21 replies to this topic

[R NESAMANI]

We are operating the cross country LPG pipeline. We have Filter , pumps. We have 2 filters(1+1)A & B, If filter-A DP is high, then take the filter-B in line.Isolate filter-A, and empty the LPG(@ 20 Kg/cm2, 1.5 MT qty) by flaring, thru blowdown line.

1) I came to know that we can flush the filter with the high pr. water. LPG can be transfered to the process piping, then isolate the filter with water inside.we can extract the water from filter,then do cleaning.
Is it safe...?
I want to know the details about this flushing job.
2) I want the evacuation system to transfer this LPG into the process pipeline, which is at 15 to 20 kg.cm2.
see the drawing of the station.

My idea is not to flare the LPG, precious energy.

Attached Files

•  IPS.pdf   15.3KB   176 downloads

[ankur2061]

Nesamani,

It is difficult and probably uneconomical to recover the LPG from the isolated filter because of the following reasons:

1. LPG being a clean liquid the chances that the filter will get plugged in a short time duration are very remote. If you are cleaning the filter even after say 6 months on a preventive maintenance schedule you need to check out if the economics are favorable to recover the small quantity of LPG in the filter. Most likely any recovery like pumping out the LPG from the filter or a vapor recovery system will not be justifiable economically due to the infrequent nature of the filter change.

2. LPG is a saturated liquid. Any reduction in the system pressure will cause the LPG to flash to vapor.When you isolate the filter there will be reduction in pressure in the filter body which will lead to partial flashing of the LPG inside the filter. LPG pumps are special design pumps which can handle liquid + vapor and thus are expensive and to installl such pumps for recovery of a small quantity of LPG and that too probably in a six-month duration seems to be unjustifiable to me.

The option to vent it to a flare or even a cold vent system (based on dispersion analysis for ground-level concentration) to me seems to be a more economic approach in your case. However, you may be required to undertake a techno-economic feasibility exercise to actually have cost of a recovery system for the LPG from the filters.

Hope this helps.

Regards,
Ankur.

[kkala]

LPG should contain no water, see specs at http://www.nationalg...ecification.pdf. Otherwise water can freeze during pressure reduction (e.g. through a drain, vent, reducing station, or just at the valve before consumption) and block the corresponding valve. Relevant accidents have happened, see http://www.sozogaku....n/HC1300001.pdf.
Thus it is rather risky to displace LPG in or around the filter with water; some water may pass to downstream LPG, some LPG may remain in water. The former may be more risky, as water (even in drops) will pass into distribution network. Is there any LPG vessel with water settling downstream of filters?
I have heard of LPG (not as a final product) mixed with water in refineries, e.g. in caustic washing. But conditions and provisions in refineries are different than here.
So this is another reason, beside those reported by Ankur, for sending dry LPG of isolated filter directly to flare (LPG release to atmosphere may not be permitted).

Edited by kkala, 11 September 2011 - 01:03 AM.

[ankur2061]

Kostas,

API 2510 - "Design & Construction of LPG Installations" permits LPG discharge to atmosphere if it is only vapor. It however explicitly prohibits discharge to atmosphere if liquid LPG might be released and suggests design and operational steps to be taken to prevent this.

I have senn many examples of cold or atmospheric vents from relief valves of stand-alone LPG bullets or spheres. The height and diameter of these cold vents is dependent on the dispersion calculations to assess ground-level concentration of the LPG constituents which are heavier than air (C3 & C4).

The conclusion is that you can vent LPG vapor discharges to atmosphere with due dispersion considerations.

Regards,
Ankur.

[R NESAMANI]

Thank you for your reply.

In our pipeline, we get LPG from 2 Refineries & one import terminal. We get huge amt of black color sand like carbon particle. this causes the filter DP increase frequently. also not only filter, we do maint. of pumps, flow meters. for ref. last year total venting is 8.5 MT, energy loss is Rs.4 lakhs, approx. for one year.

Thats why i am planning for this....

[ankur2061]

Nesamani,

As explained earlier you need to do a cost-benefit analysis of a LPG recovery system versus flaring / venting. Based on the cost-benefit analysis and "Return Over Investment" (ROI) you will exactly know the payback period for a new LPG recovery system.

Do this exercise and you will know whether a LPG recovery system is economically justifiable.

