Incorporation of biomass fly ash and biological sludge in the soil: effects along the soil profile and in the leachate water

Purpose This work aimed to study the effect of the application of biomass fly ash in the soil profile and percolate water, which is a novel feature. The results produced by this work pose a useful contribute for by-products’ valorization for the pulp and paper industry, namely fly ash and sludge, diverting them from landfills and achieving significant savings. Materials and methods Soil profiles (0.60 m) were collected in the field and into laboratory-scale vessels. Four soil profiles were used in this work. One of the profiles was used as control. To each of the other three, 7.5 Mg ha−1 of biomass fly ash, fly ash combined with sludge (50:50%wt.), or a conventional liming agent (CaO) were added. A simulation of the daily natural watering of the soils has been made throughout 1 month, with collection of the daily percolating from the bottom of the vessels. After this period, soil profiles were divided into three equal-sized depth layers (0.20 m each). Soil pH, electrical conductivity, and available Ca, Mg, K, P, Na, Mn, Fe, Zn, and Cu contents were determined in the three layers for each of the four soil profiles used. A parallel experiment was conducted in which additional pots of soil were prepared with the same amendment. Ryegrass (Lolium perenne) was sown in order to evaluate the effect on biomass growth and possible phytotoxicity. Results and discussion Amendment with biomass fly ash elevated soil pH slightly, to values within the most adequate range for plant growth. Results showed small raises in the availability of the essential plant macronutrients Ca, K, and Mg, especially in the top layer of the soils, where the amendment materials were applied. The mobilization of cations to the groundwater was always minimal, which is promising since it means little contamination to the groundwater. Ash and ash + sludge amendments produced similar plant growth results when compared to the control. However, biomass grown in Cao-amended pots showed the higher root size. Conclusions Incorporation in the soil proved to be a viable way to manage fly ash and sludge from pulp and paper industry, which could mean considerable savings. The effect on soil fertilization was similar to the conventional liming agent. No obvious hazardous effect on the soil or groundwater was found.publishe

Controlo de emissões gasosas poluentes resultantes da conbustão de carvão em leito fluidizado

