Life Cycle Assessment of Using Straw to Produce Industrial...

Life Cycle Assessment of Using Straw to Produce Industrial

Energy in New Zealand

Prepared by:

Vicky Forgie Robbie Andrew

May 2008

Life Cycle Assessment and Costing of Landcare Research and Industrial Energy from Straw in NZ New Zealand Centre for Ecological Economics

Contents Introduction...................................................................................................................................1

Goal and scope of study........................................................................................................1 Functional unit ......................................................................................................................1 Data quality requirements .....................................................................................................1 Allocation procedures ...........................................................................................................1 Study limitations ...................................................................................................................2

Background...................................................................................................................................4 New Zealand life cycle inventory analysis ...................................................................................5

LCA boundary ..........................................................................................................................7 Growing ....................................................................................................................................7

Straw baling and storage.......................................................................................................8 Straw transport to plant.........................................................................................................9

Plant operation ........................................................................................................................10 Residue waste......................................................................................................................11 Capital .................................................................................................................................12 Capital embodied energy ....................................................................................................12 Operating and maintenance.................................................................................................13

Potential impacts of alternative production systems...................................................................14 Sustainability impacts .............................................................................................................15

Results and discussion ................................................................................................................16 Combined heat and power ......................................................................................................16 Interpretation...........................................................................................................................17 Scenario analysis.....................................................................................................................18 Straw-fired heat-only ..............................................................................................................20 Interpretation...........................................................................................................................22 Scenario analysis.....................................................................................................................23

References...................................................................................................................................25 Appendix 1: Overview of LCA method from Beer et al. (2007)................................................28 Appendix 2: Ash data from Newman, 2003 ...............................................................................29 Appendix 3: Transport energy consumption...............................................................................31 Appendix 4: Electricity...............................................................................................................32 Appendix 5: Common factors.....................................................................................................33


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Introduction Landcare Research has been contracted under Bioenergy Options for New Zealand Contract ID C04X0601 Proposal No. PROJ-12011_ORI-FRI to carry out life cycle assessments (LCAs) to explore potential options for producing bioenergy in New Zealand.

Goal and scope of study

The purpose of the study is to provide input into the strategic direction New Zealand takes with regard to:

1) dependence on imported energy (energy security, balance of trade)

2) dependence on non-renewable energy resources (energy security)

3) emissions of greenhouse gases (environment)

The goal of the study was to determine the energy inputs, greenhouse gas emissions, and costs for conversion of waste straw to heat, and, combined heat and power. Energy inputs are disaggregated into total primary, fossil-fuel based (non-renewables), and imported. Associated environmental impacts are discussed but not quantified.

The intended audiences are local and central government policy-makers and business interests. These parties will need information to assess the best policy or business investment for New Zealand.

Functional unit

The functional unit for the study is 1 GJ of energy.

LCA (life cycle analysis) is a holistic approach that helps achieve sustainability standards by accurate life-cycle measurements of, for this report, the energy requirements and greenhouse gas impacts of a given bioenergy. It helps provide transparency from field to final use.

Data quality requirements

The LCA and LCC (life cycle costing) are based on the ‘average’ system of production for the defined system boundary. The system boundary determines what to include and what to exclude. For example, with straw, if the system boundary is drawn to include soil, reincorporated straw remains within the system and is not treated as a co-product. If soil is outside the system boundary then all straw constitutes a co-product regardless of whether it is baled or reincorporated (Clift et al., 1995).

This report presents LCAs and LCCs based on production processes that are feasible in New Zealand. Where the production process currently takes place in New Zealand, relevant New Zealand based data have been sourced if possible. Where New Zealand specific data are not available (as for example, producing heat and electricity from straw) overseas data have been adapted.

Allocation procedures

In LCA, environmental impacts and benefits are calculated for economic goods. These goods are generally produced by a number of manufacturers that use a range of production systems. In many cases there is joint production where two or more products are outputs from the process. In economic costing, and LCA, an approach is needed to proportion the environmental impacts of the production system to the economic goods. The choice of method used for accounting for co-products can have a substantial impact on the results. There are two main approaches: allocation and system extension.


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Allocation is based on allocating the burdens arising from the overall production between co-products in some appropriate ratio. When a production process contributes to several products, the total system environmental load has to be shared between these by allocation. This is usually economic value, mass or other attributes of the system (for example protein content). The choice of allocation method may impact on the outcome (Bernesson, 2004). Allocation LCA measures the average impact of production.

System extension LCA measures the consequence of a product or process substitution by extending the system boundary to include the use of a product. If the product is no longer available, what are the impacts of producing a good that will be a substitute product? System expansion is performed to maintain comparability of product systems in terms of product outputs. This is done by separating the unit process into two or more subprocesses and collecting the input and output data related to these subprocesses. The product system is expanded to include the additional functions related to the co-products. If production output is reduced in one area (for example kiwifruit going to stockfood is redirected to biogas production) the net impact is measured by adding an equivalent production in the other systems (replacement stockfood production). System extension LCAs attempts to measure the marginal impacts of production.

This study has used economic allocation as the method for analysis, as required by Scion.

Study limitations

While there are many advantages to using LCA to provide a holistic comparison of bioenergy forms considering the whole production chain, there are also limitations. Results should be interpreted cognisant of the following limitations (following Zah et al., 2007):

- The focus of the life cycle assessment (LCA) has been material and energy flows relating to greenhouse gas production, fossil fuel use and economic costs. Other environmental and economic impacts will also result. These would be quantified by the impact assessment stage of an LCA, which has not been included in this report.

- The assessment approach calculated only the primary environmental impacts of the process chain, e.g., energy consumption and pollutant emission during the cultivation of energy canola. Secondary effects were not covered. For instance, if the demand for canola results in the conversion of forest land or wetlands, the environmental impact of this has not been included.

- Economic allocation is based on current prices. The price of goods depends on market dynamics and will change over time.

- The process chains investigated represent only a subset of all production processes; many more production paths are conceivable. The paths chosen, however, are considered especially relevant for the current situation in New Zealand.

- The most recently available existing New Zealand data has been used as much as possible. Where this is not available overseas data have been used.

- Future and alternative process chains have been discussed and some have been explored in the scenario analysis section.

- Results may not apply to individual plants, because the environmental impacts in individual cases may differ greatly from the average situation.

- The study does not address future consequences of a shift to renewable fuels; for example, the environmental impacts should agricultural products be grown on such a large scale for bioenergy that agricultural production as a whole is intensified. The


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effects of change in demand have not been covered either; for example, if biofuels are regarded as environmentally friendly and preferred to fossil fuels, demand for biofuels may increase; the opposite impact on demand is also possible if biofuel production is linked to unwanted social and environmental practices.


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Background Each season, arable cropping in New Zealand produces large volumes of excess straw that are not used. Unwanted straw is generally disposed of by cutting up and leaving on cropped fields to break down into organic matter. It can also be burnt to reduce both the cost of establishing the next crop and vulnerability to pests. However, burning has become less common, given tighter restrictions imposed by local authorities.

Sustainability criteria for various soil types and local climates are being developed from multi-year experiments by soil scientists. For typical New Zealand cropped soils, current understanding is that an average of 50% of the crop residue can be removed without impacting on fertility. This finding has been confirmed in research on black soils in western Canada that showed repetitive straw recovery did not reduce soil carbon levels. Stubble and root contribution was regarded as sufficient to offset carbon losses (Hartman, 1999 cited in Cameron et al., 2004). It has therefore been assumed that 50% of crop residue has no fertility value to farmers and that leaving straw on the soil surface is purely a means of disposal.

Large volumes of surplus straw are used to fire combined heat and power (CHP) plants in Europe, with many of these located in Denmark. The long-term policy of the Danish government is to be entirely independent of fossil fuels – coal, oil and natural gas – to improve energy security and minimise greenhouse effects (Danish Energy Authority, 2007). A new straw-fired CHP unit at Fynsværket is planned to be commissioned in 2009 (Energinet, 2007).

