Biomass Conversion Technologies Gasification, Pyrolysis, Hydrothermal Carbonisation

Dr. Bodo Groß; gross@izes.de

Mahbod Shafiei; shafiei@izes.de

Future World Energy Demand

Industrialisation and population growth of emerging countries has increased the world wide

energy demand to an alarming rate

It is expected that energy demand surge up with app. 44 % from current total of 138,000

TWh to 198,000 TWh by the year 2030 (Ref.: Renewable and Sustainable Energy Reviews 16

(2012) 3084– 3094)

World Energy Outlook Report (WEO) 2012, has cited that fossil fuel will remain the main

source of energy with app. 80 % by the year 2035

Ref: http://jcwinnie.biz/wordpress/

World Energy Outlook Report 2012 (WEO)

Ref: World energy outlook 2012, ISBN: 978-92-64-18084-0

Rapid increasing amount of CO2 in the atmosphere since 1900

CO2 Emission to Atmosphere

World atmospheric concentration of CO2 and average global temperature change

Ref: World energy outlook special report 2013

According to renewable global status report in the year 2012, app 19 % of total

energy demand is produced by renewable energies

Share of Global Final Energy Consumption

Ref:: Renewables 2013 Global statues report ISBN 978-3-9815934-0-2

Renewable Energies in the World in 2012

Share of renewable energies in primary energy consumption in the world shows that

Europe had around 40 % of share in global renewable energy consumption in 2012.

Eurasia contain Europe and Azerbaijan, Belarus, Kazakestan, Turkey, Turkemenistan, and Uzbekistan

Reference : BP statistical Review of World Energy June 2013. Bp.com/statistical review

Share of total energy production in Europe area in 2010 (%)

Renewable energy by 26 % had the second place in total energy production in Europe area

in 2010

Reference : European commission, eurostat. . www.epp.eurostat.ec.europa.eu

Energy Production in Europe Area

Renewable Energy Production in Europe

Primary prodcution of renewable energy in Europe area in 2010

Biomass and waste has the first place in Renewable energy Production

Reference : European commission, eurostat. . www.epp.eurostat.ec.europa.eu

Biomass

Biological structure derived form living or recently living organism.

Biomass composed carbohydrate polymers (cellulose and hemicellulose) and

aromatic polymer (lignin).

Cellulose (C6H10O5) is the most important structural component of the primary cell

wall of green plants and the most abundant organic polymer on earth.

Hemicellulose present with cellulose in almost all plant cell walls.

Cellulose is crystalline, strong and resistant to decomposition in presence of

heat, but hemicellulose has a little strength in front of heat.

Unique characteristics of biomass as the only renewable and carbon based

resource, makes it more attractive for energy purposes.

Divided into; wet and dry Biomass.

Neutral Carbon Cycle of Biomass

Ref.: Center for Environmental Research and Technology, Bourns College of Engineering University of California

Future Energy Demand via Biomass

In future energy trends, a major role in the energy supply has been pointed to

biomass

Biomass has been used widely as feedstock for thermal conversion processes

such as combustion, gasification, pyrolysis, and hydrothermal carbonisation to get

various phase of products (solid, liquid and gas) to get energy

Ref: https://ukerc.wordpress.com/

Slow Heating of Biomass

Slow heating of biomass can be categorised to five levels of temperature and pressure

that end in various products in each level

Conversion technologies, subdivided into these five groups, which end in different phase

of products in quantity depend on nature of biomass and process condition

Slow Heating of Biomass

Temperature Pressure zone Gases – phase products

< 200 °C 1- 5 bar Drying Mainly H2O in phase of vapour releases from biomass

180 °C – 250 °C

1- 5 bar Devolatilization Removing –OH Structures, acetic acids, organics, CO2

releases from biomass, decomposition of cellulose starts

5 - 20 bar Hydrothermal

Carbonization of

Biomass (HTC)

Main product is char

Pre-treatment for gasification

250 °C – 300 °C 1- 5 bar Torreffaction Deoxygenation, removing O2 from reaction mixture,

complete decomposition of hemicelluloses, decomposition of

cellulose starts

300 °C – 500 °C 1- 5 bar Pyrolysis Char coal is the main product

> 500 °C 1- 5 bar gasification

combustion

Aromatics,H2O,syngas, higher hydrocarbons

Typical Yield of Thermo-Chemical Processes

Process Reaction

Conditions

(Temperature [°C],

residence time)

