Search

The interaction between volatile and char is widespread in combustion. The effect of this interaction on the conversion of fuel-N to NO x is significant, but the mechanism remains to be comprehensively unveiled. Thus, in this paper, the NO and N 2 O conversion of nitrogen-containing biomass models (glutamate, glycine, phenylalanine) during combustion at high temperatures (800–1500 °C) is investigated using two combustion modes, separated combustion (in which volatile and char are burned separately) and coupled combustion (in which volatile and char are burned simultaneously), in an O 2 /Ar atmosphere. A new pathway for N 2 O formation resulting from the interaction between volatile and char is identified. At low temperatures, this interaction facilitates the conversion of fuel-N to N 2 O. For instance, during the separated combustion of glutamate at 800 °C, the conversion rates of fuel-N to N 2 O and NO are 26.3 % and 20.4 %, respectively. However, in coupled combustion, these conversion rates shift to 48.1 % for N 2 O and 3.6 % for NO. At high temperatures, this interaction promotes the conversion of fuel-N to NO. For instance, during the separated combustion and coupled combustion of glutamate at 1500 °C, the conversion rates of fuel-N to NO are 6.2 % and 16.6 %, respectively. Similar patterns are observed for the other two amino acids. In both combustion modes, the co-firing of cellulose, lignin, and hemicellulose with glutamic acid significantly suppresses the production of N 2 O. The conversion rate of N 2 O decreases by about 7 %–10 %, while the impact on NO release shows either a suppressive or promotive effect in different temperature intervals. These results play a crucial role in the development of efficient and clean combustion technology for biomass. [Display omitted] • A novel N 2 O formation pathway from volatile-char interaction has been identified. • Volatile-char interaction enhances NO formation at 1300–1500 °C. • Accurate volatile-NO/N 2 O and char-NO/N 2 O contributions were determined. • Co-firing with cellulose, lignin, and hemicellulose inhibits the formation of N 2 O. [ABSTRACT FROM AUTHOR]

Grate boilers are widely applied in biomass combustion for heat and energy generation. However, grate-firing systems often suffer from low efficiency and high emission. Computational fluid dynamic (CFD) becomes increasingly popular as a flexible method to obtain the detailed combustion behaviors in the furnace, and to optimize the performance of existing grate boilers. This paper presents efforts toward a reliable baseline CFD model for an industrial biomass-fired grate boiler, where the structure of the fuel-bed was sufficiently considered. The combustion performances in the furnace were investigated experimentally and numerically by coupling the fuel bed and freeboard, to clarify the impact of bed structure on the simulation accuracy. Results show that when the bed structure has been taken into account, the predictions are in better agreement with the various measurements, as the deviations between them are all within 10 %. Moreover, the flame center drops, the total heat transferred to the water-cooled walls increases, and the residence time of flue gas is greatly prolonged from 2.76 s to 3.90 s, resulting in a distinct difference of the temperature and species patterns in the freeboard. The simulations will provide valuable theoretical guidance for the accurate modeling of grate-fired boiler. [Display omitted] • A baseline model is proposed for accurate modeling of biomass-fired grate boiler. • Effect of fuel-bed structure on the simulation of grate boiler is clarified in detail. • Bed structure greatly affects the predicted temperature and species patterns. • Flue gas residence time and heat transfer are also highly impacted by bed structure. [ABSTRACT FROM AUTHOR]

