• Energy Research

Measurements of the intrinsic reaction rates of two Australian coal chars (made under laboratory conditions) with O2, CO2, and H2O at increased pressures (up to 30 atm) have been made using a pressurized thermogravimetric analyzer (TGA). It was found that the reaction order in CO2 and H2O was not constant over the pressure range investigatedvarying from 0.5 to 0.8 at atmospheric pressure and decreasing at pressures above approximately 10 atm. The apparent reaction order in oxygen was less affected by pressure over the range 1 to 16 atm. Char surface area after reaction at higher pressures was generally greater than that after reaction at lower pressures. This resulted in a reduced effect of pressure on the intrinsic rates at 10% conversion. Activation energies for all three reactions were not significantly affected by an increase in reaction pressure. The intrinsic rate data obtained in this work were used to estimate the high-temperature reactivity of the chars using a basic knowledge of the pore structu...

Measurements of the intrinsic reaction rates of two Australian coal chars (made under laboratory conditions) with O2, CO2, and H2O at increased pressures (up to 30 atm) have been made using a pressurized thermogravimetric analyzer (TGA). It was found that the reaction order in CO2 and H2O was not constant over the pressure range investigatedvarying from 0.5 to 0.8 at atmospheric pressure and decreasing at pressures above approximately 10 atm. The apparent reaction order in oxygen was less affected by pressure over the range 1 to 16 atm. Char surface area after reaction at higher pressures was generally greater than that after reaction at lower pressures. This resulted in a reduced effect of pressure on the intrinsic rates at 10% conversion. Activation energies for all three reactions were not significantly affected by an increase in reaction pressure. The intrinsic rate data obtained in this work were used to estimate the high-temperature reactivity of the chars using a basic knowledge of the pore structu...

Abstract By exploring the links between laboratory-scale gasification data (e.g. slag viscosity measurements, char reactivity considerations) and the performance of the same coals under realistic pilot-scale conditions, we are provided with a dataset that allow us to refine coal test procedures for entrained flow gasification, understand the entrained flow gasification process in significantly more detail than previously, and gain some new insight into how coal reactivity and slag viscosity properties interact to define operating envelopes for specific gasification technologies. The first paper in this two-part series presented a detailed characterisation of a suite of Australian coals using laboratory-scale gasification facilities. This paper presents gasification data obtained from pilot-scale testing of these same coals, and explores the links between laboratory data, coal assessments made using these data, and the performance of the coals under realistic conditions. The results demonstrate a high degree of consistency between laboratory indications of coal reactivity and coal gasification behaviour at pilot scale. This work also demonstrates the impact of interactions between coal conversion properties and slag formation and flow behaviour, and how these interactions dictate operational parameters for the gasifier.

Abstract By exploring the links between laboratory-scale gasification data (e.g. slag viscosity measurements, char reactivity considerations) and the performance of the same coals under realistic pilot-scale conditions, we are provided with a dataset that allow us to refine coal test procedures for entrained flow gasification, understand the entrained flow gasification process in significantly more detail than previously, and gain some new insight into how coal reactivity and slag viscosity properties interact to define operating envelopes for specific gasification technologies. The first paper in this two-part series presented a detailed characterisation of a suite of Australian coals using laboratory-scale gasification facilities. This paper presents gasification data obtained from pilot-scale testing of these same coals, and explores the links between laboratory data, coal assessments made using these data, and the performance of the coals under realistic conditions. The results demonstrate a high degree of consistency between laboratory indications of coal reactivity and coal gasification behaviour at pilot scale. This work also demonstrates the impact of interactions between coal conversion properties and slag formation and flow behaviour, and how these interactions dictate operational parameters for the gasifier.

Abstract Interactions between feedstocks during pyrolysis of coal–biomass blends, and their impacts on product distribution and conversion behavior during utilization, need to be understood if we are to successfully develop systems for the effective co-utilization of biomass and coal. A novel two-stage fixed-bed reactor containing three quartz tubes was designed and used in this study to investigate these interactions, with particular emphasis on the impact on product distribution and char properties. The results show that interactions exist during co-pyrolysis of corncob and lignite blends, which increase overall tar yields and decrease overall gas yields compared with those obtained from pyrolysis of unblended feedstocks, with the interactions between corncob volatiles and lignite playing a dominant role. It is also shown that interactions between chars and volatiles can impact on the reactivity of chars to O2. Consistent with our expectations, there is a link between potassium content in char and its reactivity; however, it is found that for lignite chars in particular the potential impact of potassium is dominated by the changes of char chemical structure. The effect of potassium content is the opposite to that of char chemical structure, leading to significant complexity in determining the net result of any co-pyrolysis interactions on char reactivity. This highlights the importance of understanding these complex interactions to develop the industrial scale co-gasification systems and adjust the distributions of products.

