• Energy Research

Despite their obvious benefit in terms of energy efficiency and their potential benefit on pollutant emissions, Flue Gas Condensers (FGCs) are still not widely spread in biomass combustion plants. Although their costs have significantly decreased during the last decade, the economic viability of FGC retrofits is not straightforward and their return on investments is mainly dependent on the temperature of the available heat sink and the moisture content of the fuel. Based on a new techno-economic model of a FGC validated with recent industrial data, this paper presents a methodology to assess the economic viability of an FGC retrofitting in a medium-scale biomass combustion plant. The proposed methodology is applied to the case of a typical District Heating plant for which real data was collected. For the first time, the usual assumptions of constant process data generally used are challenged by considering the variability of the return temperature and heat demand over the year. Furthermore, a new concept of optimal configurations in terms of energy savings is introduced in this paper and compared to a strictly economic optimum. The economic feasibility is mainly evaluated by means of the Net Present Value (NPV), Discounted Payback Period (DPP), and the Modified Internal Rate of Return (MIRR). As expected, results show that the higher the humidity level and the lower the return temperature, the higher the economic profitability of a project. The NPV is, however, increased when considering variable inputs: Even with an average return temperature of 60 °C, a mixed operation of the FGC as a condenser and an economizer along the year is predicted, which results in an increased profitability assessment. Considering a constant return temperature over the year can lead to a 20% underestimation of the project NPV. An alternative averaging method is proposed, where two distinct temperature zones are considered: above and below the flue gas dew point. The discrepancy with a detailed temperature variation is reduced to a few percents. Our results also show that increasing the FGC surface beyond the highest NPV can lead to substantial energy savings at a reasonable cost, up to a certain level. The energetic optimum we defined can lead to an increase in energy savings by 17% for the same relative decrease of the NPV.

This work compares the economic viability of active and passive condensation in a medium-scale biomass combustion plant considering the variability of the return temperature and heat demand over the year. A typical District Heating plant with a total installed power of 9.5 MWth is considered. The economic feasibility is evaluated by means of the Net Present Value (NPV), Discounted Payback Period (DPP), and the Modified Internal Rate of Return (MIRR). Compared to passive condensation, the NPV of an active condensation plant is 66% higher and reduces the primary energy consumption by more than 50%. However, a higher initial investment and a higher DPP are calculated. Assuming constant return temperature and average heat demand over the year lead to an overestimation of the NPV by more than 110% for an active condensation plant and by more than 160% for a passive condensation plant. The NPV, DPP and MIRR are strongly impacted by a variation of the return temperature of the network.

AbstractThe Energy Return On Investment (EROI) is a recognised indicator for assessing the relevance of an energy project in terms of net energy delivered to society. For woody biomass divergences remain on the right methodology to assess the EROI leading to large variations in the published estimates. This article presents an in‐depth discussion about the EROI of woody biomass in three different forms: woodchips, pellets and liquid fuels. The conceptualisation of EROI is further developed to reach a consistent definition for biomass post‐processed fuels. It considers, on top of the external energy investments, the grey energy associated with the energy used to enrich the fuel. With the proposed methodology, all woodchips have an EROI of the same order of magnitude, between 20 and 37, depending on forestry types, operations and machineries. For secondary residues, the first estimate is 170 if, as co‐products, no energy investment is allocated to the forestry operations and transport. On the basis of a mass allocation for forestry operations and transport, the EROI for secondary residues becomes of the same order of magnitude as that for wood chips. Woodchips can be further post‐processed into pellets or liquid fuels. Pellets have an EROI of 4–7 if the heat is externally supplied and 8–23 if internally supplied (self‐consumption of part of the raw material). Liquid fuels derived from primary wood and residues through gasification and Fischer‐Tropsch synthesis have an EROI between 4 and 16. Fuel enhancement with hydrogen (Power & Biomass to Liquids) impacts negatively the EROI due to the low EROI of hydrogen produced from renewable electricity. However, these fuels offer other advantages such as improved carbon efficiency. A correct estimate of EROI for forestry biomass, as proposed in this work, is a necessary dimension in assessing the suitability of a project.

Abstract Flue Gas Condensers (FGC) are used to increase the thermal output of biomass boilers. This reduces the emissions per unit of produced energy but furthermore, fine dust particles will be collected in the condenser. These condensers therefore have a double effect on the specific particulate matter emissions. In addition to the mechanisms that cause particle capture such as thermophoresis and diffusiophoresis, other agglomeration or condensation growth mechanisms also influence the size of the emitted particles. Due to the combination of these mechanisms, the capture efficiency depends on particle size. A size range presenting a lower capture efficiency, called a penetration window, is generally observed. Measurements on a 5 MWth boiler showed that this penetration window is in size range 0.07–0.49 μm where the capture efficiency is reduced by around 20%. Measurements on an 18 kWth boiler showed that the penetration window is in the size range 0.04–0.49 μm and the capture efficiency can even be negative in this window. For the medium-scale boiler, the condenser reduces the overall particulate emissions by 64% in number and 62% in mass per m3, and 70% in number and 69% in mass per MJ. For the small-scale boiler, the condenser reduces the overall particulate emissions by 4% in number and 50% in mass per m3, and 14% in number and 55% in mass per MJ.

