METHOD FOR REDUCING SUGAR LOSS DURING THE SEPARATION OF A COAGULATE FROM PRE-CALCIFICATION JUICE AND FOR THICKENING THE COAGULATE

Description

[0001] The present invention relates to the provision of a method for producing an optimal clear sugar beet pre-liming juice, wherein the clear sugar beet pre-liming juice has a significantly reduced solids content, and for improved separation of the coagulate separated from the pre-liming juice.

[0002] Traditionally, sugar is extracted from beets by first cleaning the harvested beets, removing most of the remaining soil and leaf debris. After washing, the beets are shredded into slices using cutting machines. Sugar is then extracted from these slices using countercurrent extraction with hot, slightly acidified water. Acidifying the extraction liquid facilitates the filtration of the raw sugar beet juice and improves the pressing of the extracted slices. The raw sugar beet juice obtained during extraction is then subjected to extract purification. This purification typically involves a lime-carbon dioxide extraction process, consisting of pre-liming, main liming, first and second carbonation, and the separation of the precipitate after the first and second carbonation.The purpose of extract purification is to remove as many non-sucrose substances, especially high-molecular-weight substances, as possible from raw sugar beet juice. Ideally, the non-sucrose substances to be removed should not be degraded, so that no additional low-molecular-weight substances enter the extract or raw sugar beet juice.

[0003] In pre-liming, the raw sugar beet juice is gradually alkalized under gentle conditions by adding lime milk. Pre-liming is carried out by adding defined quantities of calcium hydroxide (lime milk). As a result of the alkalization of the raw sugar beet juice, the organic and inorganic acids present in the extract are neutralized, and anions that form insoluble or sparingly soluble salts with calcium precipitate. Phosphate, oxalate, citrate, and sulfate, for example, are largely removed. Furthermore, colloidally dissolved non-sucrose substances coagulate and precipitate. The precipitation of individual components, such as anions like oxalate, phosphate, citrate, and sulfate, or colloids like pectin and proteins, occurs within specific pH ranges. Within these pH ranges, the precipitate also compacts.The addition of lime milk during pre-liming also leads to protein coagulation. Due to this protein content, the aforementioned separated non-sucrose substances are also referred to as the protein-containing fraction of raw sugar beet juice.

[0004] The primary purpose of the subsequent main liming, carried out by adding lime milk, is the chemical degradation of invert sugar and acid amides, which would otherwise occur during juice thickening, forming acids. The lime milk added during the main liming also plays a crucial role in the first and second carbonation stages. Through the conversion of calcium carbonate, a strong absorbent for a range of soluble non-sucrose substances and a suitable filter aid are provided. The lime milk not consumed in the main liming process is converted to calcium carbonate in the two carbonation steps by introducing carbon dioxide as the carbonation gas. Carbonation occurs in two stages. In the first carbonation, the precipitated and flocculated non-sucrose substances and some of the pigments contained in the raw sugar beet juice are bound to the calcium carbonate formed.The first sludge juice obtained in the initial carbonation is filtered or passed through decanters and concentrated into sludge juice concentrate. In the subsequent second carbonation, the second sludge juice is produced, which is also filtered and concentrated. The calcium carbonate sludges (sludge juice concentrate) concentrated in the first and second carbonation processes are typically combined and pressed. This process yields what is known as carbocalc. This carbocalc is a storable product with a dry matter content of more than 70%. The sugar beet pre-liming juice, purified in the extract purification stage, is further processed to obtain white sugar.

[0005] A significant disadvantage of conventional lime-carbon dioxide extraction purification is its relatively low purification efficiency, as it removes only a maximum of 40% of all non-sucrose substances from raw sugar beet juice. Another drawback is the large quantities of lime milk required. However, the production of the lime milk used in lime-carbon dioxide extraction purification processes and the disposal of the waste generated during quicklime production are relatively expensive. Furthermore, carbon dioxide emissions from lime kilns and juice purification plants are very high. In addition, the carbolime produced in the lime-carbon dioxide extraction process, consisting of lime and separated juice impurities, can only be used as fertilizer.

