Crude Oil Distillation Systems Research Articles

Process design Optimisation, heat integration, and techno-economic analysis of oil refinery: A case study

ABSTRACT This paper outlines a comprehensive analysis of the optimal design and simulation of a crude oil distillation system within a refinery process, including pre-treatment and blending of two crude oils to increase the refinery’s annual profit. This distillation process is currently in operation, and the desired amount of feedstock is obtained from Iraqi Basra light-2015 and Kirkuk-2011 crude oil. To improve the energy efficiency of the utilization rate of crude oil, an atmospheric distillation process unit in this refinery with a capacity of 150,000 barrels per day (bpd) is considered. Aspen HYSYS simulation is used to optimize the distillation unit configuration and its operating performance. This paper also deals with three scenarios by comparing the feedstock compositions to the distillation process and the produced product compositions to minimize utility consumption. A heat integration approach was applied to the 3rd scenario by recycling hot outlet streams to the heat exchangers to increase the temperature of the inlet stream of the distillation column. Results indicated that about £2.29 million per year (Mpy) could be saved from the heat integration systems. Economic analysis and cut yields were carried out for each scenario to investigate the cost-effective and economically viable. Based on the economic analysis, scenario three showed better performance with a comparatively high cumulative cash flow of £31,886 M.

An advanced Grid Diagram for heat exchanger network retrofit with detailed plate heat exchanger design

This paper presents a method for heat exchanger network (HEN) optimisation considering plate heat exchangers (PHEs), incorporating detailed PHEs design. The developed method starts from a mathematical model based on the Advanced Grid Diagram, which can optimise the HEN structure. The model minimises the energy consumption cost with the constraints that enable a solution thermodynamically feasible. Then comes the heat exchanger type selection part, which is provided by a graphical tool helping to identify which types of the heat exchanger are feasible. The feasible temperature range can be easily visualised to avoid the temperature violation of PHEs. This selection part integrates the area calculation and cost calculation with the detailed heat exchanger design. The method has been tested by a case study of crude oil distillation system illustrating that the application of brazed plate heat exchangers (BHEs) of CB series manufactured by Alfa Laval can save 6.6% of the investment cost for new heat exchangers compared with the retrofit plan that only shell-and-tube and double pipe heat exchangers are used.

Adaptive MPC Controller based Cascade Control of Distillation Column Parameters Estimation and Optimization

One of the key element of many industrial process plants is a crude oil distillation system. This system requires heat for the vaporization of a mixture of feed to the distillation column in vapor form. In the existing process of distillation, an abnormal change of heat is exhibited due to improper control and monitoring of disturbances affecting the plant. This would result for undesired loss of product and product purity to be reduced. The parameters that are expected to be considered in the analysis, model and control of a distillation system described under the proposed study are inlet feed temperature, distillation column temperature, feed composition, internal liquid and vapor composition, feed flow rate, reboiler temperature and an external reflux temperature to the distillation tower. Controlling distillation column parameters with Adaptive model predictive control allows for the determination of the predicted future instant values of the plant outputs. Using such control technique, the controlled plant outputs such as the temperature of distillation column, feed preheater, re boiler and the upper reflux is properly controlled and their parameters are estimated using recursive least squares approach in the entire process adaptation mechanism. From the analysis and optimization work made on the proposed system, the efficiency of the plant outputs in tracking their corresponding set point has improved based on the value of the transient system parameters as well as the value of relative volatility of feed mixture to the column. As per the finding in the analysis of the process, 95.4% and 93.5% improvement on the set point tracking and to amount of evaporation liquid feed has been obtained respectively. On the other hand an improvement on transient parameters has been achieved to all plant outputs. As per the result obtained from the analysis, the peak overshoot, settling time and peak time of the system response has found to be less than 40% including the effect of measured disturbance to the plant. Hence, entire process variable optimization has been performed using the parameters of the model predictive controller to provide the proper degree of stability. Finally the proposed method of study has compared with with other control strategies through which the performance the proposed design has been ensured.

A fuzzy DEMATEL-ANP-VIKOR analytical model for maintenance strategy selection of safety critical assets

In most industries, such as aerospace, manufacturing, transport and energy sectors, maintenance plays a vital role in improving the performance of safety critical equipment and facilities. It also helps industries achieve the largest possible efficiency, ensure workplace and environmental safety, and reduce unnecessary breakdowns and costs. Therefore, it is crucial for industries to adopt an optimal maintenance strategy for their critical systems and infrastructure. In this study, we aim to propose a novel analytical multi-criteria decision-making (MCDM) methodology for selecting the most suitable maintenance strategy in distillation units of oil refinery plants. The alternative maintenance strategies include run-to-failure (RTF), preventive maintenance (PM), condition-based maintenance (CBM), and reliability centered maintenance (RCM), which are evaluated with respect to 12 sub-criteria in three categories of economical, safety, and sustainability issues. The MCDM methodology consists of a DEMATEL-based analytic network process (ANP) method to determine the importance weights of decision criteria and a VIKOR method to rank the maintenance strategies. Also, interval type-2 fuzzy sets are used to capture uncertainty in experts’ individual judgments. Finally, a real case study is provided to show the applicability of the proposed methodology to an oil refinery plant. The results show that, thanks to advances in degradation modeling, sensor technology, and data analytics platforms, the RCM and CBM are the superior maintenance strategy for crude oil distillation systems.

