Operating process water systems involves managing many factors to ensure that your operating goals are achieved in the most technically and financially efficient method possible. The heat transfer fluid (water) itself provides a number of those factors, including how well the water is treated for the specific application. In fact, you may not realize the full impact that water treatment has on achieving your goals. Following are the top three problems that you may not have realized were related to water treatment.
1. Water Consumption
Operating a steam or evaporative cooling system requires that water loss occur due to “vent losses” or evaporation in the case of cooling. What does water treatment have to do with it? In both cases, the concentration of minerals (Total Dissolved Solids or TDS) increases as water is evaporated for steam or cooling. The ratio of system TDS to makeup water TDS is called the Cycles of Concentration (COC) and should be a major focus point in your water treatment program.
If your water bill is high, you may want to check on the Cycles of Concentration of your system, since poor control of TDS can lead to a huge difference in water consumption that hits right in the pocketbook.
As an example, a cooling tower system that brings in makeup water at a TDS of 250 ppm and maintains a circulating water concentration of 1000 ppm is running at 4 Cycles of Concentration. At this controlled level, a system that evaporates 10,000 USG/day (which is a function of heat rejection), will need to bleed 3,333 USG/day and will therefore makeup 13,333 USG/day.
As an example, let’s assume that due to a malfunctioning level control, the level is allowed to rise and water is lost continuously from the overflow outlet of the cooling tower basin. Now, when measured, the circulating water concentration will be 350 ppm. Therefore, the Cycles of Concentration of the system will be 350 ppm/250 ppm = 1.4 COC. Under these operating conditions, the system will still evaporate 10,000 USG/day, but bleed (or in this case, water loss) would be 25,000 USG/day for a total makeup of 35,000 USG/day!
At current typical municipal water rates, a problem like this could cause a spike in your water bill of $5,000 per month!
2. Cooling Capacity
Modern HVAC systems are designed to operate very efficiently. Chillers, which are a significant component in many large building systems, have evolved with many design efficiencies being implemented, including the emergence of super-enhanced tubes that maximize the surface area available for heat transfer. The enhancing is similar to rifling – ridges and valleys are machined into the tubes to greatly increase the surface area for heat transfer available in tubes of the same diameter. Machines with this enhancement are certainly much more efficient – but did you realize that now your water treatment plays an even greater role in ensuring you maintain your cooling capacity as initially designed?
Chiller condenser tubes transfer heat from the refrigeration cycle to cooling tower water, where heat is finally rejected through evaporation. Imagine what will happen if those tubes become fouled. Under average conditions the chiller will expend more energy, but will still be able to reject the necessary heat from the system. However… put it under stress on a very hot and humid day and suddenly you will no longer be able to maintain your temperature setpoint! The problem is not design related – we’re assuming the system is properly designed and capable of handling the load. The problem and the solution is with water treatment!
Due to the emergence of super-enhanced condenser tubes, it is no longer acceptable to have any fouling, since the impact of “filling in” the rifling results in a very large impact on cooling capacity. Scaling, insufficient filtration, and bio-fouling are all potential causes for decreasing cooling capacity and dealing with them should be the focus of a well-designed water treatment program.
3. Production Output
Let's consider the following scenario - You operate a mid-size industrial steam plant. Steam is used in your production application in a 24/7 process. Your water treatment professional has recently been recommending the replacement of your aging boiler blowdown controls, which are failing to control accurately anymore. They point to evidence of carryover in your steam condensate that is occurring because sometimes boiler blowdown is insufficient. What’s the big deal?
As a manufacturing facility trying to maximize output, you may have a big problem! Steam boilers that produce saturated steam will never make steam that is 100% dry. A small percentage of the steam that is produced will still be liquid water. The goal is to keep this to a minimum, since by weight liquid water carries much less energy than steam (Water at 100psig – 67.97 BTU/lb, Steam at 100psig – 1037.2 BTU/lb).
The term Steam Dryness is typically used to define the relative dry steam content vs. liquid water content. For this case, let’s say normal conditions are 98% dry steam, 2% liquid. Therefore, the energy content will be 1017.9 BTU for every pound of steam produced.
Next, let’s consider a failing blowdown controller allowing TDS and alkalinity levels in the boiler to rise, leading to excess foaming of the boiler water and carryover. In this case, let’s look at a relatively mild scenario where Steam Dryness drops to 90%. Now, the energy content will be 940.3 BTU per pound of steam produced, or 7.6% less.
What is the impact of 7.6% percent less energy delivered to your process application? It could mean a noticeably increased time to manufacture product and lost profit for the plant!
The chemistry of the water in your system can have unexpected consequences for your operation. These examples illustrate the value of working with a trusted and reliable water treatment company.