Description

Capture efficiency is defined as the percentage of emissions captured and vented to a control device. Various capture systems may be used to capture emissions and direct them to a control device. These systems include enclosures and local exhaust ventilation measures.

1. Any natural draft opening (NDO) shall be at least four equivalent opening diameters from each VOC emitting point;
2. The total area of all NDOs shall not exceed 5 percent of the surface area of the enclosure four walls, floor, and ceiling;
3. The average face velocity (FV) of air through all NDOs shall be at least 3,600 m/hr (200 ft/min);
4. All access doors and windows whose areas are not included in the calculation in item No. 2 shall be closed during routine operation of the process; and
5. All VOC emissions must be captured and contained for discharge through a control device.

Other specific information about PTEs can be found from the following Air Pollution Control Technology Fact Sheet.

You can view a training video on capture systems here: Pollution Controls and Available Monitoring Techniques Part 2 - High Resolution (WMV).

• Method 204 A - Volatile Organic Compounds Content in Liquid Input Stream
• Method 204 B - Volatile Organic Compounds Emissions in Captured Stream
• Method 204 C - Volatile Organic Compounds Emissions in Captured Stream (Dilution Technique)
• Method 204 D - Volatile Organic Compounds Emissions in Uncaptured Stream from Temporary Total Enclosure
• Method 204 E - Volatile Organic Compounds Emissions in Uncaptured Stream from Building Enclosure
• Method 204 F - Volatile Organic Compounds Content in Liquid Input Stream (Distillation Approach)

Alternative protocols and test methods for determining capture efficiency also may be used. EPA has established data quality objectives that must be met for alternative protocols and test methods; these are presented in Appendix A to Subpart KK to Part 63 - Data Quality Objective and Lower Confidence Limit Approaches for Alternative Capture Efficiency Protocols and Test Methods.

The second type of control measure used to capture emissions and vent them to a control device is the application of local exhaust ventilation. Local exhaust ventilation systems typically consist of a hood, or hoods, that captures the contaminant at the point of generation and a duct system and exhaust fan that move the VOC-laden air to the control device.

For both types of capture systems (enclosures and local exhaust ventilation systems), maintaining the integrity of the capture device (i.e., enclosure, hood) and the airflow (ventilation) through the system are the critical operating/maintenance parameters with respect to maintaining capture system performance.

(The official version of the methods is available from the GPO's Electronic Code of Federal Regulations, Subpart BB—Data Requirements for Characterizing Air Quality for the Primary SO2 NAAQS:Appendix M to Part 51—Recommended Test Methods for State Implementation Plans)

• Method 204 - Criteria For And Verification of a Permanent or Temporary Total Enclosure (40 CFR 51, Appendix M) (7 pp, 59 K, About PDF)
• Method 204 A - Volatile Organic Compounds Content in Liquid Input Stream(22 pp, 116 K, About PDF)
• Method 204 B - Volatile Organic Compounds Emissions in Captured Stream(16 pp, 88 K, About PDF)
• Method 204 C - Volatile Organic Compounds Emissions in Captured Stream (Dilution Technique)(17 pp, 90 K, About PDF)
• Method 204 D - Volatile Organic Compounds Emissions in Uncaptured Stream from Temporary Total Enclosure(18 pp, 92 K, About PDF)
• Method 204 E - Volatile Organic Compounds Emissions in Uncaptured Stream from Building Enclosure(15 pp, 72 K, About PDF)
• Method 204 F - Volatile Organic Compounds Content in Liquid Input Stream (Distillation Approach)(19 pp, 94 K, About PDF)
• Appendix A to Subpart KK to Part 63 - Data Quality Objective and Lower Confidence Limit Approaches for Alternative Capture Efficiency Protocols and Test Method(Exits to GPO's Electronic Code of Federal Regulations)
• Air Pollution Control Cost Manual, Section 2, Chapter 3 - Permanent Total Enclosures (37 pp, 158 K, About PDF)

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Monitoring Information

Maintaining the integrity of the capture device (i.e., enclosure, hood) and the airflow (ventilation) through the system are the critical operating/maintenance parameters with respect to maintaining capture system performance. The indicators of performance for capture systems relate to these two parameters and, for purposes of discussion, monitoring approaches can be divided into two subcategories:

1. Indicators of capture by the enclosure or hood (e.g., enclosure differential pressure, NDO velocity, hood face velocity); and
2. Indicators of system air flow (e.g., fan rpm, duct pressure differential) measured downstream of the capture device combined with a system integrity inspection.

Costs

Information on the costs of Permanent Total Enclosures is presented in the EPA Air Pollution Control Cost Manual^*, Section 2, Chapter 3 - Permanent Total Enclosures(41 pp, 125 K, About PDF). Costs of monitoring systems, both Continuous Emission Monitors and parametric monitoring systems, are addressed in the EPA Air Pollution Control Cost Manual^*, Section 2, Chapter 4 - Monitors.(42 pp, 542 K, About PDF).

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