Mar-2018

Refining-petrochemicals integration: an Indian view

Integrating a refinery with a petrochemicals complex offers high value products and a boost to gross margin.

VAHIDUNNISA QURESHI, VIVEK CHATE and PRABHAT SRIVASTAVA
Fluor Daniel India

Article Summary

The refining industry has been undergoing evolution triggered by internal competition and the pursuit of higher gross refinery margin. These two factors have been shaping the complexity of today’s refining industry with respect to:
•    The dynamics of the downstream market
•    Advances in refining processes/configurations.

Interestingly, it is not just market forces that have given direction to the path in which refining technologies are moving; technologies have themselves given shape to market scenarios. The number of end products from crude processing has increased enormously over time while various technologies have been driving the conversion of heavy and sour crude to lighter and sweeter products in response to market demand. Complex blending of multiple streams began meeting the requirement for high quality fuels in the latter half of the 20th century. Meanwhile, utilisation of the byproducts of fuel processes to produce other chemical products pushed up growth in the petrochemicals industry. Batch to process, heavy to lighter, thermal to catalytic, standalone to integrated have been the directional shifts in refineries as markets have diversified and technologies have evolved.

Stricter emission norms have been regulating refinery processes since the late 1980s and today most brownfield projects are solely driven by these regulations. While there is cost associated with these projects for improving fuel quality, only a small fraction of these costs could be recovered from fuel product price hikes. Extracting more value from new products rather than just augmenting the existing product slate is the way to go for such revamps. Also, while standalone refineries are gradually exploring integration opportunities with petrochemical complexes, it is only right for new refineries to feature such integration from the start.

Integrated refinery and petrochemical complex
Integration of a refinery and petrochemical complex implies identifying synergies and optimising them for operational and economic gains where they share and exchange many streams such as feedstocks, byproducts and utilities. The integrated complex provides optimum molecule management for better return on investment. Refineries have traditionally been aimed at maximising fuels as final products and, in the process, under-
utilising opportunities for extracting higher value. For example, naphtha streams in a refinery are reformed to produce reformate that is used as a gasoline blend, and propylene produced in the FCC is used to produce alkylate that again is used as blendstock in the gasoline pool. Optimally, reformate can be used to produce aromatics, and the propylene stream can be further processed to produce polypropylene which has a higher value (see Table 1).

Refinery and petrochemical complexes can typically be integrated as follows:
I)    Refinery Integrated with a steam cracker to produce ethylene, propylene and other derivatives.
II)   Refinery integrated with an aromatics complex to produce benzene, toluene, and xylene
III)   Refinery integrated with an aromatics complex and a steam cracker.

The extent of integration between any of the above depends on technical feasibility and the resulting economic benefits. This is a complex discussion and requires further detailed study on a case by case basis.

Refinery integrated with an olefin complex/steam cracker
A refinery produces a wide range of process streams with the potential to be used as cracker feedstock, depending upon the quantities in which they are produced, their utilisation and their availability in the refinery. Adequate flexibility at the design stage of the cracker, for handling varying feedstock types (gas based or liquid feedstock), provides a long-term buffer against market volatility. Many streams and byproducts can potentially be transferred in either direction between the refinery and the steam cracker. Naphtha from the refinery can be fed to the cracker as main feed. Dry gas, which is mixture of C1/C2 components, is better utilised in the cracker as petrochemical feedstock than as a fuel in the refinery. An olefin complex produces ethylene as the main product and propylene as a byproduct; it produces pygas, which is sent back to the refinery complex for further treatment. Another major stream from an olefins complex is hydrogen, which is sent back to the refinery complex and is of great importance for various hydroprocessing units. Other byproducts of the olefin complex are fuel gas and C4s (see Figure 1).

More than 98% of ethylene is produced from stream cracking globally. Steam cracking technology has evolved, diversified and matured to process multiple feedstocks. Naphtha and mixed feed based steam crackers represent the highest number of installations. Ethane based crackers have gained ground in the Middle East, Africa and North America in recent years. One of the reasons for the increasing number of gas crackers is discovery and production of shale gas, better yield, and hence more attractive economics. But profit per unit installed capacity is not the only criteria for feedstock selection. It is often limited by regional constraints and reliability and availability of feedstock. Consumption of naphtha as feedstock in Indian petrochemical complexes has increased by ~75% from 5900000 t/y to 10300000 t/y between 2008-09 and 2015-16.

Most propylene is produced from steam crackers as a byproduct along with ethylene. Propylene yield in a steam cracker increases with heavier feedstock to the cracker. The FCC is the next largest contributor of propylene. FCC technology developments have enabled operations in propylene mode where propylene yield from the unit is in excess of 20 wt%. Other technologies are used for propylene production where these feedstocks are not available. On-purpose propylene production (for instance, propane dehydrogenation) is increasing in regions where ethane cracking is used for ethylene production and propylene byproduct yield from the process is negligible.

Refinery integrated with an aromatics complex to produce BTX
Aromatics like benzene, toluene and xylene (BTX) are key building blocks for several petrochemicals. These are precursor materials for food containers and synthetic fibres among many other end products. Refinery integration with an aromatic complex is more common than with an olefins complex. The only other source of aromatics production is coke oven gas generated from coal coking. Heavy naphtha from the refinery is used to produce reformate, rich in aromatics, and other byproducts which can be back integrated with the refinery. Figure 2 shows this relationship.

A naphtha hydrotreating catalytic reforming chain produces reformate that is the source stream for maximum aromatics in the refinery. Reformate is used as gasoline blendstock to improve octane and/or is sent to an aromatics complex for BTX recovery. The trade-off between octane enhancement and BTX production due to routing of reformate is partly settled by the byproducts of the aromatics complex – raffinate and heavy aromatics streams returning to the refinery.

By comparison with ethylene and propylene, paraxylene production is highly integrated. In east Asia, a significant amount of paraxylene production is based on imports of condensate and subsequent splitting to produce naphtha for feedstock. A larger percentage of this capacity is not integrated with a refinery, leaving further scope for integration.