SDS720 Coulomb Sulfur Analyzer

The SDS720 Coulomb Sulfur Analyzer is a fully automatic instrument designed for the rapid and accurate determination of total sulfur in coal, coke, petroleum products, solid biomass fuels, cement, minerals, catalysts, and other combustible materials.

Based on the coulometric titration method, the instrument combusts the sample in a purified air stream at a controlled high temperature. Sulfur compounds are converted into sulfur oxides and transferred to the electrolytic cell, where the sulfur content is automatically determined according to Faraday’s law of electrolysis.

With capacity for up to 21 samples, the analyzer automatically completes sample feeding, combustion, coulometric titration, result calculation, sample discharge, and waste crucible removal. Its optimized combustion system, hardware-based charge integration, stable sample introduction mechanism, and intelligent control software deliver precise, repeatable, and reliable sulfur results with minimal operator involvement.

Key Features

Accurate and Reliable Sulfur Determination

A high-precision, low-drift hardware integration circuit records the electrolytic charge in real time. Unlike software-only integration, the dedicated hardware system minimizes the risk of missing signal data and ensures complete charge integration for accurate sulfur determination.

Complete Combustion and Electrolysis

The optimized high-temperature combustion system promotes complete decomposition of sulfur compounds. Enlarged and reinforced electrode plates improve electrolysis efficiency and ensure more complete titration of the generated sulfur dioxide.

High-Throughput Unattended Operation

Up to 21 samples can be loaded at one time. The analyzer automatically performs sample feeding, testing, discharge, and disposal, allowing unattended operation and significantly improving laboratory productivity.

Flexible Sample Queue Management

Samples can be added or replaced during operation, enabling laboratories to handle urgent samples without interrupting the entire testing sequence.

Stable Sample Introduction

The dual-rod sample introduction mechanism improves feeding stability, while the specially designed chain system helps prevent crucible tipping, scratching, and jamming.

Wide Application Range

The analyzer supports total sulfur determination in:

  • Coal and coke
  • Petroleum products and heavy oils
  • Solid biomass fuels
  • Cement
  • Pyrite, minerals, and rocks
  • Catalysts and other combustible materials

Low Maintenance and Reduced Operating Costs

The optimized gas-path design minimizes moisture entering the drying tubes. Large-capacity drying tubes and a long-life, maintenance-free air pump reduce consumable replacement frequency, routine maintenance, and operating costs.

Safe and User-Friendly Design

The high-temperature furnace is enclosed within the instrument housing. Convenient leak testing, electrolyte leakage protection, automatic alarms, temperature protection, and a built-in noise-reduction device improve operational safety and user comfort.

Intelligent Software and Data Management

The control software supports automatic furnace heating, temperature stabilization, cooling, sample-weight input, result calculation, calibration, data storage, and maintenance reminders. Ethernet communication provides stable data transmission and strong resistance to interference.

Fast Analysis

A typical sulfur determination takes approximately 200 seconds, depending on the sample type and sulfur concentration.

Applicable International Standards and Methods
StandardStandard TitleApplicable Samples
ISO 20336Coal and coke — Determination of total sulfur by Coulomb titration methodSolid mineral fuels
Model Selection Guide
ParameterSDS720SDS-V
Picture
Sulfur Measurement Range0.01%–40%0.01%–40%
Sulfur Resolution0.001%0.001%
Temperature Control Accuracy±1°C±1°C
Sample MassReference sample mass: 50 mg, depending on the sample typeReference sample mass: 50 mg, depending on the sample type
Operating Furnace TemperatureCoal and coke: 1150 ± 5°C; oil and pyrite: 900 ± 5°C; cement: 1150–1200°CCoal and coke: 1150 ± 5°C; oil and pyrite: 900 ± 5°C; cement: 1150–1200°C
Maximum Sample Capacity21 samples; continuous sample loading supported1 sample
Analysis TimeApprox. 200 s, depending on the sampleApprox. 200 s, depending on the sample
Automatic Tungsten Trioxide AdditionNoNo
Maximum Power4 kW3.5 kW
Sample ContainerSlender crucibleNo. 77 porcelain boat
Gas-Tightness CheckManualManual
Flow AdjustmentManualManual
Digital FlowmeterNoNo
Application Notes

We are compiling our practical application experience into a growing collection of technical articles that will be published here regularly.

If you have an immediate analytical challenge before then—whether in mining, energy, advanced materials, or PFAS analysis—contact the Sundy Technology Application Laboratory. We provide customized method development, application optimization, and technical support to help you achieve reliable analytical results.

Software & Schematic Diagram
On-site Photos
Videos
Customer Testimonials

We have provided a complete set of Sundy testing solutions, including bomb calorimeter, sulfur analyzer, and thermogravimetric analyzer, to the fuel analysis laboratory of Kavçim Cement, a leading integrated cement plant on Turkey’s Black Sea coast. Sundy’s standardized instrument performance bring outstanding practical value to end users. The upgraded solution significantly simplifies daily operations, lowers manual intervention and maintenance costs, and unifies data consistency for routine fuel analysis.

We are very satisfied with Sundy’s product quality and technical support, and will continue to promote and recommend Sundy analytical instruments for more industrial laboratory projects in Turkey.

Dr. Karahan, POTANTEK

After more than 10 years of continuous cooperation and market verification, we confirm that Sundy’s products, especially its automatic calorimeters and elemental analyzers, have high precise temperature control, accurate testing results, and ultra-low failure rate. All products are fully compliant with international ISO and ASTM standard, completely meeting the testing demands of coal laboratories, power plants, industrial enterprises, universities and scientific research institutions.

