Combustible Gas Concentration Research Articles

Thermal and Combustion Properties of Biomass-Based Flame-Retardant Polyurethane Foams Containing P and N.

Biomass has been widely used due to its environmental friendliness, sustainability, and low toxicity. In this study, aminophosphorylated cellulose (PNC), a biomass flame retardant containing phosphorus and nitrogen, was synthesized by esterification from cellulose and introduced into polyurethane to prepare flame-retardant rigid polyurethane foam. The combustion properties of the PU and PU/PNC composites were studied using the limiting oxygen index (LOI), UL-94, and cone calorimeter (CCT) methods. The thermal degradation behavior of the PU and PU/PNC composites was analyzed by thermogravimetric analysis (TGA) and thermogravimetric infrared spectroscopy (TG-IR). The char layer after combustion was characterized using SEM, Raman, and XPS. The experimental results showed that the introduction of PNC significantly improved the flame-retardant effect and safety of PU/PNC composites. Adding 15 wt% PNC to PU resulted in a vertical burning grade of V-0 and a limiting oxygen index of 23.5%. Compared to the pure sample, the residual char content of PU/PNC15 in a nitrogen atmosphere increased by 181%, and the total heat release (THR) decreased by 56.3%. A Raman analysis of the char layer after CCT combustion revealed that the ID/IG ratio of PU/PNC15 decreased from 4.11 to 3.61, indicating that the flame retardant could increase the stability of the char layer. The TG-IR results showed that PNC diluted the concentration of O2 and combustible gases by releasing inert gases such as CO2. These findings suggest that the developed PU/PNC composites have significant potential for real-world applications, particularly in industries requiring enhanced fire safety, such as construction, transportation, and electronics. The use of PNC provides an eco-friendly alternative to traditional flame retardants. This research paves the way for the development of safer, more sustainable, and environmentally friendly fire-resistant materials for a wide range of applications.

Experimental Study and Process Simulation on Pyrolysis Characteristics of Decommissioned Wind Turbine Blades

The development of wind power has brought about increasing challenges in decommissioning, among which DWTBs (decommissioned wind turbine blades) are the most difficult component to deal with. To enable the cost-effective, energy-efficient, and environmentally friendly large-scale utilization of DWTBs, an experimental study on thermogravimetric and pyrolysis characteristics of DWTBs was carried out. A new process involving recycling glass fiber with pyrolysis gas re-combustion and flue gas recirculation as the pyrolysis medium was innovatively proposed, and the simulation calculation was carried out. Thermogravimetric experiments indicated that glass fiber reinforced composite (GFRC) was the main heat-generating part in the heat utilization process of blades, and the blade material could basically complete pyrolysis at 600 °C. As the heating rate increased, the formation temperature, peak concentration, and proportion of combustible gas in the pyrolysis gas also increased. The highest peak concentration of CO gas was observed, with CO2 and C3H6 reaching their peaks at 700 °C. The solid product obtained from pyrolysis at 600 °C could be oxidized at 550 °C for 40 min to obtain clean glass fiber. And the pyrolysis temperature increased with the increase in the proportion of recirculation flue gas. When the proportion of recirculation flue gas was 66%, the pyrolysis temperature could reach 600 °C, meeting the necessary pyrolysis temperature for wind turbine blade materials. The above research provided fundamental data support for further exploration on high-value-added recycling of DWTBs.

Simulation of Dispersion and Explosion Characteristics of LiFePO4 Lithium-Ion Battery Thermal Runaway Gases.

In recent years, as the installed scale of battery energy storage systems (BESS) continues to expand, energy storage system safety incidents have been a fast-growing trend, sparking widespread concern from all walks of life. During the thermal runaway (TR) process of lithium-ion batteries, a large amount of combustible gas is released. In this paper, the 105 Ah lithium iron phosphate battery TR test was conducted, and the flammable gas components released from the battery TR were detected. The simulation tests of the diffusion and explosion characteristics of lithium iron phosphate battery's (LFP) TR gases with different numbers and positions in the BESS were carried out using FLACS simulation software. It was found that the more batteries TR simultaneously, the shorter the time for the combustible gas concentration in the energy storage cabin to reach the explosion limit. When 48 batteries were in TR simultaneously in the energy storage cabin, the shortest time was 9.8 s, and the further the location of the fire is from the hatch, the largest explosion overpressure is generated to the hatch, up to 583 kPa. When the gas generated by the TR of 48 batteries explodes, the maximum explosion overpressure at 5 m outside the energy storage cabin hatch is more significant than 40 kPa, which will cause serious injury to humans. The causes of TR of batteries in prefabricated chambers are complex, and the location and amount of thermal runaway of batteries as well as the diffusion of combustible fumes can have different effects on the external environment. The research results can provide support for the safety design of BESS.

