Work recently came out in a publication with CAPES classification of A1; results suggest that production from vinasse could supply 16.6% of the consumption of natural gas in the State of São Paulo

Researchers from the FAPESP Shell Research Centre for Gas Innovation (RCGI), led by Professor Suani Coelho, recently published in the Journal of Cleaner Production the results of an investigation of the technologies of cleaning and upgrading processes for removing contaminants from biogas (such as H2S and CO2). The article was published in the July issue with a QUALIS System CAPES classification of A1, with a great national and international impact (click here to read the paper). At the RCGI, Suani is Coordinator of the project “Perspectives on the contribution of Biomethane for increasing the offer of Natural Gas.”

“There is a considerably large number of technologies available for performing these processes, which could be a barrier for those who develop policies and do energy planning to make quick estimates, with few certainties and little satisfactory precision, of biomethane potentials taking into account the norms and standards established by regulatory agencies. Therefore, the main objective of the article was to propose a short-cut model, based only on mass balances, which could assess the efficiency of the cleaning and upgrading process, irrespective of the source of organic feedstock or the technology used,” explains Caio Joppert, the lead author of the paper.

According to him, the idea was to facilitate the work of decision makers and planners by creating a model that would be able to estimate how much gas would be available for use after the cleaning (in terms of volume) and what would be the energy content (calorific value) of this fuel.

“These parameters can vary considerably, according to the technology utilized, because each technology is like a black box, so to speak. What we know is that there will never occur a total purification of the methane from other gases and vapors that que comprise the biogas. And it is common to lose methane during these upgrading processes.”

Joppert, who is a chemical with a degree from the Polytechnic School of the University of São Paulo (Poli/USP) and is working on his Master’s degree at the Institute of Energy and the Environment at the same University (IEE/USP) under the orientation of Professor Marilin M. Santos, states that the parameters for the loss of methane are very well established in the literature. “This parameter for loss influences the quantity of gas found at the end of the upgrading process, the methane content that the gas will have…. And this is not taken into consideration by energy planners and those who develop public policies,” he cautions.

The group analyzed the main purification technologies: washing with water, scrubbing with amine, physical absorption, and PSA (pressure swing adsorption), as well as newer technologies, such as separation with membranes and cryogenic separation (during which the gas mixture is held at cryogenic temperatures for CO2 liquefaction, which occurs prior to the liquefaction of CH4, and thus separates one from the other).

Results – The model created by the team was validated with data obtained from the literature (simulations and experiments) and, according to Joppert, satisfactory correlations occurred with that data, even for technologies experiencing high levels of methane loss.

It was used in a case study for the State of São Paulo, in which the team used biogas produced from vinasse to generate biomethane that would meet ANP norms.

“Besides the volume and composition of the biomethane, we assessed how much of the biogas produced would be needed to generate enough energy to supply the upgrading process. This is an important parameter, because the process could consume a considerable fraction of the biogas that will be upgraded to biomethane. Cryogenics, for example, demand very high energy consumption levels: the cryogenic process is the one that most consumes energy and, therefore, leaves less biogas available for producing biomethane.”

The author added: “Taking into consideration the mass balance of the process, plus the energy mass balance, we calculated that the volume of biomethane the would remain available to substitute diesel oil in the farming machinery and the trucks used at the mills, and also to be injected into the pipeline and make energy available to the sugar and alcohol mills near the State’s gas pipeline network.”

According to him, the model allowed making a prior choice of the technology that could meet the requirements. “The model assisted in making a prior choice of the technology that would be adequate to the needs of the biomethane standard imposed by the regulatory agency, and made it possible to estimate that 1.975 billion Nm³/year of biomethane could be produced from vinasse, thus supplying 16.6% of the natural gas consumption of the entire State and potentially all of the consumption of diesel oil at the sugar and alcohol mills. Furthermore, the substitution of natural gas and diesel oil could prevent the release of 3.965 million tons of CO2eq into the atmosphere (5.48% of the emissions of the entire State of São Paulo).”

He adds that, at the present time, Brazilian norms for injecting biomethane into the system are being established and that it would be an opportune moment to present the methodology to decision makers and planners, which the group intends to do.