Ethylene Recovery Unit

An Ethylene Recovery Unit is a declination of the classic Flare Gas Recovery System (FGRS). Normally FGR systems are used in refineries or oil production plants to reduce flare emissions and recover waste gasses (most of the times carbon dioxide or H2S) that otherwise would be burnt and released into the atmosphere through the flare systems.

Gas flaring is not only necessary in the Oil & Gas industry, but also at some chemical and petrochemical facilities, like ethylene or olefins plants.

Nowadays, this industry is taking serious efforts to reduce this occurrence.

The aim is not only to help reduce emissions of air pollutants, noise and light coming from flare stacks, but also to recover usable resources.

Moreover, in some countries, the regulations on the GHG emissions or the so-called carbon taxes are bringing operators to think about unnecessary gas flaring.
For all these reasons, it is easy to understand that it is convenient to recover rather than burn the flare gases.

Flare Gas Recovery Systems in Ethylene Production Plants

In ethylene production plants, an FGR package aims to compress the gas and conveys it to further use into the production plant.

The gas from the flare header passes through the Ethylene Recovery System. Like the classic FGRS, this consists of three main elements: a liquid ring compressor, a separator, and a cooler, all connected through pipings and valves.

Ethylene Recovery Package processes a gas mixture coming from different units of the plant. The volumes and the composition of this stream depend on the capacity, nature of the processes and the raw material used for the ethylene production.

Despite its specific composition, this fuel gas often contains valuable components like hydrogen, ethylene, propylene, propane and other olefins. By not burning these elements, olefins plants can reduce their emissions and enhance savings for the plant.

Benefits & Payback

Installing an FGRS in an ethylene or more generically in an olefin plant can bring several benefits:

Reduction of dangerous emissions, noise, light, and odors coming from burning flares
Recovery of valuable olefins and gasses, which can bring additional cost benefits
Enhanced sustainability and social commitment towards environment and local communities

Another important consideration is that the investment taken for adding a flare gas recovery unit can be offset by costs reduction over time.

How it Works

The gas (1) coming from the flare Process Unit enters the Liquid Ring Compressor (2) along with the process water (3). After the compression phase, the process gas and the water enter the separator (4) where they are parted: the gas passes through a demister (5) to have minimum water and leaves the vessel from the top, while possible condensed hydrocarbons and water are separated by gravity due to lower gas speed. The water is pushed back to the compressor, after being cooled again by a cooler (6).
Moreover, a continuous process water make up line (7) in the compressor suction line is provided to ensure a continuous water ring in the compressor. The gas exiting the separator heads to further use in the plant.

Liquid Ring Compressors for Flare Gas Recovery

Liquid ring compressors are generally considered the most feasible option for the classic Flare Gas Recovery Systems because of their reliability and intrinsically safe design. They are ideal for toxic, aggressive and explosive gasses like those present in oil & gas environments.

The main reason behind the LR compressor’s reliability is the fact that it uses a liquid as a compression element, avoiding any metal-to-metal contact typical of other types of compressors. This unique feature naturally reduces the vibration and noise levels and makes it possible to handle liquid or particulates carryovers with no effects. Downtimes and possibly mechanical failure statistically occur less, and in this case any maintenance can be performed easily, just removing the front of the compressors thanks to the Garo overhung design.

As second major features, a liquid ring compressor can ensure a near isothermal compression and oil free service.

Finally, a liquid ring compressor and its components can be constructed in different materials ensuring the maximum flexibility and reliability.