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• Osas Uwoghiren

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REFRIGERATED GAS PLANT HYSYS SIMULATION REPORT 1.0 Introduction The purpose is to find the LTS (Low Temperature Separator) temperature at which the hydrocarbon dewpoint target is met for the Gas plant 2.0 Design Basis The incoming gas is first routed to an Inlet Separator. It is then cooled in two stages: 1) By heat exchange with product Sales Gas in a gas-gas exchanger (Gas-Gas Exch.) 2) and via a propane chiller (Chiller) After cooling, it is routed to a LTS and sent to Sales line after heat exchange with the incoming gas stream. Required Sales Gas Hydrocarbon Dewpoint = -15 oC at 6000kPa Incoming Feed Stream (To Refrig) parameters and composition are shown below in Table 1.0 and Fig 1.0 respectively Table 1.0: Incoming Stream Parameters Parameter Temperature (oC) Pressure (kPa) Flow Rate (kgmole/hr)

Value 15 6200 1440

Fig 1.0: Incoming Feed Stream Composition

3.0 Simulation Window The base case simulation run is shown below in Fig 2.0.

Fig 2.0: Simulation Window for Refrigerated Gas Plant The specifications used for the base case are as follows: Table 2.0 Specifications used in Base case simulation Gas-Gas Exchanger Min Temp Approach 5 oC Chiller Pressure Drop 35 kPa Gas to LTS Stream Temperature -20 oC

Exercises Parameter

Table 3.0: Parameters obtained from Simulation Exercise Value

Flowrate of Gas to Chiller Sales Gas Pressure Sales Gas Temperature

1440kgmole/hr 6125 kPa 10 oC

Using Balance Operation The Balance Operation (see Fig 3.0) was used in determining the current Hydrocarbon Dew point for the Sales Gas Stream.

Fig 3.0: Using the Balance Operation Mole Balance was selected to provide molar flow rate and composition for the Sales Gas stream. In determining the HC Dewpoint at specified pressure of 6000kPa, the Vapour fraction was set to 1.0 as seen below in Fig 4.0.

Fig 4.0: HC Dewpoint for Sales Gas (Base Case) HC Dewpoint = -19.75oC. This current dewpoint is lower than the specified dewpoint of -15 oC which is required. Assuming the pressure is fixed, other parameters that affect the dewpoint is the composition of the gas. Gas with more heavy ends will have higher dewpoint temperature.

Using Adjust Operation The Adjust Operation was used to manipulate the Gas to LTS Stream Temperature so as to arrive at the Specified HC Dewpoint Temperature of -15oC. See iterations done in Fig. 5.0. The required temperature for Gas to LTS stream is -15.22oC

Fig 5.0: Calculations using Adjust Operation

Linking Propane Loop to Refrigerated Gas Plant The Propane loop template from Module 2 was linked to the Refrigerated Gas Plant simulation via a Sub-Flowsheet as seen in Fig. 6.0. The Chiller duty from the Refrigerated Gas Plant was linked to that of Chiller in the Propane loop The new flow rate of propane = 162.4 kgmole/hr at 1,464,000 KJ/hr as opposed to 111kgmole/hr at 1,000,000 KJ/hr in previous case.

Fig 6.0: Linking Propane Refrigeration loop to Refrigerated Gas Plant Modifying the Heat Exchanger The UA for the Heat Exchanger was set to active and modified to 2e5 kJ/ oC.h. The summary for the base case and modification results are given below

Min Temp Approach LMTD UA (kJ/ oC.h)

(oC)

Previous Case 5 (Specified) 7.144 2.83e5

New Case 7.4 (Calculated) 9.2 2e5

The lower the UA, the higher the temperature approach between the outlet gas to be cooled and cold gas from the LTS. This shows the impact on the heat transfer between hot and cold gas. More heat transfer occurs with higher overall conductance (UA). Challenge Exercise Converting the Chiller to a Heat Exchanger. The Chiller E-101 in the Refrigerated Gas plant simulated was changed to a Heat exchanger, E-100. (Ref: Refrigertaed Gas Plant Challenge.hsc). The Gas to Chiller Stream was routed to the Tube side while the Propane Stream was routed to the Shell side of the Heat Exchanger. See Fig 7.0 for the specifications used

Fig. 7.0: Heat Exchanger Specifications Summary of the Streams for the Heat Exchanger is shown in Fig. 8.0

Fig 8.0: Summary of Streams to and from the HEX