Product gasifier

Although the gasifier product itself has low levels of NOx, the total systems emissions of this product must be carefully scrutinized. When clean biogas is eventually burned, NOx will be produced, as it is in most combustion systems with all fuels. The use of biogas rather than solid biomass fuels provides the opportunity to better control the combustion process, which can potentially result in lower NOx emissions. As such, gasification offers potential environmental emissions advantages over combustion alternatives. However, NOx may still occur as the gas is burned, and appropriate NOx control technologies may be needed. 

Air-blown gasifiers benefit from a low-cost (free) source of oxidant, but produce a gasifier product gas that has a very low heating value (approximately 5MJ/m3 for air-blown gasification of coal, compared to 38MJ/m3 for a typical natural gas) and which is too dilute to use for liquid fuel synthesis. 

Table 6-3 shows the contaminants and their impact on MCFC operation. The table denotes the species of concern and what cleanup of the fuel gas is required to operate on coal gas. Confidence in operation with coal will require the use of an actual gasifier product. An FCE MCFC stack was installed (fall of 1993) using a slipstream of an actual coal gasifier to further clarify the issues of operation with trace gases (46). 

Midilli, A., Dogru, M., Akay, G., Howarth, C.R. 2002. Hydrogen production from sewage sludge via a fixed bed gasifier product gas. Int J Hydrogen Energy 27 1035-1041. 

If the gasifier product stream is intended for downstream use as the feedstock for further upgrading such as methanation, methanol or Fischer Tropsch synthesis, very thorough desulphuri-sation is essential since the catalysts in these upgrading processes are highly sensitive to sulphur poisoning. The methanation catalysts normally cannot tolerate more than 0.05 ppm of sulphur in the feedstock. In addition to H2S sulphur values in the gasifier product it may contain COS, CS2, mercaptans and thiophenes. These are normally removed by activated carbon or zinc oxide filters ahead of the sensitive synthesis catalyst beds. 

Dinitrosopentamethylenetetramine (II) is used as a gasifiable product for the production of porous plastics and rubber (e.g. Unical ND, Vulkacel BN). 

Several methods of gasification were patented outside of Russia, For example, in the process patented in USA (Ref 5) elec current, passed bet" electrodes introduced into underground coal seam, generates enough heat to carbonize part of coal and creates low resistance path. Continued heating causes direct gasification of nart of the fuel, and subsequent introduction of air permits recovery of addnl gasified products... 

Note Others consist of unidentified products, gasified products and wata doived from dehydration of saccdiarides. Not detected. 

The existence of mercaptans, thiophenes, and other organic sulfur compounds in (gasifier) product gas will probably be a function of the degree of severity of the process, contacting schemes, and heat-up rate. Those processes that tend to produce tars and oils may also tend to drive off high-molecular-weight organic sulfur compounds into the raw product gas. 

Battelle Memorial Institute (1986) Engineering analysis of biomass gasifier product gas cleaning technology, in Biofuels and Municipal Waste Technology Division, PNL-5534, Richland, Washington. 

The fire property associated with corrosion damage is defined as corrosion index (Cl), which is the corrosion rate per unit mass concentration of the products [(A/min)/(g of polymer gasified products/m of air flow)] [2,3] ... 

Approximate Percentage Number of Number of of Worldwide Coal Gas Plants Gasifiers Production ... 

The Koppers-Totzek (K-T) gasifier produces a medium-Btu gas (in the general range of 300 Btu/scf) and has been commercially employed in many different syngas applications, with particular emphasis in the area of ammonia synthesis. The process is carried out at just over atmospheric pressure but at very hi temperatures of over 1870°C. The data in Table 3 [16] give the expected K-T gasifier product composition for an Illinois coal (62% C, 19.1% ash, 4.4% H2, and 5% S plus 02 and H20) that has been ified with a steam-coal ratio (wt/wt) of 0.27 and an oxygen/coal ratio (wt/wt) of 0.7. K-T units vary in size between those that convert about 300 t coal per day and those that convert over 750 t coal per day. 

The gasifier product is scrubbed with water to cool the gas and remove any ash particles. A portion of the gas stream is sent to a water-gas shift reaction to increase the hydrogen content. Finally, low-pressure steam is generated as the product gas is cooled before additional purification. The full recovery of this heat increases the thermal efficiency of the process and is important for economical operation of the chemical processes that utilize the steam. 

---