Condensate Management

Compressed air always contains water. When air is compressed and cooled, this moisture condenses and must be properly removed and treated.

Condensate Generation

How Much Water Does a Compressor Produce

Compressor Capacity	Typical Condensate*
25 HP	5-10 gal/day
50 HP	10-20 gal/day
100 HP	20-40 gal/day
200 HP	40-80 gal/day
500 HP	100-200 gal/day

*Conditions: 80°F, 60% RH, 8 hours operation

Factors Affecting Quantity

Factor	Effect
Ambient relative humidity	Higher RH = more condensate
Ambient temperature	Higher temp = more absolute humidity
Operating pressure	Higher pressure = more condensation
Cooler efficiency	Better cooling = more condensation
Dryer type	Refrigerated vs desiccant

Estimation Formula

\text{Condensate (gal/h)} = \frac{CFM \times 60 \times (W_1 - W_2)}{8.33 \times 7{,}000}

Where:

$CFM$ = Compressor flow
$W_1$ = Inlet specific humidity (grains/lb)
$W_2$ = Outlet specific humidity (grains/lb)
$8.33$ = Weight of water (lb/gal)
$7{,}000$ = Grains per pound

Drain Points

Required Locations

Location	Reason
Aftercooler	Highest condensate volume
Receiver tank	Accumulation from cooling
Before dryer	Protects the dryer
After dryer	Captures residual condensate
Filters	Accumulate separated water
Pipe low points	Gravity accumulation
Drip legs	Designed to capture water
Dead-end lines	No flow = accumulation

Drip Leg Design

    Main line
    ━━━━━━━━━━━━━━━━━━━━━━━
                │
                │ Minimum 6"
                │ drop
                ▼
    ┌───────────────────────┐
    │                       │
    │   Accumulation        │
    │   pocket              │  Minimum
    │   (min 2× diameter)   │  12"
    │                       │
    └───────────┬───────────┘
                │
              ┌─┴─┐
              │ D │ ← Drain
              └───┘

Drain Types

Manual Drain

Feature	Description
Type	Ball valve or petcock
Operation	Periodic manual opening
Cost	$20-50
Reliability	Depends on operator

Disadvantages:

Requires staff discipline
Frequently forgotten
If left open, wastes air
Not appropriate for critical systems

Timer Drain

Feature	Description
Type	Solenoid valve with timer
Operation	Opens at programmed intervals
Cost	$100-300
Adjustments	Frequency and opening interval

Typical configuration:

Frequency: Every 5-30 minutes
Opening duration: 1-10 seconds

Disadvantages:

Wastes compressed air
Doesn't respond to actual condensate amount
May over-drain or under-drain

Level Drain (Zero Loss)

Feature	Description
Type	Float or capacitive sensor
Operation	Drains only when condensate present
Cost	$200-800
Air loss	Zero or minimal

Types:

Mechanical float: Buoy opens valve
Magnetic float: Buoy activates switch
Capacitive: Sensor detects liquid level
Smart electronic: Monitoring and diagnostics

Advantages:

No compressed air loss
Drains only what's needed
Higher reliability
Lower operating cost

Drain Comparison

Type	Initial Cost	Air Loss	Reliability	Maintenance
Manual	$	Variable	Low	None
Timer	$$	High	Medium	Low
Mechanical float	$$$	None	Medium-High	Medium
Electronic	$$$$	None	High	Low

Condensate Composition

Typical Contaminants

Contaminant	Source	Typical Concentration
Oil	Lubricated compressor	50-500 mg/L
Solid particles	Corrosion, environment	Variable
Heavy metals	Pipe corrosion	Traces
Hydrocarbons	Degraded oil	Variable
Bacteria	Environment, stagnation	Variable

Legal Classification

In most jurisdictions, condensate from lubricated compressors is considered hazardous waste due to oil content.

Region	Oil Limit for Discharge
EPA (USA)	10-40 mg/L (varies by state)
European Union	10-20 mg/L
Canada	15 mg/L (varies by province)

Oil-Water Separators

Operating Principle

Separators take advantage of density differences:

Water: 1.0 g/cm³
Oil: 0.85-0.95 g/cm³

    Condensate inlet
           │
           ▼
    ┌──────────────────────────┐
    │ ░░░░░░░░░░░░░░░░░░░░░░░░ │ ← Floating oil
    ├──────────────────────────┤
    │                          │
    │   Separation zone        │
    │                          │
    │ ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓ │ ← Coalescing media
    │                          │
    │   Clean water            │
    │                          │
    └────────────┬─────────────┘
                 │
                 ▼
           Water discharge
          (< 10-20 mg/L)

Separator Types

Type	Capacity	Efficiency	Application
Simple gravity	Low	80-90%	Small systems
Coalescing	Medium-High	95-99%	Standard industrial
Adsorption (carbon)	Medium-High	99%+	Strict requirements
Membrane	High	99.9%	Critical

Sizing

Compressor Capacity	Separator Size
Up to 50 HP	50-100 gal/day
50-100 HP	100-200 gal/day
100-250 HP	200-500 gal/day
250-500 HP	500-1,000 gal/day

Maintenance

Component	Frequency	Action
Oil level	Weekly	Check, drain if needed
Filters/media	3-6 months	Replace per saturation
Activated carbon	6-12 months	Replace
General inspection	Monthly	Check leaks, connections

Condensate Disposal

Legal Options

Method	Requirements	Cost
Separator + discharge	Periodic testing, permits	Low
Third-party collection	Contract, manifests	Medium
Evaporation	Treated water only, permits	Low
Oil recycling	Recycler certification	Variable

Required Documentation

For environmental compliance:

Discharge permits (if applicable)
Records of treated volumes
Periodic effluent analysis
Hazardous waste manifests
Authorized handler certificates

What NOT to Do

Prohibited

Discharge untreated condensate to drain
Pour on ground or water bodies
Mix with other waste
Burn condensate
Ignore local regulations

Synthetic Oils and Condensate

Impact of Synthetic Oils

Synthetic oils (PAO, ester, PAG) present special challenges:

Oil Type	Separability	Emulsification
Mineral	Good	Low
PAO	Good	Low
Ester	Difficult	High
PAG	Very difficult	Very high

Emulsions

When oil forms an emulsion with water, gravity separation doesn't work.

Solutions:

Membrane separators
Chemical treatment (demulsifiers)
Evaporation
Collection as hazardous waste