Annex E. Pellet production for fertilising – Life Cycle Inventory data – Environmental Project No. 1298 2009 – Life Cycle Assessment of Slurry Management Technologies

Life Cycle Assessment of Slurry Management Technologies

Annex E. Pellet production for fertilising – Life Cycle Inventory data

E.1 System description

This appendix contains Life Cycle Inventory data for fibre pellet production in a Samson Bimatech Plant MaNergy 225.

The system in this Annex E is very close to the system in Annex D, however, the fibre pellets are not used for heat production as in Annex D, but for application to the field as fertiliser.

The scenario containing the Energy Plant producing energy based on fibre pellets is shown in figure E.1. The process numbers refer to the heading of the section in this Annex E.

Figure E.1. Flow diagram for the scenario with production of fibre pellets for fertilising.

Click here to see Figure E.1

E.2 In-house storage of slurry

This process is identical to process C.2 in Annex C.

E.3 Storage of slurry in pre-tank

This process is identical to process C.3 in Annex C.

E.4 Mehcanical separation and Fibre pellet production

In the Samson Bimatech Energy Plant, the slurry is separated into a liquid fraction and a fibre fraction, as described in Annex D. The processes for the fibre pellet production in the energy plant are described in Annex D.

When producing fibre pellets as the “primary product” instead of heat, the emissions per 1000 kg slurry is different, as there is less combustion. Approximately 40% of the fibres are used for producing the heat required for drying the fibres. The emissions correspond to approximately 50% of the amount of emissions from when all the fibre pellets are combusted for heat production (Annex D), as the efficiency is slightly lower when the plant is not used to its full capacity.

Accordingly, it is assumed that the emissions are reduced by 50% when producing fibre pellets as the main product and the heat is only for drying the pellets.

The life cycle data for the Fibre pellet production in the Energy Plant are shown in table E.1

As decribed in Annex D, the mechanical separation separates the slurry into 51.98 kg fibre fraction and 948 kg liquid fraction (“reject”).

From Annex D (table D.1) it can be seen that when 1000 kg of pig slurry undergoing mechanical separation and pellet production, 23.19 kg fibre pellets are produced, based on the mass balances. However, approximately 40% of the fibres are used for producing the heat required for drying the fibres (as described in section E.4 in Annex E).This means that the treatment of 1000 kg pig slurry gives approximately 13.9 kg fibre pellets.

The amount of ash produced is 1.94 kg ¹.

Table E.1. Life cycle data for treatment of slurry in the Samson Bimatech energy. Data per 1000 kg slurry treated.

	Fattening pig slurry	Comments
Input
Slurry (ex pre-tank)	1000 kg	Slurry directly from the pre-tank under the pig housing units. This is the reference amount of slurry, i.e. the emissions are calculated relative to this.
Output
Fibre pellets	13.9 kg	In this Annex, all fibre pellets are used for fertilising.
Liquid fraction of the slurry	948 kg	Reject slurry / liquid phase of the slurry
Ash	1.94 kg
Heat production, surplus.	0 MJ	No surplus heat in this scenario.
Heat production used in the plant	120 MJ	Used in the plant for drying fibres, see 3 lines below
Energy consumption
Electricity	19 kWh	Personal correspondence with J Mertz, 2008.
Heat	120 MJ	Used in the plant for drying fibres, produced by the plant, see 3 lines above
Wooden pellets	0.078 kg	Wooden pellets are used for heating when starting the plant.
Consumption of materials and chemicals
Wooden pellets	0.078 kg	For starting the process
Emissions to air
Carbon dioxide (CO₂)	18.1 kg	Information from J. Mertz (2009)
Carbon monoxide (CO)	0.0355 kg	Information from J. Mertz (2008)
Methane (CH₄)	No data	Assumed to be negligible.
Non-methane volatile organic compounds (NMVOC)	No data
Ammonia (NH₃-N)	-	Assumed to be insignificant.
Nitrous oxide (N₂O-N)	No data
Nitrogen oxides (NO_X)	0.05 kg	Information from J. Mertz (2009)
Nitrogen(N₂)	0.178 kg	Calculated according to mass balances, see text.
Particulates	0.015 kg	Information from J. Mertz (October 2008) Size of the particulates not specified.
Hydrogen sulphide (H₂S)	No data
Sulphur dioxide (SO₂)	No data
Odour	No data
Emissions to water
		No emissions to water

E.5 Outdoor storage of the liquid fraction

This process is identical to process C.5 in Annex C.

