Over-temperature of the boiler water-wall poses significant operational safety risks, particularly during deep peak shaving, making accurate prediction of the water-wall temperature crucial for boiler combustion regulation. The water-wall temperature prediction model using the hiking optimization algorithm-based stochastic configuration network (HOA-SCN) was proposed in this study. To create high-quality input features, Light gradient boosting machine (LightGBM) was utilized to evaluate feature variables with correlation. Considering the delay characteristics of boiler working medium, the delay time of the characteristic variables was estimated. To improve the efficiency of traditional SCN searching for weights and biases, to alleviate the ill-posed problem, and to improve the generalization and robustness, the SCN is improved with HOA algorithm and L2 Norm Regularization. Simulation experiments were conducted by extracting actual operating data from an in-service 660 MW coal-fired boiler. The results showed that the improved HOA-SCN achieves significantly better prediction than the conventional models, such as BP and Long Short-Term Memory (LSTM). The training time of HOA-SCN is 3.927 s, compared to 169.464 s and 13.868 s for BP and LSTM. Compared to the baseline model, the RMSE for HOA-SCN was only 2.06 degrees C, while the RMSE for SCN and Greedy-SCN was 4.484 degrees C and 3.628 degrees C.

Chemical looping is an economically advantageous technology for reducing carbon emission from energy, fuels, and chemicals conversion systems utilizing a variety of feedstocks including fossil fuels, renewable materials, and industrial and municipal wastes. Its development relies on two key areas of core competency, i.e., metal oxide reaction engineering, and particle science and technology. The reaction kinetics and the transport phenomena in chemical looping reactors are intrinsically twined with the specific system operational conditions, configuration, and their integration. The optimal design and successful operation of chemical looping systems necessitate a comprehensive consideration of both the reaction rates and multiphase flow characteristics within each reactor. In this article, we analyze the impact of particle hydrodynamic characteristics on optimizing the operational conditions of a syngas-fueled chemical looping (SCL) process, which aims to co-produce hydrogen and electricity. Using this SCL process as an illustrative example, we examine how the particle hydrodynamics influence the system performance and efficiency. The outcome of these effects on the system performance is discussed.

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.

Chemical looping is broadly defined to represent processes that use chemical intermediates to decompose a reaction into two or more sub-reaction steps. Metal oxides are the typical chemical intermediates used for the chemical looping reactions although other metal derivatives are also used. Based on its intended applications, chemical looping encompasses calcium looping for CO2 capture and redox looping for clean energy conversion applications. The redox looping has a longstanding history and has been demonstrated at multiple scales under various operating conditions since its conceptual inception about 120 years ago. Even with such extensive and prolonged efforts, redox looping is yet to be realized sustainably at a commercial level, while the calcium looping has been demonstrated for commercial applications. With growing concerns of climate change due to emissions of industrial greenhouse gases, efforts in developing redox looping processes as a promising fossil energy conversion technology with CO2 emission control have been invigorated since the beginning of the 21st century. Metal oxide reaction engineering and particle science and technology have been the two enabling technical thrust areas, pivotal to advance the chemical looping concept to industrial practice. This article highlights some salient features of the chemical looping processes including a description of their historical development and illustration of the material screening and synthesis of oxygen carrier particles along with the representative process operational behavior. Recognizing that the configuration of chemical looping systems in their key operational scheme is established on the framework of circulating fluidized bed (CFB) systems, this article emphasizes the relevant characteristics of fluidization and fluid-particle systems with which the chemical looping technology is conducted. Both the fundamental and applied aspects of chemical looping processes and their associated CFB operation are discussed.

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.

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.

The United States Energy Information Administration has projected that the global natural gas consumption will rise by 50% between 2010 and 2035. Chemical Looping Reforming for reforming natural gas to syngas represents a potentially efficient means of producing electricity, hydrogen, syngas, and/or liquid fuels with minimal carbon emissions compared to traditional natural gas reforming schemes. Chemical looping reforming represents a potentially efficient way for reforming natural gas to syngas as compared to traditional natural gas reforming schemes. The chemical looping reforming concept refers to the use of a metal oxide to partially oxidize natural gas to syngas while regenerating the reduced metal with air and/or steam. The solar thermochemical process for methane reforming to produce syngas replaces fossil fuels with solar energy to supply the energy for the endothermic heat of reaction. Iron-based oxygen carriers are particularly attractive in chemical looping systems as they are abundantly available and low in cost.