Abstract In this paper, a novel methodology is proposed for the online monitoring of the air-fuel ratio in large pulverised-fuel boilers at the burner level. Using standard measurements, this parameter can only be estimated, as the fuel distribution between burners is generally missing. The detailed air flow distribution to the burners can also be unknown depending on the available measurements. An accurate control of local and global air-fuel ratios is however crucial in terms of boiler efficiency and various pollutant emission reductions, leading to lower overall operational cost, improved performance and increased fuel and load flexibility. It is here proposed to combine two advanced techniques to quantify air and fuel flow rates per burner: microwave probes for fuel particles and smart soft sensors for air. When combined, those measurements allow for the calculation of the local air-fuel ratios. The proposed methodology was successfully applied to the boiler of a 660 MWe coal-fired power plant. While the burner equivalence ratios predicted by the standard equipments were in the range 0.9 - 1.05 , it was shown that the actual range was significantly broader ( 0.65 - 1.25 ). Looking at the averaged ratios per burner level, it was concluded that the expected values were globally overestimated compared to the measured values ( > + 14 % ). The performed air flow measurements were also used to partially tune the combustion process by solving hardware and software issues. Oxygen, flue gas flow rate, temperature and NO x imbalances at the outlet of the furnace were significantly reduced.

Energy systems design is challenged by uncertainties in energy carrier costs. This study explores hydrogen and conventional energy carrier costs, providing global insights with a focus on Belgium. Over two years, European natural gas prices surged 55-fold, while solid biomass prices varied only 1.8-fold over 13 years. Regression analysis (adjusted [Formula: see text]>0.9) reveals mutual correlations among energy carriers, allowing for cost ranking relative to the natural gas price. The relationship between electricity and natural gas prices underscores financial challenges for heat pumps in Belgium. Hydrogen cost estimations for 2024 are 43.7, 48.8, 16.4, and 17.5 €/GJH2,LHV for green, yellow (grid), grey and blue hydrogen, respectively. Achieving cost parity between blue and grey hydrogen requires a carbon tax of 67.5–123 €/tonCO2. Present approach incorporates uncertainties in energy carrier costs by varying natural gas price scenarios, facilitating prompt identification of cases for in-depth evaluation in future energy systems.

The decarbonisation of the building heating sector requires a shift from decentralised fossil fuel heating appliances to systems converting energy carriers with low greenhouse gas (GHG) emissions. However, for certain energy carriers, a considerable portion of GHG emissions arises upstream during production, processing and transportation, rather than during energy conversion. Accurately quantifying these indirect GHG emissions typically requires life cycle assessments, which are often resource-intensive and impractical during the early stages of energy system design. This study introduces operational GHG emissions as a pragmatic metric for the preliminary assessment of energy carrier environmental impact in building heating applications. These operational GHG emissions include both direct CO2 emissions and indirect CO2, CH4 and N2O emissions. Based on a comprehensive literature analysis, average estimates are proposed for the operational GHG emissions of various energy carriers within a European context, including natural gas, oil, coal and wood, as well as the average European and Belgian electricity grid, and hydrogen from various production methods. The findings underscore the significant contribution of indirect GHG emissions, as the selection of the energy carrier with the lowest environmental impact hinges on whether direct emissions alone or the broader operational GHG emissions are considered. By integrating operational GHG emissions into the early design stages of energy systems, stakeholders can make more informed decisions about which energy systems warrant further investigation, thereby facilitating more sustainable energy system development from the outset.

AbstractEstimates of the energy potential of the different energy sources are essential for modelling energy systems. However, the potential of biomass is debatable due to the numerous dimensions and assumptions embedded. It is thus important to investigate further the final potential to understand their implications. Therefore, this study analyses European studies assessing biomass potential and proposes a critical discussion on the different results to converge to a realistic range of potentials for 2030. Biomass is divided into four categories: forestry products, agricultural residues, energy crops and other waste, each with sub-categories. Belgium is used as a case study to highlight the convergences and divergences of the studies. Having a national case study allows for more precise analyses through in-depth comparisons with national data and reports. The potential estimates are compared with the current production for each category in order to have a better view of the gap to be bridged. From these national perspectives, the European potential can be better apprehended. The results show that the realistic potentials for 2030 for Belgium and Europe are somewhat in the lower range of the estimates of the different studies: from 30 to 41 TWh and from 2000 to 2500 TWh, respectively. The forestry biomass is already well exploited with a slight potential increase, while the agricultural residues present the most significant potential increase. The realistic potential for energy crops in Belgium turned out to be close to the minimum estimates. Indeed, the implications of those crops are considerable regarding the agricultural structure and logistics. This article emphasises that no energy potential is neutral, as it involves a specific system in terms of agriculture, forestry or waste management, with broader social, economic or environmental implications. Consequently, using one estimate rather than another is not a trivial matter; it has an impact on the system being modelled from the outset.