Trickle Bed

Heat transfer between solid particles and liquid droplets is a key phenomenon encountered in many industrial applications. We investigate the fluid dynamics and heat transfer between a liquid droplet and a static solid particle by means of direct numerical simulations. The presence of the solid particle is represented through a sharp interface immersed boundary method (IBM) on a Cartesian computational grid, whereas the motion of the gas-liquid interface is tracked by a mass conservative volume of fluid method (VOF). To account for the thermal coupling between the gas and the liquid, and more specifically the conjugate heat transfer between the fluid and the solid, a second order accurate diffused interface formulation is proposed for the conduction term in the energy equation. A detailed validation of the method is also presented. We have studied the effect of wettability and solid conductivity both of which have been found to have significant effect on the total heat transfer rate.

The hydrodynamic parameters were determined for two different three-phase systems (fluidized-bed and trickle-bed) through the experimental evaluation of the dynamic residence time distribution in the gas or liquid phase. For different fluid phase flow rates the fluidized-bed system was operated with a tracer in the gas phase and in the trickle-bed with a tracer in the liquid phase. The analysis of the processes was achieved through the application of different models representing the dynamic behavior of tracers present in the gas and liquid phases with a simulation of experimental operations of the three-phase reactors. The transfer functions developed for the two systems made it possible to estimate the hydrodynamic parameters providing the gas holdup (2.22 x 10-2 to 8.42 x 10-2) and the gas phase Peclet number (54.18 to 41.20) for the fluidized-bed and the liquid holdup (0.16 to 0.25), the liquid phase Peclet number (20.37 to 4.52) and wetting efficiency (0.34 to 0.56) for the trickle-bed.

Three very different techniques for measuring the catalyst wetted fraction-or wetting efficiency-in trickle bed reactors have been carried out and compared. The first one based on pressure drop data performed successively in single gas then liquid phase, then in gas-liquid phase is experimentally very simple but did not result in meaningful wetting efficiency estimation. The other ones, based on RTD analysis and on dye adsorption on wetted surfaces, gave similar results, and were used to investigate different parameters: liquid velocity and gas molecular weight and pressure by RTD, liquid-solid interaction or affinity (contact angle) and particle shape and diameter by dye fixation. The main operating parameter is the liquid velocity while the effect of gas flow is very weak. Higher solid-liquid affinity (heptane versus water) improves wetting efficiency only at very low liquid velocity (<2•10-3 m/s).

Heat transfer was investigated in an insulated packed bed column with co-current downflow of gas and liquid under constant and periodically modulated gas-liquid feed temperature. Bed temperatures at three axial positions were assessed at steady state for different insulating systems, different gas and liquid flow rates and system pressure. The experimental profiles recorded were modeled with a dynamic pseudo-homogeneous one parameter model to analyze the effect of operating conditions and to deduce coefficients of overall (U) and bed to wall (h W ) heat transfer. It appears that the heat transfer is strongly affected by the system pressure, whereas the liquid flow rate has a smaller influence. The experimental data of h W were correlated with the operating conditions leading to a small average error of 7% in the correlation. Condensation of water vapor occurring in the column seems to contribute to the heat transfer inside the packed bed. Several dynamic experiments modulating the feed temperature were also conducted and described with the help of the dynamic model. Predictions with the fitted values of U were in good agreement with experiments and give confidence to apply this model in the investigation of the catalytic wet air oxidation of phenol over carbon conducted in a trickle bed reactor under temperature feed modulation.

Three very different techniques for measuring the catalyst wetted fraction-or wetting efficiency-in trickle bed reactors have been carried out and compared. The first one based on pressure drop data performed successively in single gas then liquid phase, then in gas-liquid phase is experimentally very simple but did not result in meaningful wetting efficiency estimation. The other ones, based on RTD analysis and on dye adsorption on wetted surfaces, gave similar results, and were used to investigate different parameters: liquid velocity and gas molecular weight and pressure by RTD, liquid-solid interaction or affinity (contact angle) and particle shape and diameter by dye fixation. The main operating parameter is the liquid velocity while the effect of gas flow is very weak. Higher solid-liquid affinity (heptane versus water) improves wetting efficiency only at very low liquid velocity (<2•10-3 m/s).

