دانلود رایگان مقاله عملیات بهینه سازی سطح بی از فرآیند مایع سازی گاز طبیعی

Abstract

The production of liquefied natural gas (LNG) is a highly energy intensive process, as required liquefaction temperature is approximately −160 °C at atmospheric pressure. In this study, we propose a novel bi-level optimizing operation system for an LNG process, which consists of a real-time steady-state optimizer (RTSSO) and a decentralized control system. The RTSSO computes the optimal operating conditions such that the compressor power is minimized, while the decentralized control system performs real-time feedback actions to attain the target operating points against various disturbances. Special attention was given to the decentralized control system so that i) the process operation can be rapidly stabilized, and ii) the developed system can be seamlessly applied to an actual process. The performance of the proposed operation system was validated in a numerical LNG plant that precisely replicates an actual plant that produces 100 t of LNG per day.

6. Conclusions

In this study, we proposed a novel bi-level optimizing operation system for an LNG process. The proposed structure is composed of an RTSSO that determines the optimal compression ratio and warm end delta temperature and a decentralized control system that conducts the regulation of the process. Numerical studies showed thatthe proposed decentralized control systems for liquefaction and refrigeration units cope well with various disturbances and successfully fulfilled the tracking of large set point changes. The processes were stabilized in a relatively short transient for different scenarios in the process changes, and the product specification represented by the LNG temperature was met at all times, especially even in the case that refrigerant cold duty is not sufficient to cool and liquefy the entire feed NG. The superiority of the proposed control system was also demonstrated via comparison with alternative control scheme. A special feature of the LNG process is that refrigeration and liquefaction units are closely related to each other in energy balance, while each is operated under separately-designed local controllers. To accommodate these features, the integrated control system that balances the energy supply and demand between the two units was developed. Numerical studies showed thatthe proposed integrated control systemworks quite satisfactorily, steering theprocess operations into the prescribed stable region.