Rice Quarterly: A modern Greek classic

by Emily Buckley
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Spanos Bros began planning to build its new rice milling facility in early 2000 and soon after contracted F.H. Schule Mühlenbau GmbH of Reinbek, Germany, to equip the plant. Built in the industrial area of Sindos, next to Thessaloniki, Greece, this new facility is one of the most modern rice processing plants in Europe.

Construction started in 2000, equipment was installed in 2001 and 2002, and the facility came online in October 2002. With an input capacity of 7.5 tonnes per hour, the rice mill includes a parboiling plant with output capacity of 6 tph. Other components include pre-cleaning systems, a silo system, husk conveying, a husk burning plant, a steam plant, bran conveying, packing and final product storage. The new mill also incorporated an existing silo plant including 8 silos with a total 8,000 tonnes capacity for paddy.

Spanos Bros took over the processing reigns in late 2002. Here, we take a look inside to see how this facility manages to exceed all performance expectations.

 

THE PARBOILING SYSTEM

Paddy that has been dried down to 14% humidity is delivered to the facility by truck. A weigh bridge before and after unloading measures the delivered product quantity and registers the amount into a computer program. From the intake hopper, paddy is conveyed by elevator to a 35 tph pre-cleaning system to remove coarse and fine impurities. The paddy, depending on rice type and intended purpose, is distributed to different silos by a chain conveying system. From storage, paddy is conveyed either to the rice mill for the production of cargo or white rice or to the parboiling plant for the production of parboiling rice.

Paddy on its way to the parboiling plant is conveyed to the fine cleaning and sorting section, first reaching two gravity separators where the cargo kernels are separated. A special fine cleaner classifies over- and undersized product and highly efficient aspiration removes the last light particles. Next, an indented cylinder removes any brokens. The cleaned and classified paddy is conveyed to the day bin of the parboiling plant.

From there, it moves to the soaking section. A special computer-controlled scale precisely fills the four soaking tanks and determines soaking cycles. The water quality — as well as the soaking temperature of up to 71°C (160°F) — greatly affects the soaking time required. In order to reduce the soaking time further, the tanks are operated with a pressure of up to 87 psi. In addition, Schule’s system ensures that the water temperature remains consistent with the pre-programmed level to maximize soaking quality.

Once the projected soaking time is reached, the tank pressure is released, the water drained and the tank outlet opened to the intermediate bin below the four soaking tanks. After a defined time, the outlet will be automatically closed and a new soaking cycle starts.

The product in the intermediate bin runs onto a de-watering screen, the surplus water is removed and the product is fed continuously into a stainless steel bucket conveyor. An attached cleaning device uses compressed air to ensure that the back-flowing buckets are completely discharged.

At the heart of every Schule parboiling plant is the continuous, computer-controlled vertical cooker. This cooker is installed on special weighing cells that transmit every weight change to the main computer, and Schule’s specially designed software reacts according to the pre-programmed parameters.

As product comes from the bucket conveyor into a pre-bin, it enters a feeding lock. The computer calculates the cooking time for the height of the product column. From the discharge lock, the paddy flows onto a vibratory feeder that provides an even product flow onto the first of three fluid bed dryers.

The fluid bed dryer is driven by powerful vibratory motors. Hot air systems supply the dryer with warm air that directly flows through the product and dries the paddy down to 22% to 24%. A specially designed aspiration system disperses the warm, humid air.

Schule prefers a three-stage drying system and believes the drying process has a decisive influence on the quality of the parboiled end product. Tempering cells are located between the individual drying steps. The dimensions of the tempering cells are designed for a product flow that lasts a minimum of 8 hours, operating on the first-in, first-out principle.

From the last tempering cell, the parboiled paddy is conveyed to separate silos, which allow for both the required 48-hour resting time for the paddy and continuous operation of the rice mill.

The steam plant feeds the parboiling plant, the fresh water tanks, soaking tanks, the continuous cooker and the drying plant. The steam generator is fueled by a husk burning plant that burns the husks obtained from the rice mill. Operation with gas or oil is also possible.

THE RICE MILL

The facility’s Rizomat rice mill 3075 produces cargo, white, or parboiled rice.

From the day bin of the rice mill, the paddy first flows through the cleaning section. Afterwards, the paddy is conveyed through a control unit that manages the input of material into the mill. The computer records the hourly capacity and the throughput capacity per shift. Next, paddy is conveyed to two destoners, which are each equipped with a special aspiration system.

The shelling (debranning) process begins as paddy is distributed to the shelling section and separated onto three Combihulls, CH10/1260 — a complex combination of high-capacity rubber roll sheller S10 PR and the closed circuit husk separator UHS 1260.

The rubber roll sheller is automatically activated and controlled exclusively by a pneumatic system. The movable rubber roll is equipped with a patented linear slide that moves against the fixed roll.

With the separator, husk and light particles can be separated from the paddy-cargo mix. The separation chamber is illuminated and inspection windows permit easy observation.

Three products leave the separator. Husks are blown from a separate fan into a husk silo. The mixture of light rice grains is supplied to the shelling (debranning) department or table separator depending on the quality. After the husk separation, the cargo still contains unshelled rice that has to be separated by the Schule table separator and again applied to the shelling process.

Schule’s new all-steel table separator model TH3 offers new dropping channels with large cross-section areas for uniform feeding of all compartments. The table separator is equipped with a three-point stroke adjustment as well as a fine adjustment of table inclination.

Finally, the paddy-free cargo is transported to the whitening section, which consists of three rice whitening machines. The Verticone VPC 470 rice whitening machines operate vertically from top to bottom using abrasive conical whitening discs with air-feed openings between them. The smaller diameter conical whitening rotor is placed at the top, while the larger diameter is placed at the bottom, before the outlet section. The product is fed evenly by a conical distributor and into a ‘feeding worm’ that lifts the product to the whitening chamber between the whitening rotor and sieve. The rotation of the whitening rotor, the pressure of the worm, the position of the steel brakes and the counter pressure of the outlet section connected by three springs ensure a gentle and uniform whitening.

A ventilator cools the product during the whitening procedure, and the bran is blown out of the working chamber. Bran is then separated and used for the production of compound feed. The whitened rice is conveyed to the sorting section.

A high-capacity square plansifter with an indent cylinder separates head rice and brokens, which are stored in different silos depending on their dimensions.

The whitened and sorted rice is conveyed to the polishing machine RPM 200W. During the abrasive whitening process, grooves are made on the rice kernel surface. During processing, these grooves become filled with bran, which gives the rice a dull appearance. Because the bran is subject to rancidity, the rice flavor and quality can deteriorate badly during storage. The polishing machine removes the polishing bran and flattens the grooves to give rice a shiny appearance.

Keeping the operation highly efficient, the bran is routed to a special collector and also used for feed. The regulation of the fresh water supply to the polisher is managed automatically.

Polished rice is stored in silos. In the blending station, it is mixed to the defined sales quality. The final product flows through a color sorting machine to the bagging plant.

The whole plant, including the parboiling plant, is managed and controlled from a central control room.

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