Treating and Testing your boiler and what we look for and what we use.
As you saw in our previous blog about understanding NYC feed water and what happens to it in your Low-Pressure Steam Boiler, we saw this water carries impurities that concentrate and will need to be controlled and their potential effects mitigated. Water treatment plays a pivotal role in preventing corrosion, scaling, and fouling/deposition within the boiler system, ultimately enhancing its lifespan and performance. Regular testing of the water used in steam boilers is vital to maintaining optimal conditions and identifying potential issues promptly. In this blog post, we will explore the importance of steam boiler water treatment and testing, the key parameters to monitor, and the various testing methods employed in the industry to control and clean your boiler and its water content.
Water treatment in steam boilers is crucial due to the adverse effects of impurities on the system’s efficiency and longevity. Untreated water can contain dissolved solids, minerals, suspended particles, and gases that, when left unchecked, lead to detrimental consequences.
Let’s take a look at some issues that occur.
Suspended particles and dissolved solids can accumulate as sludge or sediment within the boiler, obstructing flow paths and impairing heat transfer. This buildup not only reduces efficiency but can also cause localized overheating, leading to tube failures and reduced operational lifespan. Furthermore, untreated water can introduce dissolved oxygen and carbon dioxide, which accelerate corrosion processes within the system.
These impurities can cause scaling, which deposits layers of mineral-based compounds on heat transfer surfaces, reducing heat transfer efficiency and leading to higher energy consumption. When Calcium Carbonate, Silica and Magnesium are concentrated, they drop out of solution and form a coating on heat transfer surfaces. Because you are having to over fire the boiler to achieve the same energy output, this stresses the boiler leading to unforeseen repairs.
There are a few potential causes of Carryover of water into the steam lines from bulk water surging in the vessel. One of those is water chemistry. Besides mechanical reasons such as deposits of residual oil, grease, mill scale and protective coating inherent in manufacturing and installation or repairs, or the flame being too big for the combustion chamber, or faulty level controls, there are some water chemistry factors that can cause it.
Too high alkalinity: If this condition occurs the concentration of alkalinity forms a crude type of soap. As the alkalinity in the boiler increases, the viscosity of the boiler water increases. This in turn increases the surface tension on the surface of the boiler water. So, once the surface tension becomes too high, steam that is exiting the boiler will pull water with it. This results in surging of the bulk water up and down, and eventually carryover of boiler water. Carry over pulls water out of the boiler into the steam line. With this type of surging foaming is common.
TDS (total dissolved solids) TSS (total suspended solids): As impurities in the feed water concentrate or if corrosion byproducts from tanks and pipes/lines that feed the boiler or return water to the boiler come back in, it drives up the levels of TDS and TSS causing uneven heating of the water, and similar issues.
Your sensors and alarms will indicate if water levels are fluctuating or if you have a sight glass you will see the level rise up and down. Skim-line blow down will help alleviate the issue.
To maintain optimal boiler performance, several key parameters must be regularly tested and monitored. These parameters provide valuable insights into the water quality and the overall condition of the steam boiler. Some of the following are essential parameters that should be analyzed during water treatment testing:
- pH Level: pH is a measure of the water’s acidity or alkalinity. Maintaining the correct pH range helps prevent corrosion and scale formation. The acceptable pH range typically falls between 8.5 and 9.5, depending on the boiler design and materials.
- Conductivity: Conductivity is a measure of the water’s ability to conduct electricity and indicates the concentration of dissolved ions. High conductivity levels suggest the presence of dissolved solids. Monitoring conductivity helps assess the effectiveness of water treatment processes and determine the need for further treatment.
- Total Alkalinity: Alkalinity can occur in three different forms depending on the pH levels of the water. These can come in the form of carbonate (CO3), bicarbonate (HCO3), or hydroxide (OH).
- Total Dissolved Solids (TDS): TDS refers to the sum of all inorganic and organic substances dissolved in water. Excessive TDS levels contribute to scale formation, reducing heat transfer efficiency and promoting corrosion. Regular testing ensures that TDS levels remain within acceptable limits.
- Total Hardness: Hardness is a measure of the concentration of calcium and magnesium ions in the water. These ions contribute to scale formation and can reduce the effectiveness of water treatment chemicals. Monitoring and controlling hardness levels prevents scale accumulation and minimize the associated problems.
