Consumption of compressed air in chemical plants
The amount of compressed air used by chemical plants varies depending on process complexity, equipment size and capacity requirements, and usually requires a comprehensive combination of theoretical calculations, measured data and empirical estimates. The following are specific analysis methods and industry cases:
1. Usage estimation method
- theoretical calculation method
- formula: Actual consumption = theoretical consumption × 1.3~2.0 (including 30% leakage loss).
- case: In the production of viscose fiber, the theoretical daily air consumption for pressing viscose is 178Nm³, but the actual need is 231.4 Nm ³.
- Gas storage tank test method
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step: Close the outlet valve of the air storage tank and record the time required to pump air from 0.48MPa to 0.69MPa.
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formula：
Among them,is the volume of the gas storage tank (m³),is the final pressure (MPa),is the initial pressure (MPa),is the time (s),Atmospheric pressure (0.1MPa).
- empirical estimation
- total amount = equipment gas consumption + aftertreatment gas consumption + leakage + reserve volume.
- experience points: Leakage accounts for 5% of the system’s gas volume, and reserves increase by 10 – 20% based on future demand.
2. Core influencing factors
- plant scale
- large chemical plant(For example, annual output of 300,000 tons of ethylene): 5,000 – 8,000 Nm ³/h.
- Small fine chemicals workshop：500-1000Nm³/h。
- process flow
- High gas consumption link：
- Pneumatic conveying (e.g., powder conveying requires 20 – 50 Nm ³/min).
- Instrument air source (pressure 0.6 – 0.8MPa).
- Equipment purging (10 – 30 Nm ³ per operation).
- Low air consumption link: Laboratory analysis (<5 Nm ³/h), small pneumatic valve (<0.1Nm ³/min).
- device type
- reciprocating compressor: Low pressure and small flow (<100Nm³/min), low efficiency.
- screw compressor: Medium and high pressure (0.7-1.5MPa), the efficiency is 20-30% higher than that of the reciprocating type.
- centrifugal compressor: Large flow (>1000Nm³/min), but high start-up energy consumption.
- production load
- For every 10% increase in load rate, compressed air consumption increases by 8-12%.
3. Industry Cases
- petrochemical enterprises
- scene: PTA plant with an annual output of 600,000 tons.
- dosage: The total demand is about 6500Nm³/h, of which instrument gas accounts for 30%, transmission gas accounts for 45%, and purge gas accounts for 25%.
- chlor-alkali plants
- scene: purging of electrolytic cells in electrolysis workshop.
- parameters: Pressure 1.2MPa, air consumption per tank is 5Nm³/min, and total demand for the entire workshop is 800Nm³/h.
- Pharmaceutical Intermediate Factory
- scene: Stir the reaction kettle.
- parameters: Pressure is 0.6MPa, gas consumption per reactor is 20Nm³/h, and total demand of the whole plant is 1200Nm³/h.
4. Optimization suggestions
- leakage management
- For every 1% reduction in leakage volume, 0.5-1.0% energy is saved.
- detection method: Gas tank pressure drop method (it takes less than 10 minutes to drop from 0.69MPa to 0.62MPa).
- system matching
- Configure a compressor combination (such as 1 large-flow screw machine +2 frequency converters for peak shaving) to save energy by 30-50%.
- waste heat recovery
- Compression heat is used to heat the boiler to replenish water, and the recovery efficiency is 60-80%.
summary: The amount of compressed air used in chemical plants needs to be comprehensively estimated based on process requirements, equipment type and load rate, and a margin of 10-20% is reserved. Through leak detection and system optimization, energy consumption can be reduced by 8-15% and system efficiency can be improved.