428
DESTRUCTORS A dust-catching apparatus has been designed and erected at the temperature in main flues, &c. (y) The chimney draught Edinburgh, by the Horsfall Furnace Syndicate, in order to over- must be assisted with forced draught from fans or steam jet to come difficulties in regard to the escape of flue dust, &c., from a pressure of 1^ inches to 2 inches under grates by water-gauge. the destructor chimney. Externally, it appears a large circular (h) Where a destructor is required to work without risk of block of brickwork, 18 ft. in diameter and 13 ft. 7 in. high, nuisance to the neighbouring inhabitants, its efficiency as a refuse connected with the main flue, and situated between the destructor plant must be primarily kept in view in designing the destructor cells and the boiler. Internally it consists of a spiral works, steam-raising being regarded as a secondary consideration. flue .traversing the entire circumference and winding upwards to Boilers should not be placed immediately over a furnace so as tothe top of the chamber. There is an interior well or chamber present a large cooling surface, whereby the temperature of the 6 ft. diameter by 12 ft. high, having a domed top, and com- gases is reduced before the organic matter has been thoroughly municating with the outer spiral flue by four ports at the top of burned, (i) Where steam-power and a high fuel efficiency are the chamber. Dust traps, baffle walls, and cleaning doors are also desired a large percentage of C02 should be sought in the furnaces, provided for the retention and subsequent weekly removal of the with as little excess of air as possible, and the flue gases should flue dust. The apparatus forms a large reservoir of heat main- be utilized in heating the air-supply to the grates, and the feedtained at a steady temperature of from 1500° to 1800° F., and is water to the boilers, (j) Ample boiler capacity and hot-water useful in keeping up steam in the boiler at an equable pressure storage feed-tanks should be included in the design where steamfor a long period. It requires no attention, and has proved power is required. successful for its purpose. As to the initial cost of the erection of refuse destructors, few Travelling cranes for transporting refuse and feeding cells are trustworthy data can be given. The outlay necessarily depends, sometimes employed at destructor stations, as, for example, at amongst other things, upon the difficulty of preparing c Hamburg. Here the transportation of the refuse is effected by the site, upon the nature of the foundations required, means of specially constructed water-tight iron waggons, con- the height of the chimney-shaft, the length of the inclined or taining detachable boxes provided with two double-flap doors at approach roadway, and the varying prices of labour and materials the top for loading, and one flap-door at the back for unloading. in different localities. As an example may be mentioned the case There are thirty-six furnaces of the Horsfall type placed in two of Bristol, where, in 1892, the total cost of constructing a 16-cell ranks, each arranged in three blocks of six in the large furnace Fryer destructor was £11,418, of which £2909 was expended on hall. An electric crane running above each rank lifts the boxes foundations, and £1689 on the chimney-shaft; the cost of the off the waggons and carries them to the feeding-hole of each cell. destructor proper, buildings, and approach road was therefore Here the box is tipped up by an electric pulley and emptied on £6820, or about £426 per cell. The cost per ton of burning reto the furnace platform. Where the travelling crane is used, fuse in destructors depends mainly upon—(a) The price of labour the carts (four-wheeled) bringing the refuse may be constructed in the locality, and the number of “shifts ” or changes of workso that the body of the carriage can be taken off the wheels, men per day ; (b) the type of furnace adopted ; (c) the nature of lifted up and tipped direct over the furnace as required, and the material to be consumed ; (d) the interest on and repayment returned again to its frame. The adoption of the travelling of capital outlay. The cost of burning, ton for ton consumed, in crane admits of the reduction in size of the main building, as less high-temperature furnaces, including labour and repairs, is not platform space for unloading refuse carts is required ; the inclined greater than in slow-combustion destructors. The average cost roadway may also be dispensed with. Where a destructor site of burning refuse at twenty-four different towns throughout Engwill not admit of an inclined roadway and platform, the refuse land, exclusive of interest on the cost of the works, is Is. l^d. may be discharged from the collecting carts into a lift, and thence per ton burned ; the minimum cost is 6d. per ton at Bradford, and elevated into the feeding-bins. the maximum cost 2s. lOd. per ton at Battersea. At Shoreditch the cost per ton for the year ending 25th March 1899, including The general arrangement of a battery of refuse cells at labour, supervision, stores,- repairs, &c. (but exclusive of interest a destructor