stack new.pdf
- 1. STACK MONITORING PRESENTED BY SRUTHEESH SOMANATH NAMP OPERATOR 1
- 2. • The main pollutants are:- • CO • NOx • CO2 • SOx • SPM, etc. • The gases emitted from the stack impair the composition of the atmosphere. Thus causes air pollution. Therefore, analysis & monitoring of pollutants is done.
- 3. STACK • A stack is a structure for venting hot flue gases or smoke from a boiler, stove, furnace or fireplace to the outside atmosphere. • These are typically vertical to ensure that the gases flow smoothly through them. • The height of stack plays an important role in their ability to transfer flue gases and it varies for different industries. • The dispersion of pollutants at a higher altitude helps reduce the influence of pollutants in the surroundings. • In the case of chemically aggressive output, the tall stack allows partial or complete self- neutralization of chemicals in the air before they reach the ground. • The dispersion of pollutants over a large area reduces their concentration in compliance with regulatory limits.
- 4. STACK EMISSION MONITORING • Stack monitoring is performed by inserting a measuring device into the stack to obtain a sample of fume. • The purpose of stack sampling is to determine the quantity, quality & the type of pollutants emitted from a specific source, efficiency of the pollutant collector & to determine an appropriate design for air pollution control equipment.
- 5. Devices for general use Meters • They are used to determine accurately the volume of the gas collected. They are fitted with manometers and thermometers to indicate the pressure and temperature of the gas stream sampled. Probes • These are tubes suitable for penetrating into the gas stream and should be constructed of materials which are noncorrosive and which can withstand special temperature conditions. • Also, they should be constructed of materials which do not react with the substances to be sampled.
- 6. Therefore, they should be made of stainless steel or preferably of glass or quartz. • A probe should have suitable length and diameter. • To ensure isokinetic sampling conditions, the opening of the probe should face the gas stream to be sampled. Suction Devices • Any suction device which has the required volumetric capacity can be used. Vacuum pumps driven by electric motors are very commonly used.
- 8. Selection of Sampling location and Minimum Number of Traverse Points • Select the sampling location at any cross section of the stack at least eight stack diameters downstream (8D) and two stack diameters upstream (2D) from any point of flow disturbance (bend, expansion, contraction, visible flame, or stack exit) • Cross section of stack is divided into a number of equal areas where traverse points are located • Determine the number of traverse points required. Inside diameter of stack or duct (m) Number of points I.D. ≤ 0.3 4 0.3 ≤ I.D. ≤ .6 8 0.6 ≤ I.D. ≤ 1.2 12 1.2 ≤ I.D. ≤ 2.4 20 2.4 ≤ I.D. ≤ 5 32 8
- 9. Location of traverse points on circular cross section 9 For circular stack divide the cross section into equal parts by two right-angle diameters, locate half the traverse points symmetrically along each diameter.
- 10. Location of traverse points on diameters of cross section of circular stacks 10
- 11. Example showing circular stack cross section divided into 12 equal areas, with location of traverse points 11
- 12. • For stack having dia. > than 0.61 m , no traverse point shall be located within 2.5 cm of stack wall. • For stack diameters < than 0.61 m , no traverse point shall be located within 1.3 cm of stack wall. • If any traverse points falls within 2.5/1.3 cm of stack wall, relocate them away from stack wall. • For elliptical stacks having unequal perpendicular diameter, separate traverse points shall be calculated along each diameter. • Use same traverse points and locations for velocity and particulate measurements. 12
- 13. Location of sampling port • To ensure laminar flow, 8D- 2D i. Number of sampling port – min. 2 ports are required, so that full cross- sectional area of stack can be covered for measurements. ii. Dimensions of sampling port – standard flanged pipe of 0.10 m inside diameter with 0.15 m bolt circle diameter. Port should extended outward from the exterior stack wall not less than 40mm, installed at height between 0.90 and 1.2 m above the floor of working platform. iii. Platform – If two ports are required at 90o , half of stack circumference and If four ports are required, entire circumference ; minimum platform width shall always be 1.2 m iv. Platform access – caged ladder, stairway, rooftop v. Platform loading – support load of at least three men and equipments vi. Power supply – At platform and stack base 13
- 14. 14 ˃ Position of sampling ports in a circular stack
