Qatar Foundation Annual Research Forum Volume 2012 Issue 1

Gas-to-liquid (GTL) projects form an important part of Qatar's energy industry due to the country's extensive natural gas reserves. At present, commercial GTL plants in Qatar account for 36% of the total worldwide GTL production, but suffer from high operational costs due to limitations in the existing Fischer-Tropsch synthesis (FTS) reactor technologies, which are at the heart of the GTL process. Of the two FTS reactor types currently in use commercially, fixed-bed reactors (i.e. gas-phase FTS) offer poor temperature control while slurry-bed reactors (i.e. liquid-phase FTS) suffer from difficult catalyst separation and other challenges. The utilization of supercritical fluids (SCF) as solvents in FTS (SCF-FTS) provide several advantages over the existing commercial technologies. SCF-FTS can improve the heat transfer properties relative to fixed-bed reactors, while also offering high diffusivity of the reactants relative to slurry-bed reactors. The results presented here summarize multidisciplinary research activities, led by our research team at Texas A&M University at Qatar, in collaboration with top scientists from institutions around the word and supported by an industrial advisory board. The work was funded by different agencies and combined several projects, which have been undertaken over the past four years. This work was unique in that it focused on understanding both the micro- and macro-scale behaviours of the FTS chemistry and reactor. The micro-scale studies enabled better understanding of the reaction mechanism and kinetics, FTS thermodynamics and phase behavior (via experimental and modeling studies), and intra-particle catalyst effectiveness factor. The macro-scale investigations covered: 1) identifying the overall (heat/mass/hydrodynamic) profile inside the reactor, 2) selecting an appropriate supercritical solvent, and 3) building a lab scale reactor unit. The outcome of these studies is that we were able to identify the most applicable solvent(s) while providing a detailed techno-economic and safety evaluation of this process. Furthermore, the overall structure of the separation process for solvent recovery and recycle has been completed based on energy optimization. Currently, we are at the stage of developing an upgraded design for this technology based on the data to be generated from our demo-scale FTS reactor unit.

The process industry utilizes thermal energy on a massive scale and rejects a significant proportion into the environment as a low grade heat. The definition of low grade heat is fuzzy and is somewhat related to the temperature of the stream carrying such thermal energy. Estimates of low grade heat emissions are hard to compile accurately on a global scale but these are likely to be of the order of thousands of trillions of BTUs. In some cases, up to 50% of thermal energy consumed is eventually rejected as low grade heat. This waste is not only uneconomical but also environmentally damaging since it carries a carbon footprint. Modern process plants reduced a great deal of thermal energy losses through heat integration and energy recovery. However, due to process temperature requirements, a vast amount of thermal energy denoted as low grade heat is still rejected. The objectives of this work include evaluating the possibility of utilizing the low grade heat outside the process generating, in a useful manner that has both economic and environmental benefits. In the Middle East where the oil and gas industry rejects vast amounts of low grade heat, recovery and utilization for desalination is becoming a serious option. This work proposes utilization of low grade heat in membrane distillation for desalination and establishes a balance between capital and operating costs as well as carbon footprint reduction. The work is based on a couple of case studies involving well established processes, namely the vinyl chloride monomer and gas-to-liquids processes. The recovery of low grade heat will be coupled with seawater cooling thus providing a warm source of salty water feed to the membrane distillation system. The work indicated that quality potable water may be produced for the petrochemical plants and neighboring living quarters at a reasonable cost. This approach may reduce the demand for fresh water from desalination plants in major industrial complexes making these self-sufficient in fresh water. Benefits are both economic and environmental.

Background: The use of fish embryos for toxicity testing (FET) is under consideration as an alternative to traditional acute fish toxicity tests. For the past two years, a marine fish embryo test (mFET) has been under development in our laboratory as a routine ecotoxicological test for risk assessment of potential contaminants around the Qatari coastal area. Objective: The objectives of this study were to: a) develop and use a flow-through system to optimize the mFET test conditions to maintain stable concentration of volatile compounds; b) correlate the flow-through mFET to the conventional acute fish test; c) investigate changes in sensitivity of Arabian Killifish embryos to toxicity of chlorine-produced oxidants under flow-through conditions compared to the previous static mFET. Methods: The flow-through system was carried out using custom designed glass chambers. Peristaltic pumps were used to ensure constant flow conditions. To investigate the effect of the flow-through mFET on toxicity of chlorine, fertilized eggs were exposed to aqueous concentrations of calcium hypochlorite for up to 240 hours. The investigated endpoints included; coagulated eggs, somite development, heartbeat, tail detachment, hatchability and post-hatch mortality. Results: The present investigation demonstrated that the custom designed flow-through system enhanced the FET conditions compared to the static FET. The flow-through system stabilized chlorine concentration and provided a larger volume which allowed an increase in the number of test embryos and sufficient test media for chemical analysis. Conclusions: Our data showed that the flow-through system improved the mFET assay for conditions like control survivability and for the main goal of bringing the sensitivity of the embryos into alignment with published data on the effects of chlorine-produced oxidants. This dataset, in conjunction with our previous work on static test conditions provides a wider range of applicability for the assay. In order to further support the mFET as an alternative to acute fish testing, the flow-through FET is currently being extended to other potential compounds of interest.

