Modern Gasworks Practice

RETORT-BENCH APPURTENANCES 249 from some types of charging machines) which, by adhering to the tarry surfaces of the interior of the pipe, promote obstruction. Once started, such obstruction grows apace. When the temperature of the issuing gases is high.—such, as with light charges or layer carbonization—the escaping tarry vapours undergo distillation and redistillation in the pipe until a pitchy mass capable of no further volatilization remains. The most satisfactory means to avoid stoppage is to ensure that every pipe is augered each. time the retort is opened for charging, whether there is any apparent obstruction or not. Some engineers prefer to arrange for an auger gang to pass right through a definite row of pipes an hour or so before the charges are withdrawn. In this way the work of charging and drawing is not delayed, and it is claimed that the time is favourable for the operation owing to the con-dition of the tarry mass. Many ideas have been introduced with. the ob] eet of avoiding trouble from stopped pipes, and one of the earliest of these was the admission of a small trickle of water to the apex of the ascension pipe by means of a gooseneck (Fig. 154), or by the Darwen pipe (Fig. 155). In this way the temperature of the pipe is lowered, whilst the steam produced aids in carrying away a portion of the Fig. 154.—Wateb-keed roa Ascension Pipe. tarry vapours before their distillation can take place. Another means of arriving at the same result is to add a small proportion of water to the coals before carboni-zation, but this is not to be recommended. In some cases a small steam supply has been admitted direct to the base of the pipe, but its use appears to be attended with mixed results, although. the process of steaming on. orthodox principles appears whilst ampie room should be circulation of air. to be followed by decidedly beneficial results. A precaution, however, which calls for attention is the avoidan.ee of entting draughts arotind the pipes, and local cooling. Where the latter occurs in any degree, trouble will nearly always be experienced; and in some works provision has been made for ensuring uniform temperatures by jacketing the pipes with non-conducting material. This would certainly seem unnecessary in. any but very cx-ceptional cases; but care should be given in the design of the liouse so that draughts are avoided, left around the ascension. pipes for the eflective Some interesting work in connection with been carriecl out by M. Coudelou 1 in France. 1 Proc. Société Technique du Gaz, July, 1919. stoppages in ascension pipes has This investigator found thai the See also Gas J„ CXLVI, p. 243.