유동층 환원로내에서 분철광석의 유동특성 및 분화거동에 관한 연구 = (A) study on the characteristics of fluidization and the behaviors of degradation for iron ore fines in a fluidized-bed reduction furnace

다국어 초록 (Multilingual Abstract)

- Characteristics of a cold fluidization -
In this study, a cold fluidized-bed for sinterfeed of wide size range 1∼5 mm has been comprehensively characterized in terms of minimum fluidization velocity, fluidized-bed regime, variation in pressure drop, degradation and holdup of axial direction using manometers and differential pressure transmitters(DPTs). In the experiment, a acryl tube was employed as a cold reactor and nitrogen and reducing gas, which was synthesized to have similar composition to a coal-gasified gas, were used as gas media. The range of superficial gas velocity in the reactor was 0∼3.5 Nm/s. The measured values of minimum fluidization velocity were compared with those calculated from the equation proposed by Wen & Yu and fairly good agreement was obtained. From the measurement of pressure drop(△P) in the reactor using seven DPTs installed along the vertical length of reactor, it was found that the degradation of iron ore is almost in the early stage of fluidization, within 5 minutes. In addition, the superficial gas velocity required for a optimal bubbling fluidization is 1.2∼1.4 times minimum fluidization velocity and the solid holdup in the bubbling fluidized-bed ranged 0.2~0.3 depending on the particle size and size distribution. The amount and size distribution in each section between DPTs can be predicted from the measurements of △P. Calculating the solid holdup in the bed from the measurements, the variation in the bed height with ore weight can be also predicted. The results from the present study could be used as basic data for hot fluidized-bed.
-Characteristics of a hot fluidization -
Characteristics of a fluidized bed with iron ore fines in the size range of 1 to 5mm have been investigated at high temperature (700∼850℃) in terms of the minimum fluidization velocity, fluidization patterns, the pressure drop, the solid hold-up in the reactor, etc. using a laboratory scale fluidized bed reactor. It was observed that the minimum fluidization velocity of particles in wide size range is equivalent to that of the particle of harmonic mean size. The measured values of minimum fluidization velocity were compared with those calculated from the equation proposed by Wen & Yu, Richardson and Grace fairly good agreements were obtained. The minimum fluidization velocity for fine ore particles smaller than 1500㎛, of which fluidization behavior is governed by the viscosity of gas, decreases with a increase in temperature while that for coarse ore particles larger than 1500㎛, of which fluidization behavior is governed by the force of inertia, increases with temperature. In addition, the optimum gas velocity for fluidization is about 1.25 times of the minimum fluidization velocity and this is similar to the result observed in the minimum fluidization velocity and this is similar to the result observed in the experiments in a cold state. During heat-up and reduction in the reactor, iron ore particles are degraded due to the thermal shock and reduction reaction. It was also fond that the degradation of ore particles was completed in the early stage of reduction reactions.
- Degradation behaviors of iron ore fines -
Three mechanisms of the degradation behavior of iron ore fines(IOF) sized 1 mm to 5 mm during fluidized-bed reduction have been investigated: mechanical degradation(MD), thermal degradation(TD) and reductional degradation(RD). The effects of operational parameters such as ore type, temperature, superficial gas velocity, and reducing gas composition have also been studied. The degradation in three mechanisms has been quantitatively evaluated by the amount of IOF smaller than 1mm which was produced and by the weight change of IOF in the bed during fluidization. The reductional degradation become the most predominant aspect among the three and the thermal degradation is the least when the IOF has a low water content, while the degradations of all three aspects are not much different in contribution when the IOF has a high water content. For the effect of operating parameters, the IOF of a lower sphericity showed a higher degradation in the cold fluidization under inert atmosphere but this effect was lessened or negligible under a fluidized-bed reduction at a high temperature. A higher water content in the IOF demonstrated a higher degradation at a high temperature. In the fluidized-bed reduction, the degradation was little affected by the reaction temperature, the superficial gas velocity, and the reducing gas composition. In addition, all three aspects of degradation were mostly completed in the early stage, within 15 minutes, of the reduction reaction.
- Elutriation characteristics of iron ore fines -
The reduction behavior of iron ore fines of multi-sized distribution in a fluidized-bed has been extensively investigated in the aspects of degradation and elutriation. The present study has endeavored to obtain fundamental data for effective plant operations and improvements of devices in fluidized-bed systems through fully understanding the effects of operating parameters and dimension or design of reactor on the degradation and elutriation of ore fines during the fluidized-bed reduction. The abrasion and degradation during fluidized-bed reduction are more severe when the ore particles are coarse, and in this study, the weight percent of ore particles smaller than 250㎛ increased from 27wt% to 45wt% and that of ore paricles smaller than 500㎛ increased from 42wt% to 57wt% after the fluidized-bed reduction. It has been confirmed with a mathematical model of elutriation loss that as the superficial gas velocity increases, the fluidization of coarse ore becomes more vigorous but the elutriation rate and concentration of iron ore fines entrained in gas also increase and it finally results on a high elutriation loss.
These results could be used as basic data for interpretating the reduction behavior of fine iron ore of wide size range. The present study is also expected to provide useful parameters critical in the determination of reactor size in a scale-up of a fluidized-bed system.

