Document 2B54qQ0r53LRmv2B2bZ3j2Ng

FILE NAME: Concrete (CONC) DATE: 1939 Apr DOC#: CONC004 DOCUMENT DESCRIPTION: Journal Article - Dust-Collecting Systems Charter Member CEMENT MILL SECTION of Associated Business Papers C o n c r e t e , with which has been com bined Cement Age, New York, and Concrete Engineering, Cleveland, is devoted to the Proper Use of Concrete and the Manufacture of Cement. Volume 47 Established 19Q4 ApriL 1939 Number 4 Published Monthly by Concrete Publishing Corporation 400 West Madison Street Chicago, Illinois Telephone CENtral 8822 Louis Brookman. Jr., Business M anager L Moeller, Circulation M anager Harold 0 . Hayes, Promotion M anager Representatives New York City E, Macdonald Bacon 17 West 45th--Room 909 Longacre 5-5260 Detroit Parker & Tarbell 419 Curtis Bldg., 2842 W. Grand Blvd. Madison 1540 San Francisco: Don Harway Room 1009,155 Montgomery St. Exbrook 6029 Los Angeles: Don Harway & Co. 318 West Ninth Street Tucker 9706 # T h e Cem ent M ill Edition o f Concrete The Cement Mill Edition of Concrete is edited exclusively for those interested in the manufacture of Portland cement and related products. Its pages are devoted to discussions of plant design, management, operation, production effi ciency, chemical research and control, quarry op eration, progress and news of the industry. The Cement Mill Edition also contains all the material published in the corresponding Regular Edition and so provides news of the rises and merchandising of the materials whose manufacture is discussed in the Mill Edition. The Regular Section furnishes mill operating officials and mill executives valuable points of con tact with the users of the materials they produce. The subscription price is $4.00 a year in the United States and its possessions, and Mexico. One dollar additional for postage in all other countries. Current copies, 50 cents each. Norman M. S tinem an, Editor J- C. Witt, Consulting Editor A. C. Bam bercer, Assistant Editor CONTENTS Major Trend la Mechanical Phases of Cement Manufacture-- By C, S. Lincoln____________________________________ __ _____ 143 What Happen In a Rotary Cement Kiln....... ......................................145 Dust-CoUectfaq S y ste m s.............................. ..................- ....................147 Influence of G lass Content on Heat of Hydration............................ ISO Editorial D iscussion_________________________ ___ _________ _15l Shipments Make Good Start Room for More Slurry Filters Safety a Product of Patience Another Forecast on Production Good Housekeeping Means Safety In Q u arries_________ __ ____ 152 Atlantic City Gets Next Safety C ooqreaa__ __________ ___ ____154 Universal Atlas Headquarters Movinq to New York__ _________155 Dust-Sampiinq Methods and A pparatus_______________________155 Ideal's Vice-President P asses Away____________ ____ __________ 155 Men and M ills___ _________________________________________156 y Advertisers' Index, Page 40 Charter Member Copyright, 1939, by Concrete Publishing Corp. CONCRETE is indexed in INDUSTRIAL ARTS INDEX, which may be consulted in any Technical or Public Library. Audit Bureau of Circulations C O N C R E T E -- Cement Mill Section -- ApriL 1939 Page 141 UHM H - T . i l D u st -C o llec t in g S y st e m s Discuss Various Types in Engineering Report DUST collection in all its engineer ing phases is discussed in the final report of the committee on the preven tion of silicosis through engineering con trol, presented to the National Silicosis Conference sponsored by the United States Department of Labor. Warren A. Cook, of the Connecticut State Depart ment of Health, Hartford, Conn., is chair man of this committee. The full report has been published by the Department of Labor as Bulletin No. 21, Part 2. A complete dust-exhaust and colleclection system, the report emphasizes, consists of the following four parts: (1) Exhaust hoods. (2) Piping or duct system. (3) Air-cleaning plant. (4) Source of suction. Each of these parts contributes essen tially to the smooth working of the whole system, and no part can be used alone. For convenience in presentation, how ever, the report discusses the four items separately. Exhaust Hoods.