Gas-to-liquid (GTL) products have increasingly become a promising energy resources over the past two decades. Qatar possesses the third largest proven reserve of natural gas in the world, with a net capacity approaching 900 tcf (trillion cubic foot). This has motivated Qatar to develop a long term vision, involving the investment of huge expenditures into world-class commercial plants that convert natural gas into value-added liquid hydrocarbon products. This vision was translated into the Oryx GTL plant in late 2006 and the Shell Pearl GTL plant reported to be the largest in the world, which began operations officially at the end of 2011, leading Qatar to be described as the world capital of GTL. The substantial usage of energy in Fischer-Tropsch (FT) GTL processes and the complexity of energy distribution throughout the process offer opportunities for heat integration and waste heat recovery. The objective of this paper is to carry out an energy integration analysis for a typical GTL process. The approach was started with process simulation to develop the base-case data for the process. Next, energy integration tools were used to optimize energy distribution, heat exchange, and waste heat recovery. Finally, simulation and techno-economic analysis were utilized to assess the performance of the proposed design changes and their economic viability. The resultant pinch diagram showed that a single pinch case was faced with a fixed driving force of 10 oC, in which both external cooling and heating utilities were required to satisfy energy needs. Meanwhile, the Grand Composite Curve (GCC) showed that flue gases cover most of the heating utility while cooling water covers all the required cooling utility. Moreover, the waste heat recovery study supported by HYSYS software illustrated considerable recoveries in steam qualities from discharged flue gases within the FT reactor section. In conclusion, energy integration on a GTL process was realized to be a promising one as the targets for net energy savings were found to be close to 40%. Additionally, generation of various qualities of steam can be obtained in a cost-effective manner. At the top of it, most of the recommended projects have attractive payback periods, below six years.

Background: Cobalt catalyzed Fischer-Tropsch synthesis (FTS) is a process for converting natural gas to liquid fuels. Supported cobalt catalysts are common for F-T reactions because of their high activity and selectivity for forming linear hydrocarbons. Oxide supporters affect the catalytic properties of cobalt significantly. Co and oxide support interact and lead to irreversible deactivation of the catalyst. Promoters, e.g., Pd, Ru and Pt are added to the cobalt oxide supported catalysts for various reasons, such as to increase the reducibility of Co and to act as a source for hydrogen spillover. Objectives: To investigate the oxidation isotherms of cobalt and cobalt supported oxide catalysts using coulometric titration (CT) and to examine the effect of the rhenium (Re) promoter on the reducibility of cobalt on an alumina catalyst. Methods: The sample was exposed to a gas mixture containing 10% H2, 3% H2O and 87% N2 for full reduction. The P(O2) was then established by equilibrium between H2 and H2O: P(O2)½ =K-1 * P(H2O)/P(H2) Oxygen was then pumped into the cell electrochemically by passing a current through the Pt electrodes (Fig. 1). The open-circuit potential across the electrodes (V) was measured in order to calculate P(O2) from the Nernst equation: V= RT/4F Ln PO2/0.21 Results: The oxidation isotherms obtained from the CT for reduced bulk cobalt oxide (Co3O4) (Fig. 2) and promoted catalyst (Fig. 3) exhibit two well-defined transitions. The first transition is corresponding to the oxidation of Co to CoO and the second oxidation is corresponding to CoO to Co3O4. On the other hand, the oxidation isotherms of reduced 15 wt% Co3O4/Al2O3 exhibit one transition, which is corresponding to CoO to Co3O4 (Fig. 4). It is clear that the Co/alumina compound has a limited degree of reduction, which may be due to the strong interaction between Co and alumina resulting in a non-reducible form of a Co-alumina compound (Figs. 5-7). This explains that rhenium enhanced the reduction of the cobalt/alumina catalyst to a metallic cobalt but it did not have an effect on the extent of reduction of the cobalt oxide Co3O4 to CoO. Conclusions: Coulometric titration and thermal gravimetric analysis results show that a rhenium promoter has facilitated the reduction of Co3O4 to Co (Fig. 8).

