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  • 1.
    Carlsson, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Grönberg, Carola
    Energy Technology Centre, Piteå.
    Marklund, Magnus
    Energy Technology Centre, Piteå.
    Risberg, Mikael
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhrman, Olov
    Spatially resolved measurements of gas composition in a pressurised black liquor gasifier2009In: Environmental Progress & Sustainable Energy, ISSN 1944-7442, E-ISSN 1944-7450, Vol. 28, no 3, p. 316-323Article in journal (Refereed)
    Abstract [en]

    Black liquor gasification is a new process for recovery of energy and chemicals in black liquor from the Kraft pulping process. The process can be combined with catalytic conversion of syngas into motor fuels. The potential for motor fuel production from black liquor in Sweden is to replace about 25% of the current consumption of gasoline and diesel. For Finland the figure is even higher while for Canada it is about 14% and for the USA about 2%.

  • 2.
    Gebart, Rikard
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhrman, Olov
    Energy Technology Centre, Piteå.
    Pettersson, Esbjörn
    Energy Technology Centre, Piteå.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Carlsson, Per
    Energy Technology Centre, Piteå.
    Turning a pulp mill into a biorefinery: A possible outcome from the 2nd black liquor gasification program2008In: NWBC 2008: 2008 Nordic Wood Biorefinery conference : 11-14 March, 2008 : City Conference Centre, Stockholm, Sweden, Stockholm: STFI-Packforsk AB , 2008, p. 56-61Conference paper (Refereed)
  • 3.
    Lundqvist, Petter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Air heating system design for a sub-Arctic climate using a CFD technique2019In: Building and Environment, ISSN 0360-1323, E-ISSN 1873-684X, Vol. 160, article id 106164Article in journal (Refereed)
    Abstract [en]

    The thermal comfort in a residential building equipped with an air heating system and located in a sub-Arctic region was investigated with computational fluid dynamics (CFD) software. The predicted percentage of dissatisfied (PPD) was used to identify flaws with the heating system during winter conditions. New scenarios were simulated and compared to each other to see potential improvements of the thermal indoor climate. Comparison was done by combining the discomfort spaces inside rooms, the level of the discomfort and the time spent in these spaces. The discomfort covered 8–38% of the interior volume depending on the test case. The results provide the necessary means to create a satisfactory thermal indoor climate if an air heating system is to be utilized in sub-Arctic regions during the winter. The correct heat demand for each floor and appropriate placement of the supply devices are required. Adding air transfer units or grilles in rooms from which exhaust air is removed further improves the comfort. The results also show the strength of using CFD technique when investigating the indoor discomfort with PPD, and how a fair assessment can be done by combining the PPD with time.

  • 4.
    Pericault, Youen
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Vesterlund, Mattias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Viklander, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    A novel freeze protection strategy for shallow buried sewer pipes: temperature modelling and field investigation2016In: Proceedings of the 8th International Conference on Sewer Processes & Networks, 2016Conference paper (Other academic)
    Abstract [en]

    The burial of sewer and water pipes below the maximum ground frost depth can be very costly and laborious in regions with cold winters. If a freeze protection measure is applied, the utility lines can be installed in a shallower trench to reduce the excavation needs during construction and maintenance works. One freeze protection measure, so called heat tracing, consist in supplying heat along the pipes. In this work, the use of 4th generation district heating as a heat tracing solution was investigated at a pilot site in Kiruna, Sweden. The influence of the system on sewer and water pipes temperatures was studied experimentally and numerically at a snow-free and snow-covered cross section. The study showed that, under the climatic conditions of the experiment, a heat tracing temperature of 25 ˚C allowed to prevent freezing of the pipes while keeping drinking water pipes in safe temperature range at both cross sections. The other main result was that a finite volume model of the sections was developed and showed a good fitting to the experimental data.

