| Synthetic gas produced by conversion reaction must be pressed by compressor to ensure the requirement of methanol synthesis in methanol plant with coal or natural gas as raw material. The compressor must use the seal to avoid process gas of carbon monoxide, hydrogen and other toxic, flammable and explosive gases leakage to the atmosphere from a rotating machinery. Dry gas seal(DGS) systems as the major choice have been used in most centrifugal compressor applications, because it is superior to ordinary contact type mechanical seal in many respects.Compressor units are the core equipments of methanol plant, once the compressor is shut down, the production unit will bring great impact on the time and energy consumption. It is the major fault causes of centrifugal compressor that dry gas seal is damaged, it may causes the production device downtime repair, while the whole system of coasting, which seriously restricts the normal continuous operation, and brings huge losses to chemical production. However, experience shows that DGS failures are still quite common. This dissertation made analysis and calculation on these practical problems from a methanol plant compressor made by the well-known foreign manufacturers, and made some experimental study and relevant renovations.The first part of this dissertation mainly analyzes the reasons of these problems. It was found that the abnormal increase of thrust force when compressor emergency shut down, beyond the limit of lock nut and thrust bearings can withstand. The additional thrust force influences internal components of the compressor, and causes dry gas seal destructive injury. The thrust force of the high pressure cylinder is made up with four parts of the calculation, finally obtains the compressor thrust force under the normal operation, emergency shutdown process, the calculation results and the measured data from the compressor manufacturers is similar, which proves that this calculation method on axial force of centrifugal compressor is reliable and can be used as the reference for centrifugal compressor. The seal gas source is not available at sufficient pressure to cover the entire operating range of the compressor including transient conditions such as startup, shutdown, or idle, and static conditions. Thus, the sealing surface wear and the O type ring fracture are caused by the insufficiency of the seal gas supply, and the leakage of the dry gas seal is increased.The second part is the dry gas seal operation test. The impact of compressor speed, supply gas pressure and supply gas temperature on the seal gas leakage was conducted experimentally.The third part is concerned with technical renovation taken some specific measures for the above problems. These are eliminating the abnormal thrust force through reworking the balance drum system, ensuring the supply gas pressure by adding the seal gas boosters, avoiding the moisture of the supply gas by adding the heat tracing system and thermal insulation, reducing the friction of dry gas seal faces by improving process operation modes. The service life of dry gas seal was prolonged by the above technical renovation.After the technical renovation has been completed, the dry gas seal service life is greatly extended. The compressor can be operated continuously for long cycle. The economic benefits of enterprises about 33 200000 yuan a year has been obtained. |
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