I have a system comprising of a 100 m3 tank (atmospheric vessel).

From time to time the tank has to be cleaned (CIP) by spraying hot water into the tank by means of spray nozzles.

At the start of the wash the tank can be as cold as 0°C.

My problem is then:

As soon as hot water is sprayed into the tank the air mass inside will heat up and expand. Furthermore the air will be saturated with water vapor. The increase in volume must be vented using the PVSV (consevation valve) on the tank.

Obviously the vent flow will depend on the rate of the temperature rise.

I'm trying to estimate the temperature rise in a given time (eg. 20 sec). There are 3 possible approaches:

1. Assume adiabatic and perfect mixing conditions during the time step - in other words the air, liquid water and vessel wall has the same temperature (energybalance + mass balance for humid air).

2. Assume as for 1 but neglect the influence of the vessel mass.

3. Rate controlled scenario - the liquid reaching the bottom of the tank is not in equilibrium with the air but has transferred some mass and energy to the air.

My impression is:

Re: 1. It is probably unrealistric to assume that the vessel wall reaches temperature equilibrium with the rest iof the system.

Re: 2. Probably too worst case - the vapor flow would be overestimated.

Re: 3. The correct solution - however the estimation of h(og) and k(og) for a non uniform spray system is not straight forward.

Any suggestions or past experience with similar system from any one ?

Best regards

Peter

Peter:

Please read the Forum Guideline rules. DO NOT POST MULTIPLE COPIES of the same query. I am deleting the copy you posted in the Industrial Professionals. Multiple copies create confusion in the responses.

If this is a real-life application, I would not recommend using a Pressure-Vacuum Safety Valve as a sole relief protection against an over-pressure scenario as you describe. Just about every API type tank is equipped with a roof-located emergency vent (which can be nothing more than a weighed blind flange with a hinge or a chain on it. This emergency device is what is normally relied upon for use during a maintenance, clean-out, or emergency case. That type of device, in my opinion, is what you should be employing or designing.

Yep - I know - tried to delete it but had no luck. Thanks.

Re: my case - this is a very real life app. and the tank(s) will be equipped with PSV(s) apart from the breather valve (pipe away type) as secondary protection. I agree - anything else would be foolish.

It is, however, the desire of the customer to clean without opening hatches to the outside due to sanitary considerations (Pharma production) and the fact that the caustic cleaning solution could spray through large openings.

Basically the problem boils down to estimating the rate of temperature increase as a fuction of tank temperature and water spray rate.

Best regards

Peter