Experimental study of natural brine solar ponds in Tibet

A salinity gradient solar pond (SGSP) is a simple and effective way of capturing and storing solar energy. The Qinghai-Tibet Plateau has very good solar energy resources and very rich salt lake brine resources. It lacks energy for its mineral processes and is therefore an ideal location for the development and operation of solar ponds. In China, solar ponds have been widely applied for aquaculture, in the production of Glauber’s salt and in the production of lithium carbonate from salt lake. As part of an experimental study, a SGSP using the natural brine of Zabuye salt lake in the Tibet plateau has been constructed. The pond has an area of 2500 m² and is 1.9 m deep. The solar pond started operation in spring when the ambient temperature was very low and has operated steadily for 105 days, with the LCZ temperature varying between 20 and 40 °C. During the experimental study, the lower convective zone (LCZ) of the pond reached a maximum temperature of 39.1 °C. The results show that solar ponds can be operated successfully at the Qinghai-Tibet plateau and can be applied to the production of minerals.     

Monitoring and maintaining the water clarity of salinity gradient solar ponds

A common problem encountered in salinity-gradient solar ponds is the growth of various types of algae and bacterial populations, which affects the brine clarity and hence reduces thermal performance. Algae and bacterial populations are enhanced by the presence of organic nutrient such as nitrogen and phosphorus. A comprehensive study was undertaken on three salinity-gradient solar ponds in Australia: a 3000 m² sodium chloride solar pond at Pyramid Hill in Northern Victoria; a 50 m² sodium chloride; and 15 m² magnesium chloride solar pond at RMIT University in Bundoora, Victoria. The experimental study involved monitoring the clarity of these three ponds and testing chemical and biological treatment methods to see their effect on the brine transparency. The sources of turbidity and their impacts on clarity and efficiency of salinity-gradient solar ponds are presented in detail in this paper. The initial observation showed that the amount of sunlight is reduced due to the heavy algal growth creating instability in the solar pond as it absorbs light. Two treatment methods were applied to these solar ponds and experiments were conducted to study the turbidity reduction in the solar ponds. In the RMIT magnesium chloride solar pond, diluted hydrochloric acid was injected in the pond to reduce the pH and turbidity levels. Algal blooms were observed and found in the pond where the pH was between 5.5 and 8. It was observed from the experimental study that pH values should be kept below 4.5 to maintain low turbidity and prevent algae growth. The introduction of brine shrimps was also found to be very effective and economical to control algae, provided the oxygen has not depleted due to advanced heavy algal growth. The investigation concluded that hydrochloric acid could be used initially as a shock treatment to kill all the algae and then brine shrimps could be introduced to control the growth of algal and maintain transparency. This analysis showed that by using a combination of chemical and biological treatment methods, the pond clarity can be maintained and the thermal efficiency of the solar pond can be improved.     

Helio-hydro and helio-thermal production of hydrogen

Fossil fuels account for about 80% of the world annual energy demands. Renewables contribute 14% and nuclear some 6%. These numbers will soon change as the world's population grows, energy demand rises, cheap oil and gas deplete, global warming effects continue rising and city pollution worsens the living conditions. The development of energy sources and devices will emerge more aggressively to address the world's energy and environmental situation. A concept of using hydrogen as an energy carrier or storage as a fuel, a replacement of burning fluid fossil fuels is presented. Sources of energy from which hydrogen can be produced in a massive quantity and at a low cost are briefly surveyed. A short account of devices to be employed for hydrogen production is given. Primarily the sun, sea, runoff waters, winds and fissionable materials are to be utilized. The discussion on the inexhaustibility of naturally occurring sources utilized and/or harnessed in this process will lead to the low cost for hydrogen production. Some hydrogen rich products including hydrogen sulfide and methane accompany the oil, gas and brine, when they are pumped out of the ground. While methane is used sometimes as fuel; the hydrogen sulfide is disposed off invariably. In principle, hydrogen can be extracted from these waste products. We discuss here to produce hydrogen in economically feasible manner. The use of brine as a means of usable solar energy in the form of heat and electricity was discussed earlier. Here, we aim at discussing the production of hydrogen from the brine and hydrogen sulfide gas. The brine is proposed to be utilized for two purposes: one for salt gradient solar pond to produce usable heat and electricity, and the other as an electrolyte to produce hydrogen out of itself. The hydrogen from hydrogen sulfide can chemically be extracted.     