  • 5.
    Pericault, Youen
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Vesterlund, Mattias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Viklander, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    A novel freeze protection strategy for shallow buried sewer pipes: temperature modelling and field investigation2017In: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, Vol. 76, no 2, p. 294-301Article in journal (Refereed)
    Abstract [en]

    The burial of sewer and water pipes below the maximum ground frost depth can be very costly and laborious in regions with cold winters. If a freeze protection measure is applied, the utility lines can be installed in a shallower trench to reduce the excavation needs. One freeze protection measure, so called heat tracing, consists in supplying heat along the pipes. In this work, the use of 4th generation district heating as a heat tracing solution was investigated at a pilot site in Kiruna, Sweden. The influence of the system on sewer and water pipe temperatures was studied at a snow-free and snow-covered cross section. To this end, five heat tracing temperatures were tested and the corresponding sewer and water pipe temperatures were measured. The field experiment was also simulated with a two dimensional finite volume model. The study showed that, under the climatic conditions of the experiment, a heat tracing temperature of 25 °C allowed to prevent freezing of the pipes while keeping drinking water pipes in a safe temperature range at both cross sections. The other main result was that the developed finite volume model of the sections showed a good fitting to the experimental data

  • 6.
    Pericault, Youen
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Viklander, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Temperature performance of a heat-traced utilidor for sewer and water pipes in seasonally frozen groundManuscript (preprint) (Other academic)
  • 7.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    CFD modelling of radiators in buildings with user defined wall functions2016In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 64, p. 266-273Article in journal (Refereed)
    Abstract [en]

    The most widely used turbulence model for indoor CFD simulations, the k-ε model, has exhibited problems with treating natural convective heat transfer, while other turbulence models have shown to be too computationally demanding. This paper studies how to deal with natural convective heat transfer for a radiator in order to simplify the simulations, reduce the numbers of cells and the simulation time. By adding user-defined wall functions the number of cells can be reduced considerably compared with the k-ω SST turbulence model. The user-defined wall function proposed can also be used with a correction factor for different radiator types without the need to resolve the radiator surface in detail. Compared to manufacturer data the error is less than 0.2% for the investigated radiator height and temperature.

  • 8.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Investigation of thermal indoor climate for a passive house in a sub-Arctic region using computational fluid dynamics2019In: Indoor + Built Environment, ISSN 1420-326X, E-ISSN 1423-0070, Vol. 28, no 5, p. 677-692Article in journal (Refereed)
    Abstract [en]

    There is currently an increasing trend in Europe to build passive houses. In order to reduce the cost of installation, an air-heating system may be an interesting alternative. Heat supplied through ventilation ducts located at the ceiling was studied with computational fluid dynamics technique. The purpose was to illustrate the thermal indoor climate of the building. To validate the performed simulations, measurements were carried out in several rooms of the building. Furthermore, this study investigated if a designed passive house located above the Arctic Circle could fulfil heat requirements for a Swedish passive house standard. Our results show a heat loss factor of 18.8 W/m2 floor area and an annual specific energy use of 67.9 kWh/m2 floor area, would fulfils the criteria. Validation of simulations through measurements shows good agreement with simulations if the thermal inertia of the building was considered. Calculation of heat losses from a building with a backward weighted moving average outdoor temperature produced correct prediction of the heat losses. To describe the indoor thermal climate correctly, the entire volume needs to be considered, not only one point, which normally is obtained with building simulation software. The supply airflow must carefully be considered to fulfil a good indoor climate.

  • 9.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    The impact of snow and soil freezing for commonly used foundation types in a subarctic climate2018In: Energy and Buildings, ISSN 0378-7788, E-ISSN 1872-6178, Vol. 173, p. 268-280Article in journal (Refereed)
    Abstract [en]

    Heat losses from a building foundation are affected by both the surrounding conditions and the surrounding soil properties. These include many factors that complicate the analysis of heat loss, such as thermal storage, snow and soil freezing. The effect of snow and soil freezing was studied with a 3D simulation model in a subarctic climate.