In this paper, the effect of alkaline-earth metals (AEMs, Ca, Ba, and Sr) on the performance of CuO/ZrO 2 oxygen carriers (OCs) and the hemical looping with oxygen uncoupling (CLOU) process of wheat-derived hydrochars with these Cu-based OCs were investigated. The results showed that after multiple cycles, the crystal phases of modified Cu-based OCs were the same as that of pure CuO/ZrO 2 OC without any interaction between them. Due to the catalytic effects of AEMs, an increase in the decomposition of wheat and hydrochar-235 in modified Cu-based was observed at 500 °C. The combination of Ca and HTC promotes reoxidation, while Ba and Sr inhibit reoxidation. Notably, the Cu-based OCs exhibited moderate agglomeration after 20 redox cycles at 950 °C. The results of the kinetic analysis indicate that the chemical order models and diffusion models can suitably describe the first combustion stage for wheat and hydrochars with Cu-based OCs, respectively. The geometrical contraction model was also found to most suitably describe the second combustion stage of all samples. These results suggest that a combination of hydrothermal carbonization pretreatment with AEMs modification is an efficient approach for CLOU using CuO-based OCs. [Display omitted] • AEMs enhanced the decomposition under 500 °C without interactions with CuO OC. • Simultaneous combustion and reoxidation enhancement of hydrochar-235 was observed. • The reoxidation activity of CuO was improved by Ca but inhibited by Ba and Sr. • Moderate agglomeration of CuO was observed after 20 redox cycles at 950 °C. • The kinetics of biomass combustion was estimated using the Coats-Redfern method. [ABSTRACT FROM AUTHOR]

The paper presents new approach in reducing of the CO emission in exhaust gases from small-scale wood pellet boilers. The results are obtained by control of the airflow to the boiler using a model-based nonlinear predictive controller. The complex-structure nonlinear model designed, and simplified to the nonlinear block-oriented Hammerstein system. Finally, the Hammerstein system is used to design the nonlinear predictive controller of the combustion process. The effectiveness analysis of the designed control algorithm under operating conditions at nominal heat power shows that 1) the airflow changes to the boiler is crucial for the CO concentration in the flue gasses and 2) accurate control of the airflow may lead to a significant reduction of the CO emission without any changes of the boiler design. The paper shows that reducing CO emissions from small-scale wood pellet boilers decreased by 35–50% of the original value with low implementation cost to fit industrial scale. • Complex-structure nonlinear model of small-scale boiler for biomass combustion. • Air flow nonlinear extended horizon predictive controller based on Hammerstein model. • CO emissions is decreased to 35–50% in actual operating conditions. • Low-cost modifications, easily implemented to commercially available boilers. [ABSTRACT FROM AUTHOR]

Biomass is a carbon neutral fuel and can effectively replace fossil fuels. However, its large scale application is limited by disadvantages such as low calorific value, low energy density and high alkali content. Densification, pyrolysis and adding additives are available methods to upgrade biomass fuels. Nevertheless, emission rules of nitrogen and sulfur oxides in combustion of densified biochar need to be clarified. This paper focuses on the emission and transformation mechanisms of nitrogen and sulfur pollutants during pyrolysis and combustion of biomass with phosphorus based additives by means of thermodynamic calculation and experimental research. The addition of additives promoted the emissions of H 2 S, COS and NH 3 during pyrolysis, so the treatment of H 2 S and COS needs to be considered particularly. During combustion of densified biochar at 1000 °C, increased pyrolysis temperature accelerated SO 2 emissions, while it had no obvious influence on NO emissions. NH 4 H 2 PO 4 accelerated organic sulfur release, NH 4 H 2 PO 4 and Ca(H 2 PO 4) 2 slightly reduced the emission of NO. The maximum values of NO and SO 2 release rates were about 2.81 and 1.55 g/kg, respectively, which were lower than those of most typical fuels. The upgraded densified biochars have benefits such as high calorific value, low melting point and low pollutant emission. • Emission rules of nitrogen and sulfur oxides of densified biochar were studied. • Influences of phosphorus additives on transformation of N and S were studied. • Additives promoted H 2 S and NH 3 release during pyrolysis. • SO 2 and NO emissions of densified biochar during combustion were lower than most fossil fuels. [ABSTRACT FROM AUTHOR]

