Dry running vacuum technology for phenolic resin production

Maulburg - Dynea Erkner GmbH produces phenolic resins for further processing in many areas of the industry. The chemical reactions take place in reaction facilities of different sizes as well as different temperatures and pressure ratios. In recent years, the traditionally run company has made huge investments in its production, which is based in the town of Erkner, just outside Berlin. Dynea Erkner can now proudly present itself as a modern and innovative company. The vacuum supply to the reactors has also been redesigned and the vacuum for 16 reactors is now supplied by the latest generation of a dry running vacuum system from Dr.-Ing. K. Busch GmbH.
Vacuum system for vacuum supply during phenolic resin production.
Vacuum system for vacuum supply during phenolic resin production.

Phenolic resin production has been taking place in Erkner since as far back as 1909, when the products were sold under the name "Bakelite". Following a long and varied history, with a number of different owners, the production plant in Erkner was finally taken over by the Dynea Group in 2002 and now operates under the name Dynea Erkner GmbH. As part of a three-shift operation, 115 people are now employed in the production of phenolic resin, which is used as a binding agent with grinding disks, non-woven fabrics, filter papers and fire-resistant applications. Phenolic resins are also used for producing mineral wool and rock wool, decorative laminates and derived timber products.

In 16 reactors measuring 4 to 32 cubic metres, approx. 150 different types of phenolic resin are manufactured in non-continuous operation. The batch run time is between 8 and 60 hours and the reaction takes place exothermically, with water as a by-product. In order to achieve different reaction temperatures, the boiling point of the reaction mixture is lowered using vacuum. Thanks to the lowered boiling point, the water can be expelled from the reaction mixture at temperatures of 40°C to 60°C during vacuum distillation.
Due to the large number of products with diverse parameters for processes and raw materials, and also due to the different sizes of the reactors, the demand for vacuum is highly variable. In order to capture peaks in consumption, four buffer tanks, each with a volume of 43.5 cubic metres, are used between the reactors and the vacuum system .
The central vacuum system is in use six days a week, around the clock. The operating pressure in the complete vacuum system is permanently between 50 and 60 mbar.

The vacuum supply was previously maintained by two rotary vane vacuum pumps lubricated with fresh oil, each with a pumping speed of 1000 cubic metres per hour. A Roots vacuum pump with a pumping speed of 2000 cubic metres per hour was also installed upstream of each of these pumps to provide an additional boost. This pump setup was not satisfactory for ensuring trouble-free production, as the rotary vane vacuum pumps often failed and the outlay for maintenance and repair was high. This meant that an identical, third vacuum unit had to be kept available and ready for operation as a reserve pumping station at all times. These failures were caused by phenolic and formaldehyde vapours also being sucked in, and then condensing and reacting with each other in the compression chamber. This resulted in particles and specks of phenolic resin forming in the vacuum pump. These could only partially be washed out via the fresh oil lubrication and they stuck to the compression chamber of the rotary vane vacuum pump, ultimately resulting in a shut-down period. In principle the same reaction process ran inside the vacuum pump as in the reactor. Problems were also caused by the filters installed downstream of the rotary vane vacuum pumps, which served to extract the oil sprayed on as lubrication. The fluid created due to the oil bonding with the phenolic and formaldehyde vapours completely clogged the filter elements. This meant that the filter elements had to be replaced at very short intervals of just one to two weeks.

In January 2011, the old pumping unit at Dynea Erkner, with its rotary vane vacuum pump lubricated with fresh oil and Roots vacuum pump, was replaced with a vacuum system from Busch. The new system consists of two COBRA screw vacuum pumps each with a pumping speed of 400 cubic metres per hour and a Panda Roots vacuum pump with a pumping speed of 2000 cubic metres per hour. The control system for the vacuum system is designed in such a way that the same speed as before is achieved with vacuum pumps that are much larger but with smaller aggregates, which results in huge energy savings. The previous pumping station had a connection power of 41 kW. The new vacuum system from Busch runs with just 27.5 kW, which represents a reduction of over 30 percent. This pumping station is completely dry running, which means that no oil is required in the compression chambers. As a result, a downstream oil separator is no longer required and nor are the costs for the oil and the removal of the old oil and clogged filters.
The system conforms to ATEX (Ex II 2G IIB T3). The inside is defined as zone 1; no zone is defined for the outside, around the vacuum pump. However, the process is only relevant to ATEX during the starting-up phase, because solvent vapours could be present in the system. In any case, the system makes itself inert during the start-up, after which there is no longer any risk of explosion.

According to Dynea Erkner, since it was commissioned more than two years ago the vacuum system has been operating fault-free and with very little maintenance required. In a statement the company claims: "So far we have been really satisfied". The vacuum system is maintained and checked over by Busch once a year. Oil changes in the vacuum pump gear units are carried out by in-house employees.

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