Method and device for pressing

Abstract

The invention relates to a method and a device for pressing. According to the invention, air or nitrogen, preferably in liquid form, is introduced as a coolant into the pressing chamber of a press such that the temperature of the oil cake and / or of the liquid that has been pressed out decreases during the pressing process.

Description

[0001] The invention relates to a device for pressing, in particular in the sense of a screw press.

[0002] Furthermore, the invention relates to a method for pressing.

[0003] Such methods and devices are used to extract liquids from a press cake, for example, oil from oil-containing seeds. For this purpose, the press material is fed into a pressing device, e.g., a screw press, in which liquid is extracted from the press cake by mechanical pressing, thus separating the solid and liquid components of the press material.

[0004] Screw presses have a screw shaft mounted for rotation within a press chamber. The press chamber is defined by a tubular strainer basket, with the material to be pressed being fed in at one end and the press cake being ejected at the other. The strainer basket has openings around its perimeter, usually designed as slots running parallel to the rotational axis of the screw shaft, through which the pressed liquid can escape from the press chamber. These slots are usually formed by the spaces between adjacent strainer bars.

[0005] During the pressing process, very high temperatures sometimes occur due to mechanical friction and high pressure, which affect both the quality of the press cake and the pressed liquid as well as the operational reliability of the press.

[0006] Limiting the temperature during the pressing process has a positive effect on both the press cake itself and the liquid to be pressed with regard to product quality.

[0007] After pressing, the press cake is used, for example, as animal feed or as a food supplement, so certain quality requirements apply.

[0008] For example, it is a requirement to achieve the highest possible PDI (Protein Dispersibility Index) in the press cake. This value represents the solubility of the proteins in the press cake, which is negatively affected by protein denaturation that occurs at high temperatures.

[0009] With regard to the quality of pressed liquids, for example, in mustard oil pressed from mustard seeds, one goal is to obtain the highest possible allyl isothiocyanate (AITC) content, since the AITC content causes the sharp taste.

[0010] The AITC content also decreases with increasing temperatures during the pressing process.

[0011] For both of the aforementioned objectives with regard to the product quality of press cake and pressed liquid, it is therefore of considerable importance to keep the temperature as low as possible during the pressing process.

[0012] However, particularly with regard to oils as pressed liquids, cooling the press cake during the pressing process has adverse effects on the viscosity, making it more difficult for it to flow away.

[0013] DE 10 2007 014 775 A1 proposes methods and devices of the aforementioned type which enable an improvement in the product quality of the oil obtained, in particular for use in edible oil production, which is achieved in particular by limiting the temperature of the extract to a maximum of 60°C during the entire extraction process by using supercritical CO2 as an extraction agent.

[0014] The addition of supercritical CO2 during the pressing process thus acts both as a coolant and as an extraction agent in the true sense of the word. When this principle is applied to seed oil extraction, the dissolution of carbon dioxide in the oil significantly reduces the viscosity and thus significantly liquefies the oil, thus at least compensating for the adverse effect of cooling on the oil's viscosity.

[0015] However, the disadvantages of using CO2 as a cooling medium for screw presses are the comparatively high cost of liquid CO2, the complex design of the press itself, and safety considerations. The use of CO2 requires complex sealing of the press with a closed chamber and the use of gas detectors by personnel working in the press area to prevent and / or detect a suffocating atmosphere. The closed chamber also prevents the pressed liquid from draining into this area, meaning the entire length of the press chamber cannot be fully utilized.

[0016] CN 109421307 A already discloses a method and device for pressing, according to the preamble of claim 1, using a screw press. Within a pressing chamber, the material to be pressed is transported and pressed using a screw shaft. Cooling can be achieved during the pressing process using a cold gas.

[0017] Similar methods and devices for pressing using a screw press with cooling by using a cold gas are also described in CN 107650412 A and CN 108407363 A.

[0018] It is an object of the invention to provide a device for pressing with which the material to be pressed and / or the pressed liquid can be cooled during pressing without the disadvantages occurring when using supercritical CO2.

[0019] This object is achieved according to the invention by a device for pressing according to patent claim 1.

