🔥 Total sulfur and chlorine in solid biofuels — bomb combustion or digestion, IC/ICP

Petrochemistry PN-EN ISO 16994

Overview

The standard describes methods of determining the total content of sulfur and chlorine in solid biofuels: two methods for the decomposition of the fuel and various analytical techniques for determining the elements in the solutions obtained after the decomposition; it also covers automatic apparatus, provided that a validation has been carried out and characteristics close to those of the method described in the standard have been obtained. Sulfur and chlorine occur in biofuels in various concentrations; during combustion they usually pass into sulfur oxides and chlorides, and their presence and the products of their reactions contribute significantly to corrosion and to harmful emissions. Chlorine may be present in organic and in inorganic compounds, and the total content is equal to or greater than the water-soluble content (ISO 16995). The 2016 edition (PN-EN ISO 16994:2016-10) is a minor revision of ISO 16994:2015.

The preferred method of digestion is combustion in an atmosphere of oxygen in a closed combustion vessel — it may be combined with the determination of the gross calorific value according to ISO 18125; digestion in closed vessels (ISO 16967, part A) is a suitable alternative. Other techniques may also be used, for example combustion in a tube furnace at a high temperature and the Eschka method. Automatic apparatus (elemental analysers, AOX analysers) and X-ray fluorescence require validation for the group of biomass concerned (woody, herbaceous, fruit according to ISO 17225-1) in accordance with CEN Guide 13 — either full or relative (comparison with a reference method, for example in interlaboratory tests); an instrument validated on straw, say, is not automatically suitable for wood, because of the lower concentrations and the different matrix.

The sulfur in plant biomass comes from amino acids and vitamins and its content is negligible; larger amounts (up to as much as 0.6 % by mass) are contained in biomass of municipal origin. Typical contents of sulfur and chlorine in biofuels are given in ISO 17225-1, Annex B.

Method principle

The determination proceeds in two stages, or with the use of automatic apparatus. Decomposition of the biofuel: method A — combustion in an atmosphere of oxygen in a combustion vessel and absorption of the acid constituents of the gas in an absorption solution; method B — digestion in closed vessels according to ISO 16967:2015, part A. Determination of the sulfate and chloride in the solution: ion chromatography in accordance with the principles of ISO 10304-1, or ICP in accordance with the principles of ISO 11885 (determined as sulfur and chlorine). In automatic apparatus the compounds of sulfur and chlorine may be detected as gaseous constituents (for example by IR methods). The sample for method A is pressed into a pellet of about 13 mm diameter; the combustion vessel may be the same as the one used for the gross calorific value.

Applications

• Assessment of the tendency of biofuels to cause chloride and sulfur corrosion of boilers (pellets, straw, agricultural biomass)
• Classification of pellets and wood chips according to the limits for S and Cl in ISO 17225
• Estimation of SO2 and HCl emissions from the combustion of biomass
• Analysis combined with the determination of the gross calorific value (the same bomb, ISO 18125)
• Validation of automatic analysers and of XRF for groups of biomass

Key parameters

Standard

Standard number

PN-EN ISO 16994:2016-10

Title (PL)

Biopaliwa stałe — Oznaczanie całkowitej zawartości siarki i chloru

Title (EN)

Solid biofuels — Determination of total content of sulfur and chlorine

Step-by-step procedure

1. Preparation of the sample

   Prepare the analysis sample according to ISO 14780 and determine the moisture according to ISO 18134-3 for the conversions.

2. Method A — the pellet

   Press a test portion of the sample into a pellet of about 13 mm diameter (with a combustion aid if need be) and weigh it to a resolution of 0.1 mg.

3. Method A — combustion

   Burn the pellet in an atmosphere of oxygen (≥ 99.5 %) in a combustion vessel containing an absorption solution; after the combustion collect the solution with the absorbed acid constituents of the gas quantitatively (it may be combined with the determination of the gross calorific value).

4. Method B — digestion

   Alternatively digest the sample in closed vessels in accordance with ISO 16967:2015, part A.

5. Final determination

   Determine the sulfate and chloride in the solution by ion chromatography (the principles of ISO 10304-1) or the sulfur and chlorine by ICP (the principles of ISO 11885).

6. Quality control

   Check the accuracy with a certified reference material; if the recoveries are not good, calibrate with at least two CRMs/SRMs and use others for the verification.

7. Automatic apparatus

   It is permitted after validation on reference samples of the group of biomass concerned (woody, herbaceous, fruit) according to CEN Guide 13 — a full validation or a relative one by comparison with a reference method.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• A bomb under oxygen pressure — use only vessels that have been pressure-tested, no greases in the oxygen fittings
• Digestion in closed vessels (method B) — acids under pressure and at a high temperature, shields and a fume hood
• The absorption solutions after the combustion are acidic — gloves and goggles

Frequently asked questions