These LCA and LCC analyses examine the feasibility of a CHP plant fired by straw, and a heat-only plant fired by straw as an alternative means of generating energy in New Zealand. The proposed feedstock is straw that is currently left to breakdown as a means of disposal, rather than any straw with a market value.

“CHP is the simultaneous generation of usable heat and electricity from a reciprocating engine, gas turbine, steam turbine or combined cycle system. Such units provide efficiency gains compared with the separate generation of heat and electricity. CHP units are often sized to particular heat demands and connected to lower voltage distribution systems. This reduces transmission and distribution losses compared to power stations that distribute at very high voltages to the grid” (Warwick HRI, 2007, p. 37).

To make the process economic, and fully utilise the heat generated, a straw-fired plant in New Zealand would ideally be located with an industry that required continual heat.

A new generation of smaller units is making the use of CHP more commonplace. The economics of CHP are largely determined by the cost of the fuel used to fire boilers to generate heat and by the value of the electricity sold. If the plant running the CHP unit cannot use all the electricity generated, then ability to feed excess into the national grid is needed. Reciprocating engines produce two grades of waste heat: high grade heat from the engine exhaust and low grade heat from the engine cooling. Natural gas-fired engines have an electrical efficiency of range from 28% to 40%, and waste heat recovery from CHP can increase the overall efficiency to 70%–80% (Warwick HRI, 2007).

A heat-only plant would use straw to fire a boiler to produce steam for heating or just hot water for use in a processing plant.


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New Zealand life cycle inventory analysis The region with the greatest volume of surplus straw in New Zealand is Canterbury. Timaru, located south of Christchurch on the Canterbury Plains, is a plausible location for a straw-fired plant as the town is both surrounded by arable farming, and has industries that require heat. Potential partner industries in the town using large amounts of heat and steam include the McCain vegetable processing factory currently using coal for boiler energy, and the Alliance Group freezing works. For these reasons, the scenario assumed for these LCAs is a straw-fired plant located in Timaru, supplied with surplus straw from the surrounding hinterland.

Plants generating heat and electricity from straw have been operating in Denmark since 1996. Because there are no plants in New Zealand using straw as a feedstock, data from the Masnedo plant has been used for the LCA and LCC. The Masnedo plant is one of a number of straw-fired plants in Eastern Denmark and is regarded as a reasonable representation of straw/biomass plants in Denmark (Nielsen et al., 2003). The plant capacity is 10 MW of electricity and 23 MW of heat and it consumes 40,000 tonnes of straw annually (Nielsen et al., 2003). The Masnedo plant was commissioned in 1996 and therefore represents modern technology. It is primarily fired with straw but wood chips can replace straw if needed. In 1999, the year for which the data used here applies, the input from biomass other than straw was low (Nielsen et al., 2003). The plant’s production is determined by heat demand. The electricity output is approximately 33 GWh/year and heat produced 94 GWh/year (SK Power Company, 1999). The boiler intake is 9.5 tonnes of straw per hour (SK Power Company, 1999).

The important steps in Masnedo CHP production as set out by Neilson et al. (2003) are:

1) Straw bales (about 0.5 tonnes each, 10–20% water content) are delivered to the plant in trucks and stored. On-plant storage capacity is around 1000 tonnes of straw which is just over 4 days supply.

2) Straw is transported by a crane and conveyor lines to two vertical “snails” where the straw is cut into pieces.

3) The loose straw is transported to the fire chamber through an air-tight channel and burnt to heat a boiler to 520°C with a pressure of 90 bar.

4) The walls of the boiler are pipes containing water that becomes steam at high temperature. The steam turns the turbine connected to a generator to produce electricity.

5) Flexibility in the production of heat and electricity is achieved by storing condensation heat in a heat accumulator tank.

6) Heat is distributed to local residential and business users when needed.

7) The steam is condensed back to water via heat exchangers.

8) The plant is equipped with an electrical filter for reduction of fly ash emission but no SOx and NOx filtration system has been implemented. Slag is returned to agricultural land and used as fertilizer. Due to the high content of heavy metals, fly ash is deposited.


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Figure 1: Diagram of a combined heat and power plant (Source: EHN, 2003)


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LCA boundary

Figure 2: Boundary of the LCA

Growing Canterbury is the principle region where arable crop residues are available in sufficient volume to consider using straw as a feedstock for energy generation. In 2005 106,500 ha were harvested (Statistics New Zealand, 2005). Of this area, 38,500 ha are from a variety of seed crops (and ‘other crops’), so no production figures are given, but residues may be similar to those from wheat that occupied a similar area. Table 1 lists the surplus tonnage of residues from wheat and barley crops in Canterbury.

Table 1: Available residue production in Canterbury (tonnes)

Wheat Barley Total

Crop standard moisture content 292 678 204 149 496 827

Dry weight (less 13%) 254 630 177 610 432 240

Harvest index (50%) 0.5 0.5

Residue (dry weight) 254 630 177 610 432 240

Surplus residue (dry weight) 127 315 88 805 216 120

Source: Saggar et al. (2007)

Because the crop residues removed are produced as an unwanted by-product of another farming activity, and have no economic value to the farmer, no monetary value has been

Straw baling

Farm for fertiliser

Storage and conveying

Landfill

Stack/flue

Bag filter

Cyclone

Steam for CHP

Boiler

Straw shredder

Bottom ash

Fly ash


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assigned to the straw. The proposed plant will burn 40,000 tonnes of straw leaving a surplus of at least 176,120 tonnes in the Canterbury region. Using the economic allocation method, therefore, the energy inputs and costs of the growing and harvesting operation are all allocated to the primary crop.

The cost of straw fuel for the plant is determined by the cost of baling and storage, and by the distance straw is carted. The power station operation requires a steady supply of suitable straw throughout the year. Logistics and coordination is required to maintain a reliable flow of straw and smooth out the variations in delivery, supply and storage capacity.

Straw baling and storage

Additional energy and costs are assigned to the residues for baling and storage as these processes would not be undertaken if the straw was not removed. The straw baling and handling costs given in Table 2 are a rule-of-thumb cost based on past production cost analyses of baling and handling straw (Nick Pyke, pers. comm.).

Table 2: Average residue production rate per hectare and handling costs from arable crops

Wheat Barley Field peas

Grain yield (t/ha) 8.5 7.5 3.0

Grain dry weight (t/ha)* 7.4 6.5 2.4

Harvest index (50%) 0.5 0.5 0.3

Straw/stower dry weight yield (t/ha) 7.4 6.5 5.6

Surplus straw/stover **(dry weight t/ha) 3.7 3.3 2.8

Straw cost $/tonne (fresh weight) 22 22 25 *Based on moisture content in wheat and barley = 13%; maize = 14%; field peas = 20% ** 50% of straw for typical scenario, but varies with soil and crop regime

Burtt (2006) gives the contract price in Canterbury for baling a large square bale of hay (equivalent to 15 conventional 25-kg bales) as $12.50 per bale, which puts the price of a 500-kg bale at $16.66. The $22 per bale cost is therefore a reasonable figure to use given that the larger bales should be cheaper to handle using specially designed machinery. It has been assumed a Hesston baler producing 500 kg bales at a rate of 23 tonnes per hour is used (AGCO, 2008). The $22/tonne fresh weight cost (i.e. including 13% moisture) is assumed to cover all quality control employed immediately after baling, moisture checks, bale size and shape checks, and random weight checks. For baling, a price of $1.465/litre for diesel was used (MED, 2008), at a conversion rate of 37.86 MJ/litre (MED, 2007b). The baling and storing machinery requirements used in the LCA and LCC are set out in Table 3. The embodied energy in the machinery has been calculated using 160MJ/kg of machinery with an estimated 15 year lifespan (Wells, 2001). It has been assumed that the bales are protected from the weather using polythene sheeting with a 1-year life as per Elsayed et al. (2003).


