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The substantial energy requirement of crude oil distillation columns is met partly by
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costly utilities, such as steam and fuel for red heaters, and partly by heat recovered
from the process, using process-to-process heat exchange. Energy savings, therefore,
demand not only a distillation column that is energy-ef
cient, but also a heat exchanger 5131
network (HEN) which minimizes utility costs by maximizing heat recovery. A new crude oil
distillation design procedure is presented which considers the column, the HEN and their
interactions simultaneously, to minimize utility costs. Pinch analysis is used to determine
minimum utility costs prior to the design of the HEN. In this method, the column is
decomposed into a sequence of simple columns, which enables appropriate distribution of
stages and simpli
es analysis. Modi
cations, which further increase the ef
ciency of the
process, are proposed: these are the installation of reboilers, rather than stripping steam, and the
thermal coupling of column sections. The detrimental effects of these modi
cations on the heat
recovery opportunitiesof the process are analysed for a distillation tower with side-strippers. A
new step-by-step design procedure is derived from this analysis, and is applied to a case study.
In the case study, the resulting design offers nearly 20% savings in utility costs over the base
case design. The vapour ¯ ow in the column is reduced by a similar amount, offering capital
savings, additional ¯ exibility or the opportunity to increase throughput. The new integrated
design procedure considers the column and its associated HEN simultaneously, aiming to
minimize operating costs by obtaining the best t between the process and the available
utilities.
Keywords: pinch analysis; preheat train; distillation design1. INTRODUCTION
Crude oil distillation is an energy-intensive process,
consuming as fuel 1 to 2% of the crude oil processed
(Klenner
1
). The process is highly complex and has changed
relatively little since its inception 70 years ago (Miller
2
).
Crude oil distillation design is usually governed by
experience, design guidelines and simulation trials. How-
ever, published design procedures are not systematic and do
not consider concurrently the design of the heat exchanger
network (HEN).
Energy costs are highly relevant to the crude oil
distillation process, especially since fuel combusted is
product lost from this process. Furthermore, saving energy
has the side bene
ts of reducing site emissions and
stretching further our limited crude oil reserves. The heat
duties of a distillation process can be reduced signi
cantly
by designing an energy-ef
cient system. In addition, crude
oil distillation lends itself to heat recovery through process-
to-process heat exchange since it requires heat addition and
heat removal over a wide range of temperatures. Simply
increasing the energy-ef
ciency of the distillation column
gives smaller utility savings than if the energy-ef
ciency
is improved while also maximizing the potential for energy
recovery in the context of the process and the utility
system.
1.1 Process Description
A typical crude oil distillation column consists of a main
tower with side-strippers. The crude oil fed to the distillation
tower generally comes from storage at ambient temperature
and is heated in a heat exchange network (preheat train) and
a furnace. In the preheat train, heat is transferred from hot
process streams to the crude oil feed, generally raising its
temperature to 270 to 290 C. The pressurized crude oil is
heated further, using a furnace, to about 350 to 370 C. This