Abstract

Coal plays an indispensable role in the chemical industry, in which methanol from coal is a largely crucial part. In the process of coal-to-methanol chain, a large amount of CO2 is emitted into the atmosphere, which should be captured and utilized. In this paper, firstly Aspen Plus software is used to simulate the whole process of coal-to-methanol production chain. The simulation results indicate that the carbon footprint of a certain amount of coal-to-methanol process is 3.01t CO2/t methanol, and then we compare the carbon footprint of methanol production processes with two cases which are CCS (Carbon Capture and Storage) and CCU (Carbon Capture and Utilization) with P2G (Powerto-Gas) to reduce carbon emissions. It shows that CO2 emission of methanol production after CCS is 0.64 t CO2/t methanol with reducing by 78.7% and that after CCU with P2G is 1.42 t CO2/t methanol, with reducing by 52.82%, and simultaneously increases methanol production doubly to 1378.31kt/y. The results show that CCS and CCU are effective ways to alleviate global warming.

Abstract

Full-spectrum solar energy utilization has drawn widespread attention for cascading solar energy utilization. A spectral splitting approach is described and a prototype is originally presented. Innovatively, the fullspectrum solar energy is first split and then concentrated onto photovoltaics and solar thermochemical reactor. In this case, the irreversible loss would be expected to be reduced. Here, thermodynamic evaluation of prototype is conducted. The monocrystalline silicon photovoltaics and methanol decomposing are adopted. The results show that the solar-to-electricity efficiency would be 37% in the hybrid system, 19% higher than individual concentrating solar photovoltaics and 9% higher than individual solar thermochemical system. An optimal working spectral range is about 280-1100nm for the silicon photovoltaics. The proposal of hybrid approach of solar photovoltaics and endothermal reaction leads to a feasible strategy for cascading solar energy utilization.

Abstract

The operational flexibility of coal-fired power plants during peak shaving processes becomes an urgent problem with the penetration of intermittent renewable power in the power grid. However, the original control systems for the power units have some deficiency during rapid peak shaving processes. In this paper, a revised control system by regulating high-pressure extraction steam was added to improve the operational flexibility during load change processes. Based on the transient models of a 660 MW supercritical coal-fired power unit, comparison on the original and revised control systems for the main parameters were proposed. It turns out that when compared with the original control system, the revised control system exhibits a better control performance during peak shaving processes, especially for the loading down process. The differences of the output power, live steam pressure, live steam pressure and reheat steam temperature between the original and revised control systems during load down process are −1006.41 MW·s, 21.26 MPa·s, 256.17 °C·s, and 680.17 °C·s, respectively. The study can provide a guidance for the control optimization and flexibility improvement of coal-fired power plants during peak shaving processes.

Abstract

In recent years, the subway system has experienced rapid development all over the world. However, the air quality in the station has attracted more public attention. This paper concentrates on the variation of the PM2.5 and PM10 concentrations on platformsin the entire operation periods of the train. The train frequency and piston wind are considered to investigate the influence of passing trains number, the train arrival and departure on the PM2.5 and PM10 concentrations on the platforms. The results show that the diurnal average concentrations of PM2.5 and PM10 on platforms are 81 and 147 μg/m3 , respectively. The maximum concentrations of PM2.5 and PM10 (104 and 173 μg/m3 , respectively) occur in the morning rush hours, when the number of passing trains is the largest. The piston wind can push the polluted air in the tunnel into the platform and increase the PM concentrations on platforms. Moreover, passengers walking can also cause the suddenly sharp increase of PM2.5 and PM10 concentrations when the train stops at the station. It can be deduced thatreasonable ventilation strategy and efficient air filtration system are necessary to be studied in the further research for the improvement of air quality and energy saving of the ventilation and air-conditioning system in subway stations.

Abstract

SNG (solidified natural gas) technology is a promising and potential technology for long-term and large-scale storage of methane in hydrates due to the plethora of benefits it offers in comparison to conventional methods of storage. In this study, we aim to investigate the kinetics of mixed hydrate formation using a ternary C1(93%)-C2 (5%)-C3 (2%) gas mixture representing the natural gas. The main objective is to study the effect of presence of higher hydrocarbons (ethane and propane) in influencing the mixed hydrate formation kinetics with the additional presence of thermodynamic promoter, tetrahydrofuran.
Experiments to study the effect of temperature and pressure on the mixed hydrate formation kinetics in an unstirred reactor configuration were performed. Results from this study will provide salient information in order to advance the SNG technology towards commercial implementation.

