PETROGRAPHIC CHARACTERISTICS OF COAL-BIOMASS BLENDING COMBUSTION

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1 Proceedings of the Asian Conference on Thermal Sciences 2017, 1st ACTS March 26-30, 2017, Jeju Island, Korea PETROGRAPHIC CHARACTERISTICS OF COAL-BIOMASS BLENDING COMBUSTION Isworo,Yanuar Yudhi. 1, Kim, Jong Ho. 1, Jeon, Chung Hwan 1,2* ACTS-P School of Mechanical Engineering,Pusan National University,Busan, South Korea 2 Department of Mechanical Engineering, Pusan Clean Coal Center, Pusan National University, Busan, South Korea Presenting Author: yanuar.yudhi@gmail.com * Corresponding Author: chjeon@pusan.ac.kr ABSTRACT Coal-biomass blending issues were still having attractiveness in coal power plant field up to now. One of those issues is the combustion characteristics between single and blending case for each materials. Furthermore, one of the advantages of blending coal with biomass is something very valuable for environment friendly matters, that is reducing NOx, CO 2 and other particulate emission. Based on that consideration, the characteristics of coal-biomass blending case is become important parameters to consider during combustion, such as coal-biomass reactivity, air emission (NOx, CO 2, etc). In this study, we use the petrographic microscope examination to deeply know the correlation between coal and biomass materials association include macerals and biomass particles within raw blending sample and its char respectively, and will try to correlate with combustion parameters such as ignition temperature, peak temperature, and burnout temperature, as well as also char reactivity. Different biomass type will also become focus on investigation, furthermore to conclude which biomass type indicate better combustibility if blending with different type of coals. KEYWORDS: Coal-biomass blends, petrographic microscope, macerals, ignition temperature, peak temperature, burnout temperature, char reactivity 1. INTRODUCTION The co-combustion of coal-biomass blends is a technological option for taking advantages from both fuels in term of each combustion characteristics. The main fundamental research for coal-biomass blending is the identification of single and both blending case combustion characterization. Such research will become the initial evaluation on boiler design aspects related with boiler performance and maintenance. Starting from the facts that coal is non-homogenous characters even though within the same rank, it will give different behavior during its utilization. The aspect of coal petrographic could become the solution to knowing of why coal could have different behavior during coal utilization. The reason is because coal composition must be different for each coal, and the coal composition especially the organic particles (coal macerals) are the responsible for combustion process. By knowing coal macerals composition and other petrographic characters for each coal, we could give some technological input for boiler performance and could possibly give fuel character prediction before using it as fuel feed. Up to 20% coal feed at coal fired power plant could be replaced by biomass without implying costly investment for redesigning the existing boiler units [1]. Coal-biomass blending offer advantages including: 1

2 a) reduced costs of generating electricity, b) reduced CO 2 emissions, which are responsible for the greenhouse effect, and c) reduced SO x, NO x, and particulate matter emission [2]. This study presents the results of coals from low to medium rank coal (sub-bituminous b-c, according to ASTM coal classification) representing three coals and two types of biomasses, Wood pellet and EFB (Empty fruit brunch). The results will represent the single raw coal and biomass combustion profile respectively and also the blending case within two different blending ratios. The combustion profiles will be compared and correlate with petrographic analysis (vitrinite reflectance, maceral composition, petrofactor), and the expected result will be which one in the case of reactivity will be better between two types of biomasses blending with different coals During combustion process, char is influencing most of the burnout behavior, so that the reactivity of the char is one of key points in solid fuel combustion. In this study, the characteristics of the char formed from the previous stage on combustion process called devolatilization was also studied, in order to know which char morphology was responsible for the reactivity, and which char formed from both biomasses. 2.1 SAMPLES PREPARATION 2. EXPERIMENTAL Three coals and two biomasses were selected for the study, three coals with slightly same rank, determined from it mean maximum vitrinite reflectance (Ro mean-max ), and two different biomasses, Wood Pellet and EFB (Empty fruit brunch) Chemical Analysis Proximate analysis and Gross Calorific Value was done by following ASTM standard. The chemical data of the coals and biomasses respective are shown in Table Petrographic Analysis Petrographic Analysis of coal and biomass samples were started by making polished sample by mixing each representatives single coal and biomass and also for blending case (75 90 µm), with epoxy resin (liquid) and chemical reagent hardener to fasten solidification process and molded it into special design moulder cup (31.7 mm diam). After sample dried, then grinding and polishing using automatic grinderpolisher with several grit paper steps from coarse to fine and if all grit paper already done for about 1 2 minutes, then polishing stages using special design polishing pad/material mixed with polishing liquid to produce very fine/smooth surface, until its ready as polished surface to run next microscopic analysis step. Vitrinite reflectance, coal maceral and biomasses composition were done using ZEISS Axioscopemicroscope equipped with CRAIC microspectrophotomer using white light and UV-light as source light. All the procedures for petrographic analysis were referred to ASTM D Thermal Analysis, DSC/TGA/DTG Thermogravimetric analysis was done by the TGA Q600 operating at atmospheric pressure. The system is controlled by a compatible PC, which resisters the temperature by a thermocouple placed in the alumina crucible, suspended from a highly sensitive horizontal balance located in the casing of the TGA apparatus, and heated to the reaction temperature. Sample weight is continuously recorded by the PC data acquisition system until the experiment is terminated at 100% conversion. A 15 ± 0.1 mg coal sample was heated to 850 C at 20 C/min in air atmosphere with a flow rate of 15 ml/min. The thermal parameters (e.g. characteristic temperature and maximum rate of mass loss) were derived from combustion profiles. The characteristic temperatures were designated as follows: Ti = initial temperature where mass loss reaches a rate of 1% per minute, Tp = peak temperature at the maximum weight loss rate, Tb = burnout temperature where DTG profile reaches a 1% combustion rate at the tail-end of the profile The weight loss rate was calculated by the expression: 2

