Drying and calcination are endothermic processes that require heat to evaporate bulk moisture or decompose chemical compounds. Combustion processes involve exothermic oxidation or "burning" of the feed material. Roasting processes use elevated temperature and controlled furnace atmospheres to effect desired chemical reactions in the furnace charge; roasting reactions may be either endothermic or exothermic. Although many furnace technologies exist, current industrial practice favors the rotary kiln and the fluidized-bed reactor for these applications.

Hazen can assist its clients in this area, because we understand that furnace design relies not only on an accurate definition of process operating conditions, but also on the physical characteristics of the feed materials, product specifications, gas handling requirements, and other important considerations. We can develop a well-planned program to ascertain the technical feasibility of a potential processing method, examine areas of technological uncertainty, and establish the economic viability of the venture. Once process parameters have been adequately defined, pilot-scale confirmation can generate the process design criteria needed for commercial implementation.

Hazen has an excellent assortment of equipment, including rotary kilns and fluidized-bed reactors for laboratory and pilot-scale studies. Our equipment inventory contains most conventional configurations, including both indirectly and directly heated furnaces. Our fluidized-bed studies have included evaluations of classical bubbling-bed, circulating-bed, and high-pressure reactor applications. We maintain an array of other pilot-scale equipment, including a multiple-hearth furnace, Holoflite® dryers, spray dryers, and an indirectly heated screw kiln. We can also custom design and manufacture laboratory and pilot-scale furnaces for special applications.

Since opening its doors in 1961, Hazen has completed projects over an exceptionally wide range of thermal processing applications. Some of our recent studies have involved:

• Roasting of refractory and carbonaceous gold ores
• Sulfation roasting of cobalt–copper–nickel concentrate
• Reduction roasting of nickel laterites
• Manganese carbonate calcination
• Zirconium sulfate calcination
• Selective chlorination of metals
• Antimony and arsenic fuming
• Combustion of coal, oil shale, refuse-derived fuel, and other fuels
• Combustion of municipal solid waste for energy recovery