భాషా ఎంచుకోండి:
కైల్ ఫ్లిన్, అభిషేక్ గుప్తా, ఫ్రాంక్ Hrach
నైరూప్య
Review of the relevant literature indicates that significant research has been undertaken to apply electrostatically
separation techniques to dry granular plant-based food (అంటే., organic) materials. గతంలో ఈ అభివృద్ధి వేగవంతమైంది 10 - 20 సంవత్సరాల, with many researchers in Europe and the United States applying స్థిరస్థిర విభజన techniques to a wide variety of beneficiation challenges. ఈ పరిశోధన నుండి, స్థిరవిద్యుత్ పద్ధతులు కొత్త ఉత్పత్తి సామర్థ్యాన్ని కలిగి స్పష్టమవుతుంది, అధిక-విలువ ప్లాంట్ ఉత్పత్తులు, లేదా ప్రాసెసింగ్ పద్ధతులను తడి ప్రత్యామ్నాయాన్ని ప్రతిపాదించాయి. Although encouraging separations of cereal grain, pulse and oilseed materials have been demonstrated at the laboratory and in some cases, pilot scale, the electrostatic systems used to demonstrate these results may not be suitable or cost-effective processing equipment to perform such separations on a commercial basis. Many electrostatic technologies are not suitable for process finely ground, low-density powders such as plant materials. అయితే, the ST Equipment & టెక్నాలజీ (STET) triboelectrostatic belt separator has the demonstrated capability to process fine particles from 500 - 1 μm. The STET belt separator is a high-rate, industrially proven processing device that may be suitable to commercialize the recent developments in organic material processing. The STET belt separator was tested on a sample of whole wheat flour and was found to be successful in removing the bran from the starch fraction. Future testing with the STET separator will be conducted on wheat bran samples, corn flour
and pulses such as soy and lupin.
కీవర్డ్లు: Tribo-Electrostatic, Electrostatic, ఎడబాటు, Fractionation, Wheat, Grain, Flour, Fiber, Protein, Oilseeds, Pulses
పరిచయం
Electrostatic separation methods have been utilized for the past 50 years on the commercial-scale beneficiation of
industrial minerals and recycling of waste materials. Electrostatic beneficiation of dry granular plant-based food (అనగా, organic) materials have been investigated for over 140 సంవత్సరాల, with the first patent for electrostatic separation of wheat flour middlings filled as early as 1880. [1] Electrostatic beneficiation allows for separations based on differences in surface chemistry (work function) or dielectric properties. In some instances, these separations would not be possible using size or density separations alone. Electrostatic separation systems operate on similar principles. All electrostatic separation systems contain a system to electrically charge the particles, an externally generated electric field for the separation to occur in, and a method of conveying particles into and out the separation device. Electrical charging can occur by one or multiple methods including conductive induction, tribo ఛార్జింగ్ (contact electrification) and ion or corona charging. Electrostatic separation systems utilize at least one of these charging mechanisms. [2]
High tension roll electrostatic separation systems have been used in many industries and applications where one
the component is more electrically conductive than the others. Examples of applications for high tension roll separators include titanium bearing minerals separation, as well as recycling applications, for example sorting metal from plastic. There are multiple variations and geometries used for high tension roll systems, but in general, they operate on similar principles. Feed particles are charged negatively by an ionizing corona discharge. Feed particles are dispersed onto a rotating drum, where the drum is electrically grounded. The electrically conductive particles give up their charge upon contacting the surface of the grounded drum. The rotation of the drum causes the conductive particles to be thrown from the surface of the drum and deposited in the first product hopper. The non-conductive particles retain their electrical charge and are pinned to the surface of the drum. Eventually, the electrical charge on the non-conductive particles will dissipate, or the particles will be brushed from the drum after the drum has rotated so that the non-conductive particles are deposited in the non-conductive particle hopper. In some applications, a middlings hopper is placed between the conductive and non-conductive product hopper. The effectiveness of this type of separation device is generally limited to particles which are relatively coarse and/or have high specific gravity, due to the need for all particles to contact the surface of the drum. అదనంగా, particle flow dynamics is important as angular momentum is ultimately responsible for conveying the particles from the surface of the drum to the respective product hoppers. Fine particles and low-density particles are easily influenced by air currents and thus less likely to be thrown from the drum in a predictable area. [2] [3] [4]
The high tension belt separator is a variant of the high tension roll separator described above. Feed particles are dispersed evenly across the width of an electrically grounded conveyor belt. Particles are charged, usually by a negative corona, although other mechanisms of charging are possible. Again the conductive particles give their electrical charge up to the grounded conveyor belt, while the non-conductive particles retain their charge. The conductive particles fall off of the edge of the belt by gravity, while the charged non-conductive particles are “lifted” off of the surface of the belt by electrostatic forces. Again for the separation to be effective, each particle must contact the surface of the belt to allow for the conductive particles to give up their charge to the belt. అందువలన, only a single layer of particles can be conveyed by the separator at one time. As the particle size of the feed becomes smaller, the processing rate of the device is reduced. [5] [6]
