Oilseed pressing heat recovery process

Abstract

Oilseed pressing process, which includes the following steps: a) Preheating the oilseeds to produce warm, soft oilseeds, b) Flaking the warm, soft oilseeds to produce flakes, c) Cooking the flakes, whereby the cooking process produces an initial hot steam stream and hot flakes, d) Pre-pressing the hot flakes to produce oil and partially defatted cakes, e) Solvent extraction of the partially defatted cake to produce solvent-containing oil and solvent-containing meal, f) Desolventizing the solvent-containing shot to produce hot, moist shot, (g) Drying the hot, moist meal to produce oilseed meal and a second hot steam stream, characterized in that at least part of the preheating of the oilseeds in step (a) is carried out in a preheating mechanism using a hot liquid medium having a temperature of approximately 60 to approximately 85 °C, wherein the hot liquid medium is heated by a heat transfer mechanism, wherein a condensate is formed from the hot steam stream of at least one of the hot steam streams of step (c) or (g) to produce the hot liquid medium, wherein the hot liquid medium is water.

Description

[0001] This application claims the priority right from US patent application serial no. 61 / 524,799, filed on August 18, 2011. AREA OF INVENTION

[0002] The invention relates to an improvement in the oilseed pressing process, characterized by achieving significant energy reduction with improved reliability compared to established practice. GENERAL STATE OF THE ART

[0003] Oil extraction from oilseeds, such as rapeseed or sunflower seeds, is an energy-intensive process involving several steps that require both mechanical and thermal energy. This energy is partly mechanical, for example, crushing, grinding, rolling, pressing, and pelletizing, and partly thermal, used to break down cell walls, reduce oil viscosity, and adjust the moisture content of intermediate or final process products. Before the actual oil extraction, the oilseeds must be prepared: energy is required to break down or weaken the walls of the oil-containing cells. For some seeds, such as sunflowers, dehulling is also recommended.

[0004] The oilseed pressing process is described in more detail for rapeseed, which, with a global production of over 62 million tons in 2009 and steadily increasing, is one of the most important oilseeds. The oilseed pressing process is divided into several steps: cleaning, preheating, flaking, cooking, pre-pressing, and solvent extraction. During the cleaning step, dust, oversized particles, and foreign particles are removed from the oilseeds. During the preheating step, the seeds are preheated from ambient temperature to approximately 50–70°C by indirect heating or direct contact with hot air. This preheating weakens the cell structure and softens the rapeseed, thereby improving the subsequent flaking process.During the flaking step, the preheated rapeseed is flaked between steel rollers to reduce the starch content. This allows the solvent, usually hexane, to penetrate the cellular structure in the understream solvent extraction step to dissolve and extract the oil. Before solvent extraction, the flakes must be cooked, typically in a vertical stack steam-insert cooker or a horizontal steam-tube rotary cooker at approximately 80–100°C. This cooking step not only heats the flakes but also reduces their moisture content from approximately 8–10% to approximately 4–6%. Cooking the flakes therefore generates a hot steam stream. This steam stream is contaminated with fatty material, fine particles of oilseeds (fines), and often odor components.The flakes are then pre-pressed and extracted with solvent to obtain rapeseed oil and rapeseed meal, both of which require further processing. Typically, the oil is refined through several successive steps, and the meal is desolved. After desolvation, the rapeseed meal is then dried in specific equipment, such as a vertical stack fluidized bed dryer or a horizontal steam tube rotary dryer. The meal dryer typically reduces the moisture content of the meal from about 14–18% to 10–12%. Therefore, a second stream of hot steam, usually contaminated with fine meal particles (fines) and often odor components, is emitted from the meal drying stage.

[0005] Accordingly, as illustrated above, the oilseed pressing process is energy-intensive, with a significant thermal heating step and two significant thermal drying steps, which represent the potential for energy savings.

