• Energy Research

AbstractBei allen Prozessen der Energie‐ oder der Verfahrenstechnik, in denen aus Rohstoffen höherwertige Produkte erzeugt werden, müssen Exergie und Kapital aufgebracht werden. Die exergo‐ökonomische Analyse zeigt, welche Kosten mit der Vernichtung von Exergie verbunden sind. Bei der Betrachtung von Abgasbehandlungsprozessen ergeben sich Widersprüche, da diese Prozesse häufig weder aus wirtschaftlicher noch aus energetischer Sicht sinnvoll sind, sondern aus Gründen des Umweltschutzes durchgeführt werden. Das neue Konzept der exergo‐ökonomisch‐ökologischen Prozessanalyse wird vorgestellt und auf Prozesse zur Behandlung schwefelwasserstoffhaltiger Abgase angewandt. Dabei zeigt sich, wie durch diese systematische Analyse Verbesserungspotenziale aufgedeckt werden können.

Abstract Separation of ethylene from light gas mixture is one of the most energy intensive separations in petrochemical processes, which uses distillation columns up to 100 m tall and containing over 100 trays due the very small differences in the relative volatilities and very large reflux ratios and also due to the need for sub-ambient temperatures. In recognition of these costs, several attempts have been made in the past to develop processes with less energy and equipment costs. In distillation columns with condenser temperatures significantly below room temperature, such as in ethylene separation towers, it is essential to minimize the expensive energy requirements of the refrigeration cycle that produces the tower reflux. In this work, a solution has been found by expanding the gaseous distillate to decrease its temperature. Moreover, additional solutions applied to conventional ethylene fractionation columns have been implemented here in order to study this behavior. In this contribution, an outlet stream of an Oxidative Coupling of Methane (OCM) reactor, which has been previously stripped of its CO2 content, is also introduced in a demethanizer tower to remove almost all of its CH4 content before entering the ethylene fractionating column. Then, it is cooled exchanging its heat with the distillate stream of the ethylene tower, warming the distillate. The main goal is to reduce the condenser heat duty. This objective is achieved reducing a significant amount of heat required by the condenser, maintaining the mandatory product purity. Due to this improvement, it was also possible to reduce the reboiler heat in almost the same percentage amount that is achieved with the condenser. In addition, the reflux of ethylene column decreases. The sensitivity analysis and the corresponding simulations results will be discussed in order to show the efficiency of the presented approach. These results have also been used for the design of the pilot plant which is now being built at our department. The final design for the OCM process will also be presented.

Abstract Different designs of distributed energy resources (DER) systems could lead to different performance in reducing cost, environmental impact or use of primary energy in residential networks. Hence, optimal design and management are important tasks to promote diffusion against the centralised grid. However, current operational models for such systems do not adequately analyse their complexity. This paper presents the results of a mixed-integer linear programming (MILP) model of distributed energy systems in the residential sector which builds up on previous work in this field. A superstructure optimisation model for design and operation of DER systems is obtained, providing a more holistic overview of such systems by including the following novel elements: a) Design and utilisation of a network with integrated heating/cooling pipelines and microgrid connections between neighbourhoods; b) Exploration of use of feed-in tariffs (FITs), renewable heat incentives (RHIs) and the ability to buy/sell from/to the national grid. It is shown that the (DER network mitigates around 30–40% of the CO2 emissions per household, compared with “traditional generation”. Money from FITs, RHIs and sales to the grid, as well as reduced grid purchases, make DER networks far more economical, and even profitable, compared to the traditional energy consumption.

Biodiesel has turned out to be an integral part of the discussion of renewable energy sources and has diverse advantages in terms of its flexibility and applicability. Considering the characteristics of the transesterification reaction, a laboratory-scale system has been developed in this work. Waste Vegetable Oil (WVO), mainly sunflower oil, from local sources has been used and the transesterification carried out using methanol in the presence of sodium hydroxide catalyst. Characterisation of the biodiesel produced has been carried out using a number of different techniques including rheology, calorimetry, and gas liquid chromatography. The main factors affecting the % yield of biodiesel are temperature, catalyst, and alcohol to triglyceride ratio. Thus, experimental work has been carried out so as to study the rate and yield of the reaction as a function of those factors. A model has also been developed to validate the experimental data and this should help in increasing the efficiency of these processes and reducing the energy input. Moreover, the novel use of ultrasound as a method of measuring progression of the reaction is correlated with in-situ pH monitoring of the reaction process.

Abstract Utility systems provide heat and power to industrial sites. The importance of operating these systems in an optimal way has increased significantly due to the unstable and in the long term rising prices of fossil fuels as well as the need for reducing the greenhouse gas emissions. This paper presents an analysis of the problem for supporting operator decision making under conditions of variable steam demands from the production processes on an industrial site. An optimisation model has been developed, where besides for running the utility system, also the costs associated with starting-up the operating units have been modelled. The illustrative case study shows that accounting for the shut-downs and start-ups of utility operating units can bring significant cost savings.

Deterministic optimization approaches have been well developed and widely used in the process industry to accomplish off-line and on-line process optimization. The challenging task for the academic research currently is to address large-scale, complex optimization problems under various uncertainties. Therefore, investigations on the development of stochastic optimization approaches are needed. In the last few years we proposed and utilized a new solution concept to deal with optimization problems under uncertain operating conditions as well as uncertain model parameters. Stochastic optimization problems are solved with the methodology of chance constrained programming. The problem is to be relaxed into an equivalent nonlinear optimization problem such that it can be solved by a nonlinear programming (NLP) solver. The major challenge towards solving chance constrained optimization problems lies in the computation of the probability and its derivatives of satisfying inequality constraints. Approaches to addressing linear, nonlinear, steady-state as well as dynamic optimization problems under uncertainty have been developed and applied to various optimization tasks with uncertainties such as optimal design and operation, optimal production planning as well as optimal control of industrial processes under uncertainty. In this paper, a comprehensive summary of our recent work on the theoretical development and practical applications is presented.

Profitability studies are needed to establish the potential pathways required for viable biomethane production in the Brandenburg region of Germany. This work study the profitability of a potential biomethane production plant in the eastern German region of Brandenburg, through a specific practical scenario with data collected from a regional biogas plant located in Alteno (Schradenbiogas GmbH & Co. KG). Several parameters with potential economic influence such as distance of the production point to the grid, waste utilization percentage, and investment, were analyzed. The results illustrate a negative overall net present value with the scenario of no governmental investment, even when considering trading the CO2 obtained throughout the process. Subsidies needed to reach profitability varied with distance from 13.5 €/MWh to 19.3 €/MWh. For a fixed distance of 15 kms, the importance of percentage of waste utilization was examined. Only 100% of waste utilization and 75% of waste utilization would reach profitability under a reasonable subsidies scheme (16.3 and 18.8 €/MWh respectively). Concerning the importance of investment, a subsidized investment of at least 70% is demanded for positive net present values. Besides, the sensitivity analysis remarks the energy consumption of the biogas upgrading stage, the electricity price, and the energy consumption of biogas production as major parameters to be tackled for the successful implementation of biogas upgrading plants. The results here obtained invite to ponder about potential strategies to further improve the economic viability of this kind of renewable projects. In this line, using the CO2 separated to produce added-value chemicals can be an interesting alternative.