    The heat losses from the most commonly used foundation types in Sweden were studied. This paper shows that it is possible to achieve a good thermal estimation of the air temperatures in a crawl space, with an average difference of 0.4°C compared with the validation data over a year. Snow and soil freezing reduce the annual heat losses through the different foundation types by 7-10% and the maximum heat loss rate by 13-25%. In order to describe the heat transfer correctly, snow must be included in the calculations, while soil freezing has only a minor impact. The 3D model implemented in this study shows a significant impact on the soil temperatures when these parameters are included.

    For a subarctic climate, the commonly used calculation methods based on the European standard ISO 13370 are not thorough enough to calculate the heat transfer through a foundation accurately.

  • 10.
    Risberg, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Vesterlund, Mattias
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hedström, Annelie
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Dahl, Jan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Hållbara, integrerade energi- och VA-system2014Report (Other academic)
  • 11.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Black liquor gasification: burner characteristics and syngas cooling2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Black liquor gasification at high temperature is a promising alternative to the conventional recovery boiler process used in chemical pulp mills today. Compared to a conventional recovery boiler a black liquor gasifier can increase the total energy efficiency of a chemical pulp mill and produce a synthesis gas that can be used for production of motor fuel. In Piteå, a 3 MW or 20 tons per day entrained flow pressurized black liquor gasification development plant has been constructed by Chemrec at Energy Technology Center. The plant has been run more than 12 000 h since 2005. One of the key parts in the gasification process is the spray burner nozzle where the black liquor is disintegrated into the hot gasifier as a spray of fine droplets. In this thesis the spray burner nozzle as characterized with high speed photography in order to visualize the atomization process of black liquor. The results showed that black liquor forms non-spherical and stretched ligaments and droplets with the considered nozzle. Comparison of the results with atomization of a syrup/water mixture showed that the results were qualitatively very similar which means that a syrup/water mixture can be used instead of black liquor for burner optimization experiments. This is a considerable experimental simplification. Also spatially resolved measurements of the gas composition in the development plant with a water cooled quench probe have been performed. From the gas composition measurement and the spray visualization it has been showed that the preheating of black liquor has a significant influence on the gas composition. Another important part in the gasification plant is the counter-current condenser where the gas is cooled and the water content in the gas is condensed away in vertical tubes that are cooled on the outside by a counter-current flow of water or steam. In this thesis a computational fluid dynamics model of the counter-current condenser have been developed. The model consists of a two-phase fluid model on the tube-side of the condenser and a single phase model of the shell side. Predictions from the model are in excellent agreement with temperature measurements from the condenser used in the 3 MW Black Liquor Gasification development plant. However, more validation data is necessary before a definite conclusion can be drawn about the predictive capability of the code, in particular with respect to scale up with about two orders of magnitude for commercial size gas coolers

