The research leading to these results has received funding from the European Community&#39;s Research Fund for Coal and Steel (RFCS) under grant agreement n&#176; RFCR-CT-2014-00007. This work was funded by the UK Carbon Capture and Storage Research Centre (UKCCSRC) as part of Call 2 projects. UKCCSRC is supported by the Engineering and Physical Sciences Research Council (EPSRC) as part of the Research Council&#39;s UK Energy Programme, with additional funding from the Department of Business, Energy and Industrial Strategy (BEIS - formerly DECC). The authors would also like to thank Mr. Martin Roskilly for his enormous help throughout the course of this work.

1. Material Preparation
<ol>
	<li>Sieve the limestone (~50 kg of raw material) to the desired particle size distribution (300-400 &#181;m or another distribution depending on the experiment) using a mechanical shaker. Put the sieved material in pots next to the calciner for feeding during the test.</li>
	<li>Prepare the material in batches to be introduced into the reactor. The batches are generally 0.5 L or 1 L (1 L of limestone is roughly 1.5 kg), but this can vary depending on the operating parameters.</li>
</ol>
2. Start-up Procedure
CAUTION: Extremely high temperatures are achieved here. Suitable PPE such as gloves, eye glasses, laboratory coat and safety shoes are required.
<ol>
	<li>Heat-up of Reactors
	<ol>
		<li>Start the low flow of N2 in the carbonator (60 L/min) and calciner (20 L/min) as well as the loop-seals (10 L/min) in the rotameters.</li>
		<li>Turn on the carbonator transformers manually. Set the temperature of all electrical preheaters of the carbonator at 600 &#176;C.</li>
		<li>Start acquiring data (for gas temperatures and pressures, use the recording button in the software). The data include temperatures, pressures and gas composition of both reactors. In Figure 1 and Figure 2, screenshots of the data acquisition system are shown.</li>
		<li>Turn on the calciner gas preheaters. Turn on the heater around the calciner to 600 &#176;C measured inside the BFB via a thermocouple. 
		NOTE: Data such as temperature, pressure and gas composition are already being acquired as stated in step 2.1.3.</li>
		<li>Put 3 L of the sieved limestone into the BFB in the calciner. First open the top valve, introduce the material in the down-pipe and close the top valve, then open the bottom valve so that the material flows into the reactor.</li>
		<li>Heat the material in the BFB to above 650 &#176;C (by the electrical heater around the calciner). 
		NOTE: This usually takes ~1 h, during this time check the data acquisition and the pressures in the fluidized beds.</li>
	</ol>
	</li>
</ol>
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56112/56112fig1.jpg" /> 
Figure 1: Screenshot of temperature and pressure data acquisition for both reactors. <a href="//cloudfront-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56112/56112fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56112/56112fig2.jpg" /> 
Figure 2: Screenshot of temperature data acquisition for the preheating system. <a href="//cloudfront-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56112/56112fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56112/56112fig3.jpg" /> 
Figure 3: Schematic of the 25 kWth CaL (CFB carbonator and BFB calciner). 1: carbonator; 2: calciner; 3: lower loop-seal; 4: upper loop-seal; 5: carbonator cyclone; 6: calciner cyclone. <a href="//cloudfront-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56112/56112fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<ol start="2">
	<li>Start combustion in calciner
	<ol>
		<li>Increase the oxygen concentration in the calciner from 0 to 40% vol, making sure that the concentration is stable before starting the combustion.</li>
		<li>Start the stoichiometric flow of natural gas manually using a rotameter making sure that the combustion is stable. 
		NOTE: The natural gas flow should be increased carefully. Check that the data show an appropriate level of combustion reaction.</li>
		<li>Increase the oxygen concentration in the calciner in 20% vol increments by adjusting the natural gas flow rotameter to ensure stoichiometric combustion. 
		NOTE: This process should be performed with extreme care. If any suspicion arises that the combustion is not occurring as expected from the preliminary calculations then stop the flow of natural gas and switch the oxygen flow to nitrogen for safe operation. Identify the source of this discrepancy. The overall duration of this process is about 1 h.</li>
		<li>Achieve 100% oxygen concentration natural gas combustion. 
		NOTE: The temperature and gas composition data should be carefully followed throughout all the testing, but especially when the combustion is taking place in 100% oxygen.</li>
		<li>Add limestone in 0.5 L increments until there is 7 L in the fluidized bed. Calcine all the material in the fluidized bed of the calciner (the estimated calcination temperature is 800-850 &#176;C for the batch present in the calciner and the calciner temperature for the following batches).</li>
		<li>Increase the flow of N2 in the carbonator to start the circulation. Check the circulation view port regularly to ensure proper circulation.</li>
		<li>Calcine all the available limestone circulating in the rig before starting the CO2 capture.</li>
	</ol>
	</li>
</ol>
3. Stable Operation
<ol>
	<li>Manually switch the carbonation gas from N2 to 15% vol CO2 using the rotameter, which allows the calcined limestone to begin capturing CO2.</li>
	<li>Adjust the flows in the calciner manually using the rotameters to achieve a stable 930-950 &#176;C temperature in the calciner by regulating the flow of natural gas (NG) and oxygen (within the optimal fluidization regime). The O2 flow is usually 100% with enough bed material, but it is adjusted throughout the experiment.</li>
	<li>When the material starts to decline in activity (above 5% CO2 concentration at the exit of the carbonator, which is acquired continuously by the software as described in step 2.1.3), add more limestone.</li>
</ol>
4. Shut-down Procedure
<ol>
	<li>Manually turn off the natural gas flow using the rotameter and decrease the oxygen flow, and switch the gases in both reactors to N2. Turn off all the heaters (calciner and carbonator).</li>
	<li>Allow the temperature of the inventory of the rig to decrease (normally overnight), and empty the reactors when they are at room temperature.</li>
	<li>Weigh the extracted solids and perform a standard sieve analysis. Characterize the material: porosimetry, composition (X-ray fluorescence spectrometry, XRF)21,22 and microscopic structure (scanning electron microscopy, SEM).</li>
</ol>