--The design of ex haust hoods has been worked out in con siderable detail for a number of applica tions, while representative velocities which should be attained at the face of the hoods are given in the accompanying table. If the source of dust is a device such as a tumbling mill, as used in casting clean ing, the mill itself becomes the hood. By keeping the mill under a negative pres sure, outward leakage of dust is pre vented. In the case of abrasive cleaning cab inets or rooms, the entire enclosure is ventilated, keeping it under negative pres sure, and all of the exhaust air is passed through the duct work to the dust collec tors. In order to remove the dust from such devices as mills, cabinets and rooms, it is necessary to provide properly placed openings of suitable size to permit air to flow into the device. Due to the high velocity flow of air, dust and dirt do not escape through these openings when properly designed, but instead are con veyed through the exhaust system. Exhaust hoods for rotating devices, such as grinding wheels, must overcome the fan action of the rotating wheel in addition to overcoming the energy im parted to the dust particles as they are shot off from the object being ground. Accordingly, the exhaust hood should enclose the wheel so far as is practicable. A special application of the exhaust hood is the so-called drill-dust trap used extensively in rock-drilling operations. This device consists of a small portable hood through which the drill steel is in serted. Exhaust applied to this hood re moves the dust at its source. The drilldust trap has been shown to be effective in controlling dust produced by this op eration. In designing hoods for jobs for which there are no reliable data, it is advisable to make up light models or experimental hoods and actually try them under prac tical operating conditions. From the in formation thus gained, permanent hoods may be designed. A convenient device for testing the efficacy of exhaust hoods is the ordinary flashlight equipped with a focus adjustment. If the plant illumina tion about the hood is either dimmed or cut off, the flashlight beam, brought into the region of the hood opening, permits a general indication of the accumulation, direction of motion, and speed of travel of dust. The same testing arrangement serves well in exploring elevators, chutes, conveyors, and the like for dust leaks, and thus helps to determine what air volumes must be handled in order to control dusti ness. Piping.--The duct work leading from the exhaust hoods to the dust arrester is made up of such size, shape, and weight as will accommodate the air volumes and dust loads to be handled. Obviously, it is the part of economy to handle as small air volumes at as low velocities as is prac tical. Velocities must be great enough to carry all of the dust drawn into the piping without settling in the horizontal runs. If the dust is mixed with large ma terials or noth other substances which might injure the fan or arrester, it is ad visable to place preliminary separators or traps between the hood and arrester. Equations for calculating velocities needed to transport materials pneumat ically have been worked out by Dalla Valle and Martin. In practice, it is usual to employ velocities varying from some 1,200 feet per minute for a light, fluffy material like sawdust to 5,000 feet per minute for lead dusts. It must be borne in mind, however, that the concentration of dust in the air stream greatly affects the velocities to be used. Generally, veloc ities of less than 2,000 feet per minute Pago 147 should not be used in duct work. Casting tumbling mills require about 5,000 feet per minute in the branch pipes because of heavy concentration of dust. Grinding and polishing systems generally function properly with a 4,500 feet per minute branch-pipe velocity and 3,600 feet per minute header-pipe velocity. A fair av erage found in dust-collecting installa tions is from 3,500 to 5,000 feet per minute. Lower velocities are very apt to allow settling out of dust, while higher velocities entail a needless waste of power. The cross-section area of the header pipes of an exhaust system may be somewhat greater than the sum of the cross-section area of the branch pipes, but in order to reduce friction losses and con serve power this increase in area should not be more than 20 per cent. machines, and polishing and buffing wheels. They are the simplest type of collectors made. It is common practice to install these separators in the line ahead of and as an integral part of the final separator, such as a cloth or bag filter, in order to reduce the load or dust concentration fed to the filter cloths and to remove heavy particles that excessively abrade the blowers, fans, or arresters. However, the preliminary, separators of the inertial type can not be relied upon to furnish air sufficiently clean to satisfy hygienic requirements. They must always be supplemented by secondary cleaners whose particular function is the removal of fine particles at high efficiency. Secondary Separators and Other Types of Arresters.