by A RYBKA · Cited by 3 — Key words: hop cone; drying; conditioning; moisture. INTRODUCTION. In conventional belt dryers hops are dried down to a moisture content of
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7th TAE 2019 17 – 20 September 2019, Prague, Czech Republic HOP DRYING IN BELT DRYER USING COOLING CHAMBERS Adolf RYBKA 1 1 1 1Department of Agricultural Machines, Faculty of Engineering, Czech Univ ersity of Life Sciences Prague, Czech Republic Abstract When drying hop cones, sufficient drying of strigs is the bottleneck. Bracts are then dried up to such a level which makes pressing the hops impossible. That is the reason why hops are conditioned after over -drying to reach an optimum moisture content of 1 0 to 12 %. This process does not benefit hops, therefore we suggest ed to substitute the condit ioning chamber for two cooling chambers, in which the moisture of bracts and strig s can be equilibrated. This equilibrium is essential for baling. The advantage o f this drying method is energy saving and improv ement in the quality of the hop product. On the basis of the patented design and a utility model, the apparatus was assembled at the belt dryer PCHB 750 of Ltd. Comparing the operation with conditioning and the option of the cooling chambers, the gas savings amounted to 2,356 CZK.t -1 of dry hops and the electricity savings amounted to 831 CZK.t -1 of dry hops. Assuming the reduction of the harvest period by approximately 39 %, the other cost items will be reflected in the overall saving. Key words: hop cone ; drying ; conditioning ; moisture . INTRODUCTION In conventional belt dryers hops are dried down to a moisture content of 8 up to 6 %. They are over -dried by reason of the need for adequate drying of the hop cone strig ( ; Hofmann et al., 2013 ). On the other hand, bracts are then drie d to such an extent that baling these hops is impossible. Therefore, after drying, hops are conditioned . After conditioning, the hops have an optimum moisture content of approximately 10 to 12 %. It is obvious that neither over -drying nor subsequent mois tening does not benefit the hops ( Henderson & Miller, 1972 ; ). With the current setting of belt dryers the optimum moisture content is achieved already by the end of the second belt, yet the strig moisture content being considerably higher ( Mitter & Cocuzza, 2013 ; Srivastava et al., 2006 ). Drying on the third belt, where the hops are over -dried, takes up to 1/3 of energy requirement s for drying, therefore a design has been created in which the over -drying and subsequent moistening in a conditioning chamber is substituted by a system of two cooling chambers where the hop cones will be left for approximately 4 to 8 hr. or longer if necessary. During this time the moisture levels of bracts and strigs will reach an equilibrium value. This equilibrium is essential for the final baling as the increased moisture in the cone strigs might cause the hops to deteriorate. The designed technological process responds to the requirement for an increase in the eff iciency of gentle hop drying in belt dryers, for a reduction of drying costs, and for an increase in the quality of the final product ( 3-transverse conveyor , 4 -longitudinal conveyor , 5 -conveyor to the cooling chambers , 6 -rever se sliding co nveyor , 7,8 -cooling chambers , 7a,8a -floor discharge conveyors , 9-transverse discharge conveyor , 10 -conveyor to the press , 11 -square bale press Fig. 1 Side view of the cooling chambers and system of conveyors
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7th TAE 2019 17 – 20 September 2019, Prague, Czech Republic 1-filling conveyor, 2 -belt dryer, 3 – transverse conveyor, 4 – longitudinal conveyor, 5 – conveyor to the cooling chambers, 6 -reverse sliding conveyor, 7,8 -cooling chambers, 7a,8a – floor discharge conveyors, 9 – transverse discharge conveyor, 10 – conveyor to the press, 11 – square bale press Fig. 2 Top view of the deployment of the belt dryer , cooling chambers and system of conveyors In the proposed technology (Fig. 1 and 2) the dried hop cones are conveyed from the belt dryer (2) with the conditioning switched off into the cooling chambers where t he moisture content of the bracts and strigs evens out spontaneously, and the resulting moisture of the dried hop cones rises by 2 up to 4 % to 10 up to 12 % . Chamber filling and emptying system is separated in a way that the first cooling chamber (7) is filled by dried hops which gradually cool down here, and from the other chamber (8) the hops are conveyed (10), during the filling of the first chamber after being cooled down, i.e. after the moisture levels have reached an equilibrium value of 10 to 12 % , to the square bale press (11) where they are baled. Each cooling chamber capacity is 125 m 3 (12.5 x 4.0 x 2.5 m), which corresponds to the belt dryer performance. The aim of the research, which is presented by the article, is to compare the drying curves with the existing technology of hop drying and using cooling chambers. Based on the conceptual patented designs and a utility model, in 2018 the apparatus was assembled at the PCHB 750 The proposed technology of the cooling chambers is assembled as follow -up equipment, i.e. a floor plan extension is necessary as well as roofing of the whole space , with regard to the dimensions of the cooling chambers. The assembly was put into operation in the harvest season of 2018. MATERIALS AND METHODS The implementation of the