Parboiling Plant

Schule Rice Processing Centre

Introduction:

A parboiling plant by the company F.H. Schule Mühlenbau GmbH comprises a rice mill, a parboiling plant as well as all auxiliary equipment, such as pre-cleaning, silos, husk discharge and combustion plant, steam plant, polish discharge, packing and storage of the finished products. 

From Paddy intake to the Silo plant:

The paddy dried to 14 % is delivered in trucks. The trucks are weighed on a weigh-bridge before and after loading and the delivered product quantity is registered by a computer system. The trucks dump the paddy into an aspirated intake channel which transports the paddy via an elevator to the pre-cleaning section. The special pre-cleaner removes all coarse and fine impurities whereas light particles are separated in aspiration chambers. Then, a trough chain conveying system distributes the paddy from the pre-cleaning section to the silos according to varieties and intended use. Each silo is equipped with a powerful aspiration system. From the silo plant, trough chain conveyors transport the paddy either into the rice mill to produce cargo or white rice, or into the parboiling plant to produce parboiled rice.

The product's path through the Parboilin plant:

Different transport systems transport the paddy to the fine cleaning and sorting section. This plant consists of a day silo and a special fine cleaner which is used not only for fine cleaning but also for sorting out oversized and undersized particles of the product. The machine is equipped with its own aspiration system. The paddy is transported to two light-grain separators sorting out cargo grains, chalky grains and stones. The powerful aspiration system removes the remaining light particles. A downstream indented cylinder removes broken rice and seeds.

By means of an elevator the cleaned and sorted paddy is transported to the day silo of the parboiling plant.

Soaking section:

An elevator feeds the computer-controlled special weigher which fills the four soaking tanks with precision. The soaking cycles of the four tanks are monitored by a PLC control so that a fully automatic soaking process is ensured. Equally important for the soaking time of paddy are water quality and soaking temperature. The latter should be slightly higher than the degree of starch gelatinisation which may vary depending on the type of paddy. In the soaking tanks pressures of up to 6 bars are applied, which reduces the soaking time and ensures a uniform distribution of water in the soaking tank. In order to obtain a homogeneous soaking quality of the paddy, it is important that the temperature of the soaking water constantly remains on the preprogrammed level. This is ensured by the Schule system.

The temperature of the circulating soaking water is continuously controlled in the flow and return pipe. In case of deviations from the setpoint value the water is heated again. Once the preset soaking time has been reached, the corresponding soaking tank is relieved from pressure, the water is run off and the tank outlet is opened automatically. The collecting bin under the four soaking tanks takes up the discharged product. If the soaking tank is empty, the rinsing process starts automatically. After a preset period of time, the outlet is automatically closed and a new soaking cycle starts. The product leaves the collecting bin via an outlet and falls onto a dewatering screen which removes superfluous water and uniformly feeds the product into the downstream bucket elevator. This bucket elevator is a special version completely made of stainless steel. A pneumatic cleaning device installed in the outlet ensures that the returning buckets are completely emptied.

Continuous, computer-controlled vertical cooker (the main machine of every schule Parboiling plant):

The cooker is mounted on special load cells which transmit every change in weight to the cooker computer so that the necessary regulations are made.

Via a prebin the product coming from the bucket elevator is fed into the inlet lock. The speed of the lock can be controlled according to the product quantity by means of a variable frequency drive. When the preset height of the product column has been reached, the computer starts the outlet lock and increases the speed until the height of the product column remains constant. The height of the product column corresponds to a certain cooking time. The computer converts the preset cooking time into the product column height. A specially shaped displacer arranged in the outlet area and the specially designed inlet of the outlet lock ensure gentle and uniform product feeding into the lock chamber. The outlet lock discharges the paddy into a vibration channel which proportions a uniform product veil onto the downstream fluidised bed drier driven by powerful unbalance motors. Hot-air systems provide the fluidised bed drier with hot air that flows through the fluidised bed and dries the paddy to a moisture of 22 to 24 percent. A suitably designed aspiration system eliminates the moist hot air.

Drying system:

Now, the paddy is conveyed into the first of three vertical continuous driers. Based on decades of experience, Schule prefers a three-stage drying system. Conditioning bins are arranged between the individual drying stages. The size of the bins allows a product flow for least 8 hours. The bins work according to the so-called first-in-first-out principle. Special outlets ensure a uniform product flow over the entire cross section of the individual bin.

Decades of experience and development of the parboiling process have shown that the drying process has a decisive influence on the quality of the final parboiled product. Before the parboiled paddy is fed into the silos, it is cooled to about 5 -10 °C below ambient temperature. From the last conditioning bin, the parboiled paddy is conveyed to separate silos the size of which ensures continuous operation of the rice mill despite a 48 hour retention time.

Steam plant:

The heat and steam customers in the parboiling plant, the fresh water tanks, the soaking tanks, the continuous cooker and the drying plants are supplied with steam by an amply dimensioned steam plant.

The steam generator is heated by a husk combustion plant which incinerates the husks produced in the rice mill. It can also be fuelled by gas or oil.

The entire parboiling plant is controlled and monitored centrally from a control room.

Rice mill:

The Rizomat 3075 rice mill is designed for an input power of up to 7.5 t/h and produces cargo rice, white rice or parboiled rice.

