Water and energy savings from greywater reuse: a modelling scheme using disaggregated consumption data

Municipal drinking water supplies are under great stress globally, and one way to mitigate the problems is the reutilization of wastewater in various settings. In this paper, a greywater reuse scheme and the impact of system design and configuration on water and energy savings are investigated. The objective of the paper was to investigate the impact of hydraulic design and performance of a greywater treatment and reuse system on water and energy savings. A simulation model was created based on real, disaggregated water consumption data that predicts the reuse potential. Three scenarios were investigated; (1) greywater collection from the bathroom and reuse for toilet flushing, (2) greywater collection from bathroom sinks and showers, and reuse as hot water for sinks and showers, and (3) a combination of (1) and (2) where greywater collection from bathroom sinks and showers is used for toilet flushing, sinks and shower. The results indicate hot water reductions between 55.6 and 58.2%, while cold water reductions ranged from 5.8 to 30.6%. Reductions in energy for producing hot water between 43.5 and 46.8% were observed. Recommendations per connected user for hydraulic design ranged from 0.033 to 0.1\ua0dm3\ua0min−1, 3\ua0dm3, and 0.7–10\ua0dm3\ua0for treatment capacity, collection and holding tank volume

Interactions between potassium ashes and oxygen carriers based on natural and waste materials at different initial oxidation states

One of the most essential features of an oxygen carrier is its ability to be oxidized and reduced in order to transfer oxygen in a chemical looping system. A highly reduced oxygen carrier can experience multiple performance issues, such as decreased reactivity, agglomeration, and defluidization. This is crucial for\ua0processes that require limited oxygen transfer from the air reactor to the fuel reactor. Meanwhile, biomasses as environmentally friendly fuel options contain ashes, which would inevitably react with oxygen carriers and exacerbate the performance issues. To mimic the interactions between a highly reduced oxygen carrier and biomass ash compounds, four iron-based oxygen carriers, based on natural ores and waste materials, and three potassium salts, K2CO3, KH2PO4, and K2SO4, were investigated in a tubular reactor under an atmosphere consisting of 2.5% H2 and 10% steam in Ar and N2 at 900\ub0C for 3 h. The results from the X-ray diffraction (XRD) material analysis showed that both initially fully oxidized and highly reduced materials reach the same oxidation state after the experiment. Based on the scanning electron microscopy coupled with energy dispersive X-ray spectroscopy results, K from K2CO3 and K2SO4 diffuses in the oxygen carrier particles, while K from KH2PO4 always forms a distinct layer around the particles. The initial oxidation state of an oxygen carrier surface affects the interactions with the potassium salt only to minor extents. Thus, the final state of the material and its performance in a large-scale process are only occasionally and mildly affected by its initial oxidation state

Magnetic properties of ilmenite used for oxygen carrier aided combustion

Oxygen carrier aided combustion is a combustion process that utilizes oxygen carrying particles in a fluidized bed to transport oxygen from oxygen-rich to oxygen-poor regions in the reactor. A commonly used oxygen-carrying material is ilmenite (FeTiO3) which is a naturally occurring mineral. At higher oxygen partial pressures ilmenite can react to pseudobrookite (Fe2TiO5) and thereby take up oxygen. Upon reduction of pseudobrookite in oxygen-lean locations the oxygen is released, which enhances the distribution of oxygen through the reactor. Ilmenite was used as bed material in an industrial 115 MWth circulating fluidized bed (CFB) boiler where recycled waste wood and wood chips were utilized as fuel. Bottom ash samples were extracted after one and two weeks and the samples were separated into two fractions by a magnetic separator. The magnetic fraction was expected to be enriched in iron-containing oxides and was therefore aimed to be recirculated into the boiler. The SEM-EDS analysis revealed that the non-magnetic fraction consists to the largest extent of feldspar (KAlSi3O8) particles. A significant amount of freshly introduced ilmenite particles was also classified as non-magnetic by the magnetic separator. Characteristic for these particles was a lack of ash layer, suggesting they had only recently been added to the system. In the magnetic fraction, several feldspar particles were found which were covered by a layer rich in Ca, Fe, Ti, and Si. Comparing the XRD analysis of the ash prior to magnetic separation with its magnetic fraction revealed a decrease of the peaks corresponding to feldspar. The removal of feldspar particles by magnetic separation was further corroborated by XRF analysis, where the concentration of K, Al and Si was significantly higher in the non-magnetic fraction, however, no changes were observed in the concentration of Fe. The present analyses shows that prolonged exposure time of ilmenite increases its magnetic susceptibility. Non-magnetic feldspar was shown to acquire significant magnetic susceptibility by formation of a surface layer containing Fe-rich attrition products from ilmenite