- Chloride Levels: Chloride ions can accelerate corrosion processes, especially in high-temperature environments. Elevated chloride levels can lead to pitting corrosion, stress corrosion cracking, and increased corrosion rates. Testing chloride levels helps prevent corrosion-related failures and ensures the longevity of the boiler system.
- Dissolved Oxygen: Dissolved oxygen promotes corrosion within the boiler system. Regular testing is crucial to detect and eliminate any dissolved oxygen, either through mechanical deaeration or chemical treatments such as oxygen scavengers.
- Suspended Solids: Monitoring suspended solids helps prevent sludge and sediment buildup, which can hinder heat transfer, obstruct flow, and promote corrosion. Proper filtration and periodic testing are necessary to control suspended solids levels.
- Corrosion inhibitor: is a product designed to interrupt the bond between oxygen and iron (H2O and Fe). When these combine or exchange positive and negative ions they form Red Rust or FeO2 or Hematite corrosion. These inhibitors form a film on surfaces and interrupt the oxygen and iron bond leaving a passivated surface.
Boiler Water Treatment Testing Methods: Several testing methods are commonly employed to assess the quality of water used in steam boilers. These methods provide accurate measurements of various parameters, allowing operators to make informed decisions regarding water treatment. Here are some widely used testing methods:
- Titration: Titration involves adding a reagent to a water sample until a color change occurs. This method is frequently used for pH testing, alkalinity determination, and testing the effectiveness of water treatment chemicals.
- Conductivity Meters: Conductivity meters measure the electrical conductivity of water, which indicates the presence of dissolved ions. These meters provide real-time measurements and are used to monitor conductivity levels in steam boilers.
- Colorimetric Analysis: Colorimetric analysis involves using reagents that produce color changes proportional to the concentration of a specific parameter. Colorimetric test kits are available for testing various parameters such as total hardness, chloride levels, and dissolved oxygen.
- Spectrophotometry: Spectrophotometry utilizes the absorption or transmission of light through a water sample to measure the concentration of specific parameters. This method provides highly accurate results for testing a wide range of parameters, including dissolved solids, alkalinity, and more.
- Inductive Coupled Plasma (ICP) Analysis: ICP analysis is a sophisticated technique used for analyzing trace metals and elements in water. It provides precise measurements of elements such as iron, copper, and zinc, which are crucial indicators of corrosion and scaling potential.
Steam boiler water treatment testing plays a vital role in maintaining efficient and reliable boiler operation. Regular testing allows for the detection of impurities and the assessment of water quality, ensuring that appropriate treatment measures are implemented. By monitoring parameters such as pH, conductivity, TDS, hardness, chloride levels, and dissolved oxygen, operators can prevent scaling, corrosion, and fouling issues that can compromise boiler performance and longevity. Implementing accurate testing methods, such as titration, conductivity meters, colorimetric analysis, spectrophotometry, and ICP analysis, enables operators to make informed decisions about water treatment and take proactive measures to optimize boiler efficiency and reliability. With proper water treatment testing, steam boilers can operate at their peak performance, reducing downtime, minimizing maintenance costs, and improving overall productivity in industrial and commercial applications.
Topic 2: Chemical Treatments for Steam Boiler Water: Chemical treatments play a vital role in steam boiler water treatment programs. They help prevent corrosion, control scale formation, and minimize other detrimental effects. This section will explore different chemical treatments used in boiler water treatment, including oxygen scavengers, alkalinity builders, scale inhibitors, and corrosion inhibitors. We will discuss their functions, mechanisms, and the importance of proper dosage and monitoring to ensure their effectiveness.
Oxygen scavengers remove dissolved oxygen from the feedwater to prevent oxygen pitting corrosion. Alkalinity builders help maintain the desired pH level. Scale inhibitors control the formation of mineral deposits on heat transfer surfaces. Corrosion inhibitors form a protective film on metal surfaces, preventing corrosion. Neutralizing amines and filming amines to help protect the steam and condensate return system piping. In most applications, neutralizing amines are added to neutralize the carbonic acid and raise the pH of the condensate to reduce corrosion.