A New Optimisation-based Design Methodology for Energy-efficient Crude Oil Distillation Systems with Preflash Units

In a heat-integrated crude oil distillation system with an atmospheric distillation unit and heat recovery system, pre-separation units (a preflash or prefractionator) can help to reduce the furnace duty and improve energy efficiency of the system. The high operating and equipment cost and complexity of the system motivate the development of systematic approaches for optimal design. The approach needs to consider both design of the distillation unit and the optimisation of operating conditions in the system, including those related to the preflash unit. This work introduces an optimisation-based methodology for the design of crude oil distillation systems with preflash units. The objective is to minimise fired heat demand of the system while meeting product quality and yield specifications, where pinch analysis is applied to estimate minimum utility requirements. A stochastic optimisation algorithm (a genetic algorithm) is applied to identify the feed location of the flash vapour, the number of stages in each column section and the optimal operating conditions. Operational optimisation variables include pump-around duties and temperature drops, stripping steam flow rates, the column feed temperature, reflux ratio and preflash temperature. The approach is based on the simulation–optimisation technique of Caballero et al. (2005). In order to facilitate integration of modelling and optimisation, an interface between MatLab R2016a and Aspen HYSYS v8.8 is employed. A case study illustrates how the design methodology proposed in this work can reduce demand for fired heating.

Industrial application of surrogate models to optimize crude oil distillation units

This work presents a new approach to optimize existing crude oil distillation systems. The main features of this approach are its ability to provide key insights of the main factors affecting product yields and energy consumption; and the consideration of system limitations, such as crude oil changes, column flooding, heat transfer bottlenecks and product quality specifications. The new approach showcases sophisticated and systematic modelling and optimization methodologies, namely artificial neural networks and simulated annealing. The approach has been applied successfully in a debottlenecking study for yield optimization of a medium-scale Spanish refinery. The implementation of the optimization results was carried out successfully in the refinery; initial projections confirm predicted benefits of $7.2 million per year.

Simulation–Optimization-Based Design of Crude Oil Distillation Systems with Preflash Units

In energy-intensive crude oil distillation systems, with their distillation units and heat recovery systems, preflash units can create opportunities to reduce demand for fired heating and increase heat recovery. As holistic, systematic design methodologies are not available for design of crude oil distillation systems with preflash units, this work proposes a simulation-based design approach, where the objective is to minimize fired heat demand of the system. The approach exploits interactions between the separation and heat recovery systems, considering product quality and yield. Rigorous distillation models in Aspen HYSYS, pinch analysis, and randomized optimization (a genetic algorithm) are employed, via a MatLab interface, to minimize hot utility demand by optimizing operating variables and one structural variable, namely, the feed location of the preflash vapor. A case study demonstrates the approach, showing that a preflash unit can reduce hot utility demand but that the system is vulnerable to yiel...

Feasibility bounds in operational optimization and design of crude oil distillation systems using surrogate methods

Feasibility bounds in operational optimization and design of crude oil distillation systems using surrogate methods

Conceptual insights to debottleneck the Network Pinch in heat-integrated crude oil distillation systems without topology modifications

Heat exchanger network pinch sets the limitations of heat recovery for existing network topologies. Improving the heat recovery within a pinched-network is independent of the areas of individual exchangers present in the network, rather the topology of the network must be altered. Such a change in the topology can be very capital intensive and in many cases seems not easy to implement. This research aims to overcome the Network Pinch through proposing process operation changes, avoiding network topology alterations; hence, debottlenecks the heat-integrated systems towards further energy savings beyond the maximum heat recovery limitations. A new graphical representation is recently proposed to simulate existing preheat trains/networks with all energy equipment. The recent graphical representation is employed in this work to identify the pinching matches that limit heat recovery. Therefore, such graphs are key tools to identify potential process changes by which the Network Pinch is overcome. New graphs are constructed involving hot stream temperatures against cold stream temperatures. Existing exchangers are described by straight lines, with slopes related to flows of process streams and heat capacities. Exchanger matches touching the line where hot outlet stream temperature equals cold inlet stream temperature are pinching matches; this condition corresponds to absolute maximum heat recovery (ΔT=0). Potential process changes within a distillation unit are identified to relax the Network Pinch and further heat recovery is maximised. The slope of such an exchanger match is decreased or the location of the pinching match is altered keeping the same slope. These changes are translated into process changes within the crude oil distillation unit. Accordingly, the process changes are determined based on which match is pinched besides its location within the network. An illustrative example shows that process changes overcome the Network Pinch and energy recovery is increased by 14% beyond the maximum level achieved for the existing process conditions. Capital investments imposed are minor compared with substantial energy cost savings.

