36 replies to this topic

[Dacs]

I don't see how you can have a bottoms temperature significantly higher than the temperature of the feed(s), there is no heat input to the system besides the feeds. So the assumption of a saturated liquid at relief pressure is only possible if the composition changes (more lights).

Well, you do still maintain the steam flow to the column, which will introduce heat to the system.

[invssse]

As you mentioned, you think unbalanced heat load method is not appropriate for steam stripper tower, then what method would you apply for this kind of tower to determine the relief load? thanks.

Your system is more complicated and has a bit more going on (two flashing feeds at different locations) so i would not exclude the manual heat balance method.

I think it's going to be very difficult to reproduce the liconsor's data without knowing what method they used and what their input was (flow rates, upstream pressures, mass balance case, etc., etc.). Might be easier to ask them for a detailed calculation.

I don't see how you can have a bottoms temperature significantly higher than the temperature of the feed(s), there is no heat input to the system besides the feeds. So the assumption of a saturated liquid at relief pressure is only possible if the composition changes (more lights).

I think it's going to be very difficult to reproduce the liconsor's data without knowing what method they used and what their input was (flow rates, upstream pressures, mass balance case, etc., etc.). Might be easier to ask them for a detailed calculation

That's right. will ask licensor for the details.

I don't see how you can have a bottoms temperature significantly higher than the temperature of the feed(s), there is no heat input to the system besides the feeds. So the assumption of a saturated liquid at relief pressure is only possible if the composition changes (more lights).
this is a steam stripper. in normal conditions the bottom liquid is saturated at normal pressure. According to the basic assumptions of Unbalanced Heat Load Method, the bottom liquid will become saturated at relieving pressure. So, in this specific case, the BOTTOM stream is flashed to bubble point at relieving pressure(1.43MPAG). This causes its temperature is much more higher than expected. I cannot understand what "So the assumption of a saturated liquid at relief pressure is only possible if the composition changes (more lights)" means. Can you explain more on this?

[CMA010]

I don't see how you can have a bottoms temperature significantly higher than the temperature of the feed(s), there is no heat input to the system besides the feeds. So the assumption of a saturated liquid at relief pressure is only possible if the composition changes (more lights).

Well, you do still maintain the steam flow to the column, which will introduce heat to the system.

The steam flow is not a source of heat in this case.

[CMA010]

As you mentioned, you think unbalanced heat load method is not appropriate for steam stripper tower, then what method would you apply for this kind of tower to determine the relief load? thanks.

Your system is more complicated and has a bit more going on (two flashing feeds at different locations) so i would not exclude the manual heat balance method.

I think it's going to be very difficult to reproduce the liconsor's data without knowing what method they used and what their input was (flow rates, upstream pressures, mass balance case, etc., etc.). Might be easier to ask them for a detailed calculation.

I don't see how you can have a bottoms temperature significantly higher than the temperature of the feed(s), there is no heat input to the system besides the feeds. So the assumption of a saturated liquid at relief pressure is only possible if the composition changes (more lights).

I think it's going to be very difficult to reproduce the liconsor's data without knowing what method they used and what their input was (flow rates, upstream pressures, mass balance case, etc., etc.). Might be easier to ask them for a detailed calculation

That's right. will ask licensor for the details.

I don't see how you can have a bottoms temperature significantly higher than the temperature of the feed(s), there is no heat input to the system besides the feeds. So the assumption of a saturated liquid at relief pressure is only possible if the composition changes (more lights).
this is a steam stripper. in normal conditions the bottom liquid is saturated at normal pressure. According to the basic assumptions of Unbalanced Heat Load Method, the bottom liquid will become saturated at relieving pressure. So, in this specific case, the BOTTOM stream is flashed to bubble point at relieving pressure(1.43MPAG). This causes its temperature is much more higher than expected. I cannot understand what "So the assumption of a saturated liquid at relief pressure is only possible if the composition changes (more lights)" means. Can you explain more on this?

Assuming composition of the feeds and products as per normal operation gives in your case a bubble point of the bottoms product at relief conditions higher than the temperature of the feeds (feed1, feed2 and steam). As there is no other source of heat like a reboiler this is not possible. Therefore the only way the bottoms product can leave the tower at bubble point during a relief scenario is when the assumption of composition of the products as per normal operation is not valid: The bottoms product will contain more light components (resulting in a lower bubble point).

