•Technology development must be aligned with key trends in decarbonization.•Costs reductions are needed. We rank options by value and feasibility.•Reduction in fuel cell component costs is essential ...to commercial success.•Fuel cell cost reductions are most important.•Innovations in systems design and materials can also reduce cost.
Does generation of zero-carbon electricity from coal make sense for a decarbonized grid? Coal-based integrated gasification fuel cell systems with CO2 capture have the potential to participate in future decarbonized power grids. Over the next decade, such systems are scheduled to progress from a conceptual scheme to its first demonstration projects in China and Japan. A key issue in the long-term viability of the technology will be reducing costs so they are competitive against other forms of zero-carbon electricity; in addition, the systems must be able to operate as part of low carbon grids. We systematically evaluate the major on-going research directions, and rank them according to their economic potential, degree of technical challenge, and possible synergies with other efforts to transition to low-carbon energy systems worldwide. Our analysis indicates that the most promising pathway to making integrated gasification fuel cell technologies cost-competitive against other forms of low-carbon electricity is co-deployment of solid oxide fuel cell technologies in integrated gasification fuel cell cycle and distributed energy applications to expand the scale of production to a level that benefits both areas. Other avenues based on system optimization or improvements in fuel cell performance or degradation through materials development can help, but cannot by themselves deliver cost-competitive electricity absent an order of magnitude reduction in the cost of solid oxide fuel cell components.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We here present and analyze a novel conceptual design of 550 MW-level, syngas-fueled intermediate-temperature solid oxide fuel cell (SOFC)/Air Turbine (AT) hybrid system with an oxy-fuel combustion. ...To decouple the operation of SOFC and AT and allow independent operation of each, an intermediate heat exchanger is implemented between SOFC and AT cycles to transfer only heat from SOFC to AT. To facilitate CO2 separation and capture, the gas streams from both electrodes are separately operated and pure O2 is used in the afterburner for combustion. A total of four scenarios has been analyzed to cover the effects of current density, pressure and staged SOFC design. The results show that by elevating the pressure to 10 atm and using two-stage SOFC design, the system can achieve an overall efficiency of 64% at a nominal power output. The work provides important engineering insights in SOFC staged design and operating conditions for the next-generation SOFC/turbine hybrid systems.
•A MW-level syngas-fueled solid oxide fuel cell/Air Turbine hybrid system.•An intermediate heat exchanger between SOFC and AT.•Pressure and multi-stage SOFC design effects on the overall system efficiency.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Explored the effect of practical issues in body heat thermoelectric energy harvester.•Suggested optimal/practical geometries for the heat sink and thermoelectric module.•Considered the effect of a ...boost converter’s voltage dependent efficiency.•Estimated power output of 0.48mW within a wearable area.
Recent studies on improving the thermoelectric figure of merit (ZT) have advanced research into self-powered, wearable technologies using thermoelectric generators. However, previous design approaches do not consider structurally practical heat sink and module geometries, the use of a boost converter, or the size constraint of the generator due to aesthetic appeal, all of which lower the overall power output. Additionally, the reduced efficiency in using a boost converter changes the electrical and thermal load matching conditions for maximum power. In this study, the limitations of practicality were considered for a wearable thermoelectric generator that utilizes a state-of-the-art boost converter and an optimized heat sink. Heat sink fin geometries and thermoelectric module geometries were explored to maximize the power output within a 42.0cm2 area and a 1.0cm total height, in order to justify the wearability of the energy harvester. With optimized values of fin and module heights, the system was designed to produce 0.48mW of electrical power at a boosted output voltage of 3.0V, enough to power a small heart-rate monitor.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Various metrics for HIV burden and treatment success e.g. HIV prevalence, community viral load (CVL), population viral load (PVL), percent of HIV-positive persons with undetectable viral load have ...important public health limitations for understanding disparities.
Using data from an ongoing HIV incidence cohort of black and white men who have sex with men (MSM), we propose a new metric to measure the prevalence of those at risk of transmitting HIV and illustrate its value. MSM with plasma VL>400 copies/mL were defined as having 'transmission risk'. We calculated HIV prevalence, CVL, PVL, percent of HIV-positive with undetectable viral loads, and prevalence of plasma VL>400 copies/ml (%VL400) for black and white MSM. We used Monte Carlo simulation incorporating data on sexual mixing by race to estimate exposure of black and white HIV-negative MSM to a partner with transmission risk via unprotected anal intercourse (UAI). Of 709 MSM recruited, 42% (168/399) black and 14% (44/310) white MSM tested HIV-positive (p<.0001). No significant differences were seen in CVL, PVL, or percent of HIV positive with undetectable viral loads. The %VL400 was 25% (98/393) for black vs. 8% (25/310) for white MSM (p<.0001). Black MSM with 2 UAI partners were estimated to have 40% probability (95% CI: 35%, 45%) of having ≥1 UAI partner with transmission risk vs. 20% for white MSM (CI: 15%, 24%).
