Engineering and Commissioning of the Air Pulse Blending System for an Oil Tank Farm


Project description

HIT has been given the task of developing, setting up and commissioning an Air Pulse Blending System (APBS) on the basis of the PCS7 process control system for a tank farm. A new process system had to be developed and implemented on site. HIT was able to successfully master this challenging task. The system consists of several crude oil tanks which are equipped with 3-5 skids. When needed, air with a pressure of up to 8 bar is pressed into the tanks in definable cycles. The crude oil should mix with the dilution medium that was added in advance. The system can be operated in the same central control room as the control system of the tank farm. The engineering, programming and related construction of switch cabinets was completed by HIT. The installation work regarding the pipeline construction was outsourced. Special attention was given to the control of the valves to be used in explosion-risk areas. The subsequent commissioning on site was performed by HIT’s employees.

Abb 1 Aerial photo K
Oil tank farm (aerial view 2016)


Operating principle

The APBS works with a process pressure of 2-8 bar. A central compressor station delivers a pressure of 10 bar. The pressure will then be controlled and filtered inside the supply skids according to a given set point at 2-8 bar. The supply skids will then lead the air to the tank skid. The valves control the air supply to each tank outlets. Depending on which valve is controlled, the air will be led inside a specific section of the tank. Thus, the medium can be mixed thoroughly in different ways. The hardware of the controls is located in a remote I/O cubicle. The incoming signals can be read and the valves can be triggered by using a redundant ET-200M. The S7-410H of the control system provides the necessary logic. The system doesn’t have an own PLC.

Abb 2 Operating principle of the APBS
Operating principle of the APBS


Mechanical structure

The system is made of filling lines and valve units. The filling lines include the shutoff valves, filter, flow measurement and pressure control system. This set of components is available for each tank field. The measured data and the pressure control will be processed by the existing control system. 3-5 control valves are built at the tank valve skids and can be independently controlled. This enables the mixing inside different tank sections. The compressor station will externally supply the process pressure.

Operating mode

The valves of one tank can be controlled separately. It is possible to locally control the valves from a switch cabinet located in the tank field or from the control room. The automatic mode is operated from the control room. The skid valves can be opened and closed by setting up a cycle order. This can be configured by an authorized operator. After all parameters have been entered by the operator, the program will control the valves accordingly for a specified sequence.


The visualization is based on the existing PCS7 control system and can be accessed through the overview menu. Values like flow rate, temperature and pressure can be clearly monitored. The standardised faceplates of the control system are also to be used in this case. The »Air Package« tool contains the safety-relevant information for the running operation of the compression system. The sequence diagrams for the valves can be monitored and configured using the tank visualisation.

Abb 5 Visualisation APBS   B
Visualisation of the APBS











Why HIT?

HIT successfully completed this project. A clearly arranged and improved user interface has been designed to support the operators on site. An explicit software structure has been developed. The installed equipment has shown its reliability from the beginning. These attributes increase the fail safety and productivity of the plant.