This type of corrosion inhibitor acts by forming a protective oxide film on the surface of the metal. It causes a large anodic shift that forces the metallic surface into the passivation region, which reduces the corrosion potential of the material. Some examples are Sodium Nitrite and molybdates. Sodium nitrite is an anodic inhibitor and interferes with the anodic process (metal dissolution) and reduces the corrosion rate by suppressing the anodic reaction, through the formation or maintenance of a passive film on the metal surface. Blowdown is essential to give nitrite access to surfaces under sludge deposits.
These inhibitors slow down the cathodic reaction to limit the diffusion of reducing species to the metal surface. Cathodic oxygen scavengers such as Sodium Sulfite and Diethyl hydroxylamine (DEHA) are examples of this type of inhibitor. Proper selection and dosage of these chemicals are critical to their effectiveness. Regular monitoring and testing of water chemistry, coupled with adjusting chemical dosages as necessary, ensure optimal performance and protection against scaling and corrosion.
While water treatment is invaluable and integral to keeping your boiler efficient and extending the life of the boiler, it is not magic. Impurities will concentrate, contaminants will enter your boiler and there is only one way to remove them, and that’s by releasing or draining them by opening a blowdown valve that’s piped to your drain in the boiler room. If you don’t blowdown your boiler no amount of water treatment will stop the negative impact that not blowing down has. It’s the best way to control your Total Dissolved Solids, Chlorides and your Total Suspended Solids. Besides blocking heat transfer and contributing to carryover/surging, your valves, floats, probes and sensors can get hung up and clogged.
What Does Blowing Down a Boiler Mean?
Blowing down a boiler refers to the process of removing water from the boiler with any excess bottom sludge and dissolved solids. Companies need to blow down their boilers regularly, since the concentration of dissolved solids from makeup water increases in a boiler after removing pure water as steam. A company that periodically blows down its boiler’s water can better maintain a consistent number of cycles of concentration.
Why Do I Need to Blow Down My Boiler?
Only pure water leaves the boiler as a byproduct of steam, leaving behind any dissolved solids. Even though the condensate gets pumped back into the boiler, some of this condensate inevitably becomes lost, requiring replacement with more water. Over time, the concentration of dissolved solids from the makeup water increases in the boiler as pure water off-gases as steam. Due to this increase in dissolved solids, your boiler can see more corrosion sludge and scale. “Cycles of concentration” is the technical term for the relationship between the level of dissolved solids in the boiler and the dissolved solids in the feedwater. When you periodically drain water from the boiler, you can maintain a consistent number of these cycles. This process is essential to prevent scale and corrosion buildup or sludge in your boiler. Alongside the need to remove dissolved solids to reduce scale and corrosion, boiler blowdown is critical to avoid overheating. When too much sludge or dissolved solids build up on the boiler’s heating surfaces, the metal can overheat. This overheating can cause a pressure vessel to fail, resulting in expensive repairs and lost productivity. Besides overheating, high concentrations of dissolved solids can cause boiler water to carry over into the steam, leading to damaged equipment and piping. Without proper blowdown it may become necessary to take your boiler offline and perform an emergency cleaning or boil-out. Our overall aim is to have uninterrupted steam production so preventative maintenance steps like water treatment and management of the water cycling is imperative.
What Is the Difference Between Bottom and Skimmer or Top Blowdown?
Companies can remove water from their boiler from two main points — the bottom drain valve and a skimmer drain valve that enters the boiler somewhere just slightly below the water surface. Since you can drain water from these different points, you will run into two blowdown methods — bottom blowdowns and skimmer blowdowns. While skimmer blowdown is the most efficient means of controlling cycles of concentration, bottom blowdown is essential to prevent sludge buildup.
Both boiler blowdown methods are crucial to a boiler’s proper operation, so you will want to know how each of them works.
Bottom Blowdown: The concentration of sludge is highest at the bottom of the boiler, and bottom blowdown will remove the sludge that precipitates during boiling. Since unchecked sludge can end up affecting heat transfer systems and cause tube or vessel failure, bottom blowdown is essential. When a company performs this method, they will briefly open a valve or multiple valves to allow sludge to pass out of the boiler.
