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Efficiency Enhancement through Improved Mass Transfer
Rajan K. Paradkar, GM, Business Development, KEVIN Enterprises Pvt. Ltd. There are definite strategies for revamping towers for improving mass transfer to attain higher efficiency. This needs a multi-disciplinary approach blended with industry expertise. Avoidance of pitfalls in the design, engineering, fabrication & installation demand hands on expertise for trouble-free startups and optimum tower performance. At KEVIN, experienced engineers share their practical knowledge to help the client make sure that their tower work as expected.

In spite of the abundant technical literature readily available on the subject, critical issues affecting the tower performance need careful analysis, e.g. the Liquid-Vapor-Flashing Feed Distributor design, Integral Bed Limiters with Redistributors, necessity of Hold down Grid, non-standard Tray Down comers-Weirs-Baffles, Seal Pan installation - prevention of vapour bypassing and liquid re-entrainment, Reflux entry and Pump-around/Re-boiler return, appropriateness of the Supports, achieving revamp objectives without hot work inside the tower, Safety considerations etc. Few cases of KEVIN projects for improving mass transfer are illustrated herewith.



CASE STUDY 1
Revamp of Paraffin Recovery unit in LAB plant

SCOPE: To maximise recovery of LAB, thereby, limiting the slippage to lesser than 5 percent. Improve acid color index (ACI) to a range of 20 to 25. [ACI is the measure of purity of LAB. LAB is mixed with 98 percent H2SO4 and the colour index of the LAB Sulfonate is measured]. On studying the system, the slippage of LAB in the recovery column was found to be more than 15 percent and the acid color index (ACI) was 30-35 which sometimes even reached 60.

SOLUTION: On analysis it was concluded that the existing Pall rings had performance limitation, while the distributor and redistributors were found to be inadequate to achieve the desired distribution quality. The LAB plant was hydraulically rated using Medal-Pak and high performance distributors. The LAB slippage was found to be within 5 to 7 percent.

KEVIN recommended replacement of existing Pall rings with hiperformance Medal-Pak tower packing. The existing distributor and re-distributor were to be replaced with high performance distributors and re-distributors to improve the distribution quality. Accordingly, the tower internals and tower packing were manufactured, supplied and installed.

RESULT: Plant capacity increased by 20 percent. LAB slippage reduced to less than 5 percent. and there was improvement in the ACI as per the desired level.

CASE STUDY 2
Design of DCC & Vaporisation Cooler

SCOPE: For a leading ASU designer in India (the end user is a leading steel plant). Design and optimisation of Vaporisation cooler in order to achieve close temperature approach at cold end.

SOLUTION: KEVIN selected Omni- Pak: high performance random packing, bed height was determined to suit the customer requirements. Heat transfer calculations were carried out to simulate and confirm the output flow rate conditions. Hydraulic rating of tower was carried out to confirm minimal pressure drop requirement. Mechanical designs for the high capacity column internals were generated and the equipments manufactured and supplied.

RESULT: The column is operating satisfactorily till date with guaranteed chilled water outlet temperature and the flow rate.

CASE STUDY 3
Revamp of CO2 Absorber-Regenerator in Ammonia Plant

SCOPE: Carbon dioxide slippage from the absorber was very high (~1200 ppm). This lead to an increase in the load on the methanator and simultaneously increasing the volume of purge stream from the NH3 loop. Customer wanted to revamp the system in order to reduce the slippage of CO2 and increase the capacity without sacrificing efficiency.

SOLUTION: Towers were studied, rated and existing equipment was evaluated. Accordingly, some packing and internals were replaced with techno-commercial discretion to provide an optimum and budgeted solution. Wherever appropriate, KEVIN Medal-Pak (instead of Pall rings) was installed and existing internals were modified accordingly to provide appreciably lower pressure drop even with higher loads.

RESULT: The CO2 slip reduced to 500 ppm at higher capacity of 105 percent. The steam consumption in the Regenerator reduced by 10 percent.

CONCLUSION
These cases are typical for many applications where KEVIN expertise made a difference. Similar results can be achieved for a wide variety of applications in the chemical process industries.