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Deep sea methane electrochemical in-situ long-term monitoring technology and its significance in the ocean environmental investigation and gas hydrate exploration |
Chun-Yan SUN1, Dong-Lin WANG1,2( ), Shi-Qiang ZHANG1, Hui-Ce HE1,3, Hao ZHAO1, Fan LING4,5, Wen-Bin YIN4 |
1. School of Engineering and Technology, China University of Geosciences (Beijing), Beijing 100083, China 2. No.5 Gold Geological Party of PAP, Xi’an 710100, China; 3. Guangzhou Marine Geological Survey, China Geological Survey, Guangzhou 510075,China 4. Hunan Geo-sun High-Technology Co.,Ltd, Changsha 410208, China 5. School of Geosciences and Info-Physics of Central South University,Changsha 410083, China; |
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Abstract The continuous acquisition of dissolved methane concentration data in the deep sea has important scientific significance and practical application value for dynamic monitoring of marine environment and methane diffusion in gas hydrates development. This paper introduces key technologies of electrochemical in-situ long-term monitoring technology for deep sea methane in detail, which include the technical ideas of "seawater degassing, quantitative injection of gas samples, and high-precision electrochemical detection", the technical method of "sea water circulation controlled by supercharged drainage system, decompressed steady flow, gas-liquid separation, and improvement of high precision detection technology for hydrocarbon components". Based on the long-term monitoring experiment data obtained from bottom water in Jiaozhou Bay during 94 days, the authors studied and evaluated the technical performance, data quality and geological effect of the in-situ sensors. Some conclusions have been reached: (1) In-situ sensor has an index range of 0.01~10 000 nmol/L and sensitivity reaches 0.01 nmol/L. It has good stability and selectivity for the detection of hydrocarbon components; (2) The range of dissolved methane in the monitoring area is 19.01~106.87 nmol/L, the normal methane background is 32.41 nmol/L, and the local anomalous methane background is 80.60 nmol/L. These data show that abnormality is related to sewage discharge and seawater pollution; (3) The results of measured methane data are consistent with those obtained from previous investigation and study of seawater environment in Jiaozhou Bay, which proves that the measured data are objective and scientific; (4) The sea trial monitoring results show that the in-situ sensor is reliable in testing, reasonable in structure design and scientific in design ideas, and it basically has the capability for acquiring seawater methane concentration data in marine scientific investigation. It has practical application value and scientific significance in the dynamic monitoring of methane diffusion and long-term monitoring of deep sea methane concentration during the development of marine gas hydrate in the future.
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Received: 25 June 2018
Published: 20 February 2019
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The simple working principle of deep-sea dissolved methane in-situ long-term monitoring instrument
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The overall structure and main components of deep-sea dissolved methane in-situ long-term monitoring instrument
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Interior installation layout and physical drawings of deep-sea dissolved methane in-situ long-term monitoring instrument a—side view and top view;b—physical drawings:c—layout of components
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Interior layout plan (a) and physical map (b) of the drainage tank
