Maleic and fumaric acid production runs as a continuous process at Austrian agricultural chemicals producer ESIM. The breakdown of a filter has consequences for the whole plant. The company had relied on a Funda filter in this process. But this filter pack with 28 disc filters, each 1 m in diameter, was found to offer poor process reliability and high maintenance expenditure.
To solve these issues the external apparatus was completely exchanged, the lower shaft sealing straightened and the container optimised, but this resulted in an increasing load on fumaric acid production. While, for years, the typical lifecycle of the filter had been three to four months, it now got progressively shortener until finally achieving a lifespan of just three weeks. Whenever the filtration results were bad, the filter had to be taken apart and the filter pack replaced. This led to a downtime of several hours as well as additional materials and labour costs. It was not possible to replace the Funda filter with another apparatus or procure a second filter because of the confined space in the production hall.
In addition to the process-related support of a Funda filter expert recommended by the filter manufacturer MAVAG, ECIM engineers asked GKD to optimise the filter pack. The complete filter process was subjected to testing and a plan of action was drawn up. Numerous changes to the technical settings followed. Using detailed descriptions of the filtration process, GKD's experts pinpointed the reason for the increasingly frequent breaches of the stainless steel mesh that had been used in the filter so far.
The fumaric acid solution, mixed with activated carbon, is filtered at boiling point – at a rate of about 6,000 litres per hour. Since the filter is operated in batch process, the acid with a pH of 3 regularly resides for a certain period of time in the filter. Before it is centrifuged, the filter cake is dried with process steam at a temperature of about 150°C which is fed in at a pressure of seven bars through the casing of the filter. These aggressive chemical and physical conditions had a massive impact on the twilled dutch weave mesh made of standard stainless steel that was used to screen the disc filters. GKD therefore recommended changing to a stronger KPZ mesh with a geometric pore of 60 μm made from a special material with a modified weave and finish.
Screening of the disc filters with this particular mesh construction requires special know-how, which GKD passed on to ESIM's master mechanic in an intensive training course. ESIM now gets already folded back round plates of KPZ-Microdur mesh that only need to be placed on the filter plate and tightened around the edges.
Parallel to the process-related optimisation of the Funda filter, all 28 disc filters were replaced. During the exchange, GKD also renewed the support mesh.
Within five months, the whole optimisation process had been completed. The filter pack has been in operation for over 30 months now.