Engineering consideration of surface facilities for a candidate CCS demonstration project in Japan

AbstractThis paper presents the results of careful considerations on the surface facilities at one of the most promising CCS (Carbon dioxide Capture and Storage) candidate sites in Japan in regards to process, economy and energy consumption. This site has been selected to demonstrate the feasibility of CCS total system in which CO2 is captured from natural gas processing plants, transported to the injection site (100 km away from the plants), and then stored in the saline aquifers underneath the seabed of the Japan Sea. Four technical issues have been reviewed for the surface facilities, namely CO2 transportation, removal of impurities in the CO2 gas, the liquefied CO2 heater models and the shaft seal system for CO2 pumps.As for the CO2 transportation method, tanker trucks transportation is selected compared to pipelines because of the merits in a construction period, economy, and local citizen’s understanding and acceptance which are crucial for the realization of the project. Concerning process building, removal of impurities contained in the CO2 gas has been considered first. CO2 gas separated from natural gas contains hydrogen sulfide, mercury, and BTX in addition to water. These impurities must be eliminated prior to liquefaction of CO2 because they could interfere with the process as well as for environmental considerations. The adsorption method is found to be effective for removing all these impurities. However, it is also found that adsorbent consumption rate depends largely on the process sequence with which the impurities are eliminated. After reviewing the results, it is found that the most economical sequence to eliminate these impurities is in the order of mercury, hydrogen sulfide, BTX, then water.Liquefied CO2 heater models have been considered to reduce CO2 emission. After transportation to the injection site, the liquefied CO2 is pressurized and heated from −10 °C to a super critical state of 40 °C in order to avoid phase transition inside the injection tube. Using a heat pump to utilize the heat in the air to improve the energy efficiency, CO2 emission is substantially reduced by approximately 70% compared to the conventional method using hot water from a boiler that uses heavy fuel oil.A centrifugal pump will be selected for CO2 pumps because it can handle large volumes. An effective shaft seal system is the tandem formation using vapor-liquid seal and dry gas seal for the first and the second stages respectively. However, since we have limited experience of this formation at CO2 pumps in Japan, it is identified as a critical item in the demonstration project