THE PV FLOWRATE -PROCESS OPERATOR RELATIONSHIP

She's so popular
She's so popular
She's so popular

(Mondegreen for "Games Without Frontiers," by Peter Gabriel, 1980)

SO MANY FLOWRATES!

The PV Flowrate is the Most Popular of all the major Process Variables, more popular than the PV Temperature, PV Pressure, or PV Level.

And by "Most Popular" the PTOA means that there will be more PV Flowrate sensing and measurement devices than sensing and measuring devices for the other major Process Variables.

This Outside Process Operator is checking a local Flow Indication.

The most important PV Flowrates will be displayed on the Control Board so that the Control Board Operator can easily monitor and control them. The evolution of Distributed Control Systems (DCS) which make it possible for Control Board Operators to control PV Flowrates and other Process Variables was featured in PTOA Segment #9 through PTOA Segment #16.

The local Flowrate indicated on this Flow Indicator will need to be read by an Outside Process Operator.

Other PV Flowrates are still important yet considered auxiliary to normal process operations. These PV Flowrates will be measured, detected and displayed on local Flow Indicators that the Outside Process Operators will monitor on a regular schedule.

FLOWRATES FOR "CUSTODY TRANSFER" OF FEEDSTOCKS, UTILITIES, and PRODUCTS

Brilliant PTOA Readers and Students ... meaning those who are reading the PTOA Segments in the intended, sequential order ... can recite in their sleep that the purpose of a processing plant/facility is to continuously upgrade Feedstocks and Intermediate Products into more valuable Final Products.

Purchased feedstocks and utilities are huge operating expenses.

The Feedstocks and purchased utilities that are required to operate the processing plant are a constant, huge operating expense.

PTOA Readers and Students are accustomed to purchasing items from a store. The receipt that a cash register spits out indicates that the purchased item has changed ownership from the store to the purchaser.

In a processing facility, the "custody transfer" of the Feedstocks and utilities from the seller to the purchaser (the processing plant) is likewise a formal and legal transaction.

The nearby Block Diagram of a Fuels Refinery indicates that Crude Oil is the major Feedstock to the Atmospheric Distillation Unit of the plant. Natural Gas is the feedstock to the Hydrogen Synthesis Process Unit.

Natural Gas might also be needed as a feedstock to generate electricity in a Generator that would be driven by a GT (Electrical Power generation was featured in PTOA Segment #196). Otherwise, the electrical utility would be purchased from an electrical utility company.

The Custody Transfer of Feedstocks and Purchased Utilities will rely on Flow(rate)meters which are both Repeatable and Accurate. Ditto for the most valuable sold Products.

The Flow(rate) meters selected for the Crude Feedstock, Natural Gas, and purchased electricity will be selected for their accuracy.

"Accuracy" as it pertains to the sensing and measurement of Process Variables was featured in PTOA Segment #99. The accuracy of these Flow(rate) meters will be verified on a regular maintenance schedule. These devices will be recalibrated when necessary.

The Product(s) from the processing plant must be sufficiently valuable to pay for the Feedstocks, utilities, and all the personnel needed to operate and administer the plant ... plus there must be some profit to stay in business and cover expenses during a Turnaround.

Product Sales Flow(rate) meters must also be accurate.

Obviously, the Plant Owner does not want the customer to receive more product than what has been agreed to. For this reason, the Flow(rate)meters at the point of sale will likewise be chosen for accuracy.

The nearby Fuels Refinery Block Diagram delineates Products in blue writing. The processing units in this Fuels Refinery were purchased and installed to maximize the production of Gasoline.

Jet Fuel/Kerosine is another valuable product as are two product lines of Diesel (distillate from the Crude Tower and a cracked diesel made from the Heavy Vacuum Gas Oil feedstock that flows into the Hydrocracker).

Heavy products made at this facility include Asphalt, Petroleum Coke, and Fuel Oil. Light products made at the facility include Liquified Petroleum Gas (LPG) and Butanes. Solid Sulfur is also a byproduct of this Fuels Refinery.

As was stated above and repeated here, the profit margin for the Fuels Refinery is determined by the difference in value between the Final Products and the Feedstock(s), purchased utilities, and other operating expenses (like Process Operations!).

The Outside Process Operator and Control Board Operator greatly influence whether or not the PV Flowrates within the Fuels Refinery are optimized and thus likewise impact the safe and efficient operations of the Fuels Refinery. More examples of the important PV Flowrate-Process Operator Relationship are reviewed below.

THE PROCESS OPERATOR IMPACTS THE EFFICIENCY OF CONVECTION HEAT TRANSFER BETWEEN FLOWING FLUIDS

Very easy to imagine the thermal energy of the liquids flowing through the tubes of this Fired Heater.

All flowing fluids have thermal energy. To cut down on the cost of utilities, many hot and warm flowing fluids in a processing facility transfer their heat into colder fluids that need to be heated up prior to their next processing step.

