Assessment of thermal stresses and ratchetting in reactor vessels

Reactor vessels are often subject to “hot spots” developing at certain positions on the shell, which, if they are of a cyclic nature, may result in strain growth and fatigue failure if the amplitude of the cyclic strains are not restricted.

The paper deals with an investigation of a particular vessel with the object of determining the characteristics of “hot spots” that would cause cyclic plasticity or ratchetting in order to determine the limiting criteria to avoid or restrict such effects onder continuous operational conditions.

The basis of the investigation is finite element analysis. Temperature dependent elasto-plastic material properties are taken into account and the mesh is refined in selected “hot spot” positions in order to obtain accurate strain and stress states under cyclic loading conditions.

The assessment criteria are discussed which are the basis of recommendations for continuous operation under cyclic conditions.     

Environmental assessment and extended exergy analysis of a “zero CO2 emission”, high-efficiency steam power plant

Aim of this paper is to analyze the performance of an innovative high-efficiency steam power plant by means of two “life cycle approach” methodologies, the life cycle assessment (LCA) and the “extended exergy analysis” (EEA).

The plant object of the analysis is a hydrogen-fed steam power plant in which the H₂ is produced by a “zero CO₂ emission” coal gasification process (the ZECOTECH^© cycle). The CO₂ capture system is a standard humid-CaO absorbing process and produces CaCO₃ as a by-product, which is then regenerated to CaO releasing the CO₂ for a downstream mineral sequestration process.

The steam power plant is based on an innovative combined-cycle process: the hydrogen is used as a fuel to produce high-temperature, medium-pressure steam that powers the steam turbine in the topping section, whose exhaust is used in a heat recovery boiler to feed a traditional steam power plant.

The environmental performance of the ZECOTECH^© cycle is assessed by comparison with four different processes: power plant fed by H₂ from natural gas steam reforming, two conventional coal- and natural gas power plants and a wind power plant.     

Nuclear methane reforming for coal gasification

The G.E.G.N. (Groupement pour l'Etude de la Gazéification Nucléaire) is a group which will study nuclear coal gasification and which is formed by “Commissariat à l'Energie Atomique”, “Gaz de France”, “Charbonnages de France”, “Creusot-Loire” and “Novatome”. The G.E.G.N. was created in 1976, with the approval of the French government, to determine a coal gasification process, to define a R & D programme and to evaluate the cost of the process.

The nuclear steam reforming of methane and the hydrogasification of coal were chosen as preliminary options. The hydrogasification was also chosen because the temperatue level of the steam reforming is lower than that of the coal steam gasification.

Therefore, it seems reasonable to limit the core outlet temperature to 850°C, although the core can deliver higher helium temperatures.

The use of an intermediate circuit allows a great flexibility in the reformer design and makes it easier to handle the catalyst.

In this paper the reasons for these choices are explained and the technological solutions are discussed.     

Facility risk review as a means to addressing existing risks during the life cycle of a process unit, operation or facility

In today's process industry environment, it is becoming more and more important for companies to manage the risks associated with their plants. Amongst others, some reasons for this are that 1) Process Safety is featuring high on the agenda of Trade Unions; 2) that Management is coming under increased pressure to provide a safe workplace; 3) that Companies are trying to survive in the current competitive environment by adopting the “zero accidents” ideal; 4) because the effects of accidents that do occur are becoming more devastating due to increased inventories and the exotic nature of products and 5) the fact that overseas companies are looking at safety and conservation track records before choosing business partners or considering trade agreements.