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<li>Masnadi, M. S., Grace, J. R., Bi, X. T., Ellis, N., Lim, C. J., Butler, J. W. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S0360544215001838">Biomass/coal steam co-gasification integrated with in-situ CO2 capture.</a> Energy. 83, 326-336 (2015).</li>
<li>Abanades, J. C., Anthony, E. J., Lu, D. Y., Salvador, C., Alvarez, D. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/aic.10132/abstract">Capture of CO2 from combustion gases in a fluidized bed of CaO.</a> AIChE Journal. 50 (7), 1614-1622 (2004).</li>
<li>Hughes, R. W., Lu, D. Y., Anthony, E. J., Macchi, A. <a target="_blank" href="https://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/49_1_Anaheim_03-04_0837.pdf">Design, process simulation and construction of an atmospheric dual fluidized bed combustion system for in situ CO2 capture using high-temperature sorbents.</a> Fuel Processing Technology. 86 (14), 1523-1531 (2005).</li>
<li>Lu, D. Y., Hughes, R. W., Anthony, E. J. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S0378382008001677">Ca-based sorbent looping combustion for CO2 capture in pilot-scale dual fluidized beds.</a> Fuel Processing Technology. 89 (12), 1386-1395 (2008).</li>
<li>Hawthorne, C., et al. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S1876610211000750">CO2 capture with CaO in a 200 kWth dual fluidized bed pilot plant.</a> Energy Procedia. 4, 441-448 (2011).</li>
<li>Sánchez-Biezma, A., et al. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S1876610211001317">Postcombustion CO2 capture with CaO. Status of the technology and next steps towards large scale demonstration.</a> Energy Procedia. 4, 852-859 (2011).</li>
<li>Dieter, H., Hawthorne, C., Zieba, M., Scheffknecht, G. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S1876610213000945">Progress in calcium looping post combustion CO2 capture: successful pilot scale demonstration.</a> Energy Procedia. 37, 48-56 (2013).</li>
<li>Arias, B., et al. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S1750583613002922">Demonstration of steady state CO2 capture in a 1.7 MWth calcium looping pilot.</a> International Journal of Greenhouse Gas Control. 18, 237-245 (2013).</li>
<li>Ströhle, J., Junk, M., Kremer, J., Galloy, A., Epple, B. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S0016236113011873">Carbonate looping experiments in a 1MWth pilot plant and model validation.</a> Fuel. 127, 13-22 (2014).</li>
<li>Bidwe, A. R., Hawthorne, C., Dieter, H., Dominguez, M. A., Zieba, M., Scheffknecht, G. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S0032591013006475">Cold model hydrodynamic studies of a 200kWth dual fluidized bed pilot plant of calcium looping process for CO2 Capture.</a> Powder Technology. 253, 116-128 (2014).</li>
<li>Chang, M. H., et al. <a target="_blank" href="https://www.infona.pl/resource/bwmeta1.element.elsevier-99e63a65-57e1-3ba7-a815-e16a7b8b0f88">Design and experimental testing of a 1.9 MWth calcium looping pilot plant.</a> Energy Procedia. 63, 2100-2108 (2014).</li>
<li>Reitz, M., Junk, M., Ströhle, J., Epple, B. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S1750583616304212">Design and operation of a 300kWth indirectly heated carbonate looping pilot plant.</a> International Journal of Greenhouse Gas Control. 54, 272-281 (2016).</li>
<li>Martínez, A., Lara, Y., Lisbona, P., Romeo, L. M. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S1750583611002337">Energy penalty reduction in the calcium looping cycle.</a> International Journal of Greenhouse Gas Control. 7, 74-81 (2012).</li>
<li>Perejón, A., Romeo, L. M., Lara, Y., Lisbona, P., Martínez, A., Valverde, J. M. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S0306261915013616">The calcium-looping technology for CO2 capture: on the important roles of energy integration and sorbent behavior.</a> Appl Energy. 162, 787-807 (2016).</li>
<li>Mantripragada, H. C., Rubin, E. S. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S1876610214020542">Calcium looping cycle for CO2 capture: Performance, cost and feasibility analysis.</a> Energy Procedia. 63, 2199-2206 (2014).</li>
<li><a target="_blank" href="ftp://185.72.26.245/Astm/1/Section%2004/ASTM0401/PDF/C1271.pdf">ASTM C1271-99(2012), Standard Test Method for X-ray Spectrometric Analysis of Lime and Limestone</a>. (2012), ASTM International. West Conshohocken, PA. C1271-C1299 (2012).</li>
<li><a target="_blank" href="https://www.astm.org/Standards/C25.htm">ASTM C25-11e2, Standard Test Methods for Chemical Analysis of Limestone, Quicklime, and Hydrated Lime</a>. , ASTM International. West Conshohocken, PA. C25-C11 (2011).</li>
<li>Alonso, M., Rodríguez, N., Grasa, G., Abanades, J. C. <a target="_blank" href="https://www-sciencedirect-com.remotexs.ntu.edu.sg/science/article/pii/S0009250908005903">Modelling of a fluidized bed carbonator reactor to capture CO2 from a combustion flue gas.</a> Chem Eng Sci. 64 (5), 883-891 (2009).</li>
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</ol>

