Q & A > Rotating Equipment
Date  Replies
20/04/2017 Q: In centrifugal compressor driven by steam turbine why do we have three solenoid valves: one for starting oil and another for trip oil all of them for trip valve actuator and how does it work ?  
07/04/2017 Q: In our unit DHDS we have steam turbine pump. I am unable to understand why both mechanical and electronic governors are needed. Also turbine is provided with tripping device.The maximum over speed trip value around 1600RPM. Could anyone explain why both mechanical and electronic are needed?  
25/03/2017 Q: In our hydrocracker unit we have recycle gas compressor and they are provided five ejectors to create vacuum in service condenser. Two ejectors for first stage and another two for second stage.And last ejector for start up. Why we need to use initially start up ejector and we can use first stage and second stage initially instead of start up ejector if we can there is any effect? (1)
20/03/2017 Q: We are using Compressor Type WS2/180-A1 for our Naphtha HydroTreating recycle gas compressor. During Wash water injection at the up stream of NHT reactor effluent separator, water is carrying over to the suction of Compressor. As a result of that compressor discharge, flow becomes low and load current also becomes low which suggests one of the load valve is not functioning due to dirt in water may have choked the load valve. After cleaning the load valve, flow and current becomes normal again. This problem is being faced recently when some salt has formed at the downstream of NHT reactor effluent which is dissolving with the wash water and carrying over to the suction of compressor. In addition, we are facing this problem after 3.5 years of plant life cycle. My question is whether it is happening only for dirt in water or load valve's diaphragm and O ring get old or spring has lost its tensile strength. Whether the Compressor type WS2/180-A1 is designed to handle some liquid or water as it is designed for recycle gas of NHT unit? FYI- 1. Wash water injection has been continuing in a regular interval of 15 days since the inception of plant start-up 2. Salt formation at the suction strainer is experiencing currently.


(3)
05/01/2017 Q: Recently we encountered a failure in one of the Boiler feed water pump. Observations were as below.
1. Pump tripped after running for 30 sec when it reached its full disch pressure of 100kg/cm2G.
2. Trip was due to high bearing vibration on NDE side.
3. Rotor was moved towards DE by about 2mm.
4. Rotor was seized( could not rotate with hand).
5. NDE oil decolorised slightly.
6. upon dismantling we found that NDE bearing inner race was seized to shaft. NDE bearing was totally damaged.
7. DE bearing was fine and no change in oil color too.
8. While operation, discharge valve was fully closed( according to operations min circulation as well as balancing lines were fully open).
Online probes not able to provide required spectrum.
Now we are struggling to analyze the cause. Pls suggest the way forward and also if you have link to similar failures.
(2)
03/01/2017 Q: I need information about mechanism of steam turbine associated with recycle gas compressor and also the function of dry seal gas, secondary separation and separation gas. I would also like to understand the reason of tripping in high vibration.  
31/12/2016 Q: What is purpose of primary and secondary seal in RGC compressor ? (2)
27/12/2016 Q: We have found black solid deposits upon cleaning of our CCRU Net Gas Compressor First Stage Strainer. Upon analysis of composition, we have found that the sample contains hydrocarbon plus a significant amount of Chloride and Iron and with traces of Aluminium, Magnesium, Silicon, Phosphorous and Sulfur. What could be the source of these black solid deposits? (6)
02/12/2016 Q: I'm working in hydrocraker unit and we have recycle gas compressor. Why the condensate from condensate pump which is suction from surface condenser one line goes to RV for sealing. Also why we have expansion bottle for surface condenser. The sources to expansion bottle Medium pressure steam boiler feed water using for start another sources steam turbine drains and ejectors condenser condensate.  
19/07/2016 Q: Why is a rundown block-in timer required in modern hydrogen compressors for hydrotreating applications?  
15/07/2016 Q: IN our HCU Recycle Gas Compressor Turbine, make BHEL from one month Turbine Front & Rear journal bearing vibration suddenly increase from 15 micron to 80 micron for about 10 minutes and came back to normal during this period turbine bearing temperature also increase 3-9 degree centigrade. Please suggest the root cause. We do centrifuge of lube-oil once in 24 hors about 2-3 hours and lube oil also replace in december 2015. (1)
28/06/2016 Q: What is the average energy efficiency of Steam turbine driven centrifugal compressor (Total Condensing)? (1)
13/04/2016 Q: We are facing severe choking problem in jacket cooling system of reciprocating compressors. Currently we are using service water for closed loop circulation but the effect is such that after two or three months of cleaning, the flow area available reduces by more than 60% on an average. Is anyone facing similar problems..? What may be remedial action. ? We flush the system during every available shutdown. During flushing a think slurry like liquid sometimes black in colour is discharged.
Service water we are using has similar parameter that of industrial drinking water with slight high Cl content.

