The build-up of particulate and sludge in the circulating amine solution has a negative impact on the availability, reliability, and cost effectiveness of Amine Process Trains. The removal of these contaminants through effective filtration is imperative, as their continued accumulation substantially increases the rate of fouling, foaming, erosion, corrosion, and solution degradation.

Particle size distributions found in nature and in operating fluid systems are skewed, exhibiting a log-normal form. The relationship between normal and log-normal contaminant distributions is depicted on a linear scale in Fig. 1. Typically a process stream without filtration will follow the log-normal distribution law where the majority of finely dispersed particles exhibit a skewed size-frequency distribution. However, when depth media type filtration is employed (non-backflushable), the filter system itself allows a continual build-up of small-sized particles in the fluid -- a condition called the "Rosin-Rammler" distribution (See Fig. 1) which results in accelerated silting processes and exacerbates the "foaming" phenomenon. The REI IFS backflushable system is a true surface filter that removes even sub-micron particles due to "cake" formation and surface impaction; thus in a re-circulatory amine process with 20% slip stream, we would expect the total suspended solids ("TSS") level to drop significantly in the first 2-3 months, and after 6 months to approximately 5 ppm or less, assuming the carbon bed maintains the hydrocarbon level at 10 ppm or less.

The use of leaf filters and cartridge filters on the lean solution side of the Amine Process Trains are ineffective in removing Iron based contaminants. On the lean solution side, the iron exists mainly as ferrous ions, soluble bicarbonate and other complexes. As a result, this soluble iron cannot be removed. With the presence of hydrogen sulfide in the in-coming gas, the dissolved iron reacts with the hydrogen sulfide to form insoluble iron sulfide in the contactor. The iron sulfide particles then grow from sub -micron to larger sized debris. It is this iron sulfide, along with additional inlet gas contaminants such as pipeline corrosion products, suspended solids and corrosion inhibitors, that create the above mentioned fouling problems.

These operating problems must therefore be addressed with the installation of a high performance filtration system on either the rich or lean solution side. A mechanical filter on the rich side will remove the iron sulfide contaminants which are in suspension at the source of creation and ingress. Filtration of the circulating amine solution on the lean side will remove iron oxide particulate formed in the solvent by erosion and corrosion of the metal piping and other equipment. iron sulfide cannot be removed by a mechanical filter on the lean side as it is in solution. The molar loading on the rich side usually is 0.35 to 0.40 moles of acid gas (H2S & CO2) per mole of amine, while the lean side acid gas loading can be 0.02 to 0.08 moles per mole of amine. This residual acid gas on the lean side is dependent on the efficiency of the regenerator. Installing Remediation Earth, Inc.'s ("REI") Intelligent Filtration System ("IFS") on the rich side will remove even trace amounts of iron sulfide (pipeline corrosion products) and other suspended solids. In fact, independent certified lab tests have shown that REI's backflushable IFS system effectively removes particles in the sub-micron range.

Note: The following information is based on an actual gas plant's economics, having a flow diagram as depicted in Fig. 2 below.

Rich/Lean Exchanger Fouling:

At the present time, without the benefit of amine solution filtration, excessive fouling of the tube side of the rich/lean exchangers occurs. The fouling associated with the deposition of the particulate and sludge contained within the rich amine solution reduces the heat transfer capability of the exchangers. Allowing corrosion products to accumulate on the lean side will also cause a reduction of heat exchanger effectiveness.

Typically these heat exchangers must be taken off-line and cleaned (high pressure water washed) on an average of once every 12 months in order to maintain heat transfer effectiveness at near design. The annual cost of this extra-ordinary exercise approaches $90,000 annually.

With the installation of REI's backflushable filter system, it is estimated that the cleaning frequency of the rich/lean exchangers will be reduced to once every two years. This in-turn will result in an annual O/M cost saving of $45,000.

Figure 2: Amine Treating Process

Increased Reboiler Duty:

As the heat transfer capabilities of the exchangers decrease, so does the temperature of the rich amine solution entering the regenerator reboiler or "still." This in-turn imposes a higher sensible heat duty requirement on the still reboilers. Over the six month fouling cycle of the heat exchangers, the rich amine solution temperature to the still can drop by as much as 20o F.
Assuming a linear fouling rate, the reboiler duty requirement must be increased by 7% in-order to accommodate the average 10 oF decrease in the rich amine solution temperature. As an
example, an amine train with a gas processing rate of 77 mmscfd of residue gas would require an increase in the reboiler steam rate of 7,120 lbs./hr. This can increase the Plant fuel consumption by 0.22 mmscfd.

