Crude Distillation Unit Research Articles

Integrated Analysis of the Water-Energy-Environmental Pollutant Nexus in the Petrochemical Industry.

China has set high water-conservation, energy-saving, and pollutant-reduction goals for the petrochemical industry. This represents a challenge to petrochemical enterprises because of the complex coupling between water, energy, and environmental pollutant (WEE) subsystems, elements (different types of WEE), and production units. However, there has been little research on the element-level coupling relationship. The connection and difference between the coupling relationships of the system, element, and unit levels are not well understood. Therefore, an integrated analysis method was developed to quantify the petrochemical WEE nexus (WEEN) at these three levels, including a generic WEEN model, material and energy flow analysis, and a WEEN analysis matrix. Three indicators were proposed to analyze three-level coupling quantitatively and to formulate improvement strategies for water-conservation, energy-saving, and pollutant-reduction. A case study demonstrated significant three-level coupling. The coupled percentage of WEE subsystems were 95.87%, 61.97%, and 54.99%, respectively. The dominant energy subsystem was the root of high consumption and pollution. Based on synergies and trade-offs, we proposed element optimization priorities: High priority (deoxidized water and fuel), medium priority (steam, circulating water, and wastewater), and low priority (fresh water, demineralized water, waste gas, and electricity). The identified unit improvement potential revealed overestimation (hydrotreating and delayed coking units) and underestimation (crude distillation units) of conventional methods that overlook three-level coupling.

Optimization of Crude Distillation Unit Case Study of the Port Harcourt Refining Company

An HYSYS model for the crude distillation unit of the Port Harcourt Refining Company has been developed. The HYSYS model developed includes 3 mixers, 3 heaters, 1 heat exchanger, 1 desalter (3-phase separator), 2-phase separator and the main fractionating column. The raw crude was characterized using Aspen HYSYS version 8.8 and the developed model was simulated with the industrial plant data from the Port Harcourt Refining Company. The HYSYS model gave component mole fractions of 0.2677, 0.1572, 0.2687, 0.0547, 0.2517 for Naphtha, Kerosene, Light Diesel Oil (LDO), Heavy Diesel Oil (HDO) and Atmospheric Residue and when compared to plant mole fractions of 0.2710, 0.1560, 0.2650, 0.0530, 0.2550 gave a maximum deviation of 3.2%. The HYSYS model was also able to predict the temperature and the tray of withdrawal for Naphtha, Kerosene, Light Diesel Oil (LDO), Heavy Diesel Oil (HDO) and Atmospheric Residue as follows: tray 1 (120°C), tray 12 (206°C), tray 25 (215°C), tray 35 (310°C) and tray 48 (320°C) which was also compared with plant data and gave a maximum deviation 23.2%. The HYSYS model was then optimized using Sequential Quadratic Programming (SQP) with the industrial plant data as starting values of operating conditions. The optimization increased the mass flow rate of Naphtha product from 7.512E+004 kg/hr to 7.656E+004 kg/hr, Kerosene product from 5.183E+004 kg/hr to 5.239E+004 kg/hr, Light Diesel Oil (LDO) product from 1.105E+005 kg/hr to 1.112E+005 kg/hr, Heavy Diesel Oil (HDO) from 2.969E+004 kg/hr to 2.977E+004 kg/hr while the last product being Atm Residue remained at 3.157E+005 kg/hr. The new optimum mole fraction values for the five products were as follows: 0.2713, 0.1540, 0.2635, 0.0528, and 0.2584 while corresponding optimum temperature values were as follows: 129°C, 221°C, 257°C, 317°C and 327°C.

Exergy analysis of a shell and tube heat exchanger using DETHE software

In this paper, a sensibility study of irreversibility due to geometrical parameters variation of a shell-and-tube heat exchanger is proposed by using an exergy analysis. The irreversibility calculation model has been implemented on design tubular heat exchangers (DETHE) software, where thermohydraulic calculations are based on Bell-Delaware method. A prior evaluation of thermohydraulic results of DETHE is provided against a commercial software. Through an exergetic analysis in the study case, formulation to be implemented in the software for irreversibility calculation is developed. A real case study of a heat exchanger located in a pre-heat train of atmospheric crude distillation unit is analysed. Irreversibility results due to key design parameters variation for this heat exchanger are provided and discussed.

