Fluidised bed gasification of high-ash South African coals...high-ash coal wash plant waste. Henan, China, 45 000 Nm3/h syngas for ammonia, start-up 2014, high-ash sub-bituminous coal

© CSIR 2010 Slide 1www.csir.co.za

Fluidised bed gasification of high-ash South African coals

A.D. Engelbrecht, B.C. North, B.O. Oboirien, R.C. Everson and H.W.P.J. Neomagus

July 2013

http://www.csir.co.za

© CSIR 2010 Slide 2

Outline of presentation

• Coal gasification

• Coal gasification reactors

• Fluidised bed gasification

• Characterisation of high-ash SA coals

• Pilot-scale fluidised bed gasification of high SA coals

• Gasifier modelling

• Sensitivity analysis

• Conclusions and recommendations


Products from combustion and gasification


Products from combustion and gasification


Worldwide Gasification Capacity & Planned Growth Cumulative by YearLimited oil and gas reserves with abundant coal reserves

ChinaIndiaUSASouth Africa and Australia

Increase in cost of oil and gas

Need to diversify energy resources

Greenhouse gas emission regulations

Drivers for investment in coal gasification


Source: DOE NETL Database, 2010

Worldwide Gasification Capacity & Planned Growth Cumulative by Year


End Use Applications of Syngas



© CSIR 2010 Slide 8Source: DOE NETL Database, 2007

Worldwide Gasification Capacity & Planned Growthby Region Source: DOE NETL Database, 2010


Gasification by Technology




Coal gasification reactors


KBR TRIGTM gasifier

Projects:

§ Kemper County, USA, 550 MW IGCC, start-up 2014, lignite

§ Dongguan, China ,120 MW IGCC, start-up 2014, high-ash bituminous coal

§ Inner Mongolia, China, 35 000 Nm3/h syngas for ethylene glycol, start-up 2015, high-ash lignite

Standpipe

J-Valve

Riser

Upper Mixing Zone

Lower Mixing Zone

Startup Burner

Second Separation

Device

Seal Leg

First Separation

Device

Syngas

CoalAir

SteamOxygen

Ash


GTI U-gas® fluidised bed gasifier

Projects:

§ Shadong, China, 28 000 Nm3/h syngas for methanol, start-up 2008, high-ash coal wash plant waste.

§ Henan, China, 45 000 Nm3/h syngas for ammonia, start-up 2014, high-ash sub-bituminous coal

gas

char

oxygen + steam

oxygen + steam

ash agglomerates

coal

high pressure

steam

steam


Coal properties important for fluidised bed gasification

Coal properties

Requiredfor FBG

SA coalin future

Fit

Moisture < 7.5 % < 6 %

Ash 15 - 50 % 25-50 %

AFT > 1400 °C > 1400 °C

Caking index low <2 ?

Reactivity high med-low ?

Size 1- 4 mm Fines

Volatiles >20 % ± 25 %


Information on selected coals

Colliery New Vaal Matla Grootegeluk Duvha Location of mine Free State

Province Mpumalanga Province

Limpopo Province

Mpumalanga Province

Coal field Sasolburg Highveld Waterburg Witbank Production rate (Mt/a)1 15.2 14.0 15.0 16.0 Started production 1985 1979 1985 1979 Expected lifetime (yr)1 30 - 40 40 - 50 40 - 50 30 - 40 Coal preparation Washed Raw coal Washed Raw coal Receiving Power Station Lethabo Matla Matimba Duvha Power station rating(GWe) 3.6 3.6 3.6 3.5 1 2005


Coal characterization parameters

New Vaal Matla Grootegeluk Duvha

Calorific value (MJ/kg) 15.1 18.6 19.8 21.0 Ash content (%) 40.4 33.4 34.9 32.5 Carbon (%) (maf)* 79.10 80.2 81.8 89.3 Vitrinite reflectance (%) 0.53 0.64 0.68 0.75 Surface Area (m2/g) 7.01 2.08 <1 < 1 Porosity (%) 3.2 1.3 1.5 1.1 Free swelling index (FSI)

0 0 1 0

Roga index (RI) 0 0 10 0 AFT (° C) + 1600 1500 1500 1600 * Dry ash free + Ash fusion temperature


