CONTROL OF HORIZONTAL RETORT SETTINGS 135
be running at its lowest possible speed, thus the “ pull ” is likely to be far from steady. In order to remedy this, and to put the engine under a greater load, it is advisable to open slightly the by-pass between the inlet and the outlet pipes, this having the desired steadying efl'ect.
The advantage of working in this manner, as will be seen, is that there is no actual cessation of gasmaking, and the exhauster is at work during the whole twenty-four hours. In order that this method may be adopted, liowever, it is essential that
heavy charges should be worked. If the old-fash-ioned light charges are in vogue, then gasmaking must inevitably cease, and a portion of the poor gas should be blown away as described below. With the heavy charges, the make of gas will, of course, diminish. by degrees, until, during the final hour before recharging, it will have dropped to about 7 to 10 per cent, of the normal figure. In describing this method the average conditions of |-inch seal and f-inch “ draw ” on the foul main have been assumed. If otter conditions prevail the necessary steps will vary accordingly.
Fio. 68.—Chart showing Regulation of Vacuum at Inlet of Exhauster.
Getting Rid of Inferior Gas
After the final charge of coal has been put in, it is the quality of the gas evolved which really decides the manner in which the “ draw ” is to be regulated. It is a distinct advantage to have a special recording calorimeter run. back from the outlet of the exhauster to the retort house, so that the foreman in charge has some indica-tion of the quality of the gas soon after it has been generated. When the quality is noticed to be dropping, then the “ draw ” on the hydraulic main must be regulated accordingly. Unfortunately, in some cases, when the inferior coal is being used, the quality dæops to such, an extent that it is no longer advisable to send, the gas forward to the holders. When this occurs, the continuity of the work has to be broken, and the exhauster is stopped while the poor gas is blown away. This is best done as folio ws : The main val ve at the outlet of the condensers is closed and