In this article, I will share the impurities found in the feed water, the effects of these impurities and how to prevent the effects caused by the impurities.
Feed water is needed in the boiler for steam generation.
Though feed water is important in a steam boiler, it has several issues that should be addressed.
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Without wasting time, let me share the impurities that are found in the feed water.
Impurities in feed water boiler
- Dissolved gasses like oxygen and carbon dioxide
- Solid contaminants like sediments, gravel and sand
- Dissolved solids like magnesium, calcium, iron and silica.
Effects of feed water impurities in a boiler
1. Scaling formation in a boiler.
Scaling formation is one of the effects of impurities that are present in the feed water.
The dissolved solids e.g magnesium, calcium, iron and silica cause scale formation in a boiler. When the temperature of water in the boiler has increased the precipitation of these solids will be noticed.
The precipitation will form on the metal surfaces of the boiler and even the steam distribution system.
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When this happens the heat transfer in the boiler is going to be minimal which will end up decreasing the heat energy transferred in the boiler.
The scale formation in the steam distribution system will affect the movement of the steam to the points of application if not taken care of immediately.
All these effects will end up affecting the overall efficiency of the boiler.
2. Corrosion of the boiler and steam distribution system.
Corrosion is another effect of the dissolved gasses impurities in the feed water.
Oxygen in feed water accelerates corrosion of the metallic parts of the boiler and other boiler mountings.
Also, oxygen will react with the carbon steel, boiler mountings, accessories and pipes which will end up causing oxygen pitting and this will result in leakages.
Corrosion has many negative effects on the boiler leaving alone causing leakages.
Even the overall boiler efficiency will be affected by corrosion if action is not taken immediately.
The life of the boiler will be shortened by the effects of corrosion from the dissolved gasses.
On the other side, we have also carbon dioxide that when mixed with the condensate in the steam pipelines ends up forming acidic condensate that will corrode the steam distribution system.
3. Carryover.
Carryover can be caused by mechanical issues of the boiler such as the boiler capacity and also chemical issues which are high concentrations of solid contaminants.
The contaminants can be dissolved or suspended within the boiler. Also, excessive alkalinity, grease and oil in the boiler are causes of carryover.
Carryover is when something else other than the clean steam leaves the boiler.
In this article, I will talk about the causes of carryover as a result of contaminants because we are dealing with impurities and not mechanical issues.
The carryover in the boiler causes the formation of deposits on the valves, heat exchangers, metal surfaces of the boiler, turbine and superheaters.
These deposits on these parts of the boiler will end up decreasing the rate of heat transfer in the boiler hence the thermal energy of the steam will be reduced.
The steam that will be generated will be of a low quality.
Other parts of the boiler such as the valves will be damaged and this also affects the operation of the boiler.
The steam distribution lines are also going to be affected since the protective layer of the steam line will be stripped off.
This will increase corrosion and erosion of the steam lines, all these effects will affect the quality of steam conveyed in this steam distribution system.
4. Foaming.
Foaming is the formation of bubbles on the surface of the boiler water which goes out of the boiler with the steam generated.
This is caused by the impurities from the feed water. When solid contaminants accumulate in the boiler water this foaming will occur.
Foaming in the boiler causes water hammer and erosion in steam lines.
Another problem that is caused by foaming is local overheating in the steam pipelines which will end up increasing the thermal stresses in the steam distribution line.
All these are effects that will end up affecting the efficiency of the steam boiler.
How to prevent the effects caused by boiler feed water impurities.
1. Eliminating dissolved gasses.
The effects caused by the dissolved gasses from feed water can be eliminated by heating the water.
Increasing the temperature of the feed water allows the dissolved gasses in the feed water to escape into the atmosphere.
A deaerator and feed water heaters can be used to eliminate the dissolved gasses.
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Eliminating dissolved gasses from the feed water will reduce the corrosion in the boiler and the steam distribution system.
2. Eliminating the dissolved solids.
The dissolved solids in the feed water can be eliminated by several processes namely;
- Demineralization
- Ion exchange.
- Reverse Osmosis.
- Zeolite softening.
- Dealkanization.
All these processes can be used to eliminate the solid contaminants in the feed water.
Removal of these dissolved solids contaminants will prevent scale formation, foaming and even carryover.
A chemical approach can also be taken to eliminate the dissolved solids in the boiler water without increasing the rate of the blowdown.
Anti-foam chemicals can be used to decrease carryover.
Treating feed water before it’s fed to the boiler will prevent all these effects I have talked about in this article.
3. Elimination of solid contaminants.
The solid contaminants that are not dissolved can be removed by filtration and coagulation.
The feed water should be filtered appropriately to remove any solid contaminants.
The solid contaminants can damage the valves and even hinder the transfer of feed water to the boiler.
If the boiler feed pump is damaged by the solid contaminants that will be another problem that will add to the cost of operation of the steam boiler.
Final thoughts
It’s essential that the feed water is treated before it’s fed into the boiler to avoid all these problems I have shared in this article.
I know that feed water treatment comes with a cost but it’s worth it when you invest much in treating the feed water since you will end up saving yourself from repairing the whole steam boiler.
The efficiency of the steam boiler does not only come from the energy value supplied by the fuel but also from the steam generated.
If the feed water is of the required quality then you will be in a good spot when it comes to the steam boiler operation.
Thanks for reading this article, be sure to stick around for more amazing mechanical engineering content. See you in my next article.
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