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What equipment is needed for a sampling train for trace metals and particulates in flue gases?
Date posted:
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Post Author
Patrick LaveryCombustion Industry News Editor
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1. Background
Trace metals are of environmental, legislative and maintenance concern for combustion processes. Their measurement (sampling and analysis) is complex, but obviously vital in any consideration of legislative compliance or control. Further information on trace metals can be found in CF58.
This Combustion File (CF) deals with the equipment required for a sampling train conforming to the requirements of US EPA Method 29: Determination Of Metals Emissions From Stationary Sources. Particulates can also be measured using this technique. The preparation and use of this sample train are the subject of CFs 207-209.
US EPA Method 29 draws heavily on US EPA Method 5 and US EPA Method 2.
Safety
This CF does not cover safety procedures. The reader should consult other safety literature and particularly local safety regulations before performing the acquisition of the sample.
2. Applicability
The method that this equipment is used for is applicable for the measurement of the metals antimony (Sb), arsenic (As), barium (Ba), beryllium (Be), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), lead (Pb), manganese (Mn), mercury (Hg), nickel (Ni), phosphorus (Ph), selenium (Se), silver (Ag), thallium (Th) and zinc (Zn). However, the measurement of mercury may not be accurate using this method, as it does not account properly for mercury speciation. The Ontario-Hydro method is more suited to mercury speciation measurements, but is not the subject of this CF.
This train can also be used to measure particulates.
It should be used for sampling flue gases from stacks, with temperatures expected to be not higher than around 300oC.
3. Equipment
Table 1 gives details of the equipment used in the sampling train, with materials of construction where possible and other design comments. Table 2 lists the equipment needed for sample recovery. Table 3 lists the chemicals needed for cleanup of the sampling train.
A schematic of the sampling train is shown in Figure 1. This figure shows the interrelation of the different pieces of equipment shown in Tables 1 and 2. Some equipment is shown in Figure 1 that is not contained within the two tables – this is standard equipment.
Figure 1. Sampling train for trace metals according to US EPA Method 29. (US Federal Registry)
Table 1. Equipment required for trace metal sample train.
Item |
Construction Comments |
Further Comments |
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Probe Nozzle and Probe Liner |
Borosilicate or quartz glass, or any other material free from contamination |
Fittings should be of plastic (i.e. Teflon or polypropylene) to avoid contamination. The nozzle and probe can be made of one single piece of glass if wished. |
|
Pitot Tube |
Stainless steel |
OD: 0.48-0.95cm. Type S pitot tube. |
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Teflon Tape |
Teflon |
For capping openings and sealing connections on the sampling train. |
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Differential Pressure Gauge |
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Inclined manometer or equivalent. If magnehelic gauges are used, they must be checked after each test series. |
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Filter Holder |
Borosilicate glass, with Teflon filter support and silicon rubber gasket |
Design of holder shall provide positive seal against leakage from the outside or around the filter. Attached immediately at the outlet of the probe. |
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Filter Heating System |
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Any capable of maintaining a temperature around the filter of 120 ± 14 oC |
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Temperature Sensor |
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Capable of measuring within 1oC at the outlet of the last impinger |
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Metering System |
Vacuum gauge, leak-free pump, dry gas meter (DGM) included |
Temperature sensors capable of measuring within 3oC. DGM capable of measuring volume within 2% |
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Barometer |
Mercury, Aneroid or other |
Capable of measuring atmospheric pressure to within 2.5mm Hg |
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Bypass and main-control valve |
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For control of flow |
Condenser – For condensing and collecting gaseous metals and determining the moisture content of the stack gas. Impingers connected in series with leak-free ground glass fittings or other leak free, non-contaminating fittings. If no Hg analysis planned, then Impingers 4,5 & 6 not required. |
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1st Impinger |
Empty |
Moisture Trap |
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2nd Impinger |
HNO3/H2O2 |
Greenburg-Smith design, modified by replacing the tip with a 1.3cm ID glass tube extending to about 1.3 cm from the bottom of the flask. |
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3rd Impinger |
HNO3/H2O2 |
Greenburg-Smith design with standard tip |
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4th Impinger |
Empty |
Modified same as 2nd Impinger |
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5th Impinger |
Acidified KMnO4 |
Modified same as 2nd Impinger |
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6th Impinger |
Acidified KMnO4 |
Modified same as 2nd Impinger |
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7th Impinger |
Silica gel |
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Gas Density Determination Equipment |
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Temperature Sensor |
Thermocouple or thermometer. |
Capable of measuring within 1.5% of the minimum absolute stack temperature. Permanently attached to the pitot tube in a fixed configuration such that the tip extends beyond the leading edge of the probe shaft and does not touch any metal. |
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Pressure Probe and Gauge |
Piezometer tube and mercury or water filled U-tube manometer |
Capable of measuring stack pressure within 2.5mm Hg. |
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Gas Analyser |
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For the determination of CO2 and O2 concentrations, and dry molecular weights of a sample gas |
Table 2. Equipment required for sample recovery from trace metal sampling train.
Item |
Construction Comments |
Further Comments |
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Probe Nozzle and Liner Brushes/Swabs |
Teflon or Nylon (no metal materials) |
Nylon bristles, properly shaped to clean. Extension/handle to probe brush at least as long as the probe |
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Wash Bottles (X2) |
Glass. Polyethylene also acceptable. |
Do not use polyethylene for storing acetone more than one month. |
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Glass Sample Storage Containers |
Chemically resistant, borosilicate glass bottles, with rubber backed Teflon lined screw caps |
Non-reactive to oxidising solutions. With capacities of 1000ml and 500 ml for storage of acidified KMnO4-containing samples and blanks. Polyethylene or glass can be used for other sample types. |
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Graduated Cylinder |
Glass or equivalent. Subdivisions no greater than 2 ml. |
To measure condensed water to within 1ml or 0.5g. |
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Petri Dishes |
Glass or polyethylene |
For filter samples |
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Plastic Storage Containers |
Plastic. Air tight. |
To store silica gel. |
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Funnel and Rubber Policeman |
Glass or equivalent |
To aid in transfer of silica gel to container; not necessary if silica gel is weighed in field |
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Labels |
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For identifying samples |
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Polypropylene Tweezers and/or Plastic Gloves |
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For recovery of the filter from the sampling filter holder |
Table 3. Chemicals needed for cleaning
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Chemical |
Quantity |
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Acetone |
100ml per clean, plus extra in case of spillage etc. |
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0.1 N HNO3 |
300ml per clean, plus extra in case of spillage etc. |
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Fresh acidified KMnO4 |
100ml per clean, plus extra in case of spillage etc. |
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8 N HCl |
25ml per clean, plus extra in case of spillage etc. |
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Water |
At least 500ml per clean |
Sources
[1] US EPA, US EPA Method 29: Determination Of Metals Emissions From Stationary Sources, US Federal Registry.
[2] US EPA, US EPA Method 2: Determination Of Stack Gas Velocity and Volumetric Flow Rate, US Federal Registry.
[3] US EPA, US EPA Method 5: Determination Of Particulate Matter Emissions From Stationary Sources, US Federal Registry.