Instantaneous char reaction of biomass particles in a hot gas flow with fluctuating temperature

Char reaction is an important stage of the combustion processes of biomass particles. It dominates the burnout of biomass particles. The instantaneous char reaction processes of biomass particles in a hot gas with temperature fluctuation are studied. Two types of biomass fuels, i.e. pine and thistle, are chosen for the present investigation. The instantaneous mass variations of biomass particles with initial diameters of 100, 200, and 300 μm are calculated under different conditions. The gas temperature fluctuation leads to faster mass loss for both pine and thistle particles. The char reaction of biomass particles is further enhanced by increase in the fluctuation amplitude of gas temperature.     

Lean methane premixed combustion over a catalytically stabilized zirconia foam burner

This study experimentally investigates lean methane/air premixed combustion in a catalytic zirconia foam burner. The burner is packed with an inert perforated alumina plate at the inlet preheating zone and with catalytic zirconia foams at the combustion zone. Catalytic foams are prepared by using a modified perovskite catalyst (LaMn_0.4Co_0.6O₃), in which the transition metal ion Co is partially substituted by Mn and supported by inert zirconia foam. Results indicate that the flame stability limits of both catalytic and inert burners expand with increasing equivalence ratios. The stable combustion region of the catalytic burner is larger than that of the inert burner. The heterogeneous catalytic combustion effect can decrease and increase the lower and upper flame stability limits, respectively. The central temperatures of the flame fronts are higher in the catalytic burner than in the inert burner. The pressure drops of the catalytic burner are almost equal to those of the inert burner in cold flows but are significantly higher than those in the inert burner in reaction flows. Less amounts of carbon monoxide, nitric oxides, and unburned hydrocarbon emissions are detected in the catalytic burner relative to the inert burner. The thermal radiation efficiencies of the catalytic burner vary between 0.24 and 0.39 and are favorably superior to those of the inert burner, ranging from 0.11 to 0.20.     

Litter decomposition rate and nutrient release from different litter forms in a Himalayan alpine ecosystem

Observations on above ground litter decomposition and nutrient release in alpine ecosystem of the Himalaya were carried out. Monthly variation was observed for above ground litter crop and it was higher in the protected sites (PR) when compared with unprotected sites (UNPR). Turnover rate (TR) and time (TT) was also higher in PR sites and it corresponded to maximum net accumulation of standing dead and litter biomass. This resulted into low litter disappearance and therefore, low nutrient fluxes as well. Comparatively, potassium content was a maximum followed by N and OC in above ground crop of litter with significant variation among the sites (P < 0.001 and 0.005, respectively). It was observed that only 9–12% litter of various categories was decomposed annually at the rate of 0.1–0.13%. Overall, decomposition process was a maximum during active growth season and only 13.2–16.2% of total litter was decomposed during the winter months (December–March). Release of OC and NPK to soil organic matter through the decomposition of various litter types was also observed and the pattern of release was similar to that of disappearance channel. All these parameters are reported and possible reasons are described in the present paper.     

