Capturing CO2 from ambient air - David Keith

More documents

Recommendations

Info

average surface area [m 2 -spray / m 3 reactor] 6 5.5 5 4.5 4 3.5 3 2.5 2 1.5 1 0.5 no-coalescence prediction coalescence model 0 0.1 0.2 0.3 0.4 0.5 spray flow rate [L-solution / (s · m 2 0 cross-section)] Figure 3.10: Spray surface area as a function of liquid flow rate in a hypothetical contactor. The deviation from a no-coalescence prediction increases with flow rate (i.e. spray density). Likewise, higher efficiencies (reactive surface area per unit liquid) are achieved at lower flow rates. Assumed contactor height is 120 m and air flow velocity is 2 m/s. Perhaps the most obvious parameter to adjust is the spread of the spray distribution. However, moving from the average to the narrow distribution (see Figure 3.6) has no significant effect on surface area. This may be an artifact of the model. Since it is “well-mixed”, large drops are distributed evenly throughout the volume. With the bi-model distribution in Figure 3.9, the width of the smaller mode may not matter much since most collection is probably due to drops in the large mode striking drops in the small mode. If the model were resolved with height, we would see the spray coalescing more slowly near the top of the tower, and bringing the average surface area up. This behavior was noticed in the Lagrangian model. The narrow distribution is used in the following calculations although, again, it doesn’t seem to matter. The way the curves cross in Figure 3.7 suggests there may be an optimal liquid flowrate for maximum surface area. Figure 3.10 shows S as a function of flowrate. With this model, a peak is not obtained, but the diminishing returns are obvious. In the absence of coalescence, we would expect S to increase proportionally to F. Contactor height also has an effect on spray density. Without height resolution, the model only partly captures this effect through the larger change rates for shorter contactors. The results are shown in Figure 3.11. The effect is substantial, though only impractically short towers begin to approach the nocoalescence efficiency. The last parameter we will vary in the model is mean drop size. Modest changes can be achieved with choice of nozzle, but dramatically smaller drops are only possible by moving to an air-assist nozzle. We 34
average surface area [m 2 -spray / m 3 reactor] 4 3.5 3 2.5 2 1.5 1 no-coalescence prediction coalescence model 0.5 0 20 40 60 80 100 120 140 160 contactor height [m] Figure 3.11: Spray surface area as a function of contactor height. Shorter fall distances produce higher efficiencies (reactive surface area per unit liquid or per unit contactor volume). Total absorption is still reduced in shorter towers because of reactor volume is also proportional to height. 35
Page 1 and 2: Capturing CO2 from ambient air: a f
Page 3 and 4: For my family, friends, and everyon
Page 5 and 6: etween the National Science Foundat
Page 7 and 8: Contents Acknowledgments iv Abstrac
Page 9 and 10: List of Figures 1.1 Global CO2 emis
Page 11 and 12: Chapter 1 Introduction The climate
Page 13 and 14: egeneration at a high enough concen
Page 15 and 16: 1.4 Routes to air capture 1.4.1 Org
Page 17 and 18: The NaOH approach is the primary su
Page 19 and 20: there is no compelling reason to ca
Page 21 and 22: 7Na2CO3(l)+5Na2Ti3O7(s) ⇋ 4Na8Ti5
Page 23 and 24: changing the process design to acco
Page 25 and 26: Component / source GJ/t-CO2 electri
Page 27 and 28: Chapter 3 Contactor In this chapter
Page 29 and 30: the CO2 capture rate in a spray sys
Page 31 and 32: CO 2 absorption per pass [mol/l] 10
Page 33 and 34: CO 2 absorption [mmol/pass] 16 14 1
Page 35 and 36: Figure 3.5: Water loss measured in
Page 37 and 38: 3.3.1 CO2 depletion in air With lon
Page 39 and 40: where vt,1 and vt,2 are the termina
Page 41 and 42: surface area [m 2 -surface / m 3 -r
Page 43: spray mass density [kg / ln(μm)] 1
Page 47 and 48: As a bound on the effects of coales
Page 49 and 50: Draft type Height [m] Crosssectiona
Page 51 and 52: 2. Median assumptions, no coalescen
Page 53 and 54: capture system. We can also see tha
Page 55 and 56: Multistage spray One possible solut
Page 57 and 58: Although, the cost of water loss ma
Page 59 and 60: 3.5.6 Solids formation - scaling an
Page 61 and 62: Chapter 4 Cost of air capture Altho
Page 63 and 64: Capital Capacity Electric a Thermal
Page 65 and 66: Component Capital + O&M Energy cost
Page 67 and 68: Chapter 5 Discussion Overview In th
Page 69 and 70: 5.2 Lessons for assessing of future
Page 71 and 72: Bibliography Adams, P. J. and Seinf
Page 73 and 74: IPCC (2001). Climate Change 2001: M
Page 75 and 76: Tzivion, S., Feingold, G., and Levi
Page 77 and 78: F Liquid flow rate in the contactor
Page 79 and 80: Appendix B Experimental details and
Page 81 and 82: Figure B.2: Photograph of completed
Page 83 and 84: Figure B.4: Two cranes lift the rea
Page 85 and 86: fastened together and lined, the re
Page 87 and 88: The prototype has three particle fi
Page 89 and 90: Figure B.7: Sampling points of CO2
Page 91 and 92: In order to calculate CO2 absorbed,
Page 93 and 94: Absorbed CO 2 [mol/l] 0.3 0.25 0.2
Page 95:
periodic switching of the spray on
show all

Capturing CO2 from ambient air - David Keith

Create successful ePaper yourself

Delete template?

Save as template?