Determination of Carbon, Hydrogen and Nitrogen Content in Biomass Fuels Using Sundy SDCHN636 Carbon, Hydrogen and Nitrogen Analyzer

Application Notes: SD-DN-001-01001

Introduction

Driven by the low-carbon transition in the power industry, biomass fuels, due to their clean and renewable characteristics, are gradually replacing certain conventional fuels in power generation. Accurate determination of carbon, hydrogen and nitrogen content in biomass fuels can be used to calculate the theoretical combustion temperature and the combustion heat balance, thereby providing a data basis for applications such as biomass-coal co-firing.

Testing Principle

A known mass of sample is combusted at high temperature in a stream of oxygen. Carbon and hydrogen are completely converted into carbon dioxide and water, respectively, while nitrogen is fully converted into nitrogen oxides. After sulfur oxides and halides are removed by a dedicated system, carbon and hydrogen are determined by infrared detectors. The nitrogen oxides are then reduced to molecular nitrogen in a reducing furnace and quantified by a thermal conductivity detector.

References

ISO 14780: Solid biofuels — Sample preparation

ISO 16948: Solid biofuels — Determination of total content of carbon, hydrogen and nitrogen

GB/T 28730: Method for preparation of solid biofuels sample

DL/T 568-2013: Test methods for instrumental determination of carbon, hydrogen, and nitrogen in laboratory samples of fuel

Table 1: Comparision between ISO and Sundy Instrument SDCHN636

Sample Preparation

Prepare the sample in accordance with ISO 14780.

Crush the sample from a size of less than 6 mm to less than 0.5 mm using a fine grinding mill, ensuring that the entire sample passes through a 0.5 mm sieve. Mix all the sample thoroughly. Allow the sample to stand until it reaches an air-dried state, and then transfer it into a container. For the special sample that cannot be crushed to completely pass through the 0.5 mm sieve, the entire sample shall pass through a 1 mm sieve.

During fine grinding, the principle of “small amounts, multiple batches” shall be adopted. The mass of each batch fed into the mill should generally be controlled at 50 g or less, and the grinding time should be limited to minimum duration required to achieve the specified particle size, in order to avoid excessive heat generation from prolonged grinding.

If the materials contain seeds, grains or grasses, they may spin inside the mill or adhere to the sieve. Inspect the mill after grinding. Manually grind any materials that did not pass through the sieve until all materials pass through, and add these materials to the analysis sample.

4 Biomass Fuels  Samles

Consumption and Tools

Prepare according to the instructions

Certified Reference Material

Ethylenediaminetetraacetic acid (EDTA)

Operating Procedure

ISO 16948:2015 provides an example of the typical testing procedure for an automated carbon, hydrogen and nitrogen analyzer. Clauses 3.5.2 and 3.5.3 of DL/T 568-2013 also offer guidance on instrument calibration and sample determination. The operating procedure of the SDCHN636 follows these standard methods.

2.1 Instrument Startup Preparation

Complete the startup preparation in accordance with the instrument operation manual.

2.2 Blank Test

2.2.1 Enter a sample mass of 100 mg for at least 5 blank samples on the main interface of the software.

2.2.2 Reserve the corresponding empty positions in the sample tray.

2.2.3 After the reference standards and user samples are prepared, click Start Experiment to perform the blank test.

2.2.4 At least 5 blank samples are required. If the blank samples fail to produce acceptable blank values, increase the number of blanks.

2.3 Instrument Calibration and Curve Validation — Using EDTA as an Example

2.3.1 Conditioning sample test: Weigh 1–2 EDTA samples, wrap them into a teardrop shape, and place them after the blank samples as conditioning samples to equilibrate the system. The sample mass should be similar to that of the first set of EDTA samples used for calibration.