Rank classification system using vitrinite reflectance(Du Cann)


Coal characterization parameters

New Vaal Matla Grootegeluk Duvha

Calorific value (MJ/kg) 15.1 18.6 19.8 21.0 Ash content (%) 40.4 33.4 34.9 32.5 Carbon (%) (maf)* 79.10 80.2 81.8 89.3 Vitrinite reflectance (%) 0.53 0.64 0.68 0.75 Surface Area (m2/g) 7.01 2.08 <1 < 1 Porosity (%) 3.2 1.3 1.5 1.1 Free swelling index (FSI)

0 0 1 0

Roga index (RI) 0 0 10 0 AFT (° C) + 1600 1500 1500 1600 * Dry ash free + Ash fusion temperature


Coal reactivityConversion of coals at 950°C in 100% CO2 at 87.5 kPa

0.00.10.20.30.40.50.60.70.80.91.0

0 50 100 150 200 250 300Time, t (min)

Con

vers

ion,

X (-

)

New Vaal

Matla

Grootegeluk

Duvha

© CSIR 2010 Slide 19© CSIR 2006 www.csir.co.zaSlide 19

Specification of fluidised bed gasifier pilot plant

Operating pressure : Atmospheric (90 kPa)Bed dimensions : 0.2 m X 0.2 m (square)Freeboard dimensions : 0.4 m X 0.4 m (square)Furnace height : 2m bed & 2m freeboardDynamic bed height : < 1.5 mCoal feedrate : 15 - 35 kg/h

Coal particle size : < 4 mmCoal calorific value : > 10 MJ/kgAir flow rate : 15 - 30 Nm3/hOxygen flowrate : 4 - 10 kg/hSteam flowrate : 10 - 20 kg/hBed temperature : 900 -1000 °C

Reactant temperature : 200 – 300 °CFluidising velocity : 1.5 – 2.5 m/s



Fluidised bed gasifier pilot plant

T

T

T

T

T

T

T

P

Gasifier

Coal feed

Hea

t exc

hang

er

FD fan Flare

Cyclone

ID fan

Air

Boiler

Bed char

Cyclone char

Steam

Gas cleaning

Steampurge

PFeedwater

Water to drain

LPG

Water cooled screw Oxygen

storage

Oxygenrotameter

Orificeplate

Scrubber effluentWater pump

Buffer tank

Wat

er q

uenc

h sc

rubb

er

Gas to analysers

SteamRotameter

P

TT

TT

TT

TT

TT

TT

TT

P

Gasifier

Coal feed

Hea

t exc

hang

er

FD fan Flare

Cyclone

ID fan

Air

Boiler

Bed char

Cyclone char

Steam

Gas cleaning

Steampurge

PPFeedwater

Water to drain

LPG

Water cooled screw Oxygen

storage

Oxygenrotameter

Orificeplate

Scrubber effluentWater pump

Buffer tank

Wat

er q

uenc

h sc

rubb

er

Gas to analysers

SteamRotameter

PP



Fluidised bed gasifier fixed carbon conversions

30

40

50

60

70

80

90

0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9

Vitrinite random reflectance (%)

Fixe

d ca

rbon

con

vers

ion

(%)

950 C925 C

925 °C

950 °C

New Vaal

Matla

Grootegeluk

Duvha


Fluidised bed gasifier gas quality

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9

Vitrinite random reflectance (%)

Gas

CV

(MJ/N

m3 )

950 C925 C

New VaalMatla

Grootegeluk

Duvha

Nitrogen dilution

Homogenous gas combustion

Lower fixed carbon conversion


Coal gasification reactors


Pilot-scale fluidised bed gasification testsoxygen enriched air + steam

Ten pilot-scale fluidised bed (FBG) gasification tests were carried out on two high-ash South African coals (six test on each coal) using oxygen enriched air and steam as the gasification agents.