[0006] From EP 1 682 683 A, a process for extracting raw sugar beet juice is known, comprising the following process steps: pre-liming of the raw sugar beet juice by adding milk of lime to coagulate non-sucrose substances, i.e., the protein-containing fraction; addition of at least one flocculant; separation of the coagulate from the pre-liming juice using at least one first separation device to obtain a clear pre-liming juice; main liming of the clear pre-liming juice obtained after separation of the coagulate by adding milk of lime; and carrying out a first and optionally a second carbonation.

[0007] It is known from Fasol, Zuckerindustrie 135, 2010 (5, 228-294) to use decanter centrifuges with different discharge angles to thicken the obtained coagulates and prepare them for subsequent addition to pressed beet pulp and drying.

[0008] A disadvantage of these methods, however, is the comparatively high sugar loss, meaning a relatively high proportion of sugar in the separated coagulate and an undesirably high solids content in the resulting clear pre-liming juice. Both phenomena ultimately result from the still-improving separation of the clear pre-liming juice, ideally with a high sugar content, from the coagulate. Furthermore, it proved disadvantageous that while the decanter centrifuges used according to Fasol's method ran more stably than other configurations under certain conditions, continuous operation was still not possible due to the varying viscosities of the solids fraction to be separated.

[0009] Document DE 10 2010 047995 A1 also discloses a process for producing a sugar beet pre-liming juice, wherein in one process step the separation of the coagulate from the pre-liming juice is carried out by means of a decanter centrifuge.

[0010] The present invention therefore addresses the technical problem of providing a process for producing a clear sugar beet pre-liming juice and a protein-containing fraction from raw sugar beet juice, as well as products produced by this process, which overcomes the aforementioned disadvantages, in particular providing a process by which the coagulate is reliably and precisely separated from the pre-limed raw sugar beet juice, smaller amounts of sugar are lost during the separation, and thereby a particularly clear sugar beet pre-liming juice is obtained. The process according to the invention should also be capable of continuous operation.

[0011] The present invention solves the underlying technical problem by providing the teaching of the independent claim. In particular, the present invention solves the underlying technical problem by providing a process for producing a clear sugar beet pre-liming juice and a protein-containing fraction, comprising the process steps of: a) providing raw sugar beet juice, b) pre-liming the raw sugar beet juice provided in process step a) to obtain a pre-liming juice, forming a coagulate of non-sucrose substances in the obtained pre-liming juice, c) adjusting the solids content to 15–25 vol.- % (based on the total volume of the pre-liming juice provided in process step b)) in the pre-liming juice by means of a dynamic or static decanter, d) separation of the coagulate from the pre-liming juice obtained in process step c) with a solids content of 15 - 25 vol. % using at least one decanter centrifuge, comprising a motor-driven, rotating centrifuge drum with a cylindrical section and a conical section, wherein the angle between the longitudinal axis of the centrifuge drum and the generatrix of the conical section is 6° to 10° and an extruder screw rotatably mounted in the centrifuge drum and e) obtaining the clear sugar beet pre-liming juice and a protein-containing fraction.

[0012] Also disclosed is a clear sugar beet pre-liming juice produced by means of the inventive process and a protein-containing fraction produced by means of the inventive process, preferably subsequently thickened.

[0013] The invention therefore advantageously and surprisingly provides a process in which, in a first process step a), raw sugar beet juice is provided, for example by extraction, in particular countercurrent extraction, preferably from sugar beets, especially sugar beet pulp, and in a further process step b), the pre-liming of this raw sugar beet juice is carried out, thereby producing a pre-liming juice in which a coagulate of non-sucrose substances is formed. According to the invention, the solids content of the pre-liming juice is to be adjusted in process step c) to 15 to 25 vol.% (based on the total volume of the pre-liming juice used in process step b). In a further process step d), the invention provides for separating the coagulate from the pre-liming juice thus obtained from a clear sugar beet pre-liming juice using at least one decanter centrifuge.The decanter centrifuge used according to the invention comprises a motor-driven, rotating centrifuge drum with at least one cylindrical section and one conical section, wherein the angle between the longitudinal axis of the centrifuge drum and the generatrix of the conical section is 6° to 10°, and an extruder screw rotatably mounted in the centrifuge drum. In a subsequent process step e), a clear sugar beet pre-liming juice and a coagulate in the form of a protein-containing fraction are obtained.