[0020] It is a further object of the invention to provide a method for pressing with which the material to be pressed and / or the pressed liquid can be cooled during pressing without the disadvantages occurring when using supercritical CO2.

[0021] This object is achieved according to the invention by a method for pressing according to patent claim 12.

[0022] A pressing device according to the invention is designed as a screw press and has means for supplying a coolant into the pressing chamber.

[0023] In another embodiment of the invention, the coolant is fed exclusively or additionally from the outside onto the strainer basket, at least in part.

[0024] According to the invention, air or nitrogen is used as the coolant, wherein in preferred embodiments of the invention the respective coolant can be supplied in liquid form into the pressing chamber of the pressing device.

[0025] In preferred embodiments of the invention, nitrogen is used as a coolant instead of air, since in addition to the cooling effect, this also contributes to better product quality of press cake and pressed liquid, as oxidation of the products during pressing is avoided, and the risk of fire is reduced by displacing oxygen from the press chamber.

[0026] Since the nitrogen escaping into the press interior is considered harmless and is also completely soluble in air, which consists of 80% nitrogen, there is no potential danger provided the press is connected to a sufficiently dimensioned aspiration system and the hall in which the press is installed is well ventilated. For additional safety, flap seals can be used.

[0027] Flap seals are seals for flaps that form part of the housing or casing of a pressing device. These flaps provide access to the strainer basket of a pressing device, for example, for maintenance purposes, while simultaneously shielding the interior of the pressing device from the environment. Sealing the flaps supports this shielding, preventing gases from escaping from the pressing device into the surrounding work area. In embodiments of the invention, the flap seals are designed as rubber lips arranged on the edges of the flaps.

[0028] In preferred embodiments of the invention, flap seals are combined with an aspiration of the press interior.

[0029] In embodiments of the invention, sensors are installed on side doors and cake flap to prevent the doors or flaps from opening during operation of the pressing device or during the supply of coolant.

[0030] In embodiments of the invention, the sensors are designed as proximity switches or inductive switches with which it is possible to detect whether the doors and / or flaps are closed.

[0031] In a preferred embodiment of the invention, the sensors are integrated into a process control system with which the supply of the coolant and / or the operation of the press can be stopped when a door and / or flap is detected opening.

[0032] In liquid form, the temperature of the respective coolant is lower than in the gaseous state at ambient pressure, so that the cooling effect on the press cake and / or the pressed liquid is higher.

[0033] The means for supplying a coolant comprise at least one coolant source and at least one coolant outlet arranged on the pressing device such that the coolant can be introduced into the pressing chamber.

[0034] In embodiments of the invention, the coolant source can be designed, for example, as a coolant container or reservoir in which coolant is stored under ambient pressure or, if appropriate, a higher pressure, or as a device for generating the coolant.

[0035] Particularly preferably, the pressing device has a plurality of coolant outlets.

[0036] In embodiments of the invention, the at least one coolant source and the at least one coolant outlet are connected to one another via at least one coolant line.

[0037] Preferably, at least one coolant valve is provided, via which the supply of coolant into the pressing chamber of the pressing device can be controlled.

[0038] According to the invention, the at least one coolant outlet is arranged close to the screw shaft or in the screw shaft itself, so that the coolant is injected close to the screw shaft. This maximizes the path the coolant must take through the press cake before leaving the press chamber, thus maximizing the effect of heat exchange between the coolant and the press cake. Depending on the temperature of the supplied coolant, however, the injection must not be too close to the screw shaft, as the shaft could otherwise be damaged due to the low temperatures.

[0039] In embodiments of the invention, at least one coolant outlet is arranged on the screw shaft.

[0040] In one embodiment of the invention, the coolant is injected from the interior of the screw shaft through a coolant outlet.

[0041] In other embodiments of the invention, the coolant is injected through coolant outlets extending from the outside into the press chamber. This arrangement of the coolant outlets allows for easier retrofitting of conventional press devices compared to injection from the screw shaft.

[0042] In principle, injecting the coolant from nozzles located outside the screw shaft has the advantage that the screw shaft material is not negatively affected by direct contact with the coolant at the feed temperature. For example, the screw shaft may become brittle at temperatures that are too low.

