Catalytic hydrotreating (HDT) is a mature process technology practiced in the
petroleum refining industries to treat oil fractions for the removal of impurities (such as
sulfur, nitrogen, metals, asphaltene). Hydrotreating of whole crude oil is a new
technology and is regarded as one of the more difficult tasks that have not been reported
widely in the literature. In order to obtain useful models for the HDT process that can
be confidently applied to reactor design, operation and control, the accurate estimation
of kinetic parameters of the relevant reaction scheme are required. This thesis aims to
develop a crude oil hydrotreating process (based on hydrotreating of whole crude oil
followed by distillation) with high efficiency, selectivity and minimum energy
consumption via pilot plant experiments, mathematical modelling and optimization.
To estimate the kinetic parameters and to validate the kinetic models under different
operating conditions, a set of experiments were carried out in a continuous flow
isothermal trickle bed reactor using crude oil as a feedstock and commercial cobaltmolybdenum
on alumina (Co-Mo/¿-Al2O3) as a catalyst. The reactor temperature was
varied from 335°C to 400°C, the hydrogen pressure from 4 to10 MPa and the liquid
hourly space velocity (LHSV) from 0.5 to 1.5 hr-1, keeping constant hydrogen to oil
ratio (H2/Oil) at 250 L/L. The main hydrotreating reactions were hydrodesulfurization
(HDS), hydrodenitrogenation (HDN), hydrodeasphaltenization (HDAs) and
hydrodemetallization (HDM) that includes hydrodevanadization (HDV) and
hydrodenickelation (HDNi).
An optimization technique is used to evaluate the best kinetic models of a trickle-bed
reactor (TBR) process utilized for HDS, HDAs, HDN, HDV and HDNi of crude oil
based on pilot plant experiments. The minimization of the sum of the squared errors
(SSE) between the experimental and estimated concentrations of sulfur (S), nitrogen
(N), asphaltene (Asph), vanadium (V) and nickel (Ni) compounds in the products, is
used as an objective function in the optimization problem using two approaches (linear
(LN) and non-linear (NLN) regression).
The growing demand for high-quality middle distillates is increasing worldwide
whereas the demand for low-value oil products, such as heavy oils and residues, is
decreasing. Thus, maximizing the production of more liquid distillates of very high
quality is of immediate interest to refiners. At the same time, environmental legislation
has led to more strict specifications of petroleum derivatives. Crude oil hydrotreatment
enhances the productivity of distillate fractions due to chemical reactions. The
hydrotreated crude oil was distilled into the following fractions (using distillation pilot
plant unit): light naphtha (L.N), heavy naphtha (H.N), heavy kerosene (H.K), light gas
oil (L.G.O) and reduced crude residue (R.C.R) in order to compare the yield of these
fractions produced by distillation after the HDT process with those produced by
conventional methods (i.e. HDT of each fraction separately after the distillation). The
yield of middle distillate showed greater yield compared to the middle distillate
produced by conventional methods in addition to improve the properties of R.C.R.
Kinetic models that enhance oil distillates productivity are also proposed based on the
experimental data obtained in a pilot plant at different operation conditions using the
discrete kinetic lumping approach. The kinetic models of crude oil hydrotreating are
assumed to include five lumps: gases (G), naphtha (N), heavy kerosene (H.K), light gas
oil (L.G.O) and reduced crude residue (R.C.R). For all experiments, the sum of the
squared errors (SSE) between the experimental product compositions and predicted
values of compositions is minimized using optimization technique.
The kinetic models developed are then used to describe and analyse the behaviour of an
industrial trickle bed reactor (TBR) used for crude oil hydrotreating with the optimal
quench system based on experiments in order to evaluate the viability of large-scale
processing of crude oil hydrotreating. The optimal distribution of the catalyst bed (in
terms of optimal reactor length to diameter) with the best quench position and quench
rate are investigated, based upon the total annual cost.
The energy consumption is very important for reducing environmental impact and
maximizing the profitability of operation. Since high temperatures are employed in
hydrotreating (HDT) processes, hot effluents can be used to heat other cold process
streams. It is noticed that the energy consumption and recovery issues may be ignored
for pilot plant experiments while these energies could not be ignored for large scale
operations. Here, the heat integration of the HDT process during hydrotreating of crude
oil in trickle bed reactor is addressed in order to recover most of the external energy.
Experimental information obtained from a pilot scale, kinetics and reactor modelling
tools, and commercial process data, are employed for the heat integration process
model. The optimization problem is formulated to optimize some of the design and
operating parameters of integrated process, and minimizing the overall annual cost is
used as an objective function.
The economic analysis of the continuous whole industrial refining process that involves
the developed hydrotreating (integrated hydrotreating process) unit with the other
complementary units (until the units that used to produce middle distillate fractions) is
also presented.
In all cases considered in this study, the gPROMS (general PROcess Modelling
System) package has been used for modelling, simulation and parameter estimation via
optimization process. / Tikrit University, Iraq
| Identifer | oai:union.ndltd.org:BRADFORD/oai:bradscholars.brad.ac.uk:10454/5363 |
| Date | January 2011 |
| Creators | Jarullah, Aysar Talib |
| Contributors | Mujtaba, Iqbal, Wood, Alastair S. |
| Publisher | University of Bradford, School of Engineering, Design and Technology |
| Source Sets | Bradford Scholars |
| Language | English |
| Detected Language | English |
| Type | Thesis, doctoral, PhD |
| Rights | <a rel="license" href="http://creativecommons.org/licenses/by-nc-nd/3.0/"><img alt="Creative Commons License" style="border-width:0" src="http://i.creativecommons.org/l/by-nc-nd/3.0/88x31.png" /></a><br />The University of Bradford theses are licenced under a <a rel="license" href="http://creativecommons.org/licenses/by-nc-nd/3.0/">Creative Commons Licence</a>. |
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