June 22, 2011

Liquid Analysis: Detecting Sneaky Leaks

Dave Joseph here again. Today I wanted to blog about one of the most versatile uses of online analytical measurements. Although analysis might imply determining exactly what and how much of something is present, sometimes just sensing a change in conditions can justify the analyzer installation cost. A good example of this is in leak detection.

Many chemical plants use process water for various uses such as rinsing or cooling, and attempt to reuse the water as much as possible. Eventually, the process water is discharged, but if the water has been contaminated in the meantime, the process may escape into the environment. Common industry examples are polysilicon production (chemical/semiconductor), pulping liquor spills (pulp and paper), tailings ponds (mining), and steel pickling (metals processing). Negative outcomes can include lost product, extensive cleanup, and hazardous releases. 

Frequently the releases start at low levels, but sudden releases are best observed with an online measurement like pH or conductivity. Choosing between pH and conductivity can be a little tricky because it depends on the sensitivity of the method, the baseline interference from the cooling water, and the response to increasing amount of the chemical leak. Generally, pH is preferred when the leak may be an acid (low pH) or a base (high pH) and the background does not have a lot of buffering capacity. Conductivity measurement is preferred when the leak may be a salt, the sensor location is hard to access, or when the background is relatively pure water. Measuring before and after a likely leak can increase sensitivity considerably. You can get more background on these methods by viewing the application notes Leak Detection with pH and Leak Detection with Conductivity.

Although constant monitoring for leaks can be a compelling reason to specify analyzers downstream of every possible source of water contamination, a more economical implementation of the concept is continuous monitoring of the return/used/contaminated water at headers with provision for portable measurement (of pH or conductivity) after every process unit. Thus, when a leak is detected, it can be traced to an individual source quite easily. Rosemount Analytical has excellent wireless analyzers that can be easily transferred from location to location to diagnose sources of leaks as needed. Thus, designing in an appropriate threaded connection provides for troubleshooting flexibility without the need for immediate commissioning of analyzers or untimely process shutdowns.

Have you used Rosemount Analytical products to detect leaks? Any tips? Share your experiences with others!

June 6, 2011

“What’s in it for me?”

As educated consumers, we have a tendency to read specifications more than in the past. For an appliance, we are concerned with energy efficiency (cost to operate). For cars, we look at miles per gallon, fuel grade, time between routine maintenance and warranty. All of these specs translate into savings for us, the end user. But when it comes to analyzer specs, often these numbers are used to weed out competitors, set price points (more features means higher price) and provide a vendor with some way to push the superiority of his product. Let’s look at what some of these specifications really mean to an end user – in other words, “What’s in it for me (WII-FM)?”

Speaking particularly about process gas analyzers (photometers, TCD, paramagnetic oxygen, etc.), let’s examine some of the common specifications in closer detail. What value do they offer to me as a customer?

Stability
Repeatability and zero drift are two common specs. The tighter the numbers, the more stable the analyzer, the higher the confidence level we can have in the results, and the less time will be required for preventive maintenance (time and money savings).

Span drift is a really important number that translates into frequency of recalibration. The more stable the upper level of the measurement range, the less often the analyzer needs attendance, resulting once again in reduced costs and maintenance requirements.

Temperature error and operating range
All analyzers are subject to temperature changes, even when housed in a temperature-regulated building. The greater the temperature dependency (error generated), the greater the need for temperature control. What if an analyzer can exist and perform with the same specifications throughout a large temperature range? That analyzer could then be located outside, close to the process, not only resulting in enormous cost savings in terms of shelter requirements, but also in faster real-time measurement updates since the sample has much less distance to travel to reach the analyzer itself. Sometimes this decreased lag time becomes even more important than the actual analysis time, especially if the process being measured can change rapidly. Being able to identify process upsets and react quickly means large potential cost savings, improvements in product quality and yield, as well as safety in the overall operation.

Communications options
Plants utilize a large variety of different types of data handling options. A few still use analog outputs but the data transmitted is normally limited. Increased I/O options permits greater flexibility and provides more data. However, the use of Modbus TCP/IP protocols via Ethernet is continuously growing because of the data potential, ease of monitoring, and even the ability to control, calibrate or validate an analyzer. If an operator or supervisor can perform all these functions as well as ensure his analyzer is performing correctly and identify a problem from his office or control room, how much time can he really save and how much more confidence does he have in his results? The value is immense. Consider our ability to rapidly access information and problem-solve via the Internet with all that it can provide. Compare this to the olden days when a library or collection of reference books was our main resource. Not only do we save time and effort, we have the ability to make informed decisions. This all translates into improved profits, better product and an easier life for the people responsible for plant analyzers.

These are only a few things to consider when reading a list of a product’s specifications and features. I would encourage you to ask the question – “What’s in it for me and my company?” The answers may help you make the best purchasing decisions.

What questions or answers have you come across when purchasing an analyzer?

 Carolyn Snyder

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