The ever-increasing volumes of food waste generated and the associated environmental issues require the development of new processing methods for these difficult waste streams. One of the technologies that can treat these waste streams directly is hydrothermal carbonization. In this work, olive pomace and orange peels were treated via a mild hydrothermal carbonization process (TORWASH®) in a continuous-flow pilot plant. For olive pomace, a solid yield of 46 wt% and a dry matter content of 58% for the solid press cakes were obtained during continuous operation for 18 days. For orange peels, the values were lower with 31 wt% solid yield and a 42% dry matter content during 28 days of continuous operation. These values corresponded fully with initial laboratory-scale batch experiments, showing the successful transformation from batch to continuous processing. The obtained hydrochar from both feedstocks showed an increase in higher heating value (HHV) and a significant reduction in ash content. Pellets produced from the solids met the requirements for industrial use, demonstrating a large increase in the deformation temperature and a significant reduction in the potassium and chlorine content compared to the original feedstock. These results indicate the excellent potential of these pellets for combustion applications.

Sludges from the papermaking industry represent a challenging residue stream that is difficult to dewater using conventional processes. The successful development and scale-up of innovative processes from lab- to pilot- to industrial-scale are required to tackle challenges for waste treatment, including paper sludges. Biological paper sludge was treated via a mild hydrothermal carbonization process (TORWASH®) to improve dewaterability of the sludge, including long-duration, continuous testing. Initial lab-scale experiments indicated the optimal treatment temperature for sludge dewatering was 190 °C. Dewaterability improved with increasing temperature, but the obtained solid yield decreased. Scaling-up to a continuous flow pilot plant required a temperature of 200 °C to achieve optimum dewatering. Pilot-scale hydrothermal treatment and dewatering resulted in solid cakes with an average dry matter content of 38% and a solid yield of 39%. This study demonstrates the benefits of hydrothermal carbonization for the dewatering of biological paper sludge without the use of dewatering aids such as fiber sludge or polyelectrolytes. The results also demonstrate the successful adaptation of a lab-scale batch process to a pilot-scale continuous flow process for hydrothermal carbonization of industrial wastewater sludge.

To demonstrate the benefits of upgrading biomass, six samples of unique materials were combusted under pulverized fuel conditions aiming at the demonstration of complete coal replacement. These fuels were: sugarcane bagasse (SCB) (raw and steam exploded); sugarcane trash (SCT) (steam exploded and washed + steam exploded); empty fruit bunch (steam exploded and washed + steam exploded). The study shows that volatiles dominate the NOX formation, thus with a proper air staging all upgraded biofuels can be used to reduce directly NOX formation, when replacing coal. Washing reduces slagging issues by removing most of K, however, in the case of the sugarcane based biofuels, Fe still plays a crucial role in the melting/slag behavior. The combustion of raw bagasse and steam exploded bagasse formed relatively low amounts of aerosols, nevertheless enriched in NaCl and KCl, which poses a potential operational/corrosion risk when deposited on heat-exchanger surfaces. For SCT and EFB, washing is essential to reduce the aerosol formation, e.g. for EFB the submicron-particle mass was reduced by more than 90% and the fouling decreased proportionally by a factor of 10. Without washing unacceptably high slagging, fouling and corrosion potentials were observed with the steam exploded EFB. (c) 2022 Published by Elsevier Ltd.

Purpose : This study evaluates the potential of biomass ash as raw clinker material and the influence of biomass feedstock and thermal conversion technology on biomass ash properties. Methods : A set of criteria for biomass feedstock and ash properties (i.e. CaO/SiO 2 ratio and burnability) are established. A large dataset was collected and the best combination of biomass feedstock and conversion technology regarding the desired ash quality was identified. Results : Wood biomass has the highest potential to provide the right CaO/SiO 2 ratio which is needed to form clinker minerals. Bark content and exogenous Si inclusion in wood biomass have a large influence on the CaO/SiO 2 ratio. Paper sludge is composed of Ca, Si and Al and can potentially serve as a source of cement elements. Wood fly ash from pulverized fuel combustion can substitute a considerable amount of raw clinker materials due to its similar burnability. The replacement ratio is determined by the content of adverse elements in the ash (i.e. MgO 2 and P 2 O 5 ). Conclusion : Using biomass ash to lower the CO 2 emission from clinker production depends on the joint effort of bioenergy producers, by providing higher quality biomass ash, and cement makers, by adapting the kiln operation to enable a high level of raw material replacement by biomass ash.The presented evaluation of the ash production chain, from biomass selection through combustion technology and ash management, provides new insights and recommendations for both stakeholders to facilitate this sustainable development. Graphic Abstract

