Research

15 pages, 5226 KiB

Open AccessArticle

Frequency and Inertial Response Analysis of Loads in The Chilean Power System

by Juan Quiroz, Roberto Perez, Héctor Chávez, Carlos Fuentes, Matías Díaz and José Rodriguez

Processes 2023, 11(9), 2612; https://0-doi-org.brum.beds.ac.uk/10.3390/pr11092612 - 01 Sep 2023

Viewed by 697

The integration of power electronics-interconnected generation systems to the grid has fostered a significant number of concerns on power system operations, particularly on the displacement of synchronous generators that leads to a reduction in the grid’s overall inertia and frequency response. These concerns [...] Read more.

The integration of power electronics-interconnected generation systems to the grid has fostered a significant number of concerns on power system operations, particularly on the displacement of synchronous generators that leads to a reduction in the grid’s overall inertia and frequency response. These concerns have raised a significant amount of state-of-the-art mathematical proposals on how to estimate system inertia; however, the majority of the proposals do not differentiate generator inertia from load inertia. When inertia prediction for control room applications is required in real-time, the current state-of-the-art proposals use the inertia of generators as a proxy for a minimum, overall inertia estimate, counting the number of units committed in real-time and adding up their inertia. However, as dynamic conditions are becoming challenging with the integration of power electronics-interconnected generation systems, it is important to quantify the amount of inertia from the loads, for which the state-of-the-art proposals present very limited advancement, particularly in applications with real data. This work presents a set of recorded actual events in the Chilean power system to estimate the contribution of loads to inertia and frequency response to assess whether the loads have a significant role in frequency stability. The contribution of this work is as follows: first, reporting real data of a power system from the PMU and SCADA systems that are usually classified as not public; and, second, to derive a conclusion from the data to assess the role of loads in frequency stability in a real case. Full article

(This article belongs to the Special Issue Tools, Approaches and Modeling for Energy System Design Increasing Economic and Environmental Sustainability)

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16 pages, 2361 KiB

Open AccessArticle

Uncertainty Propagation Based MINLP Approach for Artificial Neural Network Structure Reduction

by Hasan Sildir, Sahin Sarrafi and Erdal Aydin

Processes 2022, 10(9), 1716; https://0-doi-org.brum.beds.ac.uk/10.3390/pr10091716 - 29 Aug 2022

Cited by 3 | Viewed by 1518

Abstract

The performance of artificial neural networks (ANNs) is highly influenced by the selection of input variables and the architecture defined by hyper parameters such as the number of neurons in the hidden layer and connections between network variables. Although there are some black-box [...] Read more.

The performance of artificial neural networks (ANNs) is highly influenced by the selection of input variables and the architecture defined by hyper parameters such as the number of neurons in the hidden layer and connections between network variables. Although there are some black-box and trial and error based studies in the literature to deal with these issues, it is fair to state that a rigorous and systematic method providing global and unique solution is still missing. Accordingly, in this study, a mixed integer nonlinear programming (MINLP) formulation is proposed to detect the best features and connections among the neural network elements while propagating parameter and output uncertainties for regression problems. The objective of the formulation is to minimize the covariance of the estimated parameters while by (i) detecting the ideal number of neurons, (ii) synthesizing the connection configuration between those neurons, inputs and outputs, and (iii) selecting optimum input variables in a multi variable data set to design and ensure identifiable ANN architectures. As a result, suggested approach provides a robust and optimal ANN architecture with tighter prediction bounds obtained from propagation of parameter uncertainty, and higher prediction accuracy compared to the traditional fully connected approach and other benchmarks. Furthermore, such a performance is obtained after elimination of approximately 85% and 90% of the connections, for two case studies respectively, compared to traditional ANN in addition to significant reduction in the input subset. Full article

(This article belongs to the Special Issue Tools, Approaches and Modeling for Energy System Design Increasing Economic and Environmental Sustainability)

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25 pages, 3694 KiB

Open AccessFeature PaperArticle

Integration of an Absorption Chiller to a Process Applying the Pinch Analysis Approach

by Andreja Nemet, Zdravko Kravanja and Miloš Bogataj

Processes 2022, 10(5), 1028; https://0-doi-org.brum.beds.ac.uk/10.3390/pr10051028 - 21 May 2022

Cited by 2 | Viewed by 1536

Abstract

In addition to the consumption of hot utilities, there is also a significant cost associated with the consumption of cold utilities when there is a high demand for cooling. A promising solution for cooling is an absorption chiller (AC), which uses heat instead [...] Read more.