The authors have nothing to disclose.

The operation of the calciner with an inlet of 100% vol oxygen is achievable, based on exploiting the endothermic nature of the calcination reaction, as well as the fact that the solids circulate between the two reactors at different temperatures. This operating mode aims to make the CaL process more economically promising by reducing capital and operating costs. As the recycle of flue gas (mainly CO2, water vapor and unreacted O2) is reduced or even eliminated, the heat consumed to preheat this stream is lower. Therefore, less oxygen is needed and a smaller ASU would be required. As the gas flow would be lower in this configuration, the size of the calciner would be smaller for the same fluidization velocity.
A standard methodology was developed to ensure the safe operation of the high-oxygen concentration in the calciner. The results showed a capture efficiency of up to 70% in some of the performed experiments. Also, different particle size distributions were used in this reactor configuration (carbonator as a CFB; calciner as a BFB). The distributions were: 100-200 &#181;m; 200-300 &#181;m; 300-400 &#181;m. For the smallest distribution (100-200 &#181;m), however, there were elutriation issues and the majority of the bed inventory was found in the calciner&#39;s cyclone catch-pot. The best results were achieved with the largest particle size distribution (300-400 &#181;m): an Ecarb of ~70% was maintained throughout the experiment with a make-up ratio of about 6%.
This protocol was improved by minimizing the electrical heating provided to the gas and calciner when the natural gas is being combusted, in order to protect the tubes from electrical discharges caused by the heating elements. Also, it has been noted that the O2 concentration increase can be achieved more rapidly than in initial experimental campaigns, from 20% vol to 60% vol and 100% vol. It is important to highlight that the most critical steps in this process are the start of the combustion and the increase of the oxygen concentration, which can cause increased temperatures that will turn off the natural gas source if the temperature goes higher than 980 &#176;C. Also, the material make-up is a concern as it can lower the temperature of the reactor and stop the combustion process, and therefore, it should be added in small batches.
With this methodology applied to this experimental rig, it is possible to test new synthetic materials, as well as materials improved via doping, thermal pre-treatment, chemical pre-treatment, etc.26 This protocol allows these new sorbents to be tested under realistic conditions providing a standard methodology for sorbent comparison. However, there are some challenges when applying this concept at larger scale, such as the use of coal in the calciner under these operating conditions. The use of solid fuels would increase the difficulty in calciner operation due to the high temperatures, which can lead to ash agglomeration and eventually defluidizing phenomena27. This needs further study in order to determine the feasibility of this protocol; however, the concept was proved successful at pilot-scale in this work using natural gas.
Another limitation arising from this study is the duration of the tests, with ~3 h of steady state operation per test; this is due to the heating process of the plant, which is a slow process. The average number of carbonation/calcination cycles experienced by a particle when circulating between reactors is not known. It is possible that the high oxygen concentration had a negative effect causing more sintering in the limestone particles. Further investigation of these challenges would help to assess the suitability of the protocol as a novel and feasible operating mode for CaL plants at a higher scale.

