764
MODERN GASWORKS PRACTICE
COMPLETE GASIFICATION PLANT
The use of coal for the production of producer gas and water gas, a process which. h.as been referred to in the previous chapter, is comparatively common in America, and alt.hoiigh in the case of producer gas (where air and steam are blown in simultaneously) considerable success is met with, the same cannot altogether be said when th.e ordinary water-gas plant is considered, as in. this case the requirements of a fuel are far more exacting.
Several attempts have been made to gasify coal completely. One of the earliest plants designed for the purpose was the Fahnehjelm apparatus (Fig. 458). The plant consisted of a generator with a retort placed above the former. Around the retort was arranged a heating chamber filled with chequer brickwork, and from the illustration it will be observed that the whole
Stack and Valve.
'Steam
Steam
‘Seal
Fig. 458.—Thb Fahnehjelm Plant.
minutes tlie stack valve on B was opened,
apparatus bears a stnkmg resem-blance to plants which are in operation to-day.
A Contemporary plant was that known as the Rose-Hastings which appeared in many slightly different forms. The primary generator (A, Fig. 459) was charged with coal about once every hour, while the secondary chamber (B) was filled with coke. The depth of fuel in both vessels was about 8 feet. Düring the blow the stack valve attached to generator A was opened, those on. the chamber B and super-heater C being closed. The blast was admitted simultaneously to A and B, secondary air being admitted at a point just above the top of the fuel-beds and also to the brancli connection between the two chambers. After blowing for five while some two minutes later the stack'
valve on C was opened and that on B closed, secondary an mean while being admitted to the base of C. In this way both the fuel-beds and the superheater were raised to the required temperature.
The run was then commenced, steam being admitted at the base of the coal bed. The mixture of coal gas and water gas passed firstly through the chequer brickwork at the top of the generator, thence through similar chequers in the