Sequestration-ready CO2 Research Articles

Synergistic Chemical Looping Process Coupling Natural Gas Conversion and NOx Purification

We present a novel low-temperature chemical looping combustion scheme for simultaneous natural gas conversion into a sequestration-ready CO2 stream and NOx purification. The scheme employs nickel oxide (NiO) supported on ZrO2 as the oxygen carrier. In the process, CH4 reduces the oxidized carrier to Ni/ZrO2 in a co-current moving bed reactor, which is then oxidized back to NiO/ZrO2 by the NOx-laden flue gas in a fluidized bed reactor, completing the oxygen carrier loop. Thermodynamic studies demonstrate that the presence of CO2 does not significantly affect NOx purification performance at different flue gas flow rates. The operating temperatures of the reactors are selected based on NOx-temperature programmed oxidation (TPO) and CH4-temperature programmed reduction (TPR) experiments. Results show that the process can optimally operate at temperatures close to the combustion plants’ flue gas temperature of 400–500 °C, reducing the need for hot utilities. The study conducts comprehensive isothermal and autothermal analyses of the process to evaluate the effects of temperature and carrier flow rate on CH4 conversion, CO2 selectivity, carbon deposition, and NOx conversion. For the autothermal analysis, the CH4 reactor operates adiabatically, while the NOx reactor operates isothermally. Comparative studies with the conventional NOx selective catalytic reduction (SCR) process indicate an exergy efficiency and effective thermal efficiency (ETE) improvement of 9 and 18 percentage points, respectively. The findings suggest that this low-temperature chemical looping process is a promising solution for flue gas NOx treatment, utilizing cheaper natural gas as the reductant and eliminating environmental concerns, such as ammonia or urea slippage. Overall, this study contributes to the development of more efficient and sustainable methods for reducing NOx emissions.

A particle-scale reduction model of copper iron manganese oxide with CO for chemical looping combustion

Chemical looping combustion is a promising power generation technology that produces sequestration-ready CO2 and heat/power from the combustion of fossil fuels with oxygen provided by an oxygen carrier, or metal oxide, rather than air. Successful implementation of chemical looping combustion depends highly on the choice of oxygen carrier and the development of reaction rate parameters for process design and scale-up of the multi-reactor system. In this work, the reaction profile of a promising trimetallic oxygen carrier, copper iron manganese oxide with CO, a component of coal-derived synthesis gas was characterized using differential scanning calorimetry/thermogravimetric analysis and in-situ X-Ray diffraction. A unique phase formation with reactivities different from that with single metal components and phase changes during the reaction with CO were identified. Three major reactions were identified from the phase changes to use for reaction modelling. A particle-scale reaction model was selected which best described the experimental thermogravimetric analysis data to determine the valuable intrinsic reaction values for reactor design and scale-up. A particle-scale reaction model based on nucleation and growth and 1-D phase boundary behavior exhibited the most accurate correlation with the experimental data and provided intrinsic rate constants which were validated with the conventional mass transport analysis.

Reactivity improvement of ilmenite by calcium nitrate melt infiltration for Chemical Looping Combustion of biomass

Chemical Looping Combustion is a novel process that generates sequestration-ready CO2 from the combustion of woody biomass without requiring a gas separation step and without diluting the CO2 with N2 from air. This is achieved by oxidizing the fuel with lattice oxygen of a metal oxide oxygen carrier. When using cheap and abundant ilmenite ore (FeTiO3) as the oxygen carrier, the rather low reactivity towards volatiles released from the biomass upon devolatilization, as well as detrimental structural changes due to a segregation of Fe and Ti in the material, are of concern. These issues can be addressed by modifying ilmenite with Ca via melt infiltration. In this work, we demonstrate that this modification results in a good distribution of Ca throughout the ilmenite particles that a) prevents detrimental Fe/Ti segregation, b) improves the mechanical stability of the particle compared to materials prepared by solution impregnation and c) improves the reactivity of this material towards hydrogen and wet methane. Moreover, fixed bed experiments showed that the Ca modification not only resulted in increased methane conversion, but also in an increased degree of oxidation of gaseous intermediates CO and H2. We thus conclude that the performance of ilmenite in Chemical Looping processes can be significantly enhanced by Ca modification of ilmenite either prior to use or in-situ during operation of this bed material with Ca-rich fuels such as woody biomass.

