Chemical composition and physical properties of filter fly ashes from eight grate-fired biomass combustion plants

For the handling, treatment and utilization of fly ash from biomass combustion its chemical composition and physical properties are important. In this study eight filter fly ashes from different grate-fired biomass combustion plants were investigated. In fly ash from straw combustion high concentrations of(K) were found, whereas in the fly ash from wood combustion the concentrations of Ca and Mg were higher. The average concentration of PO3-4was similar in both types of fly ashes. In all wood fly ashes some measured heavy metal concentrations were above the limits for utilization. The straw fly ashes were much less contaminated and can be utilized. For wood fly ash most parameters showed little variation, except from one fly ash where the dust pre-separator is in poor condition. The average values were: mass median diameter 4.3 ± 0.8 μm, spread of particle size distribution19 ± 11, particle density 2620 ± 80 kg/m3 and angle of repose 50°± 1°. The density of the straw fly ashes is lower(2260 ± 80 kg/m3) and the spread of the size distribution is higher(72 ± 24).For one straw combustion fly ash the values of the mass median diameter and the angle of repose were similar to the values of wood combustion fly ash, for the other straw fly ash the values differed considerably. While the particle size of this fly ash was much smaller,surprisingly the angle of repose was also lower. This can be attributed to the formation of small agglomerates in this fly ash, which were not disintegrated without a certain stress.     

Energy futures and green chemistry: competing for carbon

Global energy demand is expected to increase from the current 400 ExaJ per year to as much as 700–1,000 ExaJ per year by the middle of this century. If fossil carbon resources continue to make up the bulk of the energy supply, not only will atmospheric carbon dioxide increase to levels not seen for the past 30–35 million years, but depleting fossil carbon resources will become increasingly less available for other purposes, particularly the production of chemicals on which society now depends. The chemical process industries are heavily dependent on the availability of low-price petroleum as a feedstock. Recent life-cycle analyses suggest that pursuing both strategies of renewable energy sources and renewable feedstocks (i.e. biomass) will be required to meet these competing demands. Reducing the global use of both energy and manufactured chemicals will be a challenge for sustainable development. Education of the next generation of chemists and chemical engineers will have to change significantly from its current emphasis on petrochemical-based manufacturing to include a much greater emphasis on renewable resources and bio-based processes.Brief accounts of this work were presented at the 7th International Symposium on Green Chemistry in China (Zhuhai, People’s Republic of China, May 2005) and at the Joint US–China Green Chemistry Workshop (Beijing, People’s Republic of China, May 2005; this workshop was supported by US National Science Foundation grant CHE-0522369).     

Emission factors for PCDD/PCDF and dl-PCB from open burning of biomass

The Stockholm Convention on Persistent Organic Pollutants includes in its aims the minimisation of unintentional releases of polychlorinated dibenzo-dioxins and dibenzofurans (PCDD/PCDF) and dioxin like PCB (dl-PCB) to the environment. Development and implementation of policies to achieve this aim require accurate national inventories of releases of PCDD/PCDF/dl-PCB. To support this objective, the Conference of Parties established a process to review and update the UNEP Standardized Toolkit for Identification and Quantification of Dioxin and Furan Releases. An assessment of all emission inventories was that for many countries open burning of biomass and waste was identified as the major source of PCDD/PCDF releases. However, the experimental data underpinning the release estimates used were limited in number and, consequently, confidence in the accuracy of the emissions predictions was low. There has been significant progress in measurement technology since the last edition of the Toolkit in 2005. In this paper we reassess published emission factors for release of PCDD/PCDF and dl-PCB to land and air.In total, four types of biomass and 111 emission factors were assessed. It was found that there are no systematic differences in emission factors apparent between biomass types or fire classes. The data set is best described by a lognormal distribution. The geometric mean emission factors (EFs) for releases of PCDD/PCDF to air for the four biomass classes used in the Toolkit (sugarcane, cereal crops, forest and savannah/grass) are 1.6 μg TEQ (t fuel)⁻¹, 0.49 μg TEQ (t fuel)⁻¹, 1.0 μg TEQ (t fuel)⁻¹ and 0.4 μg TEQ (t fuel)⁻¹, respectively. Corresponding EFs for release of PCDD/PCDF to land are 3.0 ng TEQ (kg ash)⁻¹, 1.1 ng TEQ (kg ash)⁻¹, 1.1 ng TEQ (kg ash)⁻¹ and 0.67 ng TEQ (kg ash)⁻¹. There are now also sufficient published data available to evaluate EFs for dl-PCB release to air for sugarcane, forest and grass/savannah; these are 0.03 μg TEQ (t fuel)⁻¹, 0.09 μg TEQ (t fuel)⁻¹ and 0.01 μg TEQ (t fuel)⁻¹, respectively. The average EF for dl-PCB release to land is 0.19 ng TEQ (kg ash)⁻¹. Application of these EFs to national emissions of PCDD/PCDF for global estimates from open burning will lower previous estimates of PCDD/PCDF releases to air and to land by 85% and 90%, respectively. For some countries, the ranking of their major sources will be changed and open burning of biomass will become less significant than previously concluded.     