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Table 3: Baling and storing of straw for the straw-fired plant

Process Description Machinery used

Baling Big baler for 500–700 kg/bale. Capacity 12–

25 tons/hour. Bale density 140–185 kg/m3

Tractor pulling baler

Loading in the field; transport

to farm; unloading at the farm

Large tractor with front-end loader for 2

bales loads the bales to truck in the field

Tractor with front end loader

Truck

Storing at the farm Storage is outdoor and requires covering

with plastic

Transport to straw-fired plant Large tractor with front-end loader for 2

bales loads truck at storage. Truck can

carry 12 bales and trailer 12 bales in two

layers. The bales have to be covered by

curtain sides to prevent straw loss on route

Tractor with front end loader

Truck and trailer unit

Unloading at straw-fired plant A crane on the plant is equipped with grip

hooks that can lift 12 bales (one layer) at a

time off the truck. Average weight and

moisture content measured and recorded

on computer

Crane for unloading 12 bales

Weighing cell for 12 bales

Equipment for moisture

content

(Adapted from: DTI, 2007)

Straw transport to plant

The plant for this analysis has been assumed to be a similar in size to Masnedo, which is a 33 MW plant capable of generating 33 GWh of electricity and 94 GWh of heat per year from 40,000 tonnes of straw. To calculate the distance to transport straw, the plant has been located at Timaru which is reasonably central in the Canterbury region.

The availability of straw was calculated using the AgriBaseTM database (AgriQuality, 2007) to find the land area in arable crops. The available straw was assumed to be 3.7 tonnes/ha (dry weight) based on the surplus straw production rate from wheat given in Saggar et al. (2007).

Table 4 shows the total area in arable cropping and the available straw within a given distance of Timaru. In calculating the available straw it was assumed that only one third of the arable cropping area would be in crops for a given year, and, that it would be uneconomic to collect crops from areas of less than 25 ha.

Table 4: Straw availability within given distance of processing plant in Timaru

Distance from Timaru

(km)

Total arable area

(ha)

Available straw

(tonnes DW pa)

50 28,017 34,550

55 31,432 38,770

60 38,026 46,900

Supplying a 40,000 tonne/year straw-fired plant in Timaru would require feedstocks from within a 60 km radius. The mean straight-line distance of each farm from Timaru is 36.7 km. The road distances were calculated using ArcGIS Spatial Analyst to calculate the shortest distance by road to Timaru for each point on every road in the region. This layer


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was then intersected with the map of the target farms to calculate the minimum road distance to Timaru for each farm. Building in an allowance for extra distance by road increases the distance to 44 km for a one-way trip.

It is assumed that large 500-kg bales are transferred from farm storage using a tractor with a front end loader. Transport to the CHP plant uses a truck (11 tonne empty) and trailer (8 tonne empty) unit which can carry 24 bales.

Figure 3: Crane unloading a delivery of straw to a CHP plant (Source: Newman (2003))

Figure 3 shows the unloading by crane of a typical delivery vehicle in England. Special grabs are used to pick up pairs of bales along the full length of the vehicle and trailer. Within each grab is a microwave moisture-measuring system that provides an automatically calibrated value of moisture for each pair of bales; this information is fed directly to the power station’s control system (Newman, 2003).

Plant operation Straw is quoted with a range of calorific values. Khor at al. (2007) give a gross calorific value of 16.36 MJ/kg. A British study on energy from biomass gives a figure of 14.8 MJ/kg (at 15% moisture content) which is said to be approximately half the value of coal and one-third that of oil (Department of Trade and Industry, 1999). Not all the calorific content of straw is converted into heat energy. The Masnedo plant had an output of 11.76 MJ/kg of straw, and this more conservative figure has been used in the analysis.

The LCA for producing energy from straw at Timaru has been based on the LCA data from the Masnedo plant as set out in Table 5. Inputs and outputs cover all processes related to heat and power production including administration and local wastewater treatment. The power and heat production, is estimated based on an average straw based CHP plant with a yearly net electricity efficiency of 25% and an overall net efficiency of 90% (Nielsen et al.,


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2003). Use and disposal of the ash and the impacts of using seawater for cooling purposes were not included in the Masnedo LCA analysis.

Table 5: Inventory data for decentralised straw based CHP production

Substance Unit Quantity

Inputs Straw t 1.0

Water litre 75

Diesel oil litre 0.18

Heat (own prod.) MJ 40

Electricity (own prod.) MJ 396

Outputs Products Electricity GJ 3.06

Heat, net GJ 8.7

Air emissions CO2 (fossil) g 687

SO2 g 680

NOx g 1900

CO g 910

HCL g 670

N2O g 20

Dioxin ug 0.32

Slag and ash Fly ash (deposit) kg 8.3

Slag (return to

farmland) kg 54

(Source: Nielsen et al., 2003)

Residue waste

Slag (or bottom ash) and fly ash are output as by-products from energy production at the plant. Both contains a number of chemical elements and the composition of each is detailed in Appendix 2 (Newman, 2003). The ash content of straw is similar to coal but with a lower sulphur content (Department of Trade and Industry, 1999).

In Denmark, slag is returned to agricultural land and used as fertiliser. It has an average composition of phosphorus (P): 0.8–2.1%, sulphur (S): 0.1–0.7%, calcium (Ca): 6–13%, nitrogen: 0.05–0.08% (all w/w) (Videncenter for halm og flisfyring, 1999b cited in Nielsen et al., 2003). For this LCA it has been assumed that slag is used as fertiliser, and for the cost and energy transport figures, that the average distance trucks travel delivering straw to the straw-fired plant is the same distance as they travel taking the slag to farms. It has also been assumed the slag is spread with other fertilisers that would have been spread, so no additional cost or energy are required for spreading costs and energy use.

Reduced fertiliser use per year from 44,000 tonnes of straw is equivalent to only 396 tonnes of superphosphate (Craig Ross, 2008, pers. comm.). As the minerals will be mixed with 2,376 tonnes of ash, savings on fertiliser costs would be negligible, and it has therefore been assumed sale of ash does not provide a revenue stream. The ash will, however, return organic content to the soil. The use of ash by farmers is taken to be a win-win situation where the plant gets rid of the ash and the farmers gain soil fertility with no money exchanging hands.

Straw biomass fly ash cannot be used directly as a nutrient source for soil due to its high heavy metal context, and fly ash from the Masnedo plant, for example, is landfilled. Electrokinetic remediation can be used to clean biomass ash. Research evaluating the concentration of cadmium in straw ash from Masnedo CHP plant in Denmark showed it


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could be cleaned to approximately 3 g of cadmium per ton of dry ash, which could then be applied to arable soils as long as only 0.5 ton of dry ash is applied per hectare every 5 years. It was estimated the cost would be lower than disposal costs in Demark (Nielsen, 2000).

Fly ash from the Masnedo plant has a cadmium content of approximately 11.2 mg/kg DM (Hansen et al., 2004). According to Ministry for the Environment guidelines for hazardous waste, ash with this level of cadmium should be accepted at Class A landfills in New Zealand (Jodie Franks, 2008, pers. comm.). If the CHP plant is located at the McCain vegetable processing plant, the return distance to deposit the fly ash at the Timaru landfill would be 17 km. An alternative location, the Alliance Group freezing works, is less than 13 km return. The cost of transferring the fly ash by truck has been calculated based on the 17 km distance. A $75/tonne (PCE, 2006) cost for landfilling has been included.

Capital

Denmark commissioned 7 straw-fired CHP plants in the period 1989 to 2000 (DTI, 2007). No plants have been commissioned since 2000. Most Danish straw-fired CHP and power plants received subsidies to cover construction costs and still receive subsidies for electricity generated. “Without these subsidies only a very small amount of straw would have been used for energy purposes in Denmark” (DTI, 2007, p.8).

