Investigation into methods for the calculation and measurement of pulverised coal boiler flue gas furnace exit temperature

The boiler flue gas furnace exit temperature (FET) is a key operating parameter of coal fired steam boilers. From the design perspective, the FET is vital for materials selection and sizing of heat transfer surfaces. From an operating perspective, it is a major indicator of the rate of combustion and heat transfer that is occurring within the furnace. Downstream of the furnace, the FET has a significant impact on both the performance and reliability of the boiler heat exchangers, which ultimately impacts on both boiler efficiency and availability. Monitoring of the FET can advise operating and engineering corrective actions which will ultimately result in better efficiency, reliability and availability together with the associated economic benefits. Therefore, methods of determining FET are investigated. Two methods are focused on for this study, one indirect and one direct. The indirect method studied is a mass and energy balance method which begins with a global boiler mass and energy balance to calculate the major boiler flow rates of coal, air and flue gas which are difficult to measure online. These parameters are then used as inputs into a furnace or backpass mass and energy balance to calculate the furnace exit temperature. The method is applied to a case study, and is evaluated in terms of the measurement uncertainties which are propagated on the intermediate parameters calculated, as well as on the final calculated FET. The main conclusions are that this indirect method contains various uncertainties, due to parameters which have to be assumed such as (i) the distribution of ingress air (also called tramp air) in the different sections of the boiler and (ii) the estimation of the share of water evaporation heat transfer occurring in the water walls of the furnace part of the boiler. The method is however still useful and can be easily applied to any boiler layout and can be used as a reference tool to verify other measurements. The direct method studied is acoustic pyrometry. The work specifically focuses on the sources of error in determining the temperature from the measurement of the time of flight of sound, the impact of particle concentration on the speed of sound through a gas-particle mixture, and the temperature profile reconstruction from acoustic time of flight measurements. A limited set of physical testing was also carried out using one acoustic generator and receiver to take measurements on a real coal power plant. As part of this physical testing, the detection of time of flight from acoustic signals was explored. Already installed radiation pyrometers were also used as a reference for interpreting the acoustic measurements. The indications are that the acoustic pyrometer provides a more representative temperature measurement than the radiation pyrometers. The uncertainty of the acoustic measurement for the same case study as the indirect method was determined and compared with the calculated result. While many aspects still need to be researched further, this initial study and experimental testing produced very promising results for future application of acoustic pyrometry for better monitoring of the coal combustion processes in power plant boilers

Biological Nutrient Removal from Municipal and Industrial Wastewater Using a Twin Circulating Fluidized Bed Bioreactor

