Feedstock Moisture Content Research Articles

Development, process optimization and assessment of sustainable mobile biochar kiln for agricultural use

A novel and energy-efficient biochar kiln that can be operated in the field with few requirements has been developed. The generated syngas are recirculated into the combustion chamber to heat biomass. This study optimized the feedstock parameters, biochar yield, and economics of producing biochar from soybean straw using the Response Surface Methodology (RSM) based on Central Composite Design (CCD). The biochar kilns had an energy conversion efficiency of 47.02% and an overall kiln efficiency of 41.03% at steady-state operation over 500 °C. It produced an average of 29.43 ± 1.42% biochar with a minimal fuel-to-biochar ratio of 0.19 ± 0.02 and a payback period of 4.02 months. The statistical analysis confirmed that the characteristics of the feedstock affect the biochar output and economic aspects of the biochar production process. Based on the optimization studies, it was concluded that the feedstock's moisture content should be 8% and particle size should be 15 mm for higher biochar yield with maximum energy efficiency and benefit-cost ratio. Biochar produced at optimal conditions obtained from the optimization process was also characterized. Physical-chemical analysis reveals that biochar has a higher carbon content (79.38 ± 1.04 %) and a lower atomic ratio of H/C (0.696), O/C (0.14), and (N + O)/C (0.08), indicating higher carbon stability and aromaticity. The TGA analysis demonstrated the high thermal stability of biochar by showing a lower (2.15%) mass loss between the 343.8 and 407.1 °C temperature range. The SEM and TEM micrographs showed the microporous structure of the soybean straw biochar with a worm-like pattern and a cylindrical shape.

Biosolid Gasification Performance Prediction Using a Stoichiometric Thermodynamic Model.

The gasification process can recover energy from biosolids produced in wastewater treatment. This paper developed a stoichiometric thermodynamic equilibrium model for biosolid gasification based on the biosolid properties, thermodynamic database, and equilibrium constants. If the calculation result showed that the quantity of char was negative, the quantity of char was put to zero, and the simulation was carried out again. The model was first verified by woody gasification under isothermal conditions, and the influence of a given temperature on biosolid gasification was simulated. The model further investigated the effects of different feedstock types, moisture contents, equivalence ratios, and reaction extensions on the adiabatic temperature, exergy efficiency, and syngas properties under autothermal conditions. The four factors were all the main factors for adiabatic temperature. The exergy efficiency depended more on the operation conditions than on the feedstock type. The H2 concentration of the dry syngas in biosolid gasification exhibited a curve both against the given temperature under isothermal conditions and against the moisture content under autothermal conditions.

Innovative Technology for Managing Biofuel Production from Timber Industry Waste

The relevance of this study is determined by the growing worldwide interest in renewable energy sources against the backdrop of depleting fossil fuel reserves. This study aims to develop an innovative technology for managing biofuel production from wood waste, including a set of interrelated economic and mathematical models focused on maximizing the fuel and energy efficiency of biofuels depending on the location of waste generation, feedstock moisture content, and distance to the biofuel production site. This technology should also combine the main directions of international research in the field of environmental responsibility of countries in terms of carbon dioxide (CO2) emissions and the Paris Climate Agreement. The methodological basis of the research comprises the authors’ innovative technology based on a set of interconnected economic and mathematical models and managerial decision-making systems, methods for nonlinear programming, system analysis, an information approach to the analysis of systems, accepted technological processes, norms, and standards established in the international practice of the timber industry. This innovative technology was implemented in practice using the capabilities of the MathCad and MS Excel software products. The article determines the optimal operating parameters of timber industry enterprises at which the specific thermal energy of the produced biofuel exceeds by at least 15% the thermal energy spent on processing this biofuel as an energy carrier. Wood waste biofuel production is profitable if the distance for feedstock transportation to the production site does not exceed 80 km and the relative humidity of the raw materials does not exceed 60%. Doi: 10.28991/ESJ-2024-08-03-03 Full Text: PDF

