Plant Technology from One Cast
Bulk solids plants are used in a wide variety of industrial sectors and, for the most part, must cover multiple conversion processes under predefined environmental conditions. Along with demanding requirements in terms of efficiency and product quality, the prevailing conditions at the site particularly have to be taken into account for the planning and construction of the plants. A current project from bulk solids specialist J. Engelsmann AG in the chemicals industry demonstrates how multiple bulk solids processes can be implemented using a plant solution with a small footprint in a potentially explosive atmosphere.
The purchaser of the multi-functional bulk solids plant, a leading manufacturer of plastic powder for film production in the chemicals industry, needed a plant solution to expand its production capacity which, alongside delivery, screening and dispensing, also carried out the filling of various types of containers with different filling weights with the final product.
The location for the multi-purpose plant made the requirement profile even more complex. Since the plant had to be integrated into existing infrastructure, the Engelsmann plant could only have a low construction height in order to take the restricted space on site into account. In addition, sections of the plant needed to be suitable for use in potentially explosive zones.
Screening technology made from stainless steel ensures high-purity product
The plant's conversion process stretches from delivery through screening to dosing and filling of the final plastic products. In the process, the plastic powder is fed through a weighing container using on-site pneumatic delivery as the first functional area of the bulk solids plant. The container, filled with powdered plastic, is weighed with the help of load cells in order to avoid feeding too much product into the process or to produce new plastic powder as required. The weighing of the container thus ensures optimal control of the product supply for the plant designed for 3 t/h capacity. After weighing, the plastic product is fed into a granulator in order to agglomerate the powder particles into granules (granulation). With a protective screener integrated into the plant, the granulated product is dehydrated with the help of a slotted sieve in the next process step and is transferred on into a storage tank which is also equipped with load cells. A sliding tube takes care of metered dosage and a continual supply of the plastic granules to the second screener which is installed for classification and screening for coarse granules. The product level within the classifying screener, driven by vibrators, is set by means of an adjustable supply tube. The screener has a screen deck on which three fractions can be screened. The screening process takes place from fine to coarse and is particularly gentle on the product in order to ensure extremely pure quality in the final product. The screened product is additionally checked using a metal separator and any metal particles are transferred into a container so that they cannot get into the final product. In order to achieve consistently high throughput and high screening quality, a ball cleaning system, which keeps the mesh permeable during the screening process, is installed on a corrugated mesh under the screen cloth. Impact knocking balls clean the individual screen surfaces as the balls are thrown against the mesh by the machine's vibrations. Owing to the sensitive product requirements, all other parts of the machine which touch the product, besides the impact knocking balls, are made from stainless steel with high surface quality (Ra value of 0.8 µm) in order to prevent abrasion of the granulated product and minimize cleaning-related downtime. The screening pan is mounted and not fully welded so that it can be removed and cleaned in a few steps. The infeed and outlet are connected using special cuffs which can be removed without using any tools.
Intelligent process technology for appropriate filling
After the screening process, the product is transferred into a buffer container with filling level measurement and, from there, is fed into the filling unit via a swinging delivery pipe. Since the client's customers are supplied with bags (25 kg), barrels (200-250 kg) and Big-Bags (1,000 kg) as required, a variable filling system which allows the plastic product to be filled into three different container types was designed. The weighing container has a capacity of 25 kg, which is identical to the filling volume of the smallest container type (bag). Once the container is completely filled with the plastic product, a filler cap seals the swinging delivery pipe so that no more product can run out. Depending on the container, the filling process is clocked in 25 kg portions, which hit one instance of the filling process for filling a bag and forty repetitions of the filling process for the largest container, the big bag, thanks to a specially developed control unit. The calibrated weighing of the final product can thus be carried out using one and the same weighing unit even though the individual filling weights of the containers differ considerably. In addition, the different connection options for the types of containers used had to be taken into account during construction. An adapter system, specially developed for this application, allows the quick changing and connection of the appropriate containers to be filled. For the filling of the 25 kg bag, this is put over the end of the filling nozzle and held firmly by a pneumatic clamping device. At the end of the filling process the clamping device opens again and the full bag can be removed. For barrel filling, up to four barrels can be filled in a single instance of the process with a pivotable filling pipe. Big Bags are firmly connected via a filling adapter with a one-hand bag clasp and fixed before the filling process starts.
The bulk solids plant delivered five months after ordering with CE marking is a turnkey solution which was designed, manufactured and delivered by Engelsmann. The Engelsmann fitters integrated the plant technology into the existing plant infrastructure on site, in which the construction height of the plant is tailored to the restricted space at the location. After commissioning, the operating personnel were trained in the control and operation of the process technology.