PTQ Q3 2023 Issue

Economic benefits of the dual stripper flow scheme vs a single stripper flow scheme 1-8

Parameters

Unit

Conventional single stripper flow scheme (base case)

Dual stripper flow scheme

Product fractionator feed

Heater duty

MMKcal/hr tonne/hr tonne/hr $MM/year

61.0 Base Base Base Base Base Base Base Base

48.8 (8.8) (2.6) (4.8)

MP steam generation LP steam generation

Utility cost

Estimated erected cost (EEC) for new equipment NPV from process improvements

$MM $MM

+ 4.2

+ 29.5

CO₂ emission (Scope 1 & 2)

tonne/year $MM/year

(~10,000) (1)

CO₂ credit

+ 0.5

NPV including CO₂ credit

$MM

+ 32.9

Notes: 1. 835 m³/hr (~126,000 BPSD) mild HCU with conversion of 45 wt%. 2. Fuel consumption is based on 90% heater efficiency. 3. CO₂ reduction credit $50/tonne. 4. Onstream hours: 8,400 hours per year. 5. NPV is for 15 years at 10% discount rate basis. 6. Simple payback period 10 months and with CO₂ credit payback period will further reduce to 9 months. 7. Utility price basis: • Fuel gas: $ 57.1/MMKcal • MP steam: $ 17.5/tonne • LP steam: $ 16.8/tonne 8. Scope 1 & 2 CO₂ emission basis: • 0.262 tonne of CO₂/MMKcal of Fuel gas • 0.208 tonne of CO₂/tonne of MP steam • 0.196 tonne of CO₂/tonne of LP steam

Table 1

vaporisation and then fed directly to the product fractiona- tor between the flash zone and diesel product draw stage. Apart from being applicable to new HCUs, the dual stripper flow scheme is a good revamp solution to reduce the exist - ing product fractionator feed heater duty. In the revamp flow scheme, the existing stripper will be utilised as hot stripper service, whereas a new cold stripper will be added in the flow scheme (see Figure 4). The dual stripper flow scheme can reduce the product fractionator feed heater duty by 20% compared with the existing conventional single stripper flow scheme. Beyond reducing product fractionator feed heater duty, another ben - efit is that it provides a reduction of carbon emissions from the existing HCU. Table 1 provides a summary of the utility consumption, economic and CO2 emission benefits with a dual stripper flow scheme as compared to a conventional single stripper first flow scheme.

The benefits described in Table 1 are based on a recently proposed revamp solution and subsequent basic engineer - ing work, which has been completed. The revamp project is currently in the detailed design phase. As summarised in Table 1, the reduction in fuel gas consumption for this 835 m 3/hr (~126,000 BPSD) mild HCU improves the facility’s net present value (NPV) by $29.5 million. If CO₂ is valued at $50 per tonne, the NPV boost attributable to the dual stripper flow scheme approaches $32.9 million. Dual stripper scheme applied to a debutaniser-first flow scheme Some of the earlier designed HCUs are operating with a debutaniser-first flow scheme. A simplified flow diagram of the debutaniser-first fractionation section flow scheme is shown in Figure 5 . This scheme typically includes a debu - taniser column to separate LPG and lighter sour off-gases

O - gas

Stabiliser

Cold ash drum liquid

Product fractionator

Naphtha

Cold stripper

LPG

Kerosene

MP steam

Naphtha

Diesel

Hot ash drum liquid

Hot stripper (formerly debutaniser)

MP steam

LP steam

Unconverted oil

Debutaniser reboiler

Product fractionator feed heater

New / modications

Figure 6 Revamp process flow scheme with the dual stripper fractionation section of an HCU

PTQ Q3 2023