[0043] Temperatures less than or equal to 5°C are critical for the material of the screw shaft, and temperatures less than or equal to 0°C are particularly critical.

[0044] In advantageous embodiments of the invention, at least one temperature sensor is arranged in the screw shaft in the area where the coolant is introduced into the press chamber. This sensor allows the local temperature of the screw shaft to be measured.

[0045] In particularly preferred embodiments of the invention, at least one temperature measurement value of the temperature sensor arranged in the screw shaft is used to control the feed quantity and / or the feed temperature of the coolant in such a way that the temperature of the screw shaft is kept above a temperature limit value in order to avoid damage to the screw shaft due to thermal stresses.

[0046] In embodiments of the invention, the injection of the coolant from the interior of the screw shaft through a coolant outlet and the injection of the coolant through coolant outlets projecting from the outside into the pressing chamber are combined.

[0047] When the coolant is injected through coolant outlets extending from the outside into the press chamber, in embodiments of the invention these outlets are arranged in areas in the conveying direction of the press behind throttle rings. In these relaxation and mixing zones, the introduced coolant can optimally contact the press cake.

[0048] Since the state of aggregation of coolants introduced in liquid form changes from liquid to gaseous in the press chamber of the press, a good mixing effect and a high heat exchange are achieved.

[0049] An additional mixing effect to the mixing of press cake and coolant caused by the press itself is achieved with coolant outlets projecting into the press chamber due to the associated flow resistance in the area of ​​the coolant outlets for the press cake.

[0050] In embodiments of the invention, the strainer basket has a sealed area in the area of ​​the coolant outlets and / or in an area immediately behind them in the conveying direction, preventing the coolant from escaping. As a result, the coolant is conveyed along with the press cake for a longer time in the conveying direction of the press, thus achieving better cooling of the press cake. This reduces the escape of trub, i.e., press cake as a solid component in the pressed liquid.

[0051] In embodiments of the invention, the means for introducing the coolant are arranged entirely or partially in a cooling ring that forms part of the press chamber. Depending on the installation length of the cooling ring, the length of the strainer bars in the installation area is adjusted accordingly in embodiments according to the invention.

[0052] By introducing the coolant in the area of ​​the screw shaft, entrainment effects occur as the press cake flows from the coolant outlet to the openings of the press chamber, causing portions of the liquid to be pressed to flow along with the coolant. This at least partially compensates for the increased viscosity of the pressed liquid associated with cooling the press cake and the resulting impaired flow of the pressed liquid. Depending on the pressure, temperature, and flow direction of the coolant, even improved yields of the pressed liquid may be achievable.

[0053] The loosening of the press cake by evaporating coolant and the flow resistance of the nozzles or coolant outlets improve the mixing of the press cake in the strainer in the expansion zones downstream of the throttle rings. This facilitates better mass transfer of the pressed liquid (e.g., oil) from the press cake out of the strainer, as the press cake now has a higher liquid content on the inside of the strainer.

[0054] In addition to the location and type of coolant, the amount of coolant supplied, particularly in relation to the flow rate of the press cake, also plays a role in achieving the effects according to the invention.

[0055] By increasing the amount of coolant supplied, the cooling effect also increases.

[0056] In embodiments of the invention, the pressing device comprises a measuring device for measuring the exit temperature of the press cake from the pressing device. Using a corresponding metering device, the amount of coolant supplied can be adjusted to set a target temperature for the press cake exiting the press.

[0057] A pressing method according to the invention comprises at least the following process steps: Providing air or nitrogen as a coolant using a coolant source. Feeding the coolant from the coolant source into the press chamber of a screw press and / or at least partially onto the outside of the strainer basket of the screw press. Cooling the press cake and / or the pressed liquid using the coolant, The coolant is introduced into the press chamber close to the screw.

[0058] In this process, a material to be pressed, or a press cake, is introduced into a screw press through a feed opening and transported through a press chamber by means of a screw shaft, where it is pressed, so that a liquid is extracted from the press cake. The extracted liquid exits the press chamber through openings.

[0059] Preferably, the coolant is supplied to the screw press in liquid form, as this is colder and results in a greater cooling effect.

