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Title: Distillation Column Flooding Predictor

Abstract

The Flooding Predictor™ is a patented advanced control technology proven in research at the Separations Research Program, University of Texas at Austin, to increase distillation column throughput by over 6%, while also increasing energy efficiency by 10%. The research was conducted under a U. S. Department of Energy Cooperative Agreement awarded to George Dzyacky of 2ndpoint, LLC. The Flooding Predictor™ works by detecting the incipient flood point and controlling the column closer to its actual hydraulic limit than historical practices have allowed. Further, the technology uses existing column instrumentation, meaning no additional refining infrastructure is required. Refiners often push distillation columns to maximize throughput, improve separation, or simply to achieve day-to-day optimization. Attempting to achieve such operating objectives is a tricky undertaking that can result in flooding. Operators and advanced control strategies alike rely on the conventional use of delta-pressure instrumentation to approximate the column’s approach to flood. But column delta-pressure is more an inference of the column’s approach to flood than it is an actual measurement of it. As a consequence, delta pressure limits are established conservatively in order to operate in a regime where the column is never expected to flood. As a result, there is much “leftmore » on the table” when operating in such a regime, i.e. the capacity difference between controlling the column to an upper delta-pressure limit and controlling it to the actual hydraulic limit. The Flooding Predictor™, an innovative pattern recognition technology, controls columns at their actual hydraulic limit, which research shows leads to a throughput increase of over 6%. Controlling closer to the hydraulic limit also permits operation in a sweet spot of increased energy-efficiency. In this region of increased column loading, the Flooding Predictor is able to exploit the benefits of higher liquid/vapor traffic that produce increased contact area and lead to substantial increases in separation efficiency – which translates to a 10% increase in energy efficiency on a BTU/bbl basis. The Flooding Predictor™ operates on the principle that between five to sixty minutes in advance of a flooding event, certain column variables experience an oscillation, a pre-flood pattern. The pattern recognition system of the Flooding Predictor™ utilizes the mathematical first derivative of certain column variables to identify the column’s pre-flood pattern(s). This pattern is a very brief, highly repeatable, simultaneous movement among the derivative values of certain column variables. While all column variables experience negligible random noise generated from the natural frequency of the process, subtle pre-flood patterns are revealed among sub-sets of the derivative values of column variables as the column approaches its hydraulic limit. The sub-set of column variables that comprise the pre-flood pattern is identified empirically through in a two-step process. First, 2ndpoint’s proprietary off-line analysis tool is used to mine historical data for pre-flood patterns. Second, the column is flood-tested to fine-tune the pattern recognition for commissioning. Then the Flooding Predictor™ is implemented as closed-loop advanced control strategy on the plant’s distributed control system (DCS), thus automating control of the column at its hydraulic limit.« less

Authors:
Publication Date:
Research Org.:
George E. Dzyacky, Principal Investigator; Seprations Research Program, University of Texas at Austin
Sponsoring Org.:
USDOE Office of Industrial Technology Program (EE-2F)
OSTI Identifier:
993101
Report Number(s):
DOEID14426
TRN: US201101%%376
DOE Contract Number:
FC36-02ID14426
Resource Type:
Other
Country of Publication:
United States
Language:
English
Subject:
02 PETROLEUM; CAPACITY; COMMISSIONING; CONTROL SYSTEMS; DISTILLATION; EFFICIENCY; ENERGY EFFICIENCY; FLOODS; HYDRAULICS; OPTIMIZATION; PATTERN RECOGNITION; REFINING; RESEARCH PROGRAMS; Distillation; separation; flooding; advanced process control; distillation column flooding; liquid flooding; jet flooding

