Presentation is loading. Please wait.

Presentation is loading. Please wait.

STEAM & WATER ANALYSIS SYSTEM

Similar presentations


Presentation on theme: "STEAM & WATER ANALYSIS SYSTEM"— Presentation transcript:

1 STEAM & WATER ANALYSIS SYSTEM
AN OVERVIEW PRESENTED BY : DEPARTMENT OF IPC & CHEM. LAB - SANTALDIH TPS - WBPDCL 10-Jan-2011 A K SARKAR Page 1 of 21

2 Most of the Power generation in India is Thermal Power. That means
WHY SWAS ? Most of the Power generation in India is Thermal Power. That means Coal or Gas is used as fuel to heat water in the boiler. This water becomes steam and this steam runs the turbine to produce electricity by means of Generator connected with the turbine. The turbine is a masterpiece of engineering. Its design is very compli- -cated and intricate. The turbine is very costly and is very carefully manufactured and installed in a power station. Boiler, various tubes and pipes that make the Power Plant are also important. All this is dependent on good quality of steam. If the steam produced is of bad quality, it starts damaging this equipment by means of corrosion. The turbine/boiler and various tubes/pipes in the power plant start getting damaged and eventually fail. It is therefore essential to arrest all the elements that cause the corrosion effects of various kinds. It calls for modern methods that keep a 24-hours-a-day vigil on these elements, however small these may be. This can be precisely done by an On-line Steam and Water Analysis System, popularly termed as SWAS. Page 2 of 21

3 THE IMPORTANCE OF MONITORING BOILER PARAMETERS
The power plants using steam need some water source. As all of us know, water is no more a free resource. Further, the quality of water available from rivers, dams or underground sources is deteriorating every day. If we use such contaminated water for generating steam, it will have an immediate impact on the complete plant and machinery in the power plant, as there will be a lot of erosion and corrosion that will take place. In any power plant running on steam, the purity of boiler feed water and steam is absolutely crucial; especially to steam turbine, steam boiler, super heater, condenser and other steam equipment. To prevent damage of steam turbine, steam boiler and other apparatus due to scaling and corrosion, on line steam and water analysis of critical parameters is inevitable. A well-engineered SWAS can measure all these parameters accurately and reliably. As we know, anything that can be measured accurately can be controlled accurately. Page 3 of 21

4 WHAT ARE THESE CRITICAL PARAMETERS ?
pH CONDUCTIVITY HYDRAZINE SILICA DISSOLVED OXYGEN SODIUM OTHER PARAMETERS Monitoring of other parameters such as alkalinity, hardness, calcium, chloride, phosphate, dissolved ozone is also required, depending on the size of the plant and the quality of water / steam equipment. Let us see the significance of each of these parameters : pH In a soln. pH approximates but is not equal to p[H], the –ive logarithm (base10) of the molar concentration of dissolved hydronium ions(H3O+); a low pH indicates high concentration of hydronium ions& a high pH indicates low concentration.It is a measure of the acidity or basicity of a soln. The pH scale ranges from 0 to 14. Ultra pure water has a neutral pH value of 7. A pH less than 7 is acidic and greater than 7 is basic or alkaline. In the steam circuit the normal practice is to keep the pH value of feed water at slightly alkaline levels. Accurate pH analysis can therefore help in preventing the corrosion of pipe work and other equipment. Page 4 of 21

5 CONDUCTIVITY Conductivity (G), the inverse of Resistivity (R) is the ability of a material to conduct electric current. Since the charge on ions in solution facilitates the conductance of electrical current, the conductivity of a solution is proportional to its ion concentration. Conductivity in water is affected by the presence of inorganic dissolved solids such as chloride, nitrate, sulfate and phosphate anions (ions that carry a -ive charge) or sodium, magnesium, calcium, iron and aluminium cations (ions that carry a +ive charge). Organic compounds like oil, phenol, alcohol and sugar do not conduct electrical current very well and therefore have a low conductivity when in water. Conductivity is also affected by temperature: the warmer the water, the higher the conductivity. For this reason, conductivity is reported as Conductivity at 25 Degrees Celsius (250C). The basic unit of measurement of conductivity is the mho(Ω) or siemens(s). Conductivity is measured in micromhos per centimeter(µΩ/cm) or microsiemens per centimeter(µs/cm). Distilled water has a conductivity in the range of 0.5 to 3.0µs/cm. Industrial waters can range as high as 10000µs/cm. Ultra-pure water or steam is almost a bad conductor of electricity. It becomes conductive only when there is some contamination. Therefore conductivity measurement can give a quick indication of steam contamination. Page 5 of 21