CO2 emissions and the resulting global warming are critical environmental issues that have attracted a large amount of research in the past years. Carbon capture and storage (CCS) has been acknowledged as a potential technology for reducing CO2 emissions to the atmosphere1,2. The most challenging part of the CCS chain is the capture of CO2, which is also the most costly stage3. In consequence, there has been a focus on developing new technologies for CO2 capture from power plants and other industrial facilities.
CaL as a post-combustion CO2 capture technology, was first proposed by Shimizu et al.4 CO2 is captured by a CaO-based sorbent at 600-700 &#176;C in a reactor called a carbonator, and released by subsequent calcination at 850-950 &#176;C (in a calciner) according to Eq. (1), to produce a high-purity CO2 stream suitable for sequestration5,6. The CaL cycle utilises fluidized beds, which represent an optimal configuration for this process, since they allow for large amounts of solids to be circulated easily from one reactor to the other4,5,6,7,8.
CaO (s) + CO2 (g) &#8660; CaCO3 (s)&#160;&#160;&#160;&#160;&#160;&#160;&#160; &#916;H25 &#176;C = -178.2 kJ/mol&#160; (1)
This concept has been demonstrated at pilot scale by various groups and with different configurations and scales, such as the 0.2 MWth pilot in Stuttgart, the 1 MWth pilot in Darmstadt, the 1.7 MWth pilot in La Pereda and the 1.9 MWth unit in Taiwan9,10,11,12,13,14,15,16. Although this process has been proven, there are still possibilities for increasing its thermal efficiency, such as by modifying the standard operating conditions and changes in the design of the reactor configuration.
The use of heat pipes between the combustor and calciner has been studied instead of oxy-combusting fuel in the calciner. The results for the CO2 capture performance are comparable with those of a conventional CaL pilot-plant, however, this process has higher plant efficiencies and lower CO2 avoidance costs17. Mart&#237;nez et al.18 investigated the heat integration possibilities in order to preheat the solid material entering the calciner and to reduce the heat needed in the calciner. The results showed 9% reduction in the coal consumption when compared with that of the standard case. Other studied possibilities for heat integration have also considered internal and external integration options19.
One of the main problems of the CaL cycle from the economic point of view is to supply the energy needed in the calciner by means of fuel combustion20. Increasing the oxygen concentration in the calciner&#39;s inlet is proposed in order to reduce or even avoid the need of CO2 recycle to the calciner. This alternative reduces the capital costs (reduced size of calciner and air separation units (ASU)), which can significantly improve the competitiveness of this process. The drastic change in the combustion conditions can be attained by exploiting the endothermic calcination reaction and the large CaO/CaCO3 flow circulating from the carbonator operating at lower temperatures (neither advantage is available with the oxy-combustion technology).
This work aims to develop a standard operating procedure for running a CaL pilot plant with a Circulating Fluidized Bed (CFB) carbonator and a Bubbling Fluidized Bed (BFB) calciner with 100% O2 concentration in the calciner&#39;s inlet. Several experimental campaigns have been run during the commissioning of the pilot plant to ensure proper operation as the oxygen concentration increased. Also, three limestone particle size distributions (100-200 &#181;m; 200-300 &#181;m; 300-400 &#181;m) were studied to investigate how this parameter affects the elutriation of particles and capture efficiency in this operating mode.

