報告書番号

U92062

タイトル（和文）

二酸化炭素の深海処分技術（その１）－構想の提示と環境影響評価手法の検討－

タイトル（英文）

DEEP OCEAN DISPOSAL OF CARBON DIOXIDE(PART 1) DISPOSAL STRATEGIES FOR MINIMIZING ENVIRONMENTAL IMPACT AND A METHOD FOR ASSESSING CARBON-DIOXIDE BEHAVIOR IN DEEP-SEA ENVIRONMENTS

概要 （図表や脚注は「報告書全文」に掲載しております）

二酸化炭素（ＣＯ２）の深海処分方策に関し，その構想を提示し，環境への影響を論ずる前提となる物理化学過程を基礎的に検討した。深海底へと貯留し周辺環境への溶け出し速度が小さいことを期待する方策とは別に，太平洋中層水に溶解希釈する方策を提案し両者を比較した。従来，高圧ＣＯ２水溶液のＣＯ２の部分モル体積（ＶＣＯ２）の直接的な測定値の報告は無かった。３４．３ＭＰａ，３．０度の条件で，ＣＯ２水溶液の密度測定を実施し，ＶＣＯ２＝３０．５立方ｃｍ／ｍｏｌｅの値を得た。溶存ＣＯ２濃度１Ｍあたりの密度増加値は１２．９ｋｇ／立方ｍである。また，深海底から実際に採取した炭酸塩堆積物を用いて液体ＣＯ２の共存下で炭酸塩の溶解が進むことを実験的に確認した。深海底の条件で液体ＣＯ２溜りから溶出したＣＯ２の底層水中での挙動を模擬する計算モデルを作成し，ＣＯ２溶解に伴う密度増加効果および炭酸塩との中和の効果を検討した

概要 （英文）

TO ASSESS THE TECHNICAL AND ENVIRONMENTAL FEASIBILITY OF DEEP OCEAN DISPOSAL OF CO2 RECOVERED FROM FLUE GASES IN ELECTRIC POWER PLANTS,THIS PAPER REPORTS THE PHYSICO-CHEMICAL PROCESSES CONTROLLING THE BEHAVIOR OF SOLUTE CO2 IN THE DEEP OCEAN. CO2 OCEAN DISPOSAL SHOULD BE BASED ON AN UNDERSTANDING OF THE GEOCHEMICAL CYCLE OF CARBON. FROM THE STANDPOINT OF GEOCHEMISTRY,THE CONCEPT OF ISOLATING CO2 IN THE OCEAN CAN BE CLASSIFIED INTO TWO TYPES:DISSOLUTION AND STORAGE. A NOVEL DISPOSAL STRATEGY MINIMIZING THE IMPACT ON BENTHIC ORGANISMS ISPROPOSED. OCEAN INJECTION OF CO2 DILUTED IN SITU WITH SEAWATER BY A FACTOR OF CA. 300 ON A WEIGHT BASIS AT 1000M IN THE INTERMEDIATE DEEP WATER MASS OF THE NORTH PACIFIC OCEAN WOULD BE A COMPROMISE OF LONG-TERM SEQUESTRATION OF CO2 IN THE OCEAN WITH A POSSIBLE HAZARDOUS IMPACT ON THE OCEANIC SEABED ECOSYSTEM. ALTHOUGH THE CO2-ENRICHED,LOW-PH SEAWATER MASS IS HEAVIER THAN AMBIENT SEAWATER,IT COULD NOT REACH THE BOTTOM DUE TO INSUFFICIENT DENSITY CONTRAST. NO EXPERIMENTAL DATA HAS BEEN REPORTED ON THE PARTIAL MOLAR VOLUME(VCO2)OF CO2 IN AQUEOUS SOLUTION UNDER HIGH PRESSURES. WE DETERMINED THE VCO2 TO BE 30.5 CM3/MOLE AT 34.3 MPA AND3 FROM DENSITY MEASUREMENTS OF WATER CONTAINING AMOUNTS OF DISSOLUTE CO2. THE PRESENT LABORATORY EXPERIMENT,COUPLED WITH COMPUTER SIMULATION,CLEARLY SHOWS THAT THE DENSITY INCREASE OF SEAWATER NEAR A LIQUID CO2 POOL FORMED ON THE OCEAN SEATED AT DEPTHS GREATER THAN 3KM WOULD CAUSE THE SOLUTE CO2 TO CRAWL OVER THE OCEAN FLOOR. A SHIPBOARD EXPERIMENT SHOWED THAT FRESHLY-RECOVERED SEDIMENT RICH IN CARBONATE REACTS WITH LIQUID CO2 UNDER HIGH-PRESSURE CONDITIONS,THUS SUPPORTING INTRODUCTION OF THE SINK TERM FOR THE SOLUTE CO2 IN THE ABOVE-MENTIONED COMPUTER SIMULATION CODE.

報告者

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