Research Scholar, National University of Singapore
Cost effective utilization of cold energy associated with LNG [Liquefied Natural Gas]
Energy has become an indispensable part of our daily lives. Energy demand is expected to grow in the years to come. Currently fossil resources are expected to meet our growing energy demand and dependence on fossil fuel will continue. With increasing exploration of various unconventional natural gas resources, the world is all set to enter the ‘golden age of gas’. Natural gas being the cleanest fossil resource, and owing to its abundant availability there is a major shift towards natural gas as an energy resource. However, natural gas reserves are not uniformly distributed all over the world. Hence, natural gas will either be transported via pipelines or in liquefied form (LNG) to meet the rising global demand for natural gas. LNG is the preferred mode of transportation for long distances and it is expected that in near future LNG trade will nearly be double. With many new LNG regasification terminals being proposed worldwide, it is worthy to investigate process integration opportunities within a LNG regasification terminal. LNG comes with a lot of cold energy that has the potential to be utilized. However, currently the entire cold energy is wasted. In this context, I am using process simulation and optimization as a tool to come up with different process configurations to cost effectively utilize this available cold energy. This is expected to increase the overall worth of a regasification terminal both in terms of sustainability as well as from economics view point.
Abstract: The main objective of this research work is to generate electric power efficiently using the cold exergy from the regasification task of LNG (liquefied natural gas) regasification plants. Thus, the article aims to propose and analyse an unconventional efficient power plant composed by cascade Rankine cycles, combined with a direct expansion power unit. The rejected heat from each cascade power unit is used to heat the liquefied natural gas in a regasification plant. The analysis of the proposed cycle is carried out by comparing some recent contributions with the proposed cascade Rankine based power plants in which argon and methane have been used due to their inherent condensation characteristics concerning the quasi-critical condensation temperatures. As the result of the optimisation of an objective function, the cascaded Rankine cycles operating with argon and methane, followed by a direct expander unit working with regasified LNG, yield a high performance index based on the ratio of the attained power to the mass flow rate of regasified LNG (approaching 235 kW/kg-LNG) with pinch point of 2 °C at 30 bar, and 145.6 kW/kg-LNG with pinch point of 6 °C at 70 bar, when compared with the most recent contributions carried out in this field.
Pub.: 09 Oct '15, Pinned: 16 Aug '17
Abstract: The LNG (liquefied natural gas) regasification process is a source of cold exergy that is suitable to be recovered to improve the efficiency of thermal power plants. In this paper, an innovative power plant with LNG (liquefied natural gas) exergy utilisation and the capture of CO2 proceeding from the flue gases is presented. It is characterised by the recovery of LNG cold exergy in a closed Brayton cycle and through direct expansion in an expander coupled to an electrical generator. Moreover, this novel power plant configuration allows CO2 capture, through an oxy-fuel combustion system and a Rankine cycle that operates with the flue gases themselves and in quasi-critical conditions. The greatest advantage of this plant is that all the recoverable LNG exergy is used to increase the efficiency of the CBC (closed Brayton cycle) and in direct expansion whereas, in other power cycles found in literature that associate LNG regasification and CO2 capture, part of the LNG exergy is used for condensing flue gas CO2 for its subsequent capture. As a result, a high efficiency power plant is achieved, exceeding 65%, with almost zero greenhouse gas emissions.
Pub.: 01 Oct '15, Pinned: 16 Aug '17
Abstract: Natural gas is one of the most important sources of energy, the demand for which increases continuously. The LNG (liquefied natural gas) market rises currently exponentially; many countries entered this market recently. Applying an efficient regasification process for LNG is now more important than in the past. At present, mainly regasification of LNG via direct or indirect heating is used for industrial applications. Regasification of LNG can also be combined with generation of electricity. Another possibility is the integration of the regasification into a processes requiring low temperatures. A new concept dealing with the integration of regasification of LNG into a cryogenic process of air separation has recently been developed at Technische Universität Berlin. This paper evaluates two options of integrating the regasification of LNG into an air separation system. Conventional and advanced exergy analyses are used in the evaluation.
Pub.: 14 May '16, Pinned: 16 Aug '17
Abstract: The generation of boil-off gas (BOG) is inevitable in liquefied-natural-gas (LNG) regasification terminals. It can be a safety concern and, in most cases, demands BOG reliquefaction before regasification. This study presents a fundamental thermodynamic analysis of the BOG reliquefaction–LNG regasification process, which consumes significant power. We propose an evolving series of schemes that exploit the cryogenic energy of the send-out LNG to reduce the total power consumption. We synergistically integrate options such as BOG precooling, recompression, interstage cooling, and recondensation in our proposed schemes. We develop a nonlinear programming (NLP) formulation to minimize the power required for each scheme for a given amount of BOG. Under some idealistic assumptions, the optimal solutions to these NLPs give lower bounds on the total power consumption, which can be used to evaluate the cost-effectiveness of terminal operations. A novel scheme consisting of BOG precooling before compression and two-stage recondensation by direct mixing has the least power consumption. For a case-study terminal, it offers 11.9% lower power consumption than the best-reported design in the literature for 15% BOG.
Pub.: 14 Jun '16, Pinned: 16 Aug '17
Abstract: A large amount of energy is consumed in the liquefaction process of LNG and is normally disposed through heat exchange with seawater in the regasification process. In this study, a cascade Rankine cycle was optimized to recover the cold energy by applying a genetic algorithm.
