Boilers Troubles PDF

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HearteningLlama

Uploaded by HearteningLlama

Allahabad Public School

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boiler engineering steam thermal engineering

Summary

This document provides detailed notes on boiler troubles, including scale and sludge formation, caustic embrittlement, and corrosion. It explains how these issues develop, their causes, and prevention measures.

Full Transcript

# UNIT-4: Boilers - For steam generation, boilers are almost employed in industries. - The water that is filled in boilers for steam generation is called boiler feed water. - The water that is filled into boilers for steam generation (boiler feed water) should satisfy the following requirements:...

# UNIT-4: Boilers - For steam generation, boilers are almost employed in industries. - The water that is filled in boilers for steam generation is called boiler feed water. - The water that is filled into boilers for steam generation (boiler feed water) should satisfy the following requirements: - Hardness of water: 1-2002 ppm - Caustic alkalinity: -0.15-0.45 ppm - Soda alkalinity: -0.15-1 ppm - Excess soda ash: -0.3- 0.55 ppm ## Boiler Troubles ### Scale & Sludge Formation: ![Image of a diagram describing boiler troubles. The diagram includes a circle labelled "Boiler Troubles in producing Steam," connected to four circles: "Caustic Embrittlement" in the top left, "Boiler Corrosion" in the bottom left, "Priming droplets of water carried out with steam" at the top right, and "Foaming (bubbles with steam)"] ### Boiler Troubles - The set up used to produce steam in the industries is known as boilers. (The water is feed into the boiler and heated to produce steam). - **Priming:** When the boiler is producing steam rapidly, some particles (droplets) of water are carried out with steam. The process of wet steaming formation is called priming. - **Caused:** Presence of large amounts of dissolved solids. - **Avoided (Prevented):** 1. Avoid rapid steam rate (Maintaining low water level in boilers) 2. High steam velocity or improper boiler design - **Foaming:** Production of persistent bubbles (foam) in boilers which do not break easily. Occurs due to the presence of oily substances. - **Removed (Prevented):** By adding antifoaming chemicals, i.e. castor oil or sodium aluminate - **Boiler corrosion:** The decay of boiler materials in the presence of acidic environments.-e.g. - **Dissolved oxygen** - $2Fe(OH)_2 + O_2 \rightarrow Fe_2O_3+2H_2O$ - **Dissolved CO2** Forms carbonic acid. - $H_2O + CO_2 \rightarrow H_2CO_3$ - **Acids** From dissolved salts. - **Removal:** - Dissolved $O_2$ is removed by adding hydrazine. $N_2H_4 + O_2 \rightarrow N_2 + 2H_2O$ - $CO_2$ is removed by adding $NH_4OH$. - $2NH_4OH + CO_2 \rightarrow (NH_4)_2CO_3 + H_2O$ - **Scales & Sludges:** Scales are hard deposits (coating) that stick very strongly to the inner surface of the boiler. Scales are difficult to remove, even with the help of a hammer. Scales are a main source of boiler trouble. - **Causes:** Caused by the decomposition of calcium bicarbonate. - $CaSO_4 (deposition) \rightarrow Ca(HCO_3)_2 \rightarrow CaCO_3 + H_2O + CO_2 $ - **Removed:** - Loose adhering: Wire brush. - Brittle: Thermal shocks - Soft scale: - **Hard scales** Of $CaCO_3$, dissolved in $HCl$ - **Disadvantages** 1. **Wastage of fuel:** Covering of boiler safety 2. **Decrease in efficiency:** Danger of explosion - **Sludges:** Soft, loose ppt formed with the boiler. It can easily be scrapped off with a brush. It is formed by substances which have a greater solubility in hot water. ## Caustic Embrittlement - Is the phenomenon (process) during which boiler material becomes brittle (destroyed due to accumulation of caustic sub ($NaOH$) in boiler water. This type of corrosion is caused due to the presence of highly alkaline water. - **Prevented:** - By adding sodium phosphate instead of $Na_2CO_3$, or by adding tannin, lignin to boiler water, it blocks micro cracks (hair cracks). ## Difference between sludge & scale | Sludge | Scale | | ----------- | ----------- | | 1. Due to heating, salt containing water will get concentrated and changes into loose and slimy ppt, called sludge. | 1. When these ppts. become hard and stick in the walls of boilers, it is called scale. | 2. Sludge is not harmful for boilers. | 2. Scales are harmful for boilers. | | 3. Sludge can be removed from the boiler time to time. | 3. Scales can be removed by internal or external treatment or by hammering. If it cannot be removed easily. | | 4. It does not cause clogging and corrosion. | 4. It causes clogging and corrosion. | | 5. Sludge increases the discarding cost of waste. | 5. Scale increases the maintenance and operation cost. |

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