ADVANCED PROCESS CONTROL
APC uses a model-based predictive control technology that drives the process towards the desired targets through the manipulation of several variables simultaneously while observing all process constraints. APC has a proven track record in delivering business objectives: reducing energy costs, increasing yields and improving operability. Axens’ Performance Programs Business Unit provides S², our State Space APC suite, designed to efficiently implement and maintain plant-wide APC applications. The benefits of these applications have been fully demonstrated on several plants.
Figure 1: APC Overview: Plant / PID / DCS / APC
AXENS’ KNOW-HOW
As a process licensor and catalyst supplier, Axens is well positioned to offer models and first-hand knowledge of the best strategies for APC projects. Axens provides services covering all phases of APC projects, including: • Detailed functional design • Implementation • Commissioning • Maintenance
CONTROL STRATEGY
Our control strategy for Prime-G+ (shown by Figure 2) consists of: • SHU: Diolefins hydrogenation
- Adjustment of hydrogen make-up - Control of temperature profile
• Splitter - Cutpoint and reboiler duty optimization - Precise control of Light Cut Naphtha (LCN) sulfur
• Selective HDS - Precise control of Heavy Cut Naphtha (HCN) sulfur - Maximization of octane retention
• HCN+LCN blend sulfur control • CO2 constraints management.
APC for Prime-G+™ A LICENSOR SOLUTION THAT INTEGRATES MODELS, CONTROL STRATEGY & THE APC TOOLBOX
Figure 2: Control objectives for Prime-G+ APC
ControlControlDiolefinDiolefin
Hydrogenation Hydrogenation
ControlControlDiolefinDiolefin
Hydrogenation Hydrogenation
Cut Point Optimization &Cut Point Optimization &
Internal Reflux Control Internal Reflux Control Cut Point Optimization &
Cut Point Optimization &
Internal Reflux Control Internal Reflux Control
Maximization ofMaximization of
Octane retention Octane retention Maximization ofMaximization of
Octane retention Octane retention
SulfurSulfurcontrolcontrolSulfurSulfurcontrolcontrol
HCN
Feed
SHU
Prime-G+ Selective HDS
BlendBlend
H2 Make-up
SPLITTER
LCN
OCTANE & SPLITTER OPTIMIZATION
Our unique HDS inferential model, schematized in Figure 3, is based on kinetic models and allows precise octane loss estimation. Consequently, octane loss is minimized.
Figure 3: Prime-G+ - APC Architecture
The optimum splitter operating point can vary significantly, depending on feed sulfur content. Fine tuning of HCN and LCN sulfur targets is used to find the best splitter cutpoint therefore minimizing the global cost of octane loss and reboiler duty. Therefore, our splitter optimizer calculates: • Optimal splitter cutpoint, • LCN and HCN sulfur targets,
- to minimize octane loss and splitter reboiler duty - to respect LCN+HCN blend sulfur specification
• Minimal splitter internal reflux target, based on feed sulfur content.
APC BENEFITS @ 10 ppm Sulfur
4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 15.5 16
$$Average No APC Average No APC
APC ON
Target
Average APC ON
Average APC OFF
Figure 4: Sulfur distribution in the product when APC
system is turned ON / OFF
As a process licensor, catalyst manufacturer and advanced control technology supplier, Axens combines all the necessary expertise for successful Prime-G+ APC projects. The main benefits, illustrated in Figures 4 and 5 and summarized below, have been demonstrated in a plant producing 10–ppm sulfur specification gasoline.
• Sulfur on-spec without give-away +/- 0.5 ppm • Minimization of octane loss - 20 % • Reduction of hydrogen make up - 20 % • Catalyst run length maximization + 3 months • Minimization of energy consumption - 5 % Achievement: 1 million € per year at 100 tons/hour (with octane cost 5 €/ton and H2 cost 1000 €/ton) Typical ROI is less than 5 months.
May
.11-
PG+A
PC
Figure 5: Sulfur controlled at 10 ppm by APC in a Prime-G+ (28 Hours)