E.6 Transport of the liquid fraction to field

This process is identical to process C.6 in Annex C.

E.7 Field processes (Liquid fraction)

This process is identical to process C.7 in Annex C.

E.8 Avoided production of mineral fertilisers

If using the fibre pellets as fertiliser at fields, the ”fertiliser replacement value” needs to be established. As the use of fibre pellets as fertiliser is a “future possibility” for a new technology and as it is not used today, there are no rules for how this is normally handled.

As described in Annex C, the “fertiliser replacement value” of the liquid fraction depends on how the fibre fraction is managed (if it is combusted, sent to a biogas plant or sent to other farms as fertiliser).

The “fertiliser replacement value” is calculated for the total system as follows:

The calculation of the fertiliser replacement value for N is based on Danish Law combined with “common practice”. When slurry is separated, the two separated fractions should have the same “fertiliser replacement value” as the non-separated slurry. The “fertiliser replacement value” of the fibre fraction is decided by the producer of the slurry – or in agreement with the receiver of the slurry (and the N content is based on measurements a couple of times a year). In practice, the fertiliser value of the N in the fibre fraction is typically set to 50% (as the receiver is not interested in more N for the N-accounts than necessary) (personal communication with Thorkild Birkmose (2009) and Jens Petersen (2009)).

The N content in the slurry substitutes mineral N-fertiliser, as described in Annex A. The substitution of mineral N-fertiliser is restricted by Danish law (Gødskningsbekendtgørelsen, 2008, and Gødskningsloven, 2006). The farmers have to make accounts on their fertiliser use, and they have to include a fixed amount of the N content of the animal slurry in their fertiliser accounts. The amounts are based on measurements by the farmer. Accordingly, they are assumed to be identical with the calculated values.

First, the “fertiliser replacement value” for the reference system is stated (see Annex A for further details):

Mineral N fertiliser: 5.00 kg N per 1000 kg slurry ex storage [the value given by the Danish Norm Data, as explained in Annex A] * 1086 kg slurry ex storage per 1000 kg slurry ex animal * 75% [the replacement value according to (Gødskningsbekendtgørelsen, 2008] = 4.073 kg mineral N fertiliser
Mineral P fertiliser: 1.04 kg P per 1000 kg slurry ex storage * 1086 kg slurry ex storage per 1000 kg slurry ex animal = 1.13 kg P
Mineral K fertiliser: 2.60 kg P per 1000 kg slurry ex storage * 1086 kg slurry ex storage per 1000 kg slurry ex animal = 2.82 kg K

Then, the “N fertiliser replacement value” for the “Fibre Pellets to field –scenario” is calculated:

The slurry is separated into 51.98 kg fibre fraction and 948.02 kg liquid fraction (see table C.3 in Annex C). As mentioned above, approximately 40% of the fibres are combusted (as fibre pellets) in order to supply the Energy Plant with heat for drying.
Accordingly, 40% of the liquid fraction is calculated as in Annex D: The amount of N in the liquid fraction of the slurry replace mineral N fertiliser by 85% according to Danish Law (Gødskningsbekendtgørelsen (2008), BEK 789, § 21) when the fibre fraction is combusted: 948.02 kg liquid fraction * 40% [corresponding to the fraction of fibres combusted] * 4.71 kg N per kg liquid fraction after storage [from table C.8 in Annex C] * 1086 kg liquid fraction after storage per 1000 kg liquid fraction before storage * 85% [the mineral fertiliser replacement value when the fibre fraction is combusted] / 1000 kg slurry ex animal = 1.6487 kg mineral N fertiliser
The theoretical fertiliser value of the fibre fraction that is not combusted (i.e. 60% of the fibre fraction) is calculated as follows: 51.98 kg fibre fraction per 1000 kg slurry ex animal * 7.17 kg N per kg fibre fraction [table C.3 in Annex C] * 60% [fraction that is not combusted] * 50% [the fertiliser value of the fibre fraction is typically 50%, as mentioned above] = 0.1118 kg mineral N fertiliser
60% of the liquid fraction is calculated in accordance with the law regarding separation of slurry, as described above. The intention of the law is that for separation of the slurry, the separated fractions should have the same “fertiliser replacement value” as the non-separated slurry. 60% of the “fertiliser replacement value” of the non-separated slurry is 60% of 4.073 kg mineral N fertiliser (see calculations for the reference system above) = 2.4438 kg mineral N fertiliser. Left for the liquid fraction is: 2.4438 kg N – 0.1118 kg N [which is the theoretical fertiliser value of the fibre fraction that is not combusted, as calculated above] = 2.332 kg mineral N fertiliser.
Accordingly, the “fertiliser replacement value” of the system is:
40% liquid fraction: 1.6487 kg mineral N fertiliser +
Fibre fraction for fertilising the field: 0.1118 kg N +
60% liquid fraction: 2.332 kg mineral N fertiliser
= 4.093 kg mineral N fertiliser for the total system.