Char

Weight %

Liquid

Weight %

Gas

Weight %

Slow pyrolysis ~400 °C h - week 35% 30% 35%

Mild pyrolysis ~500 °C 10 – 20 sec 20% 50% 30%

Fast pyrolysis ~500 °C 2 sec 12% 75% 13%

Gasification ~800 °C -1400 °C

10 - 20sec

10% 5% 85%

HTC ~180 °C - 250 °C

1-12 hour processing

time

50-80% 5-20%

Dissolved in water

2-5%

Conversion Technologies

Wood gasification plant in Güssing/ Austria

Produces 2MW of power and 4MW of heat for the

local district heating network

Torrefaction

Proceeds between 200 C to 300 C, under atmospheric condition

In absence or very limited amount of oxygen and very low heating rate

Hemicellulose deeply decomposes and cellulose and lignin partly decomposes

that starts around 250 C

Moisture of biomass will be removed by evaporation and some organic acids,

such as acetic acid will be driven off

Torrefaction removes oxygen from biomass that causes higher heating value of

the product

Around 70 % of mass is preserved which contain 90 % of initial energy

Aslo remove hydroxyl and –OH groups in biomass and makes it more hydrophobic

Torrefied biomass can be milled easily, and high porosity of biomass increases its

reactivity

More CO and H2 in syngas, but the same quantity of CO2

Torrefaction used as pre treatment for gasification reactor

Energy and Mass balance in Torrefaction

willow wood was conducted in Toreffaction process at temperature between 250 C and

300 C with residence times of 10 and 30 minutes

With increasing temperature severe decomposition of cellulose occurs at higher 300 C

Torrefied product has a lower O/C and H/C ratio, so it has properties and character

between wood and coal

Torrefaction Process as pre - treatment

Step 1 Step 2 Step 3 Step 4

Unprocessed

wood

Dried wood chips Torrefied wood chips Final wood pellets

Wood chips are

collected and stored,

so they can be used

as biomass

Wood chips are dried

before they undergo

torrefaction process

The wood chips are

heated using microwave

technology within a

rotating drum reactor,

creating a charcoal like

substance

The torrefied wood is

milled and made into

pellets that produce up

to 10 % to 20 % more

energy than untreated

one

Pyrolysis

Carry out under 300 °C to 500 °C and almost atmospheric pressure with

residence time between 0.5 second to 24 hour.

Carry out in the absence or nearly without oxygen.

Divided to four groups depend on oven temperature and residence time: Flash,

fast, mild, and slow pyrolysis

Under these conditions, hemicelluloses, cellulose, and lignin decomposes to

char as solid phase, tar as liquid phase, and gases depend on residence time

Heat transfer rate rise up, By increasing oven temperature and in short

residence time ( < 2sec ), dominate product is tar (liquid phase)

Char is the main product of slow and mild pyrolysis with low oven temperature

and high residence time

liquid fractions or condensable gaseous products are the main product of flash

and fast pyrolysis with high oven temperature (app. 500 °C), high heat transfer rate

( app. 1 °C / sec) and very low residence time ( < 2 sec)

Fast and Flash pyrolysis is an effort to maximize liquid products such as

BIO – Oil

Typical Yield of Thermo-Chemical processes

Process Oven

temperature

residence time

pressure

Particle size Heat rate Main

products

Heating value

of products

Application

area

Flash

pyrolysis

800 °C – 1000 °C

< 0.5 sec

1-5 bar

< 0.2 mm

Biomass

supply in

form of dust

Very fast

heating rate

> 1 °C/s

Tar products

Bio - Oil

-

Power plants,

diesel, boiler,

resin, fertilizer,

fine chemicals,

transport fuels,

emulsions

Fast

Pyrolysis

500 °C - 600 °C

~ < 2 second

1-5 bar

< 1 mm

High heating

rate

>100 °C/min

Tar products

Bio - oil

17

MJ/kg

Power plants,

diesel, boiler,

resin, fertilizer,

fine chemicals,

transport fuels,

emulsions

Mild Pyrolysis

315 °C – 450 °C

10-20 second

1-5 bar

5-50

mm

Controlled

heating rate to

control tar

formation

Char

Bio - coal

19 – 24

MJ/kg

Filtration (water

and air), soil

improvement,

power plant,

pharmaceutical

s

Slow

Pyrolysis

200 °C - 300 °C

30 minute / days

1-5 bar

5-50

mm

0.1 – 0.2

°C/sec

charcoal

25 - 37

MJ/kg

Char coal

(lump)

Schematic of Pyrolysis (Char and Bio-oil)

Ref: http://energyfromwasteandwood.weebly.com/

Gasification

Controlled partial oxidation of carbonaceous material with less oxygen than

required to complete combustion ( air/fuel < 0.5).

