If a bakery has to deal with a quantity of about 20 tons of flour every day, this can only be accomplished at a fully automated large-scale business, where the flour is conveyed automatically. At the wholesale bakery Sehne near Böblingen, Germany, the efficiency of the former pneumatic conveying system had reached its limit. Therefore, a considerable capacity increase became inevitable.

The solution put into practice by the end of 2007 is brilliant and convincing: An additional pneumatic conveying unit together with a new integrated weighing station was added to the previous conveying unit. It was possible to establish an especially economic and reliable new transport and weighing concept with a considerably increased number of cycles. The extra demand of conveying air is produced by two additional positive displacement blowers manufactured by Aerzener Maschinenfabrik.

The Wholesale Bakery Sehne

The bakery in Ehningen, Germany, was founded in 1957 by master baker Heinrich Sehne and has developed into a company with almost 800 employees. The second-generation family company produces on an area of 10,000 m² and offers a variety of more than 200 different products. Originally the fully-automatic weighing station at Sehne consisted of two independently working balances, which were fed by the six external silos via a pneumatic conveying unit. However, due to the continuously increasing flour consumption this system reached its limit, so that a new solution with a considerably higher capacity was mandatory. Georg Stein Process Equipment in Melle, Germany, recommended an additional "inserted" pneumatic conveying unit along with a more efficient weighing station, with the further use of the former unit components as far as possible. This proposal was planned after preliminary talks and was commissioned at the end of 2007.

Georg Stein Process Equipment supplies individual process solutions regarding raw material handling, mechanical and thermal process engineering for the food and chemical industries. Each unit is adjusted and customized to the production courses and room conditions of each customer. This includes the distances to be bypassed, the required flow rates, the quantity of parts-removal and receiving stations, and last but not least the features of the bulk goods.

Decisive participation in all fully-automatic conveying and weighing procedures within the new pneumatic conveying concept provides a superordinate control concept. It was designed and delivered by AWS Automation, Osterrönfeld, Germany. The AWS-system works fully automatically, is multifunctional, visualized via a screen and called up in the production according to the stipulations of the central control room, and is controlled via the fully automatic AWS software. The control concept for the entire unit can be telemonitored by AWS from the location at Osterrönfeld. The AWS-system fully automatically controls all formulations for more than 200 products of the company and is also responsible for the constant daily high quality of all Sehne-products. AWS Automation worked as general contractor on this project and Georg Stein Process Equipment was responsible for the entire hardware.

New Weighing Concept

In order to increase the transport capacity, an additional pneumatic conveying unit was installed with a new, more efficient weighing station between the external silos and the old weighing stations. This insertion consists of two completely independently working units. They are supplied with the necessary conveying air by two new positive displacement blowers of Aerzener Maschinenfabrik. The weighing procedure of the component parts taken off the storage silos is now being carried out exclusively in the two new weighing stations of this new pneumatic conveying unit. The two scales of the old weighing station still only work as target reservoir, and register the entries of the charges. The mixture of flour and its further processing is then carried out in different production steps according to stipulations.

Main component parts of each single station regarding the inserted weighing station are the main scale and two reservoirs switched in addition, also being equipped as scales. The system works as follows: Three of the six external silos are drained as usual by the two conveying air blowers already available. Now, the flour is led to the inserted weighing station via sieving machines. By means of monitored switch points the flour then reaches the main scale pre-selected by a computer program, to be portioned afterwards. Via an electro-pneumatically monitored folding box the portioned amount automatically enters one of the two subsequent reservoirs arranged below. These reservoirs are also designed as scales (main scale I with subsequent reservoirs A and B, main scale II with subsequent reservoirs C and D). Due to the connecting drain of the filled-in following reservoir, a new weighing procedure starts with the main scale. However, the weighed amount of flour enters the second subsequent reservoir. In the meantime, a new weighing procedure has started with the main scale and following drain into the first subsequent reservoir. This weighing cycle of the main scale with follow-on two-way drain into two subsequent reservoirs continues constantly.

