The Rise to Dominance of the Cyclone: 1950-1970

Most of the work in the mining industry up to 1950 was for dewatering or desliming. The big breakthrough application for the cyclone, however, was just around the corner. In 1951, metallurgists at the San Manuel operation of Magma Copper Corporation (San Manuel, Arizona) experimented with a specially designed cyclone for closed-circuit grinding. The results were inconclusive, but people were starting to take notice.

Late in 1951, the Dorr Company installed a 0.65-m Dorrclone for closing the grind­ing circuit at Tennessee Copper in Copperhill, and other companies—including Climax Molybdenum and Anaconda Copper Company—started to test cyclones for this applica­tion. From 1951 to 1954, numerous researchers and companies around the world started to experiment with the use of cyclones for closed-circuit grinding. Early papers on mill-cyclone closed circuits were concerned with preparing gold ore for leaching in South Africa (Dennehy and de Kok 1953) and limestone for feed to cement kilns in the United States. E. B. Fitch and F. J. Fontein published many papers on the effects of design and operating variables on the performance and selection of cyclones (Fitch and Johnson 1953; Fontein 1961). Although the Dorr Company and other manufacturers pioneered the use of cyclones for closed-circuit grinding, it was Equipment Engineers (later Krebs Engineers) that eventually took the market away from Dorr Oliver.

In 1950, when Clarkson was mill superintendent of the Bradley Mining Co. in Idaho, Cyanamid abandoned the equipment business and returned the rights of the feeder to him. Krebs and Clarkson eventually formed the Clarkson Company to manufacture and sell the feeder, with Krebs responsible for sales in San Francisco and Clarkson for manu­facturing, which was carried out at the Boise, Idaho, airport. Cyanamid also gave the Clarkson Company the rights to some design concepts for the cyclone that Krebs and Clarkson had been working on. Equipment Engineers took responsibility for cyclones and the Clarkson Company for feeders. In 1951, Equipment Engineers acquired the rights to a forced vortex cyclone, called the Centricone, from its inventor, Norris Goodwin (see Figure 9.4). The first customer was American Cyanamid, which used it to classify phosphate ores.

In 1953, wear problems with the impellor in the Centricone led to Equipment Engi­neers selling the rights to Oliver Filters, which was soon to become Dorr Oliver. Equip­ment Engineers then started work on a more conventional cyclone with an involute style feed (see Figure 9.5). This proved to be one of the features that made the Krebs cyclones manufactured by Equipment Engineers the industry standard for high-volume applica­tions. The other feature was the thick molded-rubber linings. During this time, numer­ous studies were being performed using the cyclone in industries outside coal and mining, because it was recognized as a simple yet efficient separating device. Up to this point, most of the technical research on the cyclone was limited to plant applications and, with the exception of Dahlstrom and Driessen, very little had been done to examine how a cyclone actually operated.

The Rise to Dominance of the Cyclone: 1950-1970
FIGURE 9.5 Feed entry designs for cyclones (Heiskanen 1993; reprinted by permission from Kluwer Academic Publishers)

In 1952, D. F. Kelsall published one of the first technical papers about how a cyclone operates (Kelsall 1952, 1953). This paper was the foundation for most of the future modeling work over the next 20 years. As the knowledge of cyclones increased, its uses and designs started to change. In 1953, R. C. Emmett and Dahlstrom published the first reference to open-top cyclones, which were later installed at Philex Mines in the Philip­pines and at an iron ore property in Minnesota. Also in 1953, H. Trawinski reported on the first use of cyclones in combination with centrifuges for starch separation (Trawinski 1955). He did a considerable amount of early work on cyclones in various industrial and chemical applications during the 1950s and was the inventor of the cyclones used by Amberger Kaolin Werke.

In January 1955, Equipment Engineers obtained a patent on the Krebs Model EE cyclone, which was a two-stage cyclone with the first-stage underflow feeding directly into the second-stage cyclone. This patent also included the involute-type feed for the first-stage cyclone. At this time also, the use of cyclones for closed-circuit grinding was starting to develop momentum in the United States—the Morenci concentrator being one
of the first significant operations in the country in which cyclones were used in the grinding circuit (Barker, Papin, and Barr 1955).

Applications of cyclones outside closed-circuit grinding circuits continued to grow because they were small and cheap, and easy to install and operate. Here are some examples of applications that emerged in the period from 1955 to 1958:

■ In the uranium industry they were used in the countercurrent washing process in which uranium in solution is separated from the tailings. Dorr Oliver had pat­ented the use of multiple stages of cyclones for countercurrent washing.

■ In the petroleum industry they were used for the control of drilling muds (Wuth and O’Shields 1955).

■ In the clay industry small-diameter cyclones were used in South Africa to produce paper-coating clay and in combination with gravitational settlers to remove impu­rities from China clay (Hochscheid 1955; Naylor 1958).

