May-June 2014 | Desalination & Water Reuse

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_________Petr Sudilovskiy and Dave Ciszewski GE Power & Water, Water & Process Technologies and Ilshat Valiullin, RusGazEngineering___

Editor’s Note: Expected to come online at the end of 2015, the multi-effect steam-driven evaporation system provided by GE will allow a Russian oil-producer to recycle its water from the enhanced oil recovery in the treatment of heavy oil produced water

OPERATED BY Russia’s second largest oil producer, a heavy oil field in northwest Russia has been increasing the volume of crude processing with technology that supports enhanced recovery rates and reduced environmental impact. In 2008, they took the first steps to develop a less water-intensive way of processing produced water by conducting a feasibility study comparing different water reuse strategies. By replacing traditional treatment methods with thermal evaporator technology for produced water, this will be the first entity in Russia to use recycled water from enhanced oil recovery in the treatment of heavy oil produced water.

DeSIgnIng the rIght SyStemEnhanced oil recovery requires 100% quality steam to be injected into the well. To produce such steam using drum boilers, a series of vapor-liquid separators separate the liquid water from the steam. The 100% quality steam is then injected into the well and the separated water is disposed of via deep-well injection.

RusGazEngineering (RGE), a reputable EPC company in Russian’s oil & gas industry, turned to GE Power & Water, Water & Process Technologies to provide the technology to meet their customer’s primary challenge – to find a source of water to feed boilers for steam-assisted enhanced oil recovery.

GE’s evaporation technology (brine concentrators and crystallizers) is used extensively in heavy oil-recovery operations around the world.

In addition to a decade of experience in the oil and gas industry, RGE brings an extensive history designing, manufacturing, installing, and commissioning projects in Russia. As well as assisting GE with technology evaluations, RGE provided overall plant design, is handling equipment supply and will take the lead on balance of plant support.

Engineers from GE and RGE compared solutions that involved various water treatment options. The typical treatment method for produced water is warm or hot lime softening, filtration, and weak acid

cation exchange. But as was previously mentioned, enhanced oil recovery requires 100% quality steam and evaporation technology can be used to produce high quality boiler makeup water to maximize water recycling and reuse.

More specifically, vertical-tube falling-film evaporators (brine concentrators) could help the oil producer lower lifecycle costs, minimize waste streams, and increase system reliability. Brine concentrators can recover up to 98% of the produced water as high-quality distillate (<10 ppm non-volatile inorganic total dissolved solids). The process also increases heavy oil recovery plant availability by 2-3%, directly increasing oil production.

The use of a conventional boiler system (drum boiler) further extends the benefits of evaporator technology. In addition to eliminating the need for costly vapor/liquid separation equipment, the brine concentrator reduces the size of the boiler feed system by as much as 15% and reduces boiler blowdown by as much as 90%.

A fIrSt of ItS kInD SolutIonArmed with this information and additional technology evaluations validating effectiveness, GE and RGE set out to develop the first heavy oil produced water recovery evaporator in Russia. Based on GE’s brine concentrator treatment process, the evaporator system has a design capacity to produce 700 m3/h of distillate suitable to feed medium-pressure drum boilers.

GE’s patented evaporation technology was developed in the late 1990s. The technology can employ a proprietary contaminant reduction system for the production of superior distillate quality where required, enabling efficient and reliable operation of high-pressure (>70 bar) drum boilers.

how It workS The multi-effect evaporator (brine concentrator) process is a five-effect falling-film evaporator system designed to produce 700 m3/h of high quality distillate

Russian heavy oil recoveryenhanced by water reuse

PROJECTS

Desalination & Water Reuse | May-June 2014

for reuse as boiler feedwater. More than 800 m3/h of oilfield-produced wastewater is required to feed the plant along with 160 t/h of low-pressure steam. The steam is fully condensed by the evaporation system to return pure steam condensate back to the boiler system. Evaporation blowdown of 97 m3/h is produced requiring off-site disposal.

The first-effect evaporator condenses the plant steam, while the remaining four effects utilize evaporation steam generated from previous effects. The evaporator accepts produced water as feed, concentrates it about eight times to just below the point of solids precipitation, and produces a very pure distillate.

The low-volume concentrated waste-brine discharge is disposed of off-site via deep-well injection. The vapors produced in the last effect are condensed by an air-cooled condenser to recover the distillate.

A process flow diagram for the five-effect evaporator system is shown in Figure 1.

The evaporator system is designed to condense 160 t/h of plant steam. This is sufficient steam to concentrate more than

800 m3/h of produced water to recover clean distillate and produce concentrated brine for disposal.

Table 1 shows the expected chemistry of the concentrated produced water.

The warm produced-water feed, at 45-85°C, is received by the plant, and hydrochloric acid is added into the feedwater. The hydrochloric acid lowers the pH to convert almost all of the bicarbonate/carbonate to carbon dioxide gas.

Removing the carbonates at this early stage prevents scaling on the evaporators’ heat transfer surfaces. The acidified feed is then sent to the fifth-effect evaporator.

This multiple-effect evaporation is a countercurrent design: feedwater flows in one direction whereas steam/vapor flows in the opposing direction. Feedwater first enters the fifth effect and plant steam enters the system on the first effect.

After the fifth effect, the brine is pumped in series from the fourth effect to the first effect. Therefore the first effect will contain the highest concentrated brine.

The evaporator feedwater enters the fifth effect evaporator sump and flows in series toward the first effect. The contents in the sump are pumped by the recirculation pump up to the top of the evaporator, called the floodbox.

The brine is evenly distributed into each tube through a twin-spin tube distributor and an uniform thin film is formed on the inside of the tubes. As the thin film flows down the tubes, the brine is heated to its boiling point.

Water is driven out in the form of steam vapor and flows down the center of the tube with the concentrated brine flowing into the evaporator sump. The water vapor from the fifth-effect evaporator is drawn from the space above the boiling brine (the steam cavity) through internal mist eliminator pads, to entrap any remaining salts on its way to the condenser.

The steam from the steam cavity of the fourth effect is used to drive the fifth effect. The operating sump pressure of the fourth effect is slightly higher than the condenser shell pressure in the fifth effect evaporator. The steam gives up its heat of vaporization in the condenser of the following effect (to heat the thin falling film on the inside of the tube) and condenses on the outside of the tube wall.

The feed and vapor flows for the fourth to second effects are similarly configured to the fifth effect. Feed to the fourth effect evaporator sump is drawn off the brine recirculation flow from the fifth effect.

The vapor flows through the vapor ducts and traverses through each effect in the opposite direction from the feedwater flows. For the fourth effect, the steam used to drive evaporation originates from the third effect. The steam used to drive evaporation on the third effect comes from the second effect, and so forth.

The steam used to drive the first effect evaporator is from low-pressure plant steam. The steam gives up its heat of vaporization in the condenser (to heat the thin falling film on the inside of the tube) and condenses on the outside of the tube wall. The steawm condensate collects at the bottom of the shell side of the condenser in the first effect and returns as high-quality boiler feedwater.

EnginEERing SuCCESSExpected to come online at the end of 2015, the multi-effect steam-driven evaporation system provided by GE will allow the Russian oil-producer to recycle its water from the enhanced oil recovery in the treatment of heavy oil produced water. Expected results are shown in Table 2.

GE and RGE will continue to develop new technologies and processes to facilitate smarter, more effective, and more environmentally friendly heavy oil recovery applications. l

Figure 1: Process Flow Diagram of GE’s five-effect evaporator

Table 1. Expected produced water chemistry range

Table 2. Expected System Performance Data