THE GLASS PHASE CHARACTERIZATION OF COAL ASH SLAG

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1 THE GLASS PHASE CHARACTERIZATION OF COAL ASH SLAG Hong-zhu QUAN (1), Tanosaki TAKAO (2) (1)Department of Architecture and Civil Engineering, Qingdao Agricultural University, China (2) Taiheiyo Cement Corporation, Japan Japan Coal Energy Centre, Japan Abstract In recent years, coal power generation are strongly desired lower environmental burden, emissions of SOx, NOx, and CO 2 are reduced to the level. Since high efficiency of combustion or gasification systems discharge coal ash component of complex ashes or glassy molten (also called CCP), and the other point of view is that these CCPs are expected to be effectively used for sustainable development as component for civil engineering etc. Using the CCPs for civil engineering work, Pozzolanic reactions are very important character with hydration materials, but to measure Pozzolanic reaction by mortar test is necessary to wait very long term, waiting for the new method of determining the Pozzolanic reactions. So, chemical and mineralogical investigations were carried out on these inorganic materials. The glass phase which was formed by quenching is difficult to characterize by X- ray analysis by every CCP, and discussed only how percentage of glass phases, without not good explanation of CCP reactions in each steps. Therefore, in this study, we promote the new method by optical analysis and acid extraction tests etc. Three phases are distinguished, such as glass I, glass II, and crystal phase. Glass I has low flux compositions, and glass II has high flux compositions which makes the basic character of Class C ash in ASTM and Chinese GB standards. Keywords: coal ash,, CCP, Pozzolanic reaction, mineralogical characterization, glass 1. INTRODUCTION The Asia-Pacific Partnership(APP) on Clean Development and Climate is an organization formed to accelerate the development and deployment of clean energy technologies across the region. The APP s Cleaner Fossil Energy taskforce made the proporsal of developing IGCC(Integrated Coal Gasification Combined Cycle) systems and carbon capture in There are many different types of gasifier which produce dry, fused or agglomerated ash depending on the operating temperature and the fusion temperature of the residues. In this study the main target material is entrained flow gasifiers, which work at high temperatures 378

2 and produce a vitreous, such as IGCC, a high efficiency power generation technology which gasifies coal to be used as the fuel for gas turbines. As shown Fig.1, compared with conventional pulverized coal-fired power plants, IGCC can increase power generation efficiency by approximately 20% for commercial plants. An increase in fields that can utilize ash: since IGCC discharges coal ash in the form of glassy molten. Through the IGCC system, inorganic components are withdrawn as ; therefore an investigation on utilization of the is necessary. Recently, in Japan production of natural aggregates is restricted by environmental conditions, and investigations on from sewage sludge and municipal waste have seen an increase. In addition to aggregates, it is tested as a grainy property, the usage as a fixed medium of discharge of useful element such as the fertilizer components, or adsorption of pollutant of water or air such as CO 2 gas. As a matter of fact, the research of the GC residues just started in the cord about the IGCC system as for the coal gasifies because there were not a lot of numbers about the gas collection plant too much yet. Therefore, Feasibility studies for what being possible to use it from the characterization of residues first of all is important comparing with pulverized fly ash. Fig. 1 System of Coal gasfication (IGCC type) and typical particle of 2. TESTED SAMPLES In this study, s from a bench scale plant and pulverised coal fly ash from power stations in Japan, China, Thailand, Europe and USA were tested. As reference, from municipal solid waste, sewage sludge and natural sand in Shizuoka-Japan were tested too(shown in Table1). The s, are produced by water quenching from molten. 3. EXPERIMENTAL METHODS 3.1 Physic-chemical mineralogical characterization Size distribution, specific gravity, bulk density, surface areas and water absorption were measured based on JISA1101, JISA1109 etc. The section of s was made for microscopic, 379

3 observation for purpose of shape observation and crack densities measurement (Fig.2). Chemical compositions and Insoluble percentage (Insol) were determined by JISR Table 1: Chemical compositions of samples Iglos s SiO 2 Al 2 O 3 Fe 2 O 3 Na 2 O K 2 O Mg O Ca O SO 3 P 2 O 5 TiO 2 Insol * SlagA SlagB SlagC SlagD SlagF SlagG SlagH FA FA FA FA FA FA FA Blast furnace Steel Municipa l Waste Sewage sludge JIS portland cement Shizuoka Sand

