Volatile organic compounds (VOC) - Organic compounds whose vapor pressure at 20 °C exceeds 0.13 kPa are referred to as Volatile Organic Compounds. VOC have been implicated as a major precursor in case of production of photochemical smog, which causes atmospheric haze, eye irritation and respiratory problems. Some VOC's are cancerogenic. VOC emissions are typical for oil processing, petrochemical and chemical plants.
There are two main types of VOC emissions:
- emissions from point sources - storage tanks and filling stations vents
- fugitive emissions - process equipment leaks
Emissions from storage tanks
Emissions from storage tanks can be either measured (for fixed roof tanks) or can be calculated (for all tank types) by means of the U.S. EPA AP-42 method.
The calculation is based on
- tank construction data
- stored liquid volatility data
- meteorological data
- annual turnovers of the liquid stored.
The validity of calculated results may be controlled by means of direct emission measurement.
Tank Emissions Monitoring System TEMS
Software TEMS based on EPA's AP-42 equations was developed for tanks emissions calculations. The program uses metric units of data entered. The tank construction data, liquid data and meteorological data are in most cases permanent. Annual number of turnovers of the stored liquid changes often and must be regularly updated by. The best way of updating turnovers is the linking of TEMS to a process information system containing data about tank levels.
TEMS allows to obtain emission database and create an emission report easily and rapidly even for large tank farms. TEMS helps the user to be in compliance with ever more stringent legislation requirements on emission recordkeeping and reporting.
Fugitive emissions data
Sources of fugitive emissions are leaking components of process equipment such as flanges, valve stem packings, pump and compressor sealings, etc. Total emission rate from these sources depens especially on the age of the equipment and on maintenance routine in the plant.
LDAR Program (Leak Detection And Repair)
All the accessible equipment is monitored by means of the EPA's reference method 21. Leaking components are tightened (the first attempt to repair) or repaired during the next shutdown. The correlations between measured VOC concentration near the source and the real emission rate developed by EPA allows to evaluate total emission rate (production losses) due to leaking component and achievable savings due to repairs of leaking components.
- improves a maintenance routine
- saves both money and environment,
- helps to comply with the environmental laws
- data consulting in area of VOC monitoring and minimization
- implementation of TEMS