MAX HT®

Eliminates Sodalite Scale Accumulation in Alumina Refineries

BackgroundThe problem of sodalite scale in Bayer Process alumina production is well recognized and documented. When caustic liquor is heated in digester heaters, dissolved silica reacts with the caustic and alumina to form sodalite, which precipitates as scale on the hot surfaces of the heater. As scale develops in processing equipment, the heating surfaces become less thermally conductive, resulting in lower heating efficiency, or Heat Transfer Coefficient. Heat Transfer Coefficient decays continuously over time with the accumulation of sodalite scale. This, in turn, reduces evaporation and flow. The end result for refineries is loss of caustic and alumina, increased energy consumption and higher maintenance costs, all of which leads to lower production rates and higher production costs.

Up until now, the alumina industry has been forced to deal with this ever-present problem by removing scale after it has accumulated, which is a costly and time-consuming proposition.

Cytec’s Answer Emphasizes Prevention over CorrectionCytec’s revolutionary new solution – MAX HT sodalite scale inhibitor – tackles scale through an entirely different approach: by preventing it from forming. MAX HT sodalite scale inhibitor completely eliminates sodalite scale accumulation in liquor heat exchangers and inter-stage piping. In so doing, it achieves the following:

- enables plants to maintain Heat Transfer Coefficient and, thus, efficiency in heat exchangers

- precludes the need to inject steam directly into liquor heaters or digesters

- makes acid cleaning of heat exchangers unnecessary

Simply put, MAX HT sodalite scale inhibitor helps alumina refineries realize increased operating efficiencies and significant cost savings by rendering the once ubiquitous problem of sodalite scale into a distant memory. Consider the additional benefits:

- reduce energy consumption- lower costs for sulfuric acid to clean

equipment- eliminate the danger associated with having

plant personnel manually clean equipment - eliminate downtime required for cleaning

MAX HT sodalite scale inhibitor is designed to help free refineries from operational constraints, and solve a problem which the industry currently spends significant time, manpower and expenses correcting.

How Does It Work?Very simply, if solid sodalite is not present in the liquor, then scale cannot form. Our challenge was to find a product that would prevent solid sodalite from forming. The hypothesis that precipitation is reversible if the nuclei do not grow to a critical size became the foundation of our efforts. MAX HT sodalite scale inhibitor works by having inhibitors attach to embryos, or “micronuclei,” to stop them from growing into “nuclei,” thereby reversing the precipitation process. This prevents solid particles from ever forming.

Heat Transfer Coefficient

2Think of the possibilities...

Soluble IonsEmbryos or

“Micronuclei”r < r*

MAX HT Sodalite Scale Inhibitor

Reversible r* Irreversible

Heat Transfer Coefficient decay curve of a normal heat exchanger, without use of MAX HT sodalite scale inhibitor.

Benefits to the CustomerMAX HT sodalite scale inhibitor brings a host of far-reaching benefits to alumina refineries.

In the Evaporators:

• HigherHeatTransferCoefficientpromoteshigher levels of evaporation. Depending on the economic balance between caustic and energy costs, plants may choose to either:

- run higher mud wash flows, thereby reducing soda loss (caustic savings) or

- reduce the number of evaporators in service, thus reducing energy consumption

• Improvedflashingresultsinlowerlivesteamdemand for the same evaporation rate, thereby improving evaporator economy.

•Eliminatesacidcleaning/maintenanceofsodalitescale accumulation. As a result, there is no need to change tubes that would otherwise be subjected to acid corrosion.

In the Digesters:

• Increasedflashingandevaporationresultsinthe ability to run higher mud wash water flows, which reduces soda losses.

•Higherliquortemperatureinvaporheatersreduces live steam demand in live steam heaters.

• Withcleanerlivesteamheaters,itispossibletoachieve higher liquor-to-digester temperatures. Plants no longer need to reduce liquor flows due

to low digest temperatures. Higher average liquor flows will therefore be maintained, which results in increased production.

• Higherliquor-to-digestertemperaturesreducesthe need to inject steam directly into the digesters. This results in:

- Reduction in extraneous dilution – hence, higher mud wash and improved soda recovery.

- Reduction in energy consumption – condensate associated with steam injected into the live steam heater can be recovered and returned to the power house as boiler feed make-up water (instead of being fed into the digester). The temperature of the make-up water will now be at ~90˚C, versus ambient ~20-30˚C. The chemical treatment required for this quantity of fresh make-up water is also reduced.

