Desalination Using Low-Grade Heat Sources

This study evaluated the feasibility of utilizing low-grade heat sources such as solar energy or waste heat from industrial processes for desalination. The premise of the approach is that saline waters can be desalinated by evaporation and condensation of fresh water at near-ambient temperatures at low pressures. Low pressures can be achieved naturally in the head space of water columns of height equal to the local barometric head. By connecting the head space of such a saline water column to that of a distilled water column, and by maintaining the temperature of the former about 15–20°C above that of the latter, fresh water can be evaporated from the saline column and condensed in the distilled water column. In this study, it is proposed to use a sensible heat thermal energy storage (TES) system to heat the head space of the saline water column. The TES can be maintained at the desired temperature using solar energy and/or waste heat from thermal power plants, refrigeration plants, or air conditioning units. This paper presents the feasibility of the proposed approach, where the TES is maintained at the design temperature by a solar-powered absorption refrigeration system (ARS) augmented by an electric heater. Results of this feasibility study show that the heat rejected by an ARS of cooling capacity of 3.25?kW (0.975 tons of refrigeration) along with an additional energy input of 208?kJ/kg of desalinated water is adequate to produce desalinated water at an average rate of 4.5?kg/h. The solar panel area required for this application was 25?m2. An integrated process model and performance curves of the proposed approach are presented.     

Improving Air-Cooled Condenser Performance in Combined Cycle Power Plants

It has been recognized in recent times that air-cooled condensers (ACCs) are environmentally preferable to the traditional water-cooled condensers for rejecting heat in combined-cycle power plants (CCPPs). However, a drawback of ACCs is that their performance can decline with increasing ambient air temperature. A new approach is proposed in this paper that has the potential to alleviate this drawback of ACCs. In this approach, a chilled-water thermal energy storage system (TES) is used to precool the inflow air to the ACC whenever the ambient air temperature increases above the design air inlet temperature. The temperature of the TES system is maintained by an absorption refrigeration system (ARS) driven by low-quality waste heat from the CCPP. A process model integrating the CCPP with the ARS and the TES has been developed to optimize the volume of the TES. A 500?MW CCPP with steam turbine net output of 170.9?MW was chosen to evaluate the application of this approach for a power plant to be located in southern New Mexico. This analysis showed that a tank volume of 4,500?m3 will be required to maintain the air temperature at the inlet to the ACC at the design value of 20°C throughout the year. Simulations under ambient air temperatures up to 40°C indicated that the proposed system is capable of maintaining the rated net power output of the plant with minimal fluctuations. Simulations also showed that TES tank volume is most sensitive to the design air inlet temperature to the ACC—an increase of this temperature by 1°C can result in at least 25% reduction in the volume.     

Thermal Analysis of Cover Systems in Municipal Solid Waste Landfills

Cover temperature variations were determined at four municipal solid waste landfills located in different climatic regions in North America: Michigan, New Mexico, Alaska, and British Columbia. Cover temperatures varied seasonally similarly to air temperatures and demonstrated amplitude decrement and phase lag with depth. Elevated temperatures in the underlying wastes resulted in warmer temperatures and low frost penetration in the covers compared to surrounding subgrade soils. The ranges of measured temperatures decreased and average temperatures generally increased (approximately 2°C/m) with depth. The ranges of measured temperatures (Tmax?Tmin) were 18–30°C and 13–21°C and the average temperatures were 13–18°C and 14–23°C at 1 and 2?m depths, respectively. For soil and geosynthetic barrier materials around 1?m depth, the maximum and minimum temperatures were 22–25°C and 3–4°C, respectively. Frost depths were determined to be approximately 50% of those for soils at ambient conditions. The main direction of heat flow in the covers was upward (negative gradients). The cover gradients varied between ?18 and 14°C/m, with averages of ?7?to?1°C/m. The gradients for soil and geosynthetic barrier materials around 1?m depth varied between ?11 and 9°C/m with an average of ?2°C/m. Cover thawing n-factors ranged between 1.0 and 1.4 and the cover freezing n-factor was 0.6. Design charts and guidelines are provided for cover thermal analyses for variable climatic conditions.     