Parallel plate electrostatic separators are typically based upon separating particles not on the basis of conductivity, but on differences in surface chemistry that allows for electrical charge transfer by frictional contact. Particles are electrically charged by vigorous contact with other particles, or with a third surface such as a metal or plastic will the desired tribo-charging properties. Materials that are electronegative (located on the negative end of the tribo-electric series) remove electrons from the tribo-charging surface and thus acquire a net negative charge. In contact, materials that are on the positive end of the tribo-electric series donate electrons and charge positively. The charged particles are then introduced into an electrical field generated between the two parallel plate electrodes by various transportation means (gravity, pneumatic, vibration). In the presence of the electric field, the charged particles move towards the oppositely charged electrodes and are collected at the corresponding product hoppers. మళ్లీ, a middlings fraction containing a mixture of particles may or may not be collected, depending on the configuration of the separation device. [4] [7]
మూర్తి 1: Diagram of a high tension roll separator (left) and a parallel plate free fall separator (right).
టేబుల్ 1: Summary of commonly used electrostatic separation devices.
Case 1 – Wheat and Wheat Bran Beneficiation.
Wheat bran is a by-product of conventional wheat milling, representing 10-15% of the wheat grain. Wheat bran consists of the outer layers including the pericarp, testa, and aleurone. Wheat bran contains most of the micronutrients, ఫైబర్, and phytochemicals contained in grain, which have demonstrated health benefits to humans. [8] Significant interest in separating and beneficiating wheat bran has been reported. Historical interest in separating wheat bran was to improve the quality and the value of the flour product. అయితే, more recent interest has been reported in recovering valuable components from wheat bran.
లో 1880, Thomas Osborne patented the first commercial electrostatic separator for removing bran from flour middlings. The separator consisted of rolls coated with hard rubber or equivalent material which was capable of being electrically charged via frictional tribo-charging with wool. Although not described, it is assumed the rubber rolls acquired a negative charge relative to wool, consistent with most tribo-electric series. The electrically charged rolls then attracted the positively charged bran fiber particles, conveying them on the surface of the roll until the pinned fiber particles are brushed from the surface of the roll. ఈ (assumed) positive charging of wheat bran is in conflict with results reported by others. Tribo-charging of the bran particles was assisted by fluidizing air introduced at the bottom of the device, which had the additional benefit of causing the less dense bran particles to the surface, closer to the rolls. [1]
లో 1958 an apparatus for electrostatic separation of bran and endosperm contained in flour middlings was disclosed in a patent filing by Branstad working at General Mills. The device consisted of a parallel plate separator in which particles were conveyed between the two plates by vibration. Bran particles, charged by frictional contact with endosperm particles, were then lifted to the top electrode through perforations in the top electrode. [9]
లో 1988 an apparatus and process for recovering aleurone from commercial wheat bran was disclosed in a patent filing. Commercial wheat bran with a starting aleurone content of 34% was enriched to a concentrate of 95% వద్ద 10% mass yield (28% aleurone recovery) by a combination of hammer milling, sizing by screening, air elutriation and electrostatic separation using a parallel plate electrostatic separator. Particles were charged in the air elutriator device, which has a dual role of removing fines (<40 μm) by conveying, while simultaneously tribo-charging the aleurone particles positive (reporting to the negative electrode plate) and the pericarp/testa particles negative. The particle size of the bran mixture was carefully controlled by hammer milling and multi-level screening, to obtain a feed mostly sized in the 130 - 290 µm range. [10]
Recent work on recovering aleurone from wheat bran continues. లో 2008, Buhler AG patented an electrostatic separation device for separating aleurone particles from shell particles made of commuted bran. One embodiment of the device consists of a rotor operating in a narrowly sized treatment area, which allows for particle-to-particle and particle-to-wall contact and subsequent tribo-charging. The charged particles are then conveyed mechanically into a separation vessel containing parallel plate electrodes. Particles fall through the separation vessel by gravity, as the differentially charged particles move toward the oppositely charged electrodes under the influence of the electric field. [11] When combined with proper sizing of the feed bran and mechanical sorting methods, aleurone concentrations of up to 90% have been reported. [12] [8]
మూర్తి 2: Reproduced from Hemery et al, 2007 [8].
