Cold Energy Utilization from LNG Regasification

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.