Fresh Feed Rate Research Articles

A new class of control structures for heterogeneous reactive distillation processes

There are only a handful of process control structures applied to the neat operation of both homogeneous and heterogeneous reactive distillation, for two-reactants / two-products one-reaction systems. All of these control structures employ inferential temperature control (or concentration analyzers) at some location in the column to balance the reaction stoichiometry.This original study proposes a new class of control structures applicable to heterogeneous reactive distillation. The novel idea, common to all control structures, is based on monitoring the inventory of the reactant involved in the heterogeneous azeotrope. The organic reflux (or the organic reflux / aqueous distillate ratio) is used to detect the excess or deficiency of the reactant, based on which the fresh feed rate is adjusted such that the reaction stoichiometry is balanced. This control philosophy is simple and easy to implement in different ways as illustrated by several case studies. The performance of the proposed control structures depends on the system studied. For some systems, the performance is better, as good or nearly as good as that of the literature control structures. But for other systems, the performance is poor or the structure even fails to control the process, due to the insufficient feedback from inventory measurements.

Plantwide Control for Maximum Throughput Operation of an Ester Purification Process

Plantwide control for maximum throughput operation of an ester purification process consisting of a liquid–liquid extractor (LLX), a distillation column, and material recycle is evaluated. The extractor uses water solvent and is necessary to cross a distillation boundary making pure ester product recovery feasible. Extraction capacity is the bottleneck constraint. A steady state analysis reveals the occurrence of steady state multiplicity induced infeasibility for too high fresh feed rates and for too low water feed rates. To avoid infeasibility due to the multiplicity behavior, we recommend using the extractor feed rate as the throughput manipulator (TPM) with the fresh feed rate adjusted as a makeup stream (CS1). The other control loop pairings are conventional. Rigorous closed loop dynamic results show that CS1 is significantly more robust than the conventional control structure (CS2) with the fresh feed rate as the TPM. In particular, CS1 achieves more than 25% higher maximum throughput compared to CS...

Limitation of HPGR application

Many researchers have discussed the advantages of the pressure breakage mechanism and the importance of high-pressure grinding rolls (HPGR) in the hard minerals industry but the impact of this machine on the final product of the comminution circuit at an industrial scale has been less studied. In this research, the influence of HPGR utilisation on the comminution circuit of the 4th line of the iron ore concentrator at the Golgohar Mining and Industrial Complex, Iran, was investigated. Two series of experiments were carried out: the first was performed with the HPGR in the circuit (ON) while the other was conducted with the HPGR out of the circuit (OFF). The results show that the HPGR had no significant effect on the final product of the comminution circuit from the point of view of particle size. The trommel screen overflow rate decreased by 5.1% of the fresh feed rate when the HPGR was ON. To determine the probable reasons, X-ray computed tomography analyses were carried out. These showed that cracks in the particles entering the grinding circuit were caused not only by the HPGR since some small cracks were present in the HPGR feed. It was also found that coarse particles are more susceptible to failure in the HPGR and that soft materials, such as talc, reduce the HPGR performance.

Biohydrogen and Bioethanol Production from Biodiesel-Based Glycerol by Enterobacter aerogenes in a Continuous Stir Tank Reactor.

Crude glycerol from the biodiesel manufacturing process is being produced in increasing quantities due to the expanding number of biodiesel plants. It has been previously shown that, in batch mode, semi-anaerobic fermentation of crude glycerol by Enterobacter aerogenes can produce biohydrogen and bioethanol simultaneously. The present study demonstrated the possible scaling-up of this process from small batches performed in small bottles to a 3.6-L continuous stir tank reactor (CSTR). Fresh feed rate, liquid recycling, pH, mixing speed, glycerol concentration, and waste recycling were optimized for biohydrogen and bioethanol production. Results confirmed that E. aerogenes uses small amounts of oxygen under semi-anaerobic conditions for growth before using oxygen from decomposable salts, mainly NH4NO3, under anaerobic condition to produce hydrogen and ethanol. The optimal conditions were determined to be 500 rpm, pH 6.4, 18.5 g/L crude glycerol (15 g/L glycerol) and 33% liquid recycling for a fresh feed rate of 0.44 mL/min. Using these optimized conditions, the process ran at a lower media cost than previous studies, was stable after 7 days without further inoculation and resulted in yields of 0.86 mol H2/mol glycerol and 0.75 mol ethanol/mole glycerol.