<table><tbody><tr><td>Longcal limestone</td><td>Loncliffe</td><td>Longcal SP52</td><td>n/a</td></tr><tr><td>Mechanical Shaker</td><td>SWECO</td><td>LS24S544+C</td><td>Mechanical siever to separate particles</td></tr><tr><td>Oxygen</td><td>BOC</td><td>n/a</td><td>BOC cylinders</td></tr><tr><td>Nitrogen</td><td>BOC</td><td>n/a</td><td>BOC tank</td></tr><tr><td>Carbon dioxide</td><td>BOC</td><td>n/a</td><td>BOC tank</td></tr><tr><td>Natural gas</td><td>n/a</td><td>n/a</td><td>Taken from the line</td></tr></tbody></table>

operation of a 25 kwth calcium looping pilot-plant with high oxygen concentrations in the calciner

Calcium looping (CaL) is a post-combustion CO2 capture technology that is suitable for retrofitting existing power plants. The CaL process uses limestone as a cheap and readily available CO2 sorbent. While the technology has been widely studied, there are a few available options that could be applied to make it more economically viable. One of these is to increase the oxygen concentration in the calciner to reduce or eliminate the amount of recycled gas (CO2, H2O and impurities); therefore, decreasing or removing the energy necessary to heat the recycled gas stream. Moreover, there is a resulting increase in the energy input due to the change in the combustion intensity; this energy is used to enable the endothermic calcination reaction to occur in the absence of recycled flue gases. This paper presents the operation and first results of a CaL pilot plant with 100% oxygen combustion of natural gas in the calciner. The gas coming into the carbonator was a simulated flue gas from a coal-fired power plant or cement industry. Several limestone particle size distributions are also tested to further explore the effect of this parameter on the overall performance of this operating mode. The configuration of the reactor system, the operating procedures, and the results are described in detail in this paper. The reactor showed good hydrodynamic stability and stable CO2 capture, with capture efficiencies of up to 70% with a gas mixture simulating the flue gas of a coal-fired power plant.

Watch this Scientific Journal Video about Operation of a 25 KWth Calcium Looping Pilot-plant with High Oxygen Concentrations in the Calciner at JoVE.com

Operation of a 25 KWth Calcium Looping Pilot-plant with High Oxygen Concentrations in the Calciner

This manuscript describes a procedure for operating a calcium looping pilot-plant for post-combustion carbon capture with high oxygen concentrations in the calciner in order to reduce or eliminate the flue gas recycle.

Operation of a 25 KWth Calcium Looping Pilot-plant with High Oxygen Concentrations in the Calciner

Calcium looping (CaL) is a post-combustion CO2 capture technology that is suitable for retrofitting existing power plants. The CaL process uses limestone ...

operation-25-kwth-calcium-looping-pilot-plant-with-high-oxygen

Nanyang Technological University

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JoVE Journal

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7.9K Views.  Cranfield University. Dit manuscript wordt een procedure voor de exploitatie van een calcium looping pilot-plant voor na verbranding koolstofvastlegging met hoge zuurstofconcentraties in de calciner te verminderen of te elimineren van de flue gas recycle beschreven.

Video: Operation of a 25 KWth Calcium Looping Pilot-plant with High Oxygen Concentrations in the Calciner

Evaluation of Integrated Anaerobic Digestion and Hydrothermal Carbonization for Bioenergy Production

Lignocellulosic biomass is one of the most abundant yet underutilized renewable energy resources. Both anaerobic digestion (AD) and hydrothermal carbonization (HTC) are promising technologies for bioenergy production from biomass in terms of biogas and HTC biochar, respectively. In this study, the combination of AD and HTC is proposed to increase overall bioenergy production. Wheat straw was anaerobically digested in a novel upflow anaerobic solid state reactor (UASS) in both mesophilic (37 &#176;C) and thermophilic (55 &#176;C) conditions. Wet digested from thermophilic AD was hydrothermally carbonized at 230 &#176;C for 6 hr for HTC biochar production. At thermophilic temperature, the UASS system yields an average of 165 LCH4/kgVS&#160;(VS: volatile solids) and 121 L CH4/kgVS&#160;at mesophilic AD over the continuous operation of 200 days. Meanwhile, 43.4 g of HTC biochar with 29.6 MJ/kgdry_biochar was obtained from HTC of 1 kg digestate (dry basis) from mesophilic AD. The combination of AD and HTC, in this particular set of experiment yield 13.2 MJ of energy per 1 kg of dry wheat straw, which is at least 20% higher than HTC alone and 60.2% higher than AD only.

A novel Upflow Anaerobic Solid State (UASS) reactor was used for biogas production from fibrous feedstock. Digestate from UASS reactor was hydrothermally carbonized into HTC biochar in a pressurized batch reactor. The integration of the two bioenergy concepts was applied in this study to increase overall bioenergy production.

Lignocellulosic biomass is one of the most abundant yet underutilized renewable energy resources. Both anaerobic digestion (AD) and hydrothermal ...