Regards,
Ankur.

[S.AHMAD]

Recovery of valuable LPG is a good idea.

The first step in any project is to study the economic viability as briefly explained by Ankur. As part of this study, you need to prepare the PFD and using this PFD we can study the process safety aspects (using HAZOPS or risk assessment techniques).

Ideally, if you can return the LPG back to the refinery (upstream of LPG treating unit), probably safety is less concern.

[R NESAMANI]

Thank you for your reply.

To do a cost-benefit analysis, i should know the cost of the system to be installed for LPG recovery. So first help me in the system identification for the project.

[ankur2061]

Nesamani,

As suggested by Ahmad, prepare a process flow scheme for each of the ideas you have in mind and upload it as an attachment. We can discuss the cost as well as the merits and demerits of your ideas. The final costing would be available only based on vendor quotes for the individual or package items.

Regards,
Ankur

[engg]

Thank you for your reply.

To do a cost-benefit analysis, i should know the cost of the system to be installed for LPG recovery. So first help me in the system identification for the project.

I am thinking the dangers of LPG is that it does not rise, once you open the vent after draining the filter, some LPG will come and settle on ground level, how will you ged rid of it? using an air blower? find out.

secondly from safety docs above, you shudnt clean with water else make sure its bone dry which might be very difficult for a filter. howe about cleaning with spirtits/alcohols which fly off? in any case you need to consult your filter vendor. If possible replace rather than clean....

[kkala]

API 2510 - "Design & Construction of LPG Installations" permits LPG discharge to atmosphere if it is only vapor. It however explicitly prohibits discharge to atmosphere if liquid LPG might be released and suggests design and operational steps to be taken to prevent this. I have seen many examples of cold or atmospheric vents from relief valves of stand-alone LPG bullets or spheres. The height and diameter of these cold vents is dependent on the dispersion calculations to assess ground-level concentration of the LPG constituents which are heavier than air (C3 & C4). The conclusion is that you can vent LPG vapor discharges to atmosphere with due dispersion considerations.

Ankur's post on API recommendation (not known to me) is indeed very useful, thanks for pointing it out. After that I tried to check current practice of local refineries, which may be of interest:
1. General today practice is to sent all hydrocarbon releases to flare, including PSV discharges or vents, LPG or other hydrocarbons. New installations apply this practice after (say) 1996.
2. This practice was not initially applied to older installations.
PSVs of two towers in LPG recovery unit discharged to atmosphere (due to limited flare capacity), rest PSVs to flare. Today all PSVs of the unit discharge to flare.
LPG spheres had originally PSVs discharging to atmosphere (never occurred), today they normally discharge to flare; they also have the (not normal) possibility to divert this flow to atmosphere (editing note 4 Apr 12).
3. Vents normally discharge to flare; if used e.g. for steam out, they have possibility to discharge to atmosphere.
4. There may be still a few old releases to atmosphere, concerning LPG or light hydrocarbons, "helped" by steam for good atmospheric dispersion.

Consequently, even though LPG gas can be released to atmosphere through a proper dispersion (per API 2510) , this is not always the practice of today refineries. Practices seem to vary from place to place. Stricter practices than those by API can be applied, question is whether these indicate a general future trend.

On the other hand natural gas is released to atmosphere in a LNG terminal far from refineries. Relevant PSVs of the storage discharge to atmosphere (if it occurs sometime), while there is possibility to inject fire extinguishers (dry chemicals) to the discharge line. Natural gas (actually CH4) seems to have satisfactory "upward" dispersion in the atmosphere.

Editing note 4 Apr 12: While flare is not operating, PSV discharges of LPG are directed to a "blow down drum" located far, at safe location on the ground. They are not ignited in this case.

Edited by kkala, 04 April 2012 - 11:31 AM.

[S.AHMAD]

Dear Kkala

Thank you for the info on the refinery practices. The refinery I am currently attached to is still venting LPG from sphere to atmosphere. Routing LPG to flare may become a Good Practices in the future for LPG installation as part of effort to conserve environment. However, for safety issue the API 2510 as cited by Ankur will be good enough (unless API revises the Std).

For environmental reason, LPG should be burnt since CO2 produced is easily consumed by trees and plants to generate O2. Decaying process of hydrocarbon is slow and time consuming.

