A PROCESS FOR THE PRODUCTION OF ANIMAL FEED STUFF FROM A LIQUID RESIDUE OBTAINED BY FERMENTATION AND DISTILLATION OF GRAIN RAW MATERIAL

Abstract: A high quality animal feed stuff is produced by thermal dewatering of liquid stillage obtained from fermentation of grain raw material and distillation of the fermentation product. The liquid stillage is mixed with particles of already dewatered product and the mixture is granulated in a granulation device to form essentially spherical granules with a dry substance content of 50-70 % by weight, the major part of the granules having a particle diameter in the range of 2-6 mm, whereafter the granules are dried by being conveyed as a porous bed in a control path in contact with hot gas of a temperature less than 100<o>C, and wherafter a part of the dried granules with a desired particle size are discharged and the remaining part of the granules after possible desintegration are recirculated to the granulation step. Since all the dewatering is carried out by drying with a gas of low temperature, waste heat of low value such as condensation heat from air cooled condensors (22) in the distillation plant can be used for drying the granules.

Description: A process for the production of animal feed stuff from a liquid residue obtained by fermentation and distilla¬ tion of grain raw material It is known that fermentation of various carbohydrate materials and distillative separation of volatile product such as ethanol provides distillation residues having a considerable nutrition value and can be used for the preparation of animal feed stuff. Ethanol fermentation on grain, for example, can provide stilla¬ ge having a protein content of about 30 % of the total dry substance content. Due to the low dry substance content in the range of about 3-10 % of the stillage obtained at conventional batch fermentation, the further processing of the stillage to the dried feed stuff has not been very economical, even if never¬ theless often carried out to avoid the environment problems associated with the waste disposal. Thus, methods for concentrating the stillage from distilleries for the production of animal feed stuff are well known. At a common process solid com¬ ponents of the stillage are first separated by mecha¬ nical means, whereafter the effluent is objected to a power consuming evaporation to a certain dry sub¬ stance content to allow economical drying of the pro¬ duct in conventional dryers such as direct heated drum dryers or disc dryers heated by indirect steam. New continuous fermentation processes as for example disclosed in the Swedish patent applications 7801133-5 and 7901738-0 have made possible a reduced process water input and an output of a stillage with a dry substance content in the range Of 20-35 % . Thereby the costs for further processing of such a stillage to animal feed stuff are considerably reduced and the stillage has become a valuable by-product from the fer¬ mentation process. The positive value of the stillage to the total fermentation process economy depends main¬ ly on the feed stuff quality and the energy cost for dewatering the stillage. To convert the stillage obtained at said continuous fermentation processes, still being a viscous liquor, in such a form that it can be dried in an economical way in e.g. a drum dryer, a further evaporation to a dry substance content in the range of 30-50 % should be carried out. At a successive drying in drum dryers or disc dryers, whereat the material either is contacted with gas of 200-800°C or with heating surfaces in the range of 150-200°C, a certain degradation of substances important to the nutrition value can not be avoided, unless the drying is carried out under vacuum. Vacuum drying, however, constitutes an expensive alternative. An extremely careful and also extremely expensive drying method is freeze drying under vacuum. Among further drying methods, which are suitable for drying liquid products, spray drying should be mentioned. At spray drying the product is subjected to contact with air of high temperature (150-300°C) , but due to extre¬ mely short residence times, however, a comparatively good product quality can nevertheless be achieved. The disadvantage of the method is, however, that it is very expensive. A rather new method to dry and simultaneously granulate a liquid product is so called spray granulation in fluidized bed. According to this method the liquid pro¬ duct to be dried is sprayed over already granulated particles being maintained in fluidized state by means of a gaseous heating medium. Such processes