Making Bayer Process less emissions-intensive

Alumina, the primary raw material to make aluminum, is refined from bauxite ore through the Bayer Process. This is an energy- and emissions-intensive process, and Solvay is contributing to make it less so.

Solvay has created the MAX HT® Sodalite Scale Inhibitor to optimize energy consumption and therefore reduce emissions in the alumina processes. It reduces scaling (impurities and contaminants) from the evaporator and digester heaters during the century-old Bayer Process and maximizes heat transfers  - hence its name, which stands for Maximum Heat Transfer. MAX HT® is used in more than 30 Bayer process plants worldwide, resulting in reduced energy consumption and reduced acid waste from heater cleanings.

The Bayer Process explained

 

Aluminium-refinery

Chuck Price, Head of Solvay Technology Solution’s mining solutions business, explains the Bayer Process in a simple way: “Let’s say there’s already about 40% alumina in this bauxite ore. It’s put in a very large tank called a digester and mixed with caustic soda at high temperatures which dissolves the alumina - “pregnant liquor” in Bayer terminology.
The remaining solids are separated out as red mud. The pregnant liquor is transferred to precipitators in which seed crystals of alumina trihydrate are added to favor the precipitation of alumina trihydrate out of the liquor. The solids (alumina trihydrate) and liquids (spent liquor) are then separated, and the spent liquor is sent to evaporators to be concentrated for circulated use in the Bayer process. This is like we would concentrate a sauce by heating it to eliminate the water.”

Chuck continues: “Alumina trihydrate is then washed with water and dried, and in most cases goes to a calciner where it’s turned into aluminum oxide or alumina, the raw material used by smelters to make primary aluminum. The problem with this process is that when you try to heat Bayer liquor, scale forms on the heating surface, such as the tubes of the heat exchangers, which lowers heat transfer and reduces evaporation rate and flow.”

This is where MAX HT® kicks in: it reduces or even eliminates the scale formation in heat exchangers. The resulting annual savings per ton of alumina produced are roughly estimated to be the equivalent of a 13-92 kg reduction in CO2 emissions, and a 0.9-2.7 kg reduction in acid waste. When these savings are applied to the total alumina production from 20 plants, it leads to an estimated reduction of 0.54-3.9 billion kg of CO2 emissions, and 38-116 million kg of acid waste reduction.

Aluminium Refineries - scaling

(Pictured: severe scale formation inside a pipeline)

MAX HT® has allowed alumina refineries to operate free of sodalite scale in their heat exchangers. Solvay continues to develop products that help optimize mining operations worldwide, enabling its customers to improve productivity and reduce operating costs while meeting economic and environmental challenges.

A newer solution to Chinese aluminum refineries

Solvay has developed an improved version of the MAX HT® line specifically for the Chinese market whose bauxite is somewhat different than the rest of the world’s. “The Chinese market was using a lot more energy than necessary. Alumina refineries in China now burn less coal because they don’t need as much energy thanks to our improved MAX HT®,” explains Chuck.

Aluminium Refineries - scale-free heater tubes

(Pictured: scale-free heater tubes)

The challenge of reducing scale in alumina refineries worldwide was unsolvable until about 15 years ago with the invention of MAX HT®. It is a breakthrough product solving an unmet need for as long as the Bayer Process has existed. MAX HT® makes the Bayer Process much more efficient, allowing for billions of liters of fresh water to be saved annually, in addition to approximately 90 kg of CO2 per ton of alumina. It is the first scale inhibitor product in the market for this application.