논문 DOI: http://dx.doi.org/1.293/kfma.213.16.1.6 ISSN (Print): 2287-976 셰일가스플랜트용수처리를위한직접접촉막증발법적용가능성연구 구재욱ㆍ한지희 * ㆍ이상호 * ㆍ홍승관 *1) **2) A Feasibility Study on Shale Gas Plant Water Treatment by Direct Contact Membrane Distillation Jae-Wuk Koo *, Jihee Han *, Sangho Lee *, Seungkwan Hong ** Key Words : Shale gas( 셰일가스 ), Membrane distillation( 막증발법 ), Water treatment( 수처리 ), Plant( 플랜트 ) ABSTRACT Non-conventional oil resources such as shale gas are becoming increasingly important and have drawn the attention of several major oil companies all over the world. Nevertheless, the market-changing growth of shale gas production in recent years has resulted in the emergence of environmental and water management challenges. This is because the water used in the hydraulic fracturing process contains large amount of pollutants including ions, organics, and particles. Accordingly, the treatment of this flowback water from shale gas plant is regarded as one of the key technologies. In this study, we examined the feasibility of membrane distillation as a treatment technology for the water from shale gas plants. Direct contact membrane distillation (DCMD) is a thermally-driven process based on a vaper pressure gradient across a hydrophobic membrane, allowing the treatment of feed waters containing high concentration of ions. Experiments were carried out put in the lab-scale under various conditions such as membrane types, temperature difference, flow rate and so on. Synthetic feed water was prepared and used based on the data from literature. The results indicated that DCMD is suitable for treating not only low-range flowback water but also high-range flowback water. Based on the theoretical calculation, DCMD could have over 8% of recovery. Nevertheless, organic pollutants such as oil and surfactant were identified as serious barriers for the application of MD. Further works will be required to develop the optimum pretreatment for this MD process. 1. 서론 최근 Shale gas 등의비전통석유자원플랜트기술이세계적으로적용되고있으며, 앞으로그규모는더욱커질것으로전망되고있다. 비전통석유자원은전통적인방식으로는추출이불가능했으나기술발전과채산성개선에힘입어생산가능하게된석유자원이며, 풍부한매장량을가지고있기때문에향후국제석유시장에미치는파급력이커질것으로기대되고있다. (1) 지금까지비전통석유자원관련기술은효율적으로오일이나가스를수집하는측면이강조되어왔 * 국민대학교건설시스템공학과 ** 고려대학교건축사회환경공학과 교신저자, E-mail : sanghlee@kookmin.ac.kr 다. 그러나기술의확대적용으로인하여용수의공급과폐수의배출이환경에미치는영향에대한우려가확산되고있다. 따라서향후에는이를해결하지못하는경우실제현장적용이불가능할것으로전망된다. (2,3,4,) Shale gas 의경우에는채굴과정에서화학물질을첨가한물을대량사용해지하수를오염시킬우려가있으며, 수자원의낭비및오염된폐수처리의어려움을가지고있다. 또한다량의이온을포함하고있어기존의방법으로는처리가어려운것으로알려져있다. (6,7,8,9) 이러한문제점을해결하기위해본연구에서는 Shale gas 플랜트용수처리를위한기술로서직접접촉막증발법 (Direct Contact Membrane Distillation) 을적용하였다. 직접접촉막증발법 (Direct Contact Membrane Distillation) 은물의온도차에따른증 212 유체기계연구개발발표회발표논문, 212 년 12 월 -7 일, 부산 6 한국유체기계학회논문집 : 제 16 권, 제 1 호, pp. 6~6, 213( 논문접수일자 : 212.1.19, 심사완료일자 : 212.1.7)