In addition to the consumption of hot utilities, there is also a significant cost associated with the consumption of cold utilities when there is a high demand for cooling. A promising solution for cooling is an absorption chiller (AC), which uses heat instead of electricity for cooling. A thermodynamic approach for evaluating AC integrated with a process is presented in this work. A model for assessing the properties and duties of an AC cycle was developed. The integration of a combined process-AC system was evaluated using the Grand Composite Curve. Three different options of integration were analyzed: (i) above the Pinch, (ii) below the Pinch, and (iii) across the Pinch. AC represents the combined effect of a heat engine and a heat pump, as the generator together with the absorber and condenser has the function of a heat engine, while the evaporator combined with the absorber and condenser mimics the function of a heat pump. The comparison between the non-integrated and integrated process-AC systems has revealed that the proper placement of AC is across or below the Pinch and the improper is above the Pinch. If AC was entirely integrated below the Pinch, the integration would result in a complete (100%) reduction in the consumption of hot utility for the operation of AC. The most suitable placement of AC with double reduction of hot utility consumption and complete reduction of both hot and cold utility to operate AC is across the Pinch due to the pumping of heat through AC from below to above the Pinch. Full article

(This article belongs to the Special Issue Tools, Approaches and Modeling for Energy System Design Increasing Economic and Environmental Sustainability)

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24 pages, 3461 KiB

Open AccessArticle

Renewable Energy-Driven Desalination: New Trends and Future Prospects of Small Capacity Systems

by Lourdes García-Rodríguez and Agustín M. Delgado-Torres

Processes 2022, 10(4), 745; https://0-doi-org.brum.beds.ac.uk/10.3390/pr10040745 - 12 Apr 2022

Cited by 7 | Viewed by 2478

Abstract

New trends and future prospects for small capacity systems of Renewable Energy-driven DESalination (REDES) are reviewed and assessed in this paper over a nominal desalination capacity range of 3–1000 m³/d. A thorough literature review is reported in order to evaluate current [...] Read more.

New trends and future prospects for small capacity systems of Renewable Energy-driven DESalination (REDES) are reviewed and assessed in this paper over a nominal desalination capacity range of 3–1000 m³/d. A thorough literature review is reported in order to evaluate current research and developing activities. Outstanding commercial prospects in the near future are identified for two off-grid REDES technologies under development. First, wave energy converters with direct coupling to seawater desalination. Second, solar micro gas turbines with biofuel backup coupled to reverse osmosis (RO) desalination and/or zero liquid discharge water treatment. These systems, as well as mature REDES plants (namely PV/RO and wind turbines/RO), will benefit from forthcoming advances in energy efficiency in the RO process itself. The Closed Circuit RO desalination (CCRO^TM) concept may be a key configuration for enhancing RE-driven RO desalination. Additionally, opportunities for innovation in seawater RO desalination with variable power consumption are highlighted. On the other hand, our conclusions highlight opportunities for developing novel portable REDES systems based on solar membrane distillation with a portable linear Fresnel concentrator manufactured by SOLATOM. Additionally, the concept of portable systems could foster the commercial development of microbial desalination cells combined with solar PV energy and RO powered by tidal currents. Full article

(This article belongs to the Special Issue Tools, Approaches and Modeling for Energy System Design Increasing Economic and Environmental Sustainability)

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15 pages, 4499 KiB

Open AccessFeature PaperArticle

Recovery of N-Butanol from a Complex Five-Component Reactive Azeotropic Mixture

by Miloš Bogataj, Zdravko Kravanja and Andreja Nemet

Processes 2022, 10(2), 364; https://0-doi-org.brum.beds.ac.uk/10.3390/pr10020364 - 14 Feb 2022

Cited by 4 | Viewed by 3210

Abstract

This paper proposes a concept of a process design for the separation and recovery of n-butanol from a five-component mixture, consisting of n-butanol, isobutanol, formaldehyde, water and methanol. The mixture is a common waste stream in the production of butylated amino resins; therefore, [...] Read more.

This paper proposes a concept of a process design for the separation and recovery of n-butanol from a five-component mixture, consisting of n-butanol, isobutanol, formaldehyde, water and methanol. The mixture is a common waste stream in the production of butylated amino resins; therefore, recovery of n-butanol is crucial to the efficiency of the process. The results show that up to 94% of the n-butanol present in the waste stream can be recovered. Under the studied conditions, 99.76% pure n-butanol can be obtained, while formaldehyde, water and methanol are present only in traces. The energy intensity of the process is estimated at 2.42 MJ/kg of purified n-butanol. The economic analysis of the process shows that the process is economically viable over a wide range of production capacities, as evidenced by high net present values and high return on investment values. Full article

(This article belongs to the Special Issue Tools, Approaches and Modeling for Energy System Design Increasing Economic and Environmental Sustainability)

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19 pages, 15243 KiB

Open AccessFeature PaperArticle

Comparison of the New Refrigerant R1336mzz(E) with R1234ze(E) as an Alternative to R134a for Use in Heat Pumps

by Jan Drofenik, Danijela Urbancl and Darko Goričanec

Processes 2022, 10(2), 218; https://0-doi-org.brum.beds.ac.uk/10.3390/pr10020218 - 24 Jan 2022

Cited by 7 | Viewed by 3328

Abstract

R134a is currently the most widely used refrigerant, whose problem is the high value of the global warming potential, and which will have to be replaced in the near future. Thus far, R1234ze(E) has proven to be the most suitable alternative, but it [...] Read more.

