You are using an old browser version, please update it.

Technology / Ethylene Technology

Ethylene Technology

Ethylene is an essential component in the manufacture of many industrial and Consumer grade products.

Chemical companies have a variety of options for feedstocks as well as processes to produce ethylene.

Economics and environmental issues are the dominant factors considered in the choice of feedstock and processes of ethylene production.

Ethane rich gas is the most common feedstock used for ethylene production globally due to its higher yield, lower capital and operating costs compared to other feedstocks like Naphtha, Propane, Methane and Syn gas.

The thermal cracking process is the most common process to produce ethylene Commercially.

Ethylene as an intermediate product has to be complemented by the downstream products to maximize its value through the increased profit margins of these products also to satisfy domestic market needs, reduce the imports and supplement the value chain of other master plan projects.

 

Process Description of ABB Lummus Technology

Ethylene technology from ABB is the most widely applied process for the production of polymer grade ethylene. The process is particularly well known for its performance, including product yield and energy efficiency, low investment cost, and operating reliability. Plant owners have selected ABB`s proprietary ethylene technology for more than 175 projects, accounting for about 40% of worldwide ethylene capacity.

The ethylene processes comprise basically four sections: thermal cracking, including quenching, gas compression and gas treatment, ethylene purification, and refrigeration.

In the following sections, we will describe each step of ethylene production;

Block Flow Diagram of Ethylene process

Cracking Furnaces:

Ethane gas is fed to the furnaces and cracked at approx. 844 degree C, producing a mixture of olefins with ethylene as the major component. Ethane typically yields approx. 0.65 tons of ethylene per ton of ethane feedstock.

The cracked gas leaving the furnaces is cooled in the Transfer Line Exchangers (TLEs) to prevent further undesirable reactions and to improve the thermal efficiency of the cracking operation. The gases are then sent to the Quench Section.

Quench system:

The cracked gases from the furnaces are cooled by direct water contact cooling in the Quench Tower. The condensed hydrocarbons sent to fuel system. The condensed water accumulated in the water/oil separator is sent to the quench water strippers, to further remove the dissolved hydrocarbons from the quench water.

Cracked Gas Compression:

Cracked gas vapor from the overhead of the Quench tower is compressed. In the stages of the cracked gas compressor, suction to each compressor stage is provided with a knock-out drum. The discharge vapor from each stage is cooled with water.

Caustic Wash:

The caustic wash tower removes from the cracked gas the acid gases (CO2 and H2S) that come from the fresh feed and the cracking step where injection of sulfur compounds is done to control the carbon monoxide content in the cracked gas.

The “sweet” cracked gas is chilled with cooling water followed by Propylene refrigerant. Chilled cracked gas is sent to the primary dryer.

Drying:

Drying of the cracked gas (< 1 ppm water) is necessary to prevent freezing and hydrate formation, before it is send to the de-methanizer.

De-methanizer

Dry cracked gas from the primary dryer is chilled using Propane & Ethylene refrigerants and by vaporizing the liquid ethane recycle from the C2 splitter, before it is sent to the de-methanizer. The feeds from the charge gas chilling train (Cold Box) are sent to the de-methanizer.

The top product of the de-methanizer is mainly Methane (CH4) with concentration 99% will be delivered to the fuel system.
The bottom products of the De-methanizer enter the Cold Box in two streams and exit from the cold box to the De-ethanizer.

De-ethanizer:

The top of the de-ethanizer is cooled using propane refrigerant and delivered to the acetylene reactor. Bottoms of the de-ethanizer are sent to the Butadiene unit.

Acetylene reactors:

The top of the de-ethanizer flows to the acetylene reactor where acetylene is selectively hydrogenated to ethylene.
The effluent from the reactor is cooled and dried in a secondary dryer. Effluent from the secondary dryer is sent to the C2 Splitter.

C2 Splitter:

The top from the C2 splitter is condensed then it is fed to reflux drum, part of the reflux drum is returned to the column. 
The bottom product from the C2 splitter is the recycle ethane and is sent back to the furnaces.

Ethylene product leaves the C2 splitter as a side-draw and flows to ethylene spheres then it is delivered at the battery limit of the plant.