5 replies to this topic

[go-fish]

Hello,

I am looking for some operations information from someone who is working/ worked in a refinery. I am designing the dewatering system for crude oil tanks.

1. After the crude oil shipment is being transferred to a storage tank, generally for how much time is the shipment allowed to stand in a tank for gravity separation of water and oil?

2. Is the water settled at the bottom distinct from the crude except some emulsion phase near the oil-water interface?

3. My understanding is that dewatering is done only once after receiving the shipment when the tank is almost full. And once the shipment is dewatered, the stored crude oil is ready as feedstock. Can dewatering be also required in the same shipment after we start sending it to crude distillation unit? If yes, how often can this happen?

4. How do you address H2S exposure hazard during dewatering? Is the dewatering system designed as closed nowadays instead of as an open system going to oily water sewer?

[Skyline]

Hello,

I am looking for some operations information from someone who is working/ worked in a refinery. I am designing the dewatering system for crude oil tanks.

1. After the crude oil shipment is being transferred to a storage tank, generally for how much time is the shipment allowed to stand in a tank for gravity separation of water and oil?

2. Is the water settled at the bottom distinct from the crude except some emulsion phase near the oil-water interface?

3. My understanding is that dewatering is done only once after receiving the shipment when the tank is almost full. And once the shipment is dewatered, the stored crude oil is ready as feedstock. Can dewatering be also required in the same shipment after we start sending it to crude distillation unit? If yes, how often can this happen?

4. How do you address H2S exposure hazard during dewatering? Is the dewatering system designed as closed nowadays instead of as an open system going to oily water sewer?

1. From my experience, we settle the crude in storage tank for 12 hours.

2. Yes, you're correct

3. From my experience, we can monitor the level of water from control room. After first draining (12 hours after being loaded to the tank), we can drain it again before transferred to CDU. The reason behind this is the possibility of water leak into the storage tank from the roof through the seal and any other source.

4. We use the open system, and transfer it to a water sewer.


Hope it helps.

[go-fish]

Hello,

I am looking for some operations information from someone who is working/ worked in a refinery. I am designing the dewatering system for crude oil tanks.

1. After the crude oil shipment is being transferred to a storage tank, generally for how much time is the shipment allowed to stand in a tank for gravity separation of water and oil?

2. Is the water settled at the bottom distinct from the crude except some emulsion phase near the oil-water interface?

3. My understanding is that dewatering is done only once after receiving the shipment when the tank is almost full. And once the shipment is dewatered, the stored crude oil is ready as feedstock. Can dewatering be also required in the same shipment after we start sending it to crude distillation unit? If yes, how often can this happen?

4. How do you address H2S exposure hazard during dewatering? Is the dewatering system designed as closed nowadays instead of as an open system going to oily water sewer?

1. From my experience, we settle the crude in storage tank for 12 hours.

2. Yes, you're correct

3. From my experience, we can monitor the level of water from control room. After first draining (12 hours after being loaded to the tank), we can drain it again before transferred to CDU. The reason behind this is the possibility of water leak into the storage tank from the roof through the seal and any other source.

4. We use the open system, and transfer it to a water sewer.


Hope it helps.

Thank you for your reply. Do you remember, how big were the crude oil tanks? We have 500,000 bbl tanks. Is 12 hours good enough for my case? Also, I am assuming water content as upto 1% for design purpose. Is it a good assumption?

[Skyline]

Hello,

I am looking for some operations information from someone who is working/ worked in a refinery. I am designing the dewatering system for crude oil tanks.

1. After the crude oil shipment is being transferred to a storage tank, generally for how much time is the shipment allowed to stand in a tank for gravity separation of water and oil?

2. Is the water settled at the bottom distinct from the crude except some emulsion phase near the oil-water interface?

3. My understanding is that dewatering is done only once after receiving the shipment when the tank is almost full. And once the shipment is dewatered, the stored crude oil is ready as feedstock. Can dewatering be also required in the same shipment after we start sending it to crude distillation unit? If yes, how often can this happen?

4. How do you address H2S exposure hazard during dewatering? Is the dewatering system designed as closed nowadays instead of as an open system going to oily water sewer?