The main capital equipment required for a CHP plant to produce energy from straw are:

1. Feed-in system – crane to unload trucks and straw storage area

2. Conveyor belt to move straw

3. High pressure steam boiler

4. Steam turbine

5. Generator

6. Flue-gas recovery boiler

Danish construction costs were very high per MW of energy. The investment required for a plant with a steam turbine, grate firing and straw combustion was given as between 4.3 and 5.5 M€/MW (Danish Energy Authority et al., 2005), which is approximately $NZ200810.7m. For this reason a desktop literature search was undertaken to find costs for other CHP plants designed to use straw as a feedstock. Based on the capital cost of a CHP plant in Spain, and another in England, a cost of $NZ1.65m per MW was used in the LCA. The cost of the proposed Chinese plant was considered too low to use.

Table 6: Construction costs of existing or proposed straw-fired CHP plants

Year built Location Size

MW

Straw

(tonnes)

Cost

(million)

$NZm/MW $NZ2008m/MW Reference

2007 China* 150 373000 €55 0.64 0.7 Berstad, 2007

2002 Spain 75 160000 €51 1.39 1.6 EHN, 2003

1997 England 108 222000 £55 1.24 1.7 Select Committee,

2004

*Proposed. (Source: EHN, 2003; Select Committee on Science and Technology, 2004; Berstad, 2007)

Capital embodied energy

The calculations for the amount of energy embodied in the CHP plant are from a German 26.7 MW biomass CHP plant scaled up to a 33 MW CHP plant. The common materials used


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in the construction of the Pfaffenhofen, Bavaria CHP plant according to Moerschner and Kazmierczak (2004) are listed in Table 7. The embodied energy and CO2 emissions in the materials have been converted using Alcorn (2003).

Table 7: Energy embodied in the construction materials of CHP plants

Common materials 26.7MW CHP

tonnes used

33MW CHP

tonnes used

MJ/tonne

(Alcorn, 2003)

kg CO2/tonne

(Alcorn, 2003)

Concrete 7602 9396 1400 189

Gravel 3885 4802 40 2.3

Construction steel 1994 2464 31300 1242

Wall material (assumed aluminium,

extruded and anodized) 1012 1251 23800 887

Operating and maintenance

Maintenance costs for CHP plants burning straw are high. Straw contains higher levels of N, S, K, Cl, etc., than wood, which leads to higher emissions of NOx and particulates, increased ash, corrosion, and slag deposits. Very high temperatures increase the risk of heavy corrosion and slagging problems. CHP plants burning straw are constructed in such a way that it is relatively easy to replace corroded tubes on top of the boiler (SK Power Company, 1999). This replacement is costly and requires downtime for the plant. Recent advances in materials and boiler design allow newer plants to have higher steam temperature and efficiencies (Danish Energy Authority et al., 2005).

Annual maintenance costs were taken as 2.5% of total capital costs, as per Mortimer and Elsayed (2001). The embodied energy requirement is an estimate based on replacing half of the steel, over the 20 year lifetime of the plant (Danish Energy Authority et al., 2005).


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Potential impacts of alternative production systems The viability of a straw-fired plant is dependent on a number of factors, all of which can change overtime. These include efficient use of the energy generated, the availability of straw, and the plant size.

Efficient use of energy

Being able to use the heat produced efficiently is critical for the viability of CHP and heat-only operations. The plant, therefore, needs to be built in partnership with a process that requires a continuous supply of heat or hot water. There is less scope to cope with fluctuations in energy demand than with gas powered plants as straw-fired plants are slow to turn up and down.

The cost of the turbines to generate electricity has been included in the LCA. However, to ensure all electricity generated is used there may be additional expenses associated with connection to the grid that have not been included.

Availability of straw

The importance of a continual, steady supply of good quality straw to the power station cannot be overemphasised as the cost of cooling down and heating up a CHP plant are high. For the 36 MW Ely plant located at Sutton, near Ely, Cambridgeshire, England, a closure due to lack of straw was estimated to have cost in excess of £50,000 per day (Newman, 2003).

There is currently a limited market for straw in New Zealand but any alternative uses found may impact on the viability of the CHP plant. For example, the Keenan supplementary feed for cows system, recently introduced to New Zealand, promotes straw as a fibre source and recommends a minimum straw supply of 300 kg/cow to cover lactation plus 250 kg/cow for the dry period (AgriBusiness, 2008). Despite the growth in dairying in the Canterbury region, supplementary feed would not use large volumes of straw compared to what is produced.

There is more canola currently being grown in the Canterbury region than in the past, which has the potential to reduce the volumes of cereal straw. The technical feasibility of using oilseed rape straw and whole crop straw as alternative or supplementary fuels for a modern combustion plant designed for cereal straw has been researched. Oilseed rape straw (or canola) has significantly different combustion characteristics, but is suitable if adequate adjustments are made or the amount is restricted when co-firing with cereal straw (Newman, 2003). Depending on when it is harvested, using oilseed rape straw has the potential to extend the harvest period and makes available additional fuel at a time when stocks are almost depleted.

If farmers decide they want a return for the inconvenience of providing straw to the CHP plant they may restrict supply to achieve this once the plant is up and running. There are costs for the farmer in terms of dealing with the contractors required to bale and transport the straw to the CHP plant. There is also the land cost of the area required for storage, which can be up to 6 m2 for every hectare of cropped land. In England, for farmers supplying the Ely plant, the average time a stack of straw stands on the farm is eight months. If farmers demand an economic return for their straw there would need to be an allocation of part of the costs and energy use of growing the initial crop to the straw-fired plant, which would reduce the economic returns and energy balance.


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Plant size

The LCA has been based on a large-scale operation. There are also small-scale biomass CHP plants available that could be used on-farm or in small factories, for example, the Talbotts system, where combustion fires a micro-gas turbine indirectly via a high temperature heat exchanger. The BG100 can be operational for approximately 8000 hours per annum and is capable of producing 100 kW of renewable electricity and 200 kW of renewable heat. The electrical efficiency is claimed to be 2–3 times greater than steam-based systems at this size. The manufacturer claims the BG100 saves approximately 600 tonnes of carbon dioxide emissions per unit per year compared with conventional fossil fuel powered systems in the UK (Talbotts Biomass Energy, no date).

Sustainability impacts The optimum size for a straw-fired power station is where the total cost of delivered power is minimised by the right combination of capital costs and transport costs. Research by Bernesson et al. (2004) indicated that the efficiency of scale from larger plants was cancelled by the additional cost of biomass transport.

Straw as an energy source is CO2 neutral. When supplied by farmers who later use the slag as fertiliser for their fields, straw forms part of a natural cycle.

Use of straw-fired plants must also take into account air emissions. More modern centralised plants built in Demark are installed with desulphurication and denoxification units, so the emissions of SOx and NOx per produced unit of heat and power are presumed to be lower (Nielsen et al., 2003). Before being discharged from the stack, the flue gas passes through an electrostatic filter that removes 99% of its content fly ash, so dust and particulate, as well as toxic chemical release to the atmosphere, are minimised (CADDET, 1999).

Due to environmental regulations, fly ash is at present stored in landfills. However, systems have recently been designed to extract heavy metals from fly ash, for example, electrokinetic remediation (Nielsen, 2000), or the flue gases can pass through an economiser and be neutralised by lime injection before passage through a bag filter to remove particulates and acid gases. The resultant fly ash is rich in potassium and phosphate salts and is the basis of an organic fertiliser (Newman, 2003).


16

Results and discussion

Combined heat and power Table 8 shows the final results of the LCA and LCC broken down by each of the significant inputs.

