R J. Schick*, K J. Brown, W. Kalata Spraying Systems Co.

Transcription

1 R J. Schick*, K J. Brown, W. Kalata Spraying Systems Co.

2 Background The reduction of environmental contaminants is a worldwide goal that has seen an increased focus in recent years, especially from power plants. Among the adverse changes caused by pollutants, the effects of acid rain are far-reaching and so permanent in character that has to be prevented.

3 Technology SO 2 Reduction Throw-away Process Wet Scrubbing Dry Processes Dry Processes Lime Lime Stone Dual alkali M itsubishi Bischoff Forced oxdiation (with gypsum disposal) Lime spray drying Lime injection T rona Nahcolite Activated carbon adsorption Copper oxide adsorption Regenerative Process Absorption with water (smelters) Wellman-Lord M go Citrate Wet Processes Aqueous carbonate SULF-X Conosox Forced oxidation (with gypsum sales) Cited from Section 14.2, Air Pollution Control - A Design Approach

4 Introduction Wet-scrubber FGD is commonly used to reduce SO2 emissions. Power plants normally use a lime slurry spray tower in this process. Control of the droplets throughout the tower can ensure the maximum reduction with minimizing scale. Nozzle characteristics and placement can be helpful to optimize the system.

5 System Design and Build-Up Major mechanism - volumetric chemistry - discrete phase model - alkaline sorbent material and SO2 reaction Absorber - high velocity pilot scale - gas flow capability of 4000 acfm - SO 2 concentrations up to 6000 ppmdv Initial design - Babcock & Wilcox Company - High Velocity Absorber Module - built up the system combined with nozzle configurations

6 Empirical Equipment and Methods Phase Doppler Interferometry (PDI) - Artium 2D-MD Flux Measurement Device - drop size & velocity µm

7 Nozzle Selection - Injection Parameters The injectors were full cone, narrow Spraying Systems Co. FullJet style injectors. The target flow rate was lpm for preliminary runs and lpm for subsequent studies. Table 1. Preliminary Tests Nozzle Selection and Characteristics Nozzle ID units 1HH-SS /2GG-SS /2GG-SS /2GG-SS 3030 Pressure (dp) psi DV0.5 micron Distribution Parameter Injected Flow lpm No. of Spray Levels Table 2. Follow-up Tests Nozzle Selection and Characteristics Nozzle ID units 3/8G-9.5 3/8GANV-13 special 3/4GG-3 Pressure (dp) Pa DV0.5 micron Distribution Parameter Injected Flow lpm No. of Spray Levels 3 2 1

8 Theory-Particle Surface Reaction Core Mechanism: wet combusting particle surface reaction chemistry model In this case: particle species j (s) + gas phase species n products CaCO 3 + SO O 2 = CaSO 4 + CO 2 The particle reaction rate, R (kg/m2 s), can be expressed as where, R = D 0 (C g - C s ) = R c (C s ) N D 0 =bulk diffusion coefficient (m/s) C g =mean reacting gas species concentration in the bulk (kg/m 3 ) C s =mean reacting gas species concentration at the particle surface (kg/m 3 ) R c =chemical reaction rate coefficient N =apparent reaction order (dimensionless) Rate of reaction is given as, where, =rate of particle surface species depletion (kg/s) A p =particle surface area (m 2 ) Y j =mass fraction of surface species j in the particle ƞ r =effectiveness factor (dimensionless) =rate of particle surface species reaction per unit area (kg/m2 s) P n =bulk partial pressure of the gas phase species (Pa) D 0,r = diffusion rate coefficient for reaction r = kinetic rate of reaction r N r = apparent order of reaction r

9 Preliminary Results Velocity Inlet: 20 ft/s. Nozzle Configurations: one to three injectors with total mass flow rate of 37.9 lpm

10 Velocity Profile 1 Velocity Magnitude (m/s) Y-Velocity (m/s) 1 Nozzle 2 Nozzle 3 Nozzle 1 Nozzle 2 Nozzle 3 Nozzle 10

11 Pollutant Elimination 1 DPM Concentration (kg/m 3 ) Mass Fraction of SO 2 1 Nozzle 2 Nozzle 3 Nozzle 1 Nozzle 2 Nozzle 3 Nozzle 11