Insights of rising bubble dynamics of air‐blown biomass gasification in bubbling fluidized bed gasifier

AbstractUnderstanding the complex dynamics and spatial distribution of rising bubbles in fluidized bed gasifiers is crucial for designing, optimizing, and scaling up of the reactor. However, existing studies on bubble dynamics mainly focused on cold flow investigations, failing to capture the behavior of bubbles under the influence of chemical reactions and intricate coupling of heat transfer. Therefore, a reactive Lagrangian model is established to explore intricate bubble behaviors during biomass air gasification. The model is well validated with experiment, and the impact of operating parameters including bed temperature and equivalence ratio (ER) on the bubble behaviors is studied. The growth, coalescence, break, and eruption of rising bubbles are studied. A lower ER is recommended for better gasification performance. With an increase in the ER from 0.12 to 0.3, both the lower heating value and combustible gas concentration experienced a decrease of approximately 38.5% and 38.3%, respectively. The lateral feeding of biomass leads to asymmetrical distribution of bed temperature and bubble properties. Near the biomass inlet, a larger bubble aspect ratio is observed, possibly attributed to the hindrance in the lateral bubble growth due to the lateral biomass feeding. The bubble coordinate number is introduced to characterize the degree of bubble distribution density in a specific region. It is found that increasing the operating temperature results in a reduction in the density and an increase in the volume of bubbles at the bottom, resulting in a denser distribution of bubbles in this region. Although this concentrated bubble distribution may impact local heat and mass transfer, the differences in bubble distribution under temperature dominance gradually decrease along the reactor height. The impact of the operating conditions on the thermal properties and spatial distribution of bubbles obtained in this work can provide valuable guidance for practical gasification operations.

Simple modification of phenylphosphonic acid to construct polyester-cotton fabrics with high flame retardancy

Polyester-cotton fabrics (PTCO) have excellent properties and are ubiquitous in daily life, but their serious flammability brings great safety hazards to people's lives. This study used phenylphosphonic acid (PPOA) and urea as raw materials to prepare a flame retardant named POU. PTCO/POU was prepared by the pad-dry-cure technique, and the performance was compared with that of PTCO/PPOA, revealing many interesting phenomena. Based on the gas phase and condensed phase flame-retardant mechanism brought by P/N synergy, PTCO/POU had better flame retardancy than PTCO/PPOA did. The damaged length was 6.7 cm, and the limiting oxygen index (LOI) value was 30.1%. The char residues after burning were complete and denser with a higher degree of graphitization. Thermogravimetric analysis showed that POU can significantly reduce the Rmax of PTCO, and improve its thermal stability in high temperature zones. The CCT results showed that PTCO/POU had the longest time to ignition and the smallest fire growth index, which was of great significance for reducing fire risk. The TG-FTIR results showed that the volatile products of PTCO/POU were greatly reduced, and during the burning process, NH3 was produced to dilute the concentration of combustible gases. In addition, PTCO/POU also had better whiteness performance than PTCO/PPOA did. This work greatly improved the flame retardancy of PTCO in a simple way and expanded its application prospects.

Research on high performance combustible gas concentration sensor based on pyramid beam splitter matrix.