[0014] According to the invention, the provided method involves the use of at least one decanter centrifuge, which comprises at least one motor-driven rotating centrifuge drum with a cylindrical section and a conical section, wherein the angle between the longitudinal axis of the centrifuge drum and the generatrix of the conical section is 6° to 10° and an extruder screw rotatably mounted in the centrifuge drum, for separating a protein-containing fraction from a pre-liming juice having a solids content of 15 to 25 vol. % (based on the total volume of the pre-liming juice used in process step b).The clear sugar beet pre-liming juice obtained in this way has a lower solids content compared to a process using raw sugar beet juice of identical composition and volume at a different discharge angle, in particular 5°, and / or a different solids content in the pre-liming juice, in particular 10 vol.%. The protein-containing fraction obtained in this way has a higher solids content, a lower amount of sugar recovered per unit time (corresponding to reduced sugar loss in the clear sugar beet pre-liming juice), and a higher amount of solids recovered per unit time compared to a process using raw sugar beet juice of identical composition and volume at a different discharge angle, in particular 5°, and / or a different solids content in the pre-liming juice, in particular 10 vol.%.

[0015] The inventive method leads in a surprising way to a significantly improved, i.e. reduced, solids content in the clear sugar beet pre-liming juice obtained after separation of the coagulate, i.e. the clear run, compared to the prior art, by separating the coagulate while simultaneously obtaining an increased amount of solids per unit time and solids content as well as a lower amount of sugar in the protein-containing fraction.

[0016] In particular, without being bound to theory, it appears that in the process provided according to the invention, the specific combination of the discharge angle provided according to the invention, i.e., the angle between the longitudinal axis of the centrifuge drum and the generatrix of the conical section, with the specific solids content used according to the invention in the pre-liming juice used for separating the coagulate, leads to a significantly reduced sugar loss and a surprisingly low solids content in the clarification. In particular, the combination of discharge angle and specifically used solids content according to the invention also appears to lead, surprisingly, simultaneously to an increased solids discharge with a lower sugar content, as well as an increased solids content and solids content of the protein-containing fraction.

[0017] In a preferred embodiment, in process step b) pre-liming is carried out by adding lime milk to the raw sugar beet juice, in particular to an alkalinity of 0.1 to 0.3 g CaO / 100 ml raw sugar beet juice. In particular, the pH value is raised to 10 to 12, in particular 10.5 to 12, in particular 10.5 to 11.5, in particular 11.

[0018] According to the invention, in a preferred embodiment it is provided that after pre-liming and before separating the formed coagulate in a process step b1) at least one flocculant is added to the pre-liming juice, for example a polyanionic flocculant, for example a copolymer, for example a copolymer of acrylamide and sodium acrylate, in particular with a molar mass of about 5 million to 22 million, preferably up to a concentration of 1 to 8 ppm.

[0019] In a particularly preferred embodiment, a solids content of preferably 17 to 23 vol.%, more particularly 18 to 22 vol.%, and more particularly 20 vol.% is adjusted in process step c). It is provided that the solids content of the pre-liming juice to be used in process step d) is adjusted in process step c) by means of a dynamic or static decanter, for example a settling device.

[0020] According to the invention, the angle between the longitudinal axis of the centrifuge drum and the generatrix of the conical section of the centrifuge drum of the at least one decanter centrifuge in process step d) and / or f), also referred to here as "discharge angle" or "discharge angle of the drum", is 6 to 10°, preferably 8 to 10°, preferably 8°.

[0021] In a particularly preferred embodiment, at least a portion of the clear sugar beet pre-liming juice obtained in process step e) is mixed with pre-liming juice from process step b). In process step c), the solids content is then adjusted, and subsequently, in process step d), the coagulate is separated.

