Flare Radiation Effecting Design Temperature 1

[sjackson]

I am trying to determine if a set of pumps in a flare radiation zone will be sufficient.
The pumps are located at a distance of 100m from the base of the flare stack. According to the radiation isopleths the pumps will be exposed to a radiation of 3 kW/m2 (including solar)during full flaring.
The pumps are designed for a max. ambient temperature of 50 C. The maximum site temperature is 45 C. Therefore, I need to determine if during full flaring the air temperature will increase by more than 5 C. The pumps are equipped with a sunshield so I am not concerned with the direct radiant heat.
Is there an emperical correlation between radiation level and air temperature? I can't find one in API 520/521.

 

[MortenA]

API does not caontain a formula for converting heat radiation to acutaul surface temperature.

You can study e.g. Perry (sec 10) closer and get a relationship from there.

Other sources may also contain simple formulas/table for relationship between surface radiation and object geometry, colour, wind velocity size and many other things that will influence surface temperature.

BTW: I dont think you should be looking for air temperature - but for surface temperature - since we are talking about radiation then the surface temp of the pump may be higher than the air temp.

Best regards

Morten

 

[PAN]

sjackson,

Please consider the radiation level in

http://www.nao.com/Thermal_Radiation_Levels.htm

If the operator work space (at pump area) requires <1.58 kW/m2, your case will be unsafe.

 

[MortenA]

Pan

Human radiation where not in question - it was if the equipment could handle the radiation. The equipment could be inside a fenced off area for all that we know. most flares will have a zone where humans normally are not allowed to enter or need a special permit.

Best regards

Morten

 

[madiazr]

check the following

LEES. Loss Prevention in the Process Industries. Volume I
Radiation and Dispersion Analysis

Is the best compendium..... i was calculated the same but in an offshore facilities and i found the solution in this book

regards

 

[PAN]

Thanks MortenA.

You are right. If we can control "no operator" in the area, there will be no problem.

Should we design remote start/stop for this pump?

 

[25362]

If you are interested in assessing the expected surface temperatures, you"ll find that Heat Transfer (ed IV) by J.P. Holman brings an example (8-10) on the temperatures that surfaces may attain when exposed to radiation fluxes.

 

[MortenA]

Well that depends on a lot of issues but normally yes. If not - either the pump has to run allways or the operator has to get a permit before strating the pump. This may or may not be a problem.

If you are very strict about it then entry of an operator within the restricted area will require a total shutdown AND dlowdown of the facility (so that there is no risk of such an occurence while the operator is within the safety area). Other procedures may apply - again this requires a lot of consideration.

You can also look at this page:

http://www.thermal-wizard.com/tmwiz/

Heres a calculator for calculating natural convection (and conduction) for various geometrical objects.

View the poblem as a equlibrium problem. Fix a ambient (air) temperature (e.g. 20 deg C) and the adjust the surface area to 1 m2 (and input other constants in the form). Then change the pipe temperature until your heat transferred equal your solar input. This is your temperature at worst case condition (e.i. no wind cooling)


Best regards

Morten

 

[MortenA]

I followed my own direction and actually found that if you consider a pipe with a diameter of .3 m and the air temp is 45 deg C - and the radiation is 3000 W/m2 - then the surface temp will be around 200 deg C. This may be a littele on the high side - but it is a worst case. Im not quite sure with regards to how the calculator compensates for surface emmisivity.

Best regards

Morten

 

[Flareman]

There cannot be the easily-calculated close relationship between the air temperature and the radiant heat that you are looking for because the air temperature will increase according to the absorbtion of energy, and that is a function (in part) of the amount of solid particulate (dust) and the humidity (and any other unsymmetrical molecules floating around)

The best you could expect from the API (style) information is the transmissivity formula which implies that the radiant heat reaching a point is related to the distance it travels to get to that point.

tau = 0.79 * [(100/R)^(1/16)] * [(100/RH%)^(1/16)]
R = distance from source to receiver - ft
RH% - relative humidity
(silly formula anyway because RH% implies a reference temperature which isn't given by the book)

As this is based on a spherical model the implication is that some heat is absorbed within the sphere
= [1 - tau] * source radiation
and this, you could argue, would be distributed over
(4/3)*pi*R^3 cubic ft at an appropriate Cp for air.

You can spend time working this out if you find it meaningful and you have the basic radiated energy data.

I'm not sure it gets you anywhere because
- if the wind blows, all bets are off
- the radiated heat you have in the data sheet is probably meaningless in the first place as it's calculated for a case which may never happen in wind and solar conditions which probably won't exist even if you have that flow case
- Solar radiation heats up the air anyway at a greater rate and you can have a whole range of different air temperatures for the same local solar contribution on the basis of where the air mass is coming from.
- the calculation probably already assumes that the flame is blown (by the WIND of 30 fps!!) directly from the flare toward your pumps (what are the chances of that)
- is a wind of 30 fps consistent with no convective cooling?

In my view, there's no way you could do a calculation accurate within 5 degC without knowing more variables than you can count.

In my opinion, if you keep the pump out of the direct path of solar AND flare radiation it should be just fine. If it isn't, it's probably working MUCH TOO CLOSE to its true limiting conditions and the manufacturers rating need to be reviewed.
Have you addressed the spec with the pump man on the basis of continuous rating or short term operation.
If it is the continuous rating he may have an extra 50 - 75 degrees up his sleeve for short term.

45 deg C site temperature puts your site within the tropics with a true solar contibution as high as about 410 Btu/sq.ft_h. (1.3 kW/sq.m) on a really clear day.

 

[MortenA]

I agree with flareman - especially about screening the equipment. I must however say that when it comes to equipment protection i dont really see what the point is in calculating the air temperature (as opposed to the surface temperature where a conservative estimate is not that difficult? (allthou i can see thats what he actually asked about )

Best Regards

Morten