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EP-4289974-B1 - IMPROVED CARBONATATION PROCESS AND APPARATUS FOR IMPLEMENTING THE SAME

EP4289974B1EP 4289974 B1EP4289974 B1EP 4289974B1EP-4289974-B1

Inventors

  • AJDARI RAD, MOHSEN

Dates

Publication Date
20260513
Application Date
20230607

Claims (15)

  1. A process for producing a carbonatation product from a carbonatation educt, comprising the process steps: a) alkalisation of a carbonatation educt to obtain an alkaline carbonatation educt and b) carbonatation of the alkaline carbonatation educt comprising a first and at least one further carbonatation step b1) and b2) to obtain the carbonatation product, in the course of each of which a CO 2 -enriched carbonatation gas is introduced into the alkaline carbonatation educt and a CO 2 -depleted waste gas is discharged, characterised in that c) introducing at least a proportion of the waste gas of the at least one further carbonatation step into the alkaline carbonatation educt prior to the first carbonatation step, so that a pre-carbonatation step b0) is carried out prior to the first carbonatation step b1).
  2. The process of claim 1, wherein the carbonatation educt is a raw sugar juice and the carbonatation product is a thin juice or the carbonatation educt is a raw sugar solution and the carbonatation product is a purified raw sugar solution.
  3. The process of one of the preceding claims, wherein the process is carried out in an apparatus for producing a carbonatation product from a carbonatation educt comprising at least one first carbonatation vessel (203) and at least one further carbonatation vessel.
  4. The process of one of the preceding claims, wherein the apparatus (200) has a pre-carbonatation vessel (202) upstream of the first carbonatation vessel (203).
  5. The process of one of the preceding claims, wherein the apparatus has at least one line (240) from the at least one further carbonatation vessel to an upstream pre-carbonatation vessel (202) to introduce at least a part of the waste gas of the at least one further carbonatation step into the alkaline carbonatation educt prior to the first carbonatation step.
  6. The process of one of the preceding claims, wherein the waste gas of the at least one further carbonatation step has a CO 2 content of 1 to 40 vol%, in particular 15 to 27 vol% (based on the total volume of waste gas).
  7. The process of one of the preceding claims, wherein the waste gas of the at least one further carbonatation step after process step b) and prior to process step c) is mixed with a CO 2 -enriched carbonatation gas.
  8. The process of one of the preceding claims, wherein the CO 2 -enriched carbonatation gas is obtained from a coke- or gas-operated lime kiln or is at least a proportion of a boiler house gas.
  9. The process of one of the preceding claims, wherein the CO 2 -enriched carbonatation gas obtained according to claim 9 has a CO 2 content of 1 to 99 vol% (based on total volume of CO 2 -containing gas).
  10. The process of one of the preceding claims, wherein the carbonatation educt is obtained from sugar beet or sugar cane.
  11. The process of one of the preceding claims, wherein the CO 2 gas utilisation rate of the at least one further carbonatation step is at least 20 %.
  12. The process of one of the preceding claims, wherein the total CO 2 gas utilisation rate of the carbonatation is at least 70 %.
  13. An apparatus for producing a carbonatation product from a carbonatation educt, in particular suitable and designed for carrying out a process according to any one of the preceding claims 1 to 12, comprising at least one first carbonatation vessel (203), at least one further carbonatation vessel and at least one line (240) from the at least one further carbonatation vessel to an upstream carbonatation vessel, which is suitable for introducing at least a part of a waste gas from the at least one further carbonatation vessel into an alkaline carbonatation educt present in an upstream carbonatation vessel, wherein a pre-carbonatation vessel (202) is connected upstream of the first carbonatation vessel (203), and wherein the upstream carbonatation vessel is the pre-carbonatation vessel (202).
  14. The apparatus of claim 13, wherein the apparatus is a beet sugar or sugar cane sugar processing apparatus for producing thin juice from raw sugar juice.
  15. The apparatus of claim 13 or 14, wherein the apparatus is a sugar refining apparatus for producing a purified raw sugar solution from a raw sugar solution.

