Construction of the plant for ethylene production started in 1976, according to the licence of project house Stone&Webster (USA), and the project of installation for hydrogenation of pyrolytical gasoline was made by the Institut Français Du Pétrole (IFP), France. Complete production and getting the product in specification were realized in November 1979.
The projected annual capacities in tons are:
| Product | Capacity | Application |
| Ethylene | 200.000 | for production of polyethylene, ethylenedichloride,ethyleneoxide, ethyleneglycol, ethyl-alcohol etc. |
| Propylene | 85.000 | for production of polypropylene, propylenoxide, propylenglycol acrylonitrile, EPDM, propylendichloride, propyl-alcohol etc. |
| C4-Fraction | 45.000 | for production of styrene-butadiene rubber, latex, synthetic resins, polybutadiene rubber, ABS-powder, etc. |
| Pyrolysis oil | 38.000 | as raw material for production of industrial carbon black |
| Pyrolysis gasoline | 138.000 | for production of aromates and motor gasolines |
Production process of Ethylene Plant consists of the following parts:
• Section of pyrolytical cracking– pyrolytical furnaces
• Section of primary fractionation
• Section of compression and washing of crack-gas
• Section of cool fractionation
• Section of warm fractionation
• Section of hydrogenation of pyrolysis gasoline
Besides that,the plant has storage tanks and accessory energy,cooling and systems for process fluids.
The initial raw material in the process of getting ethylene is primary (virgin) naphtha (heavy straight-run naphtha), one of the products of atmospheric distillation of virgin naphtha. Raw material (virgin naphtha) is diluted by steam and exposed to cracking – decomposing of hydrocarbon molecules to smaller reactive units – free radicals,which are recombined in new molecules depending on the reaction conditions.This thermal reaction is happening at high temperatures above 800°C, on which occasion higher temperatures in furnaces increase the share of the main product (ethylene) in relation to the other components. The reaction is completed by sudden cooling (quenching) of outlet mixture (crack-gas) in heat exchangers ,and then,before sending to primary fractionation,outlet mixture is additionally cooled,on which occasion there is also got steam of high pressure which can be used as energy. After sudden cooling of outlet mixture,in other sections of the plant there follow series of separation of heavier and lighter hydrocarbons from the main products,as well as water elimination,acid gases and other products of reaction which can have harmful influence on the quality of basic product and especially on the quality and yield of ethylene derivatives.Separation is made by multiple consecutive distillations ,cooling and condensation of mixture components in the complex systems of columns and vessels,with compressor system and heat exchangers in the special sections of the plant. In each of these sections there is separated some useful component or fluid,with elimination of undesirable compounds and returning into process of the components which can be used as energy,raw material or reactant:
In the section of primary fractionation there are separated the products – pyrolysis oil and untreated pyrolysis gasoline,with water from which there is produced steam again for dilution and is returned to the beginning of process,in pyrolysis furnaces.
In the section of compression and washing of crack-gas they are separated at the end as liquified part C3 and all C4+ hydrocarbons (with four and more C atoms), and gaseous C2 stream is directed to the next section. In this section between third and fourth degree of compression there are eliminated harmfull acid gases.
In the part of cold fractionation on the very low temperature of -163°C, from the gaseous C2 stream there are separated methane and hydrogen.Gaseous methane is further used as fuel gas,and hydrogen as reactant for hydrogenation of acetylene into ethylene and for stabilization of pyrolysis gasoline. The liquified C2 stream contains all hydrocarbons with two C atoms –desired ethylene,but also ethane and acetylene.Acetylene in reaction with hydrogen is transformed into ethylene,and ethane is separated by distillation and is used as a part of raw material mixture. Finally there remains only ethylene of polymer purity (ethylene polymer grade) with minimum 99,9 % mol ethylene, which was the purpose of the whole process. Such ethylene is ready for usage in our polyethylene plants or for storage in cryogenic tanks and further sale.
However,it is necessary to use the rest,i.e. earlier separated stream containing C3 and C4+ hydrocarbons.
In the section of warm fractionation this stream is separated on the part containing propylene and propane and the part containing C4+ hydrocarbons.
The part containing minimum 93-95% propylene and maximum up to 7% propane represents the produced propylene of chemical purity (propylene chemical grade), which is being kept in cryogenic tank before it is delivered.
The stream containing Struja C4+ hydrocarbons is exposed to separation again ,and C4 components represent the product - C4 fraction intended for getting 1,3-butadiene and later styrene-butadiene rubber (SBR) in our plant in Elemir.
Untreated pyrolysis gasoline,created already in the section of primary fractionation,contains certain quantities of diolephins which gravitate toward hardening while standing.Therefore it is necessary to stabilize pyrolysis gasoline i.e. to hydrogenate hydrocarbons with two double connections and transform them to more stable forms ,which is being performed in the section of hydrogenation of pyrolysis gasoline.The treated pyrolysis gasoline is used as one of the components at mixing of motor gasoline or as raw material for getting aromates (benzene,toluene and xylene).