셰일가스플랜트용수처리를위한직접접촉막증발법적용가능성연구 기압차를이용하여다공성막의미세공극을통해원하는물질을분리또는제거할수있고, 고순도의물을얻을수있다는장점을가지고있다. 또한, 막증발법 (MD) 은담수화와식품산업뿐만아니라많은응용분야에서광범위하게사용될수있는가능성을가지고있다. 본연구에서는직접접촉막증발법 (DCMD) 공정의적용가능성을확인하고자실험실규모의실험을수행하였으며, 이를바탕으로실제적용시에발생할수있는문제들을미리확인하고자하였다. 2. 실험방법 본연구는실험실규모로수행되었고, 실험장치구성은 Fig. 1에나타난바와같다. 여러가지막증발법운전방식중에서본연구에서는직접접촉막증발법 (DCMD) 을적용하였으며, 이를위하여유효막면적이 인소형의평판형모듈을직접제작하여사용하였다. 막증발법을위한분리막으로는 Millipore 사의 polyvinylidene fluoride 막 ( 세공크기.22um) 을사용하였으며, 유입수와처리수의유입온도는각각 6 와 2 로고정하였다. 또한펌프로순환되는유입수와처리수의유량은 1.:1 의비율로정하여각각 4ml/min, 26ml/min 으로고정하여실험을실시하였다. 기타자세한실험조건은 Table 1에나타난바와같다. 셰일가스플랜트용수는 Table 2 (1) 과같이성분들의농도를고려하여직접제조하였다. 농도범위에따라 3가지종류의합성유입수를각각조제하여실험을수행하였다. 또한실제폐수의오일및유지성분을모사하기위해서는수용성절삭유를포함한합성유입수도같이제조하여실험을수행하였다. Fig. 1 Laboratory-scale MD system schematic diagram photography of the system Table 1 Summary of experimental conditions Item Condition Operation type DCMD membrane PVDF.22um Effective membrane area 12.2 cm 2 Cross-flow velocity Solution Temperature Feed Permeate Feed.4 L/min.26 L/min Low, Medium, High range flowback water D.I water Permeate Feed side 6 Permeate side 2 Table 2 Range of constituents in flowback water from development in the Marcellus Shale, USA (1) Constituent Low (mg/l) Medium (mg/l) High (mg/l) Total dissolved solids 66,, 261, Total suspended solids 27 38 32 Hardness (as ) 91 29,, Alkalinity (as ) 2 2 11 Chloride 32, 76, 148, Sulfate - 7 Sodium 18, 33, 44, Calcium 3 98 31, Strontium 14 21 68 Barium 23 33 47 Bromide 72 12 16 Oil and grease 1 18 26 한국유체기계학회논문집 : 제 16 권, 제 1 호, 213 7
구재욱ㆍ한지희ㆍ이상호ㆍ홍승관 3. 결과및고찰 log (1) Cond(ms/cm) 3 2 1 Low Range Medium Range High Range P: vapor pressure (mmhg) A: constant (=8.7131 mmhg) B: constant (=173.63 oc) C: constant (=233.426 oc) T: Temperature (oc) 16 14 1 2 3 4 염농도가증기압에미치는영향은다음의식으로고려할수있다. (12) (2) 12 Flux(LMH) 1 8 6 4 Pa: vapor pressure of feed water(mmhg) Pw: vapor pressure of pure water(mmhg) S: salinity (=g/kg) 2 1 2 3 4 Low Range Medium Range High Range Fig. 2 Effect of constituents range on water flux and feed conductivity in DCMD of synthetic flowback water in shale gas plants. Flux Feed water conductivity 식 (1) 과 (2) 를이용하여계산한증기압의차이와플럭스와관계를도시한결과 Fig. 3 와같은관계를얻을수있었다. 예상한바와같이증기압과플럭스가어느정도선형적인비례관계를보이는것을알수있다. Fig. 2는직접접촉막증발법 (DCMD) 에서오일및유지성분을포함하지않고제조한세일가스플랜트용수의성분범위에따라물의투과속도와유입수의전기전도도의변화를나타낸결과이다. 유입수를성분범위에따라 DCMD 로처리한결과, 유입수의농도가낮을수록물의투과속도가증가하는것을나타났다. 전기전도도값을측정한결과모든경우에서 99.99% 의높은제거율을나타냈다. Table 2에나타난조성을이용하여세가지종류의합성유입수의삼투압을계산한결과각각 44bar, bar, 161bar 으로나타났다. 따라서 Low range 의 flowback water 를제외하면역삼투공정의적용자체가불가능한것으로판단되었다. 반면 DCMD 를적용한결과 Fig. 3 에나타난바와같이플럭스는삼투압과거의영향을받지않고 1 12 L/(m 2 ㆍhr) 의값을나타내었다. DCMD 의플럭스는증기압에비례하는특성을가지고있으며, 물의증기압은온도와염농도의함수로표현할수있다. 따라서주어진조건을바탕으로다음과같은 Antoine equation 을적용하면각경우에서의이론적인증기압을계산할수있다. (11) Average Flux of MD (L/m 2 -hr) Average Flux of MD (L/m 2 -hr) 1 2 4 6 8 1 12 14 16 18 Osmotic Pressure of Feed Water (bar) 1.13.14..16.17 Difference in Vapor Pressure (bar) Fig. 3 Dependence of MD flux on osmotic pressure and vapor pressure difference. Flux vs. osmotic pressure Flux vs. vapor pressure difference 8 한국유체기계학회논문집 : 제 16 권, 제 1 호, 213
