Commercializing biomass-based technologies as an alternative to fossil fuels is necessary for a sustainable future. This study proposes a robust Biomass to Syngas (BTS) chemical looping system to gasify biomass into syngas for a range of downstream applications, with focus on liquid fuel production. The system has been demonstrated on a sub-pilot scale cumulatively for over 600 h, proving the technology's commercial viability. Pelletized corn cob, woody pellets, and unpelletized loose corn cob, were successfully tested, proving the robusticity of the process to handle untreated biomass with batch variation. Tar analysis shows that moving bed reducer can reduce the tar concentration to 0.5 g/m(3), owing to uniform residence time, high temperature, and catalytic activity of oxygen carrier, while injection of steam as an enhancer gas increases carbon conversion by char gasification. A variable syngas quality with an H-2/CO ratio of similar to 2 and a syngas purity greater >70% was achieved, making this syngas suitable for the generation of liquid fuels via Fischer-Tropsch synthesis. The biomass requirement for a chemical looping system decreases by 13.9% over the conventional biomass gasifier for generating the same amount of liquid fuels. Heat integration suggests integrating biomass drying with the combustor exhaust air for process authothermicity.

The gas-solid flow through a moving bed packed with coarse particles is investigated experimentally and theoretically in this study. By employing a bench-scale moving-bed column, different sizes of fine and coarse particles, gas flowrates, and moving-bed velocities are examined to ascertain the transport characteristics of fines. We propose models to predict the transport characteristics by performing a dimensional analysis and a regularized regression by machine learning. We observe that the transport phenomena of fines are dominated by the hydrodynamic properties of fines rather than the moving-bed velocity, and the size of coarse particles also has an impact on the transport characteristics, especially the fines holdup. Additionally, the split ratio and exiting velocity of fines are found to be a function of the gas flowrate and the size of coarse particles. Results of this study can guide the design of packed moving-bed reactors that utilize fine particles as the feedstock.

In this work, a method of producing velocity profile maps from electrical capacitance volume tomography (ECVT) measurements by reconstructing displacement from measured changes in capacitance is developed and applied to fluidized bed systems. The mapping of the reconstruction leverages the gradient of the sensitivity distribution of the ECVT sensor to circumvent the need for image cross correlation techniques. Experimental data of both bubbling and slugging fluidized beds are collected in a cold flow model. Adaptation of the technique is discussed in detail, and velocity profiles are obtained for a range of gas flow rates. The produced velocity maps are compared against the established methods of cross correlation and against empirical correlations from the literature and are found to agree well in tracking slug and bubble velocity. The exception is when the tracked object is large relative to the ECVT sensor dimensions, a scenario that can be avoided through proper sensor design. The quantities of average velocity, momentum, and solid and gas volume fraction are derived from the image and velocity profiles. The results demonstrate and extend the power of ECVT as a measurement tool for the study and monitoring of gas–solid fluidized beds by providing a computationally cheaper alternative to 3-D cross correlation for deriving velocity profiles.

—Electrical Capacitance Volume Tomography (ECVT) is a low-cost and high-speed sensing modality with great potential for industrial multiphase flow monitoring. In this work, we examine the use of the slope of the capacitance vector residual curve, as directly provided by the measurement data, to formulate a robust stopping criterion for the iterative image reconstruction in ECVT. The methodology is illustrated based on experimental data from a gas-solid fluidized bed. We show that the proposed stopping criterion can improve the performance of both the image reconstruction and the flow velocity profiling in ECVT applications. For concreteness, we focus on the popular Landweber iterative reconstruction algorithm although other reconstruction algorithms exhibiting semi-convergent behavior might benefit from the present analysis as well.

