4 replies to this topic

[Valentino111]

I am having a problem of completing my hazop analysis, can i please be helped to finish it up.

Problem Statement:
Benzene is fed to a reactor in excess to promote the production of monochlorobenzene. the reactor products are fed to a condenser, where the choloro-benzenes are condensed. the condensate is seperated from the non-condensable gases in a seperator (flash drum) the non-condensables, hydrogen chloride and chlorine leave in the upper stream. Do a hazop on the upper stream, the parameters being temperature, pressure and flow. the node being point before the vavle.

this is what i have already done:

Guide Word

Deviation

Cause

Consequence

Action

More
High Temperature
Pre-heater products enter the flash at high temperatures.
Causes to high pressure.
HCl release.
Causes injuries.

No action. Event unlikely to happen.
Hot weather.
Low Temperature
Cold Weather.
This will result in insufficient vapour leaving the tower.

More
High Pressure
Valve stuck close
High Temperature

The increase in pressure could lead to an explosion.
There should be a pressure relieve valve installed.

[S.AHMAD]

1. I am unable to help you since the problem statement (process description) does not tally with the diagram. In the problem statement you mention condenser but the drawing shows heater. If I read your description correctly, the diqagram should shows reactor followed by condenser and then by a flash drum. The upstream NODE shall be from reactor outlet to the inlet valve of the flash drum.
2. Please attached the right drawing/P&ID

Edited by S.AHMAD, 31 October 2012 - 07:22 PM.

[ankur2061]

Valentino,

If you are looking for a methodology for HAZOP then you can refer the following link:

http://www.cheresour...a-hazop-review/

If you go through the attachment in the link you will notice that HAZOP is a very detailed exercise in determining the hazards of a particular plant or unit operation. HAZOP review or analysis requires process knowledge, analytical skills and prior experience. This I can say from having attended a number of HAZOP review sessions and also having chaired some of them. Many times the HAZOP participants / attendees are required to have a minimum working experience of at least 2-3 years to comprehend the finer details of a HAZOP review.

I am a little surprised that such an advanced exercise has been entrusted to you as a student. My suggestion to you would be talk to your professor and discuss what exactly you are required to do. Per my understanding, the HAZOP exercise entrusted to you is to test your logical analytical skills on what possible hazards can exist for a given process. If such is the case, you should be analyzing all the possible hazards that can exist and then find out what can cause them and if already some safeguards exist to prevent such a hazard. This three-pronged analysis process will allow you to logically deduce what real hazards exist and what design changes are required in the process to prevent these hazards. But be sure to discuss this with your professor on what exactly is required from you as a student related to a HAZOP review.

Good luck in your HAZOP exercise.

Regards,
Ankur.

[Ahsan67]

Valentino111,

In my suggestion kindly make an Excel sheet to accurately show your Hazop work for this particular node , like


Guideword Deviation cause consequence safeguard

Flow High
Low

Pressure High
Low

Temperature High
Low

This way will help others to understand your working & also attached P&ID for this node

Thanks
Ahsan

[HSE Expert]

This exercise is not as complicated as it seems. Here is an illustrative table to indicate what a HAZOP plan looks like. Note: this is not the solution to the exercise with the chlorobenzene reactor.

In order to do a HAZOP on the upper stream (gases to be separated from the condenser) the deviations temperature, pressure and flow have to be combined with the guide words "no", "more", "less", "reverse" and so on as long as the combination makes sense. You can see how it works from the example for the deviation "flow".

Then name possbile consequences of the deviations, possible causes and the existing safeguards that there are in the diagram of the condenser.

If the existing safeguards are not sufficient to prevent the deviations, you must think of additional safeguards which could be technical, organisational and/or behaviour-based.

A HAZOP is nothing more than just a special form of a risk management plan that systematically lists possible hazards and the severity of their consequences and estimates the likelihood of occurrence based on the existing controls. If controls are insufficient, the risk will have to be reduced to an acceptable level by suitable additional controls. That's all.

 hazop-example.pdf   10.42KB   142 downloads

Best regards.