Process Control in Continuous Production' System of the Champion Porcelain Company X'rankIf. Kiddleand Herbert P. Royal Ciiixi.,"X
mLCBld*\
cuar*l.u.Dsixa'r, MiCl
16
INDUSTRIAL AND ENGINEERING CHEMISTRY
manner as the regular products of the plant. Erosive action in the mill thus introduces no foreign material into the andalusite during grinding. The product from the second mill is carried by a bucket elevator to a 30-mesh Hummer screen, which returns oversize to the mill, while the material through the screen is transferred by screw conveyors to large hoppers holding approximately 1 ton. These hoppers dump into the storage bins previously. referred to. The material a t this point shows an average of 10 per cent retained on a 100-mesh screen and over 60 per cent through a 325-mesh screen.
Vol. 22, No. 1
ard and the test cores meet speciiications, the bin of ground material is released for production. While the precautions taken to insure a steady flow of raw materials of constant composition and properties may seem excessive, it has been the experience of the Champion Porcelain Company that they are well justified. Very close dimension limits must be maintained on the principal product, spark-plug cores, and all of the sillimanite products have a high and narrow firing range. Hence a little variation in the composition of a body may produce results of a most unsatisfactory nature. The total expense involved in the close check of all raw materials over a long period of time is less than the loss and inconvenience which would ensue from the use of a faulty lot of raw material. Preparation of the Body
Figure 4-Cross S e c t i o n of H o t Zone of Dressler T u n n e l Kiln Fuel oil is burned at constant rate inside the trapezoidal doublewalled silicon carbide chambers and the hot air circulates over the ware on cars as indicated by the arrows. TFmperature control is maintained by means of thermocouples in the sides of the combustion chambers and in the top of the kiln proper.
A minus pressure equivalent to 1 inch of nTater is maintained on each of the Hardinge mills by a fan system pulling the fine dust to Dracco air filters which discharge directly into the hoppers. As a result, practically dust-free conditions are maintained and valuable h e material, which would otherwise be lost, is saved. Figure 1 shows the second mill with the classifying screen and air filters mounted above it. Control of the grinding process is maintained with the same care as that of the raw material. Every hour samples are taken of the material leaving the jaw crusher and of that leaving each of the mills. Each set of samples for each 24-hour period is combined, quartered down, and tested for fineness, and the screen analysis is plotted graphically on a record chart. A glance at the chart shows any trend in the grinding process and allows the timely adjustment of the jaw crusher for wear. I n addition to this test of the mill products, two samples are taken from each 1-ton hopperful of material just before it is dumped into the storage bin. A 1-pound sample is taken from every hopper during the filling of a bin, giving a total sample of approximately 250 pounds of material representing the 250,000 pounds discharged to storage. The sampling thief and sample storage rack and sack are shown at the right in Figure 1. Chemical and screen analyses are made on this sample, and are plotted graphically as before. In addition, a very small test body is made from it in the engineering department and processed through into finished cores, which are tested against the production standards. A second sample of several pounds is also taken from each hopper. All these samples are collected together in a special small storage bin and for each 250,000-pound lot ground there is thus available a sample sufficiently large to put through the process laboratory a large-scale test of the bin of material in question. If the records show little deviation from stand-
Production in the various departments of the plant is arranged on a continuous schedule, with a 40,000-pound batch as the unit for 1 day. All body compositions and formulas originate in the engineering department. Changes are transmitted to production through the assistant superintendent, a graduate ceramic engineer, all information relating to the changes being contained on a special printed form. The assistant superintendent in turn imparts all necessary information on other standard reference forms to his foreman in the mill room, who makes out the daily weighing-out sheets used for each batch. This sheet gives the number of the body formula, the number of the batch, the storage bins from which the various constituents are to be removed, the weight of each constituent, the mill to which the batch is to be delivered, the amount of water to be added, and the length of grind. On this sheet there are subsequently recorded the actual weights of material as weighed in on dial scales by two independent scale operators, the quantity of water added to the mill, and the time of starting and of stopping the mill. This sheet is filed in the engineering department and the progress of the batch is followed through each department by means of an accompanying batch ticket carrying the body and batch numbers and the date of preparation. The entire case history of any batch can be checked in a few minutes by consulting these records. All scales are daily checked by standard weights. Thermocouple
k Q
2 3000
3
I 2
4
5
L oca fion
6 010
12
I3
I4
15
2500
-g 2 0 0 0 IC
2
1500
/ooo 500
2 0
h
U
0
10
20
30
40
50
60
70 72
Hours
Figure 5-Temperature D i s t r i b u t i o n in Dressler Kiln of C h a m pion Porcelain Plant w h e n O p e r a t e d on 1.5-Hour S c h e d u l e T h e kiln is 305 feet lonc and contains 48 cars. When oDerated on a 1 . 5 ~ h o uschedule ~ 72 hourlarerequired for any given car to pass through the kiln. The maximum temperature is 2660' F. (1460' C.). This temperature is maintained constant within 3' F. (1.7' C.).
