Research On Key Technology Of CO₂ Compressor In Large Urea Plant

The steady and fast development of fertilizer industry is a prerequisites for improving people's quality of life and further promoting the process of industrialization. The CO2 compressor unit, as the core unit of the large fertilizer plant, is the bottleneck equipment of restricting the plant to high-end and intelligent development. The molecular of CO2 gas is large and its pressure ratio is high. The physical properties in the trans-critical process is complex, and the efficient operating condition range is narrow. For design and operation stages, the problems above-mentioned are particularly prominent. This paper mainly studied the current status of CO2 compressor that the stage performance is difficult to predict and the rotor prone to instability during oper ation. The main achievements and contributions are as follows:1. Firstly, this paper analyzed the CO2 supercritical stage under the action of real gas by using CFD numerical analysis method, and found the differences between the effects of the ideal gas and real gas on the unit components. Combined with the actual operation of the unit, this paper presented that the operating range of CO2 compressor which is designed based on ideal gas in a traditional design method is narrower than that which is designed based on actual gas, especially for the compressor stages in near-critical region. In the rated operating conditions of the compressor, the absolute flow angle of diffuser inlet in actual gas compressed condition is smaller than that in ideal gas condition, so it is more likely to cause instability.2. Secondly, the possible failure mode of the blade which may occur in the nominal operating condition of a certain compressor stage in service was analyzed, and the main reason for the failure is studied in-depth. Then, a method of how to avoid accidents through structure optimization in design, installation or other links was presented.3. In the part of damping seal, this article built six different damping sealing structure in the eye ring seal area of a certain compressor rotor. The dynamic parameters of sealing structure were calculate and then brought into the rotor system to analyze the effects on the stability of rotor. A optimal sealing structure which can be used in the alteration of compressor sealing was presented.4. Finally, the design method of centrifugal compressor model stages and the development process of the software which was used to model selection and design were both presented. The design cycle of centrifugal compressor can be greatly shorten and a reliable performance can be obtained through model stage design. The design of model stage is based on advance compressor design software NREC and CFD analysis software NUMECA. The model selection software is completed with a modular design based on the GUI feature in Mat lab.The equipment failures can be nipped in the bud through the study of the mechanism of many key issues of CO2 compressor in urea plant. The work efficiency of the compressor would be improved and the work scope would be broad. The new design method of centrifugal compressor model stages and the development process of the software which was used to model selection and design can greatly short the design cycle of centrifugal compressor and obtain a higher reliable performance and production efficiency. Thus, some technical support can be provided to the high-end, intelligent direction development of centrifugal compressor.