SCALE AND BIOENERGY PRODUCTION FROM FOREST HARVESTING RESIDUE

Transcription

1 SCALE AND BIOENERGY PRODUCTION FROM FOREST HARVESTING RESIDUE A LIFE CYCLE PERSPECTIVE Julian Cleary, Ph.D. Postdoctoral Fellow, Faculty of Forestry University of Toronto

2 SMALL SCALE VS. LARGE SCALE Efficiency Large scale plants are more efficient Wood processing Pellets vs. wood chips Transportation Distances reduced Stability of supply Shutdown of small plants would have a lesser effect on the grid But what about wood supply? Roundwood vs. wood residue Co-firing with coal in large scale facilities Not feasible since Ontario is phasing out coal completely

3 HALIBURTON FOREST Annual harvest of 35,000 tonnes of wood from a mixed hardwood forest 934 ha using selection cut ( ) Significant amounts of wood residue left after harvest Approx. 4,000 tonnes based upon estimates by Rudz By reducing the topping diametre of the cut by 5.4 cm (from 19 cm), 47% of the slash is collected, equivalent to 3227 tonnes of wood (or 1775 BDT) 9.1% more wood is collected using the biomass harvest based upon research by Wolf et al.

4 DRIVING FORCES FOR BIOENERGY FROM WOOD Regulation changes and government investment Feed in tariff for biomass energy in Ontario 13.8 cents/kwh (<10 MW) 13.0 cents/kwh (>10 MW) Compare to cents/kwh (7.7 blended rate) Increased price of energy Natural gas the exception

5 PROJECT DESCRIPTION -LCA and financial costing of forest bioenergy systems, including the displacement of conventional sources of energy. -Small scale gasification of wood chips versus large scale combustion of wood pellets in modified coal-fired power plants

6 LIFE CYCLE ASSESSMENT A method of environmental assessment First conceived in 1969 by Harry E. Teasley, Head of Packaging at the Coca-Cola Company, and used to evaluate containers Depending on the system boundary, LCA accounts for the environmental impacts from raw material extraction, processing, manufacturing, transport, use, and disposal Also avoided impacts resulting from the outputs of the system (e.g., electricity)

7 FUNCTIONAL UNIT AND SYSTEM BOUNDARIES Functional unit Allows one to compare environmental impacts using the same reference 1 kwh: Quantity of electricity generated 1 MJ: Quantity of useful energy (heat and electricity) supplied System boundary Determines which processes are included within the LCA

8 SYSTEM BOUNDARIES SMALL SCALE GASIFICATION LARGE SCALE BIOMASS FIRING

9 LCA BIOENERGY SCENARIOS 1) 2010 Reference Scenario: The system boundary is limited to the processes associated with the generation of electricity using (1.1) coal; (1.2) natural gas; and (1.3) Ontario s electricity supply mix in The forest slash is left uncollected. 2) Gasification Scenario (electricity and heat): Forest slash (equivalent to 9.1% of tonnage of collected sawlogs and firewood) are gasified using a small scale gasifier, displacing electricity and heat derived from conventional sources. 3) Large Scale Wood Pellet Combustion Scenario (electricity only): Based on the scenario by Zhang et al. (2010), the same wood biomass used in Scenario 2 is harvested, processed into wood pellets, and burned in modified coal-fired power plants (100% biomass fuel is assumed), displacing electricity derived from conventional sources.

10 RESIDUAL FOREST BIOMASS COLLECTION Biomass residue is collected by reducing the topping diameter from 19 cm to increase the tonnage of harvested wood collected by approx. 9.1%, or 1,775 ODT. Smaller topping diametre affects the efficiency of semimechanized harvesting technique, and necessitates additional cuts per tree, but increases wood collected. 6.4% increase in the time required to fell-delimb-top an equivalent volume of trees under the modified method (estimate based on Wolf et al.)