new technological process using cooling chambers was preceded by repeated in-process measurements of the depen dence of hop cone moisture content , and of bracts and strigs moisture contents separately on the drying time (drying curve) when drying the Saaz variety ( et al., 2016 ; Rybka et al., 2017 ). The samples had been taken from each inspection window (Fig. 3) of the dryer (1 -9), conditioning (10 -11) and condition ing outlet (12). The moisture contents of the whole hops, bracts and strigs were determined by means of the Mettler -Toledo HE43 moisture analyser (Jech et al., 2011 ). The drying curve shape led us to recommend setting the drying process in a way so tha t the drying kept going on still on the third belt , not over -drying the hops, with the conditioning switched off, thus the cones reached a moisture content of approximately 9 -10 % at the outlet. With the current belt dryers their technological process can be influenced, in that context, by an increased belt speed, or possibly by a change in the dried hop layer height, or even by a highly complicated adjustment of the drying air distribution. Almos t all of the adjustments lead to an increase in the hop pass age through the dryer and
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7th TAE 2019 17 – 20 September 2019, Prague, Czech Republic to a reduction of the drying time. The option covering an increased belt speed was then implemented in such a way so that the hop cone moisture content at the 9 th inspect ion window was approximately 10 %. Following the hops at the dryer outlet, they were continuously loaded into one or the other cooling chamber in which the moisture content of the bracts and strigs evened out spontaneously to a required resulting hop cone moisture, and their temperature stabili zed to ambient temperature . The hops were then conveyed to be baled and dispatched. Fig. 3 Sch eme of the belt dryer measured area with marked sampling points RESULTS AND DISCUSSION 1. Dependence of the moisture content of hop cones, bracts and strigs on the drying time (drying curve). At the beginning of the 2018 harvest season, the drying curve was determined for the Saaz semi -early red -bine hops variety. Several measurements were carr ied out the results of which did not vary significantly. Fig. 4 shows an example of a drying curve from one of the measurements. The graph makes it possible to assess the relationship between the moisture contents of the whole cones, bracts and strigs. Tab. 1 presents the belt speed and cumulative time of measurement. The drying curve character is defined by the moisture levels at individual inspection windows detected by the moisture analyser for the cones, bracts and strigs ( 2016; Rybka et al., 2016 ). In order to ensure full drying of the strigs, hops are then over -dried. The product is subsequently moistened by conditioning up to the acceptable moisture level. It is apparent that the strig moisture content declined gradually compared to the bract moisture. Since the ratio by mass of the bracts and strigs was approximately 9:1, in determining the moisture content of cones a value approaching the moisture content of bracts was obtained. The strigs by passing the conditioning were logicall y gaining a higher moisture more slowly compared to the whole cones the moisture content of which is practically identical to that of the bracts. The drying curve in Fig. 4 clearly shows that during normal drying the hop cones are considerably over -dried. Already at the beginning of the third belt (inspection window n. 7) the hops are sufficiently dried and even the hop cone strig has a moisture conten t of 8 to 10 %. Thus, any further drying leads to energy losses, cost increase s and to degradation of the hop cone quality. The drying curve illustrates that at least 200 min out of the total drying time is needless drying. The presented dependence resulte d in recommend ation to set the drying process in a way so that the drying kept going on still on the third belt, not over -drying the hops, with the conditioning switched off, thus the cones reached a moisture content of approximately 9 -10 % at the outlet a nd were subsequently stored in the cooling chambers. 2. Inclusion of the cooling chambers in the technology of hop drying. In 2018, the issued design was implemented inside the enlarged facility of the picking line and belt dryer conveyors following up the PCHB 750 belt dryer outlet (Rybka et al., 2018 ). The entire new technology was subsequently validated. The drying belt speed increased (Tab. 1) in such a way so that the hop cone moisture content at the 9 th inspection window was approx. 10 %. Owing to the ratio of the times of passage between the first and ninth inspection window at the initial and the new belt speed, the drying time was reduced by approx. 39 %. Fig. 5 depicts the drying curve of the progress of drying without