station is illustrated by Fig. 5. The cells on cost of works), was 2s. 6 9d. The quantity of refuse burned per are arranged either side by side, with a common cell per day of 24 hours varies from about 4 tons up to 20 tons. Working main flue in the rear, or back to back with the The ordinary low-temperature destructor, with 25 square feet grate area, burns about 20 lb of refuse per square foot of grate stmctors main fluo placed in the centre and leading to a area per hour, or between 5 and 6 tons per cell per 24 hours. The tall chimney-shaft. The heated gases on leaving Meldrum destructor furnaces at Rochdale burn as much as 66 lb' per square foot of grate area- per hour, and the Beaman and Deas the cells pass through the combustion chamber into the destructor at Llandudno 7l 7 lb per square foot per hour. The main flue, and thence go forward to the boilers, where amount, however, always depends materially on the care observed their heat is absorbed and utilized. Forced draught is in stoking, the nature of the material, the frequency of removal supplied from fans through a conduit commanding the of clinker, and on the question whether the whole of the refuse whole of the cells. An inclined roadway of as easy passed into the furnace is thoroughly cremated. The amount of residue in the shape of clinker and fine ash gradient as circumstances will admit, is provided for the varies from 22 to 37 per cent, of the bulk dealt with. From 25 to> conveyance of the refuse to the tipping platform, from 30 per cent, is a very usual amount. At Shoreditch, Desi^ues which it is fed through feed-holes into the furnaces. In where the refuse consists of about 8 per cent, of straw, the installation of a destructor, the choice of suitable plant paper, shavings, &c., the residue-contains about 29 per cent, clinker, per cent, fine ash, ’5 per cent, flue dust, and ‘6 per cent, old and the general design of the works must be largely de- 2'7 tins, making a total residue of 32'8 per cent. As the residuum pendent upon local requirements, and should be entrusted amounts to from Jth to gi'd of the total bulk of the refuse dealt, to an engineer experienced in these matters. The following with, it is a question of the utmost importance that some proprimary considerations, however, may be enumerated as fitable, or at least inexpensive, means should be devised for its regular disposal. Among other purposes, it has been used for materially affecting the design of such works :— bottoming for macadamized roads, for the manufacture of con(a) The plant must be simple, easily worked without stoppages, crete, for making paving slabs, for forming suburban footpaths or and without mechanical complications upon which stokers may cinder footwalks, and for the manufacture of mortar. The last is lay the blame for bad results, (b) It must be strong, must with- a very general, and in many places profitable, mode of disposal. Through defects in the design and management of many of the stand variations of temperature, must not be liable to get out of order, and should admit of being readily repaired, (c) It must early destructors complaints of nuisance frequently arose, and be such as can be easily understood by stokers or firemen of these have, to some extent, brought destructor installations into average intelligence, so that the continuous working of the plant disrepute. Although some of the older furnaces were decided may not be disorganized by change of workmen, (d) A sufficiently offenders in this respect, that is by no means the case with high temperature must be attained in the cells to reduce the the modern improved type of high - temperature furnace ; and refuse to an entirely innocuous clinker, and all fumes or gases often, were it not for the great prominence in the landscape of should pass either through an adjoining red-hot cell or through a tall chimney-shaft, the existence of a refuse destructor in a a chamber whose temperature is maintained by the ordinary neighbourhood would not be generally known to the inhabitants. working of the destructor itself at a degree sufficient to exclude A modern furnace, properly designed and worked, will give rise the possibility of the escape of any unconsumed gases, vapours, to no nuisance, and may be safely erected in the midst of a popuor particles. The temperature may vary between 1500° and 2000°. lous neighbourhood. To ensure the perfect cremation of the (e) The plant must be so worked that while some of the cells are refuse and of the gases given off, forced draught is essential. being recharged, others are at a glowing red heat, in order that a This is supplied either as air draught delivered from porce(j high temperature may be uniformly maintained. (/) The design a rapidly revolving fan, or as steam blast, as in the draught. of the furnaces must admit of clinkering and recharging being Horsfall steam jet or the Meldrum blower. With a easily and quickly performed, the furnace doors being open for a forced blast less air is required to obtain complete combustion minimum of time so as to obviate the inrush of cold air to lower than by chimney draught. The forced draught grate requires.
