6 replies to this topic

[seuenergy]

Dear all,

 

We are doing a HAZOP of reciprocating compressor(capacity is around 3000Nm³/h,  flammable gas, inlet pressure is around 2bar, outlet pressure is around 12bar). 

During discussion, some scenarios are developed:

1. no flow of lubricating oil

2. high discharge temperature 

3. low suction pressure(vacuum)

 

for the consequence of these scenarios, some think the raw risks are high, and SIL loops are needed, some think the risks are not so dangerous, and DCS loop protections are enough. 

 

 

What do you think about these risks? 

[Pilesar]

Some Hazops consider equipment damage and lost production costs, others consider only safety consequences. The scenarios presented are a partial description and do not include a consequence. In general, the compressor should operate reliably and every critical parameter measured so that appropriate action can be taken in a timely manner. I've always been able to reach consensus in Hazops with the team. It sounds like you may need more investigation and expert advice to reach a solution all can support.

[seuenergy]

Thanks for Pilesar's reply. 

 

You are right that I did not descripe the scenario completely.

 

Deviation:  low pressure of lubricating oil

Cause :  blockage of filter

Consequence:  loss lubricating of bearings, bearing damage, potentional leading to compressor damage and leakage of flammable gas. 

 

For this scenario, some colleagues think the scenario will ends as only internal damage of compressor occur, and no possilble for loss of containment.  

Others think that compressor damage is not only internal damage, integrity of damage could happen, and then leakage of flammable gas occur, potentional fire even explosion happens.

[breizh]

Hi,

For this case you should have a delta P on the filter with alarm and may be 2 sets of cartridge filters (1 spare).

This is quite standard.

Breizh 

[seuenergy]

Thanks Breizh's reply.

These sets the vendor had already provided. 

During HAZOP, safety engineers insist that the low pressure trip should be completed in SIS system. But maintenance colleagues insist DCS trip is enough. 

Actually, they have diffierent opinions about the raw risk of compressor. safety engineer thinks that large reciprocating compressor could cuase LOPC incidents, while maintenance engineer think only internal damage could happen.

 

Hi,

For this case you should have a delta P on the filter with alarm and may be 2 sets of cartridge filters (1 spare).

This is quite standard.

Breizh 

[Pilesar]

There are several other reasonable interlocks for compressors such as high vibration or high temperature which should shut down the compressor. Are these all handled the same way? Low lube oil pressure should first start an auxiliary lube oil pump, then if low pressure is not remedied, the machine should be shut down. Using a separate PLC for machinery monitoring seems a good practice. SIS may mean the requirement for an independent sensor which seems uncommon for this service. My tendency is to think this needs more than DCS, but not necessarily full SIS. Wrecking the compressor would be expensive. If the seal oil system is combined with the lube system, you might see a loss of process containment with no lube oil. I would consult compressor experts for your machine -- maybe the manufacturer can explain the consequences of operating with low lube oil pressure so that everyone on the team is satisfied. Combustible gas detectors and a fire protection system seem more important to me since putting lube oil pressure into the SIS will not stop seals from leaking.

[seuenergy]

Hi, Pilesar

 

Thanks for your kind reply!

 

The vendor always have fuzzy answer. When asked by maintenance colleagues, they gave conservative consequence. Actually, this is an big rotational machine, the raw risk is high. 

 

 

There are several other reasonable interlocks for compressors such as high vibration or high temperature which should shut down the compressor. Are these all handled the same way? Low lube oil pressure should first start an auxiliary lube oil pump, then if low pressure is not remedied, the machine should be shut down. Using a separate PLC for machinery monitoring seems a good practice. SIS may mean the requirement for an independent sensor which seems uncommon for this service. My tendency is to think this needs more than DCS, but not necessarily full SIS. Wrecking the compressor would be expensive. If the seal oil system is combined with the lube system, you might see a loss of process containment with no lube oil. I would consult compressor experts for your machine -- maybe the manufacturer can explain the consequences of operating with low lube oil pressure so that everyone on the team is satisfied. Combustible gas detectors and a fire protection system seem more important to me since putting lube oil pressure into the SIS will not stop seals from leaking.