One of the biggest integrated food industries in the Balkans, M/S Klas Ltd. is deeply rooted in the social fabric of Sarajevo. The company found a special place in the hearts of the people during the Bosnian war, when it supplied bread free of charge to the besieged community. The company’s Sarajevo premises were set in the thick of the fighting and suffered the loss of 17 of its employees in the conflict from 1992 to 1995. The mill itself was badly damaged and was forced to shut down during the last weeks of the war; in fact the marks left by the cannon balls and machine-guns on the external walls of the mill tower are still visible today. Fortunately the bakery lines had already been moved to underground rooms so that Klas was able to continue producing bread by using the flour stored in the silos, which miraculously had escaped damage.
Today, the people of Sarajevo, Bosnia Herzegovina, can take pride in a new Klas flour mill. Fully automated, and to ISO 9000 standards, it is equal to the best in the European community.
A local project team, under Project Manager, Eng. Thomas Prajo, from Splitz, Croatia, worked with milling engineers
Mill Service, Selvazzano, Padova, Italy, to complete the project in just 11 months: the whole complex was constructed within the existing tower building (47 meters above the flour silos), with a production shut down period of only 66 days. This included the dismantling of the machinery from the 200-tonne Sangati mill that had been installed in 1980.
A capacity of 450 tonnes per day of soft and hard wheat flour has been attained with a building volume of 6,300 cubic meters for the milling and cleaning sections, together with the daily and tempering silos. This equates to only 14 m3 per tonne or 9 m3 excluding the volume of the daily and tempering silos. Another major achievement is the operation of the wheat silo, the mill and the flour silos that is entirely based on the data supplied by laboratory analysis, which allows the production of different flours with constant baking yields throughout the year.
The low cost of the plant has given Klas minimal depreciation and contributes to the remarkable reduction in operating costs, made possible by the highly mechanized storage cycles for wheat, flour and bran and by the total automation of the mill.
The mill’s 65,000 tonnes of silo storage comprises 34 concrete bins of 1,200 tonnes each and 17 concrete interstice bins of 300 tonnes each and 20 metal bins of 1,000 tonnes each.
During harvest at least 60% of the wheat comes from Bosnia, Croatia and Hungary, while at other times wheat is sourced from the Balkan and Russian markets and from the United States, via the Adriatic port of Ploce. In all cases the wheat reaches Klas by road.
Prior to discharge, a rapid electronic sampler sends samples to the laboratory for analysis to determine the protein and moisture content, and also the specific weight and Falling Number index; wheat can then be stored in bins that already hold similar qualities.
Two huge hoppers, with aspiration hoods enclosed in a dust tight tunnel, serve the 100-tph pre-cleaning lines; each equipped with an electronic scale, vibrating separator, vertical aspirator with air recycle system, magnets and automatic metering unit for slow action disinfestation tablets.
Four aspiration systems with low pressure jet filters complete the installation: two of which are for the pre-cleaning lines, one for the chain conveyors installed in the room above the bins and one for those installed in the room below the bins. A fifth aspiration system serves the elevators and chain conveyors for the metal silos.
Ten of the concrete silo’s interstice bins are used for the storage of rejected wheat. Once stocks of similar quality have been stored, they are homogenized overnight by several recycling operations; the cereal is weighed by a third scale and then conveyed into the metal bins that already contain wheat with corresponding characteristics. Here the wheat is analyzed according to its baking qualities using the Brabender Farinograph and Chopin Alveograph.
These three scales and the process computer provide the means of instant stocktaking — determining either total storage, total per bin, or total for each quality of wheat.
All screenings together with the dust recovered by the filters are weighed by a fourth scale and conveyed into an interstitial bin of the concrete silo serving a hammer mill; the milled screenings are sent into another interstice bin and from there into the relevant proportioning bin located in the bran silo building.
With a full knowledge of the milling and baking qualities of the different stocks of wheat in each of the metal bins, the technical director can determine from his office the required blends by remote adjustment of the flowmeters installed underneath each metal silo bins.
