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  1. 1. Anjali Gupta, Arvind K. Nema / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 6, November- December 2012, pp.075-079 Carbon Dioxide Sequestration In Alkaline Waste Anjali Gupta*, Arvind K. Nema***(Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India. ** (Department of Civil Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016)ABSTRACT The present study focuses on exploring presence of specific gases in the atmosphere,an array of alkaline waste residues, procured denominated greenhouse gases (mainly carbonfrom diverse sources as means for sequestering dioxide, water vapour and methane) which absorbmaximal CO2. Alkaline waste residues and reemit part of the infrared radiation emitted byundertaken for the study included: (1) Cement the Earth’s surface, trapping heat in the atmosphere.Bag Filter Dust, (2) Finished Cement Sample, (3) The significant enhancement of the greenhouse gasMarble Dust and (4) Baghouse Dust. effect has been linked to the steep increase in CO2Experiments were conducted in a self fabricated atmospheric concentrations registered since theCarbonation reactor under 80% CO2 beginning of the industrial revolution [1]. Thisconcentration and at 40°C, water: solid (w/s) increase has been primarily ascribed to humanratio of 0.2 to 1.2 with relative humidity in the activities and in particular to the combustion ofreactor was maintained at 100%. Carbonation fossil fuels, which are estimated to produce aboutreactions were carried for 16hrs with sampling three quarters of anthropogenic CO2 emissions [2].done every at intervals of 4hrs. The highest The rest is mainly due to land use changes,degree of carbonation achieved with Cement Bag especially deforestation. Several industrial processesFilter Dust was 25.84% at w/s ratio of 0.4 without like oil refining and the manufacturing of cement,any amendments to the waste material. Degree of lime, and steel are also significant sources of CO2.carbonation achieved under similar conditions Carbon dioxide capture and storage (CCS)for other waste residue was 17.21% by Finished technologies have been indicated as one of the mostCement Sample followed by Marble Dust 10.98% viable and effective measures to reduce point-sourceand finally by Baghouse Dust was 7.54%. It was emissions that could be applied in the short-mediumconcluded that a low w/s ratio of 0.4 was term, at least until energy production will still relyoptimum for carbonation reaction due to on fossil fuels combustion [3]. This technologyincreased access to reaction sites. Detailed involves collection and concentration of the CO2experiments are further needed inorder to generated by industrial or energy production plants,address the inconsistency in the observed transport to a suitable storage site and subsequentcarbonation achieved by different waste due to storage in permanent, safe disposal sites such astheir heterogeneous nature. geological formations, including saline aquifers, oil reservoirs and coal seams, or oceans [4, 5].Keywords - Carbon Sequestration, carbonation, The purpose of CO2 capture is to produce aCement, mitigation, Waste Disposal concentrated stream of CO2 at high pressure that can be transported to a storage site [3]. For the energyI. INTRODUCTION sector, there are three main approaches to capture Significant evidence on currently ongoing the CO2 generated from the combustion of fossilglobal warming and related climate modifications fuels, biomass, or mixtures of these fuels, dependinghave been collected and reported by the scientific on the process or type of power plant to which CO2community in the last couple of decades, in capture is applied: post-combustion, pre-particular by the U.N. International Panel on combustion, and oxy-fuel combustion systems. Post-Climate Change [1]. An increase of almost 1 degree combustion systems separate CO2 from a flue gasCelsius of the global average surface temperature of stream, which generally contains 3-15% vol. CO2,the planet since the mid 19th century, which was typically using a liquid solvent. This