4 Fig. 2 An exterior view of thin sections and example of optical microscope of IGCC 3.2 Evaluation of mortar property Because s don t contain gravel size (Table2), mortal test was carried out in this study. Mixing with classified particles controlled grain size distribution. Air, content was measured by method of JISA1118 (alkyl sulphonic acid type agent: 2.5mg/kg, water/cement =0.45, cement/sand=0.5). Compressive strength and alkali-aggregate reaction by mortarbar method were measured following JIS A 1108, JIS A 5308, and JIS A 5011 standards. 3.3 Grinding, leaching, and cement clinker production test Grinding work index test was carried out based on JIS M Leaching test of heavy metals was measured with No.13 notification of Japanese Environment Agency. Because c he a raw material substituting to clay, IGCC of 4kg/t (Table 3) was used to produce a cement clinker at factory of Taiheiyo Cement Corp. And qualities of cement from the clinker were evaluated by JIS R Sphere (0.3wt %) are rare. Microphotograph of thin section and image processed figures are in Fig.2. The cracks develop in sewage and municipal s. 3.4 Evaluation of mortar properties Flow ratios of each fresh mortar to flow value of IGCC mortar are listed in Table 4. Except the ferro-nickel mortar, flow ratios of slug mortars are less than the natural sand mortar. As strength rations of each mortar are listed in Table 5. Because any expansion was not recognized at all test peace, rare possibilities of alkali-aggregate reaction would be considered. And no possibility of the reaction is recognized by mortarbar test. 4. RESULTS 4.1 Physic-chemical mineralogical characterization The results are shown in Table 2. By these results, fine particles are poor, and specific gravities are within the limitation of the criterion, and water absorption is less than 1.5wt/% which clear the criterion. 381

5 Chemical compositions of these s are shown in Table1. Coal F (in Table1) was used for mortar test and cement clinker production test. 4.2 Shapes and cracks As shown in Fig.1 and Fig.2, IGCC particles are composed of granular, needle-like and sphere particles. The granular is dominant (99.2wt/%), and the needle (0.5wt %) and sphere-like particles (0.3wt %) are rare. Microphotographs of thin section and image processed figures are in Fig.2. The cracks develop in sewage and municipal s. 4.3 Evaluation of mortar properties Flow rations of each fresh mortar to flow value of IGCC mortar are listed in Table 4. Except the ferro-nickel mortar, flow rations of slug mortars are less than the natural sand mortar. As strength rations of each mortar are listed in Table 5. And no possibility of the reaction is recognized by mortar-bar test. 4.4 Grinding workability, leaching and cement clinker production test Results of grinding work index test are shown in Table 3. The work index of IGCC is higher than natural sand. As shown in Table 6, leached amounts of heavy metals from IGCC are the lowest. Table 2: Grain size distribution and physical property 5.0mm 2.5mm 1.2mm 0.6mm Table 3: Cement production test's condition 0.3mm 0.15mm Unit of electric crushing power 19.7 kwh/t/clinker Volume of crush in mill 193t clinker/e Content of 0.09mm under particle 18% Output of mixing raw material 7160 t/day Using calorillic power 778 Kcal/kg HM value t=cao/ SiO 2 + Al 2 O 3 + Fe 2 O Free lime content 0.40% Density (g/cm 3 ) BET (m 2 /g) Water absorption Needle content IGCC Sewage sludge Municipal waste Ferronickel River sand Japaneses desirable sand

6 Table 4: Results from mortar test Waterabsorption Mortar flow ratio Mortar air content Crack content IGCC F IGCC (non needle) Sewadge sludge Municipal waste Ferro-nickel River sand Table 5: Results of mortar aggregate test Density (g/cm 3 ) Bulk densit (g/cm 3 ) Compressive strength raitio at 28 days IGCC A IGCC D IGCC F Sewadge sludge Municipal waste Ferro-nickel River sand Cement raw material Table 6: Chemical composition and results of leaching test (mg/l) Cd Pb Cr Zn Cu V Ni Hg As Se IGCC F ND ND Leaching test ND ND ND ND ND ND ND ND ND ND Analytical limit Table 7: Results of mortar tests by use of cement produced by test Mixing ratio of Density Brain sruface area Mortar flow Compressive strenght (MPa) IGCC (g/cm 3 ) (cm 2 /g) (mm) 3 days 28 days 91 days