Coal direct chemical looping hydrogen production with K-Fe-Al composite oxygen carrier

Hydrogen production by coal direct chemical looping (CDCL) process with iron-based oxygen carrier is an attractive option to produce H2 with sequestration-ready CO2. However, low reduction rate and high endothermicity are the two main difficulties of this process. In this work, the reduction rate of K-Fe-Al composite oxygen carrier by coal char, and the effect of Al2O3 on the endothermic property and sintering of oxygen carrier during reduction were investigated by thermogravimetric analyzer (TGA), differential scanning calorimetry (DSC), X-ray diffractometer (XRD), and scanning electron microscopy (SEM). The feasibility of this process was preliminary analyzed using a fixed-bed reactor by simulating different reaction steps. It was found that the reduction rate of composite oxygen carrier increased remarkably with higher potassium amount, but decreased with increasing Al2O3 amount. However, the addition of Al2O3 into oxygen carrier could not only mitigate the sintering, but also alleviated the endothermicity of reduction by the exothermic formation of FeAl2O4. This preliminary feasibility analysis suggests that it is possible to produce H2 using CDCL with the K-Fe-Al composite oxygen carrier

Detailed plant layout studies of oxy-enriched CO2 pulverized coal combustion-based power plant with CO2 enrichment

Coal plays a vital role in electricity generation worldwide and is expected to contribute significantly to thermal power generation for the foreseeable future, especially in countries such as India. Carbon capture and sequestration technologies therefore become imperative in order to minimize CO2 emissions. A systematic and comprehensive assessment of the most promising of these technologies—consisting of supercritical boiler parameters, oxy-coal combustion, and low temperature flashing for simultaneous CO2 and SO2 capture—for typical Indian environmental and fuel conditions has been carried out in the present study. The results show that up to 93.3 % of CO2 and 95 % of SO2 generated during combustion can be captured while producing a sequestration-ready CO2 stream of 95.5 mol% purity compressed to a supercritical pressure of 110 bar. The energy penalty for this suite of technologies amounts to about 8.5 % drop in the net power plant efficiency to 33 % despite adopting efficiency measures such as supercritical boiler technologies.

Chemical looping: To combustion and beyond

Chemical looping combustion (CLC) is a rapidly emerging technology for clean combustion of fossil and renewable fuels which allows production of sequestration-ready CO2 streams with only minor efficiency penalties for CO2 capture. While initial interest in chemical looping was almost exclusively focused on combustion, we demonstrate here that the underlying reaction engineering principle forms a highly flexible platform for fuel conversion: Replacing air with steam or CO2 as oxidizer yields the chemical looping analogue to steam and dry reforming, resulting in the production of high purity hydrogen streams without the need for further clean-up steps and a novel route for efficient CO2 activation via reduction to CO, respectively. Furthermore, by controlling the degree of carrier oxidation, incomplete, i.e. partial oxidation of the fuel to synthesis gas is attained. Finally, appropriate selection of oxygen carrier materials even allows simultaneous desulfurization of the effluent stream, resulting in a strongly intensified process for highly efficient, low-emission conversion of S-contaminated fuel streams. Based on new results from our own research, the present paper presents a brief overview over the potential of chemical looping processes for methane conversion with a particular focus on the key role of engineered carrier materials as enablers for this class of processes.

