Qatar Foundation Annual Research Forum Volume 2011 Issue 1

I. Introduction

Photovoltaic (PV) energy generation has been one of the most active research areas in the past decades, because it is essentially inexhaustible and environmental friendly with respect to the conventional energy sources.

However, nowadays the higher initial installation cost, lower efficiency and reliability of the PV system still block its widespread application. To overcome these problems, our project focuses on a novel PV system, including the novel PV interface inverter by combination of the battery into the quasi-Z-source inverter (qZSI). All of these aim at controlling output power of the PV system to the grid flexibly, thus, to extremely improve the scientific and economic developments of Qatar.

II. Methods And Results

This paper proposes the charging and discharging control of qZSI with battery for PV power generation system.

1) To monitor the battery state of charge (SOC), the output power-based SOC control is designed.

2) The closed-loop control of shoot-through duty ratio and direct power control of space-vector modulation are separately designed to acquire the stability of DC and AC voltages.

3) Related simulations and experiments are performed.

4) A 3 KW hardware experimental platform is being set up based on the TMS320F28335 32-bit floating-point DSP controller and PM100CLA120 Intelligent Power Module (IPM) for main power switching devices. We have done optimization design on the hardware circuits. Up to now, the hardware prototype has been partly set up.

III. Conclusions And Future Work

The acquired results indicate that the proposed control algorithm could stabilize the DC bus voltage and realize the battery charging and discharging without extra circuits, providing a significant method to enhance the performances of PV power generation systems.

Next step is to go on building the setup and perform related experiments, and then apply the designed control methods on the multilevel PV system, which is in accordance with our project timeline.

This paper highlights the recent work carried out at Texas A&M University at Qatar (TAMUQ) in the development of novel synthetic fuels geared towards the aviation industry's utilization. The research activities implemented involve a unique multi-disciplinary collaboration between academia and industry, which was facilitated by QF through funding provided by the Qatar Science and Technology Park (QSTP) and Rolls-Royce. This project utilizes the expertise of academia in fundamental research and the R&D expertise of world leading industrial firms (Shell and Rolls-Royce).

The broad objective of the project is to upgrade Gas-to-Liquid (GTL) derived Synthetic Paraffinic Kerosene (SPK) based fuels to meet the standards and properties as required by the aviation industry. The work done by our group at TAMUQ is concerned with formulating and testing GTL derived jet fuels for their suitability as replacements for kerosene. The SPK fuels being developed play an important role in the diversification of Qatar's natural gas resources, while also being guided by Qatar Airways inspiration on becoming the world leader in alternative clean fuel utilization.

This paper specifically looks at the relationship between the chemical compositions of SPKs and their physical properties. The chemical groups that compose SPK are normal-, iso- and cyclo- paraffins. The role these paraffins had on jet fuel properties (e.g. density, freezing point, flash point, etc…) were tested and correlated with their hydrocarbon composition. TAMUQ built a world-class Fuel Characterization Laboratory to conduct experimental investigations aimed at developing a wide array of blends using a diverse portfolio of solvents and base chemicals. The experimental data provide a basis for developing statistical models for composition vs. property relationships. Of the properties tested, the freezing point relationship was the most interesting as it showed high nonlinearity over wide range of compositions. Furthermore, a unique aspect of the freezing point testing protocol was the capturing of images of the fuel crystals as it showed a variety of crystal shapes based on blend profiles. A key aspect of the further planned studies is the inclusion of important new chemical groups such as aromatics in the preparation of blends.

