Back to the Basics: Safety and Economy

In monitoring the solvent concentration in industrial processes, the accuracy of the analyzer directly affects the safety and economy of the process.

There are two types of errors to look out for:

Back to the Basics: Flash Point, Dew Point & Temperature

The ability of the analyzer to measure the solvent concentration depends on the delivery of the solvent vapor to the analyzer through a sampling system in which all elements in contact with sample are above the dew points and flash points of all substances in the process. 

Back to the Basics: Flash Point and Dew Point

Each solvent has a characteristic “flash point.” This is the minimum temperature at which the solvent can produce sufficient vapors to form a flammable concentration in air at its surface. The flash point is determined by several test methods, giving some small variation in the published values.

Back to the Basics: Sample line leaks

Any tendency for leaking in the sample tubing or analyzer is to be avoided, as it will directly affect the accuracy of the reading. For this reason stainless steel or a similarly strong and durable material should be used for sample tubing. 

Leaks can be detected by a "probe injection" of calibration gas. In this method calibration gas is injected close to, or directly at, the very end of the sample tube, and the reading is compared to that reading obtained from the routine calibration method (injection directly at the analyzer). 

Back to the Basics: Sample Line Length and Diameter

A major delay in the response time of the analyzer comes from the length and inner diameter of the sample tubing. 

The sample transport delay is increased by the square of the sample tube’s inside radius, and in direct proportion to its length. Doubling the inside diameter of the sample tube will quadruple the time delay it causes. Although the maintenance interval can be increased by the use of a large inner-diameter tube, such delays are usually unacceptable. 

Back to the Basics: Sample pre-conditioning and filtering

Because the analyzer response time is critical, large pre-conditioning filters in the sample line are to be avoided. The delay in a filter can be estimated by dividing the filter volume by the sample flow rate through the filter. 

Back to the Basics: Location in Multi-zone Drying

When choosing the appropriate the sampling location in multi-zone drying you must consider what happens during fault conditions.  

The first or second zone might normally show the highest solvent concentration. But during an upset, it is not necessarily the zone where the peak concentration will appear. Excess solvent from an upset may very well tend to "carry over" into the next zone and produce a peak concentration there rather than in the first zone. 

Back to the Basics: Sample Probe Location

A key element in analyzer performance is the sampling location. Failure to install the sample probe in a "representative" location can lead to inaccurate or greatly delayed readings. A location representing the average solvent concentration of a single zone is desired. 

There are two basic methods of probe location: 

Back to the Basics: Sampling System Issues

The speed and accuracy of the analyzer depend equally upon the sampling system and the detector. The final development of the worst accidents occurs in seconds. It is part of the last line of defense against fire and explosion. There’s precious little time between the rise in concentration and the explosion. That’s a very good reason to pay close attention to the analyzer’s response time.

Did you know? 10 Facts about the PrevEx

 

10 FACTS ABOUT PREVEX ANALYZERS

the PrevEx is our flammability analyzer for lower flammable limit monitoring (LFL/LEL)

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