Tribo-charging and corona charging experiments on wheat bran were carried out by workers at the Electrostatics of Dispersed Media Research Unit, University of Poitiers, France in 2010. The researchers measured the surface charge and surface potential decay time on wheat bran with 10% moisture and lyophilized (freeze-dried) wheat bran. A separation test was performed on a sample of 50% freeze-dried wheat bran and 50% freeze-dried aleurone feed using a belt type corona electrostatic separator. (మూర్తి 3) Separation results for the laboratory scale corona separator indicated 67% of aleurone was recovered to the non-conductor hopper, while only 2% of the wheat bran reported to the non-conductor hopper. Tribo-charging experiments were also conducted with wheat bran and aleurone, but only to measure the specific surface charge [µC/g] generated on each fraction, as opposed to recovering products from an electrostatic separation. Both feed materials were charged using Teflon as the contact surface. Both wheat bran and aleurone are reported as charging positive relative to Teflon, which itself is very electronegative. The magnitude of the charge was found to depend on the operating pressures used on the tribo-charger, suggesting that higher turbulence leads to more contacts and more complete tribo-charging. [13]
మూర్తి 3: Reproduced from Dascalescu et al, 2010 [13]
లో 2009, researchers evaluated the electrostatic charging properties of aleurone rich and pericarp rich feed materials. [14] లో 2011 the researchers performed electrostatic separation testing on samples of finely ground wheat bran using a pilot scale electrostatic plate separator (TEP System, Tribo Flow Separations, Lexington, అమెరికా). The TEP System utilizes a charging line, where feed particles are introduced into a turbulent compressed air stream, and pneumatically conveyed through the charging line to the separation chamber. The particles are tribo-charged by the particle to particle contact, as well as particle contact with the surface of the charging line. Results obtained with the TEP System demonstrated that electrostatic separation was effective in upgrading aleurone and beta-glucan content of wheat bran. Interestingly, the fraction of material that was found to contain the highest aleurone cell content, వద్ద 68%, was the very fine (D50 = 8 μm) fraction that was recovered from the charging tube. It is not clear why this material was preferentially concentrated in the charging apparatus, అయినా, it does indicate that the ability to process aleurone cell contents may require electrostatic techniques that are capable of processing very fine powders. పైపెచ్చు, this work demonstrated that feed preparation for the wheat bran was an important consideration. Samples prepared by cryogenic grinding in a hammer mill were found to be less completely dissociated (liberated) than those ground in an impact type mill at ambient temperature. [15] [16]
మూర్తి 4: Reproduced from Hemery et al, 2011 [16]
Recent work studied the concentration of arabinoxylans from wheat bran by electrostatic methods. The researchers utilized a laboratory scale electrostatic separator consisting of a charging tube and separation chamber containing two parallel plate electrodes. Milled wheat bran was introduced into the charging tube and conveyed pneumatically into the separation chamber using compressed nitrogen. The turbulence and high gas velocity in the charging tube provided the particle contact needed for tribo-charging. The charged particles (products of the separation) were collected from the surface of the electrodes for analysis. Due to the vertical orientation of the electrodes a significant amount of material was not collected. This middlings fraction may be recycled for further processing in conventional electrostatics, అయినా, for the purposes of this experiment, material not collected on the electrodes was considered lost. The researchers reported an increase in both product grade (arabinoxylan content in the product) and separation efficiency as the conveying velocity increased. [17]
Recent efforts to beneficiate wheat bran using electrostatic methods are summarized below in Table 2.
టేబుల్ 2: Summary of electrostatic methods evaluated to beneficiate wheat bran.
