Band 21, Heft 1

Microreactors are small in size with significant heat and mass transfer. Performic acid (PFA) is an important organic compound. It has broad applications in food, oil and chemical industries because of its oxidizing properties. In the present work PFA is produced in a continuous flow Teflon spiral capillary microreactor. The PFA is produced with and without a heterogeneous catalyst. The formic acid (FA) and hydrogen peroxide (HP) are the reactants to produce the PFA. It is a reversible reaction. The aim of the present work to monitor the consequence of hydrogen peroxide concentration, temperature and heterogeneous catalyst (Amberlite) for conversion of the FA. The experimental results showed that the formation of the PFA is effected with increase in hydrogen peroxide concentration, percentage of catalyst and temperature. The PFA formed within short residence time by the use of solid catalyst. The heterogeneous catalysts are better in decreasing corrosion and segregation of the catalyst compared to homogeneous catalysts. The best conditions for the PFA synthesis reaction were noted that 10 min residence time, 30 w/v% of HP, 6 wt% of catalyst concentration based on formic acid and 30 °C. Hence, the maximum concentration of the PFA was recorded 2.8 mol/L (X FA  = 39.4%)

Unstable processes are hard to stabilize as they contain one or more positive poles which result in unbounded dynamic behavior. The occurrence of the delay and positive zeros often creates more difficulty in controlling such unstable plants. Most control strategies meant for first-order unstable processes fail to stabilize and control the higher-order unstable processes. Hence, a new dual-loop hybrid control structure is suggested for dead-time unbounded second-order processes with positive/negative zeros. Inner-loop has a stabilizing PID controller. The PID controller parameters are derived by comparing the numerator and characteristic polynomial coefficients in the transfer function for internal-loop servo action. A fractional-order internal model controller (FOIMC) is used in the external-loop. Methods for the selection of outer-loop tuning parameter and fractional-order are also discussed. By comparing the simulation results with a contemporary single-loop scheme, the usefulness of the suggested scheme is proved. The suggested scheme is capable of minimizing the overshoot and improving the overall dynamic performance. Finally, the usefulness of the suggested scheme is also demonstrated by a case study on temperature control of a continuous stirred tank reactor (CSTR) during a first-order irrevocable exothermic reaction.

This paper builds a wireless precision control function waveform pulse variable speed stirring device with point-to-point data transmission between the host computer and the microcontroller, which uses a programmable STM32 microcontroller as the system controller, superimposed with a single closed-loop static differential-free speed control system and a pulse broadband modulation (PWM) system to control the DC brush motor driving the stirring paddle based on arbitrary waveform function variable speed stirring respectively. The effects of different pulse waveform stirring systems on the purification effect of Cadmium ions (Cd 2+ ) from zinc sulfate solution were studied under the same pulse period and maximum speed. The experimental results show that when K P  = 0.012 and T i  = 100, the anti-disturbance of the motor during the variable speed stirring process can be effectively improved, and the speed adjustment time is short and robust; when the Cd 2+ purification rate reaches 92%, the purification time of the variable sine function stirring system is shortened by about 40% compared with that of the uniform speed stirring system, and that of the variable trapezoidal function stirring system is shortened by about 33.3% compared with that of the uniform speed stirring system. When the reaction is finished, the Cd 2+ concentration is reduced to 6 mg/L by the variable sinusoidal stirring system only, and the Cd 2+ concentration is lower than 10 mg/L in a shorter time compared with the time required for cadmium removal in the actual industrial production line.

This current work proposes a refined investigation on the improved sequential relay autotuning method to compute the optimal parameters of the decentralized PI controller for Two Input Two Output (TITO) system using relay feedback method. The sustained oscillation occurring in the relay response with the sequential relay autotuning and the simultaneous relay autotuning method is analyzed by taking the higher-order harmonics into consideration and the efficient performance results of the decentralized PI control systems are obtained. These methods have been applied to an Industrial-Scale Polymerization (ISP) reactor transfer function model. In closed-loop studies, comparative analysis of autotuning methods has been carried out using simulation. The effect of measurement noise and robustness are studied in the proposed work. The robustness performance of the system using improved sequential relay autotuning is enhanced by 5–25% for servo operation and 11–40% for regulatory operation. The performance of the systems with the effect of measurement noise using improved sequential relay autotuning is enhanced by 2–24% for servo operation. Comparative analysis has been carried out with the improved sequential relay autotuning and the simultaneous relay autotuning method. It is observed that the proposed method provides improved closed-loop performances and less sum of Integral square error even in presence of robustness and effect of measurement noise.

The slurry phase hydrocracking was carried out in a 150 kg/d pilot plant with a change of reaction temperature and different feedstocks including vacuum residue (VR), thermal cracking residue (TCR), 58% VR + 42% DOA (VRD) and 32% VR + 27% DOA + 41% TCR (VRDT). The results demonstrated that the conversions of residue and asphaltene, and hydrogen consumption had a linear relationship with the increment of reaction temperature. The TCR, VRD and VRDT with high content of asphaltene had the characteristic of higher asphaltene conversion and coke yield, but the coke yield was still low, and less than 1.3%. In addition, the removal rate of sulfur was much higher than that of nitrogen, while that of nickel and vanadium reach above 77 and 88%, respectively. The light liquid fraction product could further transform into high value-added chemical materials or clean transport fuel, and the heavy liquid fraction product could utilized as a very good raw material for high quality products as needle coke and carbon-based materials.