Interest in circulating fluidized bed (CFB) boilers as a power generation technology has sky-rocketed in recent years because of several advantages this technology offers over conventional boilers, such as increased gas-solid mixing, which results in higher combustion efficiency and the ability to use lower rank fuels. CFB combustors are operated at lower temperatures than conventional thermal power generation combustors, thus reducing NO x emissions, while SO 2 emissions can be conveniently controlled through the addition of Ca-based sulfur sorbents within the combustor. This paper summarizes the modeling effort on a 50 kW th CFB combustor designed, built, and operated at CanmetENERGY in Ottawa, Canada. The numerical model employs the multiphase particle-in-cell (PIC) approach in the open-source Multiphase Flow with Interphase eXchanges (MFiX) Software Suite. The MFiX-PIC model parameters for the simulation are tuned against cold-flow experiments from CanmetENERGY using olivine sand as the inert bed material. It is shown that for the relatively coarse fluid meshes and large parcel sizes necessitated by the scale of the simulation, filter size dependent corrections to the drag law must be incorporated to ensure accuracy of the simulation results. The validated cold flow model is extended to simulate reacting flow with torrefied hardwood as the feedstock and to validate the combustion reaction scheme. The species concentrations at the riser outlet are compared against CanmetENERGY's experiments and show satisfactory agreement. The simulations demonstrate the ability of MFiX-PIC to accurately capture both the physics and chemistry of a CFB combustor at bench scales, which can be further extended to pilot- and industrial-scale systems. • MFiX-PIC is employed to model the 50 kW th circulating fluidized bed at CanmetENERGY. • Calibration of PIC for a large-scale application is discussed in detail. • Filter size dependent corrections are incorporated to the drag law for accuracy. • Combustion reaction scheme is developed and validated against experiment. • MFiX-PIC model accurately captures both physics and chemistry of the CFB combustor. [ABSTRACT FROM AUTHOR]

This paper is focused on aerosol fine particle release during the thermal decomposition of beech wood samples with identical mass under an oxidizing and inert atmosphere. This thermal degradation of wood is a significant part of the biomass combustion and pyrolytic process. This contribution focuses on nanoparticles emission with specifying sizes and concentrations in the range of 18–545 nm during thermal degradation processes and determining correlations between individual thermal degradation processes of a wood sample with the same weights but with different heating rates. The flue gases' chemical composition was simultaneously analyzed using a quadrupole mass spectrometer during the thermal degradation process. The weight loss of the sample and its derivation were monitored using a thermogravimeter. This combination made it possible to identify the ranges with the highest particle emission concerning the wood sample and the sample's heating rate. The fine particle identification apparatus uses a Scanning Mobility Particle Sizer and a condensation particle counter. This experimentally obtained data were then compared with the numerical model CPD-Bio. In this case, the comparison was focused on the prediction of the temperatures of the individual pyrolysis stages, at which gaseous products and especially tars are formed. • Thermal degradation of beech induces dominantly particles in size 130 to 230 nm. • CPD-Bio calculation model is suitable for particulate mass identification of biomass. • Mass yields of tars serve as precursors for aerosol particles. • Particle number concentration increases with increase of heating rates. [ABSTRACT FROM AUTHOR]

This paper studies the technical, economic, and environmental feasibility of a standalone adsorption cooling system thermally driven by biomass combustion and solar thermal energy. The developed cooling package was benchmarked against a baseline vapour compression refrigeration system, driven by grid electricity and the widely investigated adsorption cooling system driven by solar heat. TRNSYS was utilised to imitate the integrated systems, investigate their year-round performance, and optimise their designs by employing the meteorological data for Rwanda and an existing cold room (13 m2 floor area × 2.9 m height) as a case study. The optimisation study for the system revealed that maximum chiller performance (COP = 0.62), minimum biomass daily consumption (36 kg), and desired cold room setting temperature (10 °C) throughout the year can be achieved if the boiler setting temperature, heat storage size, and heating water flow rate are 95.13 °C, 0.01 m3 and 601.25 kg/h. An optimal PV area/battery size combination of 12 modules/16 kWh was obtained from the economic, environmental, and technical viewpoints. [Display omitted] • A standalone bio-driven adsorption cooling system was developed. • A PV solar system was integrated to drive the system's auxiliaries. • The system's variables were optimised to minimise the cost and environmental impact. • The system's technical, economic, and environmental feasibility were analysed. [ABSTRACT FROM AUTHOR]

