Leaching of inorganic and organic matter from biomass and biochars under various conditions: equilibrium, kinetics and implications

This thesis investigates into the leaching phenomena in various biomass thermochemical processes. For biomass water leaching, the leachate is acidic and can interact with biomass. A method has therefore been devised for quantifying water-soluble inorganic species in biomass. For biochar leaching, partial steam gasification of biochar at low conversions is a good strategy to facilitate nutrients recycling. For biomass leaching in hot-compressed water, substantial leaching of inorganic species takes place during the hydrolysis of saccharides

Leaching Characteristics of Organic and Inorganic Matter from Biomass by Water: Differences between Batch and Semi-continuous Operations

Over 30% and ~2% (on a carbon basis) organic matter can be leached from mallee leaf and wood by water, respectively, producing acidic leachates containing organic acids. As a result, there are significant differences in the leaching characteristics of both organic and inorganic species in biomass between batch and semi-continuous leaching operations. Under conventional batch leaching, the acidic leachate continuously contacts the biomass for a prolonged period, resulting in the leaching of at least some water-insoluble inorganic species (e.g., organically bound) from biomass. Therefore, the batch leaching method clearly overestimates the amount of water-soluble inorganic species in biomass and exhibits two-step leaching kinetics, i.e. a rapid leaching step for an initial short period followed by a slow leaching step for a relatively long period. This study further develops a semi-continuous leaching method to address this issue via minimizing the contact between the leachate and the biomass sample. The semi-continuous leaching quantifies the true water-soluble inorganic species in biomass. Its leaching kinetics include only the first rapid leaching step, with the disappearance of the second slow-leaching step due to the absence of the interaction between acidic leachate and biomass.The results suggest that in the sequential extraction scheme used in chemical fractionation, semi-continuous (instead of batch) water leaching method should be used for quantifying water-soluble inorganic species in biomass. Attention should also be paid to the potentially substantial loss of fuel materials when utilizing water leaching as a pretreatment method to remove inherent inorganic species in biomass for fuel quality improvement. As result of overestimating water-soluble inorganic species and loss of organic matter, care must be taken when using water batch washing as a method for studying the effect of the inherent water-soluble inorganic species on thermochemical reactions of biomass

Trace Elements Release and Particulate Matter Emission during the Combustion of Char and Volatiles from in Situ Biosolid Fast Pyrolysis

© 2016 American Chemical Society.This paper presents a systematic study on the emission of trace elements (e.g., As, Cu, Cr, Ni, V, Co, Cd, and Pb) during the combustion of char, volatiles, and biosolid at 1300 °C using a two-stage pyrolysis/combustion reactor system. Over 50% As, Cd, and Pb in biosolid are released with volatiles during fast pyrolysis at 800-1000 °C, while other elements are mostly retained in char. During biosolid combustion, PM10 consists of mainly major elements and the contribution of trace elements is <0.5 wt %. Particulate matter (PM) produced from the combustion of volatiles produced in situ from biosolid fast pyrolysis at 800-1000 °C is dominantly PM1, contains only volatile elements (As, Cd, and Pb), and has a unimodal distribution with a fine mode diameter of 0.043 µm. Char combustion produces both PM1 and PM1-10, with the PM having a bimodal distribution (a fine mode at 0.043 µm and a course mode at 6.8 µm). It is also found that As, Cd, and Pb only contribute to PM1 emission even during char combustion. While Ni, Co, Cu, and part of V are responsible for PM1-10 emission, most Cr and some V presented in char also contribute to PM1 emission during char combustion. Significant differences are also observed in the PM between direct biosolid combustion and the sum of PM from char and volatile combustion. The results suggest that direct biosolid combustion may have produced substantially different char and volatiles, which may have experienced significant interactions during combustion

Effect of volatile–char interactions on PM10 emission during the combustion of biosolid chars under air and oxyfuel conditions