FBG operating conditions

Bed temperature (875 - 975 °C)Residence time (15 -55 min)Fluidising velocity (1.5 – 2.0 m/s)Oxygen enrichment level (33 - 37 %)


Experimental resultsEffect of bed temperature on fixed carbon conversion

20

30

40

50

60

70

80

90

100

850 875 900 925 950 975 1000Mid bed temperature (ºC)

Fixe

d ca

rbon

con

vers

ion

(%)

New Vaal Grootegeluk

Superficial gas velocity (m/s) : 1.25 - 1.84

τ = 35 minutes

τ = 25 minutes

Test 5

Test 1

Test 2

Test 3

Test 1Test 3



Experimental resultsEffect of residence time on fixed carbon conversion

50

55

60

65

70

75

80

85

90

95

100

10 15 20 25 30 35 40 45 50 55Average residence time (min)

Fixe

d ca

rbon

con

vers

ion(

%)

New Vaal Grootegeluk

Temperature = 943 °C

Temperature = 980 °CTest 3

Test 4

Test 5Test 2 Test 3

Test 4



Experimental results

Air

Oxygen enriched air

H2 - 22.7CO - 17.6CH4 - 1.2


FBG syngas flare


Experimental resultsSummary of fluidised bed coal gasification tests

Fixed carbon conversion increases with:q Fluidised bed temperatureq Residence time of char in the gasifierq Steam concentration of the reacting gasses in the gasifierq Reactivity index of the coals tested

Calorific value of the gas increases with:q Level of oxygen enrichment of the gasification airq Fixed carbon conversion

Carbon content of the elutriated char is higher than the bed char :q There is little or no oxygen present in freeboardq The concentration of CO2 and H2O are lower in the freeboard than the bed

resulting in lower gasification ratesq The concentrations of CO and H2 are higher , which inhibits the rates of the

gasification reactions q The temperature of the freeboard is lowerq The residence time of particles in the freeboard is lower than in the bed



Fluidised bed gasifier modelling

O2 flow & temperature

Steam flow & temperature

Coal flow & analysis

Bed ash flow & carbon content

Air flow & temperature

Fly ash flow & carbon content

Syngas Flow

CO2

H2

CO

CH4

H2O

N2

FBG

Temperature

Gasifier dimension

Dynamic bed height


Fluidised bed gasifier modellingMotivation

q Existing available fluidised bed coal gasifier models are in somecases not suitable for simulating the fluidised bed gasification ofhigh-ash South African coals.

q An in-depth understanding of the chemical and physical processesthat take place in a fluidised bed coal gasifier can be obtainedduring model development.

q The model can be used for process analysis, design, optimisationand scale-up.

q The model can be extended later to other gasification processes such as:

• Circulating fluidised bed gasifiers• Moving bed gasifiers• Entrained flow gasifiers• Dual fluidised bed gasifiers



Fluidised bed gasifier modellingObjectives

q Develop a fluidised bed coal gasifier model that is based on fluidised bed hydrodynamics, coal devolatilisation, rates of chemical reactions and rates of heat and mass transfer in the gasifier.

q Test the predictive capability of the model by comparing model predictions with the pilot plant data.

q Study the effect of major operating variables on gasifier performance



Fluidised bed gasifier modellingModel types

1. Mass and energy balance models

§ Conservation of mass and energy§ More unknowns than equations§ Assumptions regarding unknowns are required:

Ø Fixed carbon conversionØ CH4 and CO in the gas

2. Equilibrium models

§ Equilibrium relationships are added § Only fixed carbon conversion assumption is required§ Reactions are assumed to have reached equilibrium

3. Rate models

§ Conservation of mass and energy§ Bubbling fluidised bed hydrodynamics § Kinetics of gas-phase reaction (homogenous)§ Kinetics of char-gas reactions (heterogeneous)§ Heat and mass transfer rates in the gasifier§ Coal pyrolysis

© CSIR 2010 Slide 34© CSIR 2006 www.csir.co.za

Slide 34

Fluidised bed gasifier modellingModel equations for (FBGRM)

S u b -m o d e l C o r r e l a ti o n E q u a ti o n

H y d ro d y n a m ic s

M i n im u m flu i d is in g v e l o c it y G e l d a rt ( B .1 .1 .1 a )

B u b b le d i a m e te r M o ri a n d W e n ( 4 .3 ) D a r lt o n ( B .1 .1 .1 a )