[0060] Preferably, the coolant is injected into the press chamber in the area of ​​the screw shaft so that the cooling effect is improved and, if necessary, entrainment effects are achieved with regard to the pressed liquid.

[0061] Preferably, nitrogen is used as the coolant, particularly preferably liquid nitrogen. In embodiments of the invention, the pressing method according to the invention is designed to implement some or all of the functions of a pressing device according to the invention.

[0062] In advantageous embodiments of the method according to the invention, the coolant is supplied in such a way that the screw shaft is locally cooled to a maximum temperature greater than 0°C, in particularly preferred embodiments it is cooled to a maximum temperature greater than 5°C.

[0063] In a preferred embodiment of a pressing method according to the invention, a pressing device according to the invention is used.

[0064] Conversely, a pressing device according to the invention is also designed in embodiments to implement the method according to the invention in all disclosed variants. In a pressing method according to the invention or with a pressing device according to the invention, the following operating parameters are used in embodiments of the invention: The inlet pressure of the coolant is atmospheric pressure in embodiments of the invention. In other embodiments, a pressure below 100 bar is provided. In different embodiments of the invention, the coolant is injected under high pressure. In any case, the inlet pressure of the coolant is high enough that it can be pumped into the strainer basket in corresponding embodiments of the invention.

[0065] In embodiments of the invention, the mass flow for the press cake can be set to 100–1000 t / d seed equivalent for pre-pressing, 90–170 t / d seed equivalent for post-pressing, and 30–100 t / d seed equivalent for final pressing. However, lower mass flows can also be achieved in other embodiments.

[0066] In preferred embodiments of the invention, the ratio of the added mass fraction of coolant to the total mass flow of the press (press cake and coolant) is between approximately 0 and 25%. Excessive coolant input consumes an unnecessarily large amount of coolant and cools the press cake unnecessarily. Preferably, the press cake or the pressed liquid is cooled only to the extent that the process specifications with regard to the specified product quality are just achieved.

[0067] The essential advantage in the product quality of the press cake that can be achieved according to the invention is the higher PDI value, which indicates the percentage water solubility based on the total amount of protein in the product.

[0068] Due to the lower temperature, fewer phosphatides are transferred into the pressed oil, so that the degumming of the oil is less complex or can be completely eliminated when mixing the now higher quality post-press oil with pre-press oil.

[0069] When pressing mustard seeds, the allyl thiocyanate content is crucial for product quality. For high-quality products, a target value of 0.3 meq is targeted, although a value of up to 0.26 meq is still considered acceptable. The allyl thiocyanate content decreases with higher temperatures, so the target value of 0.3 meq can be expected at an oil temperature in the range of approximately 70 °C. The typical oil temperature in conventional secondary pressing, however, is approximately 100 °C, so a temperature reduction according to the invention is associated with a significant improvement in oil quality.

[0070] Another advantage of the invention is the use of cost-effective coolants. Liquid carbon dioxide is typically somewhat more expensive than liquid nitrogen. Extracting nitrogen from the ambient air is even more cost-effective when demand is high. Depending on the purchasing and delivery costs in a given area, savings of 40 to 75% can be achieved. Therefore, it is a case-by-case decision whether the delivery of liquid nitrogen or on-site production, which requires a higher initial investment, makes more financial sense. This also applies to air as a coolant.

[0071] Furthermore, existing conventional presses can be converted much more easily for use according to the teaching of the invention compared to the use of supercritical CO2 as a coolant, since only a few design adjustments to the presses are absolutely necessary.

[0072] With a classic shaft cooling system, in which a coolant is only passed through the screw shaft, the required temperature reductions cannot be achieved anywhere near.

[0073] In embodiments of the invention, multi-stage pressing is realized by the serial arrangement of at least two cooled pressing stages. This allows for lower residual fat contents in the press cake compared to single-stage pressing / pressing processes.

[0074] The following figures illustrate exemplary embodiments of the invention. They show: Figure 1: A schematic representation of a longitudinal section through a pressing device according to the invention, Figure 2: A detailed view of a section in the region of a coolant outlet, Figure 3: A detailed view of a section in the region of a further embodiment of a coolant outlet, Figure 4: A table with comparison values ​​for parameters of a pressing method according to the invention and Figure 5: A graphic representation of the cooling effect of two coolants in comparison.

