The Right Equipment to Ensure Efficiency, Compliance and Protection
Maintaining clean heat transfer surfaces and ultimately the success of a water treatment program depends upon matching treatment dosage to cooling water conditions and loads. To facilitate this a wide variety of chemical feed equipment is available. This equipment may include pumps, tanks, timers, water meters, flow control valves and controllers for conductivity and pH. These components can be incorporated into feed systems that automatically maintain preset treatment and system concentrations.
Chemical feed systems for cooling towers, closed loops and boiler systems will vary. The automated system of choice will depend upon system size, operational characteristics and control requirements, as well as economics. Basic feed control system components may include:
Shot or Bypass Feeder
A shot or bypass feeder is normally used to feed chemicals to closed loop or other low makeup water systems. It consists of a small tank, usually constructed of steel, equipped with an inlet, outlet, drain and vent. A feeder also has an enlarged opening or includes a funnel for the manual addition of chemicals. It provides the user with a convenient point to introduce chemicals manually into a circulating water system.
A manual feed program has certain disadvantages when used on systems where makeup requirements vary. Manual feed programs require periodic testing of the water being treated and frequent addition of chemicals to maintain treatment levels. Overtreatment, which is costly, is sometimes necessary to maintain optimum chemical residuals over a long period of time. Also, this type of program is easily neglected when manpower is short.
Chemical Feed Pumps
A chemical feed pump injects treatment into the cooling water. It has an adjustable capacity to inject relatively small amounts of chemicals accurately against system operating pressures. Positive displacement chemical feed pumps include many different types: rotary gear, peristaltic, progressive cavity, and reciprocating (piston and diaphragm). The most commonly used type is the reciprocating diaphragm pump. These pumps operate either mechanically or electronically.
A continuous feed system requires a chemical pump and is, therefore, a more cost effective system. By feeding chemicals automatically, it reduces operator chemical handling. There is a definite safety advantage also. Continuous feed with just a chemical pump is suited to a system with a constant load and where makeup, flow rates, and bleed-off fluctuate very little. However, if loads vary, this system will either undertreat or overtreat because it cannot react automatically to operating variations.
A conductivity controller is commonly used in boiler and condenser water systems to maintain cycles of concentration and to activate chemical feed. It consists of an electronic control panel with one or more set points and a probe. Since conductivity varies directly with the total dissolved solids (TDS) in a system, a suitable TDS level can be maintained by having the controller activate a bleed-off valve at a desired set point. By automatically limiting the TDS level in this manner, the controller should maintain impurities at soluble levels while feeding enough chemical to prevent scale formation on heat transfer surfaces. A conductivity controlled feed and bleed system is best suited for a system having no appreciable water losses other than controlled bleed and evaporation. The system automatically controls water quality and can adjust to load variations and incoming water quality changes.
However, if the cooling water system has uncontrolled water losses, conductivity-controlled feed and bleed will not provide good chemical residual levels. The probe must be cleaned periodically to insure correct conductivity measurement.
Water meter-based feed consists of an electric contacting head and automatic reset timer. This is installed on boiler or cooling systems to regulate chemical pumps and/or bleed valves. The meter is normally a standard totalizing meter with a special gear train and cam-operated switch. The cam on the gear closes a switch after a preselected quantity of water has been metered. This switch closure activates the automatic reset timer, and thus, a makeup signal proportional to flow is created which activates chemical feed and bleed-off devices.This is the most sophisticated system of the five types mentioned above. It embodies chemical feed regulated by proportional flow and bleed-off controlled by conductivity readings. The flow proportional chemical feed and conductivity controlled bleed system require a conductivity controller, electrically activated valve, water meter with electric contact head, automatic reset timer, and chemical pump. This control system combines the advantages of the two previously described systems; it reacts to load changes, system water losses, and changes in makeup water quality. The only disadvantages are the system’s relatively high cost and the periodic cleaning of the conductivity controller probe.
A Programmable Timer programs a chemical feed pump to supply dosages of chemicals on a daily, weekly, biweekly, monthly or more frequent basis. Application of Biocide treatments are commonly administered in this manner in conjunction with a controller. Programmable timers may be mechanically, electronically or digitally driven. They are designed to activate a switch which operates an electrical device, primarily a pump, which feeds the product into the system in a timely manner.
Used in condenser water systems requiring pH adjustment. The controller monitors the pH of the recirculating water and activates acid or caustic feed systems (depending on the desired pH of system water) to adjust pH to a preset level. The controller consists of an electronic control panel with one or more set points and a probe assembly.
It allows higher cycles of concentration. Usually used in conjunction with flow proportional to water meter feed, and conductivity bleed. Must be closely monitored because a malfunction can yield disastrous results.
In those systems utilizing an oxidizing biocide, ORP (Oxidation/Reduction Potential) is used to control the level of biocide in the system.