Study on pore evolution characteristics of gas adsorption and desorption in coal under the action of liquid nitrogen

Shuaiqi Dong,Dong Zhao,Lei Li,Xiaowei Li,Tao Chen 한국지질과학협의회 2023 Geosciences Journal Vol.27 No.1

CBM (Coalbed methane) belongs to unconventional natural gas mineral resources. The development and utilization of CBM can greatly reduce the occurrence of mine gas accidents, and how to improve the desorption capacity of CBM has always been a hot issue for researchers. Liquid nitrogen has obvious effect on coal seam cracking and permeability improvement. The purpose of this paper is to study the cracking mechanism of liquid nitrogen on coal, and provide a theoretical basis for using liquid nitrogen freezing and thawing to treat coal so as to improve the production of coalbed methane. Coal samples from Yangquan County, Shanxi Province were pretreated. The pore structure test, microscopic observation test and methane isothermal adsorption test were carried out after the coal samples with different particle sizes were treated with different liquid nitrogen freeze-thaw cycles. According to the experimental data, the evolution law of pores of coal before and after freezing and thawing with liquid nitrogen, the cracking mechanism of coal treated with freezing and thawing with liquid nitrogen, and the optimal number of freezing and thawing cycles with liquid nitrogen are analyzed. The results show that: 1) the evolution characteristics of pore structure of lower coal after liquid nitrogen freezing and thawing are that micropores in coal are promoted to develop into transition pores and mesopores, and mesopores and transition pores develop into macropores and fractures. 2) Through the observation of a metallographic microscope, the expansion degree of coal surface crack is positively correlated with the times of liquid nitrogen freeze-thaw. 3) Liquid nitrogen freeze-thaw treatment has an optimal number of cycles for the cracking degree of coal. With the increase of freeze-thaw cycles, the final adsorption capacity of coal pillar increases first and then decreases; The adsorption capacity of granular coal first increases and then decreases. After reaching freeze-thaw saturation, continued freeze-thaw is not conducive to the increase of adsorption capacity. These research results provide theoretical support for the implementation of liquid nitrogen fracturing and permeability enhancement technology in coal reservoirs.

액화질소를 이용한 인공동결공법 적용시 해성 점토지반의 동결속도 평가

최현준,이동섭,이효범,최항석 대한토목학회 2018 대한토목학회논문집 Vol.38 No.4

Nowadays, the artificial ground freezing (AGF) method has been used in many geotechnical engineering applications such astemporary excavation support, underpinning, and groundwater cutoff. The AGF method conducts the freezing process by employinga refrigerant circulating through a set of embedded freezing pipes to form frozen walls serving as an excavation support and cutoff wall. Two refrigerants of brine with the freezing temperature of –20~–40°C and liquid nitrogen with the freezing (evaporating) temperatureof –196°C are commonly being used in geotechnical applications. This paper performed a series of field experiments to evaluate the freezing rate of marine clay in application of the AGF method. The field experiments consisted of the single freezing-pipe test and the frozen-wall formation test by circulating liquid nitrogen, which is a cryogenic refrigerant, into freezing pipes constructed at a depth of 3.2 m in the ground. The temperature of discharged liquid nitrogen was maintained through the automatic valve, and the temperature change induced by AGF method was measured at the freezing pipes and in the ground with time. According to the experimental results,the single freezing-pipe test consumed about 11.9 tons of liquid nitrogen for 3.5 days to form a cylindrical frozen body with the volume of about 2.12m3. In addition, the frozen-wall formation test used about 18 tons of liquid nitrogen for 4.1 days to form a frozen wall with the volume of about 7.04m3. The radial freezing rate decreased with increasing the radius of frozen body because the frozen area at a certain depth is proportional to the square of the radius. The radial freezing rate was formulated as a simple equation. 최근 임시 지보, 보강 및 지하수 차수와 같은 다양한 지질공학분야에서 차수 및 지반보강 공법으로 인공동결공법(artificial ground freezing method)이 적용되고 있다. 인공동결공법은 지중에 매설된 동결관 내로 냉매를 순환시켜 대상 지반에 차수벽 및 지지체의 역할을 할 수 있는 동결벽체(frozen wall)를 형성한다. 본 연구에서는 해성 점토지반(marine clay)에 대한 인공동결공법 현장실증시험을 수행함으로서 인공동결공법에 따른 해성 점토지반에서의 동결속도(freezing rate)를 평가하였다. 현장실증시험은 지중에 3.2m 깊이로 매설된 동결관 내로 초저온 냉매인 액화질소를 순환시키는 방법으로 단일공 시험과 동결벽체 형성 시험을 수행하였다. 자동밸브를 통해 유출되는 액화질소의 온도를 일정하게 유지시켰으며, 동결과정에서 동결관 외벽 및 지중의 온도변화를 측정하였다. 시험결과, 단일공 시험은 부피가 약 2.12m3인 원기둥 모양의 동결체를 형성하는데 총 3.5일 동안 약 11.9ton의 액화질소가 소요되었고, 동결벽체 형성 시험은 부피 약 7.04m3의 동결벽체를 형성하는데 총 4.1일 동안 약 18ton의 액화질소가 소요된 것으로 산정되었다. 임의의 깊이에서 동결면적이 동결반경의 제곱에 비례하기 때문에 동결반경이 증가할수록 방사방향 1차원 동결속도가 감소하였고, 이를 바탕으로 방사방향 1차원 동결속도 예측식을 제시하였다.

