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When do you need to measure metals?
- Permit conditions. The environmental permit sets emission limit values for metals, often for zinc too, and how often they are to be checked.
- Waste incineration and co-incineration: the Swedish Ordinance on Waste Incineration (SFS 2013:253) has emission limit values for eleven metals and requires at least two measurements a year.
- The BAT conclusions for waste incineration have lower BAT-associated emission levels (BAT-AELs) and specify measurement according to EN 14385 every six months.
- Large combustion plants: the BAT conclusions specify measurement once a year for coal, solid biomass fuel, peat and fuel oil, more often when waste is co-incinerated.
- Metal industry, cement and glass: BAT conclusions with measurement requirements or BAT-AELs exist for non-ferrous metals, foundries, cement kilns and glass furnaces.
- Performance tests and guarantee checks after new or rebuilt flue gas cleaning.
How the sampling train is built
The measuring principle is isokinetic sampling with wet chemical absorption. The sample gas is drawn out through a nozzle facing the gas stream, at the same velocity as the flue gas, and led through a heated probe tube to a heated plane filter where the particles are caught. What passes the filter is captured in three absorption bottles in a cooling bath, filled with dilute nitric acid and hydrogen peroxide. An empty bottle catches splashes, a drying tower dries the gas, and after the control valve, pump and flow meter a dry gas meter measures the sample volume. A pitot tube, a thermocouple and pressure gauges provide the data for the isokinetic control.
- 1. Nozzle, facing the gas stream
- 2. Probe tube, heated
- 3. Filter holder with plane filter, heated
- 4. Absorption bottles with absorption solution, in a cooling bath
- 5. Empty knock-out bottle that catches splashes
- 6. Drying tower with silica gel
- 7. Control valve
- 8. Gas-tight pump
- 9. Flow meter
- 10. Dry gas meter
- 11. Temperature sensor at the gas meter
- 12. Temperature sensor, flue gas temperature (type K thermocouple)
- 13. Pressure gauge, static pressure in the duct
- 14. Pressure gauge, dynamic pressure (micromanometer)
- 15. Pitot tube (L- or S-type) for gas velocity
- 16. Barometer
Everything the sample gas meets up to the last bottle must be made of borosilicate glass, quartz glass, PTFE or titanium. Titanium, however, can contain some of the metals to be determined. When several parameters are sampled at the same time, only part of the sample gas, a side stream, is led through the bottles.
How is a metals measurement done?
Measurement plan and preliminary measurement
The measurement site must meet EN 15259, as for dust measurement. Gas velocity, temperature, oxygen and moisture are measured at the measurement points, and the nozzle is chosen for isokinetic sampling.
Clean equipment and field blank
Everything that meets the sample gas is cleaned beforehand, and the absorption solution is mixed fresh. At the measurement site a field blank is taken: the whole sampling train is assembled and rinsed as after a sample, without drawing flue gas through it.
Isokinetic sampling
After the leak test (at most 2 % of the sample gas flow), the probe is moved between the measurement points. The flow is adjusted at least every five minutes so that the deviation from isokinetic sampling stays within −5 to +15 %. The probe and filter are kept at least 20 °C above the temperature and the dew point of the flue gas.
Rinsing
The nozzle, probe and filter holder are rinsed with dilute nitric acid, and the tube to the first bottle is rinsed into it. The filter, the rinse solution and the absorption solution are handled separately.
Analysis
An accredited laboratory digests the filter in acid under pressure and analyses all the solutions by ICP-MS, ICP-OES or atomic absorption.
Calculation and report
For each metal, the amounts on the filter, in the rinse solution and in the bottles are added up and divided by the volume of dry sample gas, which gives mg/Nm3 (dry gas at 0 °C and 101.3 kPa). The concentrations are converted to the reference oxygen content and reported per metal and as sums, with their measurement uncertainty.
The requirements in EN 14385
These requirements decide whether a metals sampling is valid. They are essentially the same in the 2004 and 2024 editions of the standard.
| Requirement | Value |
|---|---|
| Deviation from isokinetic sampling | −5 to +15 %, according to EN 13284-1 |
| Materials in contact with the sample gas | Borosilicate glass, quartz glass, PTFE or titanium, from the nozzle to the last bottle |
| Probe and filter | At least 20 °C above the temperature and the dew point of the flue gas |
| Filter | Plane filters from the same batch, with a low and even metal content |
| Absorption bottles | At least three in series, with less than 1 m of line from the probe |
| Absorption efficiency | At most 10 % of a metal's total amount in the last bottle |
| Leak rate | At most 2 % of the sample gas flow, before each sample |
| Field blank | At most 10 % of the emission limit value. Not subtracted from the measured value; lower measured values are reported as ≤ the field blank |
Which metals are included?
EN 14385 is validated for eleven metals, which the regulations split into two sums. Mercury has a standard of its own. Other metals are sampled in the same way, but the standard is not validated for them and we report them without accreditation.
| Metals | In EN 14385 | In the regulations |
|---|---|---|
| Cadmium (Cd) and thallium (Tl) | Yes | The sum Cd + Tl |
| Antimony (Sb), arsenic (As), lead (Pb), chromium (Cr), cobalt (Co), copper (Cu), manganese (Mn), nickel (Ni) and vanadium (V) | Yes | The sum of the nine |
| Selenium (Se), zinc (Zn) and tin (Sn) | No | Selenium and zinc are in the measurement requirements for large combustion plants, selenium and tin in the glass industry's sums |
| Mercury (Hg) | No, EN 13211 | Emission limit value of its own |
Particle-bound and gaseous
Metals occur in the flue gas in and on particles, dissolved in droplets and as gas. The filter catches the particles and the absorption solution what passes it: gas, but also very fine dust. The standard's field trials showed that most metals cannot be determined quantitatively in the gas phase on its own, so the result is always the total concentration.
