Scale-up and trial management at an industrial pilot plant

Yes, Germany has a well-developed landscape of pilot plants and pilot facilities that can be used specifically for scale-up trials, process development and process validation. These facilities close the critical gap between laboratory trials at gramme to kilogramme scale and industrial production at tonne scale. They are operated by specialised engineering service providers, plant builders and machine manufacturers as well as by manufacturer-independent research institutions and universities.

Regional focal points lie, among others, in chemistry-oriented regions (e.g. Rhine-Main, Rhine-Ruhr, central Germany) as well as in Bavaria and Baden-Württemberg. Many providers work under strict confidentiality (NDA) and supply product-specific trial reports including measured data and design recommendations.

Typical objectives of scale-up trials at the pilot plant

The central aim of pilot-plant operation is to minimise technological and financial risk when scaling up from the laboratory to the production plant. At the pilot plant:

• process engineering trials are carried out at scales typically between 1:10 and 1:100 of the later production plant
• process characterisation is undertaken under conditions close to production (temperature, pressure, throughput)
• material tests are carried out on relevant product quantities for statistical assurance
• design parameters such as specific energy input, residence time and heat and mass transfer coefficients are determined
• formulations are adapted to industrial process conditions

The focus is on validating the data determined at laboratory scale under realistic conditions, since geometric similarity alone is usually not sufficient to ensure identical process behaviour at a large scale.

Methodological principles of scale transfer

Technical scaling is essentially based on similarity theory and dimensional analysis. Correlations are developed using dimensionless characteristic numbers and then verified at the pilot plant, for example:

• the Reynolds number for flow and mixing behaviour
• the Nusselt number for heat transfer
• the Damköhler and Froude numbers for the ratio of reaction kinetics to transport or movement processes
• further scale-up characteristic numbers for assessing dynamic and thermal similarity

The Froude number relates to rotating free-fall, drum and throw mixers as well as to systems with a horizontally mounted mixing tool. In vertical mixers with forced restratification it is not a design or scale-up criterion. What is decisive there is that the mixing principle remains the same across all sizes and that the restratification covers the entire mixing chamber independently of the fill level; transferability is secured in the pilot plant with the original product.

At the pilot plant it is determined experimentally which of these characteristic numbers are limiting for the specific process. On this basis, scale-up factors for the industrial plant are defined and potential transfer risks identified.

Typical technical equipment at German pilot-plant sites

Pilot-plant systems are generally of modular construction in order to represent different unit operations and process steps flexibly. Typical plant types and equipment include:

Reactor systems

• batch and continuous reactors, including under pressure and inert gas
• variable agitator geometries, temperature control and cooling concepts

Mixing and processing technology

• mixing and agitator systems (continuous and batchwise)
• extrusion and compounding plants

Size reduction and classifying technology

• mills, classifiers, screening machines

Drying and forming units

• spray, fluidised bed and contact dryers
• granulating and compacting plants

Downstream processing / separation technology

• filtration, centrifugation and membrane systems
• rectification columns and further thermal separation processes

Analysis and process monitoring

• online process analytical technology (PAT) for real-time monitoring of concentrations, particle size distributions, viscosities and so on
• laboratory analysis for quality control and product characterisation

Infrastructure and safety

• supply of technical gases, vacuum, steam and process media
• design to relevant safety standards (e.g. ATEX zones for flammable media)
• compliance with European and national standards and directives (e.g. the Machinery Directive, the Pressure Equipment Directive, the German Federal Water Act)

Advantages of a local pilot-plant site in Germany

A pilot-plant site in Germany offers the manufacturing and process industry several advantages:

• logistical proximity to the company's own works and to supply chains, with reduced transport and coordination effort
• direct involvement of internal engineering teams in planning, trial management and evaluation, which markedly shortens iteration cycles between calculation, trial and optimisation
• documentation and trial execution in conformity with European rules, which facilitates the transfer of the results into plant concepts capable of approval within the European Economic Area
• confidentiality and IP protection through cooperation governed by NDA and detailed, project-specific trial reports

Recommended approach for a successful scale-up at the pilot plant

A structured preparation is advisable before the pilot-plant trials begin:

• definition of the target variables and quality criteria of the end product
• specification of the starting materials and assessment of their batch consistency
• description of the boundary conditions of the later production plant, e.g. capacity, energy and media supply, safety requirements
• selection of the relevant measured variables for balancing and process monitoring (mass and energy balances, critical process parameters)
• definition of scale-up criteria (geometric, dynamic and thermal similarity)

Systematic trial planning, for example according to the principle of design of experiments (DoE), increases the informative value of the results and reduces the number of trials required.