Otherwise it is only possible when the temperature of the feeds increaeses. For example when the pressure and temperature in the upstream separators increases during the relief scenario (e.g. in case there is a compressor downstream of the separators which stops functioning as a result of the power failure) and the feeds enter the tower at a higher temperature.

[Bobby Strain]

You never indicated whether the licensors relief was vapor or liquid.

Bobby

[invssse]

You never indicated whether the licensors relief was vapor or liquid.

Bobby

The relief is VAPOR, thanks.

[Dacs]

I don't see how you can have a bottoms temperature significantly higher than the temperature of the feed(s), there is no heat input to the system besides the feeds. So the assumption of a saturated liquid at relief pressure is only possible if the composition changes (more lights).

Well, you do still maintain the steam flow to the column, which will introduce heat to the system.

The steam flow is not a source of heat in this case.

It will go inside the column and this steam will still strip with the liquid from the feed and think this is also plausible even during relief scenario.

[CMA010]

I don't see how you can have a bottoms temperature significantly higher than the temperature of the feed(s), there is no heat input to the system besides the feeds. So the assumption of a saturated liquid at relief pressure is only possible if the composition changes (more lights).

Well, you do still maintain the steam flow to the column, which will introduce heat to the system.

The steam flow is not a source of heat in this case.

It will go inside the column and this steam will still strip with the liquid from the feed and think this is also plausible even during relief scenario.

The required heat of vapourisation for the stripping comes from the feeds: normal operating temperature of feed1 is 207 °C and of feed 2 291 °C, normal bottoms temperature is 266 °C and temperature of the steam feed is 227 °C.

Unless the temperatures of the feeds do not change the bottoms temperature of 321 °C at relief conditions is not possible.

[invssse]

The required heat of vapourisation for the stripping comes from the feeds: normal operating temperature of feed1 is 207 °C and of feed 2 291 °C, normal bottoms temperature is 266 °C and temperature of the steam feed is 227 °C.

Unless the temperatures of the feeds do not change the bottoms temperature of 321 °C at relief conditions is not possible.

I agree on this.
So for strippers, it's improper to calculate heat imbalance based on bottom stream at bubble point under relieving pressure. But the problem is that it is still not clear how to estimate bottom stream's enthalpy at relieving condition.

[CMA010]

The required heat of vapourisation for the stripping comes from the feeds: normal operating temperature of feed1 is 207 °C and of feed 2 291 °C, normal bottoms temperature is 266 °C and temperature of the steam feed is 227 °C.

Unless the temperatures of the feeds do not change the bottoms temperature of 321 °C at relief conditions is not possible.

I agree on this.
So for strippers, it's improper to calculate heat imbalance based on bottom stream at bubble point under relieving pressure. But the problem is that it is still not clear how to estimate bottom stream's enthalpy at relieving condition.

Simulation of your system at relief pressure will be the easiest option i guess.

[invssse]

The required heat of vapourisation for the stripping comes from the feeds: normal operating temperature of feed1 is 207 °C and of feed 2 291 °C, normal bottoms temperature is 266 °C and temperature of the steam feed is 227 °C.

Unless the temperatures of the feeds do not change the bottoms temperature of 321 °C at relief conditions is not possible.

I agree on this.
So for strippers, it's improper to calculate heat imbalance based on bottom stream at bubble point under relieving pressure. But the problem is that it is still not clear how to estimate bottom stream's enthalpy at relieving condition.

Simulation of your system at relief pressure will be the easiest option i guess.

Do you mean this tower is simulated at system pressure = relieving pressure to get the specific enthalpy of the BOTTOM stream?

[CMA010]

The required heat of vapourisation for the stripping comes from the feeds: normal operating temperature of feed1 is 207 °C and of feed 2 291 °C, normal bottoms temperature is 266 °C and temperature of the steam feed is 227 °C.

Unless the temperatures of the feeds do not change the bottoms temperature of 321 °C at relief conditions is not possible.

I agree on this.
So for strippers, it's improper to calculate heat imbalance based on bottom stream at bubble point under relieving pressure. But the problem is that it is still not clear how to estimate bottom stream's enthalpy at relieving condition.

Simulation of your system at relief pressure will be the easiest option i guess.

Do you mean this tower is simulated at system pressure = relieving pressure to get the specific enthalpy of the BOTTOM stream?

Yes, that's how I would approach it. But i thought you have already done a dynamic simulation, so you can use that value. You can also compare the results from the unbalanced heat calaculation with your dynamic simulation.