Im projecting a heat treater as shown below.
In my study Im using a 30API oil with an inlet flow rate of 3800bbl/d, 1170bbl/d water flow rate and 0.8MMscfd gas flow rate, the operating temperature is 120F and field temperature 68F. The fuel used in the firetube is natural gas and the Inferior calorific value is 47MJ/kg. The capacity for the firetube in our project needs to be 1,75MMBTU/hr and we would like a firetube with 24 diameter.

Vessel Size 8x25: Diameter 8 ft x Length 25 ft
Inferior calorific value: 1,75MMBTU/hr
Firetube diamater: 24 inches
Oil: 30API
Field ( ambient) temperature(inlet): 68F
Vessel Operating temperature: 120F
Oil flow rate: 3,800bbl/d (barrels per day)
Water flow rate: 1170bbl/d
Gas flow rate: 0.8MMscfd
Inferioc caloric value: 47MJ/kg

i)Which would be the firetube length ? How do I calculate this?
ii)About the convection section of the firetube, do you include a firetube turbulator? If yes, how do you evaluate the influence of this in the firetube length?
iii)Which would be the firetube flux (Q/A)?
iv)If I use a forced draft blower the firetube flux(Q/A) would increase ? If yes, what is the ideal air flow rate forced by the blower?
v)What would be the operation pressure inside the firetube?