Two important patents during this time were by Bradley (1957), who patented the use of two stages of cyclones to make liquid-liquid separation, and Sharples Centrifuges Ltd., which obtained a British patent (date unknown) that generally describes the advantages of using cyclones in combination with centrifuges and filters in chemical applications.

The potential for cyclones in closed-circuit grinding, however, was far greater than for other applications, and researchers continued to study cyclones for this process. The spiral or rake classifier was the standard classifier still being used at that time in most grinding circuits around the world, but as work progressed with the cyclone and early researchers installed test cyclones in grinding circuits, they found that cyclones had some significant advantages over classifiers:

■ High-capacity and relatively small floor area for the larger tonnage mills.

■ The percentage of solids in the coarse product that returned to the mill was close to the preferred grinding mill pulp density.

■ Preferential classification of the higher specific-gravity middlings so that they were returned to the mill.

In copper concentrators, the cyclones provided a higher flotation feed density, and this helped to limit the volume of the flotation cells that were required for the larger concentrators.

For iron ore plants, cyclones were better able to provide the finer separations that were required to liberate the iron minerals for concentration and to produce suitable feed for the pellet plant.

Because cyclones preferentially placed the high specific-gravity middling particles into the coarse product for further grinding, the early work at copper concentrators in Chile and the United States showed that cyclones offered significant advantages in terms of copper recovery and feed tonnage over standard classifiers. As a result, copper con­centrators were among the first to make full use of cyclones in grinding circuits. Some of the first installations of cyclones in copper grinding circuits occurred in 1955 at Acjoe in the Philippines, Majdenpek in Yugoslavia, and Chuquicamata in Chile.

The first major copper installation in North America was in 1956 at American Smelt­ing and Refining Companies’ Silver Bell Concentrator (about 40 miles north of Tucson, Arizona). Cyclones were tested in the grinding circuit in 1955-1956 when Russ Salter, mill superintendent, and Ed King, metallurgist, were open minded enough to replace rel­atively new twin 1.3-m spiral classifiers with four 0.5-m model D20B Krebs cyclones. Ironically, Dorr Oliver received the initial order for 0.6-m cyclones, but because of a very long delivery of 1 year, Silver Bell decided to cancel the order with Dorr and place it with Equipment Engineers. At the time the Silver Bell decision was made, the design of the

Pima Mining Company concentrator was being finalized. Pima was partially owned by Utah Construction (later Utah Mining), and its plant engineering group (now Fluor Daniel) was located in Palo Alto, California. Utah Construction’s metallurgical depart­ment shared the test laboratory with Equipment Engineers, and they were kept well informed of the work at Pima. A last-minute decision was made by Utah Construction to retain the building design for classifiers but to install cyclones initially. If cyclones did not work, the classifiers could be put in. This led to the second major installation of cyclones in a copper concentrator and resulted in the second largest order of cyclones for Equipment Engineers.

The first major installation of cyclones in an iron ore grinding circuit was in 1955 at Reserve Mining (headquartered in Silver Bay, Minnesota; mine in Babbitt, Minnesota) where Dorr Oliver supplied Dorrclones that were 0.3 m in diameter. Early work on iron ore was carried out from 1951 to 1953 at pilot plants for Reserve Mining and Erie Com­pany Mining (Auroa, Minnesota), and this proved that cyclones had advantages over spiral classifiers in the grinding circuit. In 1956, Erie Mining followed with an installation of cyclones with diameters of 0.375 m, which were built by the Gallagher Co. Following the early installations in copper and iron ore in 1955 and 1956, cyclones became the standard classifier in grinding circuits, and numerous installations followed in the next 10 years.

In 1957, Equipment Engineers split into two separate companies. Kelly and Dick Krebs retained the rights to the hydrocyclone and continued with Equipment Engineers. Clarkson retained the rights to the Clarkson reagent feeder and the slurry control valve and the Clarkson Co. became a very successful valve company. Equipment Engineers supplied most of the cyclones for grinding circuits in the late 1950s and early 1960s and in 1965 changed the name of the company to Krebs Engineers to honor Kelly and Dick Krebs.

Cyclones were being installed in numerous applications around the world in the late 1950s and early 1960s, and H. L. Bradley of the Sharples Centrifuge Co. investigated them in detail. His work resulted in many patents and, more importantly, in the book entitled The Hydrocyclone, which was published in 1965 (Bradley 1965). This book was the most comprehensive work ever published on the cyclone and today is still the bible for cyclones. Bradley was the first researcher to carry out detailed tests on many aspects of the cyclone including the effect of change in inlet, vortex finder and apex diameters, cylinder length, and cone angle. He also developed one of the first mathematical models of the cyclone, which other researchers later used to study the cyclone further.

Updated: 24.03.2016 — 12:06