Nov-2023

Simulation VGO and waste lubricating/cooking oil co-hydroprocessing

Software used to build a simulation case for industrial hydrocracking of VGO, WCO, and WLO validates predicted values of gasoline and middle distillates product yields.

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

Article Summary

This study presents simulation and analytical studies on vacuum gas oil (VGO), waste lubricating oil (WLO), and waste cooking oil (WCO) co-hydroprocessing over commercial hydrocracking catalyst. It follows 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 individual separate hydroprocessing units because there is a high degree of similarity between units used to hydroprocess petroleum cuts and units to hydroprocess waste oils mixtures with VGO.

A conceptual design of an industrial hydrocracking unit is simulated and validated using the proprietary special built-in tool RefSYS from the proprietary Aspen HYSYS V.11 (or HYSIS V.11) program. The calibrated and validated hydrocracking model is run with operating conditions and feed compositions. These parameters are pre-selected during experimental trials executed in previous experimental work. The model runs forecast process variables (hydrogen consumption, quenching rate, heating duty, cooling duty), helping in process optimisation and energy saving.

Waste recycling
Many countries were highly affected by the COVID-19 pandemic and its consequences on global markets and economics. This usually led to intensively trying to use all available resources. One of these resources is waste oils and their application for fuels conversion with traditional esterification for WCO, distillation followed by extraction for WLO or hydroprocessing of both. Waste recycling has several benefits, including the use of waste as an energy source to 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 social structure aiding, especially in developing countries. Furthermore, many challenges are facing the refining industry aiming to produce high-quality fuels with considerable costs. Products from hydroprocessing waste oils or VGOs are frequently tackled by cold flow properties.¹

The hydroprocessing unit generally consists of a reaction section and a fractionation section to separate reaction products into desired product streams. Hydroprocessing units’ reactors widely use the trickle bed reactor (TBR) configuration due to its simplicity, reliability, and good operability. 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 down, forming a laminar stream around catalyst pellets and hydrogen distributed through available voids in the catalyst bed. Reactions start by diffusing dissolved hydrocarbon feed mixture and hydrogen in catalyst pores reaching active sites. On the active sites, cracking and hydrogenation reactions occur and are enhanced by increasing reaction temperature and hydrogen partial pressure.²

Modelling and simulation of an existing industrial hydroprocessing unit needs 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 course in the simulation model building up is the kinetic model calibration, which is the core of the simulation model.
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 a hydroprocessing reactions kinetic model, many studies and technical papers recommend using commercial software to execute the modelling and simulation of hydroprocessing units.³

Many recent studies depend on commercial software to simulate hydroprocessing units aiming to use these simulation models in process optimisation and profit maximisation. In 2018, Eslam S. Sbaaei and Tamer S. Ahmed modelled and simulated a hydrotreating unit that processes middle distillates produced from a delayed coker unit (DCU). This model allows them to find room for energy saving, productivity increase, and fuel consumption reduction.^4,5 Saeid Shokri et al. studied the application of particle swarm optimisation (PSO) algorithm using Visual Basic 6.0 in modelling an existing industrial hydrocracking unit in 2017.

The produced model gives good predictions regarding product yield distribution with an error of less than 1% for operating parameters within building model limits. In 2009, a fluid catalytic cracking (FCC) unit was modelled using the fourth-order Runge-Kutta algorithm (Visual Basic) to optimise the FCC naphtha yield of this industrial unit processing mainly VGO in a riser reactor by Kenneth Dagde. This study depends mainly on the five-lump kinetic scheme to describe the cracking reactions.⁶

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 of them blended with petroleum feedstock. Axens recently started marketing its new proprietary technology (Revivoil) developed jointly by Axens and Itelyum (formerly Viscolube Italiana SpA), which goes a long way to put WLO re-refining on the fast track to success. UOP also has its proprietary Ecofining technology developed by UOP and ENI for hydroprocessing plant-derived oil.