Comparative evaluation of batch and continuous process biogas production from animal wastes

The production of biogas, an alternative source of energy from animal wastes, was investigated in the laboratory scale using the simple single-state digesters. In this study, a comparison between two feed processes, a batch feeding process and a continuous feeding process, both within mesophilic temperature ranges was carried out. The digesters were fed with mixture of cow dung and poultry droppings and operated at ambient temperature of 30°C as baseline and temperatures of 32?45°C for 30 days. In this study, the optimum temperature for biogas production from the blends of the animal wastes was determined as controlled heat was supplied to the digester. Results obtained indicate maximum biogas yield of 3.603 litres from the digestion of the animal wastes at temperature of 370°C in the continuous process while maximum biogas yield of 2.685 litres was obtained at temperature of 400°C for the batch process.     

Effect of temperature on the biodiesel yield from Nigerian physic nut,castor bean,dika nut and sandbox seed oils

Biodiesel fuels were synthesised from Nigerian physic nut seed (Jatropha curcas), castor bean seed (Ricinus communis), dika nut (Irvingia gabonensis) and sandbox seed (Hura crepitans) oil. The direct base-catalysed transestetification process was employed in the biodiesel production using methanol and sodium hydroxide (NaOH) as alcohol and catalyst, respectively. The trans esterification process involved 500 ml of J. curcas, castor bean seed, dika nut and sandbox seed oils, 100 ml of methanol and 1.0% of NaOH by weight for each oil. The process was carried out at different reaction temperatures in order to examine the effect of temperature on biodiesel yield of the oils. An average maximum biodiesel yield of 89.00% at 50°C, 61.50% at 45°C, 74.33% at 50°C and 88.50% at 55°C were obtained for Jatropha, castor, dika nut and sandbox oils, respectively. The result showed that the biodiesel yield from the various oils increased with temperature up to certain points beyond which it decreased.     

Effect of co-digestion agricultural-industrial residues: various slurry temperatures

The main objective of this study is to investigate the effect of co-digestion using industrial-agro waste and operating temperature of digester slurry to enhance the biogas and methane yield. The anaerobic digestion process is carried out by using a floating dome type bio-digester with the capacity of 1?m³. The co-digestion of press mud and rice straw with the ratio of 1:1, slurry temperature mesophilic range of (30–40°C) and thermophilic raange of (41–55°C) is used in this study. The maximum generation of daily biogas and weekly methane yield obtained were about 190?L/day and 55% in the case of the thermophilic condition. The lowest generation of daily biogas and weekly methane yield obtained were about 130?L/day and 33% in the case of mesophilic condition. The 10 percentage of cow dung is used as an inoculum of the digester and 30 days of hydro retention time for both the temperature ranges. The methane and biogas yield is at its peak and there was a faster hydro retention time in thermophilic range temperature at 52°C.     

Effect of inlet charge temperature on a diesel-fuelled homogeneous charge compression ignition engine

In this work, experimental investigations were carried out on a diesel-fuelled homogeneous charge compression ignition (HCCI) engine with different inlet charge temperatures such as 80°C, 90°C, 100°C, 110°C and 120°C. Initially, the HCCI engine was operated under normal room temperature from no load to full load. Secondly, the HCCI engine was operated with different inlet charge temperatures and the effect of charge temperature on the HCCI engine output was analysed. In general, the HCCI engine has ultra-low NO_x and smoke emissions. From this study, it was observed that the level of NO_x emission increased with increasing inlet charge temperature within a certain limit and then reduced. However, smoke emission was reduced with increasing inlet charge temperature. The charge temperature of 100°C shows the maximum reduction of smoke emission is about 23 HSU. Similarly the exhaust emissions of CO and HC were reduced than the other charge temperatures. The specific fuel consumptions were increased with increasing charge temperature.     