Techno-economic and environmental analyses of the pyrolysis of food waste to produce bio-products

Food waste has become a source of concern as it is generated abundantly worldwide and needs to be valorised into new products. In this study, cucumber, tomato, and carrot wastes were investigated as pyrolysis feedstocks as a single component (cucumber), a binary component mixture (cucumber and tomato), and a ternary component blend (cucumber, tomato, and carrot). Fourteen scenarios were simulated and evaluated based on varying the feedstock blend (single, binary, and tertiary), temperature (300 and 500 °C), and feedstock moisture content (5, 20, and 40%). Using an established empirical model, the effect of these parameters on product yields, techno-economic implications, energy requirements, and life cycle analysis (LCA) outcomes were investigated. The best performers of each scenario were determined, and their strengths and weaknesses were identified and compared with other scenarios. In terms of product yields, all three systems (single, binary, and tertiary) followed a similar pattern: bio-oil yields increased as temperature and feedstock moisture content increased, while biochar yields decreased as temperature and feedstock moisture content increased. The production of syngas, on the other hand, was only observed at elevated temperatures. The total energy requirement exhibited an increase with increasing temperature and feedstock moisture content. The economic evaluation revealed that the return on investment (ROI) value for the single component at 5% moisture content at 300 °C is 29%, with a payback period (PB) of only 3.4 years, which is potentially very appealing. The water footprint increased with increasing pyrolysis temperature but decreased with increasing moisture content in all scenarios. The land footprint is observed to remain constant despite changes in process conditions. The study's findings contribute to the pyrolysis process's scalability, technological advancement, and commercialisation.

Experimental study on thermal modification characteristics of entrained-flow gasified fine ash using circulating fluidized bed

Gasified fine ash (GFA) exhibits poor reactivity due to its low carbon content and high ash content, which restricts its potential for combustion utilization. To enhance the reactivity of GFA, we employed a circulating fluidized bed (CFB) as a thermal modification unit (TMU) to thermally modify GFA from different entrained-flow gasifiers. We also experimentally investigated the impact of equivalence ratio, temperature, and feedstock moisture content on the thermal modification of GFA. After thermal modification of GFA, the pore structure of modified fine ash (MFA) was significantly improved, the proportion of active sites in residual carbon increased, and the proportion of graphitized structures decreased. An appropriate increment in the equivalence ratio increased the number of carbon active sites in MFA. A good thermal modification effect was found on the GFA produced by different types of gasification furnaces. The temperature rise promoted gasification reaction in the TMU and restricted carbon conversion, thus decreasing the consumption of combustible residual carbon. An increase of water content in the GFA improved the pore structure, but excessive water caused adverse effects.

Development of a Combined Milling and Sifting Machine for use in Pupuru (Cassava flour) Processing Plant

The concern of the entire nation over the need to ensure food security is continually becoming more apparent every day. Hence, this has led researchers, industrialists, investors and government agencies to begin aggressively develop series of devices to reduce the level of drudgery associated with processing, and formulation of varieties of food items to enhance food productivity and quality. Pupuru, a derivative of cassava, is one of the foodstuffs whose global demand is on the increase but its production is at low pace as a result of the crude techniques and implement utilize in its post-processing. Post-processing of cassava into pupuru involves series of stages, ranging from peeling to packaging. Combination of two or more of these processing stages is one of the potential measures of enhancing the productivity of the product, and financial benefits of the stakeholders. This study focused on the development and performance evaluation of a combined milling-sifting machine for use in 5.0 kg/batch Pupuru processing plant. the machine comprises a gear reduction motor, milling chamber, vibrating tray and sets of extension spring connected in parallel for magnifying the vibration produced during operation. The results of the performance revealed that the throughput capacity and sifting efficiency of the machine range between 69.30 – 82.92 kg/h and 86.30 – 95.30 % when used to process feedstock with moisture content in the range of 5 – 6 %. It was observed that the performance of the machine improves with reduction in the feedstock moisture content. It was concluded that the incorporation of the machine into pupuru processing line would enhance the yield and quality to meet the ever-increasing global demand for cassava flour