We highly recognize Hunan Sundy Science and Technology’s strong production capacity, standardized quality management system, professional technical support team and excellent business credibility. In all our cooperation cases, Sundy has always demonstrated professionalism, reliability and a customer-oriented service attitude.

Dr. Kim, YEONJIN
FAQs

The analyzer uses the coulometric titration method. The sample is combusted in a purified air stream, converting sulfur compounds mainly into SO₂ and a small amount of SO₃. These gases enter the electrolytic cell, where the consumed iodine or bromine is regenerated electrolytically. The total sulfur content is calculated from the electrical charge consumed according to Faraday’s law.

The analyzer is suitable for determining total sulfur in coal, coke, coal residue, petroleum products, heavy oil, solid biomass fuels, pyrite, cement, catalysts, minerals, rocks, and other combustible or inorganic materials compatible with the configured test method.

The specified total sulfur measurement range is 0.01% to 40%. The sample mass should normally be selected according to the expected sulfur concentration and the combustion characteristics of the material.

The permitted sample mass range is 10–110 mg, with approximately 50 mg commonly used as a reference mass. Solid samples should normally be ground to a particle size of less than 0.2 mm to promote representative sampling and complete combustion.

The operating temperature depends on the selected test type:

  • Coal and coke: 1150 ± 5°C
  • Heavy oil and pyrite: 900 ± 5°C
  • Cement: approximately 1190 ± 5°C

The software allows the constant-temperature setpoint to be configured within the supported range of 900–1200°C for different test methods.

The manual specifies purified air as the carrier and combustion gas. A relatively low oxygen partial pressure favors the conversion of sulfur compounds into SO₂ rather than excessive SO₃ formation. The air must also be clean and dry; otherwise, sulfur oxides may react with moisture and be retained on the internal tubing, resulting in low sulfur values.

Tungsten trioxide acts as a catalyst that promotes the decomposition of sulfate sulfur at approximately 1150–1200°C. It helps ensure that sulfur in difficult-to-decompose forms is completely released without requiring an excessively high furnace temperature, which would shorten the service life of the combustion tube and heating element.

Vanadium pentoxide is recommended as a catalyst for cement samples because it accelerates the decomposition of sulfate compounds. When the catalyst itself contains measurable sulfur, its sulfur content should be entered into the software so that it can be included in the result calculation.

The analyzer uses a dedicated hardware integration circuit to record the electrolytic current and total charge during titration. Compared with software-only integration, this reduces the risk of signal loss or incomplete data acquisition and improves the accuracy, stability, and repeatability of the sulfur result.

Rapid stirring disperses the electrolytically generated iodine or bromine throughout the electrolyte and maintains reliable endpoint control. If stirring is too slow, the titrant cannot diffuse quickly enough, which may cause endpoint instability and inaccurate sulfur results. The speed should be set close to, but below, the point at which the magnetic stir bar begins to jump or strike the electrodes.

The nominal working flow is approximately 1000 mL/min. For instruments using manual rotameters, a reading between approximately 900 and 1000 mL/min is regarded as normal. Unstable or insufficient flow may indicate leakage, bent tubing, blocked absorbent cotton, or desiccant entering the gas line.

The main pump is started and the gas-tightness test device is manually actuated. If the rotameter float falls below approximately 250 mL/min, the gas path is considered adequately sealed. If it does not, the tubing connections, purification tubes, electrolytic-cell seal, dust-filter cover, gaskets, and O-rings should be inspected.

The electrolyte should be replaced when:

  • Its pH falls below 1
  • Its color becomes red or dark reddish-brown
  • The software issues a replacement reminder
  • Measurement stability or accuracy begins to deteriorate

The manual also gives an indicative replacement interval of approximately 200 tests, although the actual service life depends on the samples and sulfur loading.

The electrolytic cell should be cleaned periodically. Contamination on the platinum electrodes may be removed carefully with cotton or gauze and alcohol, followed by thorough rinsing with distilled water. After completing a series of tests, the electrolyte may be drained into a sealed amber glass bottle and stored away from light, while the cell should be rinsed with distilled water.

The indicating silica gel should be replaced or regenerated when approximately 70% of the material has changed color due to moisture absorption. Excessively wet desiccant reduces drying efficiency and may allow moisture to interfere with sulfur oxide transport and coulometric titration.

Possible causes include incomplete sample combustion, insufficient catalyst, air leakage, excessive moisture in the gas path, adsorption of sulfur oxides in contaminated tubing, blocked filters, deteriorated electrolyte, low gas flow, or a cracked or heavily coked porcelain boat. The furnace position, sample introduction parameters, and constant-temperature zone should also be verified.

Unstable results may be associated with fluctuating gas flow, leakage, incorrect stirring speed, contaminated electrodes, deteriorated electrolyte, excessive moisture in the purification system, unstable furnace temperature, or unsuitable sample mass. Reference materials should also be tested to distinguish an instrument condition from sample heterogeneity.

The SDS720 can hold up to 21 samples. Its chain-type feeding mechanism automatically completes sample feeding, combustion, analysis, discharge, and disposal in sequence, allowing substantially unattended operation. Samples may also be added or replaced during the analytical sequence, provided the operating area and current test position are not disturbed.

Certified reference materials with known sulfur values are entered into the software. The system can generate and apply a calibration equation containing a constant and slope. Calibration must be enabled for the selected test type before the equation is applied to the reported results.

The software supports automatic furnace heating, temperature stabilization and cooling, sample-weight acquisition, test-type configuration, calibration, result calculation, data storage, recalculation of modified records, user and permission management, maintenance counters, and instrument alarms. Protective functions include warnings for overtemperature, thermocouple disconnection, and incorrect thermocouple polarity.

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