Special Issue "Renewable energy solutions for the Baltic–Nordic region"

A special issue of Energies (ISSN 1996-1073).

Deadline for manuscript submissions: closed (31 August 2019).

Special Issue Editor

Prof. Dr. Timo Kikas
E-Mail Website
Guest Editor
Chair of Biosystems Engineering, Institute of Technology, Estonian University of Life Sciences, Tartu, Estonia
Interests: bioeconomy; biofuels; biomass conversion; biomethane; bioethanol; lingnocellulosic biomass; pretreatment; renewable transport fuels
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Special Issue Information

Dear Colleagues,

Biosystems Engineering (BSE) aims to become the leading annual conference in the Baltic region in fields related to traditional and modern engineering techniques and technical solutions applied to biological systems. The goal of BSE 2019 is to gather scholars from all over the world to present advances in the fields of biosystems engineering and to foster an environment conducive to exchanging ideas and information. This conference will also provide an ideal environment to develop new collaborations and meet experts on the fundamentals, applications, and products of the mentioned fields.

Among the more prominent topics of the conference are energy and fuels from renewable sources, bioenergy, waste-to-energy, etc.

Prof. Dr. Timo Kikas
Guest Editor

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Smart energy systems
  • Energy policy
  • Energy system analysis
  • Renewable energy resources
  • Advanced sustainable energy conversion systems
  • Renewable heat systems
  • Biofuels and biorefineries
  • Alternative fuels
  • Hybrid and electric vehicles
  • Energy storage
  • Energy efficient appliances
  • Energy efficiency in buildings

Published Papers (8 papers)