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Waste pool appearance (a) and interior (b) design
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液位情况 | 液室内探针长度/cm | 液位高度/cm | 液体容积/mL | 内部气压/MPa | 初始 | | 0 | 0 | 0.101 | 接触T1 | 4.5 | 1.0 | 80 | 0.105 | 接触T2 | 4.0 | 1.5 | 146 | 0.109 | 接触T3 | 2.5 | 3.0 | 400 | 0.129 | 接触T4 | 1.0 | 4.5 | 714 | 0.168 | 液室充满 | | 5.5 | 943 | 0.210 |
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Design of waste liquid pool and liquid probe parameters
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液位情况 | 探针间电平信号 | 系统工作情况 | T1-T2 | T1-T3 | T1-T4 | 0~T1 | 高 | 高 | 高 | 不排液 | 达到T1及T1~T2间 | 高 | 高 | 高 | 不排液 | 达到T2及T2~T3间 | 低 | 高 | 高 | 启动排液,将液位排至T2以下 | 达到T3及T3~T4间 | 低 | 低 | 高 | 优先排液,将液位排至T3或T2以下 | 到达T4 | 低 | 低 | 低 | 强制排液,强制排液至T3或T2以下 |
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Automatic control design of drainage system
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Structure design of pressurized drainage pump
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Overall installation of the drainage system
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压力 /MPa | 排量 /(mL·次-1) | 电流 /A | 功率 /W | 0 | 6.8 | 0.62 | 14.88 | 7 | 6.1 | 0.71 | 17.04 | 10 | 5.6 | 0.75 | 18.00 | 15 | 5.0 | 0.81 | 19.44 | 20 | 4.5 | 0.84 | 20.16 |
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The displacement, current and power of drainage pump under different pressure
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The power (left) and the displacement (right) of drainage pump with the change of pressure
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压力/MPa | 温度/℃ | 脱气前顶空CH4浓度/(μL·L-1) | 脱气后顶空CH4浓度/(μL·L-1) | 脱气效率/% | 5 | 3~4 | 38.70 | 16.88 | 56.4 | 10 | 3~4 | 49.25 | 18.38 | 62.7 | 15 | 3~4 | 53.75 | 25.91 | 51.8 | 20 | 3~4 | 83.63 | 28.67 | 65.7 |
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Degassing efficiency of the degassing system at 5 mL/min
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柱材质 | 固定相 | 规格(长×直径) | 载气流速 | 老化 | PTFE | 1.5%阿皮松+ Al2O3颗粒(60~80目) | 1.5 m×φ3 mm | 7~8 mL/min | 马弗炉150℃ 高温老化3~5 h |
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Technical indexes of optimal chromatographic column
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Spectral peak curve of separation of methane, ethane and propane
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Schematic diagram of power supply structure
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Schematic diagram of system integration control
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Work interface of gaseous hydrocarbon detection software
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样品编号 | 甲烷传感器测试浓度/(μL·L-1) | 气相色谱仪测试浓度/(μL·L-1) | 相对误差/% | 甲烷 | 乙烷 | 丙烷 | 甲烷 | 乙烷 | 丙烷 | 甲烷 | 乙烷 | 丙烷 | 1 | 0.531 | 0.401 | 0.437 | 0.347 | 0.282 | 0.279 | 21.31 | 34.64 | 44.15 | 2 | 0.948 | 1.015 | 1.096 | 0.896 | 0.790 | 0.774 | 5.64 | 24.99 | 34.50 | 3 | 1.839 | 1.634 | 1.672 | 2.105 | 2.079 | 2.029 | 13.49 | 23.97 | 19.29 | 4 | 3.631 | 3.549 | 3.658 | 4.005 | 3.725 | 3.705 | 9.80 | 4.84 | 1.29 | 5 | 9.444 | 9.054 | 9.088 | 10.315 | 9.840 | 9.820 | 8.82 | 8.33 | 7.75 | 6 | 20.891 | 20.480 | 19.887 | 21.360 | 21.275 | 21.290 | 2.22 | 3.81 | 6.81 | 7 | 40.003 | 40.002 | 39.999 | 39.645 | 39.640 | 39.630 | 0.92 | 0.46 | 0.44 | 8 | 60.187 | 60.384 | 58.221 | 56.760 | 56.620 | 56.805 | 6.03 | 6.43 | 2.46 | 9 | 89.300 | 90.705 | 86.755 | 91.820 | 91.380 | 91.240 | 2.78 | 0.73 | 5.04 | 10 | 134.846 | 134.620 | 125.893 | 143.990 | 143.620 | 平峰 | 6.55 | 6.73 | | 11 | 150.925 | 150.899 | 142.537 | 163.350 | 平峰 | 平峰 | 7.90 | | | 12 | 175.900 | 175.100 | 164.300 | 196.050 | 平峰 | 平峰 | 10.83 | | | 13 | 181.200 | | | 146.000 | | | 21.51 | | | 14 | 214.200 | | | 174.640 | | | 20.35 | | | 15 | 308.000 | | | 251.240 | | | 22.71 | | | 16 | 300.700 | | | 260.600 | | | 14.29 | | | 17 | 453.200 | | | 371.820 | | | 19.73 | | | 18 | 463.700 | | | 380.000 | | | 19.84 | | | 19 | 539.300 | | | 463.100 | | | 15.20 | | | 20 | 738.300 | | | 585.300 | | | 23.12 | | | 21 | 1340.000 | | | 1130.300 | | | 16.98 | | | 22 | 3722.000 | | | 3262.400 | | | 13.16 | | | 23 | 6584.000 | | | 4932.500 | | | 28.68 | | |
