Week 2 Assignment

Q1. To estimate line sizing, first in Aspen simulation environment one must selct a stream, converge the stream with proper conditions and go to the equipment design option and select line sizing manager from the drop down. Then the detailed line sizing can be continued.

The first stream for line sizing is given as a pump suction line.

The conditions and composition of the stream are as follows:

The second stream for line sizing is a pump discharge line

The conditions and composition of the stream are as follows:

The third stream for line sizing is a compressor suction line

The conditions and composition of the stream are as follows:

The fourth stream for line sizing is a separator inlet line

The conditions and composition of the stream are as follows:

The detailed line sizing for all the above streams is shown as follows:

Please ignore the fifth stream as it was just a practice for me. The first four line sizing are the answers.

Q2. In this question it is asked to determine the pressure drop of the above four lines. To determine the pressure drop of a stream for a particular length of pipe run, pipe segment feature can be used for that purpose.

In this question for the four different lines i have used four different line segments as shown below:

The first stream for pressure drop calulation is a pump suction line.

The conditions, composition and detailed pipe features used through the pipe segment option to calculate the pressure drop is shown as images:

The second stream for pressure drop calulation is a pump discharge line.

The conditions, composition and detailed pipe features used through the pipe segment option to calculate the pressure drop is shown as images:

The third stream for pressure drop calulation is a compressor suction line.

The conditions, composition and detailed pipe features used through the pipe segment option to calculate the pressure drop is shown as images:

The fourth stream for pressure drop calulation is a separator inlet line.

The conditions, composition and detailed pipe features used through the pipe segment option to calculate the pressure drop is shown as images:

For all the streams above the pressure drop can be calculated from the worksheet tab, where the pressure of the startpoint stream and pressure of the endpoint stream is given along with the energy line. Thus, from there the pressure drop for the four lines can be calculated.

Q3. To determine the pump NPSH we have to define a stream then use the pump option from models and streams.

In this question there are some modifications made for determining the final answer.

The pump network is shown below:

Firstly, due to given conditions of the pump suction i have chosen a pipe segment to incorporate the pressure loss associated with the pipe lenth and pipe fittings. Also adding to it the losses due to elevation changes. The strainer losses were given in pressure terms (psi) so the additional control valve is fitted with the pressure loss of same value as the strainer. After incorporating all the pressure losses the stream (5B) is still in two phase which cant be directly feed into a pump. To avoid further errors i used a vapour liquid separator and fed the liquid part into the pump. This explains the above network.

The given conditions and composition of the startpoint stream is as follows:

Now to incorporate pressure losses the details of the pipe segment is as follows:

To incorporate strainer losses the control valve option is used. The details are as follows:

The conditions and composition of the stream after the strainer losses:

;

Now, to convert the stream into single phase a phase separator is used.

The details are as follows:

The liquid stream from the separator is the pre final stream feed into the pump.

The pump system is as follows:

The NPSH for the pump is given in the final image.

Q4. Choked flow is a limiting condition where the mass flow will not increase with a further decrease in the downstream pressure environment for a fixed upstream pressure and temperature.

By trial and error method in a pipe segment choked flow can be determined.

The conditions and composition of the inlet stream are as follows:

The details of the pipe segment are as follows:

As it is seen from the images that the current flow is the limiting choked flow condition for the given upstream temperature and pressure.