Cold Energy Utilization from LNG Regasification

• Main Author: Mazri, Mohd Zafri
• Format: Final Year Project
• Language: English
• Published: Universiti Teknologi PETRONAS 2013
• Subjects: TP Chemical technology
• Online Access: http://utpedia.utp.edu.my/8475/1/Mohd%20Zafri%20bin%20Mazri_12694_Chemical%20Engineering_Cold%20Energy%20Utilization%20from%20LNG%20Regasification.pdf; http://utpedia.utp.edu.my/8475/

report deals with Liquefied Natural Gas (LNG) cold energy utilization by integrating the system with gas power plant and Rankine cycle to generate electricity. There is a waste of cold energy available during the LNG regasification due to the use of seawater and returning it back to ocean. The cold energy available is better converted into useful energy such as electricity via Rankine power cycle implementation. Another aspect to look at is on the system performance of ordinary Rankine cycle utilizing water as working fluid which is quite low. The objectives of this research is to develop an integrated system to fully utilize cold energy available via Rankine cycle in existing gas power plant and to experiment with other working fluids to be utilized in the cycle taking pure ammonia as the basis. Two case studies are developed with first being an integration of the LNG regasification process with gas power plant to yield a targeted amount of power generation which is about 404 MW. The second case study integrates the Rankine cycle into previous system to utilize the LNG cold available. Simulation work is carried out using Aspen Hysys to check for the system’s feasibility. The efficiency of the overall system is analysed based on thermal and exergy efficiency respectively for both case studies. The effect of the inlet and outlet pressure of the gas turbine on overall system efficiency is investigated which resulted in highest efficiency when the expansion ratio of the gas turbine is at the highest. It is found that the second case study improves the thermal and exergy efficiency by 5.1 % and 2.4 % respectively. Five working fluids are used to study their effects on system efficiency which are ammonia, water, ammoniawater mixture, ethane and propane. As expected from various literature reviews, ammonia yields the highest system’s efficiency compared to other working fluids with improvement of about 0.64 % over pure water but with penalty of higher mass flow required approximately 5.2 tonnes h-1 to achieve operating specification as discussed in results section later in this paper. Based on the results obtained, it is proven that the efficiency of gas power plant can be further increased by integrating with Rankine power cycle and at the same time effectively utilizing the LNG cold energy available.