Biomass assessment and small scale biomass fired

b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 2 5 8 9 e2 5 9 9

Available at www.sciencedirect.com

http://www.elsevier.com/locate/biombioe

Biomass assessment and small scale biomass fired electricity generation in the Green Triangle, Australia Luis C. Rodriguez a,*, Barrie May b, Alexander Herr a, Deborah O’Connell a a b

CSIRO, Sustainable Ecosystems, Bellenden Street, Crace, Gungahlin, Canberra GPO BOX 284, Australia CSIRO, Sustainable Ecosystems, Clayton, Victoria, Australia

article info

abstract

Article history:

Coal fired electricity is a major factor in Australia’s greenhouse gas emissions (GHG)

Received 21 July 2010

emissions. The country has adopted a mandatory renewable energy target (MRET) to

Received in revised form

ensure that 20% of electricity comes from renewable sources by 2020. In order to support

11 February 2011

the MRET, a market scheme of tradable Renewable Energy Certificates (RECs) has been

Accepted 11 February 2011

implemented since 2001. Generators using biomass from eligible sources are able to

Available online 21 March 2011

contribute to GHG emission reduction through the substitution of coal for electricity production and are eligible to create and trade RECs. This paper quantifies the potential

Keywords:

biomass resources available for energy generation from forestry and agriculture in the

Forest

Green Triangle, one of the most promising Australian Regions for biomass production. We

Agriculture

analyse the cost of electricity generation using direct firing of biomass, and estimate the

Residue

required REC prices to make it competitive with coal fired electricity generation. Major

Feedstock

findings suggest that more than 2.6 million tonnes of biomass are produced every year

Renewable energy certificates

within 200 km of the regional hub of Mount Gambier and biomass fired electricity is viable using feedstock with a plant gate cost of 46 Australian Dollars (AUD) per tonne under the current REC price of 34 AUD per MWh. These findings are then discussed in the context of regional energy security and existing targets and incentives for renewable energies. ª 2011 Elsevier Ltd. All rights reserved.

1.

Introduction

Renewable energy and reducing greenhouse gas emissions are now established priorities worldwide. Australia is committed to ensure that 20 per cent of electricity is produced from renewable sources by 2020 [1]. Australia’s electricity requirements are projected to grow at an average rate of 2.2 per cent per year, reaching 415 TW h by 2030 [2]. Electricity generation contributes 33.4 per cent of Australia’s GHG emissions mainly because of the use of coal-fired power stations [3]. The current Australian electricity sector is extremely dependent on fossil fuels, with 92 per cent of the electricity generated from coal, oil and gas, while only 8 per cent is from

renewable sources, including hydro, wind, biomass, biogas and solar [2]. Substantial research and investment in renewable electricity generation will be required to reach the Australian Mandatory Renewable Energy Targets (MRET) of 20% by 2020. In order to support the MRET, a market scheme of tradable Renewable Energy Certificates (RECs) has been implemented since 2001. Each REC represents 1 MW h of “new renewable electricity generation” that is produced by accredited new generators or by increasing the output of existing ones. The liable parties (energy retailers and large consumers who purchase directly from the national electricity market) are obliged to acquire enough RECs every year to cover the required target of electricity from renewable

* Corresponding author. E-mail address: [email protected] (L.C. Rodriguez). 0961-9534/$ e see front matter ª 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2011.02.030

2590


sources, with a penalty for shortfall of 65 Australian Dollars (AUD) per MWh. Since burning of biomass from eligible sources is considered to be GHG neutral, generators are able to contribute to GHG emission reduction through the substitution of biomass for coal for electricity production and by creating and trading RECs. The estimation of the bioenergy potential of a region depends on the land available for growing biomass, the production levels of the different biomass types, and their energy yields, and also on the economic competitiveness of the energy generated from biomass. Several studies evaluating the biomass potential have been done around the world at both at the regional [4,5] and national [6] levels. Based on its current timber and agricultural production, the Green Triangle, an area of southeast South Australia and south-west Victoria is a promising region in terms of biomass production for electricity generation. The aim of this paper is to quantify the potential biomass resources available for energy production in the Green Triangle, analyse the cost of electricity generation using biomass and estimate the required REC prices to make it competitive with coal-fired electricity generation. The paper is structured as follows: Section 2 presents the methodology to estimate the availability of biomass and costs of the different feedstocks existing in the Green Triangle. Section 3 develops an ex ante analysis of comparative electricity generation costs and estimates the breakeven price of

RECs and biomass. Finally, section 4 discusses major findings in the context of regional energy security and Australian energy policies and draws conclusions.

2.

Biomass availability and costs

2.1.

Case study region

The Green Triangle region covers an area of about 6 million ha in south eastern South Australia and Western Victoria and included three separate statistical divisions (SD): South East, Wimmera and Western District. This region was selected because it already has a large, well developed forest industry in the south based on softwood and hardwood plantations, and a major grain growing industry in the north (Fig. 1). The climate is mostly temperate, with average annual rainfall varying from below 400 mm in the north (Warracknabeal) to over 800 mm in the southeast (Portland), while mean maximum temperatures range from 14 to 22 C in the south to 14e31 C in the north. The region is well connected by roads and rail and the port of Portland is an important export terminal. The total population is 210,000 with Mount Gambier in South Australia and Warrnambool in Victoria the largest towns each with populations in excess of 20,000.Forestry industries include saw milling, wood panels, pulp and paper manufacture, and wood chip export while agricultural industries include beef, dairy, wheat, canola, viticulture, and horticulture.

