Controls the accumulation or build up of dissolved solids in the recirculating water brought on by the evaporation. The bleed-off control operates a bleed-off valve to drain water from the system, allowing further make-as much as dilute the system water and cut back the dissolved solids level.
Conductivity bleed-off methods measure the electrical conductivity of the recirculating water, which is directly related to the level of dissolved solids. As the conductivity rises above a set level, the bleed-off valve is opened, when the conductivity stage drops below the set point the bleed-off valve is closed. This ensures the bleed-off charge is managed in proportion to the obligation or load on the cooling tower to minimise wastage of water.
Proportional bleed-off methods operate by opening the bleed-off valve in proportion to the make-up water volume. By definition, the amount of bleed-off required is a direct proportion of the make-up price. For instance, to take care of a concentration factor of 2 the amount of bleed-off required will be 50%, or one half, of the make-up rate and to keep up a concentration factor of 4 the amount of bleed-off required can be 25%, or one quarter, of the make-up.
Proportional bleed programs operate from a water meter within the make up provide to the cooling tower and open the bleed-off valve for a set time duration relative to a set quantity of make-up.
Both methods have their benefits and disadvantages:-
Conductivity bleed-off programs require conductivity devices and can’t differentiate between dissolved solids from the make-up and water treatment chemicals. When shot doses of biocides are added they cause a rise in the conductivity activating the bleed-off. A bleed lockout timer is required to stop bleed-off for a set period following biocide dosage to forestall wastage of expensive biocide chemicals.
Proportional bleed-off systems can not compensate for any leakage or different unexpected water losses from the system, nor will they detect any course of contamination. Proportional techniques don’t, however, require bleed lockout techniques as they are unaffected by slug doses of biocides and different chemicals.
2. Inhibitor dosage
Corrosion and scale inhibitors are dosed in proportion to the make-up to take care of a set level within the recirculating water. Inhibitor dosage systems subsequently use a water meter in the make-up supply to the cooling tower to function chemical dosing pumps so as to add chemicals in direct proportion to the make up water flow.
3. Biocide dosage
Two options can be found:-
Non-Oxidising Biocides Normally shot dosed on an alternating basis, often once or twice per week utilizing timer controlled dosing pumps. Sometimes, non-oxidising biocides require a contact time of four hours at a set concentration to destroy micro organism. As previously indicated, where conductivity bleed-off methods are fitted a bleed lockout system is required to stop dilution and loss of biocide to bleed-off.
Oxidising biocides Chlorine or Bromine. Chlorine ought to solely be used where pH ranges are between 6.5 and 7.8. At higher pH, chlorine is relatively unreactive and a poor biocide. Its use is therefore confined to industrial cooling towers incorporating pH management. Bromine is effective at pH levels up to 9.0, above which its biocidal effect drops considerably requiring excessive dosage rates.
Oxidising biocides are normally dosed repeatedly at a low stage to maintain a set disinfectant level within the recirculating water. The extent of disinfectant will be monitored electrically utilizing Redox (Oxidation Discount Potential ORP) or a particular chlorine monitor. Because of their price and sensitivity to contamination specific chlorine or bromine monitors are not often used.
Redox (ORP) management measures the oxidation and reduction potential in millivolts in the water over a variety of zero to one thousand mV. This is related to the extent of bromine oxidant present and makes use of easy know-how much like pH measurement. Whilst Redox is affected by adjustments in pH this has no vital effect on their performance in cooling water remedy as most cooling towers operate at a stable pH stage.
Bromine biocides are available in two primary kinds, as liquid or slow dissolving tablets. Liquid bromine is dosed using chemical dosing pumps. Bromine tablets or briquettes are dosed utilizing a brominator or erosion feeder device.
Chemical dosing pumps
Two fundamental sorts of dosing pumps can be found:-
Diaphragm pumps using both an electromagnetic solenoid operator or motor. Diaphragm pumps are capable of injecting into high pressures as much as 20 bar depending on the motor driver used. If allowed to pump dry they are going to lose their prime and will require handbook repriming.
Peristaltic pumps use a system of rollers compressing a tube to create a move. These have the advantage that they do not require non return valves to operate and will readily self prime even if run dry. The output strain of peristaltic pumps is however restricted by their design to 1.5 bar on most fashions and 5 bar on high stress units.
Towerpack MTD items
Use greater stress diaphragm pumps (5 bar injection pressure on normal units with 10 bar possibility) together with conductivity bleed-off management using electrodeless upkeep free probe.
Bleed lockout or bleed inhibit timer included as commonplace. Redox control on oxidising biocide items utilizing liquid or tablet bromine.