Page 174 - Fluid Catalytic Cracking Handbook

Unit Monitoring and Control 147

4. The flow rate of each stream should be converted to weight units.
5. The quantity of inert gases and extraneous streams should be
subtracted from the FCC gas plant products.
6. The raw mass balance should be reported, including the error,
Then the feed/products should be normalized to 100%. The error
will be distributed in proportion to flow rates or a known inac-
curate meter will be adjusted.
7. Gasoline and LCO rates will be adjusted to standard cut points.
8. The feed characterization correlations discussed in Chapter 2
should be used to determine the composition of fresh feed.

Analysis of Results

1. The yields and quality of the desired products should be reported
and compared with the unit targets.
2. The results of this test run should be compared with the results
of previous test runs; any significant changes in the yields and/
or operating parameters should be highlighted.
3. The final step is to perform simple economics of the unit opera-
tion and make recommendations that improve short- and long-
term unit operation.
The following case study demonstrates a step-by-step approach to
performing a comprehensive material and heat balance.

A test run is conducted to evaluate the performance of a 50,000 bpd
3
(331 m /hr) FCC unit. The feed to the unit is gas oil from the vacuum
unit. No recycle stream is processed; however, the off-gas from the
delayed coker is sent to the gas recovery section. Products from
the unit are fuel gas, LPG, gasoline, LCO, and decanted oil (DO).
Tables 5-2 and 5-3 contain stream flow rates, operating data, and
laboratory analyses. The meter factors have been adjusted for actual
operating conditions.
The mass balance is performed as follows:

1. Identification of the input and output streams used in the overall
mass balance equation.
2. Calculation of the coke yield.