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  • 1.
    Finnerman, Oskar
    et al.
    Chalmers University of Technology.
    Razmjoo, Narges
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Guo, Ning
    Chalmers University of Technology.
    Strand, Michael
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Ström, Henrik
    Chalmers University of Technology.
    Reactor modelling assessment for urea-SNCR applications2017In: International journal of numerical methods for heat & fluid flow, ISSN 0961-5539, E-ISSN 1758-6585, Vol. 27, no 7, p. 1395-1411Article in journal (Refereed)
    Abstract [en]

    Purpose

    This work aims to investigate the effects of neglecting, modelling or partly resolving turbulent fluctuations of velocity, temperature and concentrations on the predicted turbulence-chemistry interaction in urea-selective non-catalytic reduction (SNCR) systems.

    Design/methodology/approach

    Numerical predictions of the NO conversion efficiency in an industrial urea-SNCR system are compared to experimental data. Reactor models of varying complexity are assessed, ranging from one-dimensional ideal reactor models to state-of-the-art computational fluid dynamics simulations based on the detached-eddy simulation (DES) approach. The models use the same reaction mechanism but differ in the degree to which they resolve the turbulent fluctuations of the gas phase. A methodology for handling of unknown experimental data with regard to providing adequate boundary conditions is also proposed.

    Findings

    One-dimensional reactor models may be useful for a first quick assessment of urea-SNCR system performance. It is critical to account for heat losses, if present, due to the significant sensitivity of the overall process to temperature. The most comprehensive DES setup evaluated is associated with approximately two orders of magnitude higher computational cost than the conventional Reynolds-averaged Navier–Stokes-based simulations. For studies that require a large number of simulations (e.g. optimizations or handling of incomplete experimental data), the less costly approaches may be favored with a tolerable loss of accuracy.

    Originality/value

    Novel numerical and experimental results are presented to elucidate the role of turbulent fluctuations on the performance of a complex, turbulent, reacting multiphase flow.

  • 2.
    Razmjoo, Narges
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Characterization of conversion zones in a reciprocating grate furnace firing wet woody biomass2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Grate-firing systems are a common and popular combustion technology for burning biomass. However, combustion of biomass in these furnaces may emit a large amount of pollutants in the form of CO, CH4, PAH, NOx, and particles. These furnaces need to be further developed to increase their efficiency and improve the overall system performance while ensuring environmental compatibility. To improve the combustion of biomass in grate furnaces, it is vital to understand the processes occurring inside both the fuel bed and the gas phase above the bed (freeboard).

    The aim of this study was to characterize the conversion zones in two reciprocating-grate furnaces, with 4 and 12 MW maximum thermal outputs, firing wet woody biomass, mainly by measuring the temperature and gas concentration distributions. Measurements in the freeboard were conducted in both of the furnaces. However, measurements in the fuel bed were carried out only in the 4-MW furnace, in which the influence of two parameters, i.e., the fuel moisture and the primary airflow rate, on the bed conversion was investigated. Furthermore, a simplified model of the drying of wet biomass on a grate was developed and used to estimate the drying rate and to simulate the extent of the drying zone along the grate. The model was then validated against measurements of the fuel moisture and flue gas water vapor concentration made by NIR and FTIR, respectively.

    Measurements of temperature and gas concentration (i.e., CO, CO2, O2, CH4, and NO) profiles in the fuel bed were carried out through ports located in the wall of the furnace, by means of a stainless steel probe incorporating a K-type thermocouple. The temperature distribution along the height of the fuel bed was measured through a view-glass port, using a bent probe. High temperatures within a layer of about 0.1 m from the grate surface indicated the existence of a combustion layer at the bottom of the fuel bed (co-current combustion pattern). The drying rate of the moist fuel was calculated by the model to be about 0.0211–0.0235 kg water/m2s, under a certain condition. Therefore, the drying layer of the moist fuel was estimated to occupy almost two-thirds of the total grate length.

    Measurements of temperature and gas concentration profiles in the freeboard of the two furnaces were carried out by means of a water-cooled stainless-steel suction pyrometer. The pyrometer was introduced into the furnaces through the measuring ports, located along the pathways of the hot gas flow, and positioned at several locations between the wall and the furnace width center. For both of the furnaces, the temperature varied mainly in the 600–1000°C range in the primary combustion chamber, and reached about 1100–1200°C in the secondary chamber. A significant rise in NO concentration was observed in the transition sections between the primary and secondary combustion chambers of the furnaces. There was a positive correlation between NO and O2 at the ports in the secondary combustion chambers, which implied that in this high temperature region, the O2 concentration was the limiting factor for oxidation of N-volatiles to NO.