Assuming a fuel cost of $3.95/mscf (late May 2009), the net increase in annual fuel cost as a result of the increased reboiler duty is estimated at $313,000.

Vent Tank Chimney Tower Fouling:

A vent tank chimney tower (if used) can contain structured Glitsch packing that is susceptible to iron sulfide fouling. The counter-current contacting of the sour vent tank flash gas with the lean amine solution (containing soluble iron) results in the creation of iron sulfide through the same mechanism as discussed previously. The iron sulfide slowly plugs the packing of the vent tank chimney tower to the point of rendering the unit completely ineffective in sweetening the flash gas from the vent tank.

Previous attempts at cleaning the tower packing through acidizing have only provided limited short term success. As a result, the sour flash gas from such units must be injected into the acid gas stream to the sulfur plant, as opposed to being utilized as boiler fuel. In addition, inclusion of these hydrocarbons in the sulfur plant can also cause catalyst coking, producing carbonyl sulfide (COS). This increases the sulfur emissions in the tail gas.

Furthermore, this flash gas (containing methane) passes through the sulfur plant and enters the thermal oxidizer along with H2S. Previous thermal oxidizer studies have shown that the combustion efficiency of the methane contained within the flash gas is only 25%.

The vent tank tower generates approximately 0.32 mmscfd of equivalent fuel gas (methane). Assuming 25% combustion efficiency, an equivalent of 82 mmscf/year of fuel remains un-combusted and is vented through the thermal oxidizer stack. At a fuel cost of $3.95/mscf, this equates to an annual fuel cost of $324,000.

With the installation of a rich solution filter, the iron level in the amine solution will be significantly reduced, thereby mitigating the potential of fouling the vent tank chimney tower and the above problems. It is estimated that the vent tank chimney tower packing can then be
acidized at a one time cost of $72,000 (amortized over 5 years), and the unit be returned to normal service. The sweetened fuel will then be directed to the power boilers, where 100% combustion is achieved. This, in turn, will reduce the annual plant fuel cost by $252,000.

Foaming:

Iron sulfide and other particulates have been known to be good foam stabilizers. The buildup of these solids in the rich/lean amine solution, combined with hydrocarbon contaminants that enter the plant with the inlet gas, result in an unacceptable number of foaming incidences within the contactor. This in turn adversely affects the processing train capacity and reliability.
The installation of an REI backflushable filter system will "clean up" the circulating amine solution, thereby greatly reducing the frequency and duration of foaming incidences. It should be noted that the REI IFS backflushable unit is so efficient, that plate and frame heat exchangers can be substituted for less effective tube and shell heat exchangers when using high performance MDEA at high recirculation rates, thus increasing the overall efficiency of the gas plant.

Solution Degradation and Corrosion:

It has been well-documented that the thermal degradation of amine increases with increasing temperature. The practice of increasing the reboiler duty as a "band-aid" for exchanger fouling results in increased still bottom temperature, which directly increases the amine degradation rate, and potentially the system corrosion rate.

Failure to adjust the reboiler duty on the other hand, will result in the under stripping of the amine solution. This in-turn increases the reboiler and lean solution piping corrosion rates, and may lead to acid gas break-out in the sweet product gas.

In addition, the presence of iron sulfide (FeS) particulate, dirt and corrosion products causes erosion of the protective FeS layer on the metal surfaces (especially at elbows, bends, pump casings and impellers) thus exposing fresh metal surfaces to further accelerated metal corrosion. Removal of this particulate through efficient filtration will mitigate the above cyclical phenomenon thus increasing the equipment life.

Other:

Particulate build-up in the rich amine solution has also resulted in the fouling of contactor (bottom) and still (top) trays. In addition to decreased tray efficiencies, equipment cleaning costs have correspondingly increased.

If contactor and "still" cleaning is required once every 2 years using a high-pressure water wash, chemicals and surfactants, the cost (including small related repairs) could be as high as $160,000. If an REI Intelligent Backflushable Filtratrion System is installed, high pressure cleanings can be extended to once every 4 years. The annual O/M cost for cleaning a single train is now estimated at $40,000 instead of $80,000, for a savings of $40,000 per year.

REI's backflushable filtration will remove particulates as they form, thereby mitigating the contactor and still fouling rates.

PROJECT ECONOMICS:

This filtration system will utilize fully regenerable Etched Disc (EDF) or LonglifeTM filter elements, thereby eliminating any safety and environmental concerns associated with the replacement and disposal of filter elements.

Either filter element system can use 300 psig steam, nitrogen or fuel (sales) gas as the backflushing medium. At steady state operation (using steam), it is anticipated that the filter system will backflush every 2-3 hours with a utility requirement of 15 lbs. of steam/backflush. The annual fuel cost associated with this steam demand is estimated at $400, which is negligible.