Additional:
The iron content of service water used in the closed loop system is 0.4ppm. We don't suspect any tube leakage in exchanger as well. But surely there should be a problem with the quality of water we are using.
The type of deposit we observed is muddy type hardened along the inner wall as lumps. Breaks down if we hammer the outer surface of pipe during flow inside.
http://sailinchemicals.com/wp-content/uploads/2015/05/02_Corroded_potable_pipe_-_Credit_-_Nu_Flow_America.jpg
The appearance is similar to above image except that the colour is slight orange in nature and more like globular lumps.
(8)
05/04/2016 Q: In our crude distillation unit, Main Fractionator bottom pump (Service RCO) is having frequent primary seal leak, period varying from 8 hours to around 2 weeks. The crude processed is North Gujarat Crude which is a high TAN crude having RCO potential of about 65%. Suction specific speed was checked which is well above its rated value.
How this problem can be solved ?
(1)
28/03/2016 Q: I am looking in the possibility of replacing the let down valves after the CHPS and HHPS bottoms (in Hydrocracker), with Power Recovery Turbines. Is there way to estimate how much power would I get?
And is it reliable to use the power recovery turbines instead of let down valves?
Other than that, are there other alternatives to recover that power?
(1)
25/01/2016 Q: Our Deep Catalytic Cracking unit Wet Gas Compressor (WGC) seems to be an over-designed one as its operating at the minimum governing speed(MGS) with the anti-surge valves around 35% open even at 90% plant capacity. Due to this the speed/performance controller is operated in manual mode making it difficult to control the reactor pressure.
Is it possible to change/lower the MGS of turbine so as to bring the speed control in the unit's operating range and thus keeping the reactor pressure control in AUTO. If not, is it advisable to tune the ASVs so that they close at a lower load?
(5)
18/12/2015 Q: 1) Does the higher hydrocarbon condensing at the discharge side due to the increase in pressure in a liquid ring compressor can go back to the suction side if the volume of condensation of the hydrocarbon is more due to the change in the vapour composition?
2) Which affects the capacity of the liquid ring compressor a) heavier hydrocarbon like C5 & C6 in the suction or b) Heavier hydrocarbon vapour in the discharge port due to increase in the discharge pressure due to compression.

 
08/10/2015 Q: What happens if I put a Reciprocating compressor in a loop i.e The discharge of the compressor is sent to its suction? What do you think will happen to the temperature, wattage and pressure in the circuit? (2)
01/09/2015 Q: Currently I'm doing pump test with water, I want to know what is the best way to compare the flow from the FT and the flow in the pump curve, the Flow Transmitters are set for hydrocarbon with SG of 0.65 but I'm doing the test with water which SG is 1. Do I have to correct the flow to HC flow at conditions or standard conditions in order to compare the flows with the curve?. How can I do that?
(2)
31/07/2015 Q: In our wet Gas compressor we experience frequent seal oil migration/leak into lube oil. Wet seals exhibit low MTBF. How can we eliminate seal leak and enhance sealing performance? Is dry gas seal a reliable solution in wet gas compressor? (4)
06/06/2015 Q: We have a screw chiller compressor which is for refrigeration in recontact section of CCR naphtha Hydrotreating unit. We are trying to start it after TA but getting tripped after 3-4 sec. All electrical and rotary side are fine. It is having Interlock of PDI between lube oil discharge pressure and gas discharge pressure. Every time it trips on this and sometimes feed alarm fail comes.
Also filter on pump discharge was choked earlier.
Please suggest troubleshooting this problem.
(3)
04/06/2015 Q: In our single stage centrifugal compressor primary seal gas is ethylene. N2 is provided as backup in case C2 pressure drops due to any reason. What is the safe logic for seal changeover from C2 to N2? Primary Seal gas flow control valve and flow transmitter is in vendor package. There are individual on/off valves in C2 and N2 supply lines, these are in client's scope. Differential pressure transmitter is available across N2 supply on/off valve. (1)
15/05/2015 Q: I am working in a Divalproex sodium production plant where we are producing by spray drying of that solution to make the form of powder. Sometimes there is powder choked in the spray chamber. Then we have to shut down the whole system and trying to clear choke. When the choking is cleared, again the process started. So I just want to know why it happens. Is there any rectification for this trouble? If anybody knows about it please help me.... (1)
01/05/2015 Q: In a centrifugal pump the seal flushing oil is supplied from external source. But whenever the discharge valve of the pump is closed the seal flushing becomes zero.
What is the probable cause?
(3)
23/04/2015 Q: I was asked for evaluation of doing the leak test and pressurization step in the Hydrocracking unit start up with Nitrogen instead using Hydrogen. We have 1 reciprocant compressor for make up and one centrifugal compressor for recycle gas, I would like to know what do I have to consider to make this evaluation, what I know by now is that my recycle gas molecular weight is 4 and N2 is 28, so my centrifugal compresor could not be able to increase the pressure more than 250 psi (aprox). what should I take in account?. Is there any gain doing this? (4)
12/03/2015 Q: Why does API 618 not cover plant or instrument air compressors that discharge at a gauge pressure of 9 bars (125 psi) or less?  