B u b b le v e lo c i ty D H ( 4 .4 ) B u b b le f ra c t io n D H ( 4 .6 ) S l u g fra c t io n O rm is to n ( 4 .8 )

D e v o la t il isa t io n C S I R b e n c h - sc a l e ( B .2 .8 ) L o i so n a n d C h a u v i n ( 4 .1 2 )

H e t e ro g e n e o u s

re a c t io n s

C h a r c o m b u s ti o n L a N a u z e a n d Ju n g ( 4 .1 7 ) F i e ld ( 4 .1 9 )

C h a r-s te a m g a s i fi c a ti o n Jo h n so n ( 4 .2 5 ) L H (4 .5 5

C h a r-C O 2 g a s i fi c a ti o n A r r h e n i u s e q u a t io n ( 4 .5 8 ) C h a r-H 2 g a s if ic a t io n Jo h n so n ( 4 .3 0 )

H o m o ge n e o u s

re a c t io n s

N o n - c a ta l y ti c W G S R 3 K a r im a n d M o h i n d ra ( 4 .3 5 ) C a ta l y ti c W G S R W e n a n d T se n g ( 4 .3 8 ) C O c o m b u s t io n H a s l a m ( 4 .4 0 ) H 2 c o m b u sti o n H a s l a m ( 4 .4 1 ) C H 4 c o m b u s ti o n H a s l a m ( 4 .4 0 )

I n te r -p h a s e m a ss

t ra n sf e r

E m u l s io n t o b u b b le t ra n sf e r

b y d if fu s i o n

S it a n d G r a c e ( 4 .4 4 ) W e n a n d F a n ( B .1 .5 .1 d )

N e t fl o w D e r iv e d f ro m Y a n ( B .2 .1 4 )

In t e r- p h a se h e a t t ra n sf e r

P a rt ic l e to e m u l s io n R a n z a n d M a r sh a ll ( 4 .4 6 )

E m u l s io n to b u b b l e K u n i i a n d L e v e n s p ie l ( 4 .4 9 )

A t tri ti o n M a ( 4 .5 0 ) E l u t ria t io n G e l d a rt ( B .1 .6 )

F re e b o a rd v o i d fr a c ti o n H o ri o ( 4 .5 2 ) T ra n sp o r t a n d t h e rm o d y n a m ic p r o p e rt ie s A p p e n d i x (B .2 .6 ) s e v e ra l



Fluidised bed gasifier modellingSub models developed by CSIR and NWU

βCO

CO0CO X)(1)p

RTE

exp(kdtdX

2

2

2−

−=

Char - CO2 reaction : Arrhenius equation

Char - H2O reaction : Langmuir-Hinshelwood

Coal devolatilisation

TGA - NWU

2 “ Ø reactor

CSIR( )

=

−

− gvfvevdv

.

0111cv120bv202

av010

nQ

VVV 1

1

OH

CO

H

2

2

2


Fluidised bed gasfier modellingModel development

q Sub-models are combined into an overall gasifier model by carrying differential mass and energy balances over the reactor.

q Mass and energy balances produce 18 first order ODE’s with the reactor height (Z) being the independent variable.

q Equation were solve using Matlab with computational times varying between 5 and 10 minutes


Fluidised bed gasifier modellingParameter estimation

Parameter New Vaal Grootegeluk

fL - Relative reactivity factor for the char-H2Oreaction (-) 24.64 1.04

Ln(ko) - Ln (pre-exponential factor of the char-CO2reaction)(s-1) 11.29 16.07

fwgs- Catalytic water-gas shift reaction rateparameter (-) 1.2 1.0

Q - Fluidised bed heat losses (MJ/h) 28.93 40.43

Estimated model parameters for New Vaal and Grootegeluk coals

q Model parameters for New Vaal and Grootegeluk coals were estimated using 7 test on each coal (5 tests O2 enrichment, 1 test air/steam and 1 test oxygen/steam)

q Sum of squared deviation between measured and predicted performance variables were minimized for each coal



Fluidised bed gasifier modellingModel validation

Temperature – New Vaal

Fixed carbon conversion – New Vaal



Fluidised bed gasifier modellingModel validation

Gas calorific value – New Vaal

q For temperature and fixed carbon the predictive capability of the model was validated within 5 % and for calorific value of the gas within 10 %.

