Recirculation System Research Articles

Behaviour of dissolved inorganic salts in the cooling water of a nuclear power plant open recirculation system and formation of water discharge.

The main problem in the operation of nuclear power plants (NPPs) is the scale formation of mineral impurities in an open recirculating system (ORS). The discharge of water from an ORS into natural water bodies can alter the chemical equilibrium of wastewater components, necessitating continuous monitoring. The purpose of this study was to analyse the behaviour of dissolved inorganic salts (DIS) in water within an ORS during water treatment, using the Rivne Nuclear Power Plant (RNPP) as a case study. Moreover, the analysis impact of their discharge with return water in the Styr River. The DIS concentration has a significant impact on the efficiency of the system and the environmental of an ORS power plant. Altogether, each of the DIS components was analysed separately using the standard measurement methods, statistical methods of data processing and correlation analysis. In addition, the annual discharge of the DIS components was calculated, and the amount of discharge was assessed for compliance with the maximum discharge limit. Thus, the impact of the formation of DIS and the variations in their concentration levels upon the discharge of wastewater into a natural water body were examined.

One-year old European perch (Perca fluviatilis)-specific in vitro digestion studies in special regard to feed optimization

The aim was to investigate the effect of water temperature on digestive enzyme activities of perch, to determine at which temperature their digestion process is more suitable. European perch (Perca fluviatilis) (1 year old, 50–60 g, 10 cm) were kept in recirculation system with the stocking density of 9 kg/m3 in 150 litre-sized-tanks, at 16°C, 18°C, 20°C, 22°C. Fish were kept for 1 week acclimatization, starved for 72 hours before feeding (crude protein: 45 %, crude fat: 16 %, crude fiber: 2.6 %; digestible energy: 18.5 MJ). Feeding was twice, with a 6 hours interval. There were 3 tanks for each proper temperature treatment; every tank contained 100 fish. 10 fish were moved out from all the tanks (30 fish per treatments). Stomach, intestine of fish was separated and their walls were washed with 1 ml of distilled water (pH 2.5), with 1 ml of 50 mM Tris-HCl, containing 0.5 M NaCl, 20 mM CaCl2 (pH 7.8), respectively, to retrieve gastric and intestinal digestive extracts. Extracts were used for pepsin, trypsin. total alkaline proteolytic, lipase, α-amylase activity tests. We have succeeded in developing protocol for gaining enzyme-containing extracts to monitor the realistic physiological conditions of perch based on enzyme activity measurements. The protocol was considered to be easy to implement and to provide sufficient enzyme extract to simulate subsequent in vitro digestion. The ambient temperature affected enzyme activities significantly: pepsin (40480.14; 69245.91; 79305.86; 40236.32 U/mg protein), trypsin – (7.77; 9.88; 11.12; 5.42 U/mg protein), total alkaline proteolytic - (1.47; 1.14; 1.25; 0.84 U/mg protein), lipase – (0.40; 1.16; 0.72; 0.76 U/mg protein) and α-amylase (0.29; 0.395; 0.98; 1.17 U/mg protein) activities, respectively at 16, 18, 20 and 22°C. Based on protease activities, 18–20°C was chosen to be the most appropriate rearing temperature, which contributes the most to the proper growth of the fish.