목차 (Table of Contents)

• 목차
• 제1장 서론 = 1
• 1.1 서언 = 1
• 1.2. 유동층환원기술 개발동향 및 문제점 = 3
• 1.2.1 제철공정 분류 = 3
• 1.2.2 개발동향 및 문제점 = 7
• 1.3 연구목적 및 내용 = 13
• 제2장 유동층 이론 = 19
• 2.1 유동층 환원기술 특징 = 19
• 2.2 입자의 유동화특성 = 20
• 2.3 유동화특성에 따른 고체분율 = 26
• 2.4 유동화속도 = 28
• 2.4.1 최소유동화속도 = 28
• (1) 측정에 의한 방법 = 28
• (2) 상관식에 의한 방법 = 28
• 2.4.2 종말속도 = 33
• 제3장 상온 유동화특성 = 35
• 3.1 서언 = 35
• 3.2 실험 = 37
• 3.2.1 시료 및 가스매체 = 37
• 3.2.2 실험장치 = 40
• 3.2.3 실험방법 = 40
• 3.2.4 실험조건 = 42
• 3.2.5 입도범위 결정 = 44
• 3.3 실험결과 및 고찰 = 46
• 3.3.1 최소유동화속도 측정 = 46
• 3.3.2 상관식의 계산치와 측정치의 비교 = 46
• 3.3.3 기포유동화 상태의 적정유속 결정 = 51
• 3.3.4 차압측정에 의한 고체분율 = 56
• 3.4 결언 = 61
• 제4장 고온 유동화특성 = 62
• 4.1 서언 = 62
• 4.2 실험 = 64
• 4.2.1 실험장치 및 시료 = 64
• 4.2.2 가스매체 = 66
• (1) 혼합가스의 점도 및 밀도계산 = 66
• (2) 혼합가스의 조성변화 계산 = 69
• 4.2.3 실험방법 및 조건 = 73
• 4.3 실험결과 및 고찰 = 75
• 4.3.1 최소유동화속도 측정 = 75
• 4.3.2 실험식과 측정치와의 비교 = 75
• 4.3.3 적정 유동화속도 결정 = 85
• 4.3.4 높이방향의 차압 및 중량변화 = 87
• 4.3.5 반응기내 고체분율 = 93
• 4.3.6 고체밀도 변화 = 93
• 4.4 결언 = 97
• 제5장 분철광석의 분화거동 = 99
• 5.1 서언 = 99
• 5.2 실험 = 101
• 5.2.1 실험장치 및 시료 = 101
• 5.2.2 실험방법 = 104
• 5.3 분화 및 환원율의 평가방법 = 105
• 5.3.1 분화평가 = 105
• 5.3.2 환원율의 평가방법 = 107
• (1) 배가스에 의한 평가 = 107
• (2) 화학성분에 의한 평가 = 108
• 5.4 실험결과 및 고찰 = 109
• 5.4.1 분화기구 = 109
• (1) 기계적 분화 = 111
• (2) 열간 분화 = 111
• (3) 환원 분화 = 114
• 가. 광종의 영향 = 114
• 나. 환원시간의 영향 = 114
• 다. 환원온도의 영향 = 117
• 라. 가스유속의 영향 = 122
• 마. 환원가스조성의 영향 = 122
• 5.4.2 분화발생량의 정량적 비교 = 127
• 5.4.3 차압측정에 의한 분화평가 = 130
• 5.4.4 분화를 고려한 반응기 설계 = 133
• 5.5 결언 = 136
• 제6장 분철광석의 비산특성 = 137
• 6.1 서언 = 137
• 6.2 실험 = 138
• 6.2.1 실험장치 및 시료 = 138
• 6.2.2 실험방법 = 138
• 6.3 실험결과 및 고찰 = 140
• 6.3.1 분화와 비산 = 140
• 6.3.2 미립광석의 비산모델 = 142
• 6.3.3 시스템구성에 따른 비산손실 해석 = 152
• 6.4 결언 = 159
• 제7장 총괄 = 160
• 참고문헌 = 164
• Abstract = 172