Aluminum silicate scale formation and inhibition: Scale characterization and laboratory experiments

Amorphous silica scale enriched in aluminum is deposited from a variety of geothermal brines. Scale deposits examined in the present study are formed by tetrahedrally-coordinated aluminum substitution within an amorphous silica framework. There is no evidence that aluminum in these scales derives from distinct aluminum minerals, such as gibbsite, or from aluminum silicate minerals transported in brine from the reservoir. The formation of aluminum-rich amorphous silica scale is dependent on brine pH, temperature and aluminum concentration. Silica and aluminum exhibit concentration minima in brines at near-neutral pH. Aluminum-rich silica scales dissolve more slowly than pure amorphous silica in water and brine. Lowering brine pH below 5 or increasing it above 9 retards the kinetics of silica polymerization and the formation of aluminum-rich silica. Laboratory studies demonstrate that sequestering agents such as citric acid, acetic acid, and ethylenediaminetetraacetic acid (EDTA) may inhibit aluminum silicate scale formation.     

Solar ponds in alkaline lake and oil well regions

Solar ponds are probably the simplest technology available for the useful conversion of solar energy. The basic technology is proven. Solar ponds have been shown to be technically feasible and economically viable for many applications, particularly for thermal use. The electrical conversion and use of solar energy via solar ponds is still questionable, in general, for economic viability. By putting the untapped sources together in the South Plains region, it looks promising economically both for thermal and electrical conversions and applications. There are a number of alkaline lake basins randomly scattered in the South Plains region of the U.S.A. In that area, there are thousands of crude oil producing wells that produce brine in abundance. The selection of suitable alkaline lake basins as a solar pond site and as depository sites of brine from oil wells and the using of this brine and salty water from alkaline lakes makes the solar pond economically viable for both thermal and electrical demands in the area.     

Maintenance strategy for a salt gradient solar pond coupled with an evaporation pond

In a previous study, the authors presented a simple mathematical model for predicting the ratio of the evaporation pond area to that of a salt gradient solar pond area. The evaporation pond idea provides a very attractive method of salt recycling by evaporation, especially in areas of high evaporation and low rates of rain as it is the case for North Africa.In this paper, the model was elaborated upon and applied to two types of surface water flushing (fresh water and seawater) under the prevailing conditions of Tripoli, Libya (latitude=32.86°N). All the results presented were predicted for the first three years of operation. The daily variations of brine concentration in the of Tajoura's Experimental Solar pond and those based on different designs were predicted and discussed under different scenarios. The quantities of brine provided by the evaporation pond and that required by were predicted for both cases of surface water flushing (fresh water and seawater) under the different design conditions. It was predicted that the can provide 20–40% during the first year and 45–95% during the third year depending on the design selected.     

