CO2 study

This Study Is taken Directly from the Folkecentre For Renewable Energy

BASED ON EMBIO, THE DANISH ENERGY AGENCY'S
MODEL FOR ECONOMIC AND ENVIRONMENTAL
ASSESSMENT OF BIOFUELS

Jacob Bugge, 9/11 2000. Translation August 2001

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SUMMARY:

Rape has a strongly positive energy and CO₂ balance, and rape seed oil can be termed genuinely CO₂ neutral because the CO₂ reductions just from the rape straw by far surpasses the CO₂ emission by cultivation and processing.

The energy balance has been calculated from actual fossil gross energy consumption and energy content in the crop for conventionally cultivated winter rape. The gross energy consumption including industrial fertilizer and pesticides by cultivation and processing of rape corresponds to the average gross energy consumption excluding fertilizer and pesticides within Danish agriculture in general.

Correspondingly, the CO₂ balance has been calculated from the actual CO₂ emission by cultivation and processing and the reductions in CO₂ emission obtainable by using the crop for energy purposes.

In both cases, a gross calculation based on full use of fossil energy as well as a net calculation with utilisation of renewable energy from the crop itself for cultivation and local processing have been carried out. And in both cases, supplementary calculations excluding the contribution from the rape seed cakes have been included.

No matter whether gross or net calculations are used, and no matter whether the contribution from the rape cake is included or excluded, the conclusion is that the energy balance is strongly positive.

The corresponding conclusion is that no matter whether gross or net calculations are used, and no matter whether the contribution from the rape cake is included or excluded, rape seed oil is genuinely CO₂ neutral because the rape straw alone gives a CO₂ saving which by far exceeds the total CO₂ emission from cultivation and processing.

The calculations have been based upon the Danish Energy Agency´s EMBIO model with corrections for the differences between cold pressed rape seed oil and biodiesel.

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CONTENTS:

Summary

1. Energy Balance

1.1. Energy Consumption
1.2. Energy Contnet in the crop
1.3. Calculation of energy balance

2. CO2 balance

2.1. CO2 emission
2.2. CO2 reductions from the crop
2.3  Calculation of CO2 balance.

3.References and Key Figures

 

1. ENERGY BALANCE:

The energy balance has been calculated from fossil energy consumption and energy content in the crop.

A gross calculation based on full use of fossil energy as well as a net calculation with utilisation of renewable energy from the crop itself for cultivation and local processing have been carried out.

 

1.1. ENERGY CONSUMPTION:

Calculated with the Danish Energy Agency's method [1] with correction for the differences between cold pressed rape seed oil and biodiesel [2], the gross energy consumption for cultivation and processing amounts to 10,83 MJ/l rape seed oil, corresponding to 3,922 GJ/ton rape seed or 11,765 GJ/ha.

Of this, 5,187 GJ/ha comprises process energy for sowing seed, machinery, fertilizer, and pesticides [1]. The remaining 6,578 GJ/ha comprises local energy consumption at the farm, with 4,482 GJ/ha diesel/oil and 2,096 GJ/ha electricity [1], [2].

According to the alternative-cost approach of [1], 411 MJ/ha in the form of diesel/oil for soil preparation connected with fallow has been excluded. Thus the actual gross energy consumption is 3,5% higher, totalling 12,176 GJ/ha.

With this, the total actual gross energy consumption according to the Danish Energy Agency's method [1] with corrections [2] is 12,176 GJ/ha; this figure corresponds to the Danish agriculture's average gross energy consumption excluding fertilizer and pesticides of 12,5 GJ/ha [3]. Of the 12,176 GJ/ha, 6,989 GJ/ha comprises local energy consumption in the form of 4,893 GJ/ha diesel/oil and 2,096 GJ/ha electricity; this local fossil energy consumption can be replaced by renewable energy from the crop in the form of rape seed oil and electricity produced from rape straw.

Consequently, the fossil net energy consumption can be put at 5,187 GJ/ha, in return for a reduction of 6,989 GJ/ha from gross to net energy content in the crop.