An Artificial Freezing Technique to Facilitate Shield Tail Brush Replacement under High Pore-Water Pressure Using Liquid Nitrogen

Ping Yang,Jiling Zhao,Lin Li 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.4

During tunnelling, with the progression of the shield tunnelling machine, the shield tail brush, which is an important accessory required to seal the shield tail and prevent the tunnel from ground water or grouting fluid discharging, will gradually be worn-out/damaged and inevitably lead to safety problems. As a result, problematic tail brush needs to be replaced to prevent more serious problems from happening before any further tunnelling. The replacement of this shield tail brush can be very risky, especially when the shield tunnelling machine is located at a soil layer under high pore-water pressure. This study introduces an engineering practice to facilitate the shield tail brush replacement under high pore-water pressure through the development of a frozen soil wall with the help of an artificial freezing technique using liquid nitrogen. A case study is adopted to demonstrate the implementation of this technique. For the specific site condition, a numerical simulation is usually performed first to determine the design parameters (e.g., liquid nitrogen temperature, length and spacing of the freezing pipes) required for artificial freezing process. Several holes along the radial direction of the tunnel were then made to monitor the temperature of the soil around the tunnel. Subsequently, the artificial freezing process was performed according to the design. The replacement of the tail brush was initiated when the frozen soil wall developed during freezing met the requirements for tail brush replacement. The artificial freezing technique using liquid nitrogen proved to be a reliable and time-effective option to facilitate the tail brush replacement under high pore-water pressure.

Influence of In-Situ Cryogenic Freezing on Thermal and Mechanical Characteristics of Korean Marine Clay

최현준,이동섭,원종묵,이효범,최항석 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.11

The artificial ground freezing (AGF) method has been used in many geotechnical engineering applications such as temporary excavation support, underpinning and groundwater cutoff. The AGF method utilizes a refrigerant such as liquid nitrogen or brine, circulating through embedded freezing pipes in order to freeze the ground. In this paper, two in-situ cryogenic freezing experiments (i.e., single freezing-pipe test and frozen-wall formation test) were performed using liquid nitrogen to simulate the AGF in a Korean marine clay deposit, in which the freezing rate was evaluated. The thermal conductivity of frozen and unfrozen marine clay was evaluated by performing typical laboratory experiments. In addition, the strength and stiffness of frozen-thawed deposits were comparatively measured by sounding tests (i.e., piezocone penetration test and lateral loading test). The freezing rate of the frozen-wall formation test in the Korean marine clay deposit was approximately twice as high as that of the single freezing pipe test. Compared to the original marine clay deposit, the frozen-thawed marine clay showed a significant reduction in strength and stiffness.

