www.ecn.nl

CHALLENGES in BIOMASS

GASIFICATION

Bram van der Drift

Regatec, Barcelona, 7-8 May 2015

ENERGY BALANCE gasification process (e.g. at 800°C)

Gas

ifie

r

Solid fuel (LHV)

Gaseous fuel (LHV)

Heat in gaseous fuel

Heat loss

Carbon loss (in ash)

100%

70-95%

10-20%

1-5%

0-20%

LHV: Lower Heating Value Excluding electric energy use of: pumps, fans, oxygen production (if any), … Excluding energy recycle: e.g. air preheat and tar recycle

Main target!

Useful

COMPOSITION biomass is much different from coal

Clean wood Waste wood Straw Coal RDF

water wt% wet 20-60% ~20% ~20% ~10% ~10%

C wt% daf 50.7% 50.5% 48.8% 79.2% 60-65%

H wt% daf 6.1% 5.9% 5.9% 5.3% 8-9%

O wt% daf 42.8% 42.6% 44.0% 13.5% 25-30%

N wt% daf 0.28% 0.73% 0.85% 1.53% ~0.5%

S wt% daf 0.06% 0.14% 0.14% 1.30% ~0.2%

Cl wt% daf 0.04% 0.09% 0.43% 0.14% ~1%

volatiles wt% daf 82% 81% 81% 42% 85-90%

HHV MJ/kg daf 20.1 20.2 19.3 31.8 27-29

ash wt% dry 1.6% 6% 7% 12% 10-15%

main ash components Ca Ca, Si, Fe K, Ca, Si Si, Al Al, Ca, Si

Wet/dry/daf: based on wet/dry/dry-and-ash-free mass RDF: Refuse Derived Fuel Waste wood: excluding particle board

Straw: wheat, rye, barley Coal: average Dutch coal plants Source: www.phyllis.nl

HEATING VALUE in combustion, differences disappear

0

1

2

3

0

10

20

30

40

50

60

methane coal ethanol wood

Low

er H

eati

ng

Val

ue

[MJ/

k g

fuel

/air

mix

]

Low

er H

eati

ng

Val

ue

[MJ/

k g

fuel

]

LHV [MJ/kg fuel] - left axis LHV [MJ/kg fuel/air mix] - right axis

VOLATILES biomass has high volatile content: ~80% daf

Good:

• “Instant gas”: Good conversion at already low residence time, low temperature, low steam

• Valuable hydrocarbons in the gas (methane, ethylene, BTX)

• That also means that efficiency is better

• High calorific gas

Bad:

• Quickly responding to changes in e.g. feed

• Carbon remaining is porous and reactive: spontaneous ignition

• Tars

This presentation focuses on fluidized bed processes: 700-900°C

HYDROCARBONS modest in volume, but dominating in energy

“instant” natural gas: efficiency benefit

Ind

irec

t fl

uid

ized

bed

ga

sifi

cati

on

(M

ILEN

A)

of

wo

od

~8

00

°C

sometimes challenges, but certainly opportunities

METHANE CONTENT is BENEFIT efficiency from biomass to bioSNG

• Entrained Flow (oxygen-blown)

• CFB: Circulating Fluidized Bed (oxygen-blown)

• MILENA: Indirect Fluidized bed

53%

64%

70%

50%

60%

70%

Entrained Flow CFB MILENA

eff

icie

ncy

C. M

. van d

er

Meijd

en e

t.al., B

iom

ass

an

d B

ioe

ne

rgy 3

4, pp 3

02

-311

, 2

01

0.

CIRCULATING FLUIDIZED BED carbon conversion of CFB gasifier plants (2002 study)

Car

bo

n C

on

vers

ion

[%

]

Not only ~10% energy is lost, but also it poses a waste and safety issue

TAR defined as hydrocarbons larger than benzene

0 100 200 300 400 g/mol

Hydrocarbons

Tar (larger than benzene)

PAH (Poly-Aromatic-Hydrocarbons)

gasoline jet fuel diesel

Causing dew point >200°C

CH0.8O0.01N0.0001 …

TAR larger molecules = lower content

100

1 000

10 000

100 000

1 000 000

0 100 200 300hydro

carb

on c

oncentr

ation [m

g/N

m3]

hydrocarbon molecular weight [g/mol] per interval of 50

waste - indirect gasifier - 804C

wood - indirect gasifier - 820C

waste - CFB - 820C

wood - CFB - 840C

But also: if you want methane, you will have to deal with tars

TARS EVALUATION e.g. evaluate effect of gasifier temperature

TARS EVALUATION condensation behavior on “cold” surfaces

0

1

10

100

1 000

10 000

100 200 300 400 500 600 700

tar

that

co

nd

ense

s [

mg

/Nm

3]

temperature [degC]

819°C

775°C

735°C

861°C

COMPOSITION NOT CONSTANT during operation the bed material (olivine) “activates”

0

5

10

15

20

25

30

35

40

0 24 48 72 96 120

Co

nce

ntr

atio

n in

dry

gas

[vo

l%]

Time on stream [hour]

MIL_CH4_P

MIL_CO_P

MIL_CO2_P

MIL_H2_P

CO2

H2

CO

CH4

Ind

irec

t fl

uid

ized

bed

ga

sifi

cati

on

(M

ILEN

A)

of

wo

od

~8

00

°C

BED MATERIAL ACTIVATION caused by migration of Fe to the surface

TAR REMOVAL

• Catalytic conversion

• Plasma conversion

• Scrubbing with water

• Scrubbing with biodiesel

• Scrubbing with another liquid

- Ideal in sense that it removes tar before cooling - Sensitive to poisons like S (limits fuel flexibility) - Inevitable also destroys part (~30%) of methane