Chemical-looping with oxygen uncoupling for combustion of solid fuels

Chemical-looping with oxygen uncoupling (CLOU) is a novel method to burn solid fuels in gas-phase oxygen without the need for an energy intensive air separation unit. The carbon dioxide from the combustion is inherently separated from the rest of the flue gases. CLOU is based on chemical-looping combustion (CLC) and involves three steps in two reactors, one air reactor where a metal oxide captures oxygen from the combustion air (step 1), and a fuel reactor where the metal oxide releases oxygen in the gas-phase (step 2) and where this gas-phase oxygen reacts with a fuel (step 3). In other proposed schemes for using chemical-looping combustion of solid fuels there is a need for an intermediate gasification step of the char with steam or carbon dioxide to form reactive gaseous compounds which then react with the oxygen carrier particles. The gasification of char with H₂O and CO₂ is inherently slow, resulting in slow overall rates of reaction. This slow gasification is avoided in the proposed process, since there is no intermediate gasification step needed and the char reacts directly with gas-phase oxygen. The process demands an oxygen carrier which has the ability to react with the oxygen in the combustion air in the air reactor but which decomposes to a reduced metal oxide and gas-phase oxygen in the fuel reactor. Three metal oxide systems with suitable thermodynamic properties have been identified, and a thermal analysis has shown that Mn₂O₃/Mn₃O₄ and CuO/Cu₂O have suitable thermodynamic properties, although Co₃O₄/CoO may also be a possibility. However, the latter system has the disadvantage of an overall endothermic reaction in the fuel reactor. Results from batch laboratory fluidized bed tests with CuO and a gaseous and solid fuel are presented. The reaction rate of petroleum coke is approximately a factor 50 higher using CLOU in comparison to the reaction rate of the same fuel with an iron-based oxygen carrier in normal CLC.     

Pyrolysis of commingled waste textile fibers in a batch reactor: Analysis of the pyrolysis gases and solid product

The main object of this study was the investigation of the thermal recycling of commingled waste textile fibers, with the aim of the production of useful end products. Differential scanning calorimetry/Thermo gravimetric analysis (DSC/TGA) was applied to determine the thermal degradation characteristics of the commingled waste textile fibers and there are two peaks located at the temperature ranges of 299–360°C and 399–500°C. Commingled waste fiber was pyrolyzed in a nitrogen atmosphere in relation to three different temperatures (500, 600, and 700°C), heating rates (25 and 50°C min^?1), and retention times (15 and 30 min). The effect of the experimental conditions such as pyrolysis temperature, heating rates, and retention time on the formation of char and gas--liquid products was investigated and the product yields were determined from the rate of the weight loss. The highest conversion rate 82.9 wt.% liquid--gas product and 17.1 wt.% char product was achieved at 700°C. Pyrolysis gases were taken for every 7, 15, and 25 min and were analyzed for major components such as CO, CO₂, CH₄, and H₂ by gas chromatography. The pyrolysis char called as carbon black derived from the pyrolysis of commingled waste textile fibers was analyzed for a range of properties, including the elemental analysis, moisture content, ash content, calorific value, and trace metal analysis.     

Combustion features under different center of heat release of a diesel engine using dimethyl carbonate/diesel blend

Experiments were performed in a single cylinder common-rail diesel engine that adopts a low temperature premixed charge compression ignition (PCCI) mode. Combustion features of dimethyl carbonate (DMC)-diesel blends under various centers of heat release (COHRs) were revealed in details. With retarding of COHR, all the peaks of pressure and pressure rise rate and bulk gas temperature are postponed and declined in sequence. Normally, the crank angle of peak pressure is quite close to the COHR, while the peak of bulk gas temperature appears about 7°CA after COHR as a rule. The prolongation can be demonstrated at every stage of combustion such as q₁₀ and q₉₀ with the COHR being put backward. In addition, the heat release of diesel is completely slower than that of D10 fuel at various stages. Unfortunately, retarding of COHR implies a declining thermal efficiency of engines as well as a higher cyclic variation in general. Nevertheless, D10 blend has higher thermal efficiency than diesel thanks to high oxygen content of DMC and low boiling point that prompts better fuel atomization and complete combustion. Meanwhile, the cyclical variation of D10 is greater than diesel fuel owing to the low heat value, high latent heat of vaporization, and poor flammability of DMC. As a total, a comprehensive understanding of PCCI combustion features under different COHRs can be conducive to conducting effective management of combustion process and manipulating the subsequent emission performance to a favorable level.     

