🔥 Volatile matter in solid biofuels — heating at 900 °C for 7 min

Petrochemistry PN-EN ISO 18123

Overview

The standard specifies the requirements for and the method of determining the volatile matter content in solid biofuels; it is intended for the producers, sellers and users of biofuels and of the equipment for burning them. The volatile matter content is determined as the loss of mass, reduced by the loss due to moisture, when a solid biofuel is subjected to partial pyrolysis under standardised conditions. The test is empirical: for the results to be reproducible the rate of heating, the final temperature and the total time have to be strictly controlled and the access of air excluded, so as to prevent oxidation — the fit of the crucible lid is critical. The description is based on the preview of ISO 18123:2015; the Polish Committee for Standardization has published PN-EN ISO 18123:2023-10 (EN ISO 18123:2023), whose content has not been checked.

The moisture of the analysis sample is determined at the same time as the volatile matter (ISO 18134-3), so that the proper correction can be made. Automatic apparatus validated on reference samples of the appropriate type of biomass is permitted, provided it meets the requirements of clauses 5–8 as to the mass of the sample, the atmosphere, the temperatures and the accuracy of weighing; according to LECO both the ISO method and a TGA analyser determine the loss of mass in a prescribed time at 900 °C, the thermogravimetric analyser requiring additional heating time after the moisture stage (~105 °C).

The volatile matter of biomass is high (70–80 % Vdaf according to the Wrocław University of Science and Technology) and together with the ash and the fixed carbon characterises the fuel; GIG determines it by the gravimetric method over a range of 59.30–87.30 % (the scope of accreditation gives the edition PN-EN ISO 18123:2023-05, while the catalogue card of the Polish Committee for Standardization gives 2023-10).

Method principle

A test portion of the general analysis sample is heated essentially with no access of air at (900 ± 10) °C for 7 min; the furnace usually has no vacuum, but during the heating a partial vacuum arises, depending on the inflow of air as the charge is put in and on the air trapped in the crucible before the lid is put on. The percentage of volatile matter is calculated from the loss of mass of the test portion after subtracting the loss due to moisture. The electric furnace is to maintain a zone of uniform temperature of (900 ± 10) °C and to recover it within 4 min after a cold stand with crucibles is put in; the temperature is measured by a permanently installed sheathed thermocouple, checked regularly with a calibrated unsheathed thermocouple. The crucible is cylindrical with a well-fitting lid, both of fused silica, of a mass of 10–14 g; the horizontal clearance of the lid is ≤ 0.5 mm, and the crucible and the lid are ground in together and marked as a pair.

Applications

• Characterisation of solid biofuels (pellets, wood chips, straw) for the design of combustion and gasification
• Calculation of the fixed carbon from the moisture–ash–volatile matter balance
• Quality control and proficiency testing of biomass laboratories (GIG: 59.30–87.30 %)
• Validation of thermogravimetric analysers against the crucible method

Key parameters

Standard

Standard number

PN-EN ISO 18123:2023-10

Title (PL)

Biopaliwa stałe — Oznaczanie części lotnych

Title (EN)

Solid biofuels — Determination of volatile matter

Step-by-step procedure

1. Preparation of the sample

   Prepare a general analysis sample (nominal particle size ≤ 1 mm) according to the rules for the preparation of biofuel samples; at the same time weigh out a portion for the determination of the moisture according to ISO 18134-3.

2. Crucibles

   Use matched and ground-in crucible–lid sets of silica (10–14 g, clearance ≤ 0.5 mm); weigh the empty crucible with its lid.

3. Weighing out

   Weigh a test portion of the sample into the crucible, put the lid on and weigh; place the crucibles on the stand.

4. Heating

   Put the stand with the crucibles into the middle of the furnace heated to (900 ± 10) °C; the furnace is to recover its temperature within 4 min. Heat for 7 min with no access of air (the well-fitting lid).

   ⏱ Time: 7 min • 🌡 Temperature: 900 ± 10 °C

5. Cooling and weighing

   Take the stand out, cool the crucibles with their lids and weigh them.

6. Calculation

   Calculate the volatile matter from the loss of mass of the test portion after subtracting the loss of mass due to the moisture determined at the same time; give the result on the dry basis.

7. Check of the furnace

   Check the readings of the furnace thermocouple regularly with a calibrated unsheathed thermocouple placed as close as possible to the permanent one; the characteristic of a thermocouple at a high temperature changes with time, so the determination should not last longer than necessary.

Required equipment and apparatus

Health and safety (OHS)

• A furnace at 900 °C — long-handled tongs, heat-resistant gloves, a face shield when opening it
• The pyrolysis of biomass gives off flammable gases and tar — the flue of the furnace with its valve, ventilation of the room
• Silica crucibles are brittle and hot — cool them on a stand, do not put them on a cold bench top

Frequently asked questions