18 December 2019
The AGROinLOG project deals with utilization of non-used resources and residues to create new business lines and products at agro-industries, taking advantage of their variations in seasonal operation. In the Swedish demonstration case, straw-based second generation ethanol production will be enhanced by improved logistics and better utilization of the lignin residue remaining after ethanol production. In the demonstration case, 80,000 tonnes of winter wheat straw are supplied annually to the ethanol plant of Lantmännen Agroetanol in Norrköping, Sweden.
Based on statistics, the potential quantity of straw in Sweden as well as all 21 counties was compiled. In the whole of Sweden approximately 1,255,000 tonnes of winter wheat straw are produced yearly. Of this total potential, about 67 % or 835,000 tonnes are estimated to remain after the amount used as feed and bedding in animal production has been removed. The assumptions made in the calculations are subjected to uncertainties and the straw available for ethanol can be underestimated.
For the demonstration case to supply the ethanol plant in Norrköping with 80,000 tonnes of winter wheat straw per year, a more detailed analysis of the straw potential was made by evaluation of the sustainability in removing straw from a soil fertility aspect by using the model “Odlingsperspektivet”. Sustainable, in this context, means that soil fertility is not allowed to decrease as an effect of straw removal. It was concluded that winter wheat straw, by a comfortable margin to the planned 80,000 tonnes, could be removed from arable farms in surrounding counties without affecting yields negatively in a 50-year perspective.
In a 2050 perspective, climate-change will result in a change regarding which crops will be cultivated in different Swedish regions. Based on estimates of these changes, the total straw potential in Sweden would increase by 509,000 tonnes until 2050, corresponding to 16 %. The potential of winter wheat straw would increase with 461,000 tonnes (33 %).
Interviews with both farmers and entrepreneurs and contractors was performed to catch their practical experiences from handling of straw. According to the interviews with farmers, their incentive to harvest straw was depending on timeliness effects, effects on soil fertility and the straw price. For a system with reliable deliveries of straw it is important that there is a win for the farmer to make it worth the effort to harvest the straw. Most of the farmers wanted one-year contracts to a fixed price coupled to the cost for replacing the nutrients removed. The contractors thought Lantmännen should sign long 5 year-contracts with farmers to deliver straw from a certain area (ha) and not a certain amount of straw, since it is impossible to know the yield in advance.
A field study was made to evaluate anaerobic straw storage in wrapped bales at three different moisture contents, in terms of dry-matter losses and hygienic quality. Bales at high-moisture were characterized by a more thorough ensiling process and a higher packing density than medium and low-moisture bales. The loss of dry matter in high-moisture straw was low and in the range for acceptable. The anaerobic storage in wrapped round bales confirmed to be an efficient method for wet straw storage.
With a supply chain model developed within the project, the supply of 80,000 tonnes of winter wheat straw to the ethanol plant in Norrköping was simulated. The model is based on GIS-data on field level in the counties surrounding the ethanol plant. The model optimizes from which farms the straw should be collected to minimize the costs for purchase and transport. Straw supply was examined in following four scenarios:
- Scenario 0 – Base: 80,000 tonnes of winter wheat straw collected from arable farms in three nearby counties.
- Scenario 1 – Drought: As 0, but with 18-30 % reduced straw yield based on the “dry year” of 2018.
- Scenario 2 – Unfavorable weather at harvest: As 0, but available amounts of straw were reduced with 30%.
- Scenario 3 – Hub Vadstena: As 0, but restricted to one harvest area surrounding Vadstena municipality.
The straw supply was simulated based on the analysis of sustainable removal (no negative effects on future yields) of winter wheat straw. The simulation results confirmed that the 80,000 tonnes of winter wheat straw needed for the ethanol plant can be delivered without negative yield effects, also during years with less favourable weather conditions. In the base scenario 489 farmers, out of 1,876 available in the database, were selected for the supply and the average supply cost (purchase and transport) was €90.5 per tonne straw. All straw was supplied within an average distance of 35 km from the ethanol plant. When restricting the straw supply due to weather conditions as in scenario 1 and 2, costs increased with approx. €1-3 per tonne. The alternative to supply the plant only with straw from the area around Vadstena (Scenario 3) almost managed to reach the 80,000 tonnes of winter wheat straw, however with a higher total supply cost due to longer transports.