Self-Heating of Biochar during Postproduction Storage by O2 Chemisorption at Low Temperatures

Biochar is attracting attention as an alternative carbon/fuel source to coal in the process industry and energy sector. However, it is prone to self-heating and often leads to spontaneous ignition and thermal runaway during storage, resulting in production loss and health risks. This study investigates biochar self-heating upon its contact with O2 at low temperatures, i.e., 50–300 °C. First, kinetic parameters of O2 adsorption and CO2 release were measured in a thermogravimetric analyzer using biochar produced from a pilot-scale pyrolysis process. Then, specific heat capacity and heat of reactions were measured in a differential scanning calorimeter. Finally, a one-dimensional transient model was developed to simulate self-heating in containers and gain insight into the influences of major parameters. The model showed a good agreement with experimental measurement in a closed metal container. It was observed that char temperature slowly increased from the initial temperature due to heat released during O2 adsorption. Thermal runaway, i.e., self-ignition, was observed in some cases even at the initial biochar temperature of ca. 200 °C. However, if O2 is not permeable through the container materials, the temperature starts decreasing after the consumption of O2 in the container. The simulation model was also applied to examine important factors related to self-heating. The results suggested that self-heating can be somewhat mitigated by decreasing the void fraction, reducing storage volume, and lowering the initial char temperature. This study demonstrated a robust way to estimate the cooling demands required in the biochar production process.

Post-arc current measurement and interruption performance of vacuum interrupter in DC interruption

In the DC grid, fault current rises very fast due to low impedance. Fast DC circuit breakers are needed to isolate faults and avoid a collapse of the common DC grid voltage. Based on the forced current zero (CZ) technology, the vacuum interrupter (VI) equipped with fast electromagnetic repulsion mechanism is a very promising solution of fast DC interruption. The experimental research on the DC interruption characteristics of a VI, namely by examining the post‑arc current (PAC) is presented in this paper. The dependence of the interruption capability on the PAC is analysed. What’s more, the failure modes of the VI under various experiment conditions are summarized. A former finding was that not all the arcing history which starts from the electrodes separating to the CZ has influence on the PAC but only a very short duration of several microseconds right before the CZ takes effects. New experiment results are added in this paper to support the former finding. Another former finding was that a longer electrode separation will bring about higher PAC. In this paper, both the influence of the arcing memory time and the electrodes separation are owed to a higher residual plasma density, which is verified by a model for calculating the residual plasma density and the continuous transient model (CTM) for calculating PAC.

Effects of Using Air Curtains on Energy Consumption During Cooling Season Under Different Climate Conditions

In zones separated by doors with many entrances and exits, it is crucial in terms of energy consumption to protect the conditioned air in the indoor environment from the effects of outside air. The increase in door dimensions and opening frequency make this effect even more evident. Various methods are used to prevent leakage of outside air into the indoor environment. In this study, we investigated the effects of using air curtains on energy consumption during the cooling season in a factory building. The door width and height in this building, which has a high story height, were also large. These 26 doors must remain open all the time because of the production process. With a transient model developed on Transient System Simulation Tool (TRNSYS) coupled with Contaminant Transport Analysis Software (CONTAM), we showed the effects of using the air curtains in different climate conditions. As a result, we demonstrated that using air curtains will provide great savings, especially in cities with high cooling requirements.

Study on a New Transient Productivity Model of Horizontal Well Coupled with Seepage and Wellbore Flow

Digital transformation has become one of the major themes of the development of the global oil industry today. With the development of digital transformation, on-site production will surely achieve further automated management, that is, on-site production data automatic collection, real-time tracking, diagnosis and optimization, and remote control of on-site automatic adjustment devices. In this process, the realization of real-time optimization work based on massive data collection needs to be carried out combined with oil and gas well transient simulation. Therefore, research of the horizontal well capacity prediction transient model is one of the important basic works in the work of oil and gas digital transformation. In this paper, the method and process of establihing the transient calculation model of single-phase flow in horizontal wells are introduced in detail from three aspects: reservoir seepage, horizontal wellbore flow (taking one kind of flow as an example), and the coupling model of two flows. The model is more reliable through the verification of pressure recovery data from multiple field logs. The transient model of single-phase seepage in horizontal wells will lay the foundation for the establishment of transient models of oil-gas two-phase seepage and oil-gas-water three-phase seepage.

