6 replies to this topic

[process12]

Dear All

Propane/Butane products shall be cooled down in the Propane/Butane Refrigeration Unit and then will be sent to the tanks and stored at atmospheric pressure for export.

My question is about method of Refrigeration; as I know there are 2 methods open loop and closed loop.

Would you please help me about difference of these methods?

tanx

[Art Montemayor]

Process:

We've done a lot of threads on propane/butane refrigeration. What, exactly do you mean by "open" and "closed" loops. Please be specific and explain how you intend to refrigerate - using the C3-C4 fluids themselves, or other fluids?

A schematic diagram of your process, together with capacities, temperatures, pressures, etc. would be essential basic data.

[process12]

Many tanx
Please find below a short description:

C₄ will be cooled by C₃ (coolant) via tow chillers (kettle type), but for cooling of propane there are two ways:

• Closed loop: c₃ is coming from upstream unit and then will be cooled via 3 kettle type chillers in difference pressure and temperature. Coolant fluid in this method is separated propane loop. This coolant propane will be vaporized so will be sent to refrigeration unit (compressor, after cooler, condenser, and separator) for resending to the coolant loop.
• Open Loop: In this method there is no separated loop for coolant in the other hands instead of 3 chillers there are 3 suction drums in different pressure and temperature: part of coming propane will be change to the vapor and the others will be sent to the next suction drum. Gathered vapor will be come back to the cycle through the compressor, after cooler, condenser, and separator

Design condition can be as follow:


Fluid
Propane
Butane
Flow rate
23 Ton/h
77 Ton/h
Pressure
17 barg
6 barg
Temperature
40 °C
40 °C

[Art Montemayor]

Process12:

It is very difficult to understand your last post. Please heed what I requested in my last post: A schematic diagram of your process, together with capacities, temperatures, pressures, etc. would be essential basic data.

It would be extremely expedient if you used a spreadsheet to supply your information - including the flow schematic drawing. That way, you can tabulate your information and we can understand it.

Thank you.

[Robert Montoya]

Dear Process12;

Please don´t think more, choose loop closed, the different between loop closed and open, is that the loop closed offers more control in the compressor system and cooling temperature and products, the internal re-circulation of the refrigerant in the compressor system provide a better control in the outlet temperature of the products (C3-C4) for any disturbance in the system and thus prevent the compressor system is out of service due to low suction flow, etc.

Edited by Art Montemayor, 22 April 2012 - 11:48 AM.

[process12]

Dear All
Please find attached a schematic diagram for refrigeration system. Please be noted that these drawings are estimated and completed. I need criteria / design guideline / references to choose one system. Which factors are important to select one of them: capacity , efficiency ,...
Many tanx






 C3&C4refrigeration.pdf   121.54KB   146 downloads

[Robert Montoya]

Process 12; This is my point of view regarding two system:
Power requirements: The main consumer of energy in the cooling system is the refrigeration compressor while the condenser coolant input will have almost the same energy requirement in both systems (open and closed loop), the main point of comparison to the energy consumption is represented by the compressor power in both systems. The refrigeration system of closed cycle requires less power compared to compression open loop system. Energy savings can be more than 1MW per train compression when using the closed cycle cooling. Higher content of ethane caused by rapid vaporization and increasing the condensing pressure in the open system cooling may explain the difference in power of compression between the two systems.

Efficiency of the process: closed refrigeration will work with efficiency higher than the open system, for which the closed system gets more cooling per unit of energy consumption.
Ease of operation: It was determined that the open method of cooling is less tolerant to the possible presence of ethane and lighter contaminants in the feed of NGL. The ethane is accumulated during the stages of expansion to reach very high concentrations (17% molar in some cases) in the steam inlet of the last compression stage, therefore increases the pressure of condensation. This fact significantly increases the total power required in the compression cycle.
The light contaminants in the NGL feed needs to be continuously purged when selecting the open loop system.
The closed loop system is more complex but that the open loop by using additional coolers. However, the closed refrigeration system works independently without being affected by operational problems or disruptions that may occur upstream.
Reliability
In the closed cooling system, propane refrigerant composition is not affected by any disturbance that might occur upstream. Thus, the refrigeration cycle should function independently. Also, the composition of the propane product does not change during the cycle.

Open system with respect to cooling, propane refrigerant composition will be affected by any disturbance that might occur upstream, in this way, the refrigeration cycle does not operate independently. Additionally, propane product composition is slightly modified during the cycle due to successive sprays. This discussion reflects the benefits of independence and availability of closed-loop system in comparison to the open loop system.

In general, the refrigeration system closed loop is not affected by the quality of the product fractionation propane or by the same amount as it is a closed cycle with propane storage system refrigerant. Therefore, the closed loop system has much greater availability and reliability

Finally, it is obvious that the closed loop system provides increased major investment, because the number of equipment is higher, but costs are lower operational as discussed above.
Is recommended to make a selection matrix factors including: initial investment, operating costs, reliability, operability and efficiency of the process. In the end everything will depend on customer requirements.
Regards.