Expanded outlet

Onee expander ease pressure is above 150 psi or equal to tower pressure, aetivate XYZ. This will open both expander outlet (diseharge) and eompressor inlet valves. 

At the rated duty point, the differential pressure eontroller is aetive. The inlet eontrol valve and trip valve are eompletely open. The main bypass valve is eompletely elosed and the small bypass valve eontrols the differential pressure. Approximately 96%-98% of the flue gas flows through the expander, with the rest passing through the small bypass valve, orifiee ehamber, and double slide valve to the expander outlet to rejoin the main flue gas flow. 

Nozzle C small,pierced heoder Nozzle A expanded outlet tube Nozzle in. plain tube Nozzle venturi type... 

Refrigerant pressure at the expander inlet [MPa] Refrigerant pressure at the expander outlet [MPa] Pressure at the outlet of the multi-phase turbine [MPa] Temperature [°C]... 

This chapter begins with a problem to find the expander outlet temperature when given the expander efficiency. The user will operate an expander operation in HYSYS to model the expansion process. At the end of this chapter, the user will determine the expander outlet temperature when given expansion efficiency or vice versa. 

At the end of this chapter, the user was trained to determine the expander outlet temperature when the expansion efficiency was given. 

The gas turbine size is set by mass flow rate at the expander outlet. In all cases, this parameter is kept constant. 

Presence of excessive CO2 in the sweetened feed gas to cryogenic section possibly leads to formation of Dry Ice, most probably over the trays below the feed tray of Demethanizer column where conditions are favorable for CO2 to reach stages of top equilibrium concentrations rather than at expander outlet conditions. Close monitoring of column differential pressure and other operating conditions is necessary for early identification of any onset of CO2 solidification. 

The methane K-value shows very good agreement for all the correlations, but the ethane and propane K-values exhibit a large variation. Variation in the amount of liquid condensed at the expander outlet and the expander horsepower are directly related to the amount of vapor separated at high pressure separator. The magnitude of this variation can affect the expander design quite significantly. 

The liquids condensed by the expansion are listed in Table V along with the total liquids. The total liquid condensed is the sum of expander outlet liquid and high pressure separator liquid. Since the ethane recovery is directly proportional to the total liquids condensed, the wide variation is significant. Also, the total amount of liquids has a large effect on the design of the demethanizer. 

The results listed in Table VII vary from -29.0% to -5.8%. The major contributor to these differences is the reboiler duty. The calculated low temperature (expander outlet) conditions are markedly different. 

Any freeze-up will occur in the demethanizer. The feeds to this column are the expander outlet to the top of the column and the liquid from the high pressure separator at the fourth theoretical tray. A detailed tray-to-tray calculation was made for 8 theoretical trays using the Soave K-value correlation. At tray conditions, the limiting CO2 content in the liquid phase was found from Figure 2. 

The major effect is seen in the calculated demethanizer reboiler duty, which varies from 8.4% to 12.2%. This is largely a result of the large differences in calculated enthalpy at the expander outlet conditions. If the enthalpy balance is in error, sufficient refrigeration will not be available and the expected recovery will not be obtained. 

When discussing efficiencies, the two most important design parameters are the isentropic enthalpy drop across the expander and the volumetric flow rate at the expander outlet. Stress limits the rotor tip speed to a certain extent, but more often the speed is determined by the enthalpy drop. The outlet volumetric flow rate likewise controls the expander wheel flow area. These parameters within mechanical limits determine the basic configuration of the hydraulic channel, which in turn directly affects the turboexpander efficiency. 

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