3 replies to this topic

[Ir Kavi]

hai there. i have some doubts and im stuck on it. please someone advice me. im currently doing audit in steam consumption in refinery plant. first task is i have to calculate steam rate in plate heat exchanger. the only information that i can obtained is outlet temperature of oil. what im supposed to do? what measurement that can i used for measure this pressure and temperature? what type of thermometer that i can used?any idea?

regards,
kavi

[Art Montemayor]

Kavi:

Yours is a common, recurring problem that confronts young Chemical Engineers. The answer to your dilemma is found in the advice given me by my first Chemical Engineering professor, over 54 years ago: "When in doubt about how to start the solution to a ChE problem, do a heat and material balance."

Study carefully the simple, basic aspects of what you are confronting. You have a steady-state, sensible heat transfer, Unit Operation. From simple Physics and basic engineering, you know the relationship for sensible heat transfer that states that the heat transfered is equal to the specific heat of the substance heated multiplied by its mass and the temperature increase. I am not going to write the familiar, well-known equation. Rather, Í'll let you write it out or research it.

If you know the mass of the oil, its specific heat, and the temperature difference you can solve for the heat transferred. If you know the specifications of your steam supply (or more importantly, the conditions of the steam in the shell side(?) of the heat exchanger you also know its thermodynamic properties - such as its latent heat of condensation. With these known quantities you can easily solve for the amount of steam condensate formed by heating up the oil - which is the same as the amount of steam used to heat the oil.

[kkala]

..im currently doing audit in steam consumption in refinery plant. first task is i have to calculate steam rate in plate heat exchanger. the only information that i can obtain is outlet temperature of oil. what im supposed to do? what measurement that can i used for measure this pressure and temperature? what type of thermometer that i can used?any idea?

I would try to measure oil inlet temperature and flow, in order to calculate steam rate through a heat balance (conditions of steam used must be known). Look upstream of the exchanger for a temperature indicator (TI), and upstream / downstream of it for a flow meter. In the (improbable) case of no flow meter, try to measure the level of feeding or destination tank/drum (under stable operation) on the condition that there is no other branch flow on oil piping. In the (improbable) case of no TI upstream, try to measure oil temperature in feeding tank; even a pocket for a local thermometer (Mercury or thermocouple) may be installed.
Above may be sufficient for a student work. If you aim at a result more precise than a preliminary estimate, "every measurement should be verified by some sort of balance", as the Operations manager of my first job (in fertilizer factory) used to say. This means that in this case steam flow rate should be also measured directly (not only calculated). An orifice on steam feeding line could do the job. Measuring outlet condensate (even by placing some pot downstream of trap and measuring time of filling) would give a value close to calculated steam rate, but would not take any steam escaping from trap into account.
Probably action needs cold blood and discussion with plant supervisors / foremen, who could show details not apparent at first look.
The task is rather complex for a whole refinery plant, requiring occupation of several people. In the local fertilizer plant mentioned, this was tried in 1978, making numerous local measurements and selecting "approved" data. The audit concluded that there was waste of produced steam, adequate for two air preheaters. These were installed but not enough steam was available for them. We were told that audit was precise for a plant at steady state, but has not considered unsteady state conditions having disproportional (high) waste / consumption of steam.

Edited by kkala, 27 March 2010 - 11:55 AM.

[breizh]

Kavi ,
To support your study , I attached some equations you may find useful to perform the mass & energy balances .
Hope it helps
Breizh

http://www.spiraxsar...tions.asp#head1