CO2 as moderator for biomass gasification

Biomass can be converted into gaseous fuel by high-temperature reactions with a gasifying agent. The gasifying agent consists, in most cases, of oxygen and of a moderator, which is usually water vapour. Here we show that waste CO2 can be used instead of, or together with, water vapour to moderate the process of biomass gasification in a catalytic fluidized bed of dolomitic limestone. Such use of CO2 increased substantially the carbon and energy conversion efficiency and decreased the amount of tars in the produced gas

Transient catalytic activity of calcined dolomitic limestone in a fluidized bed during gasification of woody biomass

Calcined dolomitic limestone mixed with silica sand in a fluidized bed can catalytically enhance the gasification of woody biomass. The lime is prone to attrition and carry over from the reactor and to deactivation caused by pore sintering; therefore, it has to be replenished continuously or periodically to maintain catalytic activity of the fluidized bed. The main aim of this paper was to explore the level of the decrease of the catalytic activity of the fluidized bed if the limestone is not replenished and to estimate a critical period for its top-up. Wood chips were gasified first in a silica sand fluidized bed (1080 g), to obtain background data without the catalytic effect of limestone. After 5 h of operation, dolomitic limestone (1050 g) was added to the fluidized bed and left to calcine. Its catalytic activity was monitored during the following 6 h. During the second part of the experiment, the yield of the main gases (H2, CO, CH4, CO2, and H2O) remained almost unchanged. The yield of minor organic gases and tars rose slightly but still remained far below the value attained with only silica sand. The heavy polyaromatic tar compounds were effectively decomposed during the first 3 h after the addition of dolomitic limestone. It was concluded that the catalytic activity of dolomitic lime remains in an acceptable level during the first 3 h after its addition into the fluidized bed, suggesting that periodic rather than continuous replenishment of limestone should be sufficient

Charakterystyka popiołu dennego z MSWI oraz ocena odzysku

Municipal solid waste incineration (MSWI) bottom ash contains valuable components that can be recovered as secondary materials, such as ferrous and non-ferrous metals, some rare earth elements, glass etc. Metal-free mineral fraction can be used in construction industry as a substitute for natural materials. Important benefit of bottom ash recycling for the plant operator is also in reduction of fees for solid residuals landfilling. The composition of bottom ash is highly dependent on the composition of incinerated waste but in average can be around 5–13% ferrous metals, 2–5% non-ferrous metals, 15–30% glass and ceramics, 1–5% unburned organics and 50–70% mineral fraction. Several incineration plants in Europe are equipped with advanced systems for metals recovery, mostly based on magnetic separation of ferrous metals and separation of non-ferrous metals usually by eddy-current separators. To assess the possibilities of the bottom ash treatment in the Czech Republic it is necessary to obtain data about the bottom ash composition and evaluate its resource recovery potential. This paper summarizes characteristics of bottom ash samples from waste-to-energy plant in Prague. Emphasis of the study was primarily placed on the material composition. Bottom ash samples were dried and sieved into eight size fractions in the first step. It must be said that particle size distribution plays a decisive role for further utilization of bottom ash. In the second step, individual size fractions were sorted, using magnetic separation and the set of grinding, sieving, and manual separation processes, into the following materials: glass, ceramics and porcelain, magnetic particles with ferrous scrap, non-ferrous metals, unburned organic material, and residual fraction.Miejskie spalarnie odpadów stałych (ang. skrót MSWI) wytwarzają popiół, który zawiera cenne składniki, które można odzyskać w postaci materiałów wtórnych, tj. metali żelaznych i nieżelaznych, niektórych metali ziem rzadkich, szkła itd. Pozbawiona metalu frakcja mineralna może być użyta w przemyśle budowlanym jako zamiennik dla materiałów naturalnych. Ważną korzyścią płynącą z recyklingu popiołu dennego dla zarządzających spalarnią jest obniżenie kosztów składowania stałych pozostałości pospalaniu. Skład popiołu dennego w dużej mierze zależy od składu odpadów i średnio zawiera około 5-13% metali żelaznych, 2-5% metali nieżelaznych, 15-30% szkła i ceramiki, 1–5% niespalonych składników organicznych i 50-70% frakcji mineralnej. Kilka spalarni w Europie jest wyposażonych w zaawansowane systemy odzysku metali, głównie oparte o separacje magnetyczną. Aby ocenić możliwości odzysku popiołu dennego w Republice Czeskiej, zebrano dane na temat składu popiołu dennego i określono potencjał odzysku. Niniejsza praca podsumowuje charakterystykę próbek popiołu dennego pobranych ze spalarni generującej energię z odpadów znajdującej się w Pradze. Nacisk był przede wszystkim położony na skład materiału. W pierwszym etapie próbki popiołu dennego zostały osuszone i przesiane na 8 różnych frakcji. Warto uwzględnić, że rozkład wielkości ziaren ma decydujący wpływ na dalszą utylizację popiołu dennego. W drugim kroku, poszczególne frakcje zostały poddane separacji magnetycznej oraz innym procesom tj. rozdrabnianie, przesiewanie oraz separacja ręczna, na poszczególne frakcje: szkło, ceramika i porcelana, cząsteczki magnetyczne ze skrawkami żelaza, metale nieżelazne, niespalone materiały organiczne i pozostałe frakcje

Does micro-sized pyrogenic carbon made in lab affect earthworm mortality in restrained water content?

Micro-sized pyrogenic carbon (PyC) is expected to interact more efficiently with soil biota such as earthworms than coarse pyrogenic carbon. Little is known about whether the micro-sized PyC poses a threat to earthworms. We investigated the effects of hydrophilic micro-sized PyC on earthworm mortality in two contrasting soil substrates from young and old reclaimed soils of a successional chronosequence. These two soil substrates had different hydraulic properties, total organic carbon, pH, and nutrient status. Lower earthworm survival rates were observed in both soil substrates receiving dry micro-sized soil particles and the micro-sized PyC. Specifically, the addition of micro-sized PyC resulted in the lowest survival rate compared to the addition of micro sized soil particles and the control from day 8 to 11. The decreased earthworm survival rate due to micro sized PyC was more pronounced in the old soil substrate than in the young substrate. Fully moistened soil substrates containing micro-sized PyC or dry micro-sized soil substrate particles did not result in decreased earthworm survival. Micro-sized PyC turned from hydrophilic to hydrophobic when mixed with rhamnolipids, possibly hindering the uptake of dissolved oxygen by earthworm skins. Our results thus provide a new explanation for the negative effects of micro-sized PyC on earthworms and demonstrate the importance of assessing the hydraulic properties of both the micro-sized PyC and soil prior to PyC's application to soils