[0022] In a particularly preferred embodiment of the present invention, it is provided that in process step f) the protein-containing fraction obtained in process step e) is thickened, i.e., concentrated, particularly after prior dilution of the protein-containing fraction obtained in process step e) to a solids content of the protein-containing fraction of 15 to 25 vol.%, particularly 20 vol.%. In particular and preferably, process step f) is carried out using at least one further decanter centrifuge.In a particular embodiment, this further decanter centrifuge comprises a motor-driven, rotating centrifuge drum with at least one cylindrical section and at least one conical section, wherein the angle between the longitudinal axis of the centrifuge drum and the generatrix of the conical section is 6 to 10°, preferably 8 to 10°, more preferably 8°, and at least one extruder screw rotatably mounted in the centrifuge drum is present. In a particularly preferred embodiment, for concentrating the protein-containing fraction obtained in process step e), the aforementioned at least one further decanter centrifuge is operated with at most 50% of the permissible maximum torque.

[0023] The method according to the invention provides for the sequence of process steps a) to e), optionally also process step f). In a particularly preferred embodiment, the method according to the invention consists of process steps a) to e), in particular a) to f), meaning that no further process steps take place between process steps a) to e), in particular between process steps a) to f). In a particularly preferred embodiment, a method according to the invention is provided in which the process steps a) to e), in particular a) to f), are carried out in exactly the specified order a), b), c), d), e) or a), b), c), d), e), f). According to the invention, it is further provided that the process steps are carried out simultaneously, overlapping in time, or sequentially.In particular, process steps b) and c) as well as process steps d) and e) can be carried out simultaneously or partially overlapping in time.

[0024] The present invention also discloses a protein-containing fraction that can be produced, in particular produced, according to one of the methods according to the invention.

[0025] The present invention also discloses a clear sugar beet pre-liming juice that can be produced, in particular produced, according to one of the methods according to the invention.

[0026] The present invention also discloses the use of a decanter centrifuge comprising a motor-driven rotating centrifuge drum with a cylindrical section and a conical section, wherein the angle between the longitudinal axis of the centrifuge drum and the generatrix of the conical section is 6° to 10°, and an extruder screw rotatably mounted in the centrifuge drum, for obtaining a clear sugar beet pre-liming juice and a protein-containing fraction.

[0027] In connection with the present invention, "raw sugar beet juice" is understood to mean the juice, i.e., the aqueous sugar-containing medium, that can be obtained from sugar beets, for example from beet slices, by means of extraction or pressing processes, in particular by thermal extraction processes such as countercurrent extraction at, for example, 65 to 75°C in the so-called diffusion process, electroporation-assisted extraction processes, or pressing processes. This sugar-rich raw sugar beet juice contains, in addition to sugar (sucrose), various organic and inorganic components of the beet, which are referred to as non-sucrose substances.

[0028] In connection with the present invention, "clear sugar beet pre-liming juice" is understood to mean the juice, i.e., the aqueous sugar-containing medium, which is obtained as the clear liquid after separation of the protein-containing fraction. According to the invention, this juice is characterized in that, in a preferred embodiment, it has a low solids content (in vol. %), that is, a solids content of less than or equal to 12 vol. %. According to the invention, in a preferred embodiment, a solids content of 1–12 vol. %, in particular 1–10 vol. %, in particular 1–6 vol. %, in particular 2–12 vol. %, in particular 2–10 vol. %, in particular 2–6 vol. %, in particular 4–12 vol. %, in particular 4–10 vol. %, in particular 4–6 vol. % is achieved in the clear sugar beet pre-liming juice.

[0029] In connection with the present invention, the term "non-sucrose substances" contained in raw sugar beet juice refers to high-molecular-weight substances such as proteins, polysaccharides, and cell wall components, as well as low-molecular-weight compounds such as inorganic or organic acids, amino acids, and minerals. The cell wall components include, in particular, pectins, lignin, cellulose, and hemicellulose. These substances, like the proteins, which include, in addition to proteins, nucleoproteins and glycoproteins in particular, are present as hydrophilic macromolecules in colloidally dispersed form. Examples of organic acids include lactates, citrates, pectic acid, and oxalates. Examples of inorganic acids include sulfates and phosphates.

