Energy Procedia最新文献

The majority of household food waste in the EU is sent to landfill or incinerated; a slowly-increasing fraction is collected separately and utilised for anaerobic digestion (AD) or in-vessel composting (IVC). This study evaluates life cycle environmental impacts of these four options to identify the most sustainable alternatives. The results are compared to waste prevention, inclusive of upstream supply-chain impacts. The results suggest that AD has the lowest, net-negative carbon footprint of –40 kg CO₂ eq. per tonne of waste treated and the highest life cycle energy recovery efficiency of 12% with respect to the total primary energy recovered. If all of the heat can be utilised, then both AD and incineration can achieve maximum energy recovery efficiencies of around 25%. Waste landfilling has the highest carbon footprint at 193 kg CO₂ eq./t and a recovery efficiency of 3% through the combustion of landfill gas. IVC, credited for the production of fertiliser, has a carbon footprint of 80 kg CO₂ eq./t and it has the lowest recovery efficiency at 1%. Under the best conditions, the greatest CO₂ eq. savings are achieved by the incineration of food waste, with a net-negative carbon footprint of –221 kg CO₂ eq./t. However, this is eclipsed by the 2,800–3,100 t CO₂ eq. that can be avoided by preventing the avoidable and potentially avoidable food waste. Thus, while unavoidable food waste may be best treated via AD or incineration, the savings are negligible compared to the benefits of waste prevention. Therefore, food waste may be used within a circular economy to reclaim a limited amount of resources, but it should not be considered an alternative to prevention.

Reducing food waste and increasing resource efficiency have become worldwide targets as highlighted by the United Nations Sustainable Development Goal 12 – Responsible consumption and production. Food packaging, in particular plastics-based, is a key component of food-related waste: packaging increases the amount of total waste, but also reduces potential food waste by protecting food products and prolonging their shelf life. Therefore, it is important that packaging is designed as to satisfy both technical and environmental criteria. Hence, this paper seeks to develop a decision-support framework and key metrics to aid development and selection of new innovative food packaging within a circular economy context. A set of indicators is proposed, integrating techno-environmental and circular economy criteria to help designers as well as food and packaging manufacturers develop more sustainable products. The methodology is illustrated through a prototype new plastic packaging developed as part of this project, considering its use for two types of product – raspberries and meat – as illustrative examples.

This paper addresses the need of bridging between fundamental energy research and industrial exploitation of technologies by presenting a state of the art experimental facility to investigate pilot heat exchangers and plants dealing with high temperature waste heat recovery and conversion. The facility comprises a 830 kW process air heater with an exhaust mass flow rate of 1.0 kg/s at 70 mbar_g and maximum temperature of 780 °C. The heater has a 2.0 m long test section for the installation and characterization of waste heat recovery heat exchangers. The heat sink is a 500 kW water dry cooler with full control of flow rate and temperature of the cooling stream. The high-temperature heat to power conversion facility hosts a 50 kWe power conversion unit based on the simple recuperated Joule-Brayton cycle with supercritical CO₂ (sCO₂) as working fluid. The packaged, plug and play sCO₂ system utilizes a single-shaft Compressor-Generator-Turbine unit. The paper discusses the main design features of the test facility as well as operation and safety considerations.

An approach considered in recent years to improve the efficiency of open-type refrigerated display cabinets is to install air guiding strips at the front face of the shelves with a single layer air curtain. This paper presents experimental results comparing a conventional open-type vertical refrigerated cabinet and a cold shelf innovation, which integrates both air-guiding strips and air supply at the front of individual shelves. In addition, a comprehensive and detailed Computational Fluid Dynamics model using ANSYS Fluent has been created to further investigate the influence of the cold shelve innovation on the performance of vertical multi-deck refrigerated display cabinets. The experimental results showed energy savings of 16.7 kWh/24 hrs for the guiding strips and cold shelf innovation compared to the conventional cabinet due to the more efficient air curtain and lower air temperature entering the evaporator coil.

Over the years, the use of air curtains has been considered as one of the most effective ways of preventing warm-air infiltration in cold storages and now in refrigerated trucks as well. It is estimated that energy savings of almost 40% can be achieved using an air curtain. Previous studies have suggested that the energy efficiency of air curtains could be further improved through several mechanical adjustments, including the adjustment of discharge angle. This study focuses on the influence of different discharge angles on air curtain mechanisms and energy performance for an air curtain with warm-air suction (ambient air intake). The results suggest that adjusting the angle in the positive direction (outwards) can help prevent the bending in the discharge jet- created as a result of dominating natural convection showing a discharge angle of 10° to be more effective in controlling the bend than 0°. However, the effectiveness of the discharge angle is highly dependent on the discharge velocity. When the discharge velocity is low (2 m/s), the released jet is too weak and hence the effect of the discharge angle is also small, resulting in similar recovery energy for both the 0° and 10° cases. However, when the discharge velocity is medium to high (above 4 m/s in this case), the bending effect is also significant and hence adjusting the discharge angle can prove to be more advantageous, providing an energy saving of up to 17.6%.

