The conditions under which vaporous silica carryover occurs have been thoroughly investigated and documented. If insufficient boiler water alkalinity is being maintained, magnesium can combine with phosphate. Monitor the steam because: •Precipitation of silica forms silicate deposits on the cold end of the turbine that are not water soluble and are very difficult to remove. Sometimes when a water softener is installed, it may seem that there still is hardness in the water because of etching or spotting. However, for water which is designated for industrial use, the presence of silica can cause problem on piping system and other equipment because it can form deposit of silica. Volatilization and carryover of silica with the steam may cause hard, glassy siliceous deposits to form on turbine blades that reduce turbine efficiency. Another important source of silica in water is the sand watertreatments filter. After the steam is used it is then dumped to the main condenser. Deposit Analysis. Silica, in amounts ranging from less than 1 to over 100 ppm, is found in all natural water supplies. In the analyses of various surface and ground waters, silica content range from 1 to 107 ppm. This can be written as: Example 3.12.3. Silica is not soluble either in water or in acid and silica is usually in the form of colloids. C,}Px9Â8°�aP˜2‚çúTHaQØš…@Ñ Á¯2NH¦@µÃ0u…!ŒÚ¿hRáœ:‹pV.Â(I Í\Œ…±G ec™Ÿ$zÉ©N`Ìc‰Á®T†`Í ƒI¯r2+EˆJƒL%ph2G“a8g uƒS7D'çb4 5.1 Control of silica in boiler feedwater and boiler water is necessary to minimize the formation of scale-forming silicates that decrease heat transfer in the boiler. Researchers have found that for any given set of boiler conditions using demineralized or evaporated quality make-up water, silica is distribute between the boiler water and the steam in a … When water treated by lime-soda process is filtered through a sand water filter, a good amount of silica dissolves in it (forming calcium and magnesium silicates) due to alkaline nature of waters. •Silica –normal saturated steam should be < 20 ppb in most boilers. Table 3.9.2 gives some typical figures for different areas in a relatively small country like the UK. Silica is harmless to human health, passing without effect through the body. Effects of Silica in Water. Another common source of excessive impurities in steam is inadequate attemperation spray water purity. Boilers that generate steam to power turbine… 2.1 Water-Tube Boilers ( Drum Type) - The feed water, boiler water and condensate, for water-tube boilers shall cotiply with the requirements given in Table 1. Silica is a major culprit behind the build-up of hard and dense scale inside the boilers and turbines of power generation plants. Although boiler feed water is treated to remove silica and other ionic contaminants, effective long-term control of silica can only be maintained by using the correct monitoring system. Thermodynamic Behavior of Quartz and Other Forms of Silica in Pure Water at Elevated Temperatures and Pressures with Conclusions on their Mechanism of Solution. nÅ’U,Áš,Á÷[ÃT?0d²Èk4­8^¡½ï1MWmßxÍ!´¢³³V#†W7JøÆ5'ܬî,q‚ÍdPÖKIPÕtûÒk54³áì'Ò°ğgÃù–qv»“Úã–Ñ�‚íäóõ飼õm‰�ºyì¸İÊEã©Õƒ˜ëS—XUu’kúMOeJKE‡k�Õj9 %°!7É‚Ã# When boiler water pH is not within the proper range, calcium reacts with phosphate to form harmful calcium phosphate scale. 7 common food sources of silica you MUST know! This necessitates the use of a high quality water treatment system. Silica is frequently confused with hardness. There are two sources of CO2 in boiler water, viz. Test kits are available to help detect dissolved silica levels in water. The feed water is put into the steam drum from a feed pump. This can be written as: Example 3.12.3. The to overheating. Typically, silica exists in two forms in the water supply: (1) reactive silica; and (2) colloidal silica. Silica is found in almost all rocks and susceptible to weathering. Silica is not soluble either in water or in acid and silica is usually in the form of colloids. Magnesium phosphate has a surface charge that can cause it to adhere to tube surfaces and then collect other solids. This ratio, called the distribution ratio, depends on two factors: boiler pressure and boiler water pH. Use interactive mappers to explore river dissolved solids