다양한 냉동 및 해동공정 조합이 표고버섯의 품질에 미치는 영향

심준보 ( Jun Bo Shim ),조연지 ( Yeon Ji Jo ),최미정 ( Mi Jung Choi ),민상기 ( Sang Gi Min ),유선미 ( Seon Mi Yoo ),천지연 ( Ji Yeon Chun ) 한국산업식품공학회 2015 산업 식품공학 Vol.19 No.3

In this study, the potential of various freezing and thawing combinations was investigated for frozen storage of mushroom (Lentinula edodes). Lentinula edodes were sliced (5×5×50 mm) and then blanched in boiling water for 1 min. Samples were frozen by either natural air convection freezing (NCF, -24℃), air-blast freezing (ABF, -45℃), or liquid nitrogen freezing (LNF, -100℃). Frozen Lentinula edodes were thawed to a central temperature of 4℃ using either flowing water thawing (FT, 10℃), microwave thawing (MT, 400 W), sonication thawing (ST, 40 kHz, 10℃), or natural air convection thawing (NT, 20±5℃). In LNF Lentinula edodes, MT showed the most rapid thawing within 2.5 min followed by ST (30 min), FT (37 min), and NT (75 min). Quality attributes were evaluated by thawing loss, texture (hardness), water content, water holding capacity, pH, and color. A combination of LNF and MT induced the lowest thawing loss among tested combinations of each freezing and thawing. Thawing loss of frozen Lentinula edodes by LNF method was the lowest by MT. pH values NT of ABF method were significantly higher than blanched Lentinula edodes. In our study, MT minimized the quality changes of frozen Lentinula edodes when it was combined with ABF or LNF.

다양한 냉동 및 해동방법을 이용한 당근의 물리적 특성 관찰

김재형 ( Jae Hyeong Kim ),민상기 ( Sang Gi Min ),최미정 ( Mi Jung Choi ),유선미 ( Seon Mi Yoo ),조연지 ( Yeon Ji Jo ),천지연 ( Ji Yeon Chun ) 한국산업식품공학회 2015 산업 식품공학 Vol.19 No.4

This study investigated the combination effects of various freezing and thawing methods on the quality attributes of frozen carrot. Carrot samples were frozen by either individual air blast freezing (ABF, -45oC), liquid nitrogen freezing (LNF, -80oC) or natural freezing (NF, -24oC). Frozen carrots were thawed until the center temperature reached 4oC using natural air convection thawing (NT), flowing thawing (FT), sonification thawing (ST), or microwave thawing (MT). Changes in the quality of freezing and thawing combination were determined. In LNF, MT showed the most rapid thawing time (9.4 min) followed by ST (73 min), FT (87 min), and NT (84 min). LNF showed minimal thawing loss compared to those of ABF and NF (p<0.05). Hardness and water-holding capacity were decreased after all the tested combinations of freezing and thawing methods as compared to the control (blanched carrot). The highest thawing loss was observed at all the thawing combinations with NF. In the textural qualities, LNF-FT combination showed the best retention of hardness. In our study, LNF resulted in better quality attributes when it was combined with each thawing method compared to those of ABF and NF.

액체질소를 이용한 강관압입공법의 역학적 수리학적 안정화공법

지수빈(Subin Ji),이기철(Kicheol Lee),이주형(Ju-hyung Lee),김동욱(Dongwook Kim) 한국지반신소재학회 2016 한국지반신소재학회 논문집 Vol.15 No.3

