Johan E. Hustad

Experimental studies of lower flammability limits of gases and mixtures of gases at elevated temperatures

Abstract Experimental studies of lower flammability limits for methane, butane, hydrogen, carbon monoxide, in addition to mixtures of these gases are performed at temperatures up to 450°C and at atmospheric pressure. The experimental tests are mostly carried out for upward propagation. The flammability limits for each gas are found to decrease linearly with increasing temperature in the temperature range tested. A new mixing rule for calculating lower flammability limits for mixtures at elevated temperatures in suggested. The mixing rule is a simplification of that of Le Chateliers and is based on the established equations for each gas component in the mixture.

Biomass combustion research and utilisation in IEA countries

Abstract Projects and achievements within the activity “Wood Combustion and Oxidation of Wet Biomass” in the triennium 1992–1994 are reviewed. The projects include modelling of wood combustion and pyrolysis, characterisation of biomass fuels and ashes, emission comparisons, emission reduction techniques, measurement techniques, comparison of test standards, utilisation of contaminated wood waste, oxidation of wet biomass, condensing systems and co-generation and co-firing techniques.

Biomass combustion in IEA countries

Abstract Bioenergy use and potential, biofuels and bioenergy systems including combustion equipment and technology development are reviewed in the IEA member countries participating in the combustion activity. Focus has been put on pollutant emissions, emission measurement and reduction techniques, energy and emissions from contaminated wood combustion and fuel reactivity and modelling of pyrolysis and combustion. The paper describes the status on these topics within the IEA cooperation agreements.

Emissions from Wood Stoves and Fireplaces

New emission standards for wood stoves have been developed and introduced in several countries. To meet these emission regulations, new technology such as wood stoves with catalytic combustors and staged combustion units have been developed and introduced into the stove market. Three traditional wood stoves, one fireplace, one stove with a catalytic afterburner on the norwegian market have been tested in accordance with national testing procedures. In addition also a new none catalytic stove, two catalytic stoves and a non catalytic laboratory stove have been tested. The emissions of CO, particles, tar and hydrocarbons have been measured at different average wood consumption.

Burning rates of coke particles in the freeboard above a fluidized bed reactor

Abstract Experiments with coke particles of various sizes ranging from 90 to 360 μm in the gas temperature range from 1050 to 1350 K were performed in the freeboard region of a relatively large (250-kW) fluidized bed reactor. Burning rates and kinetic parameters have been calculated (based on external surface) by use of both the shrinking particle model and the constant diameter model. The calculations of burning rates give values less than the diffusion limit, indicating the combustion to be limited in various degrees by heterogeneous kinetics and/or pore diffusion, depending on the temperature. The calculations give an overall apparent activition energy of 38 735 cal/mol for the shrinking particle model and 36 500 cal/mol for the constant-diameter model, indicating combustion in the transition between zone I and zone II. The kinetic constants are independent of particle size. The measurements of particle size and apparent density show that the smallest particles burn more internally with an initial sharp decrease in apparent density; the larger particles, however, burn with only a small decease in apparent density but with a sharper decrease in particle diameter. The experiments support an overall apparent reaction order in the range of 0.83–1.0.

The evolution of porosity and intrinsic reactivity of coke particles

Abstract Experiments have been performed with coke particles in the freeboard region of a 250 kW Atmospheric Fluidized Bed Combustor (AFBC) with particle sizes ranging from 90 μm to 360 μm in the gas temperature range from 1050 K to 1350 K. Partially burned particles were collected at various heights and residence times. The observed morphological development during combustion indicates clear effects of internal burning resulting in an increase of pore volume and internal surface area. A pore model has been developed to describe the evolution of pores and total surface area, and to calculate the intrinsic reactivity and burning rates. The model is based on a combination of a Thiele analysis and the random pore model.

Biomass Gasification for Industrial Production of Tar and Charcoal

Process conditions in a retort prototype plant for production of tar and charcoal is evaluated. Experiments were carried out with a batch load of 810 kg wet biomass. The biomass used in this production is resinous pine root with particle size similar to chunkwood. The total duration of the experiment was approximately 15 hours with a mean biomass conversion rate of 53 kg/hr. The retort had a transient period of approximately 2 hours with an increasing amount of tar production followed by an 11 hour period with a steady state production rate of tar in the order of 8 kg/hr. Test results show a tar yield of 0.21 kg/kg dry biomass and a charcoal yield of 0.08 kg/kg dry biomass. Temperature measurements in the retort indicate heating rate in the area of 6 °C/min in the temperature range of 200 °C – 300 °C, and a high temperature zone moving downward in the retort with an average speed of 0.2 m/hr.