Case 2 – Protein Recovery from Lupin Flour
Researchers at the Food Process Engineering Group in Wageningen, The Netherlands, evaluated the potential for protein enrichment using legumes. Pea and lupin flour were used as feeds for a variety of protein enrichment techniques including air classification combined with electrostatic separation. Untreated pea and lupin seeds were first milled to approximately 200 μm. Feed materials for classification and electrostatic separation were subsequently milled using an impact type mill with an internal classifier (Hosokawa-Alpine ZPS50). Median particle size (d50) was reported as approximately 25 µm for the pea flour, and approximately 200 µm for the lupin flour, prior to air classification. చివరగా, a subset of each sample, pea and lupin flour, was then air classified (Hosokawa-Alpine ATP50). The feed to the electrostatic separator consisted of both untreated flours, as well as the course and fine product from air classification. [18]
The electrostatic separation device used during the experiments was a parallel plate type, with charging carried out via triboelectric charging in a 125 mm length charging tube, with particles conveyed pneumatically by compressed nitrogen. The device is similar in configuration to the device used by Wang et al (2015). [17] Electrostatic separation experiments were conducted on ground pea flour and lupin flour, as well as the course and fine fractions of pea flour and lupine flour obtained from air classification. The pea flour demonstrated only minor movement of protein during electrostatic testing. అయితే, the lupin flour demonstrated significant movement of protein in all three samples tested (milled flour – 35% ప్రోటీన్, milled classified fines – 45% ప్రోటీన్, milled classified coarse – 29% ప్రోటీన్). Protein-rich products of approximately 60% were recovered on the grounded electrode for each of the three lupin samples tested. [18]
Case 3 – Fiber Removal from Corn
Researchers at the Department of Agricultural and Biological Engineering, Mississippi State University performed electrostatic testing on ground corn flour, with an objective of removing fiber. The electrostatic separation device consisted of a conveyor belt with a negative electrode placed at the end of the conveyor. The positively charged particles, fiber particles, in this case, were lifted off the conveyor belt and sorted into a second hopper. The non-fiber particles fell off of the conveyor belt by gravity and were deposited into the first product hopper. The authors do not describe how the electrical charging is carried out. The feed material to this separator was relatively coarse, with particle sizes of the feed ranging from 12 మెష్ (1,532 μm) కు 24 మెష్ (704 μm). It does not appear that the undersize (<704 μm) material was processed during this study. Each test condition was completed using 1 kg of feed material which was uniformly dispersed across the belt. [6]
మూర్తి 5: Reproduced from Pandya et al, 2013 [6]
The Mississippi State researchers completed electrostatic separation testing on the unscreened corn flour, the screened corn flour fractions and the fiber-rich fractions recovered from air classification. Electrostatic testing was not completed on the low-fiber streams recovered from air classification. Analysis of the results of the electrostatic separation is provided below:
టేబుల్ 3: Results of fiber separation reproduced from Pandya et al, 2013 [6]
Case 4 – Protein Concentration from Oilseeds
Oilseeds such as rapeseed (canola), sunflower, sesame, mustard, soybean-corn germ, and flaxseed generally contain a substantial amount of both protein and fiber. Processing technologies to remove the fiber, and thus increase the protein content, of oilseeds will become increasingly important as global demand for protein increases. [19] Recent work by researchers at the French National Institute for Agricultural Research examined ultrafine milling combined with electrostatic processing of sunflower seed meal, to concentrate protein. The feed sunflower meal samples were ground in an impact mill operating at ambient temperature to a particle size (D50) ఆఫ్ 69.5 μm. The electrostatic separator used for the testing was a parallel plate device where the primary charging mechanism was tribo-charging. The tribo-charging was carried out upstream of the electrodes in a tribo-charging line, with particles conveyed through the charging line, and to the electrodes, via pneumatic transport. Protein was found to charge positive (reporting to the negative electrode) and the fiber-rich fraction was found to charge negatively. Protein selectivity was found to be high. Feed protein was 30.8%, with the protein-rich product measuring 48.9% and the protein depleted (fiber-rich) product measuring only 5.1% ప్రోటీన్. Protein recovery was 93% to the positive product. Cellulose, hemicelluloses, and lignin were measured and found to report to the negatively charged product, opposite that of protein. [20]
టేబుల్ 4: Results of sunflower seed meal separation reproduced from Barakat et al, 2015 [20]
లో 2016, an additional study was completed using finely ground rapeseed oil seed meal, or rapeseed oil cakes (ROC), as the feed to an electrostatic separation process. Again ultrafine milling at ambient temperature was performed using a knife mill device (Retsch SM 100). The milled material, with a median particle size (D50) of approximately 90 μm, was processed using a pilot scale parallel plate separator (TEP System, Tribo Flow Separations). The TEP System utilizes triboelectric charging by pneumatic conveying of particles through a high pressure charging line under turbulent conditions. A single pass separation test with the TEP System resulted in the significant concentration of protein, with a feed protein of 37%, a positively charged product protein level of 47% and a negatively charged product protein level of 25%. Additional separation stages were performed, ultimately producing a protein-rich product with 51% protein after 3 successive separation stages. [21]
టేబుల్ 5: Results of rapeseed oil seed meal separation reproduced from Basset et al, 2016 [21]
చర్చ
Review of the relevant literature indicates that significant research has been undertaken to develop electrostatic separation techniques for organic materials. This development has continued or even accelerated in the past 10 - 20 సంవత్సరాల, with many researchers in Europe and the United States applying electrostatic separation techniques to a wide variety of beneficiation challenges. ఈ పరిశోధన నుండి, it is apparent that electrostatic methods have the potential to generate new, అధిక విలువ కలిగిన మొక్క ఉత్పత్తులు, లేదా ప్రాసెసింగ్ పద్ధతులను తడి ప్రత్యామ్నాయాన్ని ప్రతిపాదించాయి.
