 Today we will learn one topic water technology and a particular beat from that topic that is scale and sludge formation in boiler. So this particular beat is related with what happened when we use hard water for creating a steam in industry. This is the learning outcome for today's session. At the end of this session students will be able to describe effect of hard water used in boiler that is scale and sludge formation, its effects and treatment. This is the content we are going to learn in this session. First we will learn the definition of hardness of water, types of hard water, then formation effect and treatment of scale and sludge formation. So first we will see what do you mean by hardness of water. Water sample which is free from any impurity easily reacts with soap solution and forms corresponding acid and base molecule with plenty of foam and such water sample is known as soft water. Whereas water sample which consists of impurity such as carbonates, bicarbonates, chloride and sulphates of the metal ions like calcium and magnesium does not react with soap solution and therefore instead of forming foam it forms precipitation of calcium and magnesium salts and such water sample is known as hard water. So it is hardness of water. Actually we know that the rain water is the single source of water on earth planet and it is one of the purest source of water but when such rain water joins to earth it gets dissolved with the impurity like carbonates and bicarbonates, chlorides and sulphates and then it may acquire the hardness. Water sample when treated with soap solution does not produce leather radially but forms a white curd like precipitate is called as hard water. Thus hardness of water sample is the tendency to resist to form foam with soap solution. The same we have expressed with the help of chemical reaction. First we have shown the sodium stearate molecule that is a sodium salt of higher fatty acid that is nothing but the soap. When it is mixed with the hardness causing impurity and one of the impurity we have mentioned here is calcium chloride. So there is a reaction in between these two molecules and instead of forming a acid base molecule and foam it forms a curd like precipitate and that is calcium stearate. So this is the behavior of the water which is known as hardness of water. Now after learning what do you mean by hardness of water now we will see what are the types of hard water. One is temporary or carbonate hardness and second one is known as permanent or noncarbonate hardness. Now what do you mean by temporary or carbonate hardness? This type of hardness is due to the presence of dissolved bicarbonates of calcium and magnesium. Temporary hardness is also caused by the presence of trace amount of other heavy metal ions and the carbonates of iron also. Temporary hardness is mostly destroyed by boiling of water when bicarbonates are decomposed yielding insoluble carbonates or hydroxides which are deposited at the bottom of vessel. So in short a temporary hardness is a hardness that is caused by the presence of bicarbonates and carbonates of calcium and magnesium along with some another metal ion also. Whereas temporary hardness can be removed by just boiling the water sample. The same we have expressed with the help of chemical reaction the first molecule is a calcium bicarbonate. On boiling we will get a precipitation of calcium carbonate. Now this is the second type of hardness of water that is permanent or noncarbonate hardness. So permanent type of hardness is due to the presence of chloride sulfates of calcium and magnesium. Also it is caused by trace amount of iron and other heavy metal ion also. Unlike temporary hardness permanent hardness cannot be removed or destroyed by only boiling. For the removal of this type of hardness some chemical methods such as ion exchange, zeolite and reverse osmosis methods are required. Temporary is caused by carbonates and bicarbonates of calcium and magnesium that can be removed by just boiling. Whereas permanent type of hardness is caused by chlorides and sulfates of calcium and magnesium and that cannot be removed by just boiling. Now we will see one of the effect of hard water when it is used in boiler for creating a steam that is scale and sludge formation. In number of industries they are using steam as a source of energy for completing different kinds of work. For steam generation water boilers are almost invariably used and if the hard water is fed to the boiler for creating the steam. There arises many troubles in mechanism of working of the boiler and one of the major trouble is known as scale and sludge formation. In boiler water evaporates continuously and concentration of dissolved salts increases progressively. When their concentration reaches to saturation point they are thrown out of water in the form of precipitate and which get deposited on the inner wall of the boiler. So if the water used for creating a steam in boiler is hard water and just we have learned that hard water consists of different impurity and as the effect of boiling the impurity gets precipitated and that will be deposited inside the coil. If the precipitation takes place in the form of loose and slimy type it is called a sludge and on the other hand if the precipitate is hard adhering on the inner walls of the boiler it is called a scale. So these are the two terms we are learning sludge and scale. So sludge is initial stage of this process where due to the evaporation of water just the solids are thrown out of the water and that initial stage where the precipitation is very loose that stage is known as sludge. But if you ignore and if you use continuously the boiler the next step will come when the amount of the saturated salts are more and that will convert into a hard and permanent deposit and that is known as scale. So sludge is a loose deposit and scale is a permanent deposit. So sludge can be easily removed by blowdown operation with water. Scales are hard deposits which stick very firmly to the inner surface of the boiler. Formation of scales may be due to decomposition of calcium bicarbonate, calcium sulphate, hydrolysis of magnesium salts and presence of silica also. So scales cannot be easily removed sludge can be easily removed by washing the coil with water. Now here I would like to ask you one question if the precipitation that is scale and sludge takes place in the form of loose and slimy type of precipitate which is called as and the correct option is option A sludge. That is if the precipitation is loose then that is called as sludge. Now we will see what are the disadvantages of scale and sludge. So first one is wastage of heat sludge and scale are poor conductors of heat. As a result of boiling of water the dissolved hardness causing impurities gets precipitated inside the coil and because of insulating nature it causes wastage of heat. So one of the effect is that wastage of heat sludge and scale that precipitate is a bad conductor so it will not conduct the heat and therefore it may cause the wastage of heat. Second one is efficiency of boiler excessive sludge and scale formation disturb the working of boiler. It settles in the region of water circulation such as pipe concentration, plug opening etc. thereby causing choking of the pipes. So the boiler loses its working efficiency. So second effect is that adversely it affect on the working of the boiler that boiler loses its efficiency. Blasting of boiler due to the decomposition of carbonates inside the coil circulation of water is not happening and the water circulation coil gets heating in dry state. Therefore due to the overheating of the coil sometimes blasting of boiler may take place. So this is particularly is related with the safety if the scale and sludge formation if you ignore then what happens the coil gets overheated and it may cause the blasting of the boiler. Now how to avoid the formation of scale and sludge formation? The first point is that by using well softened water if you use well softened water there is no possibility of formation of sludge and scale. Second one by frequently blow down operation that is drawing of portions of concentrated waste. Sludge can be removed by washing the coil with pressure of water. Sludge can be removed easily if you wash the coil with water. Removal of scale with the help of scrapper, wood or wire brush. Removal of scale by giving thermal shock. And removal of scale by dissolving the scale in a suitable chemical. So this is the comparison in short again we will conclude that what is sludge and scale. So sludge is the soft and non-adherent deposit. Scale is hard and permanent deposit which stick very firmly to the inner surface of boiler. Sludge can be removed easily by washing water, circulation coil with water. Scales are very difficult to remove but up to certain extent it can be removed with brush, scrapper or with thermal shock treatment. Sludge can transfer heat to some extent and is causing comparatively less wastage of fuel whereas scales are bad conductors of heat and causes more wastage of fuel. Sludges are formed by substances like magnesium chloride and calcium chloride whereas scales are formed by substances like calcium sulphate, magnesium hydroxide etc. This is the diagrammatic representation. So first one is a scale, second one is a sludge. So scale and sludge we have represented here diagrammatically. It is a cross-sectional area of the coil of the water. So all this I have prepared by Ray Fring a textbook of engineering chemistry written by Jain and Jain. Thank you.