Examination of temperature probe setup using computational fluid dynamics simulators

Engineering problem solving such as process design, process optimization, safety analysis, etc.; relies widely on mathematical models of the process. One of the most important aspects in a chemical plant is the safety protocols assuring the safety of workers and equipment. In this study Computational Fluid Dynamics (CFD) methods are used to model different temperature probe positions in a pipe elbow. Different models were computed together in order to solve heat transfer model: heat transfer in fluid and solid substances and momentum balance model. Three probe geometries are defined to obtain different results containing velocity field, and heat transfer. Based on the results the geometries and positions are compared to each other in order to find out which position is the most suitable for control studies, based on the time response of the probes. COMSOL Multiphysics was used to implement and to couple of the physics models. Due to the number of the geometries and model parameters (position and the geometry of the probe; inlet velocity) the COMSOL model was connected to MATLAB via COMSOL MATLAB LiveLink for solving the repeatable steps

Analysis of Mixing Efficiency of Rushton Turbines Based on CFD Models

The required power and flow pattern in a vessel mostly depend on the impeller geometry. In literature, there are only recommendation and no indices to help choosing the proper impeller for a defined mixing task. And it isn't possible to determine the optimal rotating speed for impellers applied in different mixing tasks. The primary goal of our research is to compare the quantitative characterization of the level of homogeneity in a stirred system obtained by using different impeller geometries and rotating speed. Therefore, the developed flow patterns are characterized by logarithmic histogram of the distribution of velocity field. To validate the proposed characterization technique the mixing time resulted by the different geometries are also calculated. The comparison of the mixing efficiency based on the determined power number. All these models require some measurements to be validated. Hence, a laboratory experimental system was built to measure the power consumptions of the investigated impellers

Laboratory and Computational Fluid Dynamics Investigation of Homogenization in a Tank Stirred by External Pump

The scope of this study was to investigate the homogenization of a two-layer stratified liquid in a tank where liquid stirring was achieved by carrying out external recirculation. Furthermore, the aim of the research was to observe the effect of the height of the outlet during the time of mixing one. The experimental fluid was two-layer, density stratified liquid. From the perspective of homogeneity, the effect of the height of the outlet was investigated in laboratory. Moreover, the experimental device was modeled in CFD. In simulation examination, laminar - and k-ε-model were used, and the influence of the outlet position was observed. The difference was remarkable in the first part of the measurement caused by the presence of sharp concentration variation in the tank. After the operating time, the expected homogeneity was fulfilled at the outlet in all cases. Regarding of CFD research, the results suggest that the laminar model is more effective to describe the concentration changes at the sampling point in the tank investigated

Failure Analysis of Heat Exchangers with a Valid CFD Simulation

Energy efficiency, safety and stable operation of units are the most crucial aspects in every industrial process. In this study, Computational Fluid Dynamics (CFD) simulations were used to study heat transfer in a laboratory-sized tubular heat exchanger. A partly 2D axisymmetric and mainly 3D model of the heat exchanger was created and validated with several simulation in different operating points of heating capacity and volume flow. The results of the simulations were compared to experimental data to validate the model. The inlet and outlet temperatures were measured with Pt100 temperature probes, and the surface temperatures were measured with an infrared camera. The heat transfer coefficient was determined based on the surface measurements The validated model was applied for the investigation of performance losses of heat exchanger due to fouling caused by particle deposits along the tube which caused reduced heat transfer surface or performance and a failure of heating wire which caused reduced heating performance, hence altered heat and flow characteristics through the equipment. The results provide useful information not only in the design processes but the operational lifetime as well

CFD Based Qualification of Mixing Efficiency of Stirred Vessels

In this work, we focus on the most crucial units in a chemical technology, the chemical reactors. Using a commercially available CFD software package, COMSOL Multiphysics, 3D mathematical models of a batch reactor with different impeller geometries have been investigated. The reasonable agreement between the experimental and simulation results indicates the validity of the developed CFD model. The effect of the impeller design, e. g. number of blades on the mixing efficiency is evaluated based on the simulation studies. The proposed measure to determine the energy efficiency of mixing (i. e. mixing index) is based on the calculated velocity field and energy usage. The information about the homogeneity of the mixed phase in the system can be extracted from the developed velocity field. Hence, we proposed histograms of velocity fluctuations on a logarithmic scale as an efficient tool to measure the achieved homogeneity of the phase in case of different impellers and rotational speeds

