Efficiency Penalty Research Articles

Light management for ever-thinner photovoltaics: A tutorial review

Ultra-thin solar cells, an order of magnitude thinner than conventional technologies, are an emerging device concept that enables low-cost, flexible, lightweight, and defect-tolerant photovoltaics. However, the advent of ultra-thin technologies is hindered by the fundamental challenge of poor light harvesting in thinnest absorber layers, which entails prohibitive photocurrent and efficiency penalties. Here, from a tutorial perspective, we review different light-management platforms that can overcome this inherent limitation, namely, antireflection coatings, rear mirrors, and light-trapping textures. We then review the state-of-the-art performances that have been achieved with these strategies and that have led to records of ∼20% efficiency in ∼200 nm absorbers. Finally, we identify persisting challenges and potential development avenues for attaining competitive performance with ever-thinner photovoltaic devices.

Passive flow control at impeller radial bend for stall delay in centrifugal compressors with fishtail pipe diffusers

This paper proposes a new strategy for extending centrifugal compressor stall margin through shroud passive flow control placed at the impeller radial bend. Relative to the usual leading-edge location, the radial bend presents fewer geometrical constraints for flow control devices and allows them to have potentially more impact on low-momentum flow structures that lead to stall. Two centrifugal compressors with fishtail pipe diffusers are chosen for study: a high-speed transonic design exhibiting diffuser stall and a low-subsonic design with exducer stall. Four passive flow control techniques placed on the impeller shroud at the radial bend are evaluated for each compressor, in terms of stall margin improvement and efficiency penalty at design mass flow, using unsteady RANS CFD simulations. These are circumferential groove, slots, impeller recirculation pipe and diffuser-impeller recirculation pipe. The results indicate that passive flow control at the impeller shroud radial bend can be significantly more effective than at the impeller leading edge. For each compressor, the flow mechanisms associated with stall initiation and its delay by the most effective studied flow control technique as well as the associated efficiency penalty are elucidated. The findings indicate that techniques having flow injection with high spanwise penetration and low relative streamwise momentum are most effective for delaying diffuser stall, while the opposite applies to exducer stall. The design point efficiency penalty is due to mixing/shear losses from the jet-in-cross flow phenomenon in the impeller and shear losses from flow redistribution in the diffuser.

Thermodynamic investigation of an integrated near-zero CO2 emission power generation system with SOFC, MGT, SCO2BC, and CO2 capture

In response to the imperative to reduce carbon emissions in power generation, a novel near-zero CO2 emission power generation system integrating solid oxide fuel cell (SOFC), micro gas turbine (MGT), supercritical carbon dioxide recompression Brayton cycle (SCO2BC) and CO2 capture (CC) is proposed and investigated. The innovation lies in the utilization of oxy-combustion for CO2 capture from the anode off-gas and the strategic harnessing of waste heat from the cathode off-gas through sequential MGT and SCO2BC processes. A comprehensive mathematical model is developed to assess the thermodynamic performance of the integrated system. The results indicate that the electrical efficiencies of the individual components, SOFC, SOFC-MGT, and SCO2BC, are 56.52%, 66.00%, and 40.76%, respectively, and the integrated system demonstrates an impressive overall efficiency of 70.15% under a current density of 5000 A/m2. The efficiency penalty incurred by CC on the integrated system is approximately 2%. A sensitivity analysis of key parameters highlights the potential for optimizing individual components to enhance power output or efficiency. Notably, the optimal overall efficiency is achieved when the SOFC operates at 0.25 MPa, the fuel utilization ratio is 85%, and the SCO2BC compressor pressure ratio is 2.6. This research not only establishes the viability of the proposed integrated system but also provides insights into optimizing its components for improved performance in power output and efficiency.

