We are Ph.D students at the University of Western Macedonia in Kozani, Greece and our research field is the study of processes for thermochemical energy conversion. Upon recommendation from one of our colleagues, who had previously collaborated with members of CENER, we decided to get in touch with CENER and apply for a transnational access within BRISK2, since the possibility of conducting experiments at a MW-scale gasification unit could be materialized.
As a first step, the experimental project was planned in collaboration with the experienced members of CENER team, in order to maximize the scientific output and overall experience that could be obtained and consider all the possibilities in terms of equipment utilization. Considering our lab experience with olive kernel (OK) as feedstock in gasifiers and Direct Carbon Fuel Cells, the aim of the visit was to perform experiments and familiarize ourselves with a MW-scale gasification unit, in order to gain insights for a potential large-scale implementation of similar gasification units in Greece for the production of syngas and advanced biofuels. Beside , valuable operation data was obtained for father assessment at this demo scale. Currently, no such facility in which the required tests can be conducted exists in Greece. The necessary olive kernel quantity was acquired by CENER from local suppliers and was stored on-site. Subsequently, OK fuel was characterized in terms of ultimate analysis, heating value, density and granulometry (pore size distribution) analyses (Table 1).
During the first week of the visit (14/06-18/06), several preliminary tests were conducted in all systems (main and auxiliary) in order to ensure their proper operation before the gasification experiments. Two of the most crucial parameters that were validated before the start of the gasification unit was the calibration of the biomass tank (in order to ensure proper flow conditions of the olive kernel) and check of several parameters concerning the operation of the combustion chamber (e.g., pressure, temperature, natural gas supply). Notably, it was the first time that CENER used this type of biomass for gasification tests. During operation some problems occurred, mostly attributed to the high density (ca. 750 kg/m3) and calorific value of olive kernel. During these initial tests, the main challenge was overcoming a security plant shutdown after a minimum ΔP value inside the combustion chamber was reached. The proposed solution composed of two parts:
- Addition of a small flow (ca. 3 Nm3/h) of CO2 (as inert gas) with the biomass in the gasifier, for increasing the total gas flow entering the combustion chamber.
Change of the lower limit for ΔP to 2 mbar (the default value was 3 mbar)
During the second week (i.e., 21/06 – 25/06), the main gasification experiments were conducted, including the following;
- Start-up and heating of the ABFB gasifier and the combustion chamber with natural gas and heating of the pipeline system at ca. 250 oC via OK combustion
- Air gasification of raw OK at three different nominal equivalence ratios (ER) between 15-0.25.
- Shutdown and cooling of the unit. All systems were cooled naturally, in order to avoid material damage due to high temperature gradients.
The tests aimed at a screening of different ERs and the assessment of the effect on the corresponding temperature in the gasifier (700-900 oC) as well as syngas quality. The latter was monitored in-line via μ-GC. Tarry products composition was also measured during the tests, albeit their concentration was very low due to the use of a catalytically active bed material (i.e., bauxite). A summary of the most important syngas concentrations and LHV values are presented in Table 2. The various operational parameters and variables were also being monitored remotely and in real time via SCADA software. Various troubleshooting incidents were also addressed properly at the time of the experiments.
Regarding the outcome of the gasification tests and a discussion about technological and systemic integration as well as commercial implementation issues, we were able to identify that the rational design of the gasification unit and the optimum choice of feedstock fuel and bed material are two of the most crucial parameters for the operation of a biomass gasification plant. ABFB gasifiers are better candidates concerning scale effects and higher gas quality (i.e., low tar concentration). Finally, the obtained large-scale gasification experimental results and overall gained knowledge will prove valuable towards the feasibility assessment of a potential process implementation for the production of syngas and advanced biofuels. We strongly believe this is a great opportunity for transfer of knowledge for the design and evaluation of units of this scale in Greece and especially in the olive-rich island of Crete. The study will be submitted for publication in an open-access, peer-reviewed scientific journal.
Last but not least, we would like to express our gratitude to all CENER members and especially Ines del Campo Colmenar and Idoya Goni Zubillaga for all the support before, during and after the gasification tests. It was a great experience to work with them, given our very fruitful discussions and knowledge sharing throughout our visit. We firmly believe that an experience of this kind is essential for any researcher, as it enables networking expansion, combination of scientific knowledge via multi-partnered collaborations and serves as a great motivation for advancements and breakthroughs in various scientific fields.