R134a is currently the most widely used refrigerant, whose problem is the high value of the global warming potential, and which will have to be replaced in the near future. Thus far, R1234ze(E) has proven to be the most suitable alternative, but it is slightly flammable. Recently, R1336mzz(E) has emerged as a possible alternative. During the research, the mentioned refrigerants were compared with simulations using the Aspen Plus software package in the case of using groundwater as a heat source. It was found that R1336mzz(E) could be a suitable alternative to R134a since the highest value of coefficient of performance was obtained using it. However, it must be superheated with an internal heat exchanger. The problem with using an internal heat exchanger is that the superheating of the refrigerant vapors affects the isentropic efficiency of the heat pump compressor negatively and, consequently, lowers the COP value of the heat pump. It has been shown that a one percent decrease in isentropic efficiency results in a one percent decrease in the COP value. Full article

(This article belongs to the Special Issue Tools, Approaches and Modeling for Energy System Design Increasing Economic and Environmental Sustainability)

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16 pages, 1968 KiB

Open AccessFeature PaperArticle

The Influence of Variable CO₂ Emission Tax Rate on Flexible Chemical Process Synthesis

by Klavdija Zirngast, Zdravko Kravanja and Zorka Novak Pintarič

Processes 2021, 9(10), 1720; https://0-doi-org.brum.beds.ac.uk/10.3390/pr9101720 - 25 Sep 2021

Cited by 4 | Viewed by 1299

Abstract

The emission of greenhouse gasses is a major environmental problem, and efforts are being made worldwide in various ways to encourage producers to reduce their emissions. There is a need to incorporate environmental measures into process design and synthesis, as pollution prevention is [...] Read more.

The emission of greenhouse gasses is a major environmental problem, and efforts are being made worldwide in various ways to encourage producers to reduce their emissions. There is a need to incorporate environmental measures into process design and synthesis, as pollution prevention is a higher priority than waste management, and in this way, more sustainable solutions can also be achieved. One possibility is to introduce a CO₂ tax, the value of which is very uncertain in the future. This paper demonstrates how the CO₂ tax affects the optimal results of synthesizing chemical processes using mixed-integer nonlinear programming (MINLP). It was found that the tax increase promotes the use of better-quality raw materials and more efficient process units. Energy consumption and emissions are reduced and economic performance deteriorates. A multi-period, two-stage stochastic approach with recourse is suitable to incorporate the uncertainty of the CO₂ tax in the MINLP process synthesis and gives better results than a simpler deterministic approach. In the case of the heat exchanger network synthesis, the costs obtained with the stochastic approach were 5% lower, and the emissions 7% lower than with a deterministic approach. Full article

(This article belongs to the Special Issue Tools, Approaches and Modeling for Energy System Design Increasing Economic and Environmental Sustainability)

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17 pages, 3547 KiB

Open AccessFeature PaperArticle

Universal Model for the Cogeneration of Heat, Power and Char in a Decoupled Pyrolysis and Gasification Process for Techno-Economic Assessment

by Dušan Klinar, Marcel Huber, Nataša Belšak Šel and Klavdija Rižnar

Processes 2021, 9(8), 1442; https://0-doi-org.brum.beds.ac.uk/10.3390/pr9081442 - 19 Aug 2021

Cited by 4 | Viewed by 1695

Abstract

Present work aims to present a complete and detailed heat-mass balance data, streams elemental and species composition as crucial input data for Techno-Economic Assessment (TEA). Combined heat, power and char (CHPC) generation in decoupled pyrolysis and gasification processes ensures a highly efficient, reliable [...] Read more.

Present work aims to present a complete and detailed heat-mass balance data, streams elemental and species composition as crucial input data for Techno-Economic Assessment (TEA). Combined heat, power and char (CHPC) generation in decoupled pyrolysis and gasification processes ensures a highly efficient, reliable and sustainable economic use of biomass. Innovative process model based on simultaneous heat-mass balance with the elemental (C, H, O) and species (CO, H₂, CO₂, CH₄ and H₂O) composition of each stream provides reliable data with a general/average variability in a range of ±10% and ±5% for the main outputs. Thermodynamic calculations verified not only the concept but also a numerical range of the results. Comparisons with recently published, scientific and data from technology providers, prove their general applicability and consistency. TEA cases, presented in a complete and detailed table, allow selection of the relevant calculation basis providing reliable data for doubtless evaluation at investors/entrepreneurs striving for a successful business model. Full article

(This article belongs to the Special Issue Tools, Approaches and Modeling for Energy System Design Increasing Economic and Environmental Sustainability)

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