Mill wastewater has always created considerable environmental problems for countries producing olive oil. These problems, which are of increasing relevance in relation to the growing interest in protecting water resources, are of technical and economic nature and are mainly due to the quality of the wastewater (which contains a large amount of organic substances and solute or suspended minerals, and is highly fermentable), the seasonal nature of the production process, and the great territorial dislocation of the olive mills. In order to obtain wastewater which complies with current environmental legislation regarding discharge into water supply systems, it is necessary to use treatment plants with high running costs, which can be prohibitive in olive processing activities. Accumulation and subsequent distribution on the soil through irrigation plants may represent a sustainable solution to the various problems connected with olive mill wastewater (OMW) disposal. Besides allowing fo...

Subsurface drip irrigation (SDI) is regarded as the most efficient and safe technology in reclaimed water irrigation schemes as it minimizes potential human exposure to low quality water. However, the system performance is often limited due to emitter clogging by complex biophysical activities as the whole assembly is laid underground. Growing evidence suggest that soil temperature is strongly correlated with emitter clogging although the dynamics of how it affects emitter performance is yet to be understood. This study analyses the thermal variation in rhizosphere including the consequent changes in recycled water quality and their implications on bio-fouling of emitters. In the northern horticultural district of Adelaide, seasonal variation of 18°C at 20 cm below the ground is very common and the recorded variation in any 10 year period is notably high (25.8°C). Furthermore, the average diurnal variation is also important for operational purpose as the minimum and maximum soil temperature in any day would always occur in specific times. This variation in subsurface temperature affects reclaimed water quality primarily by regulating microbial growth in the labyrinth flow path of emitters. The ever changing level of microbial quality of recycled water still poses threat to sustainable practice of drip technology. The study concludes that future research, design and operation of reclaimed water irrigation schemes must account for these sustainability issues.

BACKGROUND Heterogeneous hydrogenation catalysts for fine chemical synthesis are a convenient alternative to homogeneous catalysts because of ease of separation and reuse. In order to be good catalysts they must have high activity and selectivity and good mechanical properties. Appropriate kinetic models should also be available for reactor design. Novel composite supported Pd catalysts were synthesized and tested in the liquid-phase selective hydrogenation of 2,3-butanedione to 3-hydroxy-2-butanone (acetoin). The composite support comprised a mixture of an organic polymer and γ-Al 2 O 3. The support and the Pd catalyst were further characterized by XRD, SEM, EMPA and XPS spectroscopy. Catalytic tests at various conditions were performed in order to elucidate the kinetics of the system. RESULTS The composite had better mechanical properties (resistance to radial and axial compression) in comparison to other commercial supports. Good activity and high selectivity to acetoin, a product of partial hydrogenation, were obtained at different reaction conditions. A Langmuir-Hinshelwood chemical rate expression useful for reactor design was regressed from the kinetic data.

Per capita land and water resources are decreasing at a very fast rate. These resources are also being degraded mainly due to unmanaged over-exploitation in the wake of resource exploiting green revolution. Per capita land resource has decreased from 0.33 ha in 1951 to 0.13 ha in 2001. Similarly, per capita water availability assessed at more than 5300 m3 in 1951 had decreased to 1905 m3 in 1999 and is likely to be less than 1500 m3 by the year 2025. Therefore, to conserve water resource and to utilize salt affected land resource in a most productive manner, improved irrigation techniques including drip irrigation would play a very prominent role. Though the land area is constant like water, there is scope for utilizing the same in an intensified manner in project commands and rainfed areas to increase the production. Further, this can also be achieved by reclaiming the fallow, barren and uncultivable lands. All this would need water and hence optimum use of available water is very ...

Filtration plays vital role to improve the efficacy and reduce the maintenance of drip irrigation systems. The experiment was conducted to evaluate drip irrigation filters (gravel, disk filter and their combination) for groundwater filtration. Water quality parameters responsible for emitter plugging, such as total solids, turbidity, Ca, Mg, CO3 and HCO3 were analyzed at the entry and exit points of filters. The filtration efficiency for water quality parameters was estimated with individual filters and in combination. Significant improvement was observed for turbidity, total solids, carbonate and bicarbonate. The filtration efficiency with combination filter was 14.3±8.8% for turbidity and 16.3±9.31% for bicarbonates. Gravel filter gave better results for filtration of bicarbonate in comparison to the disk filter. Emitters protected by the gravel media filter experienced the largest flow rate reductions but emitters protected by combination filters experienced least flow rate reduc...