Comprehensive experimental study of microbial respiration during self-heating in biomass storage piles

As a critical renewable energy source, biomass has substantial potential for reducing carbon emissions and promoting sustainable development. However, its long-term storage in large volumes for modern bioenergy poses challenges due to inherent self-heating driven by exothermic microbial, physical and chemical processes, which can lead to spontaneous ignition and severe fire incidents. While physical and chemical aspects of self-heating in biomass piles greatly benefit from extensive research and experience borrowed from coal pile self-heating, microbial activities in biomass self-heating have received less attention. To address this knowledge gap, we conduct a series of comprehensive studies to gain a deeper understanding of microbial activities in biomass self-heating, aiming to develop a numerical model for reliably predicting biomass self-heating and minimizing fire risks in stored biomass. This paper presents the results of our experimental investigation into microbial respiration during biomass storage. Six commonly used biomass feedstocks with varying initial moisture content are subjected to different storage conditions over a seven-day testing period, during which the main metabolic byproduct (CO2) released from microbial degradation of the biomass is continuously measured. Our findings reveal that an increase in feedstock moisture content significantly enhances microbial activity when the initial moisture content is below 136 %. However, further increases in initial moisture content do not notably enhance, and in some cases, may even weaken microbial activity. Additionally, a temperature range of 25 °C to 45 °C is identified as conducive to rapid microbial decomposition for different biomass materials, and deviation from this range results in a significant reduction in microbial activity. Furthermore, under identical temperature and initial moisture content conditions, the order of carbon dioxide evolution rate is as follows: corn stalk > soybean hull > rice straw > wheat straw > cotton stalk > pepper stalk. Our respiration intensity test results also create a fundamental experimental database for model development and validation, and contribute to the broader understanding of biomass storage and its associated challenges.

Innovative downdraft gasifier design utilizing exhaust gas as gasification agent for sustainable syngas production

This study introduces an innovative downdraft gasifier design that harnesses exhaust gas as the gasification agent, showcasing successful operation and extensive experimental investigations using various biomass feedstocks, notably wood pellets of different sizes (<20 mm to 20–50 mm). The gasification system exhibited the ability to produce clean syngas suitable for both heating and electricity generation. Experimental assessments encompassed a temperature range of (620 to 1250 ℃) and an equivalence ratio range of 0.2 to 0.5. The resulting syngas composition featured key constituents such as H2, CO, CO2, and CH4, consistent with conventional gasification processes. The incorporation of exhaust gas as the gasification agent represents a pioneering advancement. This innovative approach not only minimizes energy input but also reduces greenhouse gas emissions, rendering the system more environmentally sustainable. The flow rate of the primary gasification agent was measured at 440 m3/h, and the producer gas’s exit temperature (300–650 ℃) was analyzed based on the moisture content of the biomass feedstock. The temperature within the reaction zone varied depending on the equivalence ratio (ER) for exhaust gas (700–974 ℃) and for air (ranging from 620–850 ℃). Additionally, the temperature was influenced by the moisture content, with ranges of (830–1050 ℃) for exhaust gas and 850–1050 ℃ for air. The syngas produced consisted mainly of carbon monoxide (14.4%–19.2%), hydrogen (16%–20%), carbon dioxide (7.1%–11.2%), and a small amount of methane (2%–3%). This innovative downdraft gasifier design holds substantial promise as a renewable energy system, particularly due to its utilization of low-cost materials and reduced environmental footprint. Such advancements pave the way for the widespread adoption of downdraft gasifiers, making them an attractive technology for thermal and power applications, especially in developing nations.

