PACE Zenith Awards 2014: Oil & Gas category
WINNER: Apex Optimisation and Esso Australia
Project: Hot Oil Process Control Improvement
In late 2010, Esso Australia commissioned Apex Optimisation (Apex) to assess opportunities for improvement of the Hot Oil system process control configuration at the Long Island Point (LIP) LPG Fractionation Plant.
A number of improvements to the DCS control configuration, as well as a new multivariable predictive controller (MPC) were recommended to reduce Hot Oil temperature variance (primarily via better rejection of disturbances such as changes in Hot Oil demand and fuel gas calorific value) and improve overall efficiency of the two hot oil circuits onsite.
Reduced hot oil temperature variance leads to improved benefits on the process side where product yields are affected by the quality of this utility stream.
The project was kicked off March 2012, and Apex Optimisation conducted plant testing to determine the process dynamics required for the redesign of the DCS control schemes for the five Hot Oil heaters at the site.
The existing control scheme designs were inconsistent, so a key objective was providing a uniform approach for the operators to deal with.
Simplified flow diagram of A/B Train Hot Oil circuit.
The proposed solution consisted of well accepted approaches to furnace control and optimisation:
- An advanced regulatory control scheme for each furnace consisted of a combination of feedforward and feedback controllers, providing improved hot oil temperature control during furnace load changes and fuel gas quality changes.
- The new MPC application provided further feedforward and feedback control and optimisation of the hot oil circuits, to minimise fuel gas consumption and reject disturbances, such as those caused by changes in the overall plant load.
One of the key requirements of the project was to implement the changes to the process control schemes, without impact on the process or plant operations.
- The process control schemes and implementation procedures were developed utilising the Apex team’s expert knowledge of the client’s DCS and experience in similar significant control system changes.
- Part of this process was to conduct offline simulation and testing of the process control schemes to ensure proper initialisation and bumpless transfer of the entire integrated control scheme – it’s important to provide a robust solution that operators will love to use, as well as minimal impact on the process when the changes are commissioned.
- It was decided to make the highest impact changes during a plant shutdown in order to minimise the overall risk of the implementation phase. However, some changes were still required whilst plant was running, and this is where Apex’s combined process and systems experience was valuable.
The modifications to the first set of three heaters were implemented and commissioned in October 2012, following extensive and successful off-line functional testing.
Distribution of the MDEA Regen Column Delta Temperature (Key Controlled Variable)
This was followed by a plant test campaign to collect the data required to develop the dynamic models for the MPC application. The first version of the MPC application was commissioned in December 2012.
Following the commissioning of the MPC applications and reassessment of the process context, it was apparent that there is another opportunity for efficiency improvement in one of the major Hot Oil users – the Amine Regeneration section.
The same process was followed, in close consultation with the client engineer, to define modifications to control scheme and MPC application.
The DCS changes were tested offline, before implementation whilst the plant was running (a strategy adopted as a result of the successful and uneventful changes earlier in the project).
The DCS control modifications for the last set of two heaters were commissioned in April 2013, followed by the inclusion of these heaters and the amine regeneration section in the MPC application.
The final outcome was a successful project where all the goals and customer requirements were met.
- the DCS control schemes were now consistent across all five hot oil furnaces;
- the MPC application is continually minimising excess hot oil circulation, as well as distributing the load between the furnaces in each circuit to preference the most efficient furnace;
- the operations group were trained in the use of the new systems and were able to run the hot oil circuits in a consistent and sustained manner day in and day out.
The project was successfully completed in June 2013, with the final outcome delivering DCS control schemes and a MPC application that:
- were successfully implemented and commissioned with no impact on the process;
- were well received and accepted by the plant operators;
- improved hot oil temperature control (standard deviation reduced by 30% on some of the furnaces) which facilitated potential fractionation process yield benefits;
- reduced energy consumption of 10.7% and 8.5% for the two hot oil circuits (this included a 33% reduction in the specific duty consumption of the amine regeneration section);
- MPC controller uptimes of 88% and 94% for the two hot circuits;
- resulted in a project payback period of less than 6 months.