Abstract

It has becoming a developing trend to replace boilers with heat pumps driven by electricity under the global carbon neutrality strategy. The exergy loss and thermal performance of the conventional circulating flash heat pump steam generator (CF-SGHP) system were researched. A new direct evaporative heat pump steam generator (DE-SGHP) system was proposed in order to reduce total exergy loss. Then the exergy loss and thermal performance of the two systems was analyzed comparatively under different discharge steam temperature (Tout), condensation temperature (Tcond) and heat source water temperature (Thsw). The results are as follows: The exergy efficiency (ƞex,sys) of the CF-SGHP system is 62.98%. In addition to the exergy loss caused by the irreversible process of the compressor, the relative maximum exergy loss occurred in the flash cycle process, whose exergy loss rate is 23.24%; The exergy loss of DE-SGHP system is always lower and the COP is always higher than that of the CF-SGHP system within the range of Tout, Tcond and Thsw; There existed an optimal Tcond of 91℃ in the DE-SGHP system to maximum the ƞex,sys of 67.74% and the COP of 2.71 when Tout is 165℃ and Thsw is 60℃, that indicated to have a broader development prospect.

Abstract

Typical industrial-scale sugarcane-to-bioethanol processes are evaluated using exergy and mass-based metrics. A more robust set of energy metrics, the change in energy quality and energy yield, are applied to assess the life-cycle efficiency of sugarcane upgradation. From an energy perspective, bioethanol production is not justifiable. Bioethanol achieves a poor energy recovery from sugarcane. Sugarcane to bioethanol, and subsequent electricity/power production, results in considerable energy losses even when compared to combusting the sugarcane itself. A technoeconomic feasibility study would be required to justify the 3 % gain in energy yield achieved when incorporating 2G processes into existing 1G infrastructure.

Abstract

There are some partially penetrating inclined fractures (PPIFs) due to stress interference between fracture networks in multi-stage fractured horizontal wells (MFHWs). It would take tremendous computation time to make flow behavior analysis and well production optimization in numerical simulators. Therefore, it is an extremely urgent task to establish efficient and rigorous models of PPIF networks. In this paper, triangular elements were introduced to characterize the geometry and intersection of PPIFs. Control volume method is adopted to model the fracture flow numerically and the star-delta transformation is used to solve the interconnected fractures more accurately. The fluid flow in the matrix is analytical modeled by source function. The transient flow between PPIFs and matrix is coupled on the surface of fractures. By introduce spatial triangle numerical integral technology in source function calculation, the model efficiency can be greatly increased. Finally, the pressure transient analysis (PTA) of PPIFs can be modelled with high accuracy and less calculation time. With the aid of proposed PPIFs model, the transient pressure behaviors of different MFHWs were analyzed. The hydraulic and natural fractures in these MFHWs have different inclinations, trends, and heights. The flow regimes of PPIFs with finite conductivity are analyzed in detail. Flow regimes analysis indicates that eight flow regimes can be observed, including the wellbore storage flow, fracture linear flow, bilinear flow, formation linear flow, early radial flow, compound linear flow, pseudo-radial flow, and boundary-dominated flow. The results indicate that the formation linear flow and early radial flow would be influenced by the geometry of nature fractures, which is quite different from that of vertical penetration fractures. The introduction of numerical integral method greatly reduces the calculation time (less than 2 minutes) with high accuracy, which make it possible to analysis the fracture parameters more efficiently. The result of typical well test curves analyses shows that the duration of flow regimes will be influenced the parameters of fractures. When the penetration ratio (> 0.6) or the incline angle (>60°) is large enough, the bilinear flow will last longer, and the early radial flow will be absent.

Abstract

In this work, a Carnot Battery energy storage system based on organic flash cycle is constructed. And the thermodynamic performance of the system with two working fluids (i-Pentane and cyclopentane) is investigated. The results showed that with the increase of flash evaporation temperature, the system round-trip efficiency, thermodynamic efficiency and energy storage density exhibited a trend of first increasing and then decreasing. The performance of system with i-Pentane is better than that of system with cyclopentane. Meanwhile, the proportion of saturated steam decreases. The performance of system is affected significantly when the isentropic efficiency of the compressor and turbine increases.

Abstract

Building sector defossilization is key to achieving significant emission reductions in our society by 2045. Reducing emissions across the sector within a very limited timeframe requires executing complex transformation processes that depend on numerous options to take and multiple stakeholders. However, conventional methods make selecting the right option while integrating all stakeholders into the transformation process complex. In other research fields, integrated methods have already been established. In this work, we introduce process systems engineering and living laboratories and propose building energy, material, and social systems engineering (BEMSSE) as a powerful tool to accelerate the transformation process in the building sector.

