🔥 Carbon, hydrogen and nitrogen in solid biofuels — instrumental method (combustion)
In short
Combustion of a known mass of sample in oxygen (or in oxygen with a carrier gas), reduction of the nitrogen oxides to N2, removal of interfering substances and instrumental determination of CO2, H2O and N2 in the gas; calibration with pure organic substances, control with CRMs. The test is performed according to PN-EN ISO 16948:2015-07; The GIG range (carbon): 10.00–72.00 % (combustion with IR detection). The procedure comprises 6 steps; it is used for: Calculation of the net calorific value of biofuels (hydrogen) and of CO2 emissions (carbon), Assessment of the potential for fuel NOx emissions (nitrogen) in the combustion of biomass, Quality control of pellets, wood chips and agricultural biomass.
At a glance
- Standard: PN-EN ISO 16948:2015-07
- Category: Petrochemistry
- Procedure steps: 6
- Principle: Combustion in O2 or O2/carrier gas → CO2, H2O, N2 (after the reduction of the NOx) → instrumental detection
- Carrier gas: Helium or another according to the manufacturer; the oxygen according to the manufacturer
- Calibrants: Pure organic substances > 99.9 %, dry; the contents according to the certificate (for example acetanilide 71.1 % C, 6.7 % H, 10.4 % N)
Overview
The standard describes a method of determining the total content of carbon, hydrogen and nitrogen in solid biofuels. Instrumental methods of the analysis of C, H and N are in general use, often instead of the older chemical methods. A reliable determination of these elements is important for quality control, and the results serve as input data for the calculations of the combustion of biofuels: nitrogen is connected with NOx emissions (fuel NOx), hydrogen is needed for the calculation of the net calorific value and carbon for the determination of CO2 emissions. For nitrogen below 0.1 % the Kjeldahl method is the most reliable.
The standard does not prescribe the construction of the instrument — there are many components and configurations with which the test can be carried out — but sets functional requirements: the combustion conditions are to convert all the carbon (including that of mineral carbonates), the hydrogen (including the constitutional water of minerals) and the nitrogen respectively into CO2, water vapour and N2 and/or nitrogen oxides; the gases have to be freed of interfering constituents, the hydrogen of halogen compounds and of the oxyacids of sulfur has to be released as water vapour, the nitrogen oxides have to be reduced to nitrogen, and the detection system is to give a response correlated with the concentrations (preferably linear) and to allow the results to be calculated.
Pure organic substances (purity > 99.9 %, dry) serve for the calibration, for example acetanilide, atropine, benzoic acid, cystine, diphenylamine, EDTA, phenylalanine, sulfanilamide, sulfanilic acid, TRIS — with the C, H, N contents according to the certificate and not the theoretical ones. The accuracy of the calibration is checked with certified reference materials (for example NBS 1573 tomato leaves, NBS 1575 pine needles); where there are matrix effects, calibration is carried out with at least two CRMs/SRMs and others are used for the verification. At GIG the carbon content of biofuels is determined according to PN-EN ISO 16948:2015-07 by high-temperature combustion with IR detection over a range of 10.00–72.00 %.
Method principle
A known mass of sample is burned in oxygen or in a mixture of oxygen with a carrier gas under conditions in which it passes into ash and gaseous products of combustion: mainly carbon dioxide, water vapour, elemental nitrogen and/or nitrogen oxides, the oxides and oxyacids of sulfur and hydrogen halides. The products of combustion are treated so that the hydrogen bound to the products of sulfur and of the halogens is released as water vapour; the nitrogen oxides are reduced to nitrogen and the products interfering with the analysis of the gases are removed. The mass fractions of CO2, of water vapour and of nitrogen in the gas stream are determined quantitatively by appropriate instrumental methods of gas analysis. The carrier gas is helium or another gas indicated by the manufacturer of the instrument; the oxygen and the additional reagents according to the manufacturer.
Applications
- Calculation of the net calorific value of biofuels (hydrogen) and of CO2 emissions (carbon)
- Assessment of the potential for fuel NOx emissions (nitrogen) in the combustion of biomass
- Quality control of pellets, wood chips and agricultural biomass
- Elemental analysis for combustion and gasification balances
- Conversion of the results to other bases according to ISO 16993
Key parameters
| Parameter | Value |
|---|---|
| Principle | Combustion in O2 or O2/carrier gas → CO2, H2O, N2 (after the reduction of the NOx) → instrumental detection |
| Carrier gas | Helium or another according to the manufacturer; the oxygen according to the manufacturer |
| Calibrants | Pure organic substances > 99.9 %, dry; the contents according to the certificate (for example acetanilide 71.1 % C, 6.7 % H, 10.4 % N) |
| Check of the accuracy | CRMs/SRMs, for example NBS 1573 (tomato leaves), NBS 1575 (pine needles); where there are matrix effects, calibration with ≥ 2 CRMs |
| Limitation | Nitrogen < 0.1 % — the Kjeldahl method is the most reliable |
| The GIG range (carbon) | 10.00–72.00 % (combustion with IR detection) |
Standard
- Standard number
- PN-EN ISO 16948:2015-07
- Title (PL)
- Biopaliwa stałe — Oznaczanie całkowitej zawartości węgla, wodoru i azotu
- Title (EN)
- Solid biofuels — Determination of total content of carbon, hydrogen and nitrogen
Step-by-step procedure
-
Preparation of the sample
Prepare the analysis sample according to the rules for the preparation of biofuel samples (ISO 14780) and determine the moisture for the conversions (ISO 16993).
