Ultra-early prediction of the process parameters of coal chemical production.

Most accidents in a chemical process are caused by abnormal or deviations of the process parameters, and the existing research is focused on short-term prediction. When the early warning time is advanced, many false and missing alarms will occur in the system, which will cause certain problems for on-site personnel; how to ensure the accuracy of early warning as much as possible while the early warning time is a technical problem requiring an urgent solution. In the present work, a bidirectional long short-term memory network (BiLSTM) model was established according to the temporal variation characteristics of process parameters, and the Whale optimization algorithm (WOA) was used to optimize the model's hyperparameters automatically. The predicted value was further constructed as a Modified Inverted Normal Loss Function (MINLF), and the probability of abnormal fluctuations of process parameters was calculated using the residual time theory. Finally, the WOA-BiLSTM-MINLF process parameter prediction model with inherent risk and trend risk was established, and the fluctuation process of the process parameters was transformed into dynamic risk values. The results show that the prediction model alarms 16 min ahead of distributed control systems (DCS), which can reserve enough time for operators to take safety protection measures in advance and prevent accidents.

A chemical accident cause text mining method based on improved accident triangle.

BACKGROUND: With the rapid development of China's chemical industry, although researchers have developed many methods in the field of chemical safety, the situation of chemical safety in China is still not optimistic. How to prevent accidents has always been the focus of scholars' attention. METHODS: Based on the characteristics of chemical enterprises and the Heinrich accident triangle, this paper developed the organizational-level accident triangle, which divides accidents into group-level, unit-level, and workshop-level accidents. Based on 484 accident records of a large chemical enterprise in China, the Spearman correlation coefficient was used to analyze the rationality of accident classification and the occurrence rules of accidents at different levels. In addition, this paper used TF-IDF and K-means algorithms to extract keywords and perform text clustering analysis for accidents at different levels based on accident classification. The risk factors of each accident cluster were further analyzed, and improvement measures were proposed for the sample enterprises. RESULTS: The results show that reducing unit-level accidents can prevent group-level accidents. The accidents of the sample enterprises are mainly personal injury accidents, production accidents, environmental pollution accidents, and quality accidents. The leading causes of personal injury accidents are employees' unsafe behaviors, such as poor safety awareness, non-standard operation, illegal operation, untimely communication, etc. The leading causes of production accidents, environmental pollution accidents, and quality accidents include the unsafe state of materials, such as equipment damage, pipeline leakage, short-circuiting, excessive fluctuation of process parameters, etc. CONCLUSION: Compared with the traditional accident classification method, the accident triangle proposed in this paper based on the organizational level dramatically reduces the differences between accidents, helps enterprises quickly identify risk factors, and prevents accidents. This method can effectively prevent accidents and provide helpful guidance for the safety management of chemical enterprises.

Effect of N2 and CO2 on the Explosion Properties of High Equivalence Ratios of Hydrogen.

The explosion characteristics of premixed gases under different equivalence ratios (1.0-3.0) and inert gas addition (5-20%) are experimentally investigated, and sensitivity analysis of the radical reactions is carried out using the USC Mech II model to analyze the molar fraction of radicals. The results show that at high equivalence ratios, inert gas has little effect on flame stability. The addition of an inert gas reduces the tensile rate in the early stage of flame growth. At high equivalence ratios, CO2 inhibits explosive flame propagation twice as effectively as N2. Due to the large heat capacity and chemical kinetic effects, CO2 has a stronger inhibitory effect on the explosion pressure than N2, and the inhibition efficiency on the explosion strength is nearly twice that high. To further analyze the effect of different inert gas addition ratios on chemical kinetics, sensitivity analysis, and molar fraction simulations were performed. The thermal and chemical kinetic effects of CO2 cause later generation of H and OH radicals and the partial chain reaction involving CO2 causes a lower peak of H radicals than the peak of H radicals generated under an N2 atmosphere. However, CO2 is a direct reactant and the third body to produce a small chemical kinetic effect.