  • 12.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Entrained flow gasification of biomass: On atomisation, transport processes and gasification reactions2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Since the energy consumption in the world is increasing together with an increase of greenhouse gas emission it is of importance to find alternatives to fossil fuels. Biomass is one of the alternative energy sources which is both renewable and CO2 neutral. However, due to the large variability of biomass and the influence from different types of contaminations it is important to find processes that can work with a range of biomass and preferably transform the energy in the biomass into higher value energy forms. Gasification is one of the most robust processes that can achieve this by transforming solid biomass (e.g. wood, bark or rice husks) or liquid byproducts from the forest products industry (black liquor) into a uniform synthesis gas that can be further upgraded into electric power or synthetic motor fuels. This thesis is focused on a specific class of gasifiers called entrained flow gasifiers that converts the biomass to syngas in a reactor where the fuel is entrained in a gas flow.In entrained flow gasification, small fuel particles are gasified together with an oxidizing medium like air or pure oxygen. The fuel particles are either formed a priori by milling of solid biomass or in situ by atomisation of a liquid fuel. In both cases the fuel is thoroughly mixed with a carrier gas and distributed into a hot gasification reactor. One type of entrained flow gasification that is of high relevance for countries with a significant pulp and paper industry is black liquor gasification. Black liquor is a by-product from pulping that is available in large quantities in chemical pulp mills. The energy in the black liquor is normally utilized for steam production in the mill but this steam can easily be produced from low grade biomass, thereby freeing the black liquor for other purposes. The most interesting process is when black liquor is gasified with pure oxygen at high temperature. This process creates a clean synthetic gas with very low concentration of tars that is suitable for catalytic conversion into transportation fuels, e.g. dimethyl ether or methanol.One of the key parts in a black liquor gasifier is the burner nozzle that is used to produce a spray of fine black liquor droplets inside the gasifier. This is a difficult task since black liquor has a very high viscosity. The black liquor atomisation process has therefore been studied with high speed photography to be able to visualize the process and thereby making it possible to optimize the burner nozzle so that it produces a spray with near uniform particle size and appropriate distribution in space. The results show that the fuel particles formed from the considered nozzle consisted of non-spherical and stretched ligaments that in some cases were further broken down into more spherical droplets. The experiments with black liquor were difficult and hazardous since the black liquor is caustic and hot since it needs to be preheated to around 120 °C before it can be atomised. It is therefore of interest to find non-hazardous substitute liquids that will have the same behaviour as black liquor in a nozzle. In a comparison between black liquor at 120 °C and a syrup/water mixture with equal viscosity and surface tension at room temperature it was found that the syrup/water mixture behaved nearly identical to the black liquor in a real burner nozzle.Connected to the atomisation studies, measurements of gas composition in a 3MW black liquor gasifier were made for different black liquor preheat temperatures. The results showed that preheating of black liquor had a significant influence on the syngas composition and the conclusion when this was combined with the results from spray visualization was that the main reason for the observed differences is the smaller droplet size that is achieved with higher preheating temperatures.In a large syngas plant where the goal is to catalytically convert the syngas into motor fuels or chemicals in a catalytic process, the raw syngas from the gasifier must be cleaned and conditioned in several steps. In all contemporary downstream processes the gas must be much colder than when it leaves the gasifier. Hence, gas cooling is an important unit operation in the syngas process. In order to optimize the overall efficiency of the syngas plant it is very important to recover the latent heat in the syngas at the highest possible temperature. One way to do this is to use a counter current condenser that cools the syngas and condenses most of the steam that is mixed with the syngas while at the same time steam that can be used by other processes is produced. The sizing of counter current condensers is therefore of high importance and one part of the thesis work was to develop a computational model that can be used for optimization of these units. In order to validate the code, measurements were carried out in the counter-current condenser in the 3 MW black liquor gasification pilot plant that was mentioned above. The predictions from the model were found to be in very good agreement with the temperature measurements from the pilot plant for the cases that were investigated.Another type of entrained flow gasification process is air-blown cyclone gasification where biomass powder is gasified in a cyclone shaped reactor. This gasification process can be used in combination with a gas engine to produce both heat and power that can be used in district heating applications or as prime mover and heat source in industrial processes where low grade biomass is available at low cost. This type of gasifier has the possibility to operate with ash rich fuels since it operates below the ash melting temperature and the majority of the ash is separated in the bottom of the cyclone.One of the objectives in this thesis was to evaluate the fuel flexibility of the cyclone gasifier by experiments with different fuels in a 500 kW pilot gasifier. From the gasification test it was found that torrefied spruce, peat, rice husk, bark and stemwood powder can be used as fuel to produce a syngas that can be used as fuel in a gas engine.To be able to understand the cyclone gasification process and be able to optimize different sizes of cyclone gasifiers a computational fluid dynamics model of the process has been developed and compared against experimental measurements, both in a 500 kW plant and a 4 MW plant. The results show that the model predicts the main gas species in the product gas and the amount of unconverted fuel reasonably well. It also predicts the effect of increased gasifier size and fuel power well. Therefore the model could be used as a tool for designing cyclone gasifiers in arbitrary sizes and to optimise operating parameters in existing gasifiers.

