2013 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association

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1 Coal Combustion and Gasification Products is an international, peer-reviewed on-line journal that provides free access to full-text papers, research communications and supplementary data. Submission details and contact information are available at the web site The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association Web: ISSN# Volume# 5 (2013) Editor-in-chief: Dr. Jim Hower, University of Kentucky Center for Applied Energy Research CCGP Journal is collaboratively published by the University of Kentucky Center for Applied Energy Research (UK CAER) and the American Coal Ash Association (ACAA). All rights reserved. The electronic PDF version of this paper is the official archival record for the CCGP journal. The PDF version of the paper may be printed, photocopied, and/or archived for educational, personal, and/or non-commercial use. Any attempt to circumvent the PDF security is prohibited. Written prior consent must be obtained to use any portion of the paper s content in other publications, databases, websites, online archives, or similar uses. Suggested Citation format for this article: Behera, Snehasis, Sahu, A.K., Das, Sudipta, Senapatil, P.K., Mishra, S.K., 2013, Scale-Up Design and Erosion Studies of Bottom Ash in Pneumatic Conveying System. Coal Combustion and Gasification Products 5, 1-8, doi: /CCGP-D

2 ISSN journal homepage: Scale-Up Design and Erosion Studies of Bottom Ash in Pneumatic Conveying System Snehasis Behera*, A.K. Sahu, Sudipta Das, P.K. Senapati, S.K. Mishra Institute of Minerals and Materials Technology (CSIR), Bhubaneswar , Odisha, India ABSTRACT Pneumatic conveying characteristics and scale-up studies of the bottom ash from three thermal power plants, i.e., M/s Orissa Power Generation Corporation (M/s OPGC), M/s Indian Metals & Ferro Alloys Ltd. (M/s IMFA), and M/s Jindal Stainless Ltd. (M/s JSL), were carried out in a pneumatic conveying test rig at the Institute of Minerals and Materials Technology, Bhubaneswar, Odisha, India. A minimum conveying line inlet air velocity of approximately m/s was required for M/s OPGC, M/s IMFA, and M/s JSL bottom ash. The erosion rate of M/s OPGC and M/s JSL bottom ash was less in cast-iron bend compared with mild-steel bend, but for M/s IMFA the erosion rate was high and similar for both types of bends. Scale-up design was used to determine the variation in pressure drop and phase density at constant mass production flow rate in plant scale. Particle degradation size distribution studies also were carried out after conveying 2 t of bottom ash out of a total conveying of 16 t for each source of bottom ash. f 2013 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association All rights reserved. ARTICLE INFO Article history: Received 18 May 2012; Received in revised form 30 November 2012; Accepted 8 December 2012 Keywords: bottom ash; pressure drop; velocity; phase density; erosion; degradation 1. Introduction In thermal power plants in India, 593 Mt of coal is used to produce GW of power, and approximately 207 Mt of total ash is generated per year (Shah et al., 2005). Because bottom ash generation is 20% of total ash, approximately 41 Mt of bottom ash is generated per year. This ash is generally collected in a waterimpounded hopper and sluiced into a storage lagoon in slurry form. It can be conveyed pneumatically to the intermediate silo after crushing to,45 mm and then sent to the user industries for making building materials and for other construction purposes (Shah et al., 2005). Erosion of the plant by the conveyed product is the first problem during installation of a pneumatic conveying system. To minimize plant erosion, the abrasive products, such as silica, sand, fly ash, bottom ash, and alumina, must be conveyed at low velocity. Because the conveying air velocity increases along the length of a pipeline, the bends at the end of the pipeline are * Corresponding author. Tel.: snehasis_behera@ yahoo.com, sbehera@immt.res.in likely to fail first. While transporting bottom ash pneumatically through the pipeline, particle degradation takes place when particles hit the walls. Particle degradation that occurs during particle wall collision is dependent upon particle impact velocity, impact angle, number of impacts, size, the form and material of the particle, thickness, and deformation of the pipeline walls (Salman et al., 1992). This article presents the results of conveying and scale-up studies of the bottom ash from three power plants in Bhubaneswar, Odisha, India: M/s Orissa Power Generation Corporation (M/s OPGC), Jharsuguda District; M/s Indian Metals & Ferro Alloys Ltd. (M/s IMFA), Choudwar District; and M/s Jindal Stainless Ltd. (M/s JSL), Jajpur District. Before conveying of the bottom ash, characterization studies were conducted to examine particle size, particle density, bulk density, and moisture content. The scale-up studies were carried out from the results of conveying characteristics of the bottom ash. Erosion rate studies of mild-steel and cast-iron pipe bends were conducted at the last bend of the conveying pipeline. Approximate design equations and their comparison with scale-up design studies and particle degradation size analysis were made by doi: /CCGP-D f 2013 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association. All rights reserved.