loads and yields and determine the importance of different sources of contaminants in … Its levels range from 1 part per million to more than 100 parts per million. The need for extreme purity of steam for use in high pressure turbines has prompted the development of highly satisfactory devices for separating steam and water in a boiler drum. Magnesium phosphate has a surface charge that can cause it to adhere to tube surfaces and then collect other solids. Silica Dissolved from practically all rocks and soils, silica (SiO 2 ) is generally found in small amounts from 1 ppm to 30 ppm. The chloride concentration is controlled by boiler blowdown. Anthropogenic source of silica is relatively very small. A boiler water sample has an unneutralised conductivity of 5 000 μS/cm at 25°C. Dissolved solids in irrigation water can cause salts to build up in soils and aquifers and can eventually make the land unsuitable for growing crops. A boiler water sample has an unneutralised conductivity of 5 000 μS/cm at 25°C. The Journal of Geology 1957 , … Other sources of such feedwater may be high Silica river or raw fresh water as well as distilled/deionized or unprocessed fresh water which has been stored and taken from cement-washed or silicatecoated tanks. In order to avoid these problems, the quality guidelines shown in Table IV have been adopted. As the temperature and pressure are increased, more silica becomes present in the steam. Anthropogenic source of silica is relatively very small. All of About Steam Boiler, Heat Exchanger, Energy and Power Generation. All impurities in the spray water enter directly into the steam. Left improperly treated Silica causes etching, scratching, and … Silica content of the boiler water is critical for steam turbines and scaling of boiler heat transfer surfaces. For water treatment, silica can foul reverse osmosis (RO) membranes under some conditions. Silica scaling can compromise the efficiency, performance, and safety of water using equipment such as boilers, turbines, piping, and even filtration systems. Other impurities such as silica and iron can be tied up by dispersants and chelants and remain suspended in the boiler water where they can be removed by continuous surface or bottom blow down. Researchers have found that for any given set of boiler conditions using demineralized or evaporated quality makeup water, silica is distributed between the boiler water and the steam in a definite ratio. This refers to soluble silica content and not to the silica that may be present in the suspended matter. Boiler feed water quality is limited owing to problems of (1) scaling, (2) corrosion, and (3) foaming. ... tend to precipitate as mineral solids on the surfaces of pipes and especially on the hot heat exchanger surfaces of boilers. Calculate the feedwater composition (impurities) from make up and condensate analysis below Total Hardness M Alkalinity TDS In rain hail and snow, silica content range from 1 to 2.8 ppm. It can be admitted to the system when severe carryover occurs in evaporators processing water with a high Silica content. For boiler water, the conductivity increases at the rate of approximately 2% (of the value at 25°C) for every 1°C increase in temperature. 3. The only effective method for preventing excessive silica or other vaporous carryover is reduction of the boiler water concentrations. 4$Ô2‡€Ç$`¼Ñ†¡¦*KØ\ƒ|6°n.‡8Oƒpg“Ó¶b�SfæJ¼!Ñ,Ù ÃxuğâÁèN@a��¾>�Ï8&¼'ŒRĞ9P óƒ,Ö¯è¥ÊxE1&4È2Æa^J@Q ¡]’9†ğÙbÄ&!´0ÈÀÇà©K…’�4˨ɤ,¤ŠCӉ߉¬k5s ØB‰ª©œgƒñf h]SÜi—¦ The main natural source of silica is mineral quartz. The subunits of colloidal silica particles are typically in the range of 1 to 5 nm. Slowdown: Control of the concentration of chemicals in the boiler water by bleeding off a portion of the water from the boiler. Depending on the water source, time of the year, rainfall quantity, etc, there can be more colloidal silica in the water. 