In this study, we performed a life cycle assessment of the reuse of biomass fly ash as secondary cementitious material in cement mortars as alternative to a reference landfill scenario of the ash. Since biomass ash does contain enhanced levels of elements that are of potential concern for the environment or human exposure, the performed Life Cycle Assessment (LCA), in addition to CO2 savings, takes into account the impact on all non-toxic categories and human toxicity/carcinogenicity during service and second life stages. Results showed that utilization of biomass ash in cement is preferable over landfill for all the non-toxic categories at both cement replacements rates of 20 and 40 wt%. In detail, the reduction of CO2-eq. was found to be between 11 and 26% when biomass ash was blended with cement instead of being landfilled. The hydraulic activity of biomass ashes was found to be a critical parameter in this scenario, as it had impacts on the global warming potential (and all other investigated non-toxic categories), and it is therefore crucial to consider the uncertainty related to this aspect in LCA studies. Cement containing biomass ash performed better, on average, when compared with the reference landfill scenario regarding the impact to human toxicity (carcinogenic) category. Contrary, only the utilization in cement for one particular ash type (from paper sludge combustion) showed a better performance than the reference scenario for the ecotoxicity (ET) category. The impact to human toxicity carcinogenic (HTc) and ecotoxicity (ET) was mainly dominated by the leaching of Cr from landfilling of pure biomass fly ash (reference scenario) and the leaching of Ba, Cu, Cr (VI) and Zn from the second life stage of cement products (i.e., reuse of the crushed cement after service life in road base applications). However, this impact was acceptable when emissions are compared to existing EU landfill directive and regulations on the reuse of secondary materials in construction works. The novel LCA approach performed in this study, which includes impacts of leached contaminants during both the service and second life phase of cement, has shown that the reuse of biomass ash as secondary cementitious materials has a beneficial effect on the majority of the impact categories, with no unacceptable leaching risks. (C) 2019 Elsevier Ltd. All rights reserved.

The pH-dependent availability and leaching of major and trace elements was investigated for a wide range of biomass ash from different fuels and conversion technologies. A technical and environmental assessment of selected biomass ash for application in soil or cement mortars was performed, using both the total content and leaching of elements. A large variation in biomass ash composition, yet consistent pH dependent leaching patterns were observed for most elements and conversion technologies. Chromium showed a distinct behaviour which was hypothesized to reflect redox conditions during conversion of the biomass. The leaching based approach was found to provide a more realistic assessment of the availability of desired (i.e. nutrients) and undesired elements (i.e. contaminants) in soil systems. When applied to a reference soil at a rate of 2% by weight, the selected biomass ash increased the concentration of particularly Cr, Mo and Zn in soil solution to a level of concern. For cement applications, the release of Ba, Cr and Mo can become of concern during the second life stage, but the release was not attributed to the included biomass ash. Both soil and cement matrixes were found to control the release of elements such as Cu, V and Ni (soil) and As, Cr and Mo (cement) when compared to the released from pure biomass ash, underlining the importance of evaluating the availability and leaching of desired and undesired elements in the application scenario. Given current regulatory criteria, beneficial utilization of biomass ash in cement may be more feasible than in soil, but regulatory criteria based on leaching rather than total content of elements may widen the application potential of biomass ash.

This study evaluated the mechanical and environmental properties of cement mortars containing fly ash from biomass combustion as a secondary cementitious material. Cement mortars with 20 and 40% wt. replacement of Portland cement with fly ash from two types of installations were tested for their compressive strength and leaching behaviour. Substitution of 20% Portland cement with wood fly ash complied with the reference standard for compressive strength of 42.50 MPa at 280 days. Replacement rates of 40% developed a lower strength (30 and 33.50 MPa), but were still suitable for applications. The pulverized fuel ash perform substantially worse. We conclude that the biomass fly ash from fluidized bed combustion performs as a functional secondary cementitious material in cement, whereas the functionality of pulverized fuel fly ash is insufficient. The release of environmentally relevant elements from all the tested specimens fulfilled the Dutch leaching criteria for reuse. During second life as a granular construction material the release of Ba, Cr, Mo and V increased to a level of concern. However, this release was found to be similar to that of existing blended cements and was controlled by cement chemistry. The technical performance of cement mortars was influenced by the type and ratio of fly ash mixed with cement. However, the environmental performance was driven by the cement matrix that controlled the release of contaminants. Using biomass fly ash as a secondary cementitious material can reduce the carbon footprint of concrete by 40% while maintaining good technical and environmental performance.

