Study of the reaction mechanism for preparing powdered activated coke with SO_(2)adsorption capability via one-step rapid activation method under flue gas atmosphere

In this study,the impact of different reaction times on the preparation of powdered activated carbon(PAC)using a one-step rapid activation method under flue gas atmosphere is investigated,and the underlying reaction mechanism is summarized.Results indicate that the reaction process of this method can be divided into three stages:stage I is the rapid release of volatiles and the rapid consumption of O_(2),primarily occurring within a reaction time range of 0-0.5 s;stage II is mainly the continuous release and diffusion of volatiles,which is the carbonization and activation coupling reaction stage,and the carbonization process is the main in this stage.This stage mainly occurs at the reaction time range of 0.5 -2.0 s when SL-coal is used as material,and that is 0.5-3.0 s when JJ-coal is used as material;stage III is mainly the activation stage,during which activated components diffuse to both the surface and interior of particles.This stage mainly involves the reaction stage of CO_(2)and H2O(g)activation,and it mainly occurs at the reaction time range of 2.0-4.0 s when SL-coal is used as material,and that is 3.0-4.0 s when JJ-coal is used as material.Besides,the main function of the first two stages is to provide more diffusion channels and contact surfaces/activation sites for the diffusion and activation of the activated components in the third stage.Mastering the reaction mechanism would serve as a crucial reference and foundation for designing the structure,size of the reactor,and optimal positioning of the activator nozzle in PAC preparation.

Effects of sulfur dioxide on growth， gas exchange rate and leaf sulfur content of massion pine seedlings

The effects of sulfur dioxide(SO_2) on the dry weight growth gas exchange rate and leaf sulfur content of massion pine(Pinus massoniana Lamb. )were investigated. The results obtained in this study show that the dry weight growth and net photosynthetic rate of masson pine seedlings are reduced by exposure to SO_2 at ≥100 ppb. From these results,one of the main causes in the dieback of masson pine forest reported in Chongqing,China may be relatively high concentrations of atmospheric SO_2 in the relevant area.

Preparation of gangue ceramsite by sintering pot test and potential analysis of waste heat recovery from flue gas

Preparation of ceramsite from solid waste based on the sintering process is a new technology and had a high efficiency in improving producing capability, decreasing consumption of liquefied petroleum gas (LPG), and recovering waste heat of flue gas. An experiment sintering gangue ceramsite was conducted in a 25 kg scale sintering pot with a 100 cm height. The combustion characteristics, phase transformation, and the release profile of SO_(2)^(*) (SO and/or SO_(2)) and NO_(x)^(*) (N_(2)O, NO, and/or NO_(2)) of gangue ceramsite during the sintering process were studied by X-ray diffraction analysis, X-ray fluorescence spectrometry, thermogravimetry–differential thermogravimetry–differential scanning calorimetry, and measurement of physical properties of ceramsite and gas components of flue gas. The results showed that the gangue ceramsite had excellent properties, and its compressive strength and water absorption were 8.2–9.6 MPa and 8.9%–9.8%, respectively, far exceeding the requirement of standard (GB/T 17431.1–2010). The ignition temperature of gangue ceramsite was 443 ℃, and the ignition loss was 14.60 mass% at 1000 ℃. Kaolinite and calcite disappeared at 600 and 800 ℃, respectively. Albite disappeared and mullite formed at 1000 ℃. Two peaks of SO_(2)^(*) emissions emerged in the range of 311–346 mg m^(-3) near 500 ℃ of upper layer ceramsite and 420–489 mg m^(-3) near 1000 ℃ of lower layer ceramsite, respectively. NO_(x)^(*) emissions peak emerged in the range of 227–258 mg m^(-3) near 550 ℃ of the upper layer ceramsite, which was related to the oxidation of sulfide and the combustion of LPG. Gangue is a direct heat source for sintering of ceramsite as well. During sintering process, the heat of flue gas above and below 400 ℃ accounts for 55.9% and 30.0% of the all-output heat, respectively, and was potentially used for producing waste-heat steam or electricity as by-products and drying raw materials during its own initial sintering process, which can realize combined mass and heat utilization for the gangue and further reduce the cost of sintered gangue ceramsite.

纯氧配风在硫回收应用中的问题及解决方法

某甲醇合成项目配套硫磺回收装置采用Claus+SCOT工艺,制硫炉采用纯氧配风操作。运行过程中一级转化器温升达到180℃;烟气SO_(2)排放200~400mg/m^(3),且波动较大。制硫炉调整为富氧操作后上述问题得到解决,烟气SO_(2)排放稳定在100mg/m^(3)以下。

Study on SO_2 Emission Mitigation of Thermal Power Plants in China

With the rapid development of electricity production, SO 2 from coal fired power stations causes severe air pollution problem. In 1997, the SO 2 emitted from thermal power plants reached 7.0 Mt, accounting for about 33% of the national emissions. At present and in the future, thermal power stations will still be the primary pollution sources. The Chinese government and power departments accord considerable importance to the SO 2 emissions from thermal power plants. New sets of environmentally friendly policies have been formulated. But, enforcement of laws and regulations needs to be further improved and broadened, especially those responding to market conditions. This paper focuses particular attention on the analysis of strategy, policies, and measures that have been or should be taken against SO 2 emissions from thermal power plants so as to achieve the environmental protection targets, on the basis of which the technical options for the future are given.