technique isestimated to be the largest temperature increase currently used to absorb CO2 from part of the flueoccurred in the past 1300 years, has been confirmed gases generated from a number of existing power[1], as well as other effects correlated to climate plants. It is also commercially used in the naturalchange such as the shrinking of mountain glaciers, gas processing industry. Pre-combustion systemsthe increase in the frequency and intensity of remove CO2 before combustion by employingdraughts and tropical storms and the rise of the gasification, water-shifting, and CO2 separation.average sea level. This technology is widely applied for fertiliserThe measured global warming has been associated manufacturing and hydrogen production. Oxy-fuelto a sharp increase in the greenhouse gas effect, combustion systems use oxygen, instead of air, forwhich is a natural phenomenon related to the 75 | P a g e
  2. 2. Anjali Gupta, Arvind K. Nema / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 6, November- December 2012, pp.075-079the combustion of the primary fuel to produce a flue infinite supply (ideal condition). The humidity wasgas that consists mainly of water vapour and CO2. maintained to 100% using an aqueous chemicalThe extent of carbonation in alkaline wastes, such as solution placed in troughs and placed inside thecoal fly ash, municipal solid waste incinerator ash, carbonation reactor.and steel slag has been investigated in preliminary The temperature in the reactor wasexperiments [6, 7, 8, 9] with favourable results. The maintained at 40°C for experimentation. Theutilization of alkaline waste materials provides samples were oven dried at 100⁰C to ensure thereseveral advantages: (1) waste materials supply a were no traces of initial moisture content. Thirtyreadily available source of calcium or magnesium grams of CBF sample, forty grams of FCS sample,mineral matter without the need for pre-processing; fifty gram of Marble Dust sample and fifty grams of(2) they are typically fine-grained with high reactive BHD samples were used for carrying out thesurface areas; and (3) the environmental quality of carbonation reaction. Distilled water was used tothe waste materials can be improved through pH- obtain the definite water to solids ratio (0.2 to 1.2).neutralization and mineral transformation [8, 10]. In Thus the effect of different water to solids ratio ataddition, alkaline industrial wastes are typically constant temperature, humidity and flow of CO2 wasgenerated at or near point sources of CO2. determined. The present paper focuses on the study of The post-carbonated samples were ovenfeasibility of mineral carbonation in the selected dried at 100°C, crushed, mixed to a homogenousalkaline wastes residues namely Cement Bag Filter form, weighed and then stored at room temperatureDust (CBF); Finished Cement Sample (FCS); in air tight bags. The carbonation reaction resultsMarble Dust (MD); and Baghouse Dust (BHD). The were noted at a regular interval of 4hrs, 8hrs, 12hrsresults were analyzed by determining their and 16hrs for different water to solid ratio. The dryrespective sequestration capacity based on their mass change of the samples was determined andmineral and elemental complementary analysis. was further used to calculate their respective degreeCarbonation reactions were carried out in a self of carbonation achievable with respect to reactionfabricated Batch reactor. Samples were subjected to time.standardized conditions of temperature and humiditywith sampling done at a regular interval of 4 hrs 2.3 MATERIAL CHARACTERIZATIONupto 16hrs. Further the optimum water: solid ration The theoretical extent of carbonation wasfor different alkaline waste residue was determined calculated for the samples using the elementalby varying the water to solid ratio from 0.2 to 1.2. compositions obtained from XRF analysis for theirCO2 sequestration capacity was established by representative subsets. The estimation of theoreticalcomparing their respective degree of carbonation extent of sequestration was based on stochiometricwith respect