Estimation of spontaneous waste ignition time for prevention and control of landfill fire

Openmunicipal solid waste(MSW) dumpsites in India are significant hotspots of spontaneous fire and associated air and ground water pollution. Unscientific dumping of MSW poses a major threat to the surrounding environment and human health. One-year-old biodegradable waste components comprised of paper, cardboard, newspaper, textile, wood, grass leaves and coconut shell were analyzed for the determination of the moisture content (MC), smoldering temperature, ignition temperature, and ignition time. Principal component analysis of the old waste components revealed that cardboard, paper, newspaper and leaves are most susceptible waste components for spontaneous ignition. In contrast, MC was the most influential parameter for resulting changes in ignition temperature (⁰C) on ignition time (min). A numerical equation was developed to estimate the time required for the spontaneous waste ignition at MSW dumpsite. The results of the study showed that the aged waste (age ≥ 3 year) having MC below 6 % and initial surface temperature of 78 ⁰C might smolder and ignite during the hottest time of the day in ∼ 6 and ∼ 26 days, respectively. Estimates showed that the time required for spontaneous waste ignition of aged waste is moderately dependent on waste MC (∼5-55 %), surface temperature (∼40-100 ⁰C), monthly pattern of average high temperature (∼36.6-42.6 ⁰C), biodegradable waste components having smoldering temperature ≤ 150 ⁰C and ignition temperature ≤ 270 ⁰C. The present study also showed that the occurrence of landfill fire events at MSW dumpsites is more prominent during the pre-monsoon season i.e. during the elevated temperature level.

Highly efficient adsorptive removal of toluene using silicon-modified activated carbon with improved fire resistance

Activated carbons (ACs) are widely applied in the removal of volatile organic compounds (VOCs) emitted from industrial processes, because of their high adsorption capacity, low cost and reusability. Their poor thermal stability under oxidative conditions is a limiting factor and often leads to fire risk in real applications. Here, Si-modification was performed over a wood-derived AC material, and a series of modified ACs with different Si/C mass ratios (0.1-0.9) were prepared via a hydrothermal route. Physicochemical characteristics of Si/C samples was examined by XRD, SEM, TEM, XPS, FTIR and N₂-physisorption measurements. As compared to pristine AC, Si-modified ACs showed enhanced fire resistance, and an increase of ignition temperature by 79 ℃ was achieved at a Si/C mass ratio of 0.9. A combination of TEM, XPS and FTIR characterization suggests that the formation of amorphous SiO₂ nanoparticles and SiC species on the surface was responsible for the enhanced fire resistance of Si-modified ACs. By increasing microporosity, Si-modification also significantly improved the adsorption capacity of toluene as a model VOC molecule. Static and dynamic adsorption experiments were performed to understand the adsorption kinetics of the Si-modified ACs. Reusability tests showed that the desorption rate of the modified AC remained at nearly 80% even after five cycles of repeated adsorption-desorption, indicating that the modified AC has a great potential for industrial applications.

Starch bio-template synthesis of W-doped CeO2 catalyst for selective catalytic reduction of NOx with NH3: influence of ignition temperature

A novel tungsten-doped CeO₂ catalyst was fabricated via the sweet potato starch bio-template spread self-combustion (SSC) method to secure a high NH₃-SCR activity. The study focuses on the influence of ignition temperature on the physical structure and redox properties of the synthesized catalyst and the catalytic performance of NO_x reduction with NH₃. These were quantitatively examined by conducting TG-DSC measurements of the starch gel, XRD analysis for the crystallites, SEM and TEM assessments for the morphology of the catalyst, XPS and H₂-TPR measurements for the distribution of cerium and tungsten, and NH₃-TPD assessments for the acidity of the catalyst. It is found that the ignition temperature shows an important role in the interaction of cerium and tungsten species, and the optimal ignition temperature is 500 °C. The increase of ignition temperature from 150 °C is beneficial to the interactions of species in the catalyst, depresses the formation of WO₃, and refines the cubic CeO₂ crystallite. The sample ignited at 500 °C shows the biggest BET surface area, the highest surface concentration of Ce species and molar ratio of Ce³⁺/(Ce³⁺+Ce⁴⁺), and the most abundant surface Brønsted acid sites, which are the possible reasons for the superiority of the NH₃-SCR activity. With a high GHSV of 200,000 mL (g h)^-1 and the optimal ignition temperature, Ce₄W₂O_z-500 can achieve a steadily high NO_x reduction of 80% or more at a lowered reduction temperature in the range of 250~500 °C.

Determination of ignition temperature of municipal solid waste for understanding surface and sub-surface landfill fire

Open dumping of municipal solid waste (MSW) is a common practice in India which leads to a number of problems like non-uniform compaction, slope failure, percolation of water during rainy seasons, abrupt leachate generation and stability issues. It also leads to various other issues, such as manual scavenging and deliberate waste burning. During the waste degradation process, an enormous amount of heat and landfill gases (LFGs) like carbon dioxide (CO₂) and methane (CH₄) are generated. Biological and chemical reactions happening at the surface and inside the landfill contribute to the heat generation. Initiation of waste ignition is a major cause of spontaneous landfill fire. The risk posed by landfill fires is high in India as most of the landfills are non-engineered. The present study aims to determine the ignition temperature of waste dumped at Bhandewadi dumpsite located at Nagpur, India which will enable a better understanding of the initiation of fires in non-engineered landfill (surface and sub-surface fires), especially in Indian condition. The results of the present study showed that ignition temperature is directly proportional to the moisture content of MSW for its values ranging from 5 to 55% by mass. The correlation of smoldering time (Ts) and ignition time (Ti) of MSW with its age under gradual temperature rise in a muffle furnace (i.e., 3 °C/min) were also studied and it was found that Ts and Ti are directly proportional to the age of MSW and the values ranged from 23 to 34 min for Ts and 27 to 48 min for Ti.

Experimental study on the minimum ignition temperature of coal dust clouds in oxy-fuel combustion atmospheres

BAM furnace apparatus tests were conducted to investigate the minimum ignition temperature of coal dusts (MITC) in O2/CO2 atmospheres with an O2 mole fraction from 20 to 50%. Three coal dusts: Indonesian Sebuku coal, Pittsburgh No.8 coal and South African coal were tested. Experimental results showed that the dust explosion risk increases significantly with increasing O2 mole fraction by reducing the minimum ignition temperature for the three tested coal dust clouds dramatically (even by 100°C). Compared with conventional combustion, the inhibiting effect of CO2 was found to be comparatively large in dust clouds, particularly for the coal dusts with high volatile content. The retardation effect of the moisture content on the ignition of dust clouds was also found to be pronounced. In addition, a modified steady-state mathematical model based on heterogeneous reaction was proposed to interpret the observed experimental phenomena and to estimate the ignition mechanism of coal dust clouds under minimum ignition temperature conditions. The analysis revealed that heterogeneous ignition dominates the ignition mechanism for sub-/bituminous coal dusts under minimum ignition temperature conditions, but the decrease of coal maturity facilitates homogeneous ignition. These results improve our understanding of the ignition behaviour and the explosion risk of coal dust clouds in oxy-fuel combustion atmospheres.