2 replies to this topic

[sherveen65]

Hello,
Could anyone please guide me with some source of information about starting up, shuting down and maintenance of the pressure vessel like a decanter, I am doing a design project of two phase liquid liquid separation by decanter and I need to mention about start up, shut down and maintenance.
Thank you very much

[Art Montemayor]

What you are confronting is a typical situation for Chemical Engineering students who have dedicated themselves to going through at least 3 years of academic preparation without having the opportunity or priviledge of experiencing a hands-on, cooperative industrial student job. Therefore, you have little or no concept of what to expect during a starting up, shuting down and maintenance procedure because you simply have never been exposed to it.

If that is your case, then you have to resort to conceptual response, based only on what information you have absorbed in your academic training and research. This is not an easy chore, but it can be done.

Start visualizing, for example what these operations would require – based solely on basic, elementary facts that you know to be true:

A decanter deals only with liquids – usually two of them, each one with a different specific gravity.

The separation of one liquid from the other is based on the residnece time both liquids spend in the vessel.

The method of separating the resulting two liquid layers formed in the vessel is by using selective, designed liquid level detectors that detect the level of each liquid (by using mechanical floats that are calibrated for the specific gravity of the fluids) and operate a control valve that allows the outlet of the liquid that accumulates in the vessel after separation.

Taking the above in consideration, you can logically then form certain needs to fulfill a startup or a shut down of such a system. For the startup, it is essential that you establish working levels, in the vessel before being able to establish steady state and an “on-line” condition.

For the shut down, you can also identify the need to maintain an equilibrium and steady state of the fluids in the vessel. This might involve you by-passing the incoming feed to a stand-by “day tank” in order to not upset the decanter operation.

For maintenance requirements you should focus on what “makes” the decanter work: the liquid level detectors and the signals they generate, together with the outlet control valves. The nature or characteristics of the fluids also may present a need for inspection (cleanliness, contaminants, etc.) Obviously, we are addressing a confined vessel entry – a very special and potentially hazardous work assignment for any maintenance crew. You should pay particular attention to the fact that, as engineer, you are responsible for the safety and welfare of the maintenance crew and should focus on the need to ensure safety during the time that humans are inside that vessel.

I am not going into the details of each of one of the above points because I believe that is YOUR job. That is what, I believe, your instructors are going to be looking for: your ability to focus on the importance issues in carrying out an assignment and how you logically apply the necessary common sense and ingenuity to design a safe and effective operation.

[sherveen65]

Thank you very much for your help.
Actually I 've got another uncertainty. I have designed a two phase liquid liquid decanter. I must mention controlling strategy. I know that the interface must be controlled. As I think the most of the design methods assume the interface is located at the center of the decanter, and I actually designed it based on the centeral interface. But in order to control it, I don't know how much offset from the center is allowed in case disturbance occured. Moreover, should this interface e controlled by the outflow which is higher in the flowrate?
Apart from this, in design books, the normal level of the liquid inside the decanter is not mentioned and I don't know whether it is important or not and how much offset is allowed for that?
Thank you