Design Modification For CO₂ Absorber In Ammonia Plant Capacity Increasing From 1000T/d To 1500T/d

Most 300.000MTPA Ammonia Plant imported in the 1970s adopted Benfield Process to remove CO2. Having run for 30 years, these kinds of plant need to be revamped and retrofitted to satisfy the requirements of production technical development. One of the important choice for revamping is to increase plant capacity from current 1000T/d to 1500T/d. Imported Benfield Process of 300.000MTPA Ammonia Plant in Lutianhua was modified to Low Heat Benfield Process in 1988. Based on Low Heat Benfield Process, in this paper, different methods for further increasing capacity are described and analyzed, material/heat balance, hydromechanics and mass transfer ' performance of CO2 Absorber under 1500T/d are calculated in detail. The hydromechanics and mass transfer performance of CO2 Absorber under current 1000T7d is rechecked in Appendix.Revamping method one is to use more efficient CO2 solvent. However, by comparing the energy consumption, initial investment cost and long-term operation cost between UOP's Low Heat Benfield Process and BASF's aMDEA CO2 Removal Process, and considering UOP's Low Heat Benfield Process has put into use in Lutianhua, it's better to increase the plant capacity to 1500T/d by continuously using UOP's Low Heat Benfield Process.Revamping method two is to rebuilt or install a new CO2 absorber to increase CO2 removal capacity. But this choice has disadvantages of huge investment, difficult equipment layout, large quantity of revamping works and complex operation after revamping. Normally, this method will not be adopted if there is more economic one.Revamping method three is to use high efficient packing and improve internal structure of CO2 absorber. This method has advantages of small modification of system, small investment, and modification work can be performed during overhaul of the plant. However, since there is no change of column body, the system needs to be redesigned and recalculated when gas-liquid load is increased. The calculation is made for hydromechanics and packing of CO2 absorber by using Carrier Point Algorithm and classical Flood Point Algorithm. The calculation result shown that by using UOP's Low Heat Benfield Process and by replacing packing at lower part to structured one, CO2absorber could remain stable operation under load of 1500T/d, and pressure drop, gas velocity at flood point and gas capacity are within safe range. By calculating mass transfer coefficient and packing volume, it's found that with packing height remained same, CO2 absorption load requirement for capacity increasing can be satisfied.All calculations in this paper are made by Excel. This design calculation has been used as basis in choosing method for CO2 removal in ammonia revamping project of Lutianhua and can be used for reference in other capacity increasing item.