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Research

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Open AccessArticle
Enhancing Bioenergy Yields from Sequential Bioethanol and Biomethane Production by Means of Solid–Liquid Separation of the Substrates
Energies 2019, 12(19), 3683; https://doi.org/10.3390/en12193683 - 26 Sep 2019
Abstract
The production of second-generation ethanol using lignocellulosic feedstock is crucial in order to be able to meet the increasing fuel demands by the transportation sector. However, the technology still needs to overcome several bottlenecks before feasible commercialization can be realized. These include, for [...] Read more.
The production of second-generation ethanol using lignocellulosic feedstock is crucial in order to be able to meet the increasing fuel demands by the transportation sector. However, the technology still needs to overcome several bottlenecks before feasible commercialization can be realized. These include, for example, the development of cost-effective and environmentally friendly pretreatment strategies and valorization of the sidestream that is obtained following ethanol distillation. This work uses two chemical-free pretreatment methods—nitrogen explosive decompression (NED) and synthetic flue gas explosive decompression—to investigate the potential of a bioethanol production sidestream in terms of further anaerobic digestion. For this purpose, samples from different stages of the bioethanol production process (pretreatment, hydrolysis, and fermentation) and the bioethanol sidestream went through a separation process (involving solid–liquid separation), following which a biomethane potential (BMP) assay was carried out. The results show that both factors being studied in this article (involving the pretreatment method and the separation process) served to influence methane yields. Liquid fractions that were obtained during the process with NED gave rise to methane yields that were 8% to 12% higher than when synthetic flue gas was used; fermented and distillation sidestream gave rise to the highest methane yields (0.53 and 0.58 mol CH4/100 g respectively). The methane yields from the liquid fractions were between 60–88% lower than those that were obtained from solid fractions. Samples from the bioethanol sidestream (solid fraction) that were pretreated with NED had the highest methane yield (1.7 mol CH4/100 g). A solid–liquid separation step can be a promising strategy when it comes to improving the energy output from lignocellulosic biomass and the management of the ethanol distillation sidestream. Full article
(This article belongs to the Special Issue Renewable energy solutions for the Baltic–Nordic region)
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Open AccessArticle
The Impact of Substrate–Enzyme Proportion for Efficient Hydrolysis of Hay
Energies 2019, 12(18), 3526; https://doi.org/10.3390/en12183526 - 13 Sep 2019
Abstract
Fuel alcohol production yields can be influenced by lignocellulosic biomass loading. High solid loadings (>20 wt%) are suggested to have the potential to produce more products. However, most often, low substrate loadings (<5% solids, w/w) are used to ensure good wetting and [...] Read more.
Fuel alcohol production yields can be influenced by lignocellulosic biomass loading. High solid loadings (>20 wt%) are suggested to have the potential to produce more products. However, most often, low substrate loadings (<5% solids, w/w) are used to ensure good wetting and enzyme accessibility, and to minimize any inhibitory effect on the hydrolysis products. Here, we analyzed the effect of substrate loading on the enzymatic hydrolysis of hay with non-commercial enzyme products obtained from white-rot fungi. A significant negative effect on hydrolysis was observed when 10 wt% hay loading was used with the commercial enzyme, however, non-commercial enzyme products from white-rot fungi had no impact on hydrolysis in biomass loading rates from 1 to 10 wt%. Moreover, it was estimated that enzymes extracted from white-rot fungi could be used at a concentration of 0.2 FPU/mL at a biomass loading from 1–10 wt%, resulting in 0.17–0.24 g of released reducing carbohydrates per gram of biomass. Higher concentrations did not result in any significant conversion increase. A mixing impact was only observed in test runs at a substrate loading of 10 wt%. The apparently positive features of the non-commercial enzyme mixes give rise to their future use. The combination and upgrade of existing technologies, e.g., efficient pre-treatment, membrane purification, and concentration and efficient product recovery, should result in even higher conversion yields. Full article
(This article belongs to the Special Issue Renewable energy solutions for the Baltic–Nordic region)
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Open AccessArticle
Contribution to the Energy Situation in Tajikistan by Using Residual Apricot Branches after Pruning as an Alternative Fuel
Energies 2019, 12(16), 3169; https://doi.org/10.3390/en12163169 - 18 Aug 2019
Abstract
A lack of access to energy in the rural areas of Tajikistan is one of the current problems of the country. Tajikistan’s goal is to reach energy independency, and the main prospects for the country’s energy sector, which relies on energy imports during [...] Read more.
A lack of access to energy in the rural areas of Tajikistan is one of the current problems of the country. Tajikistan’s goal is to reach energy independency, and the main prospects for the country’s energy sector, which relies on energy imports during the long heating periods, are: higher exploitations of hydropower and development of other renewables, mainly biofuels. Tajikistan is a highly agrarian country, where agriculture is the dominant source of income for the majority of the population. Apricot belongs to the primary agricultural commodities; however, the cultivation and management of apricot orchards is associated with the annual accumulation of significant amounts of wood waste (residual branches after pruning), which represent a source of easily available biomass. Thus, the main focus of the present research was to investigate the properties (physical, chemical and mechanical) of densified briquettes and pellets from the residual apricot tree branches through the laboratory measurements by the standard methodologies and to calculate the energy yield and potential of this material for Tajikistan as a similar study has not been conducted yet. The results showed a good quality of apricot-based biofuels characterised by the high calorific value (NCV dry basis of 19.3 MJ kg−1), relatively low ash content (1.7%) and suitable values of the main chemical elements that fulfil the standard requirement on graded wooden biofuels. The total yearly energy yield of residual apricot branches was calculated to be 3245 TJ. Full article
(This article belongs to the Special Issue Renewable energy solutions for the Baltic–Nordic region)
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Open AccessArticle
Feasibility of New Liquid Fuel Blends for Medium-Speed Engines
Energies 2019, 12(14), 2799; https://doi.org/10.3390/en12142799 - 20 Jul 2019
Abstract
Several sustainable liquid fuel alternatives are needed for different compression ignition (CI) engine applications. In the present study, five different fuel blends were investigated. Rapeseed methyl ester (RME) was used as the basic renewable fuel, and it was blended with low-sulfur light fuel [...] Read more.
