The main component of biogas is methane, which usually contains a certain amount of carbon dioxide, hydrogen sulfide and other gases. Compressing biogas generally has the following main steps and related points:
Biogas pretreatment
Desulfurization: Hydrogen sulfide in biogas will corrode the compression equipment and may also affect subsequent use. Common desulfurization methods include dry desulfurization and wet desulfurization. Dry desulfurization generally uses desulfurizers such as iron oxide to remove hydrogen sulfide through chemical reactions; wet desulfurization uses solutions to absorb hydrogen sulfide, such as sodium hydroxide solution as an absorbent.
Dehydration: The moisture in biogas will form liquid water during the compression process, affecting the compression effect and equipment operation. Cooling method, adsorption method, etc. can be used for dehydration. The cooling method is to condense the moisture into liquid water and separate it by lowering the temperature of biogas; the adsorption method is to use adsorbents such as silica gel and molecular sieves to adsorb the moisture in biogas.
Removal of impurities: Solid impurities in biogas can be removed by filtering and other methods to prevent impurities from entering the compression equipment and damaging equipment components. Generally, filters and other equipment are used.
Compression process
Choose the right compressor
Piston compressor: suitable for compression occasions with small and medium flow and high pressure. It changes the cylinder volume through the reciprocating motion of the piston in the cylinder to achieve the compression of biogas. It has a high compression ratio and high efficiency, but it has large vibration during operation and relatively large maintenance workload.
Screw compressor: commonly used for compression of medium flow and medium and low pressure. The rotation of the screw is used to continuously change the volume between the teeth to compress the gas. It has the advantages of smooth operation, small vibration, large and continuous exhaust volume, but it is more sensitive to impurities in the gas.
Centrifugal compressor: suitable for compression of large flow and medium and low pressure. Relying on the high-speed rotation of the impeller, the gas obtains kinetic energy, which is then converted into pressure energy in the diffuser. It has a large flow, high speed, and reliable operation, but the efficiency is relatively low, and surge may occur at low flow.
Compression operation
Startup preparation: Before starting the compressor, check whether the various components of the equipment are normal, whether the lubrication system and cooling system are working well, and whether the opening and closing status of the valve is correct.
Gradually pressurize: After starting the compressor, increase the pressure slowly to avoid sudden pressure increase and shock to the equipment. Generally, according to the operating procedures of the compressor, gradually adjust the operating parameters of the compressor to gradually increase the biogas pressure to the required pressure value.
Monitor operating parameters: During the compression process, closely monitor the temperature, pressure, flow and other parameters of the compressor to ensure that it operates within the normal range. If abnormal parameters are found, timely measures should be taken to adjust or shut down for inspection.
Storage and transportation
Storage: Compressed biogas is generally stored in special gas storage tanks, which must have good sealing and pressure resistance. Depending on the storage pressure and capacity, different types of gas storage tanks can be selected, such as high-pressure spherical storage tanks, cylindrical storage tanks, etc.
Transportation: The compressed biogas is transported to the place of use through pipelines. During the transportation process, attention should be paid to factors such as pressure loss and temperature changes in the pipeline to ensure that the biogas can be stably and safely transported to the user end. At the same time, the transportation pipeline should be regularly inspected and maintained to prevent accidents such as pipeline leakage.
Safety during the biogas compression process is extremely important. The following are specific safety precautions:
Equipment safety
Equipment selection and installation
Compressors and supporting equipment of appropriate specifications and performance must be selected according to the flow rate, pressure and other parameters of biogas to ensure that the equipment can operate safely and stably under the designed working conditions.
The compressor and related equipment should be installed in a dedicated machine room with good ventilation, away from fire sources and flammable materials. The machine room building should meet the requirements of fire prevention and explosion prevention and have sufficient pressure relief area.
Equipment maintenance and inspection
Formulate a strict equipment maintenance plan, regularly inspect, maintain and repair compressors, valves, pipelines, instruments, etc., and replace worn and aging parts in time to prevent safety accidents caused by equipment failure.
Focus on checking the sealing system of the compressor to ensure that there is no biogas leakage; check safety devices such as safety valves and pressure gauges to ensure that they are sensitive and reliable, and conduct regular calibration and debugging.
Gas safety
Prevent explosions
Biogas is a flammable and explosive gas. Before compression, ensure that its purity meets the requirements and strictly control the oxygen content in the biogas, which should generally be controlled below 1% to prevent the formation of explosive mixed gases.
Static electricity should be avoided during the compression process. All equipment and pipelines should be reliably grounded, and the grounding resistance should meet the requirements of relevant standards.
Harmful gas protection
Biogas may contain toxic and harmful gases such as hydrogen sulfide. Gas detection alarms such as hydrogen sulfide should be installed in the compression workshop to promptly issue an alarm when the gas concentration exceeds the standard.
Operators should be equipped with necessary personal protective equipment, such as gas masks, air respirators, etc. When entering areas where high concentrations of harmful gases may exist, they must wear protective equipment and be supervised.
Operational safety
Personnel training
Operators must undergo professional training and be familiar with the biogas compression process, equipment operation methods and safety precautions. They can only take up their posts after passing the assessment.
Regularly organize operators to conduct safety knowledge and skills training to improve their safety awareness and emergency response capabilities.
Standardized operation
Strictly follow the operating procedures to start, run and shut down the compressor. Before starting, check whether the valve opening and closing status of the equipment and pipelines, instrument indications, etc. are normal.
During the compression process, we should pay close attention to various operating parameters, such as pressure, temperature, flow, etc., and strictly prohibit over-temperature, over-pressure, and over-speed operation. When abnormal conditions occur, appropriate measures should be taken immediately to deal with them and report them in time.
Environmental safety
Fire and explosion prevention
Fireworks are strictly prohibited in the compression workshop. Obvious fire and explosion prevention signs are set up, and sufficient fire-fighting equipment, such as dry powder fire extinguishers, carbon dioxide fire extinguishers, etc., are equipped, and regular inspections and maintenance are carried out.
It is prohibited to carry out hot work in the workshop. If hot work must be carried out, strict hot work approval procedures should be carried out, reliable fire and explosion prevention measures should be taken, and the operation should be carried out under the premise of ensuring safety.
Ventilation and emergency evacuation
Maintain good ventilation conditions in the compression workshop, install ventilation equipment, and ensure that the concentration of biogas in the workshop does not exceed the standard. Ventilation equipment should be explosion-proof to prevent biogas explosions caused by electrical sparks.
Obvious safety evacuation signs and emergency lighting facilities should be set up in the workshop to ensure that operators can evacuate the site quickly and safely in an emergency.