본 연구에서는 강관압입 공법 적용 시 굴착 선단부에서 수리학적 또는 역학적 불안정으로 인해 발생 가능한 붕괴를 방지하는 목적으로 액체질소를 주입하여 굴착선단부를 안정화하는 공법에 관하여 연구하였다. 강관압입 공법 적용 시 오거 내 중공(中空)에 액체질소 주입관(호스)를 넣어 오거 선단부에 액체질소를 분사하는 방식을 고안하였다. 실내 실험을 위해 직경이 1,000 mm인 강관압입관을 기준으로 1/5축소 모형오거 및 토조를 제작하였다. 화강풍화토로 지반을 조성하여 함수비를 변화시켜가며 액체질소를 주입한 결과 오거 선단부에 동결 구근이 형성되어 강관압입공법 시공 시 발생 가능한 붕괴를 막을 수 있는 것으로 확인되었다. 액체질소를 이용한 동결공법은 지반이 모래일 때 보다는 소성이 있는 화강풍화토일 경우 더 효과적이었으며, 화강풍화토 지반의 경우 함수비가 최적함수비 이상일 경우 동결효율이 증가하는 것을 확인하였다. 액체질소 분사시간이 길어질수록 동결범위가 더 커졌으며 인위적으로 함수비를 급격히 증가시켜 수리학적 불안정을 유발해 보았더니 강관과 오거 전면의 지반이 약 120~300초 이내에 동결 되어 관으로 흙이 유입되지 않았으며, 차수효과가 있는 것으로 분석되었다. 이번 연구에서는 강관압입공법 안정화에 미치는 주요 인자에 대하여 액체질소를 이용하여 강관압입공법 시공 시 역학적 수리학적인 불안정이 발생할 경우, 화강풍화토 지반의 경우 붕괴를 막을 수 있는 효율적인 방법이 될 수 있다는 것을 확인하는데 큰 의의를 둔다. In this study, to prevent possible collapse caused by hydraulic or mechanical instability, liquid nitrogen injection method is developed and implemented at the tip of drilling auger of steel pipe propulsion tunneling. In this study, 1/5-scale model auger and sand chamber were manufactured. The prototype diameter of steel pile (or casing) is assumed about 1,000 mm. For the frictional sandy soils and plastic weathered soils, liquid nitrogen injection methods were tested varying water contents of the soils. For the induced hydraulic instability, the ground near the drilling auger was frozen within approximately 5 minutes preventing mechanical collapse and water infiltration. Securing stability of steel pile propulsion tunneling using liquid nitrogen was much more effective for which the water content of the soil somewhat exceeds the optimum water content.

Thermal and Mechanical Response of Soil and Tunnel during Replacement of Shield Tail Brush by Freezing Method

Xu-Yang Wang,Da-Jun Yuan,Da-Long Jin,Wei-Lin Su 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.5

In the long-distance shield tunneling process, the shield tail brush needs to be replaced after wear failure, especially in cross-river and cross-sea tunnel projects. Taking the shield tail brush replacement project of Qingchun Road tunnel in Hangzhou, China as the research background, a three-dimensional sequential thermo-mechanical coupled numerical simulation was carried out to study the shield tail brush replacement with liquid nitrogen freezing by ABAQUS software. The development of temperature fields and displacement fields of soil, and the deformations of the tunnel sections along the longitudinal direction induced by freezing were obtained. The numerical model was further validated by site measurement. In addition, the effects of the frozen wall thickness, buried depth, excavation radius, and coefficients of linear thermal expansion of soils on the frost heave were studied.

Development of a novel decal transfer process for fabrication of high-performance and reliable membrane electrode assemblies for PEMFCs

Cho, H.J.,Jang, H.,Lim, S.,Cho, E.,Lim, T.H.,Oh, I.H.,Kim, H.J.,Jang, J.H. Pergamon Press ; Elsevier Science Ltd 2011 International journal of hydrogen energy Vol.36 No.19

