Determination of Total Nitrogen in Urea for Power Plant DeNOx Systems Using the SDDN636 Dumas Nitrogen Analyzer
Abstract
The SDDN636 Dumas Nitrogen Analyzer provides stable analytical performance, low measurement bias, and a high degree of automation. Based on the Dumas combustion principle and the analytical capabilities of the instrument, this application establishes a standardized procedure for determining the total nitrogen content of urea used in thermal power plant DeNOx systems.
The method provides reliable analytical data for DeNOx process quality control, incoming raw-material inspection, and commercial settlement.
Application Note No.: SD-DN-001-01002
Introduction
In thermal power plant flue-gas DeNOx systems, urea is used as a precursor for producing the reducing agent. Through thermolysis and hydrolysis, urea releases ammonia, which then selectively reduces nitrogen oxides in the flue gas.
The effectiveness of this process depends directly on the amount of reducing agent that can be generated from the urea. Total nitrogen content is therefore a key quantitative indicator of urea quality. It affects both DeNOx efficiency and ammonia slip and is an important control parameter for achieving ultra-low emission requirements.
Accurate determination of total nitrogen is essential not only for DeNOx process quality control but also for incoming material acceptance and commercial settlement.
In this application, the SDDN636 Dumas Nitrogen Analyzer is used to determine the total nitrogen content of solid urea through high-temperature combustion, reduction, and thermal conductivity detection. The method enables rapid, accurate, and automated analysis, providing reliable data for urea quality evaluation and compliance management.
Test Principle: Dumas Combustion Method
In the Dumas combustion method, the sample is completely combusted in a high-temperature, oxygen-rich environment. The nitrogen contained in the sample is converted into nitrogen oxides, or NOₓ.
The combustion gases then pass through a reduction furnace, where the nitrogen oxides are reduced to molecular nitrogen, N₂. The nitrogen signal is measured using a thermal conductivity detector, or TCD.
The total nitrogen content of the sample is calculated quantitatively from a calibration curve.
Referenced Standards
GB/T 46133-2025
General Principles for Nitrogen Determination by the Dumas Combustion Method
GB/T 42955-2023
Determination of Total Nitrogen Content in Fertilizers — Dumas Combustion Method
NY/T 2542-2014
Fertilizers — Determination of Total Nitrogen Content
Sample Preparation
For solid urea, accurately weigh approximately 10 g of representative sample and place it in an agate mortar.
Grind the sample thoroughly until no obvious particles are visible, ensuring a uniform particle size. Immediately transfer the ground sample into a clean, dry, airtight container.
Before analysis, shake or mix the sample thoroughly again. Avoid taking material from caked portions of the sample, and do not analyze agglomerated urea directly.
Reference Materials
- Urea, CAS No. 57-13-6
- Ethylenediaminetetraacetic acid, EDTA, CAS No. 60-00-4
- Glycine, CAS No. 56-40-6
- Aspartic acid, CAS No. 56-84-8
Reagents
Combustion aids: Nitrogen-free carbohydrate reagents, such as sucrose or cellulose
Reducing reagents: Copper and catalyst
Adsorbents: Magnesium perchlorate and soda asbestos
Absorbent: Magnesium oxide
Consumables and Auxiliary Tools
Consumables
- Tin cups
- Tin foil
- Tin capsules
Auxiliary tools
- Agate mortar
- Tweezers
- Weighing spoon
Method Parameters
| Parameter | Setting |
|---|---|
| Combustion Tube Temperature | 950°C |
| Reduction Furnace Temperature | 700°C |
| Urea Sample Mass | 30 mg |
| Oxygen Pressure | 0.26 MPa |
| Helium Pressure | 0.18 MPa |
| Nitrogen Pressure | 0.26 MPa |
Sample Analysis Procedure
1. Sample Weighing
Weigh approximately 30 mg of the prepared urea sample into a tin cup.
2. Sample Encapsulation
Fold and compress the tin cup into a compact spherical package. Place the encapsulated samples sequentially into the autosampler tray.
3. Automated Analysis
Enter the corresponding sample mass in the instrument software. Click the start button on the main software interface. The instrument then completes the combustion, reduction, detection, calculation, and result generation processes automatically.
Calibration and Method Validation
The method was calibrated using EDTA reference material with the following information:
- Product number: AR2092-250
- Batch number: 1122V
- Certified nitrogen content: 9.55%
The EDTA masses used for linear calibration were:
- 125 mg
- 140 mg
- 155 mg
- 170 mg
- 185 mg
EDTA was also used as the validation material. The validation masses were:
- 150 mg
- 160 mg
Experimental Results
The analytical results were generated using the established linear calibration. Seven replicate measurements were performed on the solid urea sample.
| Sample No. | Sample Mass (mg) | Nitrogen Content (%) |
|---|---|---|
| 1 | 29.41 | 46.43 |
| 2 | 29.48 | 46.39 |
| 3 | 29.76 | 46.32 |
| 4 | 29.24 | 46.26 |
| 5 | 30.38 | 46.46 |
| 6 | 29.21 | 46.48 |
| 7 | 30.77 | 46.32 |
| Average | 46.38 | |
| Standard Deviation | 0.08 |
Conclusion
The average total nitrogen content of the solid urea sample was 46.38%, with a standard deviation of 0.08 percentage points. The close agreement among the seven replicate results demonstrates excellent measurement repeatability.
The SDDN636 Dumas Nitrogen Analyzer provides a rapid, accurate, and highly automated solution for determining total nitrogen in urea used for power plant DeNOx applications. The method is suitable for routine raw-material inspection, DeNOx process quality control, and commercial settlement.
