The overall principle of the transformation utilizes the existing conditions of the compressor unit, adopts the advanced technology of the current compressor design and manufacture, and improves the capacity of the compressor and reduces the energy consumption to meet the expansion needs of the urea plant with minimal changes to the unit; As far as possible, leave appropriate margins for future expansion, and try to minimize the risk of retrofitting. Reconstruction plan 1) Directly connect the carbon dioxide compressor unit with the piston type carbon dioxide compressor of the 750t/d urea unit, or directly connect a new piston compressor to solve the problem of insufficient capacity of the existing carbon dioxide compressor. 2) Inductive turbocharger at the inlet of carbon dioxide compressor to reduce the compression ratio of the existing compressor and increase the amount of air pumping to achieve the purpose of capacity expansion. 3) Parallel one multi-axis carbon dioxide compressor, which is combined with the capacity expansion of the device. 4) Improve the carbon dioxide output pressure of the synthetic ammonia boundary zone and combine with the internal structure of the modified compressor. The transformation plan determines the scheme of paralleling one multi-axis compressor. No improvement is made to the existing unit. The operation is flexible, the elasticity is large, and the construction time is short. However, the expansion capacity of the device cannot be too low, and the investment is larger than other schemes. . In the two solutions to increase the inlet pressure of the carbon dioxide compressor, the internal parts of the compressor need to be modified. After the series booster is used, the adjustment and control of the supercharger and the main engine will bring new difficulties and problems to the operation. Due to different adjustment methods, it is difficult to achieve the best working conditions of the two machines. Therefore, there is a clear advantage in choosing to increase the carbon dioxide output pressure scheme in the synthetic ammonia boundary zone. When selecting the ammonia desulfurization system reforming scheme, fully consider the CO2 pressure requirements of the urea boundary zone and increase the carbon dioxide output pressure as much as possible. Only the internal parts of the compressor are modified, so that the reliability of the unit itself and the whole unit can be easily ensured, and the operation and maintenance are more convenient. At the same time, the investment and construction time are much more economical than the series supercharger. The optimal solution in the program. Determination of process conditions When determining the modification plan of the decarbonization system of the ammonia plant, the CO2 parameters entering the urea boundary area are determined by careful accounting: absolute pressure 014 MPa, temperature 3040. In addition, the following factors are also considered: at least 2000t after the unit transformation The /d capability is required and, where possible, a margin of further increase to 2200 t/d is allowed. The reliability and safety of the whole machine must be fully guaranteed, including the safety factor of the steam turbine, the speed increasing box, the oil system and other auxiliary systems. The operational flexibility of the unit is guaranteed. Transform the control system into an integrated control system to achieve comprehensive control of load, anti-surge and interlocking systems. % The advanced technology of today's centrifugal compressors should be applied to the unit. After the transformation, the energy consumption of the unit should reach the level of the late 1990s. On the basis of comprehensive consideration of five factors, through repeated accounting and multiple exchanges, the process conditions for the transformation of carbon dioxide compressors were finally determined. The modification content determines the modification of the cooler separator of the high and low pressure cylinder internals, the unit control system and the auxiliary system of the unit. The turbine rotor is partially improved, and the rest of the cylinder block of the unit remains unchanged. The new body of the company completed the transformation of the compressor body and control part, and the domestic company completed the transformation of the compressor auxiliary system. Unit part 1) High and low pressure cylinder rotor and internal parts are all replaced with new components. The structural design and thermal design of the new impeller have been greatly improved on the original basis to improve efficiency. The low-pressure cylinder section has two ternary impellers, the section is four binary impellers, and the six impellers of the high-pressure cylinder are binary impellers. The main characteristic parameters of the high and low pressure cylinders before