Modern Gasworks Practice

RETORT-BENCH APPURTENANCES 251 THE SINGLE ASCENSION PIPE In. recent years there has been some tendency to work with. only one ascension. pipe for the removal of the gas from a through, retort, instead of providing a pipe at each end, as is the more common practice. Whcn the single pipe is used it should, for the standard sizes of through retorts, never be less than 8 inches in diameter.. The following are the advantages which may be claimed for the single-pipe system :— (a) Owing to th.e necessity of providing only one set of ascension pipes, dip pipes, hydraulic main, tar towers, foul main, etc., to each. retort setting, the saving in initial cost is considerable. It must be remembered, however, that two hydraulic mains should. be used when there are ten or more retorts to the setting, also with. settings of “ eight ” in. two rows. This is owing to the limitations imposed by the width. of the arcli. (6) There are fewer pipes to keep clear. At .the same time the pipes are larger, aad the labour, therefore, is more arduous. When the pipes are all on one side, the men can keep away from the stoking machinery, and are thus out of the way, whilst there is less liability of coal dust being carried up the pipe. (c) There is said to be greater immunity from stopped pipes. (d) The system lends itself admirably to steaming. With regard to statement (c), it must be taken with. a certain amount of reserve,. as experience with. single pipes has hardly been such as to definitely establish this, faet. The disadvantages of the system are :— (e) It cannot be satisfactorily employed wli.cn the retorts are fully charged, for although a vacuum may obtain in the end of the retort nearer the pipe, there may be a heavy pressure at the other end, owing to the gas way being clioked by swelling of the coal, uneven charging, etc. (f) With light charges the gas travelling from the farther end of the retort is in contact with the hot walls for a considerably longer period than is the case when two pipes are employed. Hence the effect of degradation will be more noticeable. (c) If the single pipe becomes clioked there is no alternative outlet for the gas ; but, as previously noted, no well-managed works should have a completely choked pipe. BRIDGE PIPES The change of direction of flow of the gas from the ascension pipe to the dip-pipe is efEected by means of the bridge, arch, or saddle pipe. When direction has to be altered in this manner a certain amount of friction is inevitable. The change must be effected as gradually and smoothly as possible, so as to avoid mechanical deposition of the tarry vapours and suspended particles. To this end sharp angles must be avoided. An equally important feature in connection with. the bridge pipe is that of ensuring easy access to all sections of the pipe way. Various types of bridge pipes are illustrated (Figs. 156 to 161). Fig. 156 is chiefly found in the smaller works. The design shown in Fig. 158 should be avoided, for, in spite of easy access to all sections, the change of direction is far too abrupt. The “ Bournemouth ”