氯化镁溶液太阳池的动态研究

对广西大学圆形斜壁氯化镁溶液太阳池的动态运行过程进行了长期的观察和测试，并对不同系统的提热量和换热速率进行了分析和计算。     

Effects of porous media on thermal and salt diffusion of solar pond

Laboratory and field experiments were carried out along with numerical simulations in this paper to study the effects of porous media on thermal and salt diffusion of the solar ponds. From our laboratory experiments simulating heat transfer inside a solar pond, it is shown that the addition of porous media to the bottom of a solar pond could help enhance its heat insulation effect. The experiment on salt diffusion indicates that the upward diffusion of the salt is slowed down when the porous media are added, which helps maintain the salt gradient. Our field experiments on two small-scaled solar ponds indicate that when porous media are added, the temperature in the lower convective zone (LCZ) of the solar pond is increased. It is also found that the increase in turbidity is repressed by porous media during the replenishment of the salt to the LCZ. Thermal diffusivities and conductivities of brine layers with porous media such as pebble and slag were also respectively measured in this paper based on the unsteady heat conducting principles of a semi-infinite body. These measured thermal properties were then used in our numerical simulations on the effect of porous media on thermal performance of a solar pond. Our simulation results show that brine layer with porous media plays more positive role in heat insulation effect when thermal conductivity of the ground is big. On the other hand, when the ground has a very small thermal conductivity, the performance of solar pond might be deteriorated and total heat storage quantity of solar pond might be reduced by brine layer with porous media.     

Heat extraction methods from salinity-gradient solar ponds and introduction of a novel system of heat extraction for improved efficiency

Heat has generally been successfully extracted from the lower convective zone (LCZ) of solar ponds by two main methods. In the first, hot brine from the LCZ is circulated through an external heat exchanger, as tested and demonstrated in El Paso and elsewhere. In the second method, a heat transfer fluid circulates in a closed cycle through an in-pond heat exchanger, as used in the Pyramid Hill solar pond, in Victoria, Australia. Based on the experiences at the El Paso and Pyramid Hill solar ponds, the technical specifications, material selection, stability control, clarity maintenance, salt management and operating strategies are presented. A novel method of extracting heat from a solar pond is to draw the heat from the gradient layer. This method is analysed theoretically and results of an experimental investigation at Bundoora East, RMIT, are presented. An in-pond heat exchanger made of polyethylene pipe has been used to extract heat for over 2 months. Results indicate that heat extraction from the gradient layer increases the overall energy efficiency of the solar pond by up to 55%, compared with conventional method of heat extraction solely from the LCZ. The experimental results are compared with the theoretical analysis. A close agreement has been found. From this small-scale experimental study, convection currents were found to be localised only and the density profiles were unaffected. An experimental study using an external heat exchanger for brine extraction and re-injection at different levels within the gradient layer still needs to be conducted to determine the effect of the heat extraction from the non-convective zone (NCZ) on the stability of the salinity gradient (both vertically and horizontally) and an economic analysis needs to be conducted to determine the economic gains from increased thermal efficiency.     

Chemistry of silica in Cerro Prieto brines

We have studied the precipitation of amorphous silica from synthetic geothermal brines that resemble the flashed brine at Cerro Prieto. We found that part of the dissolved silica quickly polymerizes to form suspended colloidal silica. The colloidal silica flocculates and settles slowly at unmodified brine pH values near 7.35. Raising the pH of the brine to about 7.8 by adding base and stirring for a few minutes causes rapid and complete flocculation and settling. These results have been confirmed in the field using actual Cerro Prieto brine. Several commercially available flocculating agents were also tested. Both in the laboratory and in the field, we found quaternary amines to be effective with some brine compositions but not with others.These results suggest the following simple preinjection brine treatment process: age the brine for 10 – 20 min in a covered holding tank, add 30 to 40 ppm lime (Ca(OH)₂), stir for 5 min, and separate the flocculated silica from the brine using a conventional clarifier. The brine coming out of such a process will be almost completely free of suspended solids.The pilot plant tests needed to reduce this conceptual process to practice are discussed.In a separate study, we researched the rate of deposition of silica scale from synthetic brines. We found that a modest decrease in pH could significantly reduce the scaling rate at a reasonable cost.     

