Short rotary furnace

Newer secondary recovery plants use lead paste desulfurization to reduce sulfur dioxide emissions and waste sludge generation during smelting. Battery paste containing lead sulfate and lead oxide is desulfurized with soda ash to produce market-grade sodium sulfate solution. The desulfurized paste is processed in a reverberatory furnace. The lead carbonate product may then be treated in a short rotary furnace. The battery grids and posts are processed separately in a rotary smelter. 

Smelting Updraught Sinter Machine / Blast Furnace Updraught Sin Machine / Blast Furnace Updraught Sinter Machine / Imperial Smelting Furnace QSL-Process Short Rotary Furnace Sinter Machine / Blast Furnace Dross Rovorberatory... 

The number of primary and secondary smelters within a given size range is illustrated in Figure 1.7, which shows the significant difference in numbers and in plant capacities. The scale of these plants also has an impact on the technologies used for secondary smelting in comparison with primary smelting, and the most common approach is the use of the short rotary furnace. 

Coarse materials are dewatered and washed on fine mesh screens and stockpiled for further processing. Metallics may simply be melted in a pot or standard lead kettle or can be melted in a short rotary furnace, with some collection of a htharge slag to separate antimony and arsenic and produce a soft lead. Separator plastics are usually disposed of in landfill but polypropylene is thoroughly washed, and extruded as pellets for sale to battery manufacturers for new case production. 

Two broad types of rotary furnace are used - the rotary kiln and the short rotary furnace. Rotary kilns are characterised by large length to diameter ratios of the order of 10 to 15 1, whereas for the short rotary furnace the length to diameter ratio rarely exceeds 1.5 1. 

The mixed granulated material is then processed in a short rotary furnace with coal or coke for reduction to lead bullion. 

The construction of the short rotary furnace is relatively simple. It consists of a drum fitted with two steel ring tyres resting on trunnion rollers and driven through a ring gear. Diameters range from 2 to 5 m with lengths from 2.5 to 7 m, and usually have a burner fitted in one end with the gas exit flue... 

Short rotary furnaces have been used for processing whole batteries as well as mixed components and separated pastes and metalUcs. The furnace has been widely used for processing pastes with the production of soda slags. A typical sulfur balance for a short rotary furnace is given in Table 11.3. 

Table 11.4 illustrates performance of a short rotary furnace of 3.5 m diameter for various feeds and with the production of a soda slag. 

Performance data fora typical short rotary furnace (Schenker, 1990). 

The bismuth-rich slags from the converter operation and from dord cupellation can be reduced in a short rotary furnace with coal and some sulfur addition to give a bismuth-lead alloy and a copper matte. The bismuth-lead alloy can be refined by a similar sequence as used for the thermal refining of lead, as follows ... 

The kettle is drossed periodically by manual skimming and the dross can be recycled to a short rotary furnace for reduction and conversion back to metallic lead. Depending on the alloying components it may be necessary to recycle the lead bullion so produced back to the refinery feed. 

As an example, indicative costs are provided for the treatment of scrap lead-acid automotive batteries to produce refined lead using battery breaking and paste desulfurisation, followed by melting and reduction in a short rotary furnace, as described in Chapters 10 and 11. A typical small scale unit handling 35 000 tonnes per year of batteries is considered with a lead production of around 19 000 tonnes per year. Relevant production data is as follows ... 

---