518 



[December, 1000. 



TIMBERS. 



UTILISATION OP WASTE WOOD. 



(From the Indian Trade Journal, Vol. 

 XIV., No. 175, August, 1000.) 



Inquiries are from time to time re- 

 ceived at the Imperial Institute from 

 firms engaged in working forest con- 

 cessions in British possessions as to the 

 possibility of utilising waste wood pro- 

 duce in the ordinary timber- working 

 operations. It has been thought desir- 

 able, therefore, to compile a short article 

 on this subject with a view to affording 

 general information as to the possibili- 

 ties in this direction. The article in 

 question is published in the Bulletin of 

 the Imperial Institute, Vol. VII., No. 1, 

 and fiom it we take the following parti- 

 culars : — 



Apart from its use for structural pur- 

 poses there are two main ways in which 

 wood eau be utilised at present, viz,, in 

 the manufacture of wood pulp for paper 

 making, and by destructive distillation 

 for the production of wood spirit, Stock- 

 holm tar and wood charcoal. For these 

 purposes the cheaper woods are avail- 

 able, and for destructive distillation espe- 

 cially the waste products of the various 

 timber industries are suitable, 



Much of the wood refuse generally 

 available, such as shavings, sawdust, 

 chips, spent dye and tan woods, etc., is 

 at present used as fuel, its value for 

 this purpose being a few shillings per 

 ton- In considering the disposal of such 

 material it is important to ascertain 

 whether local conditions will permit of 

 the disposal of distillation at a higher 

 rate than would be obtained for the raw 

 material as fuel. Indeed, in undevelop- 

 ed communities where wood spirit, tar 

 and charcoal are not saleable in large 

 quantities, the destructive distillation 

 of wood refuse is not likely to be remu- 

 nerative or even feasible. 



From air-dried wood about one-third 

 of its weight of charcoal can, as a rule, be 

 obtained, this having an average value 

 of from 17s. to 22s. per ton in districts 

 where coal is not readily obtainable. 

 Thus, from one ton of air-dried wood 

 refuse, containing from 20 to 25 per 

 cent, of water, and consequently worth 

 from 4s. to 5s., the value of the charcoal 

 would be about 6s. In most countries 

 there is little difficulty in disposing of 

 the charcoal, as its uses are numerous. 

 Besides being largely employed in the 

 manufacture of iron and steel and in the 

 extraction of other metals, such as cop- 

 per and tin, it can be used in sugar re- 

 fineries for filtration and for various 



domestic purposes. Special uses for the 

 "small" charcoal obtained by distilling 

 wood refuse are found in the manufacture 

 of certain kinds of "smokeless" fuels, 

 calcium carbide, and for packing cold 

 storage chambers. 



Wood refuse can be carbonised more 

 rapidly and at a lower final temperature 

 than blocks of wood, a temperature only 

 300° C being adequate. One result of 

 this is that the pyroligneous acid ob- 

 tained in the distillate is of good quality, 

 and fairly readily purified to yield acetic 

 acid. Wood refuse is also more readily 

 dried by exposure to the air, and does 

 not require to be stored for a year or 

 two before its content of water is 

 reduced to from 20 to 25 per cent, which 

 gives the best results, as is the case 

 with blocks of freshly-cut wood. 



Destructive Distillation op Wood. 



In the destructive distillation of wood 

 the blocks or refuse are heated in a 

 suitable vessel provided with a small 

 aperture fitted with a pipe. In modern 

 practice the carbonising vessel is general- 

 ly a eyclindrical wronght-iron retort 

 built into brick-work in a horizontal 

 position. The retorts are of an average 

 size of 3 metres long by 1 metre in 

 diameter, and are made to hold any- 

 thing up to about four tons of wood 

 (a quarter of a "cord"). They are 

 generally set up in "batteries" of two, 

 and heated by the same fire from below. 

 The naked flame is not allowed to im- 

 pinge directly on the iron retorts, which 

 are heated only by the hot furnace 

 gases, this result being obtained by 

 utilising iron or brick shields or arches. 

 Before the application of heat all the 

 orifices and connections are plugged with 

 clay. The batteries of retorts are set 

 up in rows, and the exit of each retort 

 is connected with a warm condenser 

 made of copper, and cooled externally 

 by means of running water. 



When the wood to be distilled is 

 sawdust or scraps of very small size, 

 such as spent tanning materials, dye 

 woods-, etc., it is generally advisable to 

 have the plant arranged in a special 

 manner owing to the necessity of having 

 the wood quite dry, This result is 

 frequently obtained by building the 

 retorts in such a manner that the hot 

 gases from the one distillation are used 

 to dry the wood refuse ready packed 

 in another retort. The retorts are also 

 sometimes made on a rotary system to 

 facilitate even drying, and thus pre- 

 vent unequal carbonisation. 