12 Spray Effects 1 Particle Tracking By Droplet Resident Time Wall Impingement 1 Nozzle 2 Nozzle 3 Nozzle 1 Nozzle 2 Nozzle 3 Nozzle 12

13 Plume Visualization 1 nozzle 2 nozzle 3 nozzle 13

14 Simulation Results 1 1 Nozzle 2 Nozzle 3 Nozzle 14

15 Simulation Results 1 Case Name net species mass flow O2 SO2 CO2 CaCO3 Slurry Consumption 1 Nozzle Injection kg/s % 2 Nozzle Injection kg/s % 3 Nozzle Injection kg/s % The above result of 3 nozzle injection is for 11.4 lpm case. As the higher injection quantity 15.1 lpm does not improve removal process, which might due to efficacy limitation. The marginal reduction in drop size may not have significant effect on slurry consumption at this level. The efficiency could be deducted by flow accumulation in L/D effect. These results may need further research to determine cause and effect. 15

16 Further Research Goals Slurry Injection Quantity Study reduced slurry amount & efficiency. Gas Velocity Ranges Study high inlet velocities & efficiency Relationship of Impact Factors vs. Efficiency Study Can we find some rules? 16

17 Follow-up Study Results Velocity Inlet Ranges: 16 ft/s, 18 ft/s and 20 ft/s. Nozzle Configurations: one to three injectors with total mass flow rate of lpm. -Same D 32 17

18 Velocity Profile 2 Velocity Magnitude (m/s) Y-Velocity (m/s) 1 Nozzle 2 Nozzle 3 Nozzle 1 Nozzle 2 Nozzle 3 Nozzle

19 Pollutant Elimination 2 DPM Concentration (kg/m 3 ) Mass Fraction of SO 2 1 Nozzle 2 Nozzle 3 Nozzle 1 Nozzle 2 Nozzle 3 Nozzle

20 Spray Effects 2 Particle Tracking By Droplet Resident Time Wall Impingement 1 Nozzle 2 Nozzle 3 Nozzle 1 Nozzle 2 Nozzle 3 Nozzle

21 Simulation Results 2 1 Nozzle 2 Nozzle 3 Nozzle 21

22 Simulation Results 2 Case Name Inlet Velocity Net Species Mass Flow O2 SO2 CO2 CaCO3 Slurry Lime Consumption Consumption Average SO2 Removal 1 Nozzle Injection 2 Nozzle Injection 3 Nozzle Injection 4.88 m/s % 10.57% 90.67% 5.49 m/s kg/s % 10.78% 82.18% 6.10 m/s % 4.71% 32.32% 4.88 m/s % 9.18% 79.45% 5.49 m/s kg/s % 8.93% 68.96% 6.10 m/s % 6.29% 43.76% 4.88 m/s % 10.46% 92.03% 5.49 m/s kg/s % 10.50% 82.09% 6.10 m/s % 6.28% 44.21% Wall impingement is heavier when there are multiple nozzles. Multiple-nozzle applications lead to much quicker pollutant removal than single-nozzle. Optimal nozzle locations will effect on removal efficiency and wall impingement benefiting from well droplet distribution.

23 Conclusion Benefits of High Velocity Inlet and Multiple Nozzle Applications High speed inlet velocity helps forward reaction. Multiple nozzle application helps removal process as the slurry droplets have a well and wide distribution. Find the Optimum Set-up for Your System The balance of high speed inlet gas flow and nozzle selection, locations will optimize removal process, increase the pollutant removal efficiency, and save the capital on slurry consumption. Nozzle performance test should get focus before it is applied to scrubber.

24 Acknowledgement The authors would like to acknowledge Fang Li, of Spraying Systems Co. and Muhammad Sami of ANSYS Fluent for their assistance with research and editorial contributions for this project. 24

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