Reception and cleaning:

From the day silo of the rice mill, the paddy is fed into a speed controlled belt conveyor which regulates the input of the rice mill. While the coarse and fine impurities are removed by the downstream mill cleaner, the light particles are separated in aspiration chambers. The machine is equipped with its own aspiration system. Subsequently, the paddy is transported to the reception weigher which controls the input capacity of the plant. The computer system of the weigher stores the hourly capacity and the throughput per shift.

Dry stoner:

The paddy is then transported to two dry stoners which sort out stones and other heavy particles. The powerful aspiration system removes the remaining light particles. Each of the dry stoners is equipped with a special aspiration system.

Shelling:

Via a screw conveyor the paddy is fed into the shelling section and distributed to three Combihull CH10/1260 machines. The Combihull is a combination of the rubber roll sheller S 10 PR and the closed circuit husk separator UHS 1260. The rubber roll sheller S 10 PR is activated and controlled by an exclusively pneumatically controlled automatic inlet regulation. Intensive cooling of the rubber rolls is realised by one fan each. The movable rubber roll is run on four-point bearings and is moved  in a straight line towards the stationary rubber roll. The double V-belt drive with constant belt length ensures utmost operational reliability. The sheller housing and the drive unit are arranged separately.

These outstanding features of the S 10 PR ensure a consistently high shelling degree with a low percentage of broken rice and long service lives of the rubber rolls.

Husk separation:

The UHS 1260 separates husks and light grains from the paddy/cargo mixture. Due to the utilisation of the entire width of the suction case and a new separating chamber concept, a very high degree of separation is obtained. The process in the illuminated separating chamber can be observed through inspection windows. The machine works according to the circulated air principle and does not require downstream separators or filters. A maximum of 5 % of the circulating air is discharged into the pipe system by discharge screws.

Three different products leave the husk separator:          

  • The husks are blown into a husk silo by a downstream fan.
  • Depending on the properties, the light grain mixture is transported either to the shelling section or to the table separators.
  • The cargo rice obtained after husk separation still contains unhusked rice kernels which are sorted out on the Schule table separators and returned to the shelling machine.

Table separator:

The new table separator design ensures a significantly improved precision of separation at high throughputs. In addition to the robust all-steel construction, partly in stainless steel, the TH3 offers a new feeding principle including vertical channels with large cross sections which provide uniform loading of the individual chambers.

The table separator is equipped with a three-point-stroke adjustment as well as with a precise adjustment of the table inclination.

Further advantages:

  • Electronic speed control for exact speed adjustment.
  • Guide and carrying rollers ensure a precise longitudinal table guide and smooth running. Of course, the machine is easy to maintain and to operate. The Schule table separator is patented several times.

The cargo free from paddy is transported into the whitening section consisting of three whitening machines VPC 470.

The SCHULE whitening MACHINE – VERTICONE:

For vertical whitening from top to bottom, the machine VPC 320 is equipped with an abrasive conical whitening rotor interrupted by air openings. The conical whitening rotor has a small diameter at the top in the inlet area and a large one at the bottom in the outlet area. The product is fed into the machine via a vertical piping. Via the inlet slide the intake capacity is adjusted and the product is fed into the inlet bin. A conical distributor feeds the product uniformly onto the circumference of the product draw-in screw arranged underneath. This screw conveys the product into the whitening chamber between the whitening cone and the screens. Due to the rotation of the whitening cone, the pressure of the screw, the position of the steel brakes, and the counterpressure of the outlet cone freely suspended in 3 springs, the product is whitened gently. The whitened product leaves the machine via the product outlet.

The compressed air of the fan is pressed into the working chamber via the hollow shaft and through the air openings. As a result, the product is cooled during the whitening process and the whitening bran is blown out of the working chamber. This supports the aspiration system which sucks off the whitening bran. The whitening bran is discharged via special separators and used for feed production. The whitened rice is then transported to the sorting section.

Separation of broken rice:

A high-performance plansifter with downstream indented cylinder separates head rice from the different types of broken rice. Depending on their size, the broken rice kernels are intermediately stored in different silos and added again if required.

Polishing:

The whitened and sorted rice is transported to the polishing machine RPM 200 W. During the whitening process of rice using abrasive whitening machines, scorings are produced on the surface of the individual rice grains. These scorings are filled with whitening bran making the rice grain look dull. Furthermore, this whitening bran rancidifies, which is strongly detrimental to the taste and reduces the storability. Polishing machines remove the adhering whitening bran, smooth the scorings and provide a bright rice surface. The polishing process is described by means of a water polisher. The polisher RPM 200 W is equipped with a specially designed polishing rotor. The rice is fed into the machine via a vertical piping. A screw conveys the rice into the working chamber.

Here, atomized water, i.e. fog, is supplied through the polishing rotor. This fog is generated by means of a special nozzle which is installed centrically in the inlet of the hollow shaft. The fog charges the compressed air of the blower which transports the fog through the hollow shaft into the working area where the rice is polished gently.

The residual rice bran is sucked off. The polishing bran is discharged via special separators and used for feed production.

The fresh water supply is controlled automatically. If the empty indicators arranged in the buffer bins above the RPM 225 W indicate lack of product, the impulse is transmitted to the solenoid valve of the automatic system and the water and compressed air supply is switched off automatically.

When the product supply restarts, the RPM 225 W also again changes into automatic mode. The polished rice is intermediately stored in silos. In the mixing station, the rice is mixed according to the required quality for sale. Now, the finished product passes through a high-performance colour sorting machine and from there is transported into the packing plant.

The entire plant is controlled and monitored centrally from a control room.