Investigating TheInvestigating The Effects Of Char Physical Structure On Blast Furnace CoalBlast Furnace Coal Injection jPerformanceDane SextonPhD StudentCardiff University School of Engineering

Supervisors: Dr. Richard Marsh, Dr. Julian Steer

Coal analysis and operability in iron and steel

OverviewOverview Background/Industrial contextBackground/Industrial context

Investigation aims

Methods

Experimental results

Conclusions Conclusions

I d t i l t tIndustrial context

Coal is injected into the blast furnace as a substitute for expensive coke

Provides heat & carbon for reducing gasesg g

Steelmakers want effective coal burnouts to allow higher coal injection rates

The more coal injected into the furnace, the less coke required

Coal cannot replace coke completely as coke forms a permeable bed for gases to ascend through

Background/Industrial contextBackground/Industrial context Project aim: consider how to allow higher coal

injection rate with no negative performance implications

This will allow a higher coke replacement ratio

A reactive high burnout coal with high carbon content is ideal

Project simulates BF coal injection and tests a f i bl t d t i f trange of variables to determine factors

influencing BF performance

Agglomeration investigationAgglomeration investigation

Agglomeration of coal particles found during devolatilisation in drop tube furnace

Certain coals more susceptible than others

Agglomerates found in 35ms char

Agglomerates disappear after 100ms gg ppin DTF air environment

Wide agglomerate size range 1mm-1cm+

Agglomeration investigation

Study contains analysis of coal agglomerates vs char powder collected

Assessed ash contents and gasification reactivity

Considerations towards impact of agglomerates leaving the raceway regiony g

Potential impacts of coal iagglomeration

Stable BF performance relies on maintaining furnace permeability

Char accumulation can lower furnace permeability

Gas flow hindered in raceway, cohesive zone, and stack

A l t t t i i d Agglomerates can penetrate pig iron and carburise the metal to saturation impacting productivity

Agglomerates are preferentially gasified to coke, lowering coke degradation rates

Unburnt char eventually emitted in offgas Unburnt char eventually emitted in offgas

M th dMethods

Drop Tube Furnace to simulate blast furnace raceway environment (initial coal injection) inraceway environment (initial coal injection) in order to create coal chars/agglomerates

SEM to visually distinguish differences in physical SEM to visually distinguish differences in physical structure between char and char agglomerates

TGA used to assess reactivity as char particles TGA used to assess reactivity as char particles leave the raceway environment and transition to carbon-rich atmosphere

Methods: SamplesMethods: Samples Four coals of varying volatile content (1 low, 2 mid, 1 high)

i ifi i Two coal size specifications:

Granulated coal (100%

Char creation: Drop TubeChar creation: Drop Tube Furnace

Used to replicate BF raceway with short residence time & high heating rate

Residence times: 35ms, 100ms

Laminar air flow: 20 l/min

Furnace temperature: 1100°C

Feed rate: 30g/hour Feed rate: 30g/hour

Agglomerate quantification

Agglomerates categorised/separated using sieve classification at 1mm

Agglomerate percentage of char calculated by weight

MV4 and HV1 see consistent agglomeration. MV3 sees minor l ti t ll ti l iagglomeration at smaller particle size.

The amount of agglomerates formed are not purely dependent on volatile content – MV4 – large agglomeration MV3 – little to novolatile content – MV4 – large agglomeration, MV3 – little to no agglomeration

Volatile (%) Agglomerates in 35ms char (wt%)LV1 pulverised 9.1 0LV1 granulated 0MV4 pulverised 17.6 26MV4 granulated 9.2MV3 pulverised 3 5MV3 pulverised 20.2 3.5MV3 granulated 0HV1 pulverised 34.5 6.6HV1 granulated 6.8

A l t tifi tiAgglomerate quantification

30)

LV1 Agglomeration30)

MV4 Agglomeration

10152025

omer

atio

n (%

)

Char10152025

omer

atio

n (%

)

Char

05

10

LV1 granulated LV1 pulverised

Agg

lo

Coal Sample

Agglomerate

05

10

MV4 granulated MV4 pulverised

Agg

lo

Coal Sample

Agglomerate

Coal Sample

2530

(%)

HV1 AgglomerationCoal Sample

2530

(%)

MV3 Agglomeration

5101520

gglo

mer

atio

n (

Char

Agglomerate5

101520

gglo

mer

atio

n

Char

Agglomerate

05

HV1 granulated HV1 pulverised

Ag

Coal Sample

05

MV3 granulated MV3 pulverised

Ag

Coal Sample

Agglomeration IndexAgglomeration Index Simple test to rank coals on their propensity to agglomerate

Index analyses volatile matter test residue based upon strength, swelling, cell structure, lustre

Stanton, Fieldner, and Selvig (1939), Speight (2005)

Agglomeration Index results

Index Result Index Score Coal Sample Agglomerate quantificationquantificationaverage (%)

LOWAGGLOMERATION

NA-non-agglomerate, LV1 0AGGLOMERATION RATING

non-coherent residue

A, AF-little swelling or cell structure

MV3 1.75structure

C, Cf-medium swelling,light caking

HV1 6.7

A l ti i d lt l t ith th t f

HIGH AGGLOMERATION RATING

C, Cg-strong caking MV4 18

Agglomerating index results correlate with the amounts of agglomerates found in the coal chars