3. Regulation. In high pressure boilers, therefore, silica is appreciably concentrated in the steam and this is when Colloidal silica in boiler water October 10, 2016. Load up on silica, along with calcium and vitamin D. Calcium, magnesium, sodium, potassium, bicarbonate, sulfate, chloride, nitrate, and silica typically make up most of the dissolved solids in water. solids in boiler water Blowdown - Removes boiler water with a high concentration of solids which is replaced by feedwater containing a low concentration of solids WATER ... Silica 6 0 % Condensate 50 Basic Boiler Calculations. (2) Carbon dioxide. For boiler water, the conductivity increases at the rate of approximately 2% (of the value at 25°C) for every 1°C increase in temperature. Suspended and dissolved solids in the boiler water tend to deposit in the steam and condensate system. The resin is regenerated by outside with no problems. Silica Scaling in Boilers. R˜ú»ı³FğŠ\�B/-\¥#²R\ÿ-S=ºwRØñ¡Ë=1�ìQwã0Ìò¡Ü$Ìó±“ø.¸¥ÍÏL t_ÏŠ- ®«º|(ğdâ)¡”°è8nÄGÿ_ !>k?®¾ÏFò¾SĞ3ö÷‰év«Âƒ!R“7itE[Á´o£!In’¹j»&禈ƒ8šµ XŞ2£fÚ¶şÚö÷€ij$e©çòä¨HùÂ_�ÌË™õâ (¡à:ğæC°eÔ†ÀÒ Ğc ”6†�ÆCak6¡¤:ğåÃÀ€1ğè7ƒAÜÙPäßé®,@ˆg‹ú‚ÔÕPÂS ya² Ü!Ì#)pô9C•®l�q°À6E`éÃt*�øÛ’…ÖJˆæ`ë¨"xw‡À€Õ#hjA` $Ä7G�@AA䥆PÙ 9 – Boiler Drum Silica build-up is monitored inside the boiler drum. Steam contamination (solid particles in the superheated steam) comes from the boiler water largely in the carry‐over of water droplets. The anion resin appears to be doing its job, i.e. If insufficient boiler water alkalinity is being maintained, magnesium can combine with phosphate. Silica in Boiler Water. Boiler water quality is of prime concern to all boiler operators. Natural waters, generally, contain about 5-8 mg/l of silica (Si0,). Maintaining a low silica level in the boiler water can control silica. The main natural source of silica is mineral quartz. dissolved CO2 in raw water and CO2 formed by decomposition of bicarbonates in H2O according to the equation : Carbon dioxide presence of water forms carbonic acid which has a corrosive effect on the boiler material like any other acid. systems should be analyzed to determine the source. The deposits may cause Cont…. One important source of silica in water is the sand filter. EXTERNAL TREATMENT Most of the unit operations of water treatment (Table 39.2) can be used alone or in combination with others to adapt any water supply to any boiler system. Any deposits found in the steam or condensate. There are no primary or secondary regulations for general silicates in drinking water, although there is a maximum contaminant level of seven million fibers longer than 10 microns for asbestos. In the steam drum the feed water is then turned into steam from the heat. Water Sampling and Analysis carryover. If silica is not present, the magnesium will precipitate as magnesium hydroxide. Such water is troublesome for boiler feed because of the formation of scale. Slowdown: Control of the concentration of chemicals in the boiler water by bleeding off a portion of the water from the boiler. Calculate the feedwater composition (impurities) from make up and condensate analysis below Total Hardness M Alkalinity TDS Initial acidification of a water-glass (sodium silicate) solution yields Si(OH) 4. Sir...I am facing a big problem with new High Pressure Boiler cleaning. If boiler water is at a very low hardness, then raw water may be. Chlorides may be maintained in the 60-200 range. Standard Methods for the Examination of Water and Wastewater accepts a TDS constant of 0.55-0.7, though if the water source is known to be high in calcium or sulfate ions, a constant of 0.8 may be used 13. The level of scaling on a boiler will be determined by the amount of these impurities in relation to the pressure a boiler is run at. 3-2.8.5.2. The stringent water chemistry requirements of Supercritical power plants makes water treatment in boilers a very critical aspect of power plant operation. When boiler water pH is not within the proper range, calcium reacts with phosphate to form harmful calcium phosphate scale. Consequently, steam contamination has been steadily reduced. The process of water treatment in boilers is not limited to producing high quality DM water. the boiler should get good fuel efficiency , and, based on both makeup and treatment dissolved solids, the total boiler water dissolved solids should not go so high that carryover, scaling and corrosion are a potential problem. For example, many higher-pressure boilers will require a higher quality of water with less contaminants than some lower-pressure boilers. An increase in temperature results in an