Department of Energy and Environment – Heat and Power Technology

Optimising the efficiency of

processes for the production

of Bio-SNG Process integration’s role in

achieving high efficiency production

Stefan HeyneChalmers Energy Conference

2011-01-26

Department of Energy and Environment – Heat and Power Technology

Outline

• Synthetic Natural Gas (SNG)– some definitions and numbers

• Identifying efficient production pathways– process integration a key methodology

• Integration of SNG production with existing CHP plants

• Conclusions• Outlook

Department of Energy and Environment – Heat and Power Technology

Potential in Sweden• biogas (waste, manure, sewage sludge)

– production (2005)1 1.3 TWh– near future potential2 14-17 TWh

• bio-SNG (forest residues)– conservative estimate2 59 TWh– optimistic long term estimate2 up to 200 TWh

• Primary energy supply in 20083 612 TWh

• Transport sector energy consumption (2008)3 129 TWh

50%

1 Clementsson, Biogas – basic data on biogas – Sweden, 20072 Svensson et al., Renewable Methane – An Important Aspect when Establishing a More Diversified Sourcing and Distribution of Energy Gas in Sweden, 20093 Swedish Energy Agency, Energiläget 2009

Department of Energy and Environment – Heat and Power Technology

Process integration for SNG production

• Identification of efficient pathways for SNG production using process integration tools

– conversion efficiency of biomass into SNG– use of recoverable heat for cogeneration of power and heat

• Economic performance of optimized SNG production alternatives against future energy market scenarios

• CO2 emission consequences related to production and use of SNG

Department of Energy and Environment – Heat and Power Technology

SNG production process

Drying

Gasification

Gascleaning

Methanation

Gas upgrade

Biomass

SNG

recoverable by-products

heat

electricityexcess heat

heat

electricity

heat demand

power demand

CO2

sulphur

Department of Energy and Environment – Heat and Power Technology

Base case SNG processHeatWorkFuel

el

DH

Department of Energy and Environment – Heat and Power Technology

Pinch analysis

Evaluation(Thermodynamics,

Economics &CO2 emission

balances)

Process modifications

Process modelling & validation (Aspen Plus)

Process integration

study

2

3

1

4

Methodology

Department of Energy and Environment – Heat and Power Technology

Pinch theory - Grand Composite Curves

Q (kW)0

0

Tin

terv

al (

ºC)

minimumexternalheatingdemand

“heat pockets”potential for internal

heat exchange

mimimum external cooling demand

Department of Energy and Environment – Heat and Power Technology

Heat stream representation

externalcooling

(high temp)

internal heat exchange potential

external cooling (low temp)

Department of Energy and Environment – Heat and Power Technology

Indirect gasification

Gasificationfluidised

bed combustion

hot bed material

bed material, ash & char

fuel gasificationmedium

product gas

fuel

flue gas

air

heatfuel

Department of Energy and Environment – Heat and Power Technology

Chalmers gasifier

Hot

bed

mat

eria

l

Heat, Electricity, Steam

Air

Flue gas

Biomass

Fluidization gas(Steam or Bio Producer Gas or …)

Bio Product Gas

Fuel

Hot

bed

mat

eria

l

Heat, Electricity, Steam

Air

Flue gas

New concept

Fuel

Source: H.Thunman

Department of Energy and Environment – Heat and Power Technology

Biomass SNG(extension)

Integration with existing infrastructure

boile

r

gasi

fierpower

heat

fuel fuel

heatchar

gas processing SNG

excess heat

steam

Biomass CHP(existing)

Thermalintegration

Department of Energy and Environment – Heat and Power Technology

Integration with steam cycle

00

T(°

C)

Q (kW)

Internal heat recovery

heatto

steamcycle

external cooling

Department of Energy and Environment – Heat and Power Technology

Increased integration

00

T(°

C)

Q (kW)

steam

heatto

cycle

heat recovered from steam cycleexternal cooling

Department of Energy and Environment – Heat and Power Technology

Integration cases studied

• Integrated feedstock drying applied for the SNG process• Both boiler and gasifier sized for a thermal load input of 100 MW

1Abalancing integration

1Bincreased integration

Case 1steam drying 2A

balancing integration

2Bincreased integration

Case 2low

temperature air drying

Department of Energy and Environment – Heat and Power Technology

Process performance indicators

• Overall SNG, power and heat production & efficiency

• Heat and power production associated to SNG process

SNGfuelCHPfuel

DHelSNGtot QQ

QPQ

,,

+++

=η

CHPelCHPfuelelSNGel QPP ,,, η⋅−=

CHPqCHPfuelDHSNGDH QQQ ,,, η⋅−=

all indicators based on lower heating value (LHV) of wet fuel

Department of Energy and Environment – Heat and Power Technology

Results integration SNG & CHP

0

10

20

30

40

50

60

70

80

90

100

MW

CHP 1A 1B 2A 2B

PelCHP SNG

Qfuel,LHV QDH QSNG,LHV

CHPref

Department of Energy and Environment – Heat and Power Technology

Results integration SNG & CHPCHP Case

1ACase

1BCase

2ACase

2B

[MWLHV] 100 71.5 (all four cases)

[MWLHV] - 90.3 (all four cases)

Pel [MW] 31.7 24.7 27.6 23.2 28.3

[MW] 76.8 68.4 64.1 60.1 54.9

[MWLHV] - 62.7 (all four cases)

ηtot [%] 108.6 96.3 95.4 90.2 90.1

Pel,SNG [MW] - 2.0 4.9 0.5 5.6

[MW] - 13.5 9.1 5.2 0.0

SNGfuelQ ,

SNGDHQ ,

SNGQ

CHPfuelQ ,

DHQ

• SNG process net power producer for all cases

• SNG production unaffected by choice of drying technology and level of thermal integration

• Increased level of thermal integration leads to substantial increase in power production

• Overall efficiency decrease misleading performance indicator

Department of Energy and Environment – Heat and Power Technology

Conclusions• Bio-SNG via gasification can be produced at high thermal

efficiency with cold gas efficiencies at around 70%

• Efficient use of the excess heat from the SNG process is essential for good overall efficiencies

• Electricity production can be efficiently realised when integrating SNG production with existing CHP steam power plants

• Pinch analysis is a very useful tool for a systematic analysis of the heat recovery system of the SNG process (and biorefinery concepts in general)

Department of Energy and Environment – Heat and Power Technology

Conclusions• Thermal integration can help substantially to increase the

electricity produced from the available excess heat of the SNG process

• Integrated feedstock drying improves the process efficiency considerably, low temperature air-drying being the most favourable option

• Integrating gasification in general and SNG production in particular with existing infrastructure can result in a faster introduction of gasification technology

Department of Energy and Environment – Heat and Power Technology

Outlook• Definition of appropriate performance indicators for just

comparison to other biofuel process alternatives

• Economic evaluation against possible future energy market scenarios– identification of economically robust process alternatives

• Assessment of CO2 consequences

• Improved modelling of key conversion steps– Gasification– Tar reforming collaboration with Energy Technology

Department of Energy and Environment – Heat and Power Technology

Thank you for you attention!!