Factory Engineering A -ROLLER MlLL SELF-SETTNG EXTRACTON UNT E.F? de Assis M. Dedini S.A. MetalOrgica, Brazil Key words: -roller mill, milling, innovation ABSTRACT A new milling unit with self-setting characteristics consists of the combination of two conventional mill units, resulting in an optimal design with a small specific power consumption; automatic opening adjustment between the rollers depending on bagasse blanket thickness; easy installation; imbibition efficiency; reduced floor space in the plant; better extraction efficiency; and a lower milling plant cost. A -roller pilot mill unit with 80 X 80 mm (15"X15") rollers performed excellently justifying the prelimina;y assumptions on which the proiect was based and encouraging the extrapolation of this concept to bigger units. NTRODUCTON Process continuity, high mill capacity, a good imbibition rate and low maintenance costs all have to be considered when extraction of sugarcane juice by milling is under consideration. A -roller mill requires much less floor space than two conventional mills, eliminating part of the intermediate conveyors and reducing gears. As a result, the cost of the plant is also less. BREF DESCRPTQN OF A -ROLLER MlLL As shown in Fig 1, the -roller mill is a combination of two conventional mills. t comprises five main rollers (1 to 5) and a sixth () secondary feed roller (press-roller). The lower roller bearings (1, and 5) are directly supported by a monobloc frame (7) of lighter and more simple construction than the housings of conventional -roller mills. The bottom rollers (1 and 5) are set by means of the positioning bolts (8), and the intermediate roller () is fixed, thus allowing the opening between rollers to be adiusted. The self-setting features of the unit are due to the multidirectional floating of the upper rollers (2 and 4), which are supported by hydraulic pistons (9), properly articulated in ball-and-socket ioints. Thus, the upper rollers can be displaced on a plane and not only on a straight line, as is the case in the conventional mills. Movement is restricted on one side by the hydraulic piston, and on the other by the articulation of the upper roller to the press-roller in the case of the first upper roller (2), and to the monobloc in the case of the second upper roller (4). For a better understanding of a -roller mill, a unit can be divided into two stages, A and B, as shown in Fig. 1. Each stage can be regarded as a conventional -roller mill. The intermediate lower roller () is common to both stages, being the discharse roller of the 1st stage and the feed roller of the 2nd stage. The bagasse blanket is thus submitted to four successive compressions in the unit, the same number provided by two conventional -roller mills carrying out an equivalent amount of work. The movement of bagasse through the mill is guided by two turn plate sets (10) placed between the three lower rollers, and by a rd set (ll), mounted upside down between the two upper rollers (2 and 4). This rd turn plate set limits the expansion of bagasse released by the 1st stage, transferring it to the 2nd stage with a degree of compaction comparable with that provided by the press-roller, besides keeping the upper roller of the 1st stage (2) properly clean.
FACTORY ENGNEERNG Figure 1. Elevation view of -roller mill mbibition is applied at two points, one being at the upper part of the Donnelly chute, 1 and the other where the bagasse expands at the outlet of the 1st stage. This procedure provides very effective imbibition. All the rollersare individually driven, with the exception of the press-roller, whose movement is transmitted through a pair of pinions from the upper roller of the 1st stage (2). Fig 2 shows the typical -roller mill driving system through pinion boxes, which eliminates the inconvenience of transmission by pinions without affecting the flexibility of roller adjustment. n Table 1 a comparison is given between a tandem with conventional 4-roller mills and an equivalent tandem of -roller mills. As can be seen from Table 1, the -roller mills reduce the total number of rollers of the tandem, the number of intermediate carriers and the number of drives. The latter are fewer although more powerful. This certainly results in lower maintenance costs, besides providing a compact plant of lower initial cost. The length of the -roller mill tandem is approximately half the length of a conventional tandem of similar capacity. DESCRPTON OF THE PLOT PLANT 1 With the obiective of testing the performance of a -roller mill, an autonomous pilot plant was erected close to the industrial facilities of the Sdo Luis Distillery, in Pirassununga, in the State of Sdo Paulo. t was constructed so that it did not interfere with the independent operation of Sdo Luis Sugar Mill, and so that reliable results could be obtained from the tests. The only inter-connections between the pilot and the Sdo Luis Sugar Mill were the mixed iuice line from the prototype mill and the energy supply. Separate deliveries of cane were arranged through the main weighbridge. The pilot plant operated for 1 000 hours in the 1984 season and 1 800 hours in the 1985 season, performing excellently both from the mechanical and process points of view, as can be seen from the results (see Table 2).