Otherwise stated, Convection Heat Transfer is used to both add heat to a flowing fluid and remove heat from a flowing fluid.

Convection Heat Transfer was featured in PTOA Segment #64. The most brilliant PTOA Readers and Students know that the three components that impact Convection Heat Transfer are:

The rate of convection heat transfer (q) depends mostly upon the ΔT between the hot fluid and cold fluid, the mass flowrate of the fluid (m), and the heat capacity of the flowing fluid (C_p).

The mass flowrate of the flowing Fluid (m).
The heat Capacity of the flowing Fluid (C_p).
The difference in Temperature (ΔT) between a hot flowing fluid and a cold flowing fluid.

Consider the Shell and Tube Heat Exchanger the nearby animated schematic. Assume this Shell and Tube Heat Exchanger is a "Trimmer Cooler" which means that the liquid that enters the exchanger cold and exits hot is none other than Cooling Water supplied by the Cooling Tower/Cooling Water System utility.

If the Cooling Water Utility is not operated efficiently, the water flowing through Trim Cooler Shell and Tube Heat Exchangers will not be transferred the optimal amount of heat.

If the Cooling Water Tower is not operated efficiently, the heat transfer from the hot process fluid (more than likely the Tube Side flow) into the Cooling Water (probably the Shell Side flow) will not be optimal because the ΔT between the hot flowing fluid that needs to be cooled and the heat sink provided by the flowing Cooling Water will not be optimal.

Since the less-hot effluent that flows out of the Tube Bundle and exits the Heat Exchanger will not be optimally cool, more cooling load will be borne by the downstream Fin Fan Heat Exchanger. The electricity to power the fans increases operating expenses.

Conclusion: By understanding how to optimize PV Fluid Flowrates, the Process Operator greatly impacts the rate of Convection Heat Transfer and thus the thermal efficiency of the plant.

THE PROCESS OPERATOR IMPACTS THE KINECTIC ENERGY EFFICIENCY OF FLOWING FLUIDS

The optimal Condition to operate this Pump is at the Black Triangle. The Triangle is indicating the Total Dynamic Head (TDH) right before the Efficiency of the Pump starts to decline. The Capacity (aka Flowrate through the Pump) is optimized at this Best Efficiency Point (BEP).

All brilliant PTOA Readers and Students can also recite in their sleep that "Pressure Energy" is infused into flowing liquids as the fluid whirls around in a Centrifugal Pump. Another term for "Pressure Energy" is "kinetic energy." The amount of kinetic energy in the liquid discharged from the Centrifugal Pump is determined by the mass and velocity of the flowing liquid.

A Performance Curve for a Centrifugal Pump appears in the nearby graphic. PTOA Readers and Students learned about decoding Centrifugal Pump Performance Curves in PTOA Segment #168.

PTOA Readers and Students will remember that the optimal condition at which this pump should be operated is at the maximum Capacity (aka Liquid Flowrate) attainable before the Efficiency Curve begins to decline.

This "Best Efficiency Point" (BEP) is where the liquid flows into and out of the Centrifugal Pump with the minimum amount of flow separation, turbulence, and other losses.

The Outside Process Operator will be notice if a Pump is making an unusual sound. Unusual noises from a pump are often the first sign of trouble.

When the Pump's Capacity is greater than BEP Capacity, the pump is being inefficiently operated at a Capacity (aka Flowrate) higher than the pump was designed for. If the pump is operated too far off BEP the other way, the resulting imbalance will cause premature wear of the pump internals.

In summary, a Centrifugal Pump that is operated outside of BEP will cause premature wear on the pump's internals plus waste the expense of operating the pump's motor.

Outside Process Operators routinely check pump operations and thus greatly impact whether or not the pump is operating efficiently at the optimal Capacity (aka Flowrate).

TAKE HOME MESSAGES: The PV Flowrate is the most popular Process Variable. There will be more Flowrate detecting and measuring devices in a processing facility than other Process Variable devices.

The relationship between the PV Flowrate and the Process Operator directly impacts the operating efficiency and run length between scheduled shutdowns.

Process Operators may participate in Flowmeter proving, wherein the accuracy of Flowmeters in the service of feedstock or product custody transfer is confirmed.

Process Operators directly impact the efficiency of Convection Heat Transfer of flowing fluids. Convection Heat Transfer is directly related to the thermal efficiency of the plant.

Process Operators directly impact the kinetic energy efficiency of pumped liquids. Centrifugal Pumps should always be operated at the Capacity (aka Flowrate) that coincides with the Best Efficiency Point (BEP). The Best Efficiency Point is just prior to a decline in the Efficiency Curve on a Pump Performance Curve. The BEP is also where the liquid flows into and out of the Centrifugal Pump with the minimum amount of flow separation, turbulence, and other losses.

PTOA PV FLOWRATE FOCUS STUDY AREA
THE RELATIONSHIP OF THE PV FLOWRATE WITH PV TEMPERATURE, PV PRESSURE, AND PV LEVEL

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