Optimization of Heat-Integrated Crude Oil Distillation Systems. Part III: Optimization Framework

This paper is the third of a three-part series that applies optimization to maximize the productivity and minimize operating costs of heat-integrated crude oil distillation systems. The approach presented in this paper implements simulation models for the distillation process and heat exchanger network (HEN), and HEN retrofit models into the overall optimization framework. The optimization approach is formulated in two levels. In the first level, simulated annealing is used to optimize the operating conditions of the crude oil distillation unit (e.g., distillation products and stripping steam flow rates, pump-around duties and temperature drops, and furnace exit temperatures) and to propose HEN structural modifications (e.g., adding, removing, relocating heat exchangers; adding, removing stream splitters, etc.). The second level is a nonlinear least-squares problem used to enforce HEN constraints. Three case studies illustrate the application of this approach to increase net profit and reduce annualized c...

Optimization of Heat-Integrated Crude Oil Distillation Systems. Part I: The Distillation Model

This work presents a methodology for optimizing heat-integrated crude oil distillation systems. Part I of this three-part series presents a modeling strategy where artificial neural networks are used to represent the distillation process. Part II presents a new methodology to retrofit heat exchanger networks (HENs) and Part III presents the application of this distillation model to perform operational optimization of the crude oil distillation unit while proposing retrofit modifications to the associated HEN. Independent variables of the distillation model include flow rates of products, stripping steam, pump-around specifications, and furnace exit temperature. Dependent variables include those related to product quality, and temperatures, duties, and heat capacities of process streams involved in heat integration. The resulting neural network model is able to overcome convergence problems presented by rigorous or simplified models. Simulation time is significantly improved using neural networks, compared to rigorous models, with practically no detriment to model accuracy.

Optimization of Heat-Integrated Crude Oil Distillation Systems. Part II: Heat Exchanger Network Retrofit Model

This is the second part of a series that applies optimization to maximize the productivity and minimize operating costs of existing heat-integrated crude oil distillation systems. This paper presents a two-level retrofit approach for heat exchanger networks. In the first level, simulated annealing proposes topology modifications to the existing network (e.g., adding, removing, and relocating heat exchangers; changing the heat loads of heat exchangers, adding and removing stream splitters, and changing the split fraction of stream splitters). In the second level, a repair algorithm addresses the violation of constraints. These constraints consider the minimum temperature approach, stream enthalpy balances, and existing heat transfer areas. The repair algorithm is formulated as a nonlinear least-squares problem. Temperature-dependent thermal properties are considered in this work for the accurate prediction of stream temperatures. Two case studies illustrate the application of the proposed methodology to decrease total annualized costs.

Simultaneous optimization of heat-integrated crude oil distillation systems

Crude oil distillation is important in refining industry. Operating variables of distillation process have a critical effect on product output value and energy consumption. However, the objectives of minimum energy consumption and maximum product output value do not coordinate with each other and do not lead to the maximum economic benefit of a refinery. In this paper, a systematic optimization approach is proposed for the maximum annual economic benefit of an existing crude oil distillation system, considering product output value and energy consumption simultaneously. A shortcut model in Aspen Plus is used to describe the crude oil distillation and the pinch analysis is adopted to identify the target of energy recovery. The optimization is a nonlinear programming problem and solved by stochastic algorithm of particle warm optimization.

Retrofit of heat-integrated crude oil distillation columns

Engineering projects to increase the capacity of existing heat-integrated crude oil distillation columns are commonplace. Retrofit projects aim to exploit the processing capacity of existing units by changing operating parameters and/or modifying equipment. Operational modifications can be effective and usually incur little capital expenditure, but equipment changes may also be needed to achieve retrofit objectives. Existing retrofit methodologies for crude oil distillation systems mainly focus on increasing heat recovery, increasing crude oil throughput and/or increasing the yield of most valuable products by optimising column operating parameters. However, methodologies that also consider hardware modifications are lacking. The present work proposes a systematic retrofit methodology based on distillation column and heat exchanger network (HEN) simulation. Hydraulic correlations are used to consider replacing existing distillation column internals with high-capacity trays and/or structured packings. Industrially relevant case studies illustrate the benefits of the proposed methodology to analyse and assess hardware modifications for the retrofit of distillation systems when increasing capacity.

