Modern Gasworks Practice

CONTROL OF HORIZONTAL RETORT SETTINGS 129 should. be taken to see that they are frequently attended to so that tlie free action of the vanes is maintained. RELIABLE TESTS A word is necessary liere with. regard to the manner in which tests on settings are made. When drawing oflE samples of waste gases it is advisable not to make use of the bottom or damper section of the regenerator for the purpose, as misleading analyses may be the outcome, owing to the by-passing of the secondary air. In many regenerator settings it is quite common to find that the vacuum in the secondary-air and waste-gas flues is practically equal, which is commendable as far as short-circuiting and by-passing are concerned. When. such is the case, however, it rarely occurs to those responsible to analyse the ingoing secondary air at a section near the top of the regenerator. A point worth noticing with. regard to regenerators which show signs of serious short-circuiting is that of isolating the defective sections by transposing the air-box to a position higher up in the tiers of the regenerator. A certain amount of regeneration is, of course, sacrificed ; but usually the loss is more than. balanced. by the restric-tion of the short-circuiting. This alternative should only be turned to when repairs to the lower sections are impossible. Here, again, the engineer must be thoroughly conversant with the constructional details of his setting ; for, in more than one type of regenerator, the raising of the secondary-air inlet in this way would completely cut ofl the secondary supply to many of the nostril holes. In connection with these systems, the advantages accruing from the multiple regulation are undoubtedly significant, for there is frequently a tendency for the rush, of air to be greatest towards the centre nostrils of the furnace arch. This entails irregulär distribution of heat and duil mouthpieces. With the separate adjustments, however, the mouthpiece temperature is well under control. As regards the regulation of waste-gas flue draught, it is as well to provide two dampers to each regenerator, as shown in Kg. 66. The upper damper can then be regulated until the best results are given, while chiring temporary stops or clinkering the lower damper is brought into play. The Fig. 66.—Double Damper Contbol. latter can then be opened again to its füll- est extent, and the draught is governed as originally by the upper damper, which has not been movecL Care must be taken, however, to see tliat the lower damper is properly sealed, otherwise air will be dæawn past it, and tlie chimney draught on the setting correspondingly reduced. It may be mentioned here that in the ordinary way the draught on the chimney of a regenerator setting should not exceed from to incli of water. The actual vacuum is usually measured by a special direct-reading instrument, the connecting pipe of which is thrust into the sight-box at the base of the chimney. It is usual to calibrate these instruments in hundredth parts of an inch, so that for correct working