Vida N. Sharifi

Tar reduction in pyrolysis vapours from biomass over a hot char bed

The behaviour of pyrolysis vapours over char was investigated in order to maximise tar conversion for the development of a new fixed bed gasifier. Wood samples were decomposed at a typical pyrolysis temperature (500 degrees C) and the pyrolysis vapours were then passed directly through a tar cracking zone in a tubular reactor. The product yields and properties of the condensable phases and non-condensable gases were studied for different bed lengths of char (0-450 mm), temperatures (500-800 degrees C), particle sizes (10 and 15 mm) and nitrogen purge rates (1.84-14.70 mm/s). The carbon in the condensable phases showed about 66% reduction by a 300 mm long char section at 800 degrees C, compared to that for pyrolysis at 500 degrees C. The amount of heavy condensable phase decreased with increasing temperature from about 18.4 wt% of the biomass input at 500 degrees C to 8.0 wt% at 800 degrees C, forming CO, H(2) and other light molecules. The main mode of tar conversion was found to be in the vapour phase when compared to the results without the presence of char. The composition of the heavy condensable phase was simplified into much fewer secondary and tertiary tar components at 800 degrees C. Additional measures were required to maximise the heterogeneous effect of char for tar reduction.

Pyrolysis and combustion of oil palm stone and palm kernel cake in fixed-bed reactors

The main objective of this research was to investigate the main characteristics of the thermo-chemical conversion of oil palm stone (OPS) and palm kernel cake (PKC). A series of combustion and pyrolysis tests were carried out in two fixed-bed reactors. The effects of heating rate at the temperature of 700 degrees C on the yields and properties of the pyrolysis products were investigated. The results from the combustion experiments showed that the burning rates increased with an increase in the air flow rate. In addition, the FLIC code was used to simulate the combustion of the oil palm stone to investigate the effect of primary air flow on the combustion process. The FLIC modelling results were in good agreement with the experimental data in terms of predicting the temperature profiles along the bed height and the composition of the flue gases.

Ash deposit characterisation in a large-scale municipal waste-to-energy incineration plant

The deposition of ash - combustion residues - on superheaters and heat exchanger surfaces reduce their efficiency; this phenomenon was investigated for a large-scale waste-to-energy incineration facility. Over a period of six months, ash samples were collected from the plant, which included the bottom ash and deposits from the superheater, as well as flyash from the convective heat exchanger, the economiser and fabric filters. These were analysed for particle size, unburned carbon, elemental composition and surface morphology. Element partitioning was evident in the different combustion residues, as volatile metals, such as cadmium, antimony and arsenic, were found to be depleted in the bottom ash by the high combustion temperatures (1000+°C) and concentrated/enriched in the fabric filter ash (transferred by evaporation). Non-volatile elements by contrast were distributed equally in all locations (transported by particle entrainment). The heat exchanger deposits and fabric filter ash had elevated levels of alkali metals. 82% of flyash particles from the fabric filter were in the submicron range.

The Use of Tree Bark as a Passive Sampler for Polychlorinated Dibenzo- p -Dioxins and Furans

The potential of using tree bark as a passive sampling medium for detection of Polychlorinated dibenzo- p -dioxins and furans (PCDD/F) in an urban environment has been investigated. Bark samples (∼ 30 g) were extracted with toluene using accelerated solvent extraction. Extracts were then cleaned up via a multi-bed silica column and a Florisil column followed by GC-MS/MS analysis. It is shown that PCDD/F are present in tree bark collected from sites close to a municipal waste incinerator, a crematorium, a hospital and a chemical incinerator. Furthermore, characteristic patterns for dioxin congeners were observed for the suspected emission sources.

Experimental Investigation of Indoor Air Pollutants in Residential Buildings

Indoor air quality is affected by many factors, including energy provision/use. The main objective of this research was to investigate indoor air pollutant emissions due to energy use in residential buildings, with a specific focus on particulate matter (PM). Three environments were compared: (a) a rural house with an electric cooker; (b) a city-centre flat with a gas cooker; and (c) an urban flat on a main road, also with gas appliances. Concentrations of PM, CO, NO2 and VOCs were measured in the kitchens and emission rates were calculated for cooking periods. Although there has been a great deal of research examining the effects of gaseous pollutants in the indoor environment, this is one of the first studies to specifically focus on PM. Most particles were small (≤2.5 µm) and thus respirable. The elemental analysis of the PM revealed high metal concentrations (Fe/Na/Zn), whilst their morphologies indicated these were present as salt, skin and particles of biological origin. Gaseous emissions, particularly NO2 and CO, were more prevalent in homes with gas appliances, since these are a significant source of both pollutants.