Fuel Production from Sewage Sludge using TORWASH for highly efficient dewatering and salt removal

Invasive water plants are harvested in The Netherlands in order to keep waterways open. It is expected that due to improved water quality the growth of these water plants will increase significantly. Waternet, the watercycle company of Amsterdam and surrounding areas, wishes to turn this material into useful products. One of the investigated options was TORWASH, a technology under development by ECN for converting wet, saltcontaining biomass into clean solid biofuel suitable for energy production, e.g. by co-firing in power plants. Elodea nuttaliiand Cabombacaroliniana were harvested and directly processed. Samples were chopped into a slurry and then subjected to TORWASH conditions. The resulting product was filtered and pressed into disks. All inputs and outputs were weighed and analysed to make mass balances and to determine the fate of key elements like potassium, chlorine, nitrogen and phosphorus. The pressed disks were assessed for their suitability as solid biomass fuel. Both water plants are suitable feedstock for the TORWASH process. Chopping turns these plants into a slurry with 90% water and reduces the volume by a factor of four. Chopping and milling when applied onsite will therefore result in substantial lower transport costs. The slurry has the right consistency to be introduced into the TORWASH reactor. No addition of water is needed. After wet torrefaction the slurry can be mechanically dewatered to a level of more than 70% dry matter. The dewatered solids are suitable for direct combustion in a fluidized bed system. Alkali and chlorine content are in the same order as fresh wood chips. For applications in co-firing in a pulverized fuel plant, additional drying and probably an extra washing of the product is needed to further remove alkaline and chloride. It is recommended to investigate how sand and other inert ash-forming constituents can be removed. To make the fuel comparable to clean wood pellets, an extra washingto remove alkali and chloride may need to be included.

In Nederland worden woekerende waterplanten geoogste om de waterwegen open te houden. Het is de verwachting dat door verbeteringen in de waterkwaliteit de groei van deze planten nog verder zal toenemen. Waternet, het bedrijf wat verantwoordelijk is voor de waterwegen in en rond Amsterdam en zich richt op de hele watercyclus, wil de geoogste waterplanten nuttig en duurzaam gebruiken. Een van de opties, die daarbij onderzocht is betreft TORWASH, een technologie die door ECN (Energieonderzoek Centrum Nederland) ontwikkeld wordt. TORWASH is een natte torrefactie technologie, die natte, zoute biomassa omzet in een vaste bio-brandstof die geschikt is als brandstof voor energiecentrales. In dit rapport worden onderzoeksresultaten gepresenteerd die zijn verkregen met Waterpest (Elodea nuttalii) en Cabomba (Cabomba caroliniana). De monster zijn geoogst aan het einde van de zomer van 2012 en direct naar ECN gebracht om daar te worden verwerkt. Het materiaal is gehakseld en de slurries die daaruit resulteerden zijn onderworpen aan TORWASH testen in een autoclaaf. Het natte product is gefilterd en mechanisch ontwaterd. Na een set verkennende proeven zijn de optimale condities vastgesteld om de experimenten op te schalen en uit te voeren in de 20 liter autoclaaf. Van deze grotere tests zijn massabalansen opgesteld en is de distributie van relevante elementen bepaald, zoals kalium, chloor, stikstof en fosfor. Het uitgeperste materiaal is tevens onderzocht op brandstofkwaliteit. Beide waterplanten blijken een geschikte grondstof te zijn voor het TORWASH proces. Het hakselen tot een slurry met 90% water resulteert in een vermindering van het volume met een factor 4. Dit alleen al kan leiden tot aanzienlijke besparingen op de logistieke kosten voor het afvoeren van de waterplanten. Na het hakselen is de slurry direct geschikt om te TORWASHen. Er is geen toevoeging van water nodig. Na de TORWASH stap kan het product mechanisch ontwaterd worden tot 70% droge stof. De massaopbrengst (aan droge stof) ligt rond 50%, wat een normale waarde is voor TORWASH. Alkali en chloor worden efficient verwijderd tot een niveau wat vergelijkbaar is met dat van houtchips zonder bast. Het uitgeperste product is geschikt voor meestoken in kolencentrales, maar het chloorgehalte is nog net een fractie boven de IWPB standaard voor I2 industriele houtpellets. Het is de verwachting, dat een eenvoudige nawas-stap dit kan verhelpen. De uitgeperste producten bevatten 20-40% as, wat veel meer is dan hout of steenkool. Veel van deze as is echter silica omdat bepaalde elementen selectief worden uitgewassen. Het hoge asgehalte beperkt meestoken in kolencentrales, maar het blijft mogelijk om de bio-brandstof in wervelbedinstallaties of roosterovens te gebruiken. Het is dus wel een geschikte brandstof, maar voor sommige toepassingen een minder aantrekkelijke brandstof.

