KEP ES749 - 3.3 Steam Net Heat

ES749 Flow Computer
13
3.3 Steam Net Heat
Measurements:
A owmeter measures the actual volume ow in a steam line. A temperature and a
pressure sensor are installed to measure temperature and/or pressure. All measurement
are made on the steam side of a heat exchanger.
Calculations:
• Density, mass ow and net heat ow are calculated using the steam tables stored in the
ow computer. The net heat is dened as the difference between the heat of the steam
and the heat of the condensate. For simplication it is assumed that the condensate
(water) has a temperature which corresponds to the temperature of saturated steam
at the pressure measured upstream of the heat exchanger.
• With square law device measurement the actual volume is calculated from the
differential pressure, taking into account temperature and pressure compensation.
• Saturated steam requires either a pressure or temperature measurement with the other
variable calculated using the saturated steam curve.
• Optional steam trap monitoring using compensation input.
Input Variables:
Superheated Steam: Flow, temperature and pressure
Saturated Steam: Flow, temperature or pressure
Output Results:
• Display Results
Heat, Mass or Volume Flow Rate, Resettable Total, Non-Resettable Total,
Temperature, Pressure, Density, (optional: peak demand, demand last hour,
time/date stamp)
• Analog Output
Heat, Mass or Volume Flow Rate, Temperature, Pressure, Density, Peak
Demand, Demand Last Hour
• Pulse Output
Heat, Mass or Volume Total
• Relay Outputs
Heat, Mass or Volume Flow Rate , Total, Pressure, Temperature Alarms, Peak
Demand, Demand Last Hour
Applications:
Monitoring the thermal energy which can be extracted by a heat exchanger taking into
account the thermal energy remaining in the returned condensate. For simplication
it is assumed that the condensate (water) has a temperature which corresponds to
the temperature of saturated steam at the pressure measured upstream of the heat
exchanger.
STEAM NET HEAT
Net Heat Flow
Net Heat Flow = Volume ow • density (T, p) • [E
D
(T, p)– E
W
(T
S(p)
)]
E
D
= Specic enthalpy of steam
E
w
= Specic enthalpy of water
T
S(p)
= Calculated condensation temperature
(= saturated steam temperature for supply pressure)
Calculations
Steam Net Heat
Illustration
FlowmeterTemperature
Transmitter
PRINT
5
0
–
TIME
CLEAR
•
MENU
ENTER
HELP
TEMP
4
PRE 1
3
RATE
2
TOTAL
1
GRAND
6
SCROLL
7
PRE 2
8
DENS
9
Pressure
Transmitter
Water
Steam
*
* or Steam Trap Monitor