-- Dust particles which can MINIMUM AIR VELOCITIES REQUIRED TO CAPTURE CERTAIN INDUSTRIAL DUSTS Industry Process Required air velocity At point At face of of origin hood Criterion Granite cutting_______ Hand pneumatic tool______ '2 0 0 Surfacing machine.... All tools Paint spraying?.____ ___Spraying booth___________ Sand pulverizing... . Bagging machine . Quarrying and minmg-Horizontal drilling, drill dust trap. Quarrying and mining_Vertical drilling with drill dust trap. 1 1,500 1 400 1 60 1 200 L500 50-200 Reduced concentration to sale level. Do. Do. Do. Do. Safe concentration. -- Do. 'F e e t per minute. Piping and duct systems should a l ways he provided with clean-out facilities in order that the system may be examined internally andcleaned out when required. Inertial and Other Primary Separators. --Inertial and other primary dust sep arators, such as cyclones and other de vices, depend for their air-cleaning ac tion on centrifuging out the dust par ticles by rotary motion or on imparting to the transporting air stream a quick change in direction, accompanied by a reduction in velocity. These devices are probably the oldest of the mechanical dust collectors, and have had a wide use in industry. Their principal appeal has been that they are relatively cheap, are easy to install, and the resistance is usu ally low, resulting in moderate power consumption. They are furnished by prac tically every firm engaged in the ventilat ing or dust-collecting business. In ca pacity they range from a few hundred cubic feet per minute to many thousands. They are handling dusts of practically every kind and description, and are admirably adapted to exhaust systems from such equipment as woodworking not he caught in inertial separators are removed by one of the following methods: 1. Filtration. 2. Scrubbing by water or other fluids. 3. High-tension electric precipitation. 4. Dynamic precipitation. Filtration.-- Industrial air filters han dle concentrations of 4 milligrams to 50 grams per cubic meter (0.004 to 50 ounces or 1.7 to 20,000 grains per 1,000 cubic feet) at a velocity of about 0.5 to 10 feet per minute at the filter. In indus trial processes with heavy dust loadings, velocities of 3 feet per minute or less are recommended. If the arrester is to op erate efficiently, the velocity should never exceed 3.5 feet per minute. The collected dust may have a cash value, which helps defray the operating costs, but usually this dust is worthless and its disposal is something of a problem. It does not matter whether industrial filters are in the form of flat screens or bags. Many examples o f both can be seen today, and either type, when properly designed and maintained, has a high op erating efficiency. When new, all-cloth filters emit some dust in the discharge air, but this leak age soon stops. As dust piles up on the upstream side of the cloth, resistance to air flow increases and less air goes through the system. The rate at which the resistance of a filter cloth builds up depends upon the rate at which particles are deposited upon the cloth. In order to reduce this resistance, it is customary to shake the accumulated dust off the fabric at regular intervals or whenever suitable pressure gages or manometers show that resistance has become prohibitive. Unless the filter manufacturer gives specific di rections to the contrary, filter cloths should not be shaken when air is passing through them. There are few pieces of standard equip ment that will deteriorate faster than cloth filters that are neglected. Routine inspection, routine shaking, and routine cleaning out of the units are imperative if the expense of upkeep is to be kept within reasonable limits. Wet Collection.-- It has been common practice for years in power-plant and blast-furnace operation to clean the dust from large volumes of gas by passing the gas through scrubbing or washing devices of various kinds. Such wet collectors, however, have had little application for industrial dust of hygienic interest. Re cently new designs of wet arresters have been introduced which cause the dirty air to be impinged against wetted surfaces or which utilize other means of bringing the air into intimate contact with the liquid. Wet collectors are particularly applic able where much moisture is present in the air being exhausted. One of the most valuable features is that the resistance, which is relatively low, is constant for a given exhaust system, so that the system always functions the same under the con ditions for which it was designed. These wet arresters are now beginning to find considerable application in industrial dust collection. Electric Precipitation.