Applying pinch and exergy analysis for energy efficient design of diesel hydrotreating unit

Pinch Analysis (PA) and Exergy Analysis have been used, either independently or in combination, for energy integration of process plants. This paper discusses a methodology to apply PA and Exergy Analysis during design of a new process plant to make it energy efficient, using Diesel Hydrotreating Unit (DHT) as an example. PA has been used to estimate the Minimum Energy Requirement (MER), to select utilities and to design the optimal Heat Exchanger Network (HEN). Exergy Analysis is then performed to pinpoint the sources of energy inefficiency in the whole plant and suggest improvements. The application of these two techniques has helped in energy integration of the plant during the design phase itself. Two common layouts of diesel hydrotreating unit-the 'hot separator layout' and the 'cold separator layout'-have been studied. The minimum Total Annualized Cost (TAC) is similar to 7.6 M(sic)/y and similar to 10 M(sic)/y for the hot separator layout and the cold separator layout respectively. Exergy destroyed is 27.15 MW (7.9% of exergy input) and 50.18 MW (6.7% of exergy input) respectively for the hot separator layout and the cold separator layout. Exergy Analysis reveals that the energy efficiency can be improved for air coolers, fired heaters and letdown valves. (C)2019 Elsevier Ltd. All rights reserved.