Introduction

A delayed Coker is a part of an oil refinery system whose process consists of heating a residual oil feed to its thermal cracking temperature in a furnace with multiple parallel passes.

The term "delayed" refers to the fact that coke formation is not supposed to happen in the furnace itself. Instead, the heated oil is transferred to large vessels called coke drums, where the cracking reaction continues, and coke accumulates on the bottom of the drum. The coke drums are operated in a batch mode, meaning that one drum is being filled with hot oil while the other drum is being emptied of coke.

This is an essential part of the oil refining process, as it allows refineries to extract the maximum amount of valuable products from crude oil.

Figure 1. The Coke Drum

Due to the repeated cycles of extreme temperatures, coke drums accumulate fatigue damage, which can compromise their structural integrity.

With Akselos Integra:

1. Monitor Coker Drum Status in Operational Conditions: Simulate and capture the behaviors of the Coker Drum using a Digital Twin solution under the complex conditions of the coking procedure.
2. Fatigue Assessment and Life Extension: Apply the API 579 Fatigue Assessment procedure to compute damage and predict the drum's lifespan. This information is provided to the operational team to schedule inspections and maintenance plans.
3. Modify Coking Procedure: Make adjustments to the coking procedure based on the simulation results to enhance the drum's performance and longevity.

In this article, you will know

Akselos implemented a workflow to facilitate simulating the behavior of a Coke Drum under operational conditions. Below is the two available journeys that a new user can take to familiarize themselves with the Thermal analysis on Coke Drum model.

• Journey 1: This process utilizes a pre-made collection by Akselos to help speed up the process of learning the inner working of the model.
• Journey 2: This process allows users to start from scratch, and is intended for users with more time to learn the ins and out of the simulation and model building process using Akselos Modeler.

Figure 2. Akselos simulation workflow

This article aims to introduce you to the Coke Drum model by exploring the steps involved when using a Sample Collection. For more detailed information on building a complete model within Akselos Modeler, please refer to the materials linked below.

Before we start

This article is aimed for users with basic knowledge of the Akselos Modeler and have access to Akselos Customer Dashboard. If not, these articles below might help:

Need help navigating the Akselos Dashboard? Get started by creating an account, and then check this article.

Akselos Dashboard for New Users

Need help downloading Akselos Modeler? Check out this article.

Akselos Modeler - Installing, Updating and Managing the Akselos Simulation Software

We have prepared a sample Coke Drum collection, import it here.

Coke Drum model in Akselos Modeler

On the coke drum, there are sensors to measure temperature and pressure in real time. These are recorded to be used as an input data into this simulation, the simulation is then ran to output Stress and Displacement of the model under operational conditions. These result at different time intervals is then used to estimate the fatigue damage over time on this model, and output the remaining fatigue life on the Akselos Dashboard.

Overview

Akselos Modeler Interace

Below is an overview of how the Akselos Modeler UI is laid out. These terms will serve as future references for describing these areas as well.

Figure 3. Akselos Modeler UI overview

Ribbons: This is where different views modes can be selected, Such Solution, Component, or Model view.

Structure Tree: This is where the Model Setup for simulation can be adjusted and modified. Here you can find Loads, Boundary Conditions, Solve Options and Scenarios setup.

Property Tree: When a property is selected in the Structure Tree, this area will be populated with the available options associated with it. Users can then directly modify the applicable parameters in this area.

Graphic Window: This is where the visual representation of the model is displayed. Whenever a change is made in the Structure Tree, the model here will be updated to show the changes made.

Right Panel: Akselos Modeler offers a variety of specialty tools to simplify the model setup process for complex models. These tools can be accessed from this area.

Log Screen: While using Akselos Modeler, it may need to let you know if there are any problems during setup, if you haven't completed all the steps, or if the solve request is completed successfully. This area is specifically for this purpose to help user trouble shoot any potential issues.

Working Folder

For more information regarding working folders please check out this article.

Importing Coke Drum Collection

You can find the sample Coke Drum collection here and follow these steps to import it into your local Akselos Modeler instance.

