Water Treatment in Boilers

Summary of the Discussion Process in the Oil and Gas Mailing List for September 2006, discussing water treatment in Boilers.

Question:

Dear all, In connection with the contract I will enter with a Boiler supplier, Please enlighten me for Water Treatment in the Boiler, Working pressure 8 Bar and Design Pressure 10 Bar. 1. Parameters measured for water boiler, feed water boiler and condensate boiler. 2. Can provide these STD parameters. Thank you for the conversation

Response 1:

Dear

very interesting issue that was raised, indeed after the boiler itself feed water affairs are on the top list of decisions to buy a boiler or buy electricity. The following parameters you should see carefully:

a. scaling tendency from feed water, if it forms a scale you must first treat it. b. corrosion tendency c. foaming tendencies d. oxigen content, the higher the corrosive e. silica, so it scales in the boiler tube, in the long run low efficiency, hot spots, can also be a tube failure. f. there is volatile material in the WTR, causing carry over, sometimes causing erosion g. PH, Hardness, CO2, silicate, solid disolved.

For that, a significant amount of capital investment must be put in water treatment to produce a suitable boiler feed water, for example via ion exchange, reverse osmosis, chemical dosing, dearation, condensate recicle, etc. the interaction is a bit too complicated, but advise me to hire a professional consultant, or who you think knows to write a few sheets of your water quality and water treatment requirements. The water treatment should be made to purpose, depending on the raw water, so it varies from one area to another. I think other millis will share their experiences.

Response 2: Greetings, When starting a new contract for a plant with a chemical supplier for boiler treatment, it is very sensitive because it concerns the convenience of the Plant from the service provided by the Supplier. It concerns both technical and competitive prices given, the intention is that the costs incurred by the factory to buy chemicals must be balanced with the results of treatment and can save maintenance costs. Why did it happen?

The answer: We need to know that the problem of water treatment includes 2 major problems: Suspended Solid solid material that is still visible to the eye; mud, moss, sand, etc. Dissolved Solid solid material that is no longer visible to the eye because it is in the form of ions dissolved in water.

Suspended Solid treatment is usually done by treating raw water with sedimentation and filtering processes. The tools used are also varied; sedimentation can be by clarification with injected Alum (coagulant), NaOH (pH control) and Polymer (floculant). For Polymers (floculants), Suppliers usually recommend their products. Filter tools are also many kinds. Some have already been mentioned above. Can the tank that contains silica and anthracite sand, can filter from the membrane (RO) and more. Agung can ask directly to the supplier. The parameters; Turbidity is usually <1, pH 6.5 – 7.5 to produce clear water which is good for Feed Water for Boilers. My suggestion, you ask the supplier to also analyze water quality (besides the laboratory of your father) periodically (1 month 1x or 1 month 2x). The goal is to make sure that we get good quality of clear water that fits with supplier control limits and supplier recommendations for feed water of the boiler.

Dissolved Solid Handling After a good pretreatment, it does not mean that the water quality is safe for the boiler, because there are still ions contained in clear water which can cause 3 major problems in pipes, tubing, and drum boilers, namely Corrosion, Deposite, and carry over. For this reason it is necessary to have a demin plant or softener (the use is dependent on raw water quality). Demin Plant usually has 2 tanks (Anode and Cathode Tank). Inside the tank there is Resin, Cathode Resin captures positive ions and Anodes captures negative ions. I mean ion2 is usually Ca + 2, Mg + 2, Fe + 2, SiO2-2, Cl-1 etc. and these ions are parameters that must be measured to determine the high quality of feed water. Usually each parameter has a different limit control for the condition of the water source or clear water produced. Below this is generally a guide to Demin water.

pH = 8, Conductivity <10 micromhos, Total Hardness = Trace, Silica <2.5, Fe <1

The above parameters can also apply to water from Softener. The difference is only in the tank, Softener is only a cathode tank. One more thing, sir, to reduce the dissolved O2, the feed water needs to be heated to 100 C to ensure the remodeling of O2 in the Deaerator. Now, if it is confirmed that the quality of boiler feed water has been OK, then it needs more handling.

First shield: good pre-treatment (more or less as described above) Second shield: Special chemical to recapture ions that escape the demin / softener or deaerator in the drum boiler. Usually this chemical is recommended by the supplier. The purpose of Chemical Boiler injection 1. capture the escape of ions that cause deposits (deposite inhibitors) or can (deposit dispersant) for boilers that have started to crust. the chemical component contains PO4 (phosphate base), this is the parameter measured in boiler water in addition to the parameters in the pretreatment. This chemical is also very important to bind silica which can go into the steam line so that Carry Over does not occur and there is a deposit after boiler equipment (such as Turbine) 2. capture Oxygen which is still dissolved after the Tank Deaerator so that no corrosion occurs in the Drum boiler (corrosion inhibitor), this Chemical is divided into 2 namely Food Grade and Non Food Grade. Then there is a chemical that has the same role but neutralizes the acid which causes corrosion in the condensate line.

