Development of new technology for coal gasification purification and research on the formation mechanism of pollutants

Coal-fired power generation is the main source of CO_(2)emission in China.To solve the problems of declined efficiency and increased costs caused by CO_(2)capture in coal-fired power systems,an integrated gasification fuel cell(IGFC)power generation technology was developed.The interaction mechanisms among coal gasification and purification,fuel cell and other components were further studied for IGFCs.Towards the direction of coal gasification and purification,we studied gasification reaction characteristics of ultrafine coal particles,ash melting characteristics and their effects on coal gasification reactions,the formation mechanism of pollutants.We further develop an elevated temperature/pressure swing adsorption rig for simultaneous H_(2)S and CO_(2)removals.The results show the validity of the Miura-Maki model to describe the gasification of Shenhua bituminous coal with a good fit between the predicted DTG curves and experimental data.The designed 8–6–1 cycle procedure can effectively remove CO_(2)and H_(2)S simultaneously with removal rate over 99.9%.In addition,transition metal oxides used as mercury removal adsorbents in coal gasified syngas were shown with great potential.The techniques presented in this paper can improve the gasification efficiency and reduce the formation of pollutants in IGFCs.

Hollow ZSM-5 encapsulated with single Ga-atoms for the catalytic fast pyrolysis of biomass waste

The development of efficient metal-zeolite bifunctional catalysts for catalytic fast pyrolysis(CFP) of biomass waste is highly desirable for bioenergy and renewable biofuel production.However,conventional metal-loaded zeolites often suffer from metal sintering during pyrolysis and are thus inactivated.In this study,single-site Ga-functionalized hollow ZSM-5(GaO_x@HS-Z5) was synthesized via an impregnationdissolution-recrystallization strategy without H_(2) reduction.The Ga atom was coordinated to four oxygen atoms in HS-Z5 frameworks.Benefitting from the highly dispersed single-Ga atoms and hollow zeolite framework,3GaO_x@HS-Z5 performed the best in producing hydrocarbon-rich bio-oil compared to impregnated 3GaO_x/HS-Z5 and H_(2)-reduced 3Ga@HS-Z5 in the maize straw CFP.In particular,3GaO_x@HS-Z5 delivered the highest bio-oil yield(23.6 wt%) and hydrocarbon selectivity(49.4 area%).3GaO_x@HS-Z5 also retained its structural integrity and catalytic activity after five pyrolysis-regeneration cycles,demonstrating its advantage in practical biomass CFP.The elimination of H_(2) reduction during the synthesis of catalyst provides an additional advantage for simplifying the CFP process and reducing operating costs.The retained Ga micro-environment and anti-sintering properties were unique for 3GaO_x@HS-Z5,as severe metal sintering occurred during pyrolysis for other metals(e.g.,NiO_x,ZnO_x,FeO_x,and CoO_x) that encapsulated HS-Z5.

Modification of CaO-based sorbents prepared from calcium acetate for CO_2 capture at high temperature

CaO-based sorbent is considered to be a promising candidate for capturing CO_2 at high temperature. However,the adsorption capacity of CaO decreases sharply with the increase of the carbonation/calcination cycles. In this study, CaO was derived from calcium acetate(CaAc_2), which was doped with different elements(Mg, Al,Ce, Zr and La) to improve the cyclic stability. The carbonation conversion and cyclic stability of sorbents were tested by thermogravimetric analyzer(TGA). The sorbents were characterized by N_2 isothermal adsorption measurements, scanning electron microscopy(SEM) and X-ray diffraction(XRD). The results showed that the cyclic stabilities of all modified sorbents were improved by doping elements, while the carbonation conversions of sorbents in the 1st cycle were not increased by doping different elements. After 22 cycles, the cyclic stabilities of CaO–Al, CaO–Ce and CaO–La were above 96.2%. After 110 cycles, the cyclic stability of CaO–Al was still as high as 87.1%. Furthermore, the carbonation conversion was closely related to the critical time and specific surface area.

Effect of pre-calcination for modified CaO-based sorbents on multiple carbonation/calcination cycles

In the present work,the effect of pre-calcination on carbonation conversion and cyclic stability of modi fied CaObased sorbent was investigated by thermogravimetric analyzer(TGA).The modi fied CaO-based sorbents with CaAc_2 as precursor were respectively doped with different elements(Mg,Al,Ce,Zr and La).The speci fic surface area,pore volume and pore size distribution were tested by N_2 isothermal adsorption measurements.The phase compositions of sorbents were characterized by X-ray diffraction(XRD).The results showed that the cyclic stabilities of the sorbents were improved by pre-calcination.The pre-calcination was conducted at 900°C for 5 h in air by the muf fle furnace.With pre-calcination,the cyclic stabilities of sorbents could be as high as 96% after 22 cycles,such as CaO-Al,CaO-Ce and CaO-La.After contact with air,the carbonation conversions of spent sorbents with pre-calcination suddenly increased by about one-sixth due to the change of channel structure by hydration.Both the cyclic stability of sorbent and the durability of reactivation were related to the structural stability of sample,especially the stability of mesopores between 2 nm and 5.5 nm.The present work also provided an easy and low-cost method for reactivating the spent CaO-based sorbents.

