Glass-lined reactors and their components have been geometrically defined in technical standards (mainly DIN and DIN EN standards) for many decades. For example, the main dimensions of glass-lined reactors in the volume range from 63 to 40,000 l are defined in DIN 28136-1. The nozzle patterns for the corresponding apparatus sizes can be found in DIN 28136-3. Further standards defining the geometry of glass-lined components are listed in Figure 1 below.

In the 80's of the last century, a manufacturer-independent standardization was promoted in the former Federal Republic of Germany, in particular by the then large chemical industry, in order to establish the interchangeability and the manufacturer-independent comparability of different offers.

In addition, a large number of quality and tolerance standards were developed, enabling quality requirements to be effectively and unambiguously agreed between customer and manufacturer.

In the meantime, the basic features of many German standards have also been adopted in standards bodies of other countries or standardized at European level. In other countries, the direct use of DIN standards has become established.

THALETEC has been working in the standardization committees of DIN for many years in order to incorporate its own know-how and expertise into the standardization work.

Standards and manufacturer-independent norms ensure the long-term interchangeability of existing equipment with new equipment in the field of glass lined apparatus. Furthermore, manufacturer-neutral standardization can ensure that new spare parts for existing apparatus are guaranteed to "fit".

On the other hand, strict compliance with standard specifications also has disadvantages:

• Standardized components and equipment do not always meet the requirements of special applications, such as the manufacture of active pharmaceutical ingredients. GMP and purification requirements are difficult or impossible to achieve with DIN containers.
• The "environment", i.e. the installation situation and the connection points to standardized enameled equipment, must be adapted, which can often lead to suboptimal solutions, complex piping, cleaning problems, etc.
• Often the installation situation in the process plant requires an adaptation of the apparatus and thus a deviation from the standard specifications.
• Optimization of the process is only possible within narrow limits.

Analyzing THALETEC's customer orders of the past years, it can be stated with regard to "compliance with standards" that the most frequent modifications to glass lined stirred vessels concern the following areas:

• Design pressure in the glass lined inner vessel and/or in the shell chamber.
• design temperature
• the nozzle pattern of the glass lined inner vessel: size, number and position of nozzles at the top bottom, including the size of the manhole opening
• main dimensions, especially the length of the apparatus
• additional (off-center) nozzles at the bottom of the vessel
• additional nozzles in the jacket area of the stirred tank
• the position and number of the shell nozzles
• the supporting structure

Design pressure and/or temperature

Common "standardized" glass lined stirred vessels are designed for pressures of -1/+6 bar in the inner vessel and in the outer shell area for a temperature range of -60°C to +200°C and the wall thicknesses are dimensioned and standardized accordingly.

In some cases, customers deliberately deviate from the "usual" design conditions, with deviations relating to the design temperatures occurring more frequently than those relating to the pressure range.

Increasing the design pressure

Increasing the design pressure of the equipment (inner vessel and outer shell) results in an increase in the wall thicknesses of the pressure-bearing components. As an example, consider a calculation for a BE 6300 vessel to DIN 28136. If the permissible operating pressure of the apparatus is increased to values above 6 bar, the increases in the wall thicknesses of the inner vessel (IK) and outer jacket (AM) shown in Figure 4 result:

Figure 5 shows, as an example for a BE 6300 reactor to DIN 28136, the increase in the wall thicknesses of the inner vessel and outer jacket when the design temperature is increased from 200°C to up to 300°C. Since the yield strength of the equipment’s material decreases with increasing temperatures, the wall thickness of the reactor (outer jacket) increases by up to 15% (at a design temperature of 300° compared with 200°C).

If not only the design temperature but also the actual operating temperature is to be higher than 200°C, further measures are required.

Effect on supporting structure and costs

All the above-mentioned modifying measures, such as increasing the pressure, lengthening the apparatus and increasing the design temperature, lead to an increase in wall thickness and thus to an increase in the weight of the equipment. Lengthening the reactor body also leads to a larger possible filling volume and thus also to an increase in weight. The increase in weight is essentially linear with the wall thicknesses and also linear with the reactor’s volume. The higher weight must be taken into account in the dimensioning of the supporting structure and may also lead to reinforced designs.

The above-mentioned modifying measures also have an influence on the cost of the reactor. The costs increase essentially linearly with the wall thickness of the tank (material input). Further non-linear influences result from the additional engineering effort, adaptation of the supporting structure as well as any necessary modifications and adaptation of the installation parts (agitator, baffle, etc.).

Side nozzles are very rarely used. The reason for this is that such nozzles, if they are located in the jacketed area of the glass lined vessel, have to be routed through the jacket space at great expense. Corresponding recessed areas reduce the heating/cooling surface of the reactor. Finally, lateral nozzles in the glass lined inner vessel also influence the flow profile of the heating/cooling media in the shell space and change the flow pattern, despite the use of flow nozzles (Flyer K062).

However, lateral nozzles at the rim of the upper bottom can be useful when stirred vessels are used in cascades and the lateral nozzle serves as an "overflow".

The DIN 28136 standard specifies the main dimensions (diameter as well as length of the glass lined reactors) for agitated reactors. In some cases, the customer wishes to deviate from these specifications. The diameter of the vessel is usually not changed, but in many cases the length of the reactor is. By increasing/decreasing the length, the useful volume of the apparatus can be adapted within certain limits without requiring major changes to the plant or infrastructure.

If a reactor is to be lengthened compared to the specifications of the standard, this usually leads to a new calculation of the wall thicknesses of the tank frame (this is the cylindrical area of the stirred tank) and the wall thickness of the shell in the case of jacketed reators.

Furthermore, the agitator and the built-in parts, such as the baffles, must be checked with regard to mechanical strength and vibration behavior: Lengthening a stirrer shaft reduces the critical speed of the stirrer, at which potentially dangerous oscillations of the stirrer shaft can occur. In the case of the baffle, the applied loads increase proportionally to the length and cause a higher bending moment at the nozzle flange. In addition, the critical excitation frequencies due to vortex formation must also be considered for the baffle.

Further modifications

The modifications described so far mainly concern the so-called "inner keel" of the glass lined stirred tank. If such modifications or adaptations are necessary, they must be specified at a very early stage during order processing, ideally already when the order is placed, since the glass lined inner vessel is the component that determines the delivery time. Adaptations in the areas of

• supporting structure
• shell nozzle

Can often be defined or adapted later in the manufacturing process.

Support structure

Supporting structures are defined in several standards, depending on the design:

• Support brackets in DIN 28145-7
• Support rings in DIN 28145-4
• Feet in DIN 28145-4

In practice, however, it is the case that the reactor must be integrated into existing installations. In order to avoid structural measures in the plant, it is advisable to adapt the supporting structure of the container to the surroundings.

As described above, the support structure must also be adapted if the weight of the apparatus increases as a result of changes in operating pressure, calculation or operating temperature, or the length of the apparatus.

Jacket nozzles

The type, number and position of the shell nozzles of glass-lined apparatus are specified in DIN 28151 and depend, among other things, on the size of the reactor and the supporting structure. Here, too, it is easy to make adjustments or deviating specifications during order processing, which are then taken into account in the manufacture of the equipment.

Conclusions

Modification, i.e. targeted deviation from the specifications of the standard designs of glass lined reactors, can be useful in many cases. However, there are a number of things to consider when making modifications, which makes competent advice from a specialist company such as THALETEC highly recommendable. However, if all aspects are analyzed systematically and implemented accordingly, the customer receives a reactor that "fits like a glove".