Anil K. Mehrotra

Axial dispersion in the three-dimensional mixing of particles in a rotating drum reactor

Horizontal drum reactors are widely used in industry for the processing of granular material. They are ideally suited for chemical processes that require high temperatures at near-atmospheric pressure. However, the complexities of these reactors have resulted in empirical design procedures that lead to very conservative and costly reactors. This study first reviews critically the extensive literature on experimental results obtained on rotary kilns (without flights) and proposes new design equations for the axial-dispersion coefficient in terms of rotational speed, degree of fill, drum diameter, and particle diameter. A total of 179 data points from the literature, encompassing both the batch and the continuous operational modes, yielded design correlations for slumping, rolling/cascading and cataracting bed behaviours. Additionally, new measurements were made on a pilot-scale rotary drum by tracking a single radioactive particle (emitting gamma-rays) using a battery of nine scintillation counters; these data confirmed the correctness of the proposed design correlations.

A review of practical calculation methods for the viscosity of liquid hydrocarbons and their mixtures

This paper reviews methods for the prediction and correlation of Newtonian viscosity for pure components and mixtures of liquid hydrocarbons and petroleum fluids, which are suited for practical engineering use. The methods reviewed were chosen because they are well known and accepted or appear potentially promising. The methods are categorized as semi-theoretical or empirical and further distinguished as predictive or correlative. The applicability and average deviations for each method are discussed, with the recommended methods identified.

Alkaline hydrothermal conversion of cellulose to bio-oil: Influence of alkalinity on reaction pathway change

The effects of alkalinity on alkaline hydrothermal conversion (alkaline-HTC) of cellulose to bio-oil were investigated in this study. The results showed that the initial alkalinity greatly influenced the reaction pathways. Under initial strong alkaline conditions with final pH greater than 7, alkaline-HTC only followed the alkaline pathway. However, under initial weak alkaline conditions with final pH of less than 7, acidic as well as alkaline pathways were involved. The main mechanism behind this change of reaction pathways under weak alkaline conditions was that carboxylic acids were first formed from cellulose via the alkaline pathway and then neutralized/acidified the alkaline solutions. Once the pH of the alkaline solutions decreased to less than 7, the acidic instead of the alkaline reaction pathway occurred. This change of the reaction pathways with initial alkalinity partly explained the inconsistent results in the literature of alkaline-HTC bio-oil compositions and yields.

Comparison of chemical solvents for mitigating CO2 emissions from coal-fired power plants

Abstract There is a growing concern about the effect of greenhouse gases on global warming. Among the many greenhouse gases, CO 2 produced from burning fossil fuels is a major contributor due to the huge volumes emitted into the atmosphere. According to the estimates of the Intergovernmental Panel on Climate Change (IPCC), a worldwide reduction in the emission of greenhouse gases by more than 60% is necessary to avert significant global climate changes. This paper examines the key issues involved in greenhouse gas emissions from coal-fired power plants. At the present time, absorption by chemical solvents appears to be best option for the separation of CO 2 from low pressure flue gas streams. The costs of separation and disposal of CO 2 from existing coal fired, air blown boilers are estimated to increase the cost of electricity by about 75%. Therefore, there is a need to optimize the selection of processing solvents and operating parameters to minimize the cost of separation. Increasing the inlet flue gas pressure did not improve mass transfer rates sufficiently to compensate for the higher compression costs. The effects of other process variables were also examined. In this work, we have examined the cost effectiveness of six ethanolamine-based solvents. Overall, monoethanolamine (MEA) was found to be the best solvent.

Non-isothermal crystallization kinetics of n-paraffins with chain lengths between thirty and fifty

The non-isothermal crystallization kinetics of four high-purity even-number n-paraffins, namely n-C&&2, n-&HrO, n-C,H, and n-CsOHloz, have been studied using differential scanning calorimetry (DSC). The data are treated in terms of the Ozawa theory utilizing, for the first time, a semi-empirical formulation for the so-called Ozawa cooling crystallization function. The derivations are based on the theories of surface nucleation and growth rate of extended-chain crystals. Predictions from the proposed model are in excellent agreement with the experimental data for the four n-paraffins at relatively low supercooling.