Carry out under 600 °C to 1500 °C and almost atmospheric pressure.

CO2, CO, CH4, H2 and H2Og and trace of higher hydrocarbons such as ethane

(C2H6) and ethene (C2H4) exists in produced gas.

Generally air, steam, air/steam and oxygen are used as gasification agent.

Final produced gas is a function of type of gasifier, operating condition, and

gasification agent.

Different gasification processes, classified by the regime of flow inside gasifier.

Divided to three main groups of fixed bed, fluidized bed, and entrained flow.

low cost and simple design and operation is fixed bed advantageous, but Non

uniform mass and heat transfer in fixed bed gasifier causes high amount of tar and

char in produced gas.

Good mixing and solid contact causes, higher conversion efficiency in fluidized

bed gasifiers, but higher cost of operation is its disadvantageous.

Gas Composition and Calorific Value

Calorific value Numerical value Agent Application

Low CV 4 - 6

MJ/Nm3

Air

Steam/ Air

Directly in combustion or

engine fuel

Medium CV 12 -19

MJ/Nm3

Oxygen/ Steam Utilizes as feedstock for

subsequent conversion into

basic chemicals such as

methane or methanol

High CV 40

MJ/Nm3

Hydrogen Mainly in chemical industry

Typical gas composition in gasification process Produced gas Bio fuel gas (Vol %) Charcoal (Vol %)

N2 50-54 55-65

CO 17-22 38-32

CO2 9-15 1-3

H2 6-22 15-20

CH4 2-3 0-2

LHV (MJ/M3) 5-5.9 4.5-5.6

Main Characters of Gasification Process

Gasification Process

Drying the feed stock

Happens in temperatures up to 200°C and only water driven off

At 180°C carbon dioxide and acetic acid with –OH structure starts to decompose,

which is called Devolatilization, without chemical or physical decomposing of

biomass

Pyrolysis to produce char

Takes place between 300°C to 500°C, produces a large quantity of tar and gases

containing carbon dioxide

Natural structure of the fuel is broken through exothermal reactions which

release steam, methanol, acetic acid and a considerable amount of heavy

hydrocarbons, depend on residence time

Gasification (combustion and reduction)

Combustion contains both exothermic and endothermic reactions which give a

theoretical oxidation temperature of 1450°C

In reduction area, a number of incombustible gases are converted into

combustible products through a series of reactions, depending on the temperature,

pressure and concentration of the reacting species

Main Gasification Reactions

Syngas Produced by Various Gasifiers

Fuel

feedstock

Gasification

reactor

Gasification

conditions

CO

Vol %

H2

Vol %

CH4

Vol %

CO2

Vol %

N2

Vol %

LHV

MJ/m3

Wood saw

dust pellets

Downdraft GA: air

RT: 900 -

1100 °C

21.3

17.5

3.1

13.3

44.2

6.0

Wood chips

Up draft

1.5 MW

RT:

800-900 °C

GA: air +

steam

29

15.4

1.6

6.8

47.2

5.54

Wood pellet

Bubbling

fluidized bed

BM: ofite

GA: air/

oxygen/

steam

BT: 755-840 °C

28.5

25.7

8.1

9.2

28.5

9.28

Wood

pellets

Circulating

fluidised bed

GA: air

BM: sand

23.8

21.7

0.08

9.4

41.6

5.03

Coal

Flow rate:

76.66 g/sec

Entrained

flow

gasification

GA: oxygen

and steam

57.55

39.13

0.12

2.95

0.12

10.83

Gasifing Reactors

Fixed Bed Gasifiers

Downdraft gasifier

Updraft gasifier

Crossdraft gasifier

Downdraft gasifier Updraft gasifier Crossdraft gasifier

Gasifing Reactors

Fluidised Bed Gasifier

Bubbling fluidised bed

Circulating fluidised bed

Circulating fluidised bed Bubbling fluidised bed

Gasifier Reactors

Entrained flow gasification

Entrained flow gasification

Quality of the produced gas in gasifiers

Gasification

technology

Feed stock

property

Tar and particle

content

Quality of

produced Syngas

Rank

Down draft Less than 55 mm in size

Up to 25% moisture

Low tar content

Moderate particle

High amount of N2, low

amount of CH4, moderate

amount of CO and H2

●●

Up draft Less than 55 mm in size

Up to 60% moisture

High tar content

Moderate particle

High amount of N2, low

amount of CH4, moderate

amount of CO and H2

●●

Cross draft

10 % to 25% moisture

High tar content

High particle

content

- ●●

Bubbling

fluidized bed

Less than 6 mm in size

< 50% moisture

Depend on the bed

material

C2+ , tar, and particles are

present

High amount of CH4 in

compare with other

technologies, higher CO

and H2

●●●

Circulating

fluidized bed

Less than 6 mm in size

< 50% moisture

High particle in circulating

C2+ , tar, and particles are

present

High amount of N2, low

amount of CO and H2

●●

Entrained flow Less than 0.15 mm in

size

< 15% moisture

Low tar and C2+

In Syngas.

Ash slagging

High amount of CO and

H2, low amount of N2,CO2,

and CH4

●●●

• (poor quality) •••• ( good quality)

Mass Balances

Increasing performance variables needs useful measures of mass and energy balances

Reactor Input materials Output materials MCE*

(Without

tar and

ash) % Feed

stock

Air steam Tar Char,

Ash

Dry gas Water

H2Og

Down

Draft

gasifier

20% Reject

pellets, 80 %

wood chips

3.70

(kg/hr)

Air

7.39

(kg/hr)

-

0.04

(Kg/hr)

0.08

(kg/hr)

9.26

(kg/hr)

0.17

(kg/hr)

83 %

Up draft

gasifier

RDF pellets1

5.16

(kg/hr)

Air

12.97 (kg/hr)

0.58

(kg/hr)

0.18

(kg/hr)

0.13

(kg/hr)

16.96

(kg/hr)

0.93

(kg/hr)

90 %

Bubbling

fluidised

bed

Wood pellets

11.5

(kg/hr)

Air

20.4

(kg/hr)

-

< 3.46

(kg/hr)

28.44

(kg/hr)

-

89 %

Circulating

fluidized bed

Olive oil

waste

60

(Kg/hr)

P* Air

130

(Kg/hr)

S* Air

32

(kg/hr)

-

< 43

(kg/hr)

179

(kg/hr)

-

-

80 %

Entrained

flow

Saw dust

0.6

(kg/hr)

Air

0.8

(kg/hr)

-

< 0.27

(kg/hr)

laboratory experiment

1.13

(kg/hr)

-

80 %

Carbon Conversion

Carbon conversion is defined as the fraction of carbon in the feedstock

converted to gaseous products

Nature of biomass, air ratio, reaction temperature, pressure and

present of catalyst effects the carbon conversion rate

Higher (ER) leads to lower heating value of gases, but lower (ER),

increases carbon conversion

Steam increases gas quality and heating value of the gases, but

decreases the gas yield because it doesn’t take part in gasification

reactions, so a lower carbon conversion rate is attained

Low operating temperature is equal to incomplete carbon conversion.

High temperature favored the carbon conversion efficiency.

High pressure has negative effect on carbon conversion, however the

experiments show that optimum carbon conversion is reached at low

pressure around 1 bar

Carbon Conversion Gasifier Input feed stock

(carbon flow rate)

Output carbon flow rate

Feed stock

(kg/hr)

Carbon

content

Wt %

Carbon flow

rate

(kg/hr)

Carbon flow

rate

(kg/hr)

Carbon

conversion1

%

Accessible

carbon2

%

Gas yield LHV

(MJ/M3)

Downdraft

gasifier

With air

RT: 900 °C

20% paper

reject pellets

80% wood chips

ER: 0.36

3.70 kg/hr

48.66

Wt %

1.8

(Kg/hr)

1.49

(Kg/hr)

82 %

1.03

(kg/hr)

57 %

8.81

(m3/hr)

5.79

(MJ/M3)

Updraft gasifier

With air/steam

RT: <1200 °C

Wood chips

5.2 (kg/hr)

ER: 0.36

55.72

Wt %

4.29

(kg/hr)

3.24

(kg/hr)

75 %

2.15

(kg/hr)