Regulatory directives such as OHSA'S (Occupational Health and Safety Act, Act 85 of 1993) Major Hazard Installation Regulation in conjunction with SABS 0228 (hazard group 1) is another newcomer entering the playing fields of South African Companies and is in the future going to have a serious impact on Company philosophies and policies. In this Regulations “Risk Assessment” is defined as “a planned programme to reduce, to remove, and to control a major incident”. This can be interpreted as having the meaning/objective to involve some type of Risk Management programme which will co-ordinate inter alia the risk assessment function. Also defined is “Major Incident”, which reads: “It is an occurrence (including in particular, a major emission, fire or explosion) resulting from uncontrolled developments in the course of an industrial activity, leading to a serious danger to persons, whether immediate or delayed, inside or outside the installation, or to the environment, and involving one or more dangerous substance”

To address this problem of managing the risks in a facility/plant/operation is no mean feat. Cost factors, time constraints, manpower availability, legislatory pressures and uncertainty on the most applicable risk assessment method to use, are just some of the problems facing management. Adding to this dilemma is the fact that the reviewing specialist has to choose from a variety of risk assessment methods that have varying degrees of complexity, cost and applicability. Past experience has however shown that Hazard and Operability Analysis (Hazop), Failure Mode and Effects Analysis (FMEA), Fault Tree Analysis and Event Tree Analysis are the most widely used and well accepted.

Choosing the right assessment method which will provide the information management needs to address the facility's risks is often the most difficult part in the whole assessment process. With this paper we are providing an overview of such a risk assessment method, namely Facility Risk Review (FRR) which uses a combination of techniques of a qualitative and quantitative nature.

These methods are similar to those currently being used with great success in the risk assessment process at the facilities of the Sasol Group of Companies. These methods are in use from the initial conceptual design stage of any project or change up to the stage where the facility has been in operation for many years.     

New prospects in the political economy of inner-Caspian hydrocarbons and western energy corridor through Turkey

This paper makes a new conceptualization on Caspian energy system and the transit routes that pass through Turkey. Firstly, it puts forward the term of “inner-Caspian”, comprising Azerbaijan, Kazakhstan and Turkmenistan. Secondly, it identifies sub-systems of “western energy corridor through Turkey” (WECT) by diversifying: (1) “WECT inner-Caspian”, which includes hydrocarbon transportation from Azerbaijan, Kazakhstan and Turkmenistan; (2) “WECT Russia”, which is currently composed of Blue Stream gas pipeline and oil transportation by tankers through Turkish straits; and (3) “WECT Middle East”, which refers to Iranian, Iraqi and Egyptian hydrocarbons. Thirdly, this paper makes a comparative analysis on WECT systems through selected economic (reserves, supply/demand, production and transportation costs), geo-political (e.g. moves of the concerned actors), political (e.g. recent developments in government structures) and security (especially in terms of transport) indicators which bring out that “it is more reasonable for the EU to first embrace WECT inner-Caspian, then develop WECT Middle-East in order to diversify its energy supply”.     

Enhancing the elevated temperature performance of Li/LiMn2O4 cells by reducing LiMn2O4 surface area

Lithium-rich spinels were obtained with the same structure but different surface area by two different synthesis routes, namely the “once-annealed” and the “twice-annealed” methods. The elevated temperature performance of Li/Li_1+xMn₂O₄ cell is significantly improved using a spinel cathode with a small surface area: the cell at 50°C lost 5% of the initial capacity over the first 100 cycles based on a spinel cathode with the small surface area of 1.2 m²/g compared to 8% based on a large one of 6.2 m²/g. Also the mechanism responsible for the reaction of LiMn₂O₄ with LiOH to form lithium-rich spinel has been investigated.     

Conditional probabilities of daily relative sunshine data and the dependence on the weather of the previous day

In this paper, the conditional probabilities p₁₁(m, x) and p₀₁(m, x) of the daily relative sunshine (DRS) are estimated for each month m, using available data for 30 years. p₁₁(m, x) (p₀₁(m, x)) is the probability that the DRS of a day for a certain month is greater than x, (o < x < 1), given that the DRS of the previous day is greater (smaller) than x. The empirical curves for p₁₁(m, x) and p₀₁(m, x) are fitted and the fitting parameters are estimated for each month. The results show a good agreement between the empirical and the calculated values. The vertical distance between the curves p₁₁(m, x) and p₀₁(m, x) shows a strong dependence of the weather on that of the previous day. A method to estimate a sequence of k consecutive days of “good” or “bad” weather is also given.     

The use of waste heat in a solar still

There are instances in remote areas where heat is being wasted, e.g., in internal combustion, engines, etc. Some of this heat can be recovered to produce distilled water in solar stills.

