Effect of bed particle size on heat transfer between fluidized bed of group b particles and vertical rifled tubes

The effect of bed particle size on the local heat transfer coefficient between a fluidized bed and vertical rifled tubes (38mm-O.D.) has been determined in a large-scale circulating fluidized bed (CFB) reactor. Bed particles with different Sauter mean particle diameter within the range of 0.219-0.411mm and particle density in the range of 2660-2750 kg/m3 were used as bed material in this heat transfer study. A gas fluidized bed furnace with 27.6´10.6m cross-section above refractory line and 48m in height was used. Air coal firing conditions at the membrane wall in the form of water tubes welded with lateral fins corresponded to a suspension density covering the range of 1.36-6.22kg/m3, furnace temperatures in the range of 1080-1164K, a superficial gas velocity varied from 3.13 to 5.11m/s and solids circulation flux covered a range of 22.3-26.2kg/m2s. For these operating conditions, the heat transfer analysis of CFB reactor with detailed analysis of bed-to-wall heat transfer coefficient along furnace height was investigated. In this work, the overall heat transfer coefficient was estimated using a mechanistic heat transfer model based on cluster renewal approach (1,2). The experimental results (Figs. 1-4) show that: (1) higher heat transfer coefficients along furnace height were found under finer bed particles size dp\u3c0.241mm, (2) heat transfer data confirms strong dependency of the overall heat transfer coefficient on suspension density and also hydrodynamic conditions within CFB furnace, (3) for small bed particles, dp\u3c0.233mm, the particle convection component plays dominant role in heat transfer mechanism, (4) for large bed particles, dp\u3e0.366mm, the effect of particle size on contribution of radiation from dispersed phase become essential with particle diameter increasing, and (5) for all bed particles with diameters in the range of 0.240-0.411mm, the gas convection heat transfer coefficient between the fluidized bed (Geldart B particles) and the rifled tubes increased as the bed particles size increased. REFERENCES 1.A. Blaszczuk, W. Nowak and Sz. Jagodzik. Bed-to-wall heat transfer coefficient in a supercritical circulating fluidised bed boiler. Chem. Process. Eng., 35(2):191-204, 2014. 2.A. Blaszczuk, W. Nowak. Heat transfer behavior inside a furnace chamber of large-scale supercritical CFB reactor. Int. J. Heat Mass Transfer, 87:464-480, 2015 Please click Additional Files below to see the full abstract

The Research of CFB Boiler Operation for Oxygen Enhanced Dried Lignite Combustion

The paper presents the research of CFB boiler operation for oxygen-enhanced dried lignite combustion. The combustion in oxygen-enhanced conditions generally leads to reducing the emissions of CO and NOx and N2O due to reduced volume of flue gas. The maximum oxygen content for oxygen-enhanced combustion in O2/N2 conditions should not exceed 60%, however, the maximum drying extent of fuel should not be higher than 50% of the initial moisture content in an examined lignite

The Research of CFB Boiler Operation for Oxygen Enhanced Dried Lignite Combustion

ABSTRACT The paper presents the research of CFB boiler operation for oxygen-enhanced dried lignite combustion. The combustion in oxygen-enhanced conditions generally leads to reducing the emissions of CO and NO x and N 2 O due to reduced volume of flue gas. The maximum oxygen content for oxygen-enhanced combustion in O 2 /N 2 conditions should not exceed 60%, however, the maximum drying extent of fuel should not be higher than 50% of the initial moisture content in an examined lignite

Artificial intelligence model of fuel blendings as a step toward the zero emissions optimization of a 660 MWe supercritical power plant performance

Accurately predicting fuel blends' lower heating values (LHV) is crucial for optimizing a power plant. In this paper, we employ multiple artificial intelligence (AI) and machine learning-based models for predicting the LHV of various fuel blends. Coal of two different ranks and two types of biomass is used in this study. One was the South African imported bituminous coal, and the other was lignite thar coal extracted from the Thar Coal Block-2 mine by Sind Engro Coal Mining Company, Pakistan. Two types of biomass, that is, sugarcane bagasse and rice husk, were obtained locally from a sugar mill and rice mill located in the vicinity of Sahiwal, Punjab. Bituminous coal mixture with other coal types and both types of biomass are used with 10%, 20%, 30%, 40%, and 50% weight fractions, respectively. The calculation and model development procedure resulted in 91 different AI-based models. The best is the Ridge Regressor, a high-level end-to-end approach for fitting the model. The model can predict the LHV of the bituminous coal with lignite and biomass under a vast share of fuel blends

