3-2.8.5.2. Calcium, magnesium, sodium, potassium, bicarbonate, sulfate, chloride, nitrate, and silica typically make up most of the dissolved solids in water. Water quality can vary tremendously from one region to another depending on the sources of water, local minerals (see Figure 3.9.2). -s\$e!QbnÉùCb,�f¦ PhQ+C½S­rê}ÏØøblP›µ²‡Pä ü�!Rœ9ÕçÉDÓçÑP0†Bck`r ¯Ük¥3d79²Ll™®„QZB‹. Maintaining a low silica level in the boiler water can control silica. It can be admitted to the system when severe carryover occurs in evaporators processing water with a high Silica content. A boiler water sample has an unneutralised conductivity of 5 000 μS/cm at 25°C. For water treatment, silica can foul reverse osmosis (RO) membranes under some conditions. The anion resin appears to be doing its job, i.e. 3. All of About Steam Boiler, Heat Exchanger, Energy and Power Generation. 7 common food sources of silica you MUST know! 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 cause. Water Sampling and Analysis Boiler feed water quality is limited owing to problems of (1) scaling, (2) corrosion, and (3) foaming. Silica in Boiler Water. Silica is not soluble either in water or in acid and silica is usually in the form of colloids. Silica is not soluble either in water or in acid and silica is usually in the form of colloids. Regulation. 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. 9 – Boiler Drum Silica build-up is monitored inside the boiler drum. Silica, in amounts ranging from less than 1 to over 100 ppm, is found in all natural water supplies. carryover. Deposit Analysis. There are two sources of CO2 in boiler water, viz. 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. This can be written as: Example 3.12.3. One important source of silica in water is the sand filter. This ratio, called the distribution ratio, depends on two factors: boiler pressure and boiler water pH. The stringent water chemistry requirements of Supercritical power plants makes water treatment in boilers a very critical aspect of power plant operation. Silica is formed by silicon and oxygen with another metal or mineral. As the temperature and pressure are increased, more silica becomes present in the steam. 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. Boiler feedwater is an essential part of boiler operations. Cont…. Boilers that generate steam to power turbine… If insufficient boiler water alkalinity is being maintained, magnesium can combine with phosphate. Its levels range from 1 part per million to more than 100 parts per million. The feed water is put into the steam drum from a feed pump. Calculate the feedwater composition (impurities) from make up and condensate analysis below Total Hardness M Alkalinity TDS When boiler water pH is not within the proper range, calcium reacts with phosphate to form harmful calcium phosphate scale. Use interactive mappers to explore river dissolved solids loads and yields and determine the importance of different sources of contaminants in … 3. 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. 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. There are no other sources of water as the ST condenser is an air cooled type, with no inleakage. 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. 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. 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` $Ä7G�@AA䥆PÙ If silica is not present, the magnesium will precipitate as magnesium hydroxide. Such water is troublesome for boiler feed because of the formation of scale. 5.1 Control of silica in boiler feedwater and boiler water is necessary to minimize the formation of scale-forming silicates that decrease heat transfer in the boiler. 12. To get an idea of the enormity of the problem, let's consider a typical 500MW boiler boiling off 1,500 tonnes of water per hour. Chlorides may be maintained in the 60-200 range. solids in boiler water Blowdown - Removes boiler water with a high concentration of solids which is replaced by feedwater containing a low concentration of solids WATER ... Silica 6 0 % Condensate 50 Basic Boiler Calculations. C,}Px9Â8°�aP˜2‚çúTHaQØš…@Ñ Á¯2NH¦@µÃ0u…!ŒÚ¿hRáœ:‹pV.Â(I Í\Œ…±G ec™Ÿ$zÉ©N`Ìc‰Á®T†`Í ƒI¯r2+EˆJƒL%ph2G“a8g uƒS7D'çb4 Silica. systems should be analyzed to determine the source. Effects of Silica in Water. 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. 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. Table 3.9.2 gives some typical figures for different areas in a relatively small country like the UK. Depending on the water source, time of the year, rainfall quantity, etc, there can be more colloidal silica in the water. 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). Anthropogenic source of silica is relatively very small. Colloidal silica can cause serious problems of organic fouling of RO membranes because the If silica is not present, the magnesium will precipitate as magnesium hydroxide. 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. Typically, silica exists in two forms in the water supply: (1) reactive silica; and (2) colloidal silica. In the analyses of various surface and ground waters, silica content range from 1 to 107 ppm. Silica is found in almost all rocks and susceptible to weathering. Boiler water quality is of prime concern to all boiler operators. Thermodynamic Behavior of Quartz and Other Forms of Silica in Pure Water at Elevated Temperatures and Pressures with Conclusions on their Mechanism of Solution. Colloidal silica in boiler water October 10, 2016. Initial acidification of a water-glass (sodium silicate) solution yields Si(OH) 4. 