My experience of Transnational Access with BRISK2 at CENER was very important for my career. CENER’s facilities include a biomass laboratory, facilitating biomass and biofuels characterization and process development at lab scale, as well as a second generation biofuel centre in Aoiz, which is a semi-industrial pilot scale test facility. These times were very helpful for me since I do not have the same facility in my University. I could perform all experiments I had planned and also do all analytical analyses necessary.
The gasification unit is a pilot plant with a nominal power of 2 MWt capable of generating a fuel gas suitable for the following cleaning and synthesis processes of 2nd generation biofuels. This unit is based on the technology of atmospheric bubbling fluidized bed (ABFB) working at 0.3 bar pressure and using air as gasifying agent.
The duration I spent there was divided into two weeks. The first week is to prepare the biomass feeding feedstock (Pretreatment unit), which are pellets and milled straw for gasification tests. In this unit a feed a wide range of biomass from low to high density are prepared. To achieve this goal, there are three independent lines, two for treated biomass and the other one for chips. Considering the first case, there is the possibility of simultaneously feeding biomass at both points; the second case is prepared to feed in two different levels (top and bottom of the bed), but not simultaneously.
The following are the sequence of the pretreatment process:
- chipping and choping
The characteristics of the pelletization pilot plant are: Production capacity: 200-700 kg/h
- Hammer mill: screen size 3-12 mm.
- 1 m³ mixer: moisture content adjustment and additive feeding
- 30 kW mill press:
- Ad Hoc die designs: pellets diameter, compression ratio, number of holes, etc.
- New roller design.
In the second week we start the gasification process for two different biomass, pellets and milled straw where this is the first time the mill straw will be used as a feed stock in CENER. CENER staff divided themselves to three shifts to operate the gasifier for five days continually. The full details of the Gasification Island are as follow:
- Biomass feeding system
- Bed materuak abd additives feeding system
- ABFB Gasifier
- Cyclone and discharge system
- Start-up combustion chamber
- Syngas combustion system
- Flue gas cooling and cleaning syster
- Steam generation
- Oxygen supply
- Carbon dioxide supply
- Compressed air supply
- Cooling water supply
- Natural gas supply
- Distributed control system for remote and automatic operation (SCADA)
This unit is based on the technology of atmospheric bubbling fluidized bed (ABFB) working at 0.3bar pressure and using air as gasifying agent.
Main characteristics of the gasifier are:
Reactor type: bubbling fluidized bed
- Nominal power: 2 MWt.
- Inertization and purge gas: CO2
- Operating pressure: 0,3 barg
- Bed temperature: 650-950ºC
- Freeboard temperature: 700-1000ºC
- Operating modes
- Operating Modes
- Bulk density 80-800 kg/m3
- Bulk density 80-800 kg/m3
- Moisture <50%
- Size < 30 mm
- Volatiles 68-87% daf
- Ash < 13% dry basis
- LHV: 16,1-20,6Mj/
The focus of our research was on gasification which converts solid biomass into a valuable fuel energy carrier or fuel known as syngas that can be directly used for heat, power and chemicals, and can be readily upgraded into higher value 2nd generation biofuels and chemicals. The purpose of my visit was to carry out gasification experiments for different feedstock (pellets and milled straw). This opportunity provided by BRISK2 will be very useful for future research and also to publish a paper with the results obtained. Besides that, I had also an opportunity to be in touch with other researchers and discussing the performance of the experiments and the results obtained with my supervisor Dr. David Sanchez Gonzalez and Idoya Goni Zubillaga. This allowed for the possibility to learn how to work under similar conditions of industry application.
Two experiments were carried out in CENER, for two different feedstock. One for pellets, the second for milled straw. Firstly, there is the start-up system is an internal refractory lined combustion chamber that uses natural gas as fuel. The hot flue gases generated during the combustion process will be sent to the gasifier in order to achieve the required thermal load to startup the unit. Secondly, This equipment has to supply the quantity of required air to fluidize the bed during the conventional gasification process and to supply the required pressure to vent flue gases out of the gasifier. The unit incorporates two internal refractory lined high efficiency cyclones. The gasifier is fully instrumented with an array of thermocouples, differential pressure transmitters with sample connections in the bed area.
Finally, the overall outcomes from these experiments provide a new database that can be used to help develop or validate numerical models of the char bed gasification zone for fluidized bed gasifier. Moreover, wood waste is a solid fuel which, during the gasification process, can be converted into a gaseous fuel. The type of biomass determines the conduct of the process and affects the performance of the gasification products. The denisfied biomass (pellets) were characterized by the highest calorific value. The gas obtained using this technology – due to its calorific value – may be used to drive gas turbines. An increase in the methane and hydrogen content in the syngas is obtained using fluidized gasification technologies and dual-layer gasification technology, which are complicated from a construction point of view.