In September 2021, the first biomethane injection was carried out into the network of Nedgia, a distributor of the Naturgy group. UNUE's objective is to produce and inject 20 GWh per year of biomethane into the gas system, which would mean a reduction in emissions of around 30.000 tons of CO2 equivalent.
The biomethane plant is located in the Villalonquejar industrial estate, on the property of Biogasnalia, a leading waste manager in the region and owner of the plant that has generated biogas since 2017.
Absorption by water. A well-known technology
The Spanish engineering company AGF Engineering of Processes, which designed and operates the Biogasnalia biogas plant, has also been in charge of expanding it and designing the biomethane plant with water absorption technology.
Francisco Guzmán, general director of AGF, points out that this technology is very old and well proven and is based on the different solubility in water of methane and carbon dioxide molecules.
“AGF is the only one at a national level that has developed this technology and one of the few that does so in Europe,” highlights Guzmán.
Absorption by water allows, under certain conditions of pressure, temperature and flow, to separate these molecules to obtain renewable gas with sufficient quality to be injected into the natural gas network. “AGF has defined the precise conditions for this to occur efficiently in the biomethane plant,” he notes.
On the other hand, he adds, "by having designed both plants, and thanks to an important development in control engineering, we have achieved that communication between them is very fluid: every half hour they exchange information and adjust the operation automatically."
The biogas plant receives up to 90 tons per day of waste from various food and agri-food industries and in variable quantities. Biogas is produced depending on the availability of materials, which results in the quality and flow of the output biogas not always being the same.
The chosen technology and the fluidity in the communication between the biogas plant and the biomethane plant enable the continuous production of renewable gas at all times, without stops or starts, or losses in efficiency, since the biomethane plant is capable of adapting to the variations in composition and flow rate of the biogas that reaches it.
"The key is that the biogas plant works constantly to ensure the supply to the biomethane plant," says Guzmán, "we inject the gas that is being produced into the network in real time."
After years of operating on self-consumption, in 2021, Biogasnalia expanded the biogas plant to undertake the biomethane project with maximum guarantees. The biogas plant is approaching its maximum production, equivalent to 1 MWe, and currently generates around 18 GWh/year, although the objective is to reach a production of 20 GWh per year.
In order to be injected into the network, the gas must meet the requirements defined by regulations for various parameters, such as the minimum methane content, maximum CO and CO2 content (2% each), hydrogen (5%) or oxygen ( 1%). The injection demonstrates that all parameters are met.
How the UNUE biomethane plant works
The biogas produced by Biogasnalia is treated at the entrance to the biomethane plant to adjust its relative humidity. Its sulfur content is always less than 200 ppm
The biogas enters through the lower part of the first column of the plant, where it rises in countercurrent to a flow of water at controlled pressure and temperature, which absorbs CO2. Finally, a gas with the quality required by gas pipeline injection emerges from the upper part of the column, while the water is led to a second column for regeneration.
In this second column, the water is depressurized and brought into contact with a current of air so that all the CO2 leaves the water. The water returns to the first column to repeat the biogas treatment cycle and the CO2 is released into the atmosphere dissolved in air. It is a cycle that lasts between 2 and 5 minutes. This CO2 has a short cycle and has a neutral balance in emissions and is completely unarmed. It would, in fact, be valorized in some nearby activity that required it, such as a greenhouse, for example. “In this case, liquefying it for transportation is not profitable,” says Francisco Guzmán.
During the gas separation process, no more than 2% of the input methane can be lost. To recover the methane dragged by the water current, flash distillation is carried out in the third column. The recovered methane and CO2 are recirculated back to the first column. In this way, the certified methane losses are 1,7%.
The biomethane is dried to a dew point of 20 degrees below zero and sent to the regulation and measurement station. Here, the chromatograph takes the fiscal reading and if all the values are within range, the injection into the gas pipeline is carried out.
Inject into virtual gas pipeline
The biomethane plant designed by AGF is arranged in containers to facilitate its assembly and shipping.
In this project, the actual gas pipeline is located next to the biomethane plant and the gas injection is done directly. When this is not possible, the solution called “virtual gas pipeline logistics” is used. In this case, the biomethane must be transported compressed at 250 bar in trucks to the actual gas pipeline, where flow and temperature must be controlled to proceed with the injection.
For these types of projects, AGF has designed biomethane plants that incorporate the high-pressure compression stage, integrated within the plant with the rest of the equipment. It has also designed a module to perform the discharge operation on the actual gas pipeline.
According to Francisco Guzmán, the option of virtual gas pipelines will be common in Spain due, among other factors, to the high cost of building a real gas pipeline and the processing difficulties.
First plant of its kind
UNUE is the first plant in Spain to inject biomethane from agri-food waste into the Nedgia Castilla y Léon gas network. The renewable gas produced contains energy equivalent to the annual consumption of more than 2.700 homes in Burgos.
Currently, there are other private projects in an advanced stage of development, such as the La Galera biomethane plant, in Tarragona, which will inject biomethane into the natural gas transportation network, and which is also developed by AGF.
In November 2021, an event to present the project was held, chaired by the mayor of Burgos, Daniel de la Rosa. They also came
Mariano Muñoz Fernández, Head of the Territorial Service of Industry, Commerce and Economy of Burgos; Marcelino Oreja, CEO of Enagás; Ruperto Unzué, Partner at Suma Capital; Narcís de Carreras, CEO of Nedgia; José Luis Alonso, Manager of Biogasnalia and Fernando Selva, Founding Partner and Solidarity CEO of AGF Procesos.
Source: AVEBIOM