06/01/2015 Q: Why is centrifugal pump discharge line smaller in diameter than suction line? (2)
25/12/2014 Q: To increase the energy efficiency of Steam turbine, we take it in extraction mode from total condensing mode. When we tried to increase the extraction steam flow, the turbine exhaust temperature increased. Why does the turbine exhaust temperature increase at these conditions? (2)
11/07/2014 Q: In our Hydrogen Generation Unit HP steam silica level is running high at about 0.1 PPM against design value of 0.045 PPM. We maintain BFW Ph-9.5, excess Phosphate - 3 PPM, Hydrazine excess 0.1 PPM and continuous blow down Gestra valve is 100% open. Conductivity and TDS is normal. How can we reduce silica? There are no BFW exchanger leakages
(2)
15/04/2014 Q: In our CCRU plant we have two net gas compressors which are discharging 38000 Nm3/ hr H2 gas (95 % H2 purity). Net gas compressors are two stage reciprocating compressors with recontacting section. We have 4500 Nm3/hr (87% H2 purity) of semi regenerative CRU off gas joining the circuit after the first stage discharge. We are facing problems with very high second stage suction strainer PDIs in our compressors (which is probably due to CRU off gas joining the circuit interstage). Recently we had conducted analysis of the muck we found on second stage suction valve plates.
The analysis is :
Sr.NO / Parameter / Unit
1 Moisture (@105ºC) % 5.4
2 Loss of Ignition at 800⁰C % 83.14
3 Ash at 800⁰C % 11.46
4 Solubility in water % 13
5 Oil Content % 16.96
6 Iron (Fe) as Fe2O3 % 8.716
7 Acid Insoluble ( ~ Silica etc) % 0.8
Can anyone provide further insights looking at these results?
(1)
04/03/2014 Q: How do we calculate viscosity values of Bitumen at 90°C and 100°C for VG-30 grade (pen 50-70mm, min. viscosity of 2400 poise at 60°C & 350 cst at 135°C)?These values are required to advise a consultant who is engaged to select & supply suitable rotary screw pump.  
22/01/2014 Q: At present we are operating a diesel column bottom pump (saturated liquid at around 300 deg C). Pump runs for 24-30 hours and suddenly discharge pressure drops beyond permissible value and pump needs to be stopped. All other operating parameters are well with in the range. We donot understand the phenomena why discharge pressure needs to be dropped suddenly when all other parameters are same. One of the idea is internal recirculation, pump is developing the vapour some how internally then vapour accumulates and after considerable time pump needs to be stopped. Please advice. (4)
11/10/2013 Q: If any reciprocating compressor is stopped, what is the condition of suction unloader valve? Suppose discharge loader valves pass why pressure not increase up to discharge pressure but same as suction pressure. (5)
09/07/2013 Q: Why is the pressure drop of a Control Valve at the discharge of a pump in a liquid hydrocarbon service taken as 0.7 bar as a first guess? (1)
11/06/2013 Q: What is the Wheel Chamber in a Steam Turbine? What is its purpose? (1)
12/03/2013 Q: Some weeks ago we saw some cracks in the FCC expander blades in one of our FCC units. The cracks appeared suddenly, from one month to another.
The fresh catalyst addition rate are very low, so catalyst turnover is slow. It has provoked the ageing of our e-cat inventory. We have measured the attrition of the e-cat, with Jet Cup method (Davison Index), and there is a decrease from 2-3 to 1-2. My question is could this decrease in DI of the e-cat (harder catalyst) be responsible for the mechanical problem in the expander?
(2)
17/02/2013 Q: Please advice about the operation practice of the reciprocating compressor in order to increase life time of discharge valves in the compressor cylinders.
We're operating a Hydrogen plant using water electolyser cells - using alkaline which is KOH, operating temp 70C and production rate 170 nm3/hr where reciprocating machines are used to suck hydrogen from a gas holder directly after the cells and discharge it to the high pressure line to the customer (200 bar).
The Gas Compressor comprises of 5 stages, where first stage is consits of 2 plate valves.
The problem always happens to first stage Gas Compressor. Just 15~30 days after starting, the discharge valves in the cylinder always develops a leak and fails. Upon dismantling, we used to find some debris and gum particle (deposits) in between valve plate and valves top. The problem occurs over and over again.
The deposits particle is KOH which comes with the hydrogen gas vapor passing through the suction filter and rest on the valve.
