Calculating Tank Wetted Area – Chemical Processing
Determine the average yearly height.
Determine the average wetted surface area and vapor contact surface area of tank (FT2).
Note: the floor area of the tank is not included however the roof area is included in the vapor surface area.
Determine BTU/HR loss per square foot of tank area for wetted surface and for vapor contact surface (BTU/HR-FT2).
Obtain value of fuel ($/MMBTU).
Establish energy conversion (%).
Calculate annual fuel savings separately for wetted surface and vapor contact surface (MMBTU/YR), basis design heat recovery.
Combine wetted surface fuel savings with vapor contact surface fuel savings for total fuel savings (MMBTU/HR).
Calculate annual cost savings ($/YR).
Savings ($/YR) = (Total annual fuel savings) x ($/MMBTU).
Consider the following crude storage tank:
Tank diameter = 40 ft
Tank height = 30 ft
Crude oil temp = 180ºF
Average ambient temp = 60ºF
Average height of crude in tank = 10 ft
Value of fuel = 4 $/MMBTU
Heater conversion efficiency = 80%
Design heat recovery = 90%
Using the procedure described:
Wetted surface are = (3.14 x 40 x 10) = 1260 ft2
Vapor contact surface area = (3.14 x 40 x 20) + (3.14 x 400) = 3770 ft2
At a temperature difference of 120ºF, the wetted surface heat loss in 265 (BTU/HR-ft2) and the vapor contact surface heat loss is 100 (BTU/HR-ft2).
Fuel savings for wetted surface:
Total fuel savings: (MMBTU/YR) = 3295 + 3720 = 7015
Annual cost savings: ($/YR) = 7015 x 4 = $28060
HEAT LOSS FROM UNINSULATED OIL TANKS