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Query: UMLS:C0344329 (
collapse
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28,634
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
Methane
gas is mainly present in coal in two forms: free and adsorbed. There are a large number of closed pores inside the coal, which makes it difficult to measure the gas content of the coal. Therefore, studying the nanoscale closed pores of coal is of great importance for gas control. To study the pore structure characteristics of coal with different deformation degrees and to analyze the volume fraction of closed pores in coal, various coal samples were analyzed by the low-temperature liquid nitrogen adsorption method (LT-N
2
GA), the carbon dioxide adsorption method, and small-angle X-ray scattering (SAXS). The variation of parameters such as the pore size, pore volume, specific surface area, and degree of metamorphism was compared by using different methods to obtain the proportion of the closed pore volume of different coal samples. The results show that with the increase of the degree of coal metamorphism, the total pore volume and specific surface area of coal samples show a decreasing trend first and then an increasing trend, while the average pore diameter of coal samples gradually increases first and then decreases sharply. When the degree of deterioration of coal is low (volatile content > 20%), the closed pores of coal account for more than 48% of the open pores. When the degree of deterioration of coal samples is relatively high (volatile content <20%), the proportion of large pores in coal bodies decreased from 59.47 to 29.07%, and the proportion of pores in mesopores decreased from 12.15 to 11.09% and finally increased to 11.65%, and the proportion of micropore diameter increased from 28.38 to 59.28%. The volume fraction of the coal sample measured by the SAXS experiment shows that when the coal quality is high, the volume of the mesopores is large, which is consistent with the results of the low-temperature liquid nitrogen and CO
2
adsorption experiments. Judging from the number of holes, the number of closed holes is 1 to 3 orders of magnitude greater than the number of open holes, and the number of closed holes of coal samples accounts for more than 94% of the total number of holes. It shows that the number of closed holes in the coal is far greater than the number of open holes, so the gas in the coal is mainly concentrated in the closed holes, and the formation of closed pores is partly because of the
collapse
of the internal structure and partly because of the volatilization of unstable substances. The research combined with LT-N
2
GA, the carbon dioxide adsorption method, and SAXS test methods can better analyze the number of closed pores of coal and characterize the nanopore fracture structure of coal. The novelties of this article are that this is a quantitative analysis performed using a scientific method of SAXS. The findings of this study can lead to a better understanding of the coal and gas outburst mechanism and the existence of gas to adopt better prevention measures.
...
PMID:Nanopore Characteristics of Coal and Quantitative Analysis of Closed Holes in Coal. 3301 81
The
collapse
of dense algal blooms is identified as a significant source of
methane
(CH
4
) emissions. When flocculation is used for algae removal, algal carbon is often turned into CH
4
and carbon dioxide (CO
2
). Here, we established a "bio-pump" to control algal blooms and reduce greenhouse gas (GHG) emissions by the introduction of submerged macrophytes to the aquatic ecosystem and combination of flocculation and capping. The results suggested that this strategy contributed to an approximately 98% algae removal and sustainably improved dissolved oxygen (DO) in the water and sediment after the 40-day incubation. The aerobic condition at the sediment-water interface and deeper oxygen penetration in the sediment inhibited the abundance of microorganisms related to anaerobic CH
4
production, then changed the metabolic pathway and fate of algal carbon. After the 40-day incubation, compared with flocculation-capping treatments, the bio-pump reduced 69.07% CH
4
and 77.57% CO
2
emissions, which was jointly contributed by the inhibition of anaerobic CH
4
production, aerobic oxidation of CH
4
and carbon sequestration of submerged macrophytes. This was also demonstrated from the finding of a decrease in methyl coenzyme M reductase (mcrA) gene, an increase in particulate methane monooxygenase (pmoA) gene and the absorption of
13
C-labeled from algae biomass by submerged macrophytes at the end of incubation. Therefore, the bio-pump established in the present study can improve DO in algal blooms water and turn algal-derived organic matter into the plant biomass, which supplied a sustainable method for algae removal and GHG reduction.
...
PMID:Addressing algal blooms by bio-pumps to reduce greenhouse gas production and emissions with multi-path. 3309 34
The internal
collapse
of deep seam drainage borehole and negative pressure loss represents a serious technical problem affecting gas drainage. To address this problem a creep model of coal around borehole was established based on the plastic softening characteristics of coal. The final
collapse
time of the borehole was determined and used to derive the three stages of the borehole
collapse
process. The model of negative pressure loss in drainage borehole was established according to the theory of fluid dynamics, the model of
methane
gas flow and the creep model of the coal around the borehole. The relationship between the negative pressure loss of drainage and the change of borehole aperture was derived, thereby revealing the main influencing factors of the negative pressure loss in the borehole. A drainage technique named "Full-hole deep screen mesh pipe" was introduced and tested to prevent the
collapse
of borehole and reduce the negative pressure loss. The result shows that after the borehole was drilled, the borehole wall was affected by the complex stress of the deep coal seam, the coal surrounding the borehole collapsed or presented the characteristics of creep extrusion towards the borehole. The "Full-hole deep screen mesh pipe drainage technology" could effectively control the
collapse
as well as the deformation of the borehole and reduced the negative pressure loss. Compared with the traditional drainage technology, the
methane
gas drainage concentration was increased by 101% and the gas flow was increased by 97% when the
methane
gas was drained for 90 days, the gas drainage efficiency increased significantly.
...
PMID:Instability-negative pressure loss model of gas drainage borehole and prevention technique: A case study. 3322 10
We review the thermodynamics of combustion reactions involved in aluminum fires in the light of the spate of recent high-profile tower-block disasters, such as the Grenfell fire in London 2017, the Dubai fires between 2010 and 2016, and the fires and explosions that resulted in the 9/11
collapse
of the World Trade Center twin towers in New York. These fires are class B, i.e., burning metallic materials, yet water was applied in all cases as an extinguisher. Here, we highlight the scientific thermochemical reasons why water should never be used on aluminum fires, not least because a mixture of aluminum and water is a highly exothermic fuel. When the plastic materials initially catch fire and burn with limited oxygen (O
2
in air) to carbon (C), which is seen as an aerosol (black smoke) and black residue, the heat of the reaction melts the aluminum (Al) and increases its fluidity and volatility. Hence, this process also increases its reactivity, whence it rapidly reacts with the carbon product of polymer combustion to form aluminum carbide (Al
4
C
3
). The heat of formation of Al
4
Cl
3
is so great that it becomes white-hot sparks that are similar to fireworks. At very high temperatures, both molten Al and Al
4
C
3
aerosol react violently with water to give alumina fine dust aerosol (Al
2
O
3
) + hydrogen (H
2
) gas and
methane
(CH
4
) gas, respectively, with white smoke and residues. These highly inflammable gases, with low spontaneous combustion temperatures, instantaneously react with the oxygen in the air, accelerating the fire out of control. Adding water to an aluminum fire is similar to adding "rocket fuel" to the existing flames. A CO
2
-foam/powder extinguisher, as deployed in the aircraft industry against aluminum and plastic fires by smothering, is required to contain aluminum fires at an early stage. Automatic sprinkler extinguisher systems should not be installed in tower blocks that are at risk of aluminum fires.
...
PMID:Thermodynamics of Tower-Block Infernos: Effects of Water on Aluminum Fires. 3328 89
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