By Iliana Colín, Emerson Gas Specialist for Analytical Measurements
Hello, I’m Iliana Colín and I’m your Analytic Expert today. I’d like to talk about some of the challenges associated with catalyst regeneration in catalytic cracking and how rethinking the approach to hydrocarbon monitoring in these processes can reduce risk and save you time and money.
Catalytic crackers have long been utilized to extract additional gasoline from heavier components resulting from the distillation process. The distillation process is the physical separation of a mixture of different molecules based upon the different boiling points of these molecules. The catalytic cracking process splits larger hydrocarbon molecules into lighter and higher value components such as gasoline by using a catalyst, which aids the reaction or “cracking” process. The cracking process produces carbon, or coke, which remains on the catalyst particle, reducing its effectiveness over time. Fluidized Catalytic Cracking Units (FCCU) will continuously route coked catalyst into a regenerator unit where oil remaining on the surface of the catalyst is stripped off with steam or solvent. The catalyst is then sent into the regenerator, where air is introduced to burn the coke off of the hot catalyst, usually in suspension. There are many different variations in the regeneration process: the semi-regenerative catalytic reformer and the continuous catalyst regeneration reformer (CCR). This last one is preferred because of the continuous regeneration of the catalyst, which allows plant operation for more than two years before a catalyst change is needed. This is important because the cost of the catalyst is very high.
One of the key parameters in the process is the purity of the nitrogen, which is required to move the catalyst from the reactor to the regenerator. The hydrogen content must be below 1% and total hydrocarbons must be below 15% in order to keep a non-explosive atmosphere in the process since high temperatures are needed. In addition, if hydrocarbons are burned they may lead to the formation of a coke lining over the catalyst, inhibiting its function, so monitoring is essential.
Challenges that arise in this application include the high quantities of dust due to the continuous flow of the catalyst that enables cracking. When older analyzers are used, it’s not uncommon for the dust to cause the sampling lines to plug, or even worse, damage the analyzer. This is often the result of a sampling system with inappropriate design for such a challenging environment. As a result, some plants use this as a reason to bypass the analyzer, and leave it without maintenance until it becomes useless. This is an extremely costly and dangerous approach, since the analyzer can signal a plant shut down, and if the signal is bypassed, the safety of the plant is threatened.
Also challenging is the fact that the area certification in these plants is classified as hazardous. This may drive users to install general purpose analyzers in high cost shelters that also require power supply, air conditioning, and safety devices. These shelters must be installed at floor level, representing larger tubing lines and the inherent time delay that affects the control of the application because the control system receives data with a delay of some minutes, and thus process safety is jeopardized.
Many analyzers currently installed on-site use analog outputs, and there is no way to know the status of the analyzer unless the tech is standing in front of it, which can be ill-advised in hazardous areas due to risks such as radioactive measurement of the flow rate of the catalyst moving bed, noise, height, and so on. New analyzers are able to send more information through a Modbus protocol to make the maintenance program of the analysis system easier.
A monitoring approach that can reduce risk and costs is to use an analyzer designed specifically for hazardous environments such as the X-STREAM Enhanced XEFD. Enclosed in a wall-mountable, flameproof housing certified for installation in CSA and ATEX hazardous areas, these modern analyzers offer communications protocols to keep the control room constantly informed of their condition as well as process feedback. The housing also means the analyzers do not require costly and space-intensive shelters, eliminating the need for additional utilities, such as power, air conditioning, etc. These systems offer the monitoring of both hydrogen and total hydrocarbons in a single analyzer, further reducing costs and time for installation, start up, maintenance and calibration. Because the systems are designed from the outset with very short sampling lines, which are far less likely to become plugged and have fewer fault points, analysis is faster and more reliable.
What kind of monitoring systems are you using in your catalytic regeneration processes? Have you experienced challenges?