Catalyst and Gas Samplers for Fluid Catalytic Cracker Regenerator Sigmund M. Csicsery," Hugh F. Harnsberger, Walter D. Hughes, and Roger D. Searle Chevrori Research Company. Richmond. California 94802
The design and operation of two catalyst samplers in one of Standard Oil Company of California's Model I V FCC regenerators are described. These samplers simultaneously sample both flue gas and partially regenerated catalyst and measure temperature within the dense bed of the regenerator. From this information one can determine the course of catalyst regeneration, mixing, and homogeneity of the dense bed and can optimize regenerator efficiency.
Introduction In Standard Oil Company of California's refineries we have had some questions about mixing and afterburning in our fluid catalytic cracking (FCC) regenerators, but until now we had no opportunity to study these questions directly. This paper describes our efforts to design and use multiport sampling devices in a Model IV FCC regenerator. These samplers simultaneously sample both partially regenerated catalyst and flue gas and measure temperatures within the dense bed of the regenerator. Sampling results and conclusions are also reported here.
Discussion Two catalyst samplers were installed in the Richmond FCC regenerator during March 1973. The regenerator is a conventional, Model IV design, 47 ft, 9 in. in diameter. The samplers are located in existing water spray nozzles about 3 f t above the grid. The average height of the dense phase bed is 16 ft. Figures 1-4 show the arrangements. A sampler consists of a 1 h-in. Schedule 40 stainless steel pipe, which houses three sampling tubes and three thermocouple wells. The longer sampler (no. 2 ) is 21 ft long and has sampling ports a t 11, 16, and 21 ft radially from the outside wall of' the regenerator. The shorter sampler (no. .i) is 14 ft long, and the sampling ports are 6, 10. and 14 ft radially from the outside wall. Two bipods support the longer sampler, and one supports the shorter one. The longest sampling tubes in each sampler are 'h in.; the others are 3/8-ln. tubes. To minimize coke combustion and the COZ conversion during sampling, each sampler is CO cooled with steam. Furthermore, we used 410 chrome steel instead of Ni-containing alloys whenever in contact with COz reaction by samples to avoid catalyzing the CO Ni. When the tubes of the sampler are not used, they are continuously flushed with steam to prevent plugging. The longer sampler samples catalyst near the spent catalyst riser. The shorter sampler is closer to the overflow well. The middle (16-ft) sampling port on the longer sampler and the outer (6-ft) port on the shorter sampler are located immediately below primary diplegs. The other four ports are about as far from diplegs as possible. The time required for the catalyst to flow through the sampling tube is short (i e . , seconds) compared to the total time spent in the FCC regenerator (minutes). This fact, and steam cooling, minimize coke combustion and CO oxidation during sampling. Catalyst samples are collected in 300-ml stainless steel Hoke cylinders. Glass collecting vessels are used to collect gas samples which are separated from hot solid catalyst in a small cyclone-type separator. Figure 1 shows a simplified drawing of the shorter sampler. Sampling Procedure. Taking a sample is very easy with this system, but taking good, representative samples -+
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requires careful attention to details to avoid reactions during and after sampling, prevent selective gas adsorption on catalyst samples, minimize air contamination of gas samples, and operate without plugging sampling lines. Although all sampling lines are continuously purged with steam, occasionally some of them become plugged with catalyst. We have always managed to unplug sampler lines by closing all lines except the plugged one and waiting 4-5 min for the full steam pressure to unclog the line, or by blowing it out with nitrogen (up to 500 psig) from an auxiliary cylinder. A. Catalyst Sampling. We followed these steps to take catalyst samples. (I) Turned off steam on sampler line and purged with Nz for at least 1 min. ( 2 ) Attached a 300-ml Hoke cylinder and purged it with Nz. (3) Turned off Nz and allowed catalyst to pass through the Hoke cylinder for about 1 min. A curved 1.-2 ft long tube should direct the catalyst into a bucket. Goggles are important for eye protection from wind-blown catalyst! ( 4 ) Closed outermost valve first, then the one on the other side of the Hoke cylinder, and finally the one closest to the regenerator. Detached Hoke cylinder. (5) Purged sampling line first with N2, then with steam. (6) Determined carbon contents of the catalyst samples using a Coleman C-H Analyzer. B. Gas Sampling. We took our first gas samples by releasing the gas collected with catalyst samples in the Hoke cylinders into evacuated glass sampling bottles. We found, however, that between sampling and gas separation the catalyst adsorbed much of the COz present in the gas sample. Therefore, we designed a small cyclone-type separator which effectively separated gas from hot catalyst before it had a chance to adsorb. The cyclone has a small filter filled with glass wool which protects the O-ring valves of the glass sampling bottles from catalyst fines. We followed these steps to take gas samples. (1)Purged the sampling line thoroughly with Nz. (2) Attached the cyclone and purged it with Nz for at least 2-3 min. (3) Attached a glass sampling bottle to the top of the cyclone and purged it very carefully with Nz. It is necessary to purge the steam completely from the sampling tuhe with h'z because it condenses in the glass sampling bottle and absorbs part of the COZ present in the sample. Air contamination in the gas sample is indistinguishable from real "unconsumed 0 2 ' ' present in the sample. Nz contamination, however, shows up in the analysis (as in excess over 79%), and results can be corrected. These corrections only approximate the gas compositions because part of the 0 2 can be consumed by reacting with hydrogen in the coke. The water produced cannot be identified in the analysis. It is, therefore, extremely important to purge the cyclone and the glass bottle thoroughly with Tz.(4) Opened the sampling valve and allowed catalyst to be Ind. Eng. Chern., Process Des. Develop., Vol. 14, No. 1, 1975
93
,Cwli ng Steam Outlet
Cwling Stearn inlet
~v~~ u 3 8
GI2
14'
-1
__
50. 5
Tubing Tubing 410 SST 410 S S T
Figure 1. Catalyst sampler no. 5 in the Richmond FCC regenerator.