• Inmanyplants,asscaleaccumulatesinthelivesteam heaters, the steam valves to these heaters open wider. This results in higher shell side pressures and, ultimately, higher condensate temperatures. As the condensate temperatures increase, more flashing occurs and significant energy is lost. MAX HT sodalite scale inhibitor eliminates this.

•Hightemperatureplantsthatoperateadirectinjection live steam heater can convert this to an indirect heater, thereby saving energy (condensate returned to power house) and soda (elimination of extraneous dilution).

When applied to the

evaporator feed, MAX

HT sodalite scale

inhibitor has been

proven effective

in the evaporators

and is still beneficial

in the digester

liquor heaters.

Heat Transfer Coefficient decay curve of a heater run with MAX HT sodalite scale inhibitor.

Heat Transfer Coefficient

3

Nucleir = r*

Scale Particlesr > r*

MAX HT Sodalite Scale Inhibitor

Extensive field and

laboratory testing

has revealed no

negative effects on:

predesilication,

digestion, extraction

efficiency, desilication,

mud settling,

hydrate precipitation,

yield, PSD, product

quality, oxalate

precipitation, and

head gases from high

temperature plants.

In addition, the product

causes no interference

with other process

chemicals such as

crystal growth

modifiers and defoamers.

Bauxite Quality/Mining:• Incertaincases,thesilicacontentofbauxite

is critical for the protection of heaters and inter-stage piping. However, with the use of MAX HT sodalite scale inhibitor, this becomes less of a concern (assuming product silica specification is not jeopardized). As a result, refineries may relax bauxite blending and mining programs to achieve acceptable silica levels for proper desilication.

Pre-desilication:

•Pre-desilicationtocontrolsilicainliquorfor the protection of heaters and pipes from scaling may also be severely relaxed (as product quality allows). This could have tremendous financial implications for Brownfield and Greenfield expansions.

- The number of tanks required for pre-desilication would be reduced.

- The pumping requirements would be significantly reduced.

•Forexistingplants–eliminatesdilutionfromdirect steam injection, allowing for higher mud wash and improved soda recovery.

•Reducesenergyforpumpingacrossthe pre-desilication circuit.

Plant Stability:

A stable alumina plant is highly desirable. The more stable the operation of the plant, the higher the rate of production and the greater the capacity to optimize processes. Clean heaters and inter-stage piping in both evaporators and digesters enhances plant stability through maintenance of constant:

•Steamflows(positiveimpactonthe power co-generating plant)

•Evaporationrates

•Liquor-to-digesterflows

•Digesttemperatures

•Digesterblow-offtemperatures (impact on thickener operations)

Extensive Testing Bears out Product EfficacyMAX HT sodalite scale inhibitor has undergone exhaustive pilot and plant testing, which has demonstrated the value of the product under actual production conditions. Dosages as low as 20 ppm have proven effective, though actual dosages depend upon equipment configuration and composition of bauxite.

Product Is Benign to the Overall System MAX HT sodalite scale inhibitor has been shown to cause no impact whatsoever on silica concentration in digester blow-off. In the presence of solids, the product will adsorb onto the solids, thereby rendering them innocuous. As MAX HT enters the digesters with the mud solids, it ceases to be effective. Thus, desilication occurs as per normal. MAX HT leaves the circuit with the mud and does not build up in the circuit.

In short, MAX HT sodalite scale inhibitor does only what it is intended to do – namely, eliminate sodalite scale – and nothing more.

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Although the information and recommendations set forth herein (hereinafter “Information”) are presented in good faith and believed to be correct as of the date hereof, no representation as to the completeness or accuracy thereof is made. Information is supplied upon the condition that the persons receiving same will make their own determination as to its suitability for their purposes prior to use. NO REPRESENTATIONS OR WARRANTIES, EITHER EXPRESS OR IMPLIED, OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR OF ANY OTHER NATURE ARE MADE HEREUNDER WITH RESPECT TO INFORMATION OR THE PRODUCT TO WHICH INFORMATION REFERS.

TRADEMARK NOTICE The ® indicates a Registered Trademark in the United States and the ™ or * indicates a Trademark in the United States. The mark may also be registered, the subject of an

application for registration or a trademark in other countries.

• Email: custinfo@cytec.com Worldwide Contact Info: www.cytec.com US Toll Free: 800-652-6013 Tel: 973-357-3193 •

© 2008 Cytec Industries Inc. All Rights Reserved MCT-1096-A

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Dosing pump to booster pump suctions

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