PRACTICAL ISSUES OF GRINDING

Transcription

1 PRACTICAL ISSUES OF GRINDING LC 3 Doctoral school PALAS KUMAR HALDAR 30 th June2015 1

2 About myself Studies Experience B.Sc in Chemistry B.Tech in Ceramics M. Tech in Ceramics MBA in Operation research PhD area- Electro ceramics Assistant general manager (technology management) in TARA from April 2014 onwards Senior Design engineer in TDK from November 2006 to March Area of experience- R&D, Quality, process, production & environment product quality management (EPQM) 2

3 Contents Introduction Objectives Types of comminution Theory of grinding Grinding energy and efficiency Grinding factors Hardness LC 3 production in India Conclusions 3

4 Introduction Grinding is a part of comminution which involves size reduction of materials by various forces like impact, shear,abrasion, compaction etc. Crushing is normally accomplished by compression/compaction of the materials against rigid surface. Grinding involves impact, shear & abrasion of particles by grinding media. Intergrinding usually implies to grind together when two or more different materials are present in the system. ( cement blending by ball mill) 4

5 Objectives To prepare the sample by reducing size for further processing To improve surface area of the particles leading to higher reactivity To separate impurities from valuable materials ( mineral processing)/ concentration 5

6 Types of Comminution Comminution Crushing Grinding Primary crushing (1m>P80>100mm) Secondary crushing (100mm>P80>6mm) Coarse grinding Fine grinding (6mm>P80>500µ) (500µ-> P80> 5µ) Ball mill Jaw crusher Cone crusher Hammer crusher Gyratory Crusher Ball mill Vertical roller mill Hammer mill Rod mill Attrition mill 6

7 Jaw crusher Ball mill 7

8 Jaw crushing Ball milling 8

9 Theory of grinding Work index The amount of energy (KWh/t) required to reduce a material from one size to another size. Higher work index indicates more hardness of the material. Kick s law (d> 50mm) W k = c K [ln(d F )-ln(d P )] Bond s law (50mm>d>0.05mm) W B = C B (1/ d P - 1/ d F ) W - work index C - Grinding coefficient d P - Product size(d 80 ) d F - Feed size(d 80 ) C K C B (d Bu ) -0.5 C R - 0.5C B (d Bu ) 0.5 Rittenger s law ( d< 0.05 mm) W R = C R (1/d P - 1/d F ) 9

10 Average work index 10

11 Grinding energy & efficiency Energy required during grinding (Bond s law) E= 10W B (1/ d P - 1/ d F ) Efficiency of different grinding devices Beater mills - 17% 25% Roller mills - 7% 15% Ball mills - 6% 10% Jaw crusher - 3%-5% 11

12 Energy consumption vs surface area of a typical cement grinding 12

13 Grinding factors Hardness Feed material needs to be softer than grinding media Brittleness coefficient (example) C 3 S(4.7)> C 3 A(2.9)>C 2 S(2.0) Ratio of grinding media to charge (by wt.) Usually grinding media : charge= 3:1 RPM of grinding mill % of critical speed ( V c = 42.29/ d, d is inner diameter of mill in m) Size ratio Dia of media: dia of feed = 6:1 (typical grinding) 13

14 Hardness Resistance to permanently indenting the surface. Large hardness means: --resistance to plastic deformation or cracking in compression. --better wear properties. 14

15 Conversion of hardness factor ASTM E Volume Standard Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, Superficial Hardness, Knoop Hardness etc. 15

16 Various hardness testers 16

17 Pilot production of LC3 in India Quantity- 130 Tones Place - Triranga Cement Industries (Gujarat) Time- January

18 Pilot production in India Process flow diagramme Picture of grinding assembly Weighing & batching Ball milling >200 µ Separating through classifier <200 µ Storage in silo Bagging 18

19 Pilot production in India Weighing Ball milling 19

20 Pilot production in India Composition Existing process parameters Clinker- 50% Calcined clay- 31% Lime stone- 15% Gypsum- 4% Weighing sequence of raw materials 1. Clinker 2.clay 3. Lime stone 4. Gypsum Capacity of ball mill- 5 T/ h RPM of ball mill- 24 Throughput time(ball mill)- 25min Feed size mm Total length of the mill 7.725( )m Grinding media- Hardened steel ball Size of grinding media in chamber mm (4 ton) Size of grinding media in chamber mm (10 ton) Inner dia. of mill 1.8 m Total electric power 397 HP 20

21 Pilot production in India Productivity of LC 3 LC3 production /h: 16 T Product Quality of LC 3 Color : Reddish grey Average Blaine value : 495 Size fraction +90µ : 4% -45µ : 16.52% LOI : 6.75% Initial setting time : 110 min Water consistency : 33.75% Final setting time : 335 min 21

22 Pilot production in India Technical Set back Limited capacity of pipe lines linked to ball mill, classifier and cement storage silo Lower capacity of classifier Lack of synchronisation between ball mill and classifier Mismatch of grindibility between OPC composition and LC 3 blend and hence the productivity Energy consumption (MJ/t of cement produced) Comparison of grinding energy consumption Restricted flowability of clay due to T Cem : Triranga Cements, Rajkot increased fineness LC3 : Low Carbon Cement Legend: Ind. Av. ACC 0 Ind. Ave. ACC (OPC) Indian Industry Average ACC (PPC) T Cem (OPC) T Cem LC3 (20/1) T Cem LC3 (21/1) : (Touil et. al) : ACC Ltd. Bhabua grinding unit (Bihar) T Cem LC3 (22/1) T Cem LC3 (24/1)

23 Conclusion Grindibility of LC 3 is higher than that of OPC from same clinker leading to higher productivity of LC 3. Grinding energy consumption of LC 3 is lower than that of OPC. Both limestone and calcined clay are softer than clinker which improve grinding efficiency and productivity. Blending process of LC 3 needs to be modified in an optimised way. 23

24 Thank you LC3 PROJECT OFFICE EPFL STI IMX LMC MXG 211 Station 12, Swiss Federal Institute of Technology Lausanne, 1015 Lausanne, Switzerland Jérôme Daniel Laffely