M.T. Munir

Plant-wide control: Eco-efficiency and control loop configuration

Since the eco-efficiency of all industrial processes/plants has become increasingly important, engineers need to find a way to integrate the control loop configuration and the measurements of eco-efficiency. A new measure of eco-efficiency, the exergy eco-efficiency factor, for control loop configuration, is proposed in this paper. The exergy eco-efficiency factor is based on the thermodynamic concept of exergy which can be used to analyse a process in terms of its efficiency associated with the control configuration. The combination of control pairing configuration techniques (such as the relative gain array, RGA and Niederlinski index, NI) and the proposed exergy eco-efficiency factor will guide the process designer to reach the optimal control design with low operational cost (i.e., energy consumption). The exergy eco-efficiency factor is implemented in the process simulation case study and the reliability of the proposed method is demonstrated by dynamic simulation results.

Phosphate recovery from hydrothermally treated sewage sludge using struvite precipitation

New technologies are needed to recover phosphate from organic wastes, such as sewage sludge. Sewage sludge can be hydrothermally treated to make it safe but this process is expensive. Recovering a valuable by-product, such as phosphate, could improve the economics of hydrothermal treatment. Therefore, the technical and preliminary differential cost analysis of combining hydrothermal treatment with phosphate recovery (by precipitation of magnesium ammonium phosphate (struvite)) was investigated. The effects of pH, magnesium ion dose, and either wet oxidation or thermal hydrolysis hydrothermal treatment were examined. Phosphate recovery was more sensitive to pH than magnesium ion concentration, with diminishing rates of recovery at high levels of both. Also, more struvite was recovered following wet oxidation treatment than thermal hydrolysis. Preliminary differential cost analysis showed that wet oxidation combined with precipitation at an optimal pH and magnesium ion dose could generate revenue.

A software algorithm/package for control loop configuration and eco-efficiency.

Software is a powerful tool to help us analyze industrial information and control processes. In this paper, we will show our recently development of a software algorithm/package which can help us select the more eco-efficient control configuration. Nowadays, the eco-efficiency of all industrial processes/plants has become more and more important; engineers need to find a way to integrate control loop configuration and measurements of eco-efficiency. The exergy eco-efficiency factor; a new measure of eco-efficiency for control loop configuration has been developed. This software algorithm/package will combine a commercial simulator, VMGSim, and Excel together to calculate the exergy eco-efficiency factor.

Variation in metals during wet oxidation of sewage sludge

Sewage sludge is a significant by-product from wastewater treatment plants but is potentially hazardous due to its pathogenic or harmful contents, such as toxic metals. Subcritical water wet oxidation (SCWO) is one method of hydrothermal processing which has recently been used in research and industry for treating sludge. This study investigated the effect of SCWO on metals such as Al, Cu, Fe, and Zn in sludge, including the content of metals in the liquid or solid phase after SCWO and their stability distributions according to Tessiers method. During SCWO, most metals were significantly accumulated and stabilised in the solid phase with very limited leaching. The temperature was found to be the most significant factor for metals immobilisation, followed by reaction time, while pH had negligible effect. The optimal conditions of SCWO on metals were found at 240°C, 60min, pH 5 in this study.

Virtual milk for modelling and simulation of dairy processes

The modeling of dairy processing using a generic process simulator suffers from shortcomings, given that many simulators do not contain milk components in their component libraries. Recently, pseudo-milk components for a commercial process simulator were proposed for simulation and the current work extends this pseudo-milk concept by studying the effect of both total milk solids and temperature on key physical properties such as thermal conductivity, density, viscosity, and heat capacity. This paper also uses expanded fluid and power law models to predict milk viscosity over the temperature range from 4 to 75°C and develops a succinct regressed model for heat capacity as a function of temperature and fat composition. The pseudo-milk was validated by comparing the simulated and actual values of the physical properties of milk. The milk thermal conductivity, density, viscosity, and heat capacity showed differences of less than 2, 4, 3, and 1.5%, respectively, between the simulated results and actual values. This work extends the capabilities of the previously proposed pseudo-milk and of a process simulator to model dairy processes, processing different types of milk (e.g., whole milk, skim milk, and concentrated milk) with different intrinsic compositions, and to predict correct material and energy balances for dairy processes.

