CEMENT PRODUCTION PROCESS

The ChallengeThe capacity of the vertical raw mill isoften the limiting factor for clinkeroutput – when a plant upgrades the kilnsystem, the raw mill frequently becomesa bottleneck. Rather than investing in anentirely new vertical mill to keep pace,there is a very limited set of possibilitiesin upgrading existing mill capacity insmaller steps. For example, older millscan achieve a modest capacity increaseby upgrading the integrated separator

ROLLER MILL

Vertical Roller Mill (VRM) - 3 Sections

1. Separation

2. Grinding

3. Drive

Separation

FeedMaterial

Grinding

Drive

Raw mealExhaust gases

Transport

Drying

gases

Energy

Hot

Vertical Roller Mill (VRM) - Detailsfeed gate(air lock)

mill casing

waterinjection

dam ring

louvre ringnozzle of

material scraper

mill outlet duct

speed reducer withtable bearingand motor

clutch

grinding table

hot gas inlet

hydraulic cylinder

table liner

roller with tyreor segments

roller axlerocker arm

discharge flapseparator

tailings cone

separatorguide vanes

cage rotorseparator

product dischargemill exhaust

VRM - Working principle

Vertical roller mill

Feed size:f (Roller Ø )

Material bed

Feed material

Max Particle size in feed: 5-8 % of roller diameter

Grinding force =

Roller weight + (pressure) Force

Table moves with drive

Roller rolls freely with table

VRM - Material Flow insideGas & Product Material

Feed Material

Separator Rejects

Internal Circulation

Large Material falls through to scraper

Internal gas flow

Material & Gas

Material

Gas

Separator:

removes fine material

rejects coarse material

VRM - Some Common Mill Configurations

G.Pfeiffer Loesche FLS Atox Polysius

static separator conventional rotor type cage rotor typewith guide vanes

F T

P

F F FT T

P

F F

T

P

T F

P

F =

P =

T = Tailings

Product

Feed

F T

VRM - Built-in SeparatorCage Rotor typeConventional

Rotor type

Static type

Separation control:

1. Vane adjustment

2. Speed control

Separators of 3rd Generation (Vertical roller mill)

Guide vane system

Reject cone

Cage rotor

VRM - Separator Fotos

Angle affects product sizing

Rotor speed affects product fineness

Rotor seal affects separator efficiency

Potential Problems/clogging

Cage rotor separator casing

partly clogged guide vane system

Material deposits due to insufficient airflow or airflow distribution

VRM - External Circulation

Used for reducing gas flow pressure lost over the mill

(less pneumatic internal circulation)

collecting conveyor

fresh feed

louvre ring

scraper

bucket elevator

VRM - Example flow-sheet

Control points

1 gas flow

2 pressure

difference

3 return gas

flow pressure

4 outlet

temperature

5 external

recirculation

VRM - Control & Maintenance

Control

Gearbox - Vibration monitor

- Temperature monitor

Gas flow - Temperatures & pressures

Hydraulics - Pressures

Maintenance

Wear - Rollers & Table

- Separator (sealing!) & Housing

Lubrication & Hydraulics (filters and seals)

grinding aid DEG

[t]

[kW]

[t/h]

[mbar]

[°C][%] [l/min]

[t/h] [t/h]

[%]

[cm2/g]sampler

[%R][l/h]

[mbar]

[°C]

[kW] [%]

[°C]

Hot gas[t][t] [%] [%] [bar]

[mbar]

[min-1]

[min-1]

[l/h]

to cementsilo

fresh air

Clinker Gypsum

[mbar]

[min-1]

grinding aid DEG

[t]

[kW]

[t/h]

[mbar]

[°C][%] [l/min]

[t/h] [t/h]

[%]

[cm2/g]sampler

[%R][l/h]

[mbar]

[°C]

[kW] [%]

[°C]

Hot gas[t][t] [%] [%] [bar]

[mbar]

[min-1]

[min-1]

[l/h]

to cementsilo

fresh air

Clinker Gypsum

[mbar]

[min-1]

grinding aid DEG

[t]

[kW]

[t/h]

[mbar]

[°C][%] [l/min]

[t/h] [t/h]

[%]

[cm2/g]sampler

[%R][l/h]

[mbar]

[°C]

[kW] [%]

[°C]

Hot gas[t][t] [%] [%] [bar]

[mbar]

[min-1]

[min-1]

[l/h]

to cementsilo

fresh air

Clinker Gypsum

[mbar]

[min-1]

VRM - Control

Outlet duct Inlet chute

Mill housing

Armour & nozzle rings

Rollers and table liners

Separator cone

Separator

Scrapers

Vertical roller mill internals suffering from wear

Roller and grinding track liners

Roller liners:

Monobloc

Segments

Grinding track liners:

Monobloc

Segments

• Nihard 4

• High Chromium alloys

Wear resistance material alternatives

% C % Cr % Ni Weldable

< 3.5 < 10 < 6.5 yes

% C % Cr % Other Weldable

< 3.6 < 17 Mo + Ni yes

< 2.6 < 20 Mn No

< 3.5 < 28 < 1.2 No

Example

Chromodur, FMU18, VegalineV16s

FMU 52

FMU 46

Wear resistance material alternatives

• Metallic inserts roller liner

Hard metallic insert

Soft material base

• Ceramic inserts roller and grinding track liners

Wear resistance material alternatives

Metallic base (High Cr)

Ceramic insert

Wear rate monitoring

Minimum allowed thickness

2’500 [h] = 50 [mm]40 [mm] = ~ 2’000 [h]

Wear resistance material alternatives

• Surface reconditioning on grinding track and roller liners

% C % Cr % Others Weldable

< 5 < 29 Ni, Mo yes

< 5.5 ~ 22 6 – 7 Ni yes

Example

Vautid 100, HC-O

CN-O, CNV-O

VRM - Accessories

Rotary valve Pendulum valve

Weigh belt Metal extraction

Reduces false air entering with feed material. Good for dry, small size material.

Reduces false air entering. Better for lumpy or humid feed material.

Weighs the passing material ensuring a continuous grinding bed in the mill

Metal objects damage the roller & table. The magnet removes them