Updraft gasifiers

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... 

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... 

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. 

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. 

Tars can also be removed as particulates (aerosols) which has only been shown for pyrolysis or updraft gasifier tars/oils using ESP s. Experience with the use of ESP for removal of tar aerosols from downdraft or CFB gasifiers is non-existing or is not reported. 

Figure 1 illustrates this equation for C = 26.5%, a value consistent with values reported for pure cellulose and municipal solid waste, and with data obtained in discussions with commercial firms. The importance of a slow heating rate to maximize the char yield is quite apparent in the figure. It follows that fluid beds and downdraft or updraft gasifiers, though excellent for maximizing gas yield, are not desirable for char production. 

Wellman Incandescent (England) Manufactures updraft gasifiers. 

In the updraft gasifier x essentially equals 1 for gasification by steam and carbon dioxide, but attains only 0.1 -0.6 for the methanation reaction, the exact figure depending on the reactivity of the coke [ U8J. 

Figure 7.8 Principle of an updraft gasifier (left) and a downdraft gasifier (right). ...

In updraft gasifiers, fuel moves downward and gas upward. 

When biomass is gasified, relatively large quantities of tar are produced, e.g., from 10 % of the fuel in an updraft gasifier to 2 to 4 % in a fluidized bed. The amount and composition of the tars are dependent on the fuel, the pyrolysis conditions and the secondary gas phase... 

While this characteristic is problematic for many applications, it is important to note that the uncracked compounds lead to an increase in heating value and carbon conversion in the product gas. In addition, the gradual heating that takes place as the biomass moves down the reactor also creates distinct reaction zones in the system. From the top to the bottom, the zones are the drying zone, the pyrolysis zone, the reduction zone, and the combustion zone. Ash removal takes place at the bottom. Figure 12 shows a schematic of a updraft gasifier. 

Gas composition and tar content in the product gas from different biomass gasification r under different conditions are reported in Tables 1.3 and 1.4. The produced gas must have a certain percentage of burnable gas (>20 % CO and >10 % H2), a minimum amount of tar content (<100 mg Nm ) and be completely free of dust and other poisonous gases (NH3, SO2, etc.). To satisfy the requirement of product gas, a comprehensive research has been done in the last decades. The entire reactor systems can be classified into two categories (1) updraft gasifier and (2) downdraft gasifier. 

Table 1.3 Gas composition and tar content in the product gas from different biomass gasification in updraft gasifier under different conditions [174]... 

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