Process Intensification (PI) is a topic receiving considerable attention recently. Using the simple definition of Stankiewicz and Moulijn (2000), PI is ‘Any chemical engineering development that leads to a substantially smaller, cleaner, safer, and more energy efficient technology.’ The improvement is expected to be substantial (tens to hundreds of percent), as the benefits from the effort are expected to be game changing. With that level of improvement, it is understandable why groups in the Americas, Asia, and Europe are advocating its use.
According to Stankiewicz and Moulijn (2000), PI can be divided into two areas:
- Process Intensifying equipment, which are special designs that optimize critical parameters (e.g., heat transfer, mass transfer), and
- Process Intensifying methods, where multiple processing steps are integrated into a single unit operation or alternative energy sources are used.
These are broad categories and overlap between the two areas is common.
Reactive distillation is one of the oldest and most widely implemented intensified operations. The unit combines a chemical reactor and a distillation column into a single unit (see Figure 1). Over 150 reactive distillation units are operating at commercial scale in the petrochemical industry, most of which have been constructed in the last 30 years. Applications have included production of MTBE, acetates (methyl, ethyl, and butyl), hydrolysis reactions, methylal synthesis, and many others. The intensification effort in the case of reactive distillation leads to a 20-80% reduction in capital costs and/or energy usage (Harmsen, 2010).
Another example would be a static mixer. The static mixer is a significant improvement over mechanical agitation due to its lower energy costs and uncomplicated design with no moving parts. Other important examples include monolithic reactors, compact/microchannel process units, divided wall column (DWC) distillation, ultrasonic and microwave units, and reverse flow reactors. These designs can lead to significant improvements in capital costs, energy usage, and process footprint.
PI has the potential of reducing energy usage, lowering equipment costs, and shrinking the required footprint of a given production facility. However, it must be recognized that significant effort is required to implement the PI methodology and validate the use of new technologies. Zanfir (2014) suggests the following steps to successfully manage a PI process:
- Identify business and process drivers
- Overview the entire process
- Identify rate-limiting steps
- Generate design concepts
- Analyze design alternatives
- Select equipment
- Compare PI solutions vs conventional equipment in a holistic manner
- Make decision on implementation
The above steps require skilled process engineers to achieve best results. This work will require literature reviews, technology evaluations, generation of heat and material balances and process flow diagrams, and cost estimating.
Once the PI study is completed, it needs to be recognized that the intensified process may operate differently from operation with conventional equipment. Equipment at both the bench and pilot scale are required to determine optimal process conditions and help with later scale-up of the intensified process. Due to the nature of PI systems, the fabricator needs to be highly experienced to build reliable test units using non-conventional technologies.
While a PI system requires more upfront effort than ‘off the shelf’ approaches, the long-term benefits in costs and efficiencies can more than offset this.
Patrick C. Joyce, Ph.D. Senior Process Engineer at Process Engineering Associates
Process Engineering Associates (PEA) is a chemical engineering company that provides design, applied chemical engineering and process safety services. EPIC and PEA work together to fully vet, design, build and install custom process systems that move industry forward, using proven methods and a turnkey approach. To find out more about either company and the services they provide, visit www.processengr.com, visit EPIC’s process intensification page or contact EPIC.
- D.K. Babi, M.S. Cruz, and R. Gani, Fundamentals of Process Intensification: A Process Systems Engineering View. Chapter 2 in Process Intensification in Chemical Engineering Design, Optimization, and Control (2016)
- Becht, R. Franke, A. Geißelmann, H. Hahn, An industrial view of process intensification, Chem. Eng. Process. 48 (2009) 329
- G.J. Harmsen, Reactive distillation: The front-runner of industrial process intensification. A full review of commercial applications, research, scale-up, design and operation. Chem. Eng. Process. 46 (2007) 774
- Harmsen, Process intensification in the petrochemicals industry: Drivers and hurdles for commercial implementation, Chem. Eng. Process. 49 (2010) 70
- A.J. Stankiewicz and J.A. Moulijn, Process Intensification: Transforming Chemical Engineering. Chem. Eng. Prog. 96 (2000) 22
- Zanfir, Process Intensification, Presentation at the NSF Process Intensification Workshop in Washington, DC (2014).