  • 13.
    Risberg, Mikael
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Carlsson, Per
    Energy Technology Centre, Piteå.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Numerical modeling of a 500 kW air-blown cyclone gasifier2015In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 90, p. 694-702Article in journal (Refereed)
    Abstract [en]

    Cyclone gasification of biomass in combination with a gas engine has been considered as a process for combined heat and power production. In this work a numerical model of the cyclone gasification process of wood powder was developed intended to be used as a tool for future engineering design of cyclone gasifiers. The model is based on an Euler-Lagrange formulation for the multiphase flow where the biomass powder was treated as a dispersed phase and the gas as a continuous phase. The results from the simulation are compared with experimental measurement in a 500 kWth cyclone gasifier that uses wood powder as fuel. The model was able to predict the gas composition change with increasing equivalence ratio. The relative error for the main gas component was between 2.5-4.4%, 2.8-5.4%, and 2.6-17.3% for CO2, CO and H2. CH4 was predicted with a relative error of between 3.8-19.2%. Also the model was able to predict the char amount out from the gasifier with reasonable accuracy. The obtained lower heating value from the model was between 3.5 – 5.2 MJ/Nm3 whereas the calculated based on measurement was 4.0-5.3 MJ/Nm3.

  • 14.
    Risberg, Mikael
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Numerical modeling of counter-current condensation in a black liquor gasification plant2013In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 58, no 1-2, p. 327-335Article in journal (Refereed)
    Abstract [en]

    Pressurized Entrained flow High Temperature Black Liquor Gasification is a novel technique to recover the inorganic chemicals and available energy in black liquor originating from kraft pulping. The gasifier has a direct quench that quickly cools the raw syngas when it leaves the hot reactor by spraying the gas with a water solution. As a result, the raw syngas becomes saturated with steam. Typically the gasifier operates at 30 bar which corresponds to a dew point of about 235 °C and a steam concentration in the saturated syngas that is about 3 times higher than the total concentration of the other species in the syngas. After the quench cooler the syngas is passed through a counter-current condenser where the raw syngas is cooled and most of the steam is condensed. The condenser consists of several vertical tubes where reflux condensation occurs inside the tubes due to water cooling of the tubes on the shell-side. A large part of the condensation takes place inside the tubes on the wall and results in a counterflow of water driven by gravity through the counter current condenser. In this study a computational fluid dynamics model is developed for the two-phase fluid flow on the tube-side of the condenser and for the single phase flow of the shell-side. The two-phase flow was treated using an Euler-Euler formulation with closure correlations for heat flux, condensation rate and pressure drop inside the tubes. The single-phase model for the shell side uses closure correlations for the heat flux and pressure drop. Predictions of the model are compared with results from experimental measurements in a condenser used in a 3 MW Black Liquor Gasification development plant. The results are in good agreement with the limited experimental data that has been collected in the experimental gasifier. However, more validation data is necessary before a definite conclusion can be drawn about the predictive capability of the code

  • 15.
    Risberg, Mikael
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Marklund, Magnus
    Energy Technology Centre, Piteå.
    Visualizations of gas-assisted atomization of black liquor and syrup/water mixtures at elevated ambient pressures2009In: Atomization and sprays, ISSN 1044-5110, E-ISSN 1936-2684, Vol. 19, no 10, p. 957-967Article in journal (Refereed)
    Abstract [en]

    Pressurized entrained flow high-temperature black liquor gasification (PEHT-BLG) is a novel technique to recover the inorganic chemicals and available energy in black liquor originating from kraft pulping. One of the key parts in the PEHT-BLG process is the spray atomizer where the viscous black liquor is disintegrated into a spray of fine droplets into the hot gasifier. In this study a high-speed photography system was used in order to visualize the spray formation of black liquor and syrup/water mixtures at elevated ambient pressures based on a conventional coaxially convergent gas-assisted atomizer. The main conclusion is that the breakup and atomization of black liquor by a gas-assisted atomizer is similar to that of a syrup/water mixture with similar physical properties. The observed difference in sphericity between black liquor and syrup/water may be explained by rapid cooling of the black liquor by the cool nitrogen gas at the nozzle exit, resulting in a sudden decrease in viscosity and possible skinning of the black liquor. Furthermore, it was found that an increased ambient pressure appeared to contract the spray to a more dense cloud of droplets compared to the corresponding atmospheric case.