(2)
26/10/2012 Q: We have hydrogen reciprocating four cylinder compressor. Every time after over hauling we take No Load trial for 2 hrs with discharge valve removed condition. Then we purge with nitrogen, then twice with Hydrogen. Now During Load trial Motor trip on Over load, (0% capacity), after barring compressor around 2 rotation, the compressor started Normal.
Why compressor started smoothly after free rotation? We already taken No load trial one day before.
(2)
23/08/2012 Q: One of our condensers --using cooling water as coolant media -- is located at elevated position. We can periodically isolate and dismantle this condenser, and upon inspection , the tube side (cooling water side) of this condenser always suffers from signifcant amount of fouling.
One of our colleagues suggests we install an "inline centrifugal pump " on the cooling water supply line into this particular exchanger in order to increase the amount of water flowing through condenser's tube hence minimizing the fouling rate.
I'm a bit doubtful about this suggestion, as this exchanger receives the cooling water supply from network header, thus the amount of water supplied to the inline pump will still be the same as the amount of water supplied directly to the exchanger without inline pump. An inline pump, in my opinion, will only increase the inlet pressure of cooling water into this particular exchanger. In my opinion, any attempt to increase the discharge valve opening of inline pump cavitate the pump if discharge flow is higher than suction flow received from network header.
I would like to hear the opinion from experts about the inline pump of cooling water network.

Additional:
Thanks for all..
The suggestion from Mr. Banik sounds interesting, and I'm going to evaluate it.
Anyway, I'm still curious with the case of inline pump installed in the cooling water supply line of an elevated exchanger, whether it will be able to pull more water supply from network.
My premises are :
1. Let's imagine an elevated exchanger is normally supplied with cooling water flow of X m3/hr.
2. The original supply pipe runs on the same elevation with main header of H m , then turning up towards exchanger.
3. If I reconfigure the supply pipe to turning down of H m below main header, then turning up again H m before further going up to reach the exchanger, the pressure profile inside this reconfigured pipe at elevation of H m will still same with pressure profile of original pipe at elevation of H m.
4. Hence flow of water in supply pipe no. 2 and 3 will still same.
5. If I put a pump in lowest section of reconfigured supply pipe no. 3, then the amount of water flowing into pump suction will still same X m3/hr.
6. As centrifugal pump doesn't suck, but it only pushes, so the amount of water pumped will still same X m3/hr. The only different thing is water inlet pressure to exchanger increases hence water outlet pressure from exchanger also increases.
7. Thus operating the pump discharge above X m3/hr will cause transient inventory loss in the pump casing hence cavitation.
Do I miss something or make mistakes in my premises above ?
(5)
07/06/2012 Q: Our recycle gas compressor has a wet sealing system. We are facing frequent problems of seal leak because of which around 2 lube drums of oil is to be topped in the seal oil reservoir.
There is negative delta P(-0.2 Kg/cm2) between seal oil & reference gas.
I want to ask is only negative delta P signifies the seal leak of RGC.?
Does it signify that our reference gas line is choked?
A seal oil Overhead tank is provided above a height of 7.5 m above the seal level. Due to this head there should always be a +0.6 delta P between seal oil & reference gas.
(2)
19/05/2012 Q: We have 2 combustion air blowers for meeting the total air demand in our FCC unit. Main air blower(MAB) is a fixed speed one while auxiliary man air blower(AMAB) contains VFD. Whenever AMAB is started, oil vapours start escaping from its antisurge vent line creating a vapour cloud. Recently the vent line silencer also caught fire because of this. What could be the reason? Is it normal for lube oil to escape from the blower antisurge vent line? There is also a small 3 inch balancing line connecting the blower casing and the blower vent line downstream of its antisurge control valve, is it a good practice to have this line? (2)
19/04/2012 Q: MEG regeneration system. In our plant we have 2 rich MEG tanks that receive MEG/Condensate/Water solution from condensate flash vessel. Last time during pigging activities we receive many sludge from offshore, and now all this sludge is settled down inside Rich MEG tanks. MEG Regeneration package performance rapidly reduced, pumps could not deliver Rich MEG to regen, strainers getting clogged very fast, HC compartment of MEG flash vessel in MEG Regen package filling rapidly. Any ideas how to improve situation with Rich MEG tanks? Maybe clean Rich MEG using hydro-cyclones, or any other equipment? Any links to useful equipment to be installed, or to similar problem anywhere? TQVM in advance.  
25/02/2012 Q: Please advice about the operation practice of the reciprocating compressor in order to increase life time of discharge valves in the compressor cylinders.
We're operating a Naphtha Hydrotreater - Platformer complex, where reciprocating machines are used as recycle gas compressors in NHT ( 2 Units ) and as Net Gas Compressors ( 2 Units ) in recontact loop of Platformer. A Net Gas Compressor comprises of 2 stages, where first stage is handling gas with 80% purity and the second stage is handling 90% H2 purity. The RG Compressor in NHT handling gas from second stage discharge of Net Gas Compressor.
