ASH HANDLING. The boilers required for generation of power in a large electric or industrial plant often burn thousands of tons of coal a day; and since perhaps io to of the average coal is incombustible ash, hundreds of tons must be removed each day. The handling of such volumes of waste material de serves careful consideration, as improper methods or apparatus may double or treble the cost. Thus, good ash handling methods and facilities may represent 2 to 1% of the total cost of power generation, whereas systems improperly applied may raise the cost to I or '1%.
In designing an ash-handling system certain precautions should be taken. In the first place all material coming in contact with the ashes should be of cast iron or other corrosive-resisting sub stances, since most ashes are alkaline and highly corrosive. It is furthermore important that all ashes should be thoroughly quenched before handling, otherwise there is danger from carbon monoxide poisoning and burns. In general two standardized methods of ash handling are now used in most large boiler houses: the hydraulic system and the purely mechanical system.
Hydraulic Ash Handling.—In this method ashes are stored in hoppers beneath the furnace for a period of eight to 24 hours, depending upon conditions. Beneath these hoppers a conduit capable of carrying water for removal of the ashes to a centrally located sump, is installed horizontally and the water is introduced from pressure mains. When the ash hoppers are filled, they are discharged into the conduit at a rate well below the carrying capacity of the flowing water. The ashes may be taken from the ash sump by centrifugal pumps, generally made of manganese steel, in which case (1) the ashes and water may be discharged to low points within half a mile of the boiler house, where the ashes are deposited and the water leaches into the ground; (2) the ashes and water may be pumped into an overhead storage bin, the water being run off the top and returned to the sump: the ashes remaining as a residue, which is dumped into cars. Alter natively, the ashes may be taken directly from the sump by means of a grab bucket or other elevating machinery, and loaded into an overhead storage bin or directly into railroad cars or motor trucks.
The hydraulic system of ash removal is applicable where coal is burned as powder. In such cases the ashes are removed either as a molten slag (which is chilled and disintegrated by the stream of water into which it falls) or as a dry powder. In the latter case it is essential to carry this material in an enclosed system, otherwise the ash dust permeates the entire boiler house with results deleterious to moving machinery. Hydraulic systems are also applicable to the continuous discharge type of mechanical stokers such as chain grate stokers or underfeed stokers equipped with mechanical grinders. The water required for a hydrau lic ash removal system will vary from 3 to 61b. of water per ton of ash moved, if the water is allowed to discharge to waste from the sump. If re-circulated, about one-tenth of a pound of water per pound of ash is required for make-up to prevent con centration.
The advantages of the hydraulic ash removal systems can be stated as follows: (1) no labour is required other than the open ing and closing of the valves controlling the flow of ash and the flow of water; (2) the ashes are handled in a totally enclosed system,—they are always under water and thus no dirt, dust or vapour can escape; (3) no moving machinery in the system comes in contact with the ashes; (4) the cost of running is low, varying from 1 to 3kw. hours per ton of ash moved; (5) the height of the power house building is generally 2 to 'of t. less since no cars run beneath the ash hoppers : the saving in building often more than pays the total cost of the ash handling system (6) where the ashes can be pumped to low outlying property, there is no rehandling of the material.
Mechanical Ash Handling.—This system is also in common use in large boiler houses. The ashes in the hoppers beneath the furnace are dropped into cars, the control generally being main tained by horizontal piston-operated gates. In large plants where the final disposal of ashes is to be made by railroad cars, these are often run directly beneath the ash hoppers. This entails large building expense, as the entire boiler room must be raised suf ficiently to allow the railroad cars to run beneath it ; however, it obviates the necessity of re-handling the ashes. In smaller plants where this expense is not warranted, industrial cars of small height may be run beneath the ash hoppers. In this case a skip hoist is installed at the end of the building, the industrial cars are dumped into the skip hoist bucket and the ashes lifted into a storage bin, which latter discharges directly into railroad cars or wagons. This system is advantageous where underfeed stokers are used and the ashes are intermittently discharged. Such practice generally results in comparatively large clinker formations, which can best be handled in cars or by skip bucket.
There are other systems of ash handling generally applied in special cases and usually in the smaller boiler houses or in densely populated sections of cities, such as in hotels and in office build ings. Steam jets, bucket conveyors and the like are then em ployed. (See MECHANICAL HANDLING.) These systems, however, usually entail a high maintenance and operating expense and are generally used where it is impossible or impracticable to apply either of the two systems outlined above. (F. B. A.) 'ASHI (352-427), Jewish 'angora, the first editor of the Tal mud, was born at Babylon. He was head of the Sura academy, and there began the Babylonian Talmud, spending 3o years of his life at it. He left the work incomplete, and it was finished by his disciple Rabina just before A.D. 500. (See TALMUD.)