The required blend of wheat is first weighed and then conveyed to the top of the mill tower, where it is stored in four daily silos with a total capacity of 720 tonnes and equipped with flowmeters that feed the first cleaning line.
A 24-tph first cleaning line is installed on six floors. It consists of a magnet apparatus, an electronic scale, a vibrating separator, a vertical aspirator with air recycle system, one gravity dry-destoner that divides the wheat flow into light and heavy, one battery of trieur cyclinders for the light flow, two spiral separators and one intensive wheat scourer.
The cleaning line also includes an intensive wheat damper which loads three first tempering silos that have a total capacity of 460 tonnes and are each equipped with a flowmeter installed at its discharge outlet.The wheat damper is connected to an automatic microwave apparatus that measures the moisture content of the cereal at inlet and doses the quantity of water to be added to obtain a constant final moisture content.
The second wheat tempering section with 22-tph capacity is equipped with an intensive wheat damper that loads two tempering silos with a total capacity of 360 tonnes, and each complete with a flowmeter at its outlet. The second cleaning section, with a matching capacity of 22 tph, is equipped with an intensive wheat scourer a vertical aspirator with air recycle, one atomizer dampening unit, one electronic scale and two magnetic apparatus.
The third tempering system, equipped with an atomizer dampening unit is installed before the first break line.
The three cleaning sections are served by an aspiration system with a low-pressure jet filter; the screenings are weighed and then pneumatically conveyed to the screening storage bin installed inside the building with the bran silos.
All the elevators and screw conveyors have automatic devices for overflow, screw control and limit switches; furthermore, in case of blockages the cereal flow is constantly monitored by fault indicators that are directly connected to the electrical switchboard by an alarm system for emergency stops. This is all connected to the central control computer.
The mill has a 450-tonne-per-day capacity for the production of flours below 140 microns; when producing French type flours with a particle size below 160 microns, it reaches a capacity of 500 tonnes per day.
Space limitations dictated the installation of two eight-roll machines for B1 and B2 passages; furthermore due to the low height of the sifting room the plansifters have 24 sieves. The flexible milling flowsheet, accommodates both separated or blended wheat streams and the simultaneous production of three types of flour and one type of fine semolina; the specific milling length is 8.92 mm/100 kg of wheat in 24 hours; the specific net sifting surface is 0.0586 m2/100 kg of wheat in 24 hours.
The milling section is made up of 21 completely automatic roller mills (two of which are eight-roller type) with variable speed feed system; four square sifters with eight channels and 24 sieves; six centrifugal detachers, five drum type detachers; four vertical vibrosifters; four multiple type semolina purifiers; eight horizontal bran finishers; two pneumatic conveying systems with two low pressure jet filters; an aspiration system with relevant low pressure jet filter; three flour infestation destroyer units; three single-channel rebolt sifters; four electronic control scales for flours (specifically for F400, F500, F710 and fine semolina); and three electronic scales for bran, fine bran and pollard. All the scales are able to signal in real time any anomaly in outputs. There is also a bran milling section with two roller mills and three centrifugal sifters.
Ambient conditions in the four rooms of the mill are kept constant by two air conditioning systems: the first produces 30,000 m3 of air per hour for the cleaning section and the second produces 70,000 m3 of air for the mill section.
A blend of 50% soft wheat and 50% hard wheat from Bosnia, Croatia, Hungary and the U.S., weighed at B1, gives a total flour extraction rate of 78%.
Sae Engineering, Limena, Padova, Italy, who supplied the electrical installation and automation, were responsible for the centralized control system that allows the mill to run — bagging and packaging excluded — with only two people per working shift and for the cleaning sections and the mill to run lights-out on weekends.
The air conditioned and soundproofed control room is equipped with three computers: two for the cleaning and milling sections and one for the bran silo.
Each section of the mill is controlled by its own switchboard with PLC, which permits intervention in one section without stopping the others.
Automatic systems start and control each machine in the cleaning section. The automatic dampener, equipped with a microwave-based continuous analyzer, meters the water to give a constant flow of wheat with the pre-set moisture content to B1. Level indicators determine when the weighed and milled screenings are pneumatically conveyed to the bran screw mixer ahead of final storage.