Abstract

Deep geothermal single well system is one of the geothermal energy utilization mode that only takes heat without consuming water. Compared with the traditional mode, this system avoids the problem of difficult sandstone reinjection, which can greatly reduce drilling costs, and is applicable to a wide range of geological conditions. Geothermal single well system can be divided into close loop and open loop system. The latter exchanges heat with the aquifer by convection heat transfer and mass transfer, the heat output is higher than that of the close loop system through conduction heat transfer. In this paper, a three-dimensional unsteady flow and heat transfer model is established for the open loop coaxial casing of the geothermal deep single well with a packer, the effect of the density of geothermal water on the aquifer temperature distribution and heat output of the single well under different aquifer permeability is numerically simulated. The result shows that when the permeability of the aquifer is greater than 1.0E-12 m2, the permeability has a great influence on the heat output of a single well, while when the permeability is less than 1.0E-12 m2, the permeability has little effect the heat output too much. The permeability has little effect on the heat output of a single well. The results can be used for calculating the heat output of a single well in different aquifers.

Abstract

In this paper, a method for arriving at an optimum design and operation of a geothermal district heating system equipped with deep downhole heat exchanger and heap pump was introduced. A theoretical heat transfer model at steady state was proposed by ignoring the heat loss of transmission pipeline and the heat storage effect of installed facilities and buildings. It shows that there is an optimum ratio of hot geothermal water flowrate to the cold circulating water flowrate through PHE or the evaporator of heat pump. In addition, based on the heat balance equations, and the given costs of PHE, terminal radiator and heat pump, the installation of those main facilities with a minimum capital investment can be obtained.

Abstract

The carbon emissions of the steel industry are enormous. In addition, a large amount of solid waste will be generated in the steelmaking industry. Therefore, the efficient utilization of solid waste in the steelmaking industry is significant for energy saving and carbon reduction. Steel slag is a by-product of the steelmaking process, a bulk industrial solid waste. At present, the comprehensive utilization rate of steel slag in China is less than 30%. Excessive f-CaO content in steel slag is one of the main factors limiting its utilization and will lead to the volume expansion of steel slag during the slow hydration process. The traditional f-CaO digestion method cannot improve the performance of the steel slag from the source, and the sensible heat recovery of the steel slag cannot be carried out. Therefore, the origin adjusting technology, which utilizes the sensible heat of steel slag and can modify the steel slag, has gradually attracted attention. This paper takes the steel slag of a steel plant in Shanxi as the research object. After analyzing its steel slag data, a scheme of origin adjusting is proposed, and the relevant influencing factors are analyzed.

Abstract

Flue gas assisted cyclic steam stimulation (CSS) has gradually gained prominence in the development of extra-heavy oil reservoirs. The flue gas produced by fuel combustion is primarily composed of CO2, N2, and steam, and it is injected directly into extra-heavy oil reservoirs to enhance oil recovery. This method is also known as multi-thermal-fluid (MTF) huff-puff technology, which is an important CCUS technology. In this paper, the effects of different CO2 and N2 ratios on the development of extra-heavy oil reservoirs are analyzed and discussed. To begin, the viscosity and components of crude oil are obtained through physical experiment. Second, the effects of different CO2 and N2 ratios on crude oil viscosity and phase state are analyzed using the phase equilibrium model and viscosity model. Finally, numerical simulation is used to optimize the CO2 and N2 ratios. The results show that the higher the CO2 ratio, the lower the viscosity of the crude oil after MTF huff-puff. The phase diagram gradually narrows as CO2 ratios rise while N2 ratios fall. Because the primary function of CO2 is to reduce viscosity and the primary function of N2 is to improve formation energy, the optimal ratio of CO2 and N2 is 7:3.

Abstract

Rapid pyrolysis of pulverized coal is an essential procedure of the coal upgrading process, but still faced with the problem of high content of heavy components in the tar. The CPD model is a kinetic model that can effectively predict the distribution of coal pyrolysis gas-liquid-solid products, but incapable of achieving a detailed description of the specific composition of the tar. Therefore, based on the fundamental assumptions of the molecular structure of coal in original CPD model, a more detailed tar cutting method is carried out. For the tar component only contains one aromatic unit, the aromatic core is divided as 2 types and the yield of tar with less molecular weight can be calculated. By adopting the modifications above, a more accurate prediction of the tar product distribution can be achieved. This study can provide theoretical guidance for the intensification of the pyrolysis process.