Impacts of Fuel Inventory on Low Temperature Ignition Risk during Handling and Storage of Biomass

As modernisation takes place, fossil fuel burning is one of the quickest ways to meet the ever rising energy demand. The increasing emissions of greenhouse gases, particularly carbon dioxide, as a result of excessive fossil fuel burning had been blamed for global climate change. Vegetation-based biomass is a form of bioenergy and a recognised solid renewable fuel with potential to replace coal in combating anthropogenic climate change in the power generation sector. Nevertheless, it is not a straight forward case for biomass to replace coal since biomass is an extremely reactive fuel prone to self-heating leading to self-ignition. Spontaneous biomass ignition leading to disastrous fires during biomass handling and storage could be avoided if the causes of biomass low temperature ignition are well understood. Detailed studies on woody and herbaceous biomass fuels commonly used in UK power stations were examined according to several British Standards. On top of characterising all the biomass samples, BS EN 50281-2-1 and BS EN 15188 were adhered to specifically in investigating low temperature ignition during biomass handling and biomass storage respectively. Many power stations use a mix of different biomass in their fuel inventories which can lead to dusts of biomass mixtures. Thus the low temperature ignition characteristics of biomass blends have been studied. Other factors that may impact on ignition risks are binders (added to give strength to briquettes or pellets) and pretreatments (washing and torrefaction). Washing aims to improve ash properties towards the end of combustion process while torrefaction is used to increase the calorific value of biomass that is naturally lower than fossil fuels. The reaction kinetics of some biomass dust layers deposited on a constant temperature hot surface and corresponding ignition delay time were estimated mathematically. Results from minimum dust layer ignition temperature determination showed that all biomass, regardless of woody or herbaceous, with or without binder, before or after pre-treatments, had critically ignited within a very small temperature range. This was consistent with the results of self-ignition propensity risk ranking that concluded that biomass possess medium-high risk of self-igniting. An exception to this is torrefied biomass which had not sustained a much higher temperature before it critically ignited as compared with the untreated counterpart; unlike many anticipations and therefore, the low temperature ignition characteristics were discussed from many other aspects, mainly on the reduced particle size or dust layer density. For biomass storage, scaling up method and Frank-Kamenetskii method derived from Thermal Explosion Theory had been applied to forecast the critical ignition temperature and ignition delay time for large-scale industrial storage from smaller laboratory scale experiments. Non-negligible error was detected when extrapolating to industrial volume especially for the ignition delay time and appropriate recommendation was made as a possible remedy. Emissions when biomass smouldered and critically ignited that happened at 10˚C apart were examined with a three-stage emission sampling and compared, with the aims of obtaining a suitable biomass self-ignition indicator. Detailed studies were required since only one organic compound was detected to be consistently different between smouldering and critically-igniting biomass dust. Within this small temperature difference, different volatile species with respective intensities had been modelled with FG-BioMass software. Towards the end of this work, conclusions were drawn for each section and suggestion of combining both pre-treatments with binder addition were recommended for further studies. The work in the thesis provides a large data-set which will help inform power plant operators in their dust management risks. The laboratory-scale experiments give a useful risk-ranking for dust layer ignition, but uncertainties in ignition-delay times, especially for large biomass quantities, indicate that improvements are required to BS EN 15188 (biomass storage test) to enable scaling-up with more certainty

Facile synthesis of carbon nanoparticles from sodium alginate via ultrasonic-assisted nano-precipitation and thermal acid dehydration for ferric ion sensing

Carbon nanoparticles have emerged as a promising alternative to the well-known quantum dots in many biological applications due to their excellent optical properties and biocompatibility. It has received considerable attentions from researchers especially in the aspects of producing these carbon nanomaterials via easier and cheaper synthetic routes. On this motivation, we hereby report an economical and facile synthesis of carbon nanoparticles from alginate via a simple two-step procedure; nano-precipitation through ultrasonication followed by thermal acid carbonisation. Nano-precipitation was first performed on the alginate stock solution to produce nanoparticles with controlled morphology. Precipitation was performed in acidic solution that has coagulated the alginate chains into nanoparticles. Ultrasonic treatment was found crucial to assist the formation of nanoparticles that were more homogenous in the size distribution at around 100 nm. The shape was also more spherical as compared to those without ultrasonic treatment. In the carbonisation step, thermal dehydration was employed using concentrated sulphuric acid that has successfully converted the preformed alginate nanoparticles into carbon nanoparticles. The carbon nanoparticles isolated showed high fluorescence even without further surface passivation. The fluorescence of these carbon nanoparticles were utilised for sensitive and selective sensing of ferric ions and it was evaluated to have a linear analytical dynamic range up to 25 μM with a limit of detection (LOD) as low as 1.06 μM. The system was successfully employed to detect ferric ions in real water sample

