| 1. |
- Hermansson, Sven, 1978, et al.
(författare)
-
On-line monitoring of fuel moisture-content in biomass-fired furnaces by measuring relative humidity of the flue gases
- 2011
-
Ingår i: Chemical Engineering Research and Design. - : Elsevier BV. - 0263-8762 .- 1744-3563. ; 89:11, s. 2470-2476
-
Tidskriftsartikel (refereegranskat)abstract
- Combustion of biomass for heat and power production is continuously growing in importance, because of incentivesfor replacing fossil energy resources with renewable ones. In biomass combustion, the moisture content of the fuel isan essential operation parameter, which often fluctuates for biomass fuels. Variation in moisture content complicatesthe operation of the furnaces and results in an uncertainty in the energy content of the fuel delivered to a plant.The fuel moisture-content in a furnace may be determined either by direct measurement on the entering fuel or bymeasuring the moisture and oxygen contents of the flue gases deriving the moisture content of the fuel. However,reliable methods of a motivated cost for the small to medium-scale furnaces are today not available. An exception isif the furnace is equipped with flue-gas condenser, which can be used to estimate the moisture content of the fluegases. A limitation of this method is, though, that not all furnaces have flue-gas condensers and that the measuredsignal has an inherent time delay.In thiswork, measurement of the relative humidity (RH) of the flue gases froma furnace is investigated as the centralcomponent in the on-line monitoring of the moisture content of the fuel in a furnace. The method was analysedwith humid air in a laboratory environment and tested for accuracy and dynamical behaviour in two biomass-firedheat-production units, one circulating fluidised-bed boiler (CFB) and one grate furnace. The results show that themethod, which is easy to calibrate on site, can be used to predict the moisture content of the biomass fuel in thegrate furnace with very good precision (
|
|
| 2. |
- Boman, Christoffer, et al.
(författare)
-
Development of innovative small(micro)-scale biomass-based CHP technologies
- 2017
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- To enhance the overall efficiency of the use of biomass in the energy sector in Europe, the large electricity production potential from small-scale biomass heating systems should be utilised. So far, no technologically sound (in terms of efficiency and reliability) and economically affordable micro- and small-scale biomass CHP technologies are, however, available. Therefore, the present ERA-NET project (MiniBioCHP) aimed at the further development and test of new CHP technologies based on small-scale biomass combustion in the electric capacity range between some W and 100 kW. Within the project, an international consortium consisting of 12 partners from 4 countries, including university institutions, institutes and industry (both engineering and manufacturing), collaborated closely to perform high level R&D on three promising micro/small-scale biomass based CHP technologies which are covering a broad range of applications in the residential heating sector. The Austrian engineering company BIOS, coordinated the international project. The project was based on earlier basic research and development work related to these promising new technologies and aimed at the achievement of a technological level which allows a first (commercial) demonstration after the end of the project. The three CHP concepts included in the MiniBioCHP project were;1. Pellet stoves with a thermoelectric generator (TEG)2. Small-scale biomass boilers (10-30 kWth) with a micro-ORC process3. High temperature heat exchanger (HT-HE) for an externally fired gas turbine (EFGT)The Swedish part of the project was focused on the development of the concept of biomass based EFGT with dedicated R&D activities related to the development of the HT-HE system. The Swedish project consisted of the research partners Umeå University (project leader), Luleå University of Technology, Chalmers University of Technology and RISE Research Institutes of Sweden, together with the industrial partners Enertech AB/Osby Parca and Ecergy. The expertise of the Swedish partners regarding ash related problems, grate boiler combustion and modelling, deposit formation and high temperature corrosion, were combined with the know-how of a Polish partner regarding HT-HE design, construction, testing and optimisation.The HT-HE is the most crucial component in EFGT processes significantly influencing the investment costs, availabilities as well as the efficiencies that can be achieved. With a thermal capacity from several hundred kW up to 2-3 MWth) the CHP technology based on a biomass boiler and an EFGT is suitable for district heating systems, or process heat consumers. The electricity produced by the gas turbine (up to some 100 kWel) can be used to cover the own electricity consumption of a company and/or fed into the grid. Even though the concept of biomass based EFGT has been an interesting alternative for small-scale CHP production for some decades, and R&D activities have been undertaken, tackling both economic and technical aspects, only a few pilot-plants have been in operation and no initiative has so far reached the level of commercial implementation. Thus, the concept of EFGT fed with biomass is still considered to be in a rather early development stage and the main technical challenges are related to alkali deposit induced corrosion and thermal stress of the HT-HE material, turbine design/operation and system integration.Within the present project, a HT-HE prototype aimed for an EFGT system was therefore designed, constructed and successfully tested at flue gas temperatures up to 900°C. Thus, appropriate guidelines for a compact design of the HT-HE and recommendations have been worked out to minimize thermal stresses as well as ash related problems regarding ash deposit formation and high temperature corrosion in a biomass boiler system. Furthermore, different concepts for the overall biomass based EFGT system have been worked out and evaluated. The outcome of the project will hopefully be used in the further development work and form the basis for a first testing and demonstration plant within the coming years.
|
|
| 3. |
|
|
| 4. |
- Ghirelli, Federico, 1971, et al.
