Biomass Thresholds for Electricity, CHP and Heat Generation Nigel Mortimer, Charlotte Hatto, Garry...

Biomass Thresholds for Electricity, CHP and Heat

Generation Nigel Mortimer, Charlotte Hatto,

Garry Jenkins and Onesmus MwabonjeNorth Energy Associates Limited

[email protected]

Outline

The QuestionsThe Basis for Calculations

The AnswersThe Headlines

NORTH ENERGY ASSOCIATES LTD

The Questions: Fundamentals - I

What is the “best” use of wood fuel in Scotland:domestic heat production (15 kWt to 320 kWt)?commercial and industrial heat production (50 kWt to 20 MWt)?combined heat and power generation (CHP; 1.8 MWt to 125 MWt, and 0.4 MWe to 50 MWe)?power only generation ( 5 MWe to 350 MWe)?

Wood fuels:forest wood fuels; roundwood and residues (bark and branchwood) waste wood; “clean” and “unclean”


The Questions: Fundamentals - II

Focus exclusively on greenhouse gas (GHG) emissions:

carbon dioxide (CO2)

methane (CH4)

nitrous oxide (N2O)

Effects of “technology” and “scale”:technology thermal efficiencyscale transport distance


The Basis for Calculations - IAttributional Life Cycle Assessment (LCA):

European Commission’s Renewable Energy Directive (extended to biomass energy)allocation excludes “wastes and residues”plant, machinery and equipment manufacture and maintenance excluded

Net carbon stock changes in forest excluded:affects each individual forest wood fuel equally comparison between different uses of same wood fuel (not between different wood fuels)avoids comparison of negative values


The Basis for Calculations - II

MS Excel workbook with 21 biomass chains:


Regeneration, Harvesting and Extraction of Roundwood

Transport in Forest

Transport to Storage and

Chipping

Storage and Chipping

Transport to End User

Combustion of Chips in

Commercial or Industrial

Boiler

The Answers: Q1 -Basics“Do wood-fired heat and CHP plants have lower total GHG emissions than those of power only plants that use the same source of wood fuel?”Comparing 1 MWh of heat with 1 MWh of electricityVariations in:

thermal efficiencies (range of current values) heat-to-power ratios for CHP plants (range of current values)round trip transport distances (possible values by road in Scotland:

within forest = 16 kmto processing = 66 kmto end users = 80 km to 600 km


The Answers: Q1 – Comparison with Fossil Fuels for Domestic

Heating


0 100 200 300 400 500 600 700

Wood-fired Heating; clean waste wood briquettes

Wood-fired Heating; forest residue pellets

Wood-fired Heating; roundwood logs

Wood-fired Heating; roundwood pellets

Wood-fired Heating; roundwood briquettes

Natural Gas-fired Heating

Oil-fired Heating

Coal-fired Heating

Total GHG Emissions (kg eq. CO2/ MWh)

The Answers: Q1 – Comparison with Fossil Fuels for Commercial

and Industrial Heating


0 100 200 300 400 500 600 700

Wood-fired Heating; clean waste wood chips

Wood-fired Heating; unclean waste wood chips

Wood-fired Heating; forest residue chips

Wood-fired Heating; roundwood chips

Natural Gas-fired Heating

Oil-fired Heating

Coal-fired Heating


The Answers: Q1 – Comparison with Fossil Fuels for Power Only

Generation


0 200 400 600 800 1000 1200 1400

Wood-fired Electricity; clean waste wood chips

Wood-fired Electricity; forest residue chips

Wood-fired Electricity; clean waste wood pellets

Wood-fired Electricity; forest residue pellets

Wood-fired Electricity; unclean waste wood chips

Wood-fired Electricity; unclean waste wood pellets

Wood-fired Electricity; whole roundwood

Natural Gas-fired Electricity

Oil-fired Electricity

Coal-fired Electricity


The Answers: Q1 – Example of Wood Fuel Comparison – Forest

Residues


0

10

20

30

40

50

60

70

80

90

0.01 0.1 1 10 100 1000

Tot

al G

HG

Em

issi

ons (k

g eq

. CO

2/M

Wh)

Output Rating (MW)

Individual Domestic Heating by Combustion of Wood Pellets from Forest Residues

Commercial or Industrial Heating by Combustion of Wood Chips from Forest Residues

Commercial or Industrial Heating from Combined Heat and Power Generation by Combustion of Wood Chips from Forest Residue

Commercial or Industrial Electricity from Combined Heat and Power Generation by Combustion of Wood Chips from Forest Residue

Power Only Generation by Combustion of Wood Chips from Forest Residues

Power Only Generation by Combustion of Wood Pellets from Forest Residues

The Answers: Q2 -Basics“What is the maximum distance for delivering wood fuel to heat and CHP plants at which their total GHG emissions equal those of power only plants using the same source of wood fuel?”Still comparing 1 MWh of heat with 1 MWh of electricityAverage values for thermal efficiencies and heat-to-power ratios (for CHP plants) Comparative radii of supply:

“local” = 50 km“regional” = 200 km“national” = 500 km


The Answers: Q2 -Idealised Modelling - Power Only Generation (most

favourable case)


Power Only Plant in Centre of Forest

Circular Section of Forest

The Answers: Q2 -Idealised Modelling –

Heating and CHP Generation (typical case)