A CO2 Concentration Gradient Facility for Testing CO2 Enrichment and Soil Effects on Grassland Ecosystem Function

Continuing increases in atmospheric carbon dioxide concentrations (CA) mandate techniques for examining impacts on terrestrial ecosystems. Most experiments examine only two or a few levels of CA concentration and a single soil type, but if CA can be varied as a gradient from subambient to superambient concentrations on multiple soils, we can discern whether past ecosystem responses may continue linearly in the future and whether responses may vary across the landscape. The Lysimeter Carbon Dioxide Gradient Facility applies a 250 to 500 &#181;l L-1 CA gradient to Blackland prairie plant communities established on lysimeters containing clay, silty clay, and sandy soils. The gradient is created as photosynthesis by vegetation enclosed in in temperature-controlled chambers progressively depletes carbon dioxide from air flowing directionally through the chambers. Maintaining proper air flow rate, adequate photosynthetic capacity, and temperature control are critical to overcome the main limitations of the system, which are declining photosynthetic rates and increased water stress during summer. The facility is an economical alternative to other techniques of CA enrichment, successfully discerns the shape of ecosystem responses to subambient to superambient CA enrichment, and can be adapted to test for interactions of carbon dioxide with other greenhouse gases such as methane or ozone.

A CO2 Concentration Gradient Facility for Testing CO2 Enrichment and Soil Effects on Grassland Ecosystem Function

The Lysimeter Carbon Dioxide Gradient Facility creates a 250 to 500 &#181;l L-1 linear carbon dioxide gradient in temperature-controlled chambers housing grassland plant communities on clay, silty clay, and sandy soil monoliths. The facility is used to determine how past and future carbon dioxide levels affect grassland carbon cycling.

Continuing increases in atmospheric carbon dioxide concentrations (CA) mandate techniques for examining impacts on terrestrial ecosystems. Most ...

Dynamic Pore-scale Reservoir-condition Imaging of Reaction in Carbonates Using Synchrotron Fast Tomography

Underground storage permanence is a major concern for carbon capture and storage. Pumping CO2 into carbonate reservoirs has the potential to dissolve geologic seals and allow CO2 to escape. However, the dissolution processes at reservoir conditions are poorly understood. Thus, time-resolved experiments are needed to observe and predict the nature and rate of dissolution at the pore scale. Synchrotron fast tomography is a method of taking high-resolution time-resolved images of complex pore structures much more quickly than traditional &#181;-CT. The Diamond Lightsource Pink Beam was used to dynamically image dissolution of limestone in the presence of CO2-saturated brine at reservoir conditions. 100 scans were taken at a 6.1 &#181;m resolution over a period of 2 hours. The images were segmented and the porosity and permeability were measured using image analysis and network extraction. Porosity increased uniformly along the length of the sample; however, the rate of increase of both porosity and permeability slowed at later times.

Synchrotron fast tomography was used to dynamically image dissolution of limestone in the presence of CO2-saturated brine at reservoir conditions. 100 scans were taken at a 6.1 &#181;m resolution over a period of 2 h.

Underground storage permanence is a major concern for carbon capture and storage. Pumping CO2 into carbonate reservoirs has the potential to dissolve ...

Engineering

Temperature-programmed Deoxygenation of Acetic Acid on Molybdenum Carbide Catalysts

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system includes a reactor, furnace, gas and vapor sources, flow control, instrumentation to quantify reaction products (e.g., gas chromatograph), and instrumentation to monitor the reaction in real time (e.g., mass spectrometer). Here, we apply the TPRxn methodology to study molybdenum carbide catalysts for the deoxygenation of acetic acid, an important reaction among many in the upgrading/stabilization of biomass pyrolysis vapors. TPRxn is used to evaluate catalyst activity and selectivity and to test hypothetical reaction pathways (e.g., decarbonylation, ketonization, and hydrogenation). The results of the TPRxn study of acetic acid deoxygenation show that molybdenum carbide is an active catalyst for this reaction at temperatures above ca. 300 &#176;C and that the reaction favors deoxygenation (i.e., C-O bond-breaking) products at temperatures below ca. 400 &#176;C and decarbonylation (i.e., C-C bond-breaking) products at temperatures above ca. 400 &#176;C.

Presented here is a protocol for the operation of a micro-scale temperature-programmed reactor for evaluating the catalytic performance of molybdenum carbide during acetic acid deoxygenation.

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system ...

