From the context of your question, it's not clear if you want to know about pressure control systems for towers operating under vacuum or about how to select between different vacuum generating devices. Since the pressure control system configuration depends upon the type of vacuum selected, we'll discuss the question of selection of the device type.
For commercial systems, the major types of vacuum devices are ejectors, liquid-ring pumps, and dry pumps. Ejectors are most often steam driven, but also include systems that use compressed gases, other vapors, and even liquid as motive energy sources. The major advantages of ejectors includes relative low to purchase, simple maintenance, and extremely reliable operation. Their major disadvantages include adding a new stream to the process and potential energy costs (for gas compression or steam generation). Multiple-stage ejector systems routinely operate at vacuum pressures down to 10-15 torr (10-15 mm Hg absolute). Some large industrial systems have operated at pressures as low as 2 torr (2 mm Hg absolute). For moderate vacuums down to 50 torr (50 mm Hg absolute), liquid-ring vacuum pumps are often useful choices. They minimize energy consumption. However, the have higher maintenance costs. Our personal experience is that relatively few liquid-ring pumps are used in petroleum refineries or petrochemical plants due to the maintenance problems. These problems seem to persist in spite of manufacturer reliability claims. Liquid-ring pumps appear to work well in systems where the operating temperatures are lower and the main source of gas load is leakage into the system rather than a process stream. Dry pumps come in various mechanical configurations. They are rarely used in large process systems. In smaller systems, often fine chemicals or other operations, they are more common. They have essentially the same benefits and problems as liquid-ring pumps except they dispense with the liquid sealing fluid. Dry vacuum pumps may also operate at much lower pressures than liquid-ring pumps.
What is the best way to simulate the process using commercial simulator: I mean that we want to control the level on chimney tray, and what type of configuration can you suggest for the simulation in steady-state and dynamic state?
Controlling level on the chimney tray is a common operation for a total draw tray. Steady-state simulation posses no particular problem. You ignore the level on the tray as you would ignore inventory considerations in most parts of the process. Dead-time inventories for storage in tanks or vessels are typically ignored in steady-state simulation.
In dynamic modeling, any standard commercial dynamic simulator package will handle problem if set up to reflect the unit configuration correctly. As a note, situations requiring dynamic modeling of chimney tray levels as part of the process are exceptionally rare. The only conceivable situations are where feed-forward or multiple-variable control is being used and either the heat shift in the pumparound section (requiring large flow rate changes) or the product rate changes are severe and rapid may require such analysis. Typically liquid level control is achieved with a SISO control loop that may include cascade control for particular applications.
How about revamping this process?
How you revamp a process depends very strongly on your specific revamp objectives. If you would care to discuss this in more detail, please forward detailed information on your specific revamp objectives and the limitations that you wish to improve.
Can you send some material regarding this type of column configuration?
Figure 1 shows a typical configuration for the pumparound section and level control for this type of column. An external (or manual reset) sets the pumparound flow rate needed for the required heat removal. External reflux is set by a manually adjusted flow regulating controller to meet process requirements. Of course, this may be reset by an advanced control system in cascade as well. Product draw is used to control inventory on the collector tray. The configuration shown is a basic configuration that works very well for most applications. Other variations are used to meet specific process needs.
Cliff Notes:
Gf and I dated for two years
she just broke up with me
get a new gf or get her back?
For commercial systems, the major types of vacuum devices are ejectors, liquid-ring pumps, and dry pumps. Ejectors are most often steam driven, but also include systems that use compressed gases, other vapors, and even liquid as motive energy sources. The major advantages of ejectors includes relative low to purchase, simple maintenance, and extremely reliable operation. Their major disadvantages include adding a new stream to the process and potential energy costs (for gas compression or steam generation). Multiple-stage ejector systems routinely operate at vacuum pressures down to 10-15 torr (10-15 mm Hg absolute). Some large industrial systems have operated at pressures as low as 2 torr (2 mm Hg absolute). For moderate vacuums down to 50 torr (50 mm Hg absolute), liquid-ring vacuum pumps are often useful choices. They minimize energy consumption. However, the have higher maintenance costs. Our personal experience is that relatively few liquid-ring pumps are used in petroleum refineries or petrochemical plants due to the maintenance problems. These problems seem to persist in spite of manufacturer reliability claims. Liquid-ring pumps appear to work well in systems where the operating temperatures are lower and the main source of gas load is leakage into the system rather than a process stream. Dry pumps come in various mechanical configurations. They are rarely used in large process systems. In smaller systems, often fine chemicals or other operations, they are more common. They have essentially the same benefits and problems as liquid-ring pumps except they dispense with the liquid sealing fluid. Dry vacuum pumps may also operate at much lower pressures than liquid-ring pumps.
What is the best way to simulate the process using commercial simulator: I mean that we want to control the level on chimney tray, and what type of configuration can you suggest for the simulation in steady-state and dynamic state?
Controlling level on the chimney tray is a common operation for a total draw tray. Steady-state simulation posses no particular problem. You ignore the level on the tray as you would ignore inventory considerations in most parts of the process. Dead-time inventories for storage in tanks or vessels are typically ignored in steady-state simulation.
In dynamic modeling, any standard commercial dynamic simulator package will handle problem if set up to reflect the unit configuration correctly. As a note, situations requiring dynamic modeling of chimney tray levels as part of the process are exceptionally rare. The only conceivable situations are where feed-forward or multiple-variable control is being used and either the heat shift in the pumparound section (requiring large flow rate changes) or the product rate changes are severe and rapid may require such analysis. Typically liquid level control is achieved with a SISO control loop that may include cascade control for particular applications.
How about revamping this process?
How you revamp a process depends very strongly on your specific revamp objectives. If you would care to discuss this in more detail, please forward detailed information on your specific revamp objectives and the limitations that you wish to improve.
Can you send some material regarding this type of column configuration?
Figure 1 shows a typical configuration for the pumparound section and level control for this type of column. An external (or manual reset) sets the pumparound flow rate needed for the required heat removal. External reflux is set by a manually adjusted flow regulating controller to meet process requirements. Of course, this may be reset by an advanced control system in cascade as well. Product draw is used to control inventory on the collector tray. The configuration shown is a basic configuration that works very well for most applications. Other variations are used to meet specific process needs.
Cliff Notes:
Gf and I dated for two years
she just broke up with me
get a new gf or get her back?
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