A review of other REI filter systems already in service has shown that this system has a proven track record, requiring minimal maintenance.

As noted earlier, the following annual O/M and fuel cost savings are anticipated with the installation of the REI filter on a single Process Train:

• Reduced rich/lean exchanger cleaning requirements = $45,000
• Fuel savings associated with eliminating the need for increasing the regenerator reboiler duty = $313,000
• Fuel savings associated with the redirection of sweetened vent tank flash gas to the power boilers = $252,000. (Please note that a one time O/M cost of $72,000 will be incurred for the acidizing of the vent tank tower packing. This has been considered in the economic evaluation by amortizing the $72,000 over 5 years.)
• Reduced contactor and still cleaning requirements = $40,000

The annual operational and maintenance costs (O&M) could add up to a savings of approximately $650,000 when compared to currently available technologies such as inferior "backwashable" filter systems operating on the "rich" side, or replaceable cartridge filter systems that operate on the "lean" side of the amine train.

PROJECT BENEFITS:

In summary, the installation of an REI automated backflushable filter will have the following benefits:

• Increased Train efficiency and reliability through:

- reduced rich/lean exchanger fouling
- reduced solution foaming frequency and tendency
- reduced contactor bottom and still top fouling rate
- reduced fouling rate for the vent tank chimney tower (if incorporated)

• An estimated Plant fuel saving of 0.28 mmscfd. The environmental benefit associated with this fuel savings will be the reduction of 3,000 to 5,000 tons/year of CO2 emissions. This assumption is based on an inlet gas with a high ratio of CO2 to H2 S as is commonly found in British Columbia and Alberta Canada
• Reduced train corrosion rates
• Prolonged amine solution life through a reduction in the amine degradation rate

COMPARISON OF CARTRIDGES TO REI BACKFLUSHABLE FILTRATION SYSTEMS:

The total potential annual cost savings for O&M ($650,000) plus cartridge procurement/replacement and disposal ($555,583) = $1,205,583.

Other additional cost savings are:

(1) Lost revenue resulting from unscheduled maintenance due to plugging of heat exchangers, contactors, and/or regenerators. This typically occurs every 2 years with a 2-day turnaround, for a revenue loss of approximately $150,000 per day, for an annualized loss of approximately $150,000. Now, any associated maintenance would be done during the scheduled turnaround every 3 or 4 years.

(2) Reduced revenue due to incidents of foaming. Throughput can be drastically reduced during foaming with the duration lasting between 1 hour to 1/2 day. We conservatively assume 2 total days of lost production per year due to foaming, or $300,000. With a 50% reduction in foaming incidents using the REI IFS system, $150,000 would be saved .

(3) Chemical additives, i.e. anti-foamant and corrosion inhibitors average $45,000 per year. None of these chemicals would now be required.

(4) Amine reclamation is required as often as once a year when the corrosion rate is elevated or if there is high iron content or excessive levels of salts or degradation products. It typically costs $10,000 dollars per day (including the per gallon process fee) and takes approximately 14 days to complete. This service would now be performed every two years for annualized cost savings of $70,000.

(5) Significant quantities of amine can be lost during the disposal of replacement cartridges. It is estimated that the amine losses are approximately 5 percent of the volume of a typical cartridge, even
with limited "drip" drying. This equates to an annual loss of approximately $31,000 (MDEA) using the cartridge replacement figures discussed earlier.

(6) Lost amine due to carryover during "foaming" can result in losses of 5% of the amine inventory. Assuming an amine inventory of fifty-thousand gallons of MDEA ($4.00 per kg) this equates to a potential loss of approximately $40,000 per year.

(7) Potential long term liability of (landfilled) spent amine cartridges, which contain trace amounts of heavy metals such as arsenic.

(8) Potential insurance claims from workers inadvertently exposed to hazards (H2S) while "changing out" cartridges.

(9) Increased costs due to erosion of piping (elbows and bends) and mechanical equipment (pump casings, seals and impellers).

Total additional costs = $486,000

When you add these total additional significant costs of approximately $486,000 to the $1,205,583 (from O&M and cartridge purchase/disposal economics) the potential annual total savings becomes $1,691,583).

For a more detailed explanation of how REI's backflush systems differs from the more inferior backwash filter systems, please see our webpage: www.remediationearth.comand look under the main heading "Technologies", then go to the sub-heading "Industrial Filtration Systems".

The Bottom Line: REI's IFS System is the cost effective choice for your total amine filtration solution.