HCl + Fe2O3 The process is an inversion of the chemical descaling (pickling) process. Main differences between different implementations of pyrohydrolytic acid regeneration Furnace Type (spray roaster, fluidised bed or combined furnace) Physical Properties of Iron Oxide By-Product (ferric oxide powder or pellets) Purity and commercial value of Iron Oxide By-Product Cl content SiO2 content (typically 40 to 1000 ppm) other impurities specific weight (typically 0.3 to 4 kg per litre) specific surface (typically 0.01 to 8 m2/g) Energy Consumption (between 600 and 1200 kcal/L) Fuel type Concentration of regenerated acid (typically approx. 18% wt/wt) Purity of regenerated acid (remaining Fe content, Cl content) Recovery efficiency (typically 99%) Rinse water utilization Stack emissions (HCl, Cl2, Dust, CO, NOx) Liquid effluents (composition, amount) Basic process flow diagram of spray roaster hydrochloric acid regeneration plant Process description of spray roaster hydrochloric acid regeneration plant Preconcentration The metal chloride solution (in the most common case waste pickle liquor from a carbon steel pickling line) is fed to the venturi evaporator (III), where direct mass and heat exchange with the hot roast gas from the roaster (reactor/cyclone) takes place. The separator (IV) separates the gas and liquid phase of the venturi evaporator product. The liquid phase is re-circulated back to the venturi evaporator to increase mass and heat exchange performance. approx. 25 to 30% of the waste acid (H2O, HCl) are evaporated roast gas is cooled down to approx. 92 to 96 °C dust particles are removed from the roast gas Roasting Preconcentrated waste acid from the preconcentrator (III / IV) is injected into the reactor (I) by means of one or more spray booms (VIII) bearing one or more injection nozzles each. Injection takes place at reactor top at a pressure between 4 and 10 bar. The reactor is directly fired by tangentially mounted burners that create a hot swirl. Temperatures inside the reactor vary between 700 °C (burner level) and 370 °C (roast gas exit duct). In the reactor the conversion of droplets of preconcentrated waste acid into iron oxide powder and hydrogen chloride gas takes place. Hydrogen Chloride leaves the reactor through the top, while iron oxide powder is removed from the reactor bottom by means of mechanical extraction devices. A cyclone (II) in the roast gas duct ensures separation and feed back of larger oxide particles carried by the roast gas. Absorption In the absorption column (V) the hydrogen chloride