Toshko Zhelev

Distributed Generation: Toward a New Energy Paradigm

This paper discusses distributed generation which is emerging as a new paradigm to produce on-site highly reliable and good quality electrical power. Thus, the DG systems are presented as a suitable form to offer highly reliable electrical power supply. The concept is particularly interesting when different kinds of energy resources are available, such as photovoltaic (PV) panels, fuel cells (FCs), or wind turbines.

Cleaner flue gas and energy recovery through pinch analysis

Abstract The paper addresses the problems of cleaner energy generation in industrial applications. Its aims further flue gas energy recovery accompanied with additional environmental impact. It shows how the widely accepted flue gas temperature of industrial coal fired boilers can be lowered substantially without increasing the risk of back-end condensation. This is possible through dehumidification and partial absorption of the flue gas in a packed-bed economiser system by circulating water. Different design contact economiser systems (CES) are presented and compared. Pinch principles are deployed for targeting, design and operation-guiding purposes, balancing the heat and mass transfer in a second generation CES of parallel type. The results are expected to make these systems more sophisticated and more suitable for industrial applications. They open the door for valuable boiler efficiency improvement and generalisation of methodology for simultaneous management of energy and water resources.

Heat integration in micro-fluidic devices

Abstract Presented paper addresses some problems of energy consumption minimisation in portable micro-total-analysis systems (μ-TAS) and more precisely in micro-polymerase chain reaction systems (MPCRS) used for on spot DNA analysis. Applied methodology takes on board two well-established heat integration concepts such as earlier developed deterministic method and the conceptual design approach, adapts them and applies them in the challenging area of micro-reactors. The focus of presented procedures is on a range of designs, proven as promising by earlier researchers. It considers three heating/cooling options: (a) a classical resistor heating and cooling case; (b) a three fluids case, when the sample droplets moving in a carrier fluid are being heated and pumped by a third fluid, and (c) a new proposed design claiming to overcome major drawbacks of mincrofluidic devices. The main optimisation objectives are the energy conservation and the minimisation of the time for DNA amplification. Additional design requirements are the high throughput and flexibility (versatility) improvement. The major control parameters are the cycle time, the ramp rate and the number of cycles. Advanced steps towards development of a computer code for temperature distribution simulation using deterministic heat transfer model are also reported. Future steps towards more precise problem formulation including the consideration of an enzyme-catalysed bio-chemical reaction and its impact on the fluidic properties are discussed.

Combined water–oxygen pinch analysis for better wastewater treatment management

Abstract The aim of this paper was to combine water pinch analysis and oxygen pinch analysis for more cost-effective wastewater treatment. Emphasis was placed on energy and resource saving. The variables that affect the cost of wastewater treatment are the quantity and the quality of the wastewater to be treated. The quantity of the wastewater to be treated was directly proportional to the treatment cost. The quality of the wastewater was inversely proportional to the treatment cost. It was found that the quantity of wastewater treated could be decreased by the application of water pinch analysis. This application also had a negative effect on the quality of the wastewater. The effect of the application of water pinch analysis decreased the quality of the wastewater being treated, hence increasing the treatment cost. This effect was negated by the application of a combined water–oxygen pinch analysis. The quality of the wastewater determined the amount of oxygen required. The oxygen pinch concept addresses this problem and in addition gives even more information about the health of the working micro-organisms. A 22.6% reduction in wastewater quantity was realised applying combination of both pinch concepts. A reduction of 23.44% in the oxygen requirement for the biodegradation of wastewater was achieved. An important feature of the combined water–oxygen pinch analysis is the balance obtained between the quantity of wastewater produced and the quality of this wastewater.

Energy efficiency optimisation of wastewater treatment: Study of ATAD

Abstract The aim of this paper is to minimise the energy requirement of autothermal thermophilic aerobic digestion (ATAD). To this end, a dynamic ATAD model is presented and assessed. A global sensitivity analysis was performed to identify the operating conditions with the strongest impact on the energy requirements, and thus to choose the most promising optimisation variables. The latter turned out to be the aeration flowrate, the reaction time, and the sludge flowrate. The optimisation problem was formulated following the sequential approach for dynamic optimisation, due to the discontinuous nature of ATAD. The problem was implemented in MATLAB® and solved for two case studies using the eSS algorithm, a global scatter search method that alternates with local algorithms (in our case fmincon) to refine the best solutions. The two selected full-scale case studies include a single-stage and a two-stage system. For the former, a 22% improvement of the energy requirement was achieved after optimisation, and 18% for the latter. Despite its advantages and common use in other fields, optimisation is still relatively rare in wastewater engineering. In the light of the high, rising cost of wastewater treatment, optimisation should become the norm when it comes to design and operation of wastewater treatment plants.

