Using Ethanol for Continuous Biodiesel Production with Trace Catalyst and CO₂ Co-Solvent

The continuous biodiesel production process under sub- and supercritical conditions using a trace amount of potassium hydroxide (KOH) as a catalyst has been studied. CO2 was added as a co-solvent to reduce the reaction time and increase biodiesel yield. The proposed procedure enables simultaneous transesterification and esterification of triglycerides and free fatty acid (FFA), respectively. The shorter reaction time and milder reaction conditions may reduce energy consumption due to the simplification of the separation and purification steps. The process variables, including reaction temperature, ethanol to oil molar ratio, catalyst amount, and process pressure, were systematically optimized. The highest biodiesel yield (98.12%) was obtained after a 25-min reaction time using only 0.11% wt. of KOH and a 20:1 ethanol to oil ratio. The process optimum temperature and pressure were 240 °C and 120 bar, respectively. The proposed kinetic model suggested a first-order reaction with an activation energy of 15.7 kJ·mol-1 and a reaction rate constant of 0.0398/min-1. The thermodynamic parameters such as Gibbs free energy, enthalpy, and entropy were calculated as 144.82 kJ·mol-1, 11.4 kJ·mol-1, −0.26 kJ·mol-1 and at 240 °C, respectively

Towards a Better Air Assisted Flare Design for Low Flow Conditions: Analysis of Radial Slot and Flow Effects

Numerical investigation of flow field characteristics of air injected through an inclined radial slot into a crossflowing stream has been studied for gas flaring applications. CFD is used to simulate turbulent mixing between the inclined slot jet and the crossflowing stream. The slot injection angle with respect to the crossflow, the slot jet velocity, and the slot height were varied in this study. Velocity profiles obtained from the simulations were compared to measured profiles. Simulation results showed that the centerline upflow axial velocities increased with decreasing injection angle and increasing slot height. Results also showed that decreasing injection angle increased the horizontal penetration of the jet flow into the crossflow stream

Two-Step Sub/Supercritical Water and Ethanol Processes for Non-Catalytic Biodiesel Production

The catalyst-free two-step process has been developed for biodiesel production using low-grade feedstocks. The first step consists of triglycerides hydrolysis under subcritical water conditions to generate and increase free fatty acid (FFA) content for ethyl ester production. In its subcritical state, water can be used as both a solvent and a reactant for the hydrolysis of triglycerides. The hydrolyzed product mixture is separated by decantation into the oil phase of FFA (upper layer) and a water phase that contains glycerol (lower layer). In the second step, the hydrolyzed products of free fatty acids were successfully esterified to their ethyl ester in supercritical ethanol conditions without any catalyst. Under the sub- and supercritical conditions of water and ethanol, the hydrolysis and the esterification reactions proceed quickly, with a conversion of greater than 98 % after 10−20 min. This two-step process for biodiesel production offers several advantages, such as milder reaction conditions and pollution reduction due to the use of water instead of organic solvents. Also, the glycerol is removed after the hydrolysis reaction so that the backward reaction between the glycerol and the ethyl ester disappears, and lead to the biodiesel yield and quality improvement. The aim of this study is making a comparison between our previous one-step process and the two-step reaction process to find the best pathway for designing and building an integrated reactor. Indeed, the two-step process is more applicable for low-grade feedstocks with a high amount of FFA and water

Toward a Better Air-Assisted Flare Design for Purge Flow Conditions: Experimental and Computational Investigation of Radial Slot Flow into a Crossflow Environment

Enhancing the flare gas/air mixing process above the flare tip is critical to optimizing flare performance in terms of emissions. A new flare tip design using an aerodynamic nozzle (such as that used in jet engines to increase thrust on takeoff) has been developed to control the flare gas exit velocity and the local mixing above the flare tip. The work described in this paper focuses on understanding the fluid mixing for the new flare tip design. The flow field of a jet injected into a crossflow is found in several systems, including combustion equipment, drying systems, quenching systems, and mixing tanks. A computational fluid dynamics (CFD) technique for simulating radial slot jet flow into crossflow has been validated with experimental results. Sets of experimental data were obtained from an experimental setup, which was designed and built in our laboratory. A hotwire anemometer was used to obtain the measurements of the radial velocity profiles at different axial positions and the centerline velocity profiles that are produced from the impingement of these axial profiles of velocity. A comparison between the simulation velocity profiles and experimental data was performed, and good agreement between the profiles was clearly observed. The obtained data showed that the centerline velocities were increased significantly just after the injection plane of the radial slot due to the reduction of cross-sectional area available for the flow