Mechanical and Economic Analysis of Conventional Aluminum Photovoltaic Module Frames, Frames With Side Holes, and Open-Source Downward-Fastened Frames for Non-Traditional Racking

Abstract Using bolts through the back of a solar photovoltaic (PV) module frames to attach them to racking is time consuming and awkward, so commercial PV installations use clamping technologies on the front. Conventional and proprietary clamps are costly and demand access to supply chains for uncommon mechanical components that limit deployment velocity. To overcome these challenges, this study presents new open-source downward-fastened and side-fastened aluminum (Al) framing designs, which are easy to install and compatible with metal and wood racks. The proposed parametric open-source designs are analyzed through finite element method (FEM) simulations and economic analysis is performed to compare to conventional PV frame at both the module and system levels. The FEM results showed all the frames have acceptable mechanical reliability and stability to pass IEC 61215 standards. The results show the new frame (with a bottom width of 29 mm and thickness of 1.5 mm) has about a 2% land use efficiency penalty, but has better mechanical stability (lower stress and deflections), is easier to install, and has reduced material economic costs compared to conventional frames. The results are promising for the use of the new PV frame designs for distributed manufacturing targeted at specific applications.

Study on the combined influence of aerodynamic sweep and casing treatment in a transonic compressor rotor

Casing treatment and three-dimensional blade design are effective techniques to remedy the deficiency of compressor stability margin, yet their combined effects on compressor performance are seldom studied. With the help of URANS simulations, this paper explored the combined influence of aerodynamic sweep and casing treatment in a transonic compressor rotor. Compared with the configurations of single sweep and single casing treatment, the combined configuration presented an outstanding advantage for improving compressor performance. For compressor overall performance, the stall margin improvement of combined configuration was up to 11.8%, larger than single forward sweep and single casing treatment. Meanwhile, peak efficiency penalty of combined configuration (−1.02%) was significantly lower than that of single casing treatment. Under the effect of casing treatment, the results showed that the pulsating axial velocity could effectively delay the interface of the tip leakage flow and main flow, preventing the overflow of tip leakage flow. The distributions of blockage coefficient and loading coefficient indicated that combined configuration was more effective due to tip unload by casing treatment and blockage resistance ability by forward sweep. Furthermore, the spatial and temporal evolutions of axial velocity at slot opening surface were discussed in detail. Compared with the single casing treatment, higher positive axial velocity excitation and smaller range of negative axial velocity were introduced by combined configuration, which contributed to better stability enhancement.

Characterizing Shrouded Stator Cavity Flow on the Performance of a Single-Stage Axial Transonic Compressor

Abstract Shrouded stator cavity flow increases the stator total pressure loss, reduces the compressor isentropic efficiency, and thus limits the compressor pressure rise capability. This paper proposes a simplified cavity flow model that consists of flow injection at the stator inlet and flow suction at the stator outlet. Based on this model, a full-factorial parametric study on the leakage flow ratio and the leakage swirl angle is performed at different rotational speeds and incidences. In the first place, the effectiveness of the numerical method is validated against the experimental data based on the full-scale cavity geometry; then, the numerical simulations on the simplified cavity geometry are validated against that of the full-scale one. Results show that the leakage flow ratio plays a dominant role in determining the compressor performance penalty. The isentropic efficiency drops almost linearly with the leakage flow ratio due to deteriorated near-hub separations, and the slope becomes steeper at higher operating speeds and incidences. The leakage swirl angle only has a pronounced effect under a high leakage flow ratio. The efficiency penalty reduces with increasing swirl angle due to an alleviated tangential flow mixing and suppressed near-hub separations. The swirl angle effect is more pronounced at lower incidence conditions. These findings advance the fundamental understanding of shrouded stator cavity flow effects and provide useful guidance for cavity seal designs.