[0006] An efficient energy recovery solution is described in the EU project LIFE04 env / d / 000051. In this energy recovery process, the thermal energy contained in the hot vapors exiting the flake cooking step is used to preheat the rapeseed in the seed preheating step. This recovery process involves cleaning the hot vapors exiting the flake cooking step to produce hot water, which is then used to preheat the rapeseed entering the pressing process using a preheater with vertical heat exchanger plates. The rapeseed flows between the plates by gravity and is preheated by conductivity. While this process is indeed efficient at recovering thermal energy contained in the hot vapors exiting the flake cooking step, the cleaning of these hot vapors produces hot water contaminated with fatty material and fine particles.Cleaning and maintaining the equipment, which comes into contact with hot water contaminated by grease and fine particles, is therefore difficult. Alternatively, the hot steam streams can be cleaned using filter media or cyclone separation, but these methods are inefficient because the sticky nature of the contaminants, formed by the protein contained in the fine particles, leads to rapid clogging of the cleaning agents.

[0007] WO98 / 01518A1 describes a process for producing glyceride oil with a low content of non-hydratable phosphatides from fatty plant material, wherein the fatty plant material is circulated in a closed, pressurized conveying circuit in superheated steam and spontaneously exposed to a high temperature at a controlled water content, after which glyceride oil is extracted. EP 2 062963A2 discloses a process for conditioning oilseeds, wherein the waste heat from at least one process step of the oil extraction is used for preconditioning the seeds fed into the process.

[0008] It is therefore the object of the present invention to describe a process for recovering thermal energy contained in the hot steam streams, which are contaminated by fatty material and / or fine matter and / or fragrances, leaving the flake cooking step or the scrap drying step of an oilseed pressing process, wherein such a process causes minimal contamination of the heat transfer mechanism in order to continuously maintain high efficiency with minimal cleaning or maintenance. BRIEF DESCRIPTION OF THE INVENTION

[0009] It has been found that significant thermal energy recovery can be achieved for an oilseed pressing process comprising the following steps. The present invention therefore provides an oilseed pressing process comprising one or more of the following steps a) to g): a) Preheating the oilseeds to produce warm, soft seeds, b) Flaking the warm, soft oilseeds to produce flakes, c) Cooking the flakes, whereby the cooking process produces an initial hot steam stream and hot flakes, d) Pre-pressing the hot flakes to produce oil and partially defatted cakes, e) Solvent extraction of the partially defatted cake to produce solvent-containing oil and solvent-containing meal, f) Desolventizing the solvent-containing shot to produce hot, moist shot, (g) Drying the hot, moist meal to produce oilseed meal and a second hot steam stream, wherein at least part of the preheating of the oilseeds in step (a) can be carried out in a preheating mechanism using a hot liquid medium having a temperature of approximately 60 to approximately 85 °C, wherein a condensate from the hot steam stream of at least one of the hot steam streams of step (c) or (g) is formed to produce the hot liquid medium, wherein the hot liquid medium is water.

[0010] It was surprisingly found that the use of a novel tubular condenser as a heat transfer mechanism for condensing the hot steam exiting the flake cooking and / or scrap drying step of an oilseed pressing process allows for substantial recovery of the thermal energy of the hot steam streams without generating problematic fouling of the heat transfer mechanism when the hot steam, contaminated with oil, fines, and / or odor components, is condensed within the tubes of the tubular condenser. Furthermore, cleaning the tubular condenser is simple and continuous. Further benefits and advantages of the invention will become apparent in the detailed description of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a representation of an embodiment of the process according to our invention. DETAILED DESCRIPTION

[0011] The present invention is defined by the appended claims. The following technical disclosure may in some respects extend beyond the scope of the claims. Elements of the disclosure that are not within the scope of the claims are provided for informational purposes.

[0012] The invention is described as applied to the processing of rapeseed, but this invention is not limited to this particular type of oilseed. All oilseeds requiring a pressing process involving a preheating step and a flaking cooking step and / or a scrap drying step will benefit from this invention. The process according to the invention makes use of a preheating device (preheater) where the rapeseed is preheated by conductivity while in contact with heated vertical plates. In such a preheater, a hot liquid medium (for example, hot water) is used instead of steam to preheat the rapeseed. The hot liquid medium flows countercurrently to the product flow through a bank of vertically arranged hollow stainless steel plates (such plates are commonly referred to as thermal plates).The rapeseed flows slowly downwards under gravity between the plates in a mass flow, being preheated to a uniform temperature. A discharge mechanism beneath the plate bank regulates the downward flow rate of the heated material, in this case the preheated rapeseed, through the preheater. During this process, the hot liquid medium, circulated in a closed loop, is cooled and must then be reheated. Preheaters of this design are manufactured, for example, by Solex Thermal Science Inc. (Calgary, Alberts, Canada). However, the invention is not limited to this particular supplier. Any preheater that uses a hot liquid medium circulated in hollow cavities of any shape or size distributed throughout the mass of oilseed can benefit from the present invention. The hot liquid medium is water.