A unique “turn-on” fluorescence signalling strategy for highly specific detection of ascorbic acid using carbon dots as sensing probe

Carbon dots (CDs) that showed strong blue fluorescence were successfully synthesised from sodium alginate via furnace pyrolysis. The single step pyrolytic synthesis was simple to perform while yielded CDs with high photostability, good water solubility and minimum by-products. In order to design the probe with “turn-on” sensing capability, the CDs were screened against a series of metal cations to first “turn-off” the fluorescence. It was found that ferric ions (Fe3þ) were most responsive and effective in quenching the fluorescence of CDs. Based on this observation, the conditioning of the probe was performed to ensure the fluorescence was completely quenched, while not overloading the system with Fe3þ. At the optimised condition, the CDs-Fe3þ mixture served as a highly specific detection probe for ascorbic acid (AA). The analytical potential of the probe was evaluated and showed a good linear range of response for AA concentration of 24–40 μg/mL. The selectivity study against other possible co-existing species was carried out and proved that our unique “turn-on” fluorescence signalling strategy was highly effective and selective towards AA as the target analyte. The probe was demonstrated for quantification of AA in real samples, which was the commercially available vitamin C supplement. The result showed good accuracy with minimum deviation from standard method adopted for validation purpose

Ignition Risks of Biomass Dust on Hot Surfaces

Combustible biomass dusts are formed at various handling stages, and accumulations of these dusts can occur on hot surfaces of electrical and mechanical devices and can pose fire risks. This study evaluates the ignition characteristics of dust from two types of biomass commonly used in the U.K. power stations: herbaceous miscanthus and woody pine. The ignition risks of the individual biomass and their blends in two different weight ratios, 90 wt % pine to 10 wt % miscanthus and 50 wt % pine to 50 wt % miscanthus, were investigated. Biomass–biomass blends represent the power plant scenario where a number of biomass are fired under daily operation, and thus, dust sedimentation could consist of material blends. The influence of washing pretreatment (particularly to remove catalytic potassium) on the ignition behavior of these dusts was investigated. Fuel characterization via proximate and ultimate analyses was performed on all fuels and combustion characteristics via thermogravimetric analysis (TGA). The risk of self-ignition propensity of both untreated and washed biomass was ranked graphically using the activation energy (Ea) for combustion and the temperature of maximum weight loss (TMWL) determined from the derivative TGA (DTG) curve. It was found that the TMWL and Ea of washed biomass were higher than those of the untreated biomass, implying a lower self-ignition risk. Similar analyses were performed on untreated and washed blends, and comparable results were observed. The ignition characteristics were studied following the British Standard test methods for determining the minimum ignition temperature of a 5 mm dust layer on a heated surface. It was found that the washed individual biomass and their blends revealed slightly higher dust ignition temperatures than their respective untreated counterparts, a 20 and 10 °C difference for individual biomass and blends, respectively. The effect of washing on the ignition delay time was more obvious for pine than for miscanthus, but the time difference between the untreated and washed biomass never exceeded 4 min for all biomass and blends. The biomass pretreatment method of washing did change the combustion and self-ignition characteristics of biomass dust, and there was evidence of potassium being leached from the fuels upon washing (particularly miscanthus). This is considered the main reason for the increase in the minimum ignition temperature. While the washed biomass is found to have a lower ignition risk, it should be noted that the result (validated for up to 5 mm thickness) is not significant enough to influence plant operations for the ignition risk from thin dust layers according to the National Fire Protection Association (NFPA) standard

