15 replies to this topic

[fallah]

Dear All,
If it is decided to vapourize the LPG(most Propane), intermittently would be accumulated in a horizontal K.O. Drum, by directly heating with submerged electrical heater,and conduct the vapours to flare or ...,may we would face with any problem(s)?
Regards

[Art Montemayor]

Fallah:

Vaporizing with an electrical element is no different than doing the same with other energy sources - such as steam, oil, etc.

HOWEVER, there is one outstanding big difference in control: the electrical element has no "brake" or inherent limit to its energy contribution and should the effective transfer of heat between the element and the fluid (LPG, in this case) be affected or negated by fouling, loss of fluid, etc., then the element will exponentially start to heat up - unless mitigated by efficient instrumentation - such as an imbedded thermocouple in the heating element.

The above is the outstanding weakness in an electrical element application - besides the energy cost. Your application inevitably will involve fouling products since there will be a differential density increase in the residuals produced in the vaporization process. This is inevitable in this application - and this increasing density/viscosity/sludge composition is the main culprit that contributes to a differentially increasing temperature at the element's wall. Heat transfer becomes increasingly more difficult with time. Continuous, intermittant purging or drainage of bottoms product is very important in these applications to ensure that the heat transfer is kept at an efficient level. Without efficient heat transfer you run the risk of actually FUSING the electrical element. Believe me that this can happen. It has happened to me on numerous occasions. And this is what you primarily want to avoid.

I always approach electrical element applications in vaporizers with a lot of caution and a very strict and detailed process design - especially on the instrumentation controls as to type and specific hardware installed.

I hope this experience helps.

[fallah]

Without efficient heat transfer you run the risk of actually FUSING the electrical element. Believe me that this can happen. It has happened to me on numerous occasions. And this is what you primarily want to avoid.
I hope this experience helps.[/font][/size]

Dear Art,
Thanks a lot for your valuable explanations,but please explain in detail about one of actually FUSING the electrical element happened to you (specially for Propane),if it is possible.
Indeed,if you were in my situation,what was your decision about selecting one of two following options:
1-Emptying the K.O. Drum, containing Propane, by pump routed to closed drain network.
2-Heating the Propane bulk by electrical heater and conducting generated gas to flare header.
Please note we have some problems in case 1 providing NPSHR for pumps,and if we will select first case we have to install the pump in a deep (5 meters) pit accompanying problems for routing the vent and drain lines of pump casing.
Your prompt reply would be highly appreciated.
Regards

[Art Montemayor]

Fallah:

I have had electrical heating elements fuse in vaporizer applications – primarily in vaporizing liquid Carbon Dioxide at -20 oF. I have also had elements fuse in gas heater applications where I was heating air from ambient to 400 oF and also in heating Nitrogen gas to 550 oF. All these electrical heater elements were Chromolox brand. The brand name has nothing whatsoever to do with the failures. The reason the elements failed and fused was all due to operations failures. I regard Chromolox as one of the best in the business – if not the best manufacturer.

My main point in this application is not the manufacturing quality of the elements. It has all to do with the application and the degree of detailed engineering that is applied. One must take into consideration that the only practical way to avert a total element failure due to over-heating (and destroying itself) is to apply the best over-temperature alarms and trips. And one must religiously always check these out to make sure they are operating properly.

I don’t know enough about your present application to make a hard, knowledgeable recommendation. I don’t know what your NPSHa limitations are and what your NPSHr is. I have pumped liquid LPG with no more than a foot of static height for NPSHa. To do that, I employed gear pumps – both internal and external gear designs.

If it were my choice – based on what I know (which is little) – I would select the pumping of the LPG out of the flare scrubber and to a safe disposal area. This is quicker and (in my opinion) much safer and more reliable. It requires less reliance on all instrumentation working 100% efficient at the precise moment it is needed.

That is my conjecture, based on what little I know of your operation.

[fallah]

I don’t know what your NPSHa limitations are and what your NPSHr is. I have pumped liquid LPG with no more than a foot of static height for NPSHa. To do that, I employed gear pumps – both internal and external gear designs.

Dear Art,
Actually, i do'nt know how i can appreciate from your complete and fast reply.
Anyway,our NPSHa limitations is related to type of pump being selected (centrifugal).Our available static head is max. 4 feet.If you propose gear pump for this conditions,please let me know the reliable brand(s) for using in mentioned situation.Finally i would like to know difference between
internal and external gear designs.
Regards

[Art Montemayor]

Fallah:

Go to:

http://vikingpump.com/en/index.html

and you will find a large amount of useful information on positive displacement pumps - primarily rotary gear pumps.

Here you will find a clear and simple explanation about the differences between internal and external gear pumps.

