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Spray roast process

Spray roasting of spent hydrochloric acids is the most common way of regeneration nowadays.

The spent acid is concentrated in the gas separator using the hot gases of the reactor. The integrated venturi allows the elimination of iron oxide particles which escaped the cyclone because of their small grain size.

Finally, the concentrated solution of HCl and FeCl₂ is injected into the reactor through spray nozzles at a pressure of 3 – 5 bar. The combustion inside the reactor usually happens at a surplus of air (λ>1).

Nearly all of the oxide produced (75-80%) drops down to the bottom of the reactor and is transported by a conveying system to the oxide storage bin. The residual part of the oxide fines are collected by a cyclone and returned to the reactor. The off gases of the spray roast process have a temperature of about 400°C. After leaving the cyclone these gases are cooled down by the venturi and the energy is used to preconcentrate the incoming pickling solution.

The process gases (now cooled down to around 100°C) pass through an adiabatic column to react with incoming water to 18% HCl. The incoming water gets added volumes of rinse waters from the pickling plant.

Additionally to this absorption system a chlorine scrubber can be applied, which acts as an effective means to extract minimum contents of chlorine gas created during the process. The combustion gases are further treated in a last scrubber column to eliminate residual HCl contents and oxide fines.

All process parameters are controlled automatically in order to maintain constant process conditions and thus constant acid and oxide quality. Oxide obtained from spray roasting technology is an essential and valuable resource for hard ferrite and pigment industry and can be obtained at low energy costs.

The ventilation system at the end of the gas transport way is designed to keep the system under negative pressure in order to transport the combustion gases through the plant by suction and to avoid leakages of HCl gases or oxide dust from the plant into the environment.

The advantages of the spray roast process are given in the lower energy costs compared with the fluidised bed process and the marketable red iron oxide (haematite). On the other hand the spray roaster needs a little more effort to keep it in smooth operation.