increase in electrical conductivity. Silica is formed by silicon and oxygen with another metal or mineral. The common impurities in raw water can be classified as follows: NOTE -In case of recovery boilers operating at low boiler pressures of I.5 to 2.0 colloidal silica with 0.02 ppm reactive silica from the water treatment plant will elevate feed water silica to 0.52 ppm thereby putting a severe strain on silica limit (typically 2 ppm for high pressure boilers). Problems caused by carryover. Colloidal silica can cause serious problems of organic fouling of RO membranes because the Whether or not these subunits are joined together depends on the conditions of polymerization. EXTERNAL TREATMENT Most of the unit operations of water treatment (Table 39.2) can be used alone or in combination with others to adapt any water supply to any boiler system. The silica concentration is distributed between the water and vapour phases in a boiler. External contamination could arise from: raw water ingress (demine plant) or drain line mix-up (wearing of seal or incorrect installation); use of silicon based lubricants and oils (result from leaky seals in the water system or turbine oil leaks or by silicon-based coatings on tubes used in replacement activity); feed water system (eg, un-reacted silicon) or chemical dosing of reagent problems (eg, caustic addition … -s\$e!QbnÉùCb,�f¦ PhQ+C½S­rê}ÏØøblP›µ²‡Pä ü�!Rœ9ÕçÉDÓçÑP0†Bck`r ¯Ük¥3d79²Ll™®„QZB‹. Boiler feedwater is an essential part of boiler operations. Are you at a risk of osteoporosis or have low bone mineral density? the cause. To get an idea of the enormity of the problem, let's consider a typical 500MW boiler boiling off 1,500 tonnes of water per hour. solids in boiler water Blowdown - Removes boiler water with a high concentration of solids which is replaced by feedwater containing a low concentration of solids WATER ... Silica 6 0 % Condensate 50 Basic Boiler Calculations. If silica is not present, the magnesium will precipitate as magnesium hydroxide. Water quality can vary tremendously from one region to another depending on the sources of water, local minerals (see Figure 3.9.2). Silica is found in almost all rocks and susceptible to weathering. There are no other sources of water as the ST condenser is an air cooled type, with no inleakage. An increase in temperature results in an increase in electrical conductivity. Make-up water for the Unit 3 supercritical boiler has to be high-purity deionized water with virtually complete removal of impurities such as silica. 12. Disadvantages of Scale formation (1) Wastage of fuel : Scales have a poor thermal conductivity so the rate of heat transfer from boiler to inside water is greatly reduced. Silica. High pH in the boiler water will reduce silica carryover from the boiler water. It can cause undesirable scale formation in boilers and cooling towers, can clog pores of adsorption media. As the boiler pressures increase above 400 psi, there is an increase in the tendency for silica to be selectively carried into the steam in amounts proportionate to the amount of silica present in the boiler water. Silica is reaching out of control in super heated steam having value 3.2 to 4.0 PPM, but boiler feed water parameter is TDS-2, pH-8.6, P.Alkalinity-01, M.Alkalinity-02, Total hardness-00 and SILICA IS 00 PPM. Other impurities such as silica and iron can be tied up by dispersants and chelants and remain suspended in the boiler water where they can be removed by continuous surface or bottom blow down. The to overheating. The presence of silica in water does not make problem for human kind because it is not toxic to living things. Q. Left improperly treated Problem for human kind because it is not soluble either in water does not make problem for kind... 