Study of vortex dynamics in a solar tower vortex generator

Vortical flows, integral to fluid mechanics, significantly influence the performance and efficiency of various engineering applications. Utilizing a validated three-dimensional computational model, this study characterizes vortex structures and examines the impact of ambient conditions and the strategic positioning of vortex generators (swirler) at critical geometric locations, such as the throat, and regions above and below it, within a converging–diverging solar tower. The research explores the influence of swirler position on recirculation zone characteristics, focusing on center-to-center (C2C) distance, penetration length, and maximum width. When the swirler is positioned above or below the throat, C2C distance shows minimal change. However, placing the swirler exit at the throat significantly reduces C2C distance at the lowest velocity (0.13 m/s), due to a stable recirculation zone. This effect diminishes at higher velocities. Swirler position greatly affects penetration length, resulting in two distinct behaviors: Behavior A, dominated by swirler position, occurs when the swirler is above or below the throat, and Behavior B, which is velocity-dependent, is observed when the swirler exit is at the throat. The study also investigates the interaction between the recirculation zone and swirler exit flow, focusing on restriction and mixing ratios. The restriction ratio is higher below the throat (31 %) compared to the throat (27 %). The mixing ratio shows minimal variation with inlet velocity but significant variation with swirler position. Among the evaluated positions, placing the swirler below the throat results in the lowest swirl strength for most axial distances, except near the exit height, rendering it less suitable for water harvesting applications. These findings provide guidance for optimal swirler placement to achieve desired recirculation zone control and system performance.

PEMANFAATAN CACING TANAH (Lumbricus rubellus) PADA PENDEDERAN LOBSTER AIR TAWAR (Cherax quadricarinatus) DENGAN SISTEM RESIRKULASI

Recirculation systems are intensive cultivation methods that offer an attractive alternative to extensive systems for lobster farming. This study aims to evaluate the utilization of earthworms (Lumbricus rubellus) in the juvenile rearing of freshwater lobsters (Cherax quadricarinatus) using a recirculation system. The research was conducted at the Wet Laboratory of the Seed and Fish Feed Production Technology Study Program, Politeknik Indonesia Venezuela, from October to November 2022. The experimental design used was a Completely Randomized Design (CRD) non-factorial, consisting of 4 treatments and 4 replications: A (control), B (10% of biomass), C (15% of biomass), and D (20% of biomass). The results showed that treatment D (20% of biomass) produced the highest absolute weight growth, with an average of 12.0 g, while treatment A (control) had the lowest weight with an average of 1.2 g. The highest absolute length growth was also observed in treatment D, with an average of 4.5 cm, while treatment A had the lowest length growth at 0.7 cm. The highest feed conversion ratio (FCR) was achieved by treatment B (10% of biomass) with an average of 2.57, whereas the lowest FCR was observed in treatment D with an average of 1.63. The highest molting frequency over 30 days was recorded in treatment D, while the lowest molting frequencies were found in treatments A and B. ANOVA test results indicated that the earthworm treatments significantly affected absolute weight growth, absolute length growth, feed conversion ratio (FCR), and molting frequency of the lobsters over 30 days. However, there was no significant effect on the survival rate (SR) of the lobsters.

Kinetics of Vanillin and Vanillic Acid Production from Pine Kraft Lignin

Vanillin (4-hydroxy-3-methoxybenzaldehyde) is the main component of natural vanilla and a relevant substance in the flavoring and aromatic industries. This study presents a kinetic model to explain both vanillin and vanillic acid concentrations achieved in the alkaline oxidation of pine kraft lignin. Considering that they come from the same precursors, this approach allows an understanding of vanillin production with reaction conditions that minimize the vanillic acid pathway directly from the lignin oligomers, thus maximizing vanillin production. This study involves the effects of oxygen partial pressure, temperature, and the presence or absence of a catalyst (CuSO4 and Fe2(SO4)3 mixture) on the vanillin and vanillic acid yields. An adapted reactor (M/K Systems Inc., Williamstown, MA, USA) with a recirculation and spray liquids system was used in the experiments. The experiments were performed using one liter of a solution of NaOH 2 M and 60 g of lignin. During the lignin oxidation reaction, liquid samples were analyzed at different times (from 0 to 200 min). The oxidation products were quantified by liquid chromatography (HPLC). The catalyzed experiments presented higher maximum vanillin yields than the non-catalyzed ones (39.2–39.6% on nitrobenzene oxidation) achieved at 150 °C. A kinetic model is proposed where the kinetic parameters were estimated using Monte Carlo methods, fitting satisfactorily to the experimental results. The statistical analysis of the kinetic parameters showed that all the studied variables significantly affect the vanillin yield.