Abstract

Several methods have been developed to enhance boiling heat transfer by surface modification, e.g., mechanical methods, chemical methods and hybrid methods. In the present study, micro-pin-fin silicon surfaces are prepared by a dry etching method. Subsequently, the micro-pin-fin surfaces are deposited with copper nanoparticles (20±5 nm) by an electrostatic deposition method. Saturated pool boiling heat transfer of FC-72 is experimentally investigated, illustrating the effect of nanoparticles on the saturated pool boiling heat transfer. Compared with the micro-pin-fin surface, the nanoparticles have slight effects on the heat transfer at low heat fluxes (< 5 W/cm2 ), while at moderate-high heat fluxes (>5 W/cm2 ), the effect of nanoparticles depends on the deposition time. In the present case, heat transfer is deteriorated on the micro-pin-fin surface with 1h deposition at moderate-high heat fluxes, but the heat transfer is slightly enhanced at moderate heat fluxes (5 – 15 W/cm2 ) and is slightly deteriorated at high heat fluxes (>15 W/cm2 ) on the micro-pin-fin surface with 2h deposition. Additionally, compared with the micro-pinfin surface, the critical heat flux (CHF) is slightly enhanced (around 7%) on the micro-pin-fin surface with 2h deposition, but is almost the same on the micro-pin-fin surface with 1h deposition. To study the reasons behind these results, SEM images are taken to characterize the surfaces and high speed visualization is conducted to compare bubble behaviors. In addition, supplementary experiments are designed to measure the wickabiltiy on these surfaces.

Abstract

Hydrogen storage is an important part in the utilization of hydrogen energy. The combination of phase change materials and hydrogen solid storage system will effectively recover and utilize the reaction heat in the process of hydrogen absorption and desorption. This paper presents a hydrogen-heat storage unit consisting of metal hydride (MH) and phase change material (PCM). The performance of hydrogen ab/desorption and heat storage/release of MH-PCM units was studied by numerical simulation. To optimize the units structure and improve performance, the amount of PCM was discussed. The results show that the sensible heat storage ratio of PCM and the average desorption rate increases with the decrease of the amount of PCM.

Abstract

In this study, a small-scale test rig of organic Rankine cycle (ORC) system driven by low-grade heat has been developed and investigated experimentally. The test rig consisted of a number of essential components including a scroll expander and squirrel cage motor, plate-type recuperator, finned-tube air cooled condenser, liquid receiver, liquid pump, two thermal oil heated evaporators and other ancillaries. Considering its zeroozone depletion potential and appropriate thermophysical properties, R245fa was selected as a working fluid in the ORC system. Correspondingly, R245fa flow was heated and evaporated through either a plate-type evaporator or a shell and tube one by hot thermal oil flow which itself was circulated and heated by exhausted flue gases from an 80 kWe microturbine CHP unit. In this paper, the experimental investigations were mainly carried out on the ORC system with different evaporators and with or without recuperator integrated. Subsequently, the effects of various types of evaporators and with or without recuperator on the system performance are evaluated, compared and analysed. The test results and analysis are essential to understand the system operation at different design structures and components which can significantly contribute towards optimal component selections and system performance controls.

Abstract

The United Arab Emirates (UAE) has embarked on an economic diversification strategy. One key priority is infrastructure development and environmental sustainability. The government is considering the integration of renewable and nuclear generation in the power sector as well as introducing electric vehicles into the transport sector to reduce fossil fuel consumption and air pollution. This research aims to determine the optimal arrangement between: electricity plants, charging stations, and power transmission and distribution interconnections. This to meet the electricity demand and production forecasts of a geographical region under operational and environmental constraints. The resulting electricity supply chain framework is modelled as a multi-period mixed integer linear programming (MILP) model. A case study of Abu Dhabi City from 2020-2030 was examined. The study results show that gas power still dominates by 2030, but at a lesser extent; whereas nearly 656 charging points are needed to cover 15,970 electric vehicles by 2030.

Abstract

The interactive grid is the basic model of the modern global power grids, analysis of users’ interaction power behavior is a core task. This paper firstly uses self-organizing map SOM neural network training and artificially separated methods to optimize the initial clustering center of K-means algorithm. Then, under the background of peak-to-valley time-of-use electricity price, the adjustment potential index based on user psychology is constructed, and the users’ electricity consumption behavior based on load data and adjustment potential index is analyzed. Finally, the clustering results of the two improved algorithms and the clustering results of classical K-means algorithm are compared. By comparing the advantages of K-means++ algorithm in accurate identification and clustering of users’ electricity consumption behavior, the effectiveness of K-means++ clustering center selection process in significantly shortening clustering time is analyzed.