Model Configuration

As mentioned above, the sensor data and environmental condition of the Coke Drum will be recorded and used as input data and initial conditions for the simulation. The data is converted into the following parameters:

• Material: This is based of the material used in the Coke Drum, the parameters is modified to best represent it.
• Boundary Conditions: The Coke drum is connected to the ground around the rims, this will be represented as fixed boundary conditions. it is also connected at the output and input pipes, but these allow for more movements, as such it will be modeled as springs boundary conditions.
• Loads: The loads are modeled based on the input sensor data and physical properties of the Coke Drum.

Further details on how to setup it up and why it is needed will be given in the following sections.

Materials

The materials used here is Alloy steel SA387, with a density of 8900 kg/m3, Poisson ratio of 0.29, and a Young modulus and Thermal Expansion that varies with temperature, which is visualized with the graph below.

Figure 4. Temperature dependent Material properties

The graph illustrate the relationship of Thermal Expansion and Young Modulus against Temperature. In which, Thermal Expansion is positively correlated to Temperature, while Young Modulus is negatively correlated to it.

There are 13 Temperature steps, each with an accompanying value for Thermal Expansion and Young Modulus. So these two properties is determined by the current temperature of the Model. If the value lies in between the 13 values, then the two nearest temperature point is used to interpolate the parameters.

These values are then fed into Akselos Modeler using the process below.

Material is applied in Subdomain; users can view Subdomain or Show properties tool to check material parameters.

Change the Selection Mode to Subdomains. In the Graphic Window, select all subdomains, the material properties will be shown in the Properties Tree. Mass density and poisson_ratio is fixed for all temperatures.

Figure 5. Viewing Material properties

Young Modulus and Thermal Expansion

Young’s modulus and Thermal Expansion of a material depend on the environment and operation input temperature. Along with the rise of the temperature, the atomic vibrations in the crystal structure will also increase, which leads to a Young’s Modulus value reduction. On the other hand, the Thermal Expansion will escalate.

With each temperature value, the material will have a corresponding Young_modulus and a Thermal Expansion value. The temperatures that are not in the below values will be interpolated.

Figure 6. Viewing Young Modulus parameter

Figure 7. Viewing Thermal Expansion Coefficient parameter

Boundary Conditions

In reality, the nozzles are mounted to the pipes, which is why it will be constrained using that surface. But this will not be enough to completely secure the structure. Therefore, a spring constant is used instead to mimic this behavior when building this model in Akselos Modeler.

Figure 8. Nozzles’ connection

Figure 9. Boundary Conditions

Checking Spring Constant

• View Component Properties and Sideset’s ID to check spring constant.
  • Change to Components mode à Select the component including nozzle(s) à View Property tree.

Figure 10. Viewing Spring Constant

Loads

As mentioned above, the loads are based on collected sensor data and physical properties of the Coke Drum. The following are needed to accurately represent the input data:

• Self-weight: This is based on the material volume weight of the Coke Drum and is calculated using the inputted density.
• Thermal Expansion: This is based on the Thermal expansion input parameter. This changes with the model temperature.
• Pressure: This is based on the pressure sensor recorded data. 

In these three load cases, Thermal Expansion and Pressure receives input data from sensor data. It includes nineteen temperature sensors and two pressure sensors:

Figure 11. Location of sensors data

For one cycle, there are thirty-seven times mapping input data to the model.

Load is defined directly in the component. To check load cases applied on a component, click on that component, load cases will be shown in the Operator of the Property Tree.

Figure 12. Viewing Thermal Expansion Coefficient parameter

• Self-Weight: Self Weight is applied to all subdomains of the model following the Z direction, the acceleration due to gravity is -9.81 m/ .

To view the Self Weight of whole model, change Selection Mode to Subdomains à Select scaling_x, scaling_y, scaling_z in the Property.

• Thermal Expansion: When temperature increases, the geometric dimensions (length, area, volume) of matter increase. This causes the thermal expansion load on the entire model. Thermal expansion load depends on temperature and material properties.

Figure 13. Temperature following the time

Temperature depends on time, so the value of thermal expansion load also depends on time.

Figure 14. Distribution of temperature following the time

• Pressure: During operation, the material causes pressure on the wall of the coke drum. It was considered as Pressure in mesh load in Software. This load type depends on the Coke level/nozzle pressure / temperature. It is applied to the inside of the coke drum wall.

Figure 15. Pressure value following the time

The value of Pressure also depends on time.