Combustible gas concentration detection faces challenges of increasing accuracy, and sensitivity, as well as high reliability in harsh using environments. The special design of the optical path structure of the sensitive element provides an opportunity to improve combustible gas concentration detection. In this study, the optical path structure of the sensitive element was newly designed based on the Pyramidal beam splitter matrix. The infrared light source was modulated by multi-frequency point signal superimposed modulation technology. At the same time, concentration detection results and confidence levels were calculated using the 4-channel combustible gas concentration detection algorithm based on spectral refinement. Through experiment, it is found that the sensor enables full-range measurement of CH4, at the lower explosive limit (LEL, CH4 LEL of 5%), the reliability level is 0.01 parts-per-million (PPM), and the sensor sensitivity is up to 0.5PPM. The sensor is still capable of achieving PPM-level detections, under extreme conditions in which the sensor's optical window is covered by 2/3, and humidity is 85% or dust concentration is 100mg/m3. Those improve the sensitivity, robustness, reliability, and accuracy of the sensor.

The Quality Status Analysis and Development Proposal of Combustible Gas Alarm

Combustible gas alarm is mainly used to detect the concentration of combustible gas in the environment and issue the corresponding level of alarm which is an effective early warning tool to prevent gas leakage. However, due to the uneven quality of combustible gas alarms sold on the market, there are certain difficulties for the government in market access, testing agencies in quality control, and users in later maintenance. In order to promote the industry of combustible gas alarm to further and improve product quality, this study selected 60 batches of combustible gas alarms from a first-tier city in China and tested them in accordance with the national compulsory standard GB 15322-2019 Combustible Gas Detectors, conducting price and quality analysis of combustible gas alarms from different procurement channels and different product types according to the test results and putting forward solutions and development suggestions for nonconforming projects.

A graphene@Cu-MOF hybrid synthesized by mechanical ball milling method and its flame retardancy and smoke suppression effect on EP

The traditional method of preparing graphene will cause serious environmental pollution, and the combustion of polymer materials will seriously harm people's health. In this paper, a Cu-MOF-coated graphene composite flame retardant (G@Cu-MOF) rich in flame retardant elements such as B and N was synthesized through green mechanical ball milling method. Flame retardants reduce the threat to the environment and people's lives and property. After adding 6 wt% G@Cu-MOF, the peak heat release rate, total heat release rate, CO production and CO2 production of epoxy resin (EP) composite samples decreased by 55, 14, 59, and 55%, respectively. This type of Cu-MOF releases incombustible gases such as boron trifluoride (BF3) and ammonia (NH3) during combustion, diluting the concentration of combustible gases and producing copper borate in the condensed phase. Cu2+ is reduced to Cu, and boron compounds are converted into boron oxides. The thermal conductivity of graphene can reduce the temperature of the matrix, and has good flame retardancy. It synergistically acts with Cu-MOF to promote the formation of high-quality residual char, and can significantly inhibit the heat and smoke release of EP. It plays a role in flame retardancy and protecting the substrate from fire. This study provides a new approach for preparing graphene hybrid flame retardants through mechanical ball milling, in order to improve the flame retardancy of EP and suppress the release of smoke and toxic gases.

Study on the inhibition mechanism of green suppressants zinc borate and zinc silicate for oil shale based on flame propagation experiment and thermodynamic analysis

The Green materials zinc borate (ZB) and zinc silicate (ZS) were adopted as suppressants. Hartmann tube was used to study the flame inhibition effect of oil shale explosion. It showed that the flame front length became shorter and the propagation velocity and acceleration gradually decreased by increasing suppressants. When 30 wt% ZB was added, the complete inhibition of oil shale explosion flame could be achieved, while the flame inhibition effect of ZS was relatively weak. Flynn-Wall-Ozawa and Starink methods were used to study the activation energy of oil shale, which showed that the activation energy increased significantly after adding the suppressant. By characterization tests, the microstructure changes of oil shale before and after the explosion were analyzed, and the mechanism of the explosion inhibition difference between two suppressants was revealed. ZS played a physical inhibiting role by absorbing heat, reducing temperature and diluting the concentration of combustible gases. While ZB not only had the physical inhibition role of absorbing heat and diluting the concentration of gases, but also had a covering physical inhibition role. Simultaneously, ZB also had the chemical effect. It played a highly effective physical and chemical synergistic inhibition role in the deflagration of oil shale.