\
%ole I?.
Tltal C a r b a r F l u e Gas %
20.66
20..5
23.47
Figure 3. Catalyst samplers in the Richmond FCC regenerator. Gas analyses on Apr 24, 1973, between 1O:OO a.m. and noon, 0 2 levels (mol YO),and COz/CO mole ratios (in parentheses).
10'
c--------i
Figure 2. Catalyst samplers in the Richmond FCC regenerator. Catalyst carbon levels (wt %I on Apr 24, 1973, between 1O:OO a.m. and noon; Coleman C-H analyses.
Table I. Typical Temperature Differences
Location
Temperature difference, "F ( A T in Figure 4 ) ( T 8 t e m v a l v e c l o s e d T s t e mvalve O p e n ) at regeneration temperature about 1100°F Sampler No. 2
11 ft from wall 16 ft from wall 2 1 ft from wall
30 20 6
Sampler No. 5 6 ft from wall 10 f t from wall 14 ft from wall
120 25 3
blown into the cyclone for a t least 1 min, but without overfilling the cyclone with catalyst. Catalyst level can be detected by carefully touching the outside surface of the cyclone because the catalyst is hot. The best time to stop sampling and close valves is a few seconds after condensation begins around the exit valve. ( 5 ) Closed the valve on the glass sampling bottle, then closed the others, always proceeding from the outermost valve toward the regenerator. (6) Removed the glass sampling bottle, detached the cyclone, and purged the sampling line first with Nz, then with steam. ( 7 ) Capped sampling bottles with rubber caps 94
Ind. Eng. Chem., Process Des. Develop., Vol. 14, No. 1, 1975
Figure 4. Catalyst samplers in the Richmond FCC regenerator; temperatures, O F , on Apr 24, 1973. at 10:50 a.m. t o 1 1 : l O a.m.
a t both ends. (8) Analyzed gas samples by gas chromatography. C. Temperature Measurements. We used a potentiometer box to measure the voltage of the chromel-alumel thermocouples with the reference junction in ice and water because the ambient temperature high up on the side of the regenerator changes frequently and erratically due to wind, vicinity to hot regenerator wall, sunshine, etc. We followed these steps to measure temperatures. (1) Turned off all steam flow by closing valves on the three sampling tubes and the main steam valve on the "cooling" system. If the sampling line steam flow is turned off only a t the main steam line valves, these lines can fill up with catalyst and plug. Thermocouples needed 4-5 min to warm u p after the steam-cooling was stopped. (2) Removed the thermocouple guard. (3) Measured tempera-
Table 11. Richmond FCC Sampling Results on Apr. 24, 1973 between 9 5 5 a.m. and 12:OO Noon A. Catalyst and Gas Analyses
2
Sample no. 1 Sampler no. 2 Sampling port distance f r o m regenerator wall, ft 11 Sampling time 9:55
3 2
2
4 5
5 5
6 5
7 5
8 2
9 2
16 21 10 14 6 10 21 11 10:14 10:21 11:15 11:22 11:28 11:38 11:47 12:OO
Regenerated catalyst; and flue gases f r o m East 9:50
Spent catalyst; and West flue gas 11:OO 11:50 10:50
~
Coleman C-H Analyzer i n analytical lab
0.68 0.68
Moisture, wt % (1 hr, 104-110°C ~
0.80 0.80