7 Table 7 shows that the use of IGCC to cement raw material doesn t cause any harmful influence. Judging from results of the cement test, the qualities of the cement is almost the same as the common cement. 5. DISCUSSION AND CONCLUSION 5.1 Glass phase The glass phase which was formed by quenching is difficult to characterize by X-ray analysis by every CCP. Earlier discussions only touched on how percentage of glass phases, without a good explanation of CCP reactions in each step. So in this study, we promote the new method by optical analysis and acid extraction tests etc. As shown in Fig.2(right) glass phase are determined by optical method. Three phases are distinguished, such as glass I, glass II, and crystal phase [1]. Glass I has low flux compositions, and glass II has high flux compositions which makes the basic character of Class C ash in ASTM standard. In 1989, Hemmings determined these Glass I and II (see Fig.3), but few research has done to promote. Relationships between Insol and SiO 2 +Al 2 O 3 +Fe 2 O 3 or Na 2 O+MgO+K 2 O+CaO(flux) in Table 1 are shown in Fig.4, that means Insol is a good parameter of showing the Glass II phases. SiO 4 AlO - 4 M n+ Fig. 3 Schematic structure of GlassI(left) and GlassII(right) [1] Insol* Insol* SiO2+Al2O3+Fe2O3 Na2O+MgO+K2O+CaO Fig. 4 Relationship between composition and Insol 5.2 Utilization to aggregates Because IGCC is lacking of fine grain (less than 0.6mm), some addition of fine particle is necessary. Or addition of simple grinding process to the IGC system will clear the 384

8 problem. Fewer amounts of Fe 2 O 3, CaO etc. compared to the Japanese criterion will not influence the use as aggregates and change of the criterion will solve this. Water absorption of IGCC is lower than other s and natural sand, this is because of low crack density. This had occurred by higher pressure and temperature (than other slug). If cooling velocity was lowered than the tested condition, crack density would decrease and crystallization would occure, and this will help achieve make desirable properties for aggregates. Since needle-like (Fig.1) is dangerous of transportation and operation of concrete work, elimination and/or crushing is in indispensable. And development of IGCC system will decrease the production of the needle-like particles. 5.3 Utilization to cement raw material The chemical composition of the IGCC is the same as the pulverized coal fly ash, which is recycled as cement raw material (2 million tons par year), and IGCC is mainly composed of glass phase that is reactive, therefore utilization to cement is in expectation. Because of the chemical component lack of SiO 2 compared to clay, addition of SiO 2 is necessary. The IGCC has particles than fly ash and has high grinding work index. These properties are demerit to utilize to cement raw material. In this case, more rapid quenching will be necessary to make cracks fragile. In our study, at least 3 phases in the IGCC, glass I, glass II, and crystal phases were recognized. Glass I has low flux compositions; Glass II has high flux compositions which makes the basic character of the. For civil engineering works, Pozzolanic reactions are important with hydration materials (ex: cement & concrete), but in the long term it is necessary to get the result of Pozzolanic reaction. But our method will need few hours with the glass content in the (Table1). It shall be useful to the possibility of changing the character of by the control of flux components. 5.4 Conclusions It will be too early to say conclusion by results of few lots, but we could find some tendencies. IGCC s have some different properties compared to pulverized coal ash. Three conditions will be important: (1) Coal and flux composition, (2) Gasification and quenching conditions, and (3) Preparation process of recycle and use. REFERENCES [1] Hemmings et al, On the glass in coal ashes, Materials Research Society Symp. Proceedings Vol113, 1989 [2] Kanazu T. et al, Study on the Application of Coal Gasification Slug to Cement and Concrete Fields, J.CRIEPI, 30, 1-50,