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7th TAE 2019 17 – 20 September 2019, Prague, Czech Republic conditioning and with the subsequent use of cooling chambers. The graph in Fig. 5 clearly shows that upon leaving the belt dryer the moisture content of the strig is relatively high, however, it gradually evens out with the moisture content of the bracts inside the cooling chambers (Fig. 6). Fig. 4 Dependence of the moisture contents of cones , bracts and strigs on the drying time (points = inspection windows ) Tab. 1 Paramet ers of hop drying in belt dryer with and without conditioning Drying with conditioning Sampling point 1st belt 2nd belt 3rd belt Conditioning Inspection window 1 2 3 4 5 6 7 8 9 10 11 Outlet 12 Belt speed m.s -1 0.0031 0.0019 0.0012 Measurement time min 0 47 81 98 153 231 256 376 461 496 526 555 Drying without conditioning Belt speed m.s -1 0.0055 0.0034 0.0019 Measurement time min 0 33 56 66 96 139 151 221 279 Fig. 5 Dependence of the moisture contents of cones, bracts and strigs on the drying time w ith the use of cooling chambers 01020304050607080900100200300400500600Hop moisture [%]Measurement time [min ]Cones Bracts Strigs 0102030405060708090050100150200250300Hop moisture [%]Measurement time [min ]Cones Bracts Strigs
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7th TAE 2019 17 – 20 September 2019, Prague, Czech Republic Following the accelerated drying process, we monitored the progress of changes in the moisture contents of cones, bracts and strigs inside the cooling chambers. The graph in Fig. 6 illustrates the gradual mutual transmission of moisture for the cones, bracts and strigs, and their approximation . Our assumption that during the cooling process the moisture content of cones increases by approx. 1 % under the influence of the external atmospheric environment has been fulfilled. The hop cone moisture content at the outlet prior to baling complies with the requirements specified by hop purchasers. Fig. 6 Dependence of the moisture contents of cones, bracts and strigs on the storage time inside the cooling chambers CONCLUSIONS The economic output concerning the inclusion of cooling chambers in the hop drying technology is directly related to the reduced drying time in the belt dryer. This reduction of drying time and elimination of over -drying has significant effects on the increase in the quality of hop cones, reduction of losses in the heat -labile substances, as well as on the final assessment of the hop product ( Krofta, 2008 ). Due to our long -standing monitoring of the day -to-day operation it was found out that the inclusion of cooling chambers in the process of hop drying will bring about savings in gas of 2,356 CZK.t -1 of dry hops, and savings in electricity of 831 CZK.t -1 of dry hops. As a consequence of the anticipated reduction of the harvest period by approx. 39 %, other cost items will be reflected in these savings, such as e.g. salary of the workers participating in the harvest, their use for other activities, savings in the fuel f or tractors and in the electrical power for other operations related to the harvest, etc. There are no negative effects that would influence the environmental quality. ACKNOWLEDGEMENT QJ1510004 research project. In the project solution, besides CULS Prague, are involved: Hop Research Rakochmel, REFERENCES 1. Henderson, S. M., & Miller, G. E. (1972). Hop Drying -Unique Problems and Some Solutions. Journal Agricultural Engineering Research, 17 , 281 -287. 2. & (2018). Determination of moisture ratio in parts of the hop cone during t he drying proces in belt dryer. Agronomy Research, 16(3), 723 -727. 3. H , P., R ybka , A., H , I., Hoffmann , D., J , B., & P , J. (2016) . Construction and verification of an experimental chamber dryer for drying hops. In 6th International Conference on 05101520250246810Hop moisture [%] Measurement time [h]Cones Bracts Strigs
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7th TAE 2019 17 – 20 September 2019, Prague, Czech Republic Trends in Agricultural Engineering I (pp. 179-185). Czech Republic: CULS Prague . 4. Hofmann, R., Weber, S., & Rettberg, S. (2013) . Optimization of the hop kilning process to improve energy efficiency and recover hop oils. Brewing Science , 66(March/April) , 23-30. 5. Moist air (in Czech) . Prague, Czech Republic: SNTL. 6. Sloboda, A., Sosnowski, S., Sypula, M. , & Machines for Crop Production 3: Machinery and equipment for post -harvesting and treatment of plant material (in Czech and Slovak) . Prague, Czech Republic: Profi Press Co. Ltd. 7. Krofta, K. (2008). Evaluation of hop quality . Hop Research Institute Co. Ltd. (in Czech). 8. & V. (2016). Hop -picking machine control based on capacitance throughput sensor. Applied Engineering in Agriculture, 32 (1), 19-26. 9. Mitter, W. & Cocuzza, S. (2013). Dry hopping – a study of various parameters. Brewing and Beverage Industry International, 4 , 70-74. 10. A method for treating the moisture of hops after drying using cooling chambers and appara tus for carrying out the method (in Czech). Industrial Property Office. Patent No. 307835. Bulletin No. 24/2019 . 11. , Hop production (in Czech). Prague, Czech Republic: SZN. 12. (2017). Theoretical analysis of the technological proce ss of hop drying. Agronomy Research, 15(3), 859 -865. 13. Hoffmann, D., & Krofta, K. (2016). Analysis of the technological process of hop drying in belt dryers. In 6th International Conference on Trends in Agricultural Engineering II (pp. 557 -563). Czech Repub lic : CULS Prague . 14. & drying temperature on the content and composition of hop oils. Plant, Soil and Environment, 64(10), 512 -516. 15. Srivastava, A. K., Goering, C. E., Rohrbach, R. P. & Buckmaster, D. R. (2006). Engineering Principles of Agricultural Machines . Michigan, USA: ASABE, 2nd Edition. Corresponding author: Doc. Ing. Adolf Rybka, CSc., Department of Agricultural Machines, Faculty of Engineering, Czech Univ ersity of Life Sciences Prague, Czech Republic ,rybka@tf.czu.cz
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