The development of clean energies is a central challenge for the sustainable development of the Gulf region. Global pressures including climate change mitigation efforts and energy security concerns are calling for strong investments in alternative sources of energy. Most of marine algae present in Qatar have no equivalents on earth and therefore could be considered as irreplaceable sources of primary and secondary metabolites. This is especially the case for hydrocolloids from red and brown algae that are cultured and used at an industrial scale for food-processing. This study analyzes the adaptability of existing biofuel production processes currently used for cooking oils or more traditional corn ethanol to algae fuel production. The potential benefits of biofuel from photosynthetic algae could be significant. Algae can be grown using land and water unsuitable for crop plant or food production, unlike some other first and second generation biofuel feedstocks. Moreover, select species of algae produce bio-oils through the natural process of photosynthesis - requiring sunlight, water and carbon dioxide, supplemented with nutrients. Growing algae therefore consume carbon dioxide, which provides greenhouse gas mitigation benefits. Finally, bio-oil produced by photosynthetic algae and the resultant biofuel will have molecular structures that are similar to the petroleum and refined products we use today. This helps ensure the fuels are compatible with existing transportation technology and infrastructure. In conclusion, if successful, bio-oils from photosynthetic algae could be used to manufacture a full range of fuels including gasoline, diesel fuel and jet fuel that meet the same specifications as today's products. This study bridges with a past survey carried out by Dr. Jean-Michel Kornprobst on the algae resources in Qatar and existing engineering processes currently developed in the United States and more specifically by the University of South Florida Polytechnic (Dr Philippidis) or the Abbess Ceter on Ecosystem Science and Policy at the University of Miami. Its objective is to assess the production capacity in Qatar as well as suggest projects and international cooperation to reach full potential.

Power generation through wind is expected to play a major role in the world's future energy portfolio. Wind power integration remains a challenging research area due to the unique characteristics of wind power generation. In particular, offshore wind has received significant attention worldwide due to the vast generation potential available. The electrical infrastructure of offshore wind farms is thus of significant importance. Multi-terminal high voltage direct current (HVDC) technology represents a preferable solution and has shown promise in solving wind farm interconnection problems. Droop control techniques have been proposed as a means to regulate the DC voltage and facilitate the automatic coordination between different converters without the need for fast communication between units. Different methodologies have been suggested to select the droop gains to satisfy the system performance specifications. In this work, a control design methodology is proposed for power sharing among the multi-terminal HVDC feeders providing that the power transmission efficiency is optimized. A simulation study on a 400 kV/1000 MW four-terminal HVDC transmission topology is conducted to determine the validity of the proposed methodology.

A user-friendly simulator based on a comprehensive computer model for slurry bubble column reactor (SBCR) developed in our laboratory was used to predict the performance of a conceptual commercial-scale (9-m ID and 50-m height) SBCR for indirect coal conversion using Fischer-Tropsch (F-T) synthesis in the presence of a cobalt catalyst. New correlations for predicting the hydrodynamic and mass transfer parameters and three different kinetic rate expressions from the available literature specifically for cobalt catalysts were incorporated in the simulator. The effects of operating conditions, including catalyst concentration, pressure, temperature, H2/CO ratio, and superficial gas velocity on the SBCR performance were predicted using the simulator. The predictions showed that the performance of the SBCR was strongly dependent on the kinetic rate expression used. At low catalyst concentration, the reactor operated in a kinetic-controlled regime with increased syngas conversion and catalyst productivity; however, increasing catalyst concentration drove the reactor to operate in a mass transfer-controlled regime with decreased syngas conversion and catalyst productivity. The transition from kinetic-controlled regime to mass transfer-controlled regime occurred at different solid concentrations depending on the kinetic rate expressions employed. High H2/CO ratios in the inlet feed gas to the SBCR led to high syngas conversion. Increasing the superficial syngas velocity in the reactor decreased the gas residence time, which decreased the syngas conversions. High operating temperature always resulted in high syngas conversion. Also, the effect of operating pressure on the SBCR performance was not clear, since increasing pressure resulted in low or high syngas conversion depending on the catalyst and kinetic rate expressions used.

Increase in energy demand and stringent emission standards drive the need for clean, alternative fuels. Gas-to-liquids (GTL), a liquid synthetic paraffinic kerosene (SPK) fuel obtained by Fischer-Tropsch synthesis has drawn global attention as an alternative aviation fuel due to its clean combustion characteristics when compared to conventional jet fuel. However, alternative fuels are expected to fulfill the key requirements such as having a quick atomization and vaporization and combustion and emission characteristics; similar to that of conventional fuels in order to qualify as a drop-in fuel in current aviation gas turbine engines. It is important to understand the atomization of these alternative fuels to better understand their combustion and emission characteristics. The key objective of this work is to evaluate the atomization characteristics of GTL-SPK which could potentially be used as a drop-in fuel in aircraft gas turbine engines in future. This work will discuss in detail the experimental facility developed, methodology and the results obtained using two GTL-SPKs having different chemical compositions. The spray characteristics such as droplet size and distribution are studied at three injection pressures using a pressure nozzle and compared to that of conventional Jet A-1 fuel. Results obtained clearly show that despite a considerable change in chemical composition, which in turn modestly altered the fluid properties among SPKs, the change in spray characteristics are found to be insignificant. This could be due to the minimal difference in fluid properties between the GTL-SPKs. In addition, the spray characteristics of the GTL-SPKs show close similarity to the spray characteristics of Jet A-1 fuel.