Table 8: Straw CHP LCA and LCC

Amount Unit Description Cost ($NZ)

Primary MJ

Fossil MJ

Imported MJ kg CO2-e

Notes


Inputs

3 MJ Fuel for tractor pulling baler - 3 3 3 0 (a)

2 MJ Fuel for tractor loading bales on trailer - 2 2 2 0 (b)

0.37 MJ Fuel for truck transport to farm storage - 0 0 0 0 (c)

1 MJ Fuel for unloading truck at farm storage - 1 1 1 0 (d)

18 MJ Plastic cover $0.69 18 18 18 1 (e)

2 $ Baling cost $2.15 (f)

4 MJ Embodied energy in equipment - 4 4 4 0 (g)

Straw transport to CHP plant

1 MJ Fuel for loading truck $0.05 1 1 1 0 (h)

88 km Transportation to Timaru $0.28 9 9 8 1 (i)

2 MJ Embodied energy in trucks and trailers $0.24 2 2 2 0 (j)

0.4 $ Wages for drivers $0.35 0 0 0 0 (k)

0.24 $ Truck and trailer maintenance $0.24 2 2 2 0 (l)

$1.15

Straw combustion

85 kg Straw (dry component) $0

0.58 MJ Diesel $0.02 1 1 1 0 (m)

13 MJ Capital $5.75 13 9 8 1 (n)

4 MJ Operating and maintenance $2.87 4 4 4 0 (o)

0.60 $ Wages $0.60 (p)

0.37 $ Rates $0.37 (q)

1.34 $ Overheads $1.34 1 1 1 0 (r)

0.57 $ Margin $0.57 (s)

6.4 litres Water $0.00 (t)

Waste removal

4.6 kg Transportation of slag to farmland $0.09 0 0 0 0 (u)

0.7 kg Transportation of fly ash to landfill $0.06 0.0 0.0 0.0 0 (v)

Output

1000 MJ Electricity and heat $16.83 63 60 58 4


17

Notes (a) 4 balers required to bale one season (estimate); lifetime of 15 years (Barber, 2003); 7-tonne

minimum tractor required (90 kW) for Hesston baler (AGCO, 2008); 40% diesel engine efficiency; Estimated 85% average load on engine; 23 tonnes of straw baled per hour (AGCO, 2008)

(b) 4 x 7-tonne tractors with front end loaders; energy requirements as for note (a) (c) 4 x 10-tonne farm truck; energy requirements as for note (a) (d) 4 x 7-tonne tractors with front end loaders; energy requirements as for note (a) (e) 2 tonnes of polyethylene sheeting used to protect each storage stack of 1000 tonnes of baled

wheat straw, with a life of 1 year and a direct energy requirement of 47 MJ/kg and a feedstock energy requirement of 46 MJ/kg for low density polyethylene (Elsayed et al. 2003); $3514/tonne (Cosio Plastics, pers. comm.)

(f) $22/tonne (Nick Pyke, pers. comm.), includes costs of fuel (g) 12 balers (8 tonne), 4 tractors (7 tonne), 4 trucks required (5 tonne); 160 MJ/kg embodied

energy (Wells, 2001); vehicles imported (h) 4 x 7-tonne tractors with front end loaders. 12 MJ of fuel required to load 1 tonne of straw

(calculated); $NZ1.465/litre diesel price at 18 April 2008 (MED, 2008); 37.86 MJ/litre (MED, 2007)

(i) Return trip calculated from AgriBase. $NZ1.465/litre diesel price at 18 April 2008 (MED, 2008); 37.86 MJ/litre (MED, 2007)

(j) 11-tonne truck and 8-tonne trailer (Chris Satherley, pers. comm.) (k) 2.5 hours per trip estimated from 88 km plus 30 minutes turnaround at each end, $20/hour,

(TVNZ, 2007) (l) 100% of purchase price of vehicle over life time (Burtt, 2006)

(m) 0.18 litres per tonne of straw (Nielsen et al., 2003); $1.465/litre diesel price at 18 April 2008 (MED, 2008)

(n) Based on Moerscher & Kazmierczak (2004) German biomass CHP 26.7 MW plant. Proposed plant is 33 MW. So inputs * 1.23; 9396 tonnes of concrete, 4802 tonnes of gravel, 2464 tonnes of construction steel, 1251 tonnes of aluminium. 1400 MJ/tonne concrete, 40 MJ/tonne of gravel, 31 300 MJ/ tonne of construction steel, 23 800 MJ/tonne of aluminium (Alcorn, 2003)

(o) Maintenance costs 2.5% of capital cost (Mortimer and Elsayed, 2001). Energy estimate based on half of steel replaced over 20-year lifetime of plant.

(p) 5 workers@ $40,000/yr,1 engineer@ $80,000/yr. Based on 24 permanent jobs Spain 160 000 tons of straw/yr (EHN,2003)

(q) Rates estimated from Lot DP 35657 (Timaru District Council website). ECAN rates estimated from Funding Impact Statement (Environment Canterbury website)

(r) Assumed to be 8% of total cost. Derived from overhead expenditure for Food and Beverage sector of I-O table

(s) Assume 10% return on investment (t) 75 litres per tonne of straw (Nielsen et al., 2003); 44 c/m3 local council water charge (Timaru

District Council) (u) Assume same distance as straw collected from (88 km) (v) Taken to local landfill, 8.7 km one way; landfill disposal charge $75/tonne (PCE, 2006)

Interpretation The main costs associated with producing energy from straw are the capital costs ($5.75 per 1000 MJ), and operating and maintenance costs ($2.87 per 1000 MJ). Together these costs account for $8.62 of the $16.83 cost of producing 1000 MJ of heat and electricity. Baling costs contribute $2.15 and transporting the straw to the CHP plant another $1.15.

As an example for purposes of comparison, if the McCain vegetable processing plant purchased the equivalent amount (1000 MJ) of energy by getting electricity from the grid and using coal to generate heat, this would cost a total of $9.38. This amount cannot be compared directly with the $16.83 cost of the electricity and heat generated by the straw


18

CHP plant as the McCain plant would have additional costs associated with energy production on-site that are not allowed for. These include a proportion of the capital cost of the existing boiler, wages, operating and maintenance, rates, and overheads.

From an energy perspective there are benefits. From 85 kg of dry straw (i.e. with all moisture removed), 260 MJ of electricity and 740 MJ of heat can be produced. The amount of primary energy required to do this is 63 MJ. This amount is almost all fossil fuel and required for plastic covers, plant construction materials, and transport. More than 90% of this fossil fuel component is imported.

The 63 MJ required compares very favourably with the primary energy needed to produce the same amount of electricity from the national grid. About 515 MJ of primary energy is required to generate 260 MJ of electricity of which 195 MJ is derived from fossil fuels (see Appendix 4). This comparison intentionally excludes energy and carbon in the straw, which is stored via photosynthesis and released through combustion of the straw.

If lignite coal were used to generate 740 MJ of heat, 51 kg, would be required. This is by definition all fossil-fuel derived, but not imported. The greenhouse gas outputs are significantly higher for electricity from the grid (15 kg CO2-e) and heat from coal (70 kg CO2-e) compared with electricity and heat from straw (4 kg CO2-e).

Table 9 shows the energy return on investment for the straw CHP plant, compared with electricity from the grid and heat using coal. The energy return on investment is calculated as energy out/primary energy in. A value greater than 1 indicates the system is a net producer of energy while a value less than 1 indicates more energy is consumed within the system than is gained.

Table 9: Energy return on investment for straw CHP plant

Energy In

(MJ)

Energy Out

(MJ)

Energy

Out/Energy

In

Straw CHP plant 63 1000 15.8

Grid electricity and coal-fired heat 1255 1000 0.8

Burning straw does generate air emissions. The significant air emissions from 1000 kg of straw have been estimated at Masnedo as: 680 g SO2; 910 g of CO; 1900 g NOx; 670 g HCl; 20.0 g N2O; and 0.320 µg of dioxin (Nielsen et al., 2003).

The Emissions Trading Scheme (ETS), which will require stationary energy providers to purchase sufficient credits to cover their greenhouse gas emissions from January 2010 onwards, will increase the cost of generating electricity and heat, from coal and natural gas, which will improve the economics of any CHP plant burning straw.

The LCA and LCC are based on a plant that used mostly straw for combustion. There are plants in Europe that use both coal and straw. Modifying an existing coal fired boiler to use straw as well would reduce the capital cost requirement compared with building a greenfields straw CHP plant.