A 1.5D model of a complex geometry laboratory scale fuidized bed clc equipment

The awareness of the climate changes has resulted in the development of new technologies allowing to increase the effectiveness and to lower the costs of CO2 separation from the flue gas. One of the most promised combustion technology of fossil fuels is Chemical Looping Combustion (CLC). The technology is considered to be one of the cheapest techniques for CO2 capture (1). Since it is still an emerging technology and the complexity of processes are still not sufficiently recognized, the development of a simple model of CLC equipment is of practical significance. The paper presents a 1.5D model of the laboratory-scale fluidized bed CLC equipment for Innovative Idea for Combustion of Solid Fuels via Chemical Looping Technology – NewLoop. The idea combines two technologies making them complementary: Chemical looping with Oxygen Uncoupling (CLOU) and In-situ Gasification Chemical Looping (iG-CLC). Experimental studies, calculations and model validation were performed for the CLC unit (Fig. 1). The unit constitutes two cycles: the main cycle and internal cycle with Air Reactor (AR) and Fuel Reactor (FR). Smooth glass microspheres with the Sauter mean diameter of particles of 141 µm and the density of 2450 kg/m3 were used during the investigation. Since the model is in the development stage the study was conducted for the cold tests at which the unit operated stably and smoothly. The model is performed by the use of Comprehensive Simulator of Fluidized and Moving Bed equipment (CeSFaMB). The CeSFaMB has its first successful version completed in 1987. Since then, various versions have been developed and validated for a wide range of cases (2). The first operational results with this CLC unit, i.e. fluidization dynamics are discussed, since the geometry of the system is rather complex. Pressure drops, void fractions, bubble diameter and rising velocity are determined. The results show good agreement between calculated and experimental parameters. On the matter of fluidization dynamics, CeSFaMB produces the parameters as function of vertical coordinate. As an example, the void fractions as well as bubble diameter and rising velocity in the dense region of the Air Reactor are illustrated in Fig 2. Please click Additional Files below to see the full abstract

First experience in operation of cold model of fb-clc-sf (fluidized-bed chemical-looping-combustion solid-fuels) facility

The first experiences with the cold model of dual fluidized bed unit designed for chemical looping combustion of solid fuels (FB-CLC-SF) will be presented. The constructed facility combines two different type reactors. The first one, which is the Air Reactor (AR) is operated in a regime of fast fluidized bed, whereas, the second one, which is the Fuel Reactor (FR) works under bubbling fluidized bed conditions. However, the integrated reactors make the whole construction being a CFB-type (Circulating Fluidized Bed) unit. The facility is made entirely of transparent material (Plexiglas). This feature supports effectively the measurements, which enables to conduct the comprehensive studies in the field of investigations. During this research, the air was used for bed fluidization in both reactors. As an inventory, the round glass beads were employed, since they size and density relate closely to the properties of the oxygen carriers developed concurrently in the project, whereas they are significantly less expensive and friendlier in use. Over a dozen ports for pressure measurements are provided along the main circulation path of the solids. These experimental data enable to determine the pressure balance around the whole CFB loop, which becomes the starting point for further studies. The cold simulations of solids flow demonstrate the conditions that are expected in the case of the hot 5 kW test rig operation, which remains under construction. Therefore, the main goal of this work and the challenge as well are to establish the operating conditions that consider both: a smooth fluidization throughout the FB-CLC-SF unit and an efficient oxidation/reduction of oxygen carriers in AR and FR, respectively. Moreover, these studies support directly the modelling work (Submitted paper: A 1.5D model of a laboratory scale fluidized bed CLC equipment), which makes the whole investigations being complementary

Enhancing EDM Machining Precision through Deep Cryogenically Treated Electrodes and ANN Modelling Approach

The critical applications of difficult-to-machine Inconel 617 (IN617) compel the process to be accurate enough that the requirement of tight tolerances can be met. Electric discharge machining (EDM) is commonly engaged in its machining. However, the intrinsic issue of over/undercut in EDM complicates the achievement of accurately machined profiles. Therefore, the proficiency of deep cryogenically treated (DCT) copper (Cu) and brass electrodes under modified dielectrics has been thoroughly investigated to address the issue. A complete factorial design was implemented to machine a 300 μm deep impression on IN617. The machining ability of DCT electrodes averagely gave better dimensional accuracy as compared to non-DCT electrodes by 13.5% in various modified dielectric mediums. The performance of DCT brass is 29.7% better overall compared to the average value of overcut (OC) given by DCT electrodes. Among the non-treated (NT) electrodes, the performance of Cu stands out when employing a Kerosene-Span-20 modified dielectric. In comparison to Kerosene-Tween-80, the value of OC is 33.3% less if Kerosene-Span-20 is used as a dielectric against the aforementioned NT electrode. Finally, OC’s nonlinear and complex phenomena are effectively modeled by an artificial neural network (ANN) with good prediction accuracy, thereby eliminating the need for experiments