Economic Assessment of a Crude Oil Hydrotreating Process

This paper presents the economic assessment of a crude oil hydrotreating process with a crude distillation unit. The hydrotreating of crude oil is a novel process that has great economic potential but has not been implemented widely in practice, where all the conventional hydrotreating processes are carried on each oil product separately. This new hydrotreating process of crude oil seeks to save costs and energy in crude oil refineries. The economics of this new process are compared with those of the conventional crude distillation unit where hydrotreating is conducted on each oil fraction individually. The results show that this new process of hydrotreating of the crude oil has an overall annual cost much less than that of the conventional process.

Emission Trading Scheme and the Effect of Carbon Fee on Petroleum Refineries

The high volume of green house gases released from petroleum refineries has contributed greatly to global warming. The crude distillation unit of a refinery being an energy-intensive unit generates high volume of greenhouse gases. Unlike solid and liquid pollutants that can easily be handled and treated, gaseous pollutants are difficult to handle once they are generated, hence an effective means of reducing their generation is paramount. Because of the cost penalty placed on defaulters, emission trading scheme has been an effective way of controlling the release of these obnoxious gases into the environment as refiners would seek alternative processing schemes that reduce emissions. The crude distillation unit of the refinery under study was simulated in Aspen Hysys. The unit was designed to process 125,000bpsd of a blend of three Nigerian crudes. Greenhouse gases from the unit were targeted from direct (heating sources) and indirect (electricity usage) respectively. The concept of global warming potential was adopted to estimate the carbon (iv) oxide equivalent of the greenhouse gases from the unit. A methodology to allocate emission quota to a refinery was developed and a carbon fee of $5 per tonne was placed for above- limit emissions. The crude distillation unit was found to have a base generation of 491576.27tonne/yr of carbon (iv) oxide equivalent while it pays $491,576.25per year for above-limit emission. The sensitivity analysis revealed that the gross profit is quite sensitive to carbon fee. Â

Evaluation of Heat Exchanger Network Retrofit Design Using Plant Data

Fouling in pre-heat trains of atmospheric crude distillation units is one of the major issues hindering the efficiency of oil refineries. This paper illustrates the benefits of using dynamic simulation, combined with plant measurements, to evaluate heat exchanger retrofit opportunities that provide the largest savings to the refinery. Once the fouling behavior of the network is well characterized and the most critical heat exchanger is identified, the performance of a retrofit design for that exchanger is assessed by re-running history using plant measurements for an extended period of operation. The comparison of the original design versus alternative ones, based on the potential reduction of fouling, provides an overall assessment of the impact on energy/economic savings for the whole network given by the proposed retrofits options. This enables the design engineer to use available plant data to evaluate and select the most beneficial design option, not simply based on expected operating conditions and fixed fouling factors, but on time-varying conditions and dynamic fouling build-up as it happens in the plant. The method is demonstrated with an industrial case study. The estimated savings in furnace duty were of 1.5–2.7 MW, resulting in expected economic benefits of $270–700 k per year.

A simplified multi-objective particle swarm optimization algorithm

Particle swarm optimization is a popular nature-inspired metaheuristic algorithm and has been used extensively to solve single- and multi-objective optimization problems over the last two decades. Several local and global search strategies, and learning and parameter adaptation strategies have been included in particle swarm optimization to improve its performance over the years. Most of these approaches are observed to increase the number of user-defined parameters and algorithmic steps resulting in an increased complexity of the algorithm. This paper presents a simplified multi-objective particle swarm optimization algorithm in which the exploitation (guided) and exploration (random) moves are simplified using a detailed qualitative analysis of similar existing operators present in the real-coded elitist non-dominated sorting genetic algorithm and the particle swarm optimization algorithm. The developed algorithm is then tested quantitatively on 30 well-known benchmark problems and compared with a real-coded elitist non-dominated sorting genetic algorithm, and its variant with a simulated binary jumping gene operator and multi-objective non-dominated sorting particle swarm optimization algorithm. In the comparison, the developed algorithm is found to be superior in terms of convergence speed. It is also found to be better with respect to four recent multi-objective particle swarm optimization algorithms and four differential evolution variants in an extended comparative analysis. Finally, it is applied to a newly formulated industrial multi-objective optimization problem of a residue (bottom product from the crude distillation unit) fluid catalytic cracking unit where it shows a better performance than the other compared algorithms.

Utility Paths Combination in HEN for Energy Saving and CO2 Emission Reduction

Energy demand and flue gas emissions, namely carbon dioxide (CO2) associated with the industrial revolution have exhibited a continuous rise. Several approaches were introduced recently to mitigate energy consumption and CO2 emissions by either grass root design or retrofit of existing heat exchanger networks (HEN) in chemical process plants. In this work, a combinatorial approach of path combination is used to generate several options for heat recovery enhancement in HEN. The options are applied to successively shift heat load from HEN utilities using combined utility paths at different heat recovery approach temperature (HRAT) considering exchangers pressure drop. Industrial case study for HEN of the preheat train in crude oil distillation unit from the literature is used to demonstrate the approach. The obtained results have been studied economically using the cost targeting of Pinch Technology. As a result, both external energy usage and CO2 emissions have been reduced from a heater device in HEN by 20% and 17%, respectively, with a payback of less than one year.

