Application challenges

Chemical industry

Basic chemicals plants are generally dominated by pumps; agitator applications can only be found in certain processes, such as HDPE (high-density polyethylene) manufacturing. The polymerization reactors used in this area are equipped with mechanical seals, as are often the centrifuges in which the HDPE is separated out downstream of the reaction. The shafts of the reactors and crystallizers used in PTA (purified terephthalic acid) production are also equipped with mechanical seals.

Fine chemicals plants generally contain discontinuous processes and many different machines and equipment and offer a wide range of possible applications for mechanical seals. Successive production steps, such as mixing, reacting and separating are typical here. The processed batches are often relatively small, while the processes are sophisticated and the products often very valuable. Flexible, multi-purpose plants, usually equipped with agitators, reactors, filters, dryers and other special equipment, are predominantly used.

The particular challenge for sealing technology arises from the different manufacturing processes and the crystallizing, paste-like, highly viscous or highly corrosive media under changing pressure and temperature conditions.

EagleBurgmann agitator seals have become the established standard in the chemical industry. They are robust and durable, significantly contributing to the plant availability.

Pharmaceutical and food industry

The pharmaceutical industry is a special area of the fine chemicals industry. In addition it requires machines, seals and supply systems which are easy to clean.

The sealing system is designed according to hygienic design rules. To achieve a hygienic design, consideration must be given to the design of the seal and installation space and to important criteria in the material selection. Parts of the seal in contact with the product must be suitable for CIP (Cleaning in Place) and SIP (Sterilization in Place). Other features of seals in this category are a minimum of dead spaces, open gaps, springs protected against the product and smooth, polished surfaces.

The materials of the sealing system must always fulfil the statutory requirements for the application. Physiological harmlessness along with chemical and mechanical resistance play a central role here. Naturally, the materials used must also not affect foodstuffs or pharmaceutical products in terms of odor, color or flavor.

EagleBurgmann uses high quality standard materials, such as silicon carbide (Q1) and food grade carbon graphite (B) as sliding materials, EPDM (E1), PTFE (T, T2), FFKM (KL) and silicone rubber (S1, S2) for the secondary seals and finally 1.4571 (316 Ti) (G), 1.4404 (316 L) (G), 1.4435 (316 L) (G) and 2.4610 (Hastelloy®-C4) (M) as construction materials.

EagleBurgmann has defined hygienic categories for mechanical seals and supply systems in order to simplify the selection of the right components for manufacturers and endusers. Hygienic requirements on the seal are linked to design features of the seal and supply system. The higher the class, the higher the requirements on materials, surface quality and secondary seals (with the corresponding consequences in terms of cost).

Steel and glass-lined vessels

The two categories of steel vessels and glass-lined vessels have a significant influence on the version of the mechanical seal. The EagleBurgmann mechanical seal series SeccoMix481 (dry-running), AGSZ481 (gas-lubricated) and M481 (liquid-lubricated) are designed for use on steel vessels. With the SeccoMix461, AGSZ461 and M461 series, the parts in contact with the product, such as the connecting flange, are glass-lined.

Vessels coated with enamel are catalytically inert. This means that they do not affect the product due to reactions with the vessel material. They are also highly resistant to chemicals and are easy to clean, which is why glass-lined devices are often used for applications with strict hygiene requirements.

Large shaft diameter, heated shafts, large axial movements

The trend is moving toward increasingly large plants and thus to larger machines and shaft diameters. In plants for manufacturing PTA (purified terephthalic acid), the standard shaft diameters for reactors and crystallizers are now 200 mm (7.87") or more. The largest shaft diameter to date for such a facility is now 480 mm (18.90").

The dimensions and weight of the corresponding mechanical seals of up to 1,500 kg sets new challenges for the seal and machine manufacturers and for the assembly team on site at the plant.

The difficulty with such large seals is to be able to control the deformation of the sliding seal parts and thus the gap geometry over the entire sliding face. This is a precondition for low and stable leakage and a minimal sliding face temperature, which has a decisive effect on the service life of the seal. To determine the optimum gap geometry, extensive calculations are carried out by our in-house experts which are then verified by means of test runs.

Heated shafts, as are often found in dryers or filter dryers, for example, are another challenge for the seal as they significantly increase the temperature at the seal. The right selection of design and sliding materials, the elastomers and the bearings and bearing grease are particularly important for guaranteeing the seal functionality.

Not least it is essential to control large axial shaft deflections of the type that occur due to thermal expansion in paddle dryers with bearings on both sides or due to active lifting movements in the case of nutsche filters.

EagleBurgmann has considerable experience in the sealing of technically challenging parameters and implements innovative and safe sealing solutions in close collaboration with manufacturers and endusers.

ATEX conformity

Solvents and other explosive substances are used in many process steps with the result that a potentially explosive atmosphere can arise. In these cases, the seals must meet the requirements of the ATEX directive (2014/34/EU). The agitator seal is generally treated as an equipment, rather than a machine component, so a separate ATEX certificate of conformity must be issued for it.

We have therefore carried out EU type examination on our standard series for agitators and special machinery and are able to issue a declaration of conformity for them. Individual acceptance tests can also be carried out for engineered seals. In this case, the seal is tested for its temperature behaviour on a test rig. EagleBurgmann is qualified by the TÜV to independently carry out its own type examinations and individual acceptance tests.