Basics Grinding Pressure Vrm Ws 2008

Basics Grinding Pressure

VRM Workshop San Sebastian 2008 Author: Karl-Heinz Boes – CMS/MPT

© 2007 Holcim/Switzerland

Overview Hydraulic system VRM - Loesche

Roller Accumulator Accumulator Piston

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Basics Grinding Pressure

30.07.2007 KHB Basics Grinding pressures.ppt

Pressure and Counter Pressure

Hydraulic Pressure

Counter Pressure © 2007 Holcim/Switzerland

Basics Grinding Pressure

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30.07.2007 KHB Basics Grinding pressures.ppt

Function of Counter Pressure  Avoids cavitations in hydraulic systems in case of

heavy vibrations  Supports stable pressure distribution  If counter pressure and working pressure are

identical, roller is slowly lifted (effect of piston rod which reduces area on working pressure side)  Counter pressure is typically 10-15 [%] of working

pressure  Too low counter pressure can lead to increased

vibration problems 4

© 2007 Holcim/Switzerland

Basics Grinding Pressure

30.07.2007 KHB Basics Grinding pressures.ppt

Working Pressure Diagram – Example Loesche

Optimum settings for this mill:

47 bar Operational pressure 10 bar counter pressure Result: 760 kN of working pressure (weight of roller not considered)

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© 2007 Holcim/Switzerland

Basics Grinding Pressure

30.07.2007 KHB Basics Grinding pressures.ppt

Leverage of Rockerarm – Example Loesche

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Basics Grinding Pressure

30.07.2007 KHB Basics Grinding pressures.ppt

Leverage of grinding Pressure Polysius / Pfeiffer

α

Here Leverage = cos α (0.98) © 2007 Holcim/Switzerland

Here Leverage = 1

Basics Grinding Pressure

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30.07.2007 KHB Basics Grinding pressures.ppt

Grinding Pressure  The Grinding Pressure is the result of:

Roller weight (plus frame etc.)

Hydraulic pressure - Counter pressure = Working Pressure

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© 2007 Holcim/Switzerland

Basics Grinding Pressure

30.07.2007 KHB Basics Grinding pressures.ppt

Specific grinding Force  Grinding Pressure per Roller: GP = Hydr. Force [kN] + Roller weight [kN] + Frame weight [kN]

Specific Pressure = WR

GP DR

WR * D R

Guide Value: < 800 kN/m2 9

© 2007 Holcim/Switzerland

Basics Grinding Pressure

30.07.2007 KHB Basics Grinding pressures.ppt

Accumulator (Nitrogen) Pressure 

‘Springs’ in the hydraulic system



Typically 50-60 [%] of operational pressure



Effect on vibrations, shocks, stresses of mechanical equipment

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© 2007 Holcim/Switzerland

Basics Grinding Pressure

30.07.2007 KHB Basics Grinding pressures.ppt

Loesche Tension Diagram of Accumulator Pressure

Operating Pressure (P2)

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© 2007 Holcim/Switzerland

Basics Grinding Pressure

30.07.2007 KHB Basics Grinding pressures.ppt

Guidelines accumulator pressure  Settings of accumulator pressure allow for certain

working pressure range (+/- 15 %) only  Uneven nitrogen pressure distribution can affect

grinding tools (uneven wear) and increase vibrations  Too high accumulator pressure can have negative

draw backs on vibration peaks (become larger, shock effect on equipment is bigger)  Too low accumulator pressure pressures can lead

to high tensions in mechanical equipment  If it is intended to change working pressure

significantly, accumulator pressure has to be adapted first (requires mill stop) 12

© 2007 Holcim/Switzerland

Basics Grinding Pressure

30.07.2007 KHB Basics Grinding pressures.ppt

Example

Operating Pressure (P2)

Example:

Pressure old 115 bar – now 95 bar N2- pressure must be reduced from 70 to 45 bar © 2007 Holcim/Switzerland

Basics Grinding Pressure

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30.07.2007 KHB Basics Grinding pressures.ppt

Vertical Roller Mill Calculations

HGRS VRM Calculation Sheet Plant : Mill :

Standard RM

Roller mill characteristics Supplier Size of Mill Material Production Fineness Moisture Spec. energy consump. mill Motor power (installed) Roller Mill Data Table diameter nominal Grinding track diameter Roller diameter Roller width Number of rollers Table speed spec. speed (relative to D m) Hydraulic cylinders number Diameter cylinder Diameter piston rod Rocker arm leverage Weight of compl. roller Gas flow estim. (fan operation) Gas flow estim. (fan dimens.) Casing diameter Open nozzle area, max. Material characteristics

G f m E sp Pi Dn D m1 D m2 Dr Wr ir n c ic dc dr l1/l2 Gr V fo V fd Dc An

Date : Visa :

Loesche Plant altitude: LM46.4 factor: Rawmaterial 330 [t/h] 10 [%] R 90 µm 12.0 [%] H2O 7.3 [kWh/t] motor shaft 3000 [kW] 4.64 [m] 3.71 [m] [m] 2.08 [m] 0.88 [m] 4 [-] 25.5 [min-1] 49.1 [-] 4 560 [mm] 229 [mm] 0.750 [-] 26 [t] 670'000 [m³/h] 737'000 [m³/h] 6.30 [m] 4.54 [m²]

out of hydr. pressure Hydraulic pressure operation ph 66 [bar] Grinding force per roller F1 1'271 [kN] Spec. grinding force k1 695 [kN/m²] Material pressure L1 5 [N/mm²] Power absorbed operation P ab1 2'409 [kW] Power ratio: absorbed - installed 0.80 [%] Reference values Density before roller r1 1.45 [t/m³] Density after roller r2 1.90 [t/m³] Alpha/Beta ratio 2.8 [-] a/b Bed thickness s 120 [mm] Nip angle 15.33 [°] a Attack angle 5.49 [°] b

© 2007 Holcim/Switzerland

May 07 KHB

80 45 42

Zf= v=

0 [m] 1 [-]

[%] D n [%] D n [%] D n [%] D r

Differ.

13.23 4.95 78 10 66

[m/s²] [m/s] [bar] [bar] [bar]

V fo spec. Dust ex mill vc vn

2.03 542 5.4 37

[m³/kg] [g/m³]

Main pr. Count. pr.

[m/s] [m/s]

out of spec. energy F2 k2 L2 P ab2

1'271 695 5 2'409 0.80

s/Dr µ

[kN] [kN/m²] [N/mm²] [kW] [%]

0.058 [-] 0.096 [-]

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Conclusions  Correct settings of grinding and accumulator

pressure are vital for stable operation  Far too low or too high accumulator pressures can

lead to  

Increased vibration Mechanical failures

 Too high hydraulic pressure increase the

fluctuations of torques and micro vibrations in the main reducer and must be avoided (increased risk of mechanical failure in main reducer)  Too low counter pressures can lead to mechanical

failures and increased vibrations 15

© 2007 Holcim/Switzerland

Basics Grinding Pressure

30.07.2007 KHB Basics Grinding pressures.ppt