CFD simulation with enhancement factor of sulfur dioxide absorption in the spray scrubber

A model describing the absorption process of SO2 into limestone slurry with a spray scrubber is presented. Both the physical performance of the spray liquid in the scrubber and the involved chemical reactions are analyzed in the model. A con- tinuous concentration change of H+ was solved by iterative coupling using Matlab, and it was found that there was a remarkable influence on the concentration of the other elements in the process of SO2 absorption. The calculations show that the enhancement factor exponentially grows with an increasing value of pH and logarithmically decays with an increasing value of the driving force. To verify the accuracy of the model, experiments were also carried out, and the results suggest that the model, after combining the physical performance of the spray and the enhancement factor, can more precisely describe SO2 absorption in a spray scrubber. Furthermore, a commercial computational fluid dynamics (CFD) tool is used to perform several simulations which describe and clarify the effects of variables on SO2 absorption. The results of numerical simulation can provide a basis for further design and optimization of the scrubber.

Experimental study on the spatial distribution of particle rotation in the upper dilute zone of a cold CFB riser

Particle rotation plays an important role in gas-solid flows. This paper presents an experimental investigation on the spatial distribution of average rotation speed for glass beads in the upper dilute zone of a cold circulating fluidized bed(CFB) riser. It is shown that in the horizontal direction,the average rotation speed in the near-wall area is larger than that in the center area,while in the vertical direction,it decreases as the height increases. The reason resulting in this distribution is analyzed by considering several factors including particle size,particle shape,particle number density,particle collision behavior,and the surrounding flow field,etc. The effects of CFB operation conditions on the spatial distribution of average rotation speed are also studied. The results show that the increasing superficial gas velocity increases the average rotation speed of particles in the near wall area but takes nearly no effect on that in the center area. The external solids mass flux,however,takes the opposite effect. It is found that the average rotation speeds of particles in both areas are increased as the total amount of bed material increases.

以14C法为基础的共燃烟气中生物质与煤的掺混比例测定方法（英文）

目的:准确且可靠的生物质燃料掺混比例数据的缺失,阻碍了生物质/煤混燃发电技术在中国的发展.本文旨在建立以14C法为基础的生物质掺混比例检测系统,并研究煤作为化石燃料的测试本底、不同生物质之间14C含量的差异以及苯合成工艺中引入的现代碳污染对测试精度的影响,以验证该方法在混燃电站中实际应用的可行性.创新点:1.建立并使用适用于在工业混燃电站中应用的计算方法;2.通过实验测试,获得了3种由制样过程污染产生的煤中14C含量;3.通过对实际过程的经验拟合,提出更为合理的污染修正公式.方法:1.自主搭建苯合成系统(图2),并以液体闪光计数技术为核心形成样品14C值测试体系;2.通过实验测试,获得6种生物质与3种煤的14C测试值(图3和4),并验证混燃测试的可行性(图5);3.通过公式推导,在考虑煤中14C含量后,更为合理地修正苯合成过程中引入的污染,以减小混燃测试的绝对误差(公式(9)).结论:1.光谱级纯苯的测试值为仪器的测试本底,而商用SrCO3制苯的测试值则反应了苯合成过程中引入的污染本底.2.对不同生物质的重复实验的测试值落点均在理论计算误差范围内,证明了实验中苯合成系统的可靠性.3.运用研究中建立的计算方法,获得了生物质混燃比例的测试值;14C法应用于生物质/煤混燃电站的绝对测试误差在1%左右.

Absorption of NO_2 into Na_2S solution in a stirred tank reactor

To understand the absorption mechanism of nitrogen dioxide into a sodium sulfide solution, a stirred tank reactor with a plane gas-liquid interface was used to measure the chemical absorption rate of diluted nitrogen dioxide into sodium sulfide solution. The absorption rates under various experimental conditions were measured and the effects of experimental conditions on nitrogen dioxide absorption rate were discussed. The results show that, in the range of this study, nitrogen dioxide absorption rate increases with increasing sodium sulfide concentration, nitrogen dioxide inlet concentration, and flue gas flow rate, but decreases with increasing reaction temperature and oxygen content in flue gas.

Impact of individual acid flue gas components on mercury capture by heat-treated activated carbon

Elemental mercury capture on heat-treated activated carbon （TAC） was studied using a laboratory-scale fixed bed reactor. The capability of TAC to perform Hg0 capture under both N2 and baseline gas atmospheres was studied and the effects of common acid gas constituents were evaluated individually to avoid complications resulting from the coexistence of multiple components. The results suggest that surface functional groups （SFGs） on activated carbon （AC） are vital to Hg0 capture in the absence of acid gases. Meanwhile, the presence of acid gas components coupled with defective graphitic lattices on TAC plays an important role in effective Hg0 capture. The presence of HC1, NO2, and NO individually in basic gases markedly enhances Hg0 capture on TAC due to the heterogeneous oxidation of Hg0 on acidic sites created on the carbon surface and catalysis by the defective graphitic lattices on TAC. Similarly, the presence of SO2 improves Hg0 capture by about 20%. This improvement likely results from the deposition of sulfur groups on the AC surface and oxidation of the elemental mercury by SO2 due to catalysis on the carbon surface. Furthermore, O2 exhibits a synergistic effect on Hg0 oxidation and capture when acid gases are present in the flue gases.

Development of non-premixed porous inserted regenerative thermal oxidizer

In this study, a porous inserted regenerative thermal oxidizer （PRTO） system was developed for a 125 kW industrial copper-melting furnace, due to its advantages of low NOr emissions and high radiant efficiency. Zirconium dioxide （ZrOz） ce- ramic foams were placed into the combustion zone of a regenerative thermal oxidizer （RTO）. Different performance characteris- tics of the RTO and PRTO systems, including pressure drop, temperature distribution, emissions, and energy efficiency, were evaluated to study the effects of the porous inserts on non-premixed CH4 combustion. It was found that the PRTO system achieved a significant reduction in the NOx emission level and a fuel saving of approximately 30% compared to the RTO system. It is most suitable for a lean combustion process at an equivalence ratio 〈0.4 with NOx and CO emission levels within 0.002%~）.003% and 0.001%q3.002%, respectively.

Behavior of alkali minerals in oxyfuel co-combustion of biomass and coal at elevated pressure

Combustion of biomass or coal is known to yield aerosols and condensed alkali minerals that affect boiler heat transfer performance.In this work,alkali behavior in the pressurized oxyfuel co-combustion of coal and biomass is predicted by thermodynamic and chemical kinetic calculations.Existence of solid minerals is evaluated by X-ray diffraction(XRD)analysis of ashes from pressure thermogravimetric combustion.Results indicate that a rise in pressure affects solid alkali minerals negligibly,but increases their contents in the liquid phase and decreases them in the gas phase,especially below 900℃.Thus,less KCl will condense on the boiler heat transfer surfaces leading to reduced corrosion.Increasing the blend ratio of biomass to coal will raise the content of potassium-based minerals but reduce the sodium-based ones.The alkali-associated slagging in the boiler can be minimized by the synergistic effect of co-combustion of sulphur-rich coal and potassium-rich biomass,forming stable solid K2SO4 at typical fluidized bed combustion temperatures.Kinetics modelling based on reaction mechanisms shows that oxidation of SO2 to SO3 plays a major role in K2SO4 formation but that the contribution of this oxidation decreases with increase in pressure.