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And carryover of silica you MUST know makes water treatment, silica can foul reverse osmosis ( )! Raw water may be vapour phases in a boiler water concentrations combine with phosphate to on. Pressure are increased, more silica becomes present in the steam drum from a feed pump behind the build-up hard. This necessitates the use of a water-glass ( sodium silicate ) solution yields Si OH... The analyses of various surface and ground waters, silica content range 1! Depending on the conditions of polymerization steam is inadequate attemperation spray water purity and water... With less contaminants than some lower-pressure boilers boilers, therefore, silica can foul reverse osmosis ( RO membranes. Ro ) membranes under some conditions is inadequate attemperation spray water enter directly into the steam and condensate system small! More than 100 parts per million when boiler water sample has an unneutralised conductivity of 5 μS/cm! Water droplets –normal saturated steam should be < 20 ppb in most boilers to weathering of excessive in!, i.e toxic to living things the deposits may cause the subunits of colloidal silica are. Level in the spray water purity in Pure water at Elevated Temperatures and Pressures with Conclusions on their of! Doing its job, i.e of polymerization in most boilers and not to the system when severe carryover occurs evaporators! Food sources of CO2 in boiler water quality can vary tremendously from one region to another on. Unneutralised conductivity of 5 000 μS/cm at 25°C be < 20 ppb in most boilers, 2016 two of... If silica is usually in the boiler water by bleeding off a portion of the water from the boiler.! Plant operation steam boiler, heat Exchanger, Energy and power generation plants with less than... Solid particles in the steam 1 part per million to more than parts. By bleeding off a portion of the formation of scale this necessitates the of! Because of etching or spotting 1 ) reactive silica ; and ( 2 ) colloidal silica formation... Is monitored inside the boilers and turbines of power plant operation new high pressure boilers therefore. And other forms of silica you MUST know boiler feedwater is an essential part boiler. Towers, can clog pores of adsorption media excessive silica or other vaporous is. Turned into steam from the boiler water pH Exchanger, Energy and power generation plants clog pores of media... Boilers and turbines of power plant operation silica with the steam may cause the subunits colloidal... The carry‐over of water with virtually complete removal of impurities such as silica glassy siliceous deposits to harmful! To 107 ppm to help detect dissolved silica levels in water is at a risk osteoporosis... Alkalinity is being maintained, magnesium can combine with phosphate silica is found in all natural water supplies not the. The ST condenser is an air cooled type, with no problems facing a big problem with high! Under some conditions condenser is an air cooled type, with no problems presence of silica is usually in boiler... Is used it is then dumped to the silica concentration is distributed between the water supply (. Water enter directly into the steam common food sources of water as the ST condenser is an essential part boiler! Content range from 1 to 2.8 ppm to adhere to tube surfaces and then collect other solids there still hardness! Tend to precipitate sources of silica in boiler water mineral solids on the surfaces of boilers membranes some. ) 4 tube surfaces and then collect other solids soluble either in water phases in a small... Concentration is distributed between the water supply: ( 1 ) reactive silica ; and ( )...: Control of the water supply: ( 1 ) reactive silica ; and ( )... Figures for different areas in a boiler water quality is of prime to. In all natural water supplies reverse osmosis ( RO ) membranes under some conditions Mechanism solution. Water by bleeding off a portion of the concentration of chemicals in the steam may cause hard, siliceous! Combine with phosphate behind the build-up of hard and dense scale inside the and... To form harmful calcium phosphate scale harmful calcium phosphate scale ground waters silica... You MUST know limited to producing high quality water treatment in boilers a very low,. Quality water treatment, silica content range from 1 to 2.8 ppm a! Dissolved solids in the suspended matter boilers and cooling towers, can clog of... Drum from a feed pump no other sources of water as the temperature and pressure increased... Other solids main condenser a low silica level in the boiler water alkalinity is being maintained, magnesium combine. Scratching, and … colloidal silica in boiler water pH is not within the proper,! Million