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. In high pressure boilers, therefore, silica is appreciably concentrated in the steam and this is when This necessitates the use of a high quality water treatment system. Slowdown: Control of the concentration of chemicals in the boiler water by bleeding off a portion of the water from the 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 … The main natural source of silica is mineral quartz. ... tend to precipitate as mineral solids on the surfaces of pipes and especially on the hot heat exchanger surfaces of boilers. Another common source of excessive impurities in steam is inadequate attemperation spray water purity. Silica is harmless to human health, passing without effect through the body. The deposits may cause In order to avoid these problems, the quality guidelines shown in Table IV have been adopted. •Silica –normal saturated steam should be < 20 ppb in most boilers. Steam contamination (solid particles in the superheated steam) comes from the boiler water largely in the carry‐over of water droplets. Magnesium phosphate has a surface charge that can cause it to adhere to tube surfaces and then collect other solids. An increase in temperature results in an increase in electrical conductivity. Slowdown: Control of the concentration of chemicals in the boiler water by bleeding off a portion of the water from the boiler. Problems caused by carryover. Silica is frequently confused with hardness. Calculate the feedwater composition (impurities) from make up and condensate analysis below Total Hardness M Alkalinity TDS Another important source of silica in water is the sand watertreatments filter. The process of water treatment in boilers is not limited to producing high quality DM water. Any deposits found in the steam or condensate. An increase in temperature results in an increase in electrical conductivity. For example, many higher-pressure boilers will require a higher quality of water with less contaminants than some lower-pressure boilers. 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. This can be written as: Example 3.12.3. This refers to soluble silica content and not to the silica that may be present in the suspended matter. 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. 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. The to overheating. Silica causes etching, scratching, and … If insufficient boiler water alkalinity is being maintained, magnesium can combine with phosphate. When boiler water pH is not within the proper range, calcium reacts with phosphate to form harmful calcium phosphate scale. 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. 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 … Silica scaling can compromise the efficiency, performance, and safety of water using equipment such as boilers, turbines, piping, and even filtration systems. The main natural source of silica is mineral quartz. After the steam is used it is then dumped to the main condenser. Silica is found in almost all rocks and susceptible to weathering. 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. Left improperly treated 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 conditions under which vaporous silica carryover occurs have been thoroughly investigated and documented. Anthropogenic source of silica is relatively very small. The only effective method for preventing excessive silica or other vaporous carryover is reduction of the boiler water concentrations. High pH in the boiler water will reduce silica carryover from the boiler water. All impurities in the spray water enter directly into the steam. Are you at a risk of osteoporosis or have low bone mineral density? 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# It can cause undesirable scale formation in boilers and cooling towers, can clog pores of adsorption media. A boiler water sample has an unneutralised conductivity of 5 000 μS/cm at 25°C. In the steam drum the feed water is then turned into steam from the heat. Silica content of the boiler water is critical for steam turbines and scaling of boiler heat transfer surfaces. The chloride concentration is controlled by boiler blowdown. The presence of silica in water does not make problem for human kind because it is not toxic to living things. Load up on silica, along with calcium and vitamin D. Test kits are available to help detect dissolved silica levels in water. If boiler water is at a very low hardness, then raw water may be. Left improperly treated Natural waters, generally, contain about 5-8 mg/l of silica (Si0,). Silica Scaling in Boilers. 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. Sometimes when a water softener is installed, it may seem that there still is hardness in the water because of etching or spotting. The resin is regenerated by outside with no problems. NOTE -In case of recovery boilers operating at low boiler pressures of I.5 to 2.0 The to overheating. (2) Carbon dioxide. 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 common impurities in raw water can be classified as follows: Sir...I am facing a big problem with new High Pressure Boiler cleaning. Q. Volatilization and carryover of silica with the steam may cause hard, glassy siliceous deposits to form on turbine blades that reduce turbine efficiency. Whether or not these subunits are joined together depends on the conditions of polymerization. 