Potential use of coconut husk-based magnetic sorbent for defoaming application

Absorption process is the most common method that is being applied to sweeten sour gas in the oil and gas industry. However, this process does have several consequences which will trigger the foam formation of foam that will reduce the mass transfer efficiency and absorption capacity as well as amine solutions carryover to the downstream processes. The removal of undesired contaminants in activated methyldiethanolamine (MDEA) was conducted by utilizing magnetic activated carbon (MAC). In this work, MAC was synthesized from coconut husk through chemical activation and co-precipitation methods. The performance of this material as an adsorbent was evaluated based on the foaming behaviour of activated MDEA solvent after being contacted with MAC at different duration and varying amounts. Nitrogen gas was introduced into the solvent through a gas diffuser to create foam. Based on the results, the foam volume generated by activated MDEA solvent was identified to decrease with the increase in both MAC contact time and amount. The highest removal efficiency by MAC was identified to be at 1 h contact time between MAC and activated MDEA solvent where the foam breaking time was reduced to 10–30 min. Meanwhile, the addition of 50 % MAC into the solvent was able to further decrease the foam breaking time to 5–10 min. The characteristics of the prepared MAC were evaluated through various instrumental analyses. This study shows that the MAC synthesized from coconut husk has a good potential as an adsorbent in removing the contaminants in activated MDEA solvent to reduce foam formation

Potential use of coconut husk-based magnetic sorbent for defoaming application

Absorption process is the most common method that is being applied to sweeten sour gas in the oil and gas industry. However, this process does have several consequences which will trigger the foam formation of foam that will reduce the mass transfer efficiency and absorption capacity as well as amine solutions carryover to the downstream processes. The removal of undesired contaminants in activated methyldiethanolamine (MDEA) was conducted by utilizing magnetic activated carbon (MAC). In this work, MAC was synthesized from coconut husk through chemical activation and co-precipitation methods. The performance of this material as an adsorbent was evaluated based on the foaming behaviour of activated MDEA solvent after being contacted with MAC at different duration and varying amounts. Nitrogen gas was introduced into the solvent through a gas diffuser to create foam. Based on the results, the foam volume generated by activated MDEA solvent was identified to decrease with the increase in both MAC contact time and amount. The highest removal efficiency by MAC was identified to be at 1 h contact time between MAC and activated MDEA solvent where the foam breaking time was reduced to 10–30 min. Meanwhile, the addition of 50 % MAC into the solvent was able to further decrease the foam breaking time to 5–10 min. The characteristics of the prepared MAC were evaluated through various instrumental analyses. This study shows that the MAC synthesized from coconut husk has a good potential as an adsorbent in removing the contaminants in activated MDEA solvent to reduce foam formation

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Facile synthesis of carbon nanoparticles from sodium alginate via ultrasonic-assisted nano-precipitation and thermal acid dehydration for ferric ion sensing

Carbon nanoparticles have emerged as a promising alternative to the well-known quantum dots in many biological applications due to their excellent optical properties and biocompatibility. It has received considerable attentions from researchers especially in the aspects of producing these carbon nanomaterials via easier and cheaper synthetic routes. On this motivation, we hereby report an economical and facile synthesis of carbon nanoparticles from alginate via a simple two-step procedure; nano-precipitation through ultrasonication followed by thermal acid carbonisation. Nano-precipitation was first performed on the alginate stock solution to produce nanoparticles with controlled morphology. Precipitation was performed in acidic solution that has coagulated the alginate chains into nanoparticles. Ultrasonic treatment was found crucial to assist the formation of nanoparticles that were more homogenous in the size distribution at around 100 nm. The shape was also more spherical as compared to those without ultrasonic treatment. In the carbonisation step, thermal dehydration was employed using concentrated sulphuric acid that has successfully converted the preformed alginate nanoparticles into carbon nanoparticles. The carbon nanoparticles isolated showed high fluorescence even without further surface passivation. The fluorescence of these carbon nanoparticles were utilised for sensitive and selective sensing of ferric ions and it was evaluated to have a linear analytical dynamic range up to 25 μM with a limit of detection (LOD) as low as 1.06 μM. The system was successfully employed to detect ferric ions in real water sample