Drip irrigation is the most effective and reliable method for reclaimed water irrigation. The water usually contains a lot of suspended particles, metal salt ions, organisms and microbial communities, which will enhance the possibility of emitter clogging or more complex clogging mechanism. Emitter clogging has become one of the key problems to the application and popularization of the drip irrigation technology. In this paper, we selected four kinds of pressure-compensating emitters and four kinds of non-pressure-compensating emitters, and executed the experiment of drip irrigation with on-site reclaimed water treated with cyclic activated sludge system (CASS). The emitter discharge ratio variation (Dra), coefficient of uniformity (CU) and clogging rate distribution were analyzed to evaluate the emitter clogging characteristics after eliminating the effect of temperature and pressure on the emitter outflow by data correction. The results showed that Dra and CU varied in three periods as system operation. The beginning of experiment was the fluctuated balance period, Dra and CU recurrent fluctuated in 5 %, and the emitters clogged at some spots after the system run 36-48 h. Then the two parameters varied linearly in 60-108 h, tuning into the initiate linear period, as the nonpressure-compensating emitters got an obvious linear change than the pressure-compensating ones with the gradient changed from -0.094 to 0.042 and -0.073 to 0.047, respectively. Some of the emitters have a significant difference on these two parameters at this stage. After the restarting in the second year, Dra and CU decreased sharply. The maximum decrement was, respectively, 9.6 and 10.7 %. Then they varied in line with a greater slope degree as all emitters reached the significant level, the gradient ranges were -0.176 to 0.115 and -0.216 to 0.117, respectively. This stage was called the accelerated linear period. Seriously clogged and completely clogged emitters appeared, and both Dra and CU dropped down to 38.7 and 41.5 %. Various degrees of clogged emitters often emerged in the end part of lateral at first then propelled to the head gradually, the completely clogged emitters in the end accounted for more than 73.0 % when the system run 540 h. Comprehensively considered, the pressure-compensating emitters and cusp-shaped saw-tooth non-pressure-compensating emitters with short flow path are recommended in reclaimed water drip irrigation. These researches are aimed to provide references explaining the emitter clogging mechanism of reclaimed water drip irrigation as well as its technological application and popularization.

Awareness of water conservation has been increasing and understandings of conservation technologies have made headway in the world agriculture. Enhancement in water productivity has been the key objective of planners and the stakeholders. Many water conservation techniques or technologies help in enhancing the water productivity also prevent salt build-up and land degradation. Laser land levelling is one of the many such techniques, which has popularized to a certain extent. Yet its spread has not been significant. Realizing the potential of laser land levelling, the ICAR-Central Soil Salinity Research Institute (ICAR-CSSRI), Karnal, Haryana, India had imported a laser operated land leveller some three decades back. Few research and field evaluation studies have been made in the context of on-farm water savings as well as to judge the impact of this technology on small and marginal farmers. The present study highlights an on-farm as well as observations made in the farmers’ fields, on the basis of scientific observations of information collected at the ICAR-CSSRI farm on the smoothness of the soil surface achieved, uniformity of soil moisture distribution, water requirement for irrigation, as well as saving of time yield differentials of the crops in conventionally levelled and laser levelled fields. A total of 19 farmers’ fields were studied in Pundrak, Zarifa and Kalayat villages in Haryana besides two controlled studies at ICAR-CSSRI farm, Karnal. The values of Levelling Index (LI) for before and after conventional levelling have been evaluated as 3.0 cm and 2.1 cm respectively, whereas in the laser levelled fields, these were 1.93 cm and 0.85 cm respectively. The application time for irrigation in laser levelled fields has reduced to 3.5-4.5 hours from about 6 hours required in conventionally levelled fields for 0.4 ha (1 Acre). The average values of water productivity in conventional and laser-levelled fields have been evaluated at 1.5 and 2.4 kg/m3, respectively for wheat and 0.4 and 0.5 kg/m3 respectively for rice. For the fields having LI of 0.75 cm, the application efficiency has been as high as 90% in comparison to 45% for the field having LI of 6.75 cm. The estimated net profit ranged Rs. 1000 – 1200 for the first year, which rose to Rs. 4000 – 5000 in the second year onwards, during the study for the laser levelled fields. Besides the technical appraisal, the paper highlights the limitations such as necessity of repeat application of laser land levelling once in three years. Fortunately more than 500 custom hiring units have already appeared in the North Indian states due to sensitization through trainings and demonstrations of this technology.