The solar still replaces the cooling tower, ponds, or radiators normally used to control the engine temperature. The diesel cooling water in such a system remains separate from the saline water in the solar still.

The advantages of using such a system compared with a conventional solar still are:

1. (a) water costs are very much reduced

2. (b) the area occupied is much less, i.e., about 1/5th

3. (c) production has much less seasonal variation

4. (d) the efficiency of the solar still is improved due to the higher operating temperatures.

From experiments conducted at Highett using a Mk VI solar still fitted with a simple heat exchanger and a separate electrically-heated source of hot water to simulate the waste heat, design data are not available for application to working systems. The information required to match a solar still to a diesel's cooling requirement is:

1. (a) engine efficiency

2. (b) hourly fuel consumption

3. (c) hourly solar radiation

4. (d) hourly ambient temperatures.

A by-product of this work has been the production of a “solar water heater” which costs less than that of the cheapest conventional system. This “solar” hot water system uses a heat exchanger similar to what is used to transfer the waste heat to the saline water. It is envisaged to have hot water productions approximately the same as the distilled water productions. The influence of hot water production on the output of the waste heat solar still is discussed.     

Thermal modeling of secondary lithium batteries for electric vehicle/hybrid electric vehicle applications

A major obstacle to the development of commercially successful electric vehicles (EV) or hybrid electric vehicles (HEV) is the lack of a suitably sized battery. Lithium ion batteries are viewed as the solution if only they could be “scaled-up safely”, i.e. if thermal management problems could be overcome so the batteries could be designed and manufactured in much larger sizes than the commercially available near-2-Ah cells.

Here, we review a novel thermal management system using phase-change material (PCM). A prototype of this PCM-based system is presently being manufactured. A PCM-based system has never been tested before with lithium-ion (Li-ion) batteries and battery packs, although its mode of operation is exceptionally well suited for the cell chemistry of the most common commercially available Li-ion batteries. The thermal management system described here is intended specifically for EV/HEV applications. It has a high potential for providing effective thermal management without introducing moving components. Thereby, the performance of EV/HEV batteries may be improved without complicating the system design and incurring major additional cost, as is the case with “active” cooling systems requiring air or liquid circulation.     

Design and construction of a one-axis sun-tracking system

This paper describes a tracking system which can be used with single-axis solar concentrating systems. The position and “status” of the Sun are detected by three light-dependent resistors (LDRs), one of which detects whether the collector is focused, whilst a second resistor determines if there is cloud cover, and the third senses whether it is day or night. The resultant signals are fed to an electronic control system which operates a low-speed 12-V d.c. motor which rotates the collector via a speed-reduction gearbox. The tracking system accuracy depends on the magnitude of the solar irradiance. The deviation from zero is 0.2 and 0.05° with solar radiation of 100 and 600 W m⁻², respectively. Both values suggest that the mechanism can be used satisfactorily for parabolic trough collectors of medium to high concentration ratios.     

Scenarios of energy demand and efficiency potential for Bulgaria

The paper presents aggregated results on macroeconomic and final energy demand scenarios developed within the Bulgarian Country Study on Greenhouse Gas Emissions Mitigation, supported by US Country Studies Program. The studies in this area cover five main stages: (1) outline of “Basic” and “Energy Efficiency” socio-economic and energy policy scenarios (2) modeling of macroeconomic and sectoral development till 2020; (3) expert assessments on the technological options for energy efficiency increase and GHG mitigation in the production, transport and households and services sectors; (4) bottom-up modeling of final energy demand; (5) estimation of sectoral and overall energy efficiency potential and policy. Within the Bulgarian Country Study, the presented results have served as a basis for the final integration stage “Assessment of the Mitigation Policy and Measures in the Energy System of Bulgaria.”     

