Biogas as renewable source of energy is becoming increasingly important since biogas has some ecological advantages mainly being CO2 neutral and hence reducing the formation of greenhouse gases.
The main components of biogas are methane (CH4) and carbon dioxide (CO2), but it also contains significant quantities of undesirable compounds such as hydrogen sulphide (H2S), ammonia (NH3) and siloxanes. These trace components can be very harmful if they become adsorbed by the oil as they may destroy the engine, e.g., due to corrosion.
Biogas engines for power generation are usually deployed in so called CHP (combined heat and power generation) units where the heat generated is used to optimise the fermentation process of wastes or biodegradable materials. Typically temperatures between 35-60 C are required. The biogas generated during the fermentation process is then used to produce electricity.
Gases derived from biological processes such as fermentation will contain contamination such as water, ydrogen supphide and siloxanes. All these contaminants can have detremental effects on the lifetime and the efficiency of the engines as tey degrade the oil in the biogas engine.
Water is present in biogas in form of water vapour due to the nature of the feedstock. The amount of water within the biogas depends on the temperature and where the biogas originates from. If the water content within the biogas becomes too high the combustion of the biogas can be very challenging and, in combination with hydrogen sulfide can condense into sulphuric acid.
Hydrogen sulphide (H2S) originates from the feedstock which is usually high in sulphur such as amino acids and proteins. H2S reacts with water to form sulphuric acid which is a very corrosive component and can cause damage to the gas engine itself.
Typical life-times of lubricants for biogas engines are 1500h and it is important to manage the lifetime of the lubricant effectively as the downtime of the engine during oil change has significant costs associated with it.