Chemistry

Two-way Valorization of Blast Furnace Slag: Synthesis of Precipitated Calcium Carbonate and Zeolitic Heavy Metal Adsorbent

The aim of this work is to present a zero-waste process for storing CO2 in a stable and benign mineral form while producing zeolitic minerals with sufficient heavy metal adsorption capacity. To this end, blast furnace slag, a residue from iron-making, is utilized as the starting material. Calcium is selectively extracted from the slag by leaching with acetic acid (2 M CH3COOH) as the extraction agent. The filtered leachate is subsequently physico-chemically purified and then carbonated to form precipitated calcium carbonate (PCC) of high purity (&lt;2 wt% non-calcium impurities, according to ICP-MS analysis). Sodium hydroxide is added to neutralize the regenerated acetate. The morphological properties of the resulting calcitic PCC are tuned for its potential application as a filler in papermaking. In parallel, the residual solids from the extraction stage are subjected to hydrothermal conversion in a caustic solution (2 M NaOH) that leads to the predominant formation of a particular zeolitic mineral phase (detected by XRD), namely analcime (NaAlSi2O6&#8729;H2O). Based on its ability to adsorb Ni2+, as reported from batch adsorption experiments and ICP-OES analysis, this product can potentially be used in wastewater treatment or for environmental remediation applications.

A protocol for the parallel production of precipitated calcium carbonate and zeolitic material from blast furnace slag via mineral carbonation and alkaline hydrothermal conversion, respectively, is presented. The performance of the zeolitic material towards nickel adsorption is tested.

The aim of this work is to present a zero-waste process for storing CO2 in a stable and benign mineral form while producing zeolitic minerals with ...

Microalgae Cultivation and Biomass Quantification in a Bench-Scale Photobioreactor with Corrosive Flue Gases

Photobioreactors are illuminated cultivation systems for experiments on phototrophic microorganisms. These systems provide a sterile environment for microalgal cultivation with temperature, pH, and gas composition and flow rate control. At bench-scale, photobioreactors are advantageous to researchers studying microalgal properties, productivity, and growth optimization. At industrial scales, photobioreactors can maintain product purity and improve production efficiency. The video describes the preparation and use of a bench-scale photobioreactor for microalgal cultivation, including the safe use of corrosive gas inputs, and details relevant biomass measurements and biomass productivity calculations. Specifically, the video illustrates microalgal culture storage and preparation for inoculation, photobioreactor assembly and sterilization, biomass concentration measurements, and a logistic model for microalgal biomass productivity with rate calculations including maximum and overall biomass productivities. Additionally, since there is growing interest in experiments to cultivate microalgae using simulated or real waste gas emissions, the video will cover the photobioreactor equipment adaptations necessary to work with corrosive gases and discuss safe sampling in such scenarios.

Bench-scale, axenic cultivation facilitates microalgal characterization and productivity optimization before subsequent process scale-up. Photobioreactors provide the necessary control for reliable and reproducible microalgal experiments and can be adapted to safely cultivate microalgae with the corrosive gases (CO2, SO2, NO2) from municipal or industrial combustion emissions.

Photobioreactors are illuminated cultivation systems for experiments on phototrophic microorganisms. These systems provide a sterile environment for ...

Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three preparation methods are described: (a) the incorporation of metal salts into silica or alumina wet gels using an impregnation method; (b) the incorporation of metal salts into alumina wet gels using a co-precursor method; and (c) the addition of metal nanoparticles directly into a silica aerogel precursor mixture. The methods utilize a hydraulic hot press, which allows for rapid (&#60;6 h) supercritical extraction and results in aerogels of low density (0.10 g/mL) and high surface area (200-800 m2/g). While the work presented here focuses on the use of copper salts and copper nanoparticles, the approach can be implemented using other metal salts and nanoparticles. A protocol for testing the three-way catalytic ability of these aerogels for automotive pollution mitigation is also presented. This technique uses custom-built equipment, the Union Catalytic Testbed (UCAT), in which a simulated exhaust mixture is passed over an aerogel sample at a controlled temperature and flow rate. The system is capable of measuring the ability of the catalytic aerogels, under both oxidizing and reducing conditions, to convert CO, NO and unburned hydrocarbons (HCs) to less harmful species (CO2, H2O and N2). Example catalytic results are presented for the aerogels described.

Here we present protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms. Methods for preparing materials using copper salts and copper-containing nanoparticles are featured. Catalytic testing protocols demonstrate the effectiveness of these aerogels for three-way catalysis applications.

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three ...