Unglazed Fiberglass Reinforced Polyester Solar Water Heater with Integrated Storage System

Theoretical and experimental investigations on an unglazed solar hot water heater with integrated storage system were conducted. The system was comprised of a collector and storage tank which was integrated into one unit. All parts of the system have been fabricated from fiberglass reinforced polyester (GFRP). The absorber plate has water tubes of semielliptical shape. The width and length of the absorber plate were 1.4 and 1.8?m, respectively. The absorber plate was fabricated from GFPR using a special resin composition that provides good thermal conductivity and absorptivity. The storage tank has a capacity of 496?L. The storage tank is of sandwich construction with a core material made of polyurethane foam that combines stiffness and lightness of the structure with very good thermal insulation properties. An average tank temperature of 53°C was achieved at an average solar radiation level of 700?W/m2 and ambient temperature of 28°C. The thermal efficiencies of the system were evaluated at 48 and 57% for cloudy and clear days, respectively. Transient performance of the system was predicted by solving the mathematical models consisting of energy balance equations of the system that have been converted to finite difference form and solved by a personal computer. The experimental results were in close agreement as has been found with the theoretical predictions.     

Emission Control of NO and SO2 for the High-Temperature and Low O2 Concentration Combustion of Coke by Urea and NH4HCO3

Urea and NH4HCO3 were used to control the emission of NO and SO2 from the combustion of coke at high-temperature and low oxygen concentration. Urea and NH4HCO3 could control NO emission only under 1100°C. Their effects disappeared above 1100°C even though the increase of urea and NH4HCO3 content from 10?to?50?wt?%. However, they showed good desulfurization effect on the emission of SO2 at all combustion temperatures and their effects showed remarkable results even at 1500°C. Only 10?wt?% of urea or NH4HCO3 could control the emission of SO2 effectively at 1400 and 1500°C. This effect was caused by ?NH and ?NH2 from the thermal decomposition of reducing agents at high temperature. Low O2 concentration showed little effect on the removal of SO2. Ammonia slip from the thermal decomposition of reducing chemical was not a considerable level.     

Applications of Low-Temperature Regenerative Thermal Oxidizers to Treat Volatile Organic Compounds

A series of plant scale low temperature regenerative thermal oxidizers (LTRTOs) equipped with heating wires were constructed to treat volatile organic compounds (VOCs) laden gas streams. All regenerative beds were packed with gravel (approximate particle size 1.25 cm, specific area 205 m2/m3, and specific heat capacity 840 J/kg?°C) and equipped with K-type thermocouples for measuring gas temperatures. Test gas streams were extracted from manufacturing sections of varnishing, semiconductor packing, and petrochemical plants, representing a variety of gas-phase pollutants, including several commercial solvents. Experimental results indicate that 98% or greater treatment of VOCs with concentrations between 100 and 7,000 ppm as methane. Analysis of gas temperature variation with time at various bed depths confirm that VOC degradation occurs at temperatures ranging from 300 to 440°C, which are much lower than autoignition points of tested compounds. A 1.0 s gas residence time in the oxidation zone of regenerative beds is required for successful LTRTO operation.     

Double-Pass Solar Collectors with Porous Media Suitable for Higher-Temperature Solar-Assisted Drying Systems

A high-performance solar collector suitable for a solar-assisted drying system was designed, fabricated, and tested. Solar-assisted drying systems consist of the solar collector array, auxiliary heater, drying chamber, and the air distribution systems. The solar collector was a double-pass solar collector and has upper and lower channels. The lower channel of the solar collector was filled up with porous media, which also acts as a storage medium. The outlet temperature and the performance of the system increased with the presence of the porous media. The collector width and length are 120 and 240?cm, respectively. The upper channel depth is 3.5?cm and the lower channel depth is 10.5?cm. The solar collector array consists of six solar collectors, arranged as two banks of three collectors in series. The collectors were joined in series using internal manifolding. A temperature of 90°C can be reached at a solar radiation level of 800?W/m2, ambient temperature of 30°C, and mass flow rate of 0.06?kg/s. The solar-assisted drying system was used for drying of oil palm fronds from moisture content of about 63% to moisture content of about 15%, for a drying time of about 7?h. The overall system efficiency is about 25%.     

