Lars Sørum

Pyrolysis Characteristics and Kinetics of Municipal Solid Wastes

The large variety in municipal solid waste (MSW) composition and differences in thermal degradation behaviour of MSW components makes modelling, design and operation of thermal conversion systems a challenge. The pyrolysis characteristics of 11 different components, representing the dry cellulosic fraction and plastics of MSW, have been investigated. The aim of this study is to obtain detailed information on the pyrolysis characteristics and chemical kinetics of the most important components in MSW. A thermogravimetric analysis including determination of kinetic parameters are performed at a constant heating rate of 10°C/min in an inert atmosphere. The cellulosic fraction of MSW was modelled by three independent parallel reactions describing the degradation of hemicellulose, cellulose and lignin. The plastics polystyrene, polypropylene, low-density polyethylene and high-density polyethylene were all modelled as single reactions describing the degradation of hydrocarbon polymers. The degradation of PVC was modelled with three parallel reactions describing the release of benzene during dehydrochlorination, dehydrochlorination reaction and degradation of remaining hydrocarbons. Possible interactions between different paper and plastic components in mixtures were also investigated. It was found that the reactivity of cellulosic matter was increased in a mixture with PVC.

On the fate of heavy metals in municipal solid waste combustion Part I: devolatilisation of heavy metals on the grate☆

The aim of this study has been to investigate the chemistry and volatility of the heavy metals As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn on the grate of a MSW fired furnace, using equilibrium calculations. Focus has been on the influence of varying MSW composition and operational parameters such as air/fuel ratio and temperature. Equilibrium distributions at 950–1600 K, under reducing and oxidising conditions on the grate, showed that Cd, Hg and Pb are fully volatilised. However, Cr is found to be stable in solid phase, in the entire temperature range. The volatile behaviour of Cd, Cr, Hg and Pb show no significant influence, while As, Cu, Ni and Zn are strongly influenced by one or more of the parameters; temperature, fuel/air and chlorine/metal ratios.

Formation of NO from combustion of volatiles from municipal solid wastes

An experimental and theoretical study has been performed on the formation of NO in the combustion of volatiles from municipal solid wastes. Single components and their mixtures were burned in a small-scale, fixed-bed reactor. Numerical simulations using the opposed flow diffusion flame program OPPDIF were performed to obtain a further understanding of the experimental results. Conversion factors for fuel-N to NO were determined for single components of newspaper, cardboard, glossy paper, low-density polyethylene (LDPE), and poly(vinylchloride) (PVC) and their mixtures, using gases with oxygen concentrations of 12, 21, and 40 vol %. For single components experiments at 100 vol % oxygen were also performed. The conversion factors for paper and cardboard varied from 0.26 to 0.99. The conversion factor for LDPE and PVC varied from 0.71 to 10.09 and 0.04 to 0.37, respectively. Conversion factors higher than 1.0 in the case of LDPE clearly show that NO is formed by thermal and/or prompt mechanisms. For mixtures, calculated conversion factors (based on a weighted sum of the conversion factors for single components) were compared with the experimentally determined conversion factors. Mixtures of paper and cardboard only gave different conversion factors with 40 vol % of oxygen. For mixtures of paper/cardboard and plastics, however, significant differences in the conversion factors were observed at all oxygen concentrations, when comparing experiments on a mixture of paper and plastics with the weighted sum of the single components. The explanation is found in the different combustion properties for paper/cardboard and plastic, which in this case make the formation of thermal NO from LDPE more favorable for the single component than in mixtures with other components. The simulations with OPPDIF confirmed the trends observed experimentally, and allowed an assessment of the contribution of the different mechanisms of NO formation.

