Water Technologies & Solutions case study

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CS1537EN.docx Aug-15

HTP-2: boiler on-line cleaning returns 3.2 m$/yr of savings by avoiding unscheduled shutdowns Authors: Guidetti Alessandro, Genc Emir Hakan - SUEZ Gulcen Çetin, Soke Osman – AKSA Akrilik Kimya Sanayi A.S

abstract

“AKSA” Acrylic Chemical Industry Co. is located in North West Turkey and