The batch is ground in a battery of 6-foot Abbe pebble mills, shown in Figure 2. Each mill charge of 4000 pounds of andalusite is ground for 19.5 hours with an equal weight of water. The plasticizer materials are then added and the grinding is continued for an additional hour. Revolution counters on the mills check the length of these periods, and the actual performance of each mill is recorded on a smoked chart by Bristol tachometers in the control laboratory in the engineering department, At the end of the grinding
niiothri~mill chargo from the same batch. After 3 hours oi miring, a ~ ~ n i p ilietaken izom the blungei mi tested in thc sainc way &F the snmple from the zriill. After the remits
witliin lhe company over D period of yrsrs, and is subject to the same CIOS~ eonlrol R S tilo p~oeessosin the manufacture o f the body. The dimensions of cores i r m the iorrning rnaehincl XFO e l m k d constantly by inspectors, and tho niaeiiines arc djua!,ed &F wear oeeilr~, Skilled meclienjea ro4re8s tiit: wheels with %, diamond-lipped tool. The DIOC~SS
INDUSTRIAL A N D ENGINEERING CHEMISTRY
20
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unit separate from the regular production units on account of the much larger grain size desired. A Herman mill, complete with Hummer screen, magnetic separators, conveyors, and storage bins, handles this material. The chemical laboratory ware uses the same material as the regular production. It is prepared as a slip and the shapes are formed by a combined jiggering and casting process. The ware is dried and fired in the same way as the spark-plug cores. An attempt has been made in this article to describe the thorough-going way in which control methods have been utilized in developing a program of continuous production. The process of improvement is still going on. One by one variable factors are being eliminated or restricted within increasingly narrow limits and as they are controlled new possibilities are being opened for the accurate understanding
Vol. 22, KO. 1
of the fundamentals in that hitherto very practical and but slightly fundamental industry which is devoted to the production of ceramic wares. Acknowledgment
The writers wish to express their indebtedness to J. A. Jeffery, president of the Champion Porcelain Company, for permission to present this article, and their thanks to L. E. Jeffery, who is in direct charge of the installation for the burning of ware, for valuable assistance in preparing the section on that process. Literature Cited (1) (2) (3) (4)
Bowen and Greig, J . A m . Ceram. 5'06, 7, 238 (1924). Greig, I b i d . , 8, 466 (1925). Peck, I b i d . , 8, 407 (1925). Riddle and Twells, I b i d . , 10, 281 (1927).
Studies on Production of Acetylene from Methane I-Cracking
under Vacuum1
Per K. Frolich, A. White, and H. P. Dayton DEPARTMENT OF CHEMICAL ENGINEERING, MASSACHUSETTS INSTITUTE
OF
TECHNOLOGY, CAMBRIDGE, MASS.
A study of the cracking of substantially pure methane tion reactions and therefore has been made at temperatures above 1000" C. and presin the economic utilizapermit a larger portion of the sures ranging from atmospheric down to 25 mm. At tion of cheap natural a c e t y l e n e to come through these high temperatures acetylene is a main primary gas available in enormous unchanged. product of the cracking but has a marked tendency It was the purpose of the quantities has led to renewed to polymerize into benzene and similar compounds, as present investigation to study attempts to convert methane well as to decompose further into carbon and hydrogen. this effect of pressure below into acetylene. Acetylene, In order to recover the acetylene as such, it becomes atmospheric on the producaside from its value as such, necessary to employ exceedingly short times of contact. tion of acetylene by cracking may be considered as a startWithin the range of conditions studied, however, it of substantially pure methane. ing material for the synthesis has not been possible to show that pressure below atof v a r i o u s o r g a n i c comExperimental Work mospheric has any appreciable effect on the acetylene Dounds, such as benzene by Methane containing from polym'erization and acetic Yield. 1.7 to 2.0 per cent et8haneand acid a n d acetaldehyde by catalytic oxidation. Of these products benzene is of particu- 0.9 to 1.0 per cent propane as impurities was passed through lar interest to the petroleum industry because as an anti- an electrically heated quartz tube in which the desired presknock for gasoline it has an almost unlimited market, pro- sure was maintained by a vacuum pump. The inlet gas rate was measured by means of a calibrated orifhe flowmeter vided it can be produced a t a sufficiently low cost. Recent patent and periodical literature has disclosed the and the exit rate with a wet gas meter. The effluent gas possibility of producing benzene from methane by a process was analyzed for acetylene by absorption in slightly ammoniaof combined cracking and polymerization a t temperatures cal cuprous chloride,2 for ethylene by absorption in saturated in the neighborhood of 1000" C. or higher. Thus, Stanley bromine water, and for hydrogen by oxidation over actiand Nash (6) report that at 1150" C. and 0.6 second time of vated cupric oxide. By combustion with oxygen the recontact a yield of 0.2 gallon of benzene per 1000 cubic feet mainder of the gas was shown to consist of methane. of methane was obtained, corresponding to a conversion of The apparatus consisted of a cylinder of methane under 4.8 per cent of the entering methane. They also state that pressure, a reducing valve to bleed the methane down to 8.8 per cent of the methane appeared in the product as acety- atmospheric pressure, a calibrated orifice flowmeter, a malene and ethylene. Results obtained in this laboratory on nometer, a second reducing valve through which the methane the production of aromatics from methane at atmospheric was let into the electrically-heated quartz tube, a waterpressure in electrically-heated tubes substantially agree with cooled condenser, and glass wool trap, followed by a vacuum the data published by these investigators and others work- pump and finally a wet meter. The pressure in the cracking ing in the same field (3, 7), pointing to the possibility of tube was measured by means of a manometer and was reguacetylene as an intermediate product when operating a t lated by the speed of the vacuum pump or by a by-pass temperatures of the order of magnitude of 1000" C. arrangement. Two types of pumps were employed, one of Jones (5) states that in passing methane through a hot the oil-vacuum and the other of the ejector type. The first quartz tube the yield of acetylene reaches a maximum a t contained only a very small quantity of oil and blank exa pressure of 30 to 40 cm. of mercury. That a reduction periments showed that the amount of gaseous products in pressure should actually favor the process might be antici- absorbed in the pump was only a negligible fraction of the pated, because the lower partial pressures in a system operat2 This method is satisfactory for the determination of acetylene in the ing under vacuum would tend to decrease the polymeriza- presence of ethylene over the concentration range covered by the present
HE widespread interest
T
1
Received October 31, 1929.
experiments.