End Use

Transport to End Use

Processing Point

Semi-Circular Section of Forest

The Answers: Q2 – Method


Tota

l GH

G E

mis

sio

ns

(kg

eq

. CO

2/M

Wh

)

Output Rating (MW)

Power Only Plant Using Roundwood

Heating Using Roundwood: round trip distance to end users = 0 km

Heating Using Roundwood: round trip distance to end users = 943 km

Point Where Total GHGEmissions Associated withElectricity and HeatGeneration are Equal

The Answers: Q2 – Results for Forest Wood Fuels


0 200 400 600 800 1000 1200 1400 1600 1800

Roundwood Pellets for Domestic Heating

Roundwood Chips for CHP Heating

Roundwood Chips for Commercial and Industrial Heating

Forest Residue Pellets for Domestic Heating

Roundwood Logs for Domestic Heating

Forest Residue Chips for CHP Heating

Roundwood Briquettes for Domestic Heating

Forest Residue Chips for Commercial and Industrial Heating

Maximum Radius of Supply (km)

The Answers: Q2 – Results for Waste Wood Fuels


0 100 200 300 400 500 600 700 800 900 1000

Unclean Waste Wood Chips for CHP Heating

Unclean Waste Wood Chips for Commercial and Industrial Heating

Clean Waste Wood Chips for CHP Heating

Clean Waste Wood Pellets for Domestic Heating

Clean Waste Wood Chips for Commercial and Industrial Heating

Clean Waste Wood Briquettes for Domectic Heating

Maximum Radius of Supply (km)

The Answers: Q3 - Basics“What Proportional Price Differential is required to ensure that the total GHG emissions of heat and CHP plants do not exceed those of a power only plant using the same source of wood fuel?”Comparison of heat with electricity:

weighting of “value” of electricity to “value” of heat

Emissions Trading Scheme:weighting = 2.0

Proportional price differential = price of electricity/price of heat


The Answers: Q3 - Method


Pro

po

rtio

na

l Pri

ce

Diff

ere

nti

al

(pri

ce

of

ele

ctr

cii

ty t

o p

rcie

of

de

liv

ere

d h

ea

t)

Average Round Trip Distance to End Users (km)

Region where GHG Emissions ofDelivered Heat < GHG Emissions of Electricity

Region where GHG Emissions ofDelivered Heat > GHG Emissions of Electricity

Values of Proportional PriceDifference at which GHG Emissionsof Delivered heat = GHG Emissions of Electricity

Average Round TripDistance at which GHGEmissions of DeliveredHeat =GHG Emissions ofElectricity

Proportional PriceDifferential Equivalentto this Average RoundTrip Distance

The Answers: Q3 – Results for National Delivery of Forest

Wood Fuels


1.85

1.52

1.18

1.05

1.04

1.01

0.92

0.63

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

Forest Residue Chips for CHP

Forest Residue Chips for Commercial and Industrial Heating

Roundwood Briquettes for Domestic Heating

Roundwood Chips for CHP

Roundwood Logs for Domestic Heating

Forest Residue Pellets for Domestic Heating

Roundwood Chips for Commercial and Industrial Heating

Roundwood Pellets for Domestic Heating

Minimum Price of Heat Relative to Price of Electricity

The Answers: Q3 – Results for National Delivery of Waste

Wood Fuels


2.94

1.45

1.39

1.18

0.83

0.81

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Clean Waste Wood Briquettes for Domestic Heating

Clean Waste Wood Chips for Commercial and Industrial Heating

Clean Waste Wood Chips for CHP

Clean Waste Wood Pellets for Domestic Heating

Unclean Waste Wood Chips for Commercial and Industrial Heating

Unclean Waste Wood Chips for CHP

Minimum Price of Heat Relative to Price of Electricity

The Answers: Q3 – Approach in Extended Renewable Energy

Directive


0

1

2

3

4

5

6

7

8

9

10

0 50 100 150 200 250 300

We

igh

ting

of

Val

ue

of

Ele

ctri

city

to

Val

ue

of

He

at

Temperature of Heat (C)

The Answers: Q4 - Basics

“Is there a GHG emissions threshold to the scale of CHP plants?”Complex considerations:

thermal efficiencyheat-to-power ratioweighting of value of electricity to value of heatscale and relationship to transport distance

Simple results not possible


The Answers: Q4 - Outcomes

Importance of “good quality” CHP for new wood-fired plants:

minimum “power efficiency” > 20%“Quality Index” ≥ 105as scale increases, higher overall thermal efficiency required

Realistic constraints on CHP scale:heat demanddistrict heating?


The Headlines - IOn a 1 MWh heat to 1 MWh electricity basis, heat and CHP plants have lower total GHG emissions than power only plantFor electricity generation, some overlap for larger scale CHP with low overall thermal efficiencies with smaller scale power only plants with high thermal efficienciesNational supply feasible with lower total GHG emissions for roundwood pellets for domestic heating, roundwood and unclean waste wood chips for commercial and industrial heating, and roundwood and clean and unclean waste wood chips for CHP


Thank you for your attentionNigel Mortimer

E-mail: [email protected]: 0114 201 2604

Biomass Thresholds for Electricity, CHP and Heat Generation Nigel Mortimer, Charlotte Hatto, Garry...

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