1 reply to this topic

[Sergio777]

Dear gents, 

I would appreciate if you will support in questions of startup, normal shutdown, . I'm interested in general philosophy and probably will miss such things as oil system, air cooling, motor and so on - i will assume that it's in normal and proper operation and sets.

below general description of compressor unit.

1.Manufacturer. (Packager: Chinese company, compressor Ariel).

2. 2 stages. 1^st – 1cyl (D=12.5in, MAWP: 5.5MPa). 2d – 3 cyl (7.875in, MAWP:13,1MPa).. Stroke:5.50.

3. Rated RPM:1200 (actual 900).

4.  

 

P (MPag)

T ©

Suction at 1^st compressor stage   -  0,5-0,6 (MPa) -  45C

After 1^st  compressor stage            1,8-1,9  -  120

After 1^st  cooling stage                    1,8-1,9 -  45

Suction at 2d compressor stage (additional line)

+

After 2d  cooling stage                     1,8-1,9   -   45

After 2d  compressor stage              7,25   -    138

After 1^st  cooling stage                      7,2    -    45

 

5. composition:

 

CH4         40%

C2H6        15

i-C4H10   12

n-C4H10   7,5

i-C5H12    2,2

n-C5H12   1,2

N2              0,2

C02           1,3

H2O           0,1

CH3OH      0,2

 

6. Electrical Motor ABB. 910kW (10kV) (constant speed)

7. No additional options just recycling valve at of each stage.

8. compressor will run continuously – in general it’s N+1 reservation. (in our case 2+1).

 

 

 

1) startup.

 

b)before to start motor: suction SDV (10037,10039) are closed. discharge SDV closed. SDV in recycle lines  (both) opened. all PV opened.  

c) we open SDV in dischhurge line. then push "start motor".

d) open SDV in suction line 

loading:

e) when we will get P>=0,55MPa we can "LOAD". ----> SDV in recycling lines closing. (LL-0,55, L-0,57, H-0,63, HH-0,66)

f) all PV and SDV (10039) in suction (2)  - in automatic mode.---->automatic regulating.

Do I understand correctly. that suction PV (10001A) and 10003A regulates pressure downstream and can ADD pressure in case if they are opened not for 100%. if they are already opened 100%, but we need to correct suction pressure in this case recycle lines PV will provide regulation? (10001B, 10003B) as I understand when SUCTION lines will provide proper pressure and suction PV will be opened 

unloading:

g) please advise.

 

Normal shutdown:

- motor stopped

suction SDV (10037, 10039) - closed 

- discharge SDV 10042- closed

- all PV opened

 - recycle lines SDV - i suppose opened.

 

 

 

I understand that it's little bit messy....but i will be glad to any response.

Attached Files

•  pid - unit.pdf   1.23MB   102 downloads

Edited by Sergio777, 02 December 2016 - 04:46 PM.

[Art Montemayor]

Sergio777:

 

Most of all reciprocating compressors - especially the size you have (910 kW) are mechanically designed to be started up and shut down under NO LOAD conditions.  What is meant by this is that the compressor must not be doing any work (or very little) at the startup and shut down operation.  This is a requirement that is based on the mechanical components of the machine being able to withstand the very large stresses imposed on the parts such as the crank shaft, the connecting rod, the piston rod(s) and all the various bearings - with maximum torque being applied.  And it is very important to ensure that all lubrication points are receiving the proper lubrication at the moment of startup.  The oil pump pressure and/or flow must be ensured before attempting a startup.

 

There are limitations that all manufacturers impose on their various models and compressor frames.  What I mean by frames here is the assembly of the crank case driving components and other key, connected mechanical parts - such as the crosshead, piston rods, etc.  I have experience with Ariel compressors and I can specifically tell you that they make it very clear in their arrangement with all "packagers" that the guidelines and instructions regarding the machines' capabilities and liabilities must be respected and obeyed or otherwise the Ariel guarantees will be forfeited.  I have had one packager in the past that did not comply with the need for intercoolers in order to keep the interstage temperature at a certain maximum and the result was a law suit.  I have always warned purchasers of packaged compressors to always communicate clearly and in detail with the actual manufacturer as well as the packager in order to ensure that the packager is well aware of what he can do and what he can't do in designing the compressor controls and assembly.  I believe it is the purchasers responsibility to ensure that the packager is applying the compressor in a manner that is approved by the compressor manufacturer.

 

The reason I mention all this is because you should have clear and detailed operating instructions from your packager and these instructions should be approved by Ariel, based on the application and the process conditions,.

 

There are many ways and schemes on starting and stopping a reciprocating compressor.  A lot depends on the process and the operating conditions.  You have a system that seems to rely on using block valves to isolate the compressor while starting and stopping the machine.  This implies that you are not venting any process gas to a flare, for example, in order to purge process gas through the machine when starting up in order to fill the compression system with process gas that replaces initial atmospheric air.  This means that you either maintain the machine always filled with process gas or you inject it initially prior to startup.

 

If that is the basic method that you have designed for your compressor, then a lot of careful instrumentation logic is involved with how you have the 2-stages of compression configured and piped up.  It is very critical to ensure that the block valves operate 100% of the time and that you have a fail-safe instrumentation system installed in the event they fail - either open or closed.

 

In order to discuss your query I recommend that you confirm what I have deduced from your P&ID and your data.  That way we can analyze your system and address your specific questions.  However, it is normal practice for the packager to furnish you with the detailed instructions and assurances regarding the safe and proper manner that the machine should be operated under.  They should also have instructions or directives regarding any Hazop or point to any potential hazards that could occur in the normal, day-to-day operation and how these are mitigated by their design of the controls.  Can you enlighten us by telling us what you have from your supplier?

 

I am presuming that you have four (4) throws on a common crankshaft.  Is that correct?