Single-Line Multi-Channel Flexible Stress Sensor Arrays.

Flexible stress sensor arrays, comprising multiple flexible stress sensor units, enable accurate quantification and analysis of spatial stress distribution. Nevertheless, the current implementation of flexible stress sensor arrays faces the challenge of excessive signal wires, resulting in reduced deformability, stability, reliability, and increased costs. The primary obstacle lies in the electric amplitude modulation nature of the sensor unit's signal (e.g., resistance and capacitance), allowing only one signal per wire. To overcome this challenge, the single-line multi-channel signal (SLMC) measurement has been developed, enabling simultaneous detection of multiple sensor signals through one or two signal wires, which effectively reduces the number of signal wires, thereby enhancing stability, deformability, and reliability. This review offers a general knowledge of SLMC measurement beginning with flexible stress sensors and their piezoresistive, capacitive, piezoelectric, and triboelectric sensing mechanisms. A further discussion is given on different arraying methods and their corresponding advantages and disadvantages. Finally, this review categorizes existing SLMC measurement methods into RLC series resonant sensing, transmission line sensing, ionic conductor sensing, triboelectric sensing, piezoresistive sensing, and distributed fiber optic sensing based on their mechanisms, describes the mechanisms and characteristics of each method and summarizes the research status of SLMC measurement.

Analysis of Risk Factors of Coal Chemical Enterprises Based on Text Mining.

Coal chemical enterprises have many risk factors, and the causes of accidents are complex. The traditional risk assessment methods rely on expert experience and previous literature to determine the causes of accidents, which has the problems such as lack of objectivity and low interpretation ability. Analyzing the accident report helps to identify typical accident risk factors and determines the accident evolution rule. However, experts usually judge this work manually, which is subjective and time-consuming. This paper developed an improved approach to identify safety risk factors from a volume of coal chemical accident reports using text mining (TM) technology. Firstly, the accident report was preprocessed, and the Term Frequency Inverse Document Frequency (TF-IDF) was used for feature extraction. Then, the K-means algorithm and apriori algorithm were developed to cluster and for the association rule analysis of the vectorized documents in the TF-IDF matrix, respectively to quickly identify the hidden risk factors and the relationship between risk factors in the accident report and to propose targeted safety management measures. Using the sample data of 505 accidents in a large coal chemical enterprise in Western China in the past seven years, the enterprise accident reports were analyzed by text clustering analysis and association rule analysis methods. Through the analysis, six accident clusters and 13 association rules were obtained, and the main risk factors of each accident cluster were further mined, and the corresponding management suggestions were put forward for the enterprise. This method provides a new idea for coal chemical enterprises to make safety management decisions and helps to prevent safety accidents.

Experimental Study of the Influence of H2/CO on the CH4 Explosion Pressure and Thermal Behaviors.

In a spontaneous coal combustion environment and in the coal chemical process, multiple gases, such as CH4, H2, and CO, coexist, and explosion accidents are prone to occur. The causes of these disasters and the explosion characteristics are key to formulating preventive measures. To explore the effect of H2/CO on the explosion pressure and thermal behavior of methane-air, CH4 with initial volume fractions of 7, 9.5, and 12%, which correspond to three states of oxygen enrichment, equivalence ratio, and oxygen depletion, was selected. Moreover, a mixed fuel system is composed of H2/CO with different volume ratios. A 20 L spherical gas explosion experimental system was used to test the peak explosion overpressure P max, the maximum explosion overpressure rise rate (dP/dt)max, and the corresponding time parameters of the H2/CO-CH4 mixed system. Combined with the thermodynamic calculation model, laminar burning velocity S L, explosion heat loss q tra, and other parameters were obtained. The results show that due to the existence of the damping effect, CO has the dual characteristic of promoting or weakening methane explosions. Compared with CO, the effect of H2 on the methane explosion is more significant, and the improvement or weakening of the laminar combustion rate of the reaction system by CO "lags" behind that of H2. The heat loss in the process of a gas explosion is affected by factors such as the heat release rate, the propagation speed of the combustion wave, and the heat dissipation effect of the container wall. When H2/CO increases the laminar burning velocity of the mixed system, the heat loss decreases accordingly. This study also found that the laminar burning velocity model of the mixed gas based on the ideal spherical flame propagation theory is not fully applicable to the H2/CO/CH4 mixed system in a spherical closed space, and the calculation results have large errors when the mixed system is close to the upper limit of the explosion.