Bamboo is a potential sustainable biomass source for renewable heat and power production as it presents common fuel characteristics with other biomass feedstocks regarding heating value and chemical composition. This paper presents an evaluation of the combustion behaviour of the bamboo species Guadua angustifolia Kunth, virgin as well as torrefied, in blends with coal or pure, comparing with other biomass feedstocks such as wood and herbaceous biomass. The bamboo pre-treatment and the combustion experiments were carried out at dedicated installations at ECN, including a laboratory scale batch torrefaction reactor and a combustion simulation test facility. The results on combustion and co-firing reveal that in terms of fouling, the untreated bamboo shows behaviour closer to herbaceous biomass rather than to wood, with specific fouling factors of wood, bamboo and herbaceous biomass of 0.91.10(-3), 2.9.10(-3), 3.1.10(-3) K.m(2).W-1-g(-1) respectively. Dry torrefaction improves its physical properties by increasing the density and grindability without improving significantly its fouling behaviour while the fouling behaviour of wet torrefied bamboo is similar to woody biomass; the specific fouling factors of dry torrefied and wet torrefied bamboo are 2.4.10(-3) and 0.89.10(-3) K,m(2.)W(-1)g(-1) respectively. The fouling behaviour of biomass and coal blends lies between the fuels of the blend. Alternative bamboo species were evaluated using the alkali index A(i) based on their fuel composition. It appears that the fouling behaviour of alternative species is better than for G. angustifolia, therefore these should be further analysed. (c) 2014 Elsevier Ltd. All rights reserved.

Bamboo is a potential sustainable biomass source for renewable heat and power production. Bamboo presents common fuel characteristics with other biomass feedstocks regarding heating value and chemical composition. Up to date, there are no studies on fuel properties of the bamboo specie Guadua angustifolia. Bamboo is a difficult fuel and most thermal conversion processes have stringent fuel specifications, which are challenging to fulfil with biomass streams. Bamboo is tenacious and fibrous which makes it difficult and expensive to grind. Furthermore, the characteristics with regard to handling, storage and degradability are not favourable for biomass in general. The thermal pre-treatment torrefaction is a promising upgrading technology that can enhance the fuel quality by addressing these issues. During torrefaction, biomass is heated to 250-320a#176;C in the absence of oxygen. At the end of the process the material is milled and compressed into pellets. In this way, the biomass becomes easy to grind, water resistant and has a high energy density. Alternatively, wet torrefaction (Torwash) allows for combined torrefaction and washing of the feedstock. Wet torrefaction, a form of hydro-thermal treatment, in addition to dry torrefaction removes salts and minerals from biomass, improving even more the quality of the product. This is in particular interesting for feedstock containing significant amounts of undesirable alkali components for combustion or gasification, as is the case of bamboo. This paper presents an evaluation of the use of Guadua angustifolia as a fuel for heat and power applications. The results of biomass fuel properties and characteristics and quality improvement via dry and wet torrefaction are assessed. Torrefaction clearly shows the improvement of fuel properties and grindability of biomass. Wet-torrefied Guadua angustifolia is chemically an attractive fuel, with favourable fuel properties, e.g. the results showed a 98% of alkali removal, and the production of a grindable solid fuel.

