The combustion of droplets of liquid fuels and biomass particles

Studies have been made of the combustion of droplets of liquid hydrocarbons, including kerosene and Diesel fuels, biofuels such as FAME and the alcohols, especially ethanol and n-butanol, and of pulverised solid biomass materials such as pine wood and Miscanthus which burn in an analogous fashion. Information is given on the burning rates of both the liquids and the solids and data given on soot formation yields for the different fuels. The mechanism of soot formation is discussed in relation to (1) volatile liquid fuels such as n-heptane, alcohols and aviation fuels, (2) liquid fuels having higher aromatic levels such as Diesel fuels, and (3) biomass particle combustion.     

Bench-scale production of liquid fuel from woody biomass via gasification

The bench-scale production of hydrocarbon liquid fuel was achieved from woody biomass via gasification. The daily production capacity of the biomass-to-liquid (BTL) plant used in this study was 7.8 L of hydrocarbon liquid from 48 kg of woody biomass (on a dry basis), corresponding to 0.05 barrels. The BTL process involved the following steps: oxygen-enriched air gasification of the woody biomass, wet and dry gas cleaning, gas compression, carbon dioxide removal, and the Fischer-Tropsch (FT) synthesis reaction. In the gasification step, oxygen-enriched air gasification was carried out using a downdraft fixed-bed gasifier. The content of oxygen, which acts as the gasifying agent, was increased from 21.0 to 56.7 vol%; maximum values of the conversion to gas on a carbon basis and cold gas efficiency-approximately 96 C-mol% and 87.8%, respectively-were obtained at an oxygen content of around 30 vol%. With the increased oxygen content, the concentrations of CO, H₂, and CO₂ increased from 22.8 to 36.5 vol%, from 16.8 to 28.1 vol%, and from 9.8 to 14.8 vol%, respectively, while that of N₂ decreased from 48.8 to 16.0 vol%. The feed gas for the FT synthesis reaction was obtained by passing the product gas from the gasification step through a scrubber, carbon dioxide removal tower, and desulfurization tower; its composition was 30.8 vol% CO, 25.2 vol% H₂, 0.9 vol% CO₂, 2.5 vol% CH₄, 40.6 vol% N₂, < 5 ppb H₂S, and < 5 ppb COS. The hydrocarbon fuel was synthesized in a slurry bed reactor using hexadecane as the solvent and a Co/SiO₂ catalyst. For hydrocarbons with carbon chain lengths of more than 5 carbon atoms (collectively referred to as C₅₊) in the liquid fuel, a selectivity of 87.5% was obtained along with a chain growth probability of 0.84 under the following conditions: 4 MPa, 280 to 340 °C, and a ratio of catalyst weight to feed gas rate (W/F) of 9.3 g·h/mol.     

Investigation of gas properties, design, and operational parameters on hydrodynamic characteristics, mass transfer, and biomass production from natural gas in an external airlift loop bioreactor

An external airlift loop bioreactor (EALB) was used for production of biomass from natural gas. The effect of riser to downcomer cross sectional area ratio (A_r/A_d), volume of gas-liquid separator, superficial gas velocity (U_sgr), and physical properties of gases and their mixtures [υ_g (μ/ρ) and D_g] were investigated on mixing time, gas hold-up, and volumetric gas liquid mass transfer coefficients (k_La). It was found that A_r/A_d has remarkable effects on gas hold-up and k_La due to its influence on mixing time. Kinematic viscosity (υ_g) showed its significant role on mixing time, gas hold-up and k_La when different gases used (mixing time changes directly whereas gas hold-up and k_La change indirectly). Moreover, it was found that diffusion coefficient of gas in water (D_g) has remarkable effect on k_La. The volumetric mass transfer coefficients for methane and its mixtures with oxygen (three different mixtures) were determined at different geometrical and operational factors. In average, the rate of oxygen utilization is approximately 1.8 times higher than that of methane. A gas mixture of 25 vol% methane and 75 vol% oxygen was the best gas mixture for biomass production in the EALB. The correlations developed for predicting the mixing time, gas hold-up, and k_La in terms of U_sgr, A_r/A_d, volume of gas-liquid separator, and gas phase properties have been found to be encouraging.     

Co-pyrolysis characteristics of coal and natural gas

A co-pyrolysis experiment of coal and natural gas was investigated on a fixed-bed reactor. SEM was used to study the structure changes of the exterior surface of char prepared in this co-pyrolysis experiment, while GC was also utilized to analyze the associated gas. The result showed that, with increasing temperature, the coal char tended to agglomerate. GC and SEM results show that the CH₄ decomposition on the exterior surface of char was turned to filamentous char and extended around like coral. It was also proved that the co-pyrolysis of coal and natural gas promoted syngas production. A synergistic effect of coal and natural gas does exist during this process. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Study of geometry and operational conditions on mixing time, gas hold up, mass transfer, flow regime and biomass production from natural gas in a horizontal tubular loop bioreactor

