Technology

Process Summary

The Proprietary Selective Cracking Optimum REcovery (SCORE) pyrolysis furnace features a single straight radiant-tube design with feed entering the bottom and cracked gas leaving the top of the furnace. This results in low practical reaction time (~0.1 seconds) in the industry, low operating pressures, and high olefins yields. Additional features of the SCORE process are hybrid cracking, online decoking and ultra low-NOx burners. The recovery section is based on a front-end acetylene reactor design pioneered by KBR combined with integration of fractionators with the major compressors^[1].

Process Flow Scheme

The pyrolysis furnace (1) cracks the feed hydrocarbon in the presence of dilution steam into large amounts of ethylene, propylene and byproducts. The furnace effluent is cooled by generating steam (2) and quenched further (3–5) to remove heavy gasoline (7), fuel oil and dilution steam. The cooled process gas is compressed (6), caustic-washed (8) and dried (9). The first fractionator is typically a deethanizer for lightgas feeds or a depropanizer for heavier feeds. Both schemes were pioneered by KBR and share common attributes leading to low cost and energy. The example which follows is for a depropanizer-first scheme. The depropanizer (10) is heat pumped by the last stage of the cracked-gas compressor (6). The acetylene in the depropanizer overhead is hydrogenated in an acetylene reactor (11), and the C₃ and lighter stream is sent to the demethanizer system (12–14) to separate methane and lighter fraction from the mixed C₂/C₃ stream. The demethanizer (13) bottoms C₂/C₃ stream is sent to the deethanizer (15), which is integrated with the heat-pumped C₂ splitter (16) and C₂ refrigeration compressor (17) in a patented design to save both energy and capital. The C₂ splitter is operated at low pressure to produce ethylene product and ethane recycle. The deethanizer bottoms (mixed C₃ stream) flows to the C₃ splitter (18) where propylene is recovered and propane recycled. The depropanizer bottoms product (C₄+ stream) flows to the debutanizer (19) for recovery of the mixed C₄ product and aromatic-rich pyrolysis gasoline.

Figure 1 - KBR SCORE Simplified PFD^[1].

Plant Configuration

KBR Score plants can be designed with a Deethanizer First (Fig. 2) or Depropanizer First (Fig. 1 & Fig. 3) configuration^[2].

Figure 2 - KBR SCORE Deethanizer First Configuration^[2].

Figure 3 - KBR SCORE Deethanizer First Configuration^[2].

Process Characteristics

Product yiels: Ethylene yields up to to 84% for ethane, 38% for naphtha and 32% for gasoils may be achieved^[1] depending depending upon feedstock character (Fig. 4) and cracking severity (Fig. 4)^[2]. 

Energy: overall specific energy per tonne of ethylene ranges from 3,000 kcal/kg to 6,000 kcal/kg, depending on feed type and battery limit conditions^[1].

Figure 4 - KBR SCORE Product Yields vs. Feedstock Type^[2].

Figure 5 - KBR SCORE Product Yields vs. Cracking Severity^[2].

References

1. Hyrocarbon Process Engineering, 5^th Jun 2018, Ethylene, SUPERFLEX Process by Kellogg Brown & Root LLC.
2. Jeff Caton, Feb 2019, KBR Olefins Technologies Providing Key Flexibility with Optimum Design to Ensure Profitability, Ethylene Middle East Technology Conference.