Pneumatic Self-Cleaning Filter for Tomato Processing Filtration Project
The customer is a large-scale tomato product deep-processing enterprise in North China, primarily producing tomato paste, crushed tomatoes, and tomato ketchup. In the upstream stage of the production line, the raw crushed tomato pulp from the crusher contains coarse impurities such as tomato skins, hard stems, uncrushed fruit chunks, and a small amount of vine debris. If these impurities are allowed to enter subsequent concentration, sterilization, and filling processes, they not only clog the flow channels of plate heat exchangers and evaporators but also affect the final product's texture uniformity and appearance quality.
The customer's existing vibrating screen filter had become a bottleneck in the entire production line due to frequent screen clogging, intensive cleaning requirements, and the inability to operate continuously online. With the peak order season approaching, the customer urgently needed a coarse filtration device capable of withstanding high temperatures, resisting acid-alkaline cleaning, and performing online automatic slag discharge.
After collecting on-site production process parameters, our technical team identified three key challenges that needed to be addressed:
First, the medium temperature is as high as 95°C. Conventional filter housing materials pose risks of thermal deformation or seal failure under prolonged high-temperature exposure, and the high temperature accelerates the aging of rubber seals. Second, the material itself is weakly acidic, and the customer uses 2% caustic soda and 2% citric acid solution for CIP in-place cleaning after daily production. This requires all components in contact with the medium to withstand the dual corrosion challenge of strong alkali and organic acids. Third, although the solids content is only 1 kg per hour (equivalent to approximately 0.1 kg of solids per ton of pulp), tomato skins and hard stems are flaky and somewhat tough, making them prone to getting stuck in the filter mesh gaps. Ordinary brush-type or backwashing methods are insufficient for thorough removal.
Based on the specific nature of the customer's operating conditions, we recommended the JYSCF-219-316L pneumatic self-cleaning filter and made targeted adjustments according to food processing industry hygiene requirements.
The housing and wedge wire screen are both made of SS316L stainless steel, which exhibits excellent corrosion resistance against the organic acids in high-temperature tomato pulp as well as the 2% caustic soda and citric acid cleaning solutions. The filtration accuracy was set at 18mm, a size that effectively retains tomato skins, hard stems, and large fruit chunks while allowing fine particles that meet process requirements to pass through, avoiding excessive filtration that could affect final product yield. The inlet and outlet were equipped with DN80 DIN11851 quick-clamp couplings to match the customer's on-site piping standards, facilitating daily disassembly and inspection as well as CIP cleaning fluid circulation.
The core cleaning mechanism of the equipment is a reciprocating scraper plate driven by an SS304 stainless steel pneumatic cylinder. The scraper edge maintains close contact with the wedge wire screen surface. During each cylinder action, the scraper forcibly removes tomato skins and fiber debris adhered to the inner wall of the filter screen, which are then discharged through the DN100 electric ball valve at the drain port. To accommodate high-temperature conditions, both the cylinder seals and electric ball valve seals were upgraded to fluoroelastomer (FKM) material rated for 150°C.
The equipment was installed on the pipeline between the crusher discharge pump and the buffer tank, in a vertical orientation with side inlet and bottom outlet. The entire installation process took only half a day, including pipeline connection, compressed air line installation, and electrical wiring for the electric ball valve.
The key challenge during commissioning was determining the optimal cleaning frequency and discharge duration. Due to the adhesive nature of tomato skins, the initially set automatic cleaning every 4 hours proved inadequate, with the filter differential pressure rising to the alarm value after only 2 hours. Our engineers adjusted the parameters on-site, changing the cylinder scraping frequency to once every 1.5 hours, with each cycle consisting of three reciprocating scraping actions, and extending the discharge valve opening time from 6 seconds to 12 seconds to ensure sufficient time for the scraped impurities to be expelled. After these adjustments, the differential pressure remained stable below 0.04 MPa throughout operation.
The customer was particularly concerned about the effectiveness of CIP cleaning after daily production. During actual validation, after the equipment was shut down and drained, a 2% caustic soda solution was circulated for 30 minutes, followed by a 2% citric acid solution for 20 minutes, and finally rinsed with clean water until neutral. After the CIP program was completed, inspection of the disassembled screen surface revealed no residual tomato fibers or scale layers. The sandblasted internal surface of the housing remained smooth with no dead corners for material adhesion. The electric ball valve operated normally throughout the acid-alkaline alternating rinse process with no seal leakage.
One month into peak season production, our follow-up data collection showed that the filter's automatic cleaning success rate reached over 98%. Only twice did larger vine fragments from the upstream crusher cause temporary clogging at the discharge port, but the cylinder scraper action promptly cleared the blockage without causing production line shutdown. The cleaning frequency of downstream heat exchangers was extended from weekly to once every three weeks, demonstrating that the 18mm coarse filtration effectively intercepted the main large-particle impurities that damage heat exchangers.
The customer's production manager commented: "The most frustrating issue before was the vibrating screen clogging during night shifts with no one available to handle it promptly. Now this filter runs automatically, and workers only need to check the discharge residue and differential pressure gauge daily. Most importantly, it withstands our daily acid-alkaline cleaning – after all this use, there are no signs of corrosion on the housing, which is far more durable than the previous stainless steel screens."