  • 3.
    Razmjoo, Narges
    et al.
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Hermansson, Sven
    RISE Research Institutes of Sweden.
    Morgalla, Mario
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Strand, Michael
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Study of the transient release of water vapor from a fuel bed of wet biomass in a reciprocating-grate furnace2018In: Journal of the Energy Institute, ISSN 1743-9671Article in journal (Refereed)
    Abstract [en]

    The present study investigates how sudden changes in fuel moisture affected the combustion characteristics of the fuel bed in a 4-MW reciprocating-grate furnace. The moisture content of the fuel fed to the furnace was monitored online using a near-infrared spectroscopy device, and the water vapor concentration in the flue gas was measured continuously. To obtain experimental data on fuel-bed conditions, the temperature and gas composition in the bed were measured using a probe. A simplified drying model was developed using the measured gas composition values as inputs. The model was then used to estimate the drying rate and to simulate the extent of the drying zone along the grate. Measurements indicated that a change in the moisture content of the fuel fed to the furnace was detected as a change in water vapor concentration in the flue gas with a delay of about 2 h. The model predicted that a portion of wet fuel would need about 2 h to become dry, in line with the measured time delay of the water vapor concentration change in the flue gas. Overall, there was good alignment between the measured and simulated results, supporting the validity of the model and the assumed mechanisms.

  • 4.
    Razmjoo, Narges
    et al.
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Hermansson, Sven
    Strand, Michael
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Characterization of the fuel bed combustion of wood residues in a 4 MW grate boiler2015In: European Biomass Conference and Exhibition Proceedings, 2015, p. 741-744Conference paper (Refereed)
    Abstract [en]

    Information about distributions of temperature and gas species within the fuel bed is of great importance in studying the formation of pollutants in an industrial-scale biomass boiler. The main objective of this study was to investigate the gas composition and temperature in some available sections of the fuel bed of a 4 MW reciprocating grate boiler, burning mixture of fresh pine wood chips, bark, and sawdust with two significantly different moisture content levels. The averageCO, CO2,CH4, and O2 concentrations measured during the combustion of the more moist fuel (about 60 mass %) were about 12, 12, 2, and 4 vol. %, respectively, whereas the corresponding values for the less moist fuel (about 45 mass %) were about15, 10, 2.5, and 5 vol. %, respectively. Higher concentration of CO and lower concentration of CO2 for the less moist fuel could originate either from the char conversion process or from the reactions of the devolatilizationgas products.

  • 5.
    Razmjoo, Narges
    et al.
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Sefidari, Hamid
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Strand, Michael
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Characterization of hot gas in a 4 MW reciprocating grate boiler2014In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 124, p. 21-27Article in journal (Refereed)
    Abstract [en]

    The gas concentration and temperature information from the combustion of biomass offer significant advantages to enhance the understanding of an industrial-scale biomass heating plant. The main objective of this study was to investigate the gas composition and temperature in a 4 MW reciprocating grate boiler. An extensive series of measurements was carried out, and the samples, which were drawn through different ports by means of a water-cooled stainless steel suction pyrometer, were analyzed for temperature and for O2, CO, and NO concentrations. The results showed that the averaged NO, CO, and O2 concentrations in the gas phase during fuel combustion in the primary chamber were 40 ppm, 3.5 and 6.5 vol.%, respectively, while the values were 80 ppm, 1.1 and 6 vol.% in the secondary chamber. Detailed gas species and temperature distributions are discussed, which provide good possibilities for the control of emissions.

  • 6.
    Razmjoo, Narges
    et al.
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Sefidari, Hamid
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Strand, Michael
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Experimental investigation of fuel bed combustion in an industrial grate boiler2015Conference paper (Refereed)
    Abstract [en]

    Information about distributions of temperature and gas species within the fuel bed is of great importance in studying the formation of pollutants in an industrial-scale biomass boiler. The main objective of this study was to investigate the gas composition and temperature in some available sections of the fuel bed of a 4 MW reciprocating grate boiler. The results showed that the temperature profiles of the grate bars and the fuel bed suggest significant temperature gradients versus the height of the fuel bed. The averaged NO, CO, CO2, and O2 concentrations measured in the fuel bed were about 80 ppm, 21, 11 and 1 vol. %, respectively.

