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LNG plant requires a lot of energy for its production especially in liquefaction process. One of the reasons is due to inefficiency on some of its major equipments, particularly on Main Cryogenic Heat Exchanger (MCHE). The efficiency of this unit can be improved by the usage of Mixed Refrigerant (MR) which matches closely the heating curve between hot and cold stream. However, the study on this refrigerant is complex and tedious due to multi component refrigerant and phase changing process inside MCHE. In this study, effect of varying MR composition towards MCHE performance is analyzed, with focus on heat transfer coefficient in shell side of MCHE. The analysis was based on single and two phase flow conditions which are gas flow and liquid falling film flow. The adjustment of binary components in MR composition was studied for each flow regime. By doing this, the best composition adjustment that gives the highest value of heat transfer coefficient was determined. It was found that the adjustment of methane-propane (C1-C3) is the best arrangement for both cases. However, it needs to be tested by applying this to actual process condition, in this case by implementing it in simulated LNG process.

Ocean Thermal Energy Conversion (OTEC) harnesses thermal energy stored at different seawater depths via power generation from a thermodynamic closed-loop cyclical system. Apart from its consistent energy generation, it could be diversified into other side industries, making OTEC an attractive and sustainable source of renewable energy. However, the process that utilises seawater as its main fluid is exposed to biofouling deposition due to unwanted growth and accumulation of biological elements on any contact surfaces, potentially affecting its efficiency and damaging equipment in the process. Considering that biofouling is an inevitable condition that may not be eliminated, a comprehensive study for assessing potential biofouling growth and deposition mechanism is a crucial step for strategizing effective biofouling management in a commercial and large-scale OTEC power plant facility. This review paper focuses on evaluating suitable biofouling assessment techniques specifically for a large-scale OTEC power plant facility. This is achieved by evaluating previous and proposed biofouling assessment techniques relevant to OTEC systems by focusing on their implementation under a realistic OTEC setup. The initial study indicated that the potential of biofouling deposition may be unavoidable in some sections in all OTEC models, despite biofouling-free design consideration. Previous OTEC biofouling studies were evaluated with reported physical and biological assessment approaches indicated the need to further improve these techniques especially in continuous and non-destructive methods. Therefore, several biofouling monitoring systems reported from other water treatment industries were considered for the OTEC systems, with findings indicated the importance of considering important OTEC operational parameters for feasible and robust biofouling monitoring systems. Two major parameters which are seawater intake flow rate and temperature variation at different seawater intake levels were evaluated under OTEC operational evaluation by considering examples of practices conducted in cooling water systems in the power plant industry. A realistic biofouling monitoring setup for mimicking continuous changes in biofouling deposition is required, in this case by side-connecting an operated OTEC power plant facility with a pilot plant setup or a side sampler. This step allows the application of proposed biofouling monitoring techniques under a realistic and uninterrupted biofouling deposition setup.

Ocean Thermal Energy Conversion (OTEC) is a renewable energy source in which energy is produced by converting the heat stored in the sea or the ocean thermal energy into valuable work, based on the temperature difference between the warm surface seawater and the cold deep seawater. One of the OTEC system requirements is to have a seawater temperature difference at a minimum of 20 °C within a depth of 1000 m below sea level. Recognizing the importance of optimum sea water temperature, several studies have been conducted to optimize the OTEC system. However, none of these studies was attempted under a hybrid ocean thermal energy conversion (H-OTEC) setup. A H-OTEC system is a combination of closed-cycle and open-cycle OTEC system. The objective of this study is to evaluate the performance of the H-OTEC process system based on the impact of seawater temperature variation by simulating H-OTEC process system. Aspen HYSYS was used as a chemical process simulation platform for conducting this study. After the model was completed, verification test was conducted before the simulated data was recorded. The data for the pump work input and the turbine work output were acquired to determine the net power output and system efficiency. The net power output, Carnot efficiency, and thermal efficiency were recorded approximately 1.39 kW, 5.7%, and 1.45%. The data for net power output and the efficiencies of the system was recorded for every 1 °C of increment in surface seawater temperature. The results showed that the net power output increased slightly by 0.5kW, with efficiency difference for both Carnot cycle and actual cycle, recorded to be less than 3% and 0.1% respectively.

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