At the end of this technicality, I only answer the question at the beginning that all of the above need to be carefully monitored both by the factory and, as a matter of fact, the Supplier as a service after sale. And also ask for inspection when after Running Boiler for 6 months or 1 year. So the costs we incur for treatment are more effective and efficient. Well, maybe there is still something that hasn’t been written in this article, I’m sorry and other colleagues from the mailing list can perfect it again.

Response 3: novianto.fitriawan @ power.alstom.com Hello, how are you sir? Without intending to patronize, I tried to add a little. I am sure there will be other friends who can add more complete and clear. Previously, maybe you could explain more specifically: boiler type, superheated or saturated steam produced, use of steam. Sometimes users have specific steam purity targets. This steam purity target will be requested from the boiler manufacturer to be guaranteed and in the end the boiler manufaturer will ask for the requirements to fulfill the steam purity target for feedwater quality.

The purpose of water treatment is 1. To minimize the accumulation of corrosion products such as metal oxides (iron, copper, or nickel from the pre-boiler piping system), 2. Control impurities such as calcium, magnesium and silica contained in feedwater or make up water which can cause scale, 3. prevents carryover from solid particles to superheater or downstream equipment such as turbine or process, 4. to prevent corrosion.

Based on 8 bar operating pressure (low pressure), approximately ʺstandardʺ (maybe exactly a recommendation or suggestion – the user may adopt or reject it) what is needed is as follows (based on the reference used):

ABMA, “Boiler Water Limits and Achievable Steam Purity For Water Tube Boilers”. Boiler Water: Maximum solid water boiler is 3500 ppm, maximum suspended solid is 15 ppm, maximum total alkalinity is 20% of boiler water solid (700 ppm) as CaCO3, Maximum Fractional carryover is 0.0003.

ASME, “Consensus on Operating Practices for the Control of Feedwater and Water Quality Boilers in Modern Industrial Boilers” a. Water Quality as per ASME Table 1 Boiler Type: Industrial water tube, high duty, primary fuel fired, drum type with superheaters and turbines drives and / or process restriction on steam purity. Make up water percentage: up to 100% feedwater Conditions: includes superheater, turbine drives or process restriction on steam purity.

Feedwater: DO before oxygen scavenger addition (max), ppm = <0.04 Total Iron (Max), ppm = 0.1 Total Cooper (max), ppm = 0.05 Total Hardness (CaCO3), ppm = 0.3 pH range @ 25 deg C = 7.5 – 10 Non Volatile TOC (max), ppm = <1 Oily Matter (max), ppm = <1

Boiler Water: Silica (SiO2), ppm = <150 Total Alkalinity (CaCO3), ppm = <350 Free Hydroxide Alkalinity (CaCO3), ppm = Not specified Specification Conductance @ 25 deg C w / o Neutralization (max), micro mho / cm = <3500

b. Suggested Water Quality Limits as per ASME table 2 Boiler Type: Industrial water tube, high duty, primary fuel fired, drum type Make up water percentage: up to 100% feedwater Conditions: no superheater, turbine drives or process restriction on steam purity. Saturated Steam Purity Target: 1 ppm TDS maximum

Feedwater: Total Hardness (CaCO3), ppm = <0.5 DO before oxygen scavenger addition (max), ppm = <0.04 DO measured after oxygen scavenger addition (max), ppm = <0.07 Total Cooper (max), ppm = 0.05 Total Iron (Max), ppm = 0.1 Non Volatile TOC (max), ppm = <1 Oily Matter (max), ppm = <1 pH range @ 25 deg C = 7.5 – 10.5

Boiler Water: Silica (SiO2), ppm = <150 Total Alkalinity (CaCO3), ppm = <1000 Free Hydroxide Alkalinity (CaCO3), ppm = Not specified Specification Conductance @ 25 deg C w / o Neutralization (max), micro mho / cm = <8000 JIS B8223, “The quality of boiler water feedwater and boiler water”.

Feedwater: pH (25 deg C) = 7 – 9 Hardness as CaCO3 (mg / L) = below 1 Oil and Fat = possibly keep 0 Dissolved oxygen (mg / L) = keep low Boiler Water (treatment method: Caustic Treatment) pH (25 deg C) = 11 – 11.8 M Alkalinity (mg CaCO3 / L) = 100 – 800 P Alkalinity (mg CaCO3 / L) = 80 – 600 Electrical conductivity (micro S / cm) = below 4000 Chloride Ion (mg Cl ions) / L) = below 400 Phosphate Ion (mg PO4 / L ions) = 20 – 40 Sulphite Ion (mg SO3 / L ions) = 10 – 20 Hydrazine (mg N2H4 / L) = 0.1 – 0.5

Hope it helps and hopes that other colleagues can add. Thanks.