- 15. Iso-kinetic sampling • Obtaining representative particulate sample • Kinetic energy of gas stream in stack should be equal to kinetic energy of gas stream through the sampling nozzle • If sampling velocity is greater than velocity in duct tube will suck extra particles, collecting higher percentage of smaller particles, the sampling will have a lower mass concentration • If the sampling velocity is less than velocity in duct then tube will became pressurized and particles will want to be expelled from the tube. The particles more easily dispelled are small particles resulted into collection of larger particles ,PM has a higher mass conc. 15
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- 17. Stack Temperature and Velocity Measurement • VVM-1 • Temperature- Has a digital pyrometer and thermocouple. • Velocity- A digital pressure cell (for measurement of pressure in mm of H2O) along with pitot tube. 17 Thermocouple Inter-connection tubings Carrying case Extension for pitot tube Pitot tube Pyrometer Digital pressure cell
- 18. Stack Temperature and Velocity Measurement • APM 602 • Temperature- Has a digital pyrometer and thermocouple. • Velocity- An inclined cum vertical manometer along with pitot tube. 18 Pitot tube Thermocouple sensor Manometer Digital pyrometer Inter-connection tubings Spirit level
- 19. Temperature Measurement • Thermocouple is connected with the Pyrometer • Switch on the pyrometer to measure the Ambient temperature (Tm) • Insert the thermocouple sensor into the stack through sampling port • Allow the temperature to stabilize for atleast 10 minutes • Record Stack temperature (Ts) from pyrometer • Remove the thermocouple • Hold the sensor by its handle, it is likely to be hot. 19
- 20. Stack gas velocity determination • Connect two ends of the manometer marked “pitot” to ends of Pitot tube (pitot end which has mark is connected to ‘+ve’ end of manometer) • Manometer sets to zero before hoses are connected • Insert pitot tube into stack keeping marked end of the tube facing the air stream • Plug the clearance between the port hole walls and pitot tube with asbestos wool to prevent air flow through port hole • Orient the pitot tube axis and search best alignment (highest reading ) • Note the manometer reading at various traverse points • Disconnect the pitot tube when entire cross-section of stack has been traversed 20
- 21. Pitot tube with Manometer 21
- 22. Type S pitot tube 22
- 23. i. Stack gas velocity V = k x (Stack Temperature x Pressure difference)1/2 where, V = Air velocity (m/sec) k = Pitot tube constant (0.1973) 23
- 24. ii. Stack gas volumetric flow Rate Qs = V x 60 x 1000 x Tm/Ts x A where, Qs = Flow rate (lpm) V = Velocity of stack gases (m/sec) A = Cross - sectional area of nozzle (m2) Tm= Absolute ambient gas temperature (K) Ts = Absolute stack gas temperature (K) 24
- 25. Nozzles • Stainless steel (SS 304) with sharp tapered leading edges. • Minimum recommended internal diameter is 7 mm. • Select the nozzle size which provides meter sampling rate up to 30 LPM. • Nozzle Sizes :- 25 Nozzle (inches) Internal diameter (mm) Area (m2) 1/2 12.58 12.4 x 10-5 3/8 8.60 5.8 x 10-5 1/4 6.32 3.1 x 10-5 1/8 3.10 7.5 x 10-6
- 26. Sampling Period for Particulate matter • A minimum of 1 m3 of dry gas has been withdrawn for sampling. • The mass of particulate matter amounts to atleast 20 percent of the mass of the filtering medium in the sampler. • Sampling period should be of lesser duration in heavy dust concentrations. • Too short time may give unreliable results and too long a time may cause resistance of sampling train to exceeds capabilities of vacuum pump. 26
- 27. Handy Stack Sampler APM-620 • The SPM is trapped and collected in a Filter media • Various gaseous pollutants are absorbed in suitable reagents, then analysed subsequently by simple wet chemistry methods to determine the concentrations. 27 Dry gas meter Vacuum pump Nozzle Filter holder Probe Sampler Hose pipes Rotameter
- 28. Handy Stack Sampler APM-620 i. Nozzles : A set of 4 stainless steel nozzles with internal diameter of 12.5mm, 98.6 mm, 6.3 mm & 3.1 mm. ii. Filter Holder : Stainless steel (SS 304), Suitable to hold (a) cellulose filtration thimble (size 28mm lD X 100mm long) (b) glass micro fibre thimble (size 19mm lD X 90mm long) iii. Sampling Probe : Made from SS 304 , 0.3m and 1 m in length iv. Impingers : 2 No. (240 ml) and 3 No. (120 ml) borosilicate glass impingers with Ball socket joints accommodated in ice tray. v. Rotameter : Used for flow measurement, Plastic body rotameter , 0 – 30 lpm for particulates and 0-3 lpm for gaseous pollutants monitoring vi. Dry Gas Meter : Mechanical Type with a range of 40 lpm flow rate. vii.Vacuum Pump : Monoblock Rotary Vane type, oil lubricated, 0.5 HP single phase motor (230V) with 50 lpm free flow capacity 28
- 29. Filter media - Thimbles • Paper thimbles – used at temp. up to 150o C • Alundum thimbles – able to withstand high temp. up to 550o C high wet strength, chemical resistance • Glass fibre thimbles – used in heavy dust loading conditions, able to withstand 550o C of temperature 29
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