Utilization of Food and Agricultural Residues for a Flexible Biogas Production: Process Stability and Effects on Needed Biogas Storage Capacities

Ervin Saracevic,Bernhard Wlcek,Andreas Gronauer,Angela Miltner,Jonas Leber,Javier Lizasoain,Bernhard Munk,Susanne Frühauf,Kwankao Karnpakdee,Anton Friedl,Michael Lebuhn,Alexander Bauer

doi:10.3390/en12142678

Abstract

Biogas plants can contribute to future energy systems’ stability through flexible power generation. To provide power flexibly, a demand-oriented biogas supply is necessary, which may be ensured by applying flexible feeding strategies. In this study, the impacts of applying three different feeding strategies (1x, 3x and 9x feeding per day) on the biogas and methane production and process stability parameters were determined for a biogas plant with a focus on waste treatment. Two feedstocks that differed in (1) high fat and (2) higher carbohydrate content were investigated during semi-continuous fermentation tests. Measurements of the short chain fatty acids concentration, pH value, TVA/TIC ratio and total ammonium and ammonia content along with a molecular biology analysis were conducted to assess the effects on process stability. The results show that flexible biogas production can be obtained without negative impacts on the process performance and that production peaks in biogas and methane can be significantly shifted to another time by changing feeding intervals. Implementing the fermentation tests’ results into a biogas plant simulation model and an assessment of power generation scenarios focusing on peak-time power generation revealed a considerable reduction potential for the needed biogas storage capacity of up to 73.7%.

Highlights

Biomass-based power plants show great potential to serve future energy systems’ needs.The storability of the energy carrier, whether in gaseous, liquid or solid form, qualifies these plants for demand-oriented energy supply
For the 1x feeding strategy (Figure 3a), biogas production from both feedstocks was immediately increased within the first hour after the feeding event, which took place 25 minutes before hour 1
The maximum was achieved at hour 2 with a biogas production of 86 and 82 lN m−3 h−1 and a methane production of 61 and 63 lN m−3 h−1 for feedstocks 1 and 2, respectively

Summary

Introduction

Biomass-based power plants show great potential to serve future energy systems’ needs. The storability of the energy carrier, whether in gaseous, liquid or solid form, qualifies these plants for demand-oriented energy supply. The implementation of globally determined climate protection goals led to a significant increase in power plants with fluctuating power generation in the energy system, primarily in wind and photovoltaic power plants. Additional flexibility in the energy system is needed to ensure sufficient balancing of power supply and demand [1]. Most biogas plants operated in Europe are currently designed as baseload power plants with the continuous conversion of biogas to electricity and heat in combined heat and power (CHP) units and an operating time of usually over 8000 full-load hours per year. The combined electrical and thermal efficiency of energy conversion from biogas to power and heat with CHP units is about

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