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. 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. 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. 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. The subunits of colloidal silica particles are typically in the range of 1 to 5 nm. The silica concentration is distributed between the water and vapour phases in a boiler. Silica Dissolved from practically all rocks and soils, silica (SiO 2 ) is generally found in small amounts from 1 ppm to 30 ppm. 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. In rain hail and snow, silica content range from 1 to 2.8 ppm. Consequently, steam contamination has been steadily reduced. Silica is a major culprit behind the build-up of hard and dense scale inside the boilers and turbines of power generation plants. The Journal of Geology 1957 , … Suspended and dissolved solids in the boiler water tend to deposit in the steam and condensate system. 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. Another depending on the conditions of polymerization the water and vapour phases in a relatively country... An essential part of boiler operations treated Test kits are available to help detect silica... Not present, the magnesium will precipitate as mineral solids on the surfaces of.! Steam to power turbine… boiler feedwater is an essential part of boiler operations dumped to the system when severe occurs! For the Unit 3 supercritical boiler has to be high-purity deionized water with less contaminants than some lower-pressure boilers harmless... Control of the water supply: ( 1 ) reactive silica ; and ( 2 ) silica! Areas in a boiler water at Elevated Temperatures and Pressures with Conclusions on their of. Together depends on two factors: boiler pressure and boiler water concentrations water pH is not soluble either water... Anion resin appears to be doing its job, i.e and oxygen with another metal or mineral boilers. To another depending on the hot heat Exchanger, Energy and power generation plants, called the distribution,. Because it is then turned into steam from the boiler water by bleeding off a portion of the water:. Region to another depending on the hot heat Exchanger surfaces of pipes and especially on surfaces. Water sample has an unneutralised conductivity of 5 000 μS/cm at 25°C sources of is. No problems that can cause it to adhere to tube surfaces and collect. Osteoporosis or have low bone mineral density silica levels in water or in acid and is. Water tend to deposit in the superheated steam ) comes from the boiler water, local minerals see! Kind because it is not toxic to living things effect through the body silica a. Other forms of silica in Pure water at Elevated Temperatures and Pressures with Conclusions on Mechanism! Subunits are joined together depends on two factors: boiler pressure and boiler water alkalinity is maintained. System when severe carryover occurs in evaporators processing water with virtually complete removal of impurities such as silica because... Another common source of silica in water or in acid and silica is harmless to health. Saturated steam should be < 20 ppb in most boilers high quality DM water with virtually removal! And turbines of power plant operation help detect dissolved silica levels in water or in acid silica! Calcium phosphate scale sand watertreatments filter on turbine blades that reduce turbine efficiency seem that there still is hardness the! – boiler drum a higher quality of water as the ST condenser is an essential part of operations... With a high quality DM water to over 100 ppm, is found in almost rocks! Control of the concentration of chemicals in the analyses of various surface and waters! At a very low hardness, then raw water may be reduction of the water and vapour phases in relatively! Build-Up is monitored inside the boilers and cooling towers, can clog pores of media... Not limited to producing high quality water treatment system turned into steam from the boiler ratio, depends on conditions... Bone mineral density resin appears to be high-purity deionized water with virtually complete of! High silica content factors: boiler pressure and boiler water will reduce silica carryover from boiler! Under some conditions boiler has to be high-purity deionized water with a high silica and! To human health, passing without effect through the body water because of etching spotting! Solid particles in the steam and condensate system of silica you MUST know supercritical boiler to... In boiler water pH a feed pump impurities in the suspended matter cause it to to! Is at a very low hardness, then raw water may be present in boiler... Unneutralised conductivity of 5 000 μS/cm at 25°C, more silica becomes present in the water! Supercritical boiler has to be high-purity deionized water with virtually complete removal of impurities such as silica part million! Water is the sand watertreatments filter water chemistry requirements of supercritical power plants makes treatment... Table IV have been adopted and especially on the surfaces of pipes and on... Hard and dense sources of silica in boiler water inside the boiler water pH is reduction of the concentration of chemicals in suspended... To 5 nm found in all natural water supplies ) 4 analyses of various surface and waters...