Energy saving and environmental improvement

Treating oil-contaminated condensate with a high-quality auto drain trap for saving energy


As to discharge of condensate generated from an air compressor, problems of high air loss and high oil content have been identified, which leads to energy loss and environmental problems.

It has been known that a condensate discharge trap has significantly low reliability, including float type and time solenoid valve type.

In case of the float type trap, the nozzle is often clogged up (with impurities such as scale due to the narrow nozzle size of 0.7mm). The time solenoid valve type trap has huge air loss and short life span less then 1 year.

If a drain trap with zero air loss and effective discharge is applied to drain lines of an air compressor such as after cooler, air dryer, air tank, etc., any accident caused by a condensate leak can be prevented in advance.

Moreover, condensate generated from an air compressor is severely contaminated by the oil within the compressor and pollutants in the air and thus has a high oil (Normal hexane) content of nearly 2,000ppm(2,000mg/L), affecting the water quality of rivers and public health.

Cause of the high oil content in condensate

Oil is generated when air (including saturated water vapor) passes through a rotor for compressing (oil is input in order to reduce frictional heat), and oil of 2,000 ppm or more is discharged through drain traps of an air dryer, air filter, air tank, and so forth. (Acceptable standards for water contamination: 5 ppm or below according to the regulations))

Discharge amount of condensate varies depending on seasons and is especially high during peak summer because of high humidity.

Demage from condensate

Incomplete discharge of condensate generated from an air compressor can cause shortened life and failure of an air compressor, air dryer, receiver tank, production facilities, and so forth.

Due to a high oil content in condensate, it can’t be discharged as regular wastewater but should be treated through outsourcing or independently (using an oil-water separator).

The amount of condensate generated?

Air compressor : 100HP

Numerical values needed for calculating the amount of condensate – Compressor horsepower, working pressure, operation hours (daily, yearly), and machine efficiency

Ex) Compressor 100hp; working pressure – 7㎏/㎠; operation hours – 24hour/day, 330day/year;

Amount of condensate – 42,822 (ℓ) / year in case of 80% efficiency

Temperature(℃) -3 -2 4 11 17 21 25 26 21 14 7 -1
Humidity(%) 65 62 62 65 69 71 79 76 72 68 63 66
Air comp" 126 149 778 1,863 2,977 3,879 5,717 5,712 4,005 2,436 1,203 330
Air Dryer 687 687 687 751 1,199 1,537 2,019 2,139 1,573 959 687 687
Total(ℓ/month) 813 836 1,465 2,614 4,176 5,452 7,736 7,851 5,578 3,395 1,890 1,017
Average(ℓ/1day) 32.5 33.4 58.6 104.6 167.0 218.1 309.4 314.0 223.1 135.8 75.6 40.7
  • Air comp"
  • Air Dryer
  • Total(ℓ/Month)

Condensate occurs POINT (Standard)


* Condensate rates

Section Air Comp" Air R/Tank R/Dryer Filter
winter 78% 11% 11% -
spring/fall 61% 13% 21% 4%
summer 61% 11% 25% 3%

Condensate discharge method


Manual Valve

Compressed air, produced by high-cost power, is discharged into the air in order to discharge condensate.

How much is the yearly loss of compressed air in case of 7㎏/㎠ working pressure and 3π bypass valve opening?

0.6559 m3/min X 60 min X 24hour X 330 days
= 311,683 m3 X KRW 11 (1m3 air production cost)
= 3,428,513 KRW/year (per 1 Point)
3,428,513 KRW/year X 1 Point = 3,428,513 KRW/year

3,428,513 Won/year X 1 Point = 3,428,513 Won/year


Float Trap

Float trap requires frequent disassembly and cleaning due to the small nozzle diameter (0.7∅). (which explains the need for opening of a bypass valve)
Impurities in the float cause air loss because the nozzle can’t be closed.
Viscosity of oil reduces buoyancy of the float for an oil-injected compressor, and this requires frequent replacement cost.


Time Control Sol V/V

Frequent failure occurs because of compression pressure directly applied to a solenoid valve.
A large amount of air is lost because condensate is discharged via time setting regardless of the amount.
Excessive noise is caused during discharge.

Analysis of a condensate drain trap (level sensor type)




Level sensor type

There is almost zero air loss, ensuring high economic efficiencyand fast recouping of initial investment.

Large-size drain prevents clogging, and self-restoration for an emergency mode improves safety.

A strainer within the product prevents collection of scale.

Automatic operation provides easy maintenance.

A variety of models are avaliable for smalland large capacity compressors air line.

Operating principle

Time to open a valve is calculated based on detection by a sensor.

An emergency mode begins after 60 sec if condensate is not properly discharged.

The emergency mode initiates the self-restoration feature, and the valve is opened for 5 sec per every 3 min as like time control valve temporally.

How much is the energy loss (caused by air loss) of the time control drain trap?

Accurate time setting based on the amount of condensate is difficult and thus compressed air is lost during the discharge time.
ex) Amount of air loss for the time sol v/v with 10Ø diameter (based on 7bar) : 7.2872㎥/min

Setting Time : 5 sec per 5 min – condensate discharged for 1 sec and air lost for 4 sec.
: 12 times/hr x 4sec/time = 48sec/hr

Operation of 24 hr per day for 365 days
: 24hr/day x 48sec/hr x 365day/year = 420,480sec/year

Annual energy loss
: 7.2872㎥/min x 420,480sec/year ÷ 60sec/min = 51,069㎥/year

Production cost of 1m3 air: KRW 11

51,069㎥/year x KRW 11 = KRW 562,000


Loss of compressed air


Loss of high-cost energy

Incomplete discharge of condensate


Failure of expensive facilities and product defects caused

Results of complete discharge of condensate?

Energy saving, protection of facilities, and products quality assurance

Analysis of drain trap usage and cost of air loss

1. Analysis of drain trap usage

Types of drain traps Analysis
Time Control Solenoid Type A large amount of air is lost because condensate is discharged via time setting regardless of the amount..
Float Type The trap has low reliability and experiences frequent clogging due to the small nozzle diameter (0.7∅).
Manual Valve Open Compressed air, produced by high-cost power, is discharged into the air in order to discharge condensate.

2. Cost of air loss per drain trap

Drain trap types Air loss calculation
Time Control Solenoid Type KRW 562,000/1 point x 9 EA = KRW 5,058,000 / year
Manual Valve Open KRW 1,686,000/ 1 point x 9EA = KRW 15,174,000 / year
Level sensor type(Drain Master) Zero

Improvement methods

Drain trap: Condensate discharged without air loss

Automatic level control drain system to be established

Application of an AI (artificial intelligence) electronic sensing system

Discharge of condensate only (Zero air loss)

No clogging (easy maintenance and high efficiency)

When installing a manual valve

Low labor cost and improved cleanness

Installed a time sol valve

Reduced power cost, low replacement cost, and no noise

Installed a float drain trap

No need for frequent disassembly and replacement

No oil content in discharged condensate

Separation of emulsified oil in condensate

Extraction and treatment of pure oil

*Reduction of the treated amount by 98%
*Condensate of 5ppm or below only discharged / regular drainage

Hence, regarding an oil injection compressor, condensate causes frequent clogging of a drain trap that lowers efficiency, affects air quality, results in high energy loss due to air loss, and contaminates water because of high oil content.

Installation of a semi-permanent drain trap and oil-water separator, which discharge condensate only without energy loss, can maximize efficiency in terms of operation and maintenance.