Pyrometallurgy

A Shaft-Electric Furnace for Melting and Smelting

The electric arc furnace has characteristics which make it attractive for a number of metallurgical applications. Some of these characteristics are: high thermal efficiency, the possibility of attaining very high temperatures, low off-gas volume compared to fuel-fired furnaces, no impurities are introduced by the heat source, and impurities in only minor amounts are introduced by the electrodes. It also has disadvantages, the chief ones being the relatively high cost of electrical energy compared to fossil-fuel energy and the fact that, when oxide ores are smelted using carbon as reductant, the off-gases emitted are rich in carbon monoxide.

Equipment

The vital components of the shaft-electric furnace are: the arc furnace, the feed-control mechanism between the arc furnace and the shaft furnace, the shaft furnace and its associated feed system, and an exhaust system capable of exhausting all the gaseous products from both the arc furnace and shaft furnace. In order to maintain countercurrent flow in the shaft, with solid charge descending and gases ascending, it is necessary that the exhaust system maintain a reduced pressure at the top of the shaft, thus it must be connected to the top of the shaft, adjacent to the incoming feed.

The 250-kVA arc furnace was

Shaft Kiln for Lime Production

New is a relative term, and when used with reference to a concept as old as shaft kilns can be applied to a number of designs. In this case the design that is the subject of this paper, is known as the ring or annular shaft kiln as developed by Mr. Karl Beckenbach of West Germany.

It is a single vertical cylinder to which are attached the required service platforms, combustion chambers, injectors and distribution piping. Auxiliaries such as recuperator, exhaust fan and dust collector are mounted on the appropriate service platform. The charging pan, feed conveyor, etc. are mounted at the kiln top. At the bottom of the kiln is the silo with a vibrator type discharger, and mounted separately is the required blower for injector air and fan for internal cooling.

Material flow begins with the stone being fed to the charging pan by conveyor. The charging pan is in the form of a ring mold and is rotated while being filled to insure an even distribution of stone sizing being fed to the annular space in the kiln. When the pan is loaded, the conveyor is withdrawn and the pan cover lowered into place. Next, the bottom of the

Remove Sulfur Dioxide from Off Gases of Coal Burning

The purpose of this article is to present design information and operating data on a pilot gas scrubber which is believed to be a new approach for removing noxious gases and particulate matter from the off gases of coal burning power plants and smelters.

In addition, gas scrubbers on stream or being developed for coal burning power plants and smelters have other undesirable aspects such as high pressure drop requiring high operating horsepower, relatively low gas velocities, demisting problems, and the production of slurry discharge, relatively low in solids content. This last places extra burden on settling basins, lagoons or mechanical dewatering equipment. Our design attempts to eliminate some of these undesirable aspects of gas scrubbers and to minimize others. Our concept is based on the following premises:-

  1. Particulate matter cannot adhere to a moving surface which is continuously bathed by a moving liquid.
  2. Low pressure drops across the scrubber will be achieved if the gas flow cannot pass through the aqueous scrubbing medium.
  3. Impingement of these gases and particulates on liquid surfaces is an efficient scrubbing procedure for the minimization of mist.
  4. The ability to control retention of the aqueous scrubbing medium within the scrubber independent of gravity and of

How to Remove Mercury from Copper Concentrate

The copper-silver-mercury orebody of Gortdrum Mines (Ireland) Limited is located 3 miles north of the town of Tipperary in the Republic of Ireland.

The first shipments of concentrates were made to the smelter in Europe in late 1967. In the spring of the following year, word was received from the smelter that these early shipments contained between 1% and 2% Hg, and that the smelter could not accept further shipments of this quality.

Roasting was the only feasible method found for removing the mercury from the concentrate, and it was decided that this should be done in an atmosphere with limited oxygen.

Early Work

One of the first requirements was to establish the extent of the problem. An initial difficulty was with analyses. It was obviously desirable to know how much mercury was in the ore, and, since arsenic and antimony were important penalty elements in the copper concentrate, it was also important to be able to analyse the ore for these elements.

Reasonably reliable techniques were soon developed for the analysis of concentrates, although doubts about the absolute accuracy persisted for a considerable time. The methods adopted were atomic absorption techniques for mercury and antimony, and a distillation technique for arsenic.

 

How to Control Briquet Quality

The application of briquetting in various chemical, mineral, mining and metallurgical processes has been rapidly increasing in the past two decades. This is, in part, due to the development of new, more economical and higher performance briquetting equipment. Some of these developments, which have reduced the operating and maintenance costs, include anti-friction bearings, hydraulically applied pressure enclosed and sealed gearing and bearings, tapered predensification feed screws, water cooling and materials of construction capable of operating at temperatures up to 1800°F, and control systems capable of maintaining optimum briquette quality control.