2.3.2 Weigh at least 8 replicate samples as calibration points for carbon and hydrogen. Place the samples in tin foil cups and wrap them into a water-drop shape. Recommended masses for the 8 samples: 60.8 mg, 73.0 mg, 85.2 mg, 97.4 mg, 109.6 mg, 121.7 mg, 133.9 mg, and 146.1 mg (corresponding to a carbon content range of 24.97%–60.00% and a hydrogen content range of 3.36%–8.06%). Weigh 6 replicate samples as calibration points for nitrogen. Place the samples in tin foil cups and wrap them into a water-drop shape. Recommended masses for the 6 samples: 5 mg, 15 mg, 25 mg, 35 mg, 45 mg, and 55 mg. The calibration curve passes through the zero point (corresponding to a nitrogen content range of 0–5.25%).

2.3.3 Place the samples sequentially into the sample tray. Reserve the corresponding blank positions and place the conditioning samples before the calibration samples.

2.3.4 Enter the sample mass information on the main interface of the software, click the Start Experiment button, and allow the program to complete all experiments automatically.

2.3.5 On the main interface, navigate to System Settings → Parameters, enter the certified values of EDTA, and save.

2.3.6 Enter Data Management, select the data of the calibration points, and generate and apply the calibration formula.

2.3.7 Return to the Data Management interface and recalculate the results of the day’s measurements.

2.3.8 Weigh EDTA samples with masses different from those of the calibration points for curve validation. For example, weigh 2–3 replicate EDTA samples of 100 mg each. The measured values shall fall within the uncertainty range of the certified values.

2.4 Sample Analysis

2.4.1 Blank samples: Refer to Section 2.2 — Blank Test.

2.4.2 Conditioning sample test: Weigh 1–2 EDTA samples of 100 mg each, wrap them into a water-drop shape, and place them after the blank samples as conditioning samples to equilibrate the system.

2.4.3 Weigh 2 additional EDTA samples of 100 mg each, wrap them into a water-drop shape, and place them after the conditioning samples as quality control samples. If the results deviate from the certified values, perform drift correction. The drift coefficient shall be between 0.9 and 1.1. If it falls outside this range, recalibrate the curve.

2.4.4 Weigh 100 mg of biomass sample into a tin foil cup, wrap it into a water-drop shape, and then place it sequentially into the sample tray. After every 10 sub-samples, test a set of replicate EDTA samples of 100 mg each to monitor for any drift in the results.

2.4.5 Enter the corresponding sample mass information on the main interface of the software, click the Start Experiment button, and allow the program to complete all experiments automatically.

Data Verification

Carbon and hydrogen data are generated via secondary calibration, while nitrogen data are generated via primary calibration. The calibration substance is EDTA (AR2092-250, lot 1122V; certified carbon content 41.07%, hydrogen content 5.52%, nitrogen content 9.55%). The carbon/hydrogen calibration points are 60.8 mg, 73.0 mg, 85.2 mg, 97.4 mg, 109.6 mg, 121.7 mg, 133.9 mg, and 146.1 mg. The nitrogen calibration points are zero point, 5 mg, 15 mg, 25 mg, 35 mg, 45 mg, and 55 mg. The verification substance is EDTA, with verification points at 100 mg and 50 mg.

Table 2 Biomass Sample Test Data

Summary

The experimental results show that, for the four biomass samples with four replicate determinations each, the ranges (maximum minus minimum) for carbon were 0.08%–0.17% with standard deviations of 0.04–0.07; for hydrogen, the ranges were 0.01%–0.05% with standard deviations of 0–0.02; and for nitrogen, the ranges were 0.02%–0.04% with standard deviations of 0.01–0.02. All these metrics are within the repeatability limits specified in DL/T 568-2013 and the typical standard deviation criteria given in ISO 16948 Solid biofuels — Determination of total carbon, hydrogen and nitrogen content. The precision is satisfactory, indicating that the SDCHN636 elemental analyzer meets the standard requirements for the determination of carbon, hydrogen and nitrogen content in biomass.

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