3 = (1) Where Wo is the initial sample mass, is the weight difference per time unit Activation Energy (E a ) was calculated by using the Arrhenius equation, =Aexp 1 x (2) Where A is pre-exponential factor, E is activation energy, T is temperature, t is time, x is weight loss fraction, that can be calculated by x= (3) Where Wo is the original coal mass prepared for each single experiment; Wt is the mass at time t or T, and Wf is the final weight mass at the end of combustion process. And for a constant heating rate H, H = dt/dt, rearranging Eq. (2) and integrating give: ln =ln 1 (4) Since it may be shown that for most values of E and for the temperature range of combustion process, the expression ln[ar/he(1-2rt/e)] in Eq.(4) is essentially constant, if the left side of Eq.(4) is plotted versus 1/T, a straight line may be obtained if the process can be assumed as a first order reaction. From the slope, -E/R, the activation energy E can be determined, and by taking the temperature at which Wt = (Wo + Wf)/2 in the place of T in the intercept term of Eq.(4), the preexponential factor A can also be determined. Fig. 1. Thermogravimetric Analyzer scheme 3. RESULTS AND DISCUSSION Table 1 Coal-Biomass Properties Samples/ Adb (wt%) Parameters WMG BERAU TRAF WOOD P EFB Moist

4 VM Ash FC Fuel Ratio C H O N S H/C GCV (Kcal/Kg) Table 2 Combustion Profile of Single Samples (Coal and Wood Pellet) SAMPLES Ti Tb T 1/2 Tp EA Max Weight Loss Rate WP WMG Berau Traf From the combustion characteristics, for single coal case, the reactivity is as follow : WP > WMG > Berau > Traf Biomass Particles Under UV-Light Biomass Particles Under White-Light Biomass Particles Under UV-Light Biomass Particles Under White-Light Fig. 1 Microscopic character of Wood Pellet particles ( mag) Sample : Berau; Ro: 0.45 Telovitrinite-Textinite Sample : Berau; Ro: 0.18 Detrovitrinite-Attrinite 4

5 Fig. 2 Vitrinite Macerals, Sample: Berau Sample : WMG; Ro: 0.25 Telovitrinite-Textoulminite Sample : WMG; Ro: 0.15 Detrovitrinite-Attrinite Fig. 3 Vitrinite Macerals, Sample: WMG Sample : TRAF; Ro: 0.65 Telovitrinite-Textinite Sample : TRAF; Ro: 0.54 Telovitrinite-Textoulminite Fig. 4 Vitrinite Macerals, Sample: TRAF 3. CONCLUSIONS Petrographic analysis in the coal combustion utility was able to explain the reactivity of different coal even within the same rank in the relation with coal macerals reactivity. For char reactivity, petrographic factor has well correlated to explain the combustion characteristic during char combustion phase, include in the blending case. Char morphology analysis could also use as prediction for combustion reactivity, for coal macerals and also biomass materials, and their correlation under petrographic microscope. REFERENCE [1] Zhou, Limin., Wang, Yiping.,Huang, Qunwu., and Cai, Junqing., Thermogravimetric Characteristics and Kinetic of Plastic and Biomass Blends Co-pyrolisis, Fuel Processing Technology 87 (2006) [2] C.A.Ulloa, A.L.Gordon, X.A. Garcia., Thermogravimetric Study of Interaction In The Pyrolysis Of Blends Of Coal With Radiata Pine Sawdust, Fuel Processing Technology 90 (2009) [3] J.G. Bailey, A. Tate, C.F.K. DIessel and T.F. Wall, A Char Morphology System With Applications To Coal Combustion, Fuel, 1990, Vol 69, February [4] Brien G.O', H.Beath, Microscopic Characterisation Of Coal/Biomass Blends, Cooperative Research Centre For Coal In Sustainable Development (CCSD), Research Report 44, February