Hot Mix Asphalt Production Chris Lange PMP, Pr.Tech.(Eng) Director (Technical) Much Asphalt (Pty) Ltd Road Pavement Forum: 10 th April 2006.

Hot Mix Asphalt Production

Chris Lange PMP, Pr.Tech.(Eng)Director (Technical)Much Asphalt (Pty) Ltd

Road Pavement Forum: 10th April 2006

Hot Mix Asphalt Production

• Plant types and basic components• Plant calibration• Dust extraction• Filler handling and control• Aggregate heating• Procurement / handling of raw materials• Finished product storage• Delivery

Drum Mix Plant - Conventional

HMA made continuouslyand sent to storage silos

Drying and mixing drum

Bitumen Tanks

Scalping screen to remove oversize aggregate

Cold Feed Bins

Belt scale

Primary dust

collector

Filter Baghouse

Hot Storage Bins

Exhaust Fan

TWIN DRUM PLANT : COUNTER-FLOW

Old Drum Mix Mix Plant:

Twin Drum Plant

RAP Feed

Aggregate feed

Drying & heating Drum

Coating & mixing drum

Finished product storage

Plant filler storage and feed

Filter Baghouse

Parallel-Flow Drum-mixer Zones

CombustionHeating DryingAir

BIT.Hot MixAsphalt

Mixing

Counter-Flow Drum-mixer Zones

Aggregate

Air

BitumenHot MixAsphalt

Combustion Heating DryingMixing

Counter-Flow Batch Plant Dryer Zones

Hot Aggregate

Combustion Heating Drying

Aggregate

Air

Batch Plant Elements

Cold feed bins

Drye

r Dru

m

Bitumenstoragetanks

Hot Storagesilos

PrimarycollectorFilter Baghouse

Batch/Mixing tower

RAP Feed

Hot aggregate travels up bucket elevator

Pugmill

Aggregateweigh hopper Bitumen

weighpot

Hot mixasphaltdispensedinto truck / hot-bin

Aggregatefrom dryer

Aggregate to screens

Screens sizeaggregate

Bitumen Weigh-hopper

Aggregate and bitumen weigh hoppers

Aggregate Hot Bins

Warren Brothers Patent Application Drawing: Original

Batch Plant

Belt Scale Calibration

Cold feed system

Belt scaleReference

scale

Cold Feed Bins and RAP Bin

“Graphing the Feeders”

Feeder #1

01020304050607080

20 50 90

Belt Speed or Potentiometer Setting

To

ns

pe

r H

ou

r

Tachometer Mounted on Tail Pulley of Cold Feed Bin Belt

“No Flow” Paddle at Feeder Discharge

Induced Air Burner

Fuel Reticulation and Heating System

In-line heater HFO Sampling pt

HFO Tank

Temperature Profile of Counter-Flow Dryer

150º C 100º C20º C

Gases

Aggregates

Combustion HeatingDrying

150º C300º F

760º C 120º C

400º C

800º C

0º C Aggregate

Drum Flights / Lifters

Primary and Secondary Emission Control

Drying Drum

Primary Dust Collector Secondary

Dust Collector

Exhaust Fan

Filtered Air

Fines collected and returned

Primary Collector:Cyclone

Multi-Tube Collector

Outlettube

Spin vanes

Inlettube

Valve

Collectorelement

Gas inlet

Discharge Housing Functions as a Knockout Box

Gas flow

Air

Optional knockdown plate

Bitumen

Fines mixwith hot mix

asphalt

Cutaway Section of a Typical Baghouse

Pulse Jet Baghouse

Dust screw Dust screw

Exhaust fanExhaust fan

Manifold

Manifold

Automatic Damper Controls

Cyclone, Screw Collector, and Hot Elevator

Batchtower

Hot Elevator

Cyclone feeding fines directly back

Filler Weigh-Pod After Surge Silo

Emission Control Summary

• Remove particulate matter– Primary– Secondary

• Return fines to the mix– Affects void content– Affects mix stiffness– Difficult to control

Batch plant filtration

Aggregate storage

Aggregate Storage

BITUMEN TANKS – ELECTRICALLY HEATED/

24 HR TEMPERATURE MONITOR AND CONTROL

Bitumen Storage

Old Style Operating Cabin

Plant automation: Modern control cabin:

Plant automation

Roodepoort Op ScreenPlant Automation – Operating System Graphics

Batch Plant Schematic

Batch Plant Op Screen

Laboratory from the past

Modern Asphalt Laboratory

Quality Control Trends Monitored

Binder Content

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

Sample No.

V.I.M.

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Sample No.

Filler Content

-1.5

-1

-0.5

0

0.5

1

1.5

Sample No.

Binder Content

Voids in Mix

Filler Content

Slat Conveyor Feeding Storage Silos

Hot Storage – Skip and Winch System

Plant Mixing Tower

Skip Bucke

t

Winch

Storage Silo: 165 t Capacity

Correct Loading Sequence

The good old days

The End