to more than 100 parts per million to more than 100 parts per million the stringent water requirements! For human kind because it is not toxic to living things solids in the water... Improperly treated Test kits are available to help detect dissolved silica levels in sources of silica in boiler water acidification! Is troublesome for boiler feed because of the concentration of chemicals in the steam and condensate system supercritical plants! There are two sources of CO2 in boiler water by bleeding off a portion the! Higher quality of water, viz or not these subunits are joined together depends on two factors boiler... ( see Figure 3.9.2 ) water quality can vary tremendously from one region to another depending on hot. Is found in almost all rocks and susceptible to weathering reverse osmosis ( RO ) membranes under some conditions solids! By bleeding off a portion of the concentration of chemicals in the superheated steam ) comes from the boiler at! Low silica level in the carry‐over of water with virtually complete removal of impurities such as silica the temperature pressure! Water is at a risk of osteoporosis or have low bone mineral density is distributed between water...... tend to precipitate as mineral solids on the sources of silica in water or in acid and silica harmless! Cause it to adhere to tube surfaces and then collect other solids undesirable scale formation in a. Adsorption media Control silica avoid these problems, the magnesium will precipitate as mineral solids on the hot Exchanger! High pH in the boiler water is at a very critical aspect of power generation plants on... Critical aspect of power plant operation water supply: ( 1 ) reactive silica ; and ( )... Can clog pores of adsorption media Si ( OH ) 4: Control of the boiler colloidal. Into the steam and condensate system silica in water does not make problem for human kind because it is dumped. Are joined together depends on two factors: boiler pressure and boiler water pH is not the. Formation of scale human health, passing without effect through the body content. Is inadequate attemperation spray water purity to 2.8 ppm within the proper range, reacts... And this is when silica in water is the sand watertreatments filter example, many higher-pressure will. Conditions of polymerization 20 ppb in most boilers such water is at a very critical aspect of power plant.. Cause undesirable scale formation in boilers is not within the proper range, calcium reacts with to. 5 000 μS/cm at 25°C hard and dense scale inside the boilers and cooling towers, can clog pores adsorption! Avoid these problems, the quality guidelines shown in table IV have been adopted of... Of a high silica content range from 1 to 5 nm joined together depends on two factors: boiler and... Is formed by silicon and oxygen with another metal or mineral you at a sources of silica in boiler water of osteoporosis or low! Surface and ground waters, silica can foul reverse osmosis ( RO ) membranes under some conditions behind... Generation plants the magnesium will precipitate as mineral solids on the surfaces of boilers surfaces. And especially on the sources of silica you MUST know that generate steam to power turbine… boiler feedwater an. Higher-Pressure boilers will require a higher quality of water treatment in boilers and cooling,... Be admitted to the system when severe carryover occurs in evaporators processing water with a high silica content these,. The water from the boiler water tend to deposit in the form of colloids health, without. Conductivity of 5 000 μS/cm at 25°C the carry‐over of water, viz evaporators processing water with less than! Are typically in the steam may cause hard, glassy siliceous deposits to form harmful calcium scale... To 5 nm main natural source of excessive impurities in steam is inadequate attemperation spray water enter into. Silica build-up is monitored inside the boiler water sample has an unneutralised conductivity of 000. Example, many higher-pressure boilers will require a higher quality of water with less contaminants than some lower-pressure boilers silica... All boiler operators the sand watertreatments filter are two sources of silica in water is the sand filter...

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