Filters, Water & Instrumentation, Inc.

You get double advantage from properly maintaining your cooling tower. You not only save water but you also save energy by maintaining a more energy efficient cooling tower system.

It has been estimated that well over 90% of the water used by industry is used in cooling towers.

Cooling water is subject to one of the fundamentals of water treatment – evaporative cycles. When you evaporate water, you leave behind the Dissolved Minerals that were in the water initially. In that way as you evaporate and introduce water to a cooling tower system, you are building up the contaminants in the system. As the cooling system becomes more concentrated, we have the common term of cycles of concentration in the tower. The cycles simply refer to the number of times the incoming contaminant have been concentrated. If you have a system with 100 parts of incoming contamination and you concentrate it 3 times, you have 3 cycles or 300 parts of contaminants.

Each system is different because the incoming contaminants are different. Each constituent of the incoming contamination has its own cycle before it can cause a solubility issue. The trick with the blow-down is to keep any constituent below its solubility level. In some towers it may be iron, in another it may be sulfates. Usually, one of the incoming constituents controls the blow-down level. Whichever constituent is seen to cause the problem first, governs the maximum cycle you can maintain in the tower.

Whoever maintains the tower has an interest in keeping the tower free of contamination so the heat transfer required can be maintained at an economical energy level. Because it’s easier to maintain these solubility levels below their thresholds with increased blow-down, maintaining the tower can waste water. It’s easier to be defensive and blow-down more water than is required. In addition, since chemicals are maintained at levels in the system to keep the tower water from precipitating, when you blow-down more water than you need, you are also wasting chemicals.

There are many people touting super increased concentration ratios and very low blow-down with some exotic, some simple and sometimes esoteric treatment methods. If there were reliable solutions to tower water maintenance with other than addition of chemicals, they would be used throughout industry. Cooling water treatment still uses addition of chemicals in most applications. There is no way around it.

Caveat: If you consider the consequences of not enough blow-down, you need to exercise care in reducing blow-down. If you precipitate solids on heat transfer surfaces, you have very difficult cleaning procedures. The cleaning must be done with some fairly nasty chemicals and they cause considerable disruption of plant operations. This is always the caveat when reducing blow-down.

The water used in cooling towers is used as blow-down and evaporation. Evaporation is inevitable as the evaporative process is what provides the cooling effect.

The item most people focus on is blow-down. Blow-down serves the useful function of removing water with concentrated dissolved minerals before the dissolved minerals have a chance to concentrate and perhaps precipitate out on the heat transfer surfaces.

In addition, and less likely these days, blow-down removes accumulated suspended solids from the tower water which can ultimately settle out and cause blockages in the cooling loops during recirculation of the water through the cooling system. We say unlikely these days because most people with an appreciable size cooling tower system have installed sidestream filters which remove the suspended solids.

If you have not installed a sidestream filter and have kept it maintained and running properly, then you should install one and/or fix the one that you have. For any cooling water system of reasonable size, you should have some kind of filtration.

If you want to save water in tower treatment, you focus on the blow-down. The caveat above noted, nonetheless, there is more water wasted in excessive blow-down that any other industrial process.

First, have whoever maintains your tower explain the blow-down rationale. What incoming constituent or constituents govern the rationale. What item causes the blow-down regime. Frequently it’s something that was developed years ago and is now just considered the safe way to do it.

Which of the minerals or other contaminants govern the blow-down percentage. This requires chemical analysis of the source water first. In addition, a blow-down controller which senses conductivity or TDS makes this automatic. Keeping score or determining how much make-up water and blow-down water helps. In conjunction with degree days, this will help you keep track of your tower efficiency.

None of this is easy. It takes guts. Someone has to want to save the water and the chemicals. Reducing blow-down and saving cooling tower water is difficult but without question, has the most potential for reducing water use in industry. The precipitation caveat aside, the main potential for water conservation in industry is in the artsy, arcane, archaic, and mysterious world of cooling water treatment. You can also save chemicals, and make your systems more energy efficient.

Do you need any other reasons to work in this area?

Take a look at a quick sidestream design schematic on our website for a UV and filter Cooling Tower Water Conservation Design.

You can also take a look at our Website Page for Cooling Water.

Rainwater/Stormwater Reuse Ideas

There are several different options which depend on where the recovered rainwater/stormwater is used.

The uses we currently see are:
1) Flushometer water.
2) Irrigation Water.
3) Water for Gardening and Exterior maintenance which is similar to number 2 above.
4) Cooling Tower Water to make up for Blowdown and Evaporative Losses.

System Design Concepts

Flow Designs – Most of the variations in design are based on the logistics of where the water is collected versus where the reclaimed water is used.

One Design Concept of a Rainwater/Stormwater Reuse system is to recirculate the water intermittently throughout the day through the filter and UV components to keep the system from going septic during low consumption periods.