Fig. 1 e Biomass feedstock sources in the Green Triangle.

2591


2.2.

Forestry biomass availability

The supply of biomass from currently planted forest land in the Green Triangle was estimated using spatial land use data from the Bureau of Rural Science (BRS) and the forest growth model 3-PG2 [7]. 3-PG2 was calibrated and validated for the predominant species in the region (Eucalyptus globulus and Pinus radiata) by [8] and [9]. Spatial datasets used to model growth of existing forests have been described in [9]. These included average monthly rainfall, solar radiation, maximum and minimum temperatures derived from ESOCLIM [10], rain days and frost days, soil depth and texture [9], and initial soil water availability [9]. Key assumptions regarding initial stocking, harvest timing and intensity, products harvested, residues and wood density are shown in Table 1. Growth of both softwood and hardwood plantations was initially estimated for the total region and then restricted to the current areas of hardwood and softwood plantations based on a 2006 land use layer from the BRS. In the absence of site quality data, the soil fertility index was assumed to be constant at 0.7 for all plantations as fertiliser application and weed control is standard practise across the region. Model outputs included stem biomass at final harvest (Sf) and stem biomass removed at thinning (St). Total stem biomass (S) was equal to the sum of Sf and St and was divided into sawlogs and pulplogs by multiplying by the proportions of these products (Table 1). Available harvest residues (stemwood material > 8 cm small end diameter) were assumed to comprise 8.3% of total stemwood harvested at clearfell (i.e. 9% of harvested logs removed, D. Turner, HVP, Pers. Comm.). All harvest residues from thinning and all foliage and branches were assumed to be left on site. Estimates for sawlogs, pulplogs and residues were converted into mean annual increment (MAI t3 ha3 year1) by dividing the totals by the time since planting (rotation length plus fallow period). Most hardwood plantations in the region were established in the period 1998e2001 resulting in an uneven age class distribution which is expected to influence future wood flows.

To account for this variation data from the National Plantation Inventory was used to estimates the percentage variation from mean wood production for the period 2010e29 for both hardwood (78e121%) and softwood (94e106%) in any 5 year period. These percentage differences were multiplied by the average wood production figures from 3PG2 to estimate the maximum, minimum and average annual dry mass produced each year in the Green Triangle. Sawmill residues include sawdust, chips, bark and shavings. No data were available on the amounts of sawmill residues or even the amounts of sawlogs processed within the Green Triangle. Thus, these figures were estimated from the amount of sawlog harvested using weighted data on the breakdown of sawlogs into sawmill residues and sawn timber from individual sawmills in the region (Table 2). Residues were separated into chips, bark, green sawdust and shavings (including sawdust and shavings from dried timber).

2.3.

Agricultural biomass

Crop stubble - the fibrous stalk, leaf and chaff material left after grain (or other products) has been harvested - is one potential source of biomass for energy purposes. Following [11], stubble production in the Greater Green Triangle was estimated using data on grain yields from the Australian Bureau of Statistics (ABS), combined with knowledge about the ratio of grain to total above-ground biomass (harvest index, HI). The annual production of harvestable stubble in the Green Triangle was estimated to about 1.75 million tonnes per annum. Harvestable stubble estimates assumed 1 tonne per ha per year of stubble remaining in the field to protect soils and 20% of chaff non harvestable for mechanical reasons.

2.4.

Biomass costs

The Green Triangle is a very competitive environment for the Australian forest industry, so the costs of biomass production,

Table 1 e Assumptions used for forest biomass modelling with 3-PG2. Species:

Softwood

Hardwood

P. radiata

E. globulus

Reference

Soil fertility index Initial stocking (stems ha1)

0.7 1500

0.7 1000

[9] K. Nethercott, Auspine; B. Bradshaw Timbercorp, Pers. Com.

Thinning age (% stems removed) T1 T2 T3 Final harvest age (years)

12 (50%) 19 (30%) 26 (25%) 32

Na Na Na 12

1

1

A. Moore, GTFP, Pers. Comm. A. Moore, GTFP, Pers. Comm. A. Moore, GTFP, Pers. Comm. A. Moore, GTFP, Pers. Comm. B. Bradshaw Timbercorp, Pers. Com. A. Moore, GTFP, Pers. Comm.

70% 30% 10%

0% 100% 10%

[39,40] [39,40] D. Turner, HVP Pers. Comm.

1.0 0.44

1.0 0.55

D. Turner, HVP, Pers. Comm. [41]

Fallow period (years) Products Sawlogs (% logs) Pulplogs (% logs) Residue (% logs) Wood density (t m3 green) Green (t m3) Dry (t m3)

2592


Table 2 e Average proportions of different sawmill residues, their estimated moisture contents (MC) and average cost at the sawmill gate. Data based on a survey mills in the region. Type

Proportion MC% % dry wt.

