Abstract

An innovative high-efficiency power generation system is developed and investigated in this paper. Based on self-sustaining supercritical water coal gasification, the thermal energy of the syngas is cascade utilized according to its temperature and pressure, both sensible and latent heat of the syngas can be recycled into the system, and thereby the net power efficiency can be about five percentage points higher than that of the traditional GE gasification based power plant. The exergy analysis shows that the exergy efficiency of the proposed system reaches 49.17%, which is 10.72% higher than that of the reference system, and the improvement in exergy efficiency of the proposed system mainly comes from the exergy destruction decline of the syngas energy recovery process and the gas compression process. The syngas combustion process is the highest exergy destruction process with a value of 183.77 MW in the proposed system. Further improvement in the system performance of the proposed system lies in the utilization of syngas.

Abstract

Air pollutants and carbon emissions are both mainly derived from energy consumption. As important policy instruments for emissions reduction, the relationship between environmental tax (SO2- and NOX- ) and carbon tax (CO2-) calls for more research. This paper compares cost-benefits of environmental tax and carbon tax under same level of GDP loss, carbon emissions reduction and carbon emissions intensity decline. A computable general equilibrium (CGE) model of China with 139 sectors based on 2012 China’s input-output table and statistical data on environment has been developed for this purpose. Simulation results show that current environmental tax in China is effective to reduce emissions (SO2 -1.34%; NOX -1.04%; CO2 -0.71%) with mild impact on GDP (-0.16%). In particular, given a constant GDP effect, current environmental tax equates to a carbon tax of 19 RMB per ton, but carbon tax would be more efficient than environmental tax to reduce CO2 emissions (-0.89%). If given a constant CO2 emission, current environmental tax equates to a carbon tax of 15 RMB per ton, while carbon tax has smaller impact on GDP (-0.12%); however, in terms of air pollutants reduction, carbon tax would be less efficient (SO2 -0.52%; NOX -0.61%). If given a constant carbon emission intensity decline, environmental tax is less cost-benefit than carbon tax. Impact on sector level are also discussed. The study suggests that the ‘embodied’ carbon tax in environmental tax policy should be considered if China apply a carbon tax in the future.

Abstract

With China’s phenomenal economic growth, the contradiction between the increasing demand for fossil energy consumption and the increasingly urgent emission reduction pressure is gradually standing out. The CO2 enhanced coal bed methane (CO2-ECBM) technology can inject the CO2 captured into the coal bed to enhance coal bed methane (CBM) recovery and store CO2, increasing the production of clean fossil fuels whilst reducing CO2 emissions. The investment benefits of the CO2-ECBM project in China under various scenarios was evaluated based on real options in this study, and the key factors influencing the economy of the CO2-ECBM technology were also identified. The results showed that (1) irrespective of carbon trading gains, the CO2-ECBM project can yield a profit of RMB 2.58 billion with sales of increased CBM and relevant government subsidies in low CO2 source price (RMB 180/ton) scenarios; (2) if CO2 source prices rise to RMB 300/ton (high CO2 source price scenarios), the CO2-ECBM project has no investment value as its revenues cannot offset the total costs on the technology; (3) for every yuan/ton increase in CO2 source prices, the net present value (NPV) of the project falls by roughly RMB 22.76 million, without regard to the critical CO2 source price of RMB 293/ton in carbon trading; (4) carbon trading can substantially raise the return on investment (ROI) in the CO2-ECBM project and in low CO2 source price scenarios, the current carbon price level (RMB 50/ton) can increase the ROI by around 44.2%, but China has not yet included CO2 utilization technologies in carbon market trading. The results in this study provide theoretical support for CO2-ECBM investment and the relevant policy-making.

Abstract

To alleviate the current shortage of natural gas resource and realize carbon-free emission step by step, a solar driven distributed energy system integrated with the combined dry and steam methane reforming is proposed in this study. In the system, the concentrated solar energy collected by a dish collector is used as heat source to drive the methane reforming reaction, which upgrades solar thermal energy into the chemical energy of the syngas products. As solar radiation intensity cannot satisfy the design requirement, the system can be operated continuously. The cascade utilization of chemical energy from syngas is achieved in the distributed energy system for trigeneration. The thermodynamics performances of the system are numerically investigated under on-design and off-design conditions. The results indicate that the proposed system has remarkable advantages from the energy and environmental evaluation, as compared with a conventional reference system. The excellent off-design thermodynamic performance under varying irradiation and user loads is achieved. The research findings provides an efficient and stable method for the reduction of natural gas consumption and the utilization of solar energy

Abstract

For off-grid islands or archipelago, especially island towns far from the mainland, it usually has disadvantages in terms of the stability and economy of traditional fuel supply chains, and waste disposal is also an important issue facing the sustainable development of islands and marine ecosystems. In addition, due to the uncertainty of the ocean climate. Isolated island energy systems often face the dilemma of redundancy or shortage of renewable power at different periods. To meet the above challenges simultaneously, a multi time scale hierarchical optimization method is introduced for the investment and operation planning of the island sustainable energy system that combines renewable energy, seasonal energy storage and waste to energy technologies. Alternative technologies includes the photovoltaic, wind turbine, seawater source heat pump, as well as boiler and gas engine that utilize the synthesis gas and biogas produced from island waste and marine biomass, thereby simultaneously satisfies the cooling, heating and power demand of the off-grid island. Multi-objective optimization and decision-making are conducted with indicators of system economy and renewable energy consumption in normal conditions and indicator of energy security under extreme climatic conditions. Meanwhile, the environmental benefits of the integrated system under different scenarios are also compared. Case studies show that the introduction of distributed waste to energy and seasonal energy storage solutions improves the flexibility of the isolated grid system, thereby increasing the penetration and consumption of renewable energy, and further reducing the need of standby fossil fuels. The proposed integrated system has multiple benefits in energy, economic, environmental and social aspects, which is an effective means for the sustainable development of smart islands.