Doutoramento: em Ciências Aplicadas ao AmbienteA existência dum elevado conjunto de informação sobre combustão de carvão em leito fluidizado em reactores laboratoriais, exige a sua verificação em condições reais de combustão, nomeadamente em instalações à escala piloto e industrial. No entanto, este tipo de ensaios é escasso, não só pelo reduzido número de instalações existentes, mas também pela dificuldade em proceder a variações nas suas condições operatórias. Neste contexto, procedeu-se à construção duma instalação à escala piloto no Departamento de Ambiente e Ordenamento da Universidade de Aveiro, e cujas potencialidades se apresentam neste trabalho. A infra-estrutura experimental tem por base um reactor de leito fluidizado borbulhante à escala piloto, projectado para a realização de estudos de combustão envolvendo uma potência nominal de 20 kW térmicos, e um sistema automático de controlo e amostragem gasosa. A câmara de combustão apresenta 0.24 m de diâmetro interno e 2.2 m de altura útil, e inclui um leito com 0.35 m de altura, constituído essencialmente por areia (partículas na gama 500-710 µm) e uma pequena quantidade de cinzas e calcário calcinado e sulfatado, no caso de adição de calcário. O leito fluidizado piloto permite efectuar a combustão de carvão em estado estacionário sob diferentes condições de temperatura, excesso de ar, adição do ar por estágios e com adição de agentes de dessulfurização. Foi estudada a combustão dum carvão betuminoso e duma antracite no reactor piloto de leito fluidizado borbulhante, com e sem adição de calcário. Os ensaios foram realizados em estado estacionário utilizando 10, 25 e 50 % de excesso de ar, e temperaturas do leito na gama 750-900 ºC. O ar de combustão foi repartido em dois estágios e a três níveis, onde o ar primário representava 100, 80 e 60% do ar total. Foram medidas concentrações de O 2 , CO 2, CO, NO, N 2O, SO 2 e temperatura, no leito e ao longo do freeboard . A análise dos resultados experimentais para os dois tipos de carvão mostra que com o aumento da temperatura a emissão de NO aumenta e a de N 2 O diminui. O reforço do estagiamento reduz a emissão de NO e N 2O, mas afecta de forma adversa a emissão de CO. O aumento do excesso de ar resulta num aumento da eficiência de combustão, mas agrava a emissão de NO e N 2O. A adição de calcário reduz a emissão de N 2O, embora o efeito só se verifique na presença de condições oxidantes no primeiro estágio. Também para o NO o efeito da presença de calcário é condicionado pela estequiometria do primeiro estágio; para condições oxidantes a emissão de NO é superior na presença de calcário, enquanto que para condições redutoras poderá inclusivamente ser inferior à observada na ausência de calcário. A emissão de óxidos de azoto (NO, N 2O) durante a combustão do carvão betuminoso é superior à observada para a antracite. Porém, quando referida à unidade de massa de azoto alimentado no combustível, a emissão de óxidos de azoto é inferior para o carvão betuminoso. No que respeita ao SO2, a adição de calcário permite obter remoções na gama 25-90%, embora bastante dependentes das condições operatórias, em especial da temperatura e estequiometria do primeiro estágio. De entre os efeitos analisados, o mais significativo revelou ser o da repartição do ar de combustão; um aumento na repartição do ar reduz substancialmente a eficiência de captura do enxofre. Relativamente ao efeito da temperatura verificaram-se diferentes comportamentos. Na gama 750-825 ºC a tendência é para um aumento na remoção do SO2 com o aumento da temperatura, embora seja possível observar também o inverso, apesar de nestes casos os valores de remoção serem próximos. Na gama 825-900 ºC ocorre uma diminuição na captura do SO2 com o aumento da temperatura. Foi ainda desenvolvido um modelo de combustão em leito fluidizado, a partir duma versão do modelo de Rajan & Wen (1980), em que se analisaram vários aspectos relacionados com a combustão de carvão, embora só para combustão num estágio. Genericamente, as tendências previstas pelo modelo são qualitativamente coerentes com os resultados experimentais. Contudo, no caso do NO e contrariamente ao observado quer experimentalmente quer referido na literatura, as previsões do modelo apontam para um efeito do aumento da temperatura na emissão de NO oposto e muito mais marcado do que o que realmente ocorre. As simulações efectuadas permitem concluir que no leito o balanço das reacções de formação/destruição dos óxidos de azoto pela via heterogénea predomina sobre a via homogénea; no freeboard o processo é dominado pela via homogénea.The existence of an enormous quantity of information about combustion of coal in fluidized beds in laboratorial reactors, demands their verification during combustion in real conditions, respectively in pilot and industrial facilities. However, this kind of information is scarce, not only due to the low number of existing facilities, but also as a result of the difficulty in introducing variations in their operational conditions. In this context, a pilot scale facility was designed and built in the Department of Environment and Planing of the University of Aveiro, and its potentialities are presented here. The experimental installation consists of a pilot scale bubbling fluidized bed reactor projected for combustion tests involving a nominal power of 20 thermal kW, and an automatic command and control system for reactor operation and gas sampling. The furnace section has an internal diameter of 0.24 m and an overall height of 2.2 m, and includes a bed with about 0.35 m height, composed mostly of sand with particle diameter in the range 500-710 µm, with a small amount of coal ash, and calcinated and sulfated limestone, in the case of limestone addition. The functionality of the installation comprises the steady state combustion of coal with continuous addition of coal and additives, at different temperatures and excess air ratios, and also air staging, with and without addition of sulfur dioxide adsorbents. The combustion of two coals (bituminous and anthracite) was studied in the pilot scale fluidized bed operating in bubbling regime, with and without limestone addition. The experiments were conducted in steady state conditions using 10, 25 and 50% excess air levels, and bed temperatures in the range 750-900ºC. The combustion air was divided in two stages and at three levels, were the primary air was 100, 80 and 60% of the total air. The gas composition in terms of O 2, CO 2, CO, NO, N 2O, SO 2 and temperature, were measured in the bed and along the freeboard . The analyses of results for the two coals tested revealed that an increase in the temperature increases NO emission and decreases N 2O. The increase in the degree of air staging reduces the emission of both NO and N 2O, but adversely affects the emission of CO. The increase in excess air promotes an increase in the combustion efficiency, but adversely affects the NO and N 2O emission. Limestone addition reduces N 2O emission, although the effect is only verified in the presence of first stage oxidant conditions. Also for NO, the effect of limestone presence is conditioned by the first stage stoichiometry; first stage oxidant conditions gives higher NO emissions in the presence of limestone, while during first stage reducing conditions the NO emission can inclusively be lower than the one observed in the absence of limestone. The emission of nitrogen oxides (NO, N 2O) during bituminous coal combustion is higher when compared with the anthracite. However, when corrected for the nitrogen content in the fuel added to the reactor, the emission of nitrogen oxides tends to be lower in the case of bituminous coal combustion, in comparison with the anthracite. In relation to SO2, limestone addition leads to sulfur retention in the range 25- 90%, although very dependent on operational conditions, in special temperature and first stage stoichiometry. Among the analyzed effects, the most significant was the air staging; an increase in air staging substantially reduces sulfur capture efficiency. In relation to the temperature effect, different behaviors have been detected. In the range 750-825 ºC although a tendency for an increase in the SO2 retention with an increase in temperature is observed, the reverse it was also possible; however, in this case the retention values are very close. In the range 825-900 ºC a decrease in sulfur capture with an increase in the temperature was observed. A fluidized bed combustion model was also developed, based on the initial version of Rajan & Wen (1980) model, for which several aspects related with combustion of coal in fluidized beds were analyzed, although just for combustion with air addition in one stage. In general, the trends provided by the model are in qualitative agreement with the experimental results obtained. However, in the case of NO emission and in contradiction with the experimental observations and the results often referred in the literature, the predictions revealed an effect of the temperature increase opposed and much more pronounced than the one that really occurs. The simulations revealed that in the bed the balance between the nitrogen oxides formation/destruction mechanisms by heterogeneous path prevails over the homogeneous path; in the freeboard the process is governed by the homogeneous path

