Abstract
A significant challenge in sustainability and development of energy systems is connected with limited diversity and availability of fuels, especially in rural areas. A potential solution to this problem is compression, transport, and storage of raw biogas, that would increase diversity and availability of energy sources in remote areas. The aim of this study was to perform experimental research on raw biogas compression concerning biogas volume that can be stored in a cylinder under the pressure of 20 MPa and to compare obtained results with numerical models used to describe the state of gas at given conditions. Results were used to determine the theoretical energy content of raw biogas, assuming its usage in CHP systems. In the study, six compression test runs were conducted on-site in an agricultural biogas plant. Compression time, pressure as well as gas volume, and temperature rise were measured for raw biogas supplied directly from the digester. Obtained results were used to evaluate raw biogas compressibility factor Z and were compared with several equations of state and numerical methods for calculating the Z-factor. For experimental compression cycles, a theoretical energy balance was calculated based on experimental results published elsewhere. As a result, gas compressibility factor Z for storage pressure of 20 MPa and a temperature of 319.9 K was obtained and compared with 6 numerical models used for similar gases. It was shown that widely known numerical models can predict the volume of compressed gas with AARE% as low as 4.81%. It was shown that raw biogas supplied directly from the digester can be successfully compressed and stored in composite cylinders under pressure up to 20 MPa. This proposes a new method to utilize raw biogas in remote areas, increasing the diversity of energy sources and increasing the share of renewable fuels worldwide.
Highlights
The modern energy sector faces numerous challenges connected with the increasing electricity demand
Results of performed experimental research on on-site raw biogas compression have provided significant and novel data regarding the volume of gas that can be stored under elevated pressure
It was shown that raw biogas can be compressed on-site to a pressure of 20 MPa and that widely known numerical models can predict the volume of compressed gas with an absolute average relative error as low as 4.81%
Summary
The modern energy sector faces numerous challenges connected with the increasing electricity demand. There is a growing need for an increase in the share of renewables and improvement in energy source diversity. Renewable energy usage in Europe reached a share of 17% in the gross final energy consumption in 2015, and the projections show that it will exceed the target of. Gaseous fuels are of great importance, and their consumption is increasing, based on current trends. In Poland, the majority of natural gas (NG) is imported (~78%), which is connected with limited capabilities to extract this gas nationwide. Despite the significant increase in renewables usage in electricity generation, there is a very limited alternative for compressed gas distribution, Processes 2020, 8, 1556; doi:10.3390/pr8121556 www.mdpi.com/journal/processes
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