A one-dimensional numerical study of the salt diffusion in a salinity-gradient solar pond

A one-dimensional transient mathematical model is used for the study of the salt diffusion and stability of the density gradient in a solar pond. A finite difference method with a diffusion coefficient dependent on both temperature and salt concentration is used to solve the salt diffusion equation. On the basis of simple considerations we analyze the influence of the salinity-gradient thickness on the useful energy which can be withdrawn from the bottom layer of the solar pond. Finally some considerations on the effect of the velocity of injected brine in rising solar ponds are presented, making use of the Rayleigh analysis of the small perturbations in order to study the stability of the system.     

Performance improvement of a single-flash geothermal power plant in Dieng,Indonesia, upon conversion to a double-flash system using thermodynamic analysis

We investigated proposed design of a double-flash system and compared it to the existing single-flash power plant in Dieng, Indonesia, which uses waste brine from a high pressure separator. The performance of the double-flash system was evaluated using the second law of thermodynamics, and this was based on energy and exergy analyses. The Engineering Equation Solver (EES) was used to solve the relevant mathematical equations.Our results indicate that the double-flash design is interesting for application in Dieng since the power output would increase by 19.97%. Moreover, the precipitation system to avoid silica deposition in the injection well does not have to change much. Therefore, the building costs associated with the new double-flash system would be minimal. The available exergy from the reservoir is 66,204 kW based on the enthalpy determined by TFT (Tracer Flow Test) measurements. The single-flash power plant has a net power output of 23,400 kW with a second law efficiency of 36.7%. In the double-flash design, components such as a LPS, a second purifier and an HPT would be added to the plant. Furthermore, our calculations indicate that the power plant's output and second law efficiency would increase to 29,155 kW and 44.04%, respectively. The waste brine disposed of using this precipitation system would decrease by 8.22% at 5443 kW.     

利用太阳能制取海盐传热过程的试验分析

测试了盐田卤水、土壤和环境芭及同期太阳辐照度等数据，计算了卤未与土壤间的导热，卤水以空的辐射换热和卤水对环境的对流换热，并分析了它们对卤水蒸发速率的影响。结果表明，卤水与土壤间采取良好的隔热措施，抑制卤水对土壤的传热，可将卤 水的蒸发速率近１０％。同时进行了试验验证。     

Use of fine-grained shredder dust as a cement admixture after a melting, rapid-cooling and pulverizing process

Shredder dust is a residue, which is removed from valuable ferrous metals found in scrap automobile and electronic waste. It is also an industrial waste byproduct which, under legislation in place since April 1996, must be disposed of in landfill sites. One method of disposing shredder dust is by scorification, however, this is a costly process and therefore impractical. Costs could be reduced if the shredder dust had a valuable use, and, in this paper, the authors examine its effectiveness as a cement admixture.

First, molten shredder dust was crushed for use as a cement admixture. However, it was difficult to crush it completely because metallic grains were mixed in with molten shredder dust. These particles were removed by sifting and the molten shredder dust was crushed once again. Eventually, a fine 75 μm and less powder type of slag was obtained. This slag was mixed with Ordinary Portland Cement (OPC) to form a cement mortar and subsequently a mortar test was conducted. From the test results, it was found that the long-term strength of the cement did not deteriorate even when it included 30% by weight of the pulverized molten shredder dust.     

Turbidity study of solar ponds utilizing seawater as salt source

A series of experiments were conducted to study the turbidity reduction in solar ponds utilizing seawater as salt source. The experiment on the turbidity reduction efficiency with chemicals indicates that alum (KAl(SO₄)₂·12H₂O) has a better turbidity control property because of its strongly flocculating and also well depressing the growing of algae and bacteria in the seawater. In comparison with bittern and seawater, our experiment shows that the residual brine after desalination can keep limpidity for a long time even without any chemical in it. Experiments were also conducted on the diffusion of turbidity and salinity, which show that the turbidity did not diffuse upwards in the solution. In the experiment on subsidence of soil in the bittern and saline with the same salinity, it was found that soil subsided quite quickly in the pure saline water, but very slowly in the bittern. In this paper we also proposed an economical method to protect the solar pond from the damage of rain. Finally, thermal performance of a solar pond was simulated in the conditions of different turbidities using a thermal diffusion model.     

