Column analysis: The inside story

Jon Lawson

Visualising hydraulic behaviour and the entire product ecosystem. Jennifer Dyment reports

We all want the inside story. Greater visibility into asset performance can help chemical and energy companies gain a competitive edge.

Having a better understanding of column hydraulic performance can significantly improve asset utilisation and reduce capital costs in revamp projects and new designs.

Predicting the performance of units is a critical component in the simulation of towers for process design, performance and reconciliation purposes. Being able to see precisely what is happening to the behaviour of trayed and packed columns means that process engineers can quickly get to the root cause of operational issues and make informed decisions that impact the entire operation.

With advanced simulation tools, new and experienced engineers can easily look inside the column to troubleshoot operational issues and evaluate the best options for efficiently designing new and existing units.

Using interactive functionalities with enhanced software calculations, engineers are able to visualise the entire column’s behaviour to better understand the occurrence of problems like flooding or weeping, as well as how the column can be affected by adjacent equipment and changing process conditions. Essentially, better decision-support reduces costs, time and project and operability risks.

A highly complex system

Distillation column analysis is one of the key areas of focus for chemical engineers. Gaining detailed knowledge of column internals is a high priority for engineers, especially with regards to the behaviour of equipment and processes. As one of the most expensive and energy consuming units in a plant, the fluid dynamics of the column can be complex.

Distillation columns represent one of the most challenging design and operational challenges in the process industry. According to the US Department of Energy, over 40,000 distillation columns are involved in plant operations in the chemical and petrochemical industries in North America and they consume approximately 40% of the total energy used. Owner operators are always looking to improve capacity, product quality and energy efficiency through de-bottlenecking or operational troubleshooting. Depending on the complexity of the task, further help from in-house column experts or engineering firms may be needed.

The availability of light crude oils and low natural gas prices particularly in the US is propelling de-bottlenecking projects related to columns in both the chemicals and energy sectors. Many process engineers typically find it difficult to optimise the column and the whole process together.

For revamp projects to increase capacity, they may face limited rating capabilities and are drawn into iterative design studies involving manual, error-prone transfer of data between the simulator and other tools. Column specialists typically want to predict when a column has a high risk of not behaving well (i.e. flooding, weeping, pressure swings) and be able to quickly evaluate across the full range of design conditions, safety margins and normal operation levels.

When capital is needed to de-bottleneck a process, engineers within engineering and construction companies (E&Cs) are similarly focused on minimising project capital expenditure CAPEX by reusing existing equipment (i.e. shell, piping), investing in lower cost adjacent equipment (like feed heaters and coolers) or replacing the column internals, as well as evaluating different internal configurations to find the most economical option.

In improving operations, process engineers are focused on driving efficiencies and ensuring they make safe, confident decisions. For owner-operators, it is vital to increase capacity, minimise operational expenditure (OPEX), optimise product quality and troubleshoot operational issues. By determining issues quickly, it is possible to reduce costly shutdowns and expensive physical investigations. Pushing the capacity of the column, while operating closely to safety constraints, is important to optimise production performance. It is also a high priority to minimise costs by optimising conditions and reducing energy usage.

In designing new columns, process engineers use process simulators and column vendor tools to ensure designs will meet operability guarantees, while also minimising capital costs when working with vendors to select columns and column internals. New columns need be properly sized to adequately perform for the process requirements, minimise operating costs and avoid future operational issues. Design rules of thumb differ for clients and process applications. Therefore, keeping track of those guidelines and applying them where needed is time-consuming.

Cutting-edge simulation technology helps users to better understand the behaviour of columns and enables them to swiftly address or predict operational issues by seeing the entire column in one view using visual presentations of inputs and results. Crucially, the tools offer clear messages to explain problems with potential solutions. In addition, engineers can look at the column as part of the larger process with an interactive solver for quick evaluations of multiple design options and operating cases.

Now users can improve workflow by creating and analysing column tray and packed sections for hydraulic design and rating using an interactive sizing mode. With intuitively designed functions, the engineers can tune their designs to perform within hydraulic limits by using hydraulic plots and clear system messages to quickly compare the results of multiple designs. It is easy with the process simulator to change operating conditions on the flowsheet, visualise and observe changes to hydraulic behaviour and make any necessary adjustments to create an optimal design. With greater functionality at your fingertips, column analysis becomes simpler to gain insights into column performance problems.

Understanding column performance

AspenTech is a pioneer in process simulation and has delivered significant benefits to engineers for over thirty years. New functionality incorporated within Aspen HYSYS and Aspen Plus allows engineers to optimise energy use in columns and quickly pinpoint potential issues affecting the unit whether at the design stage, troubleshooting poor operational performance or for revamp projects.

With enhanced hydraulic correlations, it is possible to decrease assumptions and produce more accurate modelling for column analysis. The use of intuitive, interactive and visual graphics for tray geometry or packing inputs and the resulting hydraulic plots for every stage gives greater detail on the hydraulic behaviour of the individual stages while simultaneously providing a view of performance of the whole column. The ability to easily evaluate the effects of changes in flowsheet inputs, as well as internals geometry on hydraulic performance, allows for better troubleshooting and design.

The key benefits of using Aspen Plus and Aspen HYSYS for column analysis include:

* Quicker insights into column performance problems and behaviour based on current operating conditions

* See the column as part of the larger process with an interactive solver for quick evaluations of multiple design options and operating cases

* Evaluate interactivity between columns and other equipment before making operations/revamp decisions

* Ability to evaluate multiple revamp options for more informed discussion with vendors

* Automated sizing capabilities and design templates save time and effort when designing a new column and assist less experienced users in getting up to speed

* Reduce time and manual labour iterating between process data in Aspen Plus or Aspen HYSYS and column analysis with third party tools (eg, Koch-Glitsch’s KG-TOWER and Sulzer’s Sulcol) with automatic export of geometry and process data.

Seeing the whole picture

Greater visibility into asset performance provides the platform for better decision-making. Advanced process simulation offers engineers powerful chemical engineering capabilities for column analysis. Gaining insight into key processes enables better and faster problem solving. With new column analysis capabilities, new and experienced engineers can troubleshoot operational issues at the root cause and evaluate new and revamp options with an interactive tool, offering enhanced calculations and visualisations.

The inside story is that column design and rating no longer needs to be done in isolation or viewed as a mysterious black box. Visualising operations can be achieved within an advanced process simulator to fully understand the behaviour of a critical capital and energy intensive piece of equipment. As a result, engineers can minimise capital expenditure and make discerning design decisions that affect the entire plant performance – great news for improving performance and increasing profitability.

Jennifer Dyment is Product Management, AspenTech.