Intra-cohort cannibalism and aggressive behavior in tropical gar (Atractosteus tropicus) larvae: Effects of stocking density and starvation

Cannibalism in early fish developmental stages is a biological phenomenon affecting aquaculture, so seeding density and feeding schemes play a fundamental role in its optimal control. The objective of this research was to evaluate two initial stocking densities, 0.7 larvae/L (D7) and 1.4 larvae/L (D14), which were fed (F) and not fed (NF) in tropical gar (Atractosteus tropicus) larvae on growth, attacks, survival, and digestive enzyme activity, digestive morphology, and oxidative enzymes and aggressiveness gene expression. A total of 420 larvae (0.022 ± 0.003 g; 1.52 ± 0.10 cm) were placed in 70 L tanks connected to a recirculation system. Treatment F larvae were fed a formulated food. D14F larvae had the highest final weight, total length, and specific growth rate (SGR) (p < 0.05). The highest survival percentage was in D7F larvae (46.19 ± 2.74) (p < 0.05). The highest frequency of attacks occurred in D14F larvae (26.66 ± 0.82) (p < 0.05). The coefficient of variation (CV) and size heterogeneity (SH) were higher in D7F larvae (13.56 ± 1.80; 0.81 ± 0.10) (p < 0.05). The F larvae started attacks at 8 days after hatching (DAH), while the NF larvae showed it at 10 DAH. The difference in weight between the attacker and the attacked was 16.44 ± 9.75% and in total length 12.28 ± 4.57% (p < 0.05). Acid and alkaline protease, trypsin, and lipase activities presented differences between both factors, as well as the interaction between them. D14F larvae presented the highest Glutathione peroxidase (GPX) activity (p < 0.05), while D7-NF larvae registered the highest catalase (CAT) activity (p < 0.05). Superoxide dismutase (SOD) activities only showed differences between F and NF larvae (p < 0.05). The liver presented the highest percentage of area with melanomacrophage centers (MMC) in D7-NF larvae, and hepatocytes with the highest area were recorded in D14F larvae (p < 0.05). In gut, the highest enterocytes were recorded in D14F larvae (p < 0.05). cat, cck, and gpx expression did not show difference between feeding regimes. The expression of sod1 and sod2 in D7F and D14F treatments presented the highest expressions (p < 0.05). D7F larvae presented higher expression of avp1, crh, htr1, sstr1, th and tph1 genes (p < 0.05). Our results show that A. tropicus larvae D14F presented the highest growth and morphometric parameters and decreased CV and SH, which shows a more homogeneous growth. Regarding cannibalism, fed larvae (D7F, D14F) presented cannibalism in a greater proportion than unfed larvae regardless of density, however, it is necessary to analyze other physiological and social factors that could be related to the aggressiveness and cannibalism of the species.

Control strategies for mode switching of a large marine two-stroke engine equipped with exhaust gas recirculation and turbocharger cut-off systems

To meet the stringent nitrogen oxides emissions regulations, the recent marine two-stroke engines are equipped with exhaust gas recirculation (EGR) systems. Crossing the boundaries of exhaust control areas requires switching between the engine operating modes associated with the activation or deactivation the EGR system, which imposes challenges to the engine operation. This study aims to develop and numerically test effective control strategies for improving the mode switching of marine two-stroke engines with EGR systems. The investigated engine dynamic model is developed by integrating a zero-dimensional thermodynamic model developed in GT-POWER and the control model developed in MATLAB/Simulink. This model is first validated against the experimentally measured engine performance parameters, and subsequently employed to simulate the engine dynamic operation with mode switching. The simulation results are assessed to quantify the impact of several control strategies on the engine performance. The derived perrformannce parameters time variations demonstrate that the deactivation of the EGR branch and the small engine–turbocharger result in exceeding the manufacturer limits at high loads and increasing the fuel consumption. The proposed load-based control strategies, which employ load thresholds and time delays for the control of the EGR and turbocharging systems activation/deactivation, are proved effective, as the engine performance parameters are retained within their limits and fuel consumption penalties are minimised. This study provides insights for developing the control of the marine engines after-treatment systems, hence contributing towards enhancing shipping sustainability.