Electrochemical and capacitive properties of thin-layer carbon black electrodes

Electrochemical properties and porous-structure-dependent capacitive ability of commercial carbon blacks, Black Pearls 2000^® (BP) and Vulcan^® XC 72R (XC), were investigated in H₂SO₄ solution by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The capacitance in-depth profile is correlated to microscopic appearance of carbon blacks in the form of a thin layer applied over Au substrate from water suspensions of BP and XC. The capacitance calculated from voltammetric charge was found to depend on the sweep rate, due to porosity of investigated materials. Impedance (EIS) characteristics upon frequency-dependent charge/discharge process indicate transmission line electric behavior of BP and XC. Capacitance and resistance values obtained by simulations of EIS data, enabled estimation of capacitance and resistance profile throughout carbon black porous electrodes. Capacitance of BP carbon layer increases going from the outer surface towards the bulk of the layer. External capacitance originates from capacitive characteristics of the macroscopic surface consisting of relatively large agglomerates, while internal capacitance originates from “inner” surface of micro-porous agglomerates. Contrary to BP, opposite distribution of the total capacitance to external and internal part was found for XC, caused by its loose structure and considerably lower real surface area in comparison to BP. The XC morphology makes additionally the pseudocapacitive contribution of surface functionalities more pronounced, which indirectly shifts also the “internal” double-layer capacitive response to higher frequencies through the effect of increased wettability of the layer. Thus, the capacitance of XC surface directly exposed to the electrolyte is larger than that of the inner one, which makes it a “fully-utilized” capacitor, while increased capacitive performance of BP emerges only at very low frequencies of charging/discharging process.     

Natural convection from isothermal flat surfaces

Local heat-transfer coefficients along a flat plate in natural convection in air were measured using Boelter-Schmidt type heat flux meters. Experiments were carried out for different temperature differences in heating and cooling, and with inclinations varying from the horizontal “facing upwards” position, through the vertical position, to the horizontal “facing downwards” position.

The results are presented in terms of local Nusselt number as a function of the local Grashof number “tangential component”. All runs were in the range accepted as that of laminar boundary layer flow. However, under certain conditions when the normal velocity component of the air is directed away from the surface, separated flow is indicated along the trailing part of the surface, well before turbulence sets in in the boundary layer. Separation starts at a certain point along the surface. This point is nearer to the leading edge the higher the temperature difference, and the larger the inclination of the surface to the vertical.

In a separation region, the flux density is uniform. In all other regions the results agreed closely with established theories of laminar boundary layer flow.

A leading adiabatic section, used in some of the experiments, did not affect the results. An appendix gives relations recommended for engineering calculations.     

Amorphous solar cells, the micromorph concept and the role of VHF-GD deposition technique

During the last two decades, the Institute of Microtechnology (IMT) has contributed in two important fields to future thin-film silicon solar cell processing and design:

(1) In 1987, IMT introduced the so-called “very high frequency glow discharge (VHF-GD)” technique, a method that leads to a considerable enhancement in the deposition rate of amorphous and microcrystalline silicon layers. As a direct consequence of reduced plasma impedances at higher plasma excitation frequencies, silane dissociation is enhanced and the maximum energy of ions bombarding the growing surface is reduced. Due to softer ion bombardment on the growing surface, the VHF process also favours the formation of microcrystalline silicon. Based on these beneficial properties of VHF plasmas, for the growth of thin silicon films, plasma excitation frequencies f_exc in the range 30–300 MHz, i.e. clearly higher than the standard 13.56 MHz, are indeed scheduled to play an important role in future production equipment.

(2) In 1994, IMT pioneered a novel thin-film solar cell, the microcrystalline silicon solar cell. This new type of thin-film absorber material––a form of crystalline silicon––opens up the way for a new concept, the so-called “micromorph” tandem solar cell concept. This term stands for the combination of a microcrystalline silicon bottom cell and an amorphous silicon top cell. Thanks to the lower band gap and to the stability of microcrystalline silicon solar cells, a better use of the full solar spectrum is possible, leading, thereby, to higher efficiencies than those obtained with solar cells based solely on amorphous silicon.

Both the VHF-GD deposition technique and the “micromorph” tandem solar cell concept are considered to be essential for future thin-film PV modules, as they bear the potential for combining high-efficiency devices with low-cost manufacturing processes.     

