiln was constructed at Armley Road, a mile from the center of the town in a west-southwesterly direction, which has been in use since the beginning of 1880.
Each destructor kiln has six cells, three in each face of a block of brick work 22 feet long, 24 feet through from face to face, and 12 feet high. Each cell is 8 feet long and 5 feet wide, arched over, the height being 3 feet 4 inches, and both the bottom and arch of the cell slope down to the furnace doors with an inclination of 1 in 3. The lower end of each cell has about 26 square feet of wrought-iron firebars, the hearth being 4½ feet above the ground.
FIG. 2.--CARBONIZER.
Section through furnaces.
Longitudinal section.
Cross section.
There are two floors, one on the ground level, a few feet only above the outlet for drainage, the other floor, or raised platform, being 15 feet above it. The refuse is taken in carts up an incline of 1 in 14 on cast-iron tram plates to the upper floor, and deposited upon and alongside of the destructor, and is shoveled into a row of hoppers at the head of the cells. These hoppers are in the middle of the width of the destructor, and each communicates with a cell on each side of it. The refuse is always damp, and often wet, and after being put into the cells is gradually dried by the heat reflected upon it from the firebrick arch of the cell, before it descends to the furnace. This distinguishes the system from the common furnace, and enables the wet material to be burned without other fuel. No fresh fuel is used after the fires are once lighted. The vapor passes off with the gases of combustion into a horizontal flue between the two rows of cells, through an opening at the head of each cell, alongside that through which the refuse is fed into it, the two openings being separated by a firebrick wall. The refuse is prevented from falling into the flue by a bridge wall across the outlet opening, over which the gases pass into the flue.
Between the destructor and the chimney a multitubular boiler is placed, which makes steam enough for grinding into sand the clinkers which are the solid residue of the burnt refuse. At Burmantofts an old chimney was made use of, which is but 84 feet high; but at Armley Road a new chimney was built, 6 feet square inside and 120 feet high. It is necessary to make the horizontal flue large; that at Armley Road is 9 feet high and 4 feet wide. A large quantity of dust escapes from the cells--about 7 cwt. a month--and unless the velocity of the air in the flue between the destructor and the chimney were checked, the dust would be carried up the chimney and might cause complaints; as, indeed, it has done with the 120-foot chimney, but whether with any substantial grounds is uncertain. The dust is removed from the horizontal flue or dust chamber once a month. Experience seems to indicate that there should be some sort of guard or grating to prevent the entry into the chimney of charred paper and similar light substances which do not fall to dust, and which are sometimes carried up with the draught.
A six-celled destructor kiln burns about 42 tons of refuse in twenty-four hours, leaving about one-fourth of its bulk of clinkers and ashes. The clinkers are withdrawn from the furnaces five times each day and night, or about every two-and-a-half hours, into iron barrows, and wheeled outside the shed which covers the destructor, and when cold are wheeled back to the mortar mills, of which there are two at each depot, each having a revolving pan 8 feet in diameter, with 27-cwt. rollers, the pan making twenty two revolutions a minute. Forty shovelfuls of clinkers and twelve of slaked lime make 7 cwt. of mortar in thirty-five minutes in each pan, which is sold at 5s. 6d. per ton. The engine driving the two mortar mills has a 14 inch cylinder, 30 inches length of stroke, and makes sixty revolutions per minute with 45 pounds steam pressure per square inch in the boiler, when both mortar mills are running. The boiler is 11 feet long, 8 feet in diameter, and has 132 tubes 4 inches in external diameter, which, together with the external flues, are cleaned out once a month.
At first sight it would probably appear that no good mortar could be made from such refuse as has been described, but having passed through the furnace, the clinkers are, of course, perfectly clean, and with good lime make a really strong and excellent mortar. They are also largely used for the foundation of roadways.
The number of men employed is as follows: Two furnace men in the daytime and two at night. They work from midnight on Sundays to 2 P.M. on Saturdays, the fires being fully charged and left to burn through the Sundays. One foreman, who attends also to the running of the engine, and one mortar man. A watchman attends while the workmen are off.
In addition to a destructor, there is at the Burmautofts depot a "carbonizer" kiln, in which the sweepings of the vegetable markets are burned into charcoal. The carbonizer consists of eight vertical cells, in two sets or stacks of four, separated by a space containing two double furnaces, back to back, there being a double furnace also at each end of the eight cells. Each of the stacks of four cells is 15 feet 6 inches high; the ends and middle parts, forming the tops of the furnaces, being 6 feet high. The block of brick work containing the eight cells and furnaces is 26 feet 6 inches long and 12 feet 4 inches wide at the floor level. Each cell is 3 feet 6 inches by 2 feet, and about 10 feet deep, with a chamber below about 3 feet deep, into which the charred material falls and is completely burned. The top of the cells is level with the upper platform, and they are fed through a loose cover, which is immediately replaced. Inside the cells cast-iron sloping shelves are hung upon the walls so that their upper edges touch the walls, but the lower edges are some inches off, so that the hot air of the furnaces passes upward behind the shelves round the four sides of the cell in a spiral manner, and out near the top into a vertical flue, which conducts it down to the horizontal flue at the bottom, which leads to the chimney. The charcoal is withdrawn from the bottom of the heating chamber through a sliding plate 2 feet above the floor, and is wheeled red hot to the charcoal cooler, which is a revolving cylinder, nearly horizontal, kept cool by water falling upon it, and delivers the charcoal in two degrees of fineness at the end. It is worked by a small attached engine, supplied with steam from the boiler before mentioned. Each cell of the carbonizer can reduce to charcoal 50 cwt. of vegetable refuse in twenty four hours, but at Leeds not quite so much is put through. The quantity of market refuse passed through six cells of the carbonizer varies from 3 to 10 tons a day, and averages about 4½ tons, from which 15 cwt. of charcoal is obtained. The fuel for burning the charcoal is derived from the ash pit refuse, some selected loads being for that purpose passed over a sloping screen fixed between the upper platform and the furnace floor, the fine ashes which pass through the screen being taken away to the manure heaps, and the combustible parts to the furnaces of the carbonizer. In this way a good deal of the ash pit refuse is got rid of; it is often one-twelfth part of the whole quantity.
The carbonizer and the destructor are set 33 feet apart, to allow room for drawing the furnaces and for the mortar mills, but the space is hardly sufficient. One man is employed in attending to the carbonizer.
Besides the openings at the top of the destructor through which the ash pit refuse is fed into the cells, there is a larger opening in each cell, kept covered usually, through which bed mattresses ordered by the medical sanitary office to be destroyed can be put into the cells. These openings are midway between the central openings and the furnace doors, and whatever is put into the cells through these comes into immediate contact with the fire. Advantage is taken of these openings for the destruction of dead animals and diseased meat, and as much as 20 tons in a year have been passed through the destructor.
The whole works are roofed over. The lower floor is open on two sides, but the upper one is closed in, with weather boarding at Burmantofts and with corrugated iron at Armley Road. At the former place the works were in some measure experimental, and the platform was constructed of timber, but at Armley Road it is of plate-iron girders, with brick arching, weight being considered advantageous in reducing the vibration of carting heavy loads over it.
The cost of each depot has been £4,500, exclusive of land, of which about an acre is required for the destructor, carbonizer, inclined road, weigh office, and space. A supply of water is necessary, a good deal being required for cooling the clinkers. The population of the two districts belonging to these works is about 160,000.
The author has no longer any connection with the works described, and for the recent experience of their working he is indebted to Mr. John Newhouse, the superintendent of the sanitary department of the corporation.