A two-material thermal barrier coating spatially tailored for high-efficiency GCI combustion

Continued research into thermal barrier coatings (TBCs) for internal combustion engines has generated insights into the design of TBCs that can increase fuel conversion efficiency. In this work, two low thermal inertia TBCs (a commercially available Gen 1 material, Gadolinium Zirconate, and a proprietary Gen 2 material) were experimentally tested in gasoline compression ignition (GCI) on a light-duty single cylinder research engine. Compared to a metal baseline, a 250-micron thick Gen 1 coated piston produced an efficiency benefit of 0.4 percentage points (pp) at 6 and 10 bar net indicated mean effective pressure (IMEPn) and a 0.2 pp penalty at 15 bar IMEPn. The Gen 1 coating also showed an uHC and smoke penalty. An 80-micron thick Gen 2 coated piston showed an efficiency benefit of 0.9 pp at 6 bar IMEPn and 0.4 pp at 10 bar IMEPn, but an efficiency penalty of 0.5 pp at 15 bar IMEPn. The Gen 2 coating, which has a lower thermal inertia than the Gen 1 coating, displayed durability problems while the Gen 1 coating did not. A third piston was coated with a 120-micron thick Gen 2 coating everywhere except the high failure outer bowl region, which was coated with a 120-micron Gen 1 coating. This hybrid coating displayed good durability, an uHC emission penalty, a smoke benefit, an efficiency benefit of 0.1 pp at 6 bar IMEPn, an efficiency benefit of 0.4 pp at 10 bar IMEPn, and no change in efficiency at 15 bar IMEPn. These results indicate that a durable Gen 1/Gen 2 coating can provide an efficiency benefit to GCI combustion, and that further improvements on piston-spray interaction optimization and surface sealing of the TBC, as well as increasing the coated combustion chamber surface area (e.g. head and valves) can add further improve efficiency.

A Survey of Design and Optimization for Systolic Array-based DNN Accelerators

In recent years, it has been witnessed that the systolic array is a successful architecture for DNN hardware accelerators. However, the design of systolic arrays also encountered many challenges. As DNN structures and applications become more complex, a DNN hardware accelerator based on the typical systolic array architecture suffers severe performance and efficiency penalties. So, it has motivated a significant amount of research on the redesign and optimization of the systolic array architecture. In this article, we survey these works on analyzing, redesigning, and improving the performance and efficiency of the systolic array architecture. These works are critical to the design flow of DNN accelerators based on systolic arrays. We also provide a technique classification of these works on the basis of their main research idea. Further, we attempt to compare the advantages and disadvantages of different designs and different technologies and provide quantitative results for reference. The aim of this survey is to provide researchers with knowledge of the state-of-the-art in the systolic array architecture and motivate them to design highly efficient DNN accelerators of tomorrow.

Cost Analysis of Pathways for the U.S. Shipping Fleet to Comply with the IMO 2020 Rule

Since 2020, ocean-going vessels must comply with the International Maritime Organization (IMO) mandate to reduce the sulfur content of marine fuels (outside emission control areas) to no more than 0.5%. This paper analyzes the cost of different approaches for the U.S. fleet, which has special cost considerations because of the Jones Act, to comply with the regulation. We perform a cost analysis for a suite of options for compliance by U.S. shippers, including low-sulfur petroleum-based fuels and alternative fuels (liquefied natural gas [LNG], ammonia, methanol, and ethanol). The cost analysis compares the average annual costs (capital and fuel) out to 2050 of each compliance approach for a representative U.S. tanker and U.S. containership under alternative scenarios with regard to fuel prices, policy, and technology innovation. We also consider the sensitivity of results with respect to vessel age, interest rates, and scrubber fuel efficiency penalties. We find the least costly compliance strategies across future fuel price scenarios and vessel types. The lower-cost compliance pathways typically deliver limited improvement in CO2 emissions which makes them riskier in the context of potential more ambitious emissions targets by IMO. This paper is derived from a technical report (ORNL/SPR-2021/2088) first prepared for the U.S. Maritime Administration.