Pneumatic Transport

The conveying air necessary for the pneumatic transport of the weighed flour quantities is produced by two new Aerzen conveyed air blowers. They supply each one of the two conveying lanes of the new piping system, from the new weighing station to the former weighing station. The four subsequent reservoirs of the new weighing station (main scale I with subsequent reservoir A and B, main scale II with subsequent reservoir C and D) are each connected staggered to one conveying lane of this new piping system (subsequent reservoir A and C to conveying lane I, subsequent reservoir B and D to conveying lane II). Upon request, the allocation of the compressed-air blowers to these subsequent reservoir couples can be monitored by a pneumatically automatic switch-point system. (Note: The compressed-air necessary for the control of these switch points had been produced by a separate compressed-air supply system and supplied to the users via separate system). The flour entering from the subsequent reservoirs into the piping system is then led via the conveying air of the new Aerzen positive displacement blowers to the old weighing station, which represents only the destination with registration function. Thanks to this cycle concept the weighing- and transport procedures run at tremendous speed and practically without any delay times. In addition the new solution offers a sufficient reserve performance, so that during the next development phase, it is possible to carry out two or even four additional weighing procedures without extensive additional modifications.

Due to the newly inserted pneumatic conveying system, this new concept leads to a considerable increase in the weighing rating, so that the flour supply of Sehne corresponds again to the increased production requirements. The entire system works at low-pressure range and is aligned for delta p = 1,000 mbar max. Thanks to the availability of two new Aerzen conveyed air blowers as well as the present switches and shut-off flaps in the new piping system the allocation of the conveyed air blowers can be switched to the two conveying lines upon requirement. However, according to procedure the remaining blower cannot serve both conveying lines at the same time, but only one exactly defined conveying line. Thus, the standstill of a conveyed air blower means a considerable reduction of the total capacity of the concept.

Aerzen Positive Displacement Blower Units

As producer of the conveying air required in addition for the new solution of Sehne, Georg Stein selected Aerzen positive displacement blower units of type GM 10 S of series "Delta Blower Generation 5". Aerzener Maschinenfabrik has manufactured positive displacement blowers since 1868. The new blower generation "Delta Blower Generation 5" combines the well-known and successful characteristics of the former generation with new technical innovations. Generation 5 offers customers five main advantages. At the same time they represent distinctive features of other blower models, such as:

• Decreased sound level by approx. 6 to 8 dB (A);
• Easy installation, operation and maintenance;
• Aeration without additional electric motor by mechanical fan on the blower shaft;
• Renunciation of sound-absorbing material; and
• Reduction of the linear dimension with smaller units and the space-saving side-by-side installation with all models.

Further advantages are: oil-free conveyance thanks to the piston ring labyrinth sealing in connection with neutral chambers, Aerzen base support certified as spark extinguisher for ATEX applications, blower stage with patented procedure for pulsation decrease, standardized application of energy-sufficient motors of classes EFF1, authorization as per PED-guideline, regarding encapsulated units the intake on the "cold" side of the unit, drive via high-performance narrow V-belts and automatic belt re-tension by hinged motor mounting plate.

Georg Stein does not only appreciate the brand awareness: "The machines made by Aerzener Maschinenfabrik are also famous in the foodstuff industry because of their high reliability. In addition, I appreciate the short official channels of this manufacturer, so that in special situations very quick reactions and solutions have always been possible."

Two Delta Blower Blowers of New "Generation 5"

The alignment of the required blowers was carried out depending on the case of requirement by Georg Stein Process Equipment. Two Aerzen positive displacement blower units of type GM 10 S, series Delta Blower Generation 5 were installed. An ATEX design was not necessary in this case. Aerzen units are designed for a conveyed capacity of 9,000 kg flour each/per hour. They work at a constant performance. At present, the blowers produce at an overpressure of approx. 600 mbar. However, they can be driven by an increase of the drive capacity up to an overpressure of 1,000 mbar.

Following detailed planning, the transition from the old to the new concept was carried out during company holidays one weekend in December 2007. Starting the working shift on Sunday night the new concept was already in good working condition. In case of system failures Sehne first call would be to the general contractor AWS. Looking at the remote control room installed by AWS, there are first clues about the cause of failure and the malfunctioning area. Thanks to the prompt agreement with Georg Stein Process Equipment, the further procedure has been coordinated between both partners without any time loss, so that the cause of malfunction can be eliminated as quickly as possible.

Sehne is absolutely satisfied with the results: "Since its commissioning at the end of 2007 the unit has been operated without any malfunctions. Thanks to the concept realized by Georg Stein Equipment, we could optimally adjust the required number of cycles of the weighing procedures to the considerably increased requirements of our production. The two new positive displacement blowers from Aerzener Maschinenfabrik have an essential share in the success of this concept. It has been quite pleasing that we could accomplish the new concept with the further use of the preexisting units to a large extent, with clear investment costs," emphasizes co-owner Gerd Sehne.