This is almost identical to the mineral fertiliser value of the reference system (which is 4.073 kg mineral N fertiliser).

The amount of K and P applied to soil is the same as in the reference scenario, as these are not lost in the system.

The application of fibre pellets to the soil has, however, impact on the crop yield. As the fibre pellets more act as soil structure improvement media than as actual N fertiliser due to the C:N ratio of the fibre pellets (as such a high C : N ratio will typically give rise to N immobilization as explained in section E.11 below), there will actually be less N available for plant growth. It has not been possible to identify the magnitude of a possible reduced crop yield, as the use of fibre pellets has never been tested or tried in real life. However, the amount of fibre pellets applied to field is rather low compared to the liquid fraction in this system (948 kg liquid fraction compared to 13.9 kg fibre pellets) which means that it is likely that the consequences for the overall system will be rather small. The possible consequences are discussed under sensitivity analyses.

E.9 Storage of fibre pellets

This process is identical to the storage of fibre pellets in Annex D.

E.10 Transport to field (fibre pellets)

It is assumed that the transport distance is the same as in the reference scenario in Annex A.

E.11 Field processes (fibre pellets)

The composition of the fibre pellets when they are applied to field is shown in table E.2 below (data from Annex D, table D.1).

Table E.2. Composition of fibre pellets.

	Composition of fibre pellets

Total mass	1000 kg
Dry matter (DM)	889.3 kg
Total-N	11.6 kg
Total-P	4.31 kg
Potassium (K)	3.58 kg
Carbon (C)	425.2 kg
Copper (Cu)	0.082 kg
Zinc (Zn)	0.242 kg

The field processes are calculated relative to the content of C and N in Annex A, see table E.3.

The emissions of ammonia (NH₃) are calculated by the use of the same emission factor as in Annex A, i.e. 0.138 g NH₃-N per g TAN ². Measurements made on “real life” fibre pellets (OK Laboratorium for Jordbrug, 3-2-2009), the NH₄⁺ content of the fibre pellets corresponds to approximately 15.2% of the total N. As can be seen in table E.2, the amount of total-N in the fibre pellets correspond to 11.6 kg N per 1000 kg fibre pellets. Accordingly, the NH₃ emissions can be calculated to 0.243 kg NH₃ per 1000 kg fibre pellets.

The content of C is very high, which gives rise to a large increase in soil C, over 10 years the C content in the soil increases 101.0 (JB3), respectively 106.6 (JB6) kg C per 1000 kg pellets, according to C-TOOL. The majority of the C in the pellets is released as CO₂ though (Table F.9). The above large increase in soil C gives rise to a modeled increase in soil N of 10% of the C increase, 10.1 (JB3) respectively 10.7 (JB6) kg N per 1000 kg pellets. This is only a little less than the N present in the pellets. So, according to this modeling, only 1.5, respectively 0.9 kg N are left for both plant uptake and all N losses, due to the high C : N ratio of the pellets of 39 : 1. Such a high C : N ratio will typically give rise to N immobilization. A C:N ratio of approx. 25 is usually considered the ratio where N mineralisation and immobilisation is in balance (Pierzynski et al., 2005). The present ratio of 39 can thus not be expected to contribute significantly to the N supply, in concordance with the above calculation. It means that the fibre pellets more act as soil structure improvement media then as actual N fertiliser.

After the gaseous losses (Table E.3), there is 0.74 (JB3), respectively -0.21 kg N left for harvest and leaching. The latter small negative value implies that 1000 kg pellets on JB6 will immobilize 0.21 kg N from the soil mineral N content.

