An exergy approach to efficiency evaluation of desalination

Desalination is often considered an approach for mitigating water stress. Despite the abundance of saline water worldwide, additional energy consumption and increased costs present barriers to widespread deployment of desalination as a municipal water supply. Specific energy consumption (SEC) is a common measure of the energy use in desalination processes, and depends on many operational and water quality factors. We completed multiple linear regression and relative importance statistical analyses of factors affecting SEC using both small-scale meta-data and municipal-scale empirical data to predict the energy consumption of desalination. Statistically significant results show water quality and initial year of operations to be significant and important factors in estimating SEC, explaining over 80% of the variation in SEC. More recent initial year of operations, lower salinity raw water, and higher salinity product water accurately predict lower values of SEC. Economic analysis revealed a weak statistical relationship between SEC and cost of water production. Analysis of associated greenhouse gas (GHG) emissions revealed important considerations of both electricity source and SEC in estimating the GHG-related sustainability of desalination. Results of our statistical analyses can aid decision-makers by predicting the SEC of desalination to a reasonable degree of accuracy with limited data.

Specific energy consumption of cake dewatering with vacuum filters

Numerical modeling of the vacuum membrane distillation process

Analysis of specific energy consumption in reverse osmosis desalination processes

A novel conceptual design of hydrate based desalination (HyDesal) process by utilizing LNG cold energy

Membrane distillation (MD) is an attractive separation process for wastewater treatment and desalination. There are continuing challenges in implementing MD technologies at a large industrial scale. This work attempts to investigate the desalination performance of a pilot-scale direct contact membrane distillation (DCMD) system using synthetic thermal brine mimicking industrial wastewater in the Gulf Cooperation Council (GCC). A commercial polyethylene membrane was used in all tests in the DCMD pilot unit. Long-term performance exhibited up to 95.6% salt rejection rates using highly saline feed (75,500 ppm) and 98% using moderate saline feed (25,200 ppm). The results include the characterization of the membrane surface evolution during the tests, the fouling determination, and the assessment of the energy consumption. The fouling effect of the polyethylene membrane was studied using Humic acid (HA) as the feed for the whole DCMD pilot unit. An optimum specific thermal energy consumption (STEC) reduction of 10% was achieved with a high flux recovery ratio of 95% after 100 h of DCMD pilot operation. At fixed operating conditions for feed inlet temperature of 70 °C, a distillate inlet temperature of 20 °C, with flowrates of 70 l/h for both streams, the correlations were as high as 0.919 between the pure water flux and water contact angle, and 0.963 between the pure water flux and salt rejection, respectively. The current pilot unit study provides better insight into existing thermal desalination plants with an emphasis on specific energy consumption (SEC). The results of this study may pave the way for the commercialization of such filtration technology at a larger scale in global communities.

Biomass-based energy (solid fuel or biogas) and green electricity take a growing share in today’s low-carbon/carbon-free energy sources. Contrary to industries with high-temperature energy consumption (e.g. steel or cement industries), the sugar industry uses relatively low-temperature energy (except for milk of lime production). To reach low-carbon/carbon-free reduction, the sugar industry will have to re-design its complete energetic scheme. The panorama of solutions answering the aforementioned questions are reviewed. Among these solutions, the optimization of the process by using existing well-known technologies is the 1st option: mechanical vapour re-compressors (MVR), heat pump, cogeneration technologies, by-product anaerobic digestion, etc. Combining these solutions will support the sugar industry to decrease significantly its specific energy consumption. As a reference, today’s sugar factories have a specific consumption between 900 to 1200 kWh of primary energy per tonne of sugar. A target for the future is to decrease the specific primary energy consumption to 620 kWh per tonne of sugar (without pulp drying). This new benchmark could be even improved in the case of using low-carbon electricity imported from the grid. How far could one go into the decarbonization of beets sugar factories? Is the objective of having net-zero emissions for sugar production realistic?

Different relative aerobic energy contribution (WAER%) has been reported for the 2 women's Olympic kayaking disciplines (ie, 200 and 500m). To investigate whether the adopted method of energy calculation influences the value of WAER% during kayaking time trials. Eleven adolescent female kayakers (age 14 ± 1 y, height 172 ± 4cm, body mass 65.4 ± 4.2kg, VO2peak 42.6 ± 4.9 mL·min-1·kg-1, training experience 1.5 ± 0.3y) volunteered to participate in 1 incremental exercise test and 2 time trials (40 and 120s) on the kayak ergometer. A portable spirometric system was used to measure gas metabolism. Capillary blood was taken from the ear lobe during and after the tests and analyzed for lactate afterward. The method of modified maximal accumulated oxygen deficit (m-MAOD) and the method based on the fast component of oxygen-uptake off-kinetics (PCr-La-O2) were used to calculate the energy contributions. The anaerobic energy portions from m-MAOD were lower than those from PCr-La-O2 in the 40-s (41.9 ± 8.8 vs 52.8 ± 4.0kJ, P > .05) and 120-s (64.1 ± 27.9 vs 68.2 ± 10.0kJ, P > .05) time trials, which induced differences of WAER% between m-MAOD and PCr-La-O2 (36.0% vs 30.0% in 40s, P > .05; 60.9% vs 57.5% in 120s, P > .05). The reported different WAER% in women's Olympic kayaking could be partly attributed to the adopted method of energy calculation (ie, m-MAOD vs PCr-La-O2). A fixed method of energy calculation is recommended during the longitudinal assessment on the relative energy contribution in women's Olympic kayaking.