Simultaneous production of biochar and thermal energy using palm oil residual biomass as feedstock in an auto-thermal prototype reactor

In developing countries, the technology used for biomass carbonization requires major retrofits for an efficient conversion of the residual biomass produced in the palm oil mills into biochar. This study analyzes a prototype of a small and modular auger reactor (P-SMART) that uses untreated kernel shells as feedstock to produce biochar and thermal energy. The P-SMART does not require inert gases during operation, neither diesel nor natural gas for the initial heating process. This study shows that the carbonization process can be driven by the energy generated during pyrolysis gas combustion (auto-thermal conditions) from a biomass load capacity of 30 kg/h. During the auto-thermal operation, the thermal energy generated by pyrolysis gas combustion is higher than that required by the carbonization process. The carbon monoxide concentration in the flue gas during the auto-thermal operation was 197 mg/Nm3 which is lower than the European eco-design requirement of 500 mg/Nm3 (both measured at 11% vol. O2, dry gas). The biochars produced during auto-thermal operation have a macro-porous structure with a pore radius that ranges from 0.42 to 12.48 μm. The carbon content and the molar H/Corg and O/Corg ratio of the analyzed biochars are in accordance with the European guidelines for the sustainable production of biochar of less than 0.7 and 0.4 respectively. Moreover, relevant soil nutrients were observed in the KS ash, namely: silica (30 wt%), potassium (8.2 wt%) and phosphorous (3 wt%).publishe

Potential for Farmers’ Cooperatives to Convert Coffee Husks into Biochar and Promote the Bioeconomy in the North Ecuadorian Amazon