A Paradigm Shift in Monitoring Pipeline Leaks - Combining Sensorless NPW with RTTM

Leak detection solutions in pipelines use several known methods and technologies. However, each method and its underlying technology has their benefits and drawbacks. This article will present and evaluate a hybrid solution that combines two methods based on different physical measurements and quantities to ensure a superior detection probability, short detection time, accurate localization of faults, and minimal false alarm rates. In addition, this solution also features preventive capabilities by pointing out problematic areas in a pipeline that may need more attention. The article presents a novel approach for pipeline monitoring using a combined solution with the strengths of real-time transient model (RTTM) technology and the power of next-generation fiber sensing geared towards leak detection. On top of acoustic sensing for leaks, it features continuous pipeline integrity monitoring where, using subtle characteristics of propagating negative pressure waves (NPW), pipeline sections signatures are tracked, aiming to detect changes that might expose pipeline integrity issues that can enable the operator to take preventive measures and plan maintenance events. Such a hybrid solution, from AVEVA™ (RTTM) and Prisma Photonics (fiber sensing), will obtain higher levels of performance and reliability. In addition, such a hybrid approach responds to the increasing regulatory demand to have two continuously working solutions based on different physical measures to ensure leak detection and prevention of substance spillage. This article intends to introduce such a hybrid solution with new applications in predictive maintenance for pipeline operators and shed more light on the benefits of such a solution facing further regulatory demands.

Modeling Transient Flow in CO2 Injection Wells by Considering the Phase Change

A transient model to simulate the temperature and pressure in CO2 injection wells is proposed and solved using the finite difference method. The model couples the variability of CO2 properties and conservation laws. The maximum error between the simulated and measured results is 5.04%. The case study shows that the phase state is primarily controlled by the wellbore temperature. Increasing the injection temperature or decreasing the injection rate contributes to obtaining the supercritical state. The variability of density can be ignored when the injection rate is low, but for a high injection rate, ignoring this may cause considerable errors in pressure profiles.

A Steady State Model for Burning Coal Mine Methane in a Reverse Flow Burner

In this study, a steady state model for burning of coal mine methane in a Reverse Flow Burner (RFB) with full kinetics was developed by analogy of a steady counter-flow reactor, and the developed model was used for quick prediction of the lean combustibility limit (LCL). The model was successfully validated with experimental and numerical results, and it was shown that the developed model has excellent accuracy and computational efficiency. Good agreement between the predicted temperature, LCL, and the experiments was observed. The LCL of the equivalence ratio of 0.022 for methane/air mixture was obtained by the developed model. The model was then used to evaluate LCL for the RFB, focusing on the effect of heat loss and burner length on LCL. This indicated that the computational time using the developed model can be reduced by a factor of 1560 compared to the complete transient model.

Numerical Simulation of the Influence of Different Surface Morphologies on Molten Pool Flow under Moving Heat Source

In order to study the influence of different initial topography on the molten pool flow under a moving heat source, the finite element analysis method was used to establish a two-dimensional transient model of laser polishing to simulate the evolution of the surface topography of the material during laser polishing. In the simulation process, a moving laser beam was used as the heat source, and the free surface of the actual material was profiled through a three-dimensional profiler. A very similar simulation model surface was constructed, coupled with the flow field and temperature field in the laser polishing process, and the capillary force was considered comprehensively. Combined with thermocapillary force. The results show that under the combined action of capillary force and thermocapillary force, the surface of the polished material has a peak-filling effect, which makes the surface of the material achieve a good polishing effect. The initial shape will affect the polishing effect, the greater the curvature, the faster the flow rate of the molten pool. In molten pools with large spatial curvatures, capillary forces dominate. Keywords: Laser polishing; molten pool; surface topography; numerical analysis; capillary force; thermocapillary force.

Simulation and optimization of VRPSA system based on pseudo-transient method

In order to address the challenge of pressure swing adsorption system optimization, an optimization framework based on pseudo transient continuation method was used and vacuum rapid pressure swing adsorption process for oxygen production as a typical example. A pseudo transient model library was established and a robust two-stage dynamic tearing model was proposed to deal with the cyclic steady state conditions. Furthermore, the time constants were discussed and a practical time constant strategy and expressions were proposed for the stability and efficiency of calculation. Finally, reduced successive quadratic programming and time relaxation algorithm were used for the optimization of the two systems respectively, and the optimization results showed that although the simulation time of pseudo transient system is slightly higher than that of single discretization system, the optimization expense of single discretization system in two cases were 5.7 times and 11.6 times of that of pseudo transient system respectively.