Utilization of Thermally Treated Flue Gas Desulfurization (FGD) Gypsum and Class-C Fly Ash (CFA) to Prepare CFA-Based Geopolymer

The feasibility of utilization of flue gas desulfurization （FGD） gypsum and Class-C fly ash （CFA） to prepare CFA-based geopolymer were studied. The results showed that geopolymer made from 90% CFA and 10% FGD gypsum （FGDG） which was thermally treated at 800 ℃ for 1 h obtained the better compressive strength of 37.0 MPa. The micro characteristics and structures of the geopolymer samples of CFA and CFA-FGDG were tested by XRD, FT-IR, and SEM-EDXA after these samples cured at 75 ℃ for 8 h followed by 23 ℃ for 28 d. Both the geopolymer samples of CFA and CFA-FGDG have significant asymmetric stretching of A1-O/Si-O bonds and Si-O-Si / Si-O-A1 bending band. In geopolymer sample of CFA-FGDG, a small quantity of lathy products probably being the ettringite wrapped over the spherical fly ash particle, and the concentration of sulfur is much more than that in geopolymer sample of CFA. It is indicated that FGD gypsum may react during alkali-activated and geopolymeric process.

Activation of Rejected Fly Ash Using Flue Gas Desulphurization (FGD) Sludge

Low-grade fly ash (rejected fly ash,rFA),a significant portion of the pulverized fuel ash (PFA) produced from coal-fired power plants and rejected from the ash classifying process,remains unused due to its high carbon content and large particle size (>45μm).But it is thought that the rejected ash may have potential uses in chemical stabilization/solidification (S/S) processes which need relatively lower strengths and a lower chemical reactivity.Flue Gas Desulphurisation (FGD) sludge is a by-product of air pollution control equipment in coal fired power plants whose chemical composition is mainly gypsum.As there is no effective usage of both of these two materials,it is of interest to research on the possible activation of rFA using FGD.This paper presents experimental results of a study on the properties of rFA activated by the FGD in rFA-cement pastes.Different percentages of FGD were added into the mix to study the effects of the FGD on the reaction of the rFA blended cement pastes.The results show that FGD takes effect as an activator only at late curing ages.Adding Ca(OH) 2 enhances the effect of FGD on activating the hydration of rFA.Also,10% FGD by weight of rFA is the optimal addition in the rFA-cement pastes.The results of the compressive strength measurements correlate well with the porosity results.

Influence of Thermally Treated Flue Gas Desulfurization(FGD) Gypsum on Performance of the Slag Powder Concrete

The feasibility of flue gas desulphurization （FGD） as concrete admixture was studied. A combined concrete admixture of the thermally-treated FGD gypsum and slag powder was explored. The FGD gypsum was roasted at 200℃ for 60 min and then mixed with the slag powder to form FGD gypsum-slag powder combined admixture in which the SO3 content was 3.5wt%. Cement was partially and equivalently replaced by slag powder alone or FGD gypsum-slag powder, at concentration of 25wt%, 40wt%, and 50wt%, respectively. The setting times, hydration products, total porosity and pore size distributions of the paste were determined. The compressive strength and drying shrinkage of cement mortar and concrete were also tested. The experimental results show that, in the presence of FGD gypsum, the setting times are much slower than those of pastes in the absence of FGD gypsum. The combination of FGD gypsum and slag powder provides synergistic benefits above that of slag powder alone. The addition of FGD gypsum provides benefit by promoting ettringite formation and forms a compact microstructure, increasing the compressive strength and reduces the drying shrinkage of cement mortar and concrete.

FGD Capacity Prediction of Thermal Power Plants in China

Through analyzing the proportion of SO2 emission from thermal power plants in the nationwide SO2 emis- sion in USA, Japan etc. developed countries, and the developmental course of thermal power installed capacity and the FGD capacity in USA, the FGD capacity of thermal power plants in China is forecasted from two angles. One is to predict FGD capacity in accordance with the policy in force in China. The other is to predict FGD capacity based upon the emission right trading policy. As compared, it is held that FGD equipment should be mainly installed on the large size units burning high sulfur coal according to the emission right trading policy. Such a method of work not only can economize large amount of investments and operation costs, but also can realize the same environmental effect.