Method of estimating break size in piping loop systems

The approach for determining the break size of recirculation loops in a multiple-loop power plant in the event of a loss of coolant accident (LOCA) is presented in this study. In this study, the MAAP5 simulation program was used. An approach to measuring the size of a crack or break in the cooling system is the temperature difference between the recirculation loops. This method does not require any additional facilities; it compares the temperatures of the cooling loops to determine which one has a rupture. The best data source was the loop monitoring system, which sends temperature data for analysis to the main control room. A real operating power reactor training simulator and the FSAR are applied to evaluate MAAP5, the methodology's engine. The results of the MAAP5 simulation code were consistent with those of the power plant simulator. Therefore, MAAP5 could produce enough analytical data to create the relationship diagram between temperature difference and break size.The study hypothesized that there exists a maximum value of temperature difference corresponding to each break size and suggested that applying the absolute maximum temperature difference can aid in identifying the break size. This approach proposes an assistive method for determining the size of a fracture or break in the recirculation system by leveraging the temperature difference between each loop.This approach eliminates the need for additional facilities, as temperature data from the recirculation loops can be transmitted to the main control room. After the reactor scram, operators can monitor the maximum temperature differences at the inlet to estimate the break size. Although the fitting curve used to preliminary estimate the Large Break Loss of Coolant Accident break size may overestimate the break size, it still provides valuable insights. This novel tool offers a rapid and comprehensive method for detecting LOCA events in the recirculation loops.

Effect of Replacing Fishmeal with Algal Meal on Growth Parameters and Meat Composition in Rainbow Trout (Oncorhynchus mykiss W.)

Aquafarms should reduce the use of fishmeal and fish oil in nutritional feed. One such accessible and relatively inexpensive food component that could successfully meet the challenge posed by aquaculture is algae. The objective of the present study was to evaluate the algae meal inclusion of Chlorella and Spirulina sp. in a diet for rainbow trout, evaluating its effects on fish growth, histological parameters and fillet quality. Experiments were carried out to replace 50% and 100% of fishmeal with Spirulina sp. and Chlorella vulgaris in feed for rainbow trout (Oncorhynchus mykiss W.) cultured in a recirculation system. At the end of the experimental period, the highest mean live weight was measured in rainbow trout fed a feed containing 50% algal meal in the feed. The absorptive vacuolization of cells was increased the most and lamina propria was average thickened when fed 50% algae diets. Fat droplets in the hepatocytes were larger in the 50% algae meal fed group, and their nuclei were replaced in the peripheral zone of the cells. Substitution of fishmeal with 50% algal meal in fish feed resulted in a 36.44% reduction in the lipid content of rainbow trout fillets compared to control fish.

Evaluation and economic analysis of fermented fish viscera silage in diets for tambaqui (Colossoma macropomum) and its effects on the physical quality of pellets, growth performance, health parameters