Sulfur dioxide gas sensing at room temperature based on tin selenium/tin dioxide hybrid prepared via hydrothermal and surface oxidation treatment

In this paper,a novel SnSe/SnO_(2) nanoparticles(NPs) composite has been successfully fabricated through hydrothermal method and surface oxidation treatment.The as-prepared sample was characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM).A series of morphological and structural characteristics confirm that the SnSe/SnO_(2) NPs composite shows a core-shell structure with a SnO_(2) shell with thickness of 6 nm.The prepared SnO_(2) NPs and SnSe/SnO_(2) NPs composite were applied as gas-sensing materials,and their gas-sensing properties were investigated at room temperature systematically.Experimental results show that the response value of the SnSe/SnO_(2) composite sensor toward 100×10^(-6) SO_(2) is 15.15%,which is 1.32 times higher than that of pristine SnSe(11.43%).And the SnSe/SnO_(2) composite sensor also has a detection limit as low as 74×10^(-9) and an ultra-fast response speed.The enhanced gas-sensing performance is attributed to the formation of p-n heterojunction between SnSe and SnO_(2) and the appropriate SnO_(2) shell thickness.

Gases emissions estimation and analysis by using carbon dioxide balance method in natural-ventilated dairy cow barns

Contaminated gases emissions from livestock industry are becoming one of the most significant contributors to the increasingly serious environmental pollution.To find a way to reduce gases emissions,it is essential to reveal the factors that can affect the gases emissions.In this study,the concentrations of typical gases(including ammonia(NH_(3)),carbon dioxide(CO_(2)),hydrogen sulfide(H_(2)S),and sulfur dioxide(SO_(2)))generated from naturally-ventilated dairy cow barns were detected through the sample-data method in Tianjin,northern China.Indoor environmental conditions,such as temperature(T)and relative humidity(RH),were measured simultaneously.After applying the carbon dioxide mass balance method,ammonia,hydrogen sulfide and sulfur dioxide emissions were determined.The correlation analysis and regression analysis between the climate condition and gas emissions were conducted to assess the data collected in dairy cow barns during the whole study period.There was a significant relationship between environmental conditions and gas emissions.NH3,H2S and SO_(2) emissions from the building are in the range of 0.98-2.36 g/LU·h,0-0.034 g/LU·h,and 0-0.069 g/LU·h,respectively.The numerical analysis shows that the NH3 emission is highly correlated with the temperature and relative humidity.The ventilation rate shows a positive correlation with all the three gases.

Regeneration of Fe_(2)O_(3)-based high-temperature coal gas desulfurization sorbent in atmosphere with sulfur dioxide

Regeneration of a high-temperature coal gas desulfurization sorbent is a key technology in its industrial applications.A Fe_(2)O_(3)-based high-temperature coal gas desulfurizer was prepared using red mud from steel factory.The influences of regeneration temperature,space velocity and regeneration gas concentration in SO_(2) atmosphere on regeneration performances of the desulfurization sorbent were tested in a fixed bed reactor.The changes of phase and the composition of the Fe_(2)O_(3)-based high-temperature coal gas desulfurization sorbent before and after regeneration were examined by X-ray diffraction(XRD)and X-ray Photoelectron spectroscopy(XPS),and the changes of pore structure were characterized by the mercury intrusion method.The results show that the major products are Fe3O4 and elemental sulfur;the influences of regeneration temperature,space velocity and SO_(2) concentration in inlet on regeneration performances and the changes of pore structure of the desulfurization sorbent before and after regeneration are visible.The desulfurization sorbent cannot be regenerated at 500℃ in SO_(2) atmosphere.Within the range of 600℃-800℃,the time of regeneration becomes shorter,and the regeneration conversion increases as the temperature rises.The time of regeneration also becomes shorter,and the elemental sulfur content of tail gas increases as the SO_(2) concentration in inlet is increased.The increase in space velocity enhances the reactive course;the best VSP is 6000 h^(-1) for regeneration conversion.At 800℃,20 vol-%SO_(2) and 6000 h^(-1),the regeneration conversion can reach nearly to 90%.

Sulfur dioxide sensing properties of MOF-derived ZnFe_(2)O_(4) functionalized with reduced graphene oxide at room temperature

In this paper,ZnZnFe_(2)O_(4) nanorods were prepared using Zn/Fe metal organic framework(MOF)as precursors,and ZnZnFe_(2)O_(4)/reduced graphene oxide(rGO)was prepared by hydrothermal method.The morphology and composition of the ZnZnFe_(2)O_(4)/rGO nanocomposite were characterized,and the results showed that the MOF-derived ZnZnFe_(2)O_(4) nanorods are uniformly modified on the surface of rGO.The ZnZnFe_(2)O_(4)/rGO nanocomposite exhibits better SO_(2) gas sensing performance than the single ZnZnFe_(2)O_(4) nanorods at room temperature.The sensing characteristics of single ZnZnFe_(2)O_(4) film sensor,single rGO film sensor and ZnZnFe_(2)O_(4)/rGO composite film sensor at SO_(2)gas concentration(1×10^(-6)-100×10^(-6))were tested.The response of ZnZnFe_(2)O_(4)/rGO composite sensor can reach 18.32%at room temperature.Compared with single ZnZnFe_(2)O_(4) and rGO film sensors,the ZnZnFe_(2)O_(4)/rGO composite sensor has better transient response,good sensitivity and selectivity.In this work,the improvement of the sensor performance is not only due to the p-n heterostructure between ZnZnFe_(2)O_(4) nanorods and rGO nanosheets,but also to the excellent electrical properties of rGO.It provides a new idea for the detection of SO_(2) at room temperature.