Monitoring of bed material in a biomass fluidized bed boiler using an electronic tongue

The thermal conversion of biomass fuel mixes in fluidized beds can cause agglomeration. To counteract agglomeration, bed material is gradually exchanged with virgin bed material, and this results in increased disposal of used bed material. Furthermore, the bed material exchange represents a costly option, as it involves a cost for virgin bed material, for landfill, and for unplanned downtime of the plant. This paper presents a novel method for the evaluation of bed material quality: the electronic tongue (ET). Evaluation of bed material quality can contribute toward decreasing the cost of unnecessary exchanges of bed material. The proposed method was tested on bed material sampled on an almost daily basis from a commercial fluidized bed boiler during several months of operation. A two-electrode ET was used for the evaluation of the bed material quality. The analysis relied on pulsed voltammetry measurements and multivariate data analysis with Principal Component Analysis (PCA). The results suggest that it is possible to follow bed material changes and that the ET, after further development, may be used to optimize the material flows connected to the bed material. Further research is being conducted to optimize the ET\u27s performance and its application in monitoring bed material

Interactions between Automotive Shredder Residue and Olivine Bed Material during Indirect Fluidized Bed Gasification

Thermal conversion of automotive shredder residue (ASR) using indirect fluidized bed gasification was conducted in the Chalmers semi-industrial 2-4-MWth gasifier. The bed material consisted of olivine that was activated through the deposition of biomass ash prior to a 13-day exposure to ASR. The interactions between the bed material and the ASR ash were investigated using XRD, SEM-EDS, and thermodynamic modeling. The deposition of iron (Fe) onto the olivine particles was noted, and this is likely to increase the oxygen-carrying ability of the particles. Furthermore, at the end of the campaign, about one-third of the particles in the bed were found to originate from the ASR ash. These particles were rich in Fe and Si, as well as elements found exclusively in the ASR ash, such as Zn, Ti, and Cu. Some of these particles exhibited a hollow morphology, suggesting a melt state during their formation in the gasifier. In addition, a low level of agglomeration of the ash and olivine particles was detected. Thermodynamic modeling with the FactSage software indicated the formation of slag. This study presents a detailed investigation of the interactions that occur between the bed material and an ash-rich fuel such as ASR. The findings may have applications in demonstrating the induction of oxygen-carrying ability in bed materials or for metal recycling through the separation of ash particles from the bed material

Bed material as a catalyst for char gasification: The case of ash-coated olivine activated by K and S addition

In this paper, the ability of an ash-coated olivine to catalyze the steam gasification of biomass-derived char is investigated in a laboratory reactor. The olivine investigated is a sample from the Chalmers dual fluidized bed gasifier and it has been activated by the in-bed addition of S and K 2 CO 3 . The char and bed material samples were analyzed by Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (SEM-EDS). It is shown that the ash layer coating of the olivine can catalyze the steam gasification of char by transferring catalytic potassium (K) to the char particles. The mobilities of the catalytic species from the olivine ash-layer are discussed. This work furthers the current understanding of the catalytic activities of ash-coated bed material particles during the thermochemical conversion of carbonaceous feedstocks in fluidized beds. In addition, it complements the existing literature on catalytic bed materials, which to date have focused on tar removal and improving gas quality

