Research On The Effects Of The Compound Morphological Changes Of Trace Toxic Heavy Metals Mercury And Chromium In The Process Of Co-Combustion Biomass With Coal

Toxic heavy metal mercury and chrome derived from coal combustion will cause serious damage to human living environment. The toxicity of methylmercury toxicity is maximum, it invades the human body cause the permeability changes of the cells, destroy ionic homeostasis of cellular, affect the basic function and metabolism of the cells.Chrome is easy to form a strong oxidizing, corrosive and carcinogenic substances, and Cr (+6) is a highly carcinogenic substance, so to strictly control the compounds’emissions during coal combustion. Biomass containing rich alkali metal and Cl elements, low N, S, these characteristics may also influence the formation of Hg、Cr compounds.The new combustion method can not only take full adavantage of natural resource, but also control the emission of pollutants. The research of co-combustion biomass with coal has great practical significance.Based on the oxidation mechanism of mercury and chromium, mercury and chromium compounds were studied in flue gas during co-combustion biomass with coal. The thermodynamics model of co-combustion biomass with coal was established with HSC Chemistry. The thermodynamic calculation results of mercury show that: With the attention of Biomass, concentration of Cl will arise which can promote Hg0change to Hg2+earlier. And the attention of C has played a certain role in promoting oxidation of Hg in coal.The thermodynamics calculation results suggest that in the systems of Cr/C/H/O/N/S/Cl, hexavalent chromium conversion rate is highest when the mixed fuel ratio was0:1, mixed fuel ratio of1:3, was the lowest, therefore, mixed fuel ratio of1:3was the best mixed combustion conditions. When co-combustion biomass with coal, where the presence of alkali metal cases, whichever mixed fuel ratio, the mainly chromium compounds was K2CrO4.On the other hand, created dynamic systems of mercury and chromium combined the characteristics of biomass has substantial content of alkali metals and Cl, low content of N、S with dynamic data from previous studies. Kinetics calculation which was focused on the transformation of alkali Cl2and SO2in flue gas, was performed with CHEMKIN4.1.Kinetic studies on mercury were basically the same with the thermodynamic, because of the complex mechanism of reaction, the kinetic results were closer to the reality combustion. Because the reaction mechanism of chromium is very complex, it is difficult to obtain the accurate dynamic parameters, so we just created a C/H/O/N/S/Cl/K/Na dynamic model, indirect predictive elements influence of chromium oxide. By C/H/O/N/S/Cl systems, C/H/O/N/Cl/K/Na systems and C/H/O/N/S/Cl/K/Na systems under different mixed-fuel ratio analysis, dynamics simulation results show that the s element exists mainly in the form of H2SO4and SO2, products of Cl element mainly for HCl, main product of alkali metals in flue gas is the KHSO4, KCl and NaCl, NaHSO4.Chromium oxide have relation to the content of alkali metals, chlorine, sulphur in fuel composition, and suitable mixed-fuel ratio would stead to chromium oxide. In addition, the study found that reactivity of the substance under temperature control. At different temperatures, chromium oxidation have different oxide impact, and alkali metals、Cl and S also have different effect on chromium.Oxide of chromium can play a facilitating role when select the appropriate temperature.Based on kinetics model, the physical model of combustion was established with FLUENT, a computational fluent dynamics (CFD) software. The CHEMKIN kinetics mechanism was imported to the physical model to simulate real combustion. Chemical reactions are combined with physical fields, the influence of flow field on chemical reaction was considered. The physical model calculation results are consistent with experimental datas, and it was verified to be feasible.