Despite similarities in other metrics, black MSM in our cohort are three times as likely as white MSM to have HIV transmission risk. With comparable risk behaviors, HIV-negative black MSM have a substantially higher likelihood of encountering a UAI partner at risk of transmitting HIV. Our results support increasing HIV testing, linkage to care, and antiretroviral treatment of HIV-positive MSM to reduce prevalence of those with transmission risk, particularly for black MSM.
Full text
Available for:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
OBJECTIVE:To evaluate for changes in sexual behaviors associated with daily pill use among men who have sex with men (MSM) participating in a preexposure prophylaxis trial.
DESIGN:Randomized, ...double-blind, placebo-controlled trial. Participants were randomized 1:1:1:1 to receive tenofovir disoproxil fumarate or placebo at enrollment or after a 9-month delay and followed for 24 months.
METHODS:Four hundred HIV-negative MSM reporting anal sex with a man in the past 12 months and meeting other eligibility criteria enrolled in San Francisco, Atlanta, and Boston. Sexual risk was assessed at baseline and quarterly visits using Audio Computer-Assisted Self-Interview. The association of pill taking with sexual behavior was evaluated using logistic and negative-binomial regressions for repeated measures.
RESULTS:Overall indices of behavioral risk declined or remained stable during follow-up. Mean number of partners and proportion reporting unprotected anal sex declined during follow-up (P < 0.05), and mean unprotected anal sex episodes remained stable. During the initial 9 months, changes in risk practices were similar in the group that began pills immediately vs. those in the delayed arm. These indices of risk did not differ significantly after initiation of pill use in the delayed arm or continuation of study medication in the immediate arm. Use of poppers, amphetamines, and sexual performance–enhancing drugs were independently associated with one or more indices of sexual risk.
CONCLUSIONS:There was no evidence of risk compensation among HIV-uninfected MSM in this clinical trial. Monitoring for risk compensation should continue now that preexposure prophylaxis has been shown to be efficacious in MSM and other populations and will be provided in open-label trials and other contexts.
OBJECTIVES:To evaluate the clinical safety of daily tenofovir disoproxil fumarate (TDF) among HIV-negative men who have sex with men.
DESIGN:Randomized, double-blind, placebo-controlled trial. ...Participants were randomized 1:1:1:1 to immediate or delayed study drug (TDF, 300 mg orally per day, or placebo).
METHODS:Four hundred healthy HIV-uninfected men who have sex with men reporting anal sex with another man within the previous 12 months enrolled in Atlanta, Boston, and San Francisco. HIV serostatus, clinical and laboratory adverse events (AEs), adherence (pill count, Medication Event Monitoring System, and self-report), and sexual and other sociobehavioral data were assessed at 3-month intervals for 24 months. Primary outcomes were clinical safety, assessed by incidence of AEs and laboratory abnormalities.
RESULTS:Study drug was initiated by 373 (93%) participants (186 TDF and 187 placebo), of whom 325 (87%) completed the final study visit. Of 2428 AEs reported among 334 (90%) participants, 2366 (97%) were mild or moderate in severity. Frequencies of commonly reported AEs did not differ significantly between TDF and placebo arms. In multivariable analyses, back pain was more likely among TDF recipients (P = 0.04); these reports were not associated with documented fractures or other objective findings. There were no grade ≥3 creatinine elevations; grades 1 and 2 creatinine increases were not associated with TDF receipt. Estimated percentage of study drug doses taken was 92% by pill count and 77% by Medication Event Monitoring System. Seven seroconversions occurred4 on placebo and 3 among delayed arm participants not yet on study drug.
CONCLUSIONS:Daily oral TDF was well tolerated, with reasonable adherence. No significant renal concerns were identified.
Pre-exposure prophylaxis (PrEP) trials are evaluating regimens containing tenofovir-disoproxil fumarate (TDF) for HIV prevention. We determined the baseline prevalence of low bone mineral density ...(BMD) and the effect of TDF on BMD in men who have sex with men (MSM) in a PrEP trial in San Francisco.