-
Calibration
Calibrate the instrument with pure, dry organic substances (> 99.9 %), using the C, H, N contents from the certificate of the material; the range of the calibration is to cover the concentrations expected.
-
Check of the accuracy
Analyse a certified reference material (for example NBS 1573, NBS 1575); if the recovery is unsatisfactory because of the matrix or of the range, calibrate with at least two CRMs/SRMs and use others for the verification.
-
Combustion of the sample
Weigh out a known mass of sample and burn it in oxygen or in oxygen with a carrier gas so that all the carbon (including the carbonates), the hydrogen (including the constitutional water) and the nitrogen pass into the gases.
-
Treatment of the gases
Release the hydrogen from the hydrogen halides and from the oxyacids of sulfur as water vapour, reduce the nitrogen oxides to N2 and remove the constituents interfering with the detection.
-
Detection and calculation
Determine the CO2, H2O and N2 in the gas stream instrumentally; calculate the C, H and N contents of the sample from the responses of the detectors and the mass of the sample; give the results on the basis required (ISO 16993).
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| CHN elemental analyser | A combustion furnace in oxygen, a gas cleaning system, a reducer of the nitrogen oxides, detectors of CO2, H2O and N2 with a linear (or characterised) response, software calculating C, H, N | — |
| Analytical balance | For weighing out small test portions of sample and of the calibrants | — |
| Capsules or boats for the samples | According to the manufacturer of the instrument | — |
| Oven and desiccator | For keeping the calibrants and samples dry | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Helium (carrier gas) | — | Or another gas indicated by the manufacturer of the instrument |
| Oxygen | — | Of the quality indicated by the manufacturer of the instrument |
| Additional reagents (reactor fillings, absorbents) | — | The types and quality according to the manufacturer; many of them are toxic and corrosive |
| Calibration substances | — | For example acetanilide, atropine, benzoic acid, cystine, diphenylamine, EDTA, phenylalanine, sulfanilamide, sulfanilic acid, TRIS — purity > 99.9 %, dry |
| Certified reference materials | — | For example NBS 1573 tomato leaves, NBS 1575 pine needles |
Health and safety (OHS)
- The reagents of the analyser (reactor fillings, absorbents) are often toxic and corrosive — replace them wearing gloves and goggles, in a fume hood
- The combustion furnace works at a high temperature with oxygen — operate it according to the manufacturer's instructions, check the gas tightness
- Cylinders of helium and oxygen — securing, pressure reducers, ventilation of the room
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 16948:2015-07 — “Solid biofuels — Determination of total content of carbon, hydrogen and nitrogen”.
How does this method work?
A known mass of sample is burned in oxygen or in a mixture of oxygen with a carrier gas under conditions in which it passes into ash and gaseous products of combustion: mainly carbon dioxide, water vapour, elemental nitrogen and/or nitrogen oxides, the oxides and oxyacids of sulfur and hydrogen halides. The products of combustion are treated so that the hydrogen bound to the products of sulfur and of the halogens is released as water vapour; the nitrogen oxides are reduced to nitrogen and the products interfering with the analysis of the gases are removed.
What is the measuring range and accuracy?
Principle: Combustion in O2 or O2/carrier gas → CO2, H2O, N2 (after the reduction of the NOx) → instrumental detection; Carrier gas: Helium or another according to the manufacturer; the oxygen according to the manufacturer; Calibrants: Pure organic substances > 99.9 %, dry; the contents according to the certificate (for example acetanilide 71.1 % C, 6.7 % H, 10.4 % N); Check of the accuracy: CRMs/SRMs, for example NBS 1573 (tomato leaves), NBS 1575 (pine needles); where there are matrix effects, calibration with ≥ 2 CRMs.
How long does the test take?
The procedure comprises 6 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
CHN elemental analyser, Analytical balance, Capsules or boats for the samples, Oven and desiccator.
Where is this test used?
Calculation of the net calorific value of biofuels (hydrogen) and of CO2 emissions (carbon); Assessment of the potential for fuel NOx emissions (nitrogen) in the combustion of biomass; Quality control of pellets, wood chips and agricultural biomass; Elemental analysis for combustion and gasification balances; Conversion of the results to other bases according to ISO 16993.
What safety precautions apply?
The reagents of the analyser (reactor fillings, absorbents) are often toxic and corrosive — replace them wearing gloves and goggles, in a fume hood; The combustion furnace works at a high temperature with oxygen — operate it according to the manufacturer's instructions, check the gas tightness; Cylinders of helium and oxygen — securing, pressure reducers, ventilation of the room.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-EN ISO 16948.