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