Gasification of Biomass to Second Generation Biofuels: A Review

ABSTRACT Biomass gasification has gained significant attention in the last couple of decades for the production of heat, power and second generation biofuels. Biomass gasification processes are highly complex due to the large number of reactions involved in the overall process as well as the high sensitivity of the process to changes in the operational conditions. This report reviews the state-of-the-art of biomass gasification by evaluating key process parameters such as gasifying agent, temperature, pressure, particle size, etc., for fluidized bed and entrained flow gasifiers. The pros and cons of each technology and the remaining bottlenecks are also addressed. INTRODUCTION Biomass, the renewable source which stores energy in molecular carbon bond structures, is bound to play an important role in the current challenging energy scenario to provide the energy required to meet the continuous increase in energy demand and to mitigate climate change [1-2]. The large flexibility of biomass as a feedstock has been widely recognized as, besides heat and power, it can be converted into chemicals and transportation fuels. Biofuels can be used in recent infrastructures more or less directly, while other technologies, such as fuel cells and batteries, require changes in infrastructure and thus are considered as long-term solutions. Second generation biofuels can be grouped into biochemically or thermo-chemically produced, either route using non-food crops, purpose-grown perennial grasses, trees or residues. Among the different available thermo-chemical processes for the conversion of biomass to biofuels, gasification is perceived as one of the most attractive routes, as it converts feedstock very efficiently to the highest density fuels, i.e. synthetic, resulting in the most economical viable system [3]. The biomass gasification process produces synthesis gas through the chemical conversion of biomass under partial oxidation of the feedstock in reducing atmosphere in the presence of air, oxygen and/or steam [4]. The synthesis gas produced can be then converted to second generation biofuels. Various types of gasification reactor designs have been developed up to now. Fluidized bed and entrained flow gasifiers are currently the two main categories of gasification technologies for biofuels production. Fluid bed gasifiers operate below the biomass ash melting point in order to avoid fluid bed agglomeration and eventual collapse. This technology is attractive for its relatively low cost, ease of operation and good scale-up potential. However, it has associated relatively low energy efficiencies and poorer gas qualities; it requires intensive additional gas cleaning after the gasifier, namely tars handling and hydrocarbon reforming and is limited to small scale operations. On the other hand, entrained flow gasifiers operate above the melting point of the biomass ashes and produce a product gas that is essentially fully converted to synthesis gas with very low contents of residual tar components, resulting in high efficiencies and higher gas quality. However, the feeding is a challenge, it has higher investment and operating costs than fluidized beds and therefore it is only suitable for high capacities. Thus, although substantial progress has been achieved over the last years, none of the two technologies have become commercially available and therefore a significant amount of work is still needed in this field to enable the deployment of second generation biofuels production.

The effect of kaolin on the combustion of demolition wood under well-controlled conditions.

In an attempt to look at means for reduction of corrosion in boilers, combustion experiments are performed on demolition wood with kaolin as additive. The experiments were performed in a multi-fuel reactor with continuous feed of pellets and by applying staged air combustion. A total characterization of the elemental composition of the fuel, the bottom ash and some particle size stages of fly ash was performed. This was done in order to follow the fate of some of the problematic compounds in demolition wood as a function of kaolin addition and other combustion-related parameters. In particular chlorine and potassium distribution between the gas phase, the bottom ash and the fly ash is reported as a function of increased kaolin addition, reactor temperature and air staging. Kaolin addition of 5 and 10% were found to give the least aerosol load in the fly ash. In addition, the chlorine concentration in aerosol particles was at its lowest levels for the same addition of kaolin, although the difference between 5 and 10% addition was minimal. The reactor temperature was found to have a minimal effect on both the fly ash and bottom ash properties.

Combustion Properties of Norwegian Biomass: Wood Chips and Forest Residues

Flue gas emissions and particle size distribution were investigated during combustion experiments of wood, forest residue and mixtures of these two. The combustion experiments were carried out in a grate fired multi-fuel reactor with and without air staging at stable operation conditions and constant temperature of 850 °C. The overall excess air ratio was held at 1.6, and the primary excess air ratio was 0.8 during air staged experiments. NOx emissions are reduced by air staging. Fly ash particle concentration of forest residues in the flue gas is lower than wood. Aerosols number increased in the staged experiments for fuel blends.