Capturing CO2 from ambient air - David Keith

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(Rao and Rubin, 2002; Rao, 2004). The capture of CO2 from calcination might alternatively be achieved using oxygen blown combustion in a fluidized bed. Such a system would be a hybrid of existing fluid bed calciners and oxygen-fired coal combustion with CO2 capture which has been studied (but not implemented) as a method for achieving CO2 capture at electric power plants. Such a system might offer significant energy savings over the amine system but because it introduces significantly more new engineering and so we do not include it in our base example system. Other authors estimating the energy requirements of an example air capture system have assumed an oxyfuel system (Baciocchi et al., 2006; Zeman, 2006). 2.3.4 Integrated system We argue that one may construct an air capture system essentially by stringing together the components described: a contactor, a kraft recovery system, an amine-based capture system, and a compressor. A few novel interconnections are required, like a heat exchanger between the contactor and the causticizer and heat exchange between the calciner flue gas and amine recovery boiler. We expect the capital and maintenance for this and some extra piping will be more than balanced by the capital equipment not required by an air capture system, compared with the caustic recovery system for a paper mill. Thus for the caustic recovery portion, we use a rule-of-thumb capital cost and energy requirements estimate for a “turn-key” caustic recovery system, obtained from an industry engineer (Flanagan, 2004). The capacity of this plant is 1000 ton-CaO per day, or about 300,000 ton-CO2/yr. This is comparable to the throughput of a single large contacting tower as detailed in the next chapter. However, a full-scale air capture installation would likely include dozens or hundreds of such towers, allowing for a combined caustic recovery plant one or two orders of magnitude larger in scale. There may be significant savings of capital and maintenance cost at this larger scale, as well as opportunities for more energy-efficient operation. These benefits of economy-of-scale are not considered in our example system estimates. The parameters for the amine capture plant are derived from the model used in Rao and Rubin (2002) with adjustments made for the higher CO2 concentration in calciner flue gas. Compression is included in the amine plant. The amine system is assumed 90% efficient, so that all upstream values must be adjusted up to compensate for CO2 leakage. 2.3.5 Energy requirements Table 2.4 shows energy requirements of various components of the example system, along with comparable values from the analysis of Baciocchi et al. (2006) and Zeman (2006). They both assume more optimized systems than the pulp and paper mill caustic recovery system used in our example system. Baciocchi et al. have two cases; in case A they assume a conventional dewatering system and in case B they assume a newer pellet reactor system which removes water much more efficiently. This turns out to have a substantial effect, as the reduced demand for calciner heat multiplies through other components, reducing demand for oxygen and compression. Another important factor determining total energy requirements is the handling of low-grade heat from the slaking reaction and from steam in the flue gas. Neither of these are typically utilized in a kraft mill. 14
Component / source GJ/t-CO2 electric GJ/t-CO2 thermal Contacting Packed tower (Greenwood) 0.3 - Packed tower (Baciocchi) 0.69 - Packed tower (Zeman) 1.3 - Spray tower (see Ch. 3) 1.4 (range: 0.71–3.2) - Caustic Recovery Example system (included in thermal) 13 Baciocchi A 0.11 12 Baciocchi B 0.11 8.0 Zeman - 5.13 CO2 capture Amine system in example system 0.121 (3.8) Oxygen separation (Baciocchi A) 0.62 - Oxygen separation (Baciocchi B) 0.49 - Oxygen separation (Zeman) 0.29 - CO2 compression Example system 0.43 - Baciocchi A 0.42 - Baciocchi B 0.36 - Zeman 0.34 - Totals Example system (included in thermal) 16 Baciocchi A (included in thermal) 17 Baciocchi B (included in thermal) 12 Zeman (included in thermal) 11 Table 2.4: Energy requirements of the air capture system by component. For totals, thermal energy is converted to electricity at 35% efficiency. Values are given as integrated with the indicated system, that is, per net ton CO2 captured by the given system. 15
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: changing the process design to acco
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 and 44: spray mass density [kg / ln(μm)] 1
Page 45 and 46: average surface area [m 2 -spray /
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
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Figure B.2: Photograph of completed
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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
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Figure B.7: Sampling points of CO2
Page 91 and 92:
In order to calculate CO2 absorbed,
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Absorbed CO 2 [mol/l] 0.3 0.25 0.2
Page 95:
periodic switching of the spray on
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Capturing CO2 from ambient air - David Keith

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