Abstract Interactions between feedstocks during pyrolysis of coal–biomass blends, and their impacts on product distribution and conversion behavior during utilization, need to be understood if we are to successfully develop systems for the effective co-utilization of biomass and coal. A novel two-stage fixed-bed reactor containing three quartz tubes was designed and used in this study to investigate these interactions, with particular emphasis on the impact on product distribution and char properties. The results show that interactions exist during co-pyrolysis of corncob and lignite blends, which increase overall tar yields and decrease overall gas yields compared with those obtained from pyrolysis of unblended feedstocks, with the interactions between corncob volatiles and lignite playing a dominant role. It is also shown that interactions between chars and volatiles can impact on the reactivity of chars to O2. Consistent with our expectations, there is a link between potassium content in char and its reactivity; however, it is found that for lignite chars in particular the potential impact of potassium is dominated by the changes of char chemical structure. The effect of potassium content is the opposite to that of char chemical structure, leading to significant complexity in determining the net result of any co-pyrolysis interactions on char reactivity. This highlights the importance of understanding these complex interactions to develop the industrial scale co-gasification systems and adjust the distributions of products.

The reaction rates of coal chars with CO2 is an important aspect of coal performance under gasification conditions. Most studies of the char−CO2 reaction are undertaken at temperatures (typically ∼1200 K or below) significantly lower than those found in entrained flow applications, to allow detailed investigations into the surface reaction processes. Application of these data to high temperatures therefore requires consideration of how these reaction rates are affected by gas diffusion through the pore structure of reacting particles, yet there are very few char−CO2 rate data at high temperatures and pressures against which such applications can be tested or verified. This paper presents results of measurements of the char−CO2 reaction rate at high pressures (2.0 MPa) and high temperatures (up to 1673 K) using an entrained-flow reactor and also presents analyses of the morphology of the chars sampled during reaction. Using an effectiveness-factor-based approach, the effects of pore-diffusion and surface r...

The reaction rates of coal chars with CO2 is an important aspect of coal performance under gasification conditions. Most studies of the char−CO2 reaction are undertaken at temperatures (typically ∼1200 K or below) significantly lower than those found in entrained flow applications, to allow detailed investigations into the surface reaction processes. Application of these data to high temperatures therefore requires consideration of how these reaction rates are affected by gas diffusion through the pore structure of reacting particles, yet there are very few char−CO2 rate data at high temperatures and pressures against which such applications can be tested or verified. This paper presents results of measurements of the char−CO2 reaction rate at high pressures (2.0 MPa) and high temperatures (up to 1673 K) using an entrained-flow reactor and also presents analyses of the morphology of the chars sampled during reaction. Using an effectiveness-factor-based approach, the effects of pore-diffusion and surface r...

Abstract The flow behaviour of coal mineral matter at high temperatures is an important parameter for coal use in entrained flow gasification technologies. Slag flow behaviour is characterised by the temperature dependence of slag viscosity, including the temperature of critical viscosity ( T CV ), which is strongly dependent on slag composition. Moreover, at temperatures below the liquidus temperature this compositional dependence is complicated by the precipitation of solids, and the resultant change in chemical composition of the liquid phase. In the present study, the viscosity behaviour of selected slag compositions is investigated in terms of the dynamics of solid precipitation, compositional changes, and the morphology of crystallised solids. Relationships between slag microstructure, phase composition and viscosity behaviour are described on the basis of viscosity measurements, thermodynamic calculations, and slag quenching experiments. It is shown that the viscosity–temperature behaviour of specific slag compositions was dependent on the amount and size of the solids in the slag, silica/alumina ratio (S/A) and compositional changes of the liquid phase due to solid phase precipitation.

Abstract The flow behaviour of coal mineral matter at high temperatures is an important parameter for coal use in entrained flow gasification technologies. Slag flow behaviour is characterised by the temperature dependence of slag viscosity, including the temperature of critical viscosity ( T CV ), which is strongly dependent on slag composition. Moreover, at temperatures below the liquidus temperature this compositional dependence is complicated by the precipitation of solids, and the resultant change in chemical composition of the liquid phase. In the present study, the viscosity behaviour of selected slag compositions is investigated in terms of the dynamics of solid precipitation, compositional changes, and the morphology of crystallised solids. Relationships between slag microstructure, phase composition and viscosity behaviour are described on the basis of viscosity measurements, thermodynamic calculations, and slag quenching experiments. It is shown that the viscosity–temperature behaviour of specific slag compositions was dependent on the amount and size of the solids in the slag, silica/alumina ratio (S/A) and compositional changes of the liquid phase due to solid phase precipitation.