and after the transformation. Main characteristic parameters and component structure change before and after low-pressure cylinder reforming cylinder type 2MCL607 (before transformation) 2MCL6076 (after retrofit) section/stage number I/3II/4I/2II/4 working speed/r (min-172006786 rotor impeller Diameter/mm1, 2, 3, 7504, 7505, 6, 7, 7001, 2, 7203, 4, 5, 6 700 seal type labyrinth seal labyrinth seal tooth shape change radial bearing elliptical sliding bearing tilting tile Main characteristics of the sliding bearing high-pressure cylinder before and after the transformation, component structure change cylinder type 2BCL306/a (before transformation) 2BCL306/a (after transformation) section / series) / 4/2) / 4/2 working speed / r (min-11390013181 rotor impeller outer diameter / mm3002801 grade 3502, 3, 4 grade 3205 grade 3006 grade 300 axis type optical axis with flow path shaped step shaft seal structure are flat tooth labyrinth seal interstage, shaft end is helical gear The labyrinth seal, the balance disc is a honeycomb seal 2) The control system is changed to the UNICOS integrated control system. Speed ​​control system: PGPL governor and Azonia regulator before the overall demolition and renovation, retain high and low pressure accident parking valves and oil motives; increase the PLC programmable logic controller of the UNICOS integrated control system, electricity / Components such as liquid converters and solenoid valves. Anti-surge control system: The new Billion UNICOS anti-surge control system is controlled by the parameters of section inlet pressure, section inlet temperature, section outlet pressure, section outlet temperature and section outlet flow differential pressure. A new air-open anti-surge B valve is added in parallel with the original anti-surge valve. 3) The newly purchased modified turbine rotor currently designed and manufactured by New Billund Company mainly solves the problem of the final blade fracture of the turbine rotor. 4) Condition monitoring and fault diagnosis system. Because the 7200 type condition monitoring system is backward in function and has many faults, spare parts can no longer be purchased, and it can't communicate with DCS. Therefore, it is changed to Bently3500 in the transformation, and Bently data management system DM2000 is added, and it is jointly developed by Xitianhua and Xi'an Jiaotong University. The fault diagnosis system is used for offline acquisition and analysis as a complement to the fault diagnosis system. Through the analysis of various maps such as the axial trajectory map, the spectrogram, and the waterfall graph, the state monitoring and fault diagnosis level of the unit is greatly improved, and the accuracy of the diagnosis is also verified in the commissioning and normal operation of the unit after the transformation. The energy-saving effect is remarkable. According to the statistical data, when the production load of the device is 1620t/d, the steam can be saved by 38MPa per hour for about 9t, and the lower the system load, the more significant the energy-saving effect. The root cause of the decline in energy consumption is mainly that the aerodynamic performance of the high-pressure cylinder rotor is greatly improved and the load of each section of the compressor is more rationally distributed. After the transformation, the compression ratio of the low pressure section and the CO2 outlet temperature are both reduced, indicating that the load is decreasing rather than increasing, so the energy saving is not in the low pressure section. The biggest improvement is the improvement of the performance of the high-pressure cylinder rotor. Before the transformation, the outlet flow rate of the section is controlled at 34,500 m3/h for a long time, and cannot be lower than 33,000 m3/h. Otherwise, the vibration of the high-pressure cylinder will be intensified. For this reason, it is necessary to maintain a large opening degree for the four-time three-four-four-one valve, so that a large amount of CO2 is recirculated. After the transformation, the outlet flow rate of the section can be reduced to 27,000 m3/h, which is the root cause of the reduction of steam power and steam reduction of work. In addition, due to the improvement of the speed control system, the adjustment accuracy of the steam turbine speed is improved, and the steam injection amount is reduced, which also reduces the energy loss generated by the conversion of 23 MPa superheated steam into 04 MPa steam injection. In the process of technical transformation of carbon dioxide compressors, the unit reconstruction plan was determined through repeated comparison and demonstration. After the transformation, although there are still some problems in the unit, from the current operation, the whole transformation work is relatively successful.
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March 29, 2023