Biological nutrient removal (BNR) refers to removal of carbon (C), nitrogen (N) and phosphorus (P) from wastewater (WW) by the aid of various microorganisms. Because of the public concern for the environment C, N and P effluent standards have become stricter. Different BNR processes such as suspended growth and attached growth have been studied during the last three decades in order to meet the increasingly stringent discharge standards. In this work, two novel processes called Twin Fluidized Bed Bioreactor (TFBBR) and Twin Circulating Fluidized Bed Bioreactor (TCFBBR) were developed and tested for BNR from municipal WW. Both TFBBR and TCFBBR comprise of an anoxic column and an aerobic column with particle recirculation between the two reactors achieved mechanically (TFBBR) and hydraulically (TCFBBR). Moreover, a newly developed system called Anaerobic Fluidized-Circulating Fluidized Bed Bioreactor (AF-CFBBR) was developed and tested to accomplish BNR from high strength industrial WW. AF-CFBBR comprises of an anaerobic, an anoxic and an aerobic columns. In all three aforementioned systems, fine carrier media are employed for biofilm attachment. After the development of biofilm, the particles are called biofilm-coated particles. TFBBR and TCFBBR were operated at organic, nitrogen and phosphorus loading rates (OLR, NLR and PLR) of up to 2.8 kg COD/m3×d and 4.5 kg COD/m3×d, 0.3 kg N/m3×d and 0.5 kg N/m3×d and 0.041 kg P/m3×d respectively to study the performance of the system with respect to biological nutrient removal. The nitrification rates based on biofilm surface area in TFBBR and TCFBBR were 0.91 g N/m2×d and 1.26 g N/m2×d respectively and the denitrification rates based on biofilm surface area in TFBBR and TCFBBR were 0.65 g N/m2×d and 1.32 g N/m2×d respectively. Both systems removed \u3e96% organic matter, 84%-88% nitrogen and 12%-50% phosphorus at overall hydraulic retention time of (HRT) 2h. TFBBR and TCFBBR achieved long SRTs of 72-108 d and 37-40 d respectively, which rationalized the very low observed yield of 0.06-0.07 g VSS/g COD and 0.09-0.1 g VSS/g COD. The AF-CFBBR demonstrated 99.7% COD removal, 84% nitrogen removal, with a very low sludge yield of 0.017 g VSS/g COD while treating a wastewater containing 10700 mg COD/L and 250-300 mg NH3-N/L. The system was operated at an organic loading rate (OLR) of 35 kg COD/m3·d based on the AF volume and 1.1 kg N/m3·d based on the CFBBR at an overall HRT of less than 12 h in the AF-CFBBR. The nitrification, denitrification and organic removal rates based on aerobic, anoxic and anaerobic biofilm surface area in AF-CFBBR respectively were 2.6 g N/m2×d, 9.03 g N/m2×d and 12.1 g COD/m2×d. Additionally, the inhibitory effect of nitrate on methanogenic activities in a high rate anaerobic fluidized bed with organic loading rate of above 35 kg COD/m3·d was studied in order to evaluate the feasibility of simultaneous denitrification and methanogenic activities (SDM) in a high rate anaerobic system. Terminal settling velocity and bed expansion of biofilm-coated particles as the two main hydrodynamic criteria in a fluidized bed, were studied. Archimedes was superior to Reynolds number for drag coefficient and bed expansion definitions. A new equation for determining drag force on fluidized bed bio-film coated particle (Fd) as an explicit function of terminal settling velocity was generated based on Archimedes numbers (Ar) of the biofilm coated particle. The proposed equation adequately predicted the terminal settling velocity of other literature data with an accuracy of \u3e90%. A new equation based on Archimedes number was proposed to calculate bed expansion index of biofilm-coated particles, which predicted the existing experimental data with less standard error than all other literature equations that related bed expansion to Reynolds number. A two-phase and three-phase predictive fluidization model based on the characteristics of a system such as media type and size, flow rates, and reactor cross sectional area was proposed to calculate bed expansion, solid, liquid and gas hold up, specific surface area of the biofilm particles. The model was subsequently linked to 1d AQUIFAS APP software (Aquaregen) to model two and three phase fluidized bed bioreactors. The model was validated for biological nutrient removal using the experimental data from a Twin Circulating Fluidized Bed Bioreactors (TCFBBR) treating synthetic and municipal wastewater. Two-sided t-tests showed that there were no statistically significant difference between the experimental and the modeled TCOD, SCOD, NH3-N, NOx-N

Rheological effects of a gas fluidized bed emulsion on falling and rising spheres

To enable the mechanistic description of the mixing of larger particles in gas-fluidized beds in models (e.g. fuel particles in combustors), knowledge about the rheology of the bed emulsion is required. Here, it is crucial to determine the drag on large fuel-alike particles. This work presents the experimental work on the fate of 13 different solid spheres falling or rising through a bed of air and glass beads at minimum fluidization. The trajectories of the tracer are highly resolved (sampling rate of 200 Hz) by means of magnetic particle tracking, this previously unmet accuracy allows disclosing the complex rheological behavior of gas-solids fluidized bed emulsions in terms of drag on immersed objects. The trajectories reveal that none of the tracers reach terminal velocity during their fall and rise through the bed. The shear stress is obtained through the drag force by solving the equation of motion for the tracer. The data reveal particularities of the bed rheology and clear differences of its effect on rising and falling particles. When studying the shear stress over the characteristic shear rate of each tracer, it can be seen that the stress of the bed on the tracers is dominated by a yield stress, with a somewhat smaller contribution of the shear stress. For rising tracers this last contribution is almost negligible. The falling tracers show strong interaction with the bed emulsion, resulting in a fluctuating shear stress, which increases with tracer size and density. The stagnation of some tracers at low shear rates reveals a viscoplastic behavior of the bed emulsion, exhibiting a typical yield stress that showing a clear dependence on the tracer diameter and buoyant density. The concept of yield gravity is used in order to introduce a normalized shear stress which provides additional verification of the experimental observations in relation to the influence of tracer size and relative density on the shear stress

