• 한국환경과학회:학술대회논문집
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• 한국환경과학회 1998년도 봄 학술발표회 프로그램
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• pp.144-153
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• 1998

Sorbents of calcined limestone and oyster particles having a diameter of about 0.63mm were exposed to simulate fuel gases containing 5000ppmv H2S for temperatures ranging from 600 to 800C in a TGA. The reaction between CaO and H2S proceds via an unreacted shrinking core mechanism. The sulfidation rate is likely to be controlled primarily by countercurrent diffusion through the product layer of calcium sulfide(CaS) formed. The kinetics of the sorption of H2S by CaO is sensitive to the reaction temperature and particle size, and the reaction rate of oyster was faster than the calcined limestone.

• 한국환경과학회지
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• 제8권1호
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• pp.125-133
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• 1999

Sorbents of calcined limestone and oyster particles having a diameter of about 0.63mm were exposed to simulated fuel gases containing 5000ppm $H_2S$ for temperatures ranging from 600 to 80$0^{\circ}C$ in a TGA (Thermalgravimetric analyzer). The reaction between CaO and $H_2S$ proceeds via an unreacted shrinking core mechanism. The sulfidation rate is likely to be controlled primarily by countercurrent diffusion through the product layer of calcium sulfide(CaS) formed. The kinetics of the sorption of $H_2S$ by CaO is sensitive to the reaction temperature and particle size, and the reaction rate of oyster was faster than the calcined limestone.

• Geomechanics and Engineering
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• 제35권2호
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• pp.121-133
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• 2023

The demand for cement and limestone crushed materials has increased many folds due to the tremendous increase in construction activities in Pakistan during the past few decades. The number of cement production industries has increased correspondingly, and so the rock-blasting operations at the limestone quarry sites. However, the safety procedures warranted at these sites for the blast-induced ground vibrations (BIGV) have not been adequately developed and/or implemented. Proper prediction and monitoring of BIGV are necessary to ensure the safety of structures in the vicinity of these quarry sites. In this paper, an attempt has been made to predict BIGV using artificial neural network (ANN) at three selected limestone quarries of Pakistan. The ANN has been developed in Python using Keras with sequential model and dense layers. The hyper parameters and neurons in each of the activation layers has been optimized using randomized and grid search method. The input parameters for the model include distance, a maximum charge per delay (MCPD), depth of hole, burden, spacing, and number of blast holes, whereas, peak particle velocity (PPV) is taken as the only output parameter. A total of 110 blast vibrations datasets were recorded from three different limestone quarries. The dataset has been divided into 85% for neural network training, and 15% for testing of the network. A five-layer ANN is trained with Rectified Linear Unit (ReLU) activation function, Adam optimization algorithm with a learning rate of 0.001, and batch size of 32 with the topology of 6-32-32-256-1. The blast datasets were utilized to compare the performance of ANN, multivariate regression analysis (MVRA), and empirical predictors. The performance was evaluated using the coefficient of determination (R²), mean absolute error (MAE), mean squared error (MSE), mean absolute percentage error (MAPE), and root mean squared error (RMSE)for predicted and measured PPV. To determine the relative influence of each parameter on the PPV, sensitivity analyses were performed for all input parameters. The analyses reveal that ANN performs superior than MVRA and other empirical predictors, andthat83% PPV is affected by distance and MCPD while hole depth, number of blast holes, burden and spacing contribute for the remaining 17%. This research provides valuable insights into improving safety measures and ensuring the structural integrity of buildings near limestone quarry sites.

• 공업화학
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• 제5권5호
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• pp.836-842
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• 1994

가스분사반응기(Jet bubbling reactor)에서의 가스분사관의 최적 설계조건과 $SO_2$ 제거효율에 미치는 운전변수들의 영향을 검토하였다. 효과적인 기-액 접촉을 위한 가스분사관의 설계에 있어서 가장 중요한 인자는 Reynolds number로서 Reynolds number를 12,000 이상으로 하고 가스분사관과 가스분사구멍에서의 Reynolds number가 동일하게 되도록 가스분사관을 설계하는 것이 가스분사관 설계의 최적조건인 것으로 판단된다. ${\Delta}P$, pH, 유입 $SO_2$농도, 석회석 입자크기 등 공정의 운전변수 중에서 $SO_2$ 제거효율에 가장 큰 영향을 미치는 변수는 ${\Delta}P$였으며 pH 4.0하에서 90% 이상의 $SO_2$ 제거효율을 얻기 위해서는 ${\Delta}P$를 230mmAq 이상으로 유지시켜야 하였다. 실험결과 3.0 정도의 낮은 pH 하에서도 높은 $SO_2$ 제거효율이 얻어졌으며 이러한 이유는 강제산화에 의해 흡수액내의 $HSO{_3}{^-}$이온이 $SO{_4}{^{2-}}$ 이온으로 거의 완전한 산화가 일어나 흡수액 내의 $SO_2$ 평형분압이 매우 낮은 상태로 유지되었기 때문으로 생각된다. 또한 흡수액의 pH 5.0 이하의 조건에서는 $SO_2$ 흡수에 사용된 석회석의 입자크기에 관계없이 모두 99.5% 이상의 높은 석회석 이용률을 나타내었다.