  • 16.
    Risberg, Mikael
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öhrman, Olov
    Gebart, Rikard
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Nilsson, Patrik
    Gudmundsson, Anders
    Sanati, Mehri
    Influence from fuel type on the performance of an air-blown cyclone gasifier2014In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 116, p. 751-759Article in journal (Refereed)
    Abstract [en]

    Entrained flow gasification of biomass using the cyclone principle has been proposed in combination with a gas engine as a method for combined heat and power production in small to medium scale (<20 MW). This type of gasifier also has the potential to operate using ash rich fuels since the reactor temperature is lower than the ash melting temperature and the ash can be separated after being collected at the bottom of the cyclone. The purpose of this work was to assess the fuel flexibility of cyclone gasification by performing tests with five different types of fuels; torrefied spruce, peat, rice husk, bark and wood. All of the fuels were dried to below 15% moisture content and milled to a powder with a maximum particle size of around 1 mm. The experiments were carried out in a 500 kWth pilot gasifier with a 3-step gas cleaning process consisting of a multi-cyclone for removal of coarse particles, a bio-scrubber for tar removal and a wet electrostatic precipitator for removal of fine particles and droplets from the oil scrubber (aerosols). The lower heating value (LHV) of the clean producer gas was 4.09, 4.54, 4.84 and 4.57 MJ/N m3 for peat, rice husk, bark and wood, respectively, at a fuel load of 400 kW and an equivalence ratio of 0.27. Torrefied fuel was gasified at an equivalence ratio of 0.2 which resulted in a LHV of 5.75 MJ/N m3 which can be compared to 5.50 MJ/N m3 for wood powder that was gasified at the same equivalence ratio. A particle sampling system was designed in order to collect ultrafine particles upstream and downstream the gasifier cleaning device. The results revealed that the gas cleaning successfully removed >99.9% of the particulate matter smaller than 1 μm.

  • 17.
    Sandberg, Marcus
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Industrilized and sustainable construction.
    Risberg, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ljung, Anna-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Varagnolo, Damiano
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.
    Xiong, Damiano
    Sveriges Lantbruksuniversitet.
    Nilsson, Michael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Distance- Spanning Technology.
    A modelling methodology for assessing use of datacenter waste heat in greenhouses2017Conference paper (Refereed)
    Abstract [en]

    In Sweden, the number of datacenters establishments are steadily increasing thanks to green, stable and affordable electricity, free air cooling, advantageous energy taxes and well-developed Internet fiber infrastructures. Even though datacenters use a lot of energy, the waste heat that they create is seldom reused. A possible cause is that this waste heat is often low grade and airborne: it is therefore hard to directly inject it into a district heating system without upgrades, which require additional energy and equipment that generate extra costs. One option for reusing this heat without needs for upgrades is to employ it for heating up greenhouses. But assessing the feasibility of this approach by building physical prototypes can be costly, therefore using computer models to simulate real world conditions is an opportunity. However, there is a lack of computer modelling methodologies that can assess the possibility of using waste heat from datacenters in greenhouses in cold climates.

    The objective of this paper is therefore to propose such a methodology and discuss its benefits and drawbacks in comparison with other research studies. This methodology combines computational fluid dynamics, process modelling and control engineering principles into a computer model that constitutes a decision support system to study different waste heat and greenhouse or mushroom house scenarios.

    The paper validates the strategy through a case study in northern Sweden, where we assess the amount of produced waste heat by collecting temperature, relative humidity, and fan speed data for the air discharged from the datacenter.

    The resulting methodology, composed by conducting measurements and computer models, calculations can then be used for other datacenter operators or greenhouse developers to judge whether it is possible or not to build greenhouses using datacenter waste heat.

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