Page 12 - Process Equipment and Plant Design Principles and Practices by Subhabrata Ray Gargi Das

6 Chapter 1 General aspects of process design

• Reliability of the process and mechanical design of equipment
This is ensured by following the relevant standards and codes
• Available space for the equipment or process being designed
• Scope of interchangeability with other equipment or common spare
• Ease of operation and maintenance
• Safety during erection, commissioning, operation and maintenance.
The process designer needs to be absolutely clear about the functional requirements to be met by
his design output and looks for the following minimal information at the outset:
• Input and output stream detailsdrange of flow rate, temperature, pressure, composition or any
other available information
• Required capacity of the processddefined in terms of maximum, normal and minimum flow rate
(input and/or output) of streams. In some cases, this may even be stated in terms of energy to be
supplied or removed from the system
• Spatial location and its limitations, the plot plan, and the preferred orientation of equipment. The
information of the surrounding area, its geographical details, presence of any existing habitation
around the proposed process plant, topology of the plot, details on wind direction (Wind rose),
location of effluent discharge points, preferred dimension of standard equipment or its
components like heat exchanger tube length, etc., are all to be considered in the design phase to
deliver an optimum option.
• Specific standards to be followed for designing, e.g., IS 2825/ASME Sec VIII Div.1 for unfired
pressure vessels or TEMAeR for heat exchangers. This is essential for generating a design that is
compatible with the rest of the facility, use of standard material of construction and ensuring the
reliability of the equipment. Standards greatly reduce the time to deliver a reliable design and get
it fabricated. The role of design codes and standards during the design activity, therefore, need no
further emphasis.
Based on the available information, the designer fixes the conditions at the boundary of the process.
In industry parlance, this boundary is the “battery limit.” Battery area refers to the physical area within
which the process resides. Input and output stream details are to be known at the “battery limit” before
proceeding further.

1.2 Design problem and its documentation

Design requirements emerge out of an expression of a functional need. Such a need can be expressed
for a new plant or processing facility. The need for a plant to process naphtha available from a local
refinery and convert it to some useful petrochemical product can be the example of such a functional
need for the design of a petrochemical complex. It is also possible to have the “need” for some
expansion/modification of existing processes/plants. The plant design gets completed by designing the
various equipment of the plant and its piping and utilities in an integrated fashion. The earlier
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mentioned example of an arrangement to cool a continuous (70 m /hr) stream of hot kerosene oil (from

90 to 40 C) before the same is sent to storage is a simple statement expressing the need for an
additional process facility to offer the required functionality, i.e., cooling. It is needless to say that even