Although encouraging separations of cereal grains, పప్పులో, and oilseed materials have been demonstrated at the laboratory and in some cases pilot scale, the electrostatic systems used to demonstrate these results may ultimately not serve as the most suitable or cost-effective processing equipment to perform such separations on a commercial basis. Existing commercial electrostatic systems are most commonly used in separations of minerals, metals or plastics. Minerals and metals are both relatively dense materials with high specific gravity, as compared to plant materials. Even with the high specific gravity of minerals and metals, the effective particle size limitations for the drum roll and parallel plate electrostatic separators is relatively coarse, with few particles below 100 µm for example. Plastics are of lower density than both minerals and metals but are often processed at coarse particle sizes, as plastic flakes for example. The introduction of fine particles creates operational difficulties for both high-tension roll and parallel plate separators. Fine, low-density particles are very sensitive to air currents, especially in comparison to minerals and metals. Small differences in air currents inside the separation device impact the travel path of the fine particles, subjecting them to forces other than those caused by the electrostatic field.
For most parallel plate separator systems, finely ground and low-density particles that are electrostatically charged are collected on the electrodes of the parallel plate separators. If these fine electrically attached particles are not removed on a constant basis, the electric field strength and efficiency of the device degrade. The work of the researchers at The Food Process Engineering Group Wageningen UR (Wang et al, 2015) took advantage of this phenomenon to collect samples off the surface of the electrodes of the parallel plate separator to analyze the products of the separation. Parallel plate separator systems, particularly those that rely upon gravity to convey particles through the electric field, have attempted to address this problem in several ways. Stone et al (1988) described a process in which fine particles were removed upstream of the electrostatic separator by air elutriation. [10] Others have reported maintaining a laminar stream of air flowing across the electrodes to prevent fine particles from being influenced by air currents. [22అయితే, maintaining laminar airflow becomes challenging as the separation device becomes larger, effectively limiting the processing capacity of such devices. Ultimately the particle size in which components are physically separate from other (present as discrete particles), will be the largest driver in determining the particle size at which processing must occur.
As mentioned previously, conventional electrostatic separation devices are limited in processing capacity, especially with low-density and finely ground powders such as plant materials. For high-tension drum and belt separation devices, the effectiveness is limited to particles that are relatively coarse and/or have high specific gravity, due to the need for all particles to contact the surface of the drum. As particles become smaller the processing rate is reduced. Parallel plate separators are further limited by the particle density that can be processed in the electrode zone. Particle loading must be relatively low to prevent space charge effects.
