Process intensification (PI) aims to dramatically improve manufacturing processes through the application of novel process systems and equipment. The novel approaches can be used to overcome bottlenecks, such as those imposed by thermodynamics, or to combine processing phenomena into fewer processing units with a concurrent reduction of capital and operation and maintenance costs and energy, water and materials intensity. PI approach goes beyond the incremental improvements achieved through optimizing existing equipment and process systems and achieves step changes in energy and materials efficiency, total life‐cycle cost reduction, and environmental impact by minimizing wastes at the sources via various hierarchy pollution prevention techniques (Bielenberg and Bryner 2018).
What Is PI?
PI is not well defined like many multidimensional concepts. Although PI may be best explained through examples, here are a few potential definitions to consider when thinking about PI (Bielenberg and Bryner 2018).
Well‐known experts in PI Stankiewicz and Moulijin (2000), both at Delft University of Technology, defined PI as the development of innovative apparatuses and technologies that bring dramatic improvements in chemical and allied manufacturing and processing, substantially reducing equipment volume, energy consumption, or waste minimization, less environmental and health impacts, and ultimately yields to cheaper, safer, sustainable technologies. They added four guiding principles to that definition (EFCE 2015):
- Maximize the effectiveness of intramolecular and intermolecular events
- Provide all molecules the same process experience
- Optimize driving forces at all scales and maximize the specific surface areas to which they apply
- Maximize synergistic effects from partial processes.
PI targets dramatic improvements in manufacturing and processing by rethinking existing operation schemes into ones that are both more precise and efficient than existing operations. There are a series of technologies that enable equipment sizes to be radically reduced. PI and microreaction technology, as well as reports of experimental results in the use of novel PI systems, including the static mixers, high‐gravity (HiGee) technology, cyclic and reactive distillation, compact high specific surface heat exchanger, multifunctional reactors, microchannel reaction systems, microengineering, microtechnology, the catalytic plate reactor, and a chemical microsystem for pervaporation. Such technologies enable to plant sizes to be correspondingly reduced. The very low inventories have environmental benefits and there are also claimed cost benefits (Reay et al. 2013). An incidental benefit is that the processes may be economic at a smaller scale (mostly batch processes), and that partly contributes to economic sustainability.
The European Roadmap on Process Intensification describes PI as providing “radically innovative principles (paradigm shift) in process and equipment design, which can benefit (often with more than a factor of two) process and chain efficiency, capital and operating expenses, quality, wastes, process safety, process integration and more” (EFCE 2015).
Reay et al. (2013) describe PI as a “chemical and process design approach that leads to substantially smaller, cleaner, safer, and more energy‐efficient process technology.” The common thread among these definitions is a focus on new schemes and equipment that create improved processes by combining, controlling, and/or enhancing the chemistry and transport phenomena in a chemical process.
A classic example of PI equipment is the static mixers. Although there are many different designs for static mixers, the basic concepts are the same. Stationary mixing elements placed in the path of fluid flow create locally highly mixed channels for the fluid to move through. Homogeneous mixing occurs quickly, with no external energy input other than that associated with the small pressure drop, at typically low capital costs. Static mixers can be incorporated into other unit operations (e.g. reactors) to enable the combination of processes and can be tailored to match mixing scales and times to optimize overall process efficiency. For example, static mixers can be placed in a tubular reactor for a two‐phase reaction system – creating a high level of mixing while maintaining a largely plug‐flow profile (typically found at a much smaller scale) at the larger reactor scale. Such an approach could offer many advantages over the alternative of operating a large continuous stirred‐tank reactor to maintain high levels of mixing.
There are many other examples of PI equipment, including microchannel reactors, spinning‐disc reactors, centrifugal contractors, and dividing‐wall column (Figure 9.11) to name a few. Each of these relies on a novel driving force (e.g. rotation) or nonstandard configuration (e.g. microchannels) to enable increased control over mixing, reaction, and heat, mass, and momentum transfer to bring about step changes in the reduction of energy consumption and capital costs.
The dividing‐wall column (Figure 9.11) is one form of process intensification that enables the separation of a three‐phase system in a single distillation tower. The internal wall splits the column into two halves. The three‐phase system is pumped into one side of the column and is reflected by the wall. The lightest component drops to the bottom and is withdrawn. The intermediate component is initially entrained in both streams; the intermediate component that flows upward subsequently separates and falls down on the opposite side of the wall, while the component that is entrained in the heavy component separates and flows up the back side of the column, where the entire intermediate stream is recovered through a side port.
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