Several sustainable liquid fuel alternatives are needed for different compression ignition (CI) engine applications. In the present study, five different fuel blends were investigated. Rapeseed methyl ester (RME) was used as the basic renewable fuel, and it was blended with low-sulfur light fuel oil (LFO), kerosene, marine gas oil (MGO), and naphtha. Of these fuels, MGO is a circulation economy fuel, manufactured from used lubricants. Naphtha is renewable as it is a by-product of renewable diesel production process using tall oil as feedstock. In addition to RME, naphtha was also blended with LFO. The aim of the current study was to determine the most important properties of the five fuel blends in order to gather fundamental knowledge about their suitability for medium-speed CI engines. The share of renewables within these five blends varied from 20 to 100 vol.%. The properties that were investigated and compared were the cetane number, distillation, density, viscosity, cold properties, and lubricity. According to the results, all the studied blends may be operable in medium-speed engines. Blending of new, renewable fuels with more conventional ones will help ease the technical transitional period as long as the availability of renewable fuels is limited. Full article
(This article belongs to the Special Issue Renewable energy solutions for the Baltic–Nordic region)
Open AccessArticle
Combustion Studies of a Non-Road Diesel Engine with Several Alternative Liquid Fuels
Energies 2019, 12(12), 2447; https://doi.org/10.3390/en12122447 - 25 Jun 2019
Cited by 1
Abstract
Sustainable liquid fuels will be needed for decades to fulfil the world’s growing energy demands. Combustion systems must be able to operate with a variety of renewable and sustainable fuels. This study focused on how the use of various alternative fuels affects combustion, [...] Read more.
Sustainable liquid fuels will be needed for decades to fulfil the world’s growing energy demands. Combustion systems must be able to operate with a variety of renewable and sustainable fuels. This study focused on how the use of various alternative fuels affects combustion, especially in-cylinder combustion. The study investigated light fuel oil (LFO) and six alternative liquid fuels in a high-speed, compression-ignition (CI) engine to understand their combustion properties. The fuels were LFO (baseline), marine gas oil (MGO), kerosene, rapeseed methyl ester (RME), renewable diesel (HVO), renewable wood-based naphtha and its blend with LFO. The heat release rate (HRR), mass fraction burned (MFB) and combustion duration (CD) were determined at an intermediate speed at three loads. The combustion parameters seemed to be very similar with all studied fuels. The HRR curve was slightly delayed with RME at the highest load. The combustion duration of neat naphtha decreased compared to LFO as the engine load was reduced. The MFB values of 50% and 90% occurred earlier with neat renewable naphtha than with other fuels. It was concluded that with the exception of renewable naphtha, all investigated alternative fuels can be used in the non-road engine without modifications. Full article
(This article belongs to the Special Issue Renewable energy solutions for the Baltic–Nordic region)
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Open AccessArticle
The Influence of Changing Hydropower Potential on Performance Parameters of Pumps in Turbine Mode
Energies 2019, 12(11), 2103; https://doi.org/10.3390/en12112103 - 01 Jun 2019
Abstract
Pumps as turbines (PAT) are used as an alternative to water turbines in small hydropower plants. The same devices can also be used for energy recovery in water distribution networks. They can replace pressure reduction valves that often lead to energy loss. However, [...] Read more.
Pumps as turbines (PAT) are used as an alternative to water turbines in small hydropower plants. The same devices can also be used for energy recovery in water distribution networks. They can replace pressure reduction valves that often lead to energy loss. However, PATs lack the parts that regulate flow so that when a hydropower potential change occurs, efficiency is reduced, as is economic gain. This article summarizes the influence of changing hydropower potential on PAT efficiency and presents comparisons of experimental results with the commonly used predictive model stemming from the theory of physical similarity, which presumes constant PAT efficiency. Our research indicates that the deviation between the model and the real power output calculation at varying potentials was minimal. Similarly, the affine parabola can be used to determine the relationship between total head and flow rate. Other relationships differ from reality the more the PAT efficiency changes. The flow rate and total head dependence on shaft speed are the main factors when setting the optimum operational parameters at varying hydropower potentials. Therefore, a change in efficiency must be included in predictive calculations to correctly optimize PAT operation. The problem is that a change in efficiency cannot be reliably predicted in advance, especially in the case of small-scale devices. For this reason, further research on the issue of changes in PAT efficiency is necessary. Full article
(This article belongs to the Special Issue Renewable energy solutions for the Baltic–Nordic region)
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Open AccessArticle
Effect of Alternative Liquid Fuels on the Exhaust Particle Size Distributions of a Medium-Speed Diesel Engine
Energies 2019, 12(11), 2050; https://doi.org/10.3390/en12112050 - 29 May 2019
Cited by 1
Abstract
We mainly aimed to determine how alternative liquid fuels affect the exhaust particle size distributions (PSD) emitted by a medium-speed diesel engine. The selected alternative fuels included: circulation-origin marine gas oil (MGO), the 26/74 vol. % blend of renewable naphtha and baseline low-sulfur [...] Read more.
We mainly aimed to determine how alternative liquid fuels affect the exhaust particle size distributions (PSD) emitted by a medium-speed diesel engine. The selected alternative fuels included: circulation-origin marine gas oil (MGO), the 26/74 vol. % blend of renewable naphtha and baseline low-sulfur marine light fuel oil (LFO), and kerosene. PSDs were measured by means of an engine exhaust particle sizer from the raw exhaust of a four-cylinder, turbocharged, intercooled engine. During the measurements, the engine was loaded by an alternator, the maximum power output being set at 600 kW(e) at a speed of 1000 rpm. The partial loads of 450, 300, 150 and 60 kW(e) were also used for measurements. At each load, the PSDs had a distinct peak between 20 and 100 nm regardless of fuel. Relative to the other fuels, circulation-origin MGO emitted the lowest particle numbers at several loads despite having the highest viscosity and highest density. Compared to baseline LFO and kerosene, MGO and the blend of renewable naphtha and LFO were more beneficial in terms of total particle number (TPN). Irrespective of the load or fuel, the TPN consisted mainly of particles detected above the 23 nm size category. Full article
(This article belongs to the Special Issue Renewable energy solutions for the Baltic–Nordic region)
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Review

