Study on the preparation of green suppressors and their characteristics in coal dust flame propagation inhibition

The properties of a green waste molecular sieve-based powder suppressor in inhibiting the flame propagation of coal dust were studied. Waste molecular sieve (S) was pretreated and selected as the carrier, potassium oxalate (K) and ferric citrate (T) as the active components. The reverse dissolution crystallization method was adopted and S@K/T, S@T/K, S@T-K suppressors with different core–shell structure were prepared by different loading sequences. Their particle size, morphology and thermal pyrolysis behavior were compared. The results showed that the particle distribution of three powders is uniform and the dispersity of them is good. The active components of explosion suppression are evenly loaded on the waste molecular sieve carrier and they have different coating structure. The thermal desorption heat of them is 44.64 J/ g, 66.95 J/g and 92.9 J/g, respectively. Furthermore, the flame propagation characteristics of coal dust were tested by the Hartmann flame propagation device. The results showed that all powders had the effect of inhibiting the flame propagation of coal dust and the inhibition effect is S@T-K, S@T/K and S@K/T from strong to weak. Combined with characterization results, the influence mechanism of the difference in the flame propagation inhibition effect of three suppressants was investigated.     

Suppression mechanism of micron/nano PMMA dust flame based on thermal analysis

The suppression mechanism of NaHCO₃ on micron/nano PMMA dust cloud flame based on thermal analysis was investigated. The results showed that the pyrolysis oxidation processes of 30 μm and 100 nm PMMA dusts were suppressed by NaHCO₃, and the apparent activation energy E and pre-exponential factor A were increased. The flame combustion intensity and propagation velocity of both micro and nano PMMA dusts were decreased obviously. Compared with 30 μm PMMA, NaHCO₃ maintained an efficient suppression on 100 nm PMMA with the mass ratio of NaHCO₃ increased with no suppression saturation phenomenon appeared. And 100 nm PMMA were more sensitive to particle size of NaHCO₃. In the flame preheat zone, the suppression effect of NaHCO₃ was mainly dominated by physical suppression, including the cooling effect of both pyrolysis reaction and products and the dilution effect on the concentration of combustible reactant. In the combustion reaction zone, the suppression effect of NaHCO₃ was mainly dominated by chemical suppression. The free radicals were absorbed by the active groups NaOH, forming the Na?NaOH suppression cycle. The E of nano PMMA dust flame was sustainably increased in both preheat and combustion reaction zones, contributing to the continuous high efficiency suppression and the sensitiveness to the particle size of explosion suppressant.     

A novel ATH/SBA-15 suppressant prepared by in-situ synthesis and its inhibition mechanism on PE dust deflagration flame

Recently, polyethylene (PE) dust explosions have become a serious threat to the petrochemical industry. In order to prevent the occurrence of PE dust explosion, a novel aluminum hydroxide (ATH)/Santa Barbara Amorphous type 15 (SBA-15) powder explosion suppressant with the uniform dispersion of ATH was prepared by in-situ synthesis method. For ATH/SBA-15 inhibitor, SBA-15 molecular sieve and ATH was used as the carrier and active component of explosion inhibition, respectively. The inhibition effect on PE dust deflagration was studied by flame propagation experiment. The results showed that when the addition amount of ATH/SBA-15 exceeded 40 wt%, PE dust deflagration flame was almost completely inhibited. Furthermore, the Coats-Redfern method was used to study the thermal decomposition kinetics model. It was found that the thermal decomposition kinetics model of PE before and after the addition of explosion suppressants followed the random nucleation and growth reaction mechanism (A3 model). Further fitting analysis showed the apparent activation energy of PE increased significantly after adding ATH/SBA-15 inhibitor, confirming that ATH/SBA-15 had a significant inhibitory effect on PE deflagration in thermodynamics. Finally, combining with a series of characterization results, it was founded that the ATH/SBA-15 suppressant played the efficient synergy of physics and chemistry, which was efficient in inhibiting PE deflagration. The physical inhibition mainly includes: the free radicals adsorption by SBA-15 molecular sieve, the coating effect of ATH, the endothermic effect and the reduction in O₂ concentration by H₂O decomposed from ATH. Meanwhile, the chemical inhibition mainly lies in the elimination of the free radicals O· and H· in the explosion process by ATH.     

Least cost SO2 emission minimization for a petroleum refinery by optimum use of source reduction, tail gas treatment and flue gas desulphurization

With the growing awareness on the necessity to preserve the environment, pollution standards are turning more stringent and minimization of waste at the source has become the first choice option rather than the end-of-pipe treatment. The objective of the present research is to identify the optimum combination of source reduction (SR), tail gas treatment (TGT) and flue gas desulphurization (FGD) to minimize the total cost of overall SO₂ emission from a petroleum refinery to various desired limits. It has been found that for the typical refinery considered, the TGT is the lowest cost option than either SR or FGD; however, only a maximum of ~12.5% reduction is achievable through the TGT. After full utilization of TGT, for the next range of SO₂ emission reductions from ~12.5% to ~64%, the SR is more economical than FGD. For a still stringent SO₂ emission limit, i.e. SO₂ emission reduction higher than ~64%, the full utilization of the TGT and the optimum use of SR and FGD are the best options.