Slugging represents one of the major regimes in fluidization, which occurs in small diameter beds with large bed height-to-diameter ratio or in large diameter beds with internals that resemble multiple small diameter fluidized beds. Slug types include round-nosed slug, wall slug and square-nosed slug. Studies of the slugs have been mainly focused on round-nosed or wall slugs known as half slug, typically occurring in Geldart group A particle fluidization. The square-nosed slug typically occurring for Geldart group D particles appears to be regarded as simple in its structure. The Electrical Capacitance Volume Tomography (ECVT) imaging of the square-nosed slugging phenomena conducted in this study reveals otherwise. That is the structure of the square-nosed slug is, in fact, complex, particularly with respect to its dynamic variation in fluidization. More broadly, this study examines experimentally the hydrodynamic characteristics of the square-nosed fluidization regime. Specifically, simultaneous measurements from multiple ECVT sensors provide non-invasive, continuous, 3-dimensional imaging of the entire flow region of the slugging bed and hence enabling the dynamic characterization of the evolution of the slugs. The analysis of the 3D images reconstructed for real-time gas-solid volume fraction profile of the slugging fluidized bed indicates that there are three different zones, namely, the bottom fluidization zone, the gas slug zone, and the solid slug zone, co-existing in the bed. The three zones present different hydrodynamic characteristics during the slug evolution. It is found that varying the gas velocity of the slugging bed mainly varies the maximum length of the gas slug zone, while it only has a minor effect on the lengths of the bottom fluidization zone and solid slug zone. It also has an insignificant effect on the solid volume fraction of the three zones. (c) 2021 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Chemical looping combustion (CLC) is an energy conversion technology that can produce concentrated CO2 stream without the need for a gas separation step, and thus, has the potential to drastically reduce the energy consumption and cost associated with CO2 capture in power generation. The coal-direct chemical looping (CDCL) process is a CLC technology that uses a moving bed reducer configuration that can directly consume coal as a feedstock without requiring an upstream gasification step. An integrated 250 kW(th) CDCL pilot unit using iron based oxygen carriers was constructed and demonstrated for over 1000 h of testing. The principles for the CDCL pilot unit design and operation are summarized in this article. During the 288-hour continuous operation testing, the CDCL pilot unit achieved 96% coal conversion with a CO2 purity of >97%. Low carbon carryover into the combustor, i.e. <2%, was also confirmed during the test, which shows the capability of the moving bed reactor to retain and convert coal using the oxygen available on the iron-based oxygen carrier. The results from the pilot unit testing confirms the CDCL concept as a promising coal combustion technology for heat and power generation with CO2 capture.

A novel process scheme for energy production from coal with in situ sulfur capture, known as the coal-direct chemical looping process with sulfur removal (CDCL-SR), is proposed in this study. The proposed process utilizes multimetal oxide comprising the oxides of copper and calcium supported on inert SiC as the oxygen carrier to combust coal and simultaneously produce separate streams of CO2 and SO2, thus eliminating the need for downstream processing units. The computational software ASPEN Plus has been utilized to carry out detailed reactor simulations along with a thorough thermodynamic analysis of the process. The reactor modeling results indicate that the moving bed reducer can effectively convert all the carbon present in coal into CO2 while capturing sulfur in the form of calcium sulfide in the reduced oxygen carrier. The reduced oxygen carrier can in turn be oxidized using steam to produce pure SO2 stream that can be readily utilized. Process simulation results indicate that the proposed CDCL-SR process has thermal and exergy efficiencies of 86 and 51%, respectively, significantly higher than both the conventional pulverized coal Rankine cycle and Fe-based CDCL processes.

The methane-to-syngas (MTS) chemical looping process is an advanced methane reforming technology for the production of high purity syngas. The developed MTS process utilizes metal oxide oxygen carriers in a cocurrent moving bed reactor to partially oxidize the methane such that the resulting syngas stream is undiluted by nitrogen in air or H-2 from overconversion and directly suitable for downstream processing. The oxygen carriers are regenerated with air in a separate fluidized bed reactor producing a spent air stream separate from the product syngas, circumventing the need for cryogenic air separation units. In this work, a 15 kW(th) subpilot unit is designed and operated in a continuous manner to experimentally confirm the viability of the MTS process. Reactor design considerations and methodology are discussed in detail. An iron-titanium composite oxygen carrier is used as the oxygen carrier for its ability to achieve high methane conversion while regulating the product syngas to the partial oxidation products, CO and H-2. Syngas is produced with an H-2/CO ratio of similar to 2, and a purity of similar to 97% is produced with methane conversion exceeding 99%. The coinjection of methane with H-2 and/or H2O is explored for the purpose of H-2 utilization and flexible H-2/CO ratios, allowing the MTS process to produce syngas for a variety of downstream processes without reactor modification. The results indicate that syngas with H-2/CO ratios ranging from 1.19 to 2.50 with high methane conversion and syngas purity can be produced with coinjection. No evidence of carbon deposition on the oxygen carrier is revealed, and the oxygen carrier retained structural integrity after subjection to reaction and circulation in the subpilot unit.