Optimisation study of a large waste-to-energy plant using computational modelling and experimental measurements

AbstractIn order to maximise the energy recovery efficiency of waste-to-energy plants, it is important to understand the physical processes that are occurring within the furnace. A mathematical model of the furnace section of a large waste-to-energy plant was constructed using FLIC to model combustion of the solid waste particles on the furnace grate and FLUENT to model the gas flow above the burning waste bed. The two models were coupled through their respective boundary conditions. A numerical simulation of the design-case setup of a large waste-to-energy plant was performed, which predicted the presence of a large flow recirculation zone in the radiation shaft. Further numerical simulations were performed using several different configurations of the secondary air jets, which revealed that the large flow recirculation in the radiation shaft could be avoided by changing the distribution of secondary air jets. Experimental measurements of the temperature profile within the burning waste bed of the plant ...

Identification of metal concentration fluctuations in waste-to-energy plant flue gases—a novel application for ICP-OES

A mobile continuous emissions monitoring laboratory, based on ICP-OES technology, was used to study temporal variations in metal concentrations in the flue gas of a waste-to-energy plant. The concentrations of over 30 elements were monitored prior to flue gas clean-up. Despite harsh analytical conditions, with high particulate loading, variable gas matrix and high concentrations of numerous elements, semi-quantitative measurements were made. Realistic detection limits in the range 0.007–0.06 mg m−3 were achieved. For many volatile metals, significant variations (4–18 mg m−3 for Na, 0–0.18 mg m−3 for Cd) were observed, and were linked to properties of the metal in question, to incinerator operating conditions, and to variations in the waste feed charge. The concentrations of some metals were attributable to specific sources in the waste. It was concluded that better waste segregation could significantly reduce the concentration of toxic metals in the incinerator residues, and where concentration spikes were detected, accurate real-time metal concentration measurements had the potential to provide feedback to clean-up systems, thereby minimising the overall environmental effect.

Investigation of biomass combustion systems using CFD techniques: a parametric study of packed-bed burning characteristics

In this paper, mathematical equations governing the fluid flow, heat and mass transfer and heterogeneous reactions in packed-bed combustion systems are described and sub-models for individual processes are presented. A model estimating the mixing rate between the under-grate air and the released volatile gases is described. Parametric study was carried out to assess the effects of fuel moisture content, kinetic rate of devolatilisation, primary air flow rate and particle mixing levels caused by grate movement. Useful conclusions were drawn in terms of flame temperature, reaction zone thickness, mass loss rate, combustion staging and residual carbon in ash.

Sustainable management of urban pollution: an integrated approach

This paper presents a new decision-support framework and software platform for an integrated assessment of options for sustainable management of urban pollution. The framework involves three steps: (1) mapping the flow of pollutants associated with human activities in the urban environment; (2) modelling the fate and transport of pollutants; and (3) quantifying the environmental, health and socio-economic impacts of urban pollution. It comprises a suite of different models and tools to support sustainability appraisals including life cycle assessment, substance flow analysis, source and pollutants characterisation, pollutant fate and transport modelling, health impact analysis, ecological impact assessment, and multi-criteria decision analysis. The framework can be used at different levels, from simple screening studies to more detailed assessments. The paper describes the decision-support framework and outlines several case studies to demonstrate its application. The software tool is available free of charge at www.pureframework.org. Practical applications: The PUrE framework and software platform can be applied to assess and compare the sustainability of different technologies, products, human activities or policies. Example applications of the framework have so far included sustainability comparisons of technologies for thermal treatment of municipal solid waste; generation of electricity from coal and biomass; environmental and health impacts of a mixture of pollutants in Sheffield; the role of urban green space in reducing the levels of particulate matter in London and the impacts of environmental policy on legacy pollution in Avenmouth.

Continuous analysis of elemental emissions from a biofuel gasifier

In recent years there has been significant and high-profile interest in the use of biofuels as possible alternatives to fossil fuels, as part of a move to reduce carbon dioxide emissions. Although combustion accounts for most biofuel use, there has also been significant research into biofuel gasification. However, the behaviour of trace elements during gasification can be problematic, with environmental concerns over toxic components, and process problems caused by alkali metal corrosion and fouling. Experiments have been conducted to continuously monitor the concentration of various trace elements in the raw gasification gas from an experimental reactor, in an effort to determine which elements are volatilised, using ICP-OES. Results of initial tests indicate that the concentration of some elements in the gas phase are extremely high, far higher than in combustion processes, and therefore are of significant concern. Owing to to problems with tar formation in the gasification process, the analysis proved extremely challenging, and further development of the sampling and pre-treatment procedure would be required to obtain more accurate, reliable, and long-term continuous monitoring results.