Iron-based syngas chemical looping process and coal-direct chemical looping process development at Ohio State University

The increasing demands for energy and concern of global warming are intertwined issues of critical importance. With the pressing need for clean, efficient, and cost-effective energy conversion processes, the chemical looping strategy has evolved as a promising alternative to the traditional carbonaceous fuel conversion processes. Chemical looping processes utilize oxygen carrier particles to indirectly convert carbonaceous fuels while capturing CO2 for sequestration and/or utilization. Throughout its development, multiple oxygen carrier compositions and reactor configurations have been studied and demonstrated. The Ohio State University (OSU) chemical looping technologies have received significant attention over the recent years. OSU’s unique moving-bed chemical looping technologies coupled with iron-based oxygen carrier particles capable of sustaining hundreds of redox cycles have the advantage of converting a variety of carbonaceous fuels, such as natural gas, coal and biomass, to electricity, H2, liquid fuels, or any combination thereof with zero to negative net CO2 emissions. Specifically, two chemical looping processes are being developed and studied, the syngas chemical looping (SCL) and the coal direct chemical looping (CDCL) technologies. Over the past 14years, these processes have developed from a novel concept to successful sub-pilot (25kWth) demonstrations. With the support of the Advanced Research Projects Agency – Energy (ARPA-E) of the US Department of Energy (USDOE), a 250kWth high pressure SCL pilot scale demonstration project was initiated for processing syngas to cogenerate pure H2 and sequestration-ready CO2 from a Kellogg Brown & Root gasifier at the National Carbon Capture Center. A 25kWth CDCL sub-pilot plant has been constructed and demonstrated at OSU with the support from National Energy Technology Laboratory (NETL) of the United States Department of Energy (USDOE). The combined SCL and CDCL operational time at reactive conditions well exceeds 850h. Multiple aspects of the OSU chemical looping development including the oxygen carrier properties, reaction mechanism studies, reactor design and modeling studies, the bench and sub-pilot scale process testing results, energy integration optimization, and techno-economic analyzes are discussed.

Mechanism of Methane Chemical Looping Combustion with Hematite Promoted with CeO2

Chemical looping combustion (CLC) is a promising technology for fossil fuel combustion that produces sequestration-ready CO2 stream, reducing the energy penalty of CO2 separation from flue gases. An effective oxygen carrier for CLC will readily react with the fuel gas and will be reoxidized upon contact with oxygen. This study investigated the development of a CeO2-promoted Fe2O3–hematite oxygen carrier suitable for the methane CLC process. Composition of CeO2 is between 5 and 25 wt % and is lower than what is generally used for supports in Fe2O3 carrier preparations. The incorporation of CeO2 to the natural ore hematite strongly modifies the reduction behavior in comparison to that of CeO2 and hematite alone. Temperature-programmed reaction studies revealed that the addition of even 5 wt % CeO2 enhances the reaction capacity of the Fe2O3 oxygen carrier by promoting the decomposition and partial oxidation of methane. Fixed-bed reactor data showed that the 5 wt % cerium oxides with 95 wt % iron oxide produ...

Modeling Energy Flow in an Integrated Pollutant Removal (IPR) System with CO2 Capture Integrated with Oxy-fuel Combustion

Oxy-coal combustion is one of the technical solutions for mitigating CO2 in thermal power plants. Many processes have been evolved in past the decade to capture CO2 from process industries. Researchers at the National Energy Technology Laboratory (NETL) have patented a process, integrated pollutant removal (IPR), that uses off the shelf technology to produce a sequestration-ready CO2 stream from an oxy-combustion power plant. The IPR process as it is realized at the Jupiter Oxygen Burner Test Facility is a spray tower (direct-contact heat exchanger) followed by four stages of compression with intercooling. To study the energy flows of the oxy-combustion process, a 15 MWth oxy-combustion pulverized-coal-fired plant integrated with the IPR system was simulated and analyzed using ASPEN Plus and ASPEN energy analyzer. This paper discusses flue-gas recycle, energy flow, recovery, and optimization of IPR systems. ASPEN models of heat- and mass-transfer processes in a flue-gas-condensing heat-exchanger system were developed to predict the heat transferred from flue gas to cooling water. The flue-gas exit temperature, cooling water outlet temperature, and energy flows of IPR streams were computed using ASPEN models. Pinch principles are deployed for targeting design and operation-guiding purposes and balancing the heat and mass transfer in the IPR system. The results are expected to support sophistication of the IPR system design, improving its application in a variety of settings. They open the door for valuable IPR efficiency improvements and generalization of methodology for simultaneous management of energy resources.