Chips Bark Green sawdust Shavings Sawn timber Total

42 7 10 3 38 100

53 30 55 12 21

Cost 1

AUD t AUD t1 wet weight dry weight 37 11 11 21 na

79 16 24 23 na

processing and transport might vary between operators and is commercially confidential. The costs of the different biomass types were estimated based on published literature complemented with information provided by forest managers and farmers operating in the region. For products with existing markets (i.e. sawlogs, pulplogs, chips, sawdust and bark) current market prices were obtained through a survey of forest growers and sawmills in the Green Triangle region (Table 3). The costs of collecting and processing the forest residues were calculated following [12] and [13], assuming that in the Green Triangle 50% of hardwood plantations are harvested using a “whole tree” system and the other 50% using the “cut-tolength” system, while for the softwood species it was assumed that all plantations follow the extensively used “cut-tolength” harvesting system and all forest residues would be transported to a fixed chipper located at the mill (B. Bradshaw, Timbercorp Pers. Comm., D. Turner, HVP, Pers. Comm.). Average costs (excluding transport) for each system are shown in Table 3. Transport costs were estimated using a model developed by [14] for estimating costs of logs and chip haulage in the Green Triangle. This model incorporates both fixed (i.e. capital depreciation, interest charges, labour, registration, insurance, repairs and maintenance and salaries) and variable (fuel, oil and tyres) costs to estimate average costs per tonne km1 haulage based on lead distance (one-way distance to destination) and average load mass. Key assumptions used for this model are listed in Table 4. Results for the modelling for lead distances ranging from 10 km to 200 km are shown in Table 5. The cost of transporting the logs and woodchips was estimated to be around

13 cents AUD per tonne km1 while that for forest and crop residues was 23 cents AUD per tonne km1. These values are consistent with those provided by Green Triangle forest managers (D. Turner, HVP, Pers. Comm.) and agricultural experts (Mick Poole, CSIRO, Pers. Comm.). The higher cost of transporting forest residues is due to the longer time needed to load trucks with small, non-uniform material, while the higher cost for transporting agricultural biomass is a result of longer loading time and lower bulk density of baled agricultural residues (0.5 tonnes per m3) compared with logs (1.0 tonnes per m3 green). The amount of available cheap biomass and the cost of transporting the required feedstock are strong limitations for the size of biomass based electricity generation plants [15]. Two sites in the Green Triangle were selected as case studies to assess the capacity of different biomass feedstock to contribute to energy production and GHG mitigation in Regional Australia, one at Mount Gambier, South Australia based on forestry feedstocks and the other at Warracknabeal, Victoria, mostly based on agricultural feedstocks. The bioenergy plant considered in this study was assumed to be a direct combustion 5 MW plant using condensing steam turbines. The selected low cost technology exhibits conversion efficiencies of 20e30% [16] and for small plant sizes with tends to be more profitable than other biomass based technologies for electricity generation [17]. This plant size covers the average electricity requirements of up to 7000 households, i.e. more than the size of most Australian regional towns, and will be able to use the cheapest locally produced biomass without competing with other already established industries that use the same biomass resources as raw material. Conversion efficiency was assumed to be 25% and the feedstock energy content was considered to be 16 GJ per tonne for dry wood from both hardwood and softwood plantations and 18 GJ per tonne for crop stubble [18]. The Green Triangle biomass availability per feedstock type and the plant gate costs of the different feedstock for the two locations are presented in Table 6.

2.5.

Green Triangle biomass supply curves

2.5.1.

Mount Gambier

Every year more than 2.6 million tonnes of biomass are produced within 200 km of Mount Gambier (Fig. 3). Agricultural residues represent about 38% of the total biomass. These are available at a plant gate cost between 84 and

Table 3 e Collection, chipping and other (excluding transport) costs (AUD per tonne dry weight) of forestry harvest residues either at the landing (for whole tree harvest operations) or across site (for cut to length operations). Data from [12] et al. (2001) expressed as 2009 AUD. Harvest system

Collection

Chipping

Othera

Total

AUD per tonne DW AUD per tonne DW AUD per tonne DW AUD per tonne DW Hardwood Whole tree harvest chipped at mill Hardwood Cut-to-length chipped at mill Softwood Cut-to-length chipped on site a Includes royalties and storage cost.

11 16 20

4 4 15

2 3 4

17 23 39

2593


Table 4 e Key assumptions used in a model for estimating the transport cost of different feedstocks. All values for pulplogs and woodchips and load sizes, fixed and variable costs for forest residues and crop stubble are based on values for a BDouble (Iveco, 260 kW) with two trailers (for logs, residues and stubble) or chip bins (for woodchips) from [14]. Loading times (excluding 5 min for measuring) and loading costs for forest residues and crops stubble were assumed to be three and two times that for pulplogs while load weight for wheat stubble (32.5 tonnes) is based on figures provided by hay bale transport companies. Item

Unit

Average load size Production rate Operating hours Loading time Average truck speed Max. loads where lead distance