THE CONDENSATTON OF COAL GAS 459
WxVc __
V x A x D
To ensure a fairly representative sample of the gas the sampling must be rapid, in order to prevent the falling out of the larger tar particles. With. this-object, the difference of pressure between. the two sides of the disc should be from 12 to 24 in. water column, depending on the resistance of the paper disc. Speed is also necessary to complete the removal of the finer particles of fog by impingement within the pores of the filter paper. One disc only is necessary, as a second one placed in series with the first and spaced by a metal liner is invariably unstained. The stain is always confined to the receiving surface of the first diso. Where the gas is tinder low pressure an aspirator is used to give the required pressure-difference.
As before stated the volume of gas to be passed through the filter paper to give a stain within measurable limits varies from 80 c.c. to 9,000 c.c., depending upon the proportion of tar fog present.
The following interesting series of results obtained upon gas streams on works where different manufacturing methods were employed have been given by Edwards :—
Coal Gas. Grains per cubic foot.
A. Outlet condensers following seal in hydraulic mains 30
B. Outlet condensers following part sealed and part dry mains with
C. retort-house governors 15
Outlet P. and A. tar extractors following A. 0-25
D. Outlet rotary exhausters following dry mains and condensers . 8
E. Outlet rotary exhausters following B. . 6
[■’. Outlet turbo exhausters following B. 0-6
G. Outlet Livesey washers following D. 0-6
H. Outlet P, and A. tar extractors following E. 0-17
I. Outlet P. and A. tar extractors following F. . 014
J. Outlet ammonia washers or serubbers horizontal revolving type follow-
mg G 0-4
Water Gas, Partly Carburetted.
K. Outlet rotary exhausters following relief holder . 2-3
L. Outlet Crossley tar extractor following K 0-17
It will be observed that retort-h.ou.se governors have an appreciable effect on the tar fog, and the rotary exhausters remove a fair proportion of the remainder. Tuibo-exhausters reduce the amount to as low a figure as Livesey washers following rotary exhausters. Pelouze and Audouin machines carry the removal to finer limits.