زنجیره انرژی مایع برای حمل و نقل و استفاده از گاز طبیعی برای تولید برق با جذب CO2 و ذخیره سازی - قسمت 4: تجزیه و تحلیل حساسیت از فشارهای حمل و نقل و تعیین معیار با تکنولوژی های معمولی برای حمل و نقل گاز

A novel energy and cost effective transport chain for stranded natural gas utilized for power production with CO2 capture and storage is developed. It includes an offshore section, a combined gas carrier and an integrated receiving terminal. In the offshore section, natural gas (NG) is liquefied to LNG by liquid carbon dioxide (LCO2) and liquid inert nitrogen (LIN), which are used as cold carriers. In the onshore process, the cryogenic exergy in the LNG is utilized to cool and liquefy the cold carriers, LCO2 and LIN. The transport pressures for LNG, LIN and LCO2 will influence the thermodynamic efficiency as well as the ship utilization; hence sensitivity analyses are performed, showing that the ship utilization for the payload will vary between 58% and 80%, and the transport chain exergy efficiency between 48% and 52%. A thermodynamically optimized process requires 319 kWh/tonne LNG. The NG lost due to power generation needed to operate the LEC processes is roughly one third of the requirement in a conventional transport chain for stranded NG gas with CO2 capture and sequestration (CCS).

The liquefied energy chain (LEC) is a novel energy and cost effective transport chain for stranded natural gas utilized for power production with CO2 capture and storage, which includes an offshore section, a combined gas carrier, and an integrated receiving terminal, see Fig. 1. In the offshore section, natural gas (NG) is liquefied to LNG by liquid carbon dioxide (LCO2) and liquid inert nitrogen (LIN), which are used as cold carriers. The nitrogen is emitted to the atmosphere at ambient conditions. The CO2 at high pressure is transferred to an offshore oilfield for enhanced oil recovery (EOR). LNG is transported to the receiving terminal in the combined carrier. Full-size image (28 K) Fig. 1. The liquefied energy chain. Figure options At the receiving terminal, the cryogenic exergy in LNG is recovered by liquefaction of CO2 and nitrogen. The onshore process is connected to an air separation unit (ASU) that produces nitrogen for the offshore process and oxygen for an oxyfuel power plant, where NG is converted to electricity, CO2 and water. The water is removed by condensation from the CO2 which is compressed to a pressure above the triple point (TP) and liquefied by vaporization of the remaining LNG. The LCO2 and LIN are transported offshore in a combined gas carrier. Transporting CO2 and LNG in the same ship results in an enhanced ship utilization. This paper is the last in a series of four papers that describe the liquefied energy chain. The first paper describes the concept and summarizes the results from the remaining three [1]. The second paper addresses the offshore and onshore processes [2]. The third paper describes the combined carrier [3]. This paper contains a general description of the thermo-mechanical exergy of LNG, LIN and LCO2, sensitivity analyses of the ship utilization and exergy efficiencies as a function of transport pressures, as well as a benchmarking against conventional technologies for gas transport.

The liquid energy chain is an integrated transport chain for utilization of stranded NG for power production with CO2 capture and use of CO2 for EOR. By using LIN and LCO2 as cold carriers, LNG can be produced offshore without extra power requirements and therefore no CO2 emissions. It is found that the transport pressures will influence the efficiencies of the onshore and offshore process as well as the simple transport chain. The transport pressure will also influence the ship utilization. The thermodynamically optimal transport pressures are 5.5 bar for LCO2, 6 bar for LIN and 1 bar for LNG. At these pressures, 1 kg of LNG requires 0.95 kg LIN and 2.21 kg LCO2. Hence a 12 250 m3 ship will be able to transport 8330 m3 LNG to shore and requires 7180 m3 LCO2 and 5070 m3 LIN from shore to the field, giving a ship utilization of 63.4% and a CO2 sequestration rate of 85%. With these assumptions, the chain requires 319 kWh/tonne NG and gives a total efficiency of 46.4%; which is 4.4% points higher than a conventional transport chain for utilization of stranded NG with CCS. Compared to conventional ship based concepts the LEC will increase the power production with 6%, which is important both from a cost and resource perspective.