To effectively control the flow and combustion of pulverised coal in down-fired boilers and improve their thermal efficiency while ensuring low NO x emissions, on arch secondary air (OASA) combustion technology and a smoke-tracing analysis were proposed. The aerodynamic characteristics of a 300-MWe Foster Wheeler (FW) down-fired boiler with the OASA ratios ( R OASA ) of 0%, 10%, 20%, and 30%, the flow trajectories and mixing characteristics of OASA, and fuel-rich coal/air flow (FRA) and fuel-lean coal/air flow (FLA) were studied experimentally. For the R OASA of <10%, FRA and FLA flow to furnace centre soon after they are injected into the furnace. OASA and FLA may mix with FRA before ignition. For the R OASA of 20% or higher, FRA and FLA flow to the near-wall area soon after being injected into the furnace. FRA mixes with OASA after ignition. With the increase in R OASA , the mixing distance between OASA and FRA increases first and then decreases. The penetration depth of coal/air flow and furnace airflow fullness increases. For the R OASA of 30%, the dimensionless penetration depth of coal/air flow can exceed 0.7. Furnace dimensionless airflow fullness at all the dimensionless heights can exceed 0.6. In real operation, the recommended R OASA is between 20 and 30%.

The evaluation of mixing effects is crucial in industrial production such as chemical and metallurgical industries. An improved Betti number method is proposed by using a gas-liquid top-blow mixing experiment and a direct contact heat exchange experiment. This method is adapted to the comprehensive evaluation of flow mixing and heat transfer performance under conditions of dispersed particles or bubbles where the target is identifiable. The comparison results and reveals that our method can not only portray the mixing effect by the critical point of the area integration curve of the Betti number time series but also the parameters (i.e., slope and intercept) obtained after the area integration of the Betti number curve by the logistic regression model can effectively characterize the mixing time and heat exchange performance. The intercept variation of the area integral of the Betti number curve was found to have a high correlation with the correlation coefficients of mixing time and heat transfer coefficient. Meanwhile, a new index for evaluating the mixing performance was obtained. The optimal working condition was obtained. This method is simple and easy to implement and can be extended to processes where the target is identifiable in a transparent reactor and where both mixing and heat transfer effects need to be quantified.

Biomass pyrolysis to produce bio-char is one of the scientific and effective means of utilizing biomass resources. Differ from previous studies, this paper explored the effect of pyrolysis temperature (400–1000 °C) on the adsorption capacity of hazelnut shell bio-char from two perspectives, including physical macroscopic structure and functional group microscopic adsorption, and the practical adsorption application tests on common 7 kinds of heavy metals in polluted water were further carried out. The results showed that the yield and adsorption of bio-char prepared at different pyrolysis temperatures varied significantly, as the temperature increased, bio-char yield and surface acid functional group content decreased, the adsorption rate on most of heavy metals increased firstly and then decreased (except for Cr 6+ ), the adsorption capacity of bio-char prepared at above 600 °C was mainly affected by physical macroscopic structure, and at 800 °C, bio-char had a large number of pore structures, and pore structure has been fully developed, iodine adsorption value and BET specific surface area were 595.36 mg/g and 197.32 mg/m 2 , respectively, the adsorption effect of bio-char on Cr 6+ , Cd 2+ , Zn 2+ , Cu 2+ and Ni 2+ were best, and the adsorption rates were 45.23%, 44.14%, 60.11%, 61.28% and 65.07% respectively. It revealed that although the absorption effect of bio-chars prepared at different temperatures on different heavy metals had a great variation, large specific surface area and developed pore structure still played important role in the adsorption capacity of bio-char. These provided a reference for the application of hazelnut shell bio-char based on adsorption properties, especially absorbing heavy metals in polluted water.

This study develops a general dimensionless model for a three-phase trickle bed reactor in the light naphtha isomerization process. The simulations are accomplished to study its conduct. The model brings up a one-dimensional axial dispersed flow to characterize dispersity and liquid-solid mass transfer in the forms of dimensionless Peclet and mass Stanton numbers under adiabatic conditions. It considers the essential reactions extant in the isomerization process comprising isomerization, hydrogenation, and hydrocracking reactions applying a precise approach of dimensionless kinetic equations and rate constants. The Crank–Nicolson method and a nonstandard finite difference approach are utilized for large systems of time-spatial PDEs to resolve the dynamic reactor model with MATLAB software. The aim is to elucidate how these large systems of PDEs and nonlinear ODEs can be solved with a comprehensive computation in the form of physical dimensionless numbers. The isomers compositions estimated with the suggested model are in corroboration simulation results obtained by empirical information. The dynamics are evaluated to consider the system conduct with a variation in the hydrogen concentration of the feedstock.