Feb-2024

Simulating VGO, WLO, and WCO co-hydroprocessing: Part 2

Economic analysis performed when co-hydroprocessing VGO, WLO, and WCO shows that WLO studied percentages increase hydrocracking unit net profits.

Mohamed S El-Sawy, Fatma H Ashour and Ahmed Refaat, Cairo University
Tarek M Aboul-Fotouh, Al-Azhar University
S A Hanafi, Egyptian Petroleum Research Institute

Article Summary

Part 1 of this study (PTQ, Q4 2023) presents simulation and analytical studies made on vacuum gasoil (VGO), waste lubricating oil (WLO), and waste cooking oil (WCO) co-hydroprocessing over commercial hydrocracking catalyst. This study follows our previous work which studied the co-hydroprocessing of VGO, WLO, and WCO experimentally on a lab-scale reactor, utilising the commercial hydrocracking catalyst. Most fuel producers prefer to utilise existing units to co-hydroprocess WLO, WCO, and VGO rather than install new separate hydroprocessing units because there is a high degree of similarity between units used to hydroprocess petroleum cuts and units to hydroprocess waste oils mixture with VGO.

In this discussion, market analysis and economic studies were conducted to illustrate the flexibility and prevalence of using these unconventional feed mixtures (blends of VGO with WLO and WCO) as industrial feedstock during the COVID-19 pandemic, which caused transportation limitations and market upsets. The analysis focused on the fluctuations in crude oil, petroleum fuels, and bio-diesel prices last year. By mixing WLO and WCO with VGO as hydrocracking feed, good opportunities for expense optimisation and net profit maximisation can be found, especially when crude oil prices increase.

Resource optimisation
Many countries were highly affected by the COVID-19 pandemic and its consequences on global markets and economics. Hard times usually lead to a concentrated effort to use all available resources. One of these resources is waste oils and their application to convert to fuels with traditional esterification for WCO, distillation followed by extraction for WLO or hydroprocessing of both. Waste recycling has several benefits, including using waste as an energy source, which will suppress toxic and hazardous emissions into the environment and reduce greenhouse gas (GHG) emissions. In addition, waste recycling is stimulating development in the region as well as aiding social structure, especially in developing countries. Furthermore, the refining industry faces numerous challenges in producing high-quality fuels at reasonable costs. Cold flow properties are often a concern when dealing with products derived from hydroprocessing waste oils or VGOs.^1,²

Generally, the hydroprocessing unit consists of a reaction section and a fractionation section to separate the reaction products into desired product streams. Hydroprocessing units’ reactors commonly use a trickle bed reactor (TBR) configuration due to its simplicity, reliability, and good operability. A TBR is a fixed bed reactor with a trickle flow regime of hydrocarbon and hydrogen mixture moving from the top to the bottom of the reactor, passing through catalyst bed(s). Usually, heavy hydrocarbons and middle distillates hydroprocessing reactors consist of more than one catalyst bed with intermediate hydrogen quenching streams to control reaction temperature, as all hydroprocessing reactions are exothermic.

Co-hydroprocessing of VGO, WCO, and WLO is a mixed-phase reaction where liquid moves downwards and forms a laminar stream around the catalyst pellets and hydrogen is distributed through available voids in the catalyst bed. Reactions start by diffusing a dissolved hydrocarbon feed mixture and hydrogen in the catalyst pores, reaching the active sites. On the active sites, cracking and hydrogenation reactions occur. These are enhanced by increasing the reaction temperature and hydrogen partial pressure.³
Modelling and simulation are important tools for optimising plant profit and operating conditions. Modelling and simulation of an existing industrial hydroprocessing unit need operating conditions and product yield identification. The simulation model case of the hydroprocessing unit consists mainly of a reaction section and a fractionation section. The most complicated aspect of building the simulation model is the calibration of the kinetic model, which forms the core of the simulation.

The reaction kinetics depend on many factors, such as reaction temperature, hydrogen partial pressure, liquid hourly space velocity (LHSV), feed composition, and catalyst configuration. From these data, in addition to product yields and specifications, simulation software can predict calibration factors that will be the core of the simulation model. To overcome the complexity of building hydroprocessing reactions kinetic models, many studies and technical papers recommend using commercial software to execute the modelling and simulation of hydroprocessing units.⁴

An extensive literature review has been conducted to study the technologies and equipment used industrially in the hydroprocessing of WCO and WLO individually, and the co-hydroprocessing mixture blended with petroleum feedstock. Axens has recently introduced a new proprietary technology called Revivoil, developed jointly with Itelyum (formerly Viscolube Italiana SpA). This technology is a significant step forward in waste lube oil re-refining and has the potential to accelerate its success.

UOP has also developed with ENI a proprietary technology called Ecofining for hydroprocessing plant-derived oil. Feedstocks include plant-derived oils like soybean, rapeseed and palm. The co-processing of waste oils is not only of interest to process technology developers, but also to refineries. For example, Petrobras has developed the H-BIO hydrogenation process to produce renewable diesel using a mixture of waste vegetable oil and mineral oil in existing oil refineries through hydrotreating units.

The co-processing of waste frying oils in a gasoil hydrodesulphurisation unit (HDS-I) at CEPSA’s refinery in Tenerife has been successful. CanmetENERGY’s research centre supports and funds such research activities. It has been observed that most refiners choose to inject WCO (on a large scale) or WLO (on a small scale) with VGO for co-hydroprocessing units, rather than installing a separate unit to hydroprocess pure WCO or WLO, taking into consideration the high degree of similarity between technologies and catalysts used in these units. The novelty of this work is to study the co-hydroprocessing of VGO, WCO, and WLO blend over commercial industrial hydrocracking catalyst. This will be followed by an economic study of the produced model in the recent market changes caused by COVID-19.^5,6,7

The aim of this study is to simulate a conceptual design of an industrial hydrocracking unit that utilises the same catalyst as our previous experimental work.1 This conceptual design has been performed using Aspen Hysys V.11, which comes with a built-in hydrocracker model (HCR). This model simulates the hydroprocessing of light and heavy petroleum fractions based on a built-in reaction network and kinetic lumps. This simulation can be used to evaluate technically and economically co-hydroprocessing normal unit feedstock of VGO vs blends of unconventional feedstocks of WCO and WLO with VGO.

Process simulation case
The industrial hydrocracking unit licensed by UOP (commercially called Unicracking unit) was simulated using Aspen Hysys V.11. This unit was selected because it utilises the experimentally used catalyst (TK-711 and DHC-8) and a similar reactor bed configuration. The reaction section of the unit consists of two reactors. The first reactor has three beds, with one for hydrotreating and the other two for hydrocracking. The second reactor has two beds, both for hydrocracking. All five beds are roughly equal in weight. The unit is designed to process 33,500 barrels per stream day (BPSD) of combined feed consisting mainly of vacuum gasoil (VGO) from the vacuum distillation unit and heavy cocker gasoil (HCGO) from the delayed cocker unit. The unit is targeted to produce light fuel products from heavy petroleum distillates while removing the majority of impurities such as sulphur, nitrogen, and oxygen.