Page 237 - Process Equipment and Plant Design Principles and Practices by Subhabrata Ray Gargi Das

236 Chapter 8 Interphase mass transfer

In most real life situations, the problem posed is usually ill defined, with incomplete information
that the designer fills in through discussions with the client, his own experience, and literature
survey. Experience of the designer is an invaluable component that helps to quickly conceive the
initial system configuration. This step is primarily based on heuristics. Technical information gaps
are filled later.
Complete Design Solution: A complete design solution to the problem comprises of the specifi-
cation of the system, process design of equipment with their details and the hydraulics of the complete
plant. It should also contain the instrumentation and control scheme, as well as settings for any safety
device (say, pressure safety valve)/arrangements for trips/interlocks.
Execution of the following steps leads to the final design:

• Configuring the overall system. This includes the contactor and the arrangement of the auxiliary
equipment/facilities, such as solvent regeneration in the case of absorption and adsorption, etc.
• Selection of appropriate contacting equipment among the available options and performing the
process design calculations that generate the information to estimate the cost.
• Deciding the economically optimum design choice. Minimizing only the cost of the separation
equipment may increase the cost of the rest of the system, and hence, the complete system,
including accessories/auxiliary system is optimized. This is illustrated in the optimum design of
distillation column.
• Working out the mechanical details to generate the complete specifications and fabrication
drawings.
• Detailing the plant hydraulics

8.3 Process design and detailed design of the equipment
Once a contacting equipment type for a mass transfer process is chosen, its detailed design depends on
the properties of the phases, their flow rates and process conditions. The detailed design of the con-
tacting equipment can then be carried out independently. An example of this is in the design of the
tower internals; the tray design is carried out in the same way irrespective of the process being ab-
sorption or stripping or distillation. However, in order to optimize the process, while carrying out the
process design, some shortcut/quick estimation of the equipment parameters are done to estimate their
costs.
Designs dealt in this section of the book covers the process aspects of mass transfer equipment with
the deliverables primarily being the height and diameter of the tower. The details of packed and tray
towers for contacting the phases are dealt separately in Chapter 14 entitled Column and Column
Internals.
Since the process designs, in this section, pivot around phase equilibria, the same is briefly covered
in Chapter 9. Subsequent chapters (Chapters 10e14) cover the process design of (i) absorption and
stripping, (ii) distillation, (iii) adsorption and (iv) extraction systems. In order to deliver the design
solution of mass transfer processes, one may be guided by the above chapters and Chapter 14 on
Column and Column Internals. Inputs from sections V and VI of the book will be required for a
complete design of the process system/plant.