셰일가스플랜트용수처리를위한직접접촉막증발법적용가능성연구 Fig. 4는유입수의염농도가증기압에미치는영향을고려하여, 실제 MD 공정의회수율을얼마나높일수있는지를계산한결과이다. Medium range 의합성유입수에대하여계산해본결과회수율 7% 까지는플럭스의감소가크게나타나지않지만 8% 이상에서는플럭스가감소하여정상적인운전이불가능할것으로예상되었다. 지금까지의결과는합성유입수내의이온성분에의한영향만을고려해서 MD 의적용성을분석한것이다. 실제 flowback water 에는이온외에도오일과첨가제등다량의유기물이존재하므로, 이에의한영향을살펴볼필요가있다. 따라서위의합성유입수에오일성분을추가한후에 MD 실험을수행하였다. Flux (L/m 2 -hr) 1 2 4 6 8 1 Recovery (%) Fig. 4 Dependence of MD flux on osmotic pressure and vapor pressure difference. Flux vs. osmotic pressure Flux vs. vapor pressure difference Fig 는오일및유지성분의수용성절삭유를포함하여제조한합성유입수를 DCMD 에적용하여, 물의투과속도와처리수의전기전도도를나타낸결과이다. 초기에는상대적으로높은플럭스를나타내었으나, 유입수의완전히녹지않은유지성분이 MD 막의표면에급속도로쌓이면서물의투과유속을감소시켰고, 수용성절삭유에함유된계면활성제에따라 MD 막이 wetting 되어, 처리수의전기전도도가증가하였다. 따라서오일성분과계면활성제등이들어있는경우에는 MD 의적용이어려울것으로판단되었다. 4. 결론본연구에서는셰일가스플랜트의용수관리를위한새로운공정으로 DCMD 를적용하는방법에대하여다루었다. 우선이온성분만을고려할때높은삼투압에도불구하고 DCMD 를이용하여성공적으로유입수를처리할수있는것으로나타났다. 반면에오일및유지성분이같이있는경우에는오일과계면활성제가 MD 막을 wetting 시킴에따라, 성능이빠르게감소하는현상이나타났다. 따라서이러한경우에는적절한전처리가없이는 DCMD 로셰일가스플랜트용수를적용하기어렵다는것을확인하였다. 따라서셰일가스플랜트용수처리를위한 MD막공정과전처리공정에대한많은연구가필요한것으로사료된다. 참고문헌 Product water concentration (us/cm) Flux (kg/m 2 -hr) 12 Averge Flux 1 8 6 4 2 2 4 6 8 1 12 14 1 Permeate water 8 6 4 2 1 2 3 4 Fig. Dependence of MD flux on osmotic pressure and vapor pressure difference. Flux vs. osmotic pressure Flux vs. vapor pressure difference (1) 한원희, 212, 셰일가스 (shale Gas) 개발현황및전망, 전기저널, Vol. 429, pp. 46 2 (2) JENKINS, C D, and BOYER, C M I., 28, Coalbed-and shale-gas-reservoirs, Journal of Petroleum Technology, Vol. 6, pp. 92 99. (3) GREGORY, K. B., VIDIC, R. D., and DZOMBAK, D. A., 211, Global Water Sustainability: Water management challenges associated with the production of shale gas by hydraulic fracturing, ELEMENTS, Vol. 7, pp. 181 186. (4) ARTHUR, J. D., BOHM, B., COUGHLIN, B. J., and LAYNE, M., 29, Evaluating the environmental implications of hydraulic fracturing in shale gas reservoirs, SPE Americas E&P Environmental and Safety Conference, San Antonio, Texas, Society of Petroleum Engineers. () A.B. Hubbard, 1971, Method for Reclaiming Waste Water from Oil Shale Processing, ACS Division of Fuel Chemistry, Preprint. (6) J. Arthur, B. Bohm, D. Cornue, 29, Environmental considerations of modern shale gas development, SPE Annual Technical Conference and Exhibition, 4-7. (7) LAPIDUS, A., KRYLOVA, A., and TONKONOGOV, B., 2, Gas chemistry: Status and prospects for 한국유체기계학회논문집 : 제 16 권, 제 1 호, 213 9
구재욱ㆍ한지희ㆍ이상호ㆍ홍승관 development, Chemistry and Technology of Fuels and Oils, Vol. 36, pp. 82 88. (8) WOOD, R., GILBERT, P., SHARMINA, M., ANDERSON, K., FOOTITT, A., GLYNN, S., and NICHOLLS, F., 211, Shale gas: a provisional assessment of climate change and environmental impacts, Tyndall Centre for Climate Change Research. (9) ZOBACK, M., KITASEI, S., and COPITHORNE, B., 21, Assessing the environmental risks from shale gas development, The role of natural gas in a lowcarbon economy. (Worldwatch Institute.) (1) Gregory, K. B., Vidic, R. D., and Dzombak, D. A., 211, Water management challenges associated with the production of shale gas by hydraulic fracturing, ELEMENTS, Vol. 7, pp. 181 186. (11) K.W. Lawson, D.R. Lloyd, 1996, Membrane distillation. II. Direct contact MD, Journal of Membrane Science, Vol. 12, pp. 123 133. (12) A. Alkhudhiri, N. Darwish, N. Hilal, 212, Membrane distillation: A comprehensive review, Desalination 287, pp. 2 18. 6 한국유체기계학회논문집 : 제 16 권, 제 1 호, 213