They needed a solution.
Ion Exchange Resin Analysis Reports:
Discussion of Resin Analysis (Written by Ted Begg of Purolite):
Train A & B strong base anion resin analysis concluded the samples are Type II Strong Base Anions, equivalent to Purolite A300. Both samples exhibited dramatic loss in strong base capacity and severe organic fouling. Typical Type II anions will have 90% strong base capacity when new, however, it is not uncommon to see severe reduction to the levels observed, ~ 60%, when the resin is continually subjected to temperatures well in excess of 95 degrees F. Strong base capacity is responsible for silica removal. As this capacity is lost, throughput to silica break gets lower and lower with cost of caustic for regeneration steadily increasing. Given caustic is approaching $1000/ dry ton, lost throughput due to resin degradation comes at a very high cost.
The organic fouling noted is severe and is likely contributing to lost throughput and increased rinse volume (fast rinse). The organics on the resin pick up sodium during caustic regeneration, which slowly elutes off during the fast rinse. Therefore the increased rinse volume.
The Demineralization System:
This plant was designed to mix returned hot condensate to the finished water make up storage tank. This water is used for boiler feedwater and as well as for regeneration. While the heated water is beneficial for boiler feedwater, it is not good for regeneration of the anion resins. This water can approach and possibly exceed 130 degrees F. The Type II strong base anion resin temperature limit is stated by manufacturers at 105 degrees F, however, it is more prudent to maintain the limit to a maximum of 95 degrees F. Given the plant operating conditions and the condition of the anion resin, we recommended that the anion be replaced with a more temperature stable product. A Type I porous anion resin with uniform particle size distribution is recommended as a replacement. The product, PFA400, is stable up to 140 degrees F and is more resistant to organic fouling than the incumbent resin. In this case longevity of the resin will improve. The throughput capacity of PFA400 will approach the incumbent resin as well. Thanks Ted for the detailed discussion above of the analyses.
Our Conclusions and Observations:
The conclusion is using a Type II anion in place of a Type I, where low silica water is required and the system can run above 95 degrees F, is a misapplication for the reasons stated above which are:
So how does this misapplication happen? The selection of the ion exchange resins for a demineralization system generally occurs many years before a system is started up. Depending upon the perceived complexity of the water treatment system which includes the demineralization system, an engineering company may be specifying the demineralization system components including the resins as well as a whole host of other pieces of equipment. Then these specifications will be bid on by a short or long list of OEM's each of whom wants to get the job. Most will bid to the specs, but others may suggest a cheaper alternative.
One common area to shave money from the whole job is to skimp on the demineralization system in particlar the anion system. When lowest installed cost is the driver, sometimes Res-Kem sees equipment companies selling deionization systems using a Type II anion resin. The reason they promote the use of a Type II anion is the anion portion of the system is smaller. Because the Type II anion resin has about a 10% higher initial capacity than a Type I, the equipment needs 10% less of the expensive anion resin and the size of the anion tank is smaller. The end result is several months after commissioning and transfer of the equipment from the OEM to the user, the problems begin. By then, the low budget OEM will be on to their next project and will often walk away from your problem.
Res-Kem believes the moral of the story is work work with a knowledgeable OEM with experienced personnel who will recommend the best equipment for your application and will stand behind their equipment when installed.