Eco-efficiency and control loop configuration for recycle systems

To integrate measurements of eco-efficiency with control loop configuration has become an important topic since all industrial processes/plants are requested to increase their eco-efficiency. The exergy eco-efficiency factor, a new measure of eco-efficiency for control loop configuration, has been developed recently [1]. The exergy eco-efficiency factor is based on the thermodynamic concept of exergy, which can be used to analyze a process in terms of its efficiency. The combination of the relative gain array (RGA), NI, CN, dynamic RGA, and the exergy eco-efficiency factor will help guide the process designer to find the optimal control design with low operating cost/eco-efficiency. In this paper, we validate the proposed exergy eco-efficiency factor for processes with recycles which are very common industrially.

Rheological characterisation of biologically treated and non-treated putrescible food waste

Food waste is gaining increasing attention worldwide due to growing concerns over its environmental and economic costs. Understanding the rheological behaviour of food waste is critical for effective processing so rheological measurements were carried out for different food waste compositions at 25, 35 and 45 °C. Food waste samples of various origins (carbohydrates, vegetables & fruits, and meat), anaerobically digested and diluted samples were used in this study. The results showed that food waste exhibits shear-thinning flow behaviour and viscosity of food waste is a function of temperature and composition. The composition of food waste affected the flow properties. Viscosity decreased at a given temperature as the proportion of carbohydrate increased. This may be due to the high water content of vegetable & fruits as the total solids fraction is likely to be a key controlling factor of the rheology. The Herschel-Bulkley model was used successfully to model food waste flow behaviour. Also, a higher strain was needed to break down the structure of the food waste as digestion time increased.

Effect of hydrodynamic mixing conditions on wet oxidation reactions in a stirred vessel reactor

The aim of this study was to investigate the impact of mixing intensity and mixing flow patterns on solid waste degradation, and production of valuable intermediate by-products such as acetic acid. Total suspended solids generally decreased, soluble chemical oxygen demand, dissolved organic carbon, and acetic acid concentration generally increased with the progress of the reaction and increase in the mixing intensity. The results showed that axial-radial flow pattern (using pitch blade impeller) and medium impeller speed (500 rpm) resulted in a higher degree of solid degradation and production of acetic acid.

Modelling batch bioreactions with continuous process simulators

Process models are increasingly becoming necessary for process understanding and optimizing. However, in the field of bioprocessing, modelling using a generic process simulator suffers from shortcomings given that many simulators cannot model batch mode bioreactors with varying reaction rates based on microbial metabolism. Bioprocesses, mostly batch, are difficult to model because most of the available unit operations in process simulators operate continuously. Our aim is to provide a general simulation platform to model these batch bioprocesses in commercial process simulators and explain how to transform batch processes with varying reaction rate into continuous unit operations for simulation purposes. Two typical fermentation processes, lactose fermentation and glucose/xylose co-fermentation, were simulated in steady state as case studies. The results are discussed as examples using the proposed approach. The potential of how to extend the simulation platform is also explained in detail.

Eco-efficiency of control configurations using Exergy

For general multi-input multi-output (MIMO) processes, thermodynamic properties like exergy have been previously used for the development of eco-efficiency analysis tools e.g. Relative Exergy Array (REA) [1, 2], and Exergy Eco-efficiency Factor (EEF) [3]. The REA is easy to use, compares several control scheme candidates for single units and ranks them according to their exergy interactions between control loops. The EEF provides means to determine the effect of a control scheme on the eco-efficiency of the whole process. In this paper, our intention is to justify the use of EEF and REA, compare EEF recommendations to REA, and consider EEF for the whole process eco-efficiency and discuss the similarities and differences between REA and EEF. Furthermore these results of testing REA and EEF on a realistic case study will be analysed to provide some practical recommendations on their usage.