Natural gas and oil processing, among many other applications in the chemical industry, depends on accurate predictions of the thermodynamic and transport properties for their accurate and reliable design. Especially in the energy sector, in which the flow rates of process streams are large and equipment is big, improper design can be costly, both in terms of investment and operating costs. Equations of state (EOS) enable the evaluation of thermodynamic properties over a wide range of temperature and pressures and are routinely used for chemical process design. Many EOS exist but relatively few have become widely used, most notably the Peng-Robinson EOS in the oil and gas industry. However, the Peng-Robinson EOS and most other cubic EOS are unsuitable for predicting the phase behavior of mixtures that contain polar compounds. Such mixtures occur even in industries normally associated with the processing of non-polar substances (e.g., hydrocarbons). For example, natural gas may be contaminated by small amounts of water, carbon dioxide, and hydrogen sulfide, often removed using amines and glycols. Modern models such as the SAFT (statistical associating fluid theory), and its variants, and the CPA (cubic plus association) EOS are suitable alternatives but require solving the association equations before computing any thermodynamic property. The Mattedi-Tavares-Castier (MTC) EOS is an entirely explicit model that avoids this drawback but is capable of predictions of accuracy similar to that of the SAFT and CPA EOS. In this paper, we show results of calculations of phase equilibrium and calorimetric properties with the MTC EOS for systems of interest to gas processing industries.

Many developed and developing economies are seeking to mitigate future climate change risks by developing strategies to reduce carbon emissions and the use of fossil fuels. Industrial energy use efficiency can be significantly enhanced by better energy recovery and integration promises significant potential to reduce emissions at low cost. These approaches are seen as crucial enablers of sustainable solutions in industries and are expected to reduce energy consumption significantly within existing technology. Many concepts and methods have been proposed for optimizing energy systems for individual processes and multiple processes linked through central utility systems. Pinch analysis along with other principles for process integration is the most widely applied approach to maximize process heat recovery. Systematic methods are also available for energy integration in an overall plant, or Total Site, consisting of multiple processes served by a common utility system. Scientific community also takes attention on development of sustainable industrial zone.

Even though not adequately covered by design approaches, reductions can be further advanced by energy recovery between multiple plants to exploit synergies between heating, cooling and power requirements in industrial zones or cities. In these zones significant quantities of fuel are combusted in order to provide the necessary energy for industrial activities. In many countries, substantial reductions in fuel consumption and GHG emissions at a national level would require efficiency gains in the industrial zones. Multiple processing plants are typically concentrated in a zone, with each plant consisting of one or more processes. Plants have their own independent operating and maintenance schedules, utility systems, and are owned and operated by different entities. The distances between plants can be considerable. To date, waste heat recovery and reuse across processing plants in industrial zones is a largely unexplored research area. We present an approach to enable the targeting of waste heat recovery and cogeneration potentials across plants in industrial zones and the development of concrete integration options based on economic criteria.

To face new hydrocarbon production metering systems and back allocation challenges, Total E&P Qatar and its Research Center (TRC-Q), located in the Qatar Science and Technology Park (QSTP), test novel approaches to improve current production metering system in the Al-Khalij field. This field is operated under a Production Sharing Agreement (PSA) with Qatar Petroleum (QP).

A field pilot, which involves three platforms offshore, is currently conducted to test a Data Validation and Reconciliation (DVR) software. This tool is used for production accounting, monitoring and as an alarm system related to equipments’ failure. The main outcome to be expected from this pilot will be an automatic validation of on-line production data before their final recording in the database.

The key advantage of the DVR approach is to take into account all the information redundancy and data uncertainties. In the DVR approach, a realistic uncertainty is associated with the information (measurement / model parameter) and a statistical method is applied to re-estimate and improve simultaneously the information and its subsequent uncertainty.

The current status of this study is presented along with improvements and challenges.

A few examples of on line monitoring of Al-Khalij Wells’ production are presented through a comparison between the DVR on-line virtual meter outputs and the on-site production tests. The results, obtained from sensitivity analysis are also discussed to assess the improvements achieved by applying the DVR approach.

There have been a number of studies regarding the efficiency of state-of-the-art thermal (Multi-Effect Distillation, MED), power driven (sea water reverse osmosis, SWRO) and hybrid (MED/SWRO) desalination systems. The comparisons between desalination technologies can be made on a number of critical parameters such as (i) cost of produced water, (ii) energy efficiency, (iii) environmental impact, (iv) reliability and (v) footprint. Whilst the reported relative advantages with respect to parameters (iii) through (v) are conclusive, there remain conflicting recommendations with respect to parameters (i) and (ii), partly due to energy pricing assumptions. Furthermore, existing studies work on the implicit assumption that there is demand for surplus power from integrated power generation and desalination systems.

