Comparing Attic Method with the Existing Techniques for Linear Programming

The aim of the work is to compare the performances of the novel Attic method for linear programming (Buzzi-Ferraris, 2011) with the existing algorithms of the simplex and interior point families. Potentialities of the new method are demonstrated and quantified on the linear programming problem of thermal cracking refinery

Assessment of global sustainability of bioenergy production in a water-food-energy perspective

One of most demanding problems for decision makers and for process engineers is the design of a proper energy strategy to guarantee clean energy supply. This problem is complex and cannot be assessed considering only the standard efficiency criteria used in the past. The process of energy production needs to be analyzed in its completeness, from seed to consumption. This paper deals with the issue of bioenergy production following a nexus perspective, considering the link among water, food and energy. In particular, an objective function depending on the most important resources required in bioenergy production is defined so that it can be simply optimized. Considering the parameter interrelationship among water, food and land (the so-called water-food-energy nexus) the method gives the instruments to determine, in one single function, the optimal condition with respect to these resources. Two cases of study are analysed, dissimilar regarding the geographical location, environmental resources availability for energy production and food security. Results show how the proposed method is able to describe the present sustainability of bioenergy production in a certain site. Furthermore, it can help to investigate the existence of bottlenecks related to the current situation of the site and, at the same time, it can highlight future opportunities in producing sustainable bioenergy

Energy-Process Integration of the Gas-Cooled/Water-Cooled Fixed-Bed Reactor Network for Methanol Synthesis

The paper deals with the techno-economical assessment of the gas-cooled/water-cooled fixed-bed reactor network for methanol synthesis. The study is the extension of the first-principles model for the watercooled reactor already proposed in our prior work (Manenti et al., 2013). Here, the optimization is extended to the steam generation and the reactor length ratio. As a result, basing on the integrated optimization of energy and process yield, we propose to significantly revise the common design. The traditional water/gas cooling reactor length ratio could be significantly reduced with consequent simultaneous increase in methanol production and steam generation as well, however preserving safety and operational ranges. The economic benefit deriving from the proposed design for a medium-scale process is estimated in more than 1.7 M€/y

Fuzzy Adaptive Control System of a Non-Stationary Plant

This paper proposes a hybrid fuzzy PID control logic, whose tuning parameters are provided in real time. The fuzzy controller tuning is made on the basis of Mamdani controller. In addition, this paper compares a fuzzy logic based PID with PID regulators whose tuning is performed by standard and well-known methods. In some cases the proposed tuning methodology ensures a control performance that is comparable to that guaranteed by simpler and more common tuning methods. However, in case of dynamic changes in the parameters of the controlled system, conventionally tuned PID controllers do not show to be robust enough, thus suggesting that fuzzy logic based PIDs are definitively more reliable and effective

Application of Advanced Estimation Techniques to a Chemical Plant Model

The paper is aimed at comparing some of the most promising and novel advanced techniques for estimation by assessing their effectiveness on the chemical process benchmark. Global and distributed implementations of the extended Kalman filter are the key elements of the work. In addition, the paper is also aimed at describing and developing a recursive implementation of the autocovariance least square algorithm for the on-line updating of the tuning knobs of the filter, demonstrating its relevance in the performance monitoring of chemical processes

Intensifying Air Separation Units

This research activity shows the possibility to further intensify air separation units (ASUs). Several modifications to the traditional process layout are proposed and simulated by means of well-established simulation suites. The proposed modifications deal with the upgrading of oxygen purity, the recycle of rich argon stream, and the possibility to generate energy. The novel process solutions are compared with the traditional process and techno-economic assessment is provided. The payback time on the revamping investment is estimated in the order of 5 years for Terni’s ASU, owned by Linde Gas Italia S.r.l., which has been selected as test-case

Online Superstructure Optimization for Energy Saving of an Industrial Gas Distribution System

Mixed-integer optimization is a common approach to handle decision-making problems. Nevertheless, such an approach still presents certain operational limitations, especially for online superstructures. One of these limitations is given by Jacobian singularity, which arises for certain combinations of the set of Boolean variables and which easily leads to possible infeasible numerical solutions. This paper proposes a novel approach to overcome this problem, ensuring the use of mixed-integer optimization also to solve online issues. The case of nitrogen supply for the Thyssen-Krupp steel mill placed in Terni (Italy) is considered as validation case

Kinetic Modeling of Sewage Sludge Combustion and Gasification for Energy Generation

Sewage sludge is a waste that is difficult to valorize due to its high ash content and presence of pollutants. Thermal conversion of sewage sludge in waste-to-energy systems allows to add value to this waste by exploiting its energy content and significantly reducing the amount of final waste to be disposed in landfill, but these processes must be modeled in detail to obtain reliable results. The GasDS simulation suite can be used for such purpose since it is an advanced tool for the detailed simulation of complex kinetic, mass, and energy transfer phenomena happening inside of gas-solid reacting systems. The peculiar characteristics of sewage sludge both in terms of chemical-physical properties and thermal decomposition behavior make it necessary to add new information in the GasDS database. A simplified kinetic model based on lumps (sludge, gas, tar, char, H2O) and two consecutive pyrolysis reactions is proposed and fitted on experimental data, leading to a reaction scheme that can be implemented in the modeling suite. Simulations of air-based sewage sludge thermal conversion systems working at different degrees of oxidation severity are performed, and results regarding flowrate, temperature, and composition of gaseous effluent are shown. Aspen HYSYS simulation software is used to model waste-to-energy systems for the production of electric power. Key performance indicators such as the specific net power output, energy yield, and CO2 emissions are shown. Gasification-based combined cycles perform better with increasing ER and perform worse than combustion-based Rankine cycles at low ER values

Study of direct thermal energy storage technologies for effectiveness of concentrating solar power plants

In this paper, numerical comparisons are devised among different direct thermal energy storage (TES) technologies of concentrating solar power (CSP) plants with possible alternatives in design, plantwide control and global economic considerations and therefore, leading the process up to the sustainable power production through the day and night. The first design is based on the conventional direct double-tank thermal energy storage CSP plant, and afterwards, the modification on the design of this plant is proposed. The modification on the plantwide control is followed by recycling the heat transfer fluid (HTF) through the solar field and decreasing the degradation of temperature of the storage in discharge period. In addition, the analogues analysis is performed towards the solutions of the stable behavior on dynamic of the storage and power production. Owing to the fact that the single-tank storage technology eliminates using an extra storage volume in process design, consequently, it decreases the capital cost of the plant, the dynamic design of the single-tank storage technology is presented. Avoiding the greater degradations of the parameters is considered and improved through the heat exchanger trains as a challenging issue in storage technologies along with the plantwide control. In this work, considerations of process control to improve the quality of storage, operational issues, and flexibility related to the selected TES technologies are discussed due to making decisions for optimal control and covering the demanded energy generated by CSP plant