APPLICATION OF VARIOUS HEAT RECOVERY DEVICES IN REDUCING THE STEAM CONSUMPTION WITH MODIFIED BLEEDING PATTERN EVAPORATOR CONFIGURATION TO SUITE COGENERATION PLANTS ITS EFFECT ON HEATING SURFACES

摘要

Heat recovery aspect in case of multiple effect evaporators is an important development in Sugar Industry. Application of Rellieux principles in case of vapour bleeding from intermittent effects of Multiple effect evaporators is a well known practice in steam economy, nevertheless more pronounced in the scenario of Cogeneration. Considering the present day need, this is an attempt to device an effective evaporator scheme involving Falling film Evaporators in conjunction with Continuous pans for all massecuite boiling & adopting the application of Beet Sugar Industry like taking out last effect vapours at higher temperature. The availability of Exhaust at comparatively higher Pressure in Cogeneration plants from Extraction-cum-condensing turbines, enable continuous steady supply to evaporator station at a desired pressure. We have chosen a Pressure of 1.35 kg / cm~2.g (125 saturation temperature) & limiting the last effect vapours @ 85 deg C @ 0.58 kg/cm~2.abs to have a ΔT of 40 deg. C, results in rearrangement of bleeding pattern. For this application Quadruple effect is more suited than other schemes considering the vapour loading conditions. Further we have considered various heat recovery devices such as condensate flash recovery system. Direct contact heaters & replacing medium pressure & low pressure steam applications in S'iper heated wash water system, Sulphur melting,Seed melting Molasses conditioning & pan washing etc. brings down the steam consumption at evaporator station considerably. The enthalpy balances for each effect is worked out to estimate the exact, exhaust steam requirement & when compared to regular system, results in over all steam economy to the extent of 8%, which generate substantial revenue both in terms of Bagasse saving & surplus power generation. Evaluation of heating surfaces with this modified configuration vs normal configuration is done to have cost-benefit analysis.