3 2 Behera et al. / Coal Combustion and Gasification Products 5 (2013) Table 1 Chemical analysis of bottom ash samples (%ash) Chemical compound M/s JSL M/s OPGC M/s IMFA %Vol SiO Al 2 O TiO Fe 2 O K 2 O P 2 O MgO Na 2 O SO ppm V 2 O Cr 2 O BaO ZrO NiO SrO MnO Rb 2 O Y 2 O Fig. 1. Particle size distribution of all bottom ash. conveying 16 t of materials for each source of bottom ash to see how much particle degradation had taken place after 2 t of conveying. 2. Material Characteristics 2.1. Chemical analysis of bottom ash samples X-ray fluorescence was used to determine the elemental and chemical composition of the samples (Table 1). The main chemical components of a bottom ash were silica (65 68%) and alumina (24 27%), with lesser amounts of oxides of P, S, Ti, Fe, Ca, Mg, Na, and K. Other minor elements, such as V, Cr, Ba, Zr, Ni, Sr, Mn, Rb, and Y, were present in parts per million (Table 1) Description of power plants ash generation and particle shape The M/s OPGC, M/s IMFA, and M/s JSL power plants have a total installed capacity of 420, 108, and 250 MW, respectively. These plants generate bottom ash rates of 320, 760, and 90 t/day, respectively. was conveyed in lean slurry form of approximately 40% concentration by weight in a mmdiameter pipeline, except at M/s IMFA where the ash was piled up in stockyard and later taken by truck to fill a lowland area. Because the Fig. 2. Schematic view of the test rig at Institute of Minerals and Materials Technology, Bhubaneswar, India.

4 Behera et al. / Coal Combustion and Gasification Products 5 (2013) 3 Table 2 Results of all bottom ash carried out in the test rig facility at Institute of Minerals and Materials Technology, Bhubaneswar, India source Pressure drop (bar) Air flow rate (kg/s) Conveying air velocity (m/s) Inlet Exit Solids loading ratio flow rate (t/h) Power (kw) Volumetric flow rate (m 3 /s) M/s OPGC M/s IMFA M/s JSL Energy consumption (kwh/t) boiler is stoker coal fired at the M/s IMFA power plant, the generation of bottom ash was 90% and the remaining 10% was fly ash Moisture content, particle size, and particle and bulk density All bottom ash samples were dried to bring down the moisture content to,1% before charging into the hopper for pneumatic conveying studies. The particle size distributions of M/s JSL and M/s OPGC were determined using a particle size analyzer (Malvern, Worcestershire, UK), and the M/s IMFA bottom ash size distribution was determined by manual sieving. Figure 1 shows the particle size distribution of all bottom ash samples. The particle densities of M/s OPGC, M/s IMFA, and M/s JSL bottom ash samples were 1734, 1667, and 2086 kg/m 3 and the bulk densities were 803, 750, and 978 kg/m 3, respectively. 3. Pneumatic Conveying Test Facility at Institute of Minerals and Materials Technology (IMMT) A pneumatic conveying test rig (Figure 2) with a screw air compressor (0.12 m 3 /s, 700-kPa maximum capacity) was used for pneumatic conveying trials of different bottom ash samples. The rig has a 49-mm bore pipeline, 56-m horizontal length, and 1.79-m vertical length, and six bends. The test rig is instrumented with Fig. 3. Erosion of mild-steel bends by pneumatic conveying of OPGC, JSL, and IMFA bottom ash.

5 4 Behera et al. / Coal Combustion and Gasification Products 5 (2013) Fig. 4. Erosion of cast-iron bends in pneumatic conveying of OPGC, JSL, and IMFA bottom ash. Fig. 5. Particle size degradation of M/s IMFA bottom ash. Fig. 6. Particle size degradation of M/s OPGC bottom ash.

