Role of Air Staging in a Batch-Type Fixed Bed Biomass Combustor under Constant Primary Air

Staged combustion of biomass is the most suitable thermo-chemical conversion for achieving lower gaseous emissions and higher fuel conversion rates.In a staged fixed bed combustion of biomass,combustion air is supplied in two stages.In the first stage,primary air is provided below the fuel,whereas in the later stage,secondary air is supplied in the freeboard region.The available literature on the effects of air staging(secondary air location) at a constant primary air flow rate on combustion characteristics in a batch-type fixed bed combustor is limited and hence warrants further investigations.This study resolves the effect of air staging,by varying the location of secondary air in the freeboard at five secondary to total air ratios in a batch-type fixed bed combustor.Results are reported for the effects of these controlled parameters on fuel conversion rate,overall gaseous emissions(CO_(2),CO and NO_x) and temperature distributions.The fuel used throughout was densified hardwood pellets.Results show that a primary freeboard length(distance between fuel bed top and secondary air injection) of200 mm has higher fuel conversion rates and temperatures as well as lower CO emissions,at a secondary to total air ratio of 0.75 as compared to primary freeboard length of 300 mm.However,NO_x emissions were found to be lower for a primary freeboard length of 300 mm as compared to 200 mm.An increase in secondary to total air ratio from 0.33 to 0.75 resulted in higher freeboard temperatures and lower CO as well as NO_x emissions.The outcomes of this study will be helpful in the effective design of commercial scale biomass combustors for more efficient and environmentally friendly combustion.

Real-world gaseous emission characteristics of natural gas heavy-duty sanitation trucks

As compared to conventional diesel heavy-duty vehicles,natural gas vehicles have been proved to be more eco-friendly due to their lower production of greenhouse gas and pollu-tant emissions,which are causing enormous adverse effects on global warming and air pol-lution.However,natural gas vehicles were rarely studied before,especially through on-road measurements.In this study,a portable emission measurement system(PEMS)was em-ployed to investigate the real-world emissions of nitrogen oxides(NO_(x))(nitrogen monoxide(NO),nitrogen dioxide(NO_(2))),total hydrocarbons(THC),carbon monoxide(CO),and carbon dioxide(CO_(2))from two liquified natural gas(LNG)China V heavy-duty cleaning sanitation trucks with different weight.Associated with the more aggressive driving behaviors,the ve-hicle with lower weight exhibited higher CO_(2)(3%)but lower NO_(x)(48.3%)(NO_(2)(78.2%)and NO(29.4%)),CO(44.8%),and THC(3.7%)emission factors.Aggressive driving behaviors were also favorable to the production of THC,especially those in the medium-speed range but sig-nificantly negative to the production of CO and NO_(2),especially those in the low-speed range with high engine load.In particular,the emission rate ratio of NO_(2)/NO decreased with the increase of speed/scaled tractive power in different speed ranges.

An evaluation of the emission profile for two-wheelers at a traffic junction

Two-wheeler vehicles are an important mode of transportation in developing countries. However, the emissions from two-wheeler vehicles are significant. Urban two-wheeler vehicles with gasoline-fueled engines produce NOx and particulate matter emissions that affect urban air quality. During traffic light stops and programmed stops, for instance, pollutants are emitted and are dangerous to human health. In this experimental study, two-wheeler vehicles with different makes, technologies and engine capacities were tested for exhaust emissions including gravimetric and online measurements at different engine speeds and a no load condition at a simulated traffic junction. Gravimetric measurements were performed by collecting the particulate mass （at two engine speeds： 1500 and 2500 rpm） from a diluted engine-out exhaust on quartz filter paper. Next, these collected particulates were used to determine the presence of metals, as well as the benzene soluble organic fraction （BSOF）. The total particulate mass, BSOF and trace elements were slightly higher at a higher engine speed （2500 rpm）. Online measurements were performed by sampling the engine exhaust （at four engine speeds： 1500, 2000, 2500, and 3000rpm） and using online instruments to determine the particle number and size distribution, the particle-bound polyaromatic hydrocarbons （PAHs）, the gaseous emissions and the smoke opacity. Engines with higher cubic capacity emitted a higher concentration of nano-particles. The particle-bound PAH concentration increased as the engine speed increased, but this concentration was notably low for the highest engine speed tested （3000 rpm）. The regulated gaseous emissions increased as the engine speed increased for all vehicles.

Soil conservation and ecosystem services

Accelerated soil erosion,driven by anthropogenic activities such as conversion of natural ecosystems to agroecosystems and mechanical tillage,has numerous adverse impacts on ecosystem services.In addition to degrading soil quality and reducing agronomic/biomass productivity on-site through a decrease in use-efficiency of inputs,off-site impacts of accelerated erosion include eutrophication and contamination,sedimentation of reservoirs and waterways,and emissions of greenhouse gases(e.g.,CO_(2),CH_(4) and N_(2)O).While advancing food and nutritional security,adoption of restorative land use and recommended management practices are important to strengthening numerous ecosystem services such as improving water quality and renewability,increasing below and above-ground biodiversity,enhancing soil resilience to climate change and extreme events,and mitigating climate change by sequestering C in soil and reducing the emission of CO_(2),CH_(4) and N_(2)O.An effective control of accelerated erosion is essential to sustainable development and improving the environment.

Incineration experiment of medical waste of novel coronavirus pneumonia(COVID-19)in a mobile animal carcass incinerator

Incineration experiment of medical waste was carried out in a mobile animal carcass incinerator.Simulated medical waste(69%cotton,1.5%wood product,4.5%mask and 25%moisture)was used as raw material.The temperature trend of first and second combustion chamber,the operating conditions and the emission characteristics of gaseous pollutants were studied.The results indicated that the temperature of first combustion chamber can be maintained at 550-650℃ without external heating,while in the final stage a burner was used to realize the burnout of material.The temperature of the second combustion chamber was always lower than that of the first combustion after the burner stopped working.The concentration of CO emission in flue gas was high due to the low disposal efficiency of the mobile incinerator,while NOX and SO2 emission concentrations were far below the standard limit value(GB 18484-2001).