Comparative analysis of CO2 capture technologies using amine absorption and calcium looping integrated with natural gas combined cycle power plant

Achieving net zero emissions is a crucial challenge in the global climate change policy. It requires a substantial reduction in unabated fossil fuel use, the deployment of renewable energy sources, and the development of carbon capture, utilisation and storage technologies. The aim of this study was to investigate and compare two CO2 capture retrofits for natural gas combined cycle (NGCC). First one, amine absorption, is already mature and characterised as commercial technology, whereas second one, calcium looping is a promising method but still under pilot studies. Energy required for capture process yields net efficiency penalty, which in conducted research totalled 8.4% points for amine unit and 7.4–15.5% points in calcium-looping units. The economic evaluation was performed to analyse the impact of both concepts on their profitability. Moreover, the climate change mitigation potential was assessed and indicated that carbon capture can lower the emissivity of a conventional power plant by 82–87% or even contribute to achieving negative emissions when biofuels are used. Carbon dioxide capture is one of the key elements of ongoing energy transition and its integration with NGCC power units could be determined as essential for maintaining energy security with net zero emissions.

Conceptual assessment of sustainable methane production from oxycombustion CO2 capture in waste-to-energy power plants

The worldwide deployment of renewable energy is growing exponentially. However, its intermittency limits its impact on the yearly energy contribution to the grid. Thus, coal remains the largest source of electricity generation in the world. Developing negative emissions technologies, such as Bioenergy with Carbon Capture and Utilization (BECCU), is a promising pathway. This study focuses on integrating waste biomass oxycombustion and a power-to-methane system. A proton exchange membrane electrolysis driven by photovoltaic solar energy is considered to produce hydrogen and oxygen, which is used for oxy-waste combustion in a sub-critical steam power cycle. Depending on the operation strategy, a certain amount of additional O2 would be required, produced by a cryogenic distillation air separation process. At the exit of the boiler, the almost pure CO2 stream is further purified, compressed, and sent to the methanation reactor. A quasi-stationary model of the entire plant is developed to simulate different operation conditions and assess the integration efficiency. The results show an excellent integration of the whole plant, with a yearly average efficiency penalty associated with the CO2 avoided of 6 % points. Since waste biomass is used as fuel, the system provides −610 kg CO2/MWh emissions compared to biomass plants without CO2 capture. Results from a yearly detailed techno-economic analysis show an average levelized cost of electricity of 199.56 €/MWh and an average green methane production cost of around 110.12 €/MWh. These yearly results involve a CO2 capture cost of about 65.66 €/ton CO2, which justify the potential interest in the proposed system for new and retrofitted biomass power plants.

Advanced natural gas liquefaction and regasification processes: Liquefied natural gas supply chain with cryogenic carbon capture and storage

Natural gas combined cycle power plants generate substantial amounts of CO2. Also, since natural gas is produced in limited sites, the liquefied natural gas (LNG) supply chain consumes considerable energy in transporting natural gas overwide. Herein, advanced natural gas liquefaction and regasification processes using an LNG supply chain with cryogenic CO2 capture and storage (CCS) are proposed using Aspen Plus® V11. This solves three significant problems associated with conventional LNG supply chains. First, through the utilization of LNG cold energy, the cryogenic CCS process reduces the efficiency penalty of power generation from 14.34 to 4.45%. Second, solid CO2 from cryogenic CCS is used as an additional cold source in the natural gas liquefaction process by conveying it to the liquefaction site via the returning LNG ship. As a result, the power consumption in the refrigerant cycle is reduced by up to 67.17% than single mixed refrigerant (SMR) process. Finally, the LNG supply chain with cryogenic CCS minimizes the sustained energy waste between the natural gas liquefaction and regasification stages owing to the geographical separation. LNG cold energy from the regasification stage is utilized in the form of solid CO2 in the CCS and liquefaction stages. Consequently, the exergy efficiency in the overall LNG supply chain increases from 18.18 to 46.39%. The findings of this study can potentially provide environmentally friendly design guidelines for various LNG processes that use LNG cold energy in CCS and natural gas liquefaction.