Energy-environment closed-loop through Oxygen Pinch

Abstract Oxygen Pinch emphasizes oxygen management and integration by splitting and recycling of oxygen/substrate requiring processes to achieve minimum “fresh” oxygen supply and maximum biodegradation per unit mass and hence to reduce energy consumption, to shorten operating times and to improve plant capacity. The presented approach considers not only the concentration differences that represent the mass transfer driving force between streams of varying substrate concentration but also the influence substrate utilization kinetics have on this driving force. Through the use of classical Pinch Principles, the maximum amount of substrate required to maintain a healthy sludge is identified assuming oxygen concentration is not limiting. The challenge posed by the presented case study towards improvement of an existing plant is not to reduce the oxygen supply (the oxygen is always maintained in excess), but to improve the substrate utilization for the same amount of supplied oxygen thereby increasing the capacity of the plant and lowering the energy consumption per unit volume of wastewater. It is reported that the principles introduced by the Thermal Pinch concept can work successfully for environment protection purposes and finally can again be returned to their original address leading to energy saving.

Modelling and sensitivity analysis of ATAD

Several authors have pointed out the need to identify the optimum operating conditions (OCs) of autothermal thermophilic aerobic digestion (ATAD). This study proves the hypothesis that the OCs have the potential to substantially improve the energy efficiency and plant capacity of established ATAD systems. As ATAD is a semi-batch process, its energy efficiency has to be optimized via dynamic optimization (DO). This methodology requires an adequate mathematical model, and appropriate selection of optimization variables. The paper presents an improved mathematical ATAD model based on previous models found in the literature. A global sensitivity analysis (GSA) was performed in order to identify variables with significant influence upon energy efficiency and plant capacity, thus paving the way for the DO of ATAD systems. The results of the GSA show that reactor volume, reactor temperature, and aeration flowrate are significant variables, which is consistent with reported literature. The results of the GSA also show that both energy efficiency and plant capacity of ATAD systems can be substantially improved by altering reactor volume and OCs.

Combined Pinch Analysis For More Efficient Energy And Water Resources Management In Beverage Industry

The aim of this investigation is to search for possible grassroot influence and relationship between water and energy resources efilcient utilisation, It intends to look at the possibility for fresh water saving combined with heat conservation. Our findings are showing that the analysis of energy and water sources and sinks and their integration at a total site level leads to solutions that are not conflicting and contradictory. The analysis is based on unique combination between the Water Pinch and the classical Thermal Pinch methodology at the retrofit design level. The aim of presented paper is to lay down the fundament for development of general methodology for targeting and design for minimum water/wastewater and energy consumption and to search for possible trade-offs in this dualistic optimisation problem. The complexity and large variety of processes of simultaneous heat and mass transfer related to the problem of interest, call for a classification and individual approach according to the type of processes involved. The paper highlights the management of energy and water in flue gas energy recovery systems, cooling systems and wastewater treatment systems, The area of application is the South Afi-icanbeverage industry where both energy and water resources are widely applied.

Micro reactor design for Distributed Fuel Generation

This paper presents a new concept of waste CO2 utilisation for fuel re-synthesis. It extends this challenging approach to GHG emission mitigation into distributed fuel generation concept based on micro-reactor technology. Further the paper outlines the steps taken to begin the fabrication of a series of micro reactors intended for the reverse water gas shift and Fischer-Tropsch synthesis. The design methodology for the micro channels within the reactors is also outlined. The designs theorized for the micro channels were simulated using two approaches; manual, macro-scale calculations and CFD micro-fluidic simulation. The results from these simulations allow a comparison to be made between the two methods. They also provide a solid foundation upon which to base the chosen micro reactor designs. The CFD simulation results provide insight into the expected gas flow rates and hence, the required micro channel arrangement. The micro reactors to be fabricated are described and were chosen based upon the results presented.

Using educational adventure-style game as a teaching method in a specific engineering domain

In a world of accelerated change in technologies and education, due to the impact of globalisation and the information and communication revolutions, the worldwide demand for easier and flexible learning can only be achieved through meaningful reforms and innovations in teaching/learning practices at Higher Education (HE) institutions. One possible solution to the problem that, perhaps, may become the gateway for success, is the use of interactive multimedia technologies together with a sound educational methodology. This paper discusses the application of multimedia game-based technology in the process of teaching/learning on a specific engineering domain. It reports on a component of the Virtual Learning Spaces (VLS) project designed as an adventure-style three-dimensional (3D) desktop educational tool. The project is supported by the Department of Arts, Culture, Science and Technology of the South African government. The component, or portal, “Africa as Technology Creator” reported here, attempts to promote understanding of a unique local technology for liquid I%elproduction from solid fossil, and familiarise learners with a recognised technology for energy savings and waterlwastewater minimisation, based on integration of processes and systematic resources management procedures.