6 Behera et al. / Coal Combustion and Gasification Products 5 (2013) 5 at IMMT; results are presented in Table 2. All types of bottom ash can be conveyed in dilute phase only, where the solids loading ratio (phase density) falls between 6 and 8. Conveying line inlet air velocity for M/s OPGC and M/s IMFA was,18 m/s and 25 m/s for M/s JSL. Mass product flow was highest for M/s JSL at 2.6 t/h. Power (3.05 kw) and energy consumption (2.34 kwh/t) were lowest for M/s IMFA Erosion studies of bottom ash Erosion in pneumatic conveying bends are dependent on variables such as conveying velocity, particle concentration, particle size, particle shape, and bend geometry (Deng et al., 2005; Mazumder et al., 2008). Erosion studies of all bottom ash were carried out by measuring the loss of erosion in grams per tonne of conveying in two types of bend materials, mild steel and cast iron, and these bends were located in the last part of the conveying pipeline. Fig. 7. Particle size degradation of M/s JSL bottom ash. pressure gauges, differential pressure transducers, temperature gauge, rotameters, digitizer, and air flowmeter. 4. Results and Discussion of Pneumatic Conveying of Bottom Ash Testing of erosion and particle degradation of bottom ash from M/s OPGC, M/s IMFA, and M/s JSL were carried out in the test rig Erosion studies of bottom ash using mild-steel and cast-iron bends M/s OPGC, M/s IMFA, and M/s JSL bottom ash were conveyed in the test rig by using mild-steel and cast-iron bends incorporated at the last section of the conveying line. Figures 3 and 4 show total erosion in grams after 2 t of conveying, for a total of 8 t of conveying of all bottom ash materials at different air velocities, pressure drops, phase densities, and mass product flow rates for both cases of cast-iron and mild-steel bends. Erosion in the castiron bend was less than in the mild-steel bend, particularly for M/s OPGC. For M/s IMFA, maximum erosion occurred in both cast-iron Table 3 Scale-up design results of all bottom ash source Pressure drop (bar) Air flow rate (kg/s) Conveying air velocity m/s Inlet Exit Solids loading ratio flow rate (t/h) Power (kw) Volumetric flow rate (m 3 /s) M/s OPGC M/s IMFA M/s JSL Energy consumption (kwh/t) Table 4 Input data for bottom ash Summary of data Symbol Parameter M/s OPGC M/s IMFA M/s JSL Dp Estimate total pressure drop bar Gas T Air temperature K R Characteristics gas constant J/kgK m Viscosity of air kg/ms Pipe Lh Horizontal length m Lv Vertical length m Nb No. of bends k Bend loss coefficient e Pipe surface roughness mm d Diameter of pipeline m Flow m p Product mass flow rate t/h C1 Estimate inlet air velocity m/s p 2 Exit pressure bar a b Sum of entry, exit and bend loss Material r s Particle density kg/m 3 d s Particle diameter mm Unit

