By John Avery
Summary: The following is an introductory article meant to give readers an idea of the various applications to which chemical feed pumps can be put to use to help water treatment professionals do their jobs better.
Achemical feed pump can be a critical component in a water treatment system. Used in conjunction with other equipment, these small pumps can help to correct some of the most difficult or objectionable water conditions found in the water improvement industry. There are circumstances when a chemical feed pump is a requirement to pre-treat water—be that for disinfection, oxidation, flocculation, coagulation or corrosion and/or scale control—so that a water conditioning system will operate correctly and continue to provide quality water at its optimal performance level.
Disinfection and beyond
Over many years these little wonders—i.e., chemical feed pumps—have been used primarily for disinfection of potable water systems. The addition of small amounts of sodium hypochlorite for constant disinfection of drinking water systems has probably saved more lives around the world than any other medical discovery known to modern man.
Still, as mentioned earlier, disinfection is just a small portion of the applications that can benefit from or implement the use of a chemical feed pump. Tremendous benefits can be realized from the proper application of these pumps in the water conditioning market.
Municipal water treatment plants use chemical feed pumps for many areas of their process to feed chemicals for coagulation, flocculation, corrosion control and pH control to provide us the water we use everyday. In addition, feed pumps are used as an integral part of the wastewater treatment process for disinfection, dechlorination, pH adjustment and flocculation, just to name a few. The treated wastewater can then be returned safely to the environment to repeat the hydrologic cycle.
Did you know there are applications for chemical feed pumps to improve the performance of your water treatment systems? Often, a chemical feed pump is overlooked as a way to correct objectionable water constituents and improve the overall system operation.
Water supplies with high amounts of ferrous iron (Fe), manganese (Mn) and hydrogen sulfide (H2S) can be corrected by chemical oxidation. Correction of these conditions with the use of chemical feed can greatly improve water conditioning systems performance and capacity. In extreme situations, oxidation by chemical feed may be the only way to ensure proper system operation. Obtaining the highest level of system performance will lead to improved operating efficiency of your system designs and lead to greater consumer satisfaction.
The process used to correct these objectionable water conditions is typically described as “Oxidation-Precipitation-Filtration.” A dose amount of an oxidant, typically sodium hypochlorite, or common bleach, is fed into the water stream. The bleach solution is injected prior to a retention tank of sufficient size to provide adequate contact time. The dose amount is usually much higher than the demand of the water so that a 3-5 parts per million (ppm) FCR—free chlorine residual—reading is obtained after contact. The oxidation causes the constituents to precipitate from their soluble form, converting them back to their solid form, whereby they’re more easily removed. The chlorinated water is then passed through a GAC (granular activated carbon) filter to remove the chlorine residual, potential disinfection by-products and also provide filtration for any precipitant remaining. We can then proceed to other methods of water conditioning for final polishing such as ion exchange water softening or reverse osmosis (RO).
Other diverse applications
Feed pumps can also be used for introduction of hydrogen peroxide as an oxidant and potassium permanganate as an oxidant or filter regenerant. Through proper selection, feed pumps can be used for introducing strong bases or strong acids for pH adjustment, flocculants and coagulants as filter aids to remedy collodial conditions. Poly-phosphate can be fed for boiler feed water corrosion and scale control as well as many more applications. One can begin to see that the use of chemical feed pumps extends far beyond the common disinfection applications that most people associate with chemical feed pumps.
Feed pump technology
The use of the right type of chemical feed pump for a particular application is an important decision when designing a system. In the past, the chemical feed pump market was separated into three distinct types or designs of pumps. The different types of designs available included:
- Mechanical diaphragm,
- Electromagnetic solenoid diaphragm, and
- Peristaltic (or tube style) pumps.
The mechanically driven diaphragm and solenoid diaphragm style pumps held an advantage because of pressure capability and the types of controls that could be used to drive the pumps proportional to flow. The peristaltic design capable of metering against 100 pounds per square inch gauge (psig) held an advantage of simplicity and self-priming with greater suction lift capability. Recently, the peristaltic pumps have improved their technology to provide different methods of control. There are now products available on the market that can proportionally drive peristaltic pumps via contact type water meters. The newest additions to the peristaltic pump markets have brought forward pumps that can be controlled via 4-20mA signals, increasing the applications that had been reserved to the solenoid type pumps only. In the future, new technology developments will arise in the chemical feed pump markets that will make feed pumps even more versatile than today.
Chemical feed pumps applied correctly can be a powerful tool in a water professional’s inventory. Consulting with the feed pump manufacturer of your choice is recommended for assistance in choosing the right pump for your systems and particular applications. You’ll find them a wealth of information and ready to assist you in expanding your business with the use of chemical feed pumps.
About the author
John Avery is technical services manager for G.H. Stenner & Co. Inc., a manufacturer of peristaltic chemical feed pumps located in Jacksonville, Fla. Avery has over 15 years of experience with Stenner in the manufacture, design, development and application of chemical feed pumps. He has held positions in his career with Stenner as manufacturing engineer, research and development engineer, and engineering manager. His experience covers a broad range of applications including residential, commercial and industrial water treatment markets. He can be reached at (904) 641-1666, (904) 642- 1012 (fax) or email: firstname.lastname@example.org