Post a Comment Hi all, This article is written based on practical experience.. If liked, share with others, or any suggestions leave in comment box. What do you mean by Statics? How do you calculate Boiler HP dosing system capacity.
Phosphate treatment is preferred in drum type boilers. In this Phosphate especially Tri sodium phosphate is added at the boiler drum which is operating at high pressure so called HP dosing system through HP dosing system. If it is dosed at feed pipe, it may react with impurities and sludge may be deposited at the feed line. Phosphate reacts with calcium and magnesium forms less sticky, loose and non-adherent sludge instead of hard scale.
This sludge remains in the boiler water in suspended condition and then, removed from the boiler through blow down Other than TSP, disodium phosphate Na2HPO4 and monosodium phosphate NaH2PO4 are used in boiler for dosing. Let us calculate phosphate consumption. Shows neutralising tendencies, main function however is to coat piping with a molecular water repellent protective film.
Adding in X-over pipe-reduces corrosion of copper alloys Dearator only effective as a feed heater. Adding after dearator -Dearator correctly performing as a dearator and feed heater. If possible the best system is to have a changeover to allow norm inj into the X-over at sea and injection after the dearator when the turbine shut down.
Oxygen scavengers also used to allow magnetite Fe 3 O 4 layer to form in the boiler. Due to level of decomposition of Na 2 CO 3. Continue reading. Your email address will not be published. Note: Entering wrong username in the login form will ban your IP address immediately. Entering wrong password multiple times will also ban your IP address temporarily. Log in. Boiler Water treatment. Apr 29, Posted by DieselShip. Sodium Phosphate Calcium Carbonate Calcium Sulphate Magnesium Sulphate All in this column precipitated as hydroxide or phosphate based sludges All in this column form sodium salts which remain in solution.
Tags: boiler feed water treatment , boiler water dosing , boiler water tests , boiler water treatment. Newer Marine shipboard Reverse Osmosis system.
Back to list. Sep 3, Posted by Ram Govindasamy 2 comments. Boiler basics and types of boilers Common issues found on Boiler feed water Boiler water treatment fundamentals Water Treatment P Apr 11, at Jul 19, at Once deposition starts, particles present in the circulating water can become bound to the deposit. Intraparticle binding does not need to occur between every particle in a deposit mass. Some nonbound particles can be captured in a network of bound particles.
Binding is often a function of surface charge and loss of water of hydration. Iron oxide, which exists in many hydrated and oxide forms, is particularly prone to bonding. Some silicates will do the same, and many oil contaminants are notorious deposit binders, due to polymerization and degradation reactions.
In addition to causing material damage by insulating the heat transfer path from the boiler flame to the water Figure , deposits restrict boiler water circulation. They roughen the tube surface and increase the drag coefficient in the boiler circuit.
Reduced circulation in a generating tube contributes to accelerated deposition, overheating, and premature steam-water separation. Figures and illustrate the process of boiler circulation. The left legs of the U-tubes represent downcomers and are filled with relatively cool water. The right legs represent generating tubes and are heated. The heat generates steam bubbles, and convection currents create circulation. As more heat is applied, more steam is generated and the circulation rate increases.
If deposits form Figure , the roughened surface and partially restricted opening resist flow, reducing circulation. At a constant heat input the same amount of steam is generated, so the steam-water ratio in the generating tube is increased.
The water in the tube becomes more concentrated, increasing the potential for deposition of boiler water salts. In extreme cases, deposition becomes heavy enough to reduce circulation to a point at which premature steam-water separation occurs. When this happens in a furnace tube, failure due to overheating is rapid.
When deposits are light they may not cause tube failures, but they reduce any safety margin in the boiler design. Up to the point of premature steam-water separation, the circulation rate of a boiler is increased with increased heat input. Often, as illustrated in Figure , the inflection point A is above the nominal boiler rating. When the circuit is dirty, the inflection point of the circulation-to-heat input curve moves to the left, and the overall water circulation is reduced.
This is represented by the lower broken line. Circulation and deposition are closely related. The deposition of particles is a function of water sweep as well as surface charge Figure If the surface charge on a particle is relatively neutral in its tendency to cause the particle either to adhere to the tube wall or to remain suspended, an adequate water sweep will keep it off the tube.
If the circulation through a circuit is not adequate to provide sufficient water sweep, the neutral particle may adhere to the tube. In cases of extremely low circulation, total evaporation can occur and normally soluble sodium salts deposit. Sodium carbonate treatment was the original method of controlling calcium sulfate scale.
Today's methods are based on the use of phosphates and chelants. The former is a precipitating program, the latter a solubilizing program. Before the acceptance of phosphate treatment in the 's, calcium sulfate scaling was a major boiler problem.
Sodium carbonate treatment was used to precipitate calcium as calcium carbonate to prevent the formation of calcium sulfate. The driving force for the formation of calcium carbonate was the maintenance of a high concentration of carbonate ion in the boiler water. Even where this was accomplished, major scaling by calcium carbonate was common.
As boiler pressures and heat transfer rates slowly rose, the calcium carbonate scale became unacceptable, as it led to tube overheating and failure. Calcium phosphate is virtually insoluble in boiler water. Even small levels of phosphate can be maintained to ensure the precipitation of calcium phosphate in the bulk boiler water-away from heating surfaces. Therefore, the introduction of phosphate treatment eliminated the problem of calcium carbonate scale. When calcium phosphate is formed in boiler water of sufficient alkalinity pH This does not prevent the development of deposit accumulations over time, but the deposits can be controlled reasonably well by blowdown.
In a phosphate precipitation treatment program, the magnesium portion of the hardness contamination is precipitated preferentially as magnesium silicate.
If silica is not present, the magnesium will precipitate as magnesium hydroxide. If insufficient boiler water alkalinity is being maintained, magnesium can combine with phosphate. Magnesium phosphate has a surface charge that can cause it to adhere to tube surfaces and then collect other solids. For this reason, alkalinity is an important part of a phosphate precipitation program.
The magnesium silicate formed in a precipitating program is not particularly adherent. However, it contributes to deposit buildup on a par with other contaminants. Analyses of typical boiler deposits show that magnesium silicate is present in roughly the same ratio to calcium phosphate as magnesium is to calcium in boiler feedwater. Phosphate treatment results are improved by organic supplements. Naturally occurring organics such as lignins, tannins, and starches were the first supplements used.
The organics were added to promote the formation of a fluid sludge that would settle in the mud drum. Bottom blowdown from the mud drum removed the sludge. There have been many advances in organic treatments Figure Synthetic polymers are now used widely, and the emphasis is on dispersion of particles rather than fluid sludge formation. Although this mechanism is quite complex, polymers alter the surface area and the surface charge to mass ratio of typical boiler solids.
With proper polymer selection and application, the surface charge on the particle can be favorably altered Figure Many synthetic polymers are used in phosphate precipitation programs. Most are effective in dispersing magnesium silicate and magnesium hydroxide as well as calcium phosphate.
The polymers are usually low in molecular weight and have numerous active sites. Some polymers are used specifically for hardness salts or for iron; some are effective for a broad spectrum of ions. Figure shows the relative performance of different polymers used for boiler water treatment.
0コメント