Combustion Characteristics of Hydrogen-methane Hybrid Fuels

ABSTRACT As the development and increasingly widespread use of IGCC and zero emission energy system, the development of advanced combustion capabilities for gaseous hydrogen and hydrogen rich fuels in gas turbine applications is becoming an area of much great concern. The combustion characteristics of hydrogen rich fuel is very different from nature gas in aspects such as flame stability, flame temperature, combustor acoustics, pollutant emissions, combustor efficiency, and some other important quantities. However, few of these issues are clearly understood by far. The purpose of this paper is to compare in detail the combustion performance of hydrogen-methane hybrid fuels with various volumetric H 2 fractions ranging from 0% to 100%. Meanwhile, the comparison of pure H 2 , pure CH 4 , and 80%H 2 +20%CH 4 was the emphasis. 80%H 2 +20%CH 4 hybrid gas is selected expressly because its component is approximately equal to the outcome of a hydrogen production test bed of our laboratory, and it is considered by the team to be a potential transition fuel of gas turbines between nature gas and pure hydrogen. Detailed experimental measurements and numerical simulations were conducted using a coflow jet diffusion burner. It was found that in the extent of experiments, when under equal general power, the flame length of hydrogen contained fuels wasn't much shorter than methane, and didn't get shorter with the increase of H 2 fraction as expected. That was because the shortening tendency caused by the increase of H 2 fraction was counteracted partially by the increase of fuel velocity, results of which was the extending of flame length. Maximum temperature of H 2 flame was 1733K, which was 30K higher than 80%H 2 +20%CH 4 and 120K higher than CH 4. All of the highest temperatures of the three fuels were presented at the recirculation zone of the flame. Although it seemed that the flame of CH 4 had the longest dimension compared with H 2 contained fuels when observed through photos, the high temperature region of flames was getting longer when increasing H 2 fractions. Curves of temperature distribution predicted by all the four combustion models in FLUENT investigated here had a departure away from the experimental data. Among the models, Flamelet model was the one whose prediction was comparatively close to the experimental results. Flame of H 2 and 80%H 2 +20%CH 4 had a much better stability than flame of CH 4 , they could reach a so called recirculating flame phase and never been blew out in the extent of experiments. On the contrary, CH 4 flames were blew out easily soon after they were lifted up. Distribution of OH concentration at the root of flames showed that the flame boundary of H 2 and 80%H 2 +20%CH 4 was more clearly than CH 4. That is to say, at the root of the flame, combustion of H 2 was the most intensive one, 80%H 2 +20%CH 4 took the second place, while CH 4 was the least. NOx emissions didn't show a linear relationship with the volumetric fraction of H 2 , but showed an exponential uptrend instead. It presented a fairly consistent tendency with flame

3640 Unique EST Clusters from the Medaka Testis and Their Potential Use for Identifying Conserved Testicular Gene Expression in Fish and Mammals

BACKGROUND: The fish medaka is the first vertebrate capable of full spermatogenesis in vitro from self-renewing spermatogonial stem cells to motile test-tube sperm. Precise staging and molecular dissection of this process has been hampered by the lack of suitable molecular markers. METHODOLOGY AND PRINCIPAL FINDINGS: We have generated a normalized medaka testis cDNA library and obtained 7040 high quality sequences representing 3641 unique gene clusters. Among these, 1197 unique clusters are homologous to known genes, and 2444 appear to be novel genes. Ontology analysis shows that the 1197 gene products are implicated in diverse molecular and cellular processes. These genes include markers for all major types of testicular somatic and germ cells. Furthermore, markers were identified for major spermatogenic stages ranging from spermatogonial stem cell self-renewal to meiosis entry, progression and completion. Intriguingly, the medaka testis expresses at least 13 homologs of the 33 mouse X-chromosomal genes that are enriched in the testis. More importantly, we show that key components of several signaling pathways known to be important for testicular function in mammals are well represented in the medaka testicular EST collection. CONCLUSIONS/SIGNIFICANCE: Medaka exhibits a considerable similarity in testicular gene expression to mammals. The medaka testicular EST collection we obtained has wide range coverage and will not only consolidate our knowledge on the comparative analysis of known genes' functions in the testis but also provide a rich resource to dissect molecular events and mechanism of spermatogenesis in vivo and in vitro in medaka as an excellent vertebrate model

PaLM 2 Technical Report

We introduce PaLM 2, a new state-of-the-art language model that has better multilingual and reasoning capabilities and is more compute-efficient than its predecessor PaLM. PaLM 2 is a Transformer-based model trained using a mixture of objectives. Through extensive evaluations on English and multilingual language, and reasoning tasks, we demonstrate that PaLM 2 has significantly improved quality on downstream tasks across different model sizes, while simultaneously exhibiting faster and more efficient inference compared to PaLM. This improved efficiency enables broader deployment while also allowing the model to respond faster, for a more natural pace of interaction. PaLM 2 demonstrates robust reasoning capabilities exemplified by large improvements over PaLM on BIG-Bench and other reasoning tasks. PaLM 2 exhibits stable performance on a suite of responsible AI evaluations, and enables inference-time control over toxicity without additional overhead or impact on other capabilities. Overall, PaLM 2 achieves state-of-the-art performance across a diverse set of tasks and capabilities. When discussing the PaLM 2 family, it is important to distinguish between pre-trained models (of various sizes), fine-tuned variants of these models, and the user-facing products that use these models. In particular, user-facing products typically include additional pre- and post-processing steps. Additionally, the underlying models may evolve over time. Therefore, one should not expect the performance of user-facing products to exactly match the results reported in this report

Interval Optimization-Based Optimal Design of Distributed Energy Resource Systems under Uncertainties