Experimental Study on Fire Behaviors of Kerosene/Additive Blends

The widely used fuels in practical are blended fuel whose combustion characteristics is more complex than those of the single-component fuel in real fire scenarios. The fire behaviors of aviation kerosene/diethylene glycol dimethyl ether (DGM) blends (R-D) and aviation kerosene/ethanol (R-E) blends were studied using a cone calorimeter. The parameters of pool fires, including the ignition time, burning rate, fuel temperature, heat release rate and combustion yield, were investigated. Janssens’ method was adopted to analyze the ignition times of the two blends. Two types of representative burning processes for blended fuel pool fires were identified. For R-D blends, the burning process is similar to that for typical pure fuels. The process for R-E blends, however, is novel, having two obvious burning processes due to the appearance of an intermediate decay stage. The fuel exhaust mass fraction (approximately 15%) was found to be almost constant throughout the intermediate decay stage. The fuel temperature during the experiment indicated that the liquid surface boiling temperature of R-D blends ranges from 162°C to 200°C depending upon the composition of these blends. For R-E blends, the initial boiling temperature is affected by the ethanol ratio, while the boiling temperature in the second process is equal to the boiling temperature of pure RP-3 kerosene. When the ethanol ratio is lower than 40%, the initial boiling temperature of R-E blends is approximately 120°C; when the ethanol ratio is higher than 40%, the boiling temperature is equal to the boiling point of ethanol. A method for calculating the burning rate of each component in the burning processes of the two blends is put forward, with the results agreeing well with the interpretation of the two burning processes. The ratio of the combustion yield CO₂/CO and the carbon conversion ratio increase with the oxygenated fuel ratio, indicating that the combustion is more complete when oxygenated fuel is added. These results will be useful for fire hazard assessment and firefighting in terms of fuel storage and transportation.     

Effects of membrane electrode assembly fabrication parameters on the proton exchange membrane fuel cell performance

In this paper, experimental investigation focuses on analysing the simultaneous influences of four different fabrication parameters, including carbon loading in GDL, Nafion content in CL, drying temperature of CL and hot pressing temperature. Active area of the MEAs was 25?cm² and characterisation of them was carried out by a 700?W fuel cell test station. Results show that the existence of MPL in GDL can improve performance of the PEMFC because of creating an even and steady surface which decreases ohmic resistance. The results confirm that the robustness of the optimum fabrication parameters influence performance of the cell. Optimum values of the parameters are: carbon loading in GDL, 3?mg?cm^?2; catalyst drying temperature, 60°C and Nafion content, 45%; but hot pressing temperature effect was lower than the other parameters. The expected performance of the fuel cell at optimum condition is 184.447?mW?cm^?2.     

CI engine performance during cold weather condition using preheated air and engine by waste energy

ABSTRACT

The aim of the current research is to experimentally investigate the performance, combustion and emission parameters of a compression ignition engine in the discharging and air preheating mode during the cold weather condition. For preheating the engine, a thermal energy storage device using phase-change material (PCM) and for preheating the inlet air an air preheater is used. From the results, it is observed that the engine temperature increases with time from 15°C to 27°C in 840?s. PCM temperature rises from 15°C to 60°C in 3000?s. during charging and while in discharging it decreases from 45°C to 30°C within the same time period. Brake thermal efficiency increases and brake-specific fuel consumption decreases with increase in load. Air-preheated diesel gives maximum cylinder pressure as compared to normal diesel. Carbon monoxide and hydrocarbon emissions are reduced during discharging and air preheating as compared to cold weather emission.     

Synthesis and characterisation of biodiesel from Nigerian physic nut,castor bean,dika nut and sandbox seed oils

Biodiesel fuels were synthesised from Nigerian physic nut seed (Jatropha curcas), castor bean seed (Ricinus communis), dika nut (Irvingia gabonensis) and sandbox seed (Hura crepitans) oil. The direct base-catalysed transestetification process was employed in the biodiesel production using methanol and sodium hydroxide (NaOH) as alcohol and catalyst, respectively. The transesterification process involved 500 ml of J. curcas, castor bean seed, dika nut and sandbox seed oils, 100 ml of methanol and 1.0% of NaOH by weight for each oil. The process was carried out at different reaction temperatures in order to examine the effect of temperature on biodiesel yield of the oils. An average maximum biodiesel yield of 89.00% at 50 °C, 61.50% at 45 °C, 74.33% at 50 °C and 88.50% at 55 °C were obtained for Jatropha, castor, dika nut and sandbox oils, respectively. The calorific values of diesel decreased from 42.7 to 42.475, 41.48, 42.330 and 42.13 MJ/kg with a blend of 10% of physic nut, castor bean, dika nut and sandbox seed biodiesel, respectively. The calorific values of the produced biodiesel from physic nut, castor bean, dika nut and sandbox seed oils are 40.45, 30.50, 39.00 and 37.00 MJ/kg, respectively. The cetane number, kinematic viscosity at 40 °C and pour point of the produced biodiesel are 59.4, 4.20 mm²/s and?1°C for physic nut biodiesel; 50, 10.75 mm²/s and?45°C for castor biodiesel; 52, 3.20 mm²/s and?6°C for dika nut biodiesel and 50, 4.20 mm²/s and 6 °C for sandbox seed biodiesel, respectively. The results showed that the addition of biodiesel to diesel generally increases the density, kinematic viscosity, flash point and pour point but, on the other hand, reduces the calorific value of the produced blend.     

