Riser temperature

For a given catalyst and feedstock, catalytic coke yield is a direct function of conversion. However, an optimum riser temperature will minimize coke yield. For a typical cat cracker, this temperature is... 

A high fractionator bottoms level, a low riser temperature, and a high residence time in the reactor dome/vapor line are additional operating factors that increase coke buildup. If the main column level rises above the vapor line inlet nozzle, donut shaped coke can form at the nozzle entrance. 

Operating variables Reduced stripping steam or atomizing steam higher preheat or riser temperature. Restore the steam flows this is not the right place to solve a sour water problem. 

These catalysts were evaluated in an isothermal, bench-scale, riser pilot plant at 1000 F average riser temperature, 5 seconds oil residence time (ORT) and at least four different catalyst to oil ratios varying from 4 to 10. The feedstock used was a Nigerian gas oil with properties as shown in Table III. Gases were analyzed by GC. The liquids were analyzed by a GC to give the carbon number isomer breakdown. In addition there was enough sample to analyze for mini-micro Motor octane which has a reported reproducibility of 0.75 octane for a single determination. 

In current industrial practice, reactor (or riser) temperature is usually controlled by the flowrate of hot catalyst fed to the reactor from the regenerator. A slide valve in the... 

Lower the FCC unit riser temperature. This solution indeed lowers the S level (up to 7%) in the gasoline range, but many units would require large temperature drops (30 °C) leading to octane losses and operating difficulties (19)... 

RISER TEMPERATURE CONTROL WITH STRIPPING STEAM... 

One of the primary variables that an FCCU operator can use is riser temperature. Increasing riser temperature usually results in increased conversion, though not necessarily greater yields of gasoline. For units not on automatic reactor temperature control, riser temperature can be increased by ... 

Left to his own, the shift worker operating the FCCU control panel often chooses the simplest method to hold riser temperature constant. On many units the control panel operator has discovered that changing the... 

Lower feed preheat. This will only work if the catalyst circulation also can be increased to maintain the riser temperature. 

Referring to Figure 7-1, we can see that the FCCU feed mixes with the catalyst in the V. Let us suppose that our target riser temperature is 990 F. Our FCCU feed might be 500°F and still a liquid as it flows into the Y. The catalyst might be 1,380°F. The hot catalyst cools down to 980°F and in so doing supplies energy to ... 

Remove oil of catalyst Increased regenerator air Higher regenerator temperature Loss product yield Hydrothermal deactivation Alter steam rate to test Change riser temperature with steam Check CO/CO2 ratio... 

At constant operating conditions (riser temperature, catalyst to oil ratio, etc.), cracking virgin diesel oil yields 75%-80% as much gasoline as cracking virgin gas oil. 

The riser or reactor temperature is reading too high. It s pretty easy to attribute the results of a faulty riser Tl to inactive catalyst. Note that gasoline production does not always increase with riser temperature or conversion. Excessive riser temperature results in overcracking, and gasoline output suffers. 

The effect of riser temperature on the diolefin content on FCCU butanes is correlated in Figure 6-3. One refiner also reported that an increase in regenerator temperature from 1,280°F to 1,320°F doubled the diolefin content of the alkylation unit feed. ... 

Increase LCO flash Pentanes in absorber off-gas Catalyst activity or selectivity Losses to refinery slop Riser temperature reading high... 

Most FCC units only have a few independent variables. Typically, these independent variables are the feed rate, feed preheat temperature, reactor/riser temperature, air flow rate to the regenerator, and catalyst activity. The feed rate and air flow rate to the regenerator are set by flow controllers. The feed temperature is set by the feed temperature controller. Catalyst activity is set by catalyst selection and fresh catalyst addition rate. Reactor temperature is controlled by the regenerator slide valve that regulates the catalyst circulation rate. The catalyst circulation rate is not directly measured or controlled. Instead, the unit relies on the heat balance to estimate the catalyst circulation rate. Except for these independent variables, other variables, such as regenerator temperature, degree of conversion, and carbon-on-catalyst, etc., will vary accordingly to keep the FCC unit in heat balance. These variables are dependent variables. 

Impact of Riser Temperature on FCC Gasoline Composition Constant Conversion Comparison... 

Figure 35.11 shows that the reactor riser temperature 7 can best be controlled by since the step response for a change in air flow and lSFrr,sp show a large response initially, followed by an inverse response. This is not dynamically favorable for control. 

Fig. 35.13. Response of controlled reactor riser temperature, controlled stack gas oxygen concentration and uncontrolled regenerator temperature to step change in feed.

Figure 4.35 represents a highly simplified view of a FCC unit We can consider the FCC unit as a black-box that converts different types of feed into products with varying profit margins. The LP model expects that the profits or values of the products are readily available. If we consider that only straight-run VGO enters the unit at fixed operating conditions (riser temperature, catalyst-to-oil ratio, etc.), we can represent the yield of the unit as ... 

To Study the effect of riser temperature at higher unit throughput, we must create a case where will vary the riser outlet temperature. First, we increase the feed flow rate to the unit Reactor Section of the FCC unit operation window. For this example, we set the feed flow rate to 115 tons/hr as shown in Figure 4.102 and solve the model. If the model does not converge, we can increase the number of creep and total iterations in the Solve Options Section. 

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