Integrated Equivalent Model of Permanent Magnet Synchronous Generator Based Wind Turbine for Large-scale Offshore Wind Farm Simulation

The high-speed simulation of large-scale offshore wind farms(OWFs) preserving the internal machine information has become a huge challenge due to the large wind turbine(WT) count and microsecond-range time step. Hence, it is undoable to investigate the internal node information of the OWF in the electro-magnetic transient(EMT) programs. To fill this gap,this paper presents an equivalent modeling method for largescale OWF, whose accuracy and efficiency are guaranteed by integrating the individual devices of permanent magnet synchronous generator(PMSG) based WT. The node-elimination algorithm is used while the internal machine information is recursively updated. Unlike the existing aggregation methods, the developed EMT model can reflect the characteristics of each WT under different wind speeds and WT parameters without modifying the codes. The access to each WT controller is preserved so that the time-varying dynamics of all the WTs could be simulated. Comparisons of the proposed model with the detailed model in PSCAD/EMTDC have shown very high precision and high efficiency. The proposed modeling procedures can be used as reference for other types of WTs once the structures and parameters are given.

Review on the NO removal from flue gas by oxidation methods

Due to the increasingly strict emission standards of NOx on various industries,many traditional flue gas treatment methods have been gradually improved.Except for selective catalytic reduction(SCR)and selective non-catalytic reduction(SNCR)methods to remove NOx from flue gas,theoxidation method is paying more attention to NOx removal now because of the potential to simultaneously remove multiple pollutants from flue gas.This paper summarizes the efficiency,reaction conditions,effect factors,and reaction mechanism of NO oxidation from the aspects of liquid-phase oxidation,gas-phase oxidation,plasma technology,and catalytic oxidation.The effects of free radicals and active components of catalysts on NO oxidation and the combination of various oxidation methods are discussed in detail.The advantages and disadvantages of different oxidation methods are summarized,and the suggestions for future research on NO oxidation are put forward at the end.The review on the NO removal by oxidation methods can provide new ideas for future studies on the NO removal from flue gas.

Flexible Operation Mode of Coal-fired Power Unit Coupling with Heat Storage of Extracted Reheat Steam

In order to provide more grid space for the renewable energy power,the traditional coal-fired power unit should be operated flexibility,especially achieved the deep peak shaving capacity.In this paper,a new scheme using the reheat steam extraction is proposed to further reduce the load far below 50%rated power.Two flexible operation modes of increasing power output mode and reducing fuel mode are proposed in heat discharging process.A 600 MW coal-fired power unit with 50%rated power is chosen as the research model.The results show that the power output is decreased from 300.03 MW to 210.07 MW when the extracted reheat steam flow rate is 270.70 t·h^(-1),which increases the deep peak shaving capacity by 15%rated power.The deep peak shaving time and the thermal efficiency are 7.63 h·d^(-1)and 36.91%respectively for the increasing power output mode,and they are 7.24 h·d^(-1)and 36.58%respectively for the reducing fuel mode.The increasing power output mode has the advantages of higher deep peak shaving time and the thermal efficiency,which is recommended as the preferred scheme for the flexible operation of the coal-fired power unit.

Elemental mercury (Hg^(0)) removal from coal syngas using magnetic tea-biochar: Experimental and theoretical insights

Mercury is ranked 3^(rd)as a global pollutant because of its long persistence in the environment. Approximately 65% of its anthropogenic emission (Hg^(0)) to the atmosphere is from coal-thermal power plants. Thus, the Hg^(0)emission control from coal-thermal power plants is inevitable. Therefore, multiple sorbent materials were synthesized using a one-step pyrolysis method to capture the Hg^(0)from simulated coal syngas. Results showed, the Hg^(0)removal performance of the sorbents increased by the citric acid/ultrasonic application.T5CUF_(0.3)demonstrated the highest Hg^(0)capturing performance with an adsorption capacity of 106.81 μg/g within 60 min at 200 °C under complex simulated syngas mixture (20% CO,20% H_(2), 10 ppm V HCl, 6% H_(2)O, and 400 ppm V H_(2)S). The Hg^(0)removal mechanism was proposed, revealing that the chemisorption governs the Hg^(0)removal process. Besides, the active Hg^(0)removal performance is attributed to the high dispersion of valence Fe_(3)O_(4)and lattice oxygen (α) contents over the T5CUF_(0.3)surface. In addition, the temperature programmed desorption (TPD) and XPS analysis confirmed that H_(2)S/HCl gases generate active sites over the sorbent surface, facilitating high Hg^(0)adsorption from syngas. This work represented a facile and practical pathway for utilizing cheap and eco-friendly tea waste to control the Hg^(0)emission.