q The predictive capability is considered acceptable for preliminary design, optimisation and scale-up purposes



Fluidised bed gasifier modellingModel output

Gas concentration as a function of bed height




Temperature as a function of bed height




Fixed carbon converted by combustion and gasification as a function of bed height




Void fraction of the bed as a function of bed height



Fluidised bed gasifier modellingSensitivity analysis

Reactant pre-heat temperature

3

4

5

6

7

8

200 250 300 350 400 450 500 550 600

(Air + oxygen + steam) temperature (°C)

Dry

gas

cal

orifi

c va

lue

(MJ/N

m3 )

30

40

50

60

70

80

90

100

Fixe

d ca

rbon

con

vers

ion

(%)

Gas

ifica

tion

effic

ienc

y (%

)

Dry gas calorific value Fixed carbon conversion Gasification efficiency

Mid bed temperature - 981 °CDynamic bed height - 1.2 mOxygen in enriched air - 37 %Superficial gas velocity - 1.87 m/s



Fluidised bed gasifier modellingSensitivity analysis

Dynamic bed height

3.00

4.00

5.00

6.00

7.00

8.00

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2

Dynamic bed height (m)

Dry

gas

cal

orifi

c va

lue

(MJ/N

m3 )

30

40

50

60

70

80

90

100

Fixe

d ca

rbon

con

vers

ion

(%)

Gas

ifica

tion

effic

ienc

y (%

)

Dry gas calorific value Fixed carbon conversion Gasification efficiency

Mid bed temperature - 981 °CAir + O2 + steam temperature - 274 °COxygen in enriched air - 37 %Superficial gas velocity - 1.87 m/s



Summary and conclusions

§ Four high-ash South African coals were gasified in an atmospheric pressure fluidised bed gasifier

§ No agglomeration and clinkering of the bed was observed

§ Fixed carbon conversion limited to 85 % (secondary combustor is required)


Gasifier

Coal &sorbent

To steam circuit

Pulse gas

Gascooler

Cyclone

Gasfilter

Gas turbine& generator

Combustor

Waste heatrecovery

To steam circuit

Gas tostack

Air

FD fan

Condenser

Steam turbine& generator

Air from heaterAsh

Tosteamcircuit

Pressurelet down

Steam

Char

Air

Cooler

Tosteamcircuit

Compressor

Solids toCFBC

IntercoolerReheater Air

Air heater

Air to CFBC

Steam circuit

Air

Solids

Air

Tosteamcircuit

Fluidisingair

CFBC

BHEL gasifier


Summary and conclusions

§ Four high-ash South African coals were gasified in an atmospheric pressure fluidised bed gasifier

§ No agglomeration and clinkering of the bed was observed

§ Fixed carbon conversion limited to 85 % (secondary combustor is required)

§ Calorific value of the gas during air blown gasification is limited to less than 4.0 MJ/Nm3 due to homogenous gas combustion.


Recommendations

§ Fluidised bed gasification of high-ash South African coals at higher pressures is investigated

§ Evaluation of the following options for the gasification of high-ash South African coals

Ø KBR-TRIG and GTI U- Gas gasifiers


Commercial fluidised bed gasifier designs

gas

char

oxygen + steam

oxygen + steam

ash agglomerates

coal

high pressure

steam

steamStandpipe

J-Valve

Riser

Upper Mixing Zone

Lower Mixing Zone

Startup Burner

Second Separation

Device

Seal Leg

First Separation

Device

Syngas

CoalAir

SteamOxygen

Ash

KBR-TRIG GTI – U-gas


Recommendations


§ Evaluation of the following options for the gasification of high-ash South African coals


Ø The dual fluidised bed gasification


Dual fluidised bed gasifier designs


Recommendations


§ Evaluation of the following options for the gasification of high-ash South African coal


Ø The dual fluidised bed gasification

Ø Chemical looping gasification


Chemical looping fluidised bed gasifier


Thank You

Documents

Fluidised bed gasification of high-ash South African coals...high-ash coal wash plant waste. Henan, China, 45 000 Nm3/h syngas for ammonia, start-up 2014, high-ash sub-bituminous coal