Computational Heat Transfer and Fluid Mechanics

With the advances in high-speed computer technology, complex heat transfer and fluid flow problems can be solved computationally with high accuracy. Computational modeling techniques have found a wide range of applications in diverse fields of mechanical, aerospace, energy, environmental engineering, as well as numerous industrial systems. Computational modeling has also been used extensively for performance optimization of a variety of engineering designs. The purpose of this book is to present recent advances, as well as up-to-date progress in all areas of innovative computational heat transfer and fluid mechanics, including both fundamental and practical applications. The scope of the present book includes single and multiphase flows, laminar and turbulent flows, heat and mass transfer, energy storage, heat exchangers, respiratory flows and heat transfer, biomedical applications, porous media, and optimization. In addition, this book provides guidelines for engineers and researchers in computational modeling and simulations in fluid mechanics and heat transfer

Advanced Topics in Mass Transfer

This book introduces a number of selected advanced topics in mass transfer phenomenon and covers its theoretical, numerical, modeling and experimental aspects. The 26 chapters of this book are divided into five parts. The first is devoted to the study of some problems of mass transfer in microchannels, turbulence, waves and plasma, while chapters regarding mass transfer with hydro-, magnetohydro- and electro- dynamics are collected in the second part. The third part deals with mass transfer in food, such as rice, cheese, fruits and vegetables, and the fourth focuses on mass transfer in some large-scale applications such as geomorphologic studies. The last part introduces several issues of combined heat and mass transfer phenomena. The book can be considered as a rich reference for researchers and engineers working in the field of mass transfer and its related topics

Cooling of Advanced Gas-cooled Reactor Fuel Pin Bundles – Flow Physics and Engineering Predictions

This thesis studies the cooling of rod bundles within the Advanced Gas-cooled Reactor (AGR) fuel route at non-design conditions using a variety of methods. The aims of the thesis are (i) to contribute to the general understanding of the detailed flow, heat transfer, and turbulence phenomena in AGR rod bundles. (ii) to develop a 3-D porous model software package for the thermal-hydraulics analysis of the fuel route. Of primary concern to this project are scenarios where the fuel bundle is distorted as a result of being dropped or damaged during refuelling operations. The model developed herein will complement the current 1-D thermal codes in use at EDF Energy. This is particularly for the cases where the latter would be excessively pessimistic or inaccurate due to their inability to capture the 3-D characteristics of the flow. The open-source, co-located, and segregated Computational Fluid Dynamics (CFD) solver Code Saturne developed by EDF has been used. For the first aim, three studies have been carried out, that is, (a) Large Eddy Simulation (LES) study of natural circulation in a short 0.25 m enclosed bundle (b) Large Eddy Simulation study of natural circulation in a 1 m tall enclosed bundle and (c) Reynolds Averaged Navier Stokes (RANS) study of forced convection in a damaged bundle. In a short bundle, (a) the flow is largely laminar and constrained to the thin boundary layers around the fuel rods and containment wall. Away from the walls, in the core, the flow is stagnant. The vertical temperature distribution is heavily stratified. The natural circulation flow in the 1 m domain is heavily influenced by a vertically developing boundary layer on the containment surface, which is initially laminar but transitions to turbulence at about a quarter of the height from the top. The Nusselt number on the containment wall can be correlated using a well established expression over a vertical plate in a free space. Laminar boundary layers observed in both the long and short domains compare very well with similarity solutions, though for those over the fuel rods, the curvature needs to be considered. Forced convection in a damaged WheatSheaf bundle shows the flow to swirl around the rods as it is diverted to regions of less resistance through the rod gaps. Hot spots on the fuel at any axial location are found on the leeward side of the cross-flow. To fulfil the requirements of the second aim a thermal-hydraulics code for the fuel route, named FREEDOM has been developed. FREEDOM aims to predict AGR fuel component temperatures under potential fault conditions while the fuel is being handled or stored within the AGR fuel route. FREEDOM has two modes, one for intact and another for damaged fuel. The main focus of this thesis is on damaged fuel. The model comprises of two domains, the fluid domain computed using Code Saturne and the solid domain computed using Syrthes. In the fluid domain, the porous media representation is used to simplify the mesh generation and lessen computation cost. Thermal conduction and radiation are associated with the solid domain. The two domains are coupled together through the exchange of temperatures and heat transfer coefficients. In addition, oxidation due to the fuel and carbon deposit have been modelled considering both diffusion and reaction dynamics controlled conditions. The code is validated by performing experimental and code-to-code comparisons for a variety of flow conditions and idealised geometries. Forced convection comparisons were in good agreement and natural convection comparisons ranged from good to acceptable. The validated FREEDOM has then been successfully used to support a safety case argument by taking into account the three-dimensional effects for the flow, radiation, and solid conduction