--For the past 25 years high tension electrical precipi tation has been applied successfully to the removal of dust, fumes, and mists from air and other gases. The method has many advantages over the other meth ods discussed, but so far it has not been applied extensively to the solution of the problems with which this silicosis con ference is concerned. Dynamic Precipitators.--This equip ment effects removal of entrained dusts by means of a specially designed fan in which the rotating element imparts a cen trifugal force to the dust particles up to Page 148 April. 1939 -- C O N C R E T E -- Cement Mill Section 1,000 to 1,200 times their specific grav ity and thereby separates them from the air stream. Originally these precipitators were designed for the collection of dry dust, but recently the construction has been modified to permit the introduction of water into the dirty air intake, thus extending its application to additional types of dusts. In determining the applic ability of this device, consideration must be given to the type of dust to be handled. Exhaust Fan.-- In the interest of econ omy, it is generally advisable to install the exhaust fan beyond the cloth filters rather than before them. The fan then handles clean air, and abrasion of the blades and housing is minimized. With the fan installed before the arrester any leaks in the arrester case cause escape of dust, resulting in contamination of the atmosphere. Design of Exhaust Systems.--Other considerations in the design of exhaust systems are: 1. Dampers and gates should be used only for two purposes in the ducts of an exhaust system: (a) To balance the system with respect to air flow and then be permanently adjusted; (6) to provide fire stops where necessary. 2. Once an exhaust system has been designed and installed for a certain --job, additional exhaust outlets can not be added to the original system without reducing the effectiveness of the system and lowering its efficiency-- excepting where such additions have been antic ipated and the header pipes are suffi cient to accommodate them. 3. The number of outlets on an ex haust system should not be reduced and the header pipe flanged off where the branches are removed, unless an amount of air equal to that which the system was originally designed to han dle is allowed to flow through the header pipe to the exhaust fan. 4. Several smaller exhaust systems are often preferable to one large sys tem. Appraisals of Results.-- A complete dust-collecting system is designed to handle certain volumes of air measured usually in hundreds or in thousands of cubic feet per minute and to collect cer tain weights of dust measured usually in pounds or tons per working day. De 1 Note.--See the following equation: 1 ounce per cubic loot = 1 gram per liter. 1 ounce per l t000 cubic feet = 1 milligram per liter. 1 ounce per 1,000 cubic feet = 1,000 milli grams per cubic meter. I grain per 1,000 cubic feet = 2.3 m illi gram s per cubic meter. 2 Fundamentals Relating to the Design and Operation of Exhaust Systems. Code Z9. Am erican Standards Association, New York, pre liminary edition. 1936. tailed procedures for testing and meas uring air flow in exhaust systems have been published. If the primary purpose of the system is to recover a dust that has a cash value, it may not be necessary or even advisable to exceed an over-all effi ciency of 98 or even 95 per cent. If the object in view is to achieve a certain de gree of air cleanliness in the work place or in the air discharged from the cleaning system, results are to be measured in terms of the cleanliness of this air. The air volumes handled, the tonnage of dust collected, and even the operating or air cleaning efficiency of the system are sec ondary considerations. The engineer must state what degree of cleanliness the system should attain. He should be able to show, in court if necessary, whether or not the plant is being operated accord ing to good modern practice, or prefer ably according to requirements deter mined either by competent research, or as prescribed by law or codes. In appraising the cleanliness of air one's instinct is first to compare it with clean country air (0.1 milligram per cubic meter [0.0001 ounce or 0.04 grain per 1,000 cubic feet] ) ,l with city air (0.5 to 2.0 milligrams per cubic meter [0.0005 to 0.002 ounce or 0.2 to 0.9 grain per 1.000 cubic feet]), with the air of a thick fog or haze (1 to 3 milligrams per cubic meter (0.001 to 0.0003 ounce or 0.4 to 1.3 grains per 1,000 cubic feet]), with the atmosphere of an air-conditioned theater (less than 0.2 milligram per cubic meter [0.0002 ounce