Energy Procedia最新文献

Instant coffee manufacture involves the aqueous extraction of soluble coffee components followed by drying to form a soluble powder. A challenge that arises from the process is the loss of volatile aroma compounds during evaporative drying. One method of retaining aroma is to first steam strip the volatiles from the coffee and add them back to a concentrated coffee solution just before the final drying stage. Understanding the impact of process conditions on the aroma content of the stripped solution offers engineers the ability to target desirable compounds and maximise their yield. This paper presents a multiscale model for aroma extraction that describes: (i) release from the matrix, (ii) diffusion through the coffee grain, (iii) transfer into water and steam, and (iv) advection through the stripping column. Results reveal how aroma physiochemistry determines the limiting kinetics at industrial extraction conditions. The interaction with the soluble matrix can also inhibit extraction, but this effect varies for the different aromas studied.

The human relationship with food is an under-acknowledged contributor towards climate change and environmental degradation. However, citizens’ choices and actions regarding food consumption and production in urban settings are shaped by the economic, cultural and infrastructure systems in which they live. The purpose of this paper is to examine, from the perspective of prosumers, the socio-technical factors that affect urban food production and associated energy, water and waste services. A residential development on the urban fringe of Australia’s subtropical Gold Coast was used as a case study. A mixed methods approach was utilised to gather quantitative and qualitative data through estate maps, development planning documents, visual observations, interviews and surveys. Data was analysed around the themes of food production, consumption and development infrastructure (physical and social). The estate’s food production demonstrated high biodiversity and highlighted three common challenges: biological, knowledge and water/climate. Food consumption incorporated self-consumption, sharing/trading and a range of other typical and atypical sources found in cities. An integrated approach to land-use, energy, water and waste was instrumental in enabling food production, highlighting issues that affect the ability of urban prosumers to incorporate sustainability into their food practices. The paper raises the possibility of a ‘sharing-economy’ food production typology for urban areas and proposes an initial performance indicator framework (people, planet, prosperity, governance and propagation) to understand, develop and manage urban prosumers in the context of integrated energy, water, waste and food services.

This article summarizes the design, the manufacturing and the testing of a small scale Organic Rankine Cycle using Concentrated Solar Power as the heat source. First, the choice of the nominal point of the cycle is detailed, including the operating environment of the ORC (characteristics of the solar field and ambient temperature) and the constraints of operation. The paper presents the design of a radial turbine with a power of 3 kW and the numerical simulations of flow in the fluidic part of the turbine (nozzle, wheel etc). It also deals with system engineering, the calculation and the selection methodology of main components such as exchangers, pumps, and sensors.

In the second part, the results of the laboratory tests is presented. The experiment was performed using as hot source, a thermal oil boiler. The analysis of the results shows isentropic efficiency around 40% on a rather large range of pressure drop, and a cycle efficiency of 5 % which, is encouraging in view of the first test conditions.

Food and drink processing industries are extremely large consumers of thermal energy as well as bio-wastes producers. The utilisation of bio-wastes for energy recovery appears to be a good opportunity to improve the overall efficiency of process industries. In this study, waste generation, management and energy auditing of a micro-brewery located in the north east of England is investigated. Fermented grains and hops are disposed as organic wastes after the production process. Hence, this study focuses on recovery of energy from these wastes through anaerobic digestion process. Experimental work was carried out in the laboratory for the wastes characterisation. The waste samples are then anaerobically digested at 55 ⁰C and 35 ⁰C with a 5L laboratory scale continuous stirred reactor using 5 gVSL^-1 and 25 days organic loading rates and hydraulic retention times respectively. Further to the experimental work, simulations were completed to evaluate the feasibility of the process. ASPEN plus simulation software was used to carry out the simulations using a novel approach for AD which is based on the ADM1 model. The experimental results showed that biogas can be produced at mesophilic and thermophilic conditions: 3.0 and 2.6 litres per day respectively. At thermophilic conditions, the methane content is 65 % while at mesophilic conditions, it is 55%. It is also found that the values of the final biogas production from the simulation were similar to the ones obtained in the experiments (-6.85%). However, the model would need further modifications to be able to accurately predict the biogas compositions. The result shows that the thermophilic process is able to fuel 126.01 kW boiler while mesophilic process can power 76.48kW boiler.

Warm air infiltration during door openings of refrigerated delivery trucks can account for approximately 34% of the overall refrigeration load, with this share estimated to be higher for longer and/or more frequent door openings. An increase in refrigeration load can have a direct impact on the energy usage (higher thermal loads require greater energy consumption). Many sources in the literature suggest that the use of an air curtain to reduce the impact of warm air infiltration during door openings. However, the majority of these studies focus on air curtain use in large cold rooms and warehouses. The main purpose of this study is to investigate the protective mechanisms of an air curtain against natural infiltration in a refrigerated vehicle during door openings. This study analyses the airflow behaviour in the refrigerated truck body with and without the protection of an air curtain during door openings. Different air curtain velocities have been tested for this particular investigation to study the influence of discharge velocity on energy performance. The airflow analysis suggests that natural infiltration is mainly caused by cold air flowing out from the lower part of the opening as warm air infiltrates in from the upperpart to fill the space. It has been found that an air curtain at optimum velocity (3.1 m/s in this study) can help reduce the energy consumption by almost 48%.