Pub.: 08 Dec '16, Pinned: 16 Aug '17
Abstract: Natural gas is transported in its liquid state over long distances and thus must be gasified before use. This study focused on the alternative use of cold energy in an LNG regasification power plant integrated with a cryogenic energy storage (LPCES) system that supports variation over time. Energy demands change over time; these dynamics must be considered to improve overall energy efficiency. During off-peak times, the LNG cold energy is stored in the cryogenic energy storage (CES) system. In contrast, during on-peak times, the stored cryogenic energy is released as electricity to meet higher energy demands. To evaluate the efficiency of the proposed LPCES system, the total power used in the CES system was optimized and a thermodynamic analysis was conducted. In addition, a case study was performed to investigate the effect of the LPCES system with respect to an hourly reserve margin. The results indicated a 95.2% round-trip efficiency for the proposed LPCES system, which is higher than the efficiencies (up to 75%) offered by existing bulk power management systems using hydropower and compressed air.
Pub.: 12 Jan '17, Pinned: 16 Aug '17
Abstract: Liquefied natural gas (LNG) cold utilized micro-cogeneration systems can be used as a part of small scale LNG regasification processes. The study proposes a LNG cold utilized micro-cogeneration system which combines a Stirling engine and a micro gas turbine. The combined system is compared to a conventional micro-cogeneration system the point of thermodynamic, environmental and thermoeconomic views. Parametric studies are conducted in the ranges of 288.15–313.15 K for the ambient air temperature and 3–4 for the compressor pressure ratio, respectively. Thermodynamic efficiencies and power generation rates are studied in thermodynamic analyses while carbon dioxide emission rates and the relevant emission reductions are observed in environmental analyses. An original exergy-cost matrix is produced for the combined system and thermoeconomic comparison is performed between the combined system and the conventional micro-cogeneration system. It is found that the combined system provides 7.8% higher power generation rates whereas it has 1% and 2.4% higher energetic and exergetic efficiencies, respectively at the actual pressure ratio of the micro gas turbine. Emission reductions are observed as 3.9%, 7.8% or 8% at individual pressure ratio of 3, 3.64 or 4. The unit fuel costs are calculated for the system components and it is deduced that the combined system has higher unit fuel costs at the lower pressure ratios. It is found that the single system has roundly 25% less levelized product cost than the combined system at the actual pressure ratio. A simple graphic-based thermoeconomic optimization study demonstrates that the minimum relative cost differences are at different locations for the combined cycle.
Pub.: 09 Feb '17, Pinned: 16 Aug '17
Abstract: LNG regasification terminals are the final destination of LNG carriers. This is where the liquefied natural gas is returned to the gaseous state and fed into transmission and distribution grids. While regasification process, cryogenic LNG has a great potential for cold energy recovery. This cold energy can be used in various applications such as power generation, material freezing and sea water desalination. In this study, we used the mentioned cold energy for cryogenic air separation unit to improve the performance of this cycle. Some of the most important results of this integration are 8.04% reduction in the amount of power requirement and also 17.05% reduction in initial capital cost of ASU plant. In this paper, the required LNG flow rate for applied integration was 24.43% of ASU cycle generated oxygen flow rate. Annualized cost of system was chosen as an economic approach. A year reduction of system period of return in relation to the before integration of ASU cycle with LNG, was the most important economic result of this integration. Sensitivity analysis was done on the system economic parameters (electrical energy, oxygen and nitrogen price). The results show that the considered integration will have a more positive impact on the system period of return in higher prices of electrical energy and also in lower prices of oxygen in the market.
Pub.: 21 Mar '17, Pinned: 16 Aug '17
Abstract: Natural gas is an important primary energy carrier and plays an important role for the energy supply. The growing liquefied natural gas (LNG) market enables more flexibility in the entire natural gas market. In the regasification terminal, the LNG is regasified, stored and finally distributed to the gas grid. Usually, the low-temperature exergy of the LNG is destroyed while regasified. Alternatively, there are systems where the low temperature of the LNG is used within power systems. A further option is the integration of the regasification of LNG into an air separation process. In this paper, the concepts of integration of LNG regasification into an air separation processes are developed taking into account different possible structures of air separation units (with and without a nitrogen liquefaction block) and safety-related issues. For the evaluation of the novel concepts, exergetic and economic analyses are conducted. The results show that for safety-related concepts the exergetic efficiency is reduced from 53.4% to 51.8%. The results of the economic analysis demonstrate that the systems with a nitrogen liquefaction block are by 10% more expensive, and that the systems where the safety aspect is included are 9% less expensive.
Pub.: 12 Apr '17, Pinned: 16 Aug '17
Abstract: The Asia Pacific (AP) region has experienced huge growth in the use and trade of LNG during the last decade, which is a reflection of the overall region's policies towards low-carbon development. Japan, South Korea, Mainland China, Taiwan and India (JKCTI) are the top five importers and consumers of LNG in the world. A holistic network system stability indicator, considering various risk factors, has been constructed based on ecological network analysis (ENA) to assess the stability of LNG supplies in each of the JKCTI countries and in the overall AP region. The research revealed that the increase in the number of LNG suppliers and improvements (higher values) of the risk factors have enhanced the status of the stability of LNG supplies. A comparative ranking of the overall levels of natural gas supply security was estimated and found that Mainland China is the leader within the AP region, followed by India, Japan, South Korea and Taiwan. Furthermore, the reliability of the LNG suppliers in terms of sharing their maximum LNG supplying capacity in each of the JKCTI countries and AP region was also estimated.
Pub.: 06 Jul '16, Pinned: 16 Aug '17