Modélisation de la qualité du biogaz produit par un fermenteur méthanogène et stratégie de régulation en vue de sa valorisation

摘要

Anaerobic digestion involves a complex ecosystem that progressively degrades the organic matter into carbon dioxide and (bio)methane. The biomethane is an highly energetic environmental friendly biofuel which can replace natural gas in the perspective of sustainable development. However biogas is still valorised below its potential. This is mainly due to a lack of dedicated methods that would ensure the anaerobic plant durability and the stability of the biogas composition. Two approaches are considered to improve liquid waste valorisation. On the one hand we develop methods to monitor anaerobic plants instabilities and prevent dysfunctions, and on the other hand we propose to control the biogas quality.These methods require accurate models to predict the process evolution. We propose a fine modeling of the liquid-gas exchange, and we show that the seeming transfer coefficient kLa depends on the biogas flow-rate. This leads to a linear relation between the dissolved CO2 and the biogas quality, which is used to improve an existing model for anaerobic digestion. A risk index based on a stability analysis of a simple model is introduced. This approach is applied on a real anaerobic plant and we show that the criterion allows to detect a potential destabilisation, earlier than the usual monitored parameters (pH, VFA). Eventually we present a control strategy of the biogas quality based on the regulation of the digester alkalinity. Several control laws are experimentally validated on a pilot plant.