 

1.2. ENERGY CONTENT IN THE CROP:

In 1 ha, the following can be harvested [2]:

1) rape seed, 3 ton, which gives:

rape seed oil, 1 ton = 1086 l rape seed oil, which corresponds to 1032 l diesel

rape cakes 2 ton

2) rape straw, 3,9 ton

The following gross energy contents apply:

rape seed oil : 37,53 MJ/l x 1086 l/ha = 40,76 GJ/ha [2] (30%) *)

rape cakes : 19,32 MJ/kg x 2000 kg/ha = 38,64 GJ/ha [4] (28%)

rape straw : 14500 MJ/ton x 3,9 ton/ha = 56,55 GJ/ha [1],[2] (42%)

Total: 135,95 GJ/ha (100%)

*): As substitution for diesel including process energy. The actual energy content is 34,11 MJ/l, corresponding to 28% of the gross energy content, see key figures at the end of the note.

As it appears, the energy content of the rape seed oil comprises ca. 30% of the total energy content in the crop, and there is about the same energy content in the oil and the cake, whereas the straw contains ca. 50% more energy. Actually, the energy content in the rape straw is a good 4,5 times higher than the total gross energy consumption.

With the abovementioned reduction of 6,99 GJ/ha in return for using renewable energy for cultivation and local processing, the net energy content becomes 6,99 GJ/ha with a reduction of the net energy content in oil and straw to 35,87 GJ/ha and54,45 GJ/ha.

It may be noted that, as an alternative to fodder, the energy content in the rape cakes may be used for energy production, either in a biogas plant or as fuel in CHP or heat producing plants.

If the energy content in the rape cakes is excluded, the gross energy content is reduced to 97,31 GJ/ha, whereas the net energy content is reduced to 90,32 GJ/ha.

 

1.3. CALCULATION OF ENERGY BALANCE:

As it appears, the total gross energy content in the crop is 135,95/12,18 = 11,16 times greater than the actual fossil gross energy consumption.

With local use of renewable energy, the net energy content in the crop is 128,96/5,19 = 24,85 times greater than the actual fossil gross energy consumption.

If the energy content in the rape cakes is excluded, the factor for gross energy content is reduced to 97,31/11,765 = 8,27, whereas the factor for net energy content is reduced to 90,32/5,19 = 17,40.

No matter whether gross or net calculations are used, and no matter whether the contribution from the rape cakes is included or excluded, the conclusion is that the energy balance is strongly positive.

 

2. CO₂ BALANCE:

Corresponding to the abovementioned calculation of energy balance, gross and net CO₂ balances are calculated.

The CO₂ balance is calculated from the CO₂ emission from cultivation and processing and the CO₂ reductions which may be obtained by using the crop for energy purposes.

 

2.1. CO₂ EMISSION:

Calculated with the Danish Energy Agency's method [1] with correction for the differences between cold pressed rape seed oil and biodiesel [2], the gross CO₂ emission from cultivation and processing amounts to 1,45 kg/l rape seed oil, corresponding to 524,4 kg/ton rape seed or 1573 kg/ha.

Of this, 483 kg/ha comprises emission from process energy for sowing seed, machinery, fertilizer, and pesticides, along with 509 kg/ha (CO₂-equivalents) from field and crop, totalling 992 kg/ha [1]. The remaining 581/ha are emitted by local energy consumption at the farm, with 364 kg/ha from diesel/oil and 217 kg/ha from electricity [1], [2].

According to the alternative-cost approach of [1], 31 kg/ha in the form of emission from diesel/oil for soil preparation connected with fallow has been excluded. Thus the actual gross emission is 2% higher, totalling 1604 kg/ha.

With this, the total actual gross CO₂ emission according to the Danish Energy Agency's method [1] with corrections [2] is 1604 kg/ha. Of the 1604 kg/ha, 612 kg/ha comprises emission from local energy consumption in the form of 395 kg/ha from diesel/oil and 217 kg/ha from electricity; this local fossil energy consumption can be replaced by renewable energy from the crop in the form of rape seed oil and electricity produced from rape straw, whereby the corresponding emission is annulled.

