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Proper sampling of the resin in an ion exchange unit for analysis is of paramount importance since the results of analysis should lead to positive recommendations for cleaning or replacing the resin. Resin vessels are confined spaces and may be oxygen deficient. Follow all confined space protocols during this procedure.
Follow these directions carefully to ensure that the sample taken is representative of the whole bed:
1. Operate the unit to its normal exhaustion endpoint; backwash as usual; then regenerate and rinse as normal practice.
2. Isolate the unit; then open the drain valve after opening the manhole (a hot process or condensate polishing unit must be cooled before draining to prevent dehydration of the resin).
Inspect the appearance of the top inlet distributor and regenerant distributor (e.g., are they level? Are the openings clogged with resin fines? Do they show any other signs of damage or abnormal condition?).
3. Drain the unit to a level slightly above (3-6”) the bed surface. Observe (and record) the appearance of the bed surface (e.g., clean, dirty, level, hilly, cracks, sloped to side, pulled away from shell, or other abnormal conditions).
Using a digital camera — take photographs. If bed surface is not level, location of high and low spots should be recorded. The cause should be established, if possible. (Possible causes: inlet distributor broken or damaged, regenerant distributor broken or damaged, underdrain system problems).
4. Measure and record the elevation of the top of the bed from a standard benchmark (e.g., from the inlet distributor or backwash outlet (this determines the actual backwash freeboard)). Calculate the actual resin bed depth, if possible.
5. Obtain a representative core sample (preferred) or a composite sample taken at three different elevations.
Retrieving the Sample
Survey the area for any safety interferences around and above the resin vessel (e.g., lighting, electrical conduits, etc.).
Use a 1” diameter PVC pipe with a thread end and cap at the top. Push the sampler directly down into the bed. This operation must be very carefully done gently to avoid disturbing the supporting bed or damaging the underdrain system or any mid-collector (especially if made of plastic). Attach the cap to the top and withdraw slowly with a twisting motion to retain the full depth of the core.
Empty the sample into a 5-gallon plastic bucket, and repeat sampling in a uniform pattern across the surface of the bed, if possible, until sufficient sample is collected. A minimum of 0.5 L is required for a single bed and a minimum of 1.0 L for layered or mixed beds.
For vessels 48”Ø and smaller, a sample from the middle of the vessel will provide a suitable sample. For vessels that are larger than 48”Ø, it is recommend to sample around the circumference of the bed. The samples should be kept separate in order to evaluate areas of the bed. Identify where in the bed 12, 3, 6 and 9 o’clock the samples were taken and from what reference point.
Sample Storage and Documentation