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Bewertung der fermentativen Wasserstofferzeugung aus lignocellulosehaltiger Biomasse

Evaluation of fermentative hydrogen production out of lignocellulosic biomass
 
: Schmick, Danae
: Weger, Andreas

Amberg-Weiden, 2015, X, 57 S., VII
Amberg-Weiden, TH, Bachelor Thesis, 2015
Deutsch
Bachelor Thesis
Fraunhofer UMSICHT Sulzbach-Rosenberg ()

Abstract
The massiv usage of fossile fuels leads to high carbon dioxid emissions which cause global warming. To stop climate change we have to reduce the usage of fossile fuels and substitude them by renewable energie sources. Hydrogen is one of the most promising alternatives. Today steam reforming of natural gas is the most common production process of hydrogen. But there are also several renewable processes to produce hydrogen. One of them is the fermentative hydrogen production out of lignocellulosic biomas. The main focus should be on the usage of residual or waste materials. A competition between the energetic usage and the food industry is to be avoided. In this thesis the utilizability of grass silage is tested. Earlier experiments showed that monofermentation of grass silage lead to not acceptable conversion rates. Due to this results and to have a connection to practice a mixture of corn and grass silage was used. Moreover the effects of inorganic additive and enzyme on the fermentative process, the decay rate and the quality of hydrolysis gas were tested. For the experiments a fermenter with a netto capacity of 20 liters was used. The fermentation conditions were a mesophilic temperature from about 39 °C and a pH range of 4,5 to 5,0. In anaerobic degradations organic acids are produced which lower the pH range. To stabilize the process natriumhydroxid is used. The retention time is 4 days. To gain the best results several inokula has been tested. Primary and tertiary sludge from a purification plant and digestate of biogas fermentation have been tested. There was just a small gas yield when primary sludge and digestate have been applied. Furthermore it was not possible to inhibit the methanogenesis. It was not possible to reach the goal of hydrolysis gas without methan. In the end tertiary sludge has been chosen to be the best inokula for conducting the following experiments, because there was a high gas yield with no methan in it. Three experiments were done: ► Experiment 1: Mixture of corn and grass silage (50:50) ► Experiment 2: Mixture of corn and grass silage (50:50) plus inorganic additive ► Expermient 3: Mixture of corn and grass silage (50:50) plus enzyme In Experiment 1 you gain a spezific hydrolysisgas yield of 78 l i.N/kgoTS and a hydrogen yield of 31 l i.N/kgoTS. You needed a lower amount of natriumhydroxid to stabilize the pH range because of the buffering effect of the grass silage. There was no methan in the hydrolysis gas. The addition of inorganic additive in experiment 2 lead to an lower degradation rate of the organic substrate. In comparission to experiment 1 a lower hydrolysis gas and hydrogen yield was reached. It was 61,5 l i.N/kgoTs and 19,2 l i.N/kgoTS. The inorganic additve pushed the methanogenesis. It was impossible to produce hydrolysis gas without methan. After a few days only methan got produced. The adding of this inorganic additive makes no sense for the hydrogenproduction. The best results had been reached with the addition of enzymes. The degradiation rate of the organic substrate was higher and the analyse of the gas quality showed an higher amount of hydrogen. In experiment 1 you got 37,2 Vol.-% and in experiment 3 a hydrogen amount of 41 Vol.-% was reached. There was a specific hydrolysis gas yield of 89,6 l i.N/kgoTS and a hydrogen yield of 36,9 l i.N/kgoTS. The experiments demonstrate that the fermentative production of Hydrogen by lignocellulostic bio mass like corn and grass silage is possible. The next part was an economic efficiency calculation. The target was to calculate the production costs for the fermentative production of hydrogen and to compare them to the price of steam refoming. Bachelorarbeit von Danae Schmick – VII – The reactor for hydrolysation was considered as a pre-stage of a biogas reactor. The desulfurization and gas purification was realized by a pressure swing adoption plant. Two cases have been measured. In the first one only corn silage was used as substrate. In the second case a mixture of corn and grass silage were utilized. With corn sillage as substrate production costs of about 16 €/kg were generated. Because of lower substrat cost you reach a lower production cost with the usage of the mixture of grass and corn silage. It was ca. 13 €/kg. The calculation of the production cost of hydrogen come to the conclusion that the price for fermentative produced Hydrogen is 10 times higher than the process costs of hydrogen which was produced by steam reforming. The fermentative prosuction costs can be lowered by the selling of byproducts like for example carbon dioxid, but this wasn’t part of this thesis. To put it in a nutshell: There is still a high demand of research work and big technical progress in the sector of gas purification necessary to produce hydrogen by fermentation in an economic way.

: http://publica.fraunhofer.de/dokumente/N-379613.html