Since the formation of gaseous pollutants during solid fuel combustion in circulating fluidized bed (CFB) units, especially under oxyfuel combustion and chemical looping combustion conditions, is an extremely complex process, the development of a simple predictive model of gas emissions is of practical significance. This paper introduces a novel approach based on fuzzy logic (FL), one of the main artificial intelligence (AI) methods, for the prediction of CO 2 , CO, NO x (i.e., NO + NO 2), N 2 O, and SO x (i.e., SO 2 + SO 3) concentrations in flue gases from coal and biomass combustion in various operational sceneries. The simulations are carried out for different combustion environments, i.e., air-firing, oxyfuel, iG-CLC (in-situ gasification chemical looping combustion), and CLOU (chemical looping with oxygen uncoupling), under a wide range of operating parameters. A mixture of oxygen with CO 2 was used for oxyfuel combustion. Three different oxygen carriers (OC) were examined in the study for iG-CLC and CLOU, i.e., ilmenite, copper oxide (60% wt.) with the support of carbonate waste from ore flotation, and copper oxide (60% wt.) with the support of ilmenite (20% wt.) and fly ash. The validation of the model was successfully performed on a complex geometry laboratory–scale 5 kW th Dual-Fluidized-Bed Chemical-Looping-Combustion of Solid-Fuels (DFB-CLC-SF) facility. The gaseous pollutant emissions predicted using the developed model were in good agreement with experimental results. The maximum relative error between measured and predicted by the model emissions was lower than 8%. The proposed method constitutes a quick and easy-to-run technique and a complementary tool compared to the experimental procedures and the programmed computing approach. The developed fuzzy logic-based model of gaseous emissions from advanced combustion (GasAdComb) of solid fuels can be easily applied by scientists and engineers to simulate and optimize coal and biomass combustion processes. • A comprehensive model of 5 kW th Dual-Fluidized-Bed CLC facility was developed. • Fuzzy logic approach was applied in the study. • Air-firing, oxyfuel, iG-CLC and CLOU under a wide range of operating parameters are considered. • The model was successfully validated against experimental data of gaseous pollutants emissions. • The model constitutes an easy-to-use optimization tool. [ABSTRACT FROM AUTHOR]

This paper presents the research on improving combustion of wood and agro pellets in domestic hot water boilers. The novel biomass combustion system concept consisting of rotary burner and two types of combustion intensifiers is proposed, with the aim to allow simple application in the most of existing boilers, as well as to improve the efficiency and emissions to extent the related requirements of the relevant EU standards are met. In this regard, inclusion of the combustion intensifier based on honeycomb structure into conventional combustion system is numerically and experimentally investigated and the most appropriate placement in a furnace found. The results show that, with such implementation of the combustion intensifier, significant reductions in unburned pollutant emissions (CO >40% in case of wood pellets and >30% in case of agro pellets), particulate matter emissions (28–56 mg/m n 3 at 10% of O 2 in dry flue gases) and improvements in combustion efficiency (>2.6–3.7%) can be obtained. A detailed numerical analysis of the subsequent combustion process within the combustion intensifier lead to the novel combustion intensifier design, aimed at lowering manufacturing cost. Preliminary numerical and experimental results indicate similar or slightly less reduction in unburned pollutants of novel design. • Novel combustion system concept for burning wood and agro pellets is presented. • Reductions in CO emissions above 30–40% are obtained. • Reductions in PM emissions for 28–56 mg/m n 3 are obtained. • Increase in combustion efficiency above 2.6–3.7% in case of agro pellets is achieved. • New design of combustion intensifier is proposed. [ABSTRACT FROM AUTHOR]