To improve the performance of a polymer electrolyte membrane fuel cell (PEMFC), various membrane electrode assemblies (MEAs) were fabricated by the decal process. When peeling the decal films away from a Nafion membrane, a novel liquid nitrogen (LN<SUB>2</SUB>) freezing method was employed. The results of a Fourier Transform Infrared (FTIR) analysis of the Nafion membranes demonstrate that this proposed method has no impact on the molecular structure of the Nafion polymer. In addition, the method makes it possible to achieve complete decal transferring under a wide range of hot-pressing pressures and temperatures: 9.8-15.7 MPa and 100-140 <SUP>o</SUP>C, respectively. Another approach to optimize the decal technique is to dry catalyst layers under vacuum. Catalyst layers dried under vacuum show better cell performances than atmospherically dried ones. Vacuum drying significantly facilitates the formation of small pores within Pt/C agglomerates on catalyst layers. Third, the use of Additive-A as a commercial dispersant in the catalyst ink has been investigated. From rheological characterizations, including thixotropy and catalyst ink viscosity, it is obvious that the additive plays an important role in elevating the dispersion stability of the ink. In addition, surface images of the catalyst layers revealed that the dispersing agent reduces cracks or fractures within the layers. Although adding Additive-A did not have an effect on the single-cell performance, the MEAs with the dispersant are expected to have better results for a long-term performance test of a single cell.

