Understanding Boiler Water Chemistry
Introduction: Low pressure steam boilers are widely used in commercial and residential buildings, schools, and processes in New York City to generate heat or steam to heat hot water in coils. However, without proper water treatment, steam boilers can fall foul of numerous issues that impede their efficiency and reliability. In this blog post we will delve into boiler water treatment and examine its role in maintaining optimal boiler performance. We will also discuss the importance of boiler water chemistry.
Understanding Boiler Water Chemistry: Boiler water chemistry is a critical aspect of steam boiler water treatment. It involves understanding and controlling the various parameters that influence water quality in the boiler system. These parameters include pH, alkalinity, dissolved oxygen, hardness, chlorides, and conductivity.
It’s important to first understand the make-up of Boiler Feed Water, or New York City water supply, where it comes from and what is contained in it, as this water affects your boiler water chemistry.
Here are some relevant excerpts from the New York City Drinking Water Supply and Quality Report (2022) Here is the link to the full report for anyone interested in a more detailed look: 2022-drinking-water-supply-quality-report.pdf
Where does my water come from?
As you can see above, the major source of our water supply is from the Catskill/Delaware watersheds and the Croton Watershed
What is in my water?
Detected Conventional Physical and Chemical Parameters
| PARAMETER | NYSDOH MCL (Highest Level Allowed) | EPA MCLG (Ideal Goal) | # SAMPLES | RANGE | AVERAGE | MCL VIOLATION | LIKELY SOURCES IN DRINKING WATER |
| Alkalinity (mg/L CaCO3) | – | 308 | 15 – 70 | 21 | No | Erosion of natural deposits | |
| Aluminum (µg/L) | 50 – 200 (1) | 308 | 7 – 78 | 19 | No | Erosion of natural deposits | |
| Barium (mg/L) | 2 | 2 | 308 | 0.01 – 0.04 | 0.02 | No | Erosion of natural deposits |
| Bromide (µg/L) | – (2) | 8 | 8 – 35 | 20 | No | Naturally occurring | |
| Calcium (mg/L) | – | 308 | 5 – 26 | 7 | No | Erosion of natural deposits | |
| Chloride (mg/L) | 250 | 308 | 10 – 80 | 15 | No | Naturally occurring; road salt | |
| Chlorine Residual, Free (mg/L) | 4 (3) | 15,240 | ND – 1.2 | 0.6 (3) | No | Water additive for disinfection | |
| Chromium (µg/L) | 100 | 308 | ND – 3 | ND | No | Erosion of natural deposits | |
| Color – distribution system (color units – apparent) | – | 13,413 | 3 – 54 | 7 | No | Presence of iron, manganese, and organics in water | |
| Color – entry points (color units – apparent) | 15 | 1,825 | 3 – 18 | 7 | No | Presence of iron, manganese, and organics in water | |
| Copper (mg/L) | 1.3 (4) | 1.3 | 308 | ND – 0.054 | 0.006 | No | Corrosion of household plumbing; erosion of natural deposits |
| Corrosivity (Langelier index) | – (5) | 257 | -2.88 to -1.05 | -2.25 | No | ||
| Fluoride (mg/L) | 2.2 | 4 | 2,071 | ND – 0.8 | 0.7 | No | Water additive which promotes strong teeth; erosion of natural deposits |
| Hardness (mg/L CaCO3) | – | 308 | 16 – 99 | 24 | No | Erosion of natural deposits | |
| Hardness (grains/gallon [US]CaCO3) (6) | – | 308 | 1 – 6 | 1 | No | Erosion of natural deposits | |
| Iron (µg/L) | 300 (7) | 308 | ND – 76 | 31 | No | Naturally occurring | |
| Lead (µg/L) | 15 (4) | 308 | ND – 6 | ND | No | Erosion of natural deposits | |
| Magnesium (mg/L) | – | 308 | 1 – 8.6 | 1.7 | No | Erosion of natural deposits |
| Manganese (µg/L) | 300 (7) | 308 | ND – 49 | 16 | No | Naturally occurring | |
| Nickel (µg/L) | – | 308 | ND – 1.2 (8) | ND | No | Erosion of natural deposits | |
| Nitrate (mg/L nitrogen) | 10 | 10 | 308 | 0.08 – 0.45 | 0.13 | No | Runoff from fertilizer use; leaching from septic tanks, sewage; erosion of natural deposits |
| pH (pH units) | 6.8 – 8.2 (9) | 15,240 | 6.8 – 10.1 (9) | 7.3 | No | ||
| Phosphate, Ortho- (mg/L) | 1 – 4 (9) | 11,025 | 0.8 – 4.8 (9) | 2.2 | No | Water additive for corrosion control | |
| Potassium (mg/L) | – | 308 | 0.5 – 2.6 | 0.7 | No | Erosion of natural deposits | |
| Silica [silicon oxide] (mg/L) | – | 231 | 2 – 6.4 | 2.7 | No | Erosion of natural deposits | |
| Sodium (mg/L) | NDL (10) | 308 | 7 – 53 | 12 | No | Naturally occurring; road salt; water softeners; animal waste | |
| Specific Conductance (µS/cm) | – | 15,238 | 76 – 488 | 101 | No | ||
| Strontium (µg/L) | – | 308 | 15 – 79 | 22 | No | Erosion of natural deposits | |
| Sulfate (mg/L) | 250 | 308 | 3 – 35 | 5 | No | Naturally occurring | |
| Temperature (°F) | – | 15,240 | 35 – 83 | 56 | No | ||
| Total Dissolved Solids (mg/L) | 500 (1) | 258 | 39 – 244 | 62 | No | Metals and salts naturally occurring in the soil; organic matter | |
| Total Organic Carbon (mg/L) | – | 408 | 0.7 – 2.0 | 1.7 | No | Organic matter naturally present in the environment | |
| Total Organic Carbon – source water (mg/L) | – (2) | 8 | 2.1 – 4.2 | 3.1 | No | Organic matter naturally present in the environment | |
| Turbidity (11) – distribution system (NTU) | 5 (12) | 13,413 | ND – 4.1 | 1.0 (12) | No | Soil runoff | |
| Turbidity (11) – source water (NTU) | 5 (13) | – | – | 2.0 (13) | No | Soil runoff | |
| Turbidity (11) – filtered water (NTU) | 0.3 (14) | – | – | 0.4 (14) | No | Soil runoff | |
| UV 254 (absorbance/cm) | – | 365 | 0.011 – 0.045 | 0.032 | No | Organic matter naturally present in the environment | |
| Zinc (mg/L) | 5 | 308 | ND – 0.036 | ND | No | Naturally occurring |
When this water is fed into your boiler, it is important to understand what happens to it in your boiler, how it reacts and how it transforms from the boiler’s process. See below for typical boiler feed systems.