A new leak recognition method for natural gas pipelines in the urban underground space based on probabilistic neural network

Natural gas leakage is one of the sources of combustible gas in the underground spaces, which can easily lead to dangerous explosions and fatal accidents. Recognizing the natural gas leakage accurately from underground combustible gas can improve the efficiency of early warning and maintenance process. However, the problem of poor gas pipeline leak identification efficiency in combustible gas concentration detection has to date remained unsolved. This paper proposes a novel and effective method for leak recognition of gas pipelines based on probabilistic neural network (PNN). First, the characteristics of natural gas leakage are analyzed. Then time-domain feature quantities and correlation feature quantity are extracted from the methane concentration and temperature profiles, which are used as the input vectors. Finally, the feature vectors are input to the PNN for natural gas leak recognition. The results show that the proposed leak recognition method based on PNN can effectively identify the natural gas leak, and it exhibits better accuracy (as high as 92.5%) in comparison with the random forest and support vector machine methods. This work can achieve timely natural gas leak detecting with high accuracy and provide a guideline for early warning of gas leak in the urban underground space.

Synthesis and application of a halogen-free epoxy resin flame retardant curing agent

In this study, the intermediate of SPDPC flame retardant curing agent was successfully synthesized through the reaction between phosphorus oxychloride and pentaerythritol under the catalysis of 4-dimethylaminopyridine. Using 1,2-propylenediamine and the prepared SPDPC, a novel phosphorus and nitrogen flame retardant curing agent named poly1,2-propylenediamine pentaerythritol diphosphate (PDS) was successfully synthesized. The target product was subjected to characterization using infrared spectroscopy, mass spectrometry, hydrogen NMR spectroscopy and thermogravimetric analysis. The molecular structure of the product was determined and its decomposition temperature curve obtained, leading to the conclusion that it could be cured at high temperatures. DDS was selected as the curing agent for epoxy E-51, the specific curing conditions were obtained by DSC test. Subsequently, E-51, DDS and PDS were mixed for high temperature curing resulting in obtaining test spline of PDS-E-51 flame retardant composite material. Then, the flame retardancy and mechanical properties of the spline were tested. It was observed that pure EP cured by DDS had an LOI of only 19.5%, indicating its flammability. However, upon addition of PDS as a flame retardant, the LOI significantly increased with 20 parts resulting in an LOI of 29.7%. The addition of 25 parts results in an increase in limiting oxygen index to 30.3%, while the tensile strength and impact strength are measured at 38.27 MPa and 5.087 kJ/m2 respectively. The CCT test shows that the addition of PDS can significantly reduce the HHR and THR of the system. CCT digital photos show that the addition of PDS can make the combustion residue of the system expand obviously, showing a good expansion and flame retardant effect. TG-FTIR gas phase infrared absorption indicates that the addition of PDS can reduce the concentration of combustible gas in the combustion process. Test results indicate that the mechanical properties of PDS-E-51 flame retardant composites experience a certain degree of decline, but with increasing amounts of PDS curing agent added, their flame retardancy is significantly enhanced.

Analysis of interference methods on transformers based on the results of dissolved gas analysis tests

<span lang="EN-US">In the operation of the power transformer, several maintenance efforts must be made to ensure the condition of the transformer is in good condition. The problems that usually arise are a thermal failure and electrical failure. The use of insulating media such as transformer oil and transformer insulation paper can be disrupted by this failure. Dissolved gas analysis, which identifies the types and concentrations of dissolved gas in transformer oil, can reveal details on fault indicators in power transformers (DGA). In this study, we used the interpretation of the IEEE std 2008-C57.104 (total dissolved combustible gas (TDCG), key gas, Rogers ratio method), the interpretation of IEC 2015-60599 (Duval triangle and basic gas ratio method), and the IEEE Std 2019-C57.104 interpretation (Duval pentagon method). The outcome of the DGA test is used to determine the conditions and indications of disturbances in the transformer for power. Using various gas analysis techniques also impacts the outcome of the fault indication. This variation has affected the types of gas used in the computation and the gas concentration limit value estimation. After the gas analysis, it was found that the oil purification process was also proven to reduce the concentration of combustible gases.</span>

Development and Field Application of Diagnostic Methods Based on Insulating Oil Analysis for Degradation due to Copper Compounds in Oil-Filled Cables