Unsourced Multiple Access With Random User Activity

To account for the massive uncoordinated random access scenario, which is relevant for the Internet of Things, Polyanskiy (2017) proposed a novel formulation of the multiple-access problem, commonly referred to as unsourced multiple access, where all users employ a common codebook and the receiver decodes up to a permutation of the messages. In this paper, we extend this seminal work to the case where the number of active users is random and unknown <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a priori</i> . We define a random-access code accounting for both misdetection (MD) and false alarm (FA), and derive a random-coding achievability bound for the Gaussian multiple access channel. Our bound captures the fundamental trade-off between MD and FA probabilities. It suggests that the lack of knowledge of the number of active users entails a small penalty in energy efficiency when the target MD and FA probabilities are high. However, as the target MD and FA probabilities decrease, the energy efficiency penalty becomes more significant. For example, in a typical IoT scenario with framelength 19200 complex channel uses and 25–300 active users in average, the required energy per bit to achieve both MD and FA probabilities below 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , predicted by our bound, is only 0.5–0.7 dB higher than that predicted by the bound in Polyanskiy (2017) for a known number of active users. This gap increases to 3–4 dB when the target MD probability and/or FA probability is below 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> . Taking both MD and FA into account, we use our bound to benchmark the energy efficiency of slotted-ALOHA with multi-packet reception, of a decoder that simply treats interference as noise, and of some recently proposed unsourced multiple access schemes. Numerical results suggest that, when the target MD and FA probabilities are high, it is effective to estimate the number of active users, then treat this estimate as the true value, and use a coding scheme that performs well for the case of known number of active users. However, this approach becomes energy inefficient when the requirements on MD and FA probabilities are stringent.

Green hydrogen production from decarbonized biomass gasification: An integrated techno-economic and environmental analysis

Biomass gasification represents an effective and promising conversion technology to different energy carriers/chemicals. Biomass gasification with CO2 capture will give an energy conversion system with negative CO2 emissions. This work assesses the techno-economic and environmental implications of decarbonized green hydrogen generation using the biomass gasification. Several pre-combustion decarbonization technologies were evaluated: chemical and physical scrubbing (absorption), membrane, hybrid membrane - chemical scrubbing. All evaluated biomass gasification concepts have 300 MW hydrogen output (corresponding to 100,000 Nm3/h hydrogen with purity above 99.95% vol.) with 90% carbon capture rate. Different system engineering tools were employed for the integrated assessment. As an important novelty outcome of this work, the green hydrogen production from decarbonized biomass gasification has promising potential to deliver high energy conversion efficiency (in the range of 57–59%), lower energy and cost penalties for decarbonization (about 2.2–3.5 net points), negative carbon emissions (considering that the primary fuel - biomass - is of renewable source). Among various assessed decarbonization technologies, the membrane system shows better techno-economic performances than the gas-liquid absorption (e.g., reduced CAPEX and OPEX by 7% and 7–9% respectively, inferior hydrogen production cost by about 7% etc.).

Automatic Power Factor Compensation

Paper present the project designed to correcting power factor for domestic, Commercial, Industrial. Which with hope to make the cost and energy usage efficient, because the energy source is depleting due to increase in population. Power factor is the ratio of real power and apparent power. This definition is mathematically represented as kW/kVA where kW is active power and kVA is apparent power (active + reactive). Reactive power is the non-working power generated by the magnetic and inductive load to generate magnetic flux. The increase in reactive power increase the apparent power so the power factor will decrease. Low pF will cause the industry to meet high demand thus making it less efficient. The main aim of this project is to increasing the current power factor of industries from 0.85 to 0.90. Power factor compensation contribute to reduction in current-dependent losses and increase energy efficiency while expanding the reliability of planning for future energy network. As technology develops, the gradual cost and efficiency penalty should reduce. Therefore, automatic power factor compensation device should become cost-effective and smaller device over time. That is the reason this project is using programmable device as it is a miniature architecture device.