Improving the livelihoods of communities living in fragile ecosystems, such as tropical forests, is among the main strategies to promote their conservation and preserve wildlife. In the Ecuadorian Amazon, farmers’ cooperatives are recognized as an important mechanism to improve the socioeconomic conditions of local communities. This study analyzes the integration of pyrolysis processes to convert agricultural waste into biochar as a way to implement the bioeconomy in these organizations. We found that post-harvesting processes in the studied farmers’ cooperatives are similar, and coffee husks are a potential feedstock to produce biochar. Although the environmental policies in Ecuador consider the valorization of agricultural waste, we did not find any specific standard to regulate the operation of pyrolysis facilities. Nonetheless, conversion of agricultural waste into biochar can contribute to (i) replacement of subsidized fossil fuels used in drying processes, (ii) prevention of environmental pollution caused by accumulation of waste, (iii) emergence of new income sources linked with the provision of carbon sequestration services, and (iv) the long-term maintenance of soil fertility. Currently, demonstration projects are needed to stimulate collaboration among farmers’ cooperatives, academia, the government, international cooperation agencies, and existing forest conservation initiatives.Fundação para a Ciência e a TecnologiaBundesministerium für Bildung und ForschungPeer Reviewe

Life cycle assessment of wood pellets and wood split logs for residential heating

Wood-fuelled systems are commonly used all over the world for residential heating, and recently wood pellets have been replacing traditional firewood. This article presents an environmental life cycle assessment of five wood-based combustion systems for residential heating: i) a pellet stove using maritime pine pellets; a wood stove using ii) eucalyptus (Eucalyptus globulus Labill.) and iii) maritime pine (Pinus pinaster Ait.) split logs; and a fireplace using iv) eucalyptus and v) maritime pine split logs. The functional unit is 1 MJ of thermal energy for residential heating. System boundaries include four stages: (1) forest management; (2) pellet and wood split log production; (3) distribution; and (4) thermal energy generation. Environmental impacts were calculated for seven impact categories from the ReCiPe 2016 midpoint method, and a sensitivity analysis was performed using the Product Environmental Footprint (PEF) life cycle impact assessment method and modifying the distances travelled. Of the five heating systems analysed, the fireplace presents the worst performance for all the impact categories with the exception of freshwater eutrophication and marine eutrophication, when maritime pine split logs are burned in the fireplace. Comparing the pellet stove with the wood stove, neither system is better for all the impact categories analysed. Regarding sensitivity analysis, the use of an alternative characterisation method leads to similar trends in the results in comparison with those obtained from the ReCiPe method, while changes in transport distances do not affect the total impacts to a large extent.publishe

Solid catalysts obtained from wastes for FAME production using mixtures of refined palm oil and waste cooking oils

More than 95% of biodiesel production feedstocks come from edible oils, however it may cause some problems such as the competition of land use between food production and biodiesel production. The waste cooking oils (WCO) are an alternative feedstock for biodiesel production; its usage reduces significantly the cost of biodiesel production and has environmental benefits, e.g., a waste recovery instead of its elimination. This work aims to produce a low-cost efficient solid catalyst for fatty acid methyl esters (FAME) production using mixtures of refined palm oil (RPO) and WCO. Four low cost catalysts were prepared (biomass fly ashes, natural dolomite rock, chicken eggshells and polyethylene terephthalate - PET), characterized (by SEM, EDX, XRD, BET, FT-IR and Hammett indicators) and tested regarding their performance in FAME production. The maximum yield of FAME achieved was around 96%wt. for biomass fly ashes catalyst at 60 °C, 9:1 (mol/mol) of methanol to oil mixture, 10%wt. catalyst to oil mixture, over 180 min in batch reactor. The results point out for promising bifunctional catalysts able to achieve also conversion of free fatty acids up to 100% using mixtures of RPO and WCO.publishe

Optimization of FAME production from blends of waste cooking oil and refined palm oil using biomass fly ash as a catalyst