Skimmer Blowdown: The concentration of dissolved solids is most significant at a point six to eight inches below the water surface, and a skimmer blowdown, also called surface blowdown, aims to remove water from this depth. By performing skimmer blowdowns, companies can extract the greatest amount of solids in the least amount of boiler water.
How Often Will I Need to Blow Down My Boiler?
Generally, companies that rely on boilers perform bottom blowdown once a shift or once a day. However, better-quality feedwater can extend the intervals between bottom blowdowns. Likewise, skimmer blowdown frequency and volume depend primarily on the amount of condensate returned to the boiler and the quality of your makeup water.
What Is the Proper Boiler Blowdown Procedure?
Since boiler blowdowns are so valuable, you’ll likely want to know how to complete the process. Bottom blowdowns and skimmer blowdowns have different procedures, so you must understand the distinction. Find out more about the steps you should take to perform each type of boiler blowdown below.
Bottom Blowdown Procedure:
- Open the valves: The bottom drain line on your boiler usually has two valves — a slow-opening gate valve and a quick-opening knife valve. The proper way to bottom blow down a boiler is to start with both valves fully closed. Next, open the knife valve first before completely opening the gate valve.
- Perform the blowdown procedure: With the valves open, you can then blow down the boiler. You can often determine how long to blow down your boiler by consulting with water treatment professionals, longer for larger vessels and shorter for lower volume vessels. To thoroughly blow down the boiler, you will close the gate valve after a specific amount of time has passed. You will want to pay attention to your gauge glass’ water level, as your boiler may need shorter blowdown cycles to ensure it has the right water level.
- Repeat blowdown procedure: After you close the gate valve, you’ll want to repeat the opening and closing of the gate valve three times. By repeating the blowdown procedure, you’ll rock the water in the boiler and work the sludge toward the drain line.
- Close valves in sequence as required.
Skimmer Blowdown Procedure:
- Skimmer blowdowns also have unique needs you should be aware of to get the best results possible. Some skimmer blowdowns often involve automated processes that a water treatment professional sets the rate for, you don’t need to do as much to perform the blowdown procedure. Skim line piping is at water level approximately ¾ way to top of the vessel.
- Though skimmer blowdowns don’t require as much operator interaction, you’ll still need to use a properly calibrated conductivity meter to determine the amount of skimmer blowdown needed. Based on your meter’s reading, you’ll want to use a needle valve or flow throttling valve to transfer boiler water through the valve into a skimmer pipe.
Finally, it is essential to blow down the safety valves, level switch and sight glass once every week to ensure they work when needed.
What happens if Blowdown hasn’t happened properly or at all?
While the efficiency of your boiler is not optimal because of this reason, there is a way to remedy the situation and hit the reset button from a chemistry perspective. You can add an Alkaline cleaning product such as TriSodium Phosphate or Sodium Hexametaphosphate to disperse TSS and TDS accumulations and sequester what’s in the bulk water. This is known as a Boil-out of your boiler. The cleaning compound is added for a minimum of 2 hours to the boiler and will run to circulate and have the appropriate contact time, then the boiler is drained to let the impurities out. Depending on how much sludge has accumulated it may be necessary to physically power wash the interior of the vessel.
What is the procedure for Boiling out and cleaning your boiler?
- Add the determined amount of cleaning compound.
- Remove safeties and blank off, fill the boiler to the top, close it up and fire boiler on low load. Allow it to circulate for a minimum of 2 hours.
- Shut off electrical and fuel supplies as necessary.
- Isolate the boiler by closing the main steam gate valve and boiler feed water valve, drain the boiler, and open all hand hole, manhole, and capped ports.
- Using a high-powered pressure washer, power wash the interior of the waterside through all open ports to dislodge scale and debris from the interior steel boiler tubes and flush out all dislodged scale and debris through the boiler drain.
- Replace the existing water level gauge glass equipped with necessary seals and reinstall all existing covers on opened hand hole, manhole, and capped ports equipped with new gaskets. Refill the boiler and open the main steam gate valve and boiler feed water valve.
- This boiler now has raw exposed surfaces because the cleaning remove layers of passivation, the surfaces will need to be re passivated with a dose of corrosion inhibitor as soon as possible.
- Now have unimpeded heat transfer with a reset bulk water from a chemistry point of view and the regular treatment and testing program should be continued.