On-line control of the heat exchanger network under fouling constraints

The article presents a mathematical model for on-line control of a heat exchanger network (HEN), aiming at maximization of heat recovery. The model assumes that HEN operates at steady state. The paper presents the method of processing measurement data in order to separate periods of time, which corresponds to the steady state of HEN.The existing mathematical models of the heat exchanger give an inaccurate results, due to large calculation errors in the estimation of the heat transfer coefficient (10–40%). Therefore, the authors introduced a heat exchanger model in which measurements were used to improve the correlation describing the heat transfer coefficient. The heat exchanger model with improved correlation was applied for estimation of the thermal fouling resistances. This approach allows calculating the exchanger with a much smaller calculation error (below 1%).The mathematical model and algorithm of HEN control were presented.The proposed on-line control model was tested on the example of HEN belonging to Crude Distillation Unit, processing 780 t/h of crude oil. In the proposed process control system, the manipulated variables are mass flows of crude oil flowing through HEN branches. The proposed method of HEN control gives opportunity to increase the heat recovery by 1.5%.

INTEGRATING REAL TIME OPTIMIZATION AND MODEL PREDICTIVE CONTROL OF A CRUDE DISTILLATION UNIT

This work reports the integration of Real Time Optimization and Model Predictive Control in the multi-layer control structure of an existing Crude Distillation Unit (CDU) of an oil refinery. The MPC considers output control zones and targets for the inputs or outputs. Both the infinite horizon and the finite output horizon controllers were tested. The plant results show that the infinite horizon controller tends to perform similarly or better then the finite horizon MPC when the CDU system needs to operate at quite different conditions. Although the dynamic layer based on the infinite horizon controller is nominally stable for any set of tuning parameters, in practice, it is observed that the interaction between the layers of the control structure associated to model uncertainty may result in oscillations in some variables that fail to converge to the optimum operation point. This problem can be solved with the retuning of the intermediary layer (target calculation layer), which indicates that the frequent tuning of the MPC is recommended and should be performed in conjunction with tuning of the intermediary layer.

Data reconciliation and gross error detection in crude oil pre-heat trains undergoing shell-side and tube-side fouling deposition

Fouling is a problem in crude oil refineries. The effect of fouling deposition is particularly significant in the heat exchanger network (or pre-heat train) upstream of the crude oil distillation unit. A wide variety of semi-empirical models are available for predicting the fouling behaviour. These models can be obtained by fitting experimental or industrial operating data to a specific fouling model. When industrial data are used, the effect of measurement error and presence of faulty instruments (or gross errors) should be accounted for. This work presents a new methodology that allows for data reconciliation and gross error detection, together with the estimation of fouling model parameters for a pre-heat train undergoing different fouling mechanisms on the shell and tube-sides. The methodology is tested in a simulated case study. It is shown that the data reconciliation and gross error detection algorithms are able to minimise the measurement errors and to identify the presence of single or multiple faulty instruments. The fouling models for each heat exchanger are estimated using the reconciled data, and the fouling behaviour and thermal performance of the network are predicted and analysed.

Integrated Proactive and Reactive Scheduling for Refinery Front-End Crude Movement with Consideration of Unit Maintenance

A typical front-end crude supply process of refineries encompasses many units, such as vessels, port-side storage tanks, long-distance pipeline, refinery-side charging tanks, and crude distillation units. In reality, the performance of these units will inevitably decay; thus, unit maintenance plans should be well integrated with normal crude movement schedules. In this paper, a novel methodology has been proposed to dynamically and simultaneously determine the optimal schedule of crude movement and unit maintenance operations. Specifically, both proactive scheduling for multiple preventive maintenance tasks and reactive scheduling for emergent corrective maintenance tasks are systematically integrated. Accordingly, the developed mixed-integer nonlinear programming (MINLP) model will optimize the operation schedule for the front-end crude supply process via minimizing the total operating cost during the scheduling time horizon. Meanwhile, it can also determine the optimal unit maintenance schedule, which will identify the best opportunities of not only isolating units from process system to perform maintenance but also resuming their services after maintenance. The model can simultaneously handle multiple unit maintenance tasks while satisfying all strict constraints for crude transferring, storing, blending, and processing operations. The efficacy of the developed methodology and the MINLP model has been demonstrated through various case studies.