Ash-derived burnout resultsAsh derived burnout results

60

Granulated coal char vsagglomerate burnout

60

Pulverised coal char vsagglomerate burnout

40

50

60

% 40

50

60

%20

30

40

Burn

out %

CharAgglomerate 20

30

40

Burn

out %

Char

Agglomerate

0

10

20B Agglomerate

0

10

20B

0HV1 MV4 MV3

Char sample

0HV1 MV4 MV3

Char sample

Burnout summary

Agglomerates generally register lower burnouts than char particles

Likely to be as a result of the unreacted interior of the agglomerate

A l ti d t t ti l Agglomeration does not appear to negatively impact burnout of non–agglomerate particles/char - MV4 pulverised has superior burnout to MV4 granulated despite large increase in agglomerationgranulated despite large increase in agglomeration

Lower ash contents suggest agglomerates are more likely to leave raceway unburnt thus increasing y y gcarbon carryover to upper furnace

SEM imaging – MV4 35ms char

Well developed char structure. Hollow cenospheric shape good for gas diffusion into & out of particle

SEM imaging - MV4 35ms agglomerate

Beyond surface

i l hparticles there does not appear to be a developeda developed porous interior

Reactant gas diffusion and product pdesorption are the driving mechanisms in upper BF charupper BF char reactivity

Char gasificationChar gasification Instrument: Mettler Toledo TGA851

Gasifying agent: CO2

G fl t 50 l/ i Gas flow rate: 50ml/min

Isothermal program: 900°C for 600 mins

Sample weight: 10mg

Used to simulate char having left the raceway and reacting inUsed to simulate char having left the raceway and reacting in high carbon environment

Ground char gasification- Inherent reactivityy

Sample R0.5(mins)HV1 Ground char vs agglomerate (mins)

0.8

0.9

1.0

gg

HV1 Char

HV1Char(ground)

72

0.5

0.6

0.7

vers

ion

%

(ground)

HV1 Agglomerate

HV1Agglomerate

800 2

0.3

0.4

X C

onv Agglomerate

(ground)

Agglomerate (ground)

0.0

0.1

0.2

0 200 400 600 800Time (mins)

R0.5 = 50% conversion (mins)

Ground char gasification- Inherent ti itreactivity

Sample R0.5(mins)MV4 Ground char vs agglomerate (mins)

0.8

0.9

1.0

gg

MV4Char(ground)

85

0.5

0.6

0.7

nver

sion

%

MV4 agglomerate

MV4 Agglomerate

920.20.3

0.4

X C

on (ground)

MV4 char (ground)

Agglomerate (ground)

0.0

0.1

0 100 200 300 400 500 600Time (mins)

R0.5 = 50% conversion (mins)

Char gasification – 50% conversionChar gasification 50% conversionUnground chars-apparent reactivity

Unground char gasification profilesHV1

HV1 Granulated Char vs Agglomerate 1 0

HV1 Pulverised Char vsAgglomerate

0 8

0.9

1.0gg

0.8

0.9

1.0 gg

HV1

0.6

0.7

0.8

on %

HV1 granulated char 0.6

0.7

ion

%

HV1 pulverised char

0 3

0.4

0.5

X C

onve

rsio

HV1 granulated agglomerate

0 3

0.4

0.5

X C

onve

rsi

HV1 pulverised agglomerate

0.1

0.2

0.3

0.1

0.2

0.3

0.00 200 400 600

Time (mins)

0.00 200 400 600

Time (mins)

Unground char gasification profilesMV4MV4

MV4 Pulverised Char vs Agglomerate

MV4 Granulated Char vs A l t

0.9

1.0

Agglomerate

0.9

1.0

Agglomerate

0.6

0.7

0.8

n % MV4

Pulverised0 6

0.7

0.8

n %

MV4 granulated char

0.4

0.5

X C

onve

rsio

n Pulverised char

MV4 Pulverised agglomerate

0.4

0.5

0.6

X C

onve

rsio

n

MV4 granulated agglomerate

0.1

0.2

0.3

0.1

0.2

0.3

0.00 200 400 600

Time (mins)

0.00 200 400 600

Time (mins)

I ti ti SInvestigation Summary Volatile content not overriding factor behind charVolatile content not overriding factor behind char

agglomeration

Ash content/burnouts – agglomerate lower ash content than hchars

Agglomerates do not appear to inhibit combustibility of char particlesp

Based upon ash contents it is fair to suggest agglomerates are more likely to leave the raceway region than non-agglomerate char particlesagglomerate char particles

When excluding physical parameters/structure, chars and agglomerates are similarly reactive during gasification

Chars generally more reactive (reach R0.5 in less time) when physical structure remains – though only marginally faster reactingreacting

Investigation SummaryInvestigation Summary

Agglomerates should ideally be kept to a minimum

h t t ti it t it i i bl th Ash contents & reactivity suggests it is viable they will reach cohesive zone & stack

Th h ti it t diff tl f Though reactivity may not differ greatly from chars, total size could potentially cause issues:

P t ti l i t i l di k d d ti & Potential impacts including coke degradation & metal carburisation

Crucially agglomerates have the potential to Crucially, agglomerates have the potential to accumulate and block areas, affecting permeability and thus reducing furnace

d ti itproductivity

Future workFuture work DTF & Gasification – expand on existing tests

Test potential impacts – assess likelihood of blockages, tuyere/injection issues, permeability

Study performance of agglomerating coals in the blast furnace correlating with BF operations data

Blend work to eliminate/control agglomeration effect

Investigating TheInvestigating The Effects Of Char Physical Structure On Blast Furnace CoalBlast Furnace Coal Injection jPerformanceDane SextonPhD StudentCardiff University School of Engineering

Supervisors: Dr. Richard Marsh, Dr. Julian Steer

Coal analysis and operability in iron and steel