Effective biogas conditioning is essential in the transformation of organic waste into usable energy, helping industries meet sustainability goals while protecting equipment and the environment. In this article, we explore how by removing harmful compounds and controlling moisture levels, companies can maximize biogas efficiency, reduce emissions, and contribute to a circular economy.
By Héctor Martínez, SACOME
Why go for waste recovery?
In recent years, waste recovery has become a priority and necessary activity for companies that generate and manage industrial waste. Firstly, because it is in line with the objectives of the 2030 Agenda, contributing to the promotion of the circular economy and the reduction of greenhouse gases. And secondly, because this recovery allows for more sustainable and profitable waste management, as it avoids sending large quantities of rejects to landfills, reducing the economic cost of landfilling or incineration. In general, we can classify waste recovery into two categories, depending on the objective pursued:
1. Valorisation for obtaining new raw materials.
2. Recovery for the generation of energy.
At SACOME, as specialists in the design and manufacture of tubular heat exchangers and pressure vessels, we have been developing many collaborations over the last 10 years with engineering firms and companies that generate and/or manage different types of industrial waste. Thanks to these collaborations, we have extensive experience in the supply of equipment for the valorisation of organic waste generated in wastewater treatment plants (WWTP), through the production of a biofuel called biogas from this waste. In particular, SACOME designs and manufactures the tubular heat exchangers, separator vessels and filter tanks that are necessary for the conditioning of the biogas prior to its use.
What is anaerobic digestion?
A WWTP produces a large amount of organic waste. In order to reduce its volume and limit pollution, this waste or sludge is sent to a device known as an anaerobic digester. In this equipment, the biochemical degradation of the sludge takes place thanks to bacteriological action in a temperature-controlled environment and in the absence of oxygen. This digestion transforms the sludge into biogas, which is a gas with a high calorific value due to its methane-rich composition. Although the composition of a biogas depends on the nature of the organic waste from which it is generated, the following percentages are characteristic for a biogas obtained in a WWTP:
- Methane: CH4 = 59%.
- Carbon dioxide: CO2 = 34%.
- Oxygen: O2 = 1%.
- Nitrogen: N2 = 1%.
- Water vapour = 5%.
These percentages will be different, for example, in a biogas obtained from waste from a landfill or a swamp, or in a biogas generated from industrial waste of different nature (dairy waste, sanitary waste, etc.). But in all cases, it is always advisable to carry out a biogas conditioning process, as a prior step to its use as fuel in specially prepared engines, which in turn can drive an alternator and generate electricity, which can be fed into the power grid or used for self-consumption.
radial outlet and support legs.
What is the importance of the biogas conditioning process?
First of all, biogas has a signifi cant water vapour content, which depends on the degree of humidity (usually 100% under saturated conditions), and on the operating pressure and temperature. The presence of this water vapour is particularly harmful to the engines where this biogas is consumed, but it can also damage the rest of the instruments and equipment in the WWTP valorisation system: blowers, compressors, etc. Similarly, the presence of water vapour can damage other biogas consumers, such as a gas turbine or a steam boiler. Secondly, biogas also contains a number of polluting or corrosive compounds that need to be removed because they can be very harmful to the waste recovery plant:
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- Siloxanes. These come from silicones that are present in household products such as oils, detergents, shampoos, deodorants, toothpastes, cosmetics, etc. During the combustion of biogas, siloxanes can produce silicates, silica and other crystalline compounds whose incrustations cause abrasive wear on the internal parts of engines.
- Hydrogen sulphide. The presence of sulphur in organic matter and sulphates and/or sulphites in water can produce hydrogen sulphide during anaerobic digestion of biogas. This gas is corrosive to all machinery in the system, and can sometimes act as an inhibitor, or even interrupt biogas production.
- Ammonia. The nitrogen contained in biogas can be in the form of ammonia, which in turn can
also inhibit or disrupt biogas production and form nitrogen oxides (NOx) during combustion. - Other compounds that can cause corrosion problems:
° Halogenated hydrocarbons: chlorine and fluorine mainly.
° Volatile organic compounds: benzene, toluene, ethylbenzene and xylene, among others.
° Foams.
° Suspended particles.
° Etc.
Therefore, the conditioning of biogas as a process prior to its use makes it possible to avoid corrosion and abrasion problems in consumer equipment and machines, thus improving their operation and extending their useful life. Furthermore, with this biogas conditioning, it is possible to reduce exhaust gas emissions, in compliance with the strict regulations applicable in this respect.
How is biogas conditioning achieved?
Biogas conditioning therefore consists of the partial or total removal of undesirable components (water vapour and polluting or corrosive compounds), while ensuring appropriate humidity, temperature and pressure conditions. To do this, first of all, it is necessary to dehumidify the biogas by cooling it to a temperature that allows the elimination of as much water vapour as possible in the form of condensate. At SACOME we have different types of tubular heat exchanger and separator vessel, depending on the characteristics of the process and the nature of the biogas, in order to achieve an optimum degree of dehumidification. The polluting or corrosive compounds (mainly those mentioned above: siloxanes, hydrogen sulphide and ammonia) are then removed by adsorption on activated carbon or silica gel, using graphite filters and resins, and sometimes in combination with washing using certain reagents (methanol, sulphuric acid, hydrocarbon mixtures, etc.). At SACOME we design and manufacture these filter tanks to guarantee perfect cleaning and conditioning of the biogas.
About the author
Héctor Martínez is Industrial Engineer by the Polytechnic University of Cartagena (Spain), in whose department of Thermal and Fluids Engineering he developed research works in heat transfer and computational fluid mechanics (CFD) with a collaboration grant. Since 2012 he is responsible for R&D&I in the technical-commercial department of SACOME, where he works as an expert in the design of tubular heat exchangers. You can contact Héctor for further information by email at hectorm@sacome.com.
About this Technical Story
This Technical Story was first published in Heat Exchanger World Magazine in December 2024. To read more Technical Stories and many other articles, subscribe to our print magazine.
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