Benchmarking Report on Critical Points and Influential Factors at Agricultural Biogas Plants

Abstract:

<p>To assess and improve the production from European biogas plants a specific targeted research or innovation project (Project no. 513949) entitled 'European Biogas Initiative to improve the yield of agricultural biogas plants' involved collating data from 13 biogas plants across Europe. Data was collected by four means; the use of periodic data from the biogas plant, weak-point analysis from each of the biogas plant operators; a questionnaire and a schematic of each plant. The information revealed that although the biogas plants were performing relatively well, with an average specific biogas yield 0.44 m3.methane.kg-1 VS and an average methane productivity of 1.25 m3.m3, there was considerable capacity to improve the performance of each of the biogas plants by a range of different means.</p> <p>Economic comparison of these biogas plants across Europe was difficult. However, about 90% of the revenue was realised from electricity sold. The average specific capital expenditure for the 13 biogas plants was about 4,400 &#8364; per installed electric capacity (kW) or at 5% discount rate and 15 years economic life, 5.3 &#8364;-Cent per kWh of electricity. The average costs of feedstock was 5.6 &#8364;-Cent per kWh electricity produced. Also the average cost was 67 &#8364;-Cent per Nm³ of methane produced. The average total costs were 19.5 &#8364;-Cent per kWh electricity produced which was slightly above the price paid in most of the countries involved.</p> <p>Development of improved means of both introducing and treating the feedstock was important for improved biogas yields. The hydrolysis of crops and crop residues could significantly reduce the HRT of some digesters to below 100 days. The type and mixture of feedstock also influenced the biogas yield and optimisation of the inputs would be of benefit. However each feedstock may ferment at different rate and/or require different conditions so process control could produce more biogas. High levels of manure required up to 4 times as much volume as other feedstocks to produce the same amount of biogas. There was up to 3 times the methane output per kg VS from different biogas plants. Some biogas plants had a variability (on standard deviation) of the specific methane yield as low as 7% others could be considered unstable with values over 100% of their mean values. Feedstocks were considered responsible for this variability, however such a range suggests that process monitoring and control would provide more stable biogas production and improved biogas yields. Monitoring fermentation parameters was limited to pH and volume of the various vessels for all biogas plants. Sensors did include means of measuring VFAs (36% of the total) and conductivity (18%) and redox potential (9%) for the 13 biogas plants. The outcome of this study will be used to identify demonstration projects at different biogas plants and research facilities.</p>

Author(s):

IGER