The use of reducing agents for control of ferric silicate scale deposition

A process has been developed to inhibit the deposition of ferric silicate scales from high-temperature, hypersaline geothermal brines, such as those encountered at the Salton Sea, California, geothermal field. Scale control is achieved by injecting sufficient reducing agent into the brine to effectively reduce trivalent iron to the divalent state. Scale deposition is decreased as a result of ferrous silicate being more soluble in these brines than ferric silicate. Furthermore, scaling can also be controlled by simultaneously blending into the brine a reducing agent and a small amount of acid sufficient to decrease the pH of the brine by up to 0.5 units. The use of reducing agents to control ferric silicate scale has also proven to mitigate corrosion of brine-handling equipment.     

Optimum thickness of the nonconvective zone in salt gradient solar ponds

The nonconvective gradient zone of a salt gradient solar pond tends to more effectively transmit incident solar energy to the storage brine below as its thickness is reduced. However, that same gradient zone tends to more effectively reduce heat loss from the warm brines as its thickness is increased. Therefore, there exists an optimum gradient zone thickness for which the net rate of energy collected and retained is a maximum. This report describes a technique for using a numerical simulation model to determine the optimum thickness of the gradient zone in ponds; provided other basic design, operating and climatic factors are specified. Significant improvements in pond efficiency may be obtained if the thickness of the gradient zone is adjusted monthly, seasonally or even if maintained at the annual average optimum thickness as compared with operating the pond with other than an optimum gradient zone thickness.     

Ferrous mineral enhanced anaerobic treatment of landfill leachate

Addition of inorganic materials is one of the effective methods to improve the methane production yield from wastewater and organic biomass. In the treatment of landfill leachate, the anaerobic digestion process is one of the essential steps. In the current study natural ferrous minerals of iron sulfide and iron oxides were added into the anaerobic digester, which was expected to improve the digestion efficiency of leachate and methane yields. Results confirmed that the addition of minerals was feasible for the anaerobic treatment of leachate. Chemical oxygen demand (COD) removal efficiency in the pyrrhotite dosed reactor achieved a maximum value of 85%; meanwhile, it was only about 60% in the control. A higher methane yield was also achieved in the mineral dosed reactors and CO₂ production was effectively reduced compared with the control. The promotion effect could be attributed to the adsorption and conductive characteristic of the minerals.     

Scale prevention method by brine acidification with biochemical reactors

Siliceous scale deposition often causes serious problems in geothermal power stations. In order to solve these problems, a number of scale prevention methods have been proposed to date, one of which is brine acidification. Although it is well known that silica deposition is prevented by keeping the pH of the geothermal brine acidic, the pH adjustment of the brine by mineral acid injection has not been commercially applied so far in geothermal power stations. A new method is proposed in which sulfuric acid can be biochemically manufactured from hydrogen sulfide in the gas exhausted from geothermal power stations. The applicability of this method has been experimentally confirmed in field tests with a biochemical reactor. It is believed that the method will provide an economical and environmentally-friendly acidification process to prevent siliceous scale deposition and will also contribute to the reduction of hazardous hydrogen sulfide emission from geothermal power stations.     

Development of a simple instrument for determination of salt concentration profile in the operation of solar ponds

The development and construction details of an instrument to measure densities of the brine at different depths in a solar pond are presented and discussed. Using a vertically moving sampling tube, brine is drawn from the pond and then is fed to the bottom of a conical container in which a sealed conical glass vessel is fully submerged. The bouyancy force exerted by the water on the sealed glass vessel is measured by a system of cantilever beam and strain gauges. The output of the strain gauge bridge is proportional to the density of the fluid passing through the conical container. It is shown that this instrument can be effectively used to determine the salt concentration profile in salt gradient solar ponds.