Network Size Estimation for Direct-to-Satellite IoT

The worldwide adoption of the Internet of Things (IoT) depends on the massive deployment of sensor nodes and timely data collection. However, installing the required ground infrastructure in remote or inaccessible areas can be economically unattractive or unfeasible. Cost-effective nanosatellites deployed in low Earth orbits (LEOs) are emerging as an alternative solution: on-board IoT gateways provide access to remote IoT devices, according to direct-to-satellite IoT (DtS-IoT) architectures. One of the main challenges of DtS-IoT is to devise communication protocols that scale to thousands of highly constrained devices served by likewise constrained orbiting gateways. In this article, we tackle this issue by first estimating the (varying) size of the device set underneath the (mobile) nanosatellite footprint. Then, we demonstrate the applicability of the estimation when used to intelligently throttle DtS-IoT access protocols. Since recent works have shown that MAC protocols improve the throughput and energy efficiency of a DtS-IoT network when a network size estimation is available, we present, here, a novel and computationally efficient network size estimator in DtS-IoT: our optimistic collision information (OCI)-based estimator. We evaluate OCI’s effectiveness with extensive simulations of DtS-IoT scenarios. Results show that when using network size estimations, the scalability of a frame-slotted Aloha-based DtS-IoT network is boosted eightfold, serving up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4 \times 10^{3}$ </tex-math></inline-formula> devices, without energy efficiency penalties. We also show the effectiveness of the OCI mechanism given realistic detection ratios and demonstrate its low computational cost implementation, making it a strong candidate for network estimation in DtS-IoT.

Novel BECCS implementation integrating chemical looping combustion with oxygen uncoupling and a kraft pulp mill cogeneration plant

Bioenergy with CO2 capture and storage (BECCS) is a promising negative emission technology (NET). When using sustainably produced biomass as fuel, BECCS allows the production of power and heat with negative CO2 emissions. The main technical challenges hindering the deployment of BECCS technologies include energy penalties associated with the capture process. This work evaluates the performance of an advanced CO2 capture technology, chemical looping with oxygen uncoupling (CLOU), replacing a conventional fluidized bed boiler in the power boiler role in a large, modern integrated pulp and paper mill. Results from a MATLAB/Simulink reactor model were incorporated in a plant and integration model developed in a commercial process simulation software to quantify the performance of the CLOU-integrated cogeneration plant. The results show that in this specific application, the typically already low efficiency penalty of CLOU-based carbon capture and storage (CCS) systems could be eliminated entirely, and actually even a very small efficiency gain could be obtained. The highly efficient operation is possible due to the high moisture and hydrogen contents of the biomass and the separation of combustion products and excess air streams in the CLOU process; this provides an opportunity to recover a significant amount of heat by flue gas condensation at a higher temperature level than what is possible in a conventional boiler. Together with abundant low-temperature heat sinks available at the pulp and paper application allows freeing a considerable amount of low-pressure steam for expansion in the condensing turbine. The resulting increase in gross generator output proved enough to not only match, but very slightly exceed the approximately 18 MW parasitic load introduced by the CLOU system in comparison to the conventional boiler.

An H8 Current-Source Inverter Using Single-Gate WBG Bidirectional Switches

Due to the high forward voltage drop of reverse-blocking (RB) switches, conventional current-source inverters (CSIs) typically suffer efficiency penalties. Bidirectional (BD) switches, on the other hand, can also block reverse voltages but with less conduction loss than RB switches, making them more attractive candidates for CSI switches. This article discusses the difficulties inherent in implementing BD switches in CSIs, such as dc-link overvoltage, interphase short circuit, more complicated commutation schemes, high body diode conduction loss, and additional gate control signals. To address these issues, a new CSI topology (H8-CSI-BD) is proposed, which is optimized for the use of single-gate wide bandgap (WBG) BD switches. The proposed topology and its modulation scheme guarantee safe operation of CSI, eliminate BD switch’s body diode conduction loss, and achieve significant efficiency improvement. In addition, its requirement for single-gate control signals for its BD switches simplifies control and gate drive circuits noticeably. The advantages of the H8-CSI-BD topology over the other CSIs using either RB or BD switches are confirmed by analysis, simulation, and experimental results.