Technoeconomic Analysis of a Small-Scale Downdraft Gasification-Based Cogeneration Power Plant Using Green Wastes

Abstract In this work, the technoeconomic assessment of a small-scale gasification-based cogeneration plant (25–50 kWe) fed with green wastes (fallen leaves, spent coffee grounds, and paperboard) is presented. The cogeneration power plant is modeled using Thermoflex software under thermochemical equilibrium and steady-state assumptions. Subsequently, the performance of the cogeneration plant is numerically analyzed as a function of the feedstock moisture content (6–30%), air–waste equivalence ratio (0.20–0.55), and the system load (6.25–25 kWe). The results show that the best energy performance of the cogeneration plant is achieved with a feedstock moisture of 6.05%, an equivalence ratio of 0.358, and a load of 25 kWe. At this best performance mode, the electric generation and cogeneration efficiencies are 19.33% and 49.71%, respectively, with a specific biomass consumption of 1.19 kg/kWh. Two scenarios are established for the economic assessment. The baseline scenario considers a 25-kWe cogeneration plant, while, in the second one, the generation capacity of the system was assumed to be doubled (50 kWe). The financial results show that the power generation has an energy levelized cost of 11.7 ¢$/kWh and 8.4 ¢$/kWh for 25 kWe and 50 kWe, respectively. Nevertheless, none of the proposed scenarios were found to be economically feasible based on the negative net present value obtained. Therefore, further energy laws and regulations are required seeking to support the small-scale auto-generation units based on biomass gasification.

Development and prototype testing of a novel small-scale pyrolysis system for the treatment of sanitary sludge

An innovative twin auger pyrolysis reactor for the intermediate conversion of partially wet sanitary faecal sludge generated on train toilets (mobile applications) is designed and successfully commissioned. The effects of operating temperature, feedstock feeding rates and moisture content and their interaction on the distribution and properties of product biofuels with the use of no carrier gas were assessed. Approximate yields of 50 %, 40 % and 10 % were observed for the biooil, syngas and biochar respectively at 500 °C. Meanwhile, the highest calorific value (HHV) of the syngas did not exceed 10 MJ/Nm3. Acidic compounds (10 % RPA) and nitrogen-containing hydrocarbons (18 % RPA) substituted the abundant species in biooil fraction at 500 °C with the lowest feed volumes of feedstock. Biochar presented the highest fixed carbon (58 %) and ash content (37 %) upon higher operating temperatures for the minimum and maximum volumes of feedstock. Interestingly, the retention of inorganics within the structure of char were observed. Meanwhile, the calorific value of the biochar reduced due to intensive reduction reactions at higher temperatures ranging to a minimum of 19 MJ/kg. Effects of reactor design and configuration on the pyrolytic products are discussed accordingly and further implications are provided. Overall, extensive further research for the end-use of pyrolytic products and the investigation of emissions, upon energy recovery or land-application of by-products are suggested.

Assessment of the greenhouse gas emission footprint of a biorefinery over its life cycle

Expanding the product portfolio of a biorefinery has the potential to improve the economics of the biorefinery as it not only increases revenue but also improves valuable feedstock use. Such process improvement, however, results in added complexity, energy consumption, and emissions. This study evaluated the energy consumption and greenhouse gas (GHG) emissions of an integrated multi-product biorefinery from a life cycle perspective. Six pathways were assessed in which the by-products of fast pyrolysis – biochar and non-condensable gases (NCGs) – were upgraded to produce ethanol and hydrogen, in addition to bio-oil. The six pathways include six corresponding biorefinery configurations. The configurations differ by NCG application and the kind of fuel used to supplement process heat demand. The GHG emissions intensity of the assessed pathways is between 13.54 and 43.13 gCO2eq/MJ. Our assessment shows a higher GHG emissions intensity in the assessed pathways than the base pathway, in which only bio-oil is produced. Generally, the emission intensities of biorefinery products are lower than when these products are produced from fossil sources but higher than when produced from dedicated bioenergy technologies. Also, when the products are put into an end-use application, like power generation, bio-oil shows lower life cycle GHG emissions compared to conventional fossil-based power plants. When the transportation of the products to the power plant is considered, the life cycle GHG emissions of hydrogen are higher than from the conventional generation methods. Sensitivity analyses show that reducing the feedstock moisture content and increasing ethanol titer can provide significant emission reduction potential. Outside the boundaries of the biorefineries, feedstock transportation also has an impact on the overall emissions.