Energy and Exergy Analysis of Vapor Compression Refrigeration System with Low-GWP Refrigerants

In this paper, a first- and second-law analysis of vapor compression refrigeration is presented to estimate and propose the replacement of R134 with working fluids having less global warming potential (GWP) and less exergy destruction and irreversibilities. Six different refrigerants were studied, namely, R717, R1234yf, R290, R134a, R600a, and R152a. A thermodynamic model was designed on Engineering Equation Solver (EES) software, and performance parameters were calculated. The model was deployed on all six refrigerants, while the used output parameters of performance were cooling capacity, coefficient of performance, discharge temperature, total exergy destruction, relative exergy destruction rates of different components, second-law efficiency, and efficiency defect of each component. The performance parameters were estimated at different speeds of the compressor (1000, 2000, and 3000 rpm) and fixed condenser and evaporator temperatures of 50 °C and 5 °C, respectively. The isentropic efficiency of the compressor was the same as the volumetric efficiency, and it was taken as 75%, 65%, and 55% at the compressor speeds of 1000 rpm, 2000 rpm, and 3000 rpm, respectively. A comparison of the performance parameters was presented by importing the results in MATLAB. It was found that the compressor had the highest exergy destruction compared to the other components. It was found that R152 was the refrigerant with zero ozone depletion potential (ODP) and a GWP value of 140 with less exergy destruction and irreversibilities. Moreover, it was easy to use R152a with good thermodynamic characteristics. It is estimated that R152a is a suitable replacement for R134a, as it can be used with few modifications

CO₂ Capture by Virgin Ivy Plants Growing Up on the External Covers of Houses as a Rapid Complementary Route to Achieve Global GHG Reduction Targets

Global CO2 concentration level in the air is unprecedently high and should be rapidly and significantly reduced to avoid a global climate catastrophe. The work indicates the possibility of quickly lowering the impact of changes that have already happened and those we know will happen, especially in terms of the CO2 emitted and stored in the atmosphere, by implanting a virgin ivy plant on the available area of walls and roofs of the houses. The proposed concept of reducing CO2 from the atmosphere is one of the technologies with significant potential for implementation entirely and successfully. For the first time, we showed that the proposed concept allows over 3.5 billion tons of CO2 to be captured annually directly from the atmosphere, which makes even up 6.9% of global greenhouse gas emissions. The value constitutes enough high CO2 reduction to consider the concept as one of the applicable technologies allowing to decelerate global warming. Additional advantages of the presented concept are its global nature, it allows for the reduction of CO2 from all emission sources, regardless of its type and location on earth, and the fact that it will simultaneously lower the air temperature, contribute to oxygen production, and reduce dust in the environment

Modelling of SO2 and NOx Emissions from Coal and Biomass Combustion in Air-Firing, Oxyfuel, iG-CLC, and CLOU Conditions by Fuzzy Logic Approach

Chemical looping combustion (CLC) is one of the most advanced technologies allowing for the reduction in CO2 emissions during the combustion of solid fuels. The modified method combines chemical looping with oxygen uncoupling (CLOU) and in situ gasification chemical looping combustion (iG-CLC). As a result, an innovative hybrid chemical looping combustion came into existence, making the above two technologies complementary. Since the complexity of the CLC is still not sufficiently recognized, the study of this process is of a practical significance. The paper describes the experiences in the modelling of complex geometry CLC equipment. The experimental facility consists of two reactors: an air reactor and a fuel reactor. The paper introduces the fuzzy logic (FL) method as an artificial intelligence (AI) approach for the prediction of SO2 and NOx (i.e., NO + NO2) emissions from coal and biomass combustion carried out in air-firing; oxyfuel; iG-CLC; and CLOU conditions. The developed model has been successfully validated on a 5 kWth research unit called the dual fluidized bed chemical looping combustion of solid fuels (DFB-CLC-SF)