Heat transfer modelling of semi-suspension biomass fired industrial watertube boiler at full- and part-load using CFD. (1st October 2021)

• Record Type: Journal Article
• Authors: Laubscher, Ryno; van der Merwe, Schalk
• Is Part Of: Thermal science and engineering progress. Volume 25(2021)
• Publication Date: 2021-10-01
• Subjects: Computational fluid dynamics -- Biomass boiler -- Heat transfer -- Semi-suspension combustion; Heat engineering -- Periodicals; Heat engineering; Thermodynamics; Periodicals; 621.402
• DOI: 10.1016/j.tsep.2021.100969
• Languages: English
• ISSNs: 2451-9049

Abstract

Highlights: CFD simulation of semi-suspension fired biomass industrial watertube boiler. Development of grate-particle interaction and evaporator bank sub-models. CFD model results in good agreement with plant measurements. Significant variation in furnace heat flux distribution observed for different load cases. Abstract: In the current work, a computational fluid dynamics model is presented of a semi-suspension fired bagasse boiler which pays special attention to resolving the heat transfer to the furnace walls, superheater tubes and evaporator tube bank. The boiler CFD model includes custom-developed sub-models programmed in the C language which captures the fuel particle grate interaction, cylindrical fuel particle drag effects, superheater steam side heat transfer and evaporator heat exchange using a porous media approach. The model is applied to simulate the case study boiler for 100% and 65% load cases. The CFD model results are verified using a steady-state process model which utilizes well-known empirical heat transfer correlations. The CFD model results are also validated using plant measurements. The results of the CFD model show that it can accurately predict the outlet steam temperatures of the superheaters with relative errors of between 0.89 and 1.6% compared to the site data. The model is also capable of accurately predicting the evaporator outlet gas temperatures with a relative error of approximately 1.4%. Once the model is verified and validated it is used to investigate heat flux and metal temperature distributions in the various heat exchangers. The results show that at part load conditions the combustion occurs much closer to the furnace rear wall due to deeper spreading of the fuel particles, which results in the front wall having a relatively low heat absorption rate compared to the side and rear walls.