Volatile Organic Compound (VOC) Recovery Units

VOC Recovery Units are packaged systems aimed at treating the vapors emitted during the loading or storage operations of petroleum products. They are designed to recover Volatile Organic Compounds, odor components or aromatics while avoiding emissions into the atmosphere.

What are Volatile Organic Compounds?


Volatile Organic Compounds (VOC) are light components generated from oil-based products such as gasoline, naphtha, diesel or crude oil.The typical sources of crude oil vapors are the filling of Floating Storage and Offloading vessels (FSO) near the oil platforms. Also vessels or tankers at onshore terminals or tank farms can generate vapors during the loading and unloading operations.

For what concerned refined petroleum products, typical sources of condensed vapors are:

  • Storage tank breathing and venting
  • Storage tank loading
  • Shuttle tanker and barge loading (also called marine loading)
  • Truck loading
  • Railcar loading
  • VOC Treating System: The Carbon Bed Vapor Recovery Unit (VRU)


    A vapor treating system is fundamental equipment to handle these vapors, recognized as being dangerous for the enviroment and human health. Currently, the Best Available Technique to recover these vapors is the Vapor Recovery Unit (VRU) with Activated Carbon Beds. They rely on Active Carbon Technology (also called Carbon Vacuum Adsorption), which is the most applicable solution for high volatile products.

    Gasoline, diesel, naphtha, condensates, methanol, ethanol, benzene, toluene, xylene, and also crude oil are compatible with Activated Carbons. From a design point of view, an active carbon based vapor recovery unit is equipped with the following main elements:

    1. The carbon beds. They are, typically two vessels filled with active carbons for capturing the VOC from the vapor stream and letting clean air out.
    2. The vacuum pumps. They extract the captured hydrocarbons from the active carbons bringing them to an Absorber Column. Liquid Ring or Dry Screw vacuum pumps are the most suitable for this application.
    3. The Absorber Column. It works as a liquid scrubber. Here the vapors encounter an absorbent liquid, which absorbs them. The liquid product (absorbent + recovered product) is sent back to the storage tank.

    These three main components reflect the three main process steps featuring the working principles of a Carbon Bed VRU:

    • ADSORPTION: The VOCs are adsorbed onto the actived carbons.
    • REGENARATION: The active carbons are cleaned from the adsorbed hydrocarbons through vacuum.
    • ABSORPTION: The vapors are headed to the absorber column where they are absorbed by an absorbent liquid.

    The vapors from loading or storage operations arrive at the Vapor Recovery Unit (VRU). They enter the carbon bed vessel set in adsorption/receiving mode. The hydrocarbons in the vapor are adsorbed onto the Activated Carbons (AC) and the clean air is released in the atmosphere.

    When the ACs are saturated, after 10 to 15 min on average, the vapors are directed to the second vessel. The first, saturated, vessel is isolated and put under vacuum by one or more vacuum pumps. By doing this, the adsorbed hydrocarbons are removed from the AC and, through the vacuum pumps, they enter the absorber column. In the absorber column, an absorbent fluid (e.g. gasoline) is showered down, while the extracted and highly concentrated vapors go in reverse direction.

    Most of the hydrocarbons in the vapor are absorbed in the absorbent liquid. The not absorbed vapors are redirected to the AC vessel in adsorption/receiving mode through a recycle line. The absorber with the recovered product is returned to the storage tank or pipeline. When the complete cycle is finished, the AC is clean and ready to receive a new stream of vapor. For this reason, the AC vessels switch function and the vapors are directed to the clean AC vessel in receiving mode. This sequence repeats itself every 10-15 minutes as long as hydrocarbon vapors are entering the Vapor Recovery System.


    Compliant with the Major Emission Standards


    One of the main drivers for installing a VRU is the necessity of complying with environmental legislation. For what concerns crude oil, the standard is related to the recovery efficiency, which is usually required to be between 90-95%.

    For oil-based products every country has its own standard, many countries require <10 mg/Nm3 according to the signed Gothenburg Protocol. Some countries go even lower with emission limits from 5 grams, 2 grams up to 150 or 50 mg/Nm3.Aromatics components standards range between 10mg/Nm3 up to 1mg/Nm3.


    Benefits of Active Carbons VOC Recovery Systems


    A Carbon Bed Vapor Recovery System reduces emissions levels, while recovering valuable hydrocarbons. They are able to capture about 99% of Volatile Organic Compounds generated.At a glance, a Carbon Bed VRU benefits are:

  • Compliance with environmental regulations
  • VOC emissions reduction and better air quality
  • Safer work environment for operators working at terminals
  • Reduced health effects on surrounding local communities
  • Increasing profits through the recovery of additional gasoline from the vapors
  • Fast return on the investment
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