Combustion promoters

GO Combustion. The combustion products leaving the coke-burning site consist of both CO2 and CO, typically at a CO2/CO mole ratio of 1.0. The CO formed can then be further oxidized. When a CO combustion promoter is present, the reaction of CO and O2 to form CO2 occurs readily in... 

Through the use of a combustion promoter, CO combustion occurs readily in the dense phase at temperatures well below 700°C, eg, one report was at 650°C in a commercial FCCU operation (34). 

Y. Guegan, "Use of Combustion Promoter," presented at Katalistiks IstFCCU Symposium, Bordeaux, France, Oct. 1980. 

With the advent of combustion promoter, the regeneration temperature could be reduced and still maintain full bum. Thus, intermediate temperature regeneration was developed. Intermediate regeneration is not necessarily stable unless combustion promoter is used to assist in the combustion of CO in the dense phase. Table 1-2 contains a 2 x 3 matrix summarizing various aspects of regeneration. 

Intermediate temperature (nominally 1,27.5 °F/690 C) Stable (with combustion promoter) tends to have high carbon on regenerated catalyst Stable with combustion promoter... 

Our SOx test work was done with samples which were fully promoted with Davison CP-3 Combustion Promoter (7.4 pounds per ton of cracking catalyst, 0.37%). The only exception is the data in Table II which shows the effect of not using combustion promoter. 

Davison CP-3 Combustion Promoter, by itself, has a very low SOx Index. At a 0.37% level in a catalyst blend, it contributes less than 0.3 of an SOx Index unit at regenerator temperatures of 1250 F to 1350 F. Its contribution to SOx reduction derives from its ability to catalyze the oxidation of S0 to SO (Equation 2 in Figure 1). ... 

Data on four SOx catalyst systems show that the presence of combustion promoter causes an increase in the SOx Index at a regenerator temperature of 1250 F (Table II). This implies that, without combustion promoter, the rate-controlling step in SOx reduction is the oxidation of SO to SO (Equation 2 in Figure 1). The use of combustion promoter increases the rate of oxidation of SO to SO, thereby causing an increase in the SOx Index. 

It should be noted that the effectiveness of a combustion promoter decreases with Increasing regenerator temperature. The reason is that the rate of oxidation of SO to SO increases with temperature, while the SOx adsorptive capacity of the SOx catalyst decreases. Therefore, at some temperature, the rate of oxidation of SO to SO is fast enough, without combustion promoter, to supply all the SO which the SOx catalyst can accommodate. That temperature would vary for different SOx catalyst systems. For DA-250 + Additive R it is about 1425 F. 

Since the oxidation of SO to SO is a step in the operation of SOx catalysts, an increase in oxygen concentration should favor the reaction, and thereby increase the efficiency of SOx catalysts. The evidence indicates that this occurs. Baron, Wu and Krenzke (9) have shown that an increase in excess oxygen from 0.9% to 3.4% resulted in a 20% reduction in SOx emissions. This was for a steam-deactivated catalyst in a laboratory unit at 1345 F (no combustion promoter). 

SOx emissions from FCCU s can be reduced by the use of SOx catalysts, especially SOx additives which can be added to the FCCU independently of the cracking catalyst. The effectiveness of these catalysts is favored by lower regenerator temperatures, the presence of combustion promoter, and higher oxygen concentrations. Deactivation of these catalysts occurs by loss of surface area and poisoning by silica. We believe that SOx additives will eventually be used by most refiners to control SOx emissions from FCCU s, either on a spot or continuous basis. 

SO removal Combustion promotion Octane enhancement Metal traps/passivators Bottoms cracking... 

Utilize combustion promoter to catalyze oxidation of carbon monoxide in the dense bed if already in nse, increase addition rate [7]... 

Sexton, J., and Eisher, R. Marathon Refineries Employ New ECC CO Combustion Promoter. Oil Gas Journal, April 27, 2009. 

In recent years, a shift has been made away from Pt-containing CO combustion promoters to promoters containing elements other than Pt. This was driven by the requirements of various EPA Consent Decrees for several units to conduct trials of these new promoters. The desire is to use elements that are still effective in oxidizing CO to CO2 and preventing afterburn, but that do not generate NOx in the process. Many of the non-Pt combustion promoters that are currently... 

INTERCAT s product COP-NP is one of the improved low NO promoters. Marathon conducted trials of COP-NP on four of their FCC units in a phased manner, successfully replacing first generation non-Pt promoters. The results found COP-NP to be two to three times more active than other vendor s first generation non-Pt promoters. This CO combustion promotion improvement comes without an increase in NO emissions as is seen with Pt-containing promoters. Overall, the improved combustion promotion effectiveness of COP-NP has resulted in use of significantly less additive for afterburn and CO emissions control, and has led to significant cost savings for each of Marathon s FCC units. The data are summarized in Table 17.3. 

Liu (1991) reported his experiments on the heterogeneous oxidation of CO in the presence of a FCC catalyst with Pt combustion promoters and proposed the following rate equation ... 

Three peaks are observed in evolved CO2 during TPO. The first (Pi) is associated with evolution from coke located near combustion-promoting metal sites or unpolymerized coke with a low C H ratio. This may be represented by reaction steps (3) and (7) and hence the rate, assuming a steady-state concentration of -C(02) and k-3 k7, is... 

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