Continuous cultivation of soils of the semiarid tropics has led to signi®cant land degradation. Soil erosion and nutrient loss caused by high runoff volumes have reduced crop yields and contributed to offsite damage. We compared a number of soil management practices (tillage, mulch and perennial/annual rotational based systems) for their potential to improve crop production and land resource protection in an Al®sol of the semiarid tropics of India. Runoff and soil erosion were monitored and surface soil and sediment were analysed for nitrogen and carbon to determine enrichment ratios. Amelioration of soils with organic additions (farmyard manure, rice straw) or rotating perennial pasture with annual crops increased soil carbon and nitrogen contents and reduced runoff, soil erosion and nutrient loss. Soil erosion totalled less than 7 t ha ±1 , but enrichment ratios were often greater than 2 resulting in up to 27 kg N ha ±1 and 178 kg C ha ±1 being lost in sediment. Up to an extra 250 mm of water per year in®ltrated the soil with organic additions and was available for crop water use or percolation to groundwater. The results show that there are good opportunities for reducing degradation and increasing productivity on farms.
A field experiment was conducted in the semi arid tropics to study the effects of soil structural modification on cropping systems. The aim was to improve crop production and land resource protection using innovative soil management practices. Tillage, mulch and perennial/annual rotational based systems were compared for 5 years in an Alfisol at ICRISAT in India. Crop yield parameters, including grain and biomass yield, leaf area index, crop cover, and plant height were measured. Results indicate significant benefits to annual crop yield (maize, sorghum) from improved water supply due to mulching with farmyard manure or and rice straw, and due to rotation with prior-perennial crops. Grain yields were 16 to 59% higher in mulched treatments compared to unmulched treatments, with similar increases for fodder yields. Annual crop yields after 4 years of perennials were 14 to 81% higher than unmulched treatments, except for low fertility maize grown after buffel grass. The interaction with chemical fertility was less clear than for water supply. The results have implications for soil management throughout the semi-arid tropics. 0 1997 Elsevier Science B.V.
In the Fluid Catalytic Cracking unit of refinery, erosion due to catalyst impact on wall refractories is a serious issue that affects the plant performance. In the present study, Computational Fluid Dynamics (CFD) coupled with Discrete Element Model (DEM) method is used to characterize gas-solid flow dynamics and erosion in regenerated catalyst slide pipe (RCSP). Catalyst particles size in the range of 1-180 µm were considered for the simulations. The predicted erosion profile was verified by comparing with thermography experiments and were found in a good agreement.
The predicted results revealed that due to partial opening and orientation of regenerated catalyst slide valve, the rapid alterations of flow direction of catalyst particles take place. Particles recirculate in the rear end of the pipe and continuously impinges at the 12 o'clock position upstream of the valve. This led to erosion in the pipe. The experimentally validated CFD model was used to characterize the erosion profile under different relative openings of regenerated catalyst slide valve (RSCV). It was observed that with increasing the valve opening the erosion profile was reduced due to decreases catalyst recirculation velocity and vice-versa. Further, effect of valve opening orientation was also studied and it was found that by changing the valve opening orientation from parallel to ground surface to down towards, erosion was not observed due to small recirculatory flow of catalyst with low velocity. The results presented in this work will help refiners to understand the catalyst flow dynamics inside the regenerated catalyst slide pipe, root cause of erosion in pipes, and to achieve further improvements in the performance of plant.
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