Hydrothermal Acid Regeneration Plants

Hydrothermal Acid Regeneration Plants avoid any direct combustion or pyrohydrolysis processing steps. They recover bound and unbound chlorides from metal chloride solutions by means of oxidation and hydrolysis. Opposite to spray roaster or fluidized bed plants, hydrothermal acid regeneration plants can oxidize and hydrolyze different metals separate from each other. This makes this process a sensible choice for applications where metal separation is key to success.
Applications of this technology include:

	spent pickle liquor regeneration
	iron control in hydrometallurgical base metals winning
	magnesium oxide production
	titanium dioxide production
	rare earth metal oxide production (such as cerium oxide)

Metal oxides produced by SMS Siemag's hydrothermal acid regeneration process show a high bulk density and, as one might expect from a low temperature process, an extraordinary high specific surface area, which makes them suitable reagents for many solid-solid reactions.

Two chemical reactions take place: Oxidation and Hydrolysis. In the exemplary case of spent pickle liquor regeneration, ferrous chloride is oxidized with pure oxygen into ferric chloride. In a hydrolysis reactor the ferric chloride is later reacting with water yielding ferric oxide and hydrogen chloride gas:

Reaction temperatures are comparably low - between 150 and 200 degrees Celsius. All reactions happen in a liquid environment. Energy is provided by indirect external heating. Preferable heat sources are steam or electricity. No fossile fuels are required. No combustion gases are produced or released.

SMS Siemag has developed energy recuperation techniques, that lower the energy consumption of the hydrothermal process to levels below 50% of comparable spray roaster and 30% of comparable fluidized bed plants.

Because of lower operating temperatures and the absence of directly heated reactors equipment wear and tear is minimized and maintenance cost is reduced.

One key advantage of the hydrothermal process over spray roaster or fluidised bed acid regeneration plants is its significantly larger turndown ratio. A hydrothermal ARP can be operated between 10 and 100 percent of its nominal capacity without compromising process efficiency, product quality or by-product value.

Iron oxides from hydrothermal acid regeneration plants, which are utilized for spent pickle liquor regeneration, are exraordinary pure. They contain lower amounts of manganese, copper and other alloy elements than oxides produced by pyrohydrolysis. Those elements are effectively discharged in a highly concentrated metal chloride bleed.

Process Characteristics

Process Operating Principle