Simultaneous nitrification and denitrification(SND),which is more economical compared with the tradi-tional method for nitrogen removal,is studied in this paper.In order to find the suitable conditions of this process...Simultaneous nitrification and denitrification(SND),which is more economical compared with the tradi-tional method for nitrogen removal,is studied in this paper.In order to find the suitable conditions of this process,a mixed flow activated sludge system under low oxygen concentration is investigated,and some key control parameters are exam-ined for nitrogen removal from synthetic wastewater.The results show that SND is accessible when oxygen concentra-tion is 0.3-0.8 mg/L.The nitrogen removal rate can be obtained up to 66.7%with solids retention time(SRT)of 45 d,C/N value of 10,and F/M ratio of 0.1 g COD/(g MLSS·d).Theoretical analysis indicates that SND is a physical phenomenon and governed by oxygen diffusion in flocs.展开更多
An experimental study on the ignition of single coal particles at low oxygen concentrations (XO_(2)<21%) was conducted using a tube furnace. The surface temperature (Ts) and the center temperature (Tc) of the coal ...An experimental study on the ignition of single coal particles at low oxygen concentrations (XO_(2)<21%) was conducted using a tube furnace. The surface temperature (Ts) and the center temperature (Tc) of the coal particles were obtained from the images taken by an infrared camera and thermocouples respectively. The ignition processes were recorded by a high-speed camera at different XO_(2) values and furnace temperatures Tw. Compared with literature experimental data obtained at a high XO_(2) value, the ignition delay time τi decreases more rapidly as XO_(2) increases at the low XO_(2) region. The responses of Ts and Tc to the variation of XO_(2) are different: Ts decreases while Tc remains nearly constant with increasing XO_(2) at a low XO_(2) value. In addition, τi is less sensitive to Tw while the ignition temperature Ti is more sensitive to Tw at a low XO_(2) value than in air. Observations of the position of flame front evolution illustrate that the ignition of a coal particle may change from a homogeneous mode to a heterogeneous or combined ignition mode as XO_(2) decreases. At a low XO_(2) value, buoyancy plays a more significant role in sweeping away the released volatiles during the ignition process.展开更多
The effects of chemical compositions, especially silicon and chromium contents, on the complete decarburization behaviors of steels in atmosphere of 2 vol. %O2 and 98 vol. % N2 were investigated by using a simuhaneous...The effects of chemical compositions, especially silicon and chromium contents, on the complete decarburization behaviors of steels in atmosphere of 2 vol. %O2 and 98 vol. % N2 were investigated by using a simuhaneous thermal analyzer. Complete decarburization was observed at both 750 and 800 ℃ for 60Si2MnA steel, while 750℃ only for 92A steel. For GCr15 steel, no decarburization was found at 750 or 800 ℃, and only partial decarburization was observed at 850 ℃. It indicates that silicon promotes while chromium prevents the complete decarburization of steels in atmosphere with 2 vol. % O2. The main reason is that silicon increases while chromium reduces the equilib rium concentration of ferrite at the interface of ferrite and austenite, which results in the complete decarburization.展开更多
文摘Simultaneous nitrification and denitrification(SND),which is more economical compared with the tradi-tional method for nitrogen removal,is studied in this paper.In order to find the suitable conditions of this process,a mixed flow activated sludge system under low oxygen concentration is investigated,and some key control parameters are exam-ined for nitrogen removal from synthetic wastewater.The results show that SND is accessible when oxygen concentra-tion is 0.3-0.8 mg/L.The nitrogen removal rate can be obtained up to 66.7%with solids retention time(SRT)of 45 d,C/N value of 10,and F/M ratio of 0.1 g COD/(g MLSS·d).Theoretical analysis indicates that SND is a physical phenomenon and governed by oxygen diffusion in flocs.
文摘An experimental study on the ignition of single coal particles at low oxygen concentrations (XO_(2)<21%) was conducted using a tube furnace. The surface temperature (Ts) and the center temperature (Tc) of the coal particles were obtained from the images taken by an infrared camera and thermocouples respectively. The ignition processes were recorded by a high-speed camera at different XO_(2) values and furnace temperatures Tw. Compared with literature experimental data obtained at a high XO_(2) value, the ignition delay time τi decreases more rapidly as XO_(2) increases at the low XO_(2) region. The responses of Ts and Tc to the variation of XO_(2) are different: Ts decreases while Tc remains nearly constant with increasing XO_(2) at a low XO_(2) value. In addition, τi is less sensitive to Tw while the ignition temperature Ti is more sensitive to Tw at a low XO_(2) value than in air. Observations of the position of flame front evolution illustrate that the ignition of a coal particle may change from a homogeneous mode to a heterogeneous or combined ignition mode as XO_(2) decreases. At a low XO_(2) value, buoyancy plays a more significant role in sweeping away the released volatiles during the ignition process.
文摘The effects of chemical compositions, especially silicon and chromium contents, on the complete decarburization behaviors of steels in atmosphere of 2 vol. %O2 and 98 vol. % N2 were investigated by using a simuhaneous thermal analyzer. Complete decarburization was observed at both 750 and 800 ℃ for 60Si2MnA steel, while 750℃ only for 92A steel. For GCr15 steel, no decarburization was found at 750 or 800 ℃, and only partial decarburization was observed at 850 ℃. It indicates that silicon promotes while chromium prevents the complete decarburization of steels in atmosphere with 2 vol. % O2. The main reason is that silicon increases while chromium reduces the equilib rium concentration of ferrite at the interface of ferrite and austenite, which results in the complete decarburization.
