Püskürtmeli Kurutucuda Trona Çözeltisi İle Yapılan Desülfürizasyon Çalışmaları Ve Cfd Simülasyonu

Abstract

Hesaplamalı mekanik günümüzde mühendislik eğitim programlarına girmeyi başarmış bir bilim dalıdır. Bilgisayar imkanlarının mühendislik alanında kullanılmaya başlanaması sonucu bir çok yeni eğitim alanında gelişme sağlanmıştır. Bu alanalardan bir taneside CFD'dir. Bu yeni yaklaşım akışkanlar mekaniğinin temel derlemlerinin çözümü için ileri matemetik yöntemlerin gelişmesini sağlamıştır. CFD yöntemlerinin endüstriyel uygulamalarda eşanlı mühendislik (cocurrent engineering) kavramına uygun olması sonucu imalat öncesi benzeşim ve analiz yaygınlaşmıştır. Bilgisayar teknolojisindeki gelişmeler sonucu,deneysel ağırlıklı akışkanlar mekaniği analiz yöntemleri ile bilgisayar desteğinde modelleme teknikleri arasındaki yarış her geçen gün artmaktadır. Bilgisayarların daha yaygın ve kolay elde edilebilir olması ve deneysel çalışmaların zorluklan ve uzun zaman alması ister istemez araştırıcıları CFD uygulamalarına yöneltmiştir. Çünkü deney öncesi bir çok ön sonuç yeterli hassasiyetlerle bilgisayar desteğinde hesaplanabilmektedir. PHOENICS adındaki CFD programı ile kimya mühendisliğinde sıkça kullanılan püskürtmeli kurutucu (Spray Dryer) modellenmiştir. Bu model kullanılarak püskürtmeli kurutucuda trona çözeltisi ile kükürt dioksitin tutulması incelenmiştir. Modelin kurulmasında kurulması için gerekli veriler programa yerleştirilmiştir. Trona çözeltisi programa dispers faz olarak programa yerleştirilirken, hava-SÜ2 karışımı ise sürekli faz olarak programa girilmiştir.

