Updraft gasifier

A survey of commercial thermal gasification in the United States shows that few gasifiers have been installed since 1984 (115). Most units in use are retrofitted to small boilers, dryers, and kilns. The majority of existing units operate at 0.14 to 1.0 t/h of wood wastes on updraft moving grates. The results of this survey are summarized in Table 36. Assuming all 35 of these units are operated continuously, extremely unlikely, the maximum amount of LHV gas that can be produced is about 0.003 to 0.006 EJ/yr (222—445 td /d). 

With fixed-bed updraft gasifiers, the air or oxygen passes upward through a hot reactive zone near the bottom of the gasifier in a direction countercurrent to the flow of solid material. Exothermic reactions between air/oxygen and the... 

Fixed bed gasifiers are generally used for small-scale operation with gas engines, having an electrical output of about 80-500 kWe. They divide into updraft and downdraft gasifiers. 

The underfired combustion mode corresponded to the operation of an updraft gasifier. The tests carried out on wet wood chips and peat lumps (35-60%) showed that the combustion rates are many times higher than the same conditions for the overfired mode. Koistinen et al were able to gasify wood chips with a moisture content of 58% d.b. However, the off-gas was so humid that it was not ignitable until the end of each run when the drying had ceased. Koistinen et al concluded that the combustion rate increased linearly with an increased primary air flow rate. 

Pyrolysis of biomass is known to produce a complex mixture of phenolic compounds, which are derived primarily from the lignin fraction of the biomass (1-4) Elder and Soltes (5, 6) have investigated a phenolic fraction obtained from pyrolysis oils made in an updraft gasifier by TECH AIR as a source of phenolic adhesives a phenolics fraction was separated by solubility differences of oil fractions based on solubility of acids in aqueous bicarbonate solutions and... 

Figure 2.10. Gasifier types (a) updraft (b) downdraft and (c) fluidised bed (from B. Sorensen, Renewable Energy, 2004, used with permission from Elsevier.)...

Partial Oxidation of MSW with Oxygen in a Slagging, Updraft Gasifier... 

Atmospheric Updraft Gasifiers (AUG) have practically no market attractiveness for power applications due to the high concentration of tar in the fuel gas and the subsequent problems in gas cleaning. Also the technology is considered weak for the same reasons. There is no company proposing AUG for power at present. 

No company is presently developing pressurised systems for downdraft, updraft, cyclonic or entrained bed gasifiers for biomass feedstocks and it is difficult to imagine that such a technology could ever be developed into a commercial product due to the inherent problems of scale, tar removal and cost. 

The temperature in the sampling line of the product gas of the updraft gasifier is kept at 00 250 C (to be examined) and in downdraft and fluid ised-bed gasification at 250 C. 

The comparison mentioned under 2. will result in knowledge on which method can reliably be used under which conditions. As other methods might be simpler (in terms of man-hours and equipment needed to perform the measurement) compared to the Guideline or produce online results on-site, we have named them shortcut methods . Examples of these methods are a) the solid phase adsorption (SPA) method developed by KTH (7], b) a number of solvent-free tar collection systems used by BTG, BEF, IGT [8-10] and c) the FID online tar analysing method under development at the University of Stuttgart (11,12]. Currently it is unknown under which conditions these methods give reliable results, for example it is unknown whether the SPA method can be used for updraft gasifier tars and at which conditions the solvent-free methods fail to collect ail tars, for instance as a result of aerosol formation. 

Solvent or no solvent. For tar sampling from updraft gasifier producer gases, a solvent is needed because direct condensation of the tars without diluting media can result in further reactions (polymerisation). The reactivity is suppressed by using a diluent like an absorbing liquid or an adsorbent resin. 

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