INDUSTRIAL AND ICNGINEERIAW CHEMISTRY
November, 1928
unrealieable, or even very difficult. Many forms of heatinterchange apparatus exist in which efficiencies far higher than 50 per cent, as above defined, are realized-notably steam boilers; and it would seem that a heat-exchange process, such as burning clinker in which the incoming cold raw materials absorb heat from the gases of combustion, and in which the hot finished product is in convenient form for transfer of heat to the air for combustion, would lend itself to a highly efficient operation, if gone about in a proper way. Fortunately, we do not have to depend entirely upon theoretical grounds, because Portland cement clinker has been aid is today being produced in stack kilns with far less fiiel than is employed in tlie rotary kiln. Muller2' gives a full account of this type of apparat,us and states that at that time (1919) there were in Germany over eight hundred sliaft kilns for burning Portland cement. He gives the fuel economy at 18 to 20 per cent, coal or coke, of the weight of clinker and the capacity from 100 to 250 barrels daily per kiln. Taking coal as having 13,000 B. t,. u. per pound, this corresponds to about from850,000 to 950,000 B. t. u.per barrel of clinker. HansenZatells of European development of the shaft kiln. His statements indicate an average fuel economy of betweeti 800,000 and 670,000 U. t. u. per barrel, and that with tlie better grades of fuel 50 pounds are required per barrel. The daily output per kiln is about 300 barrels. I n these kilns the raw materials are ground, mixed with the fuel and with 5 to 10 per cent of water, and briqiictted, before being introduced into the kiln. These briquets must hold up u?thout breaking under the considerable shock incident to their being charged into the top of the kiln, and it is not to be expected that all raw materials would make equally sound briquets, or even briquets having, in all cases, sufficient soundness to permit satisfactory operation. Further, the fuel employed must liave a low content of volatile matt.cr-i. e., of tlie naLure,of anthracite, semi-coke, or coke-because obviously if a bituminous coal is employed much of the valuable volatile matter will be distilled in the upper part of the kiln and lost up the stack. These practical difficulties, together with the small capacity, will prevent the widespread adoption of the improved stack kilns described by Hansen, in spite of their high thermal efficiency. The cost of making briquets is also 5 serious drawback. However, we are indebted to t.he stack kiln for furnishing a fairly large scale demonstration of the possibility of burning clinker with 40 to 50 per cent less fuel than is used in the rotary kiln, and by implioation of the correctness of the analytical results above set forth. The same comparison between fuel economy of the rotary kin and the shaft kiln has been noted by t.he writer in the closely similar process of burning dead-burned magne~ite.~9In this case the 125foot rotary kilns, using pulverized coal, employ about 9,800,000 B. t. u. per ton of 2000 pounds, while shaft kilns, fed with lump magnesite and coke, require ahout 4,200,000 B. t. u. per ton, the product being equally well burned in both cases. Symbols i i V = weight of fuel per pound of clinker, pounds C = B. t. u. per pound of fuel A = air required for combustion per pound of fuel, pounds T. = temperature of clinkcring, F. I t a = heat of calcination of CaCOa per pound of clinker, B. t. u. IIh = heat of calcination of XgCOa and dehydration of clay per pound clinker, B. t. u. II. = heat liberated in iormation of silicates. B.t.u. p a pound clinker
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II "Der Scbachtefen in der Zement 1nduettie;'prerented at 42nd zener& meeting of Verein Deutrcher Portland Cement Pabrikaiiten, 1919. $8 Kork Plodurlr, 33, 33 (August 27. 1S21). r BW. ~ i n eB~ ~. I836. . p. 57 (1825).
1163
T, = tempmature of product-,. e , of clinker discharged from
apparatus, * F.
S, = mean mecific heat of clinker at temperature T , above
atmospheric tempmature
G = weight of carbon dioxide liberated in calcination, pounds
T
=
per pound of clinker temperature of gases a t exit from heating zone, 'F.
fuel due to uncondenscd water from burn& .~ hydrozen of fuel = theoretical temperature of calcination, 'F. = temperature of gascs at exit from calcining zone, F. = mean specific heat of gases between T, and t = mean specific heat 01 f e d brtween atmospheric tempera~
I; Tz Sa
S,
S, = mean speeibc heat b i clinker bctween Trand t Acknowledgment
'The work upon which this and subsequent papers to be published in this journal are based was made possible by the unfailing interest and support of Geo. T. Cameron, president of the Santa Cruz Portland Cement Company, of San Francisco and Davenport, Cnlif.
Unbreakable Explosion Pipet' Frederick W. Isles ST-IVDAKD OIL C o r ~ a r voe X 6 w Jsnsru, BAYONNB, N.
I.
T H E pccompanying photograph shows an all-steel explosion pipet wliicti we made up not long ago to replace tile customary glass one in a Willianis improved gas analyzer. It consists of a 1-inch heavy malleable tee having a '/Finch spark plug in a i/z X 1 inch bnshing in tlie side outlet; a special I-inch steel plug with a capillary hose connection, screwed into the top of tlie tee; and an extra heavy 1-inch nipple, 7% inches long, screwed into the bottom of tile tee. The last-named tias no external threads on the lower end, but, i t is threaded internfilly to receive a special J/rinch steel p l u g w i t h capillary hose connection. AI1 threads are standard pipe t h r e a d s . T h e joints are made up with shellac. This pipet employs m e r c u r y as t,he aspirating fluid aiId has pinchcocks at both c u d s . After the explosion t h e residue gases arc transferred to an ordinary measuring buret. We have found tliis all-steel pipet very c o n v e n i e n t , as it wholly obviates the hazards and replacement costs incident to tlie use of a, glass explosion buret. in
8 Received O c i o b ~ i ,1928.
