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 with cold hydrocarbons

can be an economically attractive option for certain applications, as

it reduces compression costs [8]. One type of these processes is

based on using part of the liquid feed to quench the reaction. This

approach, also known as split-feed hydroprocessing, involves

splitting the feed into several fractions, in order to inject them

selectively at different positions of the reactor, as shown in Fig. 1.

Generally, the heaviest fraction is fed at the top of the reactor, for

extended contact time with the catalyst, whereas the lighter

fractions are injected to quench downstream bed effluents. The

special feature of this feeding method is that the light fractions are

provided with treatment in combination with the heavy fraction.

Several applications of this approach for processing light feeds

have been reported up to date [9–15], however, none for heavy oils.

Furthermore, the work in this field is limited to simplified reactor

modeling examples, which were not validated with experimental

data [16–18], and the possible economical benefits have not been

yet quantified.

The aim of this work is to extend our previous study [19] on

the modeling of residue hydroprocessing in fixed-bed reactors,

to include the effect of liquid quenching with cold hydrocarbons

streams, based on representative experimental data. The model

will allow for evaluating the overall performance of the heavy

oil upgrading process with liquid quenching in order to

determine if this alternative improves the economics of the

process.

Nomenclature

aL gas–liquid interfacial area (cm1)

aS liquid–solid interfacial area (cm1)

AS sectional area of the reactor (cm2)

Asph asphaltene

CH4 light gases (represented by methane)

Ci molar concentration of compound i (mol cm3)

cp mass heat capacity (J g1 K1)

Ea activation energy

g gas mass flowrate (g s1)

GL superficial mass velocity (kg m2 s1)

Hi Henry’s law constant for compound i

(MPa cm3 mol1)

DHR overall heat of reaction

H2 hydrogen

HC hydrocarbon

HF heavy fraction

H2S hydrogen sulfide

H2/oil hydrogen-to-oil ratio (std m3/m3)

k0 frequency factor

kapp apparent reaction rate constant

kint intrinsic reaction rate constant

kj reaction rate constant for reaction j

kLi

gas–liquid mass-transfer coefficient for compound

i (cm s1)

kSi

liquid–solid mass-transfer coefficient for compound

i (cm s1)

KH2S adsorption equilibrium constant for H2S

(cm3 mol1)

l liquid mass flowrate (g s1)

LF light fraction

...