[0013] According to the present invention, hot water of approximately 60 to 85°C, used as the heating fluid medium in the seed preheating mechanism (preheater), is produced in at least one tubular condenser, which condenses hot steam produced during the flake cooking process and / or the scrap drying process. The hot steam condenses within the tubes of the condenser, and the water is circulated in the shell of the condenser, where it is heated and routed in a closed circuit to the preheater. Preferably, a portion of the condensate that forms inside the tubes at the bottom of the tubular condenser is recycled at the top of the tubes via a suitable pump and piping. The recycled condensate brings the incoming steam stream to its dew point at the inlet to maximize heat transfer, and the water runs down the inner surface of the tubes.It was also observed that the recycled condensate has an unexpected cleaning effect, continuously removing entrained oil and / or fine particles. The portion of the condensate that is not recycled back to the top of the tubes is drained and separated. Typically, approximately 40 to 80% of the condensate is recycled back to the top of the tubes, with the remaining condensate being drained; however, the invention is not limited to this specific recycling percentage range. The recycling rate must be high enough to ensure that the top of the tubes is not dry, thus preventing contamination within the tubes of the vacuum condenser. However, an excessive recycling rate of the condensate must be avoided to prevent unacceptable cooling of the water exiting the vacuum condenser.For a large oilseed pressing plant processing 2000 tons of rapeseed per day, a tubular condenser equipped with approximately 500 to 1000 vertical tubes, each approximately 5000 to 11000 mm long and approximately 20 to 50 mm in diameter, is suitable for operating the process according to the invention. The tubes are preferably made of stainless steel. The shell of the tubular condenser is preferably equipped with baffles to increase the water velocity and improve the heat exchange coefficient between the tubes and the shell. The hot vapors are preferably introduced at the top of the tubular condenser by a blower or other means capable of providing sufficient velocity for the hot vapors to effect an additional self-cleaning effect by inhibiting the accumulation of oil and / or fine particles that would contaminate the inside of the tubes.The speed of the hot steam entering the tubes is preferably approximately 10 to 30 m / s.

[0014] According to one embodiment of the present invention, hot vapors produced during the scrap drying process can also be condensed in a similar tubular condenser to produce hot water at approximately 60 to 85°C. Preferably, it is more efficient to design a tubular condenser for each individual process that produces a hot vapor stream. Indeed, the specific temperature, concentration, and type of contamination of the hot vapor require a tailored tubular condenser adapted to the precise characteristics of the hot vapor stream to be condensed. Alternatively, separate hot vapor streams can be combined and condensed in a single tubular condenser.

[0015] The oilseeds in the lower part of the seed preheating mechanism can be fully heated by hot water and / or steam produced by a conventional boiler, in addition to the hot water produced by the tubular condenser used in the upper part of the seed preheating mechanism, especially during the winter when the incoming temperatures of the oilseeds are lower.

[0016] Optionally, the hot water exiting the tubular condenser is further heated by circulating it through one or more heat exchangers that process hot liquids produced during a step of the pressing process. Such hot liquids include, for example, hot oil produced during the pre-pressing step or hot condensate produced during the flake boiling step. Typically, the one or more heat exchangers are located on the same line that carries the hot water produced by the tubular condenser to the preheater.

[0017] Such a tubular capacitor does not require frequent production interruptions for cleaning, and if such cleaning is necessary, the time required can be reduced due to the large diameter of the tubes, which can be cleaned using conventional high-pressure cleaning equipment. The cleaning frequency depends on various factors, such as the origin of the oilseeds and the potential for contamination by foreign material. Reducing the cleaning frequency is a significant advantage of the process according to the present invention, as such cleaning involves production interruptions.

[0018] Despite the considerable cost of the required tubular condenser, the savings achieved by the process according to the present invention are substantial. For example, in a plant processing 2,000 tons of rapeseed per day, the energy recovered in a tubular condenser, which condenses the hot steam stream generated solely by cooking the flakes, avoids the consumption of 20 to 30 kg of steam per ton of rapeseed processed. At current heating oil prices, this reduction in steam consumption results in savings of €300,000 to €450,000 per year.