AbstractThe production of silage using fish viscera can be carried out with straightforward methods and permits the exploitation of nutrients that are usually discarded. This process fosters the concept of circular aquaculture. The aim of this study was to evaluate the inclusion of increasing levels of fish viscera silage (VS) on the physical quality of the feed pellets and their effects on their growth performance, health parameters and on economic indices when the experimental extruded feed was offered to tambaqui. A fermented fish VS produced in‐house was included in increasing levels on a wet‐basis in the formulation of five experimental diets (VS 0%, VS 5%; VS 10%; VS 15% and VS 20%). Juvenile tambaqui (~22.6 g) were stocked in fibreglass tanks of 700 L (n = 4; 21 fish per tank) with a recirculation system and the five experimental diets were attributed in a completely randomized design. The fish were fed with the experimental diets (to apparent satiation) for 13 weeks. At the end of the trial, no significant differences were observed for production performance. Fish fed with the highest inclusion level of VS presented the highest concentration of plasma cholesterol, but this was still within acceptable values for this species. The inclusion of fish VS in diets for juvenile tambaqui reduced the activity of the plasma ALT enzyme, confirming normal liver function. Extruded feed containing fish VS had a production cost of US$ 0.95 per kg, which does not significantly impact the economic indices. Up to 20% of fish VS can be included in the extruded feed formulation for juvenile tambaqui without impairing growth performance or affecting health parameters.

Clostridium and Cryptosporidium outbreak linked to a splash pad

Background. Splash pads for recreational purposes are widespread. Using these pads can pose a health risk if they lack installation regulation and water quality supervision. Our aim was to describe a waterborne disease outbreak caused by Clostridium perfringens and Cryptosporidium spp. in a Barcelona district and the measures taken for its control.Methods. On August 2018, 71 cases of acute gastroenteritis were detected, affecting people who used a splash pad or were in contact with a user. Microbiological and environmental investigations were carried out. A descriptive analysis of the sample and Poisson regression models adjusted for age and sex were performed, obtaining frequencies, median values, and adjusted prevalence ratios with their 95% confidence intervals.ResultsThe median age of the cases was 6.7 years, 27 (38%) required medical care, and three (4.2%) were hospitalized. The greater the number of times a person entered the area, the greater the number of symptoms and their severity. Nineteen (76%) of the 25 stool samples collected from cases showed the presence of one or both pathogens. Environmental investigations showed deficiencies in the facilities and identified the presence of both species in the splash pad. Health education and hygiene measures were carried out, and 14 days after the closure of the facilities, no more cases related to the pad were recorded.Conclusions. Specific regulations are needed on the use of splash pads for recreational purposes. Until these regulations are in place, these types of facility should comply with the regulations that apply to swimming pools and spas, including those related to the design of the tanks, water recirculation systems, and adequate disinfection systems.

Optimum stocking density of adult freshwater crayfish Procambarus clarkii in recirculation system

Optimum stocking density of adult freshwater crayfish Procambarus clarkii in recirculation system

Evaluating the Efficiency of Solar and Petrol-Powered Recirculating Aquaculture Systems for African Catfish (&amp;lt;i&amp;gt;Clarias gariepinus&amp;lt;/i&amp;gt;) Fingerling Production

Accessibility of quality fingerlings is dependable on a hatchery system with the capacity to produce all year round. There are two hatchery systems operational in Nigeria namely, the flow-through and re-circulating systems. These two systems require electricity to power periodic or constant water supply and aeration. When electricity supply fails or non-existent, this will result in anxiety and hardship to hatchery operators with the subsequent low output. This paper, therefore, assessed the production efficiency of solar and petrol-powered generator recirculating aquaculture systems for African catfish &amp;lt;i&amp;gt;(Clarias gariepinus)&amp;lt;/i&amp;gt; fingerlings production. The results obtained from the growth performance and survival percentage of &amp;lt;i&amp;gt;Clarias gariepnus&amp;lt;/i&amp;gt; reared in the two recirculating systems (solar and generator powered recirculating systems) showed no significant difference (P&amp;gt; 0.05) in the initial weight, specific growth rate (SGR) and feed conversion efficiency (FCE) of &amp;lt;i&amp;gt;C. gariepnus&amp;lt;/i&amp;gt; from the two-recirculating systems. However, the result showed significant differences (P&amp;lt;0.05) in the final mean weight, weight gained, and survival rate in the two-recirculating systems. Aligning with the guidelines outlined by the Food and Agriculture Organization (FAO), the means and range values of temperature (°C), dissolved oxygen (mg/l), pH and ammonia, observed from the two recirculating production systems indicated temperature (22.81°C - 25.11°C), dissolved pH (7.10-7.42), dissolved oxygen (6.22- 6.62mg/l), ammonia (0.04-0.08mg/l) respectively. The survival rate of fry reaching 84% for the solar group and 64% for the generator at the end of 28- 56 days. Thus, this study revealed that solar energy might become the most promising energy source that can replace the usual source of energy for hatchery operations in Nigeria. This study, therefore, recommended that Solar Powered Recirculating Systems be adopted where feasible, given their demonstrated support for increased growth rates and higher survival rates to enhance efficiency and sustainability of aquaculture production systems.