The presented assessments compare the different thermal, power driven and hybrid desalination systems for output (water/power) achieved from identical energy inputs into thermal power and co-generation cycles for different ratios of desired water and power outputs. This eliminates energy and water pricing issues from the analysis and makes the findings applicable to a range of conventional (e.g. natural gas) and renewable (e.g solar) thermal energy sources. A number of simulations studies have been performed to identify the most energy efficient and cost effective desalination technologies for different water and power generation needs. The key parameters such as power and heat requirements and capital expenditures used in the thermodynamic and economic assessments are in line with ranges reported in the literature and existing plant data. Trade-offs between capital intensity and energy efficiency, which are particularly pronounced in thermal technologies, have also been studied. The paper makes clear recommendations as to the preferred desalination technology for a given seawater quality and water and power demand situation. The paper further explores the impact of technological advances in the form of lower capital costs and higher energy efficiency in the two broad classes of (i) power driven, and (ii) thermal desalination technology. All studies have been performed for seawater qualities observed in the Arabian Gulf.

The estimated sulphur output from Qatar is around 4 Mtpa by 2012, primarily from gas processing operations(Sulphur magazine, March/April 2009). Shell is using novel technologies to utilize sulphur in various applications such as concrete (Shell Thiocrete*), asphalt (Shell Thiopave*) and fertilizers (Shell Thiogro*). The sulphur utilization programme in Qatar Shell Research and Technology Centre is part of a global research and development effort to develop Shell's sulphur concrete and sulphur modified asphalt technologies, with particular emphasis on the needs of the Gulf region. Shell's innovative sulphur concrete technology has the potential to take sulphur concrete from use in niche applications such as chemical flooring to more mainstream applications such as garden products, road construction products (e.g. pavers and traffic barriers) and marine products. This is because the relatively low cost of the modification technology allows sulphur concrete to be considered in applications previously covered only by Portland cement. The first field trial of sulphur concrete in Qatar is a 16 square metre area of sulphur concrete tiles in the Pearl GTL Worker's Village, Ras Laffan Industrial City, Qatar, laid in May 2008. Laboratory results showed that the bending strength of all the sulphur concrete mixtures was greater than the strength of the cement concrete. Moreover, the water absorption of the sulphur concrete tiles was lower than that of the cement concrete tiles. Shell's sulphur-modified asphalt is a technology developed by Shell Sulphur Solutions in 2003, enabling a portion of the bitumen in an asphalt mix to be replaced by modified sulphur, resulting in a pavement that has enhanced mechanical properties such as increased stiffness and significantly reduced permanent deformation. A trial two-lane section of roadway of asphalt mix containing sections of Shell Thiopave and conventional asphalt mixture was constructed in October 2007 at Pearl GTL Worker's Village. The results of the field monitoring study showed that the total road section (sulphur-modified asphalt and conventional mixture) was free of any moderate or major distresses. Industrial hygiene monitoring during laying operations showed that SO2 and H2S emissions remain below the maximum limits when the temperature is controlled than 1450C.The laboratory characterization showed that the sulphur-modified asphalt mixture exhibited better resistance to permanent deformation and higher stiffness than the conventional mixture.

Background: Laser - Ultrasound is a new non-contact technique used to detect the defects in the hot surfaces like hot billets etc. Determination of corrosion in the plates, using this non-contact technique seemed a promising research effort.

Objectives: In this work, an inspection system has been presented that uses Laser-Ultrasound (LU) technique for Nondestructive testing (NDT) of metallic structures with specific interest in Oil & Gas sector.