6 HYDRAZINE (N2H4) Hydrazine is an inorganic chemical compound with the formula N2H4. It is a colourless liquid with an ammonia-like odour H However, hydrazine has physical properties that are closer to those of water. Hydrazine is N N highly toxic and dangerously unstable, and is H usually handled while in solution for safety reasons H H The use of hydrazine as an oxygen scavenger and a source of Feed water alkalinity has advantages that are well known. a) It prevents frothing in the boiler. b) It minimizes deposits on metal surfaces. c) It removes the dissolved oxygen in the steam by chemical action. Hydrazine does not produce corrosive gases at high temperatures and pressures, and in application, reacts with oxygen to form nitrogen and water: N2H4 + O2 → 2 H2O + N2 Hydrazine does’nt contribute solids to the system, so boiler blowdown is reduced. Hydrazine helps to maintain a protective magnetite(Fe3O4) layer over steel surface, and maintain feed water alkalinity to prevent acidic corrosion. It is essential to doze hydrazine correctly, which can be done with the help of an on-line Hydrazine analyzer. Page 6 of 21

7 In order that the turbines are operated at maximum performance,
SILICA (SiO2) Most boilers making steam for turbines rarely have excessive carryover of boiler water in the steam. While, silica deposits in turbine can occur even when boiler water carryover is negligible. The reason is: steam selectively “picks up” silica from the boiler water, dissolves it, and carries it to the turbines, where it redeposit. The key to minimizing silica carryover is in keeping the boiler water silica content below certain levels, the concentration depending on operating pressures. Steam is a solvent for silica. The maximum solubility of silica in steam is a direct function of both the steam density and temperature. As steam temperature or density decreases, the silica solubility also decreases. Since pressure affects steam density and has a bearing on steam temperature, the solubility of silica in steam increases with pressure. The presence of silica in steam can lead to deposition in superheater tubes and on the turbine blades. Small deposits on the turbine blades can result in a loss of efficiency, whilst larger deposits can cause permanent mechanical damage. In order that the turbines are operated at maximum performance, continuous monitoring of silica in steam, boiler water and feed water is highly recommended. It is also essential to check silica levels at the source of water input to the plant. Page 7 of 21

8 At high temperatures dissolved oxygen attacks and causes corrosion
DISSOLVED OXYGEN ( DO2 ) At high temperatures dissolved oxygen attacks and causes corrosion of components and piping. The result is pitting, which may eventually causes puncturing and failures. Dissolved oxygen is also responsible for leakage at joints and gaskets. Hence it is essential to measure and control it precisely. Do you Know that 10 ppb of DO2 in a boiler of 450TPH creates 90 Kg. of rust per year ! SODIUM (Na) The presence of sodium signals contamination with potentially corrosive anions, e.g. chlorides, sulphates etc. Under conditions of high pressure and temperature, sodium salts are responsible for stress corrosion – cracking of boiler and superheater tubes. Sodium is available in abundance in the environment and it enters even from small openings. Sodium measurement can thus reveal possible leakage conditions anywhere in the steam circuit, including condenser sections. Page 8 of 21

9 Phosphate hideout is a phenomenon that causes boiler water control
PHOSPHATE (PO4) Phosphate hideout is a phenomenon that causes boiler water control difficulties. It is defined as the disappearance, by precipitation or absorp- tion, of the ionic phosphate (PO4) species, in the boiler water under high heat transfer or high load conditions. The best way to recognise phosphate hideout is to graph load changes, pH, and phosphate over a period of time. The variations of the graphs will clearly indicate that phosphate increases with decreasing load, and that the pH decreases with decreasing load. Events which may lead to phosphate hideout include: 1) Start-up after chemical cleaning. 2) Changes in unit load. 3) Changes in burner configuration. & 4) Metal oxide ingress and deposition on heat transfer surfaces. Phosphate hideout causes confusion, frustration over uncontrollable water chemistry, and corrosion. Some phosphate-related corrosion may be severe. Page 9 of 21