to the reaction time. Difference in and the reactive oxide content in the waste. Thecomposition of the samples lead to the variability theoretical stochiometric extent gives the percentagewhich further results in some uncertainty in the dry mass of sample reacted, that can be expected todegrees of carbonation calculated for each of the be converted into carbonate on reaction with CO2,sample. thus giving the extent or potential of the waste to sequester CO2. It was similar to the estimate ofII. MATERIALS AND METHODS Steinour [11] for concrete & mortars, as follows:2.1 SAMPLE COLLECTION Alkaline waste samples of (CBF), (FCS), %ThScCO2 = 0.785(%CaO – 0.56%CaCO3 –MD and BHD were procured from various sources. 0.7%SO3) + 1.091%MgO + 0.71%Na2O +The samples were collected at the point of 0.468(%K2O–0.632%KCl) (1)generation and placed in air tight bags for furtheranalysis and experimentation. The stochiometric mass factors shown in above equation assume that all of the CaO will react2.2 CARBONATION REACTION USING BATCH with CO2 to form CaCO3, all the MgO will react toREACTOR form MgCO3 and all of Na2O and K2O will convert The carbonation reaction was conducted in to Na2CO3 and K2CO3. Presence of initial CaCO3,an acrylic carbonation reactor with the working CaO in bounded form of CaSO4, and K2O involume of 393 liters. The reactor was fitted with two bounded form of KCl are discounted for. CaO wasvalves for CO2 injection, a heating rod & a digital the main oxide in the waste samples (as illustratedthermostat with a PID controller to control by XRF results shown in TABLE 1 below), and thetemperature, four fans to ensure circulation in the conditions of reaction were set for calcitewhole reactor and shelves for keeping the samples. production.A CO2 cylinder with a regulator was used to passCO2 into the carbonation reactor. A rotameterensured the gas flow was set to 10 liters /minute.CO2 was passed to stimulate a condition similar to 76 | P a g e
  3. 3. Anjali Gupta, Arvind K. Nema / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 6, November- December 2012, pp.075-079 TABLE 1: ELEMENTAL COMPOSITION OF PRE- 3.1 XRF ANALYSIS OF WASTE RESIDUES CARBONATED WASTE SAMPLES The XRF analysis of pre-carbonatedElemental samples gave their elemental composition. TheComposition Alkaline Waste Residue elemental composition of the pre-carbonated(%) samples was analyzed with a Philips PW 2404 X- Cement Marble Baghouse ray spectrometer (Cambridge, UK). Sample Finished specimens were homogenized by grinding in a Bag Dust Dust Cement SPEX Shatterbox (Edison, NJ). Portions of the bulk Filter Sample sample were ignited at 980°C to a constant mass and Dust then fused into glass disks with a LECO FX-503SiO2 21.74 22.63 5.57 5.94 automated fuser. The theoretical extent ofAl2O3 6.52 8.81 0.46 2.23 carbonation was obtained by plugging in theTiO2 0.46 0.1 0.07 0.15 percentage of various constituent compounds in the Equation 1. TABLE 2 below gives the stochiometricFe2O3 4.54 3.78 0.7 1.94 theoretical extent of carbonation achievable inMnO 0.09 0.04 0.03 0.04 selected alkaline residues. Inherent in this theoretical calculation is the assumption that theCaO 51.5 55.7 31.4 48 oxides in certain calcium and potassium phases areMgO 2.63 3.15 17.38 1.37 unlikely to react with CO2 at selected temperaturesNa2O 0.13 0.15 0.09 0.17 and humidity. The calculated stochiometric theoretical extent in the BHD sample was found toK2O 0.54 0.45 0.19 0.38 be comparatively lower to that of CBF, MD andP2O5 0.1 0.1 0.03 0.05 FCS can be attributed to its higher initial mass fraction of calcite.SO32- 1.98 1.67 0.18 0.32 TABLE 2: THE STOCHIOMETRIC THEORETICALCl- 0.01 0.01 0.01 0.01 EXTENT OF CARBONATION ACHIEVABLE INCaCO3 28 19.1 27.44 25.4 SELECTED ALKALINE RESIDUES Alkaline Residue Theoretical Stochiometric The mass of CaCO3 produced at time (t) CO2 Capture% taken to be equal to the dry mass gain between pre- Cement Bag Filter 30.24 and post-carbonated sample is as shown in equation Dust 2 below. Finished Cement 38.16 Wg(t)=W(t)–W(t=0) (2) Sample Marble Dust 31.59 Where W(t= 0) is the initial dry