Risk Assessment of Liquefied Petroleum Gas Explosion in a Limited Space.

In recent years, the explosion accidents of liquefied petroleum gas (LPG) have induced tremendous losses. To analyze the deflagration danger of LPG, the explosion pressure and flame propagation features of the premixed LPG-air mixture in a closed pipeline at increased initial pressures and temperatures were examined by the numerical method. It has been shown that with an increase in the initial temperature, the highest explosion pressure and explosion induction period decrease, while the maximum flame temperature increases. As the initial temperature rises, the formation of the tulip flame accelerates, and the depression of the flame front increases at the same time. The elevated initial pressure raises the highest explosion pressure and the maximum flame temperature. Nevertheless, when the initial pressure exceeds 0.5 MPa, its impact on the flame temperature slowly diminishes. In addition, the gray relational analysis approach was utilized to evaluate the correlation between the initial condition and the derived parameters. The findings indicate that the initial pressure exerts the largest influence on the four explosion parameters. The research finding is important for exposing the deflagration risk features of LPG under complicated working situations, evaluating the explosion risk of correlated procedures and devices, and formulating scientific and effective explosion-proof measures.

Effect of Synergistic Aging on Bauxite Residue Dust Reduction Performance via the Application of Colloids, an Orthogonal Design-Based Study.

The application of polymer colloids is a promising approach for bauxite residue dust pollution control. However, due to the existence of synergistic aging, the efficiency of colloid dynamic viscosity to predict the dust control performance of bauxite residue is unclear. Previous studies were also rarely performed under synergistic aging conditions. Thus, this paper investigates the relationship between colloids' viscosity and dust control performance under synergistic aging modes. Results illustrated that the binary colloid achieved better dust control performance than unitary colloid for their higher viscosity and penetration resistance. For both unitary and binary colloid, higher viscosity results in better crust strength. A logarithmic relationship was found for viscosity and dust erosion resistance under unitary aging. However, Only the dynamic viscosity of colloids in solid-liquid two-phase conditions, rather than dissolved in deionized water, can effectively predict the dust control performance under synergistic aging conditions.

Characterization of red sand dust pollution control performance via static and dynamic laboratorial experiments when applying polymer stabilizers.

Red sand dust pollution is of great concern for its occupational and environmental detriments. The current remediation technique includes water spray and non-traditional stabilization via the application of polymer stabilizers. The dust erosion resistance plays a significant role in quantifying the effectiveness of red sand dust suppression. The aim of this paper is to evaluate the reliability and accuracy of five static and dynamic laboratorial methods that are commonly utilized to quantify the dust erosion resistance in the presence of polymers in previous studies, which are wind tunnel simulation, dynamic viscosity test, crust thickness test, penetration resistance test, and unconfined compressive strength test. The advantages and shortcomings of these methods were comprehensively demonstrated. The results illustrated that the penetration resistance test is the most reliable method in terms of the highest accuracy and relatively simpler operation. It also reveals excellent universality for effectively quantifying the dust erosion resistance of red sand with different particle sizes and for different polymers with various concentrations, while the rest of the methods failed to identify. The application of polymers contributes to improved dust erosion resistance for longer crust failure time, higher solution dynamic viscosity and crust penetration resistance, and higher unconfined compressive strength of rending sand samples. PAM outperformed guar gum and xanthan gum on the base of polymer ionicity and molecular weight. This study offers a better understanding in guiding the selection of optimum evaluation methods and polymers for the study of bauxite residue dust control.