Disinfection by in-duct ultraviolet lamps under different environmental conditions in turbulent airflows

In this study, we investigated the effects of environmental factors such as airflow velocity, relative humidity (RH), temperature, and duct reflectance on the performance of in-duct UVC lamps. Staphylococcus epidermidis, Pseudomonas alcaligenes, and Escherichia coli were used as the test bacteria. The UV irradiance, disinfection efficacy, and UV susceptibility constant (Z value) of the test bacteria were experimentally determined. The results showed that the UV disinfection efficacy decreased as the airflow velocity and RH increased. The maximum UV disinfection efficacy was obtained at temperature of 20-21°C compared with the performance at lower temperature (15-16°C) and higher temperature (25-26°C). When the RH increased from 50% to 90%, the Z values of airborne bacteria reduced by 40%, 60%, and 38% for S epidermidis, P alcaligenes, and E coli, respectively. Besides, susceptibility constants had lower values under both cooling temperature (15-16°C) and heating temperature (25-26°C) compared with that under the temperature of 20-21°C. It was observed that S epidermidis generally had the highest resistance to the UV irradiance. The results also showed that the UV disinfection efficacy was lower in the duct with a black surface than in the clean duct.     

Effect of temperature on the anaerobic thermophilic conversion of volatile fatty acids by dispersed and granular sludge

The effect of temperature on the rate of volatile fatty acid (VFA) conversion by thermophilic methanogenic sludge, cultivated at 55°C, was studied using both batch activity tests and continuous flow experiments. The temperature dependence of acetate conversion in the range between 37–70°C could be described by an Arrhenius derived model when dispersed sludge with a low specific activity was used. For this sludge the optimum acetate conversion rate was found at 65°C. However, the maximum acetate utilization rate was not affected by temperature in the range between 50°C to 65°C when granular sludge with a high specific methanogenic activity was used. Crushing the granules led to a 2 to 3 fold increase in the maximum activity at 60–65°C, indicating that the conversion rate was very likely limited by the diffusion rate of acetate into the granules. Similar results were obtained with butyrate as the substrate. The temperature dependence of the crushed granules was similar to that of the less active dispersed sludge. In contrast, the thermophilic propionate oxidation rate was highest with the intact granular sludge while a similar temperature dependence was found for both the granular and dispersed sludges. The affinity for VFA increased with decreasing temperature. This phenomenon was most pronounced for the granular sludge. The thermophilic treatment of a VFA-mixture in a UASB reactor appeared to be only slightly affected by temperature when moderately low loading rates were applied, i.e. 20 kg COD·m⁻³·d⁻¹. However, temperature had a strong effect applying loading rates of 40–90 kg COD·m⁻³·d⁻¹ accompanied with high effluent VFA concentrations. The results reveal a high thermostability of the thermophilic wastewater treatment process in the range 45–60°C if “high-rate” reactors with a granular sludge bed are used.     

Spot Fire Ignition of Natural Fuels by Hot Aluminum Particles

The ignition of combustible material by contact with hot metal particles is an important pathway by which wildland and urban spot fires are started. This work examines how fuel characteristics such as density, morphology and chemical composition effect the ability of the fuel to be ignited by a hot metal particle. Fuels were prepared out of three materials: alpha-cellulose, a barley/wheat/oat grass blend, and pine needles. Each material was prepared as a powder and as larger, long pieces: strips of cellulose paper, loose grass, and pine needles. These fuels are representative of thermal insulation (cellulose strips), dry grasses (grass blend), forest litter (pine needles) and duff (powders). Aluminum particles ranging from 2 mm to 8 mm in diameter heated to temperatures between 575°C and 1100°C were dropped onto these fuels. The particle temperature required for ignition becomes higher as the particle size decreased. The results show that the required temperatures for ignition of powders were lower, with this trend particularly pronounced for the alpha-cellulose fuels. The biomass fuels required higher temperature particles to ignite, indicating that the presence of other ligno-cellulosic materials make ignition more difficult.     

