The applications of numerical modeling for the optimization of the operation of energy devices on the example of an air distribution system inside the biomass boiler

The paper addresses the results of a numerical – based on experimental data – study of air distribution in the manifold responsible for air supply into a combustion chamber of a biomass boiler. An analysis of the possibilities of optimizing the air distribution system using a ommercial CFD program by changing the diameter of the feeding ducts was performed and described

Analysis of selected problems of biomass combustion process in batch boilers - experimental and numerical approach

It is possible to list numerous groups of heating units that are used in households, such as boilers, stoves and units used as supporting heat sources, namely fireplaces. In each case, however, the same operational problems may be evoked [1]. To understand the causes of energy losses in a boiler system, a proper definition of significant elements of the unit’s heat balance is necessary. In the group of energy losses, the flue gas loss and the incomplete combustion loss are the most significant factors. The problem with the loss resulting from incomplete combustion, which is related to the presence of combustible substances in the exhaust, is especially significant in case of biomass boilers [2, 3]. The paper presents results of the research and the optimisation of the biomass combustion process in the 180 kW batch boiler. The studies described have been focused on the reduction of the pollutants emission, which was primarily realised by the modifications of the air feeding system. Results of the experiments and the CFD simulations have been compared and discussed. Both in case of the model as well as the experiment, positive influence of the modifications on the emission have been observed

The investigation of the impact of basic operational parameters on the dynamics of water jacket in a biomass boiler using numerical and experimental methods

Biomass boiler application, despite its many advantages, is dependent upon many technical aspects, which require tests and optimization. Because of practical constraints, one of the most problematic areas of research is the analysis of phenomena occurring inside the water jacket of the boiler during the combustion process. The issue referred to above is significant due to its direct impact on the heating up of the operating medium for current power of the device and the total efficiency. The paper presents the analytical possibilities of the operating medium in a biomass boiler water jacket. The experimental works conducted as a part of the study were performed using an actual device – EKOPAL RM 40 straw boiler. They were aimed at defining the values of significant boundary conditions. Resistance thermometers and K-type thermocouples connected to a data acquisition system were placed in selected points of the water jacket and the combustion chambers to allow the monitoring of the conditions of the water heating process during biomass combustion. A measurement of inlet water mass flow rate was performed. To develop a numerical model of heat transfer into the water jacket, ANSYS CFX software was applied. The results of the experiments and simulations were compared and discussed. The paper describes the methodology and instruments used to perform the experimental studies, as well as some optimization solutions developed based on the results of the numeric alanalysis

Application of various 'response surface' based algorithms in optimization of air manifolds for batch boilers

Correct design of air manifolds applied in biomass-fired batch boilers allows to avoid excessive emissions and high flow resistance, as well as helps achieving the required parameters of the fan supplying air to the boiler. The paper describes the process and the results of the optimization performed using selected methods based on the response surface analysis. An experimentally validated CFD model of the state of the art air manifold has been geometrically parametrized, in order to find the shape that is optimal from the point of view of the objective function. In each analysis, the objective function was linked to air flow characteristics. Selected algorithms of the interpolation of design points that were obtained as the result of the numerical experiment have been compared and evaluated. Optimization using the response surface generated using various algorithms has been performed and verified by further direct CFD computations. The obtained optimal values of the input parameters were applied in the final model of the prototype. The flow characteristics of the prototype and the reference state have been compared and discussed. Significant improvement of the operation conditions has been achieved

Processes of heat and mass transfer in straw bales using flue gasses as a drying medium

Moisture content is a main problem of using straw in form of bales for energy production. The paper presents possibility of straw drying in dedicated, innovative and patented in Poland straw dryers which using flue gasses as a drying medium. Paper presents an improved way of drying which proved to be very sufficient. Temperature and humidity of straw during the process of drying were measured. The measurements helped understand and perform numerical model of heat and mass transfer inside the straw bale. By using CFD codes it was possible to perform analysis of phenomenon occurring inside the dried straw bale. Based on the CFD model, proposals of the optimization and improvement process of drying have been discussed. Experimental and computational data have been compared in terms of convergence. A satisfying degree of agreement has been achieved. Applying improved drying method, homogenous field of moisture content and temperature in the straw bale is achieved in a very cost effective way