Low temperature gasification of poultry litter (PL) was experimentally studied in a lab scale fluidized bed reactor. The experiments were carried out at three different equivalence ratios (ER) of 0.17; 0.21; 0.25 and temperature 700 °C, to investigate its impact on cold gas efficiency (CGE), carbon conversion efficiency (CCE), gas yield, lower calorific value (LCV), and tar evolution. Maximum CGE and LCV of the produced gas was 43.4% and 3.34 MJ/m³ respectively at an ER of 0.25. The maximum CCE of 72% was attained at the highest value of ER (0.25). The gas yield showed an increasing trend with ER reaching its highest value of ~1 m³/kg_daf N₂ free. Highest amount of total tar was 2.41 g/Nm³ in the dry gas at the lowest tested ER. Styrene- xylene, phenol, and naphthalene, were the components with the highest concentrations of up to 30%, whilst the tar compounds detected but couldn’t be identified ranged between 25-30% with respect to the total tar yield. The average compositions of the main components in permanent gases (vol %, dry basis) at the indicative value of the lowest ER were as follows: H₂:7.87%, CH₄:2.04%, CO: 6.37%, CO₂:11.47%, C₂H₄:1%, and C₂H₆:0.22.

Carbon dioxide (CO₂) is becoming an important commercial and industrial working fluid as a potential replacement of the non-environmental friendly refrigerants. For refrigeration and power systems, the minichannel heat exchangers are becoming attractive for transcritical CO₂ Rankine cycle and supercritical CO₂ Brayton cycle, due to their highly compact construction, high heat transfer coefficient, high pressure capability and lower fluid inventory. This paper employs three-dimensional numerical models to investigate the heat transfer and pressure drop characteristics of supercritical CO₂ in minichannels. The models consider real gas thermophysical properties and buoyancy effect and investigate the effect of cross-section geometry on the thermohydraulic characteristics. Six minichannel cross-section geometries with the same hydraulic diameter of 1.22 mm are considered. The geometries include circle, semicircle, square, equilateral triangle, rectangle (aspect ratio = 2) and ellipse (aspect ratio = 2). The inlet temperature, outlet pressure and wall heat flux are 35 °C/75 bar/100 kW/m² and 35 °C/150 bar/300 kW/m² for heating conditions and 120 °C/75 bar/-100 kW/m² and 120 °C/150 bar/-300 kW/m² for cooling conditions. Comparisons of local Nusselt number and friction factor with those employed empirical correlations are made and useful information and guidelines are provided for the design of compact heat exchangers for supercritical CO₂ power system applications.

This research aims to investigate development of corn-oil ester and water mixtures as novel solid-liquid phase change material candidates for chilled and frozen food refrigeration applications. Thermal properties of both water and its mixture with corn-oil ester were tested by DSC and T-history methods. The results showed that corn oil could mix well in water solutions. Phase transition temperatures of the mixtures were lower than those of individual water. Corn-oil ester in the mixtures was acted as a nucleate agent and it was able to lower freezing point and to trigger ice nucleation in water which could diminish super-cooling. Addition of corn oil ester by 5% to 35% in water solutions could decrease freezing temperature from 0°C down to respectively -3.5°C to -28°C. The PCM candidates were also found to have excellent thermal properties that could fulfill requirements of thermal energy storage systems for food refrigeration applications.

The printed circuit heat exchanger is currently the preferred type of recuperative heat exchanger for the supercritical CO₂ Brayton cycle due to its highly compact construction, high heat transfer coefficients and its ability to withstand high pressures and temperatures. This paper employs a three-dimensional numerical model to investigate the thermohydraulic performance of supercritical CO₂ flow in a printed circuit heat exchanger. This numerical model considers entrance effects, conjugate heat transfer, real gas thermophysical properties and buoyancy effects. The inlet temperature and pressure are 100 °C/150 bar on the cold side and 400 °C/75 bar on the hot side while the mass flux is varied from 254.6 to 1273.2 kg/(m²·s). The overall performance of the heat exchanger and comparisons of local heat transfer and friction pressure drop with predictions from the empirical correlations are presented and discussed. Overall, this paper provides useful information that can be employed in the design of recuperators for supercritical CO₂ Brayton cycle applications.

Current environmental policies, which promote a more sustainable food sector, have boosted efforts to reduce energy demand during processing, and particularly during drying operations. One of the routes towards more sustainable and efficient drying processes is the design and implementation of optimal operational routines for the existing drying equipment. In the food industry, drum-dryers are typically employed for the production of food powders from viscous slurries (e.g. starchy slurries). Food powders are used in a wide range of applications in the food industry, from beverage powders (milk or cocoa), instant soups, spices or flours and flavours. In this framework, we propose a model-based optimisation routine for the operation of a double drum-dryer (product under atmospheric conditions) used in the manufacture of a breakfast cereal porridge. The problem defines optimal steam temperature and optimal rotation speed that minimises the energy demand of the dryer operation for a range of operating conditions that considered different: product formulation, final moisture contents, thickness and initial temperature of the wet slurry. Overall, this work demonstrates the potential of model-based approaches to the design and optimisation of more sustainable and efficient industrial drying technologies in the food sector, which can help in the achievement of short/medium-term energy reduction goals.