Scenario analysis The results presented in this report are for a single scenario of costs and production methods. However, some of these factors are volatile. Table 10 shows the chosen scenario, and


19

subsequent tables show results for selected changes in some of the most volatile factors in the LCA.

Table 10: Base case scenario

Output Cost ($NZ)

Primary MJ

Fossil MJ


1000 MJ Electricity and heat $17 63 60 58 4

The capital cost plus operation and maintenance of a CHP plant is a sizable proportion of the overall cost component. The capital cost in the LCC was based on two different straw-burning CHP plants, one in Spain and the other in England. Operating and maintenance costs are a percentage of capital costs so are directly proportional to the capital cost. It is possible that the actual cost of constructing a CHP plant in New Zealand is substantially different. If the capital cost was 20% more than the estimated $54m (i.e. $65m), the cost of producing 1000 MJ of electricity and gas from the straw CHP plant would increase by about $2. The amount of primary energy and fossil-fuel energy required to produce the output would also increase, but not significantly compared with the alternative of purchasing electricity from the grid and generating heat from coal.

Table 11: Capital cost of CHP plant increases by 20%

Output Cost ($NZ)

Primary MJ

Fossil MJ



If the capital cost was 20% lower, the estimated $54m (i.e. $43m), then the cost of producing 1000 MJ of electricity and gas from the straw CHP plant would decrease by about $2. The amount of primary energy and fossil fuel energy required to produce the output would also decrease slightly.

Table 12: Capital cost of CHP plant decreases by 20%

Output Cost ($NZ)

Primary MJ

Fossil MJ



The other cost likely to change is the cost of fossil fuel for transporting the straw. Increasing transport costs by 20% has a negligible effect.

Table 13: Transport costs for straw to CHP plant increases by 20%

Output Cost ($NZ)

Primary MJ

Fossil MJ



The Masnedo plant in Denmark, on which this LCA and LCC are based, uses truck and trailer units that carry 24 bales. The Ely plant in England has an adapted truck and trailer unit that carries 36 bales (see Figure 3). If the larger capacity vehicle was used instead of the 24-bale truck and trailer the base scenario uses this would result in reducing the transport cost from $17 to $16, as well as reducing energy use and CO2-e emissions.


20

Table 14: Transport capacity increases from 24 bales to 36 bales

Output Cost ($NZ)

Primary MJ

Fossil MJ



Straw-fired heat-only This section presents a case of producing only heat from straw combustion, without electricity generation. Straw baling and storage, straw transport to the plant, and waste removal are as in the CHP scenario. The differences between the CHP plant and heat-only plant are at the straw combustion phase.

A heat-only plant will produce more heat than a CHP plant as some of the heat energy in CHP is lost in the conversion to electricity. To calculate the expected heat output from 40,000 tonnes of straw, statistics from the performance of the Sabro plant between 1993 and 1997 were averaged. The Sabro plant is a straw-fired heat-only plant in Demark with a fuel to heat efficiency of 85% and an energy output from straw of 12 GJ/tonne (CADDET, 1998).

To generate heat, the proposed plant only requires the construction capital for stream production as illustrated in Figure 1. A CHP straw-fired unit producing combined heat and power requires the additional capital of a steam turbine and generator (as illustrated in Figure 1), and connection to the grid if surplus electricity is generated.

The capital cost for the heat-only plant is based on the CHP plant as set out in Danish construction costs were very high per MW of energy. The investment required for a plant with a steam turbine, grate firing and straw combustion was given as between 4.3 and 5.5 M€/MW (Danish Energy Authority et al., 2005), which is approximately $NZ200810.7m. For this reason a desktop literature search was undertaken to find costs for other CHP plants designed to use straw as a feedstock. Based on the capital cost of a CHP plant in Spain, and another in England, a cost of $NZ1.65m per MW was used in the LCA. The cost of the proposed Chinese plant was considered too low to use.

Table 6 less the estimated cost of a 10 MW steam turbine and generator. A recent New Zealand costing for an 11-MW wood-fired steam turbine and generator was between $20m and $25m (Steve Delve, date, pers. comm.). The $54m cost of the CHP plant was reduced by $22.5m to derive the cost for the heat-only plant. As the operating and maintenance costs are assumed to be 2.5% of the capital cost, these costs reduce accordingly.

The steam turbine and electricity generator require monitoring at the plant control room but no direct labour units to operate, so the wage cost is not expected to change for a heat-only straw-fired plant as opposed to a CHP plant.

Table 15 shows the final results of the LCA and LCC broken down by each of the significant inputs for heat-only.


21

Table 15: Straw-fired Heat LCA and LCA

Amount Unit Description Cost ($NZ)

Primary MJ

Fossil MJ


Notes


Inputs

3 MJ Fuel for tractor pulling baler - 3 3 3 0 (a)

2 MJ Fuel for tractor loading bales on trailer - 2 2 2 0 (b)

0.37 MJ Fuel for truck transport to farm storage - 0 0 0 0 (c)

1 MJ Fuel for unloading truck at farm storage - 1 1 1 0 (d)

18 MJ Plastic cover $0.69 18 18 18 1 (e)

2 $ Baling cost $2.15 (f)

4 MJ Embodied energy in equipment - 4 4 4 0 (g)

Straw transport to CHP plant

1 MJ Fuel for loading truck $0.05 1 1 1 0 (h)

88 km Transportation to Timaru $0.28 9 9 8 1 (i)

2 MJ Embodied energy in trucks and trailers $0.24 2 2 2 0 (j)

0.4 $ Wages for drivers $0.35 0 0 0 0 (k)

0.24 $ Truck and trailer maintenance $0.24 2 2 2 0 (l)

$1.15

Straw combustion

85 kg Straw (dry component) $0

0.58 MJ Diesel $0.02 1 1 1 0 (m)

10 MJ Capital $3.17 10 9 8 1 (n)

3 MJ Operating and maintenance $1.58 3 3 3 0 (o)

0.60 $ Wages $0.60 (p)

0.37 $ Rates $0.37 (q)

0.98 $ Overheads $0.98 1 1 1 0 (r)

0.32 $ Margin $0.32 (s)

6.4 litres Water $0.00 (t)

Waste removal

4.6 kg Transportation of slag to farmland $0.09 0 0 0 0 (u)

0.7 kg Transportation of fly ash to landfill $0.06 0.0 0.0 0.0 0 (v)

Output

1000 MJ Heat $12.33 59 58 56 4

Notes (a) 4 balers required to bale one season (estimate); lifetime of 15 years (Wells, 2001); 7-tonne

minimum tractor required (90 kW) for Hesston baler (AGCO, 2008); 40% diesel engine efficiency; estimated 85% average load on engine; 23 tonnes of straw baled per hour (AGCO, 2008)

(b) 4 x 7-tonne tractors with front end loaders; energy requirements as for note (a) (c) 4 x 10-tonne farm truck; energy requirements as for note (a) (d) 4 x 7-tonne tractors with front end loaders; energy requirements as for note (a) (e) 2 tonnes of polyethylene sheeting used to protect each storage stack of 1000 tonnes of baled

wheat straw, with a life of 1 year and a direct energy requirement of 47 MJ/kg and a feedstock energy requirement of 46 MJ/kg for low density polyethylene (Elsayed et al. 2003); $3514 /tonne (Cosio Plastics, pers. comm.)