An application of evolutionary algorithms for WAG optimisation in the Norne Field

Water-alternating-gas (WAG) is an enhanced oil recovery method combining the improved macroscopic sweep of water flooding with the improved microscopic displacement of gas injection. The optimal design of the WAG parameters is usually based on numerical reservoir simulation via trial and error, limited by the reservoir engineer’s availability. Employing optimisation techniques can guide the simulation runs and reduce the number of function evaluations. In this study, robust evolutionary algorithms are utilized to optimise hydrocarbon WAG performance in the E-segment of the Norne field. The first objective function is selected to be the net present value (NPV) and two global semi-random search strategies, a genetic algorithm (GA) and particle swarm optimisation (PSO) are tested on different case studies with different numbers of controlling variables which are sampled from the set of water and gas injection rates, bottom-hole pressures of the oil production wells, cycle ratio, cycle time, the composition of the injected hydrocarbon gas (miscible/immiscible WAG) and the total WAG period. In progressive experiments, the number of decision-making variables is increased, increasing the problem complexity while potentially improving the efficacy of the WAG process. The second objective function is selected to be the incremental recovery factor (IRF) within a fixed total WAG simulation time and it is optimised using the same optimisation algorithms. The results from the two optimisation techniques are analyzed and their performance, convergence speed and the quality of the optimal solutions found by the algorithms in multiple trials are compared for each experiment. The distinctions between the optimal WAG parameters resulting from NPV and oil recovery optimisation are also examined. This is the first known work optimising over this complete set of WAG variables. The first use of PSO to optimise a WAG project at the field scale is also illustrated. Compared to the reference cases, the best overall values of the objective functions found by GA and PSO were 13.8% and 14.2% higher, respectively, if NPV is optimised over all the above variables, and 14.2% and 16.2% higher, respectively, if IRF is optimised

On the integration of calcite scale management and operational optimisation of CCUS in Pre-salt carbonate reservoirs

In this thesis, we describe a simulation-based reactive transport workflow to optimise Carbon Capture Utilization and Storage (CCUS) in carbonate reservoirs. Although CCUS may play a crucial role in reducing greenhouse gas emissions, it does not come short of challenges. Here we focus on three of them: i) the economics, ii) carbon footprint and iii) inorganic scale, the latter being crucial when carbon dioxide (CO2) water-alternating-gas (WAG) is performed in reactive carbonate rocks. Our objective is to integrate reservoir engineering calculations, cash flow projections, carbon accounting and production chemistry to support field operational decisions. The analysis is made in the context of the Brazilian Pre-salt oilfields that have been pioneering deep-water CO2 utilization for Enhanced Oil Recovery (EOR) to avoid flaring. We used well-established optimisation techniques - statistical sampling and evolutionary algorithms - to identify CO2-EOR strategies with the highest potential to co-optimise profitability and CO2 storage, without triggering calcite deposition to the point of permanent jeopardy of production wells and facilities. Based on the production brine chemistry and flow rate forecasts, we assessed calcite scale risk and designed damage prevention strategies with the lowest cost of scale inhibitor “squeeze” treatment deployment. The methodology is presented through synthetic sector models and then applied to a field case for validation. We used deterministic models, but the impact of geological uncertainties on the outcomes is demonstrated using a set of representative models of the field case. The optimized CCUS strategies showed the potential to enhance profitability and offset operational emissions through adjustments of well operations, with limited additional investment. In addition, the mineral scaling assessment revealed how applying WAG schemes in carbonate reservoirs with considerable initial CO2 content will result in a lower calcite deposition risk compared to waterflooding. The proposed workflow provides valuable insights into the simulation and optimisation of CCUS projects with high calcite scaling risk. Its application demonstrated the importance of an integrated analysis that seeks to improve economic returns in a sustainable manner, with reduced production damage caused by CO2 speciation