• Advances in concrete construction
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• 제2권1호
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• pp.13-27
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• 2014

The principal objective of this study is to deepen the characterization studies already led on sand concretes in previous works. Indeed, it consists in studying the effect of the sand type on the main properties of sand concrete: fracture and mechanical properties. We particularly insist on the determination of the fracture characteristics of this material which apparently have not been studied. To carry out this study, four different types of sand have been used: dune sand (DS), river sand (RS), crushed sand (CS) and river-dune sand (RDS). These sands differ in mineralogical nature, grain shape, angularity, particle size, proportion of fine elements, etc. The obtained results show that the particle size distribution of sand has marked its influence in all the studied properties of sand concrete since the sand having the highest diameter and the best particle size distribution has given the best fracture and mechanical properties. The grain shape, the angularity and the nature of sand have also marked their influence: thanks to its angularity and its limestone nature, crushed sand yielded good results compared to river and dune sands which are characterized by rounded shape and siliceous nature. Finally, it should further be noted that the sand concrete presents values of fracture and mechanical properties slightly lower than those of ordinary concrete. Compared to mortar, although the mechanical strength is lower, the fracture parameters are almost comparable. In all cases, the sand grains are debonded from the paste cement during the fracture which means that the crack goes through the paste-aggregate interface.

• Korean Chemical Engineering Research
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• 제48권2호
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• pp.205-211
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• 2010

상 하수 응집제인 폴리염화알루미늄(polyaluminumchloride, PAC)과 가성소다(NaOH)를 이용하여 수산화알루미늄을 합성하고, 가성소다(NaOH) 첨가량 변화에 따른 합성물 특징을 고찰하였다. 이 때 합성된 수산화알루미늄의 특징을 XRD, SEM, PSA로 분석하였다. XRD 분석 결과, NaOH 15g에서는 비정질 수산화알루미늄로, NaOH 20g에서는 깁사이트(gibbsite)(37%), 바이어라이트(bayerite)(35%), 보헤마이트(boehmite)(28%)의 혼합상(mixed phase)으로 나타났으며, NaOH 25g에서는 깁사이트(gibbsite)(67%), 바이어라이트(bayerite)(33%)로, NaOH 30g에서는 깁사이트(gibbsite) (83%), 바이어라이트(bayerite)(17%)로 나타났다. SEM 분석 결과, NaOH 25, 30g에서 판형 형태로 분석되었다. PSA 분석 결과, 수산화알루미늄의 입자 크기는 NaOH 첨가량이 증가할수록 감소하였다.

• 자원리싸이클링
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• 제29권6호
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• pp.3-14
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• 2020

석탄재로부터 희토류 회수에 관한 연구 자료를 분석 및 검토하였다. 석탄재로부터 희토류 회수를 위해 적용된 선별 실험은 주로 PC 보일러로부터 발생된 석탄재를 대상으로 입도분리, 자력, 비중 및 부유선별법 등을 이용해 연구하였다. 선별 공정을 통해 희토류 성분의 농축 가능한 수준은 수 천 ppm 정도로 낮게 확인되었고, 선별 공정 이후 회수된 산물을 대상으로 습식 제련 공정을 통한 추가 농축 처리가 필요한 것으로 확인되었다. 침출 공정에서는 석탄재의 희토류 성분을 침출 향상을 위해 알칼리 용융과 같은 전처리 후, 침출공정에 적용하는 것이 효율적인 공정으로 확인되었다. 세계적 희토류 회수 시스템의 개발이 아직은 미흡한 것으로 확인되었으나, 석탄재에 포함된 희토류 회수 연구는 계속 진행될 것으로 보고되었다. 국내에서는 석탄재 중 희토류 회수를 위한 회수 기술이 매우 부족한 상황으로 선별, 침출 등의 기술 개발이 시급한 실정이다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.1041-1044
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• 2008

The addition of chemical inert filler in blended cement, such as limestone or chemical inert silica fume, will produce a physical effect on cement hydration. Due to the high surface area of inert filler in the mixtures, it provides sites for the nucleation and growth of hydration products, thus improving the hydration rate of cement compounds and consequently increasing the strength at early age. This paper proposes a model of hydration of Portland cement blended with chemical inert filler. This model considers the influence of water to cement ratio, cement particle size, cement composition and addition of chemical inert filler on hydration. The heat evolution, degree of hydration and porosity are obtained as accompanied results in hydration process. The prediction results agree well with experiment results.

• 한국환경보건학회지
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• 제30권5호
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• pp.395-401
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• 2004

In this study, lots of methods have been studing to utilize energy and decrease contaminated effluents. There has been great progress on IGCC (Integrated gasification combined cycle) to reduce thermal energy losses. The following results have been conducted from desulfurization experiments using waste shell to remove $H_{2}S$. Unreacted core model ior desulfuriration rate prediction of sorbent was indicated. These were linear relationship between time and conversion. So co-current diffusion resistance was conducted reaction rate controlling step. The sulfidation rate is likely to be controlled primarily by countercurrent diffusion through the product layer of calcium sulfide(CaS) formed. Maximum desulfurization capacity was observed at 0.631 mm for lime, oyster and hard-shelled mussel. The kinetics of the sorption of $H_{2}S$ by CaO is sensitive to the reaction temperature and particle size at $800^{\circ}C$, and the reaction rate of oyster was faster than the calcined limestone at $700^{\circ}C$.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.303-308
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• 2001

Recently, concrete structures have become larger and higher and are demanding high performance concrete with lower heat to prevent thermal cracking, far greater workability, high strength and durability, Application of low heat portland(Type IV) cement for the high performance concrete is the best solution to satisfied those requirements. Here are explained the effect on the properties of high flowing concrete using low heat portland cement by material and mixing variations. Variables for sensitivity test were selected items like finess modulus of aggregates, particle size of limestone powder, unit water, superplasticizer, viscosity agent and concrete temperature. The results of this study were be applied to slurry wall of #215 and #216 of underground LNG tank in Inchon.