In many branches of engineering, there has to be an understanding of the motion of fluids. One classic example of this is in the aircraft industry, where the aerodynamics of an aircraft must be determined; i.e., the lift, drag and sideforces of a design must be estimated before a prototype flies. This ensures that the lift available will be sufficient to carry the weight of the loaded aircraft, that the required power of the engines can be determined together with the aircraft's fuel economy and that the motion of the aircraft can be predicted. To obtain this aerodynamic data many models of the design could be built and tested in a wind tunnel, with the model positioned in many orientations to the flow. Such tests might consume many hours of wind tunnel time and cost many thousands or millions of pounds. As the equations that govern fluid motion are known, numerical approximations can be made to these equations, and, with the arrival of powerful computer hardware and software, some of the aerodynamics estimations can be made using these computer tools. This does not mean that wind tunnels are redundant. In reality, when computers and experiments are both used to produce predictions, engineers often choose to reduce the amount of wind tunnel time. Sometimes, however, the wind tunnels are used just as much as they would have been if they had been used alone. In both of these cases, wind tunnels can be used to investigate the problems that are too difficult to solve with the computational techniques, and there are many such problems. Effectively, the use of computers releases wind runnel time and this can be used to investigate the really difficult aerodynamics problems that could not be tackled before. Whilst this combination of experimental and computational investigations has been used to determine an aircraft's aerodynamics for some time, the use of computers for fluid flow prediction in other industrial areas is less advanced. Recently, however, other industries have been making the transition from purely experimental investigations to a mix of experimental and computational investigations. If we look at a variety of industrial sectors, such as aerospace, defence, power, process, automotive, electrical and civil engineering, there are many examples of areas where CFD is now used. For example, predictions can be made of the following:. Lift and drag of aircraft : Engineers need the data for performance prediction. CFD is used in conjunction with wind tunnel tests to determine the performance of various configurations.. Flows over missiles : This, again, is an area where there is a need for lift, drag and sideforce data, so that simulations of performance can be made. As with aircraft, CFD and xi wind tunnel tests are used, but because of the wide range of flows that have to be simulated for a given configuration, use is also made of semi-empirical methods which are derived from large amounts of experimental data.. Jet flows inside nuclear reactor halls : Such problems involve the simulation of fault conditions, and so engineers have great difficulty in performing actual experiments, for safety reasons. Hence, computation is the only way of trying to understand such flows.. Flames in burners : There is a need to understand the complex interactions between fluid flow and chemical reaction in flames. This can assist in the production of more efficient designs for burners in boilers, furnaces and other heating devices.. Air flow inside internal combustion engines : When air is used to burn fuel inside an internal combustion engine, be it a gas turbine engine, a petrol engine or a diesel engine, the air must be drawn into the chamber with the minimum amount of effort, and the flow of the air once it isin-the^&amber-must-be able to promote-good burning. Heneerengineers need^o - ?*? know the pressure drop through a system and the velocity distribution in the combustion chamber.. Flow of cooling air inside electrical equipment : In this problem, electrical devices, such as integrated circuits, produce heat. This heat must be dissipated if the equipment is not to become too hot. For example, the hot devices heat the air that surrounds them and this hot air rises, creating air currents that move the heat away from the sources of heat. If insufficient heat is moved away, then it may be necessary to add fans that will force air over the hot devices.. Dispersion of pollutants into rivers and oceans : Various pollutants are discharged into rivers and oceans, and computer programs can be used to predict where pollutants will travel in these naturally occurring flows and what the pollutant concentration will be at given positions in the river or sea. From this list, it is clear that the applications can be extremely varied in nature. Despite this, the computer predictions of the different problems can be made with computer software and hardware that is not specific to a given problem. Now that these computer tools are widely available, CFD has been brought out of the research laboratory and İs used by many more people. It can even be used in the engineering design process. The emphasis is, on engineering examples where the speed of the flow is low and the fluid is viscous, but where the flow does not include any heat transfer. This type of flow is very common throughout industry and it can be used as the basic model upon which can be built a number of modifications that account for other types of flow. For example, the flow speed might be such that the density of the fluid will change, or heat transfer or combustion might occur. Over the last few years, many commercial CFD packages have become available. The emergence of these packages has meant that CFD is no longer practised solely in a research xii environment by highly trained specialists, but it is also being used in many industrial organ izations as a design tool. Consequently, engineers who are not specialists in the CFD field are having to come to terms with this technology, if only in an attempt to understand what the benefits of using the technology are, and also to understand what the drawbacks are. As a subject, CFD can appear to be far removed from the experience of those who are not specialists in the field. The situation is not helped by the numerous books on the market that address the subject of CFD, which are mainly written for the theoretical engineer or applied mathematician who is interested in the details of how the equations that govern fluid flow are solved. No general text is, available for the less-specialized user of CFD techniques, or even for their managers. There is a wide variety of people that have a need to be able to understand something about CFD techniques, be they computational analysts using CFD for the first time, design engineers interested in obtaining information about fluid motion, and even engineering managers or computer managers who provide the computational resources for CFD. Such people are invariably graduates, often with no formal background in CFD, or even in basic fluid mechanics. If these people are offered some sympathetic help and guidance, then they can understand the basics of CFD. It is the author's experience that undergraduate engineering students can successfully model fluid flow situations, if they are given appropriate background information as to what the CFD solution process is and how it is used to obtain predictions of the behaviour of fluids. CFD can be used to produce predictions for a wide variety of flows, So that the basics of the subject can be clearly understood, particularly by those outside the aircraft industry, the content of this book has in the main been restricted to the class of problems that can be described as being viscous, incompressible flows. These flows are slow speed flows where the fluid is not compressed and features such as shock waves do not occur, many industrial flow problems are of this type, and so most of the available CFD packages can simulate these flows. When people use computers they can become so engrossed in the computational aspects of their work that everything else is excluded. For people who use CFD in an industrial environment this can be a disastrous mistake, as the computer hardware and software are merely tools to assist our understanding of the ways in which fluids flow and of the interaction between this flow and some object that is being or has been designed. Consequently, h is very important that everyone concerned with CFD has some understanding of the physical phenomena that occur when fluids flow, as it is these phenomena that CFD must analyse or predict. Each CFD software package has to produce a prediction of the way in which a fluid will flow for a given situation. To do this the package must calculate numerical solutions to the equations that govern the flow of fluids. For the CFD analyst, therefore, it is important to have an understanding of both the basic flow features that can occur, and so must be modelled, and the equations that govern fluid flow. These equations can be found from the xiii knowledge that the mass of fluid must be conserved, as must the momentum of the fluid. Whilst the equations will not be formally derived the underlying philosophy behind their derivation will be explained. Once these equations are known it should be a straightforward process to produce numerical prediction of all flows. This is not case, however, as various problems arise in translating the mathematics into a numerical solution. One problem concerns the physics of the flow and how to model turbulence, as this complicates matters by having a seemingly random effect at each point in a flow. One of application of CFD is scrubbing of SO2 in a spray dryer. Industrial and utility interest in the spray-dry scrubbing concept for the control of SO2 emissions has dramatically increased during the past decade. Most applications to date are on low to medium sulphur coals, while very few data are in existence which would confirm the applicability of the process to high sulphur coals. In the spray dry scrubbing process, flue gas at air-preheater outlet temperatures is contacted with a spray of an alkaline slurry or a clear solution. In most applications lime is the preferred sorbent. During evaporation, dissolved salts precipitate and, after complete drying residual solids are removed from the spray dryer to a particulate collection device, usually a fabric filter. Reaction with the alkaline material proceeds both in die spray dryer and in the fabric filter, i.e. both under wet and dry conditions. A disadvantage of the spray-dry scrubbing concept is its inapplicability to flue gases from high sulphur coals, for economic rather than process reasons More efficient sorbent utilization is required to make the spray-dry scrubbing process competitive against the established wet processes. Recently, there has been an increased interest in the modelling of the spray-dry scrubbing process. Through gaining a deeper understanding of the relevant reaction mechanisms, the applicability of the process might be extended. Although the overall reaction chemistry of a lime based system is quite simple, die simultaneous mass and heat transfer is considerably more complex. The reaction in the spray dryer involves several drying phases and consequently, reaction conditions which have to be approached differently. Furthermore, the method of gas-liquid contacting in the spray dryer must be taken into consideration. In this study, tentative modelling of spray dry scrubbing of SO2 was studied using CFD. PHOENICS is the one package program ofCFD that used in this study. There are three main part in PHOENICS. These are Satellite (pre-processor), Earth (processor) and Photon (post-processor). In Satellite, problem was described. This description of problem includes geometry of the problem, boundary conditions, properties of fluids, etc. Continuous phase is mixing of SO2 and air here. Some properties of SO2 and air was inputted in satellite. XIV There is a section in satellite named CENTRA. GENTRA is a part of satellite for disperse phase. Some properties of Trona solution was settled in GENTRA. Same time, geometry of spray dryer was define in satellite. Meshes were created this section of PHOENICS to computation. There is a file that named Ql that includes information about done in Fortran language. Advanced users can be make use of this file. This file records what user did. Second main part of PHOENICS is earth. Earth is computational part of PHOENICS. third part of PHOENICS is photon. Photon shows the results in graphical form.