Study of the fouling and slagging phenomena in the fixed combustion of biomass. Experimental and submodel development

Ministry of Economy, Industry and Competitiveness. ENE2015-67439-R

Start date: 01/01/2017; End Date: 31/12/2019

Although their huge potential, national biomasses find that, their use is generally limited due to the necessity of high quality fuels to avoid problems during their combustion. Todays biomass boilers have efficiencies and emissions comparable with conventional boilers employing fossil fuels, provided that the biomass has low moisture, low ash content (<1%) which is expensive and even scarce. A breakthrough development in recent years has been the commercialization of biomass condensation boilers, but again, the biomass they use needs to be of high quality. On the other hand, the abundant biomass is generated by forest maintenance, agriculture and industrial industries, corn, etc. and typically have a higher level of moisture, ash content and a wider granulometry. Therefore, common designs of fixed beds suffer from strong issues such as: slagging, fouling, channeling, etc. The capacity of CFD codes to assist in the study, design, analysis and optimization is unquestionable. However, severe limitations are found in those commercial software regarding beds of particles. The precise determination of the temperature, velocity and species fields in the bed can only be determined by the formulation of bespoke models.

In the recent years, several models and simulations of biomass combustion systems have been published in which the coupling of gas and solid is external to the code. This methodology has proved to be feasible and it has been initially used by the research group. Thanks to the funds obtained by the national project ENE2012-365454 between 2012 and 2015 we have managed to fully embed our modelling methodology into the CFD, which now is accessible via a GUI and totally configurable without the need of modifying the underlying code. Thanks to this development, this code takes into account most of the physical and chemical processes taking place in the bed, particle movements, feeding, vibration, etc. and now is available for other researchers that might be interested in testing submodels without having to formulate all the other physics of the bed.

With the present request, we want to continue with the line of work to include several new phenomena such as slagging, local collapses due to undersurface combustion, channelling, elutriation, etc. as we consider that we have reached a privileged position to tackle these issues.

In the development of the submodels required to extend the capabilities of our model, and to validate the new methodology, several experimental tests will be required. These tests will be made in our experimental burners and in the different boilers that we also have in our facilities. These tests must provide the information required to assess the capability of the whole methodology and of each submodel.To do so, some modifications of the plants have been considered in this request.