EFFECT OF SELECTED PYROLYSIS PARAMETERS ON THE PRODUCTION AND QUALITY OF BIOCHAR AND PYROLIGNEOUS ACID FROM BIOMASS

Pyrolysis is an efficient process by which biomass can be utilized to produce biochar and pyroligneous acid which can be used as source of energy for cooking and bio-pesticides, respectively. Current study determined the effect of feedstock moisture content (FMC) (10%, 15% and 20%), pyrolysis residence time (PRT) (90 minutes, 135 minutes, and 180 minutes) and chimney inclination angle (CIA) (30o, 45o and 60o) on the production and quality of biochar and pyroligneous acid (PA). An experimental pyrolysis system was designed, developed, and used. The biochar quality was based on pH, moisture content (MC), volatile matter (VM), ash content (AC) and fixed carbon (FC) while PA was classified using pH and density. The highest production obtained for biochar was 43.66% at FMC = 10%, PRT = 90 min and CIA = 30o and the lowest was 38.74% at FMC = 20% and PRT = 180 min and CIA = 45o while for PA the highest was 31.11% at FMC = 15%, PRT = 90 min and CIA = 30o and the lowest was 25.21% at FMC = 10%, PRT = 180 min and CIA = 60o. The best quality biochar obtained had a pH = 9.10 (FMC = 10%, PRT = 180 min, CIA = 30o), MC = 4.10% (FMC = 10%, PRT = 180 min, CIA = 45o), VM = 21.00% (FMC = 10%, PRT = 180 min, CIA = 30o), AC = 3.60% (FMC = 10%, PRT = 90 min, CIA = 30o) and FC = 70.60% (FMC = 10%, PRT = 180 min, CIA = 30o) while the PA had ρ = 1.05 gcm-3 (FMC = 10%, PRT = 180 min, CIA = 45o) and pH = 2.78 (FMC = 10%, PRT = 180 min, CIA = 30o). The selected pyrolysis parameters except CIA had a significant influence on the biochar production and quality and on the other hand, all the parameters affected the PA production but only PRT had a significant influence on its quality.

Influence of moisture content on recovery and durability of dairy manure compost pellets

This paper presents model relationships between pre-pelleting moisture content (MC) of composted dairy manure and both pellet durability (PD) and pellets recovery (PR). Pellets were produced with two dies (6-mm and 8-mm) at MC ranging from 10 to 35% (wet basis). Results showed strong correlations between PR and PD at MC between 10 and 35% (r = 0.87 for the 8-mm die, and r = 0.98 for the 6-mm die). Regression equations also revealed PD and PR were strongly dependent on feedstock MC (r2 = 0.96 and 0.96 for 6-mm die, and 0.94 and 0.95 for 8-mm die, respectively). Equations showing PD as functions of both PR and MC were also developed and verified. The percent of pellets recovered, therefore, may be used to predict the durability of the pellets at a given MC. The models have significant potential of reducing time and cost of producing pellets from dairy manure-composts.

OPTIMIZATION OF PYROLYSIS PARAMETERS IN PRODUCTION OF PYROLIGNEOUS ACID FROM ACACIA TWIGS

Biomass material is a renewable energy source that is readily available and being produced in large quantities as most of it goes to waste. These materials can be recovered through pyrolysis process in order to produce usable products like biochar and pyroligneous acid. These products can be used as bio-fertilizer and bio-pesticides. The aim of this research was to optimize the pyrolysis parameters in the production of pyroligneous acid from acacia twigs. The parameters varied were feedstock moisture content (10%, 15% and 20%), Pyrolysis residence time (90 minutes, 135 minutes and 180 minutes) and chimney inclination angle (30o, 45o and 60o). Smoke condensation system also known as heat exchanger was used for condensing the pyrolysis smoke in to pyroligneous acid. Response Surface Methodology technique by using Box-Behnken Design was used to develop a mathematical equation to predict the yield of the pyroligneous acid with respect to varied parameters which was later optimized to determine the optimal conditions for pyroligneous acid yield.