One of the problems associated with biomass combustion is the amount of fly ashes generated and its subsequent management. The search for ways of valorizing these ashes has been a challenge for the academic and industrial community. On the other hand, used cooking oils are wastes which management is quite difficult, by they have a very important energetic potential. The goal of this work was to optimize the Fatty Acid Methyl Esters (FAME) process, recovering two residual materials (waste cooking oils (WCO), and biomass fly flash (BFA)). The optimization of the process was achieved using the response surface methodology and a Box-Benhken experimental design applied to mixtures of WCO and refined palm oil (RPO), using BFA as catalyst. The influence on FAME yield of four variables (catalyst loading, methanol/oil molar ratio, RPO/WCO ratio and reaction temperature) was studied. The higher FAME yield achieved was 73.8% for the following operating conditions: 13.57 wt% of catalyst loading, 6.7 of methanol/oil molar ratio, 28.04 wt% of RPO in the oil mixture with WCO and 55 °C for the reaction temperature. The reusability of the BFA catalyst in the process was also studied through three successive usage cycles finding no loss of catalytic activity.publishe

Assessing a bio-energy system with carbon capture and storage (BECCS) through dynamic life cycle assessment and land-water-energy nexus

Nowadays, much attention is being paid to so-called Negative Emissions Technologies (NETs), designed to remove carbon dioxide from the atmosphere and keep global temperature rise below 1.5 °C. The deployment of NETs can trigger environmental impacts, which can be addressed through the lens of Life Cycle Assessment (LCA). According to the literature, there are several drawbacks when NETs are assessed under the life cycle framework. In this sense, this study aims at contributing to the literature by assessing a NET in a manner that the existing drawbacks are overcome. For such purpose, dynamic LCA and land-water-energy nexus were applied to a Bioenergy with Carbon Capture and Storage system (BECCS). The results show that harnessing residual forest biomass for electricity generation and carbon storage accomplished a great positive climate performance. In line with European climate goals, climate change impact resulted in −2.49E+04 kg CO2eq/MWhe and −3.40E+04 kg CO2eq/t Cstored at year 20. However, the BECCS system analyzed comes at the expense of impacting land, water and energy that cannot be overlooked. The land impact was 3.57E+05Pt/t Cstored and 2.61 E+05Pt/MWhe, green water impact was 11.1 m3/t Cstored and 8.16 m3/MWhe, and the Energy Return on Energy Investment (EROI) was 3.34. The sensitive analysis indicates that special attention should be paid to the efficiency of the system since it directly impacts on land, water and energy (EROI). Finally, this study contributes to increasing the knowledge on NETs, thus supporting climate-energy policymaking

Characteristics of ash and particle emissions during bubbling fluidised bed combustion of three types of residual forest biomass

Combustion of residual forest biomass (RFB) derived from eucalypt (Eucalyptus globulus), pine (Pinus pinaster) and golden wattle (Acacia longifolia) was evaluated in a pilot-scale bubbling fluidised bed reactor (BFBR). During the combustion experiments, monitoring of temperature, pressure and exhaust gas composition has been made. Ash samples were collected at several locations along the furnace and flue gas treatment devices (cyclone and bag filter) after each combustion experiment and were analysed for their unburnt carbon content and chemical composition. Total suspended particles (TSP) in the combustion flue gas were evaluated at the inlet and outlet of cyclone and baghouse filter and further analysed for organic and elemental carbon, carbonates and 57 chemical elements. High particulate matter collection efficiencies in the range of 94-99% were observed for the baghouse, while removal rates of only 1.4-17% were registered for the cyclone. Due to the sand bed, Si was the major element in bottom ashes. Fly ashes, in particular those from eucalypt combustion, were especially rich in CaO, followed by relevant amounts of SiO2, MgO and K2O. Ash characteristics varied among experiments, showing that their inorganic composition strongly depends on both the biomass composition and combustion conditions. Inorganic constituents accounted for TSP mass fractions up to 40 wt%. Elemental carbon, organic matter and carbonates contributed to TSP mass fractions in the ranges 0.58-44%, 0.79-78% and 0.01-1.7%, respectively.publishe