Robust set-point optimization of inferential control system of crude oil distillation units

The changes in the characteristics of the crude oil feed to an atmospheric distillation unit can influence the quality of the products. Also, the crude flow rate disturbances should be handled efficiently. An inferential control structure is adopted using RGA analysis where multiple tray temperatures are controlled. Then, a closed-loop stochastic optimization framework is proposed for tighter control and set of the decision variables is extended using the set-points of the decentralized PI controllers. The closed-loop simulations show improved disturbance rejection performance of the controllers against disturbances of feed flow rate and quality as well. Also, the challenges regarding the specifications of the product quality expressed as equality constraints are addressed. Both single and joint constraints cases are discussed.

Analysis and assessment of using an integrated solar energy based system in crude oil refinery

Crude oil heating is a significant and energy intensive process in crude oil production. Large amounts of heat are required to preheat crude before it processed in a crude distillation unit. This study aims to investigate a novel thermal design for an industrial heating process, study an integrated system of different components into overall plant, incorporate solar energy in heating application and assess the key performance indicators of a crude oil refinery employing three preheating stages. Around 10% percent of the required preheating is attained through solar energy instead of conventional gas-burning techniques during the crude oil heating process. To address the intermittent behavior of the sun, a thermal storage system (TES) is incorporated. The solar energy based integrated system is also used to produce electricity through an integrated Rankine cycle. Some assessments of possible improvements are suggested by the thermodynamic analysis. The performance assessment indicates that the overall energetic and exergetic efficiencies are 60.94% and 19.34%, respectively. This study also reveals that the largest exergy destruction rate occurs in the solar field system, TES and the heat exchangers.

Energy saving potential of a simple control strategy for heat exchanger network operation under fouling conditions

A real-life benchmark system comprising a Heat Exchanger Network operated as part of Crude Distillation Unit is considered. In such systems, the crude oil stream is typically split into parallel branches and the oil mass flows through the branches are kept in constant proportion, i.e., at constant split ratio, by the process control system. In this paper, linear control systems (proportional-integral-derivative controllers) are considered and the proposed control strategy is to adjust the parallel flows so that identical temperature values are maintained at the outlets from two parallel branches and consequently, the heat recovery in the network is maximized. The aim is to enhance the energy efficiency of the system and minimise greenhouse gas emissions. A mathematical model of the heat exchanger network was built and validated on the basis of real-life data recorded during operation of the crude distillation unit. Using MATLAB/Simulink, closed-loop control was simulated to enable comparative evaluation of the studied strategy of proportional-integral-derivative control and its potential to achieve energy savings in the operation of the distillation unit under fouling conditions. Compared to the strategy of constant split ratio, the proposed strategy of equal outlet temperatures from the network branches was found to increase the total heat recovery by about 1.5%. In the studied operation period, the heat-recovery increase fluctuated in the range 150–1100 kW and the average daily energy saving was estimated at 18 MWh.

Exceeding Pinch limits by process configuration of an existing modern crude oil distillation unit – A case study from refining industry

Crude Distillation Unit (CDU) represents significant challenge for retrofitting and energy optimisation as the most energy intensive consumer in a conventional crude oil refinery. Pinch Technology and its based-methodologies are found primary keys for decades to energy savings in refining industries for a range of common economic-based and environmental objectives or applications. Typical benefits in energy savings are reported within 20–40% of original designs. However, such savings are limited and questioned when modern refiners are dealt with. The current paper addresses the revamping of a modern refinery exhibiting an existing high energy efficiency (≈93%). This implies the maximum potential energy savings would only be 7% at current process conditions. The present research proposes an algorithm that tackles energy recovery of modern refiners, enabling additional savings beyond the energy targets set by the existing process. The algorithm starts by process simulation and validation against real plant data, followed by a network optimisation, e.g. stream splitting, to reach the energy targets set by Pinch Analysis. The energy targets are then moved to another lower level by performing potential process modifications to reduce the energy consumption further. Results showed that the current modern refinery unit could reach its energy targets by stream splitting modifications with hot energy savings of 2.69 MW. Process modifications resulted in additional energy savings of 31.3% beyond the current level of the existing plant alongside less than a year of payback period for estimated capital investment. An environmental assessment is performed, and comparable reductions were obtained with respect to greenhouse gas, with reduction in CO2 emissions by 45.1%. The proposed retrofit methodology is applicable to minimising energy consumptions of refiners including modern units to achieve energy levels beyond energy targets by new process modifications.

