Syngas Chemical Looping Process Research Articles

Efficient co-production of power and ammonia from black liquor

Black liquor (BL) is a by-product in the paper and pulp industry. Although it has good potential for providing energy as an industrial waste, BL's high moisture content limits its usability. In this study, an integrated system to effectively co-produce power and ammonia (NH3) from BL is modeled and evaluated. The modeling and integration are conducted using the principles of exergy recovery and process integration to effectively circulate the energy/heat throughout the whole system. The developed system involves BL evaporation, gasification, syngas chemical looping (SCL), and NH3 synthesis. During SCL process, H2, CO2, and N2-rich gas are produced consecutively in the oxidation, reduction, and combustion reactors, respectively. The designed system can achieve the total energy efficiency of ~50%. The result also suggests that N2-rich gas and pure H2 produced during SCL can be used directly for NH3 synthesis without any additional energy penalty. The additional step for CO2 separation can also be avoided, affording a cleaner and more efficient system that provides complete carbon capture.

Efficient black liquor conversion to power and H2 by adopting negative emission technology

Abstract Currently, some projects are underway to achieve high efficient conversion and reduce costs associated with H2 production. Biomass gasification is considered as a mature technology involving heat, steam, and oxygen to convert biomass to syngas including H2. Since biomass is treated as carbon neutral energy source, it can significantly reduce environmental impact. By integrating biomass conversion technology and carbon removal from environment, negative carbon emission can also be realized. In this study, co-production of H2 and power from black liquor (BL) is proposed based on enhanced process integration consisting of process integration and exergy recovery. The proposed system mainly consists of BL evaporation, gasification, syngas chemical looping (SCL), and power generation. The evaporation process employs exergy recovery using steam tube rotary evaporator. The effect of target moisture content on the evaporator performance is evaluated. Furthermore, the thermodynamics analysis of gasification is performed in circulating fluidized bed reactor based on Gibbs energy minimization. The SCL process comprises reducer, oxidizer and combustor and integrates with power generation. In addition, the concentrated CO2 can be generated during the SCL process, avoiding additional cost for separation.

Efficient black liquor conversion to power and H2 based on process integration and exergy recovery

Hydrogen (H2) is considered as a clean energy carrier in the future with high efficiency and various utilization technologies. The H2 can be produced from biomass as primary energy source to reduce environmental impact. Currently, some projects are underway to achieve efficient conversion and reduce costs associated with H2 generation. High energy efficiency can be achieved by minimizing exergy loss through process integration and exergy recovery. In this study, co-production of H2 and power from black liquor (BL) is proposed based on process integration and exergy recovery. The proposed system consists of BL evaporation, gasification, syngas chemical looping (SCL), and power generation. The evaporation process employs exergy recovery using steam tube rotary evaporator. The effect of target moisture content on the evaporator performance is evaluated. Furthermore, the thermodynamics analysis of gasification is performed in circulating fluidized bed reactor based on Gibbs energy minimization. The SCL process comprises reducer, oxidizer and combustor and integrates with power generation. The result shows that the proposed integrated system can achieve higher efficiency of nearly 70%. In addition, the concentrated CO2 can be generated during the SCL process, avoiding additional cost for separation.

250 kWth high pressure pilot demonstration of the syngas chemical looping system for high purity H2 production with CO2 capture

Chemical looping combustion (CLC) is an advanced technology for converting fossil fuel while achieving in-situ CO2 capture. The high purity CO generated in the combustion product stream is sequestration/utilization ready, which makes chemical looping one of the most attractive carbon emission control technology. In this paper, the authors present the design, simulation and experimental operation results of the 250 kWth high pressure syngas chemical looping (SCL) pilot plant. The pilot plant’s unique countercurrent moving bed design allows near-full conversion of coal-derived syngas with simultaneous production of high purity, carbon-free H2. Critical aspects of the design efforts, including heat and material balances, reactor sizing approach and solid flow control and measurement devices are presented. An ASPEN Plus® model is constructed to predict the gas and solid conversions of the SCL process the gas and solid conversions of the SCL process under different experimental conditions. The highest syngas conversion achieved was 97.95% with 16.03% oxygen carrier conversion, which were close to the thermodynamic limits for both the gas and solid phases in the reducer. Differences between the experimental results and predicted conversion values were more significant under conditions with lower oxygen carrier to fuel ratio. Greater than 99% purity H2 was produced from the moving bed oxidizer, and the scalability and feasibility of SCL process were successfully demonstrated.