are for example disclosed in the German published . patent speci¬ fications 2 231 445 and 3 007 292. One disadvantage of this method is that the fluidization requires large drying gas volume flows, which cannot be freely selec¬ ted. Further, since the product during the entire dry¬ ing procedure is constituted by dried granules, which from time to time randomly aggregate a fine droplet, the granules attain the temperature of the drying medium during practically the entire residence time in the fluidization chamber. If a careful drying is to be ob¬ tained by this method, it is realized that a combina¬ tion of low drying gas temperature and a very large apparatus volume blower capacity is unavoidable. More- over, substantially complete backmixing of the material to be dried prevails in the fluidized bed, and conse¬ quently the residence time distribution for the pro¬ cessed material cannot be controlled, except for batch processing. The object of the present invention is to achieve a method for the preparation of an animal feed stuff of high quality through careful dewatering of a liquid residue from fermentation and distillation of grain raw material. This object has been reached through a process, which is mainly characterized in that the liquid residue to¬ gether with particles of the recirculated dewatered product is subjected to granulation in a granulation device to form essentially spherical wet granules with a dry substance content of 50-70 X by weight, a major part of the granules having a particle diameter in the range of 2-6 mm, whereafter the wet granules are dried by being conveyed as a porous bed in a controlled course in contact with a drying gas having a temperatu¬ re not exceeding 100°C and a flow velocity less than the minimum velocity for fluidizing the granules, where¬ after a part of the dried granules are discharged and the remaining part after possible desintegration is recirculated to constitute said recirculated dewatered product. According to the invention granules of a relatively uniform size are first prepared from the liquid stilla- ge and already dewatered stillage. It has surprisingly been found that these wet stillage granules having such a low dry substance content as 50-70 % by weight have sufficiently mechanical strength to form a porous bed which can be conveyed in a controlled path, the bed being simultaneously passed by drying air of a velocity that can be selected freely, however being less than the minimum velocity for fluidizing the granules. For ordinary feed stuff granules having a particle size in the range of 2-6 mm, this velocity is in the range of 0.8 - 1.0 nm 3/m2/sec. with respect to the gas velo¬ city through empty section, the controlled drying time and granule size make possible a considerably more care¬ ful drying than e.g. fluidization granulation in that the granules during at least -the major part of the dry- ing period gradually emit their water contents so that the temperature of the drying material will be equiva¬ lent to the so-called temperature of the wet thermo¬ meter, i.e. essentially lower than the temperature of the ambient drying gas. Apart from the fact that a feed stuff of high nitri- tional value is obtained by the method according to the invention of dewatering liquid feed stuff raw material, also finished granules for commercial distribution are directly obtained. Thus, those handling problems asso¬ ciated with feed stuff products in powder form and those additional costs normally required for conveying a feed stuff to commercial form through pelletizing are eliminated. The introductory granulation stop can be carried out by means of any suitable granulation device. According to one embodiment of the invention, a drum granulator is used comprising a rotary drum with its shaft of rotation slightly declining from the horizontal direc¬ tion. The liquid raw material and the recirculated dried particles are fed into the upper end of the drum after a possible mixing operation in a mixer, and the granules are discharged at the lower end of the "drum. Large granules possibly formed, the large mass/surface ratio of which causing deficient drying in the success¬ ive drying step, are separated by screen means and re- turned to the granulation drum. The screen can be in¬ cluded in the drun itself, so that only granules of a certain maximum particle size can leave the drum. An other example of granulation device is an extruder device, provided with nozzle openings corresponding to the desired particle diameter and cutting means that cut the extruded strings in