Calcium Looping Process (CLP) for Enhanced Steam Methane Reforming

Carbon dioxide (CO2) capture using calcium-based sorbents for post- and pre-combustion applications has the potential to become a viable technology. When applied to a pre-combustion system, the presence of calcium sorbents facilitates process intensification by combining the CO2 removal step with the reactions generating the fuel gas [syngas, hydrogen (H2), etc.] in a single step. Such a process is also capable of producing a high-purity sequestration-ready CO2 stream. The enhanced steam methane reforming (SMR) using the Calcium Looping Process (CLP) has been investigated in this work. The CLP comprises three reactors: the carbonation reactor or carbonator where the thermodynamic constraint of the reforming and water gas shift (WGS) reaction is overcome by the incessant removal of the CO2 product resulting in the production of high-purity H2, the calciner where the calcium sorbent is regenerated and a sequestration-ready CO2 stream is produced, and the hydrator where the regenerated sorbent is reactivated to improve its multicyclic performance. The exothermic carbonation and WGS reaction convert the highly endothermic SMR into a heat neutral process, thus reducing the temperature of reforming from >900 to 650 °C. Experiments conducted using methane in a bench-scale fixed bed reactor have indicated that high purity H2 (∼95–99%, dry basis) can be produced using the CLP with in situ CO2 capture. Attempts to maintain the sorbent reactivity over multiple cycles using hydration have yielded encouraging results.

Carbon capture and utilization via chemical looping dry reforming

Chemical looping combustion (CLC) is a clean energy technology for CO 2 capture that uses periodic oxidation and reduction of an oxygen carrier with air and a fuel, respectively, to achieve flameless combustion and yield sequestration-ready CO 2 streams. While CLC allows for highly efficient CO 2 capture, it does not, however, provide a solution for CO 2 sequestration. Here, we propose chemical looping dry reforming (CLDR) as an alternative to CLC by replacing air with CO 2 as the oxidant. CLDR extends the chemical looping principle to achieve CO 2 reduction to CO, which opens a pathway to CO 2 utilization as an alternative to sequestration. The feasibility of CLDR is studied through thermodynamic screening calculations for oxygen carrier selection, synthesis and kinetic experiments of nanostructured carriers using cyclic thermogravimetric analysis (TGA) and fixed-bed reactor studies, and a brief model-based analysis of the thermal aspects of a fixed-bed CLDR process. Overall, our results indicate that it is indeed possible to reduce CO 2 to CO with high reaction rates through the use of appropriately designed nanostructured carriers, and to integrate this reaction into a cyclic redox (“looping”) process.

Testing of Ammonia Based CO2 Capture with Multi-Pollutant Control Technology

Abstract Powerspan has been developing a CO 2 capture process, called ECO 2 ® , since 2004 in conjunction with the U.S. DOE National Energy Technology Laboratory (NETL) under a cooperative research and development agreement. In December 2007 Powerspan announced it exclusively licensed a patent for the process from NETL. The ECO 2 process is a post-combustion, regenerative process, which uses an ammonia-based solution to capture CO 2 from the flue gas of a power plant and release it in a form that is ready for further compression, safe transportation, and geological storage. The technology is suitable for retrofit to the existing coal-based, electric generating fleet as well as for new coal-based plants. The CO 2 capture takes place after the sulfur dioxide and fine particulate matter are captured. Once the CO 2 is captured, the ammonia-based solution is regenerated to release CO 2 and ammonia. The ammonia is recovered and sent back to the scrubbing process, and the CO 2 is in a form that is ready for geological storage. Ammonia is not consumed in the scrubbing process, and no separate by-product is created. Powerspan has conducted extensive laboratory testing to establish the effectiveness of the process for CO 2 capture and has initiated a pilot test program with FirstEnergy at the R.E. Burger Plant. A 1-MW pilot demonstration is scheduled to begin in 2008, which will produce approximately 20 tons of sequestration ready CO 2 per day. The pilot will demonstrate CO 2 capture through integration with the ECO ® multi-pollutant control process. The pilot program will also prepare the technology for commercial scale (120-MW) CCS demonstration projects planned with NRG Energy for the WA Parish plant and with Basin Electric Power Cooperative for the Antelope Valley Station.

