Process Intensification: Transforming Chemical Engineering

Process Intensification:

Process Intensification (PI) has been defined as “a philosophy of plant design and construction whereby a given performance is achieved in very much smaller equipment - typically with a volume reduction of two or three orders of magnitude” [2]. These reductions in size can come from using smaller individual pieces of equipment or by cutting the number of unit operations or pieces of equipment used in the process. A volume reduction of a factor of two or more (not necessarily two orders of magnitude) was considered by [3] to be drastic enough to be labelled PI and this work broadened the definition of PI to include a dramatic increase in production capacity within a given volume, a significant decrease in energy consumption per ton of product, or large decreases in waste or by-product formation.

The concept of Process Intensification (PI) was developed within ICI in the late 1970’s when Colin Ramshaw began to look into various ways of reducing the size of parts of a plant. The desire for a reduction in size came from the realization that main plant items only represent approximately 20% of the cost of a production system. Items, which are essential in conventional plants, such as pipework, supporting structures and civil engineering work contribute substantially to the cost of a plant. If plant items are made smaller it is possible that they can be assembled more closely - reducing the pipework costs. In addition, costs should be reduced because smaller, lighter equipment needs less civil engineering and structural steel work. The offshore oil industry is one area where the advantages of process intensification are relevant. Lightness and compactness are important on rigs, which have weight and space limits.

The field of PI was divided into two areas by [3]: equipment and methods (shown in Figure 1) although there can be some overlap between the two areas. PI equipment either makes one operation more efficient (in terms of size as well as energy) or combines reaction with other operations. The combination of reaction with other operations can be used to improve the level of control of the reaction outcome that is possible. For example, combining reaction and heat transfer in a Heat Exchange Reactor means that heat addition or removal can be done as needed and reaction temperature can be controlled. PI methods are more efficient ways of processing. They involve the combination of reaction with another operation (such as separation of product), the combination of more than one type of separation technique, the use of alternative energy sources (such as the use of ultrasound to supply energy needed to drive a reaction), or fit into the miscellaneous category (such as the use of periodic operation of reactors to improve product yield or selectivity). 

It was suggested by [4] that in order to make a significant impact on the system, all plant items must be intensified. However [5] suggested that significant improvements in process performance can be made by adding PI equipment at strategic points in existing processes and gave the following example. A polystyrene plant in Japan achieved isothermal reaction conditions by adding an external loop to a stirred tank reactor. The loop contained a series of heat exchangers with static mixers within them. The result of the enhanced mixing and heat transfer was a 40% reduction in energy consumption compared with the conventional process. In addition, the right fluid environment was provided to give a product with a tighter molar-mass distribution.

A further example was also given by [5]. Dow Corning used partial application of PI principles and technologies to increase productivity of a process in which a key intermediate is produced in a gas-liquid reaction (carried out in a packed column). Poor gas dispersion was causing hot spots and by-product formation. The by-product reduced the catalyst performance and led to shut downs every two to three weeks and limited the productivity of the whole plant. A static mixer was introduced upstream 6 and injection arrangements were changed leading to better gas dispersion. As a result, by-product formation was completely eliminated and productivity was increased by 42%. 

Advantages of Process Intensification :

Although [1] named the reduction of the cost of a production system as the primary incentive for PI there are other advantages. They are:

• Improved safety
• more efficient use of raw materials
• reduced energy consumption
• improved product quality
• greater reliability
• reduced waste
• easier scale-up
• distributed plants

These advantages will now be discussed separately in the next post.

References:

1. Gerberich, H. R., “Formaldehyde” in Encyclopaedia of Chemical Technology, volume 11, Kroschwitz, J. I., New York, John Wiley and Sons, 1994, 929 - 951. 
2. Ramshaw, C., “Process Intensification: a game for n players” The Chemical Engineer, volume 416, 30 – 33, 1985.
3. Stankiewicz, A. I. and Moulijn J. A., “Process Intensification: Transforming Chemical Engineering”, Chemical Engineering Progress, volume 96(1), 22 – 34, 2000. 
4. Cross, W. T. and Ramshaw, C., “Process Intensification: Laminar Flow Heat Transfer”, Chemical Engineering Research and Design, volume 64(4), 293 – 301, 1986
5. Green, A., Johnson, B. and Arwyn, J., “Process Intensification Magnifies Profits”, Chemical Engineering, volume 106(13), 66 -73, 1999.