Abstract

This study was conducted to test the viability of coffee husks as a potential feedstock in a gasifier-dryer system. The projection of the total amount of waste produced is necessary in determining the input for the process modelling, together with the proximate and ultimate analyses that were conducted thru standard testing. In the tests, the proximate analysis gave 12.30% moisture content, 64% volatile matter, 23.30% fixed carbon and 12.70% ash content. On the other hand, the ultimate analysis gave 38.50% carbon, 5.89% hydrogen and 42.91% oxygen. No traces of nitrogen and sulfur were found. Aspen Plus Version 11, a package that can be used for modelling reactors for biomass gasification was used to produce a model and determine the producer gas composition. To dry 2 tons of coffee fruits in a gasifier-dryer system, it requires 50 kg/hr of the biomass feedstock. By feeding 50 kg/hr of coffee husks and 0.578 kg/hr of air in the model, it produced simulation results of 925.85 °C gasification temperature in the reactor to gasify the coffee husks and air mixture to produce the producer gas composed of 84.2851 carbon monoxide (CO), 4.7104 carbon dioxide (CO2), 0.1063 methane (CH4), 6.9086 hydrogen (H2), 1.0164 nitrogen (N), and 2.9726 water (H2O) in mass percentages. Finally, the energy efficiency of the gasifier with respect to temperature and air to biomass ratio was computed. All the inputs are based on the actual elemental analysis of coffee husks feedstock. A valid point at 704 °C was established, indicating the realistic limit of the gasifier based on the simulations. The trend of the results was found to be consistent with the experimentally validated analysis of other biomass feedstocks in published investigations. The model developed in this study is intended to be validated through experimental verification in our future studies, and the results of the modelling and validation will be used in prototyping the specific gasifier.

Abstract

The International Energy Agency (IEA) has provided the data that coal consumption is a major source of carbon dioxide (CO2) emissions. Up to now, the evolution of the global coal trade volume still tends towards increasing. However, whether there is a possibility of downward trend in global coal trade competition? This paper offers a comprehensive exploration and discussion of dynamic competitive relationship and intensity among the global coal importing trade from a continuous time series perspective. First, the results indicate that more competitive relationships regarding coal imports are being built, and the coal import competition network (CICN) has been moved from a core periphery structure towards a reticular structure. In addition, global coal trade competitive intensity has continued to rise. Next, we find that the role played by the Asian-Pacific region, led by Japan and China in sequence, in the evolution of this competitive pattern is becoming increasingly prominent. The competitive intensity of European importers has declined since 2007. In contrast, China soared from seventh in 2009 to first in 2016 in terms of coal import competition rank. Finally, based on the results, it is recommended that the policy makers in Asian countries should make out strategies such as adopting environmentally friendly technologies to decrease the CO2 emissions.

Abstract

Carbon market is established to achieve CO2 emission reduction targets cost efficiently. However, the pilot carbon markets in China emerged market downturn to certain degree with big variation of carbon price and low liquidity in trading market. The existence of transaction cost and market power affect the cost-effectiveness of the carbon market. Do different carbon emission permit allocation methods cause different efficiency losses? This paper explores whether the choice of emission permit allocation method affects the cost effectiveness of ETS when transaction cost and market power exist in carbon market, considering China pilot ETSs settings. By Stackelberg model, we find that transaction cost leads to the efficiency loss of ETS and the efficiency loss from benchmarking and grandfathering are less than auctioning. Market power causes the efficiency loss of ETS, the efficiency loss is proportional to the gap between the market power firm’s carbon emissions and its free emission permits. If both transaction cost and market power exist in carbon market, market power further exacerbates the efficiency loss caused by transaction cost. The further efficiency loss caused by grandfathering and benchmarking are less than auctioning.

Abstract

Even though all capture technologies developed for capturing CO2 from the utilization of fossil fuels can be applied to capture CO2 from the utilization of biomass, due to the obvious different properties, the performance can also be quite different. This work investigates the differences when using chemical absorption to capture CO2 from the combustion of recycled woods and coal, in order to provide suggestions on the integration of CO2 capture in the utilization of bioenergy and promote the application of bioenergy with CO2 capture and storage (BECCS). Two solvents, Monoethanolamine (MEA) and hot potassium carbonate (HPC), have been included. The results show that the flue gas (FG) from the combustion of recycled wood (RW) has a higher CO2 content, but lower O2, SOx and NOx content compared to the coal fired FG. In comparison to the coal fired FG, capturing CO2 from the RW fired FG requires less energy for both solvents, due to its higher CO2 content. The estimated oxidative and acid gas degradations are higher for FFCCS compared to BECCS, due to the higher O2, SOx and NOx contents in coal fired FG compared to those in the RW fired FG. For HPC process, FG compression work account for the largest part of the total energy consumption. Even though, the reboiler duty of the HPC process is lower than that of the MEA process, the total energy penalty is higher.

