1、 Quality requirements for generator sets

In the process of biogas power generation, the biogas generator set is particularly sensitive to the composition, temperature, pressure, and dosage of biogas. The generator set requires the intake system to maintain a constant and moderate air fuel ratio to avoid excessive air fuel ratio, which may cause stalling; It is also necessary to avoid excessively low air fuel ratio, which can cause high temperature and detonation. The air fuel ratio is one of the important factors that affect the combustion performance of biogas generators, and changes in biogas temperature, pressure, and composition can all affect the air fuel ratio. Therefore, before choosing biogas power generation, not controlling the biogas quality reasonably will lead to the inability of the generator set to operate normally and cause significant economic losses.

1. Biogas quality。

To use biogas for power generation, the first step is to meet the requirements of biogas power generation units for biogas quality. The requirements for biogas quality in the "Medium and High Power biogas power generation units" (GBT29488-2003) and "Technical Specifications for biogas power plants" (NY/T1704-2009) are as follows.

(1) The low calorific value of biogas is ≥ 14MJ/Nm, which is equivalent to a methane volume fraction of no less than 30% in biogas. The change rate of methane volume fraction in biogas within 30 seconds should not exceed 2%, and the change rate of methane volume fraction in biogas during continuous operation of the unit should not exceed 5%.

(2) The temperature of biogas shall not exceed 50 ℃.

(3) The specific requirements for biogas composition of biogas generator units are shown in the table below.

Note: The standard reference conditions for biogas volume are 101.3kPa, 20 ℃; Calculate based on the conversion of all sulfur-containing components in biogas into hydrogen sulfide.

① The impact of H2S on generator sets

During biogas power generation, the H2S in the biogas can cause serious corrosion to the intake pipes, superchargers, intercoolers, spark plugs, cylinder liners, exhaust pipes, and silencers of the biogas generator set, thereby affecting the lifespan of the unit. Therefore, before biogas enters the generator set, biogas pretreatment must be carried out to reduce the H2S to the allowable range of the unit in order to ensure the reliable operation of the unit.

② The impact of moisture on generator sets

In the process of biogas power generation, excessive moisture content in biogas can lead to excessive loss of intake pressure of the generator set. In severe cases, it can cause problems such as engine power fluctuations, cylinder knocking, and shutdown, seriously affecting its service life. Its specific manifestation is:

(a) Difficulty in engine ignition;

(b) Reduce the temperature of the combustion chamber and reduce the efficiency of the internal combustion engine;

(c) The presence of reactive gases such as water vapor can increase pressure and power consumption;

(d) The intermediate products produced by the combination of water vapor and other acidic substances can corrode the generator set, shorten its service life, and reduce its reliability.

③ The impact of dust on generator sets

Dust is a clearly restricted impurity in engines, and its main impact is:

(a) Blocking the pipeline, poor circulation, increased pressure loss, and increased operating costs;

(b) Increase mechanical wear and reduce equipment service life.

2. Biogas pressure

The biogas pressure of the biogas generator set at a distance of 1 meter from the gas branch pipe of the unit shall not be less than 3 kPa. When the gas supply pressure is less than 3 kPa, gas boosting equipment shall be equipped; When the gas supply pressure exceeds 5kPa, it is necessary to add a suitable pressure reducing valve. When the biogas generator set is running, the allowable biogas pressure fluctuation of the engine is generally less than 0.4kPa/s.

3. Biogas consumption

The amount of biogas used in a biogas generator set should be determined based on the efficiency and load of the generator set, and the supply of biogas during power generation should be relatively stable. When calculating the usage of biogas, it should be less than 1.2 times the rated power consumption of the biogas generator. The gas supply system should be equipped with facilities for regulating gas consumption and gas measuring instruments. When the biogas generator unit operates continuously, the capacity of the gas storage device should be designed based on the total rated power of the operating unit exceeding 3 hours of gas consumption. When the biogas generator unit operates intermittently, the capacity of the gas storage device should be designed based on the total amount of biogas greater than the intermittent power generation time

Among them, the gas regulation system of the biogas generator unit is generally achieved by using an electronic speed regulation system to control the opening of the disc door. The speed regulation system consists of a speed sensor, speed controller, actuator, and driver, forming a closed-loop speed regulation and control system to achieve control of the mixed gas intake volume. Gas measuring instruments generally use biogas flow meters, such as the Ruiyi self-control ultrasonic gas flow meter BF-3000/BF-3000B, to measure the instantaneous and cumulative flow of biogas in real-time, providing scientific data support for calculating biogas usage.

The ultrasonic gas flow meter BF-3000 adopts industry-leading ultrasonic gas sensing technology and can be used for flow measurement in large, medium, and small biogas engineering stations, as well as collecting on-site pressure and temperature. Its unique methane concentration measurement function can provide optimized measurement solutions for flow measurement, acceptance, and supervision within biogas engineering stations.

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