Processes of heat and mass transfer in straw bales using flue gasses as a drying medium

Moisture content is a main problem of using straw in form of bales for energy production. The paper presents possibility of straw drying in dedicated, innovative and patented in Poland straw dryers which using flue gasses as a drying medium. Paper presents an improved way of drying which proved to be very sufficient. Temperature and humidity of straw during the process of drying were measured. The measurements helped understand and perform numerical model of heat and mass transfer inside the straw bale. By using CFD codes it was possible to perform analysis of phenomenon occurring inside the dried straw bale. Based on the CFD model, proposals of the optimization and improvement process of drying have been discussed. Experimental and computational data have been compared in terms of convergence. A satisfying degree of agreement has been achieved. Applying improved drying method, homogenous field of moisture content and temperature in the straw bale is achieved in a very cost effective way

Characterization of the wood combustion process based on the TG analysis, numerical modelling and measurements performed on the experimental stand

The paper presents selected results of thermogravimetric (TG) analyses for softwood (pine) and hardwood (beech). The composition of the studied fuels has been defined and described. Both wood types used in the TG tests were studied in order to define their content of basic components such as lignin, cellulose and hemicellulose. Types of wood used in the TGA have been combusted on the experimental stand which is equipped with a set of temperature sensors and an exhaust analyser. A comparison of the TG analysis and the combustion in the heating unit has been performed to find relations between the kinetics of devolatilisation for different wood species and to determine the exhaust composition. Numerical modelling using computational fluid dynamics (CFD) has been performed for the process of carbon monoxide oxidation to supplement the tests results. The results of the comparisons of the performed analyses can be useful in all areas related to the process of optimisation and improvement of combustion, pyrolysis and devolatilisation process conditions in small scale heating units

Characterization of the wood combustion process based on the TG analysis, numerical modelling and measurements performed on the experimental stand

The paper presents selected results of thermogravimetric (TG) analyses for softwood (pine) and hardwood (beech). The composition of the studied fuels has been defined and described. Both wood types used in the TG tests were studied in order to define their content of basic components such as lignin, cellulose and hemicellulose. Types of wood used in the TGA have been combusted on the experimental stand which is equipped with a set of temperature sensors and an exhaust analyser. A comparison of the TG analysis and the combustion in the heating unit has been performed to find relations between the kinetics of devolatilisation for different wood species and to determine the exhaust composition. Numerical modelling using computational fluid dynamics (CFD) has been performed for the process of carbon monoxide oxidation to supplement the tests results. The results of the comparisons of the performed analyses can be useful in all areas related to the process of optimisation and improvement of combustion, pyrolysis and devolatilisation process conditions in small scale heating units

Steam generation unit in a simple version of biomass based small cogeneration unit

The organic Rankine cycle (ORC) is a very promising process for the conversion of low or medium temperature heat to electricity in small and micro scale biomass powered systems. Classic ORC is analogous to Clausius–Rankine cycle in a steam power plant, but instead of water it uses low boiling, organic working fluids. Seeking energy and economical optimization of biomass-based ORC systems, we have proposed some modifications e.g. in low boiling fluid circuit construction. Due to the fact that the operation of a micro steam turbine is rather inefficient from the technical and economic point of view, a specially modified air compressor can be used as a steam piston engine. Such engine should be designed to work at low pressure of the working medium. Studies regarding the first version of the prototype installation were focused on the confirmation of applicability of a straw boiler in the prototype ORC power system. The results of the previous studies and the studies described in the paper (on the new cogeneration unit) confirmed the high potential of the developed solution. Of course, many further studies have to be carried out