PTQ Q1 2026 Issue

2500

1200 800 400 200 600 1000 1400 1600 1800

2000

1500

1000

500

Hybrid conguration

Only conventional

Hybrid conguration

Only conventional

Figure 1 Comparison of weight – Case 1

Figure 2 Comparison of cost in US dollars – Case 1

restricted to 12m in comparison to 19m with a conventional valve tray configuration. Hydraulic design calculations were carried out at the dominant vapour/liquid loads to check and ensure ade - quate hydraulic performance for both options. All the hydraulic parameters were calculated and analysed: jet and downcomer floods, wet and dry pressure drops, weir load, downcomer backup, and weep velocities, to name a few. The delta of 7m in diameter was a promising margin, which was evaluated further in terms of material weight and cost. Tray fabrication and installation costs considered the difference in price between the column shell and cor - responding internals at both 12m and 19m diameters, as shown in Figures 1 and 2 . Results are based on steel prices from 2014 (year of design). Case study 2 The second case study describes the finalisation of the main fractionator column diameter connected to the refinery’s high-throughput fluid catalytic cracking (FCC) unit. Process data for the column indicated a 38-tray configuration. The main fractionator column, also known as the main column, is the first product separation step in an FCC unit. The superheated reactor vapours are first cooled and then scrubbed of entrained catalyst. The column accomplishes controlled heat removal (in pumparound sections) coupled with sufficient liquid-vapour contacting (in fractionation sections) to achieve the desired degree of fractionation into product streams, namely main column bottoms (MCB), light cycle oil (LCO), heavy naphtha (HN), unstabilised gasoline, and wet gas. Table 2 describes the main tray sections of the column. During the finalisation of the main column diameter, the biggest challenge was imposed by the pumparound sec - tions. The main column has three pumparound sections, namely HN, LCO, and heavy cycle oil (HCO) pumparounds. These streams are withdrawn from the main column on flow control and used to provide heat to the reboilers as per the designated heat network. Owing to the high throughput, the diameter of the main column was estimated to be as high as 11m. Satisfactory hydraulic performance for various fractionation sections could be met in this diameter with conventional valve trays. However, the pumparound sections could not be

accommodated in the bespoke diameter despite higher tray spacing. Conventional valve trays in this section required a diam - eter of ~14.5m for satisfactory hydraulic performance. The estimated column height was around 50m. The bottlenecks were in the pumparound sections, where the tray spacings could not be reduced any further. Hence, the height had to be maintained the same in a 14.5m diameter column. An overall diameter of 14.5m was ‘more than required’ for the fractionation section, resulting in hydraulic performance with considerable margins and lower downcomer loads. The performance was found to be worse under turndown conditions. As an optimal solution, the diameter was re-evaluated with a hybrid configuration. The fractionation trays were constituted by conventional valve trays, while the pumpa - round sections consisted of HC trays (name and model of trays not disclosed due to confidentiality) with a diameter of 11m. Similar to case study 1, weight and cost estimates were made for both diameters. Figures 3 and 4 present a com- parison of material and cost benefits for both configura - tions: only conventional trays in a diameter of 14.5m vs the hybrid configuration in a diameter of 11m. The hybrid tray configuration ultimately proved to be beneficial. The main fractionator column was subjected to an interim revamp (a revision in capacity during project exe - cution). This could be successfully accomplished by replac - ing the conventional trays of the existing design with new

Main column tray sections (numbered from bottom to top)

Tray section

Service for the section

# 1-6 # 7-9

MCB (main column bottoms) pumparound

HCO-MCB fractionation

# 10-12 # 13-17 # 18-20 # 21-31 # 32-34 # 35-38

HCO pumparound

LCO-HCO fractionation

LCO pumparound

HN LCO fractionation

HN pumparound Top tray section

Table 2

PTQ Q1 2026