제대혈에서 유핵세포 분리방법에 따른 회복률

이건수,김미정,최은진,최성민 대한조혈모세포이식학회 1998 대한조혈모세포이식학회지 Vol.3 No.2

연구배경 : 제대혈 조혈모세포 이식은 혈액 및 종양질환의 치료로 여러 가지의 이점으로 인해 많은 연구와 더불어 은행화에 대한 노력이 활발히 진행되고 있다. 그러나 이식의 성공률을 향상시키기 위한 제대혈 조혈모세포의 채집 방법과 획득, 장기간 냉동보존에 대해 표준화된 방법이 아직 제시되고 있지 못한 실정이다. 이 연구는 이러한 제대혈 조혈모세포의 획득률의 향상을 위해 시도되었다. 방법 : 건강한 산모로부터 제대혈 54례를 무균적, 노출(open) 방법으로 채혈하였다. F-H법, Gelatin법, HES법으로 적혈구 제거 또는 유핵세포를 분리하여 자동세포분석기를 이용하여 획득률을 구하였다. 세 가지 방법으로 분리된 유핵세포를 각각 2%, 10% 그리고 17% FBS 농도의 배지에서 실온에서 1시간, 2시간, 3시간, 20시간 그리고 24 시간 보관 후 회복률과 비교하였다. Gelatin법과 HES법으로 적혈구를 제거한 검체들은 세포수를 L-15배지로 2배 희석하여 각각 2%, 10% 그리고 17% FBS 농도의 배지에서 실온에서 1시간, 2시간, 3시간, 20시간 그리고 24 시간 보관 후 회복률을 확인하여 세포수를 2배 희석하기 전에 회복률과 비교하였다. 세 가지 세포분리법에 의해 얻어진 유핵세포를 프로그램냉동법을 이용하여 냉동한 후 37℃ 보육기에서 해동 후 회복률을 비교하였다. 결과 : 유핵세포분리에서 F-H법으로 분리한 총 백혈구의 획득률은 27.2%, Gelatin법 71.5%, HES법 73.7%로 Gelatin법이나 HES법이 F-H법에 비해 많았으나 다핵세포 제거율은 F-H법 92.9%, Gelatin법 38.2%, HES법 32.1%로 F-H법이 Gelatin법이나 HES법에 비해 통계적으로 유의하게 높았다.(P<0.05). 16례에서 실시된 3가지 방법에 의해 분리된 단핵세포 또는 유핵세포를 2% FBS가 섞인 L-15 배지에 희석한 후 보관시간에 따른 회복률의 비교에서 F-H법과 Gelatin법에 비해 HES법에 의한 세포분리방법에 의할 때 회복률은 시간경과에 따라 더 급격히 감소하였고, 10% FBS가 섞인 L-15 배지에 희석한 후 보관시간에 따른 회복률의 비교에서는 F-H법은 회복률이 유지되는데 비해 Gelatin법과 HES법에서는 회복률의 감소를 보이고 있으나 통계적인 유의성은 없었다. 17% FBS가 섞인 L-15 배지에 희석한 후 보관시간에 따른 회복률의 비교에서는 F-H법, Gelatin법 그리고 HES법에서 모두 회복률의 감소를 보였다. Gelatin법과 HES법에서 세포 수를 2배 희석하여 각각 2%, 10% 그리고 17%농도의 FBS가 섞인 L-15배지에 희석한 후 보관시간에 따른 회복률은 세포 수를 희석하기 전과 비교하여 통계적으로 유의한 차이를 보이지는 않았다. F-H법, Gelatin법, HES법으로 분리한 유핵세포를 프로그램냉동법으로 냉동하고 37℃에서 해동하였을 때 회복률은 각각 85.8%, 65.3%, 72.7%로 통계적으로 유의하기는 않았다. 결론 : 유핵세포분리는 Gelatin법이나 HES법이 F-H법에 비해 많았으나, 조혈모세포 이식에 불필요한 적혈구와 다핵세포의 제거율이 낮았고, 보관시간이 길수록 회복률의 감소가 현저했으며, F-H법에 의해 단핵세포를 분리한 검체를 10% FBS 농도의 배지에 보관했을 때 비교적 회복률이 유지되었다. 그러므로 세포분리 방법에 상관없이 냉동보존 전의 보관시간이 짧을수록 더 높은 회복률을 얻을 수 있었다. 프로그램냉동법을 이용하고 급속 해동을 실시할 경우 단핵세포 또는 유핵세포 분리방법에 따른 회복률의 차이는 없었다. Background: Human umbilical cord blood contains sufficient numbers of hematopoietic stem cells to provide long-term engraftment in the unrelated recipient with several advantages. The number of hematopoietic stem cells is an important factor for better results in transplantation. The purpose of this study is the development of a technique for the collection, separation and cryopreservation of the cord blood mononuclear cells for transplantation. Methods: Fifty four cord bloods were collected during deliveries at Kyungpook National University Hospital and Hana Hospital, Taegu, Korea from May, 1997 to May, 1998. The mononuclear cell separation by Ficoll-Hypaque (F-H) or red cell sedimentation by 3% Gelatin or 6% Hydroxyethyl Starch (HES) was done and the number and recovery rates were compared with hemocytometry. The recovery rates of separated cells by different cell separation methods in the L-15 medium containing 2%, 10% or 17% FBS before cryopreservation according to the suspension time were compared. The recovery rates of separated cells by Gelatin or HES which were diluted two times in the L-15 medium containing 2%, 10% or 17% FBS were compared as the same way. The recovery rates according to different cell separation methods after a programmed freezing method and thawing in the incubator were compared. Results: The mean volume of collected cord blood was 121 mL (80-155 mL). The removal of red blood cell was 99.4% by F-H, 79.6% by Gelatin and 70.3% by HES. The mononuclear cell separation was 52.6±27.2% by F-H, 91.1±28.9% by Gelatin and 89.4±27.8% by HES. The removal of polymorphonuclear cell was 92.9% by F-H, 38.2% by Gelatin and 32.1% by HES. The recovery rates of separated cells by Gelatin or HES in the L-15 medium containing 2%, 10% or 17% FBS before cryopreservation were gradually decreased according to the longer suspension time, and those by F-H in the L-15 medium containing 2% or 17% FBS before cryopreservation were also gradually decreased, but those by F-H in the L-15 medium containing 10% were relatively maintained up to 24 hours (P<0.01). The recovery rates of two times diluted separated cell concentration by Gelatin or HES in the L-15 medium containing 2%, 10% or 17% FBS were also decreased according to the longer suspension time as those of the initially separated cell concentration were done. The recovery rate after programmed freezing and thawing was 85.8% by F-H, 65.3% by Gelatin and 72.7% by HES. Conclusion: The nucleated cell separation by 3% Gelatin or 6% HES showed better yield than F-H. The red cell and polynuclear cell contaminations were higher in the former two methods. The recovery rates of separated cells were not significantly decreased in the 10% FBS by F-H method. The shorter the suspension time before cryopreservation, the better the recovery rate of separated cells regardless of cell separation methods. The programmed freezing showed good recovery rates of cells after thawing. These will be important factors in raising the success rate in hematopoietic stem cell transplantation.