Analysis of process steam and condensate are important aspects of any chemical processing or refining operation. Impurities in these systems such as silica, sodium, and chloride, or deviations from target pH values, can wreak havoc on a plant’s operations. Online analyses of parameters such as pH and cation conductivity are commonly performed to monitor the condition of process water and steam.
In order to achieve accurate analysis, EPRI, ASTM and ASME recommend cooling of water samples to 77°F (25°C) to ensure consistent, accurate analysis. Unfortunately, cooling water temperatures in process plants commonly exceed 100°F (38°C). While this is acceptable to provide rough cooling, it is insufficient to properly cool samples for online pH, cation conductivity or similar analyzers.
A Hazardous Environment and Limited Access to Cooling Water
While installing new online water analyzers, a refining plant had water at 100°F (38°C) to feed their primary sample coolers, but they lacked access to water cool enough to drop the sample temperatures any further. Knowing that this could cause sample temperatures exceeding 110°F (43°C) regularly, they were concerned about inaccurate readings, high probe maintenance, and inconsistent sample temperatures between steam and condensate samples.
Their sample points were located in a classified hazardous environment and were scattered around the plant. This made the application of a temperature control unit or process chiller impractical due to the cost of area-rated chillers as well as the number of chillers that would be needed to due to multiple locations of the sampling within a plant and the overall size of many plants.
Efficiently Sampling at High Temperatures
After a full understanding of the customer's application needs, a vortex tube - a common technology used to separate compressed air into hot and cool streams - was combined with a single helical tube sample cooler. The resulting solution is capable of dropping sample temperatures into range for proper analysis of boiler water, condensate, and feed water samples. This allowed the customer to obtain suitable samples for performing accurate analysis while avoiding the excessive analyzer maintenance that is necessary when operating at elevated temperatures.
This application solution uses compressed air in place of water to cool a sample. The vortex tube splits the plant air into hot and cold streams, of which the cold stream is then fed into the shell side of a sample cooler, while the sample to be cooled flows through the tube side of the cooler. In the absence of sufficiently cold cooling water, this combination results in significantly lower final sample temperatures and offers more capacity than ambient air cooling alone, peltier cooling, or other unproven solutions. The cooled sample can then be taken to a laboratory for analysis or piped to online process instrumentation for continuous monitoring of properties such as conductivity, pH or other chemical constituents.