Sustainability and Economics of the Advanced High-Temperature Reactor

The advanced high-temperature reactor is a new reactor concept that combines four technologies in a new way: coated-particle nuclear fuels traditionally used for helium-cooled reactors, Brayton power cycles, passive safety systems and plant designs from liquid-cooled fast reactors, and low-pressure liquid-salt coolants. The new combination of technologies may enable the development of a large high-efficiency, lower-cost high-temperature (700?to?1,000°C) reactor for electricity and hydrogen production. As the peak reactor coolant temperatures approach 700°C, several technologies (Brayton cycles, passive reactor safety systems, available materials, etc.) work together to improve total system performance while significantly reducing costs relative to those for other reactors. A window of performance and lower capital costs exists between these temperatures and the practical temperature limits of materials. The higher temperatures and efficiency of the Brayton power cycle greatly reduce the total heat rejection compared with that achieved in current light-water reactors and may allow economic heat rejection with dry cooling towers, thus radically reducing the water consumption used in energy production. The option for dry cooling is facilitated by the characteristics of Brayton cycles, which reject heat over a temperature range of 40?to?50°C and thus match the requirements of dry cooling systems.     

Thermal homeostasis in pregnant rats during heat stress.

Sprague-Dawley rats exposed to inescapable heat stress maintained a controlled hyperthermia while increasing heat loss by cutaneous vasodilatation and by grooming behavior. In nonpregnant Ss, the evaporation of saliva groomed onto the body surfaces increased exponentially as a function of ambient temperature above 36°C. In contrast, Ss in an advanced stage of pregnancy became dependent on grooming behavior for thermoregulation of ambient temperatures of 30-36°C. This was associated with a decrease in the body temperature threshold for salivary secretion from the submaxillary gland, which then began at approximately the same body temperature as cutaneous vasodilatation. The pregnant Ss maintained a lower level of controlled hyperthermia during heat stress than did nonpregnant Ss. This appeared to result from a decreased production of metabolic heat, reduced insulation on the ventral surface, and an increased motivation to keep cool during heat stress. These changes met the increased need for thermolysis during pregnancy and provided for thermal homeostasis both in the pregnant rat and in the unborn fetuses. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Injection Nozzle for Ultraviolet Light-Enhanced H2O2 Oxidation of Air Pollutants in Flue Gas

Injecting aqueous solutions of hydrogen peroxide (H2O2) into hot flue gases can split the peroxide into OH and HO2 radicals. These reactive radicals readily oxidize air pollutants such as CO, VOCs, NO, mercury, and others. H2O2 is thermally “activated” (split into free radicals) rapidly at temperatures of 500°C and above. At lower temperatures, such as found in boiler exhaust flue gases, ultraviolet (UV) light can be used to activate the peroxide molecules. However, placing the UV lamps directly in the flue gases can lead to operating and maintenance problems, and “dilutes” the UV energy due to absorption by other gases. A “UV nozzle” has been developed that produces H2O2 radicals and delivers them into a flowing stream of boiler flue gases. Using a previously constructed pilot scale system at NASA's Kennedy Space Center, experiments were run to prove the concept of the nozzle, measuring the oxidation of NO as an indicator of radical formation and delivery. Data were taken at three temperatures, with none, one, or two UV lamps on, and with various injection rates of peroxide. Flue gas temperatures ranged from 85 to 304°C (186 to 580°F), and the molar ratios (inlet peroxide to inlet NOx) ranged from about 1.5 to over 15. Conversions of NO varied from 0% (at the lowest temperature tested) to above 50% (at highest temperature). Although increasing temperature had a marked effect on conversion, the activation of hydrogen peroxide by UV light was demonstrated in the temperature range of final flue gas exhaust gases (290–350°F). These results indicate that radicals can be created from hydrogen peroxide at reasonable temperatures using UV light, and that the radicals can be delivered into a flue gas stream where they can oxidize pollutants.     

Solar Thermal Power for Lunar Materials Processing

Lunar in situ resource utilization (ISRU) processes require thermal energy at various temperatures. Chemical recovery processes (pyrolysis, gas-solid reactions, gas-liquid or three-phase reactions and desorption) require thermal energy at temperatures from 1,000?K?to?2,500?K. Manufacturing processes (hot liquid processing, sinter forming, composite forming, welding, etc.) can be accomplished with thermal energy at temperatures 1,200?K–1,800?K. For these materials, process applications or solar thermal power can be effectively utilized. Physical Sciences Inc. has been developing an innovative solar power system in which solar radiation is collected by the concentrator, which transfers the concentrated solar radiation to the optical waveguide transmission line made of low loss optical fiber. In this paper, we will review our work on the development of the solar thermal power system and its application to a lunar ISRU process.     