Experimental Investigation Of The Variation Of The Local Gas Velocities In A Cold Flow Pebble Bed Reactor (PBR) Using A Hot Wire Anemometry Technique

Obtaining accurate results and new benchmark data for the local velocity of the gas flowing within the pebble bed reactor (PBR) is a key step for understanding and benchmarking simulations of the thermal hydraulics in the PBR core as it significantly affects the design and safety operation of these reactors. Therefore, this work focused on studying the local gas velocities inside a pebble bed using a sophisticated hot wire anemometry (HWA) technique, which was supported with a novel probe-protector case that protected the probe, allowing the measurements to be conducted at various locations in a pebble bed with pebble diameter of 5cm and an aspect ratio of 6. The measurements were conducted at various superficial inlet gas velocities (0.3≤Ug≤2.4m/s), covering both transitional and turbulent flow conditions (993.78≤Re≤7950.24) at three axial levels and four radial locations (r/R=0, 0.33, 0.67, 0.9). The results highlighted the effect of the wall on the variation of the local gas velocities inside the pebble bed, as higher gas velocities were recorded at the near-wall region, where the void fractions are higher, providing a path of the least resistance to the flow of the gas, compared to the center of the bed. Furthermore, a second order polynomial correlation with an R2=93.96% and an AARE equal to 1.47% was developed for the prediction of the local gas velocity inside the bed, within the experimental range of the study. The accurate gas velocity measurements obtained in this study can serve as benchmark data for the validation of CFD simulations coupled with heat transfer calculations

Experimental Investigation of Coiled Tubing Buckling Effect on Annular Frictional Pressure Losses

Coiled tubing (CT) technology has been widely used in oilfield operations, including workover applications. This technology has achieved considerable economic benefits; however, it also raises new challenges. One of the main challenges that were encountered while using this technology is the buckling of the CT string. It can occur when the axial compressive load acting on the CT string exceeds the critical buckling loads, especially in highly deviated/horizontal and extended reach wells. Moreover, this issue becomes more critical when using non-Newtonian fluids. Therefore, the major focus of this study is to identify the frictional pressure loss of non-Newtonian fluids in an annulus with a buckled inner tubing string. In the present study, a laboratory-scale flow loop was used to investigate the influence of various buckling configurations (i.e., sinusoidal, transitional, and helically) of the inner pipe on the annular frictional pressure losses while circulating non-Newtonian drilling fluids. The experiments were conducted on a horizontal well setup with a non-rotating buckled inner pipe string, considering the impact of steady-state isothermal of laminar, transition, and turbulent flow regions on frictional pressure losses. Six different Herschel-Bulkley fluids were utilized to examine the dependence of pressure losses on fluid rheological properties (i.e., yield stress, consistency index, and flow behavior index). Experiments showed potential to significantly decrease the frictional pressure losses as the axial compressive load acting on the inner pipe increases. The effect of buckling was more pronounced when fluids with higher yield stress and higher shear-thinning ability were used. In addition, by comparing the non-compressed and the compressed inner pipe, an additional reduction in frictional pressure losses occurred as the axial compressive load increased. However, the effect of the compressed inner pipe was insignificant for fluids with a low yield stress, consistency index, and high-flow-behavior index, especially in the laminar region. The information obtained from this study will contribute toward providing a more comprehensive and meaningful interpretation of fluid flow in the vicinity of a buckled coiled tubing string. In the same manner, accurate knowledge of the predicted friction pressure will improve safety and enhance the optimization of coiled tubing operations

An air-assisted flare for biomass gasifiers

reportComputational fluid dynamics (CFD) was used to simulate the combustion practice of the gases that produce from gasification process. In this simulation a new air-assisted flare design which capable to handle low flowrates of these gases with high performance was used. The simulated cases were performed by using the gases that produced in the downdraft gasifier at our lab. Wood pellet was used as the biomass feedstock of the gasification process in the current study which results mainly CO, H2, CH4, and CO2 as gasification gases. Different low flowrates of these gases were used in the simulation. The non-premixed Steady Diffusion flamelet combustion model was used in this study with 22-species reduced reaction mechanism to predict the combustion efficiency of gasification gases. The results show a good flare performance when the new flare design is used