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Sensors and gas chromatography parallel experimental data comparison
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样品 编号 | 第1次测定 值/(μL·L-1) | 第2次测定 值/(μL·L-1) | 两次测试结果/(μL·L-1) | 重复性限r (r=0.2978m0.9145) | 是否 合格 | 平均值m | 绝对差值 | 1 | 0.117 | 0.144 | 0.131 | 0.027 | 0.046 | 合格 | 2 | 0.224 | 0.322 | 0.273 | 0.098 | 0.091 | 合格 | 3 | 0.429 | 0.445 | 0.437 | 0.016 | 0.140 | 合格 | 4 | 0.982 | 0.914 | 0.948 | 0.068 | 0.284 | 合格 | 5 | 1.743 | 1.934 | 1.839 | 0.191 | 0.520 | 合格 | 6 | 3.763 | 3.499 | 3.631 | 0.264 | 0.968 | 合格 | 7 | 9.969 | 8.919 | 9.444 | 1.050 | 2.321 | 合格 | 8 | 39.743 | 40.263 | 40.003 | 0.520 | 8.690 | 合格 | 9 | 88.590 | 90.010 | 89.300 | 1.420 | 18.112 | 合格 | 10 | 151.750 | 150.100 | 150.925 | 1.650 | 29.269 | 合格 | 11 | 174.800 | 177.000 | 175.900 | 2.200 | 33.668 | 合格 | 12 | 510.000 | 509.600 | 509.800 | 0.400 | 89.090 | 合格 | 13 | 784.600 | 776.200 | 780.400 | 8.400 | 131.510 | 合格 | 14 | 1051.000 | 996.700 | 1023.900 | 54.300 | 168.570 | 合格 | 15 | 1234.000 | 1260.000 | 1247.000 | 26.000 | 201.880 | 合格 | 16 | 1401.000 | 1410.000 | 1405.500 | 9.000 | 225.220 | 合格 | 17 | 1594.000 | 1659.000 | 1626.500 | 65.000 | 257.400 | 合格 | 18 | 1894.000 | 1807.000 | 1850.500 | 87.000 | 289.640 | 合格 | 19 | 2190.000 | 2007.000 | 2098.500 | 183.000 | 324.950 | 合格 | 20 | 2180.000 | 2202.000 | 2191.000 | 22.000 | 338.020 | 合格 |
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Sensor reproducibility test data
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The comparison chart of test data from in-situ methane sensor and gas chromatograph
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The situation of sea trial of Qingdao Marine experimental station in Shandong Province a—shore monitoring platform;b—instrument for launching and release
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The distribution diagram of the dissolved methane concentration effective data in the monitoring point seawater (The straight line is segments which eliminated the fault data)
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The daily mean data distribution of dissolved methane concentration in the monitoring point seawater
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A comparison chart of the dissolved methane concentration in seawater by in-situ sensor and laboratory test
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Comparison between the daily average value of the monitoring point sensor test and the same time point of the laboratory test sample dissolved seawater methane concentration
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本次海试数据 | 测试时间 | 2017年8月~11月 | 8/8~8/15 | 9/1~9/11 | 9/18~10/31 | 9/12~9/17 | 11/1~11/9 | 天数/天 | 8 | 11 | 44 | 6 | 9 | 均值/(nmol·L-1) | 31.84 | 34.66 | 30.73 | 82.35 | 79.44 | 数据分布状态 | 中低数值 | 局部异常 | 实测甲烷数据范围及均值(nmol·L-1) | 19.01~57.73(均值32.41) | 50.62~106.87(均值80.60) | 监测点甲烷浓度均值/(nmol·L-1) | 30.32(最大值35.11) | 73.83(仅一个数据) | 无 | 文献数据 | 测试时间 | 8月~11月 | 2008年1月 | 2014年4月 | 2008年4月 | 2008年7月 | 2006年8月 | 2008年11月 | 甲烷浓度范围/(nmol·L-1) | 6.30~203.29 | 7.00~21.90 | 6.86~702.49 | 30.73~1175.00 | 11.32~23.81 | 6.85~327.44 | 数据来源 | 杨晶[34] | 赵慧敏[31] | 杨晶[34] | 杨晶[34] | 李佩佩、张桂玲[35] | 杨晶[34] |
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Test data of dissolved methane concentration in sea trials and distribution of methane concentration in seawater in Jiaozhou Bay
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