Technical Analysis of Nitrogen Generators in Coal Mines: Core Equipment of Coal Mine Fire Prevention and Extinguishing a

In the coal mine safety production system, fires, gas explosions, and spontaneous combustion of coal seams have always been high-risk issues. Especially as the mining depth of the mine increases, risks such as air leakage in the mined-out areas, coal oxidation, and spontaneous heating of coal increase significantly. Traditional ventilation and fire suppression methods have become inadequate to meet the modern coal mine safety management requirements.

In this context, "coal mine nitrogen generator" has gradually become an important component of the mine safety system.

By on-site generating high-purity nitrogen and continuously injecting it into the underground, it can effectively reduce the oxygen concentration and establish an inert environment, thereby achieving:

• Prevention of fire in mined-out areas
• Prevention of gas explosions
• Inertization protection of fire zones
• Prevention of explosion in coal conveying systems
• Inhibition of coal oxidation

At present, most large coal mines have built centralized coal mine nitrogen generation stations and incorporated them into the long-term safety operation system of the mine.

This article will systematically analyze the working principle, system composition, core parameters, selection logic, and future development trends of coal mine nitrogen generators from an industry technical perspective.

Coal is an easily oxidizable substance.

When the coal seam is exposed to the air, it will slowly undergo oxidation reactions with oxygen and continuously release heat.

If the heat cannot be dissipated in time, it will result in:

• Smoldering
• Local high temperature
• Spontaneous combustion of the coal seam
• Fire spread

The risk of spontaneous combustion is higher in mined-out areas, sealed areas, and areas with remaining coal in the tunnels.

A gas explosion requires three conditions:

• Flammable gas
• Oxygen
• Ignition source

Among them, the concentration of oxygen is a key factor.

By injecting nitrogen into the underground, the oxygen content can be effectively reduced, thereby lowering the risk of explosion.

Therefore, nitrogen inertization has become an important safety measure for high-gas mines.

Traditional coal mine fire extinguishing mainly includes:

• Plugging with grouting
• Spraying water
• Chemical fire extinguishing
• Isolation and sealing

However, these methods have the following drawbacks:

• Limited coverage area
• Long fire extinguishing cycle
• High risk of secondary re-ignition
• Complex construction

While nitrogen fire extinguishing belongs to "gas inerting fire prevention and extinguishing", it has the advantages of wide coverage and strong persistence.

As the depth of the mine increases:

• Ground temperature rises
• Increased air leakage
• Changes in coal seam pressure
• Increased gas outflow

These factors will increase the risk of coal mine fires and explosions.

Therefore, modern mines increasingly rely on large-scale continuous nitrogen supply systems.

A coal mine nitrogen generator is an industrial equipment that continuously extracts nitrogen from the air using air separation technology.

Its core objective is:

To provide a protective inert gas source for the mine through continuous and stable output of high-purity nitrogen.

Air contains approximately 78% nitrogen, so the nitrogen generator only needs to separate oxygen, moisture, and impurities to obtain the required nitrogen.

Currently, the coal mining industry mainly uses:

The most mainstream solution.

Characteristics:

• High nitrogen purity
• Stable operation
• Strong continuous supply capacity
• Suitable for large coal mines

Suitable for:

• Low flow rate
• Mobile
• Low purity scenarios

Its characteristic is a simple structure, but the purity is relatively low.

Currently, large coal mines still mainly use PSA technology.

PSA (Pressure Swing Adsorption) is a pressure swing adsorption process.

The core principle is:

Using carbon molecular sieves to achieve air separation due to different adsorption speeds of oxygen and nitrogen.

The air compressor compresses the air to:

• 0.7 - 1.0 MPa

Then it enters the purification system.

Through:

• Cryogenic dryer
• Precision filter
• Oil removal system

Remove:

• Water
• Oil
• Dust

To avoid contaminating the carbon molecular sieve.

The compressed air enters the adsorption tower:

Carbon molecular sieves preferentially adsorb oxygen, carbon dioxide, and some impurities.

Nitrogen is retained and output.

After saturation, the adsorption tower rapidly depressurizes.

The adsorbed oxygen is released and discharged.

The carbon molecular sieve recovers its adsorption capacity.

Two adsorption towers operate alternately:

• One tower adsorbs
• One tower regenerates

Thus achieving continuous and stable nitrogen supply.

A complete coal mine nitrogen station usually consists of the following parts:

Function:

Provide stable compressed air.

Common configurations:

• Liposuction compressor
• Permanent magnet variable frequency compressor

Including:

• Cooling dryer
• Drying machine
• Precision filter
• Oil remover

Its function is to protect the molecular sieve.