© 2018 The Combustion Institute This study reports the significant effect of volatile–char interactions on the emission of particulate matter (PM) during the combustion of biosolid chars in drop-tube furnace at 1300 °C under air and oxyfuel conditions. Slow and fast heating chars were prepared from biosolid pyrolysis and then interacted with the volatiles produced in situ from the pyrolysis of polyethylene (PE) and double acid-washed biosolid (DAWB) in a novel two-stage quartz reactor at 1000 °C (limited by the operating temperature of quartz). The results clearly show that under the experimental conditions, the interactions between chars and small non-oxygenated reactive species in both volatiles substantially decrease the yield of PM with aerodynamic diameter < 1 µm (i.e. PM1), dominantly PM with aerodynamic diameter < 0.1 µm (PM0.1) during char combustion. The interactions between oxygen-free volatiles (produced from PE pyrolysis) and char also reduce char macroporosity, leading to a reduction in the yield of PM with aerodynamic diameter between 1 µm and 10 µm (i.e. PM1-10). However, the interactions between O-containing reactive species (produced from DAWB pyrolysis) and char significantly increase char macroporosity. Higher heating rate with shorter aging process during pyrolysis significantly weakens the effect of volatile–char interactions on PM1emission but intensifies its effect on PM1-10emission during char combustion. The combustion atmospheres have little effect on the net yield of PM contributed by volatile–char interactions. Combustion of chars interacted with the oxygen-free volatiles lead to a reduction in the yield of refractory elements (i.e. Mg, Ca, Al, Si, Fe, Ni, Co, Cu, Mn, V and Zn) in PM1-10but those interacted with the O-containing volatile resulted in an enhanced yield of these elements in PM1-10. Furthermore, the interactions between O-containing reactive species and chars significantly decrease Cr yield in PM0.1due to formation of volatile chromium oxyhydroxides. In addition, volatile–char interactions have little influence on the forms of alkali and alkaline earth metallic (AAEM) species and P in PM10, i.e. as (Na, K)PO3in PM1and (Mg,Ca)3(PO4)2in PM10

Effect of water vapour on particulate matter emission during oxyfuel combustion of char and in situ volatiles generated from rapid pyrolysis of chromated-copper-arsenate-treated wood

© 2018. This paper reports the effect of water vapour on particulate matter (PM) during the separate combustion of in situ volatiles and char generated from chromated-copper-arsenate-treated (CCAT) wood at 1300 °C. Combustion of in situ volatiles produces only PM with aerodynamic diameter <1 µm (i.e., PM1), dominantly PM with aerodynamic diameter <0.1 µm (i.e., PM0.1). Water vapour could significantly enhance the nucleation, coagulation and condensation of fine particles and reduce the capture of Na and K by the alumina reactor tube via reduced formation of alkali aluminates, leading to increases in both yield and modal diameter of PM0.1. Water vapour could also enhance char fragmentation hence increase the yield of PM with aerodynamic diameter between 1 and 10 µm (i.e., PM1-10) during char combustion. For trace elements, during in situ volatiles combustion, volatile elements (As, Cr, Ni, Cu and Pb) are only presented in PM1and water vapour alters the particle size distributions (PSDs) but has little effect on the yields of these trace elements. During char combustion, As, Cr, Cu and Ni are present in both PM1and PM1-10while the non-volatile Mn and Ti are only present in PM1-10. Increasing water vapour content increases the yields of As, Cr, Cu, Ni, Mn and Ti in PM1-10due to enhanced char fragmentation. During char combustion, water vapour also originates less oxidising conditions locally for enhancing As release, promotes the generation of gaseous chromium oxyhydroxides and inhabits the production of NiCl2(g), leading to increased yields of As and Cr and decreased yield of Ni in PM0.1

A Novel Two-Stage Alumina Reactor System for Burning Volatiles Generated in Situ from Biosolid: Effect of Pyrolysis Temperature and Combustion Conditions on PM1 Emission

© 2018 American Chemical Society. A novel two-stage alumina reactor system is developed for studying particulate matter (PM) emission from in situ volatiles combustion. It enables the generation of in situ volatiles at different pyrolysis temperatures (up to 1300 °C) and the subsequent combustion of in situ volatiles in air and oxyfuel at 1300 °C. It is found that the PM emitted from volatiles combustion contains only PM with aerodynamic diameter <1 µm (PM1) and has a unimodal distribution. An increase in pyrolysis temperature from 1100 to 1300 °C results in a substantial increase in PM1yield and a shift of fine mode diameter from 0.043 to 0.108 µm. The PM1emitted from the volatiles generated at 1100 °C mainly consists of Na, K, S, and P. For PM1emitted from the volatiles generated at 1300 °C, there are substantial increases in the yield of Na, K, and P; in addition, Mg and Si are present in PM1because of the release of these inorganic species from biosolid into the volatiles. For trace elements, increasing pyrolysis temperature from 1100 to 1300 °C not only increases the As and Cd yields in PM1but also results in the presence of Cr, Cu, and Mn in PM1because of increasing As and Cd volatility and the release of Cr, Cu, and Mn from biosolid into the volatiles. The yields of V and Pb remained unchanged, and there is no Ti, Ni, and Co present in the PM1. Changing the combustion atmosphere from air to oxyfuel causes a slight increase in PM1yield due to increased formation of alkali sulfates and enhanced formation of P4O10but results in no changes in the yields and particle size distributions of trace elements. Further analysis indicates the Na, K, S, and Cl are present in the PM1emitted from the combustion of volatiles produced at 1100 °C in the form of Na and K sulfates and Cl while P is present in the form of P4O10. The P in PM1is present in the forms of Na, K, and Mg metaphosphates and P4O10where higher proportion of P4O10is formed in PM0.1-1when pyrolysis temperature increases to 1300 °C. It is also evident that (Na, K)PO3and P4O10vapors can react with the alumina reactor tube to form alkali aluminophosphate glass which is then retained in the furnace, leading to only a fraction of Na and K in the volatiles being collected as PM1after combustion

