Influence of air staging strategies on flue gas sensible heat losses and gaseous emissions of a wood pellet boiler: An experimental study

Zadravec, Tomas; Rajh, Boštjan; Kokalj, Filip; Samec, Niko

doi:10.1016/j.renene.2021.05.150

Cited by 18 publications

(7 citation statements)

References 31 publications

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“…This behaviour is due to an increasing amount of secondary air supply at the later stage of the combustor. Higher concentration of O 2 in the flue gas mainly indicates the availability of excess air that may contribute to lower freeboard temperatures [25]. O 2 values reported here are generally higher than normal biomass combustion.…”

Section: Emissionsmentioning

confidence: 55%

“…Previous studies on staged biomass combustion show that the burning rate improves with a primary to secondary air ratio (Q p / Q s ) of 4:6 to 6:4 [24]. Whereas freeboard temperatures are mainly affected by primary air and Q p /Q s ratio [25]. Contrastingly, emissions appear to be mainly influenced by secondary air and Q p /Q s ratio, with a significant reduction in CO emissions achieved by reducing Q p /Q s ratio to 71% and 83% [25].…”

Section: Introductionmentioning

confidence: 99%

“…Whereas freeboard temperatures are mainly affected by primary air and Q p /Q s ratio [25]. Contrastingly, emissions appear to be mainly influenced by secondary air and Q p /Q s ratio, with a significant reduction in CO emissions achieved by reducing Q p /Q s ratio to 71% and 83% [25]. CO emissions can also be reduced by 50% in staged combustion of wood pellets as compared to non-staged, by using a uniform secondary air module at a higher position from the bed.…”

Section: Introductionmentioning

confidence: 99%

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Role of Primary Freeboard on Staged Combustion of Hardwood Pellets in a Fixed Bed Combustor

2022

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In staged fixed bed biomass combustion, primary air is supplied beneath the fuel bed with secondary air then provided above in the freeboard region. For fixed bed configurations, the freeboard is further divided into a primary freeboard length (LI), which is upstream of the secondary air and a secondary freeboard length (LII), measured from the secondary air all the way to the exhaust port. Despite extensive research into fixed bed configurations, no work has been successfully completed that resolves the effects of changing LI on fuel conversion, both in the fuel bed and within the freeboard of batch-type biomass combustors. In this study, experiments on a 202 mm diameter and 1500 mm long batch-type combustor have been conducted to determine the effects of changing primary freeboard length over three secondary to total air ratios (Qs/Qt) and two total air flow rates (Qt). The impact of these conditions has been studied on (i) intra-bed fuel conversion, measured through burning rate (kg/m−2 s−1), fuel bed temperature (°C) and ignition front velocity (mm-s−1), as well as (ii) post-bed fuel conversion in the freeboard, expressed through freeboard temperatures and emissions (NOx ppm, CO2%, CO ppm, O2%). The fuel used throughout the above experiments was Australian hardwood pelletised biomass. Results show that changes to primary freeboard length over LI = 200 mm, 300 mm and 550 mm, or LI/D = 1.00, 1.48 and 2.72, respectively, affect both intra-bed and freeboard (post-bed) performance indicators. The highest values of burning rate, ignition front velocity and fuel bed temperature were observed for interim values of LI/D = 1.48 at Qs/Qt = 0.25 and Qt = 0.358 kg/m−2 s−1. Primary freeboard lengths of LI/D = 1.00 and 1.48 were found to have higher freeboard temperatures, NOx and CO2 as well as lower CO and O2 values as compared to LI/D = 2.72 at Qs/Qt = 0.50 and 0.75. Increasing Qs/Qt from 0.25 to 0.50 for LI/D = 1.00 and 1.48 initially increased freeboard temperatures, with an accompanying increase in NOx and CO2 as well as decrease in CO values. However, further increase in Qs/Qt to 0.75 lead to lower freeboard temperatures for all primary freeboard lengths.

