Aqua-Chem offers a full range of feedwater pre-treatment equipment as part of the package with our distillation systems for Pharmaceutical/Biotech/WFI, Bottled Water and Military/Government applications. Pretreatment technologies include:
- water softening
- chemical feed systems
We evaluate feedwater chemistry to determine the appropriate pre-treatment system and can provide custom piping and vessel materials, instrumentation and controls. We also offer integration of all PLC and HMI panelview controls for the entire pre-treatment/distillation system, or we can keep them separate, as you prefer.
Multi-media filters are used to remove suspended solids from feedwater sources. These filters are very effective because of the multiple layers of media within the filter that are arranged from course to fine media. As water flows downward through the filter, large particulate matter is removed at the top of the filter and small particulate matter is removed at the bottom of the filter. The multi-media filter typically consists of a top layer of gravel followed by anthracite and sand granite. The multimedia filter can be designed with automatic backwash capabilities. Multi-media filters are used as pretreatment to water softeners, carbon filters, and reverse osmosis system to prevent these systems from prematurely clogging with suspended solids.
Carbon readily absorbs organics and chlorine, and is therefore used to filter such elements from feedwater. Chlorine must be removed from feedwater for use in reverse osmosis and all distillation systems because chlorine will attack membranes and stainless steel. Chlorine can cause stainless steel to stress crack corrode due to the elevated temperatures at which distillation systems operate. Various grades of carbon, including regular carbon, medical grade and coconut shell help to break down chloramines, a compound comprising chlorine and ammonia. These and other grades of carbon can be added to the filter for specific pre-treatment needs. The filters need to be designed for steam sterilization or hot water sanitization to kill the bacteria that can grow in carbon filters. Typically this is done on a weekly basis. Carbon filters are usually backwashed twice a week to make sure the carbon does not compact and allow feedwater to channel through the carbon filters. To meet these needs, the carbon filters are designed with stainless steel vessels and piping to handle the hot conditions caused by steam or hot water. Many municipalities today use carbon as a biocide replacement for chlorine. Because carbon filters remove chlorine from the feedwater, bacteria growth and control must be addressed in the design of carbon filters. To ensure the breakdown of chloramines, carbon beds should be sized for less than one gallon per minute of feedwater flow per cubic foot of carbon. In this process, the carbon effectively removes the chlorine portion of the chloramine, leaving the ammonium ion in the feedwater. Ammonium ions can be removed through water softening.
Water softening removes the hardness from feedwater to prevent hard water scale from coating evaporator tubes. Over time, hard water will degrade a distillation unit's capacity. Water softening of feedwater removes calcium and magnesium ions, the cause of water hardness, and replaces them with sodium ions. Water softeners should be sized for salt brine regeneration after 12 hours of operation. The regeneration process involves rinsing the water softener's cation-based resin with a salt brine solution. The concentrated sodium ions push the calcium and magnesium ions away from the resin and to drain, beginning the softening process all over again. In some applications, secondary water softeners are installed after a carbon filter to remove ammonium ions from the feedwater. The cation resin does not attract ammonium ions as readily as calcium and magnesium ions but, if not removed, the ammonium ions will produce high-conductivity distillate. Therefore, a primary water softener is used to remove calcium and magnesium while a secondary softener or softeners remove the ammonium. Because the secondary units operate in a biocide-free environment, they are typically designed for hot water sanitization.
Chemical injection processes are used ahead of distillation systems to eliminate chlorine, chloramines and ammonia from feedwater. Injection systems consist of chemical tanks, injection pumps and pump controls. Sodium bisulfite systems are used to create a chemical reaction to eliminate chlorine. However, sodium bisulfite cannot serve as a substitute for a carbon filter because it has no effect on organics. Sodium bisulfite systems are appropriate for water sources with organics that cause no foaming in the evaporation process. As with water softening, sodium bisulfite systems break down chloramines but still leave ammonium ions in the feedwater, requiring further treatment. Sodium hypochlorite chemical injection systems are also used ahead of distillation systems to destroy chloramines, a process known as break-point chlorination. Injecting enough sodium bisulfite in the presence of chlorine converts the chlorine to chlorides, but there must be sufficient contact time between the chlorine and sodium bisulfite. This is accomplished by adding a tank in the system. This process leaves a small amount of chlorine in the feedwater that needs to be removed by a carbon filter.