[0030] Prelimination refers to the addition of lime milk to raw sugar beet juice, particularly to an alkalinity of approximately 0.1 to 0.3 g CaO / 100 ml of raw sugar beet juice. During prelimination, the raw sugar beet juice is alkalized under gentle conditions, raising its pH from approximately 6 to approximately 11.5. Prelimination serves to flocculate non-sucrose substances, such as pectin and proteins, and to precipitate sparingly soluble calcium salts.

[0031] According to the invention, "lime milk" refers in particular to calcium hydroxide, which is formed in the strongly exothermic reaction of quicklime (calcium oxide) with water and is used as a liming agent in pre-liming and main liming. The addition of lime milk to the raw sugar beet juice during pre-liming causes the precipitation or coagulation of non-sucrose substances in the form of a coagulate.

[0032] In connection with the present invention, the non-sucrose substances separated from the raw sugar beet juice in process step b) by pre-liming and optionally the addition of flocculant in the form of a coagulate are referred to as the "protein-containing fraction" or "colloid fraction". This fraction is alkaline, perishable due to its organic nature, and thixotropic. It behaves like a non-Newtonian fluid; in particular, its viscosity decreases under shear stress, and after the stress is removed, the initial viscosity is restored.

[0033] According to the invention, a "coagulate" is understood to be the agglomerates of non-sucrose substances present in raw sugar beet juice that form as a result of a flocculation process. The coagulate comprises, in particular, the insoluble or sparingly soluble salts that form through reactions of the anions of organic or inorganic acids with calcium, and the excreted high-molecular-weight components of raw sugar beet juice, especially those with a hydrophilic character, such as proteins, polysaccharides, and cell wall components, which are normally colloidally dispersed in raw sugar beet juice. In particular, the coagulate, and thus the protein-containing fraction, contains anions such as oxalate, citrate, phosphate, sulfate, and pectic acid, as well as colloids, especially pectin, proteins, cellulose, and hemicellulose.The flocculation process is divided into flocculation, in which aggregation occurs through the absorption of bridging polymers, and coagulation, in which aggregation occurs through the breakdown or reduction of repulsive forces. The flocculation rate depends on the temperature, pH value, and the method of lime milk addition. The precipitation of individual juice components, such as anions like oxalate, phosphate, citrate, and sulfate, as well as colloids like pectin and protein, occurs within specific pH ranges, during which the precipitate compacts. The pH value at which a maximum amount of colloids flocculates and the precipitation of insoluble calcium salts is almost complete is referred to as the optimal flocculation point for pre-liming. If precipitation occurs at the optimal flocculation point, a uniform and stable flocculation of colloidally dispersed, high-molecular-weight juice components results.

[0034] The precipitation and coagulation of pectins and proteins requires a specific temperature-dependent residence time. According to the invention, pre-liming can be carried out as either cold or warm pre-liming. Preferably, cold pre-liming is performed at a pre-liming temperature of approximately 38 to 40°C. However, according to the invention, it is also preferably possible to carry out the addition of the lime milk to the raw sugar beet juice as warm pre-liming at a temperature of the raw sugar beet juice of 55 to 75°C. According to the invention, the addition of lime milk for pre-liming the raw sugar beet juice is preferably carried out as progressive pre-liming. Progressive pre-liming is understood to mean a gradual increase in the alkalinity or pH value of the raw sugar beet juice, preferably by a slow addition of the lime milk or by small, intermittent additions of lime milk, whereby the pH optimum is reached slowly.

[0035] According to the invention, it is preferably provided that the progressive alkalization of the raw sugar beet juice during pre-liming can be carried out in a countercurrent flow using already alkalized raw sugar beet juice, for example, by means of the sludge juice concentrate from the carbonation stages. The progressive alkalization in a countercurrent flow means that the added juice of higher alkalinity is mixed as quickly as possible with a juice of lower alkalinity, without different alkalinity gradients being able to build up within the mixing zone.