All compressors are equipped with double block-bleed on the suction and discharge piping. These double block-bleed are left open even for stand by machines in order to enable quick start up action.
The problem always happens to first stage of stand by Net Gas Compressor. Just 15~30 days after starting, the discharge valves in the cylinder always gets leak and failure. Upon dismantling, we used to find some debris and gum particle in between valve plate and valve stop. Even after suction surge drum cleaning, the problem occurs over and over again.
Please advise whether the stand by machine must be isolated and can only be onlined just before starting or can be left online as long as the suction surge drum is free of liquid ?
The gum particle is 100% olefins which is suspected due to di-olefin condensation. And the rust is 100% Carbon which is suspected from coke breakthrough from reactor. But why this olefin and coke never cause any problem to the second stage, or even to the first stage of "non stand by" one, as well as no problem so far to the NHT Recycle Gas Compressor ?
FYI, the stand by compressor suction line is 20 m distance from non stand by one. How to solve these all these problems?
(3)
28/01/2012 Q: In one of our FCC units (Kellog Orthoflow model), we are suffering severe problems of fouling (fines deposition) in the turboexpander. The scheme of the flue gas circuit is: two stage cyclones in the regenerator + Shell Third Stage Separator before turboexpander + 4th Stage Separator (cyclon) to recover flue gas from fines coming from TSS.
We have also observed high level of moisture in the fines from 4th Stage Separator (10-15%wt). So we suspect that the fouling of the expander is due a cold point in the flue gas circuit (where flue gas humidity is condensed) or an uncontrolled inlet of water / steam.
Has anyone experienced this kind of problems in an FCCU? What could be the potential causes of the severe fouling of the expander?
(2)
20/01/2012 Q: I am currently managing a high pressure water injection triplex pump in a hydro cracking unit. I am plumbed into the unit with my diesel powered pump that has taken place of two electric drive pumps that have failed for undisclosed reasons to me at this time. This particular job was given to my company on short notice and the only information i have received is that this was critical that the unit still perform at at least 50% production and in the event of a failure of the pump I'm operating the best thing I can do is run. If anyone has any experiences with these pumps could you enlighten me to the hazards involved, the use in process, and any down stream side effects on a refinery when they are out of service? Also I was told that within twenty minutes of shut down on their pumps that their unit would cease to function due to salt build up. (3)
26/12/2011 Q: My question is related to the potential problems that could appear when the feedrate in a FCCU is reduced to the technical minimum (turn-down) or below.
- According to your experience, what is the minimum feedrate that can be processed in a FCCU? 60% of nominal feedrate or does anyone operated below this point?
- Which are the most likely limitations that could appear in this point?
1. Insufficient gas flow rate to the wet gas compressor?
2. Insufficient pressure or delta P in feed nozzles? Problems to obtain a suitable vaporization?
3. Insufficient coke production to close heat balance?
4. Insufficient liquid-vapour traffic in the main fractionation?
5. Any other limitation?
(2)
26/12/2011 Q: I'm processing hydrocraker and my question is about steam turbine vibration hunting.
This is Recycle gas compressor turbine and its driving force is HP Steam.
I've noticed that HP steam Temp. & Press. was little changed after discovered the problem and controlled them.
But vibration hunting has still been occurring and I'm looking for another source of hunting.
Could you please advise about this if anything you have a similar experience or knowledge?
(1)
25/11/2011 Q: Swivel joints are used in the roof drain line of the floating roof tank. In our refinery we usually replace these during repair work on the tank. In that case the life of the joints is about 10-15 years. But I want to use these joints again. There is no testing facility for these joints. There are 20 swivel joints in each tank so a good amount of money is required to replace them. My questions are:
1. Is it a good decision to replace the joints after 10-15 years?
2. How should we test the joints if we wish to use them again?
 
23/11/2011 Q: Theoretically, what minimum flow requirement shuld be specified for selection of Recycle Valve with respect to compensate for drop in suction pressure, provided my maximum flow through the RC valve is known? (2)
05/08/2011 Q: In our refinery, we are running 5 no of Air Compressors (of Elliott make) to cater the Plant Air and Instrument Air requirement of the entire refinery. The setup is as follows:
4 nos of Big compressors of capacity 6040 NM3/hr each and 1 no of Small compressor of having 3020 NM3/hr and design pressure of 8.3 kg/cm2
All the compressors' discharge pressures are set at more or less equal pressure of ~7.2 kg/cm2.
Instrument Air pressure is maintained at ~5.8 kg/cm2
Of the 4 big compressors, 2 compressors are older by 12--15 years.
Now the question is the Suction C/V (IGV) of Old compressors is opening only 50 to 70% even if the demand is more. C/V stroke checked and observed to OK.
What could be the reason for less opening of IGV?
