30 



HARDWOOD RECORD 



February 10, 1922 



YARD AND KILN 



c^ Section Intended to Promote Efficiency^ 

 and Economy in Luinber Drying ^ 



Short Stories of the Kiln 



Automatic Dry Kilns 

 By C. J. M. 



Not the kind in which "you wind the clock, turn on the steam, 

 and the eontroUer will do the rest," but the very ordinary, "honest 

 to goodness," plain ventilated type kilns were built during the war, 

 in a block of a dozen or more, by one of our largest industrials. 

 These kilns were quite large, of compartment type, and would hold 

 about 40,000 Bf. of 4/4' stock. 



Outer walls were of brick, inner partitions and ceilings were of 

 wood. The usual heating system was placed under the piling floor, 

 but it was properly graduated for the drying of large oak dimension 

 lumber drying. 



Since the moisture removal was to be by ventilation, a fresh air 

 supply was provided for by means of two duets, located on the 

 floor of the kiln, one at each side wall, running full length, from 

 front to rear, taking air at both ends and distributing same into 

 the kiln through numerous transverse slots in these ducts, whenever 

 the inlet gates were opened. 



The moist air rejected was to be removed by a number of ver- 

 tical ducts in each side wall, their inlets were located about five 

 feet from the ceiling and these ducts were constructed so as to al- 

 most counterbalance the tendency of the heated air to rise in the 

 same. 



These vertical duets connected into a horizontal gathering duct 

 running on the side wall, below the ceiling, and the two horizontal 

 gathering ducts in turn were interconnected by means of a cross 

 duct located in the space between the ceiling and roof, to the cen- 

 ter of which duct was attached .a liberal-sized ventilator, passing 

 above roof and equipped with an adjustable damper, the amount of 

 opening of which was controlled from the floor, near the front door, 

 by means of copper chains. 



The writer, who was called in when these kilns were about 90 

 percent complete, paid particular attention to the damper arrange- 

 ments on the intake as well as the discharge, in the desire to make 

 the kiln regulation as positive and reliable as could be done. Ex- 

 treme precautions also were taken to protect the fresh air intakes 

 from influence of wind pressure and direction. 



When completed these kilns were charged with bent wheel rims 

 of oak, containing about 60 percent moisture, and were watched 

 with much interest. All dampers, of course, were closed tight at 

 the start. Drying progressed quite satisfactorily all the way past 

 the fibre saturation point, and yet no need showed itself for any 

 adjustment of the dampers from their original closed position. The 

 stock went on down to 5 percent and was unloaded, and still no 

 change in the damper position. The drying had been all that 

 could be desired, and all kilns in the block had acted alike. 



As fast as emptied the rooms were carefully inspected, but the 

 inspection failed to disclose any appreciable leakage. These kilns 

 were operated for more than a year in precisely the same manner, 

 and on the same materials, with uniformly excellent results, with- 

 out opening of either inflow or outflow dampers. Our expensive 

 ventilators, ducts, dampers and windbreaks might as well never 

 have been installed. The only argument advanced was that with 

 bent rims the proportion of actual wood content to wall, ceiling 

 and floor surface was so abnormal that any moisture coming from 

 the wood would be absorbed as fast as transfused and vaporized 

 into the kiln air. 



This argument sounded somewhat ingenious and fishy, so the 



writer determined to test the matter by reversing the proportions 

 of wood content to absorbent surfaces by loading into these kilns 

 as many green, heavy hickory axle blanks as they would hold. 

 Much to his surprise, the behavior of these kilns remained un- 

 changed. Moreover the drying was very good without any change 

 in damper position. 



Later, to further test the matter, several charges of 4/4" gum 

 lumber were placed into these rooms (about 40,000 Bf. each), and 

 these were likewise dried very well without attention beyond mere 

 adjustment of the heat. 



The writer has never fully solved the puzzle, but it may be fairly 

 assumed that, since the doors arc unusually tight, located on one 

 end only, the moisture coming from the lumber surely escaped in 

 many small ventilation leaks through the many joints of the wood- 

 work of the walls and ceilings, and also that it found its way into 

 the space between ceiling and roof, there to be carried to the open 

 through small ventilator slides left partly opened to prevent con- 

 densation in that space. Undoubtedly, also, a fair share of the 

 moisture, during high humidity period, found its way into the 

 cinder floor under the heater coils, only to be slowly reevaporated 

 during the latter drying period when the humidity percent of the 

 air became less. 



Internal circulation remained uninfluenced by ventilation streams, 

 drying conditions therefore were quite uniform throughout, and the 

 only control for the rejection of the moist air was the increasing or 

 decreasing vapor pressure, surely an ideal combination for effective 

 and economic moisture removal from a kiln. 



The balanced condition of these kilns without question was an 

 accident and no more, and we may never be able to reproduce the 

 same in their excellence, but to the writer their more than two 

 years' operation, under all conditions of season and weather, sug- 

 gests that if investigations were carried on along the lines herein 

 mentioned, we m.ay perhaps eventually hold our kiln air conditions 

 in closer harmony with their natural controlling forces, instead of in 

 opposition, as is now frequently the case. 



Questions and Answers 



[Note: Iica<}crs of Hardwood Eecord arc inviled to submit their yard 

 and I'Hn problems for answer in this column. — The Editor.] 



Question 4 — End, or Cross-Piling, WMch? 



As soon as business conditions permit, we intend to add to our 

 kUn-drying capacity six compartment kUns for hardwood drying. 

 These will probably be condensing kUns, with condenser pipes on 

 both side walls, and a heating system of cast iron wall type radia- 

 tion under the tracks. 



We seem to be unable to reach definite conclusion as to the best 

 piling system for these kilns. Since we will change around most of 

 our present tracks, and must acquire new transfer cars, we can use 

 either the cross-piling system which we now have, or install, with- 

 out much additional expense, the end-wise piling system, which 

 some of our friends advocate as more advantageous. 



We will gratefully receive any suggestions from parties who have 