Mill wastewater has always created considerable environmental problems for countries producing olive oil. These problems, which are of increasing relevance in relation to the growing interest in protecting water resources, are of technical and economic nature and are mainly due to the quality of the wastewater (which contains a large amount of organic substances and solute or suspended minerals, and is highly fermentable), the seasonal nature of the production process, and the great territorial dislocation of the olive mills. In order to obtain wastewater which complies with current environmental legislation regarding discharge into water supply systems, it is necessary to use treatment plants with high running costs, which can be prohibitive in olive processing activities. Accumulation and subsequent distribution on the soil through irrigation plants may represent a sustainable solution to the various problems connected with olive mill wastewater (OMW) disposal. Besides allowing for a considerable saving in costs, the use of irrigation plants allows optimal distribution of wastewater. With gradual and uniform distribution, phytotoxic organic substances are held and broken down in the surface layer of the soil, far from the roots of the trees and from water tables. Several experiments highlight that the effects of OMW on crops, soils and the environment depend on the quantity of OMW distributed, but very little information on optimal systems and modalities used to spread OMW is available. A gradual, uniform distribution of OMW can be obtained through microirrigation systems. However, some system management problems may occur. In fact, the small orifices of the emitters and the filters used to protect them can be clogged by small particles or growths due to the suspended solid content of OMW, mainly of organic type. The paper discusses both agronomic and operational aspects of OMW spreading. According to the analysis, some practical recommendations for agronomic OMW use by microirrigation systems are made.

Increasing urbanization in India is generating huge quantities of wastewater resulting in several environmental problems. Thus, use and dispose approach has to be dispensed with for use and reuse approach. Agriculture, a major consumer of good quality water, could be one sector to consume such marginal quality waters. Although surface irrigation is widely used for irrigation with waste water, drip irrigation could be suitable for sewage water reuse as it minimises the health risk to the farmers (avoids direct contact both of the person and the produce) and consumers. Since emitters and filter clogging would limit the performance of drip irrigation system, it might discourage the farmers from lapping up this technology. This paper gives a brief overview of the results of experimental trials for using sewage water on the behaviour of two kinds of filters i.e. sand and screen filters attached in series and using labyrinth type of emitters, considered most suitable against clogging. The performance of the filters recommended for clean water was inadequate for sewage water (suspended solid 100 mg l-1 and BOD ranging from 45-200 mg l-1). The operating time of the filters between cleaning operations in the case of screen filter was less than one hour causing inconvenience in operations while in the case of sand filter head losses increased from 3.1 m to 7.9 m. Clogging of the filters caused inconvenience in irrigation and energy loss went up to 100%, thus increasing input cost. The results also revealed that reduction in flow rate of the emitters was only 0.5% in the case of surface drippers, which increased to 12% in the case of subsurface drip irrigation. The coefficient of variation increased from an initial value of 0.08 to 0.16 for surface and from 0.08 to 0.23 for subsurface drip irrigation. As it is expected, clogging resulted in reduced application efficiency and reduction was from its initial value of 92 to 85% and 72% in the case of surface and subsurface drip irrigation, respectively.

India is facing innumerable challenging problems associated with land and water resources. Declining land resource, depleting water resource and decreasing resource productivity are matters of grave concern. While an estimated 8.5 million ha of agricultural lands have turned barren because of excess salts, the receding availability of the fresh quality water for agriculture aggravating over time. Thus, use of water saving technologies and/or technologies that would allow growing crops on salt-affected soils or with the use of poor quality waters would play an increasingly important role in the twin task of utilizing salty land and water resources for agriculture. The use of drip irrigation seems to be the most viable method of irrigation considering the limitations set forth by poor quality land and water resources. The expansion potential of drip irrigation can be gauged from the fact that only 0.36 million ha is currently under drip irrigation against a potential of 27 million ha. Concerted efforts are being made across the country to examine the suitability and adaptability of drip irrigation for growing a wide range of agricultural and horticultural crops under various agro-climatic conditions. A critical review of several research studies has been made to highlight increase in water use efficiency or water saving for several crops. On the basis of drip irrigation experiments conducted across India, the performance of drip irrigation in salt affected soils and water environments has been highlighted. An attempt to develop pitcher irrigation as an indigenous alternative to drip irrigation to minimize initial investment cost is also included.