Synthesis of Iron-Based Chemical Looping Sorbents Integrated with pH Swing Carbon Mineral Sequestration

The previously developed pH swing carbon mineral sequestration immobilizes the gaseous CO2 into a thermodynamically stable solid, MgCO3, using Mg-bearing minerals such as serpentine. This mineral carbonation technology is particularly promising since it generates value-added solid products: high surface area silica, iron oxide, and magnesium carbonate, while providing a safe and permanent storage option for CO2. By carefully controlling the pH of the system, these solids products can be produced with high purity. This study focuses on the synthesis of iron oxide particles as a chemical looping sorbent in order to achieve the integration between carbon capture and storage technologies. Since the solubility of Fe in aqueous phase is relatively low at neutral pH, the effect of the weak acid and chelating agents on the extraction of Fe from serpentine was investigated. The synthesized iron-based chemical looping sorbent was found to be as effective as commercially available iron oxide nanoparticles at converting syngas into high purity H2, while producing a sequestration-ready CO2 stream.

Analysis of the sorbent energy transfer system (SETS) for power generation and CO 2 capture

The sorbent energy transfer system (SETS) has the potential for providing a significant reduction in CO 2 emissions from gaseous fossil fuel-fired electric power plants with minimal loss in power generating efficiency. Energy transfer is accomplished in two steps so that CO 2 does not come in contact with combustion air, thereby avoiding a costly and energy intensive CO 2 separation step. In the first step, gaseous fuel is oxidized by reduction of an appropriate metal oxide sorbent. The gas product contains only CO 2 and H 2O so that pure, sequestration-ready CO 2 is obtained after removing H 2O by condensation. The reduced sorbent is then re-oxidized using excess air. Dual, circulating fluidized-bed or transport reactors provide continuous, steady state operation. Base case Aspen Plus simulations of the SETS process coupled to a natural gas combined cycle (NGCC) show that approximately 50% of the CO 2 can be captured with an energy penalty of only approximately 5%. Base case maximum operating temperature of the two SETS reactors was limited to 900 °C to maintain the structural stability of the sorbent and adhere to operating temperature limits of particulate filters. Increased reactor temperatures would permit increased capture of CO 2 with minimal additional energy penalty.

Unmixed combustion: an alternative to fire

A new form of combustion has been studied with properties that are greatly different from combustion via fire. Called unmixed combustion, it occurs when fuel and air alternately pass over a catalyst that undergoes oxidation and reduction, storing oxygen from the air and delivering it to the fuel. Examples of catalysts include finely divided Cu/CuO or FeO/Fe 2O 3 supported on γ-alumina. The full heat of combustion of the fuel is released, the fuel is converted to CO 2 and water, and the air is depleted of oxygen, all without any need for the fuel and air to mix. Thus unmixed combustion is an alternative to fire, another way of using fuel and air to generate heat. The properties and characteristics of unmixed combustion are different from those of combustion by fire in a number of ways, some obvious, some subtle, suggesting a number of applications where conventional combustion is not or cannot be used. One example are situations in which it is difficult to provide complete mixing but in which complete combustion is required; e.g., rotary kiln incinerators. These incinerators have a failure mode called “puffing” to which unmixed combustion may be relevant. In the area of pollution control unmixed combustion is capable of burning natural gas and pyridine with zero NO x production; of burning sulfur-containing fuels in a manner that facilitates subsequent removal of the SO 2; and of burning coal in a manner that directly provides sequestration ready CO 2. Greatly enhanced delivery of heat to surfaces, rapidly supplying heat for cold starting engines, and direct generation of dry inert gases are also possible. Unmixed combustion also allows the delivery of heat uniformly throughout a volume. This method of heat delivery is potentially useful for supplying heat to endothermic reactions carried out in packed beds of catalyst. Experimental evaluation of this technique for steam reforming shows that while conventional steam reforming is a strongly endothermic reaction with an unfavorable equilibrium, the use of unmixed combustion allows a redefinition of the system’s thermodynamics, making the reaction weakly exothermic with a more favorable equilibrium.