SIMULATED EFFECTS OF ALTERED SPILLWAY RELEASES ON THERMAL STRUCTURE AND KOKANEE GROWTH IN A COLORADO RESERVOIR1

ABSTRACT: In‐reservoir thermal and ecological effects of releasing some flows over the surface spillway at Blue Mesa Reservoir, Colorado, rather than routing all releases through the hypolimnetic outlet were evaluated using a calibrated and validated one‐dimensional thermal model (CE‐THERM) with a set of ecological models. Thermal model output indicated that surface water temperatures were influenced primarily by atmospheric conditions, but the release of warmer water over the spillway resulted in a thinner epilimnion and cooler metalimnetic water temperatures. Ecological model predictions indicated that spillway releases and associated temperatures resulted in lower growth rates for young‐of‐year (YOY) kokanee salmon (Oncorhynchus nerka) in the reservoir by up to 9 percent when compared with growth rates under baseline operations with no releases over the spillway. Kokanee growth rates were reduced under spillway release scenarios because lower temperatures not only affected metabolic rates, but limited the productivity of the zooplankton as well. Thus, altering the release regime with spillway discharges could have deleterious effects on Blue Mesa's YOY kokanee. However, in other reservoirs, distributing discharges among different elevations may provide managers with a mechanism to regulate temperatures to benefit species of concern that are facing challenges imposed by environmental conditions such as global warming.     

An Investigation of Thermal Decomposition Behavior of Hazelnut Shells

Turkey has a drastic potential in terms of biomass energy and it would be of utmost importance for our energy mix if this huge amount of energy is to be utilized. Thermochemical conversion is the most dominant one among the energy conversion processes. The carbonization process is the key point in determining the kinetic parameters of the fuels utilized. Thereafter, the kinetic parameters obtained from carbonization would be utilized in designing the thermochemical conversion equipments. In this study, the thermal decomposition behavior of hazelnut shells was investigated via dynamical thermogravimetry (TG) under N₂ atmosphere. In order to determine the effects of heating rate and gas flow rate, the experiments were performed in four different heating rates of 5, 20, 50, and 100 K/min and two different nitrogen flow rates of 50 and 100 cm³/min. As the heating rate was increased, peak temperature was increased, maximum temperature shifted to the right (higher T zones) and the maximum rate of weight loss was increased. In addition, lignin decomposition temperature interval was decreased whereas; cellulose decomposition temperature interval was increased. Increasing the heating rate from 5 to 20 K/min, hemicellulose decomposition temperature interval was increased. Total weight loss was slightly increased by the increase of gas flow rate. Kinetic parameters were calculated according to Coats Redfern method. It was found that activation energies of thermal decomposition reactions of hazelnut shell varied between 1.30 and 32.19 kJ/mol.     

Vermiculture and waste management: study of action of earthworms Elsinia foetida, Eudrilus euginae and Perionyx excavatus on biodegradation of some community wastes in India and Australia

The practice of vermiculture is at least a century old but it is now being revived worldwide with diverse ecological objectives such as waste management, soil detoxification and regeneration and sustainable agriculture. Earthworms act in the soil as aerators, grinders, crushers, chemical degraders and biological stimulators. They secrete enzymes, proteases, lipases, amylases, cellulases and chitinases which bring about rapid biochemical conversion of the cellulosic and the proteinaceous materials in the variety of organic wastes which originate from homes, gardens, dairies and farms. The process is odour free because earthworms release coelomic fluids in the decaying waste biomass which has anti-bacterial properties which kills pathogens. The species used in India were Indian blue (Perionyx excavatus), African night crawler (Eudrilus euginae) and the Tiger worm (Elsinia foetida). E. foetida was used in Australia. E. euginae was found to have higher feeding, growth and biodegradation capacity compared to other two species.Earthworm action was shown to enhance natural biodegradation and decomposition of wastes (60–80 percent under optimum conditions), thus significantly reducing the composting time by several weeks. Within 5 to 6 weeks, 95–100 percent degradation of all cellulosic materials was achieved. Even hard fruit and egg shells and bones can be degraded, although these may take longer.     