pellets of a length corre¬ sponding to essentially spherical particles. The granule drying is carried out in any drying device, in which the material to be dried is conveyed in a cer- tain path and thus during a controlled residence time in contact with warm air having a velocity less than the minimum velocity for fluidizing the granules. Examples on such drying plants are plate dryers, con¬ veyor screen dryers and shaft dryers. Since at the method according to the invention the dry¬ ing is carried out by means of air at a relatively low temperature, waste heat of low value can be utilized. If the drying air available has a particularly low tem¬ perature or if such a low temperature is desired for achieving an extreme high product quality, rather long residence times can be required. In such cases shaft drying is usually more economical in comparison with conveyor screen dryers or plate dryers. Since the wet granules before the drying procedure often do not have sufficient mechanical strength to be fed directly into a shaft dryer, the granules according to a preferred embodiment of the invention can be pre-dried in a con¬ veyor dryer or a plate dryer and then dried to finished product in a shaft dryer. Since the method according to the invention implies drying with a gas of a temperature less than 100°C, preferably no more than 80°C and most preferably not more than 70°C, for the drying step waste heat of low value can be provided re-- an integrated plant for fer¬ mentation and ciεtillative recover of fermentation pro¬ duct and simultaneous preparation of animal feed stuff from the stillage. According to a preferred er_bodiment of the invention the condensation heat obtained at condensing vapours from one or several of the distillation coluπ_ns of the plant is uti¬ lized for heating the drying air. The condensation is car- ried our in air cooled heat exchangers, and the air used as cooling medium in the condenser and possibly subjected to some further heating is used in a dryer for drying the WI granules. After further heat exchange between the air lea¬ ving the dryer and the air fed to the air cooled condenser, said heat of condensation can be utilized to constitute the major part of the total drying energy required. The invention will now be further illustrated by means of a few embodiments of the same shown as examples, whereat reference is made to the enclosed drawing, which shows a float chart of a continuous ethanol fermentation and distillation plant according to the Swedish patent application 7901738-0 and stillage processing according to the present invention. From a fermentor 5 a liquid flow 6 is withdrawn and se¬ parated by means of a centrifugal separator 7 in one flow 8 enriched in yeast, which is recirculated to the fermentor, and a substantially yeast free flow 9, which after heat exchange 10 with recirculated stillage 11 is fed to a distillation unit 12. Before the flow 6 is fed to the centrifugal separator 7, solid material 13 of the fermentation liquor is separated off by means of a sieve device 14 and sent directly to a stripper column 15. Of the bottom flow 16 from the distillation unit 12 a major part 11 is recirculated to the fermentor 5 and/or the saccharifying step 3, while the remaining minor part 17 is fed to the stripping column 15, which is heated by indirect steam 18. The vapours 19 from the stripper 15 are fed to the distillation unit 12 as heating medium. A vapour flow 20 from the distillation unit 12 is sent to a rectifying column 21 provided with an air cooled condenser 22 for condensation of a vapour flow 23 from the rectifying column 21. A part 24 of the ethanol con¬ densed in the condenser 22 is discharged while the re¬ maining part is recirculated to the column 21 as / tθRE ( O PI i , WIPO β reflux 25. From the bottom of the rectifying column is discharged so called still water 26, which is recircula¬ ted as process water to the saccharifying step 3. From the bottom of the stripper 15 is continuously dis- charged a stillage flow 27, which is fed to a granula¬ tion drum 28. To the drum is also fed dried particles 29 recirculated after having passed a drying plant 30, a sieve device 31 and a mill 32. Through the granulation drum is also sent an air stream 46, 47. Granules 33, a major part of which having a particle diameter in the range of 2-6 mm and a dry substance con¬ tent of 50-70 X by weight, are continuously discharged from the lower end of the drum 28, in which a sieve de¬ vice 34 is provided to retain particles above a certain size. The granule stream 33 is fed to the dryer 30, com¬ prising a number of above each, other located plates 35 sloping in the transport direction of the granules and being provided with perforations 36 for passage of dry¬ ing gas. The granules are transported in the dryer 30 along each plate 35 and from one plate to the other by means of gravity and impulses from the drying gas being passed through said perforations. A.s drying medium is used hot air 37, heated while serving as cooling medium in the air cooled condenser 22 and further heated by an additional heating device 38. The humid air 39 leaving the dryer is heat exchanged in a heat exchanger 40 with the air fed to the condenser 22. From the bottom of the dryer 30 dried granules 41 are discharged, and screened in a screening device 31. A particle fraction 42 suitable for the end product, for example in the range of 3-5 mm, is discharged and the OMPI remaining over fraction 43 and under fraction 44 are milled in a mill 32 and fed as granulation nucleus to the granulation drum 28. Example 1 Continuous ethanol fermentation was carried out in the plant shown in the drawing. As raw material wheat was used, and the plant was dimensioned for fermentation of 66 kg/h wheat and an ethanol production of 20 kg/h. All flows stated below refer to 1 kg produced ethanol. The following table 1 shows ingoing and outgoing product streams. C o m p o n e n t s k g Table 3 Flow Non-fermentabl. kg/kg Ferment- Kon- Stream Product EtOH Wate able Solubl. sol. Ethanol No. 1 Wheat 3.30 0.50 1.97 0.33 0.50 2 Water 1.45 1.45 45 Carbon 0.97 dioxide 42 Feed 0.92 0.09 0.33 0.50 stuff 37 Drying 1.82 1.82 water 24 Ethanol 1.04 0.04 1.00 (96 %) " From the bottom of the stripper 12 2.73 kg stillage with a dry substance content of 29.6 * was discharged and fed to the granulator 28 together with recirculated granules of 90 % OS which had been milled in a hammer mill 32 to granulation nucleus less than 1 mm. The amount ratio stillage/granulation nucleus was about 1:1, and the granules discharged from the granulator had a DS of 60 %. The heat energy was supplied to the process as indirect f O WIP steam of 2 atm, of which 2.75 kg was fed at 18 to the stripper column 15, .and 0.88 kg was fed to the heat exchanger 38 for additional heating of the drying air. Thus, only 0.88 kg further steam was added for drying off 1.82 kg water from the granules. For comparison is noted that for the evaporation of this amount of water in a conventional dryer generally requires at least 3 kg steam. 3 In the dryer 135 Nm /kg air was consumed and the follo- wing air temperatures were measured: Ingoing air of 10°C was heat exchanged with outgoing air to 35 C, then heated in the condenser 22 to 59 C and further heated in the heat exchanger 38 to 70°C. The temperature of the air leaving the dryer 30 was 40°C and was discharged from the heat exchanger 40 at 25°C. The granular fraction 42 discharged from the screen device 31 had a particle size in the range of 2.5-5 mm and a composition according to the following table 2: Table 2 Component % b.w. Raw protein 31 Raw f t 9 Fibres 9 Minerals (ash) 6 Glycerol 4 Carbon hydrates 32 Water 9 100 Example 2 Conventional stillage drying is carried out for com¬ parative reason. OMP * -Φ?NA The same stillage as used in Example 1 was dried in a rotary disc dryer and was heated by steam of 7 atm, and the water evaporated from the stillage was discharged by secondary air. In the outlet end of the dryer a dry product temperature of 110-120°C was measured..Outgoing secondary air had a temperature of 90-100°C and a rela¬ tive humidity of about 60 %. The dried product had a water content of 14 % by weight. Example 3 For comparison the same stillage as used in Example 1 was objected to freeze drying. Example 4-6 A decicive feature for the quality of an animal feed stuff is its so called digestability, i.e. the part of feed stuff that actually is assimilated through the intestine walls of the animals. A common method of estimating said digestability is the so called pepsin solubility. The dried products obtained according to Example 1-3 was dissolved in pepsin and hydrochloric acid during 48 hours. The solution was filtered and the filtrate was analyzed with respect to its hydrogen content of the dried product. The result is stated in the following table 3: Table 3 Pepsin solubility X Example No. Drying method of raw protein 4 Drying ace. to 84 the invention 5 Drying in a disc dryer 68 6 Freeze drying 85 It can be seen from the table that the product de¬ watered according to * the invention had not been subject¬ ed to any essential feed quality reductions.