STUDYING THE THERMOCHEMICAL CHARACTERISTICS OF SINTERING WITH ALKALI CONCENTRATE FROM WASTE COPPER TAILINGS

A long period of deposit development leads to a reduction in the volume of balance reserves of ores, while the volume of accumulation of waste (tailings) from mining and processing production increases. In connection with this, an urgent problem is the processing of waste tailings, which can serve as an additional source of commercial products of non-ferrous metals. The set objectives can be achieved by implementing comprehensive extraction of valuable components, reducing fuel, and energy costs at the stage of low-temperature sintering to produce white soot (grade BS-100). In order to determine the amount of heat of chemical reactions during sintering of rough copper concentrate with sodium hydroxide, thermochemical calculations were carried out. For the research, we used rough copper concentrate with a copper content of 4.40% and silver of 77.03 g/t. An equation has been obtained for calculating the heat of chemical reactions of rough concentrate sintering. According to this equation, the greatest contribution to the heat release is provided by the iron content (60%), three times less and equally (19%) - copper and silicon and about 0.2% is absorbed by aluminum. The thermal effect of sintering will be -920.45 kW·h/t of concentrate. From the heat balance of sintering it follows that with an alkali consumption of up to 200% of the mass of the concentrate. The heat of chemical reactions will be sufficient for the autogeneity of the process. Research has been carried out on sintering the concentrate with alkali in the temperature range of 250-500 °C and obtaining white soot from a productive leaching solution with the extraction of 60% silicon. White soot (mSiO2·nH2O) was isolated by two-stage carbonization of a silicate solution with carbon dioxide in a recirculation system with further washing of the precipitate with a solution of sulfuric acid. For citation: Karimova L.M., Kairalapov Ye.T., Makascheva G.K., Kharchenko Ye.M. Studying the thermochemical characteristics of sintering with alkali concentrate from waste copper tailings. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 7. P. 72-79. DOI: 10.6060/ivkkt.20246707.7004.

Length-weight relationship and condition factor of Nile tilapia ( Oreochromis niloticus) fed diets supplemented with guava and star gooseberry leaf extract.

Nile tilapia ( Oreochromis niloticus) is predominant cultured species in aquaculture. However, there is a scarcity of literature regarding relationship between guava and star gooseberry leaf extract and the condition factor. Thus, the present study aims to investigate the effect of guava and star gooseberry leaf extract-supplemented diets on the specific growth rate, length-weight relationship, and condition factor of Nile tilapia. Six hundred and thirty Nile tilapia (8.7±0.4 g) were randomly distributed among twenty-one tanks (30 fish per tank) within a recirculation system. Over a 60-day period, the fish were fed diets supplemented with 5g/Kg and 10g/Kg of guava leaf extract (GLE-5, GLE-10), star gooseberry leaf extract (SGLE-5, SGLE-10), and a mixture of both (MxLE-5, MXLE-10). Subsequently, specific growth rate, length-weight relationship, and condition factor were determined. After 60 days, the specific growth rate was significantly higher in all the GLE, SGLE, and MxLE groups compared to the control group. The final lengths and weights differed significantly both in the control group and all the GLE, SGLE, and MxLE groups. The analysis of the regression equation indicated a positive correlation (r = 0.970, 0.977, 0.976, 0.974, 0.974, 0.974, and 0.969) between the length and weight of Nile tilapia in the control group and in all the GLE, SGLE, and MxLE groups. The regression exponent " b" values in all the GLE, SGLE, and MxLE groups were >3, indicating a positive allometric growth pattern in Nile tilapia compared to the control ( b=2.866), which exhibited a negative allometry. The final condition factor values did not differ significantly in either the control group or any of the plant extract groups. Nile tilapia exhibited positive allometric growth patterns and maintained good health when fed with GLE, SGLE, and MxLE groups. Therefore, these plant extracts demonstrate suitability for commercial Nile tilapia production.