[0075] In Figure 1 a longitudinal section through a pressing device (1) according to the invention is shown schematically.

[0076] The illustrated embodiment of a pressing device (1) according to the invention is designed as a screw press and has a pressing chamber (2) that extends tubularly in the longitudinal direction of the pressing device (1). The pressing chamber (2) is radially delimited by a strainer basket (3) that has a plurality of openings through which a pressed liquid (8) can escape from the strainer basket (3).

[0077] A screw shaft (4) is rotatably mounted in the pressing chamber (2) and can be driven by means of a press drive (5). At a first end, the pressing device (1) has a feed opening (6) for the pressed material / press cake, which can then be conveyed through the pressing chamber (2) by means of the screw shaft (4). In the longitudinal direction of the pressing device (1), the screw flight formed between the screw shaft (4) and the strainer basket (3) becomes increasingly narrower, so that a continuously high pressure is exerted on the pressed material / press cake. At the second end of the pressing device (1) it has an outlet (7) for the press cake.

[0078] The pressing device (1) further comprises a strainer basket section designed as a cooling ring (9). In the region of the cooling ring (9), the pressing device (1) has several coolant outlets (10) through which a coolant can be introduced into the pressing chamber (2) of the pressing device (1). The coolant outlets (10) are connected to a coolant source (12) via a coolant line (11).

[0079] Furthermore, the device for pressing (1) has a coolant valve (13) via which the supply of coolant into the pressing chamber (2) can be regulated or at least switched on and off in relation to the supplied quantity per unit of time (e.g. volume flow).

[0080] Furthermore, the illustrated embodiment of a pressing device (1) has a coolant pump (14) with which the coolant can be conveyed from the coolant source (12) to the coolant outlets (10). Depending on the embodiment of the coolant source (12) and / or the coolant valve (13), variants without such a coolant pump (14) are also embodiments of a pressing device (1) according to the invention. For example, the amount of coolant fed into the pressing chamber (2) can be adjusted using a coolant pump (14). In other embodiments, this can be adjusted via the pressure of the coolant source (12) and / or a corresponding control of the coolant valve (13), which is designed, for example, as a proportional valve.

[0081] In the illustrated embodiment of the invention, the cooling ring (9) is arranged behind a throttle ring (15) in the conveying direction of the screw press, so that the coolant is supplied in a relaxation zone.

[0082] Figure 2 shows a detailed view of an embodiment of a pressing device (1) according to the invention in the region of a coolant outlet (10), wherein the coolant line (11) runs at least partially in the screw shaft (4) and the coolant outlet (10) is arranged on the screw shaft (4). Screw parts (16) are arranged on the screw shaft (4), forming various pressure zones, relaxation zones, and conveying areas.

[0083] In Figure 3An alternative embodiment of a coolant outlet (10) of a pressing device (1) according to the invention is shown, wherein the coolant outlet (10) extends from the outside through the strainer basket (3) into the pressing chamber (2). The opening of the coolant outlet (10) is arranged close to the screw.

[0084] Close to the screw in the sense of this document means in a spatially immediate proximity to the outer surface of the screw shaft (4) or the screw parts (16) arranged on the screw shaft. The representation in Figure 3 is not to scale for all dimensions of the pressing devices (1) according to the invention with regard to the distance between the screw shaft (4) and the coolant outlet (10).

[0085] In embodiments of the invention, an arrangement of a coolant outlet (10) close to the screw means that it is designed to discharge the coolant at a distance of less than 1 cm, in particularly preferred embodiments at a distance of approximately 3 mm to 10 mm from the outer surface of the screw shaft (4) or screw parts arranged on the screw shaft.