肼类燃料在大气中的迁移转化

肼类燃料（肼、甲基肼和偏二甲肼）排放于大气中时,可与大气组分;氧、二氧化碳、水、臭氧、氮氧化物、二氧化硫等发生反应,降解主要产物是氮气、水、甲烷或偏除,在紫外光照射条件下可发生光解。本文详细论述了肼、甲基肼和偏二甲肼与大气中的氧气、臭氧和氮氧化物的反应历程及降解机理,其中某些降解产物毒性比肼类燃料本身更大。     

Comparison of jatropha and karanja biofuels on their combustion characteristics

Biofuel blends produced from Jatropha (Jatropha curcas) and Karanja (Pongamia pinnata) oil were evaluated for their combustion properties. Two kinds of blends (regular diesel with Jatropha and Karanja oil) were prepared at 20% volume to the diesel and tested as alternative fuels in single cylinder (vertical), water-cooled, direct injection diesel engine at the rated speed of 1500 rpm. The performance of the engine in terms of thermal efficiency at full load for diesel was 30%. For Jatropha and Karanja biodiesel blends, the thermal efficiencies were 29.0% and 28.6%, respectively. The maximum cylinder pressure and ignition delay for biodiesel fuel blends are very close to that of regular diesel. Prolonged combustion was observed for Karanja oil blend in comparison to Jatropha oil blend. The combustion pattern also reveals the slow burning characteristics of vegetable oils and this study indicates that the blended biofuels have combustion characteristics that are similar to regular diesel fuels.     

A numerical study on the effects of EGR and spark timing to combustion characteristics and NOx emission of a GDI engine

EGR is one of the most significant strategies for reducing especially nitrogen oxides (NO_x) emissions from internal combustion engines. The thermal efficiency of spark ignition engines is lower than compression ignition engines because of its lower compression ratio. If the compression ratio is increased to obtain higher thermal efficiency, there may be a knocking tendency in spark ignition engines. EGR can be used in order to reduce NO_x emissions and avoid knocking phenomena at higher compression ratios. In-cylinder temperature at the end of combustion is decreased and heat capacity of fresh charge is increased when EGR applied. Besides EGR, spark timing is another significant parameter for reducing exhaust emissions such as nitrogen oxides, and unburned hydrocarbon (UHC). In this study the effects of EGR and spark timing on spark ignition engine were investigated numerically. KIVA codes were used in order to model combustion process. The combustion process has been modeled for a single cylinder, four stroke and gasoline direct injection (GDI) spark ignition engine. The results showed that in-cylinder pressure and heat release rate decrease as EGR ratio increase. In-cylinder pressure increases with the advancing of spark timing. Advancing spark timing increases the heat release rate and in-cylinder temperature. The simulation results also showed that EGR reduced exhaust gas temperature and NO_x emissions.     

溶剂型聚氨酯涂料废物热解特性及动力学研究

采用TG研究溶剂型聚氨酯涂料废物在不同升温速率、N2气氛影响下的热解特性规律。升温速率取5,10,20,30℃/min;气氛取N2气氛(50 m L/min);实验温度范围为20~800℃。研究表明,随着升温速率的增大,涂料废物热解反应各阶段起始温度、终止温度、最大失重速率温度均向高温方向移动。在500℃时,涂料废物的热分解已基本完成。运用Kissinger法和Flynn-Wall-Ozawa法进行热解动力学分析,得到溶剂型聚氨酯涂料废物热解阶段的表观活化能为196.053 3 kJ/mol。     

3种腐熟剂促进玉米秸秆快速腐解特征

为筛选出适宜东北寒冷区快速腐解秸秆的腐熟剂,通过网袋腐解试验明确施入3种秸秆腐熟剂对玉米秸秆生物量及养分释放的影响。结果显示：经过100 d的腐解,玉米秸秆生物量失重率随着时间的延长逐渐增加,玉米秸秆失重率为57.1%-64.1%,其中以施用3号秸秆腐熟剂的玉米秸秆生物量失重率最高,为64.1%。施入不同秸秆腐熟剂后玉米秸秆氮、磷、钾释放率分别为35.1%-57.2%、44.2%-59.6%、77.4%-89.7%,其中以3号腐熟剂的秸秆磷、钾素释放率最高。各处理有机碳矿化率呈相同的趋势,均随时间的延长逐渐增加,取样末期有机碳矿化率在65.3%-69.1%之间,且各处理间差异不明显。综上,以3号秸秆腐熟剂腐解秸秆的效果最好。     

