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Design of Crude Unit Desalters

Design of Crude Unit Desalters

Design of Crude Unit Desalters

(OP)

Hello, Guys...

Well, I am trying to prepare process design of desalters for 25 API Crude Mix.Apart of stokes law ,is there any refrence books/material/magazines/E-material which can help me to prepare design as well as which can help me to check the performance of existing desalters in terms of salts,asphaltene,efficiency etc.

Thanks in advance..

RE: Design of Crude Unit Desalters

Why not contact the designers and manufacturers of desalters for your requirements. They do this for a living and can surely make your job a lot easier. Try Petreco for a starter.

Orenda

RE: Design of Crude Unit Desalters


Just by doing a Google search on crude oil desalting you'll find a plethora of information.

RE: Design of Crude Unit Desalters

(OP)
Hello...actually, our desalters are designed for 25.5 API Crude mix.but even with 27 API Crude mix processing (of course crude is the mix of 8-10 crudes belnds depening on Economics,yield pattern etc..) we are not getting desired efficeincy specified by vendors in terms of salts and BS&W.How to face such issues...? we have analyzed calcium napthenates,na napthenates,asphaltenes,pH etc....still..there is some mistry it seems .....Can you pl. help me out...

RE: Design of Crude Unit Desalters

It sounds as though you need a specific demulsifier(s) to accomodate the napthenates, etc. in the crude blends you are running. If the desalter vendor can't help with this, I suggest you contact such companies as Baker-Hughes, Nalco, GE Betz, to name a few, who have a great deal of expertise in selecting the appropriate demulsifiers, pH control and wash water parameters....the technology to optimize desalter operations is very mature and easily tailored to each case.

Orenda

RE: Design of Crude Unit Desalters

Petro0707,

" our desalters are designed for 25.5 API Crude mix.but even with 27 API Crude mix processing (of course crude is the mix of 8-10 crudes belnds depening on Economics,yield pattern etc..) we are not getting desired efficeincy specified by vendors in terms of salts and BS&W.How to face such issues...? we have analyzed calcium napthenates,na napthenates,asphaltenes,pH etc....still..there is some mistry it seems .....Can you pl. help me out..."

I believe you have more than one desalter running.What is the configuration? Parallel or in series? What is the temperature at each desalter? What is the amount of wash water used for the operation?What is the salt content of your crude?Is it the same as the desalter originally designed for? Need more details to evaluate the situation.
Please provide as much details as you can.

Yours
Prochem

RE: Design of Crude Unit Desalters

(OP)
Dear Prochem,

We have two Desalters in series originally (Old series 1 & 2) having design of 30 API Crude mix with 570 KBPSD Crude T’put but than it was derated to 125 KBPSD with 25.7 API Crudemix T’Put.Along with that we have installed two more new desalters designed for 25.7 API with 250 KBPSD T’Put.Total there are four desalters, As shown below, Old series -1, New series -1, Newseries -2 are operated with 142-147 C and Old series -2 is operated with slightly lower temperature i.e. 135 -138 C.

     |----->Old series desalter-1---->Old series des.-2--
---->|
     |---> NEW Series desalter -1---->New series des.-2--

*After Final crudestream is clubed and sent to furthure heating.

Currenlty we are processing on an average 27.7 API Crudemix with around 30 PTB salts with 0.19 wt % BS&W with around 55 % filtratable solids  and we are getting only on an average 97.8 % desalting efficiency against targeted 99 wt % & dehydrated efficiency around 92 %.Our wash water rate is 7 % on crude.we are also adding demulsifier agent @ 7ppm concern. To breake the emulsion in the desalters.

New series deslaters are designed for 48 PTB Salts in the inlet & Old series desalters are designed for 60 PTB salts in the inlet. In the outlet we are getting 0.6 to 0.7 PTB salts.
Currently

How to improve desalting efficiency? Our current  limitation for 27.7 API Crude mix processing for desalters is 390 KBPSD for new desalters & 130 KBPSD for Old desalters,beyond that its performance gets still more detoriated.

RE: Design of Crude Unit Desalters

(OP)
Regret for inconvinience -typographical mistake.Currently New desalters is limiting with 195 KBPSD (instead above mentioned 390 KBPSD).

Thanks in advance for one and all of you...!!!

RE: Design of Crude Unit Desalters

It seems to me that your desalter throughput is a limiting function of the crude blends being run. It also appears that at the current throughput, desalting efficiency is at least very good, if not excellent....<1.0 PTB salt, <<0.1% water.

I really believe, as earlier stated, that you need the direct assistance of the desalter manufacturer(s) to sort out the options for increased throughput to design levels at reasonable desalting efficiency for the crudes being processed.

Orenda

RE: Design of Crude Unit Desalters

(OP)
Dear Orenda,

Basically,it is designed for 25.7 API Crudemix  with 99 % desalting efficiency,so ,it should get 99 % efficiency while processing 27.7 API Crudemix,while we are getting only 98 % desaling efficiency.

So,efficiency is also a critical issue.

RE: Design of Crude Unit Desalters

Not necessarily! The crude mix is altogether important in establishing the desalting efficiency....in other terms, a percent efficiency will not apply in every case of crude blends, depending on the particular composition of the blend including impurities therin.

Further, from your earlier data and my comments about what I consider to be excellent desalting efficiency, I think you are trying to obtain the "difficult if not impossible" last percentage point of efficiency. Forgetting about the derating of desalter throughput which you MUST deal with through the desalter vendors, what is the pay back for attaining the added 1% desalting efficiency?.....very little, I suspect.

Orenda

RE: Design of Crude Unit Desalters

(OP)
Thanks 0707,these are useful articles but yes,we have already gone with static mixture along with mixing valve still efficiency is not as specified/claimed.We are having conventional desalters i.e.2 grid AC supply,NATCO's technology is good,but how much is it reliable in terms of plastic electrode / detaching phenomenon of electrodes during operations are still needs to be addressed / any experience about it interms of reliability is really a issue.

RE: Design of Crude Unit Desalters

Our dessalters are Petreco type. Basically our dessalters efficiency varies between 90% and 99% it depends on crude mix density, water and salts content. For a good dessalters operation it’s important a good water mixing.

Factors to take into account on dessalters operations are:

Good cleaning condition of carbon steel electrode grids

Good parallelism between carbon steel electrode grids

No distortion of carbon steel electrode grids (in our case it is important to maintain a distance of 150mm between them).

Good condition of silica gel and oil of transformers.

The extremities of Teflon grid isolators should be free of carbon and should not show any kind of cracks.

On bottom of our dessalters to minimize under deposit corrosion we installed a water collector with multidirectional spray nozzle water injection to avoid mud stagnation.

It is also important to have the various purge levels unplugged to check correctly water phases

Heavy crude such as Maya is very difficult to dessalificate.

Regards

Luis Marques

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