Cogeneration system of power and h2 from black liquor through gasification and syngas chemical looping

One of the strategies to improve environmentally friendly energy harvesting can be realized by using biomass as a primary energy source for generating electricity and H2. In addition, high energy efficiency can be achieved by minimizing the exergy loss through process integration and exergy recovery. As an implementation, this study proposes a cogeneration system for black liquor (BL) to co-produce electricity and H2. The system primarily comprises of BL drying, circulating fluidized bed gasification, syngas chemical looping (SCL), and power generation. The Aspen Plus V8.8 software package is used for modelling and performing calculations of the proposed integrated system. Furthermore, thermodynamic analysis of gasification is performed by employing Gibbs energy minimization. The effects of target solid content on the required total work and compressor outlet pressure during drying and gasification with different steam-to-fuel ratios are evaluated. Moreover, the SCL process adopts three reactors, namely, the reducer, oxidizer, and combustor. Compared to the conventional processes, the integrated drying-gasification-SCL processes are significantly cleaner and more energy efficient. The proposed integrated system can achieve a net energy efficiency of about 70 %, with almost 100 % carbon capture.

Energy-efficient recovery of black liquor through gasification and syngas chemical looping

One of the strategies to improve environmentally friendly energy harvesting can be realized by using biomass as a primary energy source for generating electricity and H2. In addition, high energy efficiency can be achieved by minimizing exergy loss through process integration and exergy recovery. As an implementation, this study proposes a cogeneration system for black liquor (BL) to co-produce electricity and H2. The system primarily comprises BL drying, circulating fluidized bed gasification, syngas chemical looping (SCL), and power generation. The Aspen Plus V8.8 software package is used for modeling and performing calculations of the proposed integrated system. Furthermore, thermodynamic analysis of gasification is performed by employing Gibbs energy minimization. The effects of target solid content on the required total work and compressor outlet pressure during drying and gasification with different steam-to-fuel ratios are evaluated. Moreover, the SCL process adopts three reactors, namely, the reducer, oxidizer, and combustor. Compared to conventional processes, the integrated drying-gasification-SCL processes are significantly cleaner and more energy efficient. The proposed integrated system can achieve a net energy efficiency of about 70% with almost 100% carbon capture.

Syngas chemical looping process: Dynamic modeling of a moving‐bed reducer

The syngas chemical looping process coproduces hydrogen and electricity with iron oxide based oxygen carriers in a circulating moving bed system. In this article, a one‐dimensional (1‐D) dynamic model is developed to simulate the countercurrent gas–solid reactive flow in the moving‐bed reducer. This model is validated by TGA and bench‐scale experiments. Both the steady state and dynamic composition profiles are obtained to help understand the reaction and reactor behaviors. Numerical simulation on the effects of reactor length is conducted to optimize the moving‐bed reducer design. It is also found that minor variations in the feed rate ratio near a critical point that is represented by the reaction equilibrium could yield a significant difference in the time required for the reactions to reach a steady‐state operation. Such a difference has an important practical implication in that the moving‐bed reducer should be designed and operated to circumvent the critical point. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3432–3443, 2013

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.