The Energy research Centre of the Netherlands (ECN) has executed an extensive research and development programme in which the most important aspects of torrefaction and pelletisation were investigated. In this paper, some results of these investigations with different types of biomass (deciduous, herbaceous and coniferous) and interesting waste streams are outlined. ECN’s torrefaction technology comprises of a dedicated (moving-bed) reactor and process design. In the framework of the R&D programme, a 50–100 kg/h pilot plant “PATRIG” was commissioned and several 10–100 hour test runs with various types of biomass were executed to validate the design. The produced tonnes of torrefied material were used in semi-industrial milling and pelletisation trials. Results of these torrefaction, milling and pelletisation trials are highlighted as well. In general, a well-controlled torrefaction temperature proves essential for a good torrefied product quality control, which is crucial for a proper pelletisation performance. The extensive torrefaction and pelletisation test work up to pilot-plant scale forms a solid base for the scale-up and demonstration of the ECN technology. ECN has teamed up with industrial partners (e.g., Vattenfall) to first demonstrate the technology at a scale of several tonnes per hour and then pursue global commercial market introduction.

In the future, more electricity in the Netherlands will be produced using coal with co-combustion. Due to this, the generated annual ash volume will increase and the chemical composition will be influenced. One of the options for utilization if present markets are saturated and for use of fly ashes with different compositions, is as raw material for lightweight aggregates. This was selected as one of the best utilizations options regarding potential ash volume to be applied, environmental aspects and status of technology. Because of this, a study has been performed to assess the potential utilization of fly ash for the production of lightweight aggregate. Lightweight aggregate has been produced in a laboratory scale rotary kiln. The raw material consisted of class F fly ash with high free lime content. An addition of 8% clay was necessary to get green pellets with sufficient green strength. The basic properties of the produced lightweight aggregate and its behaviour in concrete have been investigated. The concrete has a good compressive strength and its leaching behaviour meets the most stringent requirements of Dutch environmental regulations. The carbon foot print of concrete will be negatively influenced if only the concrete itself is taken into account, but the reduction of the volume weight has advantages regarding design, transport emissions and isolation properties which may counteract this. In the Dutch situation the operational costs are higher than expected potential selling price for the LWA, which implies that the gate fee for the fly ash is negative.

A case study has been formulated concerning the use of ashes from combustion of cacao residues (shells) for electricity production and for nutrient recycling to the original soil. The effect in terms of kilograms of fertilizer per hectare and the environmental impact of closing the nutrient and mineral cycle are quantified. If the ashes are used as fertilizer, this fertilizer will only replace about 2% m/m of phosphorus and potassium that is necessary to fulfill the nutrient demand. This means that the contribution of the ashes is small. Furthermore, nitrogen has to be added as fertilizer. There is also a small advantage of reduction of CO2 emissions by nutrient recycling; this reduction is negligible from the point of view of the plantation, but from the point of view of the filter ash, the potential emission reduction is significant. This study shows that ashes from stand-alone combustion of certain agricultural residues are an potential valuable mineral source for elements such as phosphorus and potassium.

Useful application of ashes produced in the thermal conversion of biomass can contribute to the green image of biomass as a source of sustainable energy. This chapter gives an overview of the different forms of ash utilization that exist or are being developed for biomass ashes. The first section reviews options for ashes from co-firing of biomass and coal, both established forms of utilization in cement and concrete, and alternative options, e.g., manufacture of lightweight aggregates. The second section discusses utilization options for residues from "pure" biomass combustion. The large variation in biomass fuels and installation types makes this a complex issue. Besides recycling of clean wood ash to forests, these are all emerging forms of utilization. The third section discusses the specific issues related to the utilization of carbon-rich ashes from biomass gasification and pyrolysis.

In the Netherlands, biomass is envisaged to play a major role in fulfilling national ambitions concerning the reduction of CO2-emissions and the introduction of renewable energy sources. Ambitious targets have been set in the long-term energy research strategy programme of the Dutch Ministry of Economic Affairs, including targets of 25% and 40% biomass co-firing in 2020 and 2040 respectively. These co-firing targets cannot be met with state-of-the-art technology. Therefore, ECN and KEMA, with the assistance of Delft University of Technology, have joined forces to address the biomass co-firing R&D needs. The Dutch power generation sector is closely involved to ensure that the R&D activities are well targeted to market needs and to facilitate the implementation and exploitation of the results. This paper presents an overview of the topics considered.