Autumn 2017 EN

More documents

Recommendations

Info

English Issue Biogas Journal | Autumn_2017 Table 1: Base data for a cost comparison between maize silage and maize stover silage Removed fresh weight Removed dry matter yield Dry matter percentage Silage loss Organic dry matter percentage Organic dry matter yield after silaging Methane yield Methane yield per ha Electricity yield per ha 6) t fresh weight per ha t dry matter per ha % % dry matter % t organic dry matter per ha Nm 3 (t organic dry matter per ha) Nm 3 per ha kWh el per ha Maize silage (whole plant) Maize stover silage 51 1) 17.0 33 6 95 15.2 337 4) 5,116 20,423 9.7 2) 4.9 51 8 3) 93 2) 4.2 295 5) 1,237 4,937 1) Average yield of silo maize from 2009 though 2014 (Bavarian State Office for Statistics). 2) Two-year results of the practical harvest technology trial, which are also realistic in practice. 3) Silage loss based on expert estimates. 4) Methane yield of silo maize according to the biogas calculator of the LfL (http://www.lfl.bayern.de/iba/energie/049711). 5) Methane yield of maize stover in reference to organic dry matter: 87.5 percent of silo maize (according to the results of the batch trials). 6) Assuming a 40 percent rate of utilisation for electricity of the methane used in combined heat and power generation. the dry matter contents of the plant residues (= maize stover) were in the range of silo maize (30 to 35 percent). In contrast to the visual appearance, the dry matter contents were not high even for very ripe residual plant parts. Nevertheless, depending on weather conditions during the harvest, the crop can still dry significantly. For this reason it is advisable to recover the maize stover immediately following the grain harvest. With average crude ash contents of 7.9 percent (2014) and 6.2 percent (2015), contamination can be classified as unproblematic. The “natural” crude ash content of the plant residue is about 4 percent; the increase in crude ash contents by 2 to 4 percentage points is due to contamination during the harvest. If the stover yields that were actually removed and the crude ash content that was measured were used to calculate the methane yield per hectare, the yield would be about 1,500 Nm 3 CH 4 per hectare, i.e. about 20 to 25 percent of that of silo maize. Suitability of grain maize stover as silage To use maize stover all year round, it must be suitable for silage. Its designation as “straw” leads to the assumption that this substrate performs very poorly as silage. However, standardized silage trials have shown that maize stover generally performs very well as silage and that dry matter loss is low if oxygen exclusion is guaranteed. Even the aerobic stability was, for the most part, high after the silo was opened. This was also confirmed in the trials, even with higher dry matter contents and poorer maize stover quality (e.g. remained in the field for a long period), although in such cases, loss could have already occurred due to processes in the field. One challenge is certainly the ability to compress the maize stover in the silo. In an initial silage trial in the silage tunnel, the densities measured were about half that of silo maize. This has consequences with regard to the required space for the silage and brings with it the risk of spoilage if air should enter. The extent to which the silage tunnel results can also be applied to silage in clamp silos must be clarified in further trials. In practice, silaging maize stover seems to work well. Often professionals work with mixed silage or a “cover layer” of wetter substrates (e.g. grass or a catch crop) is applied to the silage. 16
Biogas Journal | Autumn_2017 English Issue Table 2: Costs of maize silage and maize stover silage “free input” for free maize stover “from the field” (€ rounded to whole numbers) Total costs “free standing supply” (without land costs) Harvest + Transport (5 km) + Silaging Storage in clamp silo Removal / recovery and supply Total costs “free input” (without land costs) € per ha € per ha € per ha € per ha € per ha € per t fresh weight € per t dry matter Euro cents per Nm³ CH 4 Euro cents per kWh el Maize silage 1) (whole plant) 1,245 386 147 46 1,824 38 114 36 8.9 Maize stover silage 2) 0 162 62 19 243 27 54 20 4.9 1) Costs according to the LfL online calculator (see also: https://www.stmelf.bayern.de/idb/silomais.html) 2) Assuming that maize stover silage requires 1.5 times more storage area than silo maize What does a kilowatt hour generated from maize stover silage cost? The LfL trial results regarding the amount and quality of the maize stover silage confirm that it is basically suitable as a substrate and demonstrate its potential. From an economic standpoint, should this potential be developed? And how competitive is maize stover? The large-scale trial also provided initial data regarding the costs for the machine used. The entire cost of providing maize stover from windrow to fermenter was 243 € per hectare. 4.9 tonnes of maize stover dry matter were recovered on this hectare. Then the yield processed by the field chopper was transported five kilometres to the clamp silo and stored there with the conventional technology. With storage losses of eight percent, it was removed again, and finally, supplied to the biogas plant (see also Table 1). If the methane yield per hectare of 1,237 Nm³ is converted to electricity with a degree of efficiency of 40 percent, total costs per kilowatt hour of electricity generated would be 4.9 euro cents (see also Table 2). This 4.9 euro cents per kilowatt hour make maize stover more than just a new competitor to be taken seriously in the substrate mix, taking the assumptions listed below into consideration. Maize stover actually is available in the field for free. Effects on individual operations that were not previously the case, such as the humus situation, nutrient balance, field hygiene (e.g. not mulching), and soil compaction due to additional passes with the chopper chain, as well as having to spread the returned fermentation residue, which was probably not previously required, were evaluated as economically inefficient. The situation for an individual operation, however, could result not only in costs (e.g. nutrient extraction due to maize stover removal without returning the fermentation residue), but also in credits (e.g. the fertilizer value in the returned fermentation residue is greater than the fertilizer value of the decayed maize stover remaining in the winter as an alternative). In addition to these agricultural side effects, above all the evaluation has not yet taken the side effects of the technical methods into account. Using a large proportion of the chopped maize stover brings up the question of pre-chopping the substrate, which has not yet been investigated. Is the fermentation of maize stover silage currently economical? Long-term evaluations at the LfL show that many biogas plants with an emphasis on maize as an input work with a substrate cost level (“free input”) of more than 10 euro cents per kilowatt hour. The total costs for classic maize silage without land use costs amount to 8.9 euro cents; with land use costs of 500 euro per hectare, the costs amount to 11.4 euro cents per kilowatt hour generated. At 4.9 euro cents per electrical kilowatt produced, this certainly makes the fermentation of maize stover economical; at 5 euro cents per kilowatt hour (about € 250 per hectare) to cover the side effects already mentioned for individual operations, there is plenty of room for flexibility. THERM Exhaust gas heat exchangers Steam generators Gas coolers / Gas heaters Special applications Additional components Energiepark 26/28 D-91732 Merkendorf / Germany +49 9826-65 889-0 info@enkotherm.de www.enkotherm.de INTELLIGENT INDIVIDUAL COMPETENT Our performance – Your success 18KW TO 2000KW CHP SOLUTIONS FROM ONE SOURCE WOLF Power Systems GmbH, Streßelfeld 1 D-29475 Gorleben, Tel.: +49 (0)8751/74-2266 wolf-power-systems.de 17
Page 1 and 2: www.biogas.org German Biogas Associ
Page 3 and 4: Biogas Journal | Autumn_2017 Editor
Page 5 and 6: Biogas Journal | Autumn_2017 Englis
Page 15: Biogas Journal | Autumn_2017 Englis
Page 25 and 26: AD & BIOGAS FEED TECHNOLOGY Biogas
Page 29 and 30: BIOGAS Know-how_3 Biogas Journal |
Page 51 and 52: Sonic Cut Thru Heavy 12. - 18.11.20

Autumn 2017 EN

Create successful ePaper yourself

Delete template?

Save as template?