Abstract

Climate changes and energy crisis have drawn considerable attention across the world, which called upon the urgency for new energy provision and carbon emission reduction globally. Hybrid renewable energy system (HRES) integrated with LAES is a good option to achieve the de-carbonization of energy sector. This study focuses on exploring the value of LAES in a hybrid renewable micro-grid, in which the decoupled off-design LAES energy storage model was developed and inserted into the system MILP framework, which is applicable for discussing the optimal E/P ratio of LAES, digging the value streams out and optimally sizing the different system components and LAES units separately to achieve good economics and environment benefits. The simulation results indicated three important aspects. Firstly, for a specific micro-grid equipped with LAES, there exist the optimal charge/discharge E/P ratio of LAES, corresponding to the optimal sizes of liquefaction unit, power recovery unit and storage tank when providing different services. Secondly, if wind penetration reaches about 50%, LAES annual benefits can reach about 90% of its annual investment cost when six explicit value streams are stacked, including the time shifting, renewable firming, peak shaving, flexibility and reserve value, as well as the waste heat utilization, which is totally 8.2% higher than that of battery storage at the same investment cost. Thirdly, compared with the LAES cost reduction and large electricity price difference, more renewable penetration is the major driving force to increase the value and attractiveness of LAES, the optimal charge/discharge E/P ratio and storage tank size is 27/14 h and 608 t when there is 75% of wind power, resulting in about 60% of carbon emission reduction on 2016 level for a micro-grid.

Abstract

In recent years, with the development of IOT and the use of new energy, the information security problems of energy big data are gradually revealed, to further improve the privacy and security of data, the open and transparent blockchain technology is introduced. At present, some scholars have introduced blockchain technology into big data query, and the query types are also various. This paper mainly summarizes the research on keyword search based on blockchain in recent years, and analyzes its application potential in energy information security. The general structure of this paper includes a brief introduction to blockchain, the research progress of keyword search based on blockchain. Finally, this paper makes some prospects on the storage and resource consumption of keyword search based on blockchain.

Abstract

Spatio-temporal data is two-dimensional data with time and space. In the past, centralized databases were used to store spatio-temporal data, but this way is weak to resist malicious attacks. As a distributed storage technology developed in recent years, which has the characteristics of decentralization, non-tampering, openness and transparency, security and credibility. The security of the blockchain is jointly maintained by participants, which makes the data stored in it more secure. This article aims to summarize the currently developing blockchain technologies, like blockchain 1.0, 2.0, and DAG blockchain known as blockchain 3.0, and analyze the advantages and limitations of using them to store spatio-temporal data.

Abstract

The hydrogen absorption of metal hydride (MH) is an exothermic process. For a cylindrical MH hydrogen storage reactor with a concentric tube heat exchange, the hydrogen adsorption heat is discharged by the heat transfer fluid (HTF), and the absorption reaction proceeds along the radial direction from the center to the periphery, which leads to the non-uniformity of the reaction process and limits the average reaction rate. In order to improve the hydrogen storage rate, the phase change material (PCM) is used to assist in heat transfer by surounding the reactor. This paper establishes a mathematical model to describe the heat and mass transfer process within the reactors. The results show that the surrounding PCM can absorb the reaction heat at the periphery of the reactor, and promote the reaction proceeding in this region. Thus, the average hydrogen absorption rate of the reactor surrounded by PCM is increased by about 1.5 times owing to the assisted heat transfer of PCM.

Abstract

In order to study the falling film flow process outside the horizontal circular tube, experiment is adopted in this paper to investigate the effects of liquid spray density and spray temperature on the liquid film flow pattern transformation and pattern distribution. Meanwhile, the temperature distribution characteristics of the horizontal tubes are analyzed. The high-speed camera was used to photograph the flow pattern of the liquid film, and the K-type thermocouples were used to measure the tubes wall temperature. The results show that (1) as the spray density increases, the liquid film is converted from a droplet flow to a columnar flow and then to a sheet flow; (2) the critical spray density of the flow pattern conversion will reduce with the spray liquid temperature increasing; (3) the critical spray density of 10% glycerol solution for flow pattern conversion is bigger than that of water; (4) the tube wall circumferential temperature increased with the increase of spray density, and the tubes wall circumferential temperature decreased with the increase of the circumferential angle in the range of the circumferential angle from 0° to 135° and rose slightly from 135° to 180°; (5) the tube wall circumferential temperature of water is higher than that of the 10% glycerol solution.

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. For complex fault-block reservoir, it is characterized by small oil-bearing area, incomplete well pattern and broken geological stricter. Based on the reservoir feature, synergistic mode is proposed. By using numerical simulation method, typical simulation models of CO2 synergistic huff and puff are established to simulate the effects of geological factors and development factors on CO2 huff and puff. Then we summarized well selection principle of CO2 synergistic huff and puff. The sensitivity evaluation results show that the reservoir rhythm, inter-well passage, well spacing, high-position well liquid production rate and waist well liquid production rate are extremely sensitive factors, the stratum dip and the injection volume allocation scheme are sensitive factors, and the relationship with structural isobaths is insensitive. For well selection, 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 120 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%.