Authors:
K. Adham, C. Lee
Chloride Metallurgy 2002, International Conference on the Practice and Theory of Chloride/Metal Interaction, Montréal, Canada, pp. 657-671
Abstract
Large amounts of energy leave the pyrohydrolysis reactor with the off-gas and the solids. Considering the rising cost of fuel, energy recovery is increasingly important for an economical operation. Due to the process constraints, the potential sources of energy recovery in pyrohydrolysis are limited to the following:
- Sensible heat of the roaster off-gas, which is partially recovered in existing plants
- Latent heat of the final off-gas, which is not recovered in any known plant
- Sensible heat of the hot oxides, which can be recovered by existing technologies
In modern installations, the sensible heat content of the reactor off-gas is partially recovered by pre-evaporation of the metal chloride solution. However, it is shown that the solubility limit of the metal chloride curtails a complete sensible heat recovery. Process modelling shows that increasing the pyrohydrolysis efficiency and reducing the roaster off-gas rate can increase the sensible heat recovery.
Options for latent heat recovery from the scrubbed off-gas (~65% steam) are evaluated. The use of a heat pump to lift the off-gas temperature and generate steam is possible, as is recovery in the form of hot water to provide a low-grade space heating source. Implementation of these options have high capital costs that must be justifiable by the potential energy savings.
Energy recovery from hot roaster oxides (in form of process steam) is defined. The existing fluidized bed waste heat boiler technology can be used for this purpose, except for the spray roasters that produce a very fine product.