1. From my experience, we settle the crude in storage tank for 12 hours.

2. Yes, you're correct

3. From my experience, we can monitor the level of water from control room. After first draining (12 hours after being loaded to the tank), we can drain it again before transferred to CDU. The reason behind this is the possibility of water leak into the storage tank from the roof through the seal and any other source.

4. We use the open system, and transfer it to a water sewer.


Hope it helps.

Thank you for your reply. Do you remember, how big were the crude oil tanks? We have 500,000 bbl tanks. Is 12 hours good enough for my case? Also, I am assuming water content as upto 1% for design purpose. Is it a good assumption?

Each tanks has a capacity of 800 thousand barrels oil. I you can't judge the settling time needed just by looking at the tank size. You have to consider the temperature, composition of the crude, etc. For your assumption on water content, i think you'll need the crude assay analysis (the certificate) to confirm your assumption. There'll be an analysis of water content you can use as a basis for your design. Hope it helps.

[Qalander (Chem)]

Hello,

I am looking for some operations information from someone who is working/ worked in a refinery. I am designing the dewatering system for crude oil tanks.

1. After the crude oil shipment is being transferred to a storage tank, generally for how much time is the shipment allowed to stand in a tank for gravity separation of water and oil?

2. Is the water settled at the bottom distinct from the crude except some emulsion phase near the oil-water interface?

3. My understanding is that dewatering is done only once after receiving the shipment when the tank is almost full. And once the shipment is dewatered, the stored crude oil is ready as feedstock. Can dewatering be also required in the same shipment after we start sending it to crude distillation unit? If yes, how often can this happen?

4. How do you address H2S exposure hazard during dewatering? Is the dewatering system designed as closed nowadays instead of as an open system going to oily water sewer?

1. From my experience, we settle the crude in storage tank for 12 hours.

2. Yes, you're correct

3. From my experience, we can monitor the level of water from control room. After first draining (12 hours after being loaded to the tank), we can drain it again before transferred to CDU. The reason behind this is the possibility of water leak into the storage tank from the roof through the seal and any other source.

4. We use the open system, and transfer it to a water sewer.


Hope it helps.

Thank you for your reply. Do you remember, how big were the crude oil tanks? We have 500,000 bbl tanks. Is 12 hours good enough for my case? Also, I am assuming water content as upto 1% for design purpose. Is it a good assumption?

Each tanks has a capacity of 800 thousand barrels oil. I you can't judge the settling time needed just by looking at the tank size. You have to consider the temperature, composition of the crude, etc. For your assumption on water content, i think you'll need the crude assay analysis (the certificate) to confirm your assumption. There'll be an analysis of water content you can use as a basis for your design. Hope it helps.

Dear go-fish Hello/Good Afternoon, Sorry for the delayed entering into this discussion. I presume that your under discussion Crude Storage tanks should be having more than one& Most probably four water draw-off sumps being a large diameter tank.
Accordingly

• water drain-out activity has to be done from each of these sides gradually under strict physical vigilance.
• This might be started after four to six hours of settling time and
• repeated on each on each of the provided draining arrangement
• preferably to have no water apparently coming out from the drains.
• this may "at-times" require even 24 hours operation
• depending upon the Crude Oil's water contents,crude oil pour point/viscosity ambient(storage) temperature etc.

Hope this proves somewhat helpful and guiding indeed.

[herrani]

Hi all

I am not sure if you have the information you were after, skyline, but here is my experience in this matter:

I have seen in some crude oil terminals that water can start being drained from the crude oil tanks even after only 2 hours of settling time. The total settling time, depends on many parameters but it could take a long time (24 hrs). In jet fuel tanks (in all airports and some refineries), a minimum of 24 hours of settling time is required before the tank can be cleared for use/export.

If you want to have a feeling for the required settling time you can use the stoke's settling velocity for one dropplet. This depends on the water dropplet size, density of oil and water, viscosity of crude oil and the tank diameter. The total tank volume is not so important in this case.

I am assuming that you are receiving crude oil from crude oil ships, and not from a pipeline directly from the production wells. In the second case, I have seen some problems related to the water dropplet size distribution. Centrifugal pumps and similar equipment can create very fine dropplets that are impossible to separate. Crude oil/water emulsions is another problem you want to avoid.

I hope this is relevant!

Edited by herrani, 01 June 2010 - 01:41 AM.