Chemical looping is a novel and promising technology that converts fossil fuels to electricity and high value chemicals with in-situ carbon capture without significant cost penalties. Smooth and controlled solid circulation is the key to the successful operation of the chemical looping system. Bridging or arching, which may occur in the moving bed standpipe of the system, caused by a combination of fines accumulation and gas flows, is a major impediment to the smooth solid circulation and can lead to the failure of the entire system operation. Thus, early detection of the tendency of bridging or arching is important. This paper describes a model that applies the long short-term memory based recurrent neural network scheme to detect the tendency of arching in the standpipe of a chemical looping system. The arching tendency can be ascertained by early detection of the bubble formation in the standpipe. The bubble movement or local fluidization is recognized to precede the arching formation due to local accumulation of fine particles generated from coarse particle attrition. The early detection of the bubbles thus renders it possible to prevent arching through the prompt action of fines removal from the system. In this study, the recurrent neural network model which detects the fines induced fault manifested as bubbles in the standpipe is developed. It is over the data generated from an experimental sub-pilot scale, cold-flow chemical looping unit. To improve the robustness of the diagnosis, a number of networks with different structures are considered, and an ensemble decision strategy is used to conduct the diagnosis. The recall value obtained of the diagnosed result, which represents the extent of the fraction of real bubbles that are detected, can reach higher than 86.7%. This result reflects a good accuracy of the recurrent neural network model in the fault detection for the chemical looping system.

The purpose of the project is to address the optimization and startup operation of a modular coal direct chemical looping (CDCL) combustion system integrated with a steam cycle for power generation to reduce the risks involved in further scale-up of the technology. The modular reactor design of the CDCL process provides flexibility in the fabrication of the reactor and in its operating capacity (i.e. turndown ratio) at the cost of a more complex heat exchange network (HEN) design and integration. To address the technology gaps and advance the efficiency and economic feasibility of the CDCL technology, the project will perform a detailed and comprehensive analysis of the integration of a modular CDCL reactor system and a steam cycle system under both static and transient conditions via HEN process performance simulations and system dynamic modeling, respectively. The scope of work consists of 1) Experimental and computational studies of the CDCL combustor reactor 2) Comprehensive static (i.e. steady-state) system HEN design analysis in CDCL 550 MWe commercial unit for power generation and 3) Dynamic modeling of site specific design of 10MWe CDCL large pilot plant. The project team has successfully developed and validated a kinetic model for the oxidation of oxygen carriers in the combustor using the unreacted shrinking core model (UCSM). The model is capable of capturing the oxidation kinetics of fully or partially reduced oxygen carrier particles. A computational fluid dynamics (CFD) model is developed to simulate the hydrodynamics, heat transfer, and chemical reaction occurring in the CDCL combustor. The model is developed in MFIX and ANSYS Fluent. Key aspects of CDCL combustor operation, including heat transfer, oxygen carrier oxidation, and the transport of oxygen carrier particles, are simulated using this CFD model. The HEN for a commercial scale 550 MWe CDCL power plant is simulated and optimized using ASPEN Plus. Practical design considerations are incorporated based on industrial experiences. The performance and cost for the commercial CDCL plant is updated based on these analyses. A dynamic model for the 10 MWe CDCL pilot plant is developed in ProTRAX simulation software. The model is based on the pilot plant design developed in project DE-FE0027654 “10 MWe CDCL Large Pilot Plang – Pre-FEED Study” and the steam cycle data obtained from Dover Light & Power plant. The transient behaviors during pilot plant load variation are simulated using the dynamic model.

•World’s first chemical looping pilot plant utilizing moving bed reactors.•Achieved near-full conversion of coal-derived syngas in the moving bed reducer.•Achieved 99% purity hydrogen production with in-situ carbon capture.•Validated operational results by ASPEN process simulation.