The aim of the work was to determine the influence of screw speed and variable amounts of fresh vegetable additives on selected aspects of extrusion-cooking of corn-vegetable blends. Corn grit as a basic component was supplemented with a fresh pulp of beetroot, carrot, leek and onion in amounts of 2.5-10% in the recipe. The extrusion-cooking was carried out using a single-screw extruder in the temperature range 120-145°C and extrudates were formed into directly expanded snacks. Two indicators were measured: the production efficiency (Q) and the specific mechanical energy (SME) consumption. As a result of the findings it was noted that the rotational speed of the extruder’s screw showed a greater impact on both production efficiency and SME as compared to the variable amounts of applied additives. A tendency to increased efficiency and specific mechanical energy consumption was observed along with the increase of screw speed during processing. The highest production efficiency was observed if fresh leek and onion were used as additives and the highest extrusion speed screw was applied. The largest specific energy consumption was noted during the extrusion-cooking of blends containing fresh carrot and onion addition at high screw speed.

Energy intensity development of the German iron and steel industry between 1991 and 2007

Reverse osmosis (RO) desalination is considered a viable alternative to reduce water scarcity; however, its energy consumption is high. Photovoltaic (PV) energy in desalination processes has gained popularity in recent years. The temperature is identified as a variable that directly affects the behavior of different parameters of the RO process and energy production in PV panels. The objective of this study was to evaluate the effect of temperature on energy consumption and polarization factor in desalination processes at 20, 23, 26 and 30 °C. Tests were conducted on a RO desalination plant driven by a fixed 24-module PV system that received spray cooling in the winter, spring and summer seasons. The specific energy consumption was lower with increasing process feed temperature, being 4.4, 4.3, 3.9 and 3.5 kWh m−3 for temperatures of 20, 23, 26 and 30 °C, respectively. The water temperature affected the polarization factor, being lower as the temperature increased. The values obtained were within the limits established as optimal to prevent the formation of scaling on the membrane surface. The spray cooling system was able to decrease the temperature of the solar cells by about 6.2, 13.3 and 11.5 °C for the winter, spring and summer seasons, respectively. The increase in energy production efficiency was 7.96–14.25%, demonstrating that solar cell temperature control is a viable alternative to improve power generation in solar panel systems.

The performance of a fluidized bed dryer integrated biomass furnace with air preheater (FBD with APH) and a fluidized bed dryer integrated biomass furnace without air preheater (FBD without APH) for drying of paddy have been evaluated. The FBD with APH and FBD without APH decreased the moisture of paddy from 24% (wet basis) to 14% (wet basis) within 43 and 47 minutes with average temperatures and relative humidities of 59.58 <sup>o</sup>C and 59.14<sup>o</sup>C, and 18.81% and 18.68%, respectively. The drying rate of paddy varied in the range of 0.11 kg/min-0.32 kg/min and 0.10 kg/min- 0.30 kg/min for FBD with APH and FBD without APH, with average values of 0.18kg/min and 0.17kg/min, respectively. The minimum, maximum, and average value specific moisture evaporation rate (SMER) was 0.20 kg/kWh, 0.57 kg/kWh, and 0.31 kg/kWh, respectively for FBD with APH, as well as 0.149 kg/kWh, 0.448 kg/kWh, and 0.252 kg/kWh, respectively, for FBD without APH. The specific energy consumption (SEC), the specific electrical energy consumption (SEEC), and the specific thermal energy consumption (STEC) were varied from 1.749 kWh/kg to 5.076 kWh/kg, 0.090 kWh/kg to 2.872 kWh/kg, and 0.760 kWh/kg to 2.204 kWh/kg, with average values of 3.528 kWh/kg, 1.96 kWh/kg, and 1.532 kWh/kg, respectively for FBD with APH, as well as from 2.234 kWh/kg to 6.702 kWh/kg, 1.056 kWh/kg to 3.167 kWh/kg, and 1.179 kWh/kg to 3.536 kWh/kg, with average values of 4.391 kWh/kg, 2.075 kWh/kg, and 2.316 kWh/kg, respectively, for FBD without APH. The thermal efficiencies of the FBD with APH and FBD without APH were varied between 12.4% and 37.93%, and 9.78% and 29.82%, resvectively, with average values of 20.78% and 16.61%. The thermal efficiency of FBD with APH was higher compared to FBD without APH.

In this study, an energy model based on the first law of thermodynamics is developed to evaluated energy efficiency and specific energy consumption. The influences of hot air temperature and initial weight of coffee beans on energy consumption are considered. Furthermore, a comparison between combined microwave–hot air spouted bed drying and hot air spouted bed drying methods on energy consumption is also investigated in detail. The results show that energy efficiency as well as energy consumption depends on hot air temperature, initial weight of coffee bean, and typical drying methods (combined microwave–hot air spouted bed and hot air spouted bed). The optimum drying condition is also achieved in this study.

Primary energy and exergy of desalination technologies in a power-water cogeneration scheme

A comprehensive review of energy consumption of seawater reverse osmosis desalination plants