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