Description

The present invention relates to a method for producing a carbonation product from a carbonation reactant and to a device for producing a carbonation product from a carbonation reactant, in particular suitable and designed for carrying out the method according to the invention. Carbonation plays a central role in the technological processes of a beet sugar or cane sugar factory or a raw sugar refinery. Carbonation typically comprises a first and a second carbonation step. It is a purification step in juice purification, particularly in raw sugar juice purification (whether from beets or sugar cane), or in sugar refining, especially raw sugar solution. Before carbonation, the raw sugar juice or solution used for carbonation is obtained by extraction from sugar beets (especially beet pulp) or sugar cane, or by dissolving raw sugar in water and subsequent pre-liming and/or main liming, also known as alkalization. During pre-liming and main liming, the extracted raw sugar juice or solution is mixed with milk of lime, i.e., a calcium hydroxide dispersion in water. This causes suspended solids contained in the extracted raw sugar juice or solution to flocculate. Alkalization yields an alkaline raw sugar juice or an alkaline raw sugar solution. Primary liming results in a primary alkalinity of approximately 0.6 to 1.2 g CaO/100 ml in the raw sugar juice or raw sugar solution, corresponding to a pH range of 12 to 12.8 at 20 °C. Carbonation is carried out using the alkaline sugarcane juice or alkaline raw sugar solution obtained in this way. In the first carbonation step, performed in a first carbonation vessel, the calcium hydroxide dispersion added in excess during the main liming process and present in the alkaline sugarcane juice or alkaline raw sugar solution is neutralized by introducing freshly generated lime kiln gas, i.e., a gas containing carbon dioxide. The alkaline sugarcane juice or alkaline raw sugar solution is then neutralized to a pH endpoint of approximately 11.4 to 10.8 at 20 °C, which corresponds to a final alkalinity. The calcium hydroxide, corresponding to approximately 0.06 to 0.1 g CaO/100 ml, is neutralized, and the calcium hydroxide precipitates as calcium carbonate. The precipitated calcium carbonate, especially when precipitated as calcium carbonate crystals, has an active, positively charged surface. Without adhering to a theoretical framework, this active surface enables the precipitated calcium carbonate, particularly in the form of calcium carbonate crystals, to exert a purification effect through the adsorption of precipitated colloids and other non-precipitable non-sugar substances. Simultaneously, the precipitated calcium carbonate, especially the calcium carbonate crystals, acts as a filter aid. In the second carbonation step, carried out in a second carbonation vessel, the alkaline raw sugar juice or the alkaline raw sugar solution is neutralized by introducing freshly generated lime kiln gas to a pH endpoint of approximately 9.4 to 8.6 at 20 °C, which corresponds to a final alkalinity of approximately 0.005 to 0.015 g CaO/100 ml, and the calcium hydroxide is precipitated as completely as possible as calcium carbonate, especially in the form of calcium carbonate crystals, until the optimal alkalinity is reached. CO₂ gas utilization rates, i.e., the utilization rates of the CO₂ content in the lime kiln gas, can reach a maximum value of approximately 90 to 95% in the first carbonation step and a maximum value of approximately 70 to 75% in the second carbonation step using novel carbonation tanks based on the state of the art. Therefore, despite comparatively high CO₂ gas utilization rates, a significant portion of the CO₂ released in the lime kiln is still present in the so-called carbonation vapors, i.e., the exhaust gas of the respective carbonation step. DE 29 25 283 A1 This concerns a process for improving the operation of the carbonation (saturation) stages of a sugar factory, whereby exhaust gas from a second carbonation stage is recycled into a first carbonation stage. The CO₂ gas utilization rate in the carbonation steps depends primarily on the alkaline sugarcane juice level or alkaline raw sugar solution level, temperature, mixing, alkalinity of the sugarcane juice or raw sugar solution, and the CO₂ content in the lime kiln gas. It is known that as the CO₂ content in the lime kiln gas decreases, the gas utilization rates in the carbonation steps decrease, and CO₂ losses increase. This can be observed, for example, when switching from a coke-fired lime kiln to a gas-fired lime kiln. The resulting reduction in the CO₂ content of the lime kiln gas, and the associated reduction in the gas utilization rate, particularly in the second carbonation step ( CO₂ content), Exhaust gas losses (approximately 15 to 25% by volume, based on the total volume of exhaust gas) can lead to a CO₂ deficiency in sugar production or refining and to significant fluctuations in the operation of th