or 0.09 grain per 1.000 cubic feet]), with the air of any workplace in which adequate dust con trol is being practiced (less than 10milli grams per cubic meter [0.01 ounce or 4.3 grains per 1,000 cubic feet]), with some dusty job in which no dust control is being enforced (over 100 milligrams per cubic meter [0.1 ounce or 4.3 grains per 1,000 cubic feet]) , and finally with concentrations of inflammable dust which are high enough to furnish an explosion hazard (10 to 50 grams per cubic meter [ 10 to 50 ounces or 4,000 to 22,000 grains per 1,000 cubic feet]). According to the U. S. Department of Agriculture, concen trations should not exceed from 7 to 10 ounces per 1,000 cubic feet, depending upon the composition, fineness, and other factors. If such comparisons are to be reliable, the use of a simple measuring technique as described in the report of the sub committee on determination of concentra tion and composition of industrial dust, is essential. Results can be given in any of the units listed above or else in num CEMENT MILsEL bers of particles per unit volume. It is impossible to convert numbers of parti C cles to weights with any real precision T because such conversions require parti cles of uniform size and shape. In prac I tice, dust particles are never uniform. Approximate conversions, good enough 0 for many purposes, can be made by as N suming that 0.7 milligram per cubic meter (0.0007 ounce or 0.3 grain per 1.000 cubic feet) is equivalent to 6,000,000 particles per cubic foot, or, that 1 milligram (0.001 ounce or 0.4 grain per 1.000 cubic feet) contain 300 million particles as sampled and counted by the impinger technique as given in the sub committee report referred to above. Summary.-- It is unwise to attempt too wide an application of any particular type of final dust separator, whether it be a cloth arrester, a wet collector, or a pre cipitator. Generally, the manufacturer of the particular device can define its par ticular uses and limitations. The cus tomer, in turn, should be prepared to fur nish reliable data on the physical and chemical properties of the dust to be col lected, such as particle size, hardness, hygroscopicity, solubility, and dryness, it is very important that the approximate dust concentrations or dust loadings be given. The purchaser should demand of the vendor a statement as to the probable performance of the system under definite conditions and should receive detailed in structions as to its operation, upkeep, and repair. Fundamental requirements relating to the design and operation of exhaust sys tems in general are presented in a report2 recently developed by the American Standards Association. This report is of direct use to those designing and oper ating dust-exhaust systems. Link-Belt's Interesting Exhibit at New York World's Fair I INK-BELT Company has arranged an ex- ^--* hibit of exceptional interest for New York' s World's Fair. It is arranged to portray in work ing models, photo murals, and colorful, realis tic dioramas and translites, how industry can ease labor's burdens, expedite production and reduce costs, by using mechanical conveying equipment for handling materials from where they are to where they are wanted next. A dominant central sculptured figure depicts the spirit of power transmission; and various types of driving units are shown in operation. This includes silent and roller-chain drives, three types of enclosed automatically-lubri cated speed reducers, and the Link-Belt P J.V . Gear variable-speed transmission for infinites imally and conveniently changing the speed of machinery, while it is in operation. C O N C R E T E -- Cement Mill Section -- April, 1939 Page 149 40 C O N C R E T E April, 1939 illtlllllllilUIIIII* FPoipre--BeUttseer WCoEnLcDrEetDe 1 Advertisers' Index I Reinforcing Mesh-- The Allan Portable Spot Welding Outfit can be used right on the job speedily, efficiently, dependably--on ail rises of wire. This electric welding machine dim* mates old-fashioned tying methods and prevents cracking. All Machines Now WATER COOLED Cmxm beuw eM br Allan Portable Welding M achia Writ* /or 4*toit* ALLAN M ANUFACTURING AND WELDING CO . BUFFALO NEW TORS MOST AMAZING 1939 BLOCK MACHINE The FOOTE HAMMERED STRIPPER Original in Design -- Outstanding in Perform ance -- Com pact -- High C apacity -- Low First Cost -- Quality, Low-Cost Production. Write today for descriptive bulletin T H E J . B. FO O TE FO U N D R Y CO. Fredericktown, Ohio HARSHAW CEMENT COLORS Chromium Green Oxide, Red Iron Oxide, Yellow Iron Oxtde. Ultramarine filue and other colors THE HARSHAW CHEMICAL CO. 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