Edited by S.AHMAD, 14 September 2011 - 06:51 PM.

[kkala]

The refinery I am currently attached to is still venting LPG from sphere to atmosphere. Routing LPG to flare may become a Good Practice in the future for LPG installation as part of effort to conserve environment. However, for safety issue the API 2510 as cited by Ankur will be good enough (unless API revises the Std).
For environmental reason, LPG should be burnt since CO2 produced is easily consumed by trees and plants to generate O2. Decaying process of hydrocarbon is slow and time consuming.

Thanks for the useful information, verifying that LPG gas is currently released into atmosphere or flare header depending on local practices. I wonder whether dispersion in atmosphere is promoted (e.g. by steam), since gaseous LPG is heavier than air.
I have not found evidence in WWW that Propane or Butane are green house gases (though CH4 is), but now I understand these are much less biodegradable than CO2.

Edited by kkala, 15 September 2011 - 12:39 AM.

[R NESAMANI]

Thank you for your reply.

The refinery I am currently attached to is still venting LPG from sphere to atmosphere. Routing LPG to flare may become a Good Practice in the future for LPG installation as part of effort to conserve environment. However, for safety issue the API 2510 as cited by Ankur will be good enough (unless API revises the Std).
For environmental reason, LPG should be burnt since CO2 produced is easily consumed by trees and plants to generate O2. Decaying process of hydrocarbon is slow and time consuming.

Thanks for the useful information, verifying that LPG gas is currently released into atmosphere or flare header depending on local practices. I wonder whether dispersion in atmosphere is promoted (e.g. by steam), since gaseous LPG is heavier than air.
I have not found evidence in WWW that Propane or Butane are green house gases (though CH4 is), but now I understand these are much less biodegradable than CO2.

LPG is not flared to atmoshphere, It is ignited and burnt thru hot flare system, in our plant.

[R NESAMANI]

Hi AHMED.
You said that the refinery you are currently attached to is still venting LPG from sphere to atmosphere. I am not talking abt the safety issues with venting or flaring. But here dont you feel that LPG is wasted. We should try to use this LPG back into the sphere.
Elaborate me the scenario, i will try my best to give you the solution to minimise the venting LPG.

[ankur2061]

Coming back to the topic of venting to atmosphere, as per API STD 521 (Section 6.3.2.2 - Vapour Emissions) the fundamental principle in venting to atmosphere of flammable hydrocarbon gases is that high discharge velocities are maintained from the discharge or tail pipes of relief valves. These high velocities ensure very high air-entrainment causing dilution of the hydrocarbon gas or vapor to below its Lower Explosive Limit.

As per API STD 521, studies have shown that jet velocities greater than or equal to 150 m/s (500 ft/s) have suffcient energy in the jet to cause turbulent mixing with air and effect dilution of the released gas. The equation fro dilution is given in the aforementioned section of API STD 521.

Regards,
Ankur.

Edited by ankur2061, 15 September 2011 - 01:51 AM.

[R NESAMANI]

Ankur, Thank you for your valuable post.
My doubt is how can i ensure the jet velocity > 150 m/s ?
In our plant, Vessel is connected to flare system, whenever we open the valve in blowdown line, the LPG will go to flare system exit, which is at 30 m far from the process area.

[R NESAMANI]

After some research, i could find the solution to LPG vent recovery from filters.


Purpose : LPG is being vented during the maintenance of Filters & Pumps. This has increased due to the pigging work.

How the system works:
Refer the diagram(LPG Vent recovery) attached.
Basket Filter will be connected with the downstream of PCV of RT-OMC, through compressor system. OMC line is always in pr of less than 10 kg/cm2.

1) LPG liquid recovery:

Isolate the basket filter. Close Valve-V1,V2 & V4; Open-V3. LPG will flow from filter(@ 20 kg/cm2) to HPCL pipeline (@ 10 kg/cm2).

Within 30 minutes, the filter pressure will come down to 10 kg/cm2. No further flow will occur.

2) LPG Vapor recovery:

Close Valve-V1 & V3; Open-V2 & V4.

LPG vapour(@10 kg/cm2 from top of the vessel) will flow from filter to compressor system. Reciprocating Compressor will evacuate the LPG vapour and discharge to the pipeline.