External gear (spur type) pumps have very low clearances and can pump up to 3,000 psig, easily. Internal gear types (like the famous viking pump) go up to 300-500 psig but can handle very viscous and every dirty fluids. I have used the external gear with a vertical lift of hydraulic oil from a sump (actually a negative NPSHa), but I wouldn't recommend this unless I knew a lot more details. In fact, this application is quite standard in most large hydraulic presses that use the spur gear to pump with a negative lift from a hydraulic oil sump in order to quickly fill the hydraulic cylinders on the presses. A coupled, high-pressure piston or other type of pump kicks the oil pressure to 5,000+ psig.

When using positive displacement pumps of this type, the fluid can be viscous; but it must be clean of abrasives or solids in order to maintain the close clearances. In your application, I believe you can fulfill both requirements with good pre-commissioning and cleanliness.

[fallah]

Again thanks,finally i would like to know ECONOMICAL comparison between mentioned pumps and centrifugal one using in my application.
Regards

[Art Montemayor]

Fallah:

It is very difficult to generalize a price comparison between two diffent type of pumps when we don't know all the details and particulars about the application.

We could have seal, alloy, motor, coupling, TDH, capacity, etc. all - or some - of which could call for either an expensive pump or a low-cost pump. It all depends on what only you know about the application.

The best way to make a general decision on pricing is to obtain equipment estimates for each of the types of pumps you are interested in comparing. Sometimes you can quickly reduce the comparison to a practical one: if you require very large pump flow rates at a low TDH, then the centrifugal type is a no-brainer decision. But bear in mind that you inherit some trade-offs with any decision that you make.

[fallah]

When using positive displacement pumps of this type, the fluid can be viscous; but it must be clean of abrasives or solids in order to maintain the close clearances. In your application, I believe you can fulfill both requirements with good pre-commissioning and cleanliness.[/font][/size]

Dear Art,

Excuse me for extending this topic.I have two questions:

1-If viscosity of the fluid (here Propane) would be as low as 0.2 cp, may using PD pump (here Gear pump) accompanying with some problems such as low efficiency operation,...?

2-What is your mean about "both requirement" in above?

Best Regards

[Art Montemayor]

Fallah:

For many decades, positive displacement pumps - primarily rotary gear pumps - were used in the process of transferring LPG between storage tanks, delivery tank-trucks, user storage, and other processes. The industry was developed here in the USA and was operated that way during the 1930's, the '40s and well into the '50s and '60s. Their use in LPG, Liquid Propane, Butane, and higher hydrocarbons is nothing new. I don't understand the degree of your concern or doubt.

Let us put your asserted application into a proper engineering perspective:

• You want the ability to quickly and safely dispose of LPG caught in a flare scrubber vessel;
• The operation is intermittant - only when a potential flare excursion occurs; it is NOT a continuous, operating condition.
• You want simplicity and dependability because (as is typical of all flare equipment) the operation is in a remote location and not frequented often by operating personnel. Simplicity and dependability aid in ensuring the operability of the operation since visual and maintenance attention is not that frequent.

Therefore, I directly ask you: What is the concern with "efficiency" here? Are you insuating that the selected method that brings about all your targeted intentions is subject to an efficiency review? Is efficiency going to take precedence over speed of disposal and safety of the operation? Please be kind enought to explain your thoughts on this subject.

The word "both" as used in my previous post was a typo. I intended to write:
"When using positive displacement pumps of this type, the fluid can be viscous; but it must be clean of abrasives and free of solids in order to maintain the close clearances. In your application, I believe you can fulfill both requirements with good pre-commissioning and cleanliness."

I am sorry for the bad communications on my part.

[fallah]

Thanks a lot for your clear logic caused i am to be satisfied. Indeed,"efficiency" is not my concern in my said application, and i mentioned this issue only as a general question not related to my main concern, but to know the effect of low viscosity on gear pumps performance.

Regards

[Qalander (Chem)]

Thanks Dears(fallah /Art.)

Your discussion has generated useful info on use of PD (espeally gear type/rotary) pumps in LPG or Flare related liquids pump-out.

regards
Qalander

[Technocrat]

Dear All,

I think we are going away from the original question of Fallah.

Fallah, please give us complete details of the system first. What are the utilities available in your plant, please also give us a brief on the process.

[fallah]

Dear All,

I think we are going away from the original question of Fallah.

Fallah, please give us complete details of the system first. What are the utilities available in your plant, please also give us a brief on the process.

You can read the post#3 for getting you required information.Indeed,the K.O. Drum receives the relieves from some BDVs in LPG production plant,and its HH level could be leading to plant shutdown due to overfilling to flare system.I think this information would be enough for submitting your comment(s) on my original question,but if you need another ones inform me.

[Technocrat]

Can you please tell me why don't you use LP steam for vaporization? What are the conditions of steam available in your plant?

[fallah]

Can you please tell me why don't you use LP steam for vaporization? What are the conditions of steam available in your plant?

Operating temperature -28 C,potential for steam condensate freezing.......