As a main component in a refrigeration system, finned-tube CO2 gas cooler plays an important role to the system performance and thus needs to be thoroughly investigated. To achieve this, some effective parameters including the CO2 and air fluid velocity fields, temperature profiles and heat transfer characteristics at different operating conditions are predicted and analysed by means of Computational Fluid Dynamics (CFD) modelling and simulation. It is noted that CFD modelling can accurately obtain the local heat transfer coefficients of both air and refrigerant sides, which are difficult to be predicted by conventional empirical correlations. This paper investigates the effect of varied operational parameters on local heat transfer coefficients and temperature profiles of the working fluids in a finned-tube CO2 gas cooler by means of CFD modelling. As one of the simulation results, it is found that the approach temperature decreases with increased air inlet velocity. The model has been compared and validated with experimental measurements and literature correlations. The research methods and outcomes can be used for further investigation and optimization in this area.

Surface processing of the materials used for the heat exchanging surfaces in condensing economizers and related facilities are used to deliver coatings to protect them from the corrosive condensates. By delivering increased corrosion protection, intact thermal conductivity, along with robust mechanical and wear resistance characteristics at low process costs, the lifetime of the investment is increased and the service periods become longer. However, during the past years surface processing has provided tools towards solutions for additional favorable surface features related to wetting phenomena. Coatings to enhance the dropwise condensation over the film-wise condensation, to increase the condensate collection rate and to promote the self-jumping of the condensates are far from rare. These features have a tremendous effect on the heat transfer coefficient and hence on the thermal efficiency of related heat exchange applications. Still, such features are typically not included on the testing protocols for the coatings being developed or demonstrated and they are not among the standard engineering selection criteria. In this work we briefly describe these features and provide preliminary equations for design and evaluation of their importance on the heat transfer coefficient.

The overall heat transfer coefficient of two CO₂ gas coolers was investigated through experiment and Computational Fluid Dynamics (CFD). The CFD modelling provided prediction accuracy for the overall heat transfer coefficient with a maximum error of 9% compared to the CFD predictions. Comparing the two gas cooler designs, and from the experimental and modelling results it has been shown that the performance of the gas cooler can be improved by up to 20% through optimization of the circuit design of the gas cooler. A horizontal slit between the 1^st and 2^nd row of tubes of the gas cooler can increase the overall heat transfer coefficient by 8% compared with the a fin without the slit.

In the European Union (EU), industrial sectors use 26% of the primary energy consumption and are characterized by large amounts of energy losses in the form of waste heat at different temperature levels. Their recovery is a challenge but also an opportunity for science and business. In this study, after a brief description of the conventional Waste Heat Recovery (WHR) approaches, the novel technologies under development within the I-ThERM Horizon 2020 project are presented and assessed from an energy and market perspectives. These technologies are: heat to power conversion systems based on bottoming thermodynamic cycles (Trilateral Flash Cycle for low grade waste heat and Joule-Brayton cycle working with supercritical carbon dioxide for high temperature waste heat sources); heat recovery devices based on heat pipes (flat heat pipe for high grade radiative heat sources and condensing economizer for acidic effluents).

One of the most important aspects of chilled food deterioration in delicatessen cabinets economically is associated with drying, rather than spoilage mechanism, especially for unwrapped products. Investigating the effects of the bacterial spoilage and moisture migration for chilled-unwrapped food product such as sandwiches, which have short display shelf life, and knowing the optimum boundary conditions that provide longer displays shelf life can significantly contribute to reduction of wastage of this type of product during its display, and operate refrigeration systems in the most efficient manner. Recent years have seen an increase in customer demand for fresh convenience food, which has resulted in a major increase in the volume of sales of unwrapped products. Surface drying has been identified as the main reason for commercial loss from unwrapped chilled food in display cabinets. Surface drying increases weight loss and leads to colour changes that are undesirable. A 2D Computational Fluid Dynamic model was constructed for the serve-over display cabinet that includes the weight loss from products inside the cabinet. The model was used to investigate the effect of the environmental boundary conditions on the drying rate and display shelf life. Validation was carried out by comparison of measured results of the product temperature, drying rate and display shelf life of the product inside the cabinet, to those predicted by the simulations. The results show that improving the operating boundary conditions inside the display cabinet can improve the food quality, reduce the drying rate of the food product and increase the display shelf life.