Bioremediation Kinetics of Crude Oil at 5°C

This bench scale experiment investigated the mineralization of crude oil at cold temperatures. Biodegradation rates of Alberta Sweet Mix crude oil at 5°C and at ambient temperatures (21°C) were compared. The experimental design consisted of 14 soil columns. Off-gas samples for each column were analyzed every second day using a gas chromatograph to determine CO2 production rates. The run lasted for 219 days, at which time the soil columns were sacrificed for analysis. Oil mineralization values were modeled by a number of methods, including CO2 production determination from GC measurements and gravimetrically determined hydrocarbon loss using soxhlet extraction. The results of the experiment suggested that temperature only affected the biodegradation rates of crude oil in the initial phase of the biodegradation process. After approximately 3 months, the degradation rates of crude oil at 5°C and 21°C were similar at about 11 mg hydrocarbon∕kg dry soil∕day. The conclusion of this study was that significant mineralization of Alberta Sweet Mix crude oil can occur at cold temperatures.     

Study on Pb and PAHs Emission Levels of Heavy Metals- and PAHs-Contaminated Soil during Thermal Treatment Process

The objective of this study was to use thermal treatment to treat soil contaminated with heavy metals and polycyclic aromatic hydrocarbons (PAHs). The emissions of lead (Pb) and PAHs during the thermal treatment process were evaluated. The parameters included pretreatment, temperature, and speed of the rotary kiln. Cadmium (Cd) had a higher mobility in thermally treated contaminated soil slag than other heavy metals because the primary fraction of Cd was the exchangeable fraction (90%). Of the temperatures tested in this study, the highest emission concentration of Pb occurred at 700°C. The Pb emission concentrations in the gas phase and solid phase were 44?μg/N?m3 and 138.35?μg/N?m3, respectively. In PAHs emissions, naphthalene, acenaphthene (Acp), and fluorene were the main species in the gas phase, at different operating temperatures. The concentrations of these species ranged from 615.5 to 2,002.3?μg/N?m3. Acp and chrysene were the main species in the solid phase at different temperatures, and the concentrations of these species ranged from 25.5 to 113?μg/N?m3.     

Total Coliform Survival Characteristics in Frozen Soils

Survival characteristics of total coliform bacteria in soil samples, with different moisture contents (24–49%) and at different temperatures (from ?28 to 20°C), were studied. The study showed that a significant fraction of coliform bacteria survive for more than six months in soil at subfreezing temperatures. Survival of total coliform bacteria at subfreezing temperatures decreased with an increase in moisture content and an increase in temperature. For 24% moisture, approximately 66% of the coliforms survived at ?28°C after 170 days, whereas less than 0.1% survived at room temperature. First-order die-off rate constants varied between 0.041/day at room temperature and 0.002/day from ?15 to ?28°C (for 24% moisture). The impact of temperature on the die-off rate constant was described by the Arrhenius equation. The high survival at subfreezing temperatures indicates that fecal bacteria at honeybucket dumpsites may survive throughout the Alaskan winter which may lead to the contamination of water sources during spring thaw.     

Rheology of Al-Cu-Mg pre-alloyed powder in supersolidus liquid phase sintering process

Sintering process was performed on cylindrical consolidates in dry nitrogen atmosphere at various temperatures ranging from the solidus-to-liquidus temperatures for 30?min at a heating rate of 10°C?min^?1. Beam bending technique has been used to measure the macroscopic apparent viscosity of Al-Cu-Mg pre-alloyed powder (2024 Al alloy). Slumping test has been used to measure the yield strength at temperatures above solidus temperature. Wetting angle and capillary stress were calculated. Results showed that the rheological behaviour of this system follows as Bingham model. The yield stress varies from 0.37?kPa at 580°C to 0.3?kPa at 610°C on air atomised Al-Cu-Mg having 0.1% Sn. The correlation between variations of viscosity as function of temperature has been derived. The activation energy of viscous flow was estimated to 15.164?kJ?mol^?1. Capillary and yield stress decrease by increasing temperature. Maximum densification with minimum distortion is obtained at 600–610°C.     

Influence of Subsurface Drainage on Soil Temperature in a Cold Climate

Soil temperature during springtime is an important factor for crop establishment and growth in poorly drained soils of northwest Minnesota. In this region, shallow water tables causing spring planting delays and excess water conditions during the growing season, may have contributed to significant unplanted cropland and yield reductions in recent years. Temperature is a regulating factor for many biological and chemical processes in the soil. One of the most commonly cited benefits of subsurface drainage on poorly drained soils is faster soil warm-up in the spring. Previous studies of this phenomenon do not provide definitive conclusions concerning the influence of soil drainage on soil temperature. The results of three site years of field observations of soil temperatures from drainage research plots at two locations in northwest Minnesota are presented herein. Replicated soil temperature and water table depths were measured continuously at five depths for two drain spacings and an undrained treatment. Subsurface drainage was found to significantly increase soil temperatures in both a coarser textured Vallers loam soil and a finer textured Hegne silty clay loam soil. Up to 4°C temperature increases occurred primarily between May and July with the greatest increases at 30–60?cm depths. Treatments with narrow drainage spacing showed a greater spring temperature increase than treatments with wider drainage spacings.     