(2)
05/08/2011 Q: A 8m3/hr & 35m H pump is available with us and we are using for pumping organic residues which is the regular operation carried out in day today operation. Now we are planning to use the same pump for recirculation purpose for about 3 to 4 hrs/shift.But the recirculation back to the storage vessel pipe static head is only ~ 6 - 8 meters, but the original design of the pump is 35 m head. I have checked the pump curve & found that by reducing the actual head from 35 m to ~ 8 m , flowrate will increase. So accordingly I have sized the recirculation pipe size to the recommended velocity. Should this solve the problem? What other consequences might it have? (3)
23/05/2011 Q: Recently we are facing a severe problem of frequent RGC trip in our Hydrocraker plant. Till now RGC tripped 10 times in last 3months. Now the problem is that in all these trips not a single trip logic actuated, but only the alarm received as compressor trip from governor. So we are clueless. We have HP steam driven RGC. At present we are bypassing trip lever &mechanical overspeed suspecting problem in that part.It was also observed that most of the trip occured at when governor speed incresed to 11,500 rpm.In last few occasion of trip it was also observed that turbine outboard bearing Outlet Lube oil temperature suddenly started shoot up just before RGC trip. After byassing the trip lever assembly RGC was not tripped till now,but as trubine outlet bearing lube oil temperature increased at speed 11,500,we have reduce the rpm to 11,00 and thus we are not able to run Hydrocraker unit in full capacity.From process point of view, all parameters are within normal operational range like previous normal RGC running condition.Can any one give any idea what may be the basic problem of frequent RGC trip? Also,will it be safe to run RGC by bypassing trip lever assembly & Mechanical overspeed? (5)
08/04/2011 Q: In our wet gas centrifugal Compressor (capacity-130TPH), dry gas seal system (nitrogen) is given as primary, secondary and separation gas. The N2 header pressure is 7.5 kg/cm2g. Is any back-up facility (N2 bottles, booster etc.) required for safe and smooth operation of WGC in case of header pressure low or failure of supply? (2)
07/03/2011 Q: Recently we have 6 nos of recycle gas compressor trip incident, but even after 6 nos tripping we are not able to diagnose/analyse the reason for such trip. Tripping alarm in PLC for all occasion found to be same which is trip from compressor governor & trip from LCP (local control panel). Kindly suggest what may the probable reason for such a trip without any prior alarm? Compressor is steam driven.. RGC normal RPM ~11500 RPM. Is the trip incident caused by variations in gas molecular weight?
Is it possible that surge conditions occur due to comparative lighter gas handling than design operating which ultimately force the RGC to trip?
(1)
05/11/2010 Q: Lately we had a problem on one of our old (33 years) but reliable Desalter Transformers. The Transformer is NWL 150KVA 4.16KV/23KV (3each) on top of our crude oil desalter trap. Two of these transformers experienced failure and we found the high voltage cable was burned and cut. The oil in the entrance housing was discolored (black) and the oil in the third transformer was clear. Later on we found the secondary on the third transformer was disconnected. the floating switch and the grid were OK.
What are the possible causes for such failure?
We replaced the entrance bushings with the high their high voltage power cables for the damaged bushings.
We performed Megger test and Polarization Index (PI) test on the transformers. The PI was 1.4, 1.6 and 1.5 for these transformers. Are these PI readings acceptable to put back the system in service? What are other tests shall we perform on these transformers?
 
26/10/2010 Q: We are fixing for choosing a new compressor for VRU; vapors recovery unit; the light hydrocarbon gas mixture has Mw about 42, K{Cp/Cv} =1.12 , Rc {Pd/Ps} =3.2 , Z factor is about 0.97, Inlet temperature is 43 C and flow rate Q is 600 CFM, discharge Pressure, Pd= 72 psia...
I'd be more than grateful for any tips, Equations, etc to use...
(1)
09/08/2010 Q: I work in Hydrocracking plant, where we commonly use turbine pump when running in normal condition, and backed up by motor pump as a spare pump.
But, in some equipment, we use turbine pump as primary pump and backed up by turbine pump as a spare pump. This pump transfer the bottom of low pressure separator (liquid hydrocarbon) to debutanizer.
I also found a pump configuration where both the primary and spare pump are turbine pump. This pump is diesel pump around (hot wash).
Do you know what is the reason behind these configurations?
(2)
03/07/2010 Q: What are the benefits of adding process steam in pre reformer inlet and reformer inlet separately? In some hydrogen plant it is mixed only in reformer inlet. What is the advantage of that? (2)
18/05/2010 Q: Problem: You have two reciprocating compressors in a NHT system, one service, the other on standby. When the duty trips the standby must be barred and then put into service.
To bar it, it must be depressurised, barred, pressured up and then started, this could take up to 15mins, so this makes it very tedious and labourious.
