Dave90001
Petroleum
- Oct 10, 2012
- 1
Hi,
I’ve been asked to calculate the trip set point on the outlet of an electric heater on the basis that the action of the TAHH takes 20 seconds to fully respond, therefore what is the maximum outlet temperature allowable to prevent exceeding 110oC (383K)pipe design temperature in 20 seconds based on the minimum possible flow through the heater?
Electric heater power = 1200 kW which I take to correspond to the Electric heater duty = 1200kW
Line design temperature = 110oC
Min flow through heater = 1.6 kg/s
Cp = 2.34 kJ/kgK
I believe Q=m cp dT is the equation to use. I’m getting confused because I need to factor time into the equation.
The electric heater duty = 1200 kW i.e. 1200 kJ/s. So this isn’t the total heat input in 20 seconds but the heat input per second.
T1 = T2 – (Q/m Cp) = 383 – (1200 / 1.6 * 2.34) = 62.5 K i.e. the initial temperature should be -210oC.
So really, the time does not have anything to do with the final fluid temperature, but instead it is the mass flowrate which should be set to prevent exceeding design temperature. Is this correct?
Can someone please provide some guidance on this?
Thanks.
I’ve been asked to calculate the trip set point on the outlet of an electric heater on the basis that the action of the TAHH takes 20 seconds to fully respond, therefore what is the maximum outlet temperature allowable to prevent exceeding 110oC (383K)pipe design temperature in 20 seconds based on the minimum possible flow through the heater?
Electric heater power = 1200 kW which I take to correspond to the Electric heater duty = 1200kW
Line design temperature = 110oC
Min flow through heater = 1.6 kg/s
Cp = 2.34 kJ/kgK
I believe Q=m cp dT is the equation to use. I’m getting confused because I need to factor time into the equation.
The electric heater duty = 1200 kW i.e. 1200 kJ/s. So this isn’t the total heat input in 20 seconds but the heat input per second.
T1 = T2 – (Q/m Cp) = 383 – (1200 / 1.6 * 2.34) = 62.5 K i.e. the initial temperature should be -210oC.
So really, the time does not have anything to do with the final fluid temperature, but instead it is the mass flowrate which should be set to prevent exceeding design temperature. Is this correct?
Can someone please provide some guidance on this?
Thanks.