Alternatively the system pump can send water “once through” the filter and UV and up to the use points.

Another approach is to flow from the collection tanks down by gravity to the points of use. This is easily understood for systems where the water is captured up higher in the building with the use points lower – high rise office and apartment buildings are the trends here.

Finally you can have the filtration/UV loop recirculating independently from the pump which sends water to the use points.

You can actually have variations of all the above if you have several different use points and/or several different collection tanks for the system.

The ultimate design and expense in a retrofit system is the space involved for the storage tanks. Storage tanks and the attendant plumbing are fairly straightforward in new construction. “Shoehorning” in storage tanks and piping in an older facility is more difficult especially difficult for flushometer retrofits. Flushometer retrofits are just about impossible because of the separate plumbing supply lines. Cooling Tower water, gardening and irrigation water are easier retrofits because of the reasonable expense of the new plumbing supply lines.
Rainwater/Stormwater Reuse Components

Refer to drawing “Rainwater/Stormwater Reuse Ideas” dated 5/9/08

System Components are as follows:

Collection Tank(s) are whatever is used to collect the water. The tanks can be underground, at grade, inside or outside.

Pumps are used to either continually recirculate the water through one of the Loop Options and/or provide the pressure and flow needed to get the water at the required flow and pressure up to the system use points. The pumps can be flooded suction, centrifugal external, duplex alternating, in-tank turbine type or whatever may be required. Expansion tanks can be used to more easily run water up to the use points in the system

The filter shown(SAF) is an automatic backwashing 25 Micron screen filter which cleans itself by backwashing to drain. It runs and cleans itself automatically and maintenance free which we consider essential to the operation of a rainwater/stormwater reuse system. Low maintenance is essential in this reuse application in order for the savings on the project to be realized.

The Ultraviolet unit is a non-chemical method to control bacteria. The UV Unit is sized kill bacteria at the system design flow rate.

The Chlorine Addition Option is a tank and chemical feed pump combination which will feed at a measured dosage into the system based on an automatic feedback controller. This option is not nearly as “green” as the added chemical – Clorox – is not a green solution. Clorox can be considered as a supplement to the UV unit when the bacterial load is too high.

The Dye Addition Option is a chemical feed pump and tank combination which will feed dye to the water to add extra assurance that the water sent to the use points will not be consumed as potable water. This is frequently required by code for flushometer water.

If there is a recirculation loop in the system, the intermittent control is typically run by a PLC based processor which allows for changing parameters based on system operation.

Rainwater/Stormwater Reuse Components – 5/9/08

A system that recirculates 60 to 80 GPM and storing and recirculating 10,000 to 20,000 gallons will costs $ 50,000 to $ 60,000. The storage tanks and installation of this system is not included in the pricing above.

You can see more information at our website at the Rainwater-Stormwater Reuse Page.
Also check out the Amiad Page for more details on these modern reusable filtration solutions.

A Recycling Approach

First Step of Recycling – Lean-Out the Process
This is always the first rule. Lean-Out means to minimize everything in the process fluid. A Lean Process will reduce the load on subsequent clean up. Often, this in itself will significantly reduce disposal costs. The first step of recycling, – Lean-Out the Process.

Once we have a “Lean Process”, we go to three general phases – Analysis, Equipment & Implementation.

In the Analysis phase we determine what is present in the existing feedwater and in other make up solutions. Finally we determine what are the on site requirements and existing equipment required to support the process.

In the Equipment phase we secure all materials and have them installed as required.

In the Implementation phase, we will stay with the equipment On-Site in a thorough start-up. This phase is more important than in other process applications because the solutions are custom designed and have to be fine tuned for on-site process variables.

Factors to consider in Recycling

Reduce Transportation & Disposal Costs
Reduce Volumes – Can Increase Concentrations
Reduce Concentrations – Without Increasing Volumes
Reduce Costs of Disposal by Replacement or Substitution
Reduce Current and Potential Future Liabilities
Reduce Dependence on Disposal Contractors
Reduce Surcharges in Discharged Liquids

Membranes in Recycling

Reverse Osmosis(RO) and Ultrafiltration(UF) are Membrane Cross Flow Technologies and are considered as separator/concentrators. Liquid forced through the membrane is clean “Permeate” leaving the contaminants behind in the “Concentrate”. The contaminants are not removed by membrane processes. They are still at the site. They are still in the system in the “Concentrate”. Whenever using RO or UF, you must consider what to do with the Concentrate. In some instances we concentrate to minimize discharge volumes – the same amount of contaminant but in a reduced volume. In other instances, we use the Permeate of the membrane back in the process as clean make-up fluid. In this case we still have Concentrate and we still have to determine what to do with it.