Dosing and control

Traditionally, boiler house operational duties include the monitoring of day tank chemical treatment levels and the top-up of additional chemicals as required. Also required is the checking of consumable inventory stock levels and the inspection of chemical feed pumps, injection points, automatic controllers, and other items of dosing and control equipment. 

Equipment systems are available that will, periodically during the day or week, activate two pumps to add a prescribed volume of each of these two chemicals into a mixing tank. The tank contents are stirred, HOBr is produced, and the tank contents are then pumped to the cooling water system. Such systems can also incorporate bromine monitors and chart recorders, plus other dosing and control items. 

Much the same is true for standard items of dosing and control equipment, laboratory and field analytical equipment, pretreatment plants, and much of the computer software. 

It is the medium-sized cooling system operator who tends, on average, to have the best dosing and control systems installed. 

Apart from the primary components of a cooling water system, all ancillary equipment such as level controllers, bleed systems, dosing and control systems, low-level alarms, pH controllers, and on-site biocide generation systems should be regularly inspected, cleaned, calibrated, and maintained in good working order. 

Product data information, material safety data sheets (MSDS), dosing and control equipment operating instructions, spares lists, minimum stock holding lists. 

On DAY 7, temporarily stop adding inhibitor and permit the product reserve to naturally fall to the normal level and hold at this point. Prepare the regular maintenance treatment program and check all dosing and control equipment. Remove all cleaning equipment from site. 

Also, it seems to be that, in whatever country considered, the standard method for inhibitor dosing and control tends to be upgraded every 4 to 5 years, with real-time monitoring, microprocessor-controlled systems now leading the way. 

Nevertheless, it is usually expected that such nonchemical control devices will already be in place (although it is still surprising to discover how many cooling towers fail to incorporate such basic items). As a result, we are primarily concerned with the dosing of chemical treatments and the control of program variables. And today, it sometimes appears that there are almost as many permutations of ideas and procedures for dosing and control systems as there are applications for cooling water. 

Dosing and Control Equipment for Open Cooling Systems to Meet Current Basic Needs... 

Shown in Figure 9.2 is a schematic drawing of a basic dosing and control system, with design and layout typical of many cooling systems. 

Fig. 9.2. Typical water treatment program dosing and control arrangements for industrial cooling system (schematic). Nonoxidizing biocides and biodispersant are typically periodically hand-dosed.

Chemical dosing and control systems are often supplied fully assembled and prewired on a skid, and increasingly dosing tanks are mounted inside secondary tanks to prevent the risk of chemical spillage or leaks causing pollution problems. 

These advanced dosing and control systems offer the optimum in cooling system process control. The primary functions they provide are as follows ... 

There is a growing trend for many operators not to have any direct involvement with their cooling system chemical dosing equipment (with regard to the addition of chemical, mixing and chemical dilutions, pump adjustments, and possibly even periodic equipment inspections and maintenance). The equipment may also not be owned by the customer. Rather, the water treatment service companies may lease the equipment to the customer, or provide free-on-loan equipment, together with all chemical dosing and control functions, as part of their services to the facility. 

At 12 and 18 months and prior to necropsy a blood smears obtained from all animals Smears are read in the high-dose and control only unless indicated by toxic effects... 

Changes in plasma-ChE activity in dosed and control animals are shown in Table 4. Over the course of the study, plasma-ChE activity levels in dosed and control animals appear to be more stable than RBC-AChE activity. It was reported that plasma-ChE activity was decreased by about 55% in dosed females at week 7, and by 37.5% in dosed males at week 3. Mean plasma-ChE activity in the female controls exhibited a slow increase over the 13-week test period (from 1743 lU/L at week -1 to 2891 lU/L at week 13). A similar response was seen in the two lowest dose groups of females. In males, mean plasma-ChE activity in controls was lower than preexposure levels (401 lU/L at week -1) at all weeks except week 3 (413 lU/L). In the dosed groups of males, mean plasma-ChE levels were lower than pre-exposure values at all sampling times. Statistical analysis of the plasma-ChE activity indicated that mean values were significantly lower than controls in the mid- and high-dose females at weeks -1, 1, 3, and 7 but not at week 13, and in the high-dose males at weeks 3 and 7. 

---