Influence of heat treatment conditions on the mechanical properties of Ti–6Al–4V alloy

In the current work, several heat treatments were carried out below and above the beta-transition temperature of the Ti–6Al–4V alloy followed by aging at 550 °C for 6 hours. The resultant microstructures and their effects on the mechanical properties of Ti–6Al–4V alloy were investigated. The results showed that solution treatment of Ti–6Al–4V samples followed by water quenching from β and α/β fields raised the alloy hardness from 380 to 575 and 656?HV, respectively, while no remarkable changes were observed after aging. The hot tensile strength of the as-forged sample increased from 671 to 756?MPa after water quenching from the ß- or α/ß- field, while the air cooling from β-phase field decreased the tensile strength to 644 MPa. The fracture mode of the tensile samples was more ductile in case of the solution-treated samples compared to the as-forged samples. A subsurface layer was formed due to the diffusion of oxygen into the surface at high temperatures. This layer which is known as ‘oxygen diffusion layer’ masked the differences of wear behaviour of the specimens.     

The ontogeny of feeding in rats: III. Thermal determinants of early ingestive responding.

High ambient temperatures (38°C) stimulated high spontaneous levels of activity and high frequencies of behaviors normally associated with ingestion (mouthing and probing), particularly in young, 3- and 6-day-old Charles River CD rat pups (Exp I). The level of spontaneous behavior was highly correlated with body temperature and also depended on deprivation condition. Temperature played an important role in determining responses to food stimuli as well. When Ss were fed by oral infusion (Exp II) or by placing milk on the floor beneath them (Exp III), warm ambient temperatures were required for active ingestion. In Exp IV, body temperature and ambient temperature were manipulated independently to assess their relative importance for Ss' feeding behavior. Ss with a low (29°C) or normal (34°C) core temperature at the start of testing were fed in either a 24°C or a 34°C ambience. Regardless of body temperature, Ss' levels of intake, activity, mouthing, and probing were higher in a warm than in a cool ambience. Therefore, the suppressed ingestive behavior of Ss fed at cool temperatures occurred not simply because Ss became hypothermic and inactive. Perceived warmth appears to be a significant contextual cue that regulates pups' responses to food stimuli. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of Freezing Temperature on Hydraulic Conductivity of Silty Clay

Hydraulic conductivity of thawed consolidated slurries of a silty clay from Lachute, Quebec, Canada, subjected to closed-system freezing at different temperatures ranging from ?2 to ?12°C were determined from constant-head permeability tests. The permeability index defined as the slope of the relation between log k and void ratio was found to increase with decreasing temperature. It was also established that the ultimate permeability index was related to the temperature at which no further change in unfrozen water content occurs. For the silty clay studied, the permeability index increased from 1.4 for the unfrozen soil prior to freezing to a maximum value of 8 at a temperature of ?12°C.     

Effect of Severe Environmental Exposures on CFRP Wrapped Concrete Columns

Deterioration of concrete structures caused by corrosion of reinforcing steel, aging, and weathering is a major problem in harsh environments such as coastal areas and cold regions. In addition, a hot environment, such as in the Arabian Gulf, is recognized as one of the most severe and aggressive environments that affects concrete durability. The purpose of this study is to investigate the effectiveness of strengthening plain concrete cylinders, subjected to extreme temperature variations, by wrapping with two layers of unidirectional carbon fiber-reinforced polymer (CFRP) sheets. Thirty-six plain concrete cylinders (150×300?mm) were tested. Nine specimens served as unstrengthened controls and the remaining cylinders were strengthened with two layers of CFRP sheets. Cylinders were subjected to high temperatures (45°C), to heating and cooling cycles (23 to 45°C), and to prolonged heat exposure (45°C). Some of the cylinders that were subjected to heating and cooling, were later subjected to freezing and thawing cycles, while others were submerged in fresh water or salt water. The specimens were loaded to failure under uniaxial compressive load and the axial and lateral deformations were monitored. High temperature exposure was not found to decrease the strength of the wrapped concrete cylinders.