[0019] A secondary benefit is that some of the odor components normally present in the hot steam stream(s) emanating from the cooker or shot dryer are condensed in the process according to the present invention and therefore not released into the atmosphere, which can lead to a reduction in the odor emitted by oilseed pressing plants, particularly rapeseed pressing plants. However, since the detection threshold for these odor components is very low, the reduction in perceived odor is sometimes far less important than the actual reduction in the amount of odor components released into the atmosphere.

[0020] Fig.Figure 1 is a diagram of the process according to our invention. Rapeseed stored at ambient temperature, for example in storage silos (not shown), is introduced at the top of the preheater (1). The rapeseed is preheated by slow movement between hollow vertical plates (2). The preheated rapeseed (3) exits the preheater for further processing (flaking, cooking, pre-pressing, solvent extraction, desolventing of the meal, drying of the meal). At least some of the hot water is produced in the tubular condenser (4) by condensing the hot steam (5) coming from the cooker or other equipment that generates hot steam, such as the meal dryer (not shown). At least some of the condensate produced by the tubular condenser is recycled within the tubes (11) of the tubular condenser via a suitable line (12) and circulation pump (13).

[0021] The non-recycled fraction is drained and further processed (14). The hot water is conveyed through a suitable line (6), including appropriate equipment such as an expansion tank (7) and optional additional heat exchanger(s) (8, 9) to further heat the hot water, to the preheater and the circulation pump (10). The additional heat exchanger(s) can process hot liquids produced in another step(s) of the oilseed pressing process, such as hot oil (not shown) or hot condensate from the flake cooker, or another hot liquid. Optionally, steam or hot water (15) produced by conventional means (not shown) can serve as an additional underflow heating medium for the preheater.

Claims

[1] Oilseed pressing process, which includes the following steps: a) Preheating the oilseeds to produce warm, soft oilseeds, b) Flaking the warm, soft oilseeds to produce flakes, c) Cooking the flakes, whereby the cooking process produces an initial hot steam stream and hot flakes, d) Pre-pressing the hot flakes to produce oil and partially defatted cakes, e) Solvent extraction of the partially defatted cake to produce solvent-containing oil and solvent-containing meal, f) Desolventizing the solvent-containing shot to produce hot, moist shot, g) Drying the hot, moist meal to produce oilseed meal and a second hot steam stream, characterized by, that at least part of the preheating of the oilseeds in step (a) is carried out in a preheating mechanism using a hot liquid medium having a temperature of approximately 60 to approximately 85 °C, wherein the hot liquid medium is heated by a heat transfer mechanism, wherein a condensate is formed from the hot steam stream of at least one of the hot steam streams of step (c) or (g) to generate the hot liquid medium, wherein the hot liquid medium is water. [2] Process according to claim 1, wherein the heat transfer mechanism comprises a tube capacitor, wherein the tube capacitor is arranged vertically. [3] Process according to claim 2, wherein the tube capacitor comprises a plurality of tubes, the hot vapor being condensed in the tubes. [4] Process according to a preceding claim, wherein the hot steam is introduced at the top of the tubes. [5] Process according to a preceding claim, wherein the velocity of the hot steam inside the tubes is at least 10 m / s. [6] Process according to a preceding claim wherein at least one fraction of the condensate is recycled within the tubes. [7] Process according to claim 6, wherein the recycled condensate is introduced at the top of the tubes. [8] Process according to a preceding claim, wherein the hot liquid medium is further heated by one or more heat exchangers. [9] Process according to a preceding claim, wherein the oilseeds are rapeseed. [10] Process according to a preceding claim wherein the hot liquid medium is hot water. [11] Process according to any of the preceding claims, wherein the preheating mechanism comprises a plurality of cavities, wherein the hot liquid medium flows through the cavities to heat the oilseeds by conductivity. [12] Process according to claim 11, wherein the cavities comprise hollow plates. [13] Process according to claim 11, further comprising the return of the hot liquid medium from the cavities to the heat transfer mechanism. [14] Process according to claim 13, wherein the heat transfer mechanism comprises a tube capacitor.

Images