The Syngas Chemical looping (SCL) process provides efficient and economic means to utilize the abundant fossil reserve of coal. The main problem associated with coal utilization is the CO2 emissions resulting from its combustion. Even though CO2 regulation or carbon tax is currently not in place, its enforcement is expected in the near future. Such a greenhouse gas emission control, if adopted in current power plant systems, will drive the efficiency down and increase the cost of electricity, due to the energy and capital-intensive nature of current CO2 separation techniques. This highlights the need to develop technologies that present a solution to the rising cost of electricity in the future. The integrated gasification combined cycle (IGCC) presents an improvement to the above predicament, but it is capital intensive due to the extensive unit operations involved. The efficiency for a CO2 capture incorporated IGCC system is around ~32%, resulting in approximately 45% increase in cost of electricity. This is definitely a better path to traverse than the conventional pulverized coal (PC) power plants as it has improved economics and efficiencies accompanied by product flexibility. The SCL process advances the benefits even further when integrated with the IGCC process. The SCL process removes the expensive WGS system and CO2 separation columns, thereby saving on capital and operational expenses. This integration results in a 12 – 21% increase in efficiency accompanied by a reduction in cost of electricity by 15 – 28%, over conventional IGCC systems. Therefore, SCL process provides the best route to harness the energy from coal. The overall project objective was to construct and operate a syngas chemical looping pilot scale test unit at the NCCC. The project scope of work was divided into 3 phases. In Phase I, cold flow model studies using a 1:1 scale acrylic test unit constructed at Particulate Solids Research, Inc. (PSRI) was successfully completed confirming robust solid flow control is achievable in the non-mechanical system design. In Phase II, the high pressure, high temperature, chemical looping reactor was successfully designed with all necessary equipment and safety instrumentation/controls specified to allow for fabrication, site construction, and assembly to commence in Phase III. In Phase III, the SCL pilot plant was successfully assembled and all necessary functional checks and pre-startup safety reviews completed. During unit commission over the course of 200 hours of testing, operational issues were observed with premix burner used for system startup. With the grants awarded by the National Energy Laboratory (NETL) and the Ohio Development Services Agency (ODSA) under awards DE-FE0023915 and D-14-18, the SCL pilot unit underwent three auxiliary equipment modifications to resolve all of the startup operational issues encountered. The unit was successfully demonstrated with 300+hr continuous operation. Key results obtained include high syngas conversion of 97.95% with 16.03% oxygen carrier conversion in the moving bed reducer and >99% purity H2 produced from the moving bed oxidizer.

This project is focused on supporting the use of coal for power production through the continued development of the Coal Direct Chemical Looping (CDCL) technology. The objective of the program is to evaluate the commercial viability of the CDCL technology. This report describes the results of Phase II of the project up to the date of the period of performance as listed above. The Phase II objectives are to reduce the technology gaps associated with the oxygen-carrier properties, coal conversion, and reducer design of the CDCL process. During this project, a 250 kWth CDCL pilot unit was designed, fabricated, installed and subsequently tested to demonstrate critical components. The pilot unit simulates actual design concepts envisioned for the commercial unit. The knowledge gained from laboratory and pilot-scale testing is used to refine the commercial plant design and cost analyses.

The fate of sulfur in the coal-direct chemical looping system was investigated in the sub-pilot reactor system. The sulfur balance was successfully closed during the injection of high sulfur coal. More than 69% of the total amount of atomic sulfur in coal was released as SO2 and H2S from the reducer flue gas stream while less than 5% was emitted as SO2 from the combustor spent air. The remaining atomic sulfur was retained in coal ash as inorganic sulfur compounds. The finding suggests an acid gas removal system targeting both H2S and SO2 is required to meet the recommended quality of CO2 stream for sequestration and transportation. Using the determined ratio of SO2 and H2S, a properly designed Claus plant can enable the recovery of elemental sulfur as a value-added byproduct. The combustor spent air was found to comply with the US EPA sulfur emission regulation and can be released to the atmosphere without a costly acid removal system. The relationship between the sulfur and carbon capture efficiencies was established experimentally and was found to be proportional to each other throughout the experiment at a slope of 0.8 below 93% of carbon capture efficiency and near 1 above 93%. This was attributed to the delayed release of organic sulfur during incomplete char gasification in the reducer. The finding affirms the effectiveness of the counter-current moving bed design for minimizing the amount of carbon and sulfur emission in the combustor spent air with an average carbon and sulfur capture efficiency of 96.5 and 95%, respectively. Sulfur deposition on the iron based oxygen carriers did not affect the system performance, and complete removal of deposited sulfur was observed during oxidation in a thermo-gravimetric analyzer. Compared with chemical looping systems using circulating fluidized bed configuration, the use of a moving bed reducer has the additional benefit of minimizing slippage of char into the combustor due to the use of large oxygen carrier; resulting in lower sulfur emission in the combustor spent air. The findings demonstrate the robustness of the coal-direct chemical looping system to handle high sulfur coal without a complicated acid gas cleaning scheme or severe performance penalties.