Combustion characteristics of the direct injection diesel engine fuelled with corn oil methyl ester

Petroleum-based fuels is a finite resource that is rapidly depleting. Consequently, petroleum reserves are not sufficient enough to last many years. In this research, an experimental investigation has been performed to give insight into the potential of biodiesel as an alternative fuel for direct injection (DI) diesel engines. The experimental work has been carried out to estimate the combustion characteristics of a single-cylinder, four-stroke, DI diesel engine fuelled with corn oil methyl ester (COME) and diesel blends. The COME was preheated to temperatures namely 50°C, 70°C and 90°C before it was supplied to the engine. The optimised preheated temperature of 70°C was chosen based on the higher brake thermal efficiency and lower specific fuel consumption. The performance, emission and combustion characteristics are evaluated by running the engine with COME and diesel blends at this preheated temperature. In this paper, the combustion characteristics are only discussed. The combustion characteristics such as ignition delay, maximum rate of pressure, heat release rate, cumulative heat release rate, mass fraction burned and combustion duration of COME methyl ester and diesel were evaluated and compared with neat diesel. The rate of pressure rise and maximum combustion pressure inside the cylinder were high for COME blends compared with neat diesel. The heat release rate of diesel is higher compared with COME blends. The ignition delay and combustion duration are decreased for COME blends compared with neat diesel. The cumulative heat release rate and mass fraction burnt of COME blends are higher than neat diesel.     

Electrochemical conversion of switchgrass and poplar in molten carbonate direct carbon fuel cell

One way of sustaining fuel cell technology is using renewable and sustainable energy means provided by biomass. This article explores switchgrass and poplar in a molten carbonate electrolyte direct carbon fuel cell. It investigates their electrochemical conversions and provides results of power density, current density, open circuit voltage (OCV) and other parameters. The biomasses were pyrolysed at 800°C to produce carbon fuels. Biomass carbon fuels were mixed with molten carbonate and subjected to different operating conditions (600–800°C) in the fuel cell. The electrochemical performances of the poplar fuel were better than those experienced with switchgrass fuel. At 800°C the OCV of poplar fuel (1.08?V) has higher output than switchgrass (0.87?V). The peak power density recorded for poplar fuel was 23.91?mW/cm² while switchgrass fuel was lower at 21.60?mW/cm². Poplar fuel (81.53?mA/cm²) gave a maximum current density with switchgrass fuel lower at 74.00?mA/cm².     

Experimental study and analysis of air heating system using a parabolic trough solar collector

An experimental study of air heating system was carried out using a parabolic trough collector with a U-tube aluminium heat exchanger. An evacuated tube placed at the focal length of the parabolic trough collected the solar radiations reflected from the surface of parabolic trough. The air was used as a working fluid, which was heated by passing it through a U-shaped aluminium heat exchanger placed inside the evacuated tube. It was found that efficiency of the parabolic trough collector depends on the mass flow rate, solar intensity and use of fins. It was observed that by using fins at a high mass flow rate of 4.557?kg/h, the maximum temperature of 126°C was achieved which is 13.27% more than the maximum temperature obtained without fins. Furthermore, for a low-mass-flow rate of 1.69?kg/h, the maximum temperature obtained was 149°C.     

Thermal Comfort in Nurseries

The mean skin temperatures as well as the temperatures of the hands, feet and forehead of small children were measured in nurseries at air temperatures of 20°C and 22°C. Differences were studied between babies remaining still, babies crawling on tiling, wooden floors or rubber foam groundsheets, and older walking children. The results suggest that an air temperature of 22°C leads to skin temperatures comparable to those observed for resting adults in comfort, while 20°C seems to induce a slight but overall cooling of the body and considerable cooling of the extremities for the babies remaining still. The material of floor coverings should be considered carefully and preference given to low conductivity materials. Assuming that the optimum skin temperatures are the same for children and for adults, it appears that the PMV-PPD approach can be used to predict this particular optimum comfort condition, provided an increase of 20 wm^?2 is taken into account for the metabolic rate of the small children.     

The Effects Of Air Temperature And Relative Humidity On Thermal Comfort In The Office Environment

The objective of this study was to assess the effect of air humidification and temperature on thermal comfort in sedentary office work. A blinded twelve-period cross-over trial was carried out in two similar wings of an office building, contrasting 28–39% steam humidification with no humidification, corresponding to 12–28% relative humidity. The length of each period was one working week. The study population was 169 workers who judged their thermal sensations in a weekly questionnaire. The percentage of dissatisfied was lowest when the air temperature was 22 °C. At 22 °C an increase in relative humidity raised the mean thermal sensation only slightly. At 20 °C when the air was humidified there were fewer workers who judged their air temperature as being too low. On the other hand, at 24 °C humidification increased the percentage of workers who judged their air temperature to be too high. The percentage of dissatisfied increased rapidly when the air temperature was outside of its optimum value, 22 °C. The percentage of workers complaining about draft increased when the air temperature was lower than 22 °C. Thus we consider that the temperature range from 20 to 24 °C during wintertime may be too wide without individual temperature control from the point vzew of thermal comfort. We recommend that the air temperature should be kept between 21 and 23 °C if no individual control is available. The best solution would be individual temperature control permitting adjustment of the temperature at 22 ± 2 °C.     

