The filter ash is transported by means of a heavy lorry trailer from the bioenergy plant to a mine in Germany. The distance is assumed to be 250 km. The amount of ash transported is 6.7 kg, which corresponds to 1.68 t km. The total PK nutrient demand has to be provided by synthetic fertilizer (243 kg) under the same condi­tions as described in scenario 1. The transport distance corresponds to 194 t km. In Table 8.11, an overview is given of the total emissions in scenario 2.

8.4.3 Comparison of the Two Scenarios

In Table 8.11, the emissions caused by the two scenarios are compared. The emissions caused by scenario 1 and by scenario 2 are about the same, which is not surprising because of the low level of replacement of the PK fertilizer that can be obtained. However, the potential CO2 reduction per kilogram of filter ash is significant, namely, about 0.40 kg CO2/kg filter ash.

In this study some assumptions have been made. In the sensitivity analysis, the influence of these assumptions on the emissions is determined.

• All of the phosphorous and potassium present in the ash is available as nutrient. If the availability of both elements drops below 40-45%, then the CO2 and SO2 emissions in scenario 1 will be higher than those in scenario 2.

• The transport distance within Cote d’Ivoire is 800 km. If the transport distance is 500 km, the CO2 emissions in scenarios 1 and 2 decrease to 160.3 and 161.9 kg, respectively. If the transport distance increases to 1,000 km, the CO2 emissions are 179.3 and 180.9 kg, respectively. This means that the absolute value in both scenarios will be influenced to a small extent, but the difference between the values in both scenarios remains the same.

• The transport distance within Cote d’Ivoire is the same for the filter ash and the PK fertilizer. If the transport distance of the ash is about 1,500 km more than that for the PK fertilizer, then the CO2 emissions in scenario 1 will be higher than those in scenario 2.