[0036] According to the invention, in process step e), the protein-containing fraction separated from the pre-liming juice in process step d) is obtained, preferably after collection. In a further preferred embodiment, the invention provides that the protein-containing fraction obtained in process step e) is concentrated in an optional process step f) by using a further decanter centrifuge according to the invention, preferably as used in process step d). According to the invention, this "concentration" is understood to mean the concentration of the protein-containing fraction to a preferred solids content of 35 to 50%, more preferably 38 to 45%, more preferably 45% (solids content in the protein-containing fraction is, unless otherwise specified, referred to by weight of the total composition in the present teaching).

[0037] In connection with the present invention, the "solid fraction" of the pre-liming juice is understood to be the fraction, preferably in vol. %, of the pre-liming juice obtained after centrifugation, in particular at 4000 rpm for 10 min, and removal of the supernatant.

[0038] In connection with the present invention, the "solid fraction" of the protein-containing fraction is understood to be the proportion, preferably in wt. %, of the protein-containing fraction that is obtained after removal of water, for example by drying.

[0039] In connection with the present invention, the "solids content" of the protein-containing fraction is understood to be the mass of the protein-containing fraction obtained in process step e) according to the invention per unit of time, preferably in kilograms per hour. The solids content is calculated from the measured volume per unit of time of the protein-containing fraction after determining its density.

[0040] In connection with the present invention, the "solid fraction" in the clear sugar beet pre-liming juice is understood to be the fraction of the clear sugar beet pre-liming juice obtained after centrifugation, in particular at 4000 rpm for 10 min, and removal of the supernatant.

[0041] In connection with the present invention, the "amount of sugar" of the protein-containing fraction is understood to be the mass of sugar which is present in the protein-containing fraction after the separation of the coagulate from the pre-liming juice.

[0042] A "decanter" or "decaneur", in particular a static or dynamic decanter, is understood to be a device or apparatus used for the mechanical removal of sedimented substances from a liquid according to the sedimentation principle using gravity.

[0043] A decanter centrifuge according to the invention comprises a motor-driven, rotating centrifuge drum with at least one cylindrical and at least one conical section and at least one extruder screw rotatably mounted in the centrifuge drum, as well as at least one inlet, at least one central outlet and at least one solids discharge.

[0044] In a particularly preferred embodiment, the torque during operation of the centrifuge in process steps d) and / or f) is at most 50%, and more preferably at most 40%, of the maximum permissible torque. In a further preferred embodiment, the torque during operation of the centrifuge is 10% to 50%, preferably 20% to 50%, preferably 30% to 50%, preferably 10% to 40%, preferably 20% to 40%, and preferably 30% to 40% of the maximum permissible torque.

[0045] In the context of the present invention, the "maximum permissible torque" is understood to mean the highest torque with which the centrifuge can be operated without causing permanent damage.

[0046] In connection with the present invention, "permanent damage" is understood to mean damage that significantly impairs the intended operation, in particular resulting in the centrifuge no longer being functional or its performance being reduced to such an extent that it produces a product of insufficient quality in connection with the present invention, in particular a clear sugar beet pre-liming juice with, for example, a solids content in the clear run of more than 15 vol.% or a protein-containing fraction with a solids content of less than 35 wt.%.

[0047] In the context of the present invention, a "flocculation aid" is understood to be a substance that influences the zeta potential of particles in colloidal suspensions such that they aggregate into flocs and can be removed from the system, for example, after sedimentation. Flocculation aids must therefore overcome the electrostatic repulsion of the mostly negatively charged particles. According to the invention, the flocculation aid can also be a sedimentation accelerator.

[0048] In the context of the present invention, "flocculation aids" or "sedimentation accelerators" are understood to be compounds that cause solid particles to clump together into larger units or flocs. Due to their increased mass, the solids settle significantly faster as a result of this clumping. Simultaneously, the pores between the individual particles are enlarged, allowing the water contained in the settled sludge to be easily removed by filtration or centrifugation. The polyanionic flocculants preferably used according to the invention have no coagulating effect, since they do not influence the dispersion of the particles in the liquid phase, but rather cause the aggregation of the particles through absorption-bridging polymers.

