Pressurized Fluidized Bed Test Rig

The installation consists of an autothermal fluidized-bed gasifier with a continuous lignite + waste feeding system, a cyclone, fluidizing medium preheaters, steam generator, pressure regulation valve, flare for process gas utilization and various measurement devices like:

  • mass flow controllers
  • thermocouples
  • pressure meters
  • process gas analyzers

The internal part of the reactor, which you can see in figure 1, is made of a heat-resistant steel tube with a diameter of 105 mm ID and a height of 1500 mm, coated by glass wool insulation and closed in stainless steel water jacket for excess heat removal. The bottom part of reactor is conical shape of length 300 mm tapers to a diameter of 70 mm ID that is placed in an electrically heated furnace, which allows to preheat the inventory material up to 800 °C. Fluidization medium is distributed within the reactor by means of a perforated plate. The longitudinal profile of temperatures inside reactor and freeboard is measured using five K-type thermocouples mounted vertically inside the reactor. The measurements are carried out at five levels 1470, 1375, 1275, 895 and 430 mm (from the top of the gasifier).

Figure 1: Schematic description of the experimental stand: fluidized-bed gasifier, biomass feeding unit, cyclone, pressure regulation valve, process gas, dust, water and tar sampling points, flare.

The fluidizing gas preparation unit consists primarily of an air compressor and a set of mounting points with pressure regulators for attachment of gas cylinders (oxygen, nitrogen and carbon dioxide). The flow rate of each is measured independently by means of dedicated Bronkhorst EL–FLOW SELECT mass flow controller. Additionally, the unit is equipped with Siemens Oxymat 61 analyzer for control of oxygen content in fluidizing mixture. The gas mixture flow lines are electrically heated up to ca. 320 °C. The steam flow rate is regulated by FWT di Tommaso Commonara water dosing pump (max. flow – 4 dm3 per hour, max. pressure 20 bar) positioned upstream of the steam generator and preheater.

The fuel feeding unit consists of three storage containers, two of them are equipped with knife gate valves enabling fuel loading while the experiments are conducted in over pressure. Nitrogen is introduced to upper tank when biomass is loaded. The fuel flow is regulated by changing the rotational speed of the upper screw feeders. From the fuel dosing tanks, the fuel is fed into a drop tube, where small stream of nitrogen is used to purge the system and to avoid possible ignition. The drop tube ends with the reactor feeder which conveys the raw material to the hot inventory bed where the gasification process occurs. The reactor feeder is additionally equipped with water jacket. All process parameters and variables are continuously collected by SCADA system.

The gas–solid mixture leaves the reactor through the reactor cover and enters the cyclone, where solid particles (char and ash) are separated. The char is stored in the char vessel that allows for its continuous removal during pressure tests and weighing. Syngas after cyclone is still contaminated with fine particles, tars and water which were analyzed according to a procedure described below. Its composition is continuously analyzed with use of a set of IR analyzers. Finally, the gas is combusted in a flare.