Simulation of Piping Operations (Compressible Gas Pipe , Pipe Segment, Valve, Relief Valve, Mixer, Tee) With Aspen Hysys.

1.      Compressible Gas Pipe <CGP> :

The compressible Gas Pipe (CGP) uses an algorithm that solves a vector system using the Two-Step Lax-Wendroff method with Boris & Book anti-diffusion.

∂U/∂t + ∂D/∂x = G

 The CGP unit operation primarily designed for transient calculations with streams calculations with streams. 

First we define our elements (inlet, outlet stream ).

Second we have to specify the profile of pipe (length-evaluation profile), here we specify:

• Length  of pipe
• Elavation change
• Cells o pipe  

Moreover, we can add more sections.

Third, we specify the Overall dimension of Pipe, specification of Overall dimension realized through two ways

• We pick the pipe schedule and the material from the schedule and material mentioned in the cases, after that we select the pipe size from the pipe size selections.

• Second way is to specify all parameters (Roughness, external diameter and internal diameter)

Fourth, we have to specify the ambient temperature and the Overall heat transfer coefficient (Overall HTC)

 

Finally we have the CGP converged, with calculating of Pressure drop, Max much number, Max Pressure and Max velocity 

2.      Pipe Segment :

The Pipe Segment is used to simulate a wide variety of piping situations ranging from single or multiphase plant piping with rigorous heat transfer estimation, to a large capacity looped pipeline problems.

First as usual, we have to define elements of our equipment (inlet , outlet streams and the energy stream) 

Second, we have to specify the Size of Pipe (Length, elevation charge, outer diameter, inner diameter and we pick our metal)

 

Third, we specify the heat transfer; The heat transfer can be specified by one of:

• Specify the heat loss  

• Specify the Overall Heat transfer coefficient (Overall HTC)

• Specify the sSegment heat transfer coefficient (Segment HTC)

• Estimate the heat transfer coefficient (Estimate HTC)  

• Specify the outlet temperature 

3.      Valve :

The main purpose of a valve is to control media flow through a system, Valve generally use in dynamic mode, in Steady state mode we can use Valve for decrease the outlet stream (like joule thomson valve).

First, we define the elements of operation (inlet, outlet stream).

 

Second, we have to specify the Delta P or we specify the outlet stream (must be low than the inlet stream).

      

1.      Relief Valve

Relieve valve is used to prevent dangerous situations occurring from pressure buildups in a system.

Relive valve used in Steady state mode like normal Valve (the valve is open) 

 

But in dynamic mode if the pressure of outlet stream is highest than the inlet the relieve valve will be close.

How do we can realize that?

First we define the inlet and outlet stream.

Second, we specify the set pressure and the full Open pressure.

Third, we specify the outlet stream pressure

 

After that we switch to the Dynamic mode 

If the pressure of outlet stream is low than the pressure of inlet stream the valve will be open. 

 

If the pressure of outlet stream is high than the pressure of inlet the valve will be close.

5.      Mixer :

The Mixer is used to combine two or more inlet streams produce a single outlet stream.

We define the inlet streams (at least two streams, and they must be converged) and we define the outlet stream.

Second, we pick “set outlet to lowest inlet” because we have difference pressures of inlet streams 

1.      Tee

The Tee operation splits one feed stream into multiple product streams with the same conditions and composition as the feed stream, and it used for simulating pipe tees and manifolds.

First, we define inlet stream and the outlet stream (at least two streams).

Second, we specify the splits or we specify the outlet flow directly.

       

Simulation of Rotating Operations (Pump, Compressor, Expander) with Aspen Hysys.

1.      Pump :

Pump is used to increase pressure of inlet liquid stream (the inlet stream must be liquid).

First, we define the inlet stream, and define the outlet stream, define energy stream.

Second, we specify Delta P or directly you can specify the pressure of outlet stream and we specify the adiabatic efficiency.and click on, if you don't click on pump will not boost the stream, pump will work with 0.00 Delta P.

 

Finally we get our Pump converged

One thing, it exists another method to converge pumps, method of "curves", this method works with Equation of Head.

H = A + B*flow + C*flow^2 + D*flow^3 + E*flow^4 + F*flow^5

You have to define first:

• the unit of head
• the flow basis
• the unit of flow 

Second fill out coefficients A,B,C…….

finally you have to click to "activate curves" 

For this method, it is more real in calculation, because you give the flow and Hysys will calculate automatically the Delta P, the pressure of outlet stream…….

2.      The compressor:

Compressor is used to increase the pressure of a stream (the stream must be gas, vapor).

First, we define the inlet stream, define the outlet stream, and define energy stream.

Second, we specify Delta P or directly you can specify the pressure of outlet stream and we specify the adiabatic efficiency.

      

In Hysys, it Exists 2 types of compressor:

• Centrifugal Compressor 
• Reciprocating Compressor

a. Centrifugal compressor:

Centrifugal compressor is used for high capacities of stream and low compression ratios.

Centrifugal compressor also can be used to represent a pump, when more rigorous pump calculation is required; in Hysys the pump operation assumes that the liquid is incompressible, so if you want to pump a liquid near to critical point (where it becomes compressible) here you can represent the pump by the centrifugal compressor.

In centrifugal compressor exists tow methods of calculation:

• Without curves
• With curves 

Without curves:

like the first example in Compressor, after defining elements (inlet stream, outlet stream, energy stream). After we specify efficiency (adiabatic or polytropic) with picking the method of polytropic, we specify Delta P or Pressure ratio or directly the outlet pressure 

       

With curves:

We click Rating, curves, and we pick the type of efficiency (adiabatic or polytropic), after that we click Add curve.

After clicking Add curve, we the units of flow and head after that we specify Volume flow, head and the efficiency.

After that we clock at Activate and Enable curves.

If you notice the yellow case that written on it “Efficiencies greater than 100 percent” this problem result in low flow (the centrifugal compressor used for higher flow and low compression) 

Therefore, we have to increase the flow 

b. Reciprocating Compressor:

This one type of compressor is used for applications where higher discharge pressures and lower flows are needed.

First, we have to define streams (outlet and inlet) and the stream energy.

Second, we specify Efficiency (adiabatic or polytropic) and we define the delta P or pressure ration or the Duty of compressor or directly the outlet pressure 

        

3.      The expander:

The expander is used for decrease the pressure of stream (the stream must be gas, vapor phase).

It exists two methods for calculation

• Without curves
• With curves 

Without curves:

After defining elements (streams and energy stream), we specify the efficiency (adiabatic or polytropic) and we define the duty of expander or delta P or the pressure ratio or directly the outlet pressure.

  

With curves:

First we click rating, curves, add curve.

After that, we have to define units of flow ad head; we specify the volume flow, head (here for the expander the head must be negative) and the efficiency.

And we finish by clicking Activate and enable curve  

Notice:

If we use the method of curves in the centrifugal compressor and expander, we don’t specify the outlet pressure or the duty or the Delta P………..

If we use the method of curves, Hysys will calculate all of those parameters.