Development of an electron beam- electrostatic spray hybrid process for NOx and SO2 removal in flue gas

국문 초록 (Abstract)

본 연구에서는 전자선 처리와 정전분무 기술을 결합하여 배가스 내 NOx 및 SO2 와 전자선에 의하여 생성되는 입자상 물질의 제거 효율을 향상시키는 공정을 개발하였다. 전자선 처리 과정에서는 모사 배기가스를 사용하여 NOx 와 SO2 를 동시에 처리하였으며, 정전분무 기술은 전자선 처리 과정에서 생성된 입자상 물질을 제거하기 위하여 적용되었다. 두 공정의 최적화된 운전 조건을 연구하였고, 전자선 첨가제 및 정전분무 가동 조건에 따른 영향을 평가하여 높은 제거 효율을 달성할 수 있는 조건을 도출하였다. 3 장에서는 전자선 처리에서 첨가제 조건 변화가 NOx 및 SO2 제거효율에 미치는 영향을 평가하였다. 합성 배기가스(20 m3/hr)를 이용하여 전자선 처리로 NOx 280 ppm 과 SO2 500 ppm 을 동시에 제거하였다. NaOH 용액을 첨가제로 사용하여 첨가제의 유량(312, 870, 1,260, 1,700 mL)과 농도(0.02 M, 0.2 M)를 변화시키며 그 영향을 분석하였다. 전자선만 사용하는 경우에는 NOx 와 SO2 제거 효율이 각각 0%와 16.1%로 거의 제거되지 않았으나, 흡수선량과 첨가제 유량을 증가시킴에 따라 NOx 와 SO2 의 제거 효율이 각각 80.1%와 81.7%로 크게 향상되었다. 또한, 첨가제 농도가 증가함에 따라 NO2 제거 효율이 최대 13.9%p까지 증가하였다. 최적화된 운영 조건에서는 NOx 제거 효율 88.2%, SO2 제거 효율 100%를 달성하였다. 장시간 운전 시에도 높은 효율이 유지되었다. 첨가제 유량 증가는 흡수선량이나 첨가제 농도 증가보다 NOx 제거 향상에 더 효과적이었으며, 첨가제 농도 증가는 장기 운전에서 안정적 효율 유지에 기여하였다. 4 장에서는 전자선 처리 과정에서 발생한 입자상 물질 제거를 위한 정전분무 기술의 성능을 평가하였다. NO, NO2, SO2 를 첨가제(NaOH, NH4OH)와 함께 전자선 처리 시 입자상 물질이 생성되었으며, 이는 입경 분포에서 150–250 nm 범위에서 가장 높은 개수농도를 보였다. 입자상 물질의 성분은 처리 가스에 따라 달랐으며 산소를 포함한 산화물이 형성되었다. 전극 전압을 높이면 전기장이 강화되어 직경 약 100 nm 의 미세 분무액적이 효과적으로 대전되었다. NaOH 를 첨가한 NO 및 NO2 처리 조건에서는 5 kV 에서도 86.1%–96.5%의 높은 제거 효율을 보였으나, SO2 처리 및 NH4OH 사용 조건에서는 10 kV에서 최대 64%의 효율에 그쳤다. 그러나 NaOH(0.02 mol/L)를 사용한 경우, 전압을 15 kV 로 높이면 제거 효율이 99.9%까지 상승하였다. 전압 및 분무액 농도 증가와 분무액 종류 변화는 고농도 입자 제거와 적용 가능성 확대에 기여하였다. 5 장에서는 전자선–정전분무 하이브리드 공정의 가스 및 입자상 물질 동시 제거 최적 조건을 도출하였다. 합성 배가스 유량 20 m3/hr 조건에서 다양한 운전 변수에 따른 제거 효율을 평가하였다. 전자선 처리 후 생성된 입자상 물질은 입경 1 μm 이하의 질소·황 산화물이었으며, 분무액 유량과 전압이 증가할수록 제거 효율이 향상되었다. 분무액 유량 2,000 mL/min, 전압 23 kV 조건에서 입자 제거 효율 96.5%를 달성하였으며, 반응기 내부에 폴리프로필렌 패킹 삽입에 따라 제거효율이 크게 향상되었다. 또한 Na2SO3 용액을 정전분무 분무액으로 사용했을 때 NOx 와 입자상 물질의 제거 효율도 증가하였다. 전자선-정전분무 하이브리드 공정의 최적화를 목표로, 다양한 조건에서 NOx, SO2 및 입자상 물질 제거 효율을 평가하였다. 정전분무 용액의 유량과 전압이 증가함에 따라 입자상 물질의 제거 효율이 높아졌고, 2,000 mL/min 의 용액 유량과 23 kV 의 전압에서 96.5%의 최대 제거 효율을 달성하였다. 또한, 반응기에 원통형 폴리프로필렌 패킹을 추가함으로써 입자상 물질 제거 효율이 크게 향상되었다. Na2SO3 용액을 정전분무 분무액으로 사용했을 때 NOx 와 입자상 물질의 제거 효율도 증가하였다. 결론적으로, 전자선–정전분무 하이브리드 공정은 배가스 내 기체 오염물질과 입자상 물질을 동시에 제거하는 효과적인 기술로 확인되었다. 흡수선량, 첨가제 유량, 분무액 조성, 인가 전압, 반응기 패킹 등 운전 변수를 최적화함으로써 다양한 조건에서 높은 제거효율을 안정적으로 달성할 수 있었다. 본 연구의 결과는 해당 하이브리드 공정의 기술적 타당성을 입증하였으며, 산업 규모로의 확장과 실용적 적용을 위한 기반 자료를 제공한다.