The briquets can be formed into almost any desired size and shape. To date, with present rotary briquetting presses in the 25 to 500 ton force range, briquets from ¼” to 6″ length are presently being used. The screw force feeder, which can be of various taper configurations or straight, performs several other functions in addition to feeding the material to the press rolls. Of equal and possibly greater importance, they (1) predensify or precompact the material, prior to its entry into the roll forming dies, (2) apply a precompaction pressure to the feed material and (3) deaerate the feed material by means of the precompaction pressure. These functions have a

Overcome Environmental Problems in Sinter Plants

The continuous sintering process was invented more than 60 years ago by two metallurgists, Arthur S. Dwight and Richard L. Lloyd, who saw a need for automation in mineral processing. Their specific objective was to beneficiate copper ore by desulfurizing and agglomerating it for copper blast furnace smelting at the Cananea plant in Mexico. Since their early development the process expanded widely in scope, size, and application. The current worldwide sintering applications exceed 250 million tons per year for agglomerating ores of lead, manganese, zinc, and iron. Sintering is also widely used for production of sintered lightweight aggregate from clays, shales, and fly ash.

Description of Sintering Process

An improved sintering process which offers considerable advantages over conventional sintering has been developed at the Dwight-Lloyd Research Laboratories of the McDowell-Wellman Engineering Company, The new process overcomes some of the salient air pollution problems and provides a high quality product at lower capital and operating costs. The techniques can embody the Dwight-Lloyd liquid sealed circular machine using a recycle draft and in situ cooling, the combinations of which lead to very practical and economic benefits.

A simplified diagram of the conventional sintering process is shown and illustrate the sequence of sintering, hot

Coal Drying Methods

In the past, it has more or less been a general rule that any time the total product is being washed, both mechanical and thermal drying was required. The reason for this was that a product moisture of 3 to 4% was required and thermal drying was and is the only practical method by which this can be accomplished.

Some of the items which had to be considered in the economic study were the following:

  1. Present and future thermal dryer operating costs.
  2. Product moisture required by customer.
  3. Could mechanical dryers be used to replace the thermal dryers.
  4. The operating cost of mechanical dryers.

The first step was to determine what the moisture would be if centrifugal dryers were used on some or all size fractions and the use of thermal drying was discontinued.

The following is a breakdown of the drying of each major fraction before the change: The plus ¼” material was being dewatered by use of vibrating screens to a moisture of 4. 2%, The ¼” x 28 mesh material was being mechanically dried in centrifuges to a moisture of 6.8% and then thermal dried. The minus 28 mesh material was being dewatered by a vacuum disc filter to a moisture

Blue Flame Burner

You have all seen a gas stove. Gas burns with tiny, bright-blue cones of flame; they are very hot, very clean, very quick to burn. You have also seen a hardwood fire; when the yellow flame disappears, the charcoal gives off a bright
blue, almost transparent flame. Again, this flame is hot, very clean, very quick to roast hot dogs.

How Does Our Burner Work?

High pressure air from a blower enters through the injector nozzle. Pressure is converted to velocity as this air leaves the nozzle. As the high velocity air passes into the injector, it entrains more air from the mixing chamber. Both the blower air and the entrained air are again compressed as they are driven through the injector creating a venturi effect with a resulting vacuum in the mixing chamber. The mixing chamber is connected to the flame tunnel by an open tube which we call the “Hot Gas Return Tube”.

This atomized oil is not a gas, but a vapor. Therefore, the flame burns in the flame tunnel with a distinctly yellow color – just like most oil burners. You probably wonder why we must use this conventional way to start our Blue Flame burner. If you

Selection and Combustion of Pulverized Coal in Rotary Lime Kilns

The selection of a coal for direct pulverized firing of a rotary lime kiln may be determined by trial and error, persistence of sales personnel, proximate analyses, grindability, or apparent BTU cost. Occasionally, the only question asked is, “How much lime will it make?”

The classic three T’s – time, temperature, turbulence – must be enlarged upon for a better understanding of the problem. Pulverized coal occupies only 0.01 per cent of the volume of air required for its combustion. This mixture behaves like a gas and the general laws governing the movement of solid particles in gasses are in effect.

As combustion proceeds, the weight of solid remaining becomes less, keeping the particle bouyed up longer in the gas stream. As the distance from the burner tip increases, turbulence decreases. Eventually, the particle of carbon or coke reaches its terminal velocity in the gas stream. This is a most unfortunate situation. The volatiles which burn readily are available for ignition at the point of highest turbulence in the coal-air stream and the carbon residues which burn more slowly only become available for combustion in the very low turbulence and low oxygen portion of the flame. The combustion rate of the solid

Coal Fired Lime Kilns

The combustion of pulverized coal is a century-old practice. Many people have investigated coal dust and the residual fly ash particles that remain after combustion. But the combustion process and fly ash formation mechanism are not understood. Working at our Maysville, Kentucky lime plant, the Dravo Lime Company Research team has collected samples of partially burned coal dust from the flame of a pulverized coal burner. Specimens were placed in a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). Microscopic examination of the particles, together with a large collection of micrographs of lime dust fused to fly ash particles, now make it possible to theorize as to how combustion advances through a piece of coal dust.

Sulfur content of the melted ash structure appears to be a function of the combined concentrations of calcium, potassium and sodium. Potassium and sodium are equally effective and together they must exceed 10% of the calcium concentration to maximize the sulfur content of the ash. To avoid a recirculating sulfur load in a lime kiln, it is preferable that sulfur be in the form of SO2 in the kiln gases. But there seems to be a quaternary eutectic of CaO, CaSO4, (K,

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