Performance investigation of coupling modes for hydrogen circulation in high-power proton exchange membrane fuel cell systems

The economy and stability of the hydrogen recirculation system in high-power fuel cells significantly impact the performance of the stack system. However, there is no consensus on the optimal hydrogen recirculation mode to be employed. To determine the most effective solution across the entire power range of the stack, this study compares the performance of various coupling modes. The dynamic performance variations of the system were investigated under different modes by the Computational Fluid Dynamics (CFD) method. The simulation results demonstrated that within the low and medium power range of the stack, the PUE (Pump Upstream of Ejector) mode had the lowest power consumption of all modes, at 112 W. The power of the PUE mode had a reduction of 56.3% compared to the full-power single hydrogen pump mode, and a reduction of 22.8% compared to the PDE (Pump Downstream of Ejector) mode.

Multi-mode operation of a novel dual-pressure steam rankine cycle system recovering multi-grade waste heat from a marine two-stroke engine equipped with the high-pressure exhaust gas recirculation system

As a promising technology for marine two-stroke engines satisfying the IMO Tier Ⅲ NOx regulation, the high-pressure exhaust gas recirculation (HP-EGR) systems in multi-mode operation significantly redistribute the waste heat, thereby complicating the design and control of the waste heat recovery (WHR) systems. In this paper, a novel dual-pressure steam Rankine cycle (SRC) is proposed to recover multi-grade waste heat from marine engines in multi-mode operation. The HP-EGR system is designed on the 6EX340 engine, followed by the evaluation of waste heat distribution in multi-modes. Detailed thermodynamic and economic analyses of the designed SRC and the combined cycle power plant are then conducted. The results show that the thermal efficiency of the designed SRC is 8.1 %–13.3 % in Tier II mode, increasing to 10.1 %–15.7 % in Tier III mode, attributable to a 16 %–42 % increase in waste heat exergy. Considering typical propulsion profiles, the reduction in weighted average fuel consumption for the combined cycle power plant reaches up to 3.4 % in Tier II operation and 6.1 % in Tier III operation. When 12.5 % of sailing time is spent within ECAs, the combined cycle power plant is expected to yield up to 4 % in annual fuel cost savings.

Optimization and 4E analysis of integration of waste heat recovery and exhaust gas recirculation for a marine diesel engine to reduce NOx emissions and improve efficiency

This paper proposes an integration of waste heat recovery system and exhaust gas recirculation system to break the inherent trade-offs between NOx and carbon emissions of marine low-speed diesel engine. It is significant important to break these trade-offs, because Energy Efficiency Existing Ship Index may not be met, though Energy Efficiency Design Index and Tier III can be already achieved for old ships. The waste heat recovery system consists of supercritical carbon dioxide Brayton cycle and Kalina cycle, where the integration of supercritical carbon dioxide Brayton cycle and Kalina cycle is achieved in the parallel style. This paper uses the classical thermodynamics in terms of engineering approach to carry out the parameter analysis of combined system first. The optimization is conducted in terms of efficiency, energy density and techno-economy with the introduction of global optimal policy. The results showed that the highest efficiency of 52.32% at Tier III mode can be achieved, at which the net power, exergy efficiency, area per unit power output and levelized energy cost can be achieved by 1568.57 kW, 45.75%, 0.589 m2/kW and 0.114$/kWh at main engine load of 85%. Further, the net power output of waste heat recovery system can reach 1085.76 kW and 2043 kW at Tier II mode and Tier III mode, while the recovering rate of waste heat recovery system can reach over 5% at Tier III mode. Finally, the Energy Efficiency Existing Ship Index of a container ship equipping with such combined system can be reduced from 9.50 to 9.05.

