Tank Inertization

Tank Inertization

1 Inertization

The inertization of reactors, storage tanks and pipes is an efficient system for preventing the formation

of a potentially explosive atmospheres and involves diluting combustive agents (oxygen present in the

air) with inert gases such as nitrogen, argon and carbon dioxide.

Initial Inertization

Prior to starting formulation activities requiring N2 inertization (i.e. before charging of any flammables)

a reliable and robust initial inertization has to be carried out to achieve an O2 level below 5% vol/vol. A

SOP how to achieve this value has to be developed and should be part of the risk assessment for the

implementation of N2 inertization system.

The N2 flushing has to be carried out until an O2 level below 5% vol/vol is achieved and the feed

nitrogen flow rate sufficiently high to ensure efficient mixing in the vessel and no dead areas.

Alternatively the final batch transfer of the non inerted campaign into the holding tank could be carried

out with the inertization system to replace the volume with nitrogen. This process is only possible if the

vessel has not to be opened for cleaning purposes afterwards, as this step would result in air ingress and

pose asphyxiation hazards. Cleaning by means of spray nozzles under N2 atmosphere is possible.

The liquid replacement by N2 is the most efficient way for inertization as less N2 consumption is

required to perform the inertization vs that of fixed flow/time.

For Example: Total Volume=5000 l ; liquid filling= 4000 l (to be replaced by 100%N2)

Total Volume 5000l = (4000 l N2) + (220 l O2 + 780 l N2)

= 220 l O2 + 4780 l N2

= 4,6% O2

Assuming that the volume of nitrogen necessary to reduce the oxygen concentration is not available is

possible to calculate as showed below:

Volume of Nitrogen required= Total Volume - [ Desirable oxygen concentration x ( Total Volume /

Oxygen concentration in the air)]

VN2= Vt- [ Conc. O2 x ( Vt/ Conc. O2 ar )]

2 Steps To Calculate the time of inertization

2.1 Step 1

Calculate the flow rate of nitrogen input

QN2 → Input flow of Nitrogen

V → average flow velocity of a gas

Dn → N2 inlet pipe diameter

A → N2 inlet pipe cross section area

2.2 Step 2

Calculate the volume of nitrogen required to decrease the concentration of oxygen

VN2 → Volume of nitrogen required

Vt → Total Volume of tank

Conc. O2 → Desirable oxygen concentration

Conc. O2 ar → Oxygen concentration in the air

VN2= Vt- [ Conc. O2 x ( Vt/ Conc. O2 ar )]

2.3 Step 3

Calculate the time of inertization

T → Time of inertization

VN2 → Volume of nitrogen required

QN2 → Input flow of Nitrogen

T= VN2 / QN2

T= (VN2 / QN2)

T= h

Premises:

V= 20 m/s (*)

Dn= 1 in → 0,0254 m2

A= (πDn2/4)

QN2 = V x A

3 Example

A storage vessel containing 100% air by volume and must be inerted with nitrogen until the oxygen

concentration is less than 5 % by volume. The vessel volume is 6 m3. How much nitrogen should be

added? What the time required of inertization?

Step 1

average flow velocity of a gas → V= 20 m/s (*)

N2 inlet pipe diameter → Dn= 1 in → 0,0254 m2

N2 inlet pipe cross section area → A= (πDn2/4)

Area → A(πDn2/4) = 0,0005067 m2

Input