Fluid Catalytic Cracking
Fluid catalytic cracking (FCC) is widely used in petroleum refineries to convert the high-boiling, long-molecular hydrocarbon fractions to more valuable gasoline, olefinic gases, and other products. The FCC process vaporizes and breaks the long-chain molecules into much shorter molecules by contacting feedstock, at high temperature and moderate pressure, with a fluidized catalyst.
The coke produced in cracking reactions deposits on the catalyst that very quickly reduces the catalyst reactivity. The spent catalyst is regenerated by burning off deposited coke in regenerator. The activated catalyst is then blown back to the reactor for repeated use. The flue gas exiting from the regenerator is processed through multiple cyclones to remove residual catalyst.
Critical Control of Process Gas
Catalyst regeneration control is a critical task in FCC process. The common practice is to measure oxygen(O2) concentration of the regenerator off-gas. If O2 is insufficient, the deposited coke may not completely combusted, while an excess O2 will cause over-temperature and reduce the life and activity of the catalyst.
Measure carbon monoxide(CO) and carbon dioxide(CO2) of the regenerator off-gas can help calculate how much coke formed in the process. The yield of coke formation reflects the grade of crude oil, the resulting data can be used as input to optimize FCC processes.
Ammonia(NH3) slip is detected outlet of SCR reactor to control DeNOx process.
Challenge of Instrumentation
Traditionally a paramagnetic (O2) and an infrared (CO, CO2) are used for the monitoring of regenerator off-gas. The sampling probe and sampling line are vulnerable to particulates, corrosives and high temperature, resulting in massive maintenance, high cost and not a real continuous operation. The sample gases have to be dried before measurement, which needs replacement of desiccant frequently. Besides, the extractive method is slow response that reduces its efficiency for process control.
FPI’s Laser Gas Analyzer (LGA) is seamlessly customized for the challenging FCC applications. The non-contact laser and sensor of the in-situ LGA combined with continuous purge results in virtually maintenance free, and performs well in high temperature up to 1500°C. High-speed response (down to 1s) of the LGA highlights its reliability for FCC process control. The extreme monochromaticity of laser spectrum ensures no interference with all other gas species. The sampling free system measures water-soluble gas like NH3 with no loss during the process of sampling.
Outlet of SCR
*3 measuring points are optional, either works.
NOTES: Listed are typical data FPI experienced and backed by field references. Alternate gases and ranges may be available or customizable on request.