Improvement of High-efficiency Green Catalysts for Flue Gas Denitrification

Based on the basic principle and mechanism of flue gas denitrification,the commonly used catalysts for flue gas denitrification were introduced firstly,and then the catalytic performance,stability and reaction mechanism of catalysts in the market were analyzed.Different types of catalysts were studied to look for green catalysts with high activity,sulfur resistance,water vapor resistance and other advantages.The mechanism of denitration reaction of green catalysts was discussed,and the laws of formation,propagation and consumption of active species in the reaction process were revealed to provide theoretical basis for optimizing catalyst design and improving reaction conditions.Then the research status and problems of new catalysts for flue gas denitrification were described.Finally,the future development direction of green catalysts for flue gas denitration was discussed to improve the performance and stability of catalysts and meet the performance requirements of denitration catalysts in different industries.

Comprehensive Solution to Flue Gas Desulfurization and Denitration of Circulating Fluidized Bed Boiler

With the advantages of high combustion efficiency, wide fuel flexibility and low concentrations of discharged pollutants, circulating fluid- ized bed （CFB） boiler has been widely used in recent years. However, in order to meet the requirement of new emission standard, it＇s necessary to add flue gas desulfurization and denitration devices. In this paper, the choice of flue gas purification processes for CFB boiler has been discussed firstly, and then the economy and rationality of the SNCR ＋ CFB-FGD ＋ COA comprehensive solution to flue gas desulfurization and denitration have been analyzed.

Low-temperature oxidation behavior and mechanism of semi-dry desulfurization ash from iron ore sintering flue gas

The low-temperature wet oxidation behavior of semi-dry desulfurization ash from iron ore sintering flue gas in ammonium citrate solution was investigated for efficiently utilizing the low-quality desulfurization ash. The effects of the ammonium citrate concentration, oxidation temperature, solid/liquid ratio, and oxidation time on the wet oxidation behavior of desulfurization ash were studied. Simultaneously, the oxidation mechanism of desulfurization ash was revealed by means of X-ray diffraction, Zeta electric resistance, and X-ray photoelectron spectroscopy (XPS) analysis. Under the optimal conditions with ammonium citrate, the oxidation ratio of CaSO_(3) was up to the maximum value (98.49%), while that of CaSO_(3) was only 8.92% without ammonium citrate. Zeta electric resistance and XPS results indicate that the dissolution process of CaSO_(3) could be significantly promoted by complexation derived from the ammonium citrate hydrolysis. As a result, the oxidation process of CaSO_(3) was transformed from particle oxidation to SO_(3)^(2−) ion oxidation, realizing the rapid transformation of desulfurization ash from CaSO_(3) to CaSO_(4) at low temperature. It provides a reference for the application of semi-dry desulfurization ash and contributes to sustainable management for semi-dry desulfurization ash.

Properties change of activated coke for sintering flue gas purification in cyclic removal of SO_(2) and NO_(x)

The properties of activated coke(AC)for sintering flue gas purification greatly affect the efficiency of desulfurization and denitration,but they gradually change during cycles.The change in properties of coal-based AC during cycles was studied to clarify the change law and AC optimization index.The AC oxygen content rapidly increases 13.49 to 17.87 wt.%in the early cycles to form phenol,which promotes the denitration rate 55.63%to 78.20%.The denitration performance slowly increases in subsequent cycles becaof the generation of quinone AC slow oxidation.However,the oxygen-containing groups are not conducive to adsorption capacity of AC for NO.The adsorbed NO species which can be replaced SO2 is the main NO species on AC,and its amount decreases with the decrease in CC content of AC.The AC chemical loss leads to the opening of closed pores,expansion of original pores and formation of new pores,causing micropore volume to increase 0.085%to 0.152%,compressive strength to decrease 472 to 336 N,and abrasive resistance to decrease 97.87%to 94.16%during cycles.The low oxygen content and high micropore volume are favorable to the initial desulfurization performance,and the former is more decisive.After a while,the desulfurization rate is linearly positively correlated with the micropore volume regardless of the chemistry.4-h desulfurization rate increased 69.03%to 85.91%during 25 cycles due to the increasing micropore volume.The AC properties change in cycles will greatly affect the desulfurization and denitration rate in the height direction of the flue gas purification system.Selecting the coal-based AC with moderate micropore volume,easy oxidation surface and less original oxygen-containing groups facilitates the better purification efficiency at lower cost for sintering plants.

Introduction of the DeNO_x Project in Huaneng Yuhuan Power Plant

The Selective Catalytic Reduction (SCR) system for flue gas denitration applied in Yuhuan Power Plant with 4×1 000 MW units is introduced in this paper. The technology system structure, process features, basic design data and equipment layout of the SCR flue gas denitration system of original units in the plant are briefly introduced and the retrofi t method of equipments is described, which provide valuable experience for flue gas denitrification retrofit of large-size coal-fired boilers in China.

Enhanced simultaneous absorption of NO_(x) and SO_(2) in oxidation-reduction-absorption process with a compounded system based on Na_(2)SO_(3)

Oxidation of sulfite and competitive absorption existed in Na_(2)SO_(3) solution for simultaneous removal of NO_(x) and SO_(2),inhibited the long-term high-efficiency when used for practical applications.A matching strategy was developed to solve these problems.Antioxidants combination was used to retard the oxidation of antioxidant and enhance inhibition of S(IV)(tetravalent sulfur)oxidation.Hydroquinone(HQ)and sodium thiosulfate(ST)showed a positive synergistic effect on inhibition of S(IV)oxidation.When SO_(2) concentration was 500 and 2000 ppmV,the addition of 0.1 wt.%HQ and 1 wt.%ST decreased the percentage of S(IV)oxidized by oxygen by over 30%and 40%,respectively.Alkali(Na_(2)CO_(3))alleviated the competitive absorption between NO_(x) and SO_(2).Moreover,Na_(2)CO_(3) exhibited an enhancement effect on the absorption of NO_(x) and SO_(2) when coupled with anti-oxidants.While the increase of oxygen pressure accelerated the oxidation of S(IV),the anti-oxidants can retard the oxidation.The measurement of pH suggested the removal efficiency of NO_(x) highly depended on SO_(3)^(2-) concentration rather than pH.The further investigation of the mechanism suggested the match effect was related to the interaction between ST and the intermediate product of HQ.The match strategy holds a potential for application of SO_(3)^(2-) to denitration.

Control of nitrogen oxides emission by selective non-catalytic reduction in preheating section during iron ore pellets production

Reducing the NO_(x) emission from pelletizing process is of great importance to the green development of iron and steel industry.The flue gas temperature of preheating(PH)section during grate-kiln iron ore pelletizing process typically ranges within 850–1050℃,which meets the temperature requirements of selective non-catalytic reduction(SNCR)for NO_(x).The in-bed SNCR behavior of NO_(x) in the PH section was investigated,and the influence of relevant parameters was revealed.Results show that with the flue gas temperature rising,the denitration rate reached a peak value and then declined,where the appropriate temperature range was 950–1000℃.Increasing the NH_(3)/NO ratio(NSR)contributed to improving the denitration rate,and the appropriate NSR was 1.0.Oxygen content in the flue gas also showed an important influence on denitration rate,which reached a peak value and then dropped with the oxygen content rising.Under the condition of 18 vol.%oxygen content,the denitration reaction mainly occurred in the form of 4NO+4NH_(3)+O_(2)=4N_(2)+6H_(2)O.For restricting the competitive reaction of NH_(3) oxidation,the oxygen content in flue gas of PH section should be kept at an appropriate range.In general,the denitration rate reached about 25%in the PH section through spraying ammonia.