Running Control Mode for In-Duct FGD with No-Bypass Design

The desulfuration system in the second phase project of Sanhe Power Plant is the first such system that adopts in-duct FGD with no-bypass design by domestic power plants.Different from that of the conventional FGD with bypass design,a running control mode,which is important for the security of the absorbing tower within the designed ranges,shall be made to ensure the flue gas temperature and dust concentration at the inlet of the absorbing tower.The stable running of the system shows that the control mode is feasible.

INTERACTION BETWEEN SO_2 FROM FLUE GAS AND SORBENT PARTICLES IN DRY FGD PROCESSES

Among the technologies to control SO2 emission from coal-fired boilers, the dry flue gas desulphurization (FGD) method, with appropriate modifications, has been identified as a candidate for realizing high SO2 removal efficiency to meet both technical and economic requirements, and for making the best quality byproduct gypsum as a useful additive for improving alkali soil. Among the possible modifications two major factors have been selected for study: (1) favorable chemical reaction kinetics at elevated temperatures and the sorbent characteristics; (2) enhanced diffusion of SO2 to the surface and within the pores of sorbent particles that are closely related to gas-solid two-phase flow patterns caused by flue gas and sorbent particles in the reactor. To achieve an ideal pore structure, a sorbent was prepared through hydration reaction by mixing lime and fly ash collected from bag house of power plants to form a slurry, which was first dewatered and then dried. The dry sorbent was found capable of rapid conversion of 70% of its calcium content at 700℃, reaching a desulphurization efficiency of over 90% at a Ca/S ratio of 1.3. Experiments confirmed that the diffusion effect of SO2 is an important factor and that gas-solid two-phase flow plays a key role to mixing and contact between SO2 and sorbent particles. For designing the FDG reactor, a new theoretical drag model was developed by combination of CFD with the Energy Minimization Multi-Scale (EMMS) theory for dense fluidi-zation systems. This new drag model was first verified by comparing calculated and measured drag values, and was then implemented in simulation of gas-solid two-phase flow in two circulating fluidized beds with different sizes and flow parameters. One riser has diameter and height of 0.15 m×3m and another one 0.2m×14.2m. Their superficial gas velocities are 4 and 5.2 m·s-1, respectively, and the circulating rate 53 and 489 kg·(m-2·s-1). FCC particles were used in both cases. The results show that not only the static pressure drop along the riser height, but also radial distributions of particle volume fraction have been very well predicted in comparison with experiments. The new drag model is expected to shed more light on the further improvement of SO2 diffusion to solid sorbent and optimization of reactor structure.

脱硫石膏含水率超标原因分析及控制措施

文章针对国华北京热电分公司脱硫石膏含水率超标(>10wt%)问题,从脱硫化学监测分析入手,结合实际运行情况及超标现象,从系统的运行方式、设备的运行状况以及运行方式对塔内正常反应的影响等几方面因素分析了石膏含水率超标的原因,并提出了控制石膏含水分的措施和改进方法,希望能对FGD运行和故障分析起到一定的参考作用。

Air Pollutant Emissions from Coal-Fired Power Plants

In order to investigate the factual air pollutant emissions from Henan’s power sector in 2010, SO2, NOx and PM emissions from 24 generating sets from 15 coal-fired power plants have been measured. It is shown that SO2 emission values from 22 of 24 generating sets conform to the requirements, which is causing by the high performance of the flue gas desulfurization system. Much higher NOx emissions indicate that the construction of flue gas denitrition systems is necessary. PM emissions varied from 2.3 kg to 299.9 kg per hour. Total sulfur, moisture, ash and volatile content, and net caloric value of coals were investigated to elucidate the relationship between coals and air pollutant emissions.