Operating strategies for acid phase digestion: an industrial case study

Acid phase digestion was investigated for enhanced operation in an industrial wastewater treatment plant. In particular, sludge retention time (SRT), temperature and pH were assessed for determining optimal conditions under operating constraints. Volatile fatty acid (VFA) production and soluble chemical oxygen demand (SCOD) were the key process parameters used to assess system performance. Increase in SRT from 0.8 to 1.4 days (at 22°C) had moderate effect on VFA production (approximately 15% increase), achieving a maximum VFA production of 3600 mg/L. High VFA production rate (0.101 ± 0.035 mg/mgVS.d) was obtained at the highest operating retention time during summer (27°C). The degree of solubilisation of particulate organic matter increased with temperature and retention time. Despite an increase in SCOD (6472 ± 873 mg/L max.), a corresponding increase in VFA was not observed. SCOD showed a linear correlation with decrease in pH, while acidogenesis (SCOD conversion to VFA) was found to be favourable at a pH of 4.5.     

Modelling and simulation of single- and triple-junction solar cells using MATLAB/SIMULINK

The main objective of this paper is to determine the single- and triple-junction solar cells’ I–V and P–V curves, define maximum voltage, current, and power. The paper demonstrates and analyses different environmental conditions that affect the solar cells, such as temperature and irradiance. The performance of single- and triple-junction solar cells is evaluated by analysing the fill factor. In this work, the analysis of single- and triple-junction solar cells is carried out through software simulation. Different conditions demonstrated to observe the results of this variation in both single- and triple-junction cells, such as observing the solar cell behaviour under variation of temperature between 15°C (288.315?K) and 45°C (318.15?K) for the single-junction cell and between 268.15?K (?5°C) and 348.15?K (75°C) for the triple-junction cell to observe the effect of temperature on open circuit voltage, the variation of different levels of irradiance to observe its effect on open circuit voltage and current density on both cell types, and cell performance evaluation using the fill factor concept. Practical results used in this paper are obtained from Clyde Space’s laboratories. Tests of Clyde Space were done using halide lamps to simulate the irradiation conditions with irradiance of half sun which is equivalent to 0.05?W?cm^?2. The operation was done under temperature of 40°C which is equivalent to 313.15?K.     

Thermal comfort,perceived air quality,and cognitive performance when personally controlled air movement is used by tropically acclimatized persons

In a warm and humid climate, increasing the temperature set point offers considerable energy benefits with low first costs. Elevated air movement generated by a personally controlled fan can compensate for the negative effects caused by an increased temperature set point. Fifty‐six tropically acclimatized persons in common Singaporean office attire (0.7 clo) were exposed for 90 minutes to each of five conditions: 23, 26, and 29°C and in the latter two cases with and without occupant‐controlled air movement. Relative humidity was maintained at 60%. We tested thermal comfort, perceived air quality, sick building syndrome symptoms, and cognitive performance. We found that thermal comfort, perceived air quality, and sick building syndrome symptoms are equal or better at 26°C and 29°C than at the common set point of 23°C if a personally controlled fan is available for use. The best cognitive performance (as indicated by task speed) was obtained at 26°C; at 29°C, the availability of an occupant‐controlled fan partially mitigated the negative effect of the elevated temperature. The typical Singaporean indoor air temperature set point of 23°C yielded the lowest cognitive performance. An elevated set point in air‐conditioned buildings augmented with personally controlled fans might yield benefits for reduced energy use and improved indoor environmental quality in tropical climates.     

Thermophilic aerobic wastewater treatment of waste metalworking fluids

An investigation into aerobic biological wastewater treatment was conducted over the temperature range 25–75°C in a semi‐batch bioreactor using waste metalworking fluids (MWFs) generated from Liverpool John Moores University's engineering workshop. The best treatment performance in terms of chemical oxygen demand (COD) removal occurred at 50°C (97.27%), with an operational time of 77.5 h. Cell viability was observed throughout the operation and it was found that higher temperature did not directly correlate to low viability. Effluent turbidity reduced considerably from 35 to 50°C and increased thereafter. Even when the system encountered alkaline shock, the overall performance was not affected, thus indicating how stable the system was. The results of this study indicate that an existing industrial‐activated sludge plant could be used to treat waste MWFs under thermophilic conditions. The COD reduction was significant but further investigation into biodegradation of recalcitrant compounds is needed to achieve optimum performance.