ST సామగ్రి & Technology Belt Separator
ST సామగ్రి & టెక్నాలజీ (STET) triboelectrostatic బెల్ట్ విభజించడానికి నుండి రేణువుల ప్రాసెస్ ప్రదర్శించారు సామర్ధ్యం ఉంది 500 - 1 μm. ఎస్ టిఇటి సపరేటర్ అనేది సమాంతర ప్లేట్ ఎలక్ట్రోస్టాటిక్ సపరేటర్, అయినా, ఎలక్ట్రోడ్ ప్లేట్లు నిలువుగా వ్యతిరేకంగా హారిజాంటల్ గా ఓరియంట్ చేయబడతాయి, చాలా సమాంతర ప్లేట్ సపరేటర్లలో ఉన్న విధంగా. (పటం చూడండి 6) పైపెచ్చు, ఎస్ టిఇటి సపరేటర్ పార్టికల్ ట్రైబో ఛార్జింగ్ ని సాధిస్తుంది మరియు హై స్పీడ్ ఓపెన్ మెష్ కన్వేయర్ బెల్ట్ ద్వారా ఏకకాలంలో కన్వేయింగ్ చేస్తుంది.. ఫీడ్ యొక్క అధిక నిర్ధిష్ట ప్రాసెసింగ్ రేటు రెండింటికీ ఈ ఫీచర్ అనుమతిస్తుంది., అలాగే సంప్రదాయ స్థిరవిద్యుత్ పరికరాల కంటే పౌడర్లను ప్రాసెస్ చేసే సామర్థ్యం. This type of separation device has been in commercial operation since 1995 మండని కార్బన్ ను ఫ్లై యాష్ ఖనిజాల నుండి వేరు చేయడం (సాధారణ డి50 సుమారుగా 20 μm) in coal-fired power plants. ఈ ఎలక్ట్రోస్టాటిక్ సెపరేషన్ పరికరం ఇతర అకర్బన పదార్థాలను కూడా కలిగి ఉండటంలో విజయవంతమైంది, కాల్షియం కార్బోనేట్ వంటి ఖనిజాలతో సహా, టాల్క్, బరైట్, and others.
The fundamental details of the STET separator are illustrated in Figure 7. ఎలక్ట్రోడ్ ల మధ్య ఖాళీ లోపల పార్టికల్ టూ పార్టికల్ తాడనాల ద్వారా ట్రైబోఎలక్ట్రిక్ ప్రభావం ద్వారా కణాలు ఛార్జ్ చేయబడతాయి.. ఎలక్ట్రోడ్ ల మధ్య అప్లై చేయబడ్డ ఓల్టేజి భూమికి సంబంధించి ±4 నుంచి ±10 కిలోవి మధ్య ఉంటుంది., యొక్క మొత్తం ఓల్టేజి వ్యత్యాసాన్ని ఇవ్వడం 8 - 20 నామమాత్రంగా చాలా ఇరుకైన ఎలక్ట్రోడ్ గ్యాప్ వెంబడి కెవి 1.5 సెం.మీ. (0.6 అంగుళాలు). మూడు ప్రదేశాలలో ఒకదానిలో మేత కణాలు ఎస్ టిఇటి సపరేటర్ కు పరిచయం చేయబడతాయి (ఫీడ్ పోర్టులు) via a distributor air slide system with knife gate valves. ఎస్ టిఇటి సపరేటర్ కేవలం రెండు ఉత్పత్తులను మాత్రమే ఉత్పత్తి చేస్తుంది, ధనాత్మక ఆవేశిత ఎలక్ట్రోడ్ పై సేకరించబడ్డ రుణావేశిత కణ ప్రవాహం, మరియు రుణావేశిత ఎలక్ట్రోడ్ పై సేకరించబడ్డ ధనావేశిత కణ ప్రవాహం. The products are conveyed to the respective hoppers at each end of the STET separator by the separator belt and conveyed out of the separator by gravity. STET సెపరేటర్ మిడ్లింగ్స్ లేదా రీసైకిల్ స్ట్రీమ్ ని ఉత్పత్తి చేయదు., ప్రొడక్ట్ స్వచ్ఛత మరియు/లేదా రికవరీని మెరుగుపరచడానికి బహుళ పాస్ కాన్ఫిగరేషన్ లు సాధ్యమైనప్పటికీ.
మూర్తి 6: STET Triboelectric Belt Separator
ఎలక్ట్రోడ్ గ్యాప్ ద్వారా కణాలు తెలియజేయబడతాయి. (సపరేషన్ జోన్) ఒక నిరంతర లూప్ ద్వారా, ఓపెన్ మెష్ బెల్ట్. బెల్ట్ అధిక వేగంతో పనిచేస్తుంది, variable from 4 కు 20 m/s (13 - 65 ft/s). బెల్ట్ యొక్క జ్యామితి ఎలక్ట్రోడ్ ల యొక్క ఉపరితలం నుంచి సన్నని కణాలను ఊడ్చడానికి పనిచేస్తుంది., preventing the accumulation of fine particles that degrade the performance and voltage field of traditional free-fall parallel plate type separation devices. అదనంగా, బెల్ట్ అధిక షీర్ ని జనరేట్ చేస్తుంది, రెండు ఎలక్ట్రోడ్ ల మధ్య అధిక టర్బులెన్స్ జోన్, ట్రిబో-ఛార్జింగ్ ను ప్రమోట్ చేయడం. సెపరేటర్ బెల్ట్ యొక్క కౌంటర్ కరెంట్ ట్రావెల్, సెపరేటర్ లోపల నిరంతర ఛార్జింగ్ మరియు రీ ఛార్జింగ్ లేదా పార్టికల్స్ కు అనుమతిస్తుంది., STET సపరేటర్ యొక్క అప్ స్ట్రీమ్ లో ప్రీ ఛార్జింగ్ సిస్టమ్ యొక్క అవసరాన్ని తొలగించడం.