Effects of fuel reactivity and injection timing on diesel engine combustion and emissions

Recent strategies for simultaneously reducing NOx and soot emissions have focused on achieving nearly premixed, low-temperature combustion (LTC) in diesel engines. A promising approach in this regard is to vary fuel reactivity in order to control the ignition delay and optimize the level of premixing and reduce emissions. The present study examines such a strategy by performing 3-D simulations in a single-cylinder of a diesel engine. Simulations employ the state-of-the-art two-phase models and a validated semi-detailed reaction mechanism. The fuel reactivity is varied by using a blend of n-heptane and iso-octane, which represent surrogates for gasoline and diesel fuels, respectively. Results indicate that the fuel reactivity strongly influences ignition delay and combustion phasing, whereas the start of injection (SOI) affects combustion phasing. As fuel reactivity is reduced, the ignition delay is increased and the combustion phasing is retarded. The longer ignition delay provides additional time for mixing, and reduces equivalence ratio stratification. Consequently, the premixed combustion is enhanced relative to diffusion combustion, and thus the soot emission is reduced. NO_x emission is also reduced due to reduced diffusion combustion and lower peak temperatures caused by delayed combustion phasing. An operability range is observed in terms of fuel reactivity and SOI, beyond which the mixture may not be sufficiently well mixed, or compression ignited. The study demonstrates the possibility of finding an optimum range of fuel reactivity, SOI, and EGR for significantly reducing engine out emissions for a given load and speed.     

Carbon Pool Dynamics in the Lower Fraser Basin from 1827 to 1990

/ To understand the total impact of humans on the carbon cycle, themodeling and quantifying of the transfer of carbon from terrestrial pools tothe atmosphere is becoming more critical. Using previously published data,this research sought to assess the change in carbon pools caused by humans inthe Lower Fraser Basin (LFB) in British Columbia, Canada, since 1827 anddefine the long-term, regional contribution of carbon to the atmosphere. Theresults indicate that there has been a transfer of 270 Mt of carbon frombiomass pools in the LFB to other pools, primarily the atmosphere. The majorlosses of biomass carbon have been from logged forests (42%), wetlands(14%), and soils (43%). Approximately 48% of the forestbiomass, almost 20% of the carbon of the LFB, lies within old-growthforest, which covers only 19% of the study area. Landfills are nowbecoming a major sink of carbon, containing 5% of the biomass carbonin the LFB, while biomass carbon in buildings, urban vegetation, mammals, andagriculture is negligible. Approximately 26% of logged forest biomasswould still be in a terrestrial biomass pool, leaving 238 Mt of carbon thathas been released to the atmosphere. On an area basis, this is 29 times theaverage global emissions of carbon, providing an indication of the pastcontributions of developed countries such as Canada to global warming andpossible contributions from further clearing of rainforest in both tropicaland temperate regions.KEY WORDS: Carbon pools; Global warming; Carbon release to atmosphere;Greenhouse effect     

Trace Gas Emissions from Biomass Burning from Northeast Region in India—Estimates from Satellite Remote Sensing Data and GIS