(f) $22/tonne (Nick Pyke, pers. comm.), includes costs of fuel (g) 12 balers (8 tonne), 4 tractors (7 tonne), 4 trucks required (5 tonne); 160 MJ/kg embodied


22

energy (Wells, 2001); vehicles imported (h) 4 x 7-tonne tractors with front end loaders. 12 MJ of fuel required to load 1 tonne of straw

(calculated); $NZ1.465/litre diesel price at 18 April 2008 (MED, 2008); 37.86 MJ/litre (MED, 2007)

(i) Return trip calculated from AgriBase. $NZ1.465/litre diesel price at 18 April 2008 (MED, 2008); 37.86 MJ/litre (MED, 2007)

(j) 11 tonne truck and 8 tonne trailer (Chris Satherley, pers. comm.) (k) 2.5 hours per trip estimated from 88 km plus 30 minutes turnaround at each end, $20/hour

(TVNZ, 2007) (l) 100% of purchase price of vehicle over life time (Burtt, 2006)

(m) 0.18 litres per tonne of straw (Nielsen et al., 2003); $1.465/litre diesel price at 18 April 2008 (MED, 2008)

(n) Capital cost based on Ely plant in England (Select Committee, 2004) and Sanguesa Power plant in Spain (EHN, 2003), reduced by the cost of 11 MW capacity steam turbine and generator (Steve Delve, pers. comm.). Materials required based on Moerschner & Kazmierczak (2004) German biomass CHP 26.7 MW plant. Proposed plant is 33 MW. So inputs * 1.23; Reduced for heat-only 9396 x.95 tonnes of concrete, 4802 x .95 tonnes of gravel, 2464 x .75 tonnes of construction steel, 1251 x .95 tonnes of aluminium. 1400 MJ/tonne concrete, 40 MJ/tonne of gravel, 31 300 MJ/ tonne of construction steel, 23 800 MJ/tonne of aluminium (Alcorn, 2003); import rates from Alcorn (2003); fossil fuels rates estimated

(o) Maintenance costs 2.5% of capital cost (Mortimer and Elsayed, 2001). Energy estimate based on half of steel replaced over 20 year lifetime of plant.

(p) 5 workers@ $40,000/yr,1 engineer@ $80,000/yr. Based on 24 permanent jobs Spain 160 000 tons of straw/yr (EHN,2003)

(q) Rates estimated from Lot DP 35657 (Timaru District Council website). ECAN rates estimated from Funding Impact Statement (Environment Canterbury website)

(r) Assumed to be 8% of total costs. Derived from overhead expenditure for Food and Beverage sector of I-O table

(s) Assume 10% return on investment (t) 75 litres per tonne of straw (Nielsen et al., 2003); 44 c/m3 local council water charge (Timaru

District Council) (u) Assume same distance as straw collected from (88 km) (v) Taken to local landfill, 8.7 km one way; landfill disposal charge $75/tonne (PCE, 2006) (w) Average coal price of $1.1/GJ (2005); CO2 emissions of 95.2 kgCO2/GJ (MED, 2007); indirect

energy has not been included

Interpretation As with the CHP plant, the biggest costs associated with producing heat energy from straw are capital costs ($3.17 per 1000 MJ), and operating and maintenance costs ($1.58 per 1000 MJ). Together these costs account for $5.75 of the $12.33 cost of producing 1000 MJ of heat. Baling costs contribute $2.15 and transporting the straw to the heat plant another $1.15.

The LCC shows it costs $4.50 less to produce 1000 MJ of heat-only than to produce 1000 MJ of combined heat and power.

As an example, for purposes of comparison, if the McCain vegetable processing plant was to purchase the equivalent amount (1000 MJ) of heat using coal it would cost $1.10 for the coal alone (using a lignite coal price of $1.10/GJ). While this is significantly lower, this amount cannot be compared directly with the $12.33 cost of straw-fired heat as the McCain plant would have additional costs associated with energy production on-site that are not included in this figure. For a direct comparison a proportion of the capital cost of the existing boiler, wages, operating and maintenance, rates, and overheads costs would need to be added to the $1.10 per 1000 MJ.


23

From an energy perspective there are benefits. It takes 85 kg of dry straw (i.e. with all moisture removed) to produce 1000 MJ of heat. The amount of primary energy needed to do this is 59 MJ. This amount is all fossil fuel and required for plastic covers, plant construction materials and transport. Most of this fossil fuel component is imported.

The 59 MJ compares very favourably with the 1000 MJ of fossil fuel input from coal. The 1000 MJ is an underestimate as additional amounts of fossil fuels are required to extract and transport the coal. The greenhouse gas outputs are significantly higher for heat from coal (95 kg CO2-e) compared with heat from straw (4 kg CO2-e). Again, there are also additional greenhouse gas emissions not included in the coal figure, such as emissions from energy used during quarrying and fugitive emissions during mining. This comparison intentionally excludes energy and carbon in the straw, which is stored via photosynthesis and released through combustion of the straw.

Table 16 shows the energy return on investment for heat produced by the straw-fired plant compared with heat produced using coal. The energy return on investment is calculated as energy out/primary energy in. A value greater than 1 indicates the system is a net producer of energy; a value less than 1 indicates more energy is consumed within the system than is gained.

Table 16: Energy return on investment for straw-fired heat plant

Energy In

(MJ)

Energy Out

(MJ)

Energy

Out/Energy

In

Straw-fired heat 59 1000 16.9

Coal-fired heat 1000 1000 1.0

Burning straw does generate air emissions. The significant air emissions from 1000 kg of straw have been estimated at Masnedo as: 680 g SO2; 910g of CO; 1900 g NOx; 670 g HCl; 20.0 g N2O; and 0.320 µg of dioxin (Nielsen et al., 2003).

The Emissions Trading Scheme (ETS), which requires stationary energy providers to purchase sufficient credits to cover their greenhouse gas emissions from January 2010 onwards, will increase the cost of generating electricity and heat, from coal and natural gas, which will improve the economics of any plant burning straw.

The LCA and LCC are based on a plant that used mostly straw for combustion. There are plants in Europe that use both coal and straw. Modifying an existing coal fired boiler to use straw as well would reduce the capital cost requirement compared with building a greenfields straw-fired plant.

Scenario analysis The results presented in this report are for a single scenario of costs and production methods. However, some of these factors are volatile. Table 17 shows the chosen scenario, and subsequent tables show results for selected changes in some factors in the LCA.


24

Table 17: Base case

Output Cost ($NZ)

Primary MJ

Fossil MJ


1000 MJ Heat $12 59 58 56 4

The introduction of a $30 per tonne of carbon credit would reduce the cost of producing heat from the straw-fired plant by $3 per 1000 MJ of energy, thus reducing the cost from $12 to $9 (Error! Not a valid bookmark self-reference.). The cost of using coal would increase to $4 plus on-site energy production costs not quantified.

Table 18: Carbon credit reduces production cost

Output Cost ($NZ)

Primary MJ

Fossil MJ


1000 MJ Heat $9 59 58 56 4

The Masnedo plant in Denmark, on which this LCA is based, uses truck and trailer units that carry 24 bales. The Ely plant in England has an adapted truck and trailer unit that carries 36 bales (see Figure 3). If the larger capacity vehicle was used instead of the 24-bale truck and trailer used in the base scenario, this would result in reducing the transport cost from $12 to $11, as well as reducing energy use and CO2-e emissions.

Table 19: Transport capacity increases from 24 bales to 36 bales

Output Cost ($NZ)

Primary MJ

Fossil MJ




25

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Nielsen, P., 2000. Electrokinetic remediation of biomass ash. Presented at 1st World Conference on Biomass for Energy and Industry, Sevilla, Spain, 5–9 June. http://books.google.co.nz/books?id=I4md2B_nk9UC&pg=PA1856&lpg=PA1856&dq=masnedo+CHP+&source=web&ots=sV2WEbaeBH&sig=QI6wTRAjTUic_1PU2ZYI3pttxbo&hl=en#PPA1856,M1.

Nielsen, P., Nielsen, A., Weidema, B., Dalgaard, R., and Halberg, N., 2003. LCA food data base. www.lcafood.dk [April 2008].


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PCE, 2006. Changing behaviour: Economic instruments in the management of waste. ISBN: 1-877274-60-7, Office of the Parliamentary Commissioner for the Environment, Wellington, NZ, 102 p. www.pce.govt.nz [10 August 2006].

R 'n' J Aerofoils, 1998. Road test: The figures don't lie... http://www.truckaerofoils.co.nz/road_test.html [April 2008].

