Boilers Troubles PDF

# 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. |