Abstract

In the past ten years, many artificial intelligence methods have been successfully applied to the fault detection and diagnosis of photovoltaic arrays, but most of them rely on complex manual feature extraction and a large amount of actual monitored fault data. Because the scale of the actual photovoltaic power plant is too large, it is difficult to obtain a large amount of data. In the case of small training data, it will severely limit the performance of the fault diagnosis model. In response to these problems, this paper first proposes a multi-element time series waveform based on maximum power point tracking as the fault feature. The interference data is filtered through the change point algorithm to obtain the fault feature with absolute high quality and complete information. We also designed a simulation model of photovoltaic array based on Simulink, and obtained simulation data and experimental data through simulation and actual experiment. In addition, this paper proposes a fault detection and diagnosis method based on transfer learning for densely connected convolutional neural networks (DenseNet), using simulated data for pre-training, and then using experimental data for fine-tuning. The comparison of experimental results proves that the fault diagnosis method can achieve better results in terms of accuracy, generalization performance, and reliability in the case of small samples.

Abstract

Accurately estimating the state of health (SOH) of the lithium-ion batteries (LIB), for battery management systems, plays an important role in an ensuring reliable system operation and reducing maintenance costs. Because of the complicated degradation mechanism and the complex internal electrochemical reactions, accurate SOH estimation remains challenging for battery energy management and applications. In this study, we proposed a new SOH estimation method. First, the data is preprocessed and multiple features are extracted to simulate the aging process of the LIB, and the battery capacity is selected as the state variable. Because of the strong capability to fit complex nonlinear problems, a regression model based on gradient boosting decision tree (GBDT) is proposed to estimate the SOH. In addition, a new hybrid optimization algorithm based on quantum particle swarm optimization (QPSO) algorithm and Nelder-Mead simplex (NMS) algorithm is proposed for parameter optimization of the GBDT model. Several lithium-ion battery test data sets from the NASA Ames Prognostics Center of Excellence were selected to validate the proposed method. Compared with other SOH estimation methods and other parameter optimization algorithms, the experimental results show that the proposed method is superior in terms of accuracy, generalization performance and reliability.

Abstract

The rapid development of urbanization makes the contradiction between the demand and supply of water and land resources increased gradually. Due to the intertwined relationship of water and land resources, great efforts are need to coordinate the water conservation and intensive use of land resources, in order to realize the efficiency and stability of economic development and agricultural production. This study investigates the coupling effects between water-land resources among different sectors in urban socio-economic network. Combing input-output table and ecological network analysis, the urban water-land nexus network model is constructed to analyze the coupling effects among water and land by quantifying the direct and indirect interactions within and among sub-systems. It quantifies the coupling coefficient between water-land resources and evaluate the efficiency and resilience of water-land utilization. It quantifies the control and utility relationships of water-land nexus between sectors and identifies the key sectors and critical pathways of water-land nexus network.

Abstract

With the gradual failure of CO2 huff and puff wells, the overall oil exchange rate shows a downward trend. In order to maintain the good effect of the measure and extend its technical life, CO2 synergistic huff and puff are proposed. The synergistic mode is proposed based on the peculiarity of small oil-bearing area of the fault block reservoir that geological structure is broken, and there is no completed development well pattern. By using the numerical simulation method, typical simulation models are established to simulate the effects of different geological factors and development factors on the performance of CO2 synergistic huff and puff. The well selection principle of CO2 synergistic huff and puff are proposed. The research results of the influencing factors show that the existence of inter-well channel has a negative impact on the stimulation performance, the greater the permeability contrast the worse of oil increasing and water cut decreasing. The injected CO2 has a certain sweep radius and the limitation of well spacing is 70m. There is negative interference between liquid production rate of high structural position well and the performance of lower position well. For well selection of CO2 synergistic huff and puff, the reservoir with large formation thickness and large stratum dip should be considered primarily. Then a well located in high structural position and with a well spacing of less than 70 m is the optimal choice. Field application at C2X1 block shows a good performance with a total oil increment of 1280 t and the average water cut reduction of 57.7%.

Abstract

The rapid economic development and urbanization accelerating the water consumption. Water shortage and irrational water use cause a series of questions, such as the imbalance between supply and demand and destruction of natural flow of water resources. Meanwhile, these problems will impose a height pressure over the further development of the social economy. This paper utilized the input-output model to calculate the coefficients of direct water consumption as well as indirect water consumption to explore the virtual water flows in different sectors based on data of Jiuquan City in 2012. Results show that the agriculture sector, having the highest water consumption but creating little economic benefits, virtually flows to food and tobacco manufacturing sectors and service sectors, as the main export sectors. Food and tobacco manufacturing sectors have a lot contribution to the indirect boost of economic system by water resources with the highest indirect water consumption. Finally, we should energetically increase the water saving capacity of agriculture, readjust industrial structure and strengthen the cooperation of water allocation among all sectors in order to promote coordinated and sustainable development of water resources utilization and economy.