Claims: Claims 1. A process for the production of high quality feed stuff by thermal dewatering of a liquid residue obtain¬ ed by fermentation of grain taw material and distilla¬ tion of the fermentation product, c h a r a c t e ¬ r i z e d i that the liquid residue together with particles of the recirculated dewatered product is subjected to granulation in a granulation device to form essentially spherical wet granules with a dry sub¬ stance content of 50-70 X by weight, a major part of the granules having a particle diameter in the range of 2-6 mm, whereafter the wet granules are dried by being conveyed as a poreous bed in a controlled course in contact with a drying gas having a temperature not exceeding 100°C and a flow velocity less than the mini¬ mum velocity for fluidizing the granules, whereafter a part of the dried granules are discharged and the re¬ maining part after possible desintegration is recircu¬ lated to constitute said recirculated dewatered pro¬ duct. 2. A process according to claim 1, c h a r a c t e ¬ r i z e d i n that the granules are dried through contact with gas with a temperature not exceeding 80 C. 3. A process according to claim 1, c h a r a c t e ¬ r i z e d i n that the granules are dried through contact with gas with a temperature not exceeding 70 C. 4. A process according to any of the preceding claims, c h a r a c t e r i z e d i n that the liquid resi¬ due is continuously fed to a rotary granulation drum, to which also continuously are fed particles of recir¬ culated dewatered product, which forms granulation nucleous, and that the formed granules are continuously 14 discharged from the granulation drum and dried in a separate drying plant. 5. Process according to any of the claims 1-3, c h a r a c t e r i z e d i n that the liquid residue is mixed with recirculated dewatered product, the mix¬ ture so obtained is extruded through nozzle openings of a diameter in the range of 2-6 mm and the extruded strings are cut to granules of a size and from corre¬ sponding to spherical particles, whereafter the granu¬ les are dried in a separate drying plant. 6. A process according to any of the preceding claims, c h a r a c t e r i z e d i n that the granules after being dried are separated in particles fractions, dis¬ charging granules having a size" within a range suitable for feed stuff granules while recirculating particles of sizes above and below said range. 7. A process according to claim 6, c h a r a c t e ¬ r i z e d i n that at least part of the recirculated particles are desintegrated to sizes less than 1 mm before being ciixed with the liquid residue. 8. A process according to any of the preceding claims, c h a r a c t e r i z e d i n that the wet granules are dried by being conveyed as a movable porous bed along a number of plates located above each other and being provided with perforations for passage of drying gas, the granules being conveyed from an upper plate to a lower plate by means of gravity. 9. A process according to any of the claims 1 - 7, c h a r a c t e r i z e d i n that the wet granules are dried by being conveyed as a porous bed resting on a movable support, provided with perforations for passage of drying gas. 10. A process according to any of the preceding claims, c h a r a c t e r i z e d i n that the granules are first preheated by being conveyed as a thin porous bed in a first drying step and are then dried to a finished product by being passed as a porous shaft bed by means of gravity through a drying shaft. 11. A process according to any of the preceding claims, in which said liquid residue is obtained as a bottom product (27) from one or several of distillation columns (15) used for said distillation and in which vapours enriched in volatile products such as ethanol are removed as top product from one or several of said columns (21) and are then condensed, at least part of the heat of condensation thereby obtained is used for heating air, c h a r a c t e r i z e d i n that said air (37) heated by said heat of condensation is used as drying medium for drying said granules (33) . 12. A process according to claim 11, c h a r a c t e ¬ r i z e d i n that for the condensation of said top product one or several air cooled condensors (22) are used, and that the cooling air (27) leaving said con¬ densors (22) are used as drying medium for drying said granules (33) .

Inventors: BAELING PETER, EHNSTROEM LARS, BAELING, PETER, EHNSTROEM, LARS
Applicants: ALFA LAVAL AB, SVENSKA LANTMAENNENS, ALFA-LAVAL AB, SVENSKA LANTMAENNENS RIKSFOERBUND, FOERENING U.P.A.
Application year: 1982
Main classification: A23K1
IPC codes: A23K1, B01J2