MKH1223 - Project 2 (Aug 2010)
HAZOP Study of Isomerisation Process
i.
Process Description
Isomerisation process is quite important in petroleum industry because isobutane is usually more valuable as a chemical feedstock than n-butane.
The typical amount of isobutane contained in crude oil and produced in refinery operations such as catalytic cracking is sometimes not enough to
satisfy the demand. On the other hand, supply of n-butane sometimes exceeds the demand.
The isomerisation reaction occurs in the vapour phase and is run at elevated temperature (400 oF) and pressures (600 psia). The reaction is
exothermic with heat of reaction of -3600 btu/lbmol. So, there is a temperature rise as the process stream flows through the adiabatic tubular
reactor. Following heat exchange with the reactor inlet stream and condensation with cooling water, the reactor effluent is introduced into a large
distillation column that separates the C4’s. The column that is also called debutaniser (DIB) has many trays and has 16 ft diameter.
The fresh feed stream is a mixture of both nC4 and iC4 (with some propane and isopentane impurities). It is also introduced into the column, not
directly into the reactor. The ratio of the recycle flow to the fresh flow ia about 1:2. The DIB column operates at 100 psia so that cooling water
can be used in the condenser.
The product of the DIB column is isobutene product. It has a specification of mol 2 % nC4. Since fresh feed contains propane, there is also some
propane in the distillate product.
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The bottoms from the DIB cntains most of the nC4 along with some iC4 impurities and all of the heavy sopentane impurities. Since this heavy
component will build up in the process unless it is removed, a second distillation column is used to purge out a small stream that contains the
isopentane. Some nC4 is lost in this purge stream. The purge column has 20 trays and 6 ft in diameter. The distillate product from the second
column is recycled to reactor.
ii.
Problem
You have been given a preliminary control strategy for the plant as shown in the given diagram. Having both safety and operability issues in
mind, you are required to come up with a HAZOP Report with the following Content:
Executive Summary
1.0 Introduction
1.1 Background
1.2 Purpose of study
1.3 TOR and Schedule
1.4 Team composition
1.5 Project description
2.0 Area of potential weakness (discuss any issue that may limit the study or anything that may be lacking from the study)
3.0 Comments applicable to the whole plant
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4.0 Major and priority finding
5.0 Reports and comments for other safety meetings
6.0 Conclusion
7.0 Appendices (HAZOP worksheet)
iii.
Scope for each group
Carry out the required HAZOP study . To simplify the tasks, the problem is divided into sub-tasks to be carried out based on the previous
groups.
Group
1- airiza, heng etc
Equipment
DIB Column
Parameters
Pressure, recycle feed
flow
2 – mubin, norfizar etc
Furnace
Temperature, Flow
3 – aizatul akmar, nadhilah etc
Tubular Reactor
Flow, Temperature
4 – Gaddafi, k khuzaimah etc
Purge Column
Pressure, Liquid LEvel
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Recycle
Reactor
TC
PC
FC
PC
LC
CW
LC
FC
PC
Product
LC
Fresh
Feed
FC
CC
LC
LC
DIB Column
Purge
Column
FC
Isomerization Process.
Purge
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