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A pilot plant is a small industrial system which is operated to generate information about the behavior of the system for use in design of larger facilities. Pilot plant is a relative term in the sense that plants are typically smaller than full-scale production plants, but are built in a range of sizes. Some pilot plants are built in laboratories using stock lab equipment, while others are constructed of fabricated metal on dedicated concrete slabs and cost millions of dollars. They can also be used to train personnel for a full-scale plant.
Pilot plants are used to reduce the risk associated with construction of large process plants. They do so in several ways:
- Computer simulations and semi-empirical methods are used to determine the limitations of the pilot scale system. These mathematical models are then tested in a physical pilot-scale plant. Various modeling methods are used for scale-up. These methods include:
- Chemical similitude studies
- Mathematical modeling
- Aspen/Hysys modeling
- Finite Elemental Analysis (FEA)
- Computational Fluid Dynamics (CFD)
- They are substantially less expensive to build than full-scale plants. The business does not put as much capital at risk on a project that may be inefficient or unfeasible. Further, design changes can be made more cheaply at the pilot scale and kinks in the process can be worked out before the large plant is constructed.
- They provide valuable data for design of the full-scale plant. Scientific data about reactions, material properties, corrosiveness, for instance, may be available, but it is difficult to predict the behavior of a process of any complexity. Engineering data from other process may be available, but this data can not always be clearly applied to the process of interest. Designers use data from the pilot plant to refine their design of the production scale facility.
If a system is well defined and the engineering parameters are known, pilot plants are not used. For instance, a business that wants to expand production capacity by building a new plant that does the same thing as an existing plant may choose to not use a pilot plant.
Additionally, advances in process simulation on computers have increased the confidence of process designers and reduced the need for pilot plants. However, they are still used as even state-of-the-art simulation cannot accurately predict the behavior of complex systems.
As a system increases in size, system properties that depend on quantity of matter (with extensive properties) might change. The chemical and physical properties of a system affect each other and create varying results. The surface area to liquid ratio is a good example of such a property. On a small chemical scale, in a flask, say, there is a relatively large surface area to liquid ratio. If however you scale the reaction in question up to fit in a 500 gallon tank, the surface area to liquid ratio is becomes much smaller. As a result of this difference in surface area to liquid ratio, the exact nature of the thermodynamics and the reaction kinetics of the process changes in a non-linear fashion. This is why a reaction in a beaker can behave vastly differently from the same reaction in a large scale production process.
Other factors that change during the transformation to a production scale include:
- Reaction kinetics
- Chemical equilibrium
- Material properties
- Fluid dynamics
- Equipment selection
After data is collected from operation of a pilot plant, a larger production scale facility may be built. Alternatively, a demonstration plant, which is bigger than a pilot plant, but smaller than the full-scale production plant, may be built to demonstrate the commercial feasibility of the process. Businesses sometimes continue to operate the pilot plant in order to test ideas for new products, new feedstocks, or different operating conditions. Alternatively, they may be operated as production facilities, augmenting production from the main plant.
Recent trends try to keep the size of the plant a small as possible to save costs. This approach is called miniplant technology. The flow chemistry takes up this trend and uses flow miniplant technology for small scale manufacturing.
Bench scale vs pilot vs demonstration
The differences between bench scale, pilot scale and demonstration scale are strongly influenced by industry and application. Some industries use pilot plant and demonstration plant interchangeably. Some pilot plants are built as portable modules that can easily transported as a contained unit.
For batch processes, in the pharmaceutical industry for example, bench scale is typically conducted on samples 1–20 kg or less, whereas pilot scale testing is performed with samples of 20–100 kg. Demonstration scale is essentially operating the equipment at full commercial feed rates over extended time periods to prove operational stability.
For continuous processes, in the petroleum industry for example, bench scale systems are typically microreactor or CSTR systems with less than 1000 cc of catalyst, studying reactions and/or separations on a once-through basis. Pilot plants will typically have reactors with catalyst volume between 1 and 100 litres, and will often incorporate product separation and gas/liquid recycle with the goal of closing the mass balance. Demonstration plants, also referred to as semi-works plants, will study the viability of the process on a pre-commercial scale, with typical catalyst volumes in the 100 - 1000 litre range. The design of a demonstration scale plant for a continuous process will closely resemble that of the anticipated future commercial plant, albeit at a much lower throughput, and its goal is to study catalyst performance and operating lifetime over an extended period, while generating significant quantities of product for market testing.
In the development of new processes, the design and operation of the pilot and demonstration plant will often run in parallel with the design of the future commercial plant, and the results from pilot testing programs are key to optimizing the commercial plant flowsheet. It is common in cases where process technology has been successfully implemented that the savings at the commercial scale resulting from pilot testing will significantly outweigh the cost of the pilot plant itself.
- M. Levin (Editor), Pharmaceutical Process Scale-Up (Drugs and the Pharmaceutical), Informa Healthcare, 3rd edition, ISBN 978-1616310011 (2011)
- M. Lackner (Editor), Scale-up in Combustion, ProcessEng Engineering GmbH, Wien, ISBN 978-3-902655-04-2 (2009).
- M. Zlokarnik, Scale-up in Chemical Engineering, Wiley-VCH Verlag GmbH & Co. KGaA, 2nd edition, ISBN 978-3527314218 (2006).