Experimental and numerical study of biogas,methane and carbon dioxide produced by pre-treated wheat straw and pre-digested cow dung

ABSTRACT

The biogas constituting majorly CH₄ and CO₂ has been produced by Ca(OH)₂ pre-treated wheat straw with pre-digested cow dung. Some of the key thermodynamic parameters like specific heat capacity, density and heating capacity of the biogas produced have also been calculated per day as well as throughout the hydraulic retention time. The governing equations of biogas with appropriate phase and interfacial conditions describing the physics of the biogas have been derived. The control volume approach has been used to predict the total volume (ml) of biogas, CH₄ and CO₂ throughout the experiment and on the daily basis. The effects of feedstock, temperature and pressure on the production of biogas, CH₄ and CO₂ in anaerobic digestion have also been studied. The average number of molar fraction and conversion ratio of CH₄ and CO₂ are correlated with number of carbon atoms available in feedstock. Numerical calculations by using developed model and Modified Gompertz model have shown proficient agreement with the experimental observations.     

竹柳发展现状及未来趋势——基于案例

竹柳目前已在全国普遍种植,但竹柳的产业化还不够成熟,特别是在生物质能源方面.文章针对竹柳自身优势、产生的综合效益、目前在纸浆和生物质能源产业的开发现状及未来将走的两种模式进行了综述,对其进一步的发展和研究有一定参考意义.参33.     

The Indian perspective of utilizing fly ash in phytoremediation, phytomanagement and biomass production

Coal-based power generation is a principal source of electricity in India and many other countries. About 15–30% of the total amount of residue generated during coal combustion is fly ash (FA). FA is generally alkaline in nature and contains many toxic metals like Cr, Pb, Hg, As and Cd along with many essential elements like S, B, Ca, Na, Fe, Zn, Mn and P. Dumped FA contaminates the biosphere by mobilization of its fine particles and hazardous metals. Despite the negative environmental impact of FA, coal continues to be a major source of power production in India and therefore FA disposal is a major environmental issue. To overcome this problem, FA dumping sites have been started as a potential resource for biomass production of tree species. Phytoremediation is a strategy that uses plants to degrade, stabilize, and remove contaminants from soils, water and waste FA. Phytomanagement of FA is based on the plants' root systems, high biomass, woody nature, native nature, and resistance to pH, salinity, and toxic metals. Recently Indian researchers mostly from the National Botanical Research Institute have been working on phytoremediation and revegetation of FA dykes, inoculation of bacterial strains for reducing FA stress and biomass production from FA dykes. Many international researchers have worked on reclamation, revegetation and utilization of FA. FA utilization saves resources, mainly land (topsoil), water, coal, limestone and chemical fertilizer. Safe utilization of FA is a major concern around the world and regulatory bodies are enforcing stringent rules for the proper management of FA. This article summarizes various viable avenues in India for FA utilization and environmental management.     

Growth and fecundity of earthworms: <Emphasis Type="Italic">Perionyx excavatus</Emphasis> and <Emphasis Type="Italic">Perionyx sansibaricus</Emphasis> in cattle waste solids

