Back

Liquid-liquid separation technology

In industrial process equipments liquid-liquid mixtures are produced by essentially two different mechanisms. a) Mixing of the phases in either purpose built equipment, mechanical mixers, static mixers where pressure energy is applied to increase the surface free energy of the fluids to produce droplets, or in shear flow of the fluid mixture in pipes.

b) The cooling of a saturated liquid below the solution point so that the solute phase condenses out of solution resulting in the formation of a second liquid phase. This takes place frequently in storage tanks and in processes downstream of condensers or coolers.

When two phases are formed, this mixture is most often in the form of a dispersion (droplets of one phase distributed in the second or continuous phase). The mixture is thermodynamically unstable, meaning that given time, the droplets will separate out to form two bulk liquid phases. This takes place by droplets coalescing both with “near neighbour” droplets (drop-drop coalescence) and with the bulk phase as this forms and settles from the mixture (drop-interface coalescence).

The kinetics, or rate at which these processes take place, determine the selection and design of equipment. The driving force promoting coalescence is gravity and in a given system is proportional to Δr · g, Δr being the density difference between the two liquid phases. The diameter of the droplets is a critical parameter.

DOWNLOAD LITERATURE

Sponsor:

Sulzer Chemtech

Categories:

Filtration and Separation

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 ...