Background
Topsoe designs catalytic reactors used for the production of methanol from synthesis gas. The synthesis gas contains mainly hydrogen, carbon monoxide and carbon dioxide and will be produced from eg natural gas, oil or coal.

The reactor is a vertical tubular reactor. The catalyst is contained inside the tubes (typically 2000 to 4000 tubes, 7 m long) and on the outside of the tubes, boiling water is used to remove the heat from the exothermic reaction taking place inside the tubes.

The catalyst in the tubes is loaded tube by tube through the top of the reactor. The bottom of the reactor is filled with ceramic balls acting as suppport for the catalyst inside the tubes. The catalyst must be replaced on a regular basis, say every 5 years, and with the present design unloading is carried out through a number of openings at the bottom of the reactor, whereby the ceramic balls and the catalyst will be dumped into a container placed below the reactor.

The challenge
The ceramic balls are rather costly and as they can be reused, they are separated from the catalyst in a screening process after being dumped. Then the ceramic balls are reloaded through an opening at the bottom of the reactor before loading of fresh catalyst.

As the operation during catalyst replacement is rather tiresome, the project goal was to construct a new design for support of the catalyst omitting the ceramic balls.

The solution
In this case, the catalyst support is provided by a grid arrangement located just below the catalyst tubes. The grid is divided into a number of sections and hinged in a manner that allows the grid sections to be released from the normal position and subsequently opening up for the catalyst to drop out of the reactor. The grid release can be carried out from the outside of the reactor. After the reactor has been unloaded, the grids can be swung back in their normal position and fresh catalyst can be loaded.

The project work

• function analysis of the existing solution
• function analysis of a number of alternative solutions
• detailed design of one solution comprising material selection, stress calculations, welding specifications, detailed drawings and cost estimate

Students
Dennis Daugård Hansen and Lars Lundberg Kristensen, Ingeniørhøjskolen i København (IHK), Machinery Engineering Department

Bachelor thesis in the Technology Division, Mechanical Engineering Department

Background
In the energy sector high temperature corrosion of metals due to oxidation, sulphidation, carburisation and metal dusting is a major concern.

The project investigates the degradation of high alloyed materials and coatings at temperatures above 1000°C under oxidation conditions.

Key parameters
Key parameters of the project include

• characterisation of the oxide films formed
• grain growth of the base metal
• changes in phase composition
• formation of brittle precipitates
• interdiffusion between base metals and coatings
• disbanding of coatings

Techniques
The following techniques were used:

• heat treatments under controlled conditions
• preparation of metallographic specimens
• light optical microscopy
• scanning electron microscopy
• electron dispersive X-ray analyses
• x-ray diffractometry
• microhardness measurement

Student: Stine Søndergaard, DTU, Department of Chemical Engineering
Engineering trainee in the Technology Division, Engineering development department

Background
Topsoe's WSA process - Wet gas Sulphuric Acid - is used for cleaning sulphurous off gases. The content of sulphur dioxide (SO2) in the flue gas is catalytically oxidised into sulphur trioxide (SO3) and by reaction with water converted to sulphuric acid (H2SO4) - commercial quality concentrated sulphuric acid.

Project goal
The project investigates two areas for possible improvement of the process:

Combustion of sulphur feed stocks, catalytic oxidation, hydration and condensation are all exothermal reactions. The excess heat is used for steam production and process-to-process heat recovery. The integration of energy and the degree of heat recovery in a WSA plant was investigated in order to identify possibilities for improvement.

The parameters for allowable emissions differ from Chinese environmental legislation to European legislation. As the market in China is growing, it is desirable to adapt the design of the WSA units by optimising the operating conditions to meet the Chinese environmental legislation demands in the most economical way using the advantages of the WSA process.

In order to determine an economical optimum for design of the process it was investigated how different operating conditions influence on the design of equipment and production figures.

Student
Annette Wendt, LTH, Department of Chemical Engineering

Master thesis in the Technology Division, Environmental Process Engineering Department

Background
Due to increased political pressure to improve the air quality, tighter and tighter specifications on transport fuels are being introduced. The sulphur specification for diesel in the EU is 10 wt ppm from 2009, and a similar specification has been introduced in Japan. The sulphur specification for diesel in the US has been 15 wt ppm since 2006.

Within this decade it is expected that a significant part of the world will also move towards an ultra low sulphur diesel (ULSD) specification of 50 ppm (however expected to e as low as 10 wt ppm S in the large cities). As a consequence of these tight specifications, the need for hydrotreating capacity grows.

Hydrotreating
Removal of organic sulphur is carried out in hydrotreating units, where diesel oil and hydrogen flow concurrently down through a bed of porous catalyst particles (usually CoMo or NiMo on an alumina support). Several reactions take place in a hydrotreater:

• hydrodesulphurisation (HDS)
• hydrodenitrogenation (HDN)
• hydrodearomatisation (HDA)

The saturation of aromatics (HDA) is important, since several properties of the diesel fuel, eg the cetane number and the emission characteristics, depend on the content of aromatic compounds.

Saturation of fused poly-aromatic rings is known to be fast at typical hydrotreating conditions, and the conversion is therefore often limited by thermodynamic equilibrium, whereas the saturation of mono-aromatics is much slower. The catalytic reactions take place inside the liquid-filled pores of the catalyst particles and therefore require the diffusion of hydrogen from the gas phase through a liquid film and into the particle before a reaction can take place. Thus, the conversion may be limited by mass transport of the reacting species depending on the process conditions.

Objective
Using naphthalene hydrogenation as a model reaction, the project develops a model to describe the hydrodearomatisation reactions taking place in a trickle-bed reactor, accounting for the intrinsic kinetics, thermodynamic equilibrium constraints, vapor-liquid equilibrium and mass transfer/diffusion limitations.

Student
Rasmus Risum Boesen, DTU, Department of Chemical and Biochemical Engineering
Master thesis in the R&D Division (Refinery Process)

Background
The major part of the industrialised world is trying to limit the sulphur content in transportation fuel for environmental reasons. Many researchers in the field of naphtha hydroprocessing agree that the lowest achievable sulphur level in a single stage may be dictated by the extent of recombination – a term applied for the reaction of olefins with hydrogen sulphide.

The aim of this project has been to obtain a solid understanding of recombination reaction kinetics and thermodynamics. This understanding is critical to the design and operation of ultra low sulphur hydro-desulphurisation naphtha units.

Experimental work was carried out at Topsoe's facilities. The experiments were used to collect information regarding recombination, and the reactions that directly influence recombination. These reactions are hydrogenation/dehydrogenation, hydrodesulphurisation, olefin isomerisation and cracking.

The experimental work carried out at Topsoe was planned in collaboration between the student and the project supervisors. The actual experimental work was carried out by experienced technicians in Topsoe’s pilot plants, and the data were analysed by the student.

Theoretical work
A rigorous thermodynamic model was developed from first principles and used to s imulate part of the experimental work. The model showed good predicting properties.

Many disciplines were applied in this project, eg thermodynamics, kinetics, mathematics, programming and organic chemistry. The close cooperation between the student, supervisors and laboratory technicians ensured a good workflow and provided an excellent working environment.

Student
Yassir Ghiyati, MSc, Chem. Eng.

Master thesis carried out between February and June 2007 in collaboration with
Department of Chemical and Biochemical Engineering, Technical University of Denmark
Research and Development, Refinery Process

Currently working as Technology Sales Manager at Topsoe, yizg@topsoe.dk