Coupling Carbon Capture from a Power Plant with Semi-automated Open Raceway Ponds for Microalgae Cultivation

In the United States, 35% of the total carbon dioxide (CO2) emissions come from the electrical power industry, of which 30% represent natural gas electricity generation. Microalgae can biofix CO2 10 to 15 times faster than plants and convert algal biomass to products of interest, such as biofuels. Thus, this study presents a protocol that demonstrates the potential synergies of microalgae cultivation with a natural gas power plant situated in the southwestern United States in a hot semi-arid climate. State-of-the-art technologies are used to enhance carbon capture and utilization via the green algal species Chlorella sorokiniana, which can be further processed into biofuel. We describe a protocol involving a semi-automated open raceway pond and discuss the results of its performance when it was tested at the Tucson Electric Power plant, in Tucson, Arizona. Flue gas was used as the main carbon source to control pH, and Chlorella sorokiniana was cultivated. An optimized medium was used to grow the algae. The amount of CO2 added to the system as a function of time was closely monitored. Additionally, other physicochemical factors affecting algal growth rate, biomass productivity, and carbon fixation were monitored, including optical density, dissolved oxygen (DO), electroconductivity (EC), and air and pond temperatures. The results indicate that a microalgae yield of up to 0.385 g/L ash-free dry weight is attainable, with a lipid content of 24%. Leveraging synergistic opportunities between CO2 emitters and algal farmers can provide the resources required to increase carbon capture while supporting the sustainable production of algal biofuels and bioproducts.

A protocol is described to utilize the carbon dioxide in natural gas power plant flue gas to cultivate microalgae in open raceway ponds. Flue gas injection is controlled with a pH sensor, and microalgae growth is monitored with real time measurements of optical density.

In the United States, 35% of the total carbon dioxide (CO2) emissions come from the electrical power industry, of which 30% represent natural gas ...

CO2 Photoreduction to CH4 Performance Under Concentrating Solar Light

We demonstrate a method for the enhancement of CO2 photoreduction. As the driving force of a photocatalytic reaction is from solar light, the basic idea is to use concentration technology to raise the incident solar light intensity. Concentrating a large-area light onto a small area cannot only increase light intensity, but also reduce the catalyst amount, as well as the reactor volume, and increase the surface temperature. The concentration of light can be realized by different devices. In this manuscript, it is realized by a Fresnel lens. The light penetrates the lens and is concentrated on a disc-shaped catalyst. The results show that both the reaction rate and the total yield are efficiently increased. The method can be applied to most CO2 photoreduction catalysts, as well as to similar reactions with a low reaction rate at natural light.

CO2 Photoreduction to CH4 Performance Under Concentrating Solar Light

We present a protocol for improving the performance of CO2 photoreduction to CH4 by heightening the incident light intensity via concentrating solar energy technology.

We demonstrate a method for the enhancement of CO2 photoreduction. As the driving force of a photocatalytic reaction is from solar light, the basic idea ...

Development and Validation of Chromium Getters for Solid Oxide Fuel Cell Power Systems

Degradation of cathode in solid oxide fuel cells (SOFC) remains a major concern for the long-term performance stability and operational reliability. The presence of gas phase chromium species in air has demonstrated significant cathode performance degradation during long-term exposure due to unwanted compound formation at the cathode and electrolyte interface which retards the oxygen reduction reaction (ORR). We have demonstrated a novel method to mitigate the cathode degradation using chromium getters which capture the gas phase chromium species before it is ingested in the cathode chamber. Low-cost getter materials, synthesized from alkaline earth and transition metal oxides, are coated on the cordierite honeycomb substrate for application in the SOFC power systems. As-fabricated getters have been screened by chromium transpiration tests for 500 h in humidified air atmosphere in presence of chromium vapor. Selected getters have been further validated utilizing electrochemical tests. Typically, electrochemical performance of SOFCs (lanthanum strontium manganite (LSM) &#449; yttria stabilized zirconia (YSZ) &#449; Pt) was measured at 850 &#176;C in the presence and absence of Cr getter. For the 100 h cell tests containing getters, stable electrochemical performance was maintained, whereas the cell performance in the absence of Cr getters rapidly decreased in 10 h. Analyses of Nyquist plots indicated significant increase in the polarization resistance within the first 10 h of the cell operation. Characterization results from posttest SOFCs and getters have demonstrated the high efficiency of chromium capture for the mitigation of cell degradation.

Cathode poisoning from airborne contaminants in trace levels remains a major concern for long-term stability of high-temperature electrochemical systems. We provide a novel method to mitigate the cathode degradations using getters, which capture airborne contaminants at high temperature before entering electrochemically active stack area.

Degradation of cathode in solid oxide fuel cells (SOFC) remains a major concern for the long-term performance stability and operational reliability. The ...

Operation of a 25 KW_th Calcium Looping Pilot-plant with High Oxygen Concentrations in the Calciner

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