Use of Alutal Hamilton’s Polilyte Plus in Raw Sugar Juice Carbonatation


Industry: Sugar Production
Application: Carbonatation of Raw Juice
Alutal Hamilton Products: Polilyte Plus

Crystalline sugar is the primary sweetening agent in many countries, making a reliable supply of high-quality sugar essential for a large population.

With an average sugar content of 20%, sugar beets are one of the main sources of sucrose worldwide. The extraction and purification of sucrose from beets take place in refineries through a multi-step process, where efficiency is crucial to producing high-quality sugar at the lowest possible cost.

At the refinery, freshly harvested beets are cleaned and sliced, and sucrose is extracted using hot water. The resulting raw juice is then purified in the carbonatation process, yielding thin juice. This thin juice is concentrated through evaporation into thick juice and fed into crystallizers to produce the final crystalline sugar product.

Carbonatation and pH Control

Raw juice contains about 99% of the sugar from the beets but also several organic and inorganic non-sugar compounds. These compounds can be removed by precipitation using burned lime (calcium oxide) and carbon dioxide.

In the carbonatation process, burnt lime is first added to the raw juice, forming a loose precipitate of calcium hydroxide and non-sugar compounds. Carbon dioxide gas is then introduced, reacting with calcium hydroxide to produce calcium carbonate, which forms a stable precipitate with the non-sugar compounds. The precipitate is filtered out, yielding thin juice.

Carbonatation is carried out in two stages, both requiring the addition of carbon dioxide, which affects the pH levels. pH measurement is essential to regulate the addition of carbon dioxide during carbonatation.

In the first stage, carbon dioxide is added at a temperature of 90°C to maintain the pH between 11.1 and 11.6. Most of the lime, non-sugar compounds, and some of the sugar form a precipitate, which is removed by filtration. The filter cake is washed to retain sugar, and the wash water is reintroduced to the first carbonatation step.

In the second stage, remaining lime and impurities must be removed. Carbon dioxide is added again at 90–95°C to precipitate the remaining calcium hydroxide and impurities. Maintaining an optimal pH of 9.1 to 9.2 is critical to ensure proper precipitation. If the pH is too high, filters clog quickly; if too low, the precipitate can dissolve back into the solution.

Standard pH sensors with ceramic diaphragms often become contaminated in these conditions and are difficult to clean, leading to inaccurate readings. Prolonged contamination can render the sensor unusable.

Instead of ceramic diaphragms, the Alutal Hamilton Polilyte Plus sensors feature a single pore liquid junction between the polymeric electrolyte and medium. This design resists clogging and ensures stable measurements. In the event of contamination, debris can easily be removed from the single pore. Additionally, the pH glass in the Polilyte Plus sensors provides highly accurate measurements in alkaline media.

User Benefits of Alutal Hamilton’s Polilyte Plus in Carbonatation:

  • Long durability
  • Reliable readings
  • Resistance to frequent cleaning
  • Slow clogging of the single pore
  • Easy cleaning of the single pore

Performance of Polilyte Sensors

At the Pfeifer & Langen sugar factory in Jülich, Germany, the Alutal Hamilton Polilyte Plus sensors demonstrated their effectiveness in carbonatation. Two sensors were installed in each carbonatation tank—one as the primary and the other as a backup. In 2010, the primary sensors operated continuously for at least eight weeks, with some performing flawlessly throughout the entire three-month production campaign.

Alutal Hamilton Polilyte Plus in Carbonatation

pH measurement during carbonatation presents significant challenges due to the high process temperatures (90–95°C) and the presence of solid, sticky compounds in the medium.

The sensors are mounted in automated retractable housings to avoid interrupting the ongoing carbonatation process. They are cleaned every 90 minutes with acid to remove lime and other adherent compounds, and calibrations are performed 2–3 times daily.