Session: 08-02-01: Fundamentals and Applications of Thermodynamics

Paper Number: 69268

Start Time: Wednesday, 10:05 AM

69268 - Advanced Exergetic Analysis of Preheat Train of a Crude Oil Distillation Unit 

In this investigation, exergy and advanced exergy analysis was used to obtain information about the performance of heat exchangers belonging to a preheating train to determine the most cost-efficient times for maintenance activities.

The preheater train is attached to a crude distillation unit designed to operate 150,000 barrels per day (150000 BPD). In the production process, the crude oil circulates through the preheating train before arriving at the furnace where it is heated to temperatures reaching 371 °C and then fractionated into different products such as heavy vacuum gas oil, medium vacuum gas oil, atmospheric gas oil, heavy diesel, and vacuum residue.

Since the oil temperature difference between the train inlet and the furnace outlet is about 339 °C, it is convenient to use the heat exchanger network as a regenerative process to increase the plant's energy efficiency, reduce operating costs and environmental impact, but several factors such as aging, long operating periods, crude oil composition, and fouling affect energy efficiency, which requires maintenance to restore its condition. However, most of the solutions proposed to establish the optimal execution times do not consider the limitations of the manufacturing processes, operating and environmental conditions, and relationships between the exchangers themselves as fundamental criteria for the elaboration of strategies, this causes methods to be imprecise when it comes to establishing intervention priorities and knowing the benefits obtained by performing maintenance.

To solve the problem, studies based on the second law of thermodynamics are proposed to calculate the conventional, inevitable, avoidable, endogenous, and exogenous exergy destruction rates and the combinations of the last four terms to identify sources of inefficiency. The impact of those sources is quantified and categorized. The exogenous analysis is used to individualize the equipment-to-equipment relationships in the entire network, allowing a more realistic view of the equipment conditions and the opportunity for improvement.

The effect of unavoidable exergy destruction on performance measurement of exchangers through the exergy efficiency is studied to evaluate the performance of exchangers more accurately, indicating that in some cases suppressing the unavoidable part can increase the second law efficiency by more than fifteen percentage points.

The results put the total exergy destruction at more than 61.6 MW, which 63% is avoidable. Five heat exchangers are considered critical because they concentrate the highest rates of exergy destruction, representing 39% of all exergy destruction in the network. This ranking of equipment allows focusing improvement works on exchangers that will produce a substantial increase in the network performance.

The improvement work to eliminate avoidable irreversibilities in all heat exchangers will result in a reduction of approximately 38.49 MW in exergy destruction, which means a higher inlet temperature at the furnace and reduction in fuel consumption and environmental impacts.

Presenting Author: Juan Fajardo Universidad Tecnológica de Bolívar

Authors:

Juan Fajardo Universidad Tecnológica de Bolívar
Camilo Negrete Universidad Tecnológica de Bolívar
Daniel Yabrudy Universidad Tecnológica de Bolívar
Camilo Cardona Ecopetrol