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Section: Emissionsmentioning

confidence: 55%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Role of Primary Freeboard on Staged Combustion of Hardwood Pellets in a Fixed Bed Combustor

2022

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“…The results showed that the water saving, coal saving and net present value (NPV) of this system could reach up to 95 t/h, 4.11 g/kWh and 102,739,000 RMB with investment payback within 4 years, demonstrating the profitability of mitigating the environmental problems caused by flue gas. Zadravec et al [32] introduced the flue gas extraction with an effective air-staging strategy for sensible heat recovery. A wood-pellet boiler was installed into a laboratory-sized heating system, while the operating conditions, including the airflow rate, temperatures and combustion ash inside the chamber, were measured.…”

Section: Energy Saving and Emission Reductionmentioning

confidence: 99%

Recent Advances in Low-Carbon and Sustainable, Efficient Technology: Strategies and Applications

et al. 2022

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The COVID-19 pandemic has had a significant impact on the supply chains of traditional fossil fuels. According to a report by the International Energy Agency (IEA) from 2020, oil-refining activity fell by more than the IEA had anticipated. It was also assumed that the demand in 2021 would likely be 2.6 million bpd below the 2019 levels. However, renewable markets have shown strong resilience during the crisis. It was determined that renewables are on track to meet 80% of the growth in electricity demand over the next 10 years and that sustainable energy will act as the primary source of electricity production instead of coal. On the other hand, the report also emphasized that measures for reducing environmental pollution and CO2 emissions are still insufficient and that significant current investments should be further expanded. The Sustainable Development of Energy, Water and Environment Systems (SDEWES) conference series is dedicated to the advancement and dissemination of knowledge on methods, policies and technologies for improving the sustainability of development by decoupling growth from the use of natural resources. The 15th SDEWES conference was held online from 1–5 September 2020; more than 300 reports with 7 special sections were organized on the virtual conference platform. This paper presents the major achievements of the recommended papers in the Special Issue of Energies. Additionally, related studies connected to the above papers published in the SDEWES series are also introduced, including the four main research fields of energy saving and emission reduction, renewable energy applications, the development of district heating systems, and the economic assessment of sustainable energy.

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“…He concluded that the supply of PA has an important role in combustion and more biomass fuel was burnt with increasing PA flow rate. Zadravec et al [11] aimed to obtain correlations between the emissions and combustion temperatures at different primary and secondary air ratios and excess air conditions in small-scale wood pellet boiler. They stated that air staging has great importance to decreasing harmful emissions and sensible heat losses.…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigation of the Effect of Feeding System on the Performance at Pellet-Fuelled Boilers

Sungur

2022

Erzincan Üniversitesi Fen Bilimleri Enstitüsü Dergisi

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Depending on the growing industry and the population, energy needs are increasing day by day. This issue makes it necessary the use of renewable energy sources as much as possible. There is a growing interest in pellet fuel and pellet-fired combustion systems, which are one of the renewable energy sources. In this work, performance analyzes of pellet-fueled boilers with two different feeding systems (horizontal-fed and top-fed) and two different flue gas outlet positions were carried out and results were discussed. Emissions of O2, CO2, CO and NOx and flue gas temperature were measured at a certain point of the chimney. Boiler thermal efficiencies were calculated and compared with each other. Direct and indirect methods were used to calculate thermal efficiency of boilers. Results showed that the flue gas temperatures were about 110 °C in the top-fed boiler and 138 °C in the horizontal-fed boiler. The thermal efficiency of top-fed boiler was higher than horizontal-fed boiler. In the top-fed boiler, CO and NOx emissions were lower than the horizontal-fed boiler. Generally, the top-fed boiler showed better performance and lower emission characteristics than horizontal-fed boiler.

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Influence of air staging strategies on flue gas sensible heat losses and gaseous emissions of a wood pellet boiler: An experimental study

Cited by 18 publications

References 31 publications

Role of Primary Freeboard on Staged Combustion of Hardwood Pellets in a Fixed Bed Combustor

Role of Primary Freeboard on Staged Combustion of Hardwood Pellets in a Fixed Bed Combustor

Recent Advances in Low-Carbon and Sustainable, Efficient Technology: Strategies and Applications

Experimental Investigation of the Effect of Feeding System on the Performance at Pellet-Fuelled Boilers

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