మూర్తి 7: Fundamentals of operation of STET Belt Separator
STET సపరేటర్ అనేది అధిక ఫీడ్ రేట్, వాణిజ్యపరంగా నిరూపితమైన ప్రాసెసింగ్ వ్యవస్థ. STET సపరేటర్ యొక్క గరిష్ట ప్రాసెసింగ్ సామర్ధ్యం అనేది ఎక్కువగా వాల్యూమెట్రిక్ ఫీడ్ రేట్ యొక్క విధి, దీనిని STET సపరేటర్ బెల్ట్ ద్వారా ఎలక్ట్రోడ్ గ్యాప్ ద్వారా తెలియజేయవచ్చు.. ఇతర వేరియబుల్స్, బెల్ట్ యొక్క వేగం వంటివి, ఎలక్ట్రోడ్ ల మధ్య దూరం మరియు పౌడర్ యొక్క ఏరేటెడ్ సాంద్రత గరిష్ట ఫీడ్ రేటును ప్రభావితం చేస్తుంది, సాధారణంగా తక్కువ మేరకు. For relatively high-density materials, for example, ఫ్లై యాష్, గరిష్ట ప్రాసెసింగ్ రేటు 42 అంగుళాల (106 సెం.మీ.) ఎలక్ట్రోడ్ వెడల్పు వాణిజ్య విభజన యూనిట్ సుమారుగా 40 - 45 గంటకు టన్నుల కొద్దీ మేత. తక్కువ దట్టమైన మేత పదార్థాల కొరకు, గరిష్ట మేత రేటు తక్కువగా ఉంటుంది.
టేబుల్ 6: Approximate maximum feed rate for various materials processed with STET 42 inch electrostatic separator.
Dust explosions are a major hazard in grain and other organic powder processing operations. The STET separator is suitable for processing combustible organic powders with only minor modifications. There are no heated surfaces in the STET separator. The only moving parts are the separator belt and drive rollers. The roller bearings are located outside of the powder stream on the external shell of the unit. Therefore they are not a risk for overheating/sparking in the material stream. పైపెచ్చు, the STET separator bearings are available with factory fitted temperature measurement capability to detect bearing failure well before dangerously high temperatures are reached. The separator belt and drive system pose no higher risk than other conventional rotating machinery. The STET separator high voltage components are also located outside of the material stream and contained in dust-tight enclosures. The maximum energy of a spark across the separator gap is limited by the design of the high voltage components. An additional level of safety can be introduced via nitrogen purging.
Whole Wheat Flour Processing by STET Separator
Whole wheat flour is derived from grinding the entire grain of wheat (bran, germ, and endosperm). Commercially available, off-the-shelf, whole wheat flour was purchased for use as test material to evaluate the capability of the STET separator to remove the fibrous bran and germ from the starchy endosperm fraction of wheat flour. The whole wheat flour sample was analyzed by STET prior to beginning the testing. Ash content was tested by ICC Standard 104 / 1 (900°C). Repeated ash measurements of the same sample, an unseparated feed sample, measured 10 times, were found to have an ash content of 1.61%, a standard deviation of 0.01 and a relative standard deviation of 0.7%. Particle size analysis was completed by laser diffraction using a Malvern Mastersizer 3000 with a dry dispersion apparatus. Protein analysis was conducted using the DUMAS method, with an Elementary rapid N exceed nitrogen/protein analyzer. A conversion factor of N x 6.25 was used. The various properties of the whole wheat flour sample are summarized below. (టేబుల్ చూడండి 7)
టేబుల్ 7: Analysis of whole wheat flour feed by STET
Ash content and protein content were found to be very repeatable when tested in the same sample, but significant variability was identified between the multiple bags of whole wheat flour used as the feed sample. (టేబుల్ చూడండి 8) This feed sample variability resulted in some scatter in the test data.