In recent years, breakdown failures occur in joint boxes of oil-filled cables associated with the adhesion of copper compounds, such as copper sulfide or organocopper compounds. This is the adhesion degradation of copper compounds due to electric charging. Therefore, the degradation should be diagnosed for keeping its high reliability. However, the degradation cannot be predicted by the conventional diagnostic methods based on dissolved gas analysis, because the definition of degradation aspect in the method does not assume this degradation. Therefore, a new degradation diagnosis method is developed based on insulating oil analysis and the trend of the concentration of dissolved copper in the oil and the concentration of combustible gas generated due to the degradation. However, it is not possible to measure the concentration of dissolved copper in the past 30 years, because the majority of oil-filled cables are over 30 years old. Therefore, the past concentration of dissolved copper is calculated by the dielectric loss tangent value of oil, which has been traditionally measured. As a result, the consistency rate of the diagnostic methods was confirmed to be more than 80% by comparison with the results of demolition investigations of the using joint boxes.

Study of biomass gasification in an industrial-scale dual circulating fluidized bed (DCFB) using the Eulerian-Lagrangian method

Dual circulating fluidized bed (DCFB) has emerged as an efficient reactor for biomass gasification due to its unique feature of high gas-solid contact efficiency and separated reactions in two reactors, yet the understanding of complex in-furnace phenomena is still lacking. In this study, biomass gasification in an industrial-scale DCFB system was numerically studied using a multiphase particle-in-cell (MP-PIC) method featuring thermochemical sub-models (e.g., heat transfer, heterogeneous reactions, and homogeneous reactions) under the Eulerian-Lagrangian framework. After model validation, the hydrodynamics and thermochemical characteristics (i.e., pressure, temperature, and species) in the DCFB are comprehensively investigated. The results show that size-/density-induced segregation makes solid fuels concentrate on the bed surface. Interphase momentum exchange leads to the continuous decrease of the gas pressure axially. In the gasifier and combustor, the lower heating value (LHV) of the gas products is 5.56 MJ/Nm3 and 0.2 MJ/Nm3 and the combustible gas concentration (CGC) is 65.5% and 1.86%, respectively. The temperature in the combustor is about 100 K higher than that in the gasifier. A higher solid concentration results in a smaller value of particle heat transfer coefficient (HTC). The HTCs range from 50 to 150 W/(m2 K) for a solid concentration larger than 0.3 in the combustor while the HTCs range from 100 to 200 W/(m2 K) in the gasifier. The Reynolds number of biomass particles is two orders of magnitude larger than that of the sand particle. The numerical results shed light on the reactor design and process optimization of biomass gasification in DCFBs.

Gas composition during thermochemical conversion of dry solid fuels and waste-derived slurries.

Coal has long remained a promising and widely used energy resource all over the world. Special emphasis is usually put on the research and development of environmentally friendly technologies for the use of coal and coal processing waste. The development of slurry fuels based on coal waste is one of the promising ways to use raw materials with energy potential, recover wastes, and reduce the environmental load. However, no combustion technology has yet been created for heterogeneous wastes as water-based slurries. The physical principles and parameters of the corresponding processes have not been studied adequately. In this research, the environmental combustion indicators (CO2, CO, H2, NOx, and SO2 concentrations) of slurries based on water and petrochemical, coal, and plant wastes were analyzed for the first time in a wide range of temperatures covering all the typical stages of thermochemical fuel conversion: pyrolysis (400-700°C), gasification (700-900°C), and combustion (700-1000°C). We established the key patterns and aspects of changes in gas concentrations at all the main stages during the thermal decomposition of fuels. The use of water-based fuels at the pyrolysis stage was notable for up to 96% higher concentrations of the key combustible gases (CO, H2). The temperature extrema were 50-100°C lower than those of bituminous coal. In terms of the key anthropogenic emissions (CO2, NOx, and SO2), the combustion of slurries also appeared to be 20-77% more environmentally friendly than that of coal depending on the temperature conditions and fuel composition. The maximum positive effect from adding biomass to coal-water slurries was achieved in the temperature range of 850 to 1000°C. The research findings can be used for developing the technologies for thermal recovery of waste as water slurries, in particular, by intensifying the pyrolysis, gasification, and combustion.