Thermal behaviour of polymorphic n-alkanes: effect of cooling rate on the major transition temperatures

Abstract The thermal behaviour of selected polymorphic even-numbered and odd-numbered n -alkanes, namely n -C 23 H 48 n -C 25 H 52 , n -C 28 H 58 , n -C 30 H 62 , n -C 33 H 68 , n -C 34 H 70 and n -C 37 H 76 was studied using differential scanning calorimetry (d.s.c.). Both the melting and the crystallization d.s.c. thermograms for these paraffins exhibit two major peaks, α and β, corresponding to the liquid-solid and solid-solid transitions. At the same rate of temperature change, the shape and peak height of the melting endotherms differ considerably from those of the cooling exotherms. The experimental results are explained in terms of the established crystallographic descriptions of the crystalline rotator phases for these alkanes. More importantly, the peak-to-peak temperature difference ( ΔT peak = T α − T β ) depends on the carbon number but not on the cooling rate. The following linear relation, which is independent of cooling rate, is proposed for the variation of ΔT peak with the carbon number ( C ): ΔT peak = 17 −0.42 C .

Liquid-solid-solid thermal behaviour of n-C44H90 + n-C50H102 and n-C25H52 + n-C28H58 paraffinic binary mixtures

Abstract The equilibrium phase behaviour and thermal characteristics of n-C25H52 + n-C28H58 and n-C44H90 + n-C50H102 binary systems have been studied using a differential scanning calorimeter (DSC). As in the case of pure polymorphic n-alkanes, both the melting and crystallization thermograms for n-C25H52 + n-C28H58 mixtures exhibit two major peaks, α and β, corresponding to the liquid-solid and solid-solid transitions. Hence, isomorphous solid solutions were formed for these mixtures. Interestingly, the peak-to-peak temperature difference (ΔTpeaks = Tα − Tβ) for binary mixtures does not vary linearly with the mixture composition. More importantly, ΔTpeaks does not depend on the cooling rate. For n-C44H90 + n-C50H102 mixtures, on the other hand, the likelihood to form either isomorphous or eutectic systems was dependent on the thermal history of the prepared mixture. Once formed, however, eutectic and/or isomorphous systems were found to be stable over long periods of time.

Liquid-solid phase transformation of C16H34, C28H58 and C41H84 and their binary and ternary mixtures

Abstract Differential scanning calorimetry (DSC) was used to study the phase transformations of three pure n -alkanes, namely hexadecane (C 16 H 34 ), octacosane (C 28 H 58 ) and hentetracontane (C 41 H 84 ), and their binary and ternary mixtures. The DSC results were used to investigate the liquid–solid phase equilibrium of n -alkane mixtures, all of which show eutectic behavior. The experimental liquid–solid phase transformation temperatures were compared with predictions obtained from available eutectic equilibrium models. The results show the presence of non-idealities in all of the mixtures.

Field-scale operation of methane biofiltration systems to mitigate point source methane emissions

Methane biofiltration (MBF) is a novel low-cost technique for reducing low volume point source emissions of methane (CH₄). MBF uses a granular medium, such as soil or compost, to support the growth of methanotrophic bacteria responsible for converting CH₄ to carbon dioxide (CO₂) and water (H₂O). A field research program was undertaken to evaluate the potential to treat low volume point source engineered CH₄ emissions using an MBF at a natural gas monitoring station. A new comprehensive three-dimensional numerical model was developed incorporating advection-diffusive flow of gas, biological reactions and heat and moisture flow. The one-dimensional version of this model was used as a guiding tool for designing and operating the MBF. The long-term monitoring results of the field MBF are also presented. The field MBF operated with no control of precipitation, evaporation, and temperature, provided more than 80% of CH₄ oxidation throughout spring, summer, and fall seasons. The numerical model was able to predict the CH₄ oxidation behavior of the field MBF with high accuracy. The numerical model simulations are presented for estimating CH₄ oxidation efficiencies under various operating conditions, including different filter bed depths and CH₄ flux rates. The field observations as well as numerical model simulations indicated that the long-term performance of MBFs is strongly dependent on environmental factors, such as ambient temperature and precipitation.

Effect of enzyme additions on methane production and lignin degradation of landfilled sample of municipal solid waste

Operation of waste cells as landfill bioreactors with leachate recirculation is known to accelerate waste degradation and landfill gas generation. However, waste degradation rates in landfill bioreactors decrease with time, with the accumulation of difficult to degrade materials, such as lignin-rich waste. Although, potential exists to modify the leachate quality to promote further degradation of such waste, very little information is available in literature. The objective of this study was to determine the viability of augmenting leachate with enzymes to increase the rate of degradation of lignin-rich waste materials. Among the enzymes evaluated MnP enzyme showed the best performance in terms of methane yield and substrate (lignin) utilization. Methane production of 200 mL CH(4)/g VS was observed for the MnP amended reactor as compared to 5.7 mL CH(4)/g VS for the control reactor. The lignin reduction in the MnP amended reactor and control reactor was 68.4% and 6.2%, respectively.