What are the effects of Hydrocarbon liquids on sensors?
Hydrocarbon liquids – such as hexane or benzene – condensing on sensors will usually block the sensor from making measurements by physically covering the membrane and stopping oxygen from entering the sensor. This could cause problems for the whole process if not quickly identified and resolved.
How do hydrocarbon liquids get into a gas stream?
Hydrocarbon liquids can enter gas streams a few ways.
- Incorrect sampling
Improper sample conditioning can result in hydrocarbon liquids forming in a sample. For example, where there are low ambient temperatures heat trace tubing or insulation are essential. Where these are missing, cold spots will occur in within the tubing lowering the temperature to below the hydrocarbon dew point. Under these conditions, liquid hydrocarbons may form.
- Process upsets
Process upsets can potentially cause a slug of hydrocarbon liquids to get sent downstream. This can make its way into analysers if proper precautions are not taken.
How correct sampling can avoid hydrocarbon liquids forming in a system
- Filters
There are two types of filters that can remove liquid from a system: Coalescing and Membrane filters. Both these filters work in slightly different ways, but their main purpose is to filter liquids out of a system. Positioning the filters is very important: make sure that the filter(s) are positioned before the analyser and any other component that may become clogged, such as flow meters.
- Correct temperatures
Take care to ensure that the temperature in the sampling system is above the hydrocarbon dew point by using heat-traced tubing. This heats the tubing, making sure that there are no cold spots in the tubing until the sample reaches the coalescing filter. The sample tube from the filter to the analyzer should not be heated to avoid a cold spot occurring in the analyzer itself.