Core equipment.

It mainly consists of:

• Adsorption tower
• Carbon molecular sieve
• Pneumatic valve
• Dampener

Used for:

• Stabilizing pressure
• Balancing flow rate
• Mitigating fluctuations

Realizes:

• Automatic switching
• Purity monitoring
• Pressure control
• Fault alarm
• Remote monitoring

Including:

• Pipeline
• Pressurization system
• Nitrogen injection borehole

Responsible for underground transportation.

When selecting a coal mine nitrogen generation system, the following parameters are mainly considered.

Unit: Nm³/h

Common range:

• 200 - 5000 Nm³/h

For large coal mines, it can be even higher.

Common requirements:

Usually controlled:

• ≤ 1%
• ≤ 3%
• ≤ 5%

Depending on the working conditions.

Low dew point can avoid:

• Pipeline condensation
• Underground water accumulation
• Equipment corrosion

Common requirements:

• ≤ -40℃

The pressure at the outlet of the nitrogen generation system is usually:

• 0.6 - 1.3 MPa

The core application.

By continuous injection of nitrogen:

• Reduce oxygen concentration.
• Inhibit coal oxidation.

• Prevent re-ignition.
• Maintain a long-term stable inerting environment.

• Reduce the risk of explosion limits.

Used for:

• Coal powder storage
• Coal conveying belt
• Dust space

Some coal chemical enterprises adopt centralized nitrogen supply.

This large coal mine adopts:

• 2000 Nm³/h PSA nitrogen generation system
• Nitrogen purity 98%

Used for long-term nitrogen injection into mined-out areas.

After system operation:

• CO concentration significantly decreased
• Fire zone temperature stable
• Self-ignition risk reduced

This high-gas mine adopts:

• Dual redundant nitrogen generation system

Achieve:

• Continuous nitrogen supply
• Automatic switching
• Remote monitoring

Effectively enhance mine safety level.

The core is not the size of the equipment.

But the actual nitrogen consumption.

Must calculate:

• Leakage volume
• Oxidation area volume
• Nitrogen injection duration

Higher purity means:

• Increased energy consumption
• Increased air consumption

Not necessarily the higher the better.

Coal mine equipment usually requires:

• 24-hour operation
• Annual continuous operation of more than 8000 hours

Coal mines belong to special environments.

Must meet:

• Explosion-proof electrical control
• Explosion-proof motor
• Mine safety regulations

Modern mines place more emphasis on:

• Unattended operation
• Remote control
• Data networking

The largest energy consumption source of the coal mine nitrogen generation system is:

Electricity consumption of air compressors

Usually accounts for more than 70% of the total energy consumption

Factors affecting energy consumption Including:

• Nitrogen purity
• Compression pressure
• Air humidity
• Molecular sieve efficiency
• Valve switching efficiency

How to reduce energy consumption?

• To reduce part-load losses.

• Excessive purity will significantly increase energy consumption.

• Leakage will cause huge energy waste.

• Reduce pressure drop.

Blockage will lead to:

• Increased pressure drop
• Increased energy consumption

Failure of molecular sieve will cause:

• Decreased purity
• Excessive oxygen content

Pneumatic valves are components with high-frequency operations.

They require special maintenance.

Including:

• Change the lubricating oil
• Check the bearings
• Check the cooling system

• Ensure the accuracy of purity detection.

Common reasons:

• Ageing of molecular sieves
• Valve leakage
• Excessive moisture content in air
• Unstable pressure

PSA nitrogen production relies on stable adsorption pressure.

After pressure drops:

• The oxygen adsorption capacity decreases.
• Purity will fluctuate immediately.

Quick depressurization is beneficial for:

• Molecular sieve regeneration
• Improving adsorption efficiency

Frequent starting and stopping will:

• Increase valve wear
• Affect the lifespan of molecular sieves
• Cause unstable purity

Coal mine nitrogen production equipment usually needs to comply with:

Coal mine safety standards Including:

• Explosion-proof regulations
• Mine electrical regulations
• Safety monitoring regulations

Pressure vessel regulations

Involving:

• Gas storage tanks
• Pressure pipelines

Gas purity testing standards

Ensure:

• Oxygen content meets standards
• Gas stability meets standards

In the future, coal mines tend to:

• Have centralized nitrogen generation stations.

Including:

• AI Fault Prediction
• Remote Maintenance
• Data Networking

• Reduce the electricity consumption per unit of nitrogen.

• Shorten the installation period.

• Reduce human intervention.