Important role of volatile-char interactions in enhancing PM1 emission during the combustion of volatiles from biosolid

Abstract A three-stage pyrolysis/combustion reactor was used to demonstrate the importance of volatile–char interactions in inorganic particulate matter (PM) emission from the combustion of biosolid volatiles. It consists of a two-stage quartz reactor (including an inner drop-tube/fixed-bed pyrolyser as Stage I and an outer fixed-bed as Stage II) cascaded into a large drop-tube furnace (DTF, Stage III). The unique reactor design enables the volatiles that are produced in situ from the fast pyrolysis of cellulose, polyethylene or acid-washed biosolid in Stage I to pass through a preloaded bed of slow-pyrolysis biosolid char in Stage II then be immediately combusted (achieving complete combustion) in the DTF as Stage III at 1300 °C. Limited by quartz maximum working temperature (in Stages I and II), two temperatures (800 or 1000 °C) were considered for preparing the bed of char and generating the in situ volatiles. The results clearly show that volatile–char interactions lead to significant changes in the particle size distributions (PSDs) of PM emitted from the combustion of volatiles produced in situ from cellulose, polyethylene or acid-washed biosolid pyrolysis. The volatile–char interactions increase the yield of PM1 (i.e. PM with aerodynamic diameter <1 µm), dominantly PM0.1 (i.e. PM with aerodynamic diameter <0.1 µm). The results show that small non-oxygenated reactive species (especially H free radicals) in the fresh volatiles can react with the chars to enhance the release of alkalis (Na and K) as well as P and S in the chars. The released Na, K, P and S can react to form alkali metaphosphate and sulphate which subsequently form PM1 during volatiles combustion. It is also evident that volatile–char interactions convert some of Pb and Cr in the biosolid chars into volatile forms which are released and then contribute to PM1 emission

Association of inorganic species release with sugar recovery during wood hydrothermal processing

© 2015 Elsevier Ltd. All rights reserved. Over 90% of the inherent Mg and Ca in wood can be released during wood hydrothermal processing in a semi-continuous flow reactor at 10 MPa and 150 °C. An increase in temperature to 180 °C results in rapid release of Mg and Ca, but a further increase in temperature has little effect. The release of Mg and Ca is associated with the conversion of organic matter during hydrothermal processing. In particular, the release of water-insoluble Mg and Ca correlates well with the arabinose recovery, suggesting that these species are bound to carboxylic acid functional group on hemicellulose side chains and their release requires the cleavage of these side chains

Leaching characteristics of inherent inorganic nutrients in biochars from the slow and fast pyrolysis of mallee biomass

This study compares the inherent leaching characteristics of inorganic nutrients, particularly alkali and alkaline earth metallic (AAEM, mainly Na, K, Mg, and Ca) species in biochars prepared from the slow and fast pyrolysis of mallee biomass particles at 500 C. The results indicate that, compared to slow pyrolysis, fast pyrolysis produces biochars with less water-soluble AAEM species but more plant available AAEM nutrient species (through Mehlich I extraction). Pyrolysis of different biomass components results in biochars with different water-soluble and plant available AAEM nutrient species, depending on pyrolysis conditions. Biochars produced from pyrolysis of large wood particle (2–4 mm) exhibit slower water leaching kinetics and a lower plant available nutrients than those from fine wood particles (150–250 lm). Slow pyrolysis results in a reduction in water-soluble Na and K in biochars while an increment was observed for biochars produced from the fast pyrolysis of large wood. Experimental kinetic data can be broadly fitted to a pseudo-second order model. For all biochars, a significant proportion of inorganic nutrients can be recycled, demonstrating the potential of returning biochar to soil for completing the loop of nutrient recycling and enhancing the sustainability of biomass utilisation cycle