Modern Gasworks Practice

226 MODERN GASWORKS PRACTICE impurities associated with the fuel. It is a recognized rule of retort-house practice t.hat the furnaces must not be too hot; therefore there is theoretically no need for very high refractoriness. If, however, an inferior brick was made use of, the results would undoubtedly be very far from pleasing, for the heat in the producer chiefly owing to fluctuation in the depth. of the fuel-bed.—undergoes severe changes. With regard to the construction of the regenerator flues for the circulation of secondary air and waste gases, it must be borne in mind that the arrangement is employed with. a view to abstracting the maximum of heat from the waste gases and conducting it to the secondary air. Accordingly, as the heat to be withstood is comparatively low, the bricks or blocks should be made with an eye to high thermal conductivity and mechanical strength rather than to higli refractoriness. WORKING repairs When retorts have been in operation for some time they should be carefully examined when discharged. When. holes and cracks begin to make their appear-ance they should be dealt with at once, as the cutting action of the furnace gases passing through them tends to enlarge them. This is particularly the case in the modern regenerative setting in which a pressure prevails in the combustion chamber and gas flues. Many excellent proprietary patching cements are now to be obtained, and experience with the various kinds is the best guide. For cold patching and crawling the author finds that the best method is to clean thoroughly all of the cracks, and then to.wash them out with. a solution of silicate of soda made by dis-solvmg 1 Ib. of the silicate in a gallon of water. For pugging up the cracks the above sihcate solution should be intermixed with as much of a good quality silica clay as gives a consistency suitable to work with. After the crack has been stopped. the surface should be washed over with the silicate solution. In this way the material forming the iepair tends to flux sliglitly, with. the result that it forms a close bond with the original refractory, and seldom works out when the retort beuch is put under heat again. R. L. Fletcher * has introduced a method in America whereby the repairs are effected by spraying into the cracks by means of a hand-pump a mixture of fireclay, silica cement, and a small proportion of comrnon salt. The mixture is diluted with water, so as to form a solution wliich will freely pass the spray, and it is applied at a pressure of 50 Ib. per square inch. MATERIALS FOR HEAT RETENTION The chief qualities required of the material of which the outside or front walls of the setting are composed are moderate refractoriness, but, more especially, a low abihty to conduct heat. By far the most common practice is still that of building up these walls of 9-inch or 13|-inch work in aluminous fireclay, but witliin the last few years some attempt has been made to reduce the thermal losses by radiation 1 Gas Record, July, 1919.