7 6 Behera et al. / Coal Combustion and Gasification Products 5 (2013) Table 5 Output data for bottom ash Symbol Parameter M/s OPGC M/s IMFA M/s JSL ma Air mass flow rate kg/s a Pressure loss factor Re Reynold s no f Pipeline friction coefficient L eq Equivalent length of pipe m DP a Air only pressure drop bar Dp Pressure drop bar w Phase density C 1 Inlet air velocity m/s C 2 Outlet air velocity m/s Unit and mild-steel bends. The erosion rate in the case of the cast-iron bend for M/s JSL was 2.1 g/t, for M/s OPGC it was 1.0 g/t, and for M/s IMFA it was 4.8 g/t. These values are less than those for the mildsteel bend, which were 3.7 g/t for M/s JSL, 3.7 g/t for M/s OPGC, and 5.5 g/t for M/s IMFA. At an average product flow rate of 1.6 t/h and conveying air velocity of 20 m/s, as were achieved in this pipeline, the bends would last for hours Particle degradation of bottom ash Sixteen tonnes of bottom ash from each source (M/s OPGC, M/s IMFA, and M/s JSL) was conveyed pneumatically in the test rig. Particle degradation size analyses were carried out after conveying 2 t of the total 16 t of bottom ash. The mean particle size of bottom ash from M/s IMFA (Figure 5), M/s OPGC (Figure 6), and M/s JSL (Figure 7) was reduced from 3.93 to mm, 212 to mm, and 242 to mm, respectively. Severe particle wall erosion took place in M/s IMFA bottom ash. 5. Scale-Up Design The pipeline transfers the bottom ash from intermediate reception hoppers to delivery silos. The reception hoppers are generally vacuum loaded from the duct hopper by a negative-pressure pneumatic conveying system. In total, the plant pipeline consists of 155 m of horizontal pipelines, 25 m of vertical pipeline, and eight 90u bends. The scaling parameters, i.e., horizontal distance, vertical lift, number and geometry of bends, and pipeline bore, were taken into account (see the Appendix for scaling equations). The scaling process was carried out in two stages. In the first stage, the scaling was done for pipeline geometry and included pipeline routing and bends that take into account the relative horizontal and vertical distances and the number of bends. In the second stage, scaling was in terms of pipeline bore to give the desired bottom ash flow rate (Pan and Wypych, 1992; Behera et al., 2000) Summary of scale-up design for all experiments at M/s OPGC, M/s IMFA, and M/s JSL Table 3 shows the scale-up design results for a plant pipeline of 150-mm bore pipeline, 155-m horizontal length, 25-m vertical length, and eight bends by using the data obtained in the test facility at IMMT for M/s OPGC, M/s IMFA, and M/s JSL bottom ash samples (Table 2). 6. First Approximation Design Methods The first approximation method for pneumatic conveying system design is based on air only pressure drop data. These equations (Mills, 1990; also see the Appendix) are used to find out the pressure drop and air mass flow rate value by taking into account the mass product flow rate at 7.30, 5.48, and 4.46 t/h for M/s OPGC, M/s IMFA, and M/s JSL, respectively, for plant design calculations. These figures of mass product flow rate have been taken from scale-up design results. Excel programming input and output data for all bottom ash are shown in Tables 4 and Comparison between First Approximate Equations and Scale-Up Design Equations Figure 8 shows the pressure drop and phase density values of all bottom ash. The trend lies close to the scale-up design data, but prediction of phase density or mass product flow rate values was high compared with scale-up design data because the conveying air inlet value is same for both the cases. 8. Design Calculations of a Typical Bottom Ash Collection and Conveying System Fig. 8. Comparison of pressure drop and phase density between scale-up and design equations in bottom ash conveying. A schematic of the entire ash collection and conveying system is shown in Figure 9. from the boiler is collected in three hoppers. Ash outlet is through a set of four grated doors. A single roll crusher below this gate crushes the ash to reduce the particle size to

8 Behera et al. / Coal Combustion and Gasification Products 5 (2013) 7 Fig. 9. Design results of the bottom ash collection and conveying system. 9 mm for pneumatic conveying. Crushed ash is pushed to a screw feeder that controls ash feed into the vacuum conveyor (Rastogi, 1997; Shah et al., 2005). The pneumatic conveyor consists of 250- mm pipe through which materials are transferred under vacuum to a silo approximately 180 m away. The results of vacuum conveying 9-mm bottom ash where an ash transfer truck is interposed in the pipe approximately 30 m from the feed hopper are given in Figure 9. The truck has a collection tank and a pair of pipe headers (supply and return) above it. When docked, it becomes part of the conveying path and collects coarse ash (most of the total ash), whereas fine ash continues with the return air passing on to the silo. The 45-mm fine ash design results are mentioned in Figure 9. On the top of the silo is a filter/separator that separates the fine ash and transfers it into the silo. Clean air passes on to the vacuum source, a twin lobe type mechanical exhauster. Ash from the silo is taken by trucks to a landfill site on the power plant premises. 9. Conclusions with a mean particle size of 212 mm, 3.93 mm, and 242 mm from M/s OPGC, M/s IMFA, and M/s JSL thermal power plants, respectively, can be conveyed in a dilute phase mode positive-pressure pneumatic conveying system with 50-mmdiameter pipeline. These bottom ashes were successfully conveyed with product flow rates of up to 2 t/h at a low conveying line pressure drop up to 80 kpa; a minimum conveying line inlet air velocity of 17 m/s is required. The erosion rate of M/s IMFA bottom ash is very high for both mildsteel and cast-iron bends. In other cases, cast-iron bends erode less than mild-steel bends. So, all bends must be reinforced with wearresistant materials and, even then, wear can be expected at some bends. The scale-up design studies show that this product cannot be conveyed in dense phase. The solids loading ratio value decreases by increasing conveying distance. For the plant pipeline the maximum phase density that can be expected with a conventional blow tank system is approximately 3. Acknowledgments The authors thank Prof. B.K. Mishra, Director, Institute of Minerals and Materials Technology, Bhubaneswar, India, for permission to publish this paper. We also thank Dr. Vimal Kumar, Head Flyash Mission, DST, Flyash Utilization Unit, Government of India, for funding to study the behavior of bottom ash. References Behera, S., Das, S., Jones, M.G., Mohanty, R.C., Scaling up of conveying parameters using computer aided design from test rig data to commercial design parameters for crushed bath. In: International Conference on Powder & Bulk Solids Handling. IMechE, London, U.K. Deng, T., Li, J., Chaudhry, A.R., Patel, M., Hutchings, I., Bradley, M.S.A., Comparison between weight loss of bends in a pneumatic conveyor and erosion rate obtained in a centrifugal erosion tester for the same materials. Wear 258, doi: /j.wear Mazumder, Q.H., Shirazi, S.A., McLaury, B., Experimental investigation of the location of maximum erosive wear damage in elbows. Journal of Pressure Vessel Technology 130, doi: / Mills, D., Pneumatic Conveying Design Guide. Butterworths, London, U.K. Pan, R., Wypych, P., Scale-up procedures for pneumatic conveying design. Powder Handling and Processing 4, Rastogi, S., Pneumatic conveying of bottom ash. Powder Handling and Processing 9, Salman, A.D., Verba, A., Mills, D., Particle degradation in dilute phase pneumatic conveying systems. In: Proceedings of the 18th Powder and Bulk Solids Conference, Chicago, IL, pp Shah, S.R., Rastogi, S., Mathis, O., Applications of dry bottom ash removal and transport for utilization. Fly Ash India, New Delhi, India. wikipedia.org/wiki/electricity_sector_in_india, accessed June 2012.