The use of reduced models for design and optimisation of heat-integrated crude oil distillation systems

The importance of exploiting degrees of freedom within a crude oil distillation process for improving energy performance has been a feature of process integration from the earliest days. Combining process changes with changes to the heat recovery system leads to far better results, compared with changes to the heat recovery system alone. However, in order to obtain the best results, the distillation process and heat exchanger network need to be optimised simultaneously. Whilst in principle this is straightforward, there are many difficulties. Methods for the optimisation of heat exchanger networks are well developed. In these methods, heat exchanger network models are based on network details, such as stream connections between heat exchangers, heat transfer area of individual units, etc. The consideration of these network details is important to design and optimise crude oil distillation systems. On the other hand, the distillation process model to be coupled with the heat exchanger network model needs to be simple and robust enough to be included in an optimisation framework. If distillation models and heat recovery models can be combined effectively, then there are not just opportunities for design and retrofit, but also for operational optimisation. One of the big challenges to progress the application of this approach is the effective generation of reduced distillation models. Short-cut distillation models can be used, but many other options are available, such as the use of artificial neural networks. This paper reviews various crude oil distillation modelling approaches and highlights the areas of application of these different approaches. An example illustrates the computational performance of reduced and rigorous crude oil distillation models.

Operational optimization of crude oil distillation systems using artificial neural networks

A new methodology for optimizing heat-integrated crude oil distillation systems is proposed in this work. The new procedure considers an artificial neural networks (ANN) model for representing the distillation column. Models of the distillation column and the associated existing heat exchanger network are incorporated in an optimization framework to systematically determine the operating conditions that improve the overall process economics. Of particular interest is the problem of optimizing the net value of the products obtained from the column by increasing the yield of higher-value products at the expense of less valuable products, while taking into account feasibility of the distillation specifications, heat recovery, energy and equipment constraints. A two-stage procedure is applied to first optimize the column operating conditions based on minimum utility requirements. In the second stage the heat exchanger network is designed.

06/00576 Thermodynamic analysis of crude oil distillation systems: Al-Muslim, H. and Dincer, I. International Journal of Energy Research, 2005, 29, (7), 637–655.

06/00576 Thermodynamic analysis of crude oil distillation systems: Al-Muslim, H. and Dincer, I. International Journal of Energy Research, 2005, 29, (7), 637–655.

Thermodynamic analysis of crude oil distillation systems

This work deals with a thermodynamic analysis of crude oil distillation systems to study energy and exergy efficiencies for system analysis, performance evaluation and optimization. In this regard, a new analysis methodology is proposed, and the SimSci/PRO II (2000) is employed as a simulation package for the required parametric studies, particularly to study the effects of the distillation column temperatures and pressures on the efficiencies. The simulations are carried for the operating conditions of the model. It is found that the total irreversibility losses are 608 MW for a flow rate of 507 kg s−1 [e.g. 56% by the Atmospheric Distillation Unit (ADU), 26% by the Vacuum Distillation Unit (VDU) and 18% by the heaters]. The highest irreversibility losses occur in the ADU as the main separation takes place there. Of the losses, 6.2% are due to chemical exergy losses associated with the separation process itself. The rest of the losses are due to the physical exergy losses mainly because of the temperature difference. The energy efficiencies are 0.497 for the ADU, 0.579 for the VDU and 0.519 for the overall system. The exergy efficiencies are 0.433 for the ADU, 0.501 for the VDU, 0.821 for Heater 1, 0.956 for Heater 2 and 0.233 for the overall system. The overall efficiency is not equal to the product of the components efficiencies. Copyright © 2005 John Wiley & Sons, Ltd.

Effect of reference state on exergy efficiencies of one- and two-stage crude oil distillation plants

In this paper we deal with the effects of varying reference temperature on the exergy efficiencies of one- and two-stage crude oil distillation units. Such units essentially consist of the crude oil heating furnace, the distillation column and a network of heat exchangers. Since the exergy efficiency is a key parameter to see how well the system is performing, we undertake a study on the influence of the reference temperature on such efficiencies. In this regard, a commercial software package, SimSci/PRO II program is used for the calculations. The results show that increasing reference temperature decreases the exergy efficiency in both one- and two-stage crude oil distillation systems and also increases the difference between the exergy efficiencies of both systems. Therefore, the exergy losses increase in the crude oil distillation systems.

Improvement of the operation of crude oil distillation systems

Improvement of the operation of crude oil distillation systems