An emergency task recommendation model of long-distance oil and gas pipeline based on knowledge graph convolution network

When long-distance oil and gas pipeline accidents take place, a set of requirements and constraints ought to be considered, due to the various environment, multiple accident types and hazard-bearing bodies. Compliance with the response tasks directly influences the subsequent accident development. Furthermore, attribute to geographic location or communication limitations, the accident information may be delayed or unclear. Knowledge graphs are an advantageous representation of the fusion of complex relationships. On this basis, this study aims to establish an emergency task recommendation model that can adapt to several accident information description levels. Combined with the proposed emergency case framework, a knowledge graph of long-distance oil and gas pipeline emergency cases is established for the first time. Realize embedding learning by aggregating neighbor node and relationships. The accuracy of the emergency task recommendation is improved by introducing a variety of relations in the case-feature graph. Apply this model to the 11.22 Qingdao Oil Pipeline Explosion incident. Tasks such as culvert and well boundary detection, combustible gas concentration monitoring, and response upgrading are supplemented. Compare with the accident investigation report conclusions, the recommended tasks help to prevent the explosion. The proposed model not only has a case information recording framework but is also not bound by the input format of structured cases. It solves the issue of ambiguous case feature input in the task recommendation and has good practical application value.

Экспериментально-аналитические исследования формирования пожаровзрывоопасных паровоздушных облаков в атмосфере при утечках и проливах жидкого водорода

Experimental and numerical studies of the process of formation of fire-explosive steam-air clouds in the atmosphere during leaks and spills of liquid hydrogen were carried out. Within their framework, the tasks were performed to determine the size and lifetime of a hydrogen-air cloud with a hazardous concentration of hydrogen from the point of view of explosion and fire hazard (including at the boundary of a visible cloud), and the relationship between the temperature and concentration of combustible gas in a gas-air cloud; studying the effect of cloud temperature on its parameters, the role of atmosphere involvement in the convective hydrogen jet; establishing the influence of moisture content in the atmospheric cloud and the mobility of the environment (wind exposure) on the dynamics of changes in the level of its fire and explosion hazard. It is shown that the humidity of the environment affects the concentration of hydrogen at the boundary of the visible cloud, and, consequently, its fire and explosion hazard. The assessment of the influence of humidity on the parameters of the studied turbulent convective jet indicates that the rate of change in the mass concentration of hydrogen on the axis of the low-temperature jet from the height of ascent depends on the humidity of the medium. The higher the humidity, the sharper the decrease in the mass concentration of hydrogen along the height of the convective jet becomes. In accordance with the calculations, the time for dissipation of a cloud to a fireproof hydrogen concentration in the presence of moisture condensate is reduced by 30 %, and the dissipation time to an explosive concentration of hydrogen is reduced by about 20 %. The coefficient of air involvement α in convective jets of hydrogen-air mixtures with positive buoyancy is 0.12 considering the real enthalpy and absolute humidity of the surrounding air of 15 g/m3 (90 % humidity at 20 °C). This coefficient can be used in the calculations of turbulent convective jets formed during stationary hydrogen evaporation. Wind at low speeds leads to an increase in the maximum transverse dimensions of the cloud, regardless of the concentration in the hydrogen jet, and at high speeds, to their decrease. For emergency hydrogen spills, the most dangerous case when a hydrogen-air cloud of large volumes is formed in the atmosphere, is the case with zero humidity and no wind (in a wide range of values of the initial mass flow of hydrogen: 0.1–100 kg/s).

Novel design and synthesis of bio-based polyelectrolyte complexes for enhancing the flame retardancy of epoxy resin

The flame-retardant efficiency of a single flame retardant is often not as expected, but the process of synthesizing new high-efficiency flame retardants is usually complicated and harsh. Here, a bio-based polyelectrolyte complexes (PA-Ni-PEI) was synthesized by reacting biomass phytic acid, nickel ion and polyethylenimine, and then incorporated into EP as a flame-retardant additive for improving the thermal stability and flame retardancy properties. When the adding of PA-Ni-PEI complexes is 2.0 wt%, the peak heat release rate (PHRR), the total heat release (THR), the total smoke release (TSR) and smoke factor (SF) with a reduction of 30.4%, 24.9%, 36.0% and 55.4%, respectively, and the char residue was improved by 53.9%, compared to EP. The improvement in fire safety was ascribed to the early degradation of EP catalyzed by the decomposition products of the composites, resulting in the formation of a dense, robust and stable cross-linked char layer to prevent heat and oxygen from contacting with epoxy resin. Simultaneously, water and nitrogen-containing incombustible gas are released to reduce the concentration of combustible gas. A new idea for the preparation of EP composites with excellent flame retardancy property was provided by this work.

