• Energy Research
• 6. Clean water close
• Tsinghua University close

A high performance CaO/bio-based sorbent that resists attrition was developed to reduce the calcium losses and pressure drop in a circulating fluidized bed (CFB) for flue gas desulfurization (FGD). The calcium conversion of the CaO/bio-based sorbent is higher than that of pure lime, since the biomass acts as a dispersion medium in the lime to prevent agglomeration of the lime particles and to reduce the lime particle size. The study on the attrition characteristics of the sorbent in a bubbling fluidized bed shows that the attrition fraction of the CaO/bio-based sorbent is reduced to 32% compared with 100% for the sorbent without biomass, since the biomass and lime produces hydrated calcium silicate which changes the pore structure of the sorbents. This pore structure also improves the reaction rate. Biomass ash melting rearranges the lime structure and enhances the cohesive forces between particles resulting in less particle attrition. The reduced attrition fraction of the sorbents is related to the high SiO2 and K2O fractions in the biomass. The CaO/bio-based sorbent is a promising sorbent with high calcium conversion and reaction rate, small attrition fraction and improved structural properties.

Abstract The effects of hot-water outlet temperature, compressor discharge pressure, compressor rotation speed, and expansion valve opening on the ejector and overall system performance were investigated for tap water outlet temperatures ranging from 50 to 90 °C. The coefficient of performance (COP) of the ejector–expansion heat pump system reaches 4.6 when the tap water outlet temperature is 70 °C, which is 10.3% higher than the corresponding basic cycle. Compared to the basic system, adding an ejector is more effective for the generation of high-temperature hot water. The COP of the ejector–expansion heat pump system increases; however, the COP improvement ratio ΔCOP decreases with the increase in the discharge pressure because of lower pressure lift ratio and ejector efficiency. The COP and ΔCOP increase when the compressor rotation speed decreases under our test conditions; simultaneously, the heat capacity decreases.

Abstract The induced two-phase natural circulation flow and the critical heat flux (CHF) on the outer surface of lower head are crucial factors for the assessment of the external reactor vessel cooling (ERVC) under in-vessel retention which is considered as an effective management strategy to mitigate the core degradation accident. In this work combined with the two-phase drift flux model, an analysis program for the induced two-phase circulation flow has been established based on one-dimensional steady-state mass, momentum and energy conservation equations. The calculation results are compared with the simulation results using RELAP5 within the same geometric parameters to verify the rationality and correctness of the analysis program. Combining the analysis program with the SULTAN CHF correlation, the characteristics of induced two-phase flow and the CHF on the outer surface of lower head are studied comprehensively to analyze the coolability limits of ERVC under in-vessel retention. The effects of concerned parameters including subcooling of water, decay power of molten corium, flooding levels, height of riser channel, loss coefficient at the inlet and gap clearance between the reactor pressure vessel and thermal insulation are studied.

Hydropower stations are an important source of clean energy, usually operating in sandy water flow, and the turbine wheels may suffer severe wear and tear. In addition, during the operation of the unit, it is necessary to operate at different water heads according to the actual situation, which will result in varying degrees of wear and tear. In this paper, the Lagrange method is used to study the wear characteristics of a Francis turbine under different water heads. The research object is the water turbine in Wanjiazhai Hydropower Station. Research has shown that wear on the walls of the turbine volute, guide vanes, and runner is inevitable, and the clearance walls are also vulnerable to wear. The difference in the water head mainly affects the movement trajectory and impact speed of particles. The higher the water head, the more severe the wear on the wall surface of the flow passage components. Both the crown and lower ring of the runner are worn. The impact of particles causes wear at this location, and the greater the relative velocity relative to the runner, the more severe the wall wear. This indicates that reasonable head operating conditions can effectively reduce wall wear, which provides guidance for the operation of hydraulic turbines.

Abstract Typical continental, cold climate conditions were applied to four large, laboratory columns to simulate temperatures ranging from −20 to +20 °C over summer, winter, and spring runoff. The goal of this research was to assess the seasonal effectiveness of bioretention application in cold climate regions that are currently experiencing the impacts of climate change. 1.6 years’ worth of equivalent Edmonton precipitation volume was applied over a 10-month period to evaluate the water quality improvement through two soil types (i.e., loam and sandy loam) with and without amendments intended to enhance nutrient removal. During summer, excellent removal of total suspended solids (TSS), phosphate, and ammonium (i.e., ≥90% average concentration reduction) was observed in both the loam and sandy loam columns without the nutrient removal amendments. The columns containing the amendments also reduced TSS, ammonium, and phosphate, but not as effective as the non-amended columns for TSS and ammonium. During winter and spring runoff, if infiltration occurs, physical removal of TSS, phosphate, and ammonium was still achieved, only days after the complete freezing (and subsequent thawing) of bioretention media at −20 °C. After an initial maturation and leaching period, nitrate was well removed (≥65.2% average concentration reduction) via denitrification in the columns with the nutrient removal amendments and submerged zone.