50 %

20.48

(m3/hr)

5

(MJ/M3)

Bubbling

fluidized bed

With Air

BM: Ni-alumina

BT: 780 -830 °C

Chips of pine

wood

FR: 0.4 -0.8

(kg/hr)

ER: 0.18 -0.45

50

Wt %

0.4

(kg/hr)

0.35

(kg/hr)

87 %

0.25

(kg/hr)

62 %

1.25-2.45

(m3/kg)

3.7-8.4

(MJ/M3)

Bubbling

fluidized bed

with Steam

BM: silica sand

BT: 750 -780 °C

Chips of pine

wood

FR: 1.5 – 4

(kg/hr)

ER: 0 (kg/hr)

50

Wt %

2

(kg/hr)

1.34

(kg/hr)

67 %

0.94

(kg/hr)

47 %

0.86-1.14

(m3/kg)

10.3-13.5

(MJ/M3)

accessible carbons defined as flow rate of carbon in output Syngas, which have LHV value consist of CO, CH4, and CnHm

to carbon flow rate of input biomass feedstock.

Carbon Conversion

Gasifier Input feed stock

(carbon flow rate)

Output carbon flow rate

Feed stock

(kg/hr)

Carbon

content

Wt %

Carbon flow

rate

(kg/hr)

Carbon flow

rate

(kg/hr)

Carbon

conversion1

%

Accessible

carbon2

%

Gas yield LHV

(MJ/M3)

Circulating

fluidised bed

With air

BM: silica

sand

Willow

69

(kg/hr)

ER: 0.37

BT:850 °C

48.7

Wt %

33.60

(kg/hr)

27.04

(kg/hr)

81.5 %

12.43

(kg/hr)

37 %

151

(m3/hr)

3.15

(MJ/M3)

Entrained

flow

With air and

steam

Wine

industry

waste4

0.96 kg/hr

ER: NR

RT: 1050 °C

52.61

Wt %

0.5

(kg/hr)

0.3

(kg/hr)

59 %

0.175

(kg/hr)

35 %

1.59

(m3/hr)

9.81

(MJ/M3)

Entrained

flow

With air

Wine

industry

waste4

0.96 kg/hr

ER: NR

RT: 1050 °C

52.61

Wt %

0.5

(kg/hr)

0.47

(kg/hr)

94 %

0.244

(kg/hr)

48 %

2.67

(m3/hr)

5.05

(MJ/M3)

accessible carbons defined as flow rate of carbon in output Syngas, which have LHV value consist of CO, CH4, and CnHm

to carbon flow rate of input biomass feedstock.

Hydrothermal Carbonisation (HTC)

Typically HTC of biomass is achieved in water at elevated temperatures of app.

180°C to 250°C and under pressures of about app. 20 to 25 bars for several hours

Very small amount of gas (1-5%) is generated, and most organics remain or are

transformed into solids.

Mainly water is removed from the biomass, hence energy density of the product

will raise and heating value will be increased

Variety of problematic wastes and continuously generated biomass streams are

used such as, human waste (e.g. excrement’s and faecal sludge’s), municipal solid

wastes as well as agricultural residues and algae

Compared to other conversion methods low amount of energy during

processing and low operation temperature is necessary.

In addition to the high conversion efficiency, a low amount of tar and very high

amount of H2 as well as a low CO content in the product could be achieved.

Deploying the process to industrial size has been the key obstacle until now

Schematic of Hydrothermal Carbonisation (HTC)

Ref: Suncoal hydrothermal carbonization process www.suncoal.de

http://www.suncoal.de/en/technology/carboren-technology

Feedstock Property

Characters of biomass such as moisture content, ash content, volatile

compounds, and particle size has effect on gasification performance

Fuel with moisture more than 30 % makes ignition difficult and reduces the CV

of the produced gas

Moisture content has effect on grind ability of the biomass

Moisture reduces the highest temperature in oxidation zone, leads to

incomplete cracking of hydrocarbons released from pyrolysis zone

In fast or flash pyrolysis due to the high heating rates, fine feed stock with very

low particle size is required

Feed stocks with high moisture content are mostly suitable for biological

conversion technologies such as fermentation, anaerobic digestion, but for

hydrothermal carbonisation (HTC) too

Utilisation of and special kind of pre treatment depends on the used or preferred

conversion technology

Now!

Which kind of feed stock

do you have?