- 6 - 



Changes That Lime Undergoes in the Scrubber 



There are 3 types of lime in commercial use: carbonates, hydroxides 

 and burnt or caustic lime. The carbonate forms are of no value for scrub- 

 bing, since they are naturally saturated with CO2. Because of its caustic 

 properties, burnt lime presents a potential danger to the user and may 

 prove hazardous when subjected to scrubbing conditions. Hydrated lime, 

 the hydroxide form, is the only lime that should be used for scrubbing. 



Although the expression of guarantee on the bag is in terms of CaO 

 and MgO, the Ca and Mg are actually in the hydrate form, Ca(0H)2 and 

 MgC0H)2. 



The reaction that takes place in the scrubber is as follows: 



Ca(0H)2 + CO2--- CaC03 + H2O 

 Mg(0H)2 + CO2--- MgC03 + H2O 



With the dolomitic limes, less CO2 absorption takes place than 

 with the high-calcium hydrated limes. This is due to the lower reactiv- 

 ity of the Mg(0H)2 in dolomites. Consequently, greater amounts of dolo- 

 mitic lime are needed, depending on the Mg(0H)2 content, than if high- 

 calcium hydrated limes are used. 



Preliminary Tests 



At the University storage, we tested one bag each of 3 different 

 types of lime in a small dry-lime scrubber. We realize that these results 

 cannot be regarded as representing the 3 limes, because of the small size 

 of the sample, but the data in Tables 1 and 2 are of interest from the 

 standpoint of rate and final apparent equilibrium level of CO2 absorbed. 



The high-calcium lime (lime A) absorbed CO2 to a greater degree 

 than did limes B and C (Table 1) . The CO2 absorption of limes B and C 

 did not differ appreciably. 



Table 1: Comparative carbon dioxide absorption of three types of lime, 

 19611-55 



Sampling % COp content in lime: 



date 



10/19 

 11/23 

 12/21 



1/18 



2/19 



3/19 



% CO2 uptake 



37.5 21.4 23.0 



*A High-calcium hydrate lime - (CaO, 72-74%; MgO, 0.2-0. 

 **B Hydrated dolomitic lime - (CaO, 43-45%; MgO, 26-28%) 

 ***C Dolomitic spray lime - (CaO, 45%; min. MgO, 3r " 