All those items – let’s call them impurities, in the New York City water supply, listed above end up concentrating, because pure water leaves as steam and all those impurities that have a specific gravity or weight greater than H2O or water are left behind. So as the total volume of water is evaporated, what’s left behind in the vessel is known as a “cycle”.
It’s important to blowdown your boiler to let these concentrated impurities out because they block heat transfer and increase corrosion. Keeping blowdown to lower rates (doing it in small amounts on a regular basis) reduces your water usage and energy loss. Not blowing down is detrimental to maintaining correct operation and the longevity of your boiler. These impurities can also form a coating on the surfaces of your boiler, tubes, and coils in the form of scale. Hardness and corrosion by products in water both suspended and dissolved, lead to scale formation, which reduces heat transfer efficiency. A 1/8th of an inch scale deposit can lead to a 20% loss of efficiency.
In my next blog we will delve further into how we properly measure and control these cycles.
Besides these impurities, when steam is condensed and returned to the boiler it forms carbonic acid, so we must boost the Alkalinity or pH to compensate for this. So, when we monitor your boiler and make adjustments in treatment based on testing and application of product, here is what we are looking to interpret and control.
Alkalinity helps stabilize the pH and prevent fluctuations.
pH indicates if your boiler water is in an acidic, neutral, or base state.
Dissolved oxygen can cause corrosion, so its levels or ability to bond with iron must be minimized.
Hardness and corrosion by products in water both suspended and dissolved, lead to scale formation, which reduces heat transfer efficiency. A 1/8th of an inch scale deposit can lead to a 20% loss of efficiency leading to increased water and energy usage.
Conductivity is a measure of the total dissolved solids in the water. Understanding these parameters and their desired ranges allows operators to monitor and control the water chemistry effectively, ensuring optimal boiler performance and longevity.
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.
Chlorides are the ion, Cl-, associated with common salts such as NaCl, MgCl2, and CaCl2 and at higher levels are an indicator that its time to increase blowdown or clean, drain and refill your boiler.
So, both Oxygen and Mineral deposition are problems for boilers.
Which one should I be most concerned about? The answer is both, but corrosion, more so than scaling. The mineral content of New York City (Silicate, Magnesium and Calcium Carbonate) is present at lower levels. If there were higher concentrations, we would require a water softener to remove these impurities but since NYC water is less or only moderately hard, we don’t have to worry so much about these (unless you don’t blowdown your boilers!!!).
How do we know? There is a way to predict scaling and deposition rates and rates of corrosion of any water supply by using something called the Langelier Scale Index (LSI)
| pH =7.3 Conductivity / TDS + 62 ppm (TDS) [Ca2+] = 7mg/L [HCO3–] = 17.1 mg/L Water temperature = 56 degrees F | LSI = pH – pHs pHs = (9.3 + A + B) – (C + D) where: A = (Log10[TDS] – 1)/10 = 0.15 B = -13.12 x Log10(oC + 273) + 34.55 = 2.09 at 25°C and 1.09 at 82°C C = Log10[Ca2+ as CaCO3] – 0.4 = 1.78 D = Log10[alkalinity as CaCO3] = 1.53 |
pH= 9.7
Water is undersaturated with respect to calcium carbonate. Undersaturated water has a tendency to remove existing calcium carbonate protective coatings in pipelines and equipment.
LSI = -2.4
Serious corrosion potential
In conclusion it’s important to understand you water supply and how it will affect the process you use it for so you can protect your equipment, ensure the safety of its operators, and save of the cost of water usage and the cost of the fuel medium used to fire the furnace to boil the water. Reach out to us at Controlled Combustion if you want to find out more and have us partner with you to manage your water and mitigate corrosion and deposition of impurities.