Prediction of new tightly-bound states of H2 (D2) and “cold fusion” experiments

It is suggested that in the “cold-fusion” experiments of Fleischmann and Pons and others new tightly-bound molecular states of D₂⁺ are formed with binding energies predicted to be of the order of 50 keV accounting for the heat released without appreciable fusion. Other tests of the suggested mechanism are proposed and the derivation of the new energy levels is given.     

Rebuttal to “The Marginal Cost of CO2 Emissions”: C. Azar, Energy19, p. 1255 (1994)

In “The Marginal Cost of CO₂ Emissions”, Azar criticizes my early works on the shadow price of CO₂ emissions. In this note, I refute those criticisms.     

The greenland hydropower as a source of electrolytic hydrogen

A preliminary assessment of the Greenland hydropower potential is presented. Based on classical exploitation techniques the proven mean annual power capacity is estimated at 15–40 GW while the ultimate potential is between 100 GW and 1 TW.

This potential will not only satisfy the energy needs of Greenland itself but will also allow for large scale energy export. One of the best solutions for transporting this energy is the in situ synthesis of ammonia on the basis of liquefied air and electrolytic hydrogen, a suggestion already made in the project “Energy Depot” of the U.S. army. The ammonia would then be shipped overseas by LNG-tankers in liquid form. Expected costs are comparable to current prices on the world's market.     

A focused approach to reliability, availability and maintainability for critical pressure vessels

A “Review Integrity of Critical Equipment” (RICE) programme is presented here. The programme has a systematic structure that facilitates the development of strategic maintenance plans for critical pressure vessels. The programme is based on the reliability, availability and maintainability (RAM)‘ principles and was developed and applied to Sasol's vessels in order to ensure compliance with future statutory requirements. It is believed that the presented programme will be useful for other users than Sasol.

The programme consists of a number of stages; systematic data acquisition, assessment of data and proposed principle inspection plan, acceptance of the plan followed by detailed planning, actual inspection and evaluation of results. The inspection plan is supplemented by proactive measures to solve suspected problems. The paper includes a case study of a critical scrubber vessel in order to illustrate how the programme works.     

Optical and electrochemical characteristics of niobium oxide films prepared by sol-gel process and magnetron sputtering A comparison

Electrochromic niobia (Nb₂0₅) coatings were prepared by the sot-gel spin-coating and d.c. magnetron sputtering techniques. Parameters were investigated for the process fabrication of sol-gel spin coated Nb₂0₅ films exhibiting high coloration efficiency comparable with that d.c. magnetron sputtered niobia films. X-ray diffraction studies (XRD) showed that the sot-gel deposited and magnetron sputtered films heat treated at temperatures below 450°C, were amorphous, whereas those heat treated at higher temperatures were slightly crystalline. X-ray photoelectron spectroscopy (XPS) studies showed that the stoichiometry of the films was Nb₂0₅. The refractive index and electrochromic coloration were found to depend on the preparation technique. Both films showed low absorption and high transparency in the visible range. We found that the n, k values of the sot-gel deposited films to be lower than for the sputtered films. The n and k values were n = 1.82 and k = 3 × 10⁻³, and n = 2.28 and K = 4 × 10⁻³ at 530 urn for sot-gel deposited and sputtered films, respectively. The electrochemical behavior and structural changes were investigated in 1 M LiC10₄/propylene carbonate solution. Using the electrochemical measurements and X-ray photoelectron spectroscopy, the probable electrode reaction with the lithiation and delithiation is Nb₂O₅ + x Li⁺ + x e⁻ ↔ Li_xNb₂0₅. Cyclic voltametric (CV) measurements showed that both Nb₂0₅ films exhibits electrochemical reversibility beyond 1200 cycles without change in performance. “In situ” optical measurement revealed that those films exhibit an electrochromic effect in the spectral range 300 < λ < 2100 nm but remain unchanged in the infrared spectral range. The change in visible transmittance was 40% for 250 nm thick electrodes. Spectroelectrochemical measurements showed that spin coated films were essentially electrochemically equivalent to those prepared by d.c. magnetron sputter deposition.