9 8 Behera et al. / Coal Combustion and Gasification Products 5 (2013) Appendix See Nomenclature table for an explanation of equation symbols. Scaling equations C 1 ~ _m atf T 1 2:737d 2 p 1 m=s ð1þ L e ~L h zð2 L v ÞzN b L eb m ð2þ _m ppp ~ _m ptf Dp pp Dp tf L e tf L epp ð3þ Dp~Dp a (1za) Re~ 4m a pdm a~w T 1:5 273:15 m~0:006515: (Tz105:65) ð15þ ð16þ ð17þ ð18þ _m ppp ~ _m ptf Dp pp d 2 pp ð4þ Dp tf d tf Nomenclature _m app ~ _m atf d 2 pp kg=s ð5þ d tf P~202 _V 0 ln p 1 p 0 kw ð6þ " Dp a ~ 1:0z 1:34 Y 0:5 # _m2 a tf d {1:0 100 kpa ð7þ w~ m: p tf 3:6 _m atf ð8þ y~ 4 fl z X k d First approximation design equations ð9þ _V 0 ~ m a _ RT 0 p 0 m 3 s ð10þ " # f ~0: z 20,000 e 1 d z Re L eq ~L h z2l v z bd 4f m a ~ pd2 p 1 C 1 4RT ð11þ ð12þ ð13þ Dp a ~ p 2 1 z 16 p 2 4fL eqm a RT d 5 {p ð14þ Symbol (unit) C (m/s) d (m) D (m) f k Parameter Conveying air velocity Pipeline bore Pipe bend diameter Pipeline friction Bend loss coefficient (for smooth pipe and 90u bends with D/d 5 10, k 5 0.1) Pipeline length Air mass flow rate Mass product flow rate No. of bends Air pressure Power Actual temperature L (m) m a (kg/s) m p (t/h) N p (kpa) P (kw) t (uc) T (K) Absolute temperature 5 (tuc +273) V (m 3 /s) Volumetric flow rate of air Greek a Pressure loss factor b Sum of entry, exit, and bend loss Y Pipeline friction loss coefficient D Difference w Phase density m (Pa?s) Viscosity of air e Pipe surface roughness (0.015) gk Bend losses 5 N b?k Subscripts 1 Pipeline inlet, material feed point 2 Pipeline outlet, material discharge point a Air only b Bends e Equivalent value h Horizontal min Minimum value 0 Free air conditions P kn/m 2 T K pp Plant pipeline tf Test facility v Vertically up