Distributed energy resource (DER) systems have elicited increasing attention and applications because of their excellent economic and environmental performance. However, uncertainties exist in such systems, preventing their potential advantages to be realized. In this study, an interval optimization-based model for the optimal design of DER systems is proposed, considering uncertainties in energy prices, renewable energy intensity, and load demands. Uncertainties are described as interval numbers, and the uncertain optimization model is transformed into a deterministic optimization problem using the order relationship and probability degree of interval numbers. The proposed model is applied to a typical hospital in Lianyungang, China, and its effectiveness is verified. One deterministic case and three uncertain cases are designed. The effects of uncertainties on system configuration and economic performance are also analyzed, and the optimal operation strategy under the three uncertainties is determined. A sensitivity analysis is conducted to analyze the effects of probability degree and weighting coefficient on total annual cost. Results show that uncertainties exert a cumulative effect on system optimization outcomes, and the proposed interval optimization model can obtain robust solutions to uncertainties

THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS SYSTEM OPTIMIZATION OF HUMID AIR TURBINE CYCLE

ABSTRACT The humid air turbine(HAT) cycle, proposed by Mori et al. and recently developed by Rao et al. at Flour Daniel, has been identified. as a promising way to generate electric power at high efficiency, low cost and simple system relative to combined cycle and steam injection gas turbine cycle. It has aroused considerable interest. Thermodynamic means, such as intercooling, regeneration, heat recovery at low temperature and especially non-isothermal vaporisation by multi-phase and multi-component, are adopted in HAT cycle to reduce the external and internal exergy losses relative to the energy conversion system. In addition to the parameter analysis and the technical aspect of HAT cycle, there is also a strong need for "systems" research to identify the best ways, of configuring HAT cycle to integrate all the thermodynamic advantages more efficiently to achieve high performance. The key units in HAT cycle are analyzed thermodynamically and modelled in this paper. The superstructure containing all potentially highly efficient flowsheeting alternatives is also proposed. The system optimization of the HAT cycle is thus represented by a nonlinear programming problem. The problem is solved automatically by a successive quadratic algorithm to select the optimal configuration and optimal design parameters for the HAT cycle. The results have shown that the configuration of the HAT cycle currently adopted is not optimal for efficiency and/or specific power, and the current pressure ratio are too high to be favorable for highest performance. Based on the current technical practice, the optimal flowsheeting for thermal efficiency can reach 60.33% when TIT=1533K, while the optimal flowsheeting for specific power can achieve 1300kW/kg/s air for TIT at 1533K. The optimal flowsheeting configuration is compared favorably with the other existing ones

Heat integration and optimization of direct-fired supercritical CO2 power cycle coupled to coal gasification process

Supercritical carbon dioxide (sCO(2)) power cycle is a promising power cycle that has drawn much attention in recent years. Among various layouts, the direct-fired sCO(2) power cycle achieves not only high efficiency but also near zero emission. Coal gasification and air separation process are indispensable processes when coal is used as fuel. To explore the best cycle performance, the above two processes have to be tightly integrated with the sCO(2) power cycle in both mass and energy. Key parameters that govern the heat integration should also be optimized to achieve better performance. A two-stage method is applied for simultaneous optimization and heat integration of a direct-fired sCO(2) power cycle coupled to coal gasification process. First, boundary parameters of the heat integration process are optimized. Then the heat exchanger network, which reveals viable heat integration scheme, is designed to fulfill the optimized target. The result shows that the net efficiency reaches 39.29% when heat integration of ASU is not considered. If heat integration of ASU is considered, the net efficiency increases to 40.97%, showing an efficiency increment of 1.68%. When the CO2 turbine pressure ratio is also optimized, the net efficiency increases further to 41.41%. (C) 2017 Published by Elsevier Ltd.</p

Winter snow cover influences growing-season vegetation productivity non-uniformly in the Northern Hemisphere

Abstract Ongoing changes in snow cover significantly affect vegetation productivity, but the actual effect of snow cover remains unclear due to a poor understanding of its lagged effect. Here, we used multisource datasets to investigate the lagged effect of snow cover on vegetation productivity in Northern Hemisphere ( > 40°N) ecosystems from 2000 to 2018. We found a widespread lagged effect of snow cover ( > 40%, P < 0.05) on growing season vegetation productivity (mean ~73-day lag). The effect of snow cover on vegetation productivity was underestimated by over 10% of the areas without considering regional lagged time differences. A longer lagged effect generally occurred in warm and humid areas, and areas with increased lagged time (66%) were greater than those with decreased trends. Moreover, changes in lagged effect were strongly driven by climate factors, followed by soil and topography factors. These findings emphasize the need to consider lagged time differences of snow cover when investigating snow-vegetation productivity interactions

Technical, environmental, and economic assessment of deploying advanced coal power technologies in the Chinese context

The goal of this study is to evaluate the technical, environmental, and economic dimensions of deploying advanced coal-fired power technologies in China. In particular, we estimate the differences in capital cost and overall cost of electricity (COE) for a variety of advanced coal-power technologies based on the technological and economic levels in 2006 in China. This paper explores the economic gaps between Integrated Gasification Combined Cycle (IGCC) and other advanced coal power technologies, and compares 12 different power plant configurations using advanced coal power technologies. Super critical (SC) and ultra super critical (USC) pulverized coal (PC) power generation technologies coupled with pollution control technologies can meet the emission requirements. These technologies are highly efficient, technically mature, and cost-effective. From the point of view of efficiency, SC and USC units are good choices for power industry. The net plant efficiency for IGCC has reached 45%, and it has the best environmental performance overall. The cost of IGCC is much higher, however, than that of other power generation technologies, so the development of IGCC is slow throughout the world. Incentive policies are needed if IGCC is to be deployed in China.