Cooling Tower Info.

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EnRUD Resources, Inc.

Cooling Tower Monitoring

using the

El Paso Method


Cooling tower monitoring describes the characterization of volatile organic air pollutants that are capable of being air-stripped from a water matrix. While generic or indicator monitoring may be required to identify the existence of volatile organic compound (VOC) emissions, speciated compound characterizations may also be required in some instances to characterize the specific compounds present.

Historically, a method for cooling tower water characterization was developed for use by El Paso Products Company in the early 70's. This method utilized a dynamic or flow-through system for air stripping a sample of the water and analyzing the resultant off-gases for VOC's using a common flame ionization detector (FID) analyzer, and has been the popular choice in Texas for many years.  

The El Paso Products method, however, has been overshadowed nationally by the use of purge and trap analysis of water samples utilizing gas chromatography and/or mass spectrometry techniques. While direct water analysis has been shown to be effective for cooling tower measurements of heavier molecular weight organic compounds with relatively high boiling points, Texas Commission on Environmental Quality (TCEQ) has determined that this approach may be ineffective for capture and measurement of volatile organic compounds with lower boiling points, such as ethylene, propylene, 1,3-butadiene, and butenes. VOC's with a low molecular weight and boiling point are generally lost in the sample collection step of purge/trap type analyses. 

Consequently, TCEQ requires that the air stripping method presented in this manual be used for cooling tower and other applicable water matrix emission measurements of VOC's with boiling points below 140F. Specific procedures for cooling tower sampling and analysis for VOCs with boiling points of 140F and greater must be submitted to TCEQ for approval on a case-by-case basis.

*The summary above is an excerpt from the:

TCEQ "Cooling Tower Monitoring," Sampling Procedures Manual, Appendix P, Revision No. 1


RT-201 Air Stripper System


The "VOC in Water" Air Stripper System based on the El Paso Method can aid in the measurement of fugitive volatile materials, which can escape from cooling tower water for example, and can be an indicator for process leaks and will allow plants to conform to laws limiting such emissions.



The RT-201 Air Stripper is based on a standardized method and is the preferred system for reliably testing VOC (Volatile Organic Compounds) in low PPM-concentrations with a FID-analyzer from cooling tower water. It can also be used in a wide variety of other applications where VOC concentrations in water need to be measured. When connected to a Total Hydrocarbon FID-analyzer the RT-201 is a continuous on-line or transportable monitor, which provides the measurement of low ppm concentrations of dissolved solvents in water. This could be from cooling water, industrial waste- water, groundwater, process or rain water run-off.

Continuous monitoring is a reliable and effective method to improve the process management for treating, discharging and detecting of dissolved VOCs in water. Compared to the laboratory grab sample analysis method, the technique of continuous on-line monitoring provides cost effective, remote and operator unattended measurement of volatile hydrocarbons in water. After the RT-201 stripping unit is connected via a short sample line to FIA (Flame Ionization Analyzer), it reliably measures strippable dissolved and dispersed volatile organic compounds in water.

Typical Applications

       Cooling Towers

       Condensate Water

       Holding Ponds

       Heat Exchangers

       Waste Water

       Process Stream Analysis

Spray Paint Booth

VOC in Cooling Tower Water

Leaks of volatile hydrocarbons from heat exchangers may emit large amounts of VOC which can cause emissions into the atmosphere or may create a hazard. Continuous on-line monitoring gives an early warning of possible corrosion leaks. Savings in lost product can be substantial.

VOC in Heat Exchanger Water

The continuous monitoring of volatile hydrocarbons in condensate or cooling water gives the possibly earliest warnings for the development of leaks in a heat exchanger.

VOC in Waste Water, Holding Ponds

Drainage run-offs, equipment leaks or spills can be the cause for a build up of volatile hydrocarbons. A VOC analyzer with the Model RT-201 continuously indicates the presence of VOC in such waters.


Continuous monitoring means uninterrupted real time measurement of VOCs in contaminated water.

Direct measurement does not require any sample pretreatment prior to measurement.

Monitoring process with a FID is more selective for the detection of VOC in the presence of physical and chemical interference in contaminated water.

Major Applications are Continuous monitoring (or field monitoring) of VOCs in water from cooling towers, cooling water outlets, condensers, heat exchangers, water wells, spray paint systems, extraction water run off, rain water run off.


For Additional Information:

TCEQ Sampling Procedures Manual

Appendix P, Cooling Tower Monitoring


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