  • 7.
    Razmjoo, Narges
    et al.
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Sefidari, Hamid
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology. Luleå University of Technology.
    Strand, Michael
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Measurements of temperature and gas composition within the burning bed of wet woody residues in a 4 MW moving grate boiler2016In: Fuel processing technology, ISSN 0378-3820, E-ISSN 1873-7188, Vol. 152, p. 438-445Article in journal (Refereed)
    Abstract [en]

    Moving grate firing systems are widely used for biomass combustion. The characteristics of the fuel bed combustion in moving grate boilers are of practical interest as they are directly related to the release of pollutants and affect the furnace efficiency. Measurements of temperature and gas species concentrations inside the fuel bed are necessary to improve our understanding of the highly complex processes involved in biomass combustion.There have been few experimental studies of the fuel bed of industrial scale grate furnaces. The present study measured temperature and gas species concentrations within a thick burning bed of wet woody biomass, in a  4 MW reciprocating grate boiler. Measurements were carried out under three different operating conditions through ports located in the wall of the furnace using a stainless steel probe incorporating a thermocouple. Temperatures of about 1000 °C were measured close to the grate, indicating intense combustion at the bottom of the fuel bed. The temperature distribution along the bed height showed that different stages of the combustion process take place in horizontally adjacent layers along the grate. Higher flow rates of the primary air resulted in relatively higher CO and lower CO2 and NO concentrations in the fuel bed.

  • 8.
    Razmjoo, Narges
    et al.
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Sefidari, Hamid
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Strand, Michael
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Yang, Jingjing
    Linnaeus University, Faculty of Technology, Department of Building and Energy Technology.
    Gas measurements and characterization of wood combustion in a traveling grate boiler2013In: Proceedings for 21st European Biomass Conference and Exhibition, ETA-Florence Renewable Energies , 2013, p. 591-594Conference paper (Refereed)
    Abstract [en]

    Experimental tests have been carried out on a moving grate boiler at a 4 MW heating plant located at a sawing mill in south of Sweden. In order to investigate the performance of the combustion chamber, the local concentrations of O2, NO and CO are determined in the region above the grate using two water-cooled stainless steel probes of different lengths and diameters. The fuel used was sawmill waste consisting of bark, sawdust and shavings. The results of the study provided valuable insights into the combustion process.

  • 9.
    Razmjoo, Narges
    et al.
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Strand, Michael
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    In-bed combustion charachteristics of wet wood chips and sawdust in a full-scale grate boiler2017In: Proceedings 13th International Conference on Energy for a Clean Environment, 2017Conference paper (Refereed)
  • 10.
    Razmjoo, Narges
    et al.
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Strand, Michael
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Investigation of moist fuel bed combustion in grate furnaces2017In: Proceedings of Nordic Flame Days, 10-11 October, 2017, Stockholm, 2017Conference paper (Refereed)
  • 11.
    Sefidari, Hamid
    et al.
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Razmjoo, Narges
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    Strand, Michael
    Linnaeus University, Faculty of Technology, Department of Built Environment and Energy Technology.
    An experimental study of combustion and emissions of two types of woody biomass in a 12-MW reciprocating-grate boiler2014In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 135, p. 120-129Article in journal (Refereed)
    Abstract [en]

    The gaseous emissions of primary concern from biomass combustion are nitrogen oxides (NOX), carbon monoxide, and various unburned gaseous components. Detailed characterization of the gas in the hot reaction zones is necessary to study the release, formation, and evolution of the gas components. In the present study, gas temperature and concentration were measured in a 12-MWth biomass-fired reciprocating-grate boiler operated with over-fire air and flue-gas recirculation. Temperature measurement was combined with flue gas quenching and sample gas extraction using two water-cooled stainless-steel suction pyrometers. The concentration profiles of O2, NO, and CO were experimentally determined throughout the furnace, and the profile gas temperature was measured in several positions inside the furnace for the two types of woody biomass studied. For both fuels, the gas temperature varied between approximately 450 °C (average primary chamber temperature) and 1200 °C (average secondary chamber temperature). The concentration profiles of CO and O2 suggested no conclusive difference between the two types of biomass. However, the local mean concentrations of NO and NOX emission factors (measured in the stack) were higher for Greenery fuel due to its higher nitrogen content than that of Standard fuel.

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