How long can a compressor be static until it needs to be barred? Some say it must be barred at least 1 hour before starting to ensure all liquid is displaced from the cylinders. Some say the compressor must be barred every 3-4 days.
Are there any systems that can eliminate the need for barring via reducing the chance of hydrocarbon condensation or otherwise.
(3)
13/05/2010 Q: What are the benefits of a top fired reformer versus a sided fired one? (5)
20/04/2010 Q: We want to install a Diesel generator near an already operational Gas generator located inside a gas installation for emergency power supply. As per OISD standards or other regulations is there any minimum inter-distance required?  
07/04/2010 Q: For any industrial compressor why do we assign the interlock like this:
Low pressure trip for lube oil and low flow trip for cooling water
and why not vice versa ?
(2)
19/03/2010 Q: Centrifugal pump (say A) is designed for suction pressure 2.6kgf/cm2 with plan 11. Now if in suction we route some material @10kgf/cm2 with a 1/3 of flow of the said A pump by keeping discharge OPEN, what will happen? Is there any chance of seal leak? (1)
19/03/2010 Q: I am working in DHDS unit. Recently our unit tripped because of some strange problem. I request all to suggest a reason for the problem explained below.
We have one centrifugal Recycle gas compressor (RGC) and two reciprocating make up gas compressors (MGC) one running and the other stand-by. As per the regular change over of MGC we tried to take the other one in line and spare the running one. The discharge of MGC (40 KSC) goes to suction of RGC (39.4 KSC). After starting the spare compressor and once it got 50% loaded, the make up gas rose from 25 Tons per day to 35 tons per days, simultaneously RGC amperage came down from 210 to 176 amps and discharge pressure of RGC came down from 61 KSC to 53 KSC and this dropping of amps and discharge pressure continued and unit tripped on low hydrogen pass flows. As the discharge pressure of RGC reduced the discharge flow also reduced. I didn't understand why the discharge pressure of RGC came down.

Additional Information: Separator pressure is constant and when the RGC tripped, it started raising. The suction flow was 265 Tons per day and when the RGC discharge pressure dropped, the suction flow also dropped to 255 Tons per day.
(6)
08/03/2010 Q: In our Once Through Hydrocracker Unit, the Recycle Gas Compressor is surging from 100% opening of the anti-surge valve to 0% without any change in process parameters. It was also observed that just prior to surging the total flow at the inlet of the RGC was also increasing. We have got an amine column at the inlet of RGC suction after HP separator to reduce sulphur loading. But now due to some constraints the amine flow had to be reduced. Can anybody explain the phenomenon? (3)
03/03/2010 Q: What are the implications of shell side fouling on the pulling of a VCFE/Texas Tower (Platformer) bundle for cleaning? Our client is looking to pull a VCFE which has been in-situ for 16 years and I would like to find out if others have carried out a similar exercise and any impacts fouling may have had on the activity. (2)
13/01/2010 Q: What is the optimum time for switchover between standby rotating equipment? (4)
01/11/2009 Q: What is main purpose of putting sealing steam in a turbine? (1)
01/11/2009 Q: In our DHDT recycle gas compressor primary seal vent flow at non driver end side has reduced to zero while it was previously 5 Nm3/hour. Driver end side flow is running between 30 Nm3/hour. What is the possible reason behind flow reduction? (1)
15/08/2009 Q: In Our Recycle Gas compressor turbine seal steam pressure having too much fluctuation. Some time its pressure increase and some time decreases. What are the possible causes? (1)
12/08/2009 Q: In DHDT unit suppose benzene converted to cyclohexane and then cyclohexane converted to normal hexane. What is the mechanism of this reaction? How is aromatic converted to cyclohexane then how cyclohexane ring broken and converted to n-hexane? (3)
21/07/2009 Q: For Euro-III diesel why must we maintain density 820 to 845 Kg/cube metre? How will performance be affected if this value is not maintained? (2)
21/07/2009 Q: Why must we maintain distillation of diesel 95% at 360 degrees centigrade for Euro-III ? If less or more what is the effect on engine performance? (2)
18/07/2009 Q: What is the basic difference between a thermal and pressure safety valve? (3)
16/07/2009 Q: How can one fix minimum circulation flow and scheme for a pump which is undergoing in revamp, specially when flow is going to reduce after revamp? (3)
19/04/2009 Q: To avoid surging anti surge controller is provided, while for reciprocating compressor spill-back controller is provided. What is the purpose of a spill-back in reciprocating compressor? (2)
28/03/2009 Q: What is lube oil supply temperature for any pump or compressor? Like feed pump, makeup gas and recycle gas compressor. (2)
25/03/2009 Q: Why do we need to maintain gas oil ratio in our diesel hydrotreater? (5)
22/03/2009 Q: Recently there was a case of loss of gas oil cracking unit feed resulting in unit shutdown. During troubleshooting analysis, it was observed that the centrifugal pump feeding the gas oil feed suddenly experienced a drop in the motor amperage a few seconds before the total gas oil flow to the pump started to drop below the minimum circulation flow. The minimum circulation control valve fortunately worked when it started to open to allow the circulation flow back to the pump suction.