11 TRANSPORTATION OF WOOD RESIDUE FEEDSTOCK Average distance from harvest sites to Mill/gasifier: 27 km (HRWR) Assumption of self-loading truck Atikokan: approx km Assumption of rail Nanticoke: approx. 400 km Assumption of rail Scale vs. distance

12 GASIFICATION Wood placed in high pressure/high temperature reactor with controlled/limited oxygen Endothermic reaction Fast pyrolysis Bio-oil Slow pyrolysis Biochar Gasification Syngas/Producer gas Composed of H 2, CH 4 and CO

13 GASIFICATION TRADE- OFFS Fixed bed (small-scale, <1 MWe) -Updraft -producer gas high in tars, low exit temperature -Downdraft -producer gas low in tars, high exit temperature

14 WOOD CHIP GASIFICATION -Approx. 20% of producer gas is used to supply heat for gasification process -46% of the energy content of the wood is lost in the gasification process (i.e. 54% of the original energy remains in the producer gas) Producer gas combustion -Electrical efficiency: 24% -Heat efficiency: 55%

15 WOOD CHIP GASIFICATION Overall -Electrical efficiency: 13% -Heat efficiency: 30%

16 WOOD PELLET COMBUSTION LCA scenario based upon Zhang et al. (2010) for wood pellet combustion in two modified coal fired power plants. 31.6% electrical efficiency OPG OPG

17 WOOD INPUTS AND RECOVERED ENERGY Scenario Small scale gasification Wood pellet combustion Mass of wood inputs per kwh of electricity (ODT) Note: Figures subject to revision. Net syngas production (Nm 3 ) Recovered heat (MJ) ,410,000 9,710,000 (28% of this used to dry biomass) ,610,000 (amount used to dry biomass) Electricity generated (kwh) 1,160,000 2,720,000

18 ELECTRICITY AND HEAT DISPLACEMENT Heat For gasifier and wood drying in kiln Assumed displacement of natural gas/propane Avg. 50% efficiency Electricity Average electricity supply mix (Ontario 2010): 55% nuclear, 20.4% hydro, 13.6% natural gas, 8.3% coal, 1.9% wind, 0.8% other sources Marginal sources of power in Ontario Coal, natural gas

19 PRELIMINARY LCA GHG RESULTS BY LIFE CYCLE STAGE kg CO 2 eq./kwh Harvesting and Collection Chipping and/or Pelletization Transportation Gasification / Combustion Small scale gasification Wood pellet combustion in modified coal plant (Zhang et al lack data on capital) Note: Figures subject to revision.

20 PRELIMINARY LCA GHG RESULTS (OVERALL) kg CO 2 /kwh Small scale gasification Large scale wood pellet combustion 2010 electricity grid Coal Biogenic CO Fossil CO (avoided natural gas due to recovered heat) Note: Figures subject to revision.

21 LIFE CYCLE COSTING Includes the financial costs from the following: (1) harvesting costs; (2) transportation costs; (3) processing (chipping, drying, and/or pelletization) costs; and (4) gasification/combustion costs

22 PRELIMINARY FINANCIAL COSTING RESULTS BY LIFE CYCLE STAGE $/kwh Harvesting and Collection ($/kwh) Transportation ($/kwh) Gasification / Combustion ($/kwh) Avoided carbon loss, assuming coal as the marginal source ($/t CO 2 ) Small scale gasification Wood pellet combustion in modified coal plant (chipping) (pelletization) $218 $194 (including avoided natural gas for heat) $109 Note: Figures subject to revision.

23 CONCLUSION Carbon Similar CO2 emissions per kwh at large and small scales Costs Higher costs (approximately double) for CO2 reduction at small scale Large scale Sufficient feedstock? Life cycle impacts Inclusion of heat from the small scale system

24 THANK YOU Haliburton Forest and Wildlife Reserve MITACS Accelerate NSERC Collaborative Research and Development Grant and Strategic Project Grant

25 OUTLINE Driving forces for bioenergy from wood in Ontario Background on life cycle assessment and forest management systems Project description and objectives Data collection and preliminary results CO 2 and life cycle impact assessment Life cycle costing Conclusion

26 ANALYSIS TOOLS LCA software package and unit process database SimaPro 7.2 and US EcoInvent database Life cycle inventory Accounting of emissions, but not impacts Life Cycle Impact Assessment Methods Mid-point level impacts E.g. acidification, GWP, ecotoxicity End-point level (damage) impacts E.g. damage to human health, ecosystem quality

27 CARBON NEUTRALITY DEBATE UNFCCC reporting guidelines for bioenergy exclude CO 2 emissions from biomass combustion and land use change LCAs are beginning to abandon the carbon neutrality assumption e.g., McKechnie et al. 2011

28 SMALL SCALE Can be the more appropriate technology if: There is a low supply of available biomass Insufficient electrical transmission capacity In comparison to larger scale facilities: Lower efficiency Higher cost of electricity production Mainly fixed bed gasifiers (Brown et al. 2009) Research scale pyrolyzer at Haliburton Forest