[0049] In a preferred embodiment according to the invention, the copolymers of acrylamide and sodium acrylate used as polyanionic flocculants are synthetic, organic, water-soluble polyelectrolytes with a relatively high molecular weight of approximately 5 million to approximately 22 million. These compounds are moderately to strongly ionic. Products 2440 and 2540 (Stockhausen) and NA 945 (Clarflock) are particularly preferred as flocculants.

[0050] Further advantageous embodiments result from the dependent claims.

[0051] The invention is described in more detail using the following exemplary embodiments. Example 1

[0052] Raw sugar beet juice is placed in a heated container equipped with an agitator, an inlet for raw sugar beet juice, an outlet, and a pH electrode, and heated to 55°C. Over a period of 20 minutes, lime milk is gradually added to the raw juice until the pH value of the optimal flocculation point for pre-liming is reached (approx. 0.1–0.3 g CaO / 100 ml juice). To increase the settling rate, a polyanionic flocculant (Praestol 2540TR) is then added. The pre-limed juice is drained off, adjusted to a solids content of 20% by volume using a static decanter, and fed into a decanter centrifuge. The centrifuge has an angle of 8° between the longitudinal axis of the centrifuge drum and the generatrix of the conical section and is operated at 10–30% of its maximum permissible torque. The pre-liming juice (inlet) is fed to the decanter centrifuge at a rate of 3000 L / h.The protein-containing fraction is separated from the pre-liming juice and discharged from the decanter centrifuge via the solids discharge, while the clear sugar beet pre-liming juice is discharged from the centrate outlet of the decanter centrifuge. The solids content of the protein-containing fraction is 38 to 42% by weight, and the solids rate is 192 kg / h dry matter. The sugar content of the protein-containing fraction is 15 kg / h, and the solids content in the clear sugar beet pre-liming juice is 4 to 6% by volume. Example 2 Comparison of different discharge angles between the longitudinal axis and generatrix of the conical section of the centrifuge drum

[0053] Raw sugar beet juice is pre-limed as in Example 1 and fed at a rate of 3000 L / h and a solids content of 20 vol.% to various decanter centrifuges with discharge angles of 5°, 8°, 10°, and 15° between the longitudinal axis and the generatrix of the conical section of the centrifuge drum. The different decanter centrifuges are operated at different torques to enable separation of the coagulate. The protein-containing fractions and clear raw sugar beet juices separated by the different decanter centrifuges differ in the solids content of the clear pre-limed sugar beet juice, as well as in the sugar content and the amount and proportion of solids in the protein-containing fraction (see Table 1). The use of a decanter centrifuge with an angle of 5° results in a higher sugar content and a lower solids content (dry matter in wt.).The use of a decanter centrifuge with an angle of 8° results in a particularly clear sugar beet pre-liming juice, a high solids content, a high solids quantity, and a lower sugar content in the protein-containing fraction. A decanter centrifuge with an angle of 10° also yields comparable sugar and solids quantities, as well as a comparable solids content in the protein-containing fraction. Even with a brief exceedance of the maximum permissible torque, the decanter centrifuge with an angle of 15° fails to separate the protein-containing fraction from the pre-liming juice. Table 1 discharge angle ° 5 8 10 15 Inflow (pre-liming juice) L / h 3000 3000 3000 3000 Applied torque (% of the maximum permissible torque) % very low < 40% 40-80% > 100% Solid content in pre-liming juice Vol. 20 20 20 20 Klarlauf (clear sugar beet pre-liming juice) L / h 2400 2600 2650 3000 Protein-containing fraction L / h 600 400 350 - Protein-containing fraction, solids content kg / h 148 192 164 - Protein-containing fraction (TS), solid fraction % by weight 23 38-42 38-40 - Sugar content of the protein-containing fraction kg / h 22 15 15 - Solids content in clear sugar beet pre-liming juice Vol. 12 - 14 4 - 6 8 - 12 - Example 3 Comparison of the solids content in the influent