A novel approach to studying dynamic three phase systems using Electrical Capacitance Volume Tomography (ECVT) is proposed and verified against previously published pressure gauge techniques and hydrodynamics patterns. In this three-phase study, hold up of water, glass beads, and air are measured simultaneously in a slurry bubble column reactor. Application of ECVT to investigate three phase systems holds several advantages over pressure gauges including the ability to deliver non-invasive real time direct measurements without making assumptions about the hydrodynamics. Results support the conclusion that ECVT can be used in place of pressure gauges to obtain accurate holdup measurements of three-phase flow systems in real time applications.

•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.

A three-dimensional ECVT sensing technique is applied to imaging complex slugging phenomena of a gas–solid fluidized bed under ambient and elevated temperature conditions. The study indicates that the time interval between rising slugs decreases with an increase in the gas velocity, reaching a nearly steady time interval value of about 1 s between two slugs when the gas velocity is ∼1.7 m/s above the minimum fluidization velocity. The fluidized bed behaves as a bubbling fluidized bed at low gas velocities. In slugging regime, the slug rise velocity increases with the gas velocity. A mechanistic analysis of forces around the dense phase solid particles suggests that the relationship between the slug rise velocity and the gas velocity for the square-nosed slugging bed is not strictly linear and is highly related to the interparticle forces, internal friction of particles, and gas velocity in addition to the wall stress.

Pneumatic transport of solids in a riser has a unique nonuniform flow structure, characterized by the core solids acceleration and the wall solids deceleration along the riser, which causes the down-flow of solids and hence back mixing. To predict this nonuniform flow structure, this paper presents a mechanistic model that includes two controlling mechanisms: the interparticle collision damping for axial transport of solids and the effects of collision-induced diffusion and turbulent convection for radial transport of solids. The model predictions are partially validated against available measurements, such as axial and radial distributions of concentration and velocity of solids.

The L-valve, as a solids flow control device, has been used extensively in fluidized beds and circulating, fluidized beds for controlling the solids circulation rate. Knowledge on L-valves, however, is Mostly limited to ambient flow conditions with Geldart A and B particles. Studies on the L-valve under high temperature conditions which are common in industrial applications are rare. This paper describes experimental studies that probe the characteristics of the L-valve operation under high temperature conditions using Geldart D particles. The relationships between the solids flow rate, aeration rate, and pressure drop are investigated and compared With those under ambient conditions using different groups of particles. The results indicate that the variation of the solids flow rate controlled by the L-valve aeration depends on the actual internal flow rate of the gas that flows through the L-valve rather than the external aeration flow rate of the gas that is introduced into the system. The actual aeration gas flow rate required for generating a given solids flow rate is the same so long as the location of the aeration tap is above the height-to-diameter ratio of 1.5 in the L-valve. Operating the L-valve with Geldart D particles needs more gas aeration compared to that with Geldart A and B particles for a given solids flow rate. However, under high temperature Conditions, the solids flow for Geldart D particles in the L-valve behaves like those with Much smaller particle sizes. For Geldart D particles, the aeration gag flow rate required under high temperature conditions is much less than that under ambient conditions.

结合活性焦干法烟气净化技术的优缺点以及现阶段中国燃煤电厂烟气脱硫整体发展水平,分析活性焦干法烟气净化技术应用于中国大型燃煤电厂的适应性;总结了该技术应用于燃煤电厂烟气污染治理需解决的关键问题,如工程造价、对高SO2浓度烟气的适应性、所需物料的供应及脱硫副产物处置及活性焦再生热源等,对于中国高含硫燃煤烟气条件,若采用活性焦干法烟气净化技术,需进行二次技术开发;特别指出,只有研发出中国自主知识产权的可资源化活性焦干法烟气宽谱净化技术,实现技术设备国产化,尤其是吸附塔和解析塔等核心设备的加工制造,才能大幅降低工程造价,使该技术具有较强的技术经济优势而加以推广。

•Integrated, moving bed chemical looping reactor with iron-oxide based oxygen carrier.•Coal carbon conversion from 84.8% to 99.9%, thermal capacity 7.4 to 27.7kWth, O2 demand less than 1.3%.•Dynamic temperature of moving bed reducer is established and tracked during coal injection.•CH4 and CO present at initial coal injection, eliminated after oxygen carrier activated.•Lower coal injection had higher volatiles residence time and conversion.