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The Main Methods of Biogas Composition Analysis

The main methods of component detection are austenite gas analysis method, gas chromatography GC analysis method, thermal catalytic element detection method and infrared detection method. Composition detection analyzer: CO2 is absorbed by sodium hydroxide solution, CO2 is absorbed by alkaline gallic acid solution, and CH4 is measured by absorption method after the explosion combustion method, thereby measuring the content of CH4, CO2, and O2. This method has a simple structure, but it needs to collect representative gases and cannot be analyzed on site. In addition, it needs to purchase a large amount of medicaments every year, and personnel need to be trained and labor intensive for analysis and testing. Gas chromatographic GC analysis method: The sampled gas is separated on the chromatographic column using its physical adsorption capacity difference and then the TCD sensor is used to analyze its CH4, CO2, and O2. This method is simple to test, but the chromatographic price is relatively expensive.

On-site analysis

Thermocatalytic detection method: The thermocatalytic (black and white) element-compensation element and bridge arm cathode are used to form a Wheatstone bridge with a constant voltage. Because the skeleton of the thermocatalytic element is a platinum wire material, it is heated when the current flows, so that the temperature is Around 500 degrees, when encountering gas, the chlorination reaction occurs when the gas touches the surface of the catalytic element, which generates a large amount of heat, which increases the temperature of the catalytic element and increases the resistance value. The unbalanced voltage output by the bridge reflects the Measure the concentration of methane. The advantage of this method is that it is inexpensive and suitable for coal mines to measure whether methane exceeds the standard. It has been widely used in portable gas analyzers and fixed gas sensors. Disadvantages are: frequent calibration, calibration once every 7 days, only one year of service life, poor accuracy (10%), short life, can only measure gas below 0-4%. The high concentration makes the sensor poisoned or even scrapped, and in addition does not measure CO2 energy. Infrared detection method: Using CH4 and CO2 gas will absorb 3.4um, 4.26um of the characteristics of the infrared wavelengths at home and abroad, the CH4 and CO2 content can be obtained through the change of infrared absorption rate, and the O2 and H2S content can be obtained with the electrochemical sensor. At present, it is the preferred measuring instrument for biogas measurement in foreign countries. At present, the CDM projects in China’s plot development mechanism require infrared biogas analyzers to detect the composition of biogas. The advantage is that it can be measured online in real time without the need for airbag sampling. No consumables are consumed, and the measurement accuracy is high. Frequent calibration is not required. The measurement range is 0-100%. It can measure both the gas composition of the biogas digester and the biogas leakage.

Gas analyzers cannot be analyzed on-site, and they need to purchase a large amount of reagents every year (unless the government has financial arrangements for reagent costs every year). The analysis and testing are complex and labor-intensive, so they are not suitable for analysis work. The recommended laboratory method for measuring biogas CH4 and CO2 requires laboratory analysis after sampling, but it is expensive to purchase, complicated to operate, and difficult to use on the site of biogas.

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