Consequently, the fossil net emission can be put at 992 kg/ha, in return for a reduction of 612 GJ/ha from gross to net reduction obtained from the crop.

 

2.2. CO₂ REDUCTION FROM THE CROP:

The direct CO₂ reduction from the rape seed oil as substitute for diesel is 2,78 kg/l [2], corresponding to 1006,3 kg/ton rape seed or 3019 kg/ha.

For the rape straw as substitute for coal, the direct CO₂ reduction is 1814 kg/ton rape seed or 7075 kg/ha [2]. As it appears, the reduction from the rape straw alone is 4,5 times greater than the total gross emission.

Correspondingly, a similar CO₂ reduction of (38,64/56,55) x 7075 = 4843 kg/ha applies to rape cakes as substitute for coal.

The resulting gross CO₂ reduction from the crop amounts to 14,937 ton/ha. The corresponding net reduction amounts to 14,325 ton/ha.

If the CO₂ reduction from the rape cakes is excluded, the gross CO₂ reduction is reduced to 10,094 ton/ha, whereas the net reduction is reduced to 9,482 ton/ha.

 

2.3. CALCULATION OF CO₂ BALANCE:

As it appears, the total gross CO₂ reduction from the crop is 14,937/1,604 = 9,31 times greater than the gross CO₂ emission.

With local use of renewable energy, the net CO₂ reduction from the crop is 14,325/0,992 = 14,44 times greater than the than the net CO₂ emission.

If the CO₂ reduction from the rape cakes is excluded, the factor for gross CO₂ reduction is reduced to 10,094/1,604 = 6,29, whereas the factor for net reduction is reduced to 9,482/0,992 = 9,56.

No matter whether gross or net calculations are used, and no matter whether the contribution from the rape cakes is included or excluded, the conclusion is that rape seed oil is genuinely CO₂ neutral because the rape straw alone gives a CO₂ saving which by far exceeds the total CO₂ emission from cultivation and processing.

 

3. REFERENCES AND KEY FIGURES:

REFERENCES:

[1] EMBIO Energistyrelsens Model til økonomisk og miljømæssig vurdering af BIObrændstoffer, Januar 1997, Udarbejdet af COWI. (EMBIO The Danish Energy Agency's Model for economic and environmental assessment of BIOfuels, January 1997, elaborated by COWI): 233 pages two volumes report in Danish.

[2] Jacob Bugge: ANVENDELIGHED AF RAPPORTEN EMBIO Energistyrelsens Model til økonomisk og miljømæssig vurdering af BIObrændstoffer, Januar 1997, Udarbejdet af COWI. Folkecenteret 2000. (APPLICABILITY OF THE REPORT EMBIO ... (etc), Folkecenter 2000): 30 pages report in Danish. English prologue and summary available at www.folkecenter.dk.

[3] Note: Rape seed oil for transport 2: Agriculture and energy, Folkecenter for Renewable Energy, 2001. Available at www.folkecenter.dk.

[4] Fodermiddeltabel, Sammensætning og foderværdi af fodermidler til kvæg, Rapport nr. 91. Landsudvalget for Kvæg, Oktober 2000. (Feedstuffs table, composition and fodder value of feedstuffs for cattle, Report no. 91, National Board for Cattle, October 2000): 52 pages report in Danish.

 

KEY FIGURES:

Conversion: 1 l rape seed oil corresponds to 0,95 l diesel, which has an energy content of 0,95 x 35,9 = 34,11 MJ/l and a process energy of 0,95 x 3,6 = 3,42 MJ/l, totalling 37,53 MJ/l [1], [2].

Fossil energy and CO₂ emission [1], [2]:

Renewable energy and CO₂ reduction from the crop [1], [2], [4]:

a): Energy content (heating value)

b): Energy content along with process energy for provision and transport, and refinement of diesel. The total for diesel is 3,6 MJ/l; this energy is also saved by the use of rape seed oil.

*: Substitute for diesel

**: Substitute for coal

 

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