다국어 초록 (Multilingual Abstract)

This study investigates the combined application of electron beam treatment and electrostatic spray technology for efficient removal of NOx, SO2, and particulate matter from flue gases. The electron beam treatment enables effective gas-phase pollutant removal but simultaneously induces the formation of particulate matter. Accordingly, electrostatic spray technology was applied to control the particles generated after the electron beam gas treatment. The optimization of operating conditions for both processes, including the use of electron beam additives and electrostatic spray parameters, was explored to achieve high removal efficiencies. In chapter 3, the effect of additive condition variations in the electron beam process on NOx and SO2 removal efficiency was examined. An electron beam treatment process was employed for simultaneous removal of 280 ppm NOx and 500 ppm SO2 using a synthetic flue gas at a gas flow rate of 20 m3/hr. In addition, the effect of NaOH solution as an additive was revealed by varying the flow rate (312, 870, 1,260 and 1,700 mL) and concentration (0.02 and 0.2 M) of the additive. Optimized parameters were explored to obtain high NOx and SO2 removal efficiencies under circulation of the additive solution. In an electron beam only process at an absorbed dose of 20 kGy without additive, 280 ppm NOx and 500 ppm SO2 were barely removed, with removal efficiencies of 0% and 16.1%, respectively. In contrast, removal efficiencies of NOx and SO2 increased significantly when absorbed dose of electron beam and additive flow rate were increased. In conditions with an absorbed dose of 20 kGy and an additive flow rate of 1,260 mL/min (liquid-gas ratios, 1:265), removal efficiencies of NOx and SO2 were 80.1% and 81.7%, respectively. Removal efficiency of NO2 was increased by up to 13.9% as the additive concentration was increased from 0.02 M to 0.2 M. In addition, removal efficiencies of more than 87% for NOx and 99% for SO2 were maintained during a continuous operation of the electron beam process for one hour. Consequently, the highest removal efficiencies (88.2% for NOx and 100% for SO2) were obtained under optimized operating conditions (absorbed dose: 20 kGy, additive flow rate: 1,700 mL/min, and additive concentration: 0.2 M). Increasing the flow rate was found to be more effective in increasing the NOx removal performance in the electron beam process than increasing the absorbed dose or the additive concentration. Moreover, increasing the additive concentration is an effective method to secure stable removal efficiency during long-term additive circulation. These results could serve as a cornerstone for field application of electron beam technology in flue gas treatment process. In chapter 4, the performance of electrostatic spray technology for removing particulate matter generated during electron beam treatment was evaluated. The efficacy of electrostatic spray technology was assessed for removing particulate matter emitted from flue gas treatment processes utilizing an electron beam. The electron beam treatment of target compounds (NO, NO2, and SO2) with additives (NaOH and NH4OH) produced particulate matter. This particulate matter displayed varying number concentration distributions across different particle sizes. The highest number concentration was observed in the 150-250 nm size range. Particulate matter generated from each target compound varied in elemental composition, forming oxidized species that contained oxygen. An increase in the applied voltage from 5 kV to 10 kV enhanced the electric field strength of the electrostatic spraying device, thereby charging fine spray droplets of 100 nm diameter emitted from the nozzle. In conditions with low particle number concentration (additive: NaOH, gas: NO and NO2), even at an applied voltage of 5 kV, high removal efficiencies (ranging from 86.1% to 96.5%) were achieved. Under high concentration conditions, which included the treatment of SO2 with NaOH and all cases with NH4OH, the removal efficiency peaked at 64% at 10 kV. When NaOH (0.02 mol/L) was utilized as the electrostatic spray solution, the removal efficiency decreased, yet increasing the applied voltage to 15 kV achieved a removal efficiency of 99.9%. Enhancements in the applied voltage of the electrostatic spraying device allowed for the treatment of high concentrations of particulate matter generated during the electron beam process and opened up several application possibilities through the modification of the spray solution. These results affirm that electrostatic spraying is a potent technology for treating particulate matter generated in electron beam processes. In chapter 5, the optimal conditions for simultaneous removal of gases and particulate matter in the electron beam-electrostatic spray hybrid process were derived. The removal efficiencies of gases and particulate matter were examined under various electrostatic spray flow rate (280, 750, 1,260, 1,750, and 2,000 mL/min) and applied voltage (15, 20, and 23 kV) conditions, with a synthetic gas flow rate of 20 m3/hr to optimize the electron beam–electrostatic spray hybrid process. When treated with an electron beam, the particulate matter, having particle sizes smaller than 1 μm, comprised oxidized nitrogen and sulfur compounds. The removal efficiency increased with higher flow rates of the electrostatic spray solution and applied voltages. A peak removal efficiency of 96.5% was achieved using a spray solution flow rate of 2,000 mL/min and an applied voltage of 23 kV. At higher voltages, the circular polypropylene packing in the electrostatic spray reactor significantly enhanced the removal efficiencies of particulate matter compared to the unpacked condition. Additionally, switching the electrostatic spray solution from H2O to Na2SO3 increased the removal efficiency of both NOx and particulate matter. These findings suggest an optimized approach for incorporating the electrostatic spray system into the electron beam process for efficient high-flow flue gas treatment. The results indicate that increasing the flow rate of the electrostatic spray solution and the applied voltage effectively controls particulate matter. Consequently, the electron beam–electrostatic spray hybrid process was confirmed to be an effective strategy for simultaneous removal of both gaseous pollutants and particulate matter from flue gases. By optimizing parameters such as absorbed dose, additive flow rate, spray solution type, applied voltage, and reactor packing, the system demonstrated high and stable removal efficiencies under a range of operating conditions. These results not only validate the technical feasibility of the hybrid approach but also provide a strong foundation for its scale-up and practical implementation in industrial flue gas treatment systems.