(författare)
-
Reactor residence time analysis with CFD
- 2006
-
Ingår i: Progress in computational fluid dynamics. ; 6:4/5, s. 241-247
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract: The residence time of the fluid in a reactor can be analysed with at least three differentcomputational methods:(a) Eulerian simulation of the residence time measurements(b) solution of the Eulerian transport equation for residence time(c) Lagrangian particle tracking.Methods (a) and (c) are compared with analytical and experimental data from a pilot lagoon forvalidation, and the superiority of the Eulerian approach is demonstrated. Method (b), which hasbeen validated in earlier studies, is applied to study the flow in the secondary combustionchamber of a biomass grate furnace. An inefficiently exploited zone of the furnace is identified,and a change in operating conditions, aimed at improving the reactor utilisation, is discussed.
|
|
| 5. |
- Hermansson, Sven, 1978, et al.
(författare)
-
CFD modelling of bed shrinkage and channelling in fixed-bed combustion
- 2011
-
Ingår i: Combustion and Flame. - : Elsevier BV. - 1556-2921 .- 0010-2180. ; 158:5, s. 988-999
-
Tidskriftsartikel (refereegranskat)abstract
- Combustion of fixed fuel beds in grate furnaces is common within production of heat and power fromsolid fuels. Available theoretical and experimental experience provides a solid base of knowledge onhow a conversion model of a fuel bed, using Computational Fluid Dynamics (CFD), needs to be structuredand solved. Most existing models, however, handle the conversion in one single dimension of constantbed properties; when observing a burning fuel bed in a grate furnace it becomes apparent that the fuelbed is neither homogeneous nor uni-dimensional. In this study, a two-dimensional model of the combustionof fixed fuel beds has been developed for the purpose of studying the influence of heterogeneousfuel-bed properties on the conversion. In the model, the available experience from fuel-bed modellingby means of the sub-models for fixed-bed conversion was structured into a fluid-flow scale and into afuel-particle scale, in which new formulations describing the shrinkage of the fuel bed on a multi-particlescale was introduced. Both available and new sub-models were introduced into a pre-existing CFD-platform,in which the framework for simulating fluid flow in porous media was used to solve also the conversionrelated processes acting within the particle scales as well as within the multi-particle scales. Thecomplete model was validated with good correspondence between available measurements of temperatureand species concentration in a wood-char combustor. In addition, the modelled shrinkage was foundto well describe the observed shrinkage of the fuel bed in a combustion experiment. Results of modelsimulations by using heterogeneous bed porosity show that a porous passage through the bed risks causingchannelling in the fuel bed – a phenomenon common in modern grate furnaces and suspected tocause increased emissions of nitric oxides and unburned carbon compounds. The channelling tendencycould, however, to a large extent be reduced by grates of higher flow resistance. The natural porosityincrease attributable to the packing of particles onto a wall was shown to concentrate combustion disturbancesclose to the surface of the grate. Thus, larger changes in the porosity than caused by natural fuelpacking against a wall are needed to give rise to channels that emerge through the fuel bed.
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Hermansson, Sven, 1978, et al.
(författare)
-
Combustion Disturbances Related to the Fuel Bed in Grate Furnaces
- 2005
-
Ingår i: Swedish-Finnish Flame Days 2005. - 9171781854 ; 1:1, s. 150-158
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Combustion in grate furnaces is a common method for conversion of biofuels to energy, especially in small-scale heat production. In these furnaces combustion instabilities in the fuel bed are often observed. Here, an inventory is presented of combustion disturbances found in the fuel bed in grate furnaces. The inventory was carried out by interviewing personnel responsible for operation of ten furnaces and by recording of the fuel bed in eight of them by a portable video camera. Combustion disturbances were experienced in all except one of the furnaces. The most common disturbances were burnouts in the fuel bed and channelling at the bounding furnace walls. These disturbances are affected by practical factors related to the operation of grate furnaces. Those factors are presented together with suggestions for measures to reduce the frequency and magnitude of the disturbances. Digital image analysis was used to detect and quantify the size and movement of local burnouts in the fuel bed in one of the furnaces. The method can be used to find the source of disturbances or to evaluate contra-measures against burnouts.