mass and Baghouse Dust 28.13 W(t) is the dry mass after the carbonation reaction. The change in carbonation content (referred as 3.2 CARBONATION OF ALKALINE WASTE RESIDUE extent of carbonation) can be expressed as CO2 % A simplified method was developed to (in terms of dry mass) as shown in equation 3 estimate the sequestered quantity of CO2 by below. carbonate precipitation. Once standardization was achieved, the carbonation of CBF, FCS, MD and %CO2(t)=[Wg(t)/W(t)]× 100 (3) BHD alkaline waste residue carried out in the batch reactor at 40°C maintaining a humidity of 100% with a flow of CO2 at 10L/minute for 1 hour. The The degree of carbonation (E (t)) was estimated as results are shown in Figure 1 for CBF, Figure 2 for extent of mass change due to carbonation as a FCS and Figure 3 for MD and Figure 4 for BHD. percent of the theoretical extent of carbonation The highest degree of carbonation achieved (ThCO2) based on initial composition of the sample with Cement Bag Filter Dust in the CO2 Reactor was as shown in equation 4. 25.84% at w/s ratio of 0.4, 80% CO2 and 16hrs E (t) =Wg(t) /[W(t=0)×ThCO2 ] (4) duration without any amendments to the waste material. A lower water-to-solids ratio was obtained III. RESULTS to have a higher degree of carbonation though some In the following sub-sections, the degree of amount of water is required for the reaction to carbonation with respect to time for selected waste occur. Higher water content limits the carbonation. residue has been calculated and the potential This can be attributed to the hindrance caused by candidate with highest CO2 sequestered has been water in the diffusion of CO2 and as the gas- reported. permeability of the sample is reduced, there is a decreased access to reaction sites and so CO2 cannot penetrate effectively to react to form carbonate. The 77 | P a g e
  4. 4. Anjali Gupta, Arvind K. Nema / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 6, November- December 2012, pp.075-079 stochiometric theoretical extent for the different samples types was determined as a function of 12 MARBLE DUST water-to-solids ratio with respect to time. The DEGREE OF CARBONATION% optimum water: solid ratio for different samples was 0.2 W/S determined and their corresponding degree of 9 0.4 W/S carbonation was calculated. CBF gave maximum degree of carbonation of 6 0.6 W/S 25.84% under given conditions of temperature, 0.8 W/S humidity and at 0.4 water: solid ratio as illustrated 1 W/S 3 in Fig.1 below. 1.2 W/S 0 4 8 12 16 CEMENT BAG FILTER DUST TIME(Hrs) 30 DEGREE OF CARBONATION% Figure 3. Degree of carbonation in MD as a function 27 of initial water-to solids ratio 24 0.2W/S 21 18 0.4 W/S 9 BAGHOUSE DUST 15 DEGREE OF CARBONATION% 12 0.6 W/S 9 0.2 W/S 0.8 W/S 6 6 0.4 W/S 3 1 W/S 0 0.6 W/S 4 8 12 16 1.2 W/S 0.8 W/S TIME (Hrs) 3 1 W/S Figure 1 Degree of carbonation in CBF as a function 1.2 W/S of initial water-to solids ratio 0 4 8 12 16 Degree of carbonation achieved under TIME (Hrs) similar conditions with other waste residue Figure 4 Degree of carbonation in BHD as a investigated in the present study was 17.21% by function of initial water-to solids ratio FCS followed by MD 10.98% and finally by BHD was 7.54 % as illustrated in Fig. 2, Fig. 3 and Fig. 4 respectively. The degree of carbonation was IV. CONCLUSION observed to be greater at lower water: solid ratio of In conclusion, the results presented of this 0.4 due to increased access to reaction sites. Thus study reveal that the ex-situ mineral sequestration of however higher water contents appear to decrease CO2 by carbonation of CBF, MD, FCS and MD the overall sequestration extent by slowing or could be an attractive method to reduce the CO2 hindering the transport of CO2 to reaction sites. emission in the atmosphere. Comparative study of the degree of carbonation achievable in the selected waste with respect to time has been illustrated in 21 FINISHED CEMENT SAMPLE Fig. 5 below. DEGREE OF CARBONATION AT 0.4 DEGREE OF CARBONATION% 18 0.2 W/S 15 W/S at 16hrs 0.4 W/S 12 30 25.84 DEGREE OF CARBONATION % 0.6 W/S 27 9 24 0.8 W/S 21 17.21 6 18 1 W/S 15 .10.98 3 1.2 W/S 12 9 7.54 0 6 3 4 8 12 16 0 TIME(Hrs) CBF FCS MD BHDFigure 2 Degree of carbonation in FCS as a function of initial Figure 5 Comparison of degree of carbonation withwater-to solids ratio respect to time e for selected waste sample at 0.4 water: solid ratio at the end of 16hrs. 78 | P a g e
