March 14, 2019

Candle filters for use in Russia’s gold mining industry

A BHS service engineer inspects the two simultaneously operated tube sheet candle filters in Amursk, Russia.

International renown for filtration expertise pays off: Process Plants International, an Australian company, recommended BHS-Sonthofen candle filters to a gold processing plant in Amursk, Russia. Two large filters for removing foreign particles from the condensate stream in pressure oxidation reactors were delivered at the end of April. They do not simply replace the previously used technology, but also optimize it.

Process Plants International (PPI) is an Australian consulting firm that specializes in optimizing, commissioning and maintaining plants in the mining and raw materials processing sector. Its Russian customer, Polymetal International, needed support in order to expand the capacities of its gold processing plant in Amursk. Pressure oxidization reactors with a closed water circulation system are used in one process step of gold extraction. Foreign particles must be continuously removed from the condensate coming from the flash tank to prevent clogging and wear. This is where Process Plants International came to rely on the expertise of BHS-Sonthofen.

Previous process using sedimentation tanks was not ideal

The Russian company previously used sedimentation tanks to remove sulfide dust, mineral ores and other undesirable particles from the condensate. The condensate was pumped into the tank and remained there for some time, allowing for undesirable foreign particles to sink to the bottom. However, a certain amount of particles would still end up back in the water circulation system due to the particles' small size and slow sinking behavior. This resulted in foreign particles causing increased wear to delicate system components such as heat exchangers.

PPI decided to test out an alternative process within the framework of the company's planned capacity expansion of the plant. The first pilot tests showed positive results. PPI opted for BHS-Sonthofen, an expert with over 60 years of experience in solid-liquid filtration. "Using the data we had collated from the preliminary tests, we were able to suggest a filter combination that impressed the customer," says Christian Gassen, Area Sales Manager in the Filtration Technology division at BHS-Sonthofen, summarizing the first stage of the collaborative project with PPI.

Candle filter system ensures a high degree of purity at low cost

BHS-Sonthofen decided on two simultaneously operated tube sheet candle filters to replace the sedimentation tanks. These remove almost all foreign particles from the condensate and therefore ensure a clear filtrate and less wear. The tube sheet design is usually used for applications where the filter cake comprises sludge discharge as was the case with the Russian customer. It offers the advantage of a simpler candle filter design, with only one filtrate outlet resp. a single filtrate valve and fewer fittings. For the customer this means a system with fewer fragile components as well as a less effort for automation and maintenance work. This, in turn, improves the overall process reliability. The pre-existing filter presses downstream of the BHS candle filters produce a solid filter cake for easy disposal.

The challenges in implementing this project included the high flow of approximately 400 cubic meters of water per hour and the objective of achieving a clear filtrate, as well as the highly corrosive properties of the condensate stream. This combination of factors called for durable, high-quality candle filters. "The super duplex steel built into the filters is corrosion resistant to the highest degree, but it is also difficult to process," Gassen explains. "Large metal plates are needed for a tube sheet design with a filter surface of 110 m² per filter. Given the chosen steel quality, this posed a challenge to the engineers and steel workers. That's why we're all the more satisfied with the result."

Successful international cooperation

BHS worked in close cooperation with PPI in both designing and manufacturing the filters. BHS was commissioned to produce the candle filters, including the necessary internal piping and instrumentation, but not the steel structure. The final assembly will be carried out on site in Russia with local partners. BHS-Sonthofen did not merely rely on preliminary tests when drawing up the filters' dimensions. A small pilot test system was installed in Amursk to test previously selected filter cloths in real working conditions. The tests were supervised by BHS employees and Australian employees from PPI in early 2018. They confirmed the proper design and choice of components.

PPI also performed the project acceptance in Germany and will be responsible for accompanying the candle filters to their final destination. The experts at BHS were invited to a meeting in Australia to ensure that commissioning in Russia will go as smoothly as possible. All questions related to the operation and safety of the system in particular were discussed in great detail and documented for the end customer. Gassen is very pleased with how the project has gone so far: "When you think about the fact that people from three different continents worked together on this plant, the positive results underscore the high degree of professionalism across the board."

The two BHS candle filters have a water throughput of 400 cubic meters per hour.

Filtration technology from BHS-Sonthofen was used at the capacity expansion of a goldprocessing plant, operated by Polymetals Intl. in Amursk.

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