|
|
| 9. |
- Hermansson, Sven, 1978
(författare)
-
Detecting, Modelling and Measuring Disturbances in Fixed-bed Combustion
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Combustion of fixed fuel beds in grate furnaces is one of the most common techniques within production of heat and power from solid fuels. The grate furnace used to be a working horse for combustion of hard coal, while today the incitement of using renewable fuel sources has turned biomass and municipal waste into dominating fuel types. These fuels are more conveniently managed by the robust grate furnace than by, for example, fluidised bed or suspension boilers. However, the introduction of the, in many cases, complicated and heterogeneous biomass and waste fuels have, while at the same time subjected to increasingly stringent demands on efficiency and emission of harmful substances, given rise to diffuse challenges to the operation and design of grate furnaces. The influence of the heterogeneous fuels and the low air flow rate required for low nitric oxide emissions are, to a large extent, unclear. The outcome is that different furnaces not only rely on diverging strategies of design and operation – they also show a variety of disturbance characteristics. To make way for more efficient use of modern biomass fuels in grate furnaces, by improving the understanding of the combustion situation and disturbance characteristics, the following steps were made in this study: (1) a set of grate furnaces were investigated separating hands-on problems from underlying research oriented questions, (2) three methods for detecting and measuring disturbances in grate furnaces were developed, and (3) the fundamentals behind disturbances in the part of a fuel bed of grate furnace dominated by char conversion were addressed by mathematical modelling. The outcome of the inventory of furnaces is that fuel-bed channelling and grate material deterioration are common – the first causing increased emissions of unburned carbon compounds and nitric oxides, while the latter giving rise to high material costs and operation failures. In some furnaces, the disturbances could be detected by logical reasoning and visual observations while abated by hands-on adjustments to the fuel handling, operation conditions or grate design. The continued study adds two instruments to further improve this category: (1) a method of video recording inside furnaces to detect, quantify and fend off disturbing channelling, and (2) a new method of on-line monitoring of the fuel moisture content to detect disturbing changes in fuel moisture content during operation. Furthermore, a third developed method of analysing the residence time field of the gas flow in a furnace by mathematical modelling provides an opportunity to optimise the furnace chamber for both steady conditions and transient disturbances. The inventory of furnaces also identified some fundamental question marks concerning the conversion of the fuel bed – how channels in the fuel bed arise and how these disturbances may be avoided, also during low combustion air flow, without causing grate-material deterioration. Computational Fluid Dynamics (CFD) modelling of two-dimensional conversion of a fixed char bed was developed and used for investigating these matters, in which it was confirmed that a provoked change of bed porosity may cause process disturbing channelling. An obvious solution to avoid bed-channelling is, therefore, to create an as homogeneous fuel bed as possible. However, the structure of the fuel bed may only to a certain extent be affected; the low cost of the inferior quality fuel is, to a large extent, attributable to the fact that it is heterogeneous and, furthermore, advanced fuel pre-treatments drastically reduce the economical outcome. Thus, the most powerful parameter to avoid disturbances in a heterogeneous fuel bed is to manipulate the distribution of air by means of grate design. Here, a considerable flow resistance across the grate – an effect which may be achieved by reducing the amount and/or size of the air holes in the grate rods – was found to dampen channelling. The CFD modelling, however, indicates that the placing or shaping of these holes, under certain circumstances during the char conversion, may cause thermal and/or carburizing material deterioration – one of the most common disturbances in the inventory of furnaces. Consequently, recommendations for placing of holes along the lower part of a combustion grate, counter-acting the risk of grate material deterioration, could be given from the modelling outcome. These recommendations, which also include recirculation of flue-gases into the combustion air, may in a straight forward manner be applied to the design of future grate furnaces to improve the combustion of heterogeneous fuel beds.
|
|
| 10. |
- Hermansson, Sven, 1978
(författare)
-
Disturbances in Fixed-Bed Combustion
- 2007
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Conversion of solid fuels in fixed beds is a common method for heat and power production. A frequent fixed-bed technique in small to medium scale is combustion in grate furnaces. Grate furnaces are widely used in the industrial energy branch and appreciated for their stability and simplicity of control. Also, the fuel flexibility makes the method economically attractive as an energy supplier to district heating systems. With increasing demands on combustion efficiency and fuel flexibility, it has been observed, though, that the fuel bed in grate furnaces often suffers from disturbances causing problems in the fuel bed and in the free-board above it, such as elevated emissions and increased material wear. To reduce these problems it is important to gain a deeper understanding of the processes in the fuel bed, both by practical investigations and modelling. An inventory of disturbances in the fuel bed of grate furnaces was carried out, in which interviews with operating personnel and recordings of fuel beds with a video camera, was made. The results show that disturbances in the fuel bed are very common. Most frequent is channelling in the fuel bed and at the bounding walls, which occur naturally at walls of packed beds and in connection with local changes in bed porosity. The inventory shows that a range of practical measures in the operation of grate furnaces amplify this phenomenon. Modelling of combustion in the free-board of a grate furnace and in the fixed fuel bed was performed. The free-board modelling was carried out with a numerical software, using a simplified bed model to describe the inlet conditions from the fuel bed. The results clearly emphasise the practicability of such a combination and effects that are difficult to foresee by measurements and observations are highlighted. A zone in the furnace that is poorly exploited by the combustion process was revealed by the computation, and an alternative design was evaluated. The first steps in creating a bed model that describes the processes in a burning bed of char were also taken. The model was implemented into a commercial software and enriched with model-specific functions. Emphasis was put on describing a two-dimensional flow, including spatial variations in flow conditions and their influence on bed porosity and shrinkage, which enables modelling of channel formation in fixed beds.
|
|