목차 (Table of Contents)

• Ⅰ. Introduction 1
• Ⅱ. Experimental overview 8
• Ⅲ. Efficient NOx and SO2 removal using NaOH additive in electron beam flue gas treatment process 12
• 3.1. Concept and objectives of study 12
• 3.2. Materials and methods 13
• 3.2.1. Electron beam-based NOx and SO2 treatment process 13
• 3.2.2. Preparation of additive 15
• 3.2.3. Absorbed dose and electron beam irradiation 16
• 3.2.4. Measurement and analysis 18
• 3.2.5. Experimental procedure 19
• 3.3. Results and discussion 20
• 3.3.1. Effects of absorbed dose and additive flow rate 20
• 3.3.1.1. Additive only 20
• 3.3.1.2. Electron beam with additive spray 22
• 3.3.1.3. Ion analysis 32
• 3.3.2. Effect of additive concentration 35
• 3.3.3. Changes in removal efficiency and pH during long-term operation of the electron beam treatment process 37
• Ⅳ. Innovative electrostatic spray technology for control of particulate matter emitted from electron beam flue gas treatment process 42
• 4.1. Concept and objectives of study 42
• 4.2. Materials and methods 43
• 4.2.1. Electron beam process 45
• 4.2.2. Electrostatic spray 48
• 4.2.3. Sampling and analysis 50
• 4.2.4. Simulation of electric field 52
• 4.3. Results and discussion 52
• 4.3.1. Generation of particulate matter by electron beam irradiation 55
• 4.3.2. Electrostatic spray system 59
• 4.3.2.1. Electric field simulation by applied voltage to electrode 59
• 4.3.2.2. Droplets generated by an electrostatic spray 61
• 4.3.3. Particulate matter control using the electron beam process for NOx and SO2 treatment 63
• 4.3.3.1. Impact of electrostatic spray conditions on particulate matter concentration changes 63
• 4.3.3.2. Removal efficiency of total particulate matter by electrostatic spray conditions 67
• 4.3.4. Application of electrostatic spray solution 69
• Ⅴ. Optimization of an electrostatic spray system for control of particulate matter generated from electron beam flue gas treatment processes 71
• 5.1. Concept and objectives of study 71
• 5.2. Materials and methods 72
• 5.2.1. Experimental setup 72
• 5.2.2. Electron beam process for synthetic gas treatment 74
• 5.2.3. Electrostatic spray system for particulate matter treatment 76
• 5.2.4. Analysis and sampling 78
• 5.3. Results and discussion 79
• 5.3.1. Flow rate and voltage of electrostatic spray 85
• 5.3.2 Application of scrubber packing in electrostatic spray 87
• 5.3.3. Changes in spray solution 89
• 5.3.4. Effective economic assessment of electon beam technologies for NOx and SO2 control 94
• Ⅵ. Conclusions 97
• References 99