logo


Minimize recycle and coke carryover with the coker main fractionator washspray header design

Coker Main Fractionator flash zone design is critical to reliable operation of the column and maintaining product quality. This section commonly experiences problems related to the presence of unstable heavy liquid and carryover of solids. Successful operation often hinges on the design of the wash liquid distributor. Although Sulzer utilizes several styles of wash liquid distributors, this bulletin focuses on the spray header design. The spray distributor design is a careful balance of nozzle type, number, and placement. Optimizing the wash header design minimizes natural recycle, allowing higher flow of fresh feed to the furnace for increased capacity.

Fundamental #1 – Selection of Number of Nozzles
Spray coverage diameter or overlap determines the number of nozzles required. A header with 7 is typical, but more may be required for large diameter towers. Wash spray coverage is fully developed at a vertical distance of 2 ft and no additional coverage can be obtained by increasing the nozzle distance.

Fundamental #2 – Selection of Nozzle Type
Spray coverage diameter depends on the type of nozzle chosen, defined by its desired spray angle, size of orifice, and the nozzle pressure drop. Sulzer designs typically incorporate nozzles that have sufficient pressure drop to maintain the spray pattern and have a cone angle to target the largest spray coverage diameter. Optimized coverage requires less natural recycle. Smaller angle nozzles can be used if coke carryover is an issue, as their greater downward force could potentially improve knockdown of coke. If multiple nozzle types meet the column’s specifications, select the nozzle with the larger orifice passage for increased reliability from plugging or coking off.

Fundamental #3 – Placement of Nozzles
In wash sections with a dual header design, the top distributor is rotated from the lower distributor, ensuring complete wash coverage across the column. The nozzle placement on each header is carefully determined to maximize the amount of coverage. When designing the placement, it is important to maintain some overlap of the spray nozzle coverage, but not so high that the overlapping droplets interfere with and deflect each other.

Other Design Considerations
1. Entrainment: The relatively high pressure drop through a spray nozzle is beneficial to prevent plugging, but the same pressure drop creates smaller droplets that are subject to entrainment, which must be considered when determining the wash header design flow rate.

2. Turndown: At lower than design flow rates, pressure drop through the nozzle is reduced and the spray pattern may collapse. Turndown conditions must be considered during the sizing process, or alternatively in a dual header system, the upper header can be operated with a steam purge (to prevent plugging) while the bottom header operates normally.

DOWNLOAD LITERATURE

Sponsor:

Categories:

View More

  • Tray designs for extreme fouling applications

    Today refiners experience a lot of problems with processing of opportunity or heavy crudes. Such crudes have very high sulfur content and require the addition of amine scavengers before desalting. These amines decompose in the heater and create ammonium chlorides in the presence of water in the top of ...

  • Anti-fouling trays maximize coker main fractionator profitability

    The Coker Main Fractionator is systematically subjected to harsh operating conditions that can lead to deteriorating efficiency and performance due to coking and fouling. Poor reliability results in loss of profitable coking margins for the refinery. The main fractionator vapor feed from the coke drum ...

  • Improve separation in your column by increasing the number of trays

    Refiners often face revamp challenges when trying to improve separation within an existing column. Improving diesel recovery from gas oil, splitting benzene precursors from naphtha reformer charge, or simply minimizing product overlaps after capacity creep can all be difficult when limited by a fi xed ...

  • Gain 5-10% efficiency with this simple 4-pass tray revamp

    The design of 4-pass trays can be complex. It not only requires a close evaluation of the mechanical design but also the process response to that design at various flow rates. The balancing of the fluid flows across the tray can have a substantial effect on the tray performance, namely efficiency. Many ...

  • Proper design of mass transfer internals in the FCC flue gas scrubber can help reduce PM emissions

    The EPA’s New Source Performance Standards (40 C.F.R. §60.100-1-0, subpart Ja) regulates refinery particulate emissions, including the discharge of catalyst fines from the FCCU flue gas scrubber stack. Because refiners have traditionally correlated particulate matter (PM) emissions with FCCU ...

  • Improve fouling resistance in your wastewater benzene stripper

    Benzene stripper columns, built so that refineries can meet the National Emissions Standards for Hazardous Air Pollutants (NESHAP), operate with several unique conditions – low vapor rates, high liquid loads, and a high tendency toward fouling make designing well-balanced, effective internals difficult. The ...

  • Important tray design features that improve column operating reliability

    How often does Maintenance personnel open a column during a shutdown and find tray panels fallen without any obvious damage? How about tray valves stuck in the bottoms pump suction? While the initial reaction may be to blame faulty installation where the hardware was not properly tightened, the answer ...

  • Green design practices: focus on efficiency

    Green design is more than recycling scrap materials or calculating carbon footprints. It minimizes negative environmental impact through skillful design and operating practices to produce efficient, better-functioning processes. Because green practices reduce resource requirements, in many cases, they ...

  • 4 simple ways to convert turnarounds into profitable tower upgrade opportunities

    With planned outages commonly occurring at intervals of 2-5 years, a refinery turnaround is a prime opportunity to replace column and separator internals with the newest available technology. Planning for an outage with a “replacement-in-kind” strategy will address lost performance from refinery ...

  • Maximizing light cycle oil recovery in the FCC main fractionator

    Refiners operating FCCU's have adjusted their operating strategies to maximize light cycle oil production to meet the increased demand for automotive diesel. Catalyst formulations and reactor conditions can alter yields, but the refinery cannot take full advantage of the increased LCO recovery without ...