టేబుల్ 8: Analysis of separation test results of whole wheat flour by STET
Electrostatic separation testing of the whole wheat flour sample was performed at the ST Equipment & టెక్నాలజీ (STET) pilot plant facility in Needham, మసాచుసెట్స్. The STET pilot plant contains two pilot scale STET separators along with ancillary equipment used to investigate the separation of materials from candidate sources. The pilot-scale STET separators are the same length as a commercial STET separator, వద్ద 30 అడుగులు (9.1 మీటర్ల) దీర్ఘ, అయినా, the pilot plant separator electrode width is only 6 అంగుళాలు (150 mm), or one-seventh the width of the largest commercial STET separator at 42 అంగుళాలు (1070 mm) electrode width. The feed capacity of the STET separator is directly proportional to the width of the electrodes, therefore, the feed rate of the pilot plant separator is one-seventh the feed rate of the 42-inch wide commercial separator unit. The maximum feed rate with whole wheat flour was 2.3 Tons per hour at pilot scale, which corresponds to 16 Tons per hour for the 42-inch wide commercial separator. In comparison to the scale at which the majority of the electrostatic separation studies have been conducted to date, the STET separator testing was carried out at a considerably higher feed rate. Testing was performed in 10 కిలొగ్రామ్ (20 pound) batch tests, due to the practical considerations of supplying 2.3 Tons per hour of feed continuously. For each batch test condition, the products of the separation process were weighed to calculate the mass recovery. Subsamples from each test were collected and analyzed for ash content and protein content.
మూర్తి 8: STET Pilot Plant Separator.
Particle size measurement of the whole wheat flour feed and two product samples is shown below in Figure 9.
మూర్తి 9: Particle size measurement of whole wheat flour feed, and the two separated product samples.
A picture of the recovered separation products is included below. (పటం చూడండి 10) A noticeable color shift was observed during the separation, which the high ash content product fraction considerably darker than the feed whole wheat flour sample.
మూర్తి 10: Typical products recovered from the STET separation process.
Ash content for all products from the separation process was measured. (పటం చూడండి 11)
మూర్తి 11: Ash content versus the mass recovery of low ash product for whole wheat flour separation tests by STET
Testing of the STET electrostatic separator with whole wheat flour demonstrated significant movement of the high ash (bran) fraction of the wheat kernel to the positive electrode. The reduced ash product was subsequently collected on the negative electrode. Testing was performed on a single pass scheme, అయినా, it is possible to perform further upgrading of either of the separation products by performing another separation stage. Future testing with the STET separator will be conducted on wheat bran samples, as well as corn flour and legumes such as Lupin.
తీర్మానాలు[మార్చు]
Review of the relevant literature indicates that significant research has been undertaken to develop electrostatic separation techniques for organic materials. This development has continued or even accelerated in the past 10 - 20 సంవత్సరాల, with many researchers in Europe and the United States applying electrostatic separation techniques to a wide variety of beneficiation challenges. ఈ పరిశోధన నుండి, స్థిరవిద్యుత్ పద్ధతులు కొత్త ఉత్పత్తి సామర్థ్యాన్ని కలిగి స్పష్టమవుతుంది, అధిక విలువ కలిగిన మొక్క ఉత్పత్తులు, లేదా ప్రాసెసింగ్ పద్ధతులను తడి ప్రత్యామ్నాయాన్ని ప్రతిపాదించాయి. Although encouraging separations of wheat, corn and lupin-based plant materials have been demonstrated at the laboratory and in some cases pilot scale, the electrostatic systems used to demonstrate these results may not be the most suitable or cost-effective processing equipment to perform such separations on a commercial basis. Many electrostatic technologies are not suitable for process finely ground, low-density powders such as plant materials. అయితే, the ST Equipment & టెక్నాలజీ (STET) triboelectrostatic belt separator has the demonstrated capability to process fine particles from 500 - 1 µm at high rates. The STET belt separator is a high rate, industrially proven processing device that may be suitable to commercialize the recent developments in plant material processing. The STET belt separator was tested on a sample of whole wheat flour and was found to be successful in removing the bran from the starch fraction. Future testing with the STET separator will be conducted on wheat bran samples, as well as corn flour and pulses such as soy and lupin.
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