Dynamic Simulation

March 1, 2005
Process simulation has become an indispensable tool for the design, analysis, and operation of these complex plants

Airplanes are dependent on a consistent supply of clean and dry fuel. Similarly, it is the tank farm operator's responsibility to operate safely and profitably. Process simulation has become an indispensable tool for the design, analysis, and operation of these complex plants. With a reliable simulation tool, tank farm management processes will be optimized, operational safety will be increased, and capital investment costs will be reduced to a minimum.

Process simulation allows virtual experiments to be conducted that would be too expensive or operationally unrealistic in the real plant. Defects, deficiencies, or dangerous operating conditions can be detected easily during design, avoiding significant construction retrofit cost. In the field training and service of operators dynamic simulation is an important tool.

Reduced Investment, Ooperational Costs

The success of a project is assessed by coping with budget and specifications. Cost reduction requires quality planning. Suitable planning tools are required to cope efficiently with specifications. Simulation supplies accurate benchmarks and helps to assess various technical and economic scenarios.

The designer optimizes the combination of components with regard to hydraulic, mechanic, and controlling aspects. Systems are optimized by removing unnecessary components or by creating a higher integration of functionality in single parts. CAD-techniques complete dynamic simulation by 3-dimensional illustration of flow diagrams.

It is a social and in some cases a legal responsibility to protect the environment and to save energy resources. Each plant should be efficiently operated with a minimum of resources. The operator benefits directly from lower energy costs as power consumption is an immense cost factor to operating a tank farm or hydrant system. That's why Kleopatra can calculate power consumption with various plant configurations to optimize safety and profitability.

Virtual Experiments On-Line

Kleopatra presents itself as a graphic software to design the process flow diagram. All relevant pipeline parameters are assigned to the corresponding components. This includes the nominal width of the pipes (internal diameter), nominal pressure (maximum licensed internal pressure), relevant armatures for control and regulation of flow (various valves), safety controls and measuring outlets, flow rates, etc.

Dialogue boxes and drop and drag techniques offer highest user comfort. With the start of the virtual product flow, a blotter -- in a pop-up window -- records data (e.g. pressure, flow rate) like the real plant. On virtual changing of parameters, operational conditions or configuration of the plant, the user can observe "live" the consequences of those changes. The excellent visualization enables an intuitive understanding of complex procedures and supports decision-making.

By testing hydraulic alternatives or various mechanic configurations, the user can optimize the design or operation of the system. Simulation features an enormous saving of cost and time for both configuration of the plant and an efficient automation concept.
Simulation provides an opportunity to minimize the danger of pressure surges through the control of valves with automation techniques. For example, the first 95 percent of a closing or opening may proceed more rapidly. The last 5 percent should be precisely controlled to prevent pressure surges from happening.

Operational Test Areas

Professional development of new models -- be it in the aircraft industry, sewage works, safe processing in the chemical industry, or airport hydrant systems at the airport -- can reap the benefits of saving time and money with simulation technology.
The simulation techniques reflect reality and enable experiments that would otherwise be too expensive or potentially dangerous in real scale, particularly with regard to the explosive characteristics of fuel. Pipelines of refineries, fuel depots, or airport hydrant systems are highly complex "dynamic systems".

Some of the security risks include leakages, material fatigue, or pressure surges. These factors don't depend on the size of a plant and are partly predictable.

"Pressure surges are a common fact in each plant transporting liquids," explains Dr. Leszek Juchniewicz, general manager for hansaconsult, a German-based firm which offers Kleopatra, one such simulation software program. "They result from a change of the liquid's velocity."

Pressure surges arise in running systems when valves are opened or closed, additional pumps are switched on or shut down, pumps stop working, are switched off, or power supply is interrupted. The dynamic stress of pipelines and pipeline clips, valves, and all parts of the plant cannot be avoided. The target must be to limit material stress. Damages don't occur immediately, but develop over time. There are numerous examples illustrating damages by pressure surges. One example:

-The pipeline system of an airport tank farm was to be operated with an operational pressure of 8 bar. The system was rated for 16 bar. However, during the operation the pipeline burst with severe consequences. Subsequent dynamic simulation calculated an operational pressure of more than 100 bar, leading to the disaster.

Numerous accidents due to pressure surges can be avoided. The plant-related danger can be assessed by the following rule of thumb: Risk increases with the rising velocity of fluid, length of pipeline, and velocity of opening or closure of valves. Dynamic simulation records the magnitude and extent of pressure waves.

The Conflict Of Safety and Profitability

Logistical interfaces bring additional cost, time, and risk. The downstream environment of refineries is embedded in an integrated transport system. Sea tankers transport the crude oil to the pier. The unloaded combustibles are pumped via pipeline to an intermediate tank farm for storage until further processing.

The refinery is subject to comprehensive regulation regarding safety and environment. In 2000, authorities required the installation of further safety-related devices at the sea tanker-pipeline interface. The interface features rotatable loading arms. A strong drift of the loading or unloading ship might lead to a spillage of oil due to a disconnection of the loading arm. Emergency valves at the coupling system close immediately to prevent water pollution. Depending on process conditions -- such as a sudden shutdown of pumps -- large pressure shocks or surges with incredible power could occur, causing catastrophic results. (It was hard to believe the entire plant would be demolished.)

Profitability and operational efficiencies require that these plants operate at the maximum flow rate. But the damaging effect of a pressure surge actually increases with flow rate. Short valve closure times prevent product from being spilled. But the risk of damaging pressure surges increases with the velocity of opening and closing of the valves. Pipe distances between source and valves are inevitable (here up to 3 km, depending on location of the pier). But the risk of damaging high pressures increases with the length of pipeline.

During a recent simulated relationship between pressure, flow, and valve closure of a plant with real data, hansaconsult confirmed that the closure times can be reduced significantly, without achieving inadmissibly high pressure figure.