Role of surface morphology on bed material activation during indirect gasification of wood

Olivine and alkali-feldspar were utilized in separate campaigns in an indirect dual fluidized bed gasification campaign with woody biomass as fuel. After three days, both bed materials were reported to be active towards tar removal and exhibited oxygen-carrying abilities and had formed an ash layer consisting of an outer ash deposition layer and an inner interaction layer. X-ray microtomography analysis concluded that a preferred deposition of ash happens onto convex regions of the bed particles, which results in an increase in thickness of the ash layer over convex regions. This effect is most pronounced for the outer layer which is a product of ash deposition. The inner layer exhibits a homogeneous thickness and is probably formed by interaction of Ca from the outer layer with the particles. Transmission electron microscopy revealed the presence of Fe and Mn on the surface of the particles in a solid solution with Mg. The oxygen-carrying effect which is found for aged particles is therefore attributed to the presence of Fe and Mn on the surface of aged particles. Alkali were found on the surface of both particles which are likely contributing to the catalytic activity of the material towards tar removal

Advanced biofuel production via gasification – lessons learned from 200 man-years of research activity with Chalmers’ research gasifier and the GoBiGas demonstration plant.

This paper presents the main experiences gained and conclusions drawn from the demonstration of a first-of-its-kind wood-based biomethane production plant (20-MW capacity, 150 dry tonnes of biomass/day) and 10 years of operation of the 2–4-MW (10–20 dry tonnes of biomass/day) research gasifier at Chalmers University of Technology in Sweden. Based on the experience gained, an elaborated outline for commercialization of the technology for a wide spectrum of applications and end products is defined. The main findings are related to the use of biomass ash constituents as a catalyst for the process and the application of coated heat exchangers, such that regular fluidized bed boilers can be retrofitted to become biomass gasifiers. Among the recirculation of the ash streams within the process, presence of the alkali salt in the system is identified as highly important for control of the tar species. Combined with new insights on fuel feeding and reactor design, these two major findings form the basis for a comprehensive process layout that can support a gradual transformation of existing boilers in district heating networks and in pulp, paper and saw mills, and it facilitates the exploitation of existing oil refineries and petrochemical plants for large-scale production of renewable fuels, chemicals, and materials from biomass and wastes. The potential for electrification of those process layouts are also discussed. The commercialization route represents an example of how biomass conversion develops and integrates with existing industrial and energy infrastructures to form highly effective systems that deliver a wide range of end products. Illustrating the potential, the existing fluidized bed boilers in Sweden alone represent a jet fuel production capacity that corresponds to 10% of current global consumption

Characterization of ash component desorption on novel bed material for fluidized bed boilers

The use of biomass as a renewable fuel for production of heat and electricity is regarded as a key to reduce fossil fuel dependency, and thereby to reduce net CO2 emissions. Fluidized bed (FB) technology is widely accepted as the most energy efficient process for thermal conversion of biomass. One of the often-mentioned drawbacks is the building up of agglomerates within the process because of bed material-ash interaction. To avoid unplanned operational stops due to agglomeration, bed material is continuously replenished and spent bed material is removed in the form of bottom ash. The spent bed material cannot readily be reused and is usually deposited or used as construction filler material. Sand is the primary choice for bed material but novel bed materials are being tested to improve biomass conversion. Even though agglomeration is reduced and the energy efficiency of the conversion process is improved, bottom and fly ash are still being generated and need to be managed. To conceive new management strategies there is need to improve the understanding of the composition and stability of the compounds formed from the interaction between biomass ash and the novel bed materials. In the present work four bed materials (Olivine, Ilmenite, Feldspar and Manganese ore), all minerals, have been used in a biomass fueled 10MW CFB boiler. The materials have been sampled upon similar gas composition and time exposures in order to assure similarity in bed material “activity”. Bed material characterization followed by stepwise leaching have been used to identify opportunities in terms of pretreatment prior to deposition or/and the possibilities for alternative reuse