A horizontal tubular loop bioreactor (HTLB) was used for production of biomass from natural gas. Hydrodynamic characterizations (mixing time and gas hold up) and mass transfer coefficients were considered in the HTLB (L=2.2 m, H=0.4 m and D=0.03 m) as functions of design parameters, i.e., horizontal length to diameter ratio (L/D) and volume of gas-liquid separator (S) as well as operational parameters, i.e., superficial gas and liquid velocities (U_sG, U_sL). In addition, flow regime in different gas and liquid flow rates was investigated. It was observed from experimental results that U_sL has remarkable effects on gas hold up and k_La due to its influence on mixing time. The volumetric mass transfer coefficients for oxygen (k_La_O2) and methane (k_La_CH4) were determined at different geometrical and operational factors. In average, the amount of oxygen consumption for metabolism is approximately 1.4 times higher than that of methane. In bubble flow regime, the HTLB was used for biomass production, too. A gas mixture of 50% methane and 50% oxygen (based on results of dry cell weight, optical density and doubling time) was the best gas mixture inlet for biomass production. The empirical correlations for mixing time, gas hold up and k_La in terms of U_sG, U_sL, L/D and volume of gas-liquid separator were obtained and expressed separately.     

A pillared-layer metal-organic framework for efficient separation of C3H8/C2H6/CH4 in natural gas

Metal-organic frameworks (MOFs) have great potentials as adsorbents for natural gas purification. However, the trade-off between selectivity and adsorption capacity remains a challenge. Herein, we report a pillared-layer metal-organic framework Ni(HBTC)(bipy) for efficiently separating the C₃H₈/C₂H₆/CH₄ mixture. The experimental results show that the adsorption capacity of C₃H₈ and C₂H₆ on Ni(HBTC)(bipy) are as high as 6.18 and 5.85 mmol·g^-1, while only 0.93 mmol·g^-1 for CH₄ at 298 K and 100 kPa. Especially, the adsorption capacity of C₃H₈ at 5 kPa can reach an unprecedented 4.52 mmol·g^-1 and for C₂H₆ it is 1.48 mmol·g^-1 at 10 kPa. The ideal adsorbed solution theory predicted C₃H₈/CH₄ selectivity is as high as 1857.0, superior to most of the reported materials. Breakthrough experiment results indicated that material could completely separate the C₃H₈/C₂H₆/CH₄ mixture. Therefore, Ni(HBTC)(bipy) is a promising material for separation of natural gas.     

Coproduction of acetic acid and hydrogen/power from natural gas with zero carbon dioxide emissions

A process plant flow sheet that coproduces acetic acid and hydrogen/power from natural gas with zero carbon dioxide emissions is developed. Two cases are explored: the production of acetic acid and hydrogen (Case 1) and the production of acetic acid and power (Case 2). This is realized by the selection of an appropriate reaction cluster whose sum results in the overall reaction that coproduces acetic acid and hydrogen/power. The concept of energetic self‐sufficiency is introduced and it imposes constraints on the system defined in terms of the ratio of oxygen feed to acetic acid produced. Heat and power integration of the converged flow sheet reveals an operating range for each case that guarantees energetic self‐sufficiency. Operating points are chosen to conduct a preliminary economic analysis and a carbon dioxide cost and performance metric calculation to quantify profitability and carbon capture potential of the overall process. © 2017 American Institute of Chemical Engineers AIChE J, 64: 860–876, 2018     

Production of benzene,toluene, and xylenes from natural gas via methanol: Process synthesis and global optimization

A systematic global optimization‐based process synthesis framework is presented to determine the most profitable processes to produce aromatics from natural gas. Several novel, commercial, and/or competing technologies are modeled within the framework, including methanol‐to‐aromatics, toluene alkylation with methanol, selective toluene disproportionation, and toluene disproportionation and transalkylation with heavy aromatics, among others. We propose a stand‐alone chemicals facility: the main products are aromatics with allowable by‐products of gasoline, liquefied petroleum gas, and electricity. Several case studies are discussed that produce varying ratios of para‐, ortho‐, and meta‐xylene across multiple refinery capacities. The results indicate that utilizing natural gas for the production of aromatics is profitable with net present values as high as $3800 MM dollars and payback periods as low as 6 years. The required investment for these refineries represents as much as a 65% decrease compared to published estimates of similar coal‐based capacity plants. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1531–1556, 2016     

Investigating the effect of dianhydride type and pyrolysis condition on the gas separation performance of membranes derived from blended polyimides through statistical analysis

In this study, properly designed experiments are utilized to improve and optimize the main parameters including the selection of precursors with different molecular structures, blend composition of precursors and conditions of carbonization. Optimum conditions are met for UIP-R/PBI, at blend composition of 94% and pyrolysis temperature of 620 °C at 10⁻⁷ Torr. Under such conditions, the model estimated permeability of CH₄ and CO₂ equal to 26.7 and 310 Barrer, while measured selectivity responses of CO₂/CH₄ is 77.5, respectively. As a result, greater values of separation efficiency are achieved in the range of 0.88–0.97 polyimide content in these blends.