Investigation of cryogenic biogas upgrading using innovative two-stage autocascade refrigeration cycle working with natural refrigerants

Project title: Investigation of cryogenic biogas upgrading using innovative two-stage autocascade refrigeration cycle working with natural refrigerants
Project Manager:  dr inż. Michał Sobieraj
Implementing institution: WIBHiIŚ
Source of funding:  (IDUB)

Project summary:

The goal of this project is to provide a solution for biogas purification with the
opportunity the use a by-product CO2 as an ecological refrigerant. The main object of this
project is to study a process of cryogenic biogas upgrading. Biogas – a natural fuel rich in
highly energetic methane gas, contains huge amounts of carbon dioxide and trace amounts
being residues of water vapour and sulfur, which results in inefficient burning and transport
processes. It is therefore of the utmost importance to remove the CO2 from the biogas
stream, which can be efficiently achieved with cryogenic separation. A novel two-stage
Joule-Thomson autocascade cycle providing cryogenic temperatures is proposed in this
project.
The novelty of the solution has its reflection in the cycle configuration as well as in the
refrigerants used. An upper refrigeration cycle will use medium to low boiling substances,
while in the lower cycle ultra-low boiling substances will be used. Refrigerants with low
global warming potential (GWP) will be used in the proposed solution, with the most
important aspect being the use carbon dioxide in the quantity of as much as 50% of the
overall refrigerant charge.
The proposed autocascade cycle will be based upon the two patented solutions,
developed at the Faculty, allowing the use of an environmental friendly carbon dioxide
(R744) as a low-temperature refrigerant.
Two aspects of the cryogenic biogas upgrading with a novel autocascade cycle will be
studied. The first part is to investigate the efficiency of the proposed cycle based on the
energy and exergy analysis performed in simulation and experimental means. Different cycle
configurations working with a range of mixture concentrations will be studied. The second
part will be the investigation of the heat and mass processes during the formation of solid
carbon dioxide on the tubes of the cryogenic heat exchanger. An experimental setup will be
manufactured consisting of a two-stage autocascade refrigeration unit and a visualization
section. The visualization of the formation of solid dry-ice in the temperatures as low as
-120°C will be of a great help for the mathematical description of the process.
Both the aspects of the study including the evaluation of the refrigeration cycle
performance and heat and mass transfer processes will be an important contribution to the
field of thermodynamics. The solution proposed enables an efficient separation of biogas for
further use of high purity methane as a fuel and CO2 as a refrigerant.