Page 1 of 2 H. Reuter 17.04.2014

Energiestelsels / Energy Systems M434

Tutoriaal / Tutorial 8

1. Dry saturated steam at 8 bar(g) is used in a plant and the condensate runs to a waste at a temperature 6oC below steam temperature. How much enthalpy is wasted in the process, and what is the percentage of the total enthalpy of saturated steam which is being wasted if the ambient temperature is 10 ºC?

2. If 550 litres of water are to be heated from 16oC to 88oC, how many kilojoules are needed and what does one call this type of energy addition?

3. A part of a steam heated plant operates at 14 bar(g) with a operating load of 500 kg/h. The plant is drained through a trap discharging condensate at steam temperature, directly to atmosphere. What will the temperature of the condensate be on discharge from the trap and how much flash steam will be lost per hour and at what pressure.

4. Condensate from a jacketed pan working at 1 bar(g) is discharged at an average rate of 150 kg/h, through a float steam trap. The trap is sized to pass 150 kg/h of condensate at a differential pressure of 0.35 bar. The jacket is fitted with an automatic air vent. The condensate is lifted directly from the trap up a vertical pipe 6 m high. Leaking steam traps elsewhere in the system are setting up a back pressure of 0.2 bar(g) in the condensate return. The output of the pan is reducing. What is the probable cause of the trouble and what other snags are present.

5. A flash recovery vessel is supplied at the trap draining an evaporator which works at 10 bar(g) with a steam consumption of 1000 kg/h. The flash steam from the vessel is fed to a tank heating coil at a pressure of 0.5 bar(g). What is:

(a) the quantity of flash steam to be expected? (b) the quantity of residual condensate to be discharged from the flash vessel? (c) the temperature of the condensate leaving the flash vessel.

6. Steam with a dryness fraction of 0.9 at 7 bar(g) passes through a pressure reducing valve to a pressure of 2 bar(g). What is the dryness fraction of the steam downstream of the valve?

7. A heat exchanger is supplied with steam at 7 bar and on the secondary side of the exchanger the temperature of 2.4 kg/s of water is raised from 70oC to 80oC. What mass of steam is condensed per second? If the steam supply has a dryness fraction of 0.9, how much condensate must the steam trap handle?

8. How much "flash" steam at atmospheric pressure was released from each kg of condensate leaving the heat exchanger steam traps in (7)? If this steam had been taken off at 0.5 bar, how much would be available?

9. Consider the attached Piping and Instrumentation Diagram which was converted to a Control Diagram. Provide labels for all the components on the diagram and give the type and phase of the working fluid in each pipe.

10. A steam desuperheating station is used to reduce the steam temperature in the HP line, at 130 bar, from 570 ºC to 565 ºC, in order to protect the steam turbine. From the attached P&I diagram, draw the symbol for the desuperheater and determine the steam flow required from the boiler to produce 100 kg/s of steam for the turbine if the water is supplied by the HP feedwater pump at 150 bar and 80 ºC.

11. The continuous blowdown from a HP boiler drum at 150 bar, is discharged to the environment at a flow rate of 1 kg/s. Calculate the following:

(a) The energy lost if all the water is discharged directly to the dirty water drain, and the make-up water enters the open feedwater tank at 20 ºC.

(b) Name the other losses resulting from blowdown. (c) The flash steam temperature and flow rate if the blowdown is discharged to a flash vessel at

1.5 bar(a) before flowing to the drain.

Page 2 of 2 H. Reuter 17.04.2014