Analysis of Fuel Reduction Strategies for Crude Distillation Unit

There is greater awareness today on the depleting fossil energy resources and the
growing problem of atmospheric pollution. Engineers are developing practical
techniques to ensure energy processes are designed and operated efficiently.
Inefficient furnaces and heat exchangers contribute to the problem due to higher fuel
demand and higher carbon emission. In crude preheat train (CPT), fouling causes the
reduction of heat transfer efficiency, which leads to higher furnace fuel consumption,
and exert additional cost for heat exchanger cleaning and lost production. This thesis
presents strategies to reduce fuel consumption in the furnace, which will lead to
reductions of operational cost and environmental emission. The method of exergy
analysis is applied to determine the baseline energy efficiency of the furnace and CPT
in a crude distillation unit (CDU). The strategies consist of locating and reducing
exergy lost through process modifications of the energy system and developing
optimum scheduling for retrofit and/or cleaning of heat exchangers in the CPT. There
are two options for achieving fuel savings in the furnace. The options are reduction of
heat lost from furnace stack and enhancement of heat recovery in the CPT. The
second option involves plant shutdown for overall cleaning of CPT (Case 1), online
cleaning of heat exchangers (Case 2) and combined online cleaning with retrofit of
high efficiency heat exchangers (Case 3). Reduction of heat loss from furnace stack
contributes to the smallest cost saving of 6.44% without carbon credit. With carbon
credit, the saving is increased to 6.70%. The largest energy and carbon dioxide
emission savings are found from Case 3. The installation of high efficiency heat
exchangers improves furnace inlet temperature (FIT) from 215oC to 227oC.
Furthermore, Case 3 results in the highest percentage of cost saving by about 71% and
62% with and without carbon credit, respectively. The payback period for investment
in high efficiency heat exchangers is 3 months, with carbon credit, and 4 months,
without carbon credit, respectively. Thus, Case 3 is the most cost effective option for
reductions of energy consumption and carbon dioxide emission in the CDU.