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  2. Article: Out with the bags: Big bag system easily handles heavy weights

27.10.2015

Big bag emptying system for product with poor flow characteristics

The emptying of big bags must meet the highest safety and product handling requirements. Emptying poorly pourable bulk solids and feeding them to the production process requires intelligent system solutions that are tailored to the conditions in a plant. Just like, for example, a current turnkey project in the chemical industry realised by J. Engelsmann AG, a bulk solids specialist.

The client, a leading producer of chemicals, among other things processes methacrylamide that, as a finished product, is supplied to the pharmaceutical industry and is used as binding agent in the production of medicines or thickening agent and stabiliser in the food industry. Other applications include cosmetic products such as hair spray or shampoo and washing agents, paints and adhesives. As additive for binding or thickening agents, methacrylamide, in its original form a crystalline material, tends to caking during transportation. Previously delivered in 25-kg bags by different suppliers, the methacrylamide was of differing quality with regards to caking. Only with significant manual effort and the use of lifting and conveying equipment the bags could be emptied via a bag emptying station and could be conveyed to the first processing step in a stirring tank supplied by the client where a solvent is added to dissolve the product.

A test structure was realised for clarity and safety

In order to make the emptying and feeding process of the supplied methacrylamide more efficient, the chemicals producer decided to replace the delivery in bags by a big bag solution. For this purpose the bag emptying station was to be replaced by a big bag emptying unit that is supposed to ensure complete and hassle-free emptying and conveyance of the product towards the stirring tank. The fact, that methacrylamide due to its properties is only poorly pourable after transportation and does not flow out of the bag by its own, had to be included in the planning and construction of the emptying station. For example the small room height and an uneven installation surface on site had to be taken into account. With these requirements we started the conception phase of the system. Due to the complex product and process requirements, a test structure was realised in the Engelsmann test center in coordination with the client to simulate the big bag emptying based on the conceived system solution. The test did not only produce important production data but also provided the safety that the system will run smoothly during its future operation.

To ensure smooth emptying of the big bag Engelsmann equipped the system with an emptying station. A crane track module with the corresponding chain hoist in a flat version ensures the introduction of the big bags into the emptying station. For this purpose the spring-loaded loading gear that is attached to the chain hoist is extended and lowered to the position of the big bag. Then the four loops of the big bag are hung into the loading gear, the big bag is lifted up and brought back into the station. Before the big bag is lowered onto a pneumatically operated milling device, that also serves as fall protection in case the loops of the vig bag should tear, a pneumatically operated bar crusher is used. The large tackle of the bar crusher on both sides of the big bag enables the precise capture of caked product that will be broken up before the discharging process. The big bag that hovers above the actual discharge position is lowered a bit and the bar crusher is used again in order to break up as much caking as possible. Only after the bar crusher has done its work, the outlet of the big bag will be tied over the manually operated discharge funnel without generating dust, the outlet nozzle is opened and the emptying process is started. As soon as the emptying of the big bag starts the milling device is switched on, ensuring, in conjunction with the spring loading module on the loading gear, that the poorly pourable material is completely discharged. The decreasing weight of the big bag ensures that the big bag is automatically tightened upwards via the springs which enables the almost complete emptying of the bags.

Only the emptying device provides workable product properties

After the emptying process the product is conveyed directly into a discharge device that Engelsmann developed for the removal of poorly flowing bulk solids to ensure a continuous process. Due to the negatively tapered shape of the container the product to be discharged slides down and discharge arms continuously convey the product towards the outlet nozzle. The discharge device has the function to break up the caking so that the product will regain its original crystalline shape which is required to be able to process it in a first production step in the stirring container. After the caking has been broken up, the product in its crystalline original form is conveyed to the downstream screw conveyor that transports the product to the first production step as the conditions on site impeded the installation of the emptying station directly above the stirring container. In order to ensure the exact quantity of solvent added to the stirring container, it is decisive for the process quality that always the correct quantity of methacrylamide is added to the stirring container. Usually three entire big bags have to be emptied. In order to take account of possible weight or quantity tolerances of different big bags and to precisely determine and check the feed quantity, the bags have to be weighed first. The uneven installation surface not allowing reliable weighing, a weighing unit has been integrated into the emptying frame for this purpose. Using an equalising weight the differences were levelled and thus precise weighing was ensured.

Due to the planned installation in an explosive production area the entire system was produced in accordance with ATEX. The big bag emptying station has been completed four weeks prior to the planned delivery date and is a turn-key solution with CE marking. Engelsmann was responsible for its planning, production, delivery and assembly. Upon commissioning including a site acceptance test, the operating personnel were instructed on the control and operation of this processing technology. In addition, a maintenance contract has been concluded in order to minimise the risk of downtimes by optimum maintenance and servicing.