insignificant, and may be placed at about 0.112 pounds per horse-power per hour.
It has been proven in actual practice that, both in the distilling and combustion types of apparatus, the wood, either in the green state or in the form of saw-mill waste, may contain as much as 60 per cent. of water. Either of the two systems can be operated under pressure with an air-blast, in which case a gas-holder and bell must be employed. The gas as it passes from the generator to the gas-holder is conducted through a cooler and washer and through a moss filter, which removes traces of the products that may have escaped the distillation.
Inverted Combustion.—With a few exceptions the pressure-generators which have been described, as well as suction gas-producers which will be later discussed, are fed with anthracite coal or with coke. They cannot be operated with moderately soft or bituminous coal. For this reason they limit the employment of producer-gas engines. Manufacturers have long sought generators in which any fuel whatever can be consumed.
Among the producers which seem to overcome the objections cited to a certain degree, are those which are based on the principle of inverted combustion. These apparatus embody the ideas of Ebelmen, the products of distillation being decomposed by passing them over layers of incandescent fuel.
Fig. 89.—Deschamps inverted-combustion producer.
Many writers place in the class of inverted combustion producers, apparatus of the Riché, Thwaite, and Duff type, in which this idea is also carried out. Riché
employs an independent incandescent mass to reduce the products of distillation of another mass. Thwaite employs two vessels which serve alternately as distilling retorts and reducing columns. Duff draws in the products of distillation for the purpose of blowing them under the fire. All these generators can hardly be said to be of the inverted combustion type.
Fig. 90.—Fangé-Chavanon inverted-combustion producer.