Energy Management, EN 410/607
Assignment – 2
1. A process plant generates 20 kg/s of dry saturated LP steam at 4 bar (abs). For heating and other
applications, it requires 15 kg/s of HP steam at 13 bar (abs), 10 kg/s of MP steam at 8 bar (abs),
and 5 kg/s of LP steam at 4 bar (abs). It is possible to generate VHP steam at 550°C, 45 bar
(abs) in the boiler house. Based on the Salisbury approximation, determine the cogeneration
potential for the process.
2. In a double pipe heat exchanger hot fluid is entering at 220°C and leaving at 115°C. Cold fluid
enters at 10oC and leaves at 75°C. The following data is provided for hot and cold fluids.
Mass flow rate of hot fluid
= 100 kg/hr
Cp of hot fluid
= 1.1 kcal/kg°C
Cp of cold fluid
= 0.95 kcal/kg°C
(i) Calculate LMTD
a) For parallel flow
b) For counter current flow
(ii)
Which flow arrangement is preferable and why?
(iii)
Find the mass flow rate of cold fluid if the heat loss during the exchange is 5%.
3. A process fluid at 40m3/hr, with a specific gravity of 0.95, is flowing in a heat exchanger and
is to be cooled from 38oC to 29oC. The fluid specific heat is 0.78 kCal/kg °C. Find out the
chilled water flow rate if the chilled water range across the heat exchanger is 3oC.
4. A process plant requires 28 tonnes of steam per hour. The power requirement is 2250 kW. The
plant operates for 8000 hours per annum. Steam is generated at 2 bars in a coal fired boiler with
an efficiency of 75%. The feed water temperature is 80OC. The calorific value of coal is 4000
kcal/kg. The cost of coal is Rs. 2000/tonne. Power is drawn from the grid at Rs. 4/kWh. The
contract demand is 3000 kVA and the company is charged for 100 % of the contract demand at
Rs. 300/kVA. The company is planning for a back-pressure cogeneration plant using the same
coal with the following parameters. The power and steam demand were fully met by the
cogeneration plant.
Boiler generation pressure
- 18 bar, 310OC
Boiler efficiency
- 81 %
A contract demand of 1000 kVA with the grid was kept for emergency purpose.
Investment required
- Rs. 20 crores
Generated power
= 2250 kW
Find out the IRR over a project life cycle of 6 years
5. Determine minimum hot and cold utility requirements for the following stream data
corresponds to ΔTmin = 10 °C:
Stream
Tin (°C)
Tout
(°C)
Duty (kW)
Stream
Tin (°C)
Tout (°C)
Duty (kW)
1
180
40
280
2
150
40
440
3
60
180
360
4
30
130
260
***
Page 1 of 1