Alkalized alumina process

Processes 7 to 9 in Table III have the common feature of producing sulphur as the end product. They are therefore overall reduction processes. The Cat-Redox and CO/SO2 systems are both direct conversions to elemental sulphur. The latter has a particular advantage of being able to accept effluent gas streams at temperatures of 750 F or higher thus avoiding the need for any cooling of combustion flue gases before clean-up. The Alkalized Alumina Process, however, involves concentration and catalytic... 

Alkalized Alumina Processes Bureau of Mines Proems... 

The Alkalized Alumina process was developed by the U.S. Bureau of Mines and carried through the pilot-scale testing phase (Bienstock et al., 1964 1967). It has not been applied commercially. The process uses dawsonite [NaAl(C03)(OH)2]/sodium aluminate [NaA102] as the sorbent. Ihe material is activated at 1,200°F to form a high surface area, high porosity, dry solid, which removes sulfur dioxide from flue gas at temperatures between 300° and 650°F. This process is no longer being pursued due primarily to an excessive sorbent attrition rate. 

Perhaps the most promising regenerative dry process for the removal of sulfur dioxide from stack gases is the alkalized alumina process, which has undergone extensive development by the U.S. Bureau of Mines and others. Here the absorption step takes place at 300-350°C, which is a relatively low temperature compared with the lime absorption processes discussed previously. The absorption unit, perhaps a fluidized bed, would be located between the steam generation section of the boiler and the stack. The alumina provides a support rather akin to a catalyst support for the absorbent proper, which is Na20, at a level of about 20%. The absorption reaction is... 

The major difficulty with the alkalized alumina process appears to be the attrition of the solid as it is recycled from the absorber to the regenerator. A recent report from the Bureau of Mines [83] describes the evaluation of some solid oxides, including alkalized aluminas, for this process. All of the oxides were found to show adequate capacity and reactivity but were subject to excessive attrition, as evaluated by the investigators. 

Acid Gas Removal. The aluminas that are used for acid gas removal obviously contain relatively high soda contents. Sodium is always contained in aluminas because Na(OH) is used in the Bayer process for extraction of alumina from bauxite. The typical content of Na20 in activated aluminas is 0.3% (wt). The soda content can vary considerably. The soda content in the alkalized alumina is typically >1%. The BET (Brunauer-Emmett-Teller) surface areas of activated aluminas are generally in the range 200-500 m /g, with total pore volumes near 0.5 cc/g. 

In the discussions that follow, dry sorption processes are categorized on the basis of the sorbent utilized i.e, dry lime/limestone, sodium salt injection, alkalized alumina, dry MgO-based, and copper oxide processes. 

Laboratory scale work on a copper oxide process for SO2 removal was conducted by the U.S. Bureau of Mines (McCrea et al., 1970). The effort was aimed at developiiig a dry, regen-erable sorbent for SO2 that would not have the problems of alkalized alumina, i.e., physical degradation, excessive reducing gas consumption, and a high temperature difference between... 

The CRG process operates adiabatically in a small single bed reactor. The catalyst has high nickel oxide content and is precipitated under carefully controlled conditions with alumina to give a high activity and thermally stable strac-ture. The finished catalyst is alkalized to prevent carbon formation and is reduced before operation. Steam to carbon ratio can be as low as 1.5 when reforming naphtha to produce town gas. 

Substitute natural gas (SNG) may be obtained by methanation of CRG process gas with a stable nickel-alumina catalyst after removal of the carbon dioxide formed in the conventional process. Gas containing more than 98% methane can be produced. The CRG process is operated at low steam ratio to maximize methane production. Two stages of methanation follow the CRG reactor and inter-cooling is required to control the temperature. Standard alkalized, high nickel... 

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