Biomass burning associated with shifting cultivation areas from the northeastern region of India is an important source of trace gas emissions in the Southeast Asian region. In the present study, satellite data pertaining to IRS-P4 OCM data and DMSP-OLS has been used to quantify the intensity, areal extent and amount of biomass burnt in the northeastern region states at district level. Trace gas emissions have been quantified both by using IPCC based emission ratios and ground based emission ratios obtained from field based studies. Areal estimates with respect to shifting cultivation areas from IRS-P4 OCM satellite data of 4th April 2000 suggested nearly 112.99 km² of the northeastern region of India affected due to shifting cultivation. In the study, DMSP OLS nighttime data has been used to capture the real time fires during the dry season. The results suggested high amount of fires during the March season when compared to April and May. Using the emission ratios obtained from the ground-based studies and IPCC emission ratios, the emissions for the individual non-CO₂ trace gases have been computed in a GIS framework using the biomass data, combustion factors and emission ratios. Results suggested emissions of 2.063 Mt CH₄, 17.94 Mt CO, 1.419 Mt N₂O, and 51.28 Mt NO _x and 2.643 Mt release of CH₄, 3.7204 Mt CO, 0.145 Mt N₂O, and 8.477 Mt NO _x , respectively, from biomass burning due to shifting cultivation for the year 2000, from the northeastern region in India. The study highlights the importance of Satellite Remote sensing data and GIS in quantifying the trace gas emissions from biomass burning.     

The Interactive Effects of Fire and Diversity on Short-Term Responses of Ecosystem Processes in Experimental Mediterranean Grasslands

We conducted a field experiment using constructed communities to test whether species richness contributed to the maintenance of ecosystem processes under fire disturbance. We studied the effects of diversity components (i.e., species richness and species composition) upon productivity, structural traits of vegetation, decomposition rates, and soil nutrients between burnt and unburnt experimental Mediterranean grassland communities. Our results demonstrated that fire and species richness had interactive effects on aboveground biomass production and canopy structure components. Fire increased biomass production of the highest-richness communities. The effects of fire on aboveground biomass production at different levels of species richness were derived from changes in both vertical and horizontal canopy structure of the communities. The most species-rich communities appeared to be more resistant to fire in relation to species-poor ones, due to both compositional and richness effects. Interactive effects of fire and species richness were not important for belowground processes. Decomposition rates increased with species richness, related in part to increased levels of canopy structure traits. Fire increased soil nutrients and long-term decomposition rate. Our results provide evidence that composition within richness levels had often larger effects on the stability of aboveground ecosystem processes in the face of fire disturbance than species richness per se.     

EFFECT OF pH ON PHOSPHORUS RELEASE DURING MACROPHYTE (ELEOCHARIS sp.) DECOMPOSITION1

ABSTRACT: Laboratory microcosms were used to evaluate the effect of pH on release of soluble reactive phosphorus (SRP) during aerobic decomposition of the aquatic macrophyte Eleocharis sp., which is common in oligotrophic Florida lakes. The total amount of SRP released during a 227-day incubation in the dark was independent of pH over the range 3.7 to 5.5, but initial rates of release were faster at the lowest pH. The results indicate that the low total phosphorus concentrations observed in many acidic lakes are not necessarily attributable to reduced rates of decomposition and nutrient mineralization at low pH, as some researchers have suggested.     

A Novel Solar Thermal Cycle with Chemical Looping Combustion

In this paper, we have proposed a thermal cycle with the integration of chemical-looping combustion and solar thermal energy with the temperature of about 500-600°C. Chemical-looping combustion may be carried out in two successive reactions between a reduction of hydrocarbon fuel with metal oxides and a reduced metal with oxygen in the air. This loop of chemical reactions is substituted for conventional combustion of fuel. Methane as a fuel and nickel oxides as an oxygen carrier were employed in this cycle. Collected high-temperature solar thermal energy is provided for the endothermic reduction reaction. The feature of the proposed cycle is investigated through Energy-Utilization Diagram methodology. As a result, at the turbine inlet temperature of 1200°C, the exergy efficiency of the proposed cycle would be expected to be about 4 percentage points higher than that of a conventional gas turbine combined cycle. Compared to the previous study of chemical-looping combustion energy systems, the proposed cycle with the integration of green energy and traditional hydrocarbon fuels will offer the possibility of both greenhouse gas mitigation, with green energy, and a new approach to the efficient use of solar energy.