1 ׀ INTRODUCTION
Energy conservation remains the prime concern for many process
industries considering the rising energy cost and environmental
limitations. In order to increase the profitability of the industries
and reduce their environmental impacts, several methods for analyzing
energy systems of new and existing plants have been developed. Among the
various process integration methods used to minimize excessive heat
energy consumption in different industrial processes, pinch analysis is
most commonly used . Pinch technology has made possible the design of
new plants with optimum energy and capital costs, and performance
improvement of existing processes . The technique has been used globally
to target hot and cold energy requirement for crude distillation units
(CDU) and other processes . Based on pinch analysis, the heat exchanger
network retrofitting is envisaged as one of the promising options for
reducing energy consumption which could lead to enhanced economic and
environmental sustainability .
Literature is rich on the various industrial application areas of the
pinch analysis technique. For instance, its application for general heat
integration of distillation columns has been reported by Ajay and Amiya
, and for internally heat integrated distillation columns by Nakaiwaet al. . Al-Riyami et al. studied the effects of changing
the pinch temperature of a fluid catalytic cracking plant on the hot and
cold utilities and the area of the heat exchanger networks. Ajao and
Akande investigated the energy integration of the crude pre heat train
of Kaduna refinery where they found out the optimum pinch temperature
for the pre-heat train using pinch Analysis techniques. Salomeh et
al. used the Heat-Int software which is based on methods of Pinch
Technology to design, optimize and improve the integrated heat exchanger
network of crude oil preheating process in distillation unit in Arak
refinery. With the aid of the Heat-int software, Al-Mutairi and Elkawad
also carried out energy integration of a heat exchanger network in a
plant refinery plant using pinch analysis and investigated the effects
of pinch temperature on changes in hot and cold utilities and on the
area of heat exchangers. Revamping projects using pinch design method
conducted for existing oil refineries to improve their operation and
achieve more energy savings have been reported . In addition, the stage
model has been applied to many CDUs as in the work of Promptak et
al. .
A previous study conducted by Akande indicated that several
possibilities exist for energy saving in the Nigerian industrial sector
such as the plant refineries. On heat exchanger network synthesis
(HENS), first described and formulated by Masso and Rudd , extensive
reviews have been contributed by a number of workers such as Linhoff and
Flower , Nishida et al. , Papoulias and Grossmann , Linhoff and
Ahmad , Yee et al. , Furman and Sahinidis , , Morar and Agachi ,
Klemeš and Kravanja , and Klemeš et al. . But, despite the
advancement in methodologies and tools of process modelling and
optimization, a major challenge in HENS problems is how to develop
superior models and algorithms that can optimally obtain optimal heat
exchanger network (HEN) with lower total annualized cost.
Among the several design targets for HEN synthesis proposed previously
by different workers are the findings of Hohmann , Raghavan , Linnhoff
and Flower , Papoulias and Grossmann , Cerda et al. , and O’Younget al. which demonstrated the prediction of either the minimum
utilities required for a specified minimum temperature difference
(Tmin), or the minimum number of units for specified
utilities, independent of area. But, the study conducted by Colberg and
Morari developed a pair of transshipment nonlinear programs (NLP) to
simultaneously calculate the area and capital cost targets for HEN
synthesis, making it possible to evaluate the trade-off between the area
and number of units before synthesis. Basically, Colberg and Morari
formulated the transhipment model of Papilias and Grossman as a NLP for
targeting the area on HENS. The NLP model of Colberg and Morari is able
to target for both restricted matches and those that are not restricted.
The HINT (Heat-Integration) is non-commercial software developed by
Department of Chemical engineering and Environmental Technology,
University of Valladolid, Spain that is capable of handling design of
small heat exchanger network . It is based on the principle of pinch
analysis, a reliable method that has been used in the optimization of
HENs. In the present study, the goal is to apply pinch analysis using
HINT software in energy conservation and optimization of crude
distillation unit (CDU) of Kaduna Refining and Petrochemical Company
(KRPC) Ltd and compare results with the NLP technique of Colberg and
Morari .