Regenerative Thermal Oxidation of Airborne N, N-Dimethylformamide and Its Associated Nitrogen Oxides Formation Characteristics
Abstract In this study, a two-bed electrically heated regenerative thermal oxidizer (RTO) was used to test the thermal destruction and oxides of nitrogen (NOx) formation characteristics in burning airstreams that contain either N, N-dimethylformamide or dimethylformamide (DMF) mixed with methyl ethyl ketone (MEK). The RTO contained two 0.152 m × 0.14 m × 1 m (L × W times] H) beds, both packed with gravel particles with an average diameter of approximately 0.0111 m and a height of up to 1 m with a void fraction of 0.42 in the packed section. The thermal recovery efficiency (TRE) and the gas pressure drop over the beds were also studied. Experimental results reveal that, with a valve shifting time (t s) of 1.5 min, a superficial gas velocity (U g) of 0.39 m/sec (evaluated at an influent air temperature of around 30 °C) and preset maximum destruction temperatures (T S) of 750–950 °C, no NOx was present in the effluent gas from the RTO when it was loaded with DMF-free air. When only DMF was present in the influent air, the average destruction efficiencies exceeded 96%, and increased with the influent DMF concentration from 300 to 750 mg/N∙m3. The “NOx-N formation/DMF-N destruction” mass ratios were in the range 0.76–1.05, and decreased as the influent DMF concentration increased within the experimental range. When both DMF and MEK were present in the influent gas, the NOx formation ratio was almost the same and the DMF destruction efficiency increased with the influent MEK/DMF ratio from 150/300 to 4500/300 (mg/mg) and in the preset temperature range. The NOx formation ratios were in the range 0.75–0.96. The TRE decreased as U g increased but was invariant with T s. The Ergun equation was found to suffice in the estimation of the pressure drop when the gas flowed over the packing beds.
Design of Thermal Oxidation Systems for Volatile Organic Compounds
INTRODUCTION Combustion History of Air Pollution Thermal Oxidation's Wide Applicability Air Pollutant Emissions in the United States Industrial Sources of Air Pollution ENVIRONMENTAL REGULATIONS Federal Law - State Implementation 1990 Clean Air Act Titles VOC DESTRUCTION EFFICIENCY Operating Parameters Destruction Efficiency EPA Incinerability Ranking Environmental Regulations Halogenated Compounds COMBUSTION CHEMISTRY Generalized Oxidation Reactions Highly Halogenated VOCs Chemical Equilibrium Dewpoint Products of Incomplete Combustion (PICs) Substoichiometric Combustion Emission Correction Factors MASS AND ENERGY BALANCE Fundamentals Energy Balance Lower and Higher Heating Values Auxiliary Fuels Mass-to-Volume Heat Release Conversions Mixture Heating Values VOC Heating Value Approximations Heat of Formation Water Quench Auxiliary Fuel Addition Adiabatic Flame Temperature Excess Air Wet vs Dry Combustion Products Simplified Calculational Procedures WASTE CHARACTERIZATION AND CLASSIFICATION Waste Stream Characterization Waste Stream Variability Minor Contaminants - Major Problems Classifications Liquid Waste Streams THERMAL OXIDIZER DESIGN Burners Residence Chamber Refractory Insulation Thermal Conductivity Heat Loss Mixing Plenums and Nozzles Typical Arrangements HEAT RECOVERY Heat Exchangers Waste Heat Boilers (WHB) Heat Transfer Fluids Water Heating Drying Regenerative Heat Recovery CATALYTIC OXIDATION Applications Theory Basic Equipment and Operation Gas Hourly Space Velocity (GHSV) Catalyst Design Operation Halogens Catalytic vs. Thermal Oxidation Waste Gas Heating Value Effects Catalyst Deactivation Deactivation Indicators Regeneration Performance Comparison Pilot Testing Summary REGENERATIVE SYSTEMS Evolution of the RTO Basic Concept Thermal Efficiency Number of Heat Sink (Regenerator) Beds Purge System Bed Orientation Thermal Efficiency vs Cycle Time Heat Sink Materials Flow Diverter Valve Single-Chamber Design Auxiliary Fuel Injection Pollutant Emissions Effect of Waste Stream Component on Design and Operation Exhaust Temperature Control Waste Stream Motive Force Regenerative Catalytic Oxidizers (RCO) Retrofit of RTO COMBUSTION NOx CONTROL Characterizing/Converting NOx Emission Levels NOx Formation Mechanisms Thermal NOx Equilibrium/Kinetics Parametric Affects Fuel Type Affects NOx Prediction Low NOx Burners Vitiated Air Flue Gas Recirculation (FGR) Fuel-Induced Recirculation (FIR) Water/Stream Injection Air/Fuel Staging Staged Air Oxidation for Chemically Bound Nitrogen Effect of Sulfur POST-COMBUSTION NOx CONTROL Selective Noncatalytic Reduction (SNCR) Chemistry Effect of Temperature Normalized Stoichiometric Ratio NOx Inlet Loading Effect of Residence Time Effect of POC Carbon Monoxide Concentration Practical Reduction Levels Injection Methods Computational Fluid Dynamic Modeling Ammonia Slip Reagent By-Products Selective Catalytic Reduction (SCR) GAS SCRUBBING SYSTEMS Wet Scrubbers Dry Systems Hybrid Systems SAFETY SYSTEMS Lower Explosive Limit (LEL) Minimum Oxygen Concentration Flashback Velocity Flashback Prevention Techniques Combustion Safeguards Typical Natural Gas Fuel Train Start-Up Sequence Interlocks Lead/Lag Temperature Control Electrical Hazard Classifications DESIGN CHECKLIST Primary Objectives Scope of Supply Process Conditions Design Requirements Performance Requirements Auxiliary Equipment Utilities Available Environment Preferred Equipment/Approved Vendors Start-Up Assistance Spare Parts Design Documentation Appendix A - Incinerability Ranking Appendix B - Table of the Elements Appendix C - Heats of Combustion of Organic Compounds Appendix D - Abbreviated Steam Tables Appendix E - Explosive Limits of VOCs References Bibliography Index
Mixing in the interaction zone of two free jets
Mixing in the interaction zone of two round free jets with nozzle axes intersecting at half-angles of 15, 30, and 45 deg. has been studied by the smoke scattered light technique. The fields of mean concentration and concentration fluctuation intensity were mapped with one jet marked with smoke, the other jet marked, and both jets marked. The correlation function between the concentration fluctuations associated with fluid of the two nozzle streams has been calculated from the results and is an important characteristic of the mixing field and a significant measure of molecular mixedness. A transport equation for the associated covariance function is derived, and the special features of the mathematical modeling problem for this class of mixing process are discussed. The implications of the results for processes involving chemical reactions are examined.