Once the product and by-product destinations have been set, the mill can be started up and processing begun. Blockages in the conveying systems are automatically prevented by capacitive sensors.
A scale installed before B1 controls plant output. Finished products and by-products are weighed by means of eight scales before conveying to the specified silos.
Any product or by-product can be excluded from the process cycle even during the milling operation. If required, coarse bran can be milled.
Baking flour F500 is conveyed into one of two 80-tonne homogenization bins. A recycle system automatically starts when it reaches half of the maximum capacity. Once completely full, the bin is discharged and its content pneumatically conveyed to the selected bin of the flour silo; at the same time the homogenization process starts inside the second bin. Information is reproduced in real time on the video synoptic screen.
It is also possible to control and record the mill yield during a given shift and have it graphically displayed.
The mill computer is remotely connected to another installed inside the manager’s office to allow data checks.
THE FLOUR SILO
The flour silo is located below the milling section and consists of 21 concrete bins with a total capacity of 2,100 tonnes, equal to six working days, and is complete with loading, discharging and recycle systems of 30 tph. This storage capacity allows the flour to be kept at optimum maturation level, and to be stable and uniform throughout the year. Small differences in ash and moisture content can be leveled out by homogenizing the basic flours.
A limited number of basic flours rationalizes milling performance; the larger stocks of the same quality of wheat avoids frequent adjustments of the machines.
The basic baking flours from the homogenization bins are sent to the mixing bins, where samples are taken for routine analysis of quantity, protein and ash content. Once the results are obtained, the recipe code is entered into the computer. This automatically controls the inverter of the proportioning worms of the vibratory extractors. The mix is conveyed into a continuous mixer and then pneumatically conveyed into the feed bins for the bagging stations or the packaging units.
As the two rooms under the bins are not high enough for the installation of scales above the mixer, a volume mixing system has been adopted with a 2% to 3% degree of precision.
The pneumatic lines used to feed, recycle and dispatch add product ventilation to that produced during the homogenization process, providing rapid maturation of the baking flours.
About one quarter of the production is conveyed by means of three pneumatic lines into the silos of the company’s own bakery, pasta, cake and biscuit factory after having been weighed by three specific scales.
The whole system is run by a computer that synchronizes the proportioning units, blending, the mixing process, silo levels and finished product recipe parameters and also provides historical record of all blends that have been produced.
The by-product silo, supplied by M/S Mlinoproject of Zagreb, Croatia, and its bagging line, were installed inside the old mill, constructed in 1902, near to the new mill tower.
The by-product silo consists of six metal bins of 5 meters diameter: four of them are 13 meters high and the other two are 10 meters high. Total capacity is 350 tonnes, equal to about one week’s production.
By-products are either bagged off into 40 kg bags by a 500 bag-per-hour weigher-packer or bulk loaded into trucks. A pneumatic conveyor will connect this bran silo to a 20-tph automatic feed mill that is soon to be installed.
All the loading, recycle and dispatch systems are controlled by PLC and interfaced with the mill control system.
The flour silo, together with bagging and bulk outloading can be operated by four persons during the day shift. Less than twenty workers can manage the whole milling complex, included wheat silos, during 24 hours, excluding the laboratory personnel.
M/S Klas at a glance
Established 1902, Klas is a 62% employee-owned joint stock company.
It operates in the cereal sector with:
• 65,000 tonnes wheat storage at its Sarajevo mill.
• A 450 tonne-per-day wheat mill with silos for 2,100 tonnes flour storage and 360 tonnes bran storage.
• A 60-tonne maize mill for the production of brewery grits and semolina for polenta.
• A 50-tonne barley plant for the production of pearled barley for soups and meal.
• An industrial baking facility with a daily production of 50 tonnes of bread.
• An additional 100 mini-bakeries located across Bosnia Herzegovina.
• A 20 tonne-per-day pasta factory.
• A 10 tonne-per-day biscuit factory.
• Cake industry activity with daily production of 7 tonnes.
• Active in the semi-frozen bread and general food.