Epigeic earthworms (Oligochaeta) have been appeared as key organisms to convert organic waste resources into value-added products, i.e., vermicompost and worm biomass. The assessment of reproduction potential of composting earthworm may be beneficial for large-scale earthworm production. Although, the waste minimizing potential of Perionyx excavatus and Perionyx sansibaricus is well proved, but little information is available about their fecundity rate. In this study, the efforts have been made to explore the growth and reproduction biology of P. excavatus and P. sansibaricus, using cattle waste solid as culture substrate, under laboratory conditions. Earthworms were weighed weekly and number of cocoons produced per week assessed. Biomass productions, fecundity, maturation, natality all were significantly different between P. excavatus and P. sansibaricus. The highest mean individual biomass was 767.7 ± 18.4 mg and 612.6 ± 20.6 mg, respectively in P. sansibaricus and P. excavatus. However, the highest cocoon numbers occurred in P. excavatus (492.3 ± 13.6), significantly higher than P. sansibaricus (269.6 ± 17.1). Fecundity was slightly different in both species: 1.38 ± 0.77 cocoons adult worm⁻¹ week⁻¹ (P. excavatus) and 1.58 ± 0.74 cocoons adult worm⁻¹ week⁻¹ (P. sansibaricus). The hatchling success rate (%) was highest in P. excavatus. Overall natality (juveniles adult⁻¹ week⁻¹) was highest in P. sansibaricus (1.52) than P. excavatus (1.26), which suggests that P. sansibaricus may be a better candidate for rapid propagation of earthworms in cattle waste solid.     

Application of recycled paper sludge and biomass materials in manufacture of green composite pallet

Rice straw, rice husk and paper sludge are by-products and industrial waste, and are beneficial resources as raw biomass materials used for manufacturing value-added composite products. We investigated the effect on selected mechanical properties of adding rice straw, rice husk and paper sludge to wood composites to replace wood particles for manufacturing green pallets. Results showed that increasing the contents of rice straw and rice husk dramatically decreased the mechanical strength of the composites. This is because the wax and silicate coating of these materials obstructed the strong bonding with UF resin. When 10 wt.% of wood particle was replaced with 10 wt.% of paper sludge, the wood–paper sludge composites showed similar mechanical properties to those of wood particle. Wood particle can be replaced by 10 wt.% of dried paper sludge in accordance with the minimum requirement recommended by standards in green pallet manufacturing.     

The combined effects of biomass and temperature on maximum specific ammonia oxidation rate in domestic wastewater treatment

• Actual SAORs was determined using MLVSS and temperature. • Measured SAOR decreased with increasing MLVSS 1.1‒8.7 g/L. • Temperature coefficient (θ) decreased with increasing MLVSS. • Nitrification process was dynamically simulated based on laboratory-scale SBR tests. • A modified model was successfully validated in pilot-scale SBR systems. Measurement and predicted variations of ammonia oxidation rate (AOR) are critical for the optimization of biological nitrogen removal, however, it is difficult to predict accurate AOR based on current models. In this study, a modified model was developed to predict AOR based on laboratory-scale tests and verified through pilot-scale tests. In biological nitrogen removal reactors, the specific ammonia oxidation rate (SAOR) was affected by both mixed liquor volatile suspended solids (MLVSS) concentration and temperature. When MLVSS increased 1.6, 4.2, and 7.1-fold (1.3‒8.9 g/L, at 20°C), the measured SAOR decreased by 21%, 49%, and 56%, respectively. Thereby, the estimated SAOR was suggested to modify when MLVSS changed through a power equation fitting. In addition, temperature coefficient (θ) was modified based on MLVSS concentration. These results suggested that the prediction of variations ammonia oxidation rate in real wastewater treatment system could be more accurate when considering the effect of MLVSS variations on SAOR.     

Potential Environmental Benefits from Increased Use of Bioenergy in China

Because of its large population and rapidly growing economy, China is confronting a serious energy shortage and daunting environmental problems. An increased use of fuels derived from biomass could relieve some demand for nonrenewable sources of energy while providing environmental benefits in terms of cleaner air and reduced emissions of greenhouse gases. In 2003, China generated about 25.9 × 10⁸ metric tons of industrial waste (liquid + solid), 14.7 × 10⁸ metric tons/year (t/y) of manure (livestock + human), 7.1 × 10⁸ t/y of crop residues and food-processing byproducts, 2 × 10⁸ t/y of fuelwood and wood manufacturing residues, and 1.5 × 10⁸ t/y of municipal waste. Biofuels derived from these materials could potentially displace the use of about 4.12 × 10⁸ t/y of coal and 3.75 × 10⁶ t/y of petroleum. An increased bioenergy use of this magnitude would help to reduce the emissions of key air pollutants: SO₂ by 11.6 × 10⁶ t/y, NO_X by 1.48 × 10⁶ t/y, CO₂ by 1.07 × 10⁹ t/y, and CH₄ by 50 × 10⁶ t/y. The reduced SO₂ emissions would be equivalent to 54% of the national emissions in 2003, whereas those for CO₂ are 30%. It is important to recognize, however, that large increases in the use of biomass fuels also could result in socioeconomic and environmental problems such as less production of food and damage caused to natural habitats.