Experimental study on effects of multistage reactant and air jet velocities on self-preheating characteristics and NOx emission of burning pulverized coal

To explore the NOx control strategies deeply, this study investigated the effects of multistage reactant and air jet velocities, including preheated fuel jet velocity (vpf), ratio of internal secondary air jet velocity to external secondary air jet velocity (R12) and ratio of first-staged tertiary air jet velocity to second-staged tertiary air jet velocity (M12), on combustion characteristics and NOx emission of pulverized coal on a 30 kW self-preheating combustion test rig. During preheating, as vpf increased, the temperature at different locations increased. And the concentrations of the main combustible gases (CO and H2) in the coal gas and the conversion rate of each component in the pulverized coal increased first and then decreased at the outlet. Moreover, vpf also influenced the particle characteristics greatly. The particle size of preheated coal char decreased first and then increased, while its specific surface area and reacting activity increased first and then decreased. The good self-preheating characteristics had a positive impact on the subsequent combustion and NOx emission. During combustion, vpf, R12 and M12 had different effects on the temperature distribution in the down-fired combustor (DFC). Under different vpf, the temperature distribution was relatively complex, and it was mainly regulated by the self-preheating characteristics, combustion share and jet velocity of the preheated fuel. As R12 increased, the temperature increased gradually in the upper part of the DFC, meaning the upper combustion was promoted. M12 mainly affected the position of the main combustion region, which shifted down as M12 increased. Moreover, increasing M12 could also reinforce the combustion in the main combustion region. vpf, R12 and M12 also influenced combustion efficiency and NOx emission obviously with certain change regularities. As vpf and R12 increased, the combustion efficiency increased first and then decreased, while NOx emission decreased first and then increased. As M12 increased, the combustion efficiency decreased first and then increased, while NOx emission increased first and then decreased. Moreover, compared to lower M12, it was more favorable to improve the combustion when M12 was higher.

Dual Modification of Layered Double Hydroxide by Phosphonitrilic Chloride Trimer and Aniline for Enhancing the Flame Retardancy of Polypropylene

Owing to the poor dispersion of layered double hydroxide (LDH) in a polypropylene (PP) matrix and its own flame-retardant efficiency being finite, the development of high-performance PP/LDH-based composites is still a tremendous challenge. To improve the dispersion of LDH and its inherent flame retardancy, phosphonitrilic chloride trimer (HCCP) was grafted onto the surface of LDH through the bridging effect of (3-aminopropyl)triethoxysilane and then further modified with aniline to replace the chlorine element in HCCP, so a flame-retardant (LDH@HA) was successfully synthesized. The flame retardancy and smoke suppression of LDH@HA with PP composites (PP/LDH@HA) were tested with the limit oxygen index (LOI), UL-94, and cone calorimetry tests. With a loading of 20 wt % LDH@HA, the peak heat release rate, total heat release, and total smoke rate of PP/LDH@HA composites were 300.1 kW·m–2, 57.7 MJ·m–2, and 697.5 m2·m–2, respectively, which were decreased by 64.4, 46.4, and 49.1% in comparison to those of PP, and the LOI value of PP/LDH@HA reached 30.6% and achieved the UL-94 V-0 rating. The improvements in flame retardancy and smoke suppression were due mainly to the physical barrier effect of LDH and the catalytic carbonization effect of HCCP together with the nonflammable gases formed by the decomposition of aniline, which diluted the combustible gas concentration. Compared with PP/LDH, the optimization of the mechanical properties of composites was due mainly to the introduction of HCCP and aniline, which significantly enhanced the compatibility between LDH and PP and promoted the uniform distribution of LDH in the PP matrix. In conclusion, LDH@HA has low cost, easy fabrication, and an excellent smoke suppression effect, and the strategy provides a specific idea for the preparation of fire-resistant PP composites.