[0086] In Figure 4A table is shown which shows the cooling effect of the supply of nitrogen (N2) as a coolant with two different amounts of coolant supplied in comparison with supercritical CO2. Due to the significantly lower inlet temperature of -196 °C of liquid nitrogen compared to the inlet temperature of 72.3 °C for supercritical CO2, the use of liquid nitrogen leads to greater cooling of the press cake with the same mass flows of the pressing aids or coolant, as the enthalpy difference of the pressing aid is more than three times as great. Increasing the mass flow of liquid nitrogen from 111 kg / h to 219 kg / h also results in a significant increase in the cooling effect; in the present example, the achieved temperature difference of the cooled press cake increases from 16.5 °C to 32.7 °C.

[0087] Assuming a press cake outlet temperature of approximately 140 °C after the post-pressing, which is usual for two-stage finishing presses, a calculated temperature curve results depending on the supplied quantities of CO2 or N2 as shown in Figure 5 shown.

Claims

1. Device for pressing (1) designed as a screw press having a pressing chamber (2) in which a pressed material or press cake can be pressed with the aid of a screw shaft (4) and wherein the pressing chamber (2) is bounded in the radial direction by a strainer basket (3), wherein the device has means for supplying a coolant into the pressing chamber (2) and / or from the outside onto the strainer basket (3), the coolant being air or nitrogen, wherein at least one coolant outlet (10) is arranged for introducing the coolant into the pressing chamber (2), characterized in that the at least one coolant outlet (10) is designed in such a way that the coolant can be introduced into the pressing chamber (2) close to the screw.

2. Device for pressing (1) according to claim 1, characterized in that the means for supplying a coolant are designed for supplying the coolant in a liquid state.

3. Device for pressing (1) according to one of claims 1 and 2, characterized in that the means for supplying a coolant comprise at least one coolant source (12) and at least one coolant outlet (10).

4. Device for pressing (1) according to claim 3, characterized in that the coolant source (12) is designed as a coolant container or as a device for generating the coolant.

5. Device for pressing (1) according to one of claims 3 and 4, characterized in that the means for supplying a coolant comprise a coolant valve (13) and / or a coolant pump (14), which is / are arranged in the region of a coolant line (11) connecting the coolant source (12) to the at least one coolant outlet (10).

6. Device for pressing (1) according to claim 5, characterized in that at least one coolant outlet (10) arranged for introducing the coolant into the pressing chamber (2) is arranged at the screw shaft (4).

7. Device for pressing (1) according to one of claims 5 and 6, characterized in that at least one coolant outlet (10) arranged for introducing the coolant into the pressing chamber (2) extends from the outside through the strainer basket (3) into the pressing chamber (2).

8. Device for pressing (1) according to one of the preceding claims, characterized in that the at least one coolant outlet (10) is arranged in a coolant ring (9) which is part of the strainer basket (3).

9. Device for pressing (1) according to one of the preceding claims, characterized in that the at least one coolant outlet (10) is arranged in the conveying direction of the screw press in a region downstream of a throttle ring (15).

10. Device for pressing (1) according to one of the preceding claims, characterized in that the device for pressing (1) has a sealed region of the strainer basket (3) downstream of coolant outlets (10) in the conveying direction of the device for pressing (1).

11. Device for pressing (1) according to one of the preceding claims, characterized in that it has a sealed flap in the housing.

12. Method for pressing, wherein a pressed material or a pressed cake is introduced into a screw press through a feed opening (6) and transported through a pressing chamber (2) by means of a screw shaft (4) and pressed in the process, so that a liquid (8) is pressed out of the pressed material or pressed cake, and wherein the pressed-out liquid (8) emerges from the pressing chamber (2) through openings, comprising the following method steps: - providing a coolant with the aid of a coolant source (12) - supplying a coolant from a coolant source (12) into the pressing chamber (2) of the screw press and / or at least in some areas on the outside of the strainer basket (3) of the screw press - cooling the press cake and / or the pressed liquid with the aid of the coolant, wherein air or nitrogen is used as the coolant, characterized in that the coolant is introduced into the pressing chamber (2) close to the screw.

13. Method for pressing according to claim 12, characterized in that the coolant is supplied under atmospheric pressure.

14. Method for pressing according to one of claims 12 and 13, characterized in that the coolant is liquid during feeding.

15. Method for pressing (1) according to one of claims 12 to 14, characterized in that a device for pressing (1) according to one of claims 1 to 11 is used.

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