Evaluation of the localized corrosion resistance of 316 L austenitic and 430Ti ferritic stainless steel in aqueous chloride/sulphate media for application in petrochemical crude distillation units

Corrosion problems are frequently encountered in petrochemical crude distillation units due to increased levels of chlorides and sulfur anions from the constituents of crude oil. Potentiodynamic polarization test, potentiostatic measurement, open circuit potential measurement and optical microscopy characterization was performed on 316 L austenitic and 430Ti ferritic stainless steel in 3.5 M H2SO4 solution at 0%–6% NaCl concentration to study and compared their general and localized corrosion resistance for application in industrial operating conditions simulating petrochemical crude distillation unit. Results obtained showed 316 L is significantly more corrosion resistant than 430Ti with comparable corrosion rates of 0.222 mm y−1 and 3.174 mm y−1 (316 L), and 24.218 mm y−1 and 12.238 mm y−1 at 0% and 6% NaCl concentration. Corrosion potentials of 316 L showed dominant cathodic reaction mechanisms, shifting from −0.211 VAg/AgCl to −0.290 VAg/AgCl due to higher resistance to localized corrosion reactions. Values obtained for 430Ti showed active-passive behavior resulting from general surface deterioration coupled with localized corrosion reactions. Polarization plots of 316 L displayed extensive passivation behavior during potential scanning from 0%–5% NaCl concentration. Passivation was completely absent on 430Ti plots due to accelerated destruction of the protective oxide. The morphology of 430Ti severely deteriorated with visible corrosion pits due to depassivation of specific sites on the steel surface by SO42− and Cl- anions compared to the morphology of 316 L, which starkly contrasts due to higher resistance to surface oxidation. The extent of degradation on 316 L was superficial. The open circuit potential plots of 316 L were significantly electropositive compared to 430Ti which was electronegative.

Crude Oil Desalting Using Multi-Surfactant Based on a Best Dosage, Solvent and Mixing Ratio

Crude oil desalting is the first processing step in a refinery. The objectives of crude desalting are the removal of salts, solids, and the formation of water from unrefined crude oil before the crude is introduced in the crude distillation unit of the refinery. The experimental work is divided into three schemes covering the effect of surfactant dosage, test different types of surfactants, and the effect of salt content on desalting efficiency. The results show that the crude oil desalting efficiency, increased with increasing surfactant quantity. The results indicate that desalting efficiency has lowered with increasing the salt content in crude oil. Also, the results show that the best solvent was toluene, and the best mixing ratio of solvent was 10 Vol. %.

Application of retrofitted design and optimization framework based on the exergy analysis to a crude oil distillation plant

The petroleum refining industry is one of the most complex and energy-intensive separation units that produce various petroleum products from crude oil. In this work, an entire crude oil distillation unit (CDU) process is retrofitted and optimized by a proposed theoretical retrofit-optimization framework based on established exergy loss analysis. The purpose of this analysis is to further improve the energy utilization efficiency of the process both qualitatively quantitatively. The theoretical derivation is carried out on exergy loss of key components in CDU including condensers, furnaces, and distillation columns. The locations and magnitudes of the inefficiency in the whole process are detected according to the exergy loss distribution analysis of the basic process. The exergy loss of every studied sub-unit is defined as the objective function to be minimized in the optimization of key operational parameters using the Sequential Quadratic Programming (SQP) methodology. Compared to the basic process, the exergy efficiency of improved process is increased from 28.9% to 41.4%, and the total annual consumption (TAC) is reduced by 28.7% under the same flow rates and qualities of every product. The proposed framework is able to be extended to other similar chemical separation processes to achieve a higher energy and exergy saving.

Scheduling Upstream Operations at Inland Petroleum Refineries Using a Precedence-Based Formulation

Several types of crude oils arrive at inland oil refineries to be transformed into different intermediate and finished products. Incoming crude oils should be cleverly blended to meet some quality specifications before processing them in the crude distillation units (CDUs). This requires a careful allocation of the available crude oils to the refinery tanks and a proper sequence of the tanks feeding the same CDU. This work introduces a mixed-integer nonlinear programming (MINLP) formulation that uses general-precedence sequencing variables to choose the best ordering of operations in every tank. By using a rigorous objective function, the MINLP model provides the exact operating cost of the best solution found. The replacement of nonlinear component balances by tailor-made linear constraints in the MINLP leads to a tight mixed-integer linear (MILP) model that usually yields a good MINLP feasible point. A nonlinear programming (NLP) formulation that results by fixing the 0–1 variables to their MILP-values ...