Design and Control of a Complete Azeotropic Distillation System Incorporating Stripping Columns for Isopropyl Alcohol Dehydration

As demonstrated by Pham and Doherty [Chem. Eng. Sci.1990, 45, 1823] in an ethanol dehydration process and by Arifin and Chien [Ind. Eng. Chem. Res.2007, 46, 2535] in an isopropyl alcohol dehydration process, a three-column heterogeneous distillation sequence which contains a preconcentrator column, an azeotropic column, and an entrainer recovery column is more energy saving than two-column and four-column sequences. The three-column sequence for the isopropyl alcohol (IPA) dehydration process, according to Arifin and Chien, is more energy-saving than the two-column sequence, but the capital cost of the entire sequence is more expensive than that of the two-column sequence. Because the reflux ratio used either in the preconcentration column or the recovery column of the three-column IPA dehydration system is quite small, these two conventional distillation columns are both replaced by a stripping column, and in this study a new separation scheme is thereby developed. The economic analysis of the proposed system shows there is more saving in energy and capital costs than the two- and three-column sequences aforementioned. Further, in developing a plant-wide control structure, a tray temperature control loop is implemented in each of the three columns which regulates reboiler duty in order to maintain the bottom product compositions for the new scheme, and ratio control of the organic reflux flow to the feed flow rate of the azeotropic column is used to reject feed rate disturbance. The purities of water achieved in the preconcentrator and entrainer recovery columns are greater than 99.88 mol %, and the IPA purity in the product stream is greater than 99.99985 mol %. Closed-loop responses to ±20% changes in fresh feed rate and feed H2O composition show that the proposed strategy has good control performance.

A model on chemical looping combustion of methane in a bubbling fluidized-bed process

We developed a mathematical model to discuss the performance of chemical looping combustion (CLC) of methane in continuous bubbling fluidized-beds. The model considers the particle population balance, oxidation and reduction rate of particles in fluidized beds. It also considers utilization efficiency of oxygen carrier (OC) particles, residence time of particles in each reactor, and particle size in reaction rate. The model was applied for a bubbling coreannulus fluidized-bed process. The core bed was the fuel reactor (0.08 m-i.d., 2.1 m-height) and the annulus bed was the air reactor (0.089 m-i.d., 0.15 m-o.d., 1.6 m-height). The process employed a type of Ni-based OC particles. The present model agrees reasonably well with the combustion efficiency measured in the process. Simulation was performed to investigate the effects of some variables for the process. The present model revealed that the range of circulation rate of OC particles for achieving complete combustion determined the operating range of the CLC system. The minimum circulation rate of OC particles for complete combustion decreased in the considered operating range as temperature or bed mass increased in the fuel reactor. A large mass of the fuel bed was necessary to obtain complete combustion at low fuel reactor temperature. The fresh feed rate of OC particles for steady state operation increased in complete combustion condition as temperature or static bed height or gas velocity increased.

Simulation of solid oxide fuel cell systems integrated with sequential CaO–CO2 capture unit

Abstract This paper presents preliminary simulation results from the performance analysis of the integrated systems of calcium oxide (CaO)–carbon dioxide (CO2) capture unit and solid oxide fuel cell (SOFC). The CO2 was extracted for further sequestration in the CaO–CO2 capture unit. Three configurations of the integrated systems (CaO-Before-SOFC: CBS, CaO-After-SOFC: CAS and CaO-After-Burner: CAB) were considered. It was found that the CO2 capture efficiency (Ec) is dependent on CaO fresh feed rate (F0) and CaO recycle rate (FR). The improvement of SOFC performance was only realized for the CBS system. The SOFC performance increases with increasing CO2 Ec. The preliminary economic analysis was carried out considering total additional cost per mole of CO2 captured. At a low percentage of CO2 capture ( 94%).

Improved oxygen delivery in a continuous-roller-bottle reactor

Variations to the original aeration system in a continuous roller bottle reactor of novel design have been tested and compared for optimal oxygen (O) delivery. Reactor operating parameters that affect O transfer are rotation rate, liquid-volume level, fresh-feed rate, and supplementary-aeration rate. Design modifications to enhance gas-liquid O transfer include the addition of wall baffles and center baffles. The number and location of each of these baffles are compared for their effect on k(L)a values in the reaction chamber. The liquid feed into the system has been modified to improve the axial liquid mixing and O transfer.

Instrumentation and control of a continuous 0.6-m SAG mill circuit

A 60-cm semiautogenous grinding (SAG) mill was designed for continuous wet operation in closed circuit with a vibrating screen. The circuit is fully instrumented and automated. Part of the control system incorporates Foxboro SPEC 200 controllers around the pump box to maintain level. The rest of the control system involves an ACTION model BC2 basic direct digital controller that handles all other inputs/outputs and contact closure sensing. The success of the control system is attributed to the uniqueness of specially designed mass flow metering systems. Various control strategies are possible. Employed to date has been control of a mill load setpoint by cascading the deviation from load setpoint as the setpoint to the fresh feed rate “controller”. Mill feed water is ratioed to total flow rate of solids fed to the mill. The performance of the circuit is being correlated with the performance of full scale SAG circuits in British Columbia to develop models, to assess the feasibility of scale up and to investigate the effects of design variables on responses such as circuit throughput.