Producer gas or generator gas.—Manufacture of producer gas consists in dealing separately with the generation of the gas and the combustion of the gases which arise. This is effected by admitting only so much air (primary air supply) to the fuel as is necessary to cause the gases to come off, and then admitting further air (secondary supply) at the point where the combustion is to take place; this secondary supply and the gas formed in the gas producer are heated in regenerators before combustion by bringing the gases to be burnt into contact with Siemens’s heaters, of which there are four. Two of these are always heated and serve to heat the producer gas and secondary air supply.
Fig. 15.—Horizontal Regenerative Grate (after Lueger)
A producer gas furnace, therefore, consists of a gas producer, a gas main leading to the furnace hearth, the heater, and the chimney.
Fig. 16.—Step Regenerative Grate (after Lueger)
The gas producer is a combustion chamber filled with coal in which the coal in the upper layer is burnt. Generators may have horizontal or sloping grate (see figs. [15] and [16]). The Siemens’s heaters or regenerators are chambers built of, and filled loosely with, fireclay bricks and arranged in couples. Should the gas producers become too hot, instead of the chambers subdivided air heaters are used, whereby the hot furnace gases are brought into contact with a system of thin-walled, gastight fireclay pipes, to which they give up their heat, while the secondary air supply for the furnace is led beside these pipes and so becomes heated indirectly. Previous heating of the producer gas is here not necessary; no valves are needed because the three streams of gas all pass in the same direction.
Fig. 17a.—Siemens’s Regenerative Furnace
L Air; G Gas