These amounts of surplus N are very small, so for simplicity the distribution of the surplus between harvest and leaching for JB3 is assumed to be as for pig slurry (Table A.15). For JB6, the leaching is set to zero. The 100 year leaching values cannot be calculated with the methods used in Annex A, B and C, because of the high C/N ratio. No estimates are therefore given for these values for the fibre pellets.

Table E.3. Life cycle data for application of slurry and field processes (reference scenario). All data per 1000 kg of slurry ex outdoor storage.

	Annex A Fattening pig slurry	Annex E Fibre pellets	Comments
Input
Slurry “ex storage” Fibre pellets “ex storage”	1000 kg Slurry ex storage	1000 kg Fibre pellets ex storage	This is the reference amount, i.e. the emissions are calculated relative to this.
Output
Slurry on field, fertiliser value	Fertiliser replacement value: See section E.8	Fertiliser replacement value: See section E.8.	See text in section E.8.
Energy consumption
Diesel for slurry	0.4 litres of diesel	0.4 litres of diesel	Assumed to be the same per kg.
Emissions to air
Carbon dioxide (CO₂), JB3 JB6	81.6 (99.8) kg 80.2 (99.4) kg	1188.7 (1453.1) kg 1168.2 (1447.3) kg	Modelled by C-TOOL (Gyldenkærne et al, 2007). 10 year values and 100 year values in parentheses.
Methane (CH₄)	Negligible	Negligible	The CH₄ emission on the field is assumed to be negligible, as the formation of CH₄ requires anoxic environment (the field is aerobic) (Sherlock et al., 2002).
Ammonia (NH₃-N) during application	0.02 kg	0.04 kg	NH3 emissions during application: 0.5% of NH4+-N “ex storage”, see table A.1 and A.2 and text below. Hansen et al. (2008).
Ammonia (NH₃-N) in period after application	0.48 kg	0.243 kg	NH3 emissions in the period after application are based on Hansen et al. (2008) and the current slurry distribution in the crop rotation, see text.
Direct emissions of Nitrous oxide (N₂O-N)	0.05 kg [0.015-0.15]	0.116 kg	0.01 [0.003 - 0.03] kg N₂O-N per kg N “ex storage” for application of animal wastes to soil, based on IPPC (2006, table 11.1).
Indirect emissions of Nitrous oxide (N₂O-N) Soil JB3 Soil JB6	0.005 kg 0.014 kg 0.011 kg	0.012 kg 0.003 kg 0 kg	0.01 kg N₂O–N per kg (NH₃–N + NO_X–N) volatilised (IPCC, 2006, table 11.3). Ammonia emissions given in this table. Furthermore, nitrate leaching leads to indirect emissions of nitrous oxide.
Nitrogen oxides (NO_x-N)	0.005 kg	0.012 kg	NO_X–N = 0.1 * N₂O-N according to Nemecek and Kägi (2007)
Nitrogen (N₂-N) Soil JB3: Soil JB6:	1.91 (2.12) kg N 1.50 (1.67) kg N	0.40 kg 0.00 kg	See text
Discharges to soil
Nitrate leaching Soil JB3 Soil JB6	1.91 (2.12) kg N 1.50 (1.67) kg N	0.40 kg 0.00 kg	See text
Phosphate leaching	0.113 kg P	0.431 kg P	10% of the P applied to field (Hauschild and Potting, 2005 – only 6% of this reach the aquatic environment, see text).
Copper (Cu)	0.0276 kg	0.082 kg	[No data]
Zinc (Zn)	0.0824 kg	0.242 kg	[No data]

E.12 Storage of ash

This process is identical to the storage of ash in Annex D.

E.13 Transport of Ash to Field

This is identical to the transport of ash in Annex D.

E.14 Field processes (ash)

This is identical to the field processes for the ash in Annex D.

[1] 23.19 kg fibre pellets * 40% * 0.209 kg ash per kg DM (See Annex D) = 1.09 kg ash.

[2] As explained in section “Definitions and abbreviations” in the beginning of the report, TAN and NH₄⁺is used as synonyms for each other by e.g. Hansen et al. (2008) and Poulsen et al. (2001) in spite of that it is only an approximation. This approximation is also used here.