Reactor biomass flash pyrolysis

Thermochemical Liquefaction. Most of the research done since 1970 on the direct thermochemical Hquefaction of biomass has been concentrated on the use of various pyrolytic techniques for the production of Hquid fuels and fuel components (96,112,125,166,167). Some of the techniques investigated are entrained-flow pyrolysis, vacuum pyrolysis, rapid and flash pyrolysis, ultrafast pyrolysis in vortex reactors, fluid-bed pyrolysis, low temperature pyrolysis at long reaction times, and updraft fixed-bed pyrolysis. Other research has been done to develop low cost, upgrading methods to convert the complex mixtures formed on pyrolysis of biomass to high quaHty transportation fuels, and to study Hquefaction at high pressures via solvolysis, steam—water treatment, catalytic hydrotreatment, and noncatalytic and catalytic treatment in aqueous systems. 

The Biolig process of the research center Karlsruhe FZK, Germany. Here, flash pyrolysis, with emphasis on straw as feedstock, is tested to produce a bio-oil-char slurry. The pyrolysis reactor compares to the ER reactor (Lurgi-Ruhrgas) by which sand as heat carrier is mixed and transported together with biomass in a double (twin) screw feeder. A novel unit is constructed with a biomass processing capacity of 12 t/day. 

Schematic overview of flash pyrolysis reactor technologies. (Reproduced from Meier, D., and Faix, O., Wood and Biomass Utilization for the Carbon Uptake, Seoul National University, 2005. With permission.)...

The splitting of the cyclonic combustor into reactors is shown in Figure I. The corresponding reactor network accepted in the combustion modeling is shovm in Fig. 2. The reactor network structure is largely based on the current understanding of the processes in the combustor issuing from the limited experimental observations and from the CFD calculations [4], The key assumption is a separation of the biomass pyrolysis and subsequent char and gas oxidation, Thus, the initial part of the network represents flash pyrolysis of the biomass. 

Fig. I Flash pyrolysis pilot plant for biomass (PDU-scale) (1 hopper, 2 vibration conveyor, 3 screw feeder, 4 fluidised bed reactor, 5 cyclone, 6 heat exchanger, 7 intensive cooler, 8 electrostatic precipitator, 9 flare, 10 compressor, 11 gas preheater 1, 12 gas preheater 2,13 overflow container).

Several studies have been published describing results from the flash pyrolysis of biomass. Most of these studies were carried out at higher temperatures and were intended to promote biomass gas production. However, the work of Roy and Chornet [4] reported high liquid yields from biomass pyrolysis under vacuum conditions. More recently, Roy et al. [5] have described a vacuum pyrolysis system for the production of liquids from biomass, based on a multiple hearth type of reactor. Knight et al. [6] have developed an upward flow entrained pyrolyzer for the production of liquids from the thermal pyrolysis of biomass. 

Most promising is flash pyrolysis in which fuel particles are heated very rapidly (more than 1,000 °Cs ) and remain in the hot zone for a very short time (in general less than 1 s). After this very short time period, the liquid compounds produced from the solid biomass by decomposing the organic compounds (z.e. lignin, celluloses) have to be removed and cooled rapidly to avoid further decomposition into gases. To date, flash pyrolysis reactors have reaehed laboratory stage development level and the first pilot plants are available. 

Air-dried wood or other biomass heated in the absence of oxygen can be converted into oil, gas, and other valuable fuels. The biomass feedstock, before it is fed to the pyrolysis reactor, must be ground or shredded into smaller than 14-mesh size units. Flash pyrolysis takes place at 500°C and under high pressure (101 kPa). After processing the solid char is separated from the fluids produced in a cyclone separator. The char is then used as a heating source for the reactor. 

Alternatively, flash pyrolysis processes were developed for biomass liquefaction as well [5]. On a water- and ash-free basis, from wood typically 75% liquids (including 25% of water), 10% of solid char, and 15% of gases, mainly CO2 and CO, are formed at 5 00 ° C with gas retention times of only a few seconds. Several reactor concepts such as stationary and fluidized fluidized beds, the mechanically agitated rotating cone and Auger reactors, a well as ablative and vacuum pyrolysis have been carried out and operated on a semi-technical and pilot scale. For fast pyrolytic treatment of... 

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