The cokeless cupola completely
eliminates the use of coke for melting iron with substitution by
natural gas, propane, diesel oil or other suitable fuels, even powdered coal is possible.
Existing cupolas can be readily
converted or new ones designed for specific applications.
The principle of the design is highlighted in the diagramatic drawing below.
The main features are the water cooled grate, consisting of steel tubes which may be coated with refractory for insulation on smaller cupolas as shown left. The grate supports the specially developed refractory spheres shown in right. which acts as a heat exchanger. Below the grate are the burners which are operated to give partially reducing conditions inside the cupola to reduce oxidation losses. The hot gases from the burners maintain the bed of spheres at high temperature and also preheat and melt the metal in the shaft. The metal is superheated in passing through the bed and is then collected in the well prior to tapping out in any normal way. A suitable recarburiser is continually injected into the well to give the correct carbon analysis. The carbon content of the metal can be easily altered by changing the injection rate at the control panel.
Automatic combustion control and indication of condition of all important services can be provided, as shown below. Simpler more manual systems are also manufactured.
|.........||Depending on the fuel used and the recarburiser injected there is no sulphur pick-up in melting. With correct charge materials the sulphur content of tapped iron can be below 0.01% which makes the metal ideally suited for the production of ductile iron. Picture shows metal being converted directly to ductile iron without desulphurisation. This cupola is operating on natural gas and using graphite for injection.|
|..........||An important feature of the cokeless cupola is that during operation there is no visible emission and the actual solids emitted are very low and are only dependant on the cleanliness of the charge. Only the simplest form of fume control is necessary and a simple wet cap will enable the cupola to meet all known environmental standards. This picture highlights conventional coke melting (right), and the cleanliness of the cokeless cupola also operating, (left).|
|..........||A typical installation rated at 6 tonnes per hour tapping high quality iron.|
|..........||Looking directly into charge of a gas cupola during operation - cleanliness is apparent.|
Other advantages of cokeless melting include cleaner and better quality metal, there is also less refractory lining wear and hence longer campaigns are possible. It follows that less slag is made and hence there are less disposal problems.
Because of the semi-permanent nature of the bed and the ability to control carbon content by injection as well as the precise control of the combustion process, both iron temperature and iron analysis are far more consistent than that from a coke cupola. It makes possible the production of high quality metal much easier for the foundryman, and hence his ability to produce good castings is much improved. He will also appreciate the greater flexibility of operation compared with the coke cupola. A wide variety of metal charges can be melted in the cokeless cupola and generally a similar charge to a conventional coke fired cupola can be used.
It has been shown in many instances that much cheaper metal will be obtained from the
cokeless cupola compared with other forms of melting.