Energy-saving Research Of Evaporation Process In Pharmaceutical Industry Based On Mechanical Vapor Recompression System

The secondary steam produced by evaporation concentration process in the pharmaceutical industry is often exhausted directly,which is a consequence of great energy loss in the industry.In this paper,the mechanical vapor recompression(MVR)technology is proposed,which can be used to recycle the secondary steam by recompressing the secondary steam.It can help to improve the efficiency of energy utilization and reduce the energy consumption for pharmaceutical industry.The theory and operation process of the MVR system was introduced firstly.Then the mathematical model was built by the equation of energy conservation,the relationship equation between compression ratio and heat transfer temperature difference and compressor's characteristic curve.The rotatig speed of the compressor and the heat transfer coefficient of the evaporator were simulated,and the theoretical values of the parameters under different working conditions are calculated.40%vol ethanol was chosen as the experimental medium to test MVR's performance.The results show that under the same pressure,the evaporation rate,the evaporation rate,compression ratio,transfer temperature difference will increase with a higher rotating speed of centrifugal compressor.And the maximum evaporation rate is 2870kg/h and the coefficient of performance(COP),specific moisture extraction rate(SMER)can reach 15.3 and 21.5kg/kW·h respectively when the compressor rotating speed runs up to 16000 rpm.Increasing evaporation pressure is benefit to improve evaporation rate and COP with the same compressor rotating speed.The characteristics of different types of compressors were compared theoretically.Operation efficiency of two MVR systems driven by centrifugal and vortex compressors were researched.The results show that under the same design evaporation rate,centrifugal compressor's average amount of evaporation rate is 637kg/h higher than vortex compressors',whose COP is 4.3 higher than vortex compressors'.It can be proved that under the premise of ensuring air tightness,the centrifugal compressor is more suitable for concentrating alcohol extract than the vortex compressor,and has a better energy saving effect in concentration process.Based on the second law of thermodynamics,the total energy efficiency of the MVR system and the energy loss of each part of the equipment are calculated.The total energy efficiency is about 9.1%.And the steam compressor's energy loss is 30.02 kW,which accounts for 23.1% of the total energy paid.Evaporator's energy loss is 27.38 kW,accounting for 21.1% of the total energy value.Preheater's energy loss is 48.79 kW,accounting for 37.5% of the total energy value.Auxiliary pump's energy loss is 12.08 kW,accounting for 9.2% of the total payment of the energy.Therefore,increasing the energy efficiency of plate preheater,compressor and evaporator was very important.After putting MVR system into operation,the use of steam in the plant reduced obviously but the electricity consumption has increased.The unit energy consumption of evaporation process decreases from 0.104 tons standard coal to the 0.028 tons standard coal by calculating,and it can save 391.6 tons standard coal per year for the company and the energy-saving effect is remarkable.