On the Effect of Side Clearance in the Vaned Diffuser of a Centrifugal Compressor

AbstractEnvironmental and regulatory pressures have prompted original equipment manufacturers (OEMs) to explore highly boosted internal combustion (IC) engines as a means to minimize toxic air pollutants and meet strict legislative targets. The exhaust gas turbocharger is a key technology used to achieve the boost pressures necessary for advanced engines of the future. Centrifugal compressors with vaneless diffusers have been widely implemented in turbochargers for IC engines, particularly passenger vehicles, primarily due to their compact size and ability to deliver high-pressure ratios over a wide range of flowrates. Methods to improve compressor efficiency near surge without reducing the surge margin have received considerable interest in the past. In many situations, changes to the impeller blade design and/or diffuser are limited by the need to meet the strict engine-rated power target. Such competing demands have encouraged designers to develop variable geometry compressors with the aim of improving near surge performance without sacrificing rated power performance. The on/off-type vaned diffuser is a variable geometry compressor capable of delivering a pressure ratio benefit near surge by utilizing a vaned diffuser rather than a vaneless diffuser. The vanes are retracted prior to the diffuser choking to form a vaneless diffuser in order to reach the engine-rated power condition. Diffuser vane-shaped clearances in the hub or the shroud end wall, termed side clearances, enable axial sliding variability of the vanes into and out of the diffuser passage. Unfortunately, the clearances manifest themselves as a discontinuity in the flow field which gives rise to an efficiency penalty. It is not yet clear how the side clearance geometry and position affect the compressor performance i.e., efficiency and stability. Hence, a numerical and experimental investigation was carried out to determine the impact of side clearance geometry and end wall position on compressor performance. It was found that a side clearance positioned at the shroud end wall reduced the surge margin of the investigated compressor for both types of clearance geometry considered. In contrast to this, a clearance positioned at the hub end wall improved the compressor surge margin but had the lowest efficiency benefit near surge. An experimentally validated Computational Fluid Dynamics (CFD) model was used to inspect the flow field and to elucidate the reasons behind the changes in compressor performance.

Concept design, parameter analysis, and thermodynamic evaluation of a novel integrated gasification chemical-looping combustion combined cycle power generation system

Integrated gasification chemical-looping combustion (IGCLC) is a potential combustion technology with innate CO2 separation for solid fuels. Coupling this technology with coal-fired power plants is expected to greatly alleviate the high efficiency penalty induced by CO2 capture. This study proposes an innovative system called integrated gasification CLC combined cycle (IGCLCCC) that highly integrates a gasification system, a CLC system, a combined cycle, an ultra-supercritical steam cycle, and a CO2 capture system. In the proposed system, the oxygen-depleted stream from air reactor and flue gas from fuel reactor enter the combined cycle and ultra-supercritical steam cycle, respectively, for power generation. The energy and mass balances of the proposed system are determined by process simulation. The relationship between the performance of subsystems and system efficiency is studied by parameter analysis. Results indicate that the net efficiency penalty (0.3 percentage points) of the proposed system is 4.3 to 13.2 percentage points less than those of the conventional CO2 capture power plants, and the power consumption of specific CO2 capture is minimized to 8.3 kWeh/t. Besides, its net efficiency is as high as 45.0%, which is comparable to that of the natural gas combined cycle power plant with a 90% CO2 capture rate. This work provides a new sight into the design of the low-carbon and efficient power generation system.