Modeling of a Biomass Gasification CHP Plant: Influence of Various Parameters on Energetic and Exergetic Efficiencies

Abstract

International audienceThis paper presents a theoretical assessment of energy, exergy, and syngas cleaning performances in a biomass gasification combined heat and power (CHP) plant with varying operating parameters. The analysis is carried out using a detailed model of a biomass gasification CHP plant developed with Aspen Plus. The model describes: wood drying and gasification in a dual fluidized bed (DFB) reactor, syngas cleaning, as well as combustion in a gas engine for electricity production. Heat is recovered from the CHP system for internal needs and for district and domestic water heating. An accurate prediction of tar and inorganic contaminants is developed for proper modeling of syngas cleaning efficiency. The influence of wood moisture content, drying conditions, flow rate of the sand circulating in the DFB reactor, catalyst and scrubbing agent efficiencies, as well as additional electricity production through steam turbine on the overall process performances is studied. On the basis of the comparative analysis of nine case studies, it is found that the highest energetic efficiencies are obtained when forced drying is not implemented in the CHP system. Lowering the inlet wood moisture content with natural drying (energy-free) prior to the CHP plant improves the electrical efficiency. An overall energeticefficiency of 74% (23% electric, 51% thermal; based on the lower heating value of wood on anhydrous basis) is then reached with wood fed at 30% moisture content. The best exergetic efficiency is reached when wood (naturally dried to 30%) is dried further to 15% by forced drying in the CHP plant and when some of the high-temperature heat is recovered for electricity production via steam turbine instead of district heating. In this case, the overall energetic efficiency is 63% (32% electric, 31% thermal). This model is a useful tool to assess process design improvements and life cycle inventory

Techno-economic modeling of an integrated biomethane-biomethanol production process via biomass gasification, electrolysis, biomethanation, and catalytic methanol synthesis

“…In the simulation of complex integrated flowsheets, biomass steam gasification has frequently been modeled by separating the pyrolysis-gasification process and the char combustion process. Under this approach, a mass and heat balance is calculated around the pyrolysis-gasification zone, the unconverted char is transferred to the combustion zone, and char combustion heat is set equivalent to the enthalpy requirements of the pyrolysis-gasification process, allowing for a fraction of heat loss [33,34]. Some authors have simulated the pyrolysisgasification process (gasification bed) as a single-step gas formation process, either by using experimental data to reconcile a thermodynamic model [35,36] or by directly implementing empirical correlations [37].…”

Assessing the Fate of Nutrients and Carbon in the Bioenergy Chain through the Modeling of Biomass Growth and Conversion

“…HCl and NH 3 in syngas were assumed to be entirely removed in the cleaning process, along with more than 99% of the tarry contaminants. , NH 3 and HCl absorbed in the water scrubber were burnt in the char combustor within stripped air used to clean scrubbing water. Tars removed from the scrubber were also returned to the char combustor within tar sludge (see S.3).…”

Development of the Process Model and Optimal Drying Conditions of Biomass Power Plants

“…Primary researches on this subject are most of the experimental studies focusing on the drying kinetic mechanism of biomass and the characteristic of dried products. − The mathematical modeling studies on biomass drying make it possible to predict drying behavior, diffusivity, the temperature profile of biomass, and VOCs occurred drying. − Several previous studies have reported that the integration of biomass drying and power plants has improved the thermal efficiency of boilers. − …”