Because the particles carry metals, the sample is taken isokinetically and at several measurement points, as in dust measurement; otherwise the share of heavy particles is wrong.
At low concentrations, cleanliness decides the result. The BAT conclusions' upper value for cadmium and thallium at waste incineration plants is 0.02 mg/Nm3, and the field blank may be at most a tenth of that: 2 millionths of a gram per cubic metre, for the filter, rinse solution and bottles together. Measured values below the field blank are reported as at most equal to it, so in practice the field blank sets the detection limit. Bottles and tubing from mercury sampling must therefore not be used for metals: the permanganate solution leaves manganese behind.
Which emission limit values apply to metals?
The emission limit value is set in the permit, in the Swedish Ordinance on Waste Incineration (SFS 2013:253) or in the sector's BAT conclusions, whose upper value applies as a limit value four years after publication. The values refer to sums of metals, in solid form and in the gas phase.
| Plant | Emission limit value or BAT-AEL | Rule |
|---|---|---|
| Waste incineration (11 % O2) | Cd + Tl: 0.05 mg/Nm3. Sb + As + Pb + Cr + Co + Cu + Mn + Ni + V: 0.5 mg/Nm3 | SFS 2013:253, section 64 |
| Co-incineration: combustion plant (6 % O2, solid fuel) and cement kiln (10 % O2) | 0.05 and 0.5 mg/Nm3 | SFS 2013:253, sections 69 and 95 |
| Waste incineration, BAT-AEL | Cd + Tl: 0.005–0.02 mg/Nm3. The nine metals: 0.01–0.3 mg/Nm3 | BAT 25, (EU) 2019/2010 |
| Large combustion plant co-incinerating waste with coal | The nine: 0.005–0.5 mg/Nm3 below 300 MW, 0.005–0.2 from 300 MW (average of the year's samples). Cd + Tl: 5–12 and 5–6 µg/Nm3 respectively | BAT 68, (EU) 2021/2326 |
| Large combustion plant co-incinerating waste with biomass or peat | The nine: 0.075–0.3 mg/Nm3. Cd + Tl: < 5 µg/Nm3 (average of the year's samples) | BAT 69, (EU) 2021/2326 |
| Cement kiln | Cd + Tl: < 0.05 mg/Nm3. The nine: < 0.5 mg/Nm3 | BAT 28, 2013/163/EU |
| Container glass melting furnace | As + Co + Ni + Cd + Se + Cr(VI): < 0.2–1 mg/Nm3. Together with Sb, Pb, Cr(III), Cu, Mn, V and Sn: < 1–5 mg/Nm3 | BAT 21, 2012/134/EU |
What does a metals measurement cost?
The price depends on the number of stacks or ducts and operating conditions and on the number of samples. The laboratory analysis is a large part of it: each sample gives the laboratory several portions to analyse separately (the filter, the rinse solution, the first two bottles and the third on its own), and the field blank is analysed in the same way. More metals than the standard's eleven increase the analysis cost. When mercury, dust or dioxins are measured during the same visit, travel and set-up are shared. Request a quote and we will reply within two working days. Approximate prices for the most common measurements are in the price guide.
How often must metals be measured?
As often as the permit says. For waste incineration and co-incineration, the Swedish Ordinance on Waste Incineration (SFS 2013:253) requires at least two measurements a year, and one every three months during the first twelve months of operation. The BAT conclusions specify every six months for waste incineration and once a year for large combustion plants, but every six months when waste is co-incinerated and every three months from 300 MW. The non-ferrous metals industry and foundries measure once a year.
Measure metals yourself
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DX21-103EVA Light glass probe for metals sampling
Heated glass probe with glass nozzles of 4–12 mm, S-type pitot tube and thermocouple, 1,000 or 1,500 mm long.
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GM11-101 · GM11-102CU-1-10 and CU-1-20 control units
Vacuum pump, drying tower, flow meter and gas meter in one portable unit, up to 10 or 20 l/min.
Frequently asked questions about metals measurement
Is the metals measurement accredited?
Yes, the sampling. METLAB's Swedac accreditation covers the sampling of metals according to EN 14385, and the analysis is done by an accredited laboratory. Metals beyond the standard's eleven are reported without accreditation.
How long does a metals measurement take?
A sample lasts between 30 minutes and 8 hours. Energiforsk's Emissionsmäthandbok (the Swedish emission measurement handbook) recommends at least one hour, and the BAT conclusions' values refer to the average of three consecutive samples. Add to that the set-up, the preliminary measurement, the field blank and the rinsing.
Can metals be measured at the same time as mercury and HCl?
Yes. From the same probe and filter, the sample gas is split into side streams, each with its own absorption solution: one for metals, one for mercury and more where needed, for example for HCl. The filter and the side streams for metals and mercury must have the same sampling time.
What is required of the measurement site?
The same as for dust measurement: sampling ports on a straight run of duct, normally 3-inch threaded sockets, and a safe working platform with room for the probe, bottle rack and cooling bath. Also electricity for the probe heating and the pump.
How are values below the detection limit counted in the sum?
According to the 2024 edition of EN 14385, a portion of the sample below the laboratory's limit of quantification counts as half the limit when the metals are added up. With many small portions the sum can therefore be higher than the real emission, one reason to take a large enough sample volume.