Process can revolutionize retention of gases from oil extraction at the bottom of the sea
When extracted from wells, oil is accompanied by a mixture of carbon dioxide (CO2) and gaseous hydrocarbons, particularly methane (CH4), both atmospheric pollutants, which are normally reinjected into wells, which makes the process more expensive. Ideally, these two main gaseous components would be collected and separated so that methane could be used as fuel and carbon dioxide stored conveniently.
This is the scope of the studies that have been carried out by a group of researchers from Unicamp and USP. In this case, the idea involves the formation of gas hydrates, in which solidified water retains the gases in question in its interstices. The crystalline structure formed, which resembles ice, has a large gas storage capacity: one liter of methane hydrate, for example, can contain approximately 168 liters of this gas.
Then, from these crystalline structures - obtained under appropriate pressure and temperature conditions - methane can be separated for use as fuel and the carbon dioxide trapped. There would then remain two possibilities for disposing of carbon dioxide hydrates: they would be deposited either in wells or at the bottom of the sea, where the low temperature (4 degrees Celsius) and high pressure would keep them definitively stable.
The project aimed to capture and store carbon dioxide (CO2) and methane (CH4), through the process of producing gas hydrates, was coordinated by professor Song Won Park, from the Department of Chemical Engineering at the Escola Politécnica da USP and had the technical coordination of professor José Roberto Nunhez, from the Department of Process Engineering at the Faculty of Chemical Engineering (FEQ) at Unicamp. The study included the collaboration of advisors from the two professors: from the Polytechnic School, Adriano Ferreira de Mattos Silvares (post-doctoral student), João Pedro Ferreira del Pintor and Vitor Hideyo Isume (master's students); from Unicamp, post-doctoral students Lucídio Cristóvão Farderlone and Daniela da Silva Damaceno, doctoral student Nayla Xiomara lozada Gardia and master's student Aglaer Nasia Cabral Leocádio.
This study, developed within the scope of the special participation clause of the National Petroleum, Natural Gas and Biofuels Agency (ANP), is sponsored by Petrogal Brasil, which actively participates in technical coordination through Carlos Augusto and Marcella Mathias, who work on the projects.
For the initial experimental studies, a bench system was used for the production of gas hydrates, built in Portugal, based on technology patented by the Laboratory of Separation and Reaction Engineering, of the Faculty of Engineering of Porto (FEUP) and produced by the company Paralab .
In the NETmix ® minireactor, a component of the equipment, both water and gases come into contact with each other and produce gas hydrates at appropriate pressure and temperature. The auspicious initial results led to the construction, by the same company, of pilot equipment with ten times greater capacity, already tested by FEUP, and which is coming to Unicamp. These two pieces of equipment were the first to be built in the world specifically for the production of hydrates, although NETmix has long been used in Europe for various other processes.
The differences
Professor Nunhez explains that the use of hydrates is ancient. The project aimed to propose a real, concrete and quick solution for CO capture2 and CH purification4 , using reduced-sized industrial facilities on marine platforms. Hydrates form at low temperatures, but during processing there is a large release of heat that requires the fastest possible removal for the process to continue and accelerate. In mixing tanks, which would be an option for producing hydrates, heat removal is slow and can take hours, unlike the proposed process in which hydrate formation takes place in seconds.
In fact, in tanks, as their quantities increase, the thermal exchange capacity decreases. One of the biggest problems in obtaining hydrates is the high energy released in their formation. It is abundantly mentioned in the specific literature that, with the increase in scale in mixing tanks, energy is not released with the same efficiency as in smaller tanks since the scale decreases the relationship between the heat exchange area and the volume in that the transformation occurs. Differently, the new process uses a technology that guarantees the same level of thermal exchange even with increased scale.
The great difference of the proposed equipment, whose reactor consists of a network of static mixers, is that they have structures that allow the flow of water and gases introduced to be divided several times, allowing greater contact between them. In this technology, the equipment, in thermal exchange, has characteristics of micro mixers. Depending on the scale of production, simply increase the number of mixers, a process that facilitates the dissipation of the heat necessary for the formation of hydrates. In other words, mixers are progressively added so that the production of hydrates occurs according to the flow of gases to be processed.
Another advantage of the system is its compact installation when compared to mixing tanks. In other words, the area occupied becomes smaller and the process is continuous. Naturally, carbon dioxide and methane hydrates need to be removed as they form for subsequent separation of the gases so that only carbon dioxide hydrates remain.
In fact, Nunhez explains, the idea is to first remove the hydrocarbon, in this case methane, and keep the carbon dioxide hydrate: “As the hydrates of these gases have different stabilities, methane can be released preferentially. This separation is still being studied and, although not trivial, it involves a problem that can be solved by chemical engineering using what is called thermodynamic equilibrium.”
This, in short, is the idea of the ongoing project. In tests already carried out, hydrates were obtained with the CO mixture.2 and CH4 - used in the same proportion as they are found in oil wells - and, separately, of CO hydrates2. Similar results were obtained with the use of seawater, which has a saline composition, and which could inhibit the formation of hydrates.
The professor credits the award to the very encouraging results achieved and the global potential of the technology developed. By the way, he concludes: “We have shown that the technology works and brings a great advance in terms of technological innovation because it enables a continuous process at an incomparable speed compared to what occurs in a battery process in which hydrates form over time. ”.
In 2019, the company won the ANP Technological Innovation Award, awarded in five categories in its sixth edition. It aims to recognize the results achieved by research, development and innovation (RD&I) projects that represent technological innovation for the oil, natural gas and biofuels sector developed in Brazil by research institutions accredited by the Agency, with resources from exploration contracts and production. The award received by researchers from Unicamp and USP falls into category I: “Oil and Gas Exploration and Production”.
