Modern Gasworks Practice

REFRACTORIES FOR GASWORKS PURPOSES 209 abstruse technical details, which are of chief concern to the scientist and investigator. Errors of judgment in the selection of fireclays are only too common, even in the present age ; and, undoubtedly, considerable trouble and expense could be avoided if, in the first place, the purchaser studied his requirements on methodical lines. To this end, it is suggested that the conditions which any particular material may be called upon to withstand should be subjected to a preliminary investigation on. lines such as the following :— 1. Is the temperature high or moderate? “Moderate” may be considered. up to 1,000° C. “ High,” up to 1,500° C. Äs a matter of faet, the latter temperature should seldom be necessary in the modern combustion chamber ; the figure being usually in. the iieighboiirhood of 1,400° C. 2. Will there be fluctuations of temperature ? This is one of the most trying conditions which the material can be called upon to withstand. If the setting is worked. correctly there should be nothing in. the way of violent fluctuations, except, perhaps, in the retorts. It must be remembered that there may be so great a fall in temperature as 500° C. when a retort is freshly charged. 3. Will the material come into direct contact with the flame, or will there be “ cutting heat ” ? By a “ cutting heat ” is usually understood a fierce, localized. flame, the effeet of which is exaggerated by the presence of flue dust in the gases. This dust may contain upwards of 50 per cent, of injurious iron compounds. 4. Is mechanical strength required ? Various portions of the retort beuch take their place in ensuring the stability of the structure ; hence, in addition to withstanding high temperatures, théy are called upon to withstand working stresses. 5. Is heat to be conducted or retained ? This is a point which arises chiefly when deciding upon. material for regenerators and the external walls of settings. In order to prove a good conductor of heat, the material should be dense, and manu-factured with. as close a graiii as possible. 6. Is the material likely to be affeeted by external fluxes ? The small per-centage of low-fusing constitueirts present in the fireclay is more or less harmless when left to itself ; but if incipient “ slagging ” is set up by other fusible substances introduced from outside, there is no telling where the trouble may end. Iron dust in the producer gases and clinker adhering to the sides of the furnace walls are the chief offenders in this direction. This effeet is considered more fully on page 215. 7. Will the material be subjected to an oxidizing or to a reducing atmosphere ? A reducing atmosphere (i.e., an atmosphere of carbon monoxide) is more trying than oxidizing conditions ; but if a retort bench is being correctly operated, the only possible point at which a reducing atmosphere could contiiiuously prevail, would be above the fuel in the furnace and below the nostril arcli. If carbon monoxide is found at a point beyond this, it is certainly indicative of a shortage of secondary air. Mellor says that the magnitude of the fluxi,ng effeet induced by the reducing atmosphere depends upon a number of factors. For example : (1) It depends upon the strength. of the reducing atmosphere ; that is, on the proportion (and kind) of reducing gases in the given atmosphere ; (2) it. will also depend upon the rate the gases penetrate into the interior of the brick, and this in turn depends upon the