press- roller pinions driving r - roller mlll \ st speed reduction Llntermediore speed reduction Figure 2. -roller mill driving unit As a prototype, a 80x80 mm -roller mill was constructed, together with the equip- / ment necessary for unloading, cane preparation and accessory milling operations, all in dimensions proportional to the size of the mill. The cane handling for the pilot plant was done by a ton crane with a hydraulic grab to transfer the cane from the trucks to the feed ramp of the cane conveyor where it was prepared by a rotating set of knives. The specifications were a 80 mm wide rotor with a peripheral diameter of 1 000 mm, to run at 900 rpm using 0 kw of installed power. At the discharge end of the conveyor, the cane was shredded in a vertical shredder having the same width as the knife set. The rotor was 1 000 mm diameter, running at 1 200 rpm and using 8 kw of installed power, and giving a preparation index slightly above 85%. The shredded cane was conducted on a rubber belt conveyor to the Donnelly chute of the -roller mill. The extracted juice was filtered in a conventional cush-cush, and sent to the iuice treatment plant at the sugar mill. Because only one -roller mill was installed, a simple imbibition system, with application of water in the Donnelly chute and in the turn plate between the two upper rollers, was adopted. 1
- FACTORY ENGNEERNG Table 1 - Comparison of a conventional tandem of six 4-roller mills to an equivalent tandem of -roller mills Components conventional mill Component quantities roller mill Milling units Rollers ntermediate carriers Pinions Couplings Pinion box lntermediate speed reduction First speed reduction Turbine 24 5 0/48* * The conventional mills with pinions on only one side of the shaft utilize a total of 0 pinions and 48 when the pinions are on both sides of the shafts. ** Pinions of the press-rollers. Table 2 - Results of the tests on the -roller mill prototype Avg crushing 10.15 t cane/h Fibre % cane 12.52 Reduced extraction (N.DEERR) 87.9 % Pol % bagasse 5. Moisture in final bagasse 49.4 % mbibition % cane fibre 24 18 2 * * 15 The main characteristics of the -roller mill prototype used in this pilot plant were: - roller size 80 X 80 mm (15"X15") - No. of rollers - external diameter of the roller shells 420 mm - length of the roller shells 81 mm - grooves of rollers 1, and 50 X 25.4 mm - grooves of rollers 2, 4 and 5 450 X 25.4 mm - bearing dimensions 0 10 X 140 mm - hydraulic pistons 4 - cross section of each hydraulic piston 7540 mm2 - maximum lift of the upper rollers 0 mm - maximum specific hydraulic pressure 0 MPa - hydraulic load 4. x lo5 N - power installed in the drive 5 kw - roller speed.5 to 12.0 rpm RESULTS When operating the pilot plant most difficulties were encountered in the cane handling and cane preparation sections because of the reduced dimensions of the equipment. Feeding of the cane conveyor was crucial, requiring the cane bundles to be arranged
manually so that choking at the inlet of the first set of knives could be avoided. The -roller mill gave an excellent mechanical performance, with only a few modifications to the articulated arms of the press-roller, and adiustments to roller speed and the imbibition rate being required to achieve expected performance. After 2800 hours of operation in the 1984 and 1985 seasons, the plant had been optimized and the problems associated with the reduced scale of the equipment had been overcome. Representative average performance data for the -roller mill are shown in Table 2. These were obtained over 17 consecutive days, when 12 tons of cane were crushed. t is important to highlight that the average crushing rate given in Table 2 corresponds to a roll-speed of 7.5 rpm. Tests carried out at 9 rpm also showed an excellent performance with an average of about 12 t caqe/h, and a peak value of 18 t cane/h. For feeding, three men were employed to arrange the cane bundles in the main cane conveyor. The operation showed that the capacity for imbibition water absorption was considerable, a maximum value of 400% fibre being reached. CONCLUSON The operational reliability offered by the -roller mill together with the good results obtained on a pilot scale, would appear to warrant a scale-up. All the assumptions were confirmed by the results of the tests which, in summary, indicated a slightly better performance when compared with that of two conventional 4-roller mill units. By extrapolating, a tandem with X -roller mill units of 101 X 171 mm (40" X 54"), with a performance equivalent to a tandem of conventional mills of 8 X 17 mm (4" X ") crushing 8000 t cane/day and giving a reduced extraction of at least 9%, can be proposed. Although the cost of a -roller mill set, including the drive, is nearly that of two conventional 4-roller mills, the total cost of the plant is significantly lower, if one takes into consideration the compactness of the plant, and the use of fewer carriers and other components as listed in Table 1. These features have a marked effect on the cost of buildings, and on erection and civil engineering costs. The costs of operation and maintenance of the -roller design will certainly be lower than those of conventional designs. UN MOULN A -CYLNDRES-PROJET D'ETUDE D'UNE UNT D'EXTRACTON AUTO-REGLABLE M. Dedini S/A Metalurgica, Brazil EXTRAT Description du proiet d'etude d'un moulin auto-reglable base sur la fusion de deux moulins conventionels avec les resultats.suivants: meilleure consommation de puissance, ouvertures s'adaptant automatiquement aux variations d'epaisseur de la couche de bagasse, montage facile, imbibition efficiente, encombrernent reduit, meilleure extraction et coot reduit de ['atelier de moulins. Les rksultats obtenus avec une installation pilote d'un moulin b cylindres de 80 X 80 mm (15" X 15") ont ete excellents. ls ont confirm les suppositions qui avaient ete faites pendant 'etude et nous ont encourages b extrapoler cette solution b de plus grosse unites.
FACTORY ENGNEERNG MOLNO DE SElS ROLLOS - UN NUEVO PROYECTO DE UNDADE DE EXTRACCON AUTO-AJUSTABLE M. Dedini S/A MetalDrgica, Brasil RESUMEN El trabajo describe un nuevo disetio de molino con caracteristicas de auto-ajuste. La idea bsica es la unin de dos unidades de molienda convencionales, resultando en un proyecto optimizado con: menor consumo especifico de energia, abertura autom- tica de aiuste entre 10s cilindros dependiente de las variaciones de la sabano de bagazo, facil mejor eficiencia de extracin y costo mas bajo del molino. Los resultados obtenidos en una planta piloto con un molino de seis rollos de 80 mm X 80 mm (15" X 15") ensetiaran un excelente desempetio, confirmando las expectaciones del proyecto y animando extrapolar esta solucin para unidades ms grandes.