Figure 16. Distribution of pressure following the time

To view temperature, change to Components mode, Select the temperature_id in the Property.

Figure 17. Temperatures in 37 steps

To view Pressure, change to Boundary Set mode, Select the pressure_load_id in the Property.

Figure 18. Pressure in 37 steps

Solve in Akselos Modeler

Before submitting a solve request, you should have a final check on the model configuration and make sure your credentials to access the Akselos Cloud is still valid.

First to check your credentials ensuring an established connection to Akselos Cloud to submit a solve request, follow these steps:

Next, lets check the Solve Scenario and Solve list.

Figure 21: Scenario and Solve list

Change to the Solutions ribbon, click on the Solve button. The solving request will be submitted on Akselos Cloud and the solutions will be returned in Akselos Modeler after solving successfully.

Figure 22: Solving and solutions

The available solution fields will depend on your selection during the Solver Option setup.

Solution Examination

After a successful solve request, the result will be automatically downloaded from Akselos's servers. Akselos offers a selection of tools to help with examining the simulation result, we will introduce you to a few that can be utilized to extract more information from this simulation result.

Figure 23: Solution Tab UI Layout

Summary Tab

This tab shows the user the general information regarding the simulation results, such as the run time, and simulation type.

Figure 24: Simulation summary

Inspect Tab

On the inspect tab, more details about specific nodes can be viewed. Users can select a specific node, or can use the function to locate the Maximum and Minimum value, it will automatically jump to the appropriate timestep.

Figure 25: Node details

Usage of Clip planes

Clip planes can be used to more closely inspect the cross-section of the result. Multiple clip plane can be active at once to give an extra perspective.

Figure 26: Clip planes

As you can see from the figure above, the clip plane provides an a whole new perspective to inspect problematic or hidden area which otherwise could be over looked.

Displacement Scale

The Displacement Scale can help users clearly visualize the behavior of the model under simulation conditions.

Figure 27: Displacement scale

Result Utilization

The Displacement and Stress Result of multiple time intervals will be used to calculate Fatigue Damage and remaining Fatigue Life, Which will then be displayed on Akselos Dashboard. Continue with this article to learn more about that process.

Read more

Need help understanding the Data Structure when working with Modeler?

Working Folder and Data Management

Need to import new meshes to make changes to the Model? 

Import meshed files into a Digital Twin collection

Need to add more load to the Coke Drum model? 

How to add Loads to your simulation model

Appendix

Extra reference information is contained in this section.

Import Mesh to enable Spring Constraints

View the settings of component types to check the boundaries which are imported.

• In the Collection ribbon, click on Add… à Component Type. 

Figure 28. Opening Component Type

• In the New Component Type window, change to Settings tab à view range of IDs in Sideset (Dirichlet B.C, Spring-X, Spring-Y, Spring-Z).

Figure 29. Viewing range of Sideset’s IDs

• On the Graphic Window, change to Boundary Sets mode. Move the mouse to the dark areas of the model on the graphic window to view the ID name of surface:
  • Dirichlet Boundary condition: 300 – 329
  • Spring X: 400 – 439
  • Spring Y: 440 – 469
  • Spring Z: 470 – 499

Figure 30. Viewing surface ID

Calculate Weight Data

To check weight data of the model, users can solve the model with the Calculate Weight Data solver option.

•  Create new Solver Option and set up Solver Type:
  • On Structure Tree, right click on Solver Options à Create Solver Option.
  • Click on the new Solver Option (users can rename it to easily distinguish from other options) à Set up as in the figure below.

Figure 31. Setting up the Calculate Weight Data solver option

• Create Scenario and add it to Solve list:
  • On Structure Tree, right click on Scenarios à Create Scenario.
  • Click on the new scenario (users can rename it to easily distinguish from other scenarios) à choose WeightData in the Solve Options box.

Figure 32. Setting up scenario

• In the Solve List, turn on Scenario 2 and turn off Load Combination 1.

 Figure 33. Setting up Solve List

• Solve and check data:
  • Change from Solution ribbon, click the Solve button to proceed.

Figure 34. The Solve button

• After solving successfully, click on the solution and view the Right Panel to check weight data.

Figure 35. Checking weight data in solution