What equipment is needed for a sampling train for trace metals and particulates in flue gases?

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What equipment is needed for a sampling train for trace metals and particulates in flue gases?
Date posted: 16th Dec 2002
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- Post Author
  
  Patrick Lavery
  
  Combustion Industry News Editor

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 300^oC.

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
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.
Teflon Tape	Teflon	For capping openings and sealing connections on the sampling train.
Differential Pressure Gauge		Inclined manometer or equivalent. If magnehelic gauges are used, they must be checked after each test series.
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.
Filter Heating System		Any capable of maintaining a temperature around the filter of 120 ± 14 ^oC
Temperature Sensor		Capable of measuring within 1^oC at the outlet of the last impinger
Metering System	Vacuum gauge, leak-free pump, dry gas meter (DGM) included	Temperature sensors capable of measuring within 3^oC. DGM capable of measuring volume within 2%
Barometer	Mercury, Aneroid or other	Capable of measuring atmospheric pressure to within 2.5mm Hg
Bypass and main-control valve		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.
1^st Impinger	Empty	Moisture Trap
2^nd 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.
3^rd Impinger	HNO₃/H₂O₂	Greenburg-Smith design with standard tip
4^th Impinger	Empty	Modified same as 2^nd Impinger
5^th Impinger	Acidified KMnO₄	Modified same as 2^nd Impinger
6^th Impinger	Acidified KMnO₄	Modified same as 2^nd Impinger
7^th Impinger	Silica gel
*Gas Density Determination Equipment*
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.
Pressure Probe and Gauge	Piezometer tube and mercury or water filled U-tube manometer	Capable of measuring stack pressure within 2.5mm Hg.
Gas Analyser		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
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
Wash Bottles (X2)	Glass. Polyethylene also acceptable.	Do not use polyethylene for storing acetone more than one month.
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.
Graduated Cylinder	Glass or equivalent. Subdivisions no greater than 2 ml.	To measure condensed water to within 1ml or 0.5g.
Petri Dishes	Glass or polyethylene	For filter samples
Plastic Storage Containers	Plastic. Air tight.	To store silica gel.
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
Labels		For identifying samples
Polypropylene Tweezers and/or Plastic Gloves		For recovery of the filter from the sampling filter holder

Table 3. Chemicals needed for cleaning

Chemical	Quantity
Acetone	100ml per clean, plus extra in case of spillage etc.
0.1 N HNO₃	300ml per clean, plus extra in case of spillage etc.
Fresh acidified KMnO₄	100ml per clean, plus extra in case of spillage etc.
8 N HCl	25ml per clean, plus extra in case of spillage etc.
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.