  5. 5. Anjali Gupta, Arvind K. Nema / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 6, November- December 2012, pp.075-079It can be concluded that at w: s ratio of 0.4 and at for Energy and the Environment, 27, 2002,end of 16hrs CBF shows the highest degree of 193-232.carbonation when compared with other waste [5] K.S. Lackner. Climate change: a guide toresidues selected for the present study. The degree CO2 sequestration. Science, 300, 2003,of carbonation was observed to be greater at lower 1677-1678.water: solid ratio of 0.4 due to increased access to [6] D.J. Fauth, Y. Soong, and C.M. White.reaction sites. Carbon Sequestration Utilizing Industrial This experimental investigation Solid Residues. Symposium-Americandemonstrated that 1 ton of CBF, an industrial waste Chemical Society, Division Fuelthat contains about 51.1 wt. % of lime (CaO), could Chemistry, 2002, 37- 38.sequester up to 0.302 kg of CO2 per kg of CBF with [7] M.F. Bertos, X. Li, S.J.R. Simons, C.D.maximum degree of carbonation of 25.84% at the Hills, and P.J. Carey. Investigation ofend of 16hrs at w: s ratio of 0.4. For FCS, an Acceleration Carbonation for theindustrial product that contains about 55.7 wt. % of Stabilisation of MSW Incinerator Asheslime (CaO) could sequester up to 0.381 kg of CO2 and the Sequestration of CO2. Greenper kg of FCS with maximum degree of carbonation Chemistry, 6, 2004a, 428-436.of 17.21% under similar conditions. For MD, an [8] M.F. Bertos, X. Li, S.J.R. Simons, C.D.industrial waste that contains about 31.4 wt. % of Hills, and P.J. Carey. A Review oflime (CaO) could sequester up to 0.315 kg of CO2 Accelerated Carbonation Technology in theper kg of MD with maximum degree of carbonation Treatment of Cement-Based Materials andof 10.98%. Finally for BHD that contains about 48 Sequestration of CO2. Journal ofwt. % of lime (CaO) could sequester up to 0.28 kg Hazardous Material , B112, 2004b, 193-of CO2 per kg of BHD with maximum degree of 205.carbonation of 7.56 % under similar conditions. [9] W.J.J. Huijgen, G.J. Witkamp, and R.N.J. This confirms the possibility to use these residues Comans. Mineral CO2 Sequestration byfor CO2 mitigation in punctual sources. Other Steel Slag Carbonation. Environmentaladvantages of the proposed method are (1) that the Science and. Technology, 39 (42), 2005,carbonation process takes place at low temperature 9676-9682.(40°C) and reduces the energy costs of the process [10] W.J.J. Huijgen and R.N.J. Comans. Carbonat industrial scale and, (2) the use of moderate Dioxide Sequestration by Mineralpressure in the system does not require expensive Carbonation Literature Review. Energymaterials for reactor design. Resource Center of the Netherlands, 2003, ECNC- 03-016, 2003. Available atREFERENCES www.ecn.nl (Accessed 29 December [1] IPCC (2007). Climate Change 2007: The 2010). Physical Science Basis. Contribution of [11] H.H. Steinour. Some Effects of Carbon Working Group I to the Fourth Assessment Dioxide on Motars and Concrete – Report of the Intergovernmental Panel on Discussion, Concrete Briefs, Journal. Climate Change. S. Solomon., D. Qin, M. American Concrete Institute, 1959, 905- Manning, Z. Chen, M. Marquis, K.B. 907. Averyt, M. Tignor, and H.L. Miller. (Ed.). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. [2] IPCC (2001). Climate Change 2001: The Scientific Basis. Contribution of Working Group I, Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). J.T. Houghton, Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, D. Xiaosu, (Ed.) Cambridge University Press, UK. [3] IPCC (2005). IPCC special report on carbon dioxide capture and storage. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. [4] K.S. Lackner. Carbonate chemistry for sequestering fossil carbon. Annual Review 79 | P a g e