[0054] A pre-liming juice prepared according to Example 1 is adjusted to 10, 20, and 30 vol.% solids content using a static decanter. These differently adjusted pre-liming juices are each fed into a decanter centrifuge with a discharge angle of 8°. Different results are obtained by using a pre-liming juice with different solids content: The pre-liming juice with a solids content of 10 vol.% results in insufficient separation of the protein fraction, while the pre-liming juice with 30 vol.% solids content leads to an increased solids content in the clear run (see Table 2). The pre-liming juice with 20 vol.% solids content results in a very clear sugar beet pre-liming juice and a high solids content in the protein fraction. Table 2 discharge angle ° 8 8 8 Inflow (pre-liming juice) L / h 3000 3000 3000 Applied torque (% of the maximum permissible torque) % <40% < 40% 20-60% Solid content in pre-liming juice Vol. 10 20 30 Klarlauf (clear sugar beet pre-liming juice) L / h 2780 2600 2600 Protein-containing fraction L / h 220 400 400 Protein-containing fraction, solids content kg / h 100 192 192 Protein-containing fraction (TS), solid fraction % by weight 36-40 38-42 38-42 Sugar content of the protein-containing fraction kg / h 9 15 15 Solids content in clear sugar beet pre-liming juice Vol. 2 - 3 4 - 6 16 - 20 Example 4

[0055] Preliminated sugar beet juice produced according to Example 1, with a solids content of 15% by volume, is fed into a decanter centrifuge with a discharge angle of 10° (operated as described in Example 1). The resulting clear sugar beet preliminated juice is collected and further processed. The protein-containing fraction, with a solids content of 36% by weight, is collected, diluted to 20% by volume, and fed into another decanter centrifuge. This second decanter centrifuge has a discharge angle of 8° and is operated with a torque of no more than 50% of the maximum permissible torque. The protein-containing fraction is concentrated to a solids content of 45% by weight using this second decanter centrifuge.

Claims

1. A method for producing a clear sugar beet pre-liming juice and a protein-containing fraction from sugar beet raw juice, comprising the following method steps: a) providing the sugar beet raw juice; b) pre-liming the sugar beet raw juice provided in method step a) to obtain a pre-liming juice, forming a coagulate of non-sucrose compounds forming in the obtained pre-liming juice; c) setting a solids content of 15 - 25% by volume (based on the total volume of the pre-liming juice provided in method step b)) in the pre-liming juice by means of a dynamic or static decanter; d) separating the coagulate from the pre-liming juice obtained in method step c) using at least one decanter centrifuge, comprising a motor-driven, rotating centrifugal bowl with a cylindrical portion and a conical portion, wherein the angle between the longitudinal axis of the centrifugal bowl and the generatrix of the conical portion is 6° to 10°, and an extruder screw mounted rotatably in the centrifugal bowl; and e) obtaining the clear sugar beet pre-liming juice and the separated coagulate in the form of a protein-containing fraction.

2. The method according to claim 1, wherein, in a method step f), the protein-containing fraction obtained in method step e) is thickened using at least one further decanter centrifuge.

3. The method according to any one of the preceding claims, wherein at least a part of the clear sugar beet pre-liming juice obtained in method step e) is mixed in a further method step with pre-liming juice from method step b), a pre-liming juice mixed with clear sugar beet pre-liming juice is obtained, the solids content is set in method step c) and subsequently fed to a coagulate separation in method step d).

4. The method according to any one of the preceding claims, wherein the angle between the longitudinal axis of the centrifugal bowl and the generatrix of the conical portion is 8° to 10°.

5. The method according to claim 4, wherein the angle between the longitudinal axis of the centrifugal bowl and the generatrix of the conical portion of the at least one decanter centrifuge is exactly 8°.

6. The method according to any one of the preceding claims, wherein the pre-liming juice used in method step d) has a solids content of 20% by volume.

7. The method according to any one of the preceding claims, wherein the at least one decanter centrifuge used in method step d) and / or f) is operated at a torque of at most 50% of the maximum permissible torque.

8. The method according to any one of the preceding claims, wherein the at least one decanter centrifuge used in method step d) and / or f) is operated at a torque of at most 40% of the maximum permissible torque.

9. The method according to any one of the preceding claims, wherein, following method step b), a flocculation is carried out in a method step b1), adding at least one flocculation aid.