Investigation of Mixing in Tanks of a Special Geometry

Mixing is one of the most crucial processes in the chemical industry. Homogeneity is a requirement for all feedstocks and industrial products. The degree of mixing depends on the hydrodynamic properties of the fluid in the units. The Residence Time Distribution (RTD) was investigated in a tank of a special geometry. Mixing was investigated using various geometries of the tank by applying the Heaviside function in step-response experiments. After obtaining experimental results, the RTD function was calculated. The flow structure in the tank was approximated by fitting black-box transfer function models onto the RTD function of the system. Two general model structures were defined and their fitness compared. By evaluating the fitted models, a relationship was established between the flow structure in the tank and its geometry

Model Predictive Control of CMSMPR Crystalliser

One of the most critical components of the chemical industry in terms of crystallisation is the pharmaceutical sector. Most medicine components are expensive and require complex processes for their production, so producing waste is highly inefficient. Another concern is the high-quality standards for most pharmaceutical products. Therefore, optimising the crystallisation process is critical from a quality perspective, with the main concerns being the product's crystal structure and particle diameter distribution. Regardless efficient control in batch processes such as crystallisation is a difficult task due to the inherently nonlinear behaviour of the system. Using a priori model of the system as the basis for nonlinear model predictive control could provide a useful tool for handling the crystallisation process, mitigating the effects of disturbance and noise and ensuring appropriate product quality. In this work, we wish to showcase the possibility of controlling a crystallisation process using model predictive control to enable the production of crystal products with desired particle diameter distribution and crystalline product average size. The method is shown using citric acid as a model substance in a case study of a continuous crystallisation procedure in a stirred tank reactor. The crystalliser model includes an energy balance, so the system's behaviour depends on the cooling rate and residence time. Accordingly, the control problem can be formulated as multiple inputs and multiple outputs (MIMO) system. Moreover, the two controlled (average particle size and crystal size dispersion) variables are not easily detached from each other. So, the traditional controlling strategies, for example, the decoupling controller, is challenging to apply. The MPC (model predictive control) as an advanced control algorithm can be a solution to this

Application of models with different complexity for a stirred tank reactor

Engineering problem solving such as process design, process optimization, safety analysis, etc.; relies widely on mathematical models of the process. To solve various engineering problems various models with different complexity are needed. A stirred tank reactor with a highly exothermic reaction is studied in this work, because in the modern chemical technologies mixing is one of the most important operations, and stirred reactors are widely used in industrial applications. The stirring system of a mixed tank is always an important aspect of the design, because the involved processes (such as reactions, heat and component transport) usually require proper contact and homogeneity of the existing phases. For the suitable homogeneity the design and the size of the moving parts are also important problems. In certain situations attachment of static parts to a stirred tank (such as baffles) may have an important effect too. The primary goal of this study is to create models with different level of complexity and determine which model is the best suited for solving different engineering tasks such as process design, scale-up, or optimisation. etc. To determine which model fits best for a problem, mathematical models were created and compared to find out, how the information can be extracted from these models and be applied to solve engineering problems. Three types of models have been developed: perfectly mixed reactor model, compartment model, and Computational Fluid Dynamics (CFD) models with different dimensions. The reaction of hydrogen peroxide with sodium thiosulphate in a continuously stirred tank reactor is analysed as a case study. The perfectly mixed vessel models and compartment models were solved in MATLAB/SIMULINK program package. The CFD models were implemented in COMSOL Multiphysics

Dynamic Modelling and Process Control System Development of a H2S Scrubber Used in a Coke Oven Gas Purification Technology

Coke oven gas is a by-product of coke production. Cleaned coke oven gas can be a valuable energy source, ideal as a substitute for natural gas. However, to meet increasingly stringent environmental regulations and to protect combustion equipment, the high efficiency of the coke oven gas purification process must be ensured continuously, even for existing, less up-to-date plants. Process simulators built to support technologies can be a great help in this task. At the same time, they can be used to assist operations, understand general and specific process behaviour features, and examine development suggestions. The H2S scrubber of an existing coke oven gas purification plant was investigated in this study. Previously, the steady-state model of the purification process was studied, and the impact of operating parameters was investigated. Then the dynamic model of the purification process was created in Aspen Hysys simulator software. Finally, the model was validated against laboratory analyses and daily operational plant data. Subsequently, the control structure of the purification process was studied. It was concluded that the control system used in the coke oven gas purification plant is rather elementary and is primarily designed to ensure the safe operation of the technology. However, a more complex advanced control structure is needed to continuously provide a constant gas composition, in which the dynamic model of the technology is a great support. In this study, two examples for improving the control structure of the process were presented using the dynamic model of the H2S scrubber