Saggar, S., Giltrap, D., Forgie, V., and Renquist, R., 2007. Bioenergy options report: Review of agricultural resources. Landcare Research Contract Report: LC0708/016 (prepared for SCION).

Select Committee on Science and Technology, 2004. Appendix 6: Visit to Elean and Thetford power stations. http://www.publications.parliament.uk/pa/ld200304/ldselect/ldsctech/126/12618.htm [28 April].

SK Power Company, 1999. Case study no. 4 Masnedo CHP plant. Hellerup, Denmark.

Statistics New Zealand, 2005. Agricultural production survey 2005. Compiled with the Policy Information Group, MAF, Wellington, NZ.

Talbotts Biomass Energy, no date. http://www.talbotts.co.uk/bgen.htm [28 April].

TVNZ, 2007. Just the job. http://tvnz.co.nz/view/page/1448397 [30 April].

Warwick HRI, 2007. AC0401: Direct energy use in agriculture: Opportunities for reducing fossil fuel inputs. University of Warwick, Warwick.

Wells, C., 2001. Total energy indicators of agricultural sustainability: Dairy farming case study. Technical paper 2001/3, ISBN: 0-478-07968-0, ISSN: 1171-4662, Ministry of Agriculture and Forestry, Wellington, NZ, 90 p. http://www.maf.govt.nz/mafnet/publications/techpapers/techpaper0103-dairy-farming-case-study.pdf.

Zah, R., Böni, H., Gauch, M., and Hischier, R., 2007. Life cycle assessment of energy products: Environmental impact assessment of biofuels. Empa, 20 p.


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Appendix 1: Overview of LCA method from Beer et al. (2007)

Life cycle assessment (LCA) is the process of evaluating the potential effects that a product, process, or service has on the environment over the entire period of its life cycle. The International Organization for Standardization (ISO 1997) has defined an LCA as:

A technique for assessing the environmental aspects and potential impacts associated with a product by:

• compiling an inventory of relevant inputs and outputs of a product system

• evaluating the potential environmental impacts associated with those inputs and outputs

• interpreting the results of the inventory analysis and impact assessment phases in relation to the objectives of the study.

The technical framework for life cycle assessment consists of four components, each having a vital role in the assessment. They are interrelated throughout the entire assessment and in accordance with the current terminology of the International Organization for Standardization (ISO). The components are goal and scope definition, inventory analysis, impact assessment, and interpretation.

Figure 4: The components of an LCA. Source: ISO, (1997)


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Appendix 2: Ash data from Newman, 2003 Table 20: Analysis of fly ash from wheat straw, oil seed rape (OSR) straw and whole crop straw

(Source: Newman, 2003)

The main constituents in the fly ash are compounds of calcium, potassium, sulphur, phosphorus and chlorides. The toxic heavy metal content is low on all three straw types but as a result of lime addition for acid gas retention, calcium levels are above that in the raw fuel ash. The analysis is very similar for all three straw types and within the variance levels normally encountered for cereal straw. Chloride levels are lowest for OSR in the fly ash but highest in the bottom ash (Table 4.5.2), which reflects the amount of lime dosing encountered in the combustion test.


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Table 21: Analysis of bottom ash from wheat straw, oil seed rape (OSR) straw and whole crop straw

(Source: Newman, 2003)

The main constituents in the bottom ash are compounds of calcium, potassium and chlorides but at much lower levels than encountered in the fly ash; the sulphur and chloride levels being highest with OSR straw. Whole crop straw produced more fly ash and the least bottom ash of all three straw types (23% and 77% by weight respectively) compared with cereal and OSR, which produced 15% fly ash and 85% bottom ash. This may be due to the inclusion of grain in the whole crop and the manner in which it breaks up on entry to the high temperature furnace.


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Appendix 3: Transport energy consumption There are no standard figures available in New Zealand for fuel efficiency of road freight transport. A recent report by TERNZ used 0.3 l/km for single unit trucks and 0.5 l/km for articulated vehicles (rigs), quoting figures obtained from industry (Baas and Latto, 2005). A report by the Ministry for the Environment used an average for the heavy vehicle fleet of 0.6 l/km (MfE, 2005). A 1998 demonstration of a truck aerofoil, carrying a refrigerated 20-tonne load the length of New Zealand showed an average fuel efficiency of 0.44 l/km (R 'n' J Aerofoils, 1998). Mitsubishi recently announced a new rig with a New Zealand fuel efficiency of 0.49 l/km carrying a 26-tonne payload (Mitsubishi Motors NZ, 2007). Given these last two are claims of better-than-average fuel efficiency, it appears likely the average would be higher than 0.5 l/km. Fuel efficiency in Europe appears to be significantly greater, with data from GaBi (IKP and PE, 2004) – a life-cycle assessment software – and from a 2003 UK survey (McKinnon et al., 2003) both indicating fuel efficiency of 0.34 l/km for articulated trucks.

We have used a fuel consumption rate of 0.55 l/km for an articulated truck with a maximum payload of 26 tonnes, and 0.3 l/km for a single truck with a maximum payload of 10 tonnes. Following the method used by GaBi (IKP and PE, 2004), we have used a logarithmic relationship to relate fuel consumption to truck loading (see Figure 5), with minimum fuel consumption at 10% loading. These are presented as average figures, and will vary widely depending on terrain, maintenance, driving style, and speed.

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Load

litr

es/k

m

Articulated truck(26 tonne max payload)

Single unit truck(10 tonne max payload)

Figure 5: Fuel efficiency of trucks by truck size and actual payload (source: GaBi (IKP and PE, 2004)

and Baas and Latto (2005))


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Appendix 4: Electricity Electricity supplied to the national grid is generated from a combination of fossil-based energy resources and non-fossil resources, and from a combination of imported energy and domestic energy. The two forms of fossil energy used in electricity generation are coal and natural gas. Significant amounts of coal used for electricity generation are now imported, while all natural gas is extracted domestically. Table 22 gives the total, fossil, and imported primary energy inputs into (non-cogeneration) electricity generation in New Zealand between 2002 and 2006, and shows the fossil energy, imported energy, and greenhouse gas emissions per unit of consumer electricity. All these indicators are likely to change in the near future as the New Zealand Government’s policies on climate change take effect (among other effects).

Table 22: Electricity energy contents, 2002–2006 (excluding cogeneration)

Total

primary energy (PJ)

Fossil primary

(PJ)

Imported coal (PJ)

Consumed electricity

(PJ)

Primary energy in consumer electricity (MJ/MJ)

Fossil energy in consumer electricity (MJ/MJ)

Imported energy in consumer electricity (MJ/MJ)

GHG emissions (ktCO2-e)

Implied emission

factor (kgCO2-e/MJ)

2002 241 84 2.7 119 2.02 0.71 0.02 5673 0.048

2003 243 94 10.3 126 1.93 0.75 0.08 6904 0.055

2004 247 83 20.5 129 1.92 0.64 0.16 6573 0.051

2005 269 109 25.0 133 2.02 0.82 0.19 8728 0.066

2006 272 112 28.4 135 2.02 0.83 0.21 8659 0.064

Average 1.98 0.75 0.13 0.057

Source: Ministry of Economic Development (2007b; 2007a)


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Appendix 5: Common factors Where information on fossil-energy components was unavailable, we have assumed all primary energy is derived from fossil sources to be conservative when comparing with the fossil alternative.

The primary energy content of fossil diesel is 1.193 MJ/MJ (Barber et al., 2007), which is assumed to have negligible non-fossil content. Diesel supply is 31% imported, and 5% of the New Zealand refinery’s input is local oil (both average of 2004–2006; MED, 2007), so that approximately 97% of diesel energy is imported. Fossil diesel has a gross calorific value (GCV) of 45.75 MJ/kg and 37.86 MJ/litre (MED, 2007b).

Global warming potentials (GWPs) used for methane (CH4) nitrous oxide (N2O) were 21 and 298, as required under the Kyoto Protocol.

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