Citation Formats

George E. Dzyacky. Distillation Column Flooding Predictor. United States: N. p., 2010. Web.
George E. Dzyacky. Distillation Column Flooding Predictor. United States.
George E. Dzyacky. 2010. "Distillation Column Flooding Predictor". United States. doi:. https://www.osti.gov/servlets/purl/993101.
@article{osti_993101,
title = {Distillation Column Flooding Predictor},
author = {George E. Dzyacky},
abstractNote = {The Flooding Predictor™ is a patented advanced control technology proven in research at the Separations Research Program, University of Texas at Austin, to increase distillation column throughput by over 6%, while also increasing energy efficiency by 10%. The research was conducted under a U. S. Department of Energy Cooperative Agreement awarded to George Dzyacky of 2ndpoint, LLC. The Flooding Predictor™ works by detecting the incipient flood point and controlling the column closer to its actual hydraulic limit than historical practices have allowed. Further, the technology uses existing column instrumentation, meaning no additional refining infrastructure is required. Refiners often push distillation columns to maximize throughput, improve separation, or simply to achieve day-to-day optimization. Attempting to achieve such operating objectives is a tricky undertaking that can result in flooding. Operators and advanced control strategies alike rely on the conventional use of delta-pressure instrumentation to approximate the column’s approach to flood. But column delta-pressure is more an inference of the column’s approach to flood than it is an actual measurement of it. As a consequence, delta pressure limits are established conservatively in order to operate in a regime where the column is never expected to flood. As a result, there is much “left on the table” when operating in such a regime, i.e. the capacity difference between controlling the column to an upper delta-pressure limit and controlling it to the actual hydraulic limit. The Flooding Predictor™, an innovative pattern recognition technology, controls columns at their actual hydraulic limit, which research shows leads to a throughput increase of over 6%. Controlling closer to the hydraulic limit also permits operation in a sweet spot of increased energy-efficiency. In this region of increased column loading, the Flooding Predictor is able to exploit the benefits of higher liquid/vapor traffic that produce increased contact area and lead to substantial increases in separation efficiency – which translates to a 10% increase in energy efficiency on a BTU/bbl basis. The Flooding Predictor™ operates on the principle that between five to sixty minutes in advance of a flooding event, certain column variables experience an oscillation, a pre-flood pattern. The pattern recognition system of the Flooding Predictor™ utilizes the mathematical first derivative of certain column variables to identify the column’s pre-flood pattern(s). This pattern is a very brief, highly repeatable, simultaneous movement among the derivative values of certain column variables. While all column variables experience negligible random noise generated from the natural frequency of the process, subtle pre-flood patterns are revealed among sub-sets of the derivative values of column variables as the column approaches its hydraulic limit. The sub-set of column variables that comprise the pre-flood pattern is identified empirically through in a two-step process. First, 2ndpoint’s proprietary off-line analysis tool is used to mine historical data for pre-flood patterns. Second, the column is flood-tested to fine-tune the pattern recognition for commissioning. Then the Flooding Predictor™ is implemented as closed-loop advanced control strategy on the plant’s distributed control system (DCS), thus automating control of the column at its hydraulic limit.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2010,
month =
}
  • Project fact sheet written for the Inventions and Innovation Program about an innovative technology for predicting and avoiding liquid and jet flooding in the petroleum refining process.
  • The Flooding Predictor is an advanced process control strategy comprising a patented pattern-recognition methodology that identifies pre-flood patterns discovered to precede flooding events in distillation columns. The grantee holds a U.S. patent on the modeling system. The technology was validated at the Separations Research Program, The University of Texas at Austin under a grant from the U. S. Department of Energy, Inventions & Innovation Program. Distillation tower flooding occurs at abnormally high vapor and/or liquid rates. The loss in tray efficiencies is attributed to unusual behavior of liquid inventories inside the column leading to conditions of flooding of the spacemore » in between trays with liquid. Depending on the severity of the flood condition, consequences range from off spec products to equipment damage and tower shutdown. This non-intrusive pattern recognition methodology, processes signal data obtained from existing column instrumentation. Once the pattern is identified empirically, it is modeled and coded into the plant's distributed control system. The control system is programmed to briefly "unload" the tower each time the pattern appears. The unloading takes the form of a momentary reduction in column severity, e.g., decrease bottom temperature, reflux or tower throughput. Unloading the tower briefly at the pre-flood state causes long-term column operation to become significantly more stable - allowing an increase in throughput and/or product purity. The technology provides a wide range of value between optimization and flooding. When a distillation column is not running at capacity, it should be run in such a way ("pushed") that optimal product purity is achieved. Additional benefits include low implementation and maintenance costs, and a high level of console operator acceptance. The previous commercial applications experienced 98% uptime over a four-year period. Further, the technology is unique in its ability to distinguish between different flooding mechanisms within the same tower, e.g., liquid and jet flooding.« less
  • This factsheet describes a research project whose goal is to develop the flooding predictor, an advanced process control strategy, into a universally useable tool that will maximize the separation yield of a distillation column.
  • Here is a way to estimate maximum allowable vapor velocity and entrainment in a distillation column. The method can easily be computerized. It is based on equations derived from the widely accepted correlations. The equation for flooding velocity is applicable to bubble-cup, sieve and valve trays, while the entrainment equation applies only to sieve trays.
  • UOP's McCook, IL, plant produces a great variety of chemicals, among them many antioxidants and antiozonants which are used by gasoline producers, rubber processors and other industrial customers. Low boiling oxygenated aliphatics are stripped from high boiling nitrogenous compounds in a distillation column. In order to achieve the necessary separation, very high column reflux rates were required. This sometimes caused jet flooding which led to entrainment and contamination of the overhead streams. When the overhead streams did not meet purity specs, they had to be inventoried and later recycled. The result was unacceptably high costs and low overall unit efficiency.more » To correct the problem, UOP decided to revamp the column in question. The 28 original sieve trays were removed from the 28' tall, 19 1/4'' ID column, and 27 SS304 cartridge-type fabricated screen trays were installed don 12'' spacing. The closely spaced wires from which the decks of the trays are fabricated form venturi-shaped slots that allow operation in the froth regime over a wide range of conditions. Reduced entrainment and low pressure drop combine to permit use of very high vapor and liquid rates without flooding. After the revamp, UOP found that flooding problems were eliminated in the column. Pressure drop was considerably reduced, too. An increase in separation efficiency was also noticed which permitted reboiler temperatures to be lowered by 20-50/sup 0/F, and lower reflux rates to be employed. Energy requirements of the reboiler were cut by 400,000 Btu/hr at 80% of maximum column feed rate. This represented a savings of more that $16,000/yr in fuel costs on an annualized basis, calculated on 80% efficiency in the natural gas-fired furnace.« less