Specification sheets for all major equipment to be treated. Knowledge of equipment details, size, type, internal components, operating parameters, etc., is crucial for selection of chemical treatment programs. This applies to many systems in the plant. Here’s a rundown of some key elements and necessary details.
1. Makeup water treatment system (which may include, but isn’t limited to, pretreatment screening devices, settling basins, clarifiers, micro- or ultra-filters, reverse osmosis units and ion exchangers):
• inlet water temperature range; and
• historical raw water analysis.
2a. Cooling water systems (whether once-through or cooling-tower based):
• flow rates; and
• system materials, including heat-exchanger tube materials.
2b. Cooling-tower based systems:
• tower size and materials of construction;
• tower type (typically counterflow or crossflow, mechanical draft);
• system volume;
• chemical treatment (current program, including scale/corrosion control chemicals and biocides used, as well as treatments not allowed); and
• typical operating data, including cycles of concentration (COC) being maintained in the tower, temperature difference across the tower at various seasonal conditions, and seasonal recirculating rates.
3. Process water and closed cooling water systems:
• heat exchanger and piping materials;
• heat exchanger operating temperatures; and
• basic chemistry of process fluids on the other side of the heat exchangers (to identify what impurities a leak would introduce into the condensate return).
4. Steam generators:
• type and fuel source;
• operating pressure;
• current condensate/feedwater and boiler water chemical treatment programs; and
• description of the condensate return system.
5. Waste stream discharges:
• current plant National Pollutant Discharge Elimination System (NPDES) permits;
• any permitting of particulate matter less than ten microns (PM10) in cooling tower air exhaust; and
• any cooling tower blowdown limitations.
Also important is a history of equipment upsets or failures to alert the water treatment supplier to conditions that have caused problems in the past. Due to the harsh conditions that may exist in some systems such as steam generators, chemical treatment often can be described as “walking on the razor’s edge,” where even seemingly slight upsets may have major consequences.
We have been involved in numerous pre-bid meetings where the operating company invited all the vendors to one meeting and scheduled perhaps just a couple of hours at most for equipment and system inspection. The motive is to save costs — but such an arrangement hampers knowledge transfer. For starters, placing vendors together inhibits the airing of questions and comments because suppliers want to avoid tipping off the competition. Much better information exchange will occur if vendor visits are scheduled individually. Also, make time available for the supplier to meet with plant operators and technical personnel and to tour the systems that require treatment.
Some actual examples of what not to do include:
• giving suppliers ten-day notice to inspect 35 plants;
• providing two-day notice to be at the site for a plant walkdown; and
• not doing a walkdown but instead simply handing suppliers a makeup water sample and telling them to design a program based on that analysis.
Another common mistake is not allowing the vendor to use its expertise.
Many times, an RFP will arrive in which the owner or owner’s engineer has established control parameters without giving proper, if any, thought to the technical details involved. This applies to equipment as well as chemicals. A classic example we frequently observe is an RFP that specifies an elevated COC for the cooling tower. Apparently, the designers believe that a high COC provides environmental benefits because of reduced blowdown. They don’t realize that most of the water loss from a cooling tower is due to evaporation and that as the COC increases much above six or so, the water savings in the blowdown become minimal. On the other hand, chemistry control gets much tougher as COC rises.
Another example, one particularly prevalent in the power industry, is that of RFPs blindly calling for injection of an oxygen scavenger (reducing agent) into the condensate/feedwater systems of the steam generators. Unless the feedwater system contains copper alloys — and virtually no modern combined cycle units with heat recovery steam generators (HRSGs) do — this chemistry is outmoded. In fact, it’s long been established that reducing agents induce a phenomenon known as flow-accelerated corrosion (FAC) in feedwater piping, economizers, attemperator piping and low-pressure circuits of HRSGs (Figure 2). A number of FAC-induced failures have caused fatalities over the last three decades.
We have highlighted some of the issues and omissions that undermine getting the most appropriate water treatment programs. Following the pointers presented here will help your water-treatment vendor come up with the best option for your site. The old mindset that “water is water” can lead to major failures at industrial plants.
KEVIN BOUDREAUX is a member of the technical staff of ChemTreat, Glen Allen, Va. BRAD BUECKER is a senior technical publicist for ChemTreat. Email them at email@example.com and firstname.lastname@example.org.