Long-term substitution of fish oil with alternative sources in Atlantic salmon (Salmo salar): Performance, health, and consumer appeal

Salmon farming in Chile faces the dual challenge of maintaining growth while improving sustainability. One approach to advance sustainability involves the feeds without marine-fishery inputs. This study aimed to evaluate the effect of completely replacing fish oil (FO) on the performance of Salmo salar throghout marine grow-out. The investigation involved fish ranging from 400 g to 4000 g and explored three diets without fish meal, each which included 2.2% EPA + DHA from different sources: FO (control), transgenic canola oil (Can n-3) and Schizochytrium sp. oil (AOV) as unique type of oils. Each diet was randomly distributed in triplicate among nine tanks with a recirculation system maintained at 12 °C, with automatic feeding and a 24-h light photoperiod. Fish density was 29 fish m−3 at day 133 of the experiment and seven fish m−3 at day 319. The diets were isoproteic, isolipidic and isoenergetic. Fish were evaluated at 133 and 319 days of experiment in terms of productive performance, liver health, EPA + DHA and lipid retention efficiency, fatty acid metabolism, response to acute stress, and final product quality. The results showed similar productive performance and liver health among the three diets during both sampling periods. No differences were observed in lipid or EPA + DHA retention efficiency in the whole body or fillet. Eicosanoids and receptors for anti-inflammatory mediators derived from EPA and DHA showed similar or higher capacities in fish fed with Can n-3 and AOV than those fed FO. Responses to induced stress, measured through lactate, cortisol, sodium, potassium, chloride, glucose, and the liver profile were similar between the three diets. Similarly in fillet quality between the three diets. However, sensory analysis revealed a lower intensity of “global aroma” in Can n-3-fed fish fillets and lower evaluations in “typical salmon aroma”, “oily aroma” and “fresh flavor” in AOV-fed fish fillets when they are compared with FO. The nutritional indicators of the final product were similar between the three diets, except for PUFA/SFA, the thrombogenicity index, hypercholesterolemia/hypocholesterolemia, and the health promotion index. In these specific indicators, fish fed with Can n-3 and AOV demonstrated more favorable results for consumer health than the FO-fed fish.

Numerical Studies of the Influence of Flue Gas Recirculation into Primary Air on NOx Formation, CO Emission, and Low-NOx Waterwall Corrosion in the OP 650 Boiler

Numerical calculations of the innovative flue gas recirculation (FGR) system through an inactive coal pulverizer for a 40% load of the OP 650 boiler at the Jaworzno III Power Plant were carried out. The research was conducted to determine the effect of FGR on the formation of NOx, CO emissions, and low-NOx waterwall corrosion. Using numerical modelling, the influence of the place of injection of recirculated flue gas on the formation of NOx was also investigated. The tests were carried out based on data from the boiler monitoring system and calculation results using a 0-dimensional model. Modelling of the FGR was performed for five variants. FGR equalized the temperature in the furnace, eliminating temperature peaks in the burner belt. Moreover, FGR did not increase the CO content in the flue gas and reduced the O2 concentration in the area zone of pulverized coal combustion. For FGR systems, the emission of NOx below 200 mg/m3n for 6% O2 in dry flue gas was kept. This proves that the recirculation helps to meet the BAT (best available techniques) requirements for NOx emissions. It has also been shown that FGR does not pose a risk of low-NOx corrosion in the next 20 years.