To mitigate the climate change-induced water shortage and realize the sustainable development of agriculture, drip irrigation, a more efficient water-saving irrigation method, has been intensively implemented in most arid agricultural regions in the world. However, compared to traditional border irrigation, how drip irrigation affects the biophysical conditions in the cropland and how crops physiologically respond to changes in biophysical conditions in terms of water, heat and carbon exchange remain largely unknown. In view of the above situation, to reveal the mechanism of drip irrigation in improving spring wheat water productivity, paired field experiments based on drip irrigation and border irrigation were conducted to extensively monitor water and heat fluxes at a typical spring wheat field (Triticum aestivum L.) in Northwest China during 2017–2020. The results showed that drip irrigation improved yield by 10.3 % and crop water productivity (i.e., yield-to-evapotranspiration-ratio) by 15.6 %, but reduced LAI by 16.9 % in contrast with border irrigation. Under drip irrigation, the lateral development of spring wheat roots was promoted by higher soil temperature combined with frequent dry-wet alternation in the shallow soil layer (0–20 cm), which was the basis for efficient absorption of water and fertilizer, as well as efficient formation of photosynthate. Meanwhile, drip irrigation increased net radiation and decreased latent heat flux by inhibiting leaf growth, thereby increased sensible heat, causing a higher soil temperature (+1.10 ℃) and canopy temperature (+1.11 ℃). Further analysis proved that soil temperature was the key factor affecting yield formation. Based on the above conditions, the decrease in leaf distribution coefficient (−0.030) led to the decrease in evapotranspiration (−5.7 %) and the increase in ear distribution coefficient (+0.029). Therefore, drip irrigation emphasized the role of soil moisture in the soil-plant-atmosphere continuum, enhanced crop activity by increasing field temperature, especially soil temperature, and finally improved yield and water productivity via carbon reallocation. The study revealed the mechanism of drip irrigation for improving spring wheat yield, and would contribute to improving Earth system models in representing agricultural cropland ecosystems with drip irrigation and predicting the subsequent biophysical and biogeochemical feedbacks to climate change.

The rapid development of coastal economies has aggravated the problem of pollution in the coastal water bodies of various countries. Numerous incidents of massive-scale marine life deaths have been reported because of the excessive discharge of industrial and agricultural wastewater. To investigate the diffusion of typical pollutants after discharge, in this study, a multi-process fusion simulation analysis model of pollutants under the action of ocean currents was established based on the concentration analysis method. Furthermore, key technologies involved, such as the parameter value, data selection, and visualization, were investigated. The iterative analysis and programming realization of three independent sub-processes, such as pollutant diffusion and transport, and the drift path and concentration distribution of pollutants after their discharge into the sea, were visualized. The case study revealed that the increase in the concentration of pollutants in the ocean was affected by the diffusion sub-process, and the transport sub-process plays a critical role in the long-distance transport of pollutants. The proposed method can provide technical support for marine environmental risk assessment and dynamic tracking of marine pollutants.

The water flow and movement of silt in a prototype double suction centrifugal pump was simulated using an Euler–Lagrange multiphase flow model. Back-blade and J-groove configurations were adopted to protect the impeller ring from silt abrasion. Four back-blades and four J-grooves were considered. The results show that the relative velocity of water around the impeller ring is too low to move silt out of the spacing between the impeller and the casing, which results in a high silt concentration around the impeller ring. The high silt concentration around the impeller ring is the major contributor to silt abrasion of the ring. Back-blade and J-groove configurations are effective in reducing the silt concentration around the ring but extra friction loss is also introduced and the pump efficiency is decreased. Optimization of the length, position and number of back-blades, and the shape and number of J-grooves, decreases losses in pump efficiency and effectively protects the impeller ring. Case 4 for the back-blade and Case 8 for the J-groove were the most effective configurations in this study.

Abha city is distinguished by urbanization, infrastructure, deepening watercourses, and changes in runoff flow which encourage flash floods in the urban zones of many villages in the region. AlMahalah village is prone to flash flooding due to its geographic location near the outlet of convergence streams of significant flow. The Geographic Information System (GIS), Remote Sensing (RS), Water Modeling System (WMS), and Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) were used to assess the effects of flash floods on AlMahala village. Precipitation data from 1978 to 2020 was statistically processed and analysed to provide more information about flash flood hazards. With a 3-h lag time in both watersheds, the higher peak discharge in Wadi Abha than in Wadi Al Akkas indicates that flooding was a primary concern in Wadi Abha. With an average yearly rainfall of 520 mm, the hydrograph simulation from 1 to 5 April 2020 would contribute to the junction (outlet) point of AlMahala village with a peak discharge rate of 474.14 m3/s. The vegetation cover increased by 243 km2 in 2020 compared to 2016. The HEC-RAS model was used to calculate the water depth, velocity, and elevation of the water surface with and without dam installation. The study provides the administration with practical and reasonable procedures for avoiding flash flood destruction in urban areas.