10 SWAS ON-LINE ANALYSERS
ON-LINE ANALYSERS (AT SANTALDIH TPS) Line Nos. Samples taken from SWAS ON-LINE ANALYSERS pH Ks Kc N2H4 SiO2 DO Na PO4 1. FW at Economiser I/L 2. CBD from Boiler Drum 3. Saturated Steam 4. Superheated Steam 5. Condensate bef. LP Htr. 6. CEP Discharge 7. DM Make-up Water 8. Deaerator Feed Water 9. DMCW Aux. Header O/L 10. DMCW (B) HF O/L Page 10 of 21

11 All the analyzers as mentioned, work efficiently if the temperature,
THE NEED FOR SAMPLING All the analyzers as mentioned, work efficiently if the temperature, pressure and flow conditions of sample are maintained properly. Further, the sensors are capable of handling the water / steam samples at particular pressure and temperature only. This necessitates the use of the sample conditioning system. THE SAMPLE CONDITIONING SYSTEM The sample conditioning systems have several functions. The sample must be: 1. Withdrawn from the process. 2. Transported. 3. Conditioned. 4. Introduced into the analyzer. & Disposed off. Page 11 of 21

12 Position of Sample Extract for Conductivity measurement
Page 12 of 21

13 Position of Sample Extraction Probes for pH measurement
Page 13 of 21

14 Position of Sample Extraction for Silica measurement
Page 14 of 21

15 Position of Sample Extraction Probes for DO measurement
Page 15 of 21

16 Position of Sample Extraction for Sodium measurement
Page 16 of 21

17 Position of Sample Extraction for Hydrazine & PO4
measurement Page 17 of 21

18 SAMPLE EXTRACTION PROBES – For Withdrawal of Sample
Studies by CEGB(Central Electricity Generation Board, UK) suggest a more important factor in obtaining representative particulate samples may be the maintenance of a sufficiently high transport velocity in the sample line to prevent hideout of the suspended species. Thus proper sample extraction probe selection is the first step for ensuring accurate analysis of steam / water. SAMPLE PIPE WORK – For Transport of Sample Sample lines should be kept as short as possible. Use of unnecessary large line diameters should be avoided so as to avoid delayed response and the damping-out of transients. Sample pipework must be of a material, which will not react chemically with any species in the sample. Stainless steel AISI 316 is the standard. The number of bends and joints should be kept to a minimum. Page 18 of 21

19 SAMPLE COOLERS – For Conditioning of sample
The Sample coolers form the heart of the sampling system. These should preferably be of coil-in-shell type design. This should make use of counter flow type of heat exchange principle. The coolers with Double helix type coil design give better approach temperature than conventional single coil designs, apart from being compact in size. A built-in shell relief valve takes care of possible mishap due to high pressures caused by coil rupture etc. FILTRATION : For the majority of on-line analyzers, the presence of unwanted particulate matter can be damaging. To arrest this damage, a small High-pressure Filter with a sintered stainless steel element is necessary to permit regular cleaning. Page 19 of 21

20 PRESSURE REDUCTION & REGULATION
Traditional Pressure Reducing devices do not offer pressure ‘regulation’. In such cases, any pressure fluctuations in the inlet conditions can get transmitted to analysers and this is not a healthy condition for analysis. Pressure Reduction as well as ‘regulation’ is essential to ensure accurate, reliable and stable performance of on-line analysers. CHILLED WATER Use of chilled water becomes necessary when the cooling water available on site is not capable of cooling the sample to the temperatures required by the analysers. If available cooling water is upto 400C, a well-designed sampling system can ensure sample outlet temperatures of 450C. Most of the modern analysers can work comfortably with these sample temperatures. However, if cooling water temperature exceeds 400C, use of chilled water becomes necessary. Of course for some analysers, samples are always required to be conditioned at 250C by means of Chillers. Page 20 of 21

21 SANTALDIH THERMAL POWER STATION, WBPDCL BOILER WATER CHEMISTRY REPORT
O & M (CHEMISTRY) Date_________ Shift _____________ Time ________ Page 21 of 21

22 TO SEE THE NEXT PRESENTATION Courtesy: M/s. Forbes MARSHALL LIMITED.
PLEASE WAIT TO SEE THE NEXT PRESENTATION ( ANIMATION ) Courtesy: M/s. Forbes MARSHALL LIMITED.


Download ppt "STEAM & WATER ANALYSIS SYSTEM"

Similar presentations


Ads by Google