GB468887A - Improvement in or relating to a method of and apparatus for drying and incinerating waste material - Google Patents

Abstract

468,887. Drying and incinerating furnaces. STEVENS, A. H. (Nichols Engineering & Research Corporation) March 5, 1937, No. 6612. [Class 51 (i)] [Also in Group XIII] A method of drying and incinerating waste material, such as sewage sludge, comprises passing the material downwardly through drying zones in the presence of hot vapour, then burning the dried material and mixing the products of combustion with the drying gases to destroy odour and using a substantial part of the resultant heat to heat the gases circulating in the drying zones without direct contact as by a recuperator or muffle. Filtered sludge is fed through a revolving valve 12, Fig. 1, to a multiple hearth furnace 10 provided with a rotatable hollow shaft 13 carrying rabble arms 14-21, to pass material over staggered hearths 22-29. The furnace may be enclosed within a cylindrical wall. Hearths 25-29 may be of brick and 22-24 of heat resistant alloy steel. The shaft 13 may have a conduit 30 receiving air from a blower 31 and passing it into the interior of rabble arms 18-21 or also 16-21 if desired in known manner. As material is rabbled over hearths 22-35 it comes in contact with hot vapour through various discharge ports and over the hearths in succession. A substantial portion is recirculated through a conduit 33 by fan 34 and through conduits 35 of a recuperator 36 and back by a conduit 37, being reheated in the process. As excess accumulates in this portion of the furnace it may be forced through a branch conduit 38 and heated to eliminate bad odours. The recirculated vapour absorbs considerable heat from exhaust gases and extra heat is given up in the recuperator 44 for heating intake air in the conduit 47. Recirculation of vapour in the drying hearths checks premature combustion or scorching of the partially heated sludge. Upper furnace gas comes at 39 in contact with combustion gas at its hottest about 1100‹ F. To ensure this temperature an oil or gas burner 49 may be used. Preheated combustion air comes from conduits 32, 42 to furnace inlets 40, 41. The combustion gas from chamber 48 heats the recuperators 36 and 44 and may then pass out to a stack or heating system for the plant. A number of fuel burners 52 may be used to start the plant. The speed of operations can be controlled by various fans and dampers. Ash is passed out at 53. Weights and temperatures are quoted for a plant 20 feet in diameter. Reverse flow of gases to that shown may be employed in some cases. In a modification, Fig. 2, gas and vapour mixture after passage through conduit 50 pass through recuperators 36, 44 in reverse order to that of Fig. 1. In another modification, Fig. 3, hearths 75-78 are provided with muffle heating cavities 89, 91. High temperature gas is drawn off at 87 and meets drying gas at 86 so as to consume odours. Hot gas may be passed upwards through succeeding muffles or downwardly, thence through a conduit 92 into a recuperator 93 and out to a stack. Intake air may pass through conduit 88 to incinerating parts of the furnace.