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Open AccessFeature PaperReview
Evaluation of New Genetic Toolkits and Their Role for Ethanol Production in Cyanobacteria
Energies 2019, 12(18), 3515; https://doi.org/10.3390/en12183515 - 12 Sep 2019
Abstract
Since the public awareness for climate change has risen, increasing scientific effort has been made to find and develop alternative resources and production processes to reduce the dependency on petrol-based fuels and chemicals of our society. Among others, the biotechnological fuel production, as [...] Read more.
Since the public awareness for climate change has risen, increasing scientific effort has been made to find and develop alternative resources and production processes to reduce the dependency on petrol-based fuels and chemicals of our society. Among others, the biotechnological fuel production, as for example fermenting sugar-rich crops to ethanol, is one of the main strategies. For this purpose, various classical production systems like Escherichia coli or Saccharomyces cerevisiae are used and have been optimized via genetic modifications. Despite the progress made, this strategy competes for nutritional resources and agricultural land. To overcome this problem, various attempts were made for direct photosynthetic driven ethanol synthesis with different microalgal species including cyanobacteria. However, compared to existing platforms, the development of cyanobacteria as photoautotrophic cell factories has just started, and accordingly, the ethanol yield of established production systems is still unreached. This is mainly attributed to low ethanol tolerance levels of cyanobacteria and there is still potential for optimizing the cyanobacteria towards alternative gene expression systems. Meanwhile, several improvements were made by establishing new toolboxes for synthetic biology offering new possibilities for advanced genetic modifications of cyanobacteria. Here, current achievements and innovations of those new molecular tools are discussed. Full article
(This article belongs to the Special Issue Renewable energy solutions for the Baltic–Nordic region)
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