We evaluated 1) the prevalence of low BMD using Dual Energy X-ray Absorptiometry (DEXA) in a baseline cohort of 210 HIV-uninfected MSM who screened for a randomized clinical trial of daily TDF vs. placebo, and 2) the effects of TDF on BMD in a longitudinal cohort of 184 enrolled men. Half began study drug after a 9-month delay to evaluate changes in risk behavior associated with pill-use. At baseline, 20 participants (10%) had low BMD (Z score≤-2.0 at the L2-L4 spine, total hip, or femoral neck). Low BMD was associated with amphetamine (OR = 5.86, 95% CI 1.70-20.20) and inhalant (OR = 4.57, 95% CI 1.32-15.81) use; men taking multivitamins, calcium, or vitamin D were less likely to have low BMD at baseline (OR = 0.26, 95% CI 0.10-0.71). In the longitudinal analysis, there was a 1.1% net decrease in mean BMD in the TDF vs. the pre-treatment/placebo group at the femoral neck (95% CI 0.4-1.9%), 0.8% net decline at the total hip (95% CI 0.3-1.3%), and 0.7% at the L2-L4 spine (95% CI -0.1-1.5%). At 24 months, 13% vs. 6% of participants experienced >5% BMD loss at the femoral neck in the TDF vs. placebo groups (p = 0.13).
Ten percent of HIV-negative MSM had low BMD at baseline. TDF use resulted in a small but statistically significant decline in BMD at the total hip and femoral neck. Larger studies with longer follow-up are needed to determine the trajectory of BMD changes and any association with clinical fractures.
ClinicalTrials.gov: NCT00131677.
Full text
Available for:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The present computational study investigates the effects of pressure and flow patterns on the electrochemical performance of a repeating unit in the anode-support SOFC stack using a reduced order ...model previously developed. A unique feature of the present study is that the charge, heat, and mass transport affecting the cell performance has been coupled with the temperature field. The focus of this study is to simulate how the flow patterns and operating pressure in conjunction with temperature field coupling impact the electrochemical performance and chemical reactions within syngas-fueled SOFCs. The simulation results show that the benefits of pressure on power performance do not increase linearly, but with a tapering of performance at higher pressure ranges. This indicates that an intermediate pressure operation may offer a balance between increased performance but higher cost in pressurized systems. The counter-flow design yields a narrower temperature gradient than the co-flow design across the stack, thus leading to a better overall performance. The simulations also find that pressurization significantly promotes the CO direct electro-oxidation and reverse water gas shift reaction simultaneously, thus resulting in higher power density.
•Pressurization significantly enhances the CO direct electro-oxidation.•Pressurization promotes reverse water gas shift reaction.•Pressurization does not linearly enhance the electrical performance.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
An electrochemical reduced order model (ROM) has been developed in this study to simulate the performance of syngas-fueled anode-supported SOFCs with coupled bulk chemical reactions and multi-species ...gas diffusion in the electrodes. Experimental V-I curves with syngas fuel were used to validate the model to ensure its high fidelity. The model was used to investigate the effects of fuel composition and temperature on the electrochemical performance of the cell, chemical reaction rate and concentration distributions of gaseous species across the anode. The results show that H2 electro-oxidation dominates the overall cell performance, and that CO contributes to the performance indirectly via water gas shift (WGS) reaction, especially at low CO:H2 ratio and low current densities. Increasing the temperature enhances the performance of syngas-fueled SOFCs by increasing the rates of total electrochemical oxidation and the WGS reaction. The present work provides fundamental knowledge and framework for future performance simulations of large-scale and more complex syngas-fueled SOFC systems.
In this paper, a new characterization factor for thermoelectric module design in thermoelectric refrigeration is presented with guidelines for practical design strategy. It has been general practice ...to optimize the geometric factor (G-factor), the ratio of the area to the leg length of a thermoelectric leg, and the number of leg pairs simultaneously to gain a minimum refrigeration temperature from a module for a refrigeration system. However, the B-factor, which is defined as the ratio between the leg length and the fill factor (ratio of the area filled with thermoelectric materials to the module area), allows for module optimization with only one parameter. To demonstrate, a theoretical model of a module was created with energy conservation equations. While disregarding electrical contact resistance, the number of leg pairs did not affect the obtainable maximum temperature difference or the power consumption of a module when utilizing the B-factor. The effects of contact resistance on the optimum B-factor were also evaluated and avoided when the leg length was increased. It was then found that using fewer legs in a module would produce a temperature difference that was less sensitive to a varying input current. The present theoretical approach was validated with experimental evidence.
•Presented one parameter (B-factor) module optimization strategy.•The new geometric factor is not sensitive to contact resistance.•Temperature and power consumption do not depend on number of legs.•Less number of legs is preferable for temperature control.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
PDF