Methods: The developed system is the first one of its kind in the Middle- Eastern region. The nature of signals is quite unique as well and traditional signal processing runs into a lot of algorithmic complications with them. A new approach has been developed for this setup in order to efficiently enhance signal to noise ratio for the underlying signals so that any subsequent classification/intelligent-detection system can be based on the outcomes of this algorithm. Multiform Tiltable Exponential Distribution (MTED) kernel, which is a generalization of 2nd order Cohen's class functions in Time-Frequency Representation (TFR) space, has been used in this work to isolate the essential frequency components with temporal and frequency based masking filters.

Results: While detecting defect points is quite similar to the conventional ultrasonic testing, the detection of corrosion is quite different. The reason being is the surface properties, and hence the surface vibrations, are quite different for a corroded surface as compared to a polished surface. In this respect, we have observed the propagation of the surface Rayleigh waves manifests a pattern that can be mapped to the corrosion concentration on the surface.

Conclusion: Interesting observation has been made with coated corroded surfaces where the behavior has been found to be quite similar. Thus, the underlying technique can be applied without any need to remove the coatings from the sample under study.

To adequately predict reliability and optimize the time-to-maintenance for complex system design and reliability problems, this research develops a new model for complex systems, which are subject to performance degradation and multiple dependent failure modes. In particular, the hazard rate corresponding to each failure mode depends both on time and system state. The system state stochastically degrades over time, and the degradation is described by a stochastic process. The degradation rate, in particular, depends on time and is also a function of the degradation level.

This research develops a reliability model for complex systems, which are subject to performance degradation and multiple dependent failure modes. A joint model of system degradation and failure time is constructed. The system state stochastically degrades over time, and the degradation is described by a stochastic process. Unlike existing reliability models, we consider a realistic scenario where the degradation rate is, not only a function of time, but also the degradation level at that time.

The goal of this research project is to develop the optimum Condition-Based Maintenance (CBM) schedules. The developed model will be used as the basis in our future research on CBM scheduling.

Depleting oil reserves, environmental pressure, as well as abundant reserves of coal, natural gas and biomass, have all contributed to a revived interest in Fischer-Tropsch (F-T) technology for producing ultra-clean, virtually sulfurfree, transportation fuels and chemicals. F-T technology involves conversion of synthesis gas (i.e., a mixture of H2 and CO) to a wide spectrum of hydrocarbons. In this study, the kinetics of the Fischer Tropsch (FT) synthesis reaction over 0.27 % Ru 25 % Co/Al2O3 catalyst was studied in a 1L stirred tank slurry reactor (STSR). Supported cobalt catalysts and slurry reactors are used in commercial processes for natural gas conversion to liquid fuels (e.g. ORYX GTL in Qatar). With known kinetics one can size reactors and predict their performance as a function of process conditions. Experiments were conducted at reactor pressures of 1.4 MPa and 2.4 MPa, temperatures of 205°C and 220°C, H2/CO feed ratios of 1.4 and 2.1 and gas space velocities ranging from 2 to 15 NL/g-cat*h.

Langmuir-Hinshelwood-Hougen-Watson (LHHW) type rate equations were derived on the basis of a set of reactions originating from carbide, Eley-Rideal and enolic pathways, and two empirical power laws from the literature were used to describe CO disappearance rates.

Model rate laws were fitted to isothermal experimental rates using least-squares nonlinear regression to obtain model parameter values. Physical and statistical tests were used to discriminate between rival models. Optimisations were performed by first applying bounds to obtain realistic values of the parameters and then assumptions were made regarding the degree of adsorption for some species. Finally, nonlinear regression of model rate laws using non-isothermal experimental rates was also performed by applying Arrhenius law-based constraints to obtain physically meaningful results.

Goodness of fit for the most physically significant models were compared using qualitative (parity curves) and quantitative (mean absolute relative residuals (MARR), R-square and F-test) analysis. It was found that the model based on carbide mechanism involving dissociative CO and hydrogen adsorption (M1) and the model based on hydrogen-assisted dissociative adsorption of CO followed by hydrogenation of dissociatively adsorbed CO (M3) provided the best fit to the experimental data.