After discussion with the vendor, LPG compressor is selected, which can safely evacuated up to 2.00 Kg/cm2. Which is more than 90% of LPG is evacuated.
Beyond 2.00 kg/cm2, we can’t evacuate. So close Valve-V2 & Open valve-V1 for flaring.

Compressor system: (Refer the drawing & specs of the system)
Compressor system includes, the liquid trap to prevent the entry of liquid LPG into the compressor. Suction strainer.
4 Pole FLP motor rated for 1500 rpm, 7.5 HP
a)Low suction pressure switch qty- 1
b)High discharge pressure switch qty-1
c)High discharge temperature switch qty-1


Mail me your views & suggestions on this plan.

Regards

R Nesamani

Attached Files

•  LPG vent recovery system.pdf   37.64KB   98 downloads
•  IPS.pdf   15.3KB   56 downloads
•  Compressor specs.doc   138.5KB   56 downloads

[Vivienne]

Hi evertone! I would like to ask opinion from this group as our refinery also has still some LPG spheres venting to atmosphere. I am currently working as a Process Design Engineer. I am currently evaluating a project proposal for closed loop sampling, draining, and commissioning of LPG spheres. Would like to solicit your inputs on how I can possibly design this system? Also, may I know the closed loop sampling system from other refineries? The sampling point at our sphere is located in the lowest point. We are planning to construct our sampling point system as reflected in the attached diagram. Would appreciate receiving your comments. Mail me your suggestions on this scheme@ mfcarpio@petron.com

Edited by Vivienne, 31 January 2012 - 03:49 AM.

[kkala]

Hi evertone! I would like to ask opinion from this group as our refinery also has still some LPG spheres venting to atmosphere. I am currently working as a Process Design Engineer. I am currently evaluating a project proposal for closed loop sampling, draining, and commissioning of LPG spheres. Would like to solicit your inputs on how I can possibly design this system? Also, may I know the closed loop sampling system from other refineries? The sampling point at our sphere is located in the lowest point. We are planning to construct our sampling point system as reflected in the attached diagram. Would appreciate receiving your comments. Mail me your suggestions on this scheme@ mfcarpio@petron.com

Better to have started another topic, since few might see your post in this thread. Mentioned diagram has not been attached, probably by some failure. Can you attach it, if it is not too late? My knowledge is not sufficient to reply the query, but some other member could help.

Edited by kkala, 04 April 2012 - 11:48 AM.

[kkala]

Coming back to the topic of venting to atmosphere, as per API STD 521 (Section 6.3.2.2 - Vapour Emissions) the fundamental principle in venting to atmosphere of flammable hydrocarbon gases is that high discharge velocities are maintained from the discharge or tail pipes of relief valves. These high velocities ensure very high air-entrainment causing dilution of the hydrocarbon gas or vapor to below its Lower Explosive Limit.
As per API STD 521, studies have shown that jet velocities greater than or equal to 150 m/s (500 ft/s) have sufficient energy in the jet to cause turbulent mixing with air and effect dilution of the released gas. The equation from dilution is given in the aforementioned section of API STD 521.

Having recently the chance to read API 2510 A (2nd ed, 1996), I noted that an LPG "release will not create wide area flammable clouds at grade as long as exit velocity of the vapor is 100 feet per second or more" (para 2.10.2.2).
A bigger part of the wording in API 2510 A can be found at http://www.cheresou...ief-scenarios/ , para 5.5. Besides the discharge stack should be vertical, supported independently of the relief valve, be in accordance with API 2510 (5.1.6.5) and API RP 521. Vapor release has to be diluted below its low flammability limit while still in the jet momentum release plume.
Not having access to either API RP 521 or API 2510, I wonder what is the acceptable LPG exit velocity to atmosphere (per API): 100 ft/s or 500 ft/s ? On the other hand API 521 may mean something else. The two cases (of 100 and 500 ft/s) are likely not to have the same level of risk.
Clarifications / interpretation would be appreciated.

Edited by kkala, 12 April 2012 - 04:26 PM.

[kkala]

Kindly note that post No 21 has been without a response for three months, while the subject is judged important. LPG velocity to atmosphere should be 100 ft/s or 500 ft/s as a minimum? Hopefully this reminder, referring to previous post, will be a chance for an answer. Someone having approach to latest edition of API 2510?