Hidrodesulfuracion

Modeling, simulation and analysis of heavy oil hydroprocessing in fixed-bed

reactors employing liquid quench streams

Anton Alvarez a, Jorge Ancheyta a,b,*, Jose´ A.D. Mun˜oz a

a Instituto Mexicano del Petro´leo, Eje Central La´zaro Ca´rdenas 152, Col. San Bartolo Atepehuacan, Me´xico D.F. 07730, Mexico

b Escuela Superior de Ingenierı´a Quı´mica e Industrias Extractivas (ESIQIE-IPN), Unidad Profesional Adolfo Lo´pez Mateos, Unidad Zacatenco, Me´xico D.F. 07738, Mexico

1. Introduction

Nowadays, the technologies for upgrading heavy petroleum

fractions are of vital importance to the refining industry, as a result

of the growing market of high value petroleum products and

decreasing availability of light oils [1]. Among these technologies,

catalytic hydroprocessing has the capacity to increase the yield of

distillates and to reduce the level of impurities such as sulfur,

nitrogen, metals (Ni and V) and asphaltenes [2]. Commonly, heavy

oil hydroprocessing is carried out in fixed-bed reactors loaded with

CoMo/NiMo alumina supported catalysts for hydrotreating (HDT)

and hydroconversion [3].

The main drawback of heavy oil hydroprocessing in fixed-beds

is the rapid catalyst deactivation, due to the presence of metals and

asphaltenes (coke formation precursors) in the feed, drastically

reducing the cycle length [4]. However, recent advances in this

field have led to the development of graded catalyst systems that

extend significantly the length of run [5]. Typically, these systems

comprise a front-end hydrodemetallization (HDM) catalyst, a midsection

catalyst with balanced HDM/hydrodesulfurization (HDS)

activity, and a tail-end highly active HDS/hydrocracking (HCR)

catalyst [1,5]. The principal feature of the front-end catalyst is a

high-metal uptake capacity, and its main function is to disaggregate

asphaltene molecules for metals removal, so that the

downstream catalysts can operate with low-metal content

hydrocarbons.

The other important factor is a careful selection of the reaction

severity, in order to balance the quality of the product with the rate

of catalyst deactivation (i.e. cycle length). Reaction severity also

impacts the economics of the process, as it determines the total

investment of the unit (reactors, compressors, etc.), hydrogen

make-up, and heating, cooling, pumping, and compression inputs.

The Mexican Institute of Petroleum (IMP) has taken into account all

these problems and developed a catalytic hydroprocessing

technology to convert heavy and extra-heavy crude oils, either

for obtaining upgraded crude oil or producing suitable feed for

refineries [6]. Among other characteristics, the process has an

arrangement of fixed-bed reactors in series loaded with a graded

catalyst system, which in combination with low-pressure operating

conditions minimizes sludge formation.

In commercial units, the temperature and hydrogen-to-oil

(H2/oil) ratio profiles, generated by the adiabatic operation

and hydrogen quenching/recycling, differ substantially from

those observed in bench scale reactors. Consequently, when

Applied Catalysis A: General 361 (2009) 1–12

A R T I C L E I N F O

Article history:

Received 23 December 2008

Received in revised form 28 February 2009

Accepted 4 March 2009

Available online 17 March 2009

Keywords:

Heavy oil hydroprocessing

Fixed-bed reactor

Liquid quenching

A B S T R A C T

This work presents the modeling and analysis of heavy oil hydroprocessing in a fixed-bed reactor system

with liquid quenching. Hydroprocessing tests at various operating conditions were conducted in amultireactor

pilot plant, with inter-bed injection of quench gas or liquid. Based on the experimental

information, a heterogeneous plug-flow reactor model was developed to simulate the behavior of the

process with both gas and liquid quenching. Major reactions such as hydrodesulfurization (HDS),

hydrodenitrogenation (HDN), hydrodemetallization (HDM), hydrodeasphaltenization (HDAs), and

hydrocracking (HCR) are considered. The model showed to predict quite well the experimental data in

the range of the studied operating conditions. The analysis was extended to simulate the commercial

process and to analyze different quenching schemes from an economical point of view. It was

determined that the liquid quenching scheme reduces the consumption of utilities and equipment

requirements, and thereby total costs, without affecting product quality.

 2009 Published by Elsevier B.V.

* Corresponding author at: Instituto Mexicano del Petro´ leo, Eje Central La´ zaro

Ca´rdenas 152, Col. San Bartolo Atepehuacan, Me´ xico D.F. 07730, Mexico.

Tel.: +52 55 9175 8443; fax: +52 55 9175 8429.

E-mail address: jancheyt@imp.mx (J. Ancheyta).

Contents lists available at ScienceDirect

Applied Catalysis A: General

journal homepage: www.elsevier.com/locate/apcata

0926-860X/$ – see front matter  2009 Published by Elsevier B.V.

doi:10.1016/j.apcata.2009.03.008

scaling-up experimental data, an adequate reactor configuration

must be established to represent the average temperature

and H2/oil ratio used in pilot plant tests. This is done by (1)

adjusting inlet temperatures and number of catalytic beds along

with their respective lengths and (2) properly distributing the

amount of hydrogen in the quenching/recycling streams. In a

previous study on one process alternative [7], it was found that

it is not possible to quench with hydrogen the total heat release

and at the same time to keep the design average H2/oil ratio. The

latter resulted from the low gas rate circulating in the system

(H2/oil ratio of 890 std m3/m3) and the inverse relationship

between hydrogen quenching and H2/oil ratio (i.e. every quench

stream reduces the amount of recycled hydrogen entering the

reactors, thereby decreasing average H2/oil ratio); on the other

hand, augmenting hydrogen quenching capacity implied

increasing compression. Such a technical–economical limitation,

led to evaluate other alternatives for designing the quench

system.

A recent review on quenching in fixed-bed hydroprocessing

reactors pointed out that liquid quenching

...