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Multi-stage expander refrigeration cycles were proposed and analyzed in order to develop an efficient natural gas liquefaction process. The proposed dual and cascade expander processes have high efficiency and the potential for larger liquefaction capacity and are suitable for small-scale and offshore natural gas liquefaction systems. While refrigeration cycles of conventional expander processes use pure nitrogen or methane as a refrigerant, the proposed refrigeration cycles use one or more mixtures as refrigerants. Since mixed refrigerants are used, the efficiency of the proposed multi-stage expander processes becomes higher than that of conventional expander processes. However, the proposed liquefaction processes are different from the single mixed refrigerant (SMR) and dual mixed refrigerant (DMR) processes. The proposed processes use mixed refrigerants as a form of gas, while the SMR and DMR processes use mixed refrigerants as a form of gas, liquid- or two-phase flow. Thus, expanders can be employed instead of Joule-Thomson (J-T) valves for refrigerant expansion. Expanders generate useful work, which is supplied to the compressor, while the high-pressure refrigerant is expanded in expanders to reduce its temperature. Various expander refrigeration cycles are presented to confirm their feasibility and estimate the performance of the proposed process. The specific work, composite curves and exergy analysis data are investigated to evaluate the performance of the proposed processes. A lower specific work was achieved to 1,590 kJ/kg in the dual expander process, and 1,460 kJ/kg in the cascade expander process. In addition, the results of exergy analysis revealed that cycle compressors with associated after-coolers and companders are main contributors to total exergy losses in proposed expander processes. [ABSTRACT FROM AUTHOR]

This paper focuses on the development of an integrated risk assessment system to increase the safety of gas refinery plants. This integration is important in managing the design and the operation of chemical plants and it requires significant time, effort and specialized expertise. We propose a systematic procedure to apply quantitative and qualitative hazard identification methods before constructing the refinery plants. Advantages of this assessment procedure are 1) systematic method in identifying most of the important hazards, 2) complete and rigorous analysis, and 3) reducing budget and time. The qualitative and quantitative assessment method consists of two and three steps, respectively. After these five steps, the risk of the same plant was calculated and analyzed. This method can identify risk and potential hazards from local gas refinery plants effectively and systematically. We applied the integrated qualitative and quantitative risk assessment method to remove the risk of a local gas refinery plant with 160 P&ID sheets. The result of this work confirmed that no residential population existed within the bounds of the 1×10 per annum risk contour. Therefore, the risk to the public from the gas refinery plants should be considered acceptable. [ABSTRACT FROM AUTHOR]