CHAPTEE XIII
THE CONDENSATION OF COAL GAS
Although the operation of condensation might appear to be one of extreme sim-plicity, this is by no means the case ; for the character of the final products obtained is appreciably influenced by the männer in which the gas is dealt with at this stage. Condensation may be best defmed as the reduction of the gas to normal temperatures, and the simultaneous removal of all those substances which are not permanent gases at such temperatures. In the main, the apparatus employed for the purpose is of a simple nature, and merely embodies the principle of exposing large surface areas to the action of a cooling agent. On gasworks the cooling medium employed is either air or water, or both. The atmospheric condenser was a common feature of gasworks in the past, and it is still to be found in many of the smaller and medium-sized works. As a cooling agent, however, water is infinitely more efficient. When a temperature drop of 10° Fahr, is required, the capability of water (per square unit of surface exposed) to bring about the reduction is eleven times as great as that of air, and when. the temperature drop increases to 50° Fahr, the proportional efficiency is more than 200 to 1. In addition, the water-cooled condenser is easily regulated, so that a more or less constant outlet temperature may be obtained whether the apparatus is working up to its füll capacity or not.
ATMOSPHERIC CONDENSERS
Condensers of the atmospheric type are of no stereotyped construction, and in the case of some small works are often made up from odd lengths of pipe and connections which. the manager may have at his disposal. In general, however, the chief standard varieties in conimon use may be classified as follows :—
(a) Horizontal types.
(6) Vertical types.
(c) Annular types.
(<Z) The battery condenser.
The horizontal condenser shown in Fig. 266 frequently takes the form of an extended foul main which is carried in zigzag fashion from end to end of one of the retort-house walls. As blockages from naphthalene or pitchy deposits are likely to occur at times, it is essential that flange connections should be used, so that clearing may be easily effected. The Condensed, liquids flow down the sloping pipes in the 436