Continuous high purity hydrogen generation from a syngas chemical looping 25 kWth sub-pilot unit with 100% carbon capture

The syngas chemical looping (SCL) process circulates iron-based oxygen carrier particles through three reactors, namely the reducer, the oxidizer, and the combustor, to perform reduction–oxidation reaction cycles for converting gaseous fuels to highly concentrated discrete streams of hydrogen (H2) and carbon dioxide (CO2). The counter-current moving-bed operation of the reducer enhances the extent of oxygen carrier conversion, which facilitates the generation of hydrogen as confirmed in lab and bench scale studies. The 25kWth sub-pilot SCL unit represents an integrated continuous demonstration of all 3 reactor sections. Previous studies have analyzed the design criteria, construction, and preliminary demonstration of the sub-pilot unit with promising results. In this study, the results from extended demonstrations conducted using two reactor configurations and two oxygen carrier types differing in size and iron composition are presented. In each demonstration, the solids and syngas flow rates are varied to analyze the effect on the unit performance. Steady profiles of 99.99% H2 production and nearly 100% syngas conversion are achieved. Post-experiment solids analysis on the oxygen carrier particles revealed no deterioration in oxygen carrier performance after the extended demonstration and highlights the longevity of the oxygen carrier. Additionally, the abraded oxygen carrier fines collected during operation could be reprocessed to match the fresh particle performance, making solids make-up more economically viable. Multistage equilibrium moving bed model reducer studies are conducted to compare the experimental syngas conversions for each test condition with the theoretical thermodynamic results. The experimental results matched well with the model results. A total of over 300h of integrated sub-pilot unit demonstration have been conducted with a longest continuous run of 3days validating the reliable performance of the SCL process for cogenerating high-purity H2 and electricity with 100% CO2 capture.

Syngas Chemical Looping Process: Design and Construction of a 25 kWth Subpilot Unit

The syngas chemical looping (SCL) process employing the gas–solid counter-current flow pattern demonstrates an innovative approach to generate hydrogen and/or electricity from syngas accompanied with in situ carbon capture. Iron-based oxygen carriers donate oxygen for complete syngas conversion in the reducer. The reduced oxygen carriers are then oxidized by steam and/or air to generate hydrogen and/or heat in the oxidizer and/or the combustor, respectively. Previous studies have reported the performance of the iron-based oxygen carriers, the advantages of a moving bed reducer and oxidizer, and simulation of various parametric effects on the reactor design of the reducer, oxidizer, and combustor for a continuous system. In this study, a 25 kWth subpilot SCL unit was designed based on the simulated criteria and constructed to demonstrate the feasibility of generating high purity hydrogen with in situ carbon capture. Two test runs were presented using 4.5 mm × 2.5–4.5 mm cylindrical oxygen carriers comprising of 60 wt % iron oxide (Fe2O3). The first test resulted in a syngas conversion of 99.96% and trace amounts of hydrogen generation highlighting the importance of the extent of oxygen carrier conversion. The second test demonstrated the continuous production of hydrogen with an average purity of 94.4% and a maximum of 98.4% when the conversion of the oxygen carriers exiting the reducer was 35.54%. The initial test results support the concept of continuous hydrogen generation with in situ carbon capture using the SCL process and also highlight the advantage of adopting the counter-current moving bed reactor design.

Syngas chemical looping gasification process: Bench‐scale studies and reactor simulations

AbstractThe syngas chemical looping process co‐produces hydrogen and electricity from syngas through the cyclic reduction and regeneration of an iron oxide based oxygen carrier. In this article, the reducer, which reduces the oxygen carrier with syngas, is investigated through thermodynamic analysis, experiments, and ASPEN Plus® simulation. The thermodynamic analysis indicates that the countercurrent moving‐bed reducer offers better gas and solids conversions when compared to the fluidized‐bed reducer. The reducer is continuously operated for 15 h in a bench scale moving‐bed reactor. A syngas conversion in excess of 99.5% and an oxygen carrier conversion of nearly 50% are obtained. An ASPEN Plus® model is developed which simulates the reducer performance. The results of simulation are consistent with those obtained from both the thermodynamic analysis and experiments. Both the experiments and simulation indicate that the proposed SCL reducer concept is feasible. © 2009 American Institute of Chemical Engineers AIChE J, 2010