- Simple from operational point-of-view - Consumes power (~1/3 of what is being produced)

- Tar dew point is water temperature - Produces nasty mixture of tar, particles, water

- Applied in Austrian indirect gasifier plants - Consumption biodiesel (~1 kg biodiesel/kg tar) - Only works when little tar (filter upstream and

acceptable biodiesel consumption)

- Example: OLGA

POTASSIUM (K)

Good:

• Acts as catalyst for conversion and tar reduction, allows lower temperature

• Responsible for bed material activation

Bad:

• Danger of agglomeration/melting in gasifier

• Downstream fouling by condensation of volatile salts

AGGLOMERATION

• Lower temperature

• Prevent hot spots

• Add K-getter (clay material)

• Add more surface and blow away

WHAT CHICKEN MANURE CAN DO the good thing about Potassium

0

2

4

6

8

10

12

14

840°Cwood

840°Cwood +

20% chicken manure

760°Cchicken manure

Tar

conte

nt [g

/Nm

3]

WHEN GOING CHEMICAL… sulphur removal is not just removing H2S

• Sulphur has many forms (numbers for clean wood in N2-free gas): – H2S 200 ppmv

– COS 20 ppmv

– Mercaptans 5 ppmv

– Thiophene 10 ppmv

– Benzothiophene 3 ppmv

– Dibenzothiophene 1 ppmv

• Activated carbon can remove this, but: – It will also absorb BTX and thus soon is saturated/needs regeneration

• HDS (HydroDeSulphurization) will convert the organic S, but: – Olefins will hydrogenate too (e.g. ethylene to ethane), exothermic

– Water Gas Shift reaction will occur too, exothermic

– So, temperature control is challenge

WHEN GOING CHEMICAL… hydrocarbons is more than tar and methane

• Significant amounts of olefins (mainly ethylene) and single aromatics (BTX)

• Known for their coke forming tendency

• Also: benzene emissions from engine exceed limits (e.g. Germany)

• BTX: – Can be reformed, but needs upstream S-removal to protect reformer catalyst, and

upstream activated carbon does not make sense since it absorbs the BTX

– Can be separated and used/sold, enables downstream activated carbon S-removal

• Ethylene: – Can be converted to ethane, which is much easier to handle for catalysts

– Can be converted into aromatics, and separated

– Can be separated

GREEN GAS (bioSNG)

our process choices

Smart combination of endothermal reforming and exothermal methanation

MILENA – OLGA – ESME

ECN process for biomass-to-bioSNG

Gasifier Tar

removal Up-grading

Metha-nation

CO2 removal

S removal

HDS Pre-

reformer Metha-nation Metha-

nation

Gasifier: Fluidized Bed Gasifier operating at temperature below 1000°C HDS: HydroDeSulphurization (converting organic S molecules into H2S) BTX: Benzene, Toluene, Xylene (~90%/9%/1% in case of fluidized bed gasification at ~800°C)

BTX is converted

Needed to protect reformer catalyst

Little organic-S, but too much for reformer

Ni catalyst is not able to treat BTX

<10 bar to prevent removal of methane

Prevents BTX to contaminate CO2

CO2 co-product is clean Starting point: existing catalyst and technology

MILENA OLGA ESME

MILENA – OLGA – ESME ECN process for biomass-to-bioSNG

MILENA gasifier OLGA tar removal HDS reactor Further gas

cleaning Methanation

reactors 1 bar 1 bar 6 bar 6 bar 6 bar

70% efficiency from wood to bioSNG

bioSNG PROCESS with BTX removal

Gasifier Tar

removal Up-grading

Metha-nation

Hydro-genation

BTX Metha-nation Metha-

nation

Gasifier: Fluidized Bed Gasifier operating at temperature below 1000°C BTX: Benzene, Toluene, Xylene (~90%/9%/1% in case of fluidized bed gasification at ~800°C)

S and CO2 removal

BTX removal also removes organic-S

Mainly ethylene to ethane, COS to H2S

Activated carbon guard bed is possible now

H2S and CO2 removal in one unit

No HDS required No reformer required

Starting point: existing catalyst and technology

MILENA OLGA

BTX SCRUBBER

• Removes BTX (Benzene, Toluene, Xylenes)

• Scrubbing process

• Produces liquid BTX for further use

BTX scrubber, 2 nm3/h

CONCLUDING REMARKS

• Biomass gasification has many options to make renewable energy

• And it can make money

• Main challenges: – Feeding

– Tar

– Non-conventional gas cleaning

• Fortunately, these challenges all have good solutions

• Main challenges remaining are … non-technical

CHEMICAL INDUSTRY as role model, but…

What do you get if you ask an experienced EPC in petro-chemistry to design a bioSNG plant?

What do you get if you ask an experienced car manufacturer to build a human-powered two-wheel car? Also called a bicycle.

It certainly works, but may not be the best choice

MORE INFORMATION

publications: www.ecn.nl/publications

fuel composition database: www.phyllis.nl

tar dew point calculator: www.thersites.nl

IEA bioenergy/gasification: www.ieatask33.org

Milena indirect gasifier: www.milenatechnology.com

OLGA: www.olgatechnology.com / www.renewableenergy.nl

SNG: www.bioSNG.com /www.bioCNG.com

Bram van der Drift

ECN

Westerduinweg 3 P.O. Box 1

1755 LE Petten 1755 ZG Petten

The Netherlands The Netherlands

T +31 224 56 45 15 vanderdrift@ecn.nl

M +31 610 909 927 www.ecn.nl

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