Everything was checked, from NPSHa of the pump, basket strainer and y-type pump suction strainer, total gas oil and high-pressure reactor feed controllers` transmitters, as well as the pump motor voltage, among others. But none seemed to be identified as the root cause of the unit trip.
Is there any other aspects of the centrifugal pump that needs to be evaluated? Any possibilities of internal circulation inside the pump cavity that could cause the sudden pump cavitation?
Test runs on the pump's spillback have been conducted, and based on the observation, all including the pump vibration and behaviour of the minimum circulation control valve opening, were considered normal.
Could the pump motor amperage drop result in lower suction feed to the pump?
(1)
09/03/2009 Q: Why is a minimum circulation line not provided in some centrifugal pumps? For instance, in our stripper reflux pump it is provided, while in our diesel hydrotreater stripper it is not. (2)
04/03/2009 Q: What is the exact meaning high/low severity in case of refinery catalytic unit? (5)
15/02/2009 Q: Why is the cetane index of diesel higher for high sulfur than low sulfur crude? (6)
15/02/2009 Q: What is the mechanism of aromatic saturation reaction in diesel hydrotreater reactor (i.e. step by step conversion from aromatic to paraffins)? (2)
07/02/2009 Q: What is the standard value of SOX & NOX in furnace stack outlet? Are the Values different in case of fuel oil firing and fuel gas firing? (3)
31/01/2009 Q: We have calculated EII for a long period and we have observed it was very clear that capacity and EII directly related to each other.
If you go on details to decrease bad effect of low on EII the best way to use VSD for every system. (One pump or fan for each system.)
But at this point we have two main doubts:
1. Reliability of the VSDs
2. VSD effect on control system.
Are we correct to have these concerns?
(1)
02/11/2008 Q: Sample Probes: How are the vibration calculations done (vibration calculations to ensure that the probe cannot fail to resonance effects / harsh process conditions)? Are there any software packages available to check that the sample probe selected can withstand the process parameters (pressure, temperature, flow, fluid density, etc.)?  
16/10/2008 Q: Why is the non return valve fitted on the horizontal pipe line rather than the vertical one? (2)
01/08/2008 Q: How can I design sizing of a jet mixer? what are the factors that determine its efficiency? Can a jet mixer also operate with Nitrogen? And how to calculate the consumption of Nitrogen? Is it better than conventional mechanical agitators for highly viscous fluids with congealing nature? (1)
04/03/2008 Q: How do you calculate the efficiency of a centrifugal compressor driven by a variable speed steam turbine? What equations are to be used and what input data are required from the running unit? How do you correlate this with performance curve given by the equipment manufacturer?  
07/02/2008 Q: Have hydraulic power recovery turbines (HPRTs) been included in any of the most recently completed or planned projects where core hydrocracking and amine regeneration is required? Besides energy savings incurred with the installation of an HPRT, how significant a role with HPRTs play in reducing CO2 emissions?  
07/02/2008 Q: What are some of the most successful turbomachinery management systems in use today? What documentation is available to show where turbomachinery/compressor expected life has been extended?  
06/02/2008 Q: In a cross country gas pipeline, is any passive fire protection system like fire water storage / pumps / hydrant network or fire water spray system etc are required to be installed at compressors stations and delivery stations? If, so what cooling rate should be considered for fire fighting system?  
26/11/2007 Q: I am still amazed at how few companies are using Inverter Technology on Fans and Pump applications.
Is there much demand for European manufactured Inverters within Petrochemical industry?
 
26/11/2007 Q: Is there any refiner using variable speed drivers in electrical motors of process units? (4)
19/09/2007 Q: Please advise on reduction of ammonia emissions from a fertiliser plant.
Our emissions from a urea plant stack is about 150 ppm, and we need to reduce them to 50 pp to comply with EPA regulations. I know some plants are provided with an acid washing system.
I would be grateful for advice from anyone with experience in this field.
(1)
31/07/2007 Q: Recycle gas compressor of CRU had ammonium chloride salt deposition in its impeller vanes during regeneration activities. Can we wash the rotor with DM water or steam condensate without opening the machine. If yes, can you suggest some guidelines?

(6)
24/07/2007 Q: What is the feasibility of using gas turbines in olefins plants as process compressor drivers? (1)
09/07/2007 Q: Can you comment on some of the most important aspects of recent orders for compressors and turbines? Also, with a large backlog of orders for new equipment, what are the most effective condition-monitoring and asset reliability programs for maintaining the performance of existing rotating equipment? (3)