Chemical kinetic behaviors at the chain initiation stage of CH4/H2/air mixture.

To intensively investigate chemical kinetic behaviors at the initial stage of CH4/H2/air mixture thoroughly, the density functional theory (CAMB3LYP/6-31 G) and a detailed mechanism (GRI-Mech3.0) were used to obtain kinetic and thermodynamic parameters. The reaction paths during the explosion process were analyzed, and the reaction rates of elementary reactions were compared with different ratios of CH4/H2/air mixture. The key reactions at the initiation stage of CH4/H2/air mixture explosion were determined, and their configurations were optimized. The reaction mechanism, reaction channel and configuration parameters of key reactions were obtained, which was verified by the intrinsic reaction coordinate (IRC) theory. Results show that H2 addition increases the laminar burning velocity, while it shortens the ignition delay time of H2/CH4/air mixture. The addition of hydrogen greatly accelerated the explosion reaction from sample 1 to sample 4. Moreover, CH4 still plays a key role at the chain initiation stage in H2/CH4/air mixture system; the addition of H2 would not compete with CH4 for triggering the explosion reaction, nor will it suppress the explosion of CH4. H2 could not replace or take precedence over the chain branching reactant (CH2O) of CH4 explosion to react with O2. Besides, H2 takes precedence over CH4 in the process of chain transfer after the chain reaction beginning, although CH4 has a distinct advantage in the chain initiation stage. The present results can provide theoretical guidance for the prevention and control of gas explosion, which may effectively reduce the explosion hazards.

Effects of N2 and CO2 dilution on the explosion behavior of liquefied petroleum gas (LPG)-air mixtures.

The present work aims to provide theoretical support to prevent LPG explosion accidents and reduce its hazardous effect. The explosion of LPG-air mixtures (4.0 % - 9.0 % in volume) under N2 and CO2 dilution (0.0%-30.0% in volume) was experimentally investigated by using a 20-L vessel at ambient temperature and pressure. The parameters of the maximum explosion pressure (pmax), time to reach the maximum explosion pressure (tc), maximum rate of the pressure rise ((dp/dt)max), time to reach the maximum rate of the pressure rise (tb), and average velocity of flame propagation (v) were investigated. In addition, the inerting efficiencies of N2 and CO2 were compared and analyzed. The results show that there exists a cubic function relation among pmax, (dp/dt)maxx, tc, tb and LPG volume fraction during the LPG explosion process. At the volume fraction of LPG was 5.7 %, all parameters reached peak values. The addition of N2 and CO2 effectively suppressed the explosion of LPG, reduced pmax, (dp/dt)max, and v and extended tc and tb. At a low LPG volume fraction, the inerting efficiency of CO2 was higher than that of N2. At a high LPG volume fraction, the inerting efficiency of N2 was higher than that of CO2.

Effect of Inert Gas CO2 on Deflagration Pressure of CH4/CO.

To study the effect of CO2 on the explosion characteristics of CH4/CO, the explosion experiments of the effect of different volume fractions of CO2 on CH4/CO deflagration were carried out by using the self-developed pipeline gas explosion experimental platform. The explosion characteristics of premixed gas are studied from the aspects of explosion peak pressure and time of reaching the peak pressure. The results show that the effect of CO on the deflagration of methane with a different volume fraction is the result of the interaction of the elementary reaction and the oxygen content in the reaction system. Two percent of the CO promoted the methane explosion in the oxygen-rich state, while it showed a damping effect in the oxygen-poor state. CO2 has different inhibitory effects on different volume fractions of methane. Experiments show that the addition of 20% CO2 can effectively inhibit the deflagration of methane. The addition of CO2 has a stronger inhibitory effect on the mixed gas of CH4/CO under the condition of poor oxygen but less on the mixed gas under the condition of rich oxygen.