Biochar production and quality optimization using response surface methodology technique

The dependency on fossil fuels can be reduced by the use of renewable energy sources like biomass and it can make a remarkable contribution to the reduction of CO2 emissions and as a result reducing the carbon footprint hence eliminating the greenhouse gas effect. Biomass materials that go to waste can be recovered through the pyrolysis process in order to produce biochar which can be used as a source of energy for cooking. The aim of this study was to carry out optimization of biochar production and quality using the Response Surface Methodology technique. The parameters varied were feedstock moisture content (FMC) (10%, 15% and 20%), pyrolysis residence time (PRT) (in minutes) 90, 135 and 180 and chimney inclination angle (CIA) (30o, 45o and 60o). An experimental insulated metallic carbonization kiln (1 m high and 0.5 m diameter) was developed and used. Response Surface Methodology technique by using Box-Behnken Design was used to develop a mathematical equation to predict the production and quality of the biochar with respect to varied parameters which was later optimized to determine the optimal conditions for biochar production and quality. The biochar quality was based on its moisture content (MC), volatile matter (VM), ash content (AC), fixed carbon (FC) and pH. The combined optimal conditions were 10% feedstock moisture content, 126.93 min pyrolysis residence time and 30o chimney inclination angle resulting to production of 44.35%, MC = 3.82%, VM = 23.52%, AC = 2.94%, FC = 67.89% and pH = 9.28. The mathematical equation developed had composite desirability (CD) of 0.9490 at a p-value≤0.05 which made it viable. These research findings are of importance since optimization reduces the wastage of resources resulting into increase in the efficiency of the pyrolysis system. Keywords: Renewable Energy, Pyrolysis, Biochar, Optimization, Response Surface Methodology

Thermo-economic analysis of syngas production from wet digested sewage sludge by gasification process

Digested sewage sludge (digestate) which is a by-product during treatment of municipal wastewater can be regarded as a reliable biological resource for production of bioenergy as a form of renewable energy. In this study, clean syngas production by gasification process of wet digestate is modeled and analyzed for the effluent of anaerobic digesters at Tehran South Wastewater Treatment Plant. The issues of allowable amounts of inlet feedstock moisture content into different gasifying systems and the criteria for selecting a proper type of gasifier are few in the available literature. Thus, thermal gasification technology (dual fluidized-bed (DFB) steam gasifier coupled with a dryer) and emerging supercritical water (SCW) gasification technology are modeled and investigated here. Results show that the hydrogen mole fraction in the syngas produced by dryer-DFB gasifier is about 0.55 which is almost 11% higher than that for SCW gasifier. However, the SCW gasifier has about 8% higher overall system efficiency (22.6%). Economic assessment shows that SCW gasifier has 19% lower levelized cost of clean syngas production (82.5 $/GJ) than dryer-DFB gasifier (102 $/GJ). Therefore, the SCW gasifier is generally preferred based on thermo-economic analysis of clean syngas production from very wet (75%) digestate.

Gasification characteristics of a simulated waste under separate and mixed atmospheres of steam and CO2

Downdraft gasifier is attractive for small-scale solid waste treatment, but the gasification characteristics are worthy of deep research. In this study, a two-stage continuous feeding apparatus was developed to examine the effect of moisture content of the mixed feedstock on co-gasification. Furthermore, considering the effect of CO2 from flue gas, the gasification experiments were carried out when CO2 participated in the gasification alone or in a mixed atmosphere of CO2 and steam. The pyrolysis residue plays an essential role in the gasification with steam, which can improve the syngas yield, especially the H2 yield reaches 0.345 m3/kg when steam and feedstock mass ratio (S/F) is 0.8. CO2 is inferior to steam in promoting H2 formation. But when CO2 and feedstock mass ratio (C/F) rises from 0.74 to 1.48, the gas yield increases from 60.52% to 77.15%, and the yields of tar and residue cut down correspondingly. CO2 is still an alternative gasifying agent, which can partially substitute steam in the gasification process. However, when CO2 coexists with a small amount of steam (S/F = 0.4), introducing excessive CO2 (C/F = 1.48) will intensify the competition between steam and CO2.

Physio-chemical properties of pellets using different feedstocks

This study was assumed to analysed the physico-chemical characteristics of seven dissimilar combination of biomass pellets was studied for their storage and combustion properties. The seven different proportion of soybean straw and cotton stalk feedstock T1 (80:20), T2 (70:30), T3 (60:40), T4 (50:50), T5 (40:60), T6 (30:70), T7 (20:80) were used during the experiment. the moisture content of feedstock was found ranges from 7.16 to 9.26 %. The volatile matter of feedstocks was recorded to be 69.48 to 72. 06 % and ash content was noted 8.23 to 13.46 %. The fixed carbon was recorded during the experiment 6.19 to 13.34 %. The maximum bulk density was observed 634 kg/m3 in combination of T3 (60:40). The highest and least mean for the heating value of the pellets produced different combinations ranged from 3997 to 4126 kcal/kg. It is concluded that the combination of T3 (60:40) produces better biomass pellets.

Exergy Analysis of Alternative Configurations of Biomass-Based Light Olefin Production System with a Combined-Cycle Scheme via Methanol Intermediate

Thermodynamic performance of three conceptual systems for biomass-derived olefin production with electricity cogeneration was studied and compared via exergy analysis at the levels of system, subsystem and operation unit. The base case was composed of the subsystems of gasification, raw fuel gas adjustment, methanol/light olefin synthesis and steam & power generation, etc. The power case and fuel case were designed as the combustion of a fraction of gasification gas to increase power generation and the recycle of a fraction of synthesis tail gas to increase olefin production, respectively. It was found that the subsystems of gasification and steam & power generation contribute ca. 80% of overall exergy destruction for each case, of which gasifier and combustor are the main exergy destruction sources, due to the corresponding chemical exergy degrading of biomass and fuel gas. The low efficiency of 33.1% for the power case could be attributed to the significant irreversibility of the combustor, economizer, and condenser in the combined-cycle subsystem. The effect of the tail gas recycle ratio, moisture content of feedstock, and biomass type was also investigated to enhance system exergy performance, which could be achieved by high recycle ratio, using dry biomass and the feedstock with high carbon content. High system efficiency of 38.9% was obtained when oil palm shell was used, which was 31.7% for rice husk due to its low carbon content.

Modelling and experimental investigation of small-scale gasification CHP units for enhancing the use of local biowaste.

Small-scale gasification Combined Heat and Power systems, fed by biowaste resources, have the potential to enhance local renewable energy production, reduce carbon emissions and address the challenges of waste disposal. However, there is a lack of understanding on the influence of challenging feedstocks, such as, for example, digestate, poultry litter and municipal solid waste, on the syngas quality and the incidence of the drying stage in the overall process. This paper addresses this gap by analysing and comparing 40 samples of the most common biowaste feedstocks. We developed a stoichiometric-thermodynamic one stage equilibrium model that was experimentally validated and calibrated by laboratory results, with a maximum error of 15% between real and predicted values. Simulation results show that the low heating value of the syngas produced from biowaste resources analysed ranges from 3.1 to 5.4MJ/Nm3 on a dry basis. Working at the optimal equivalence ratio increases the electricity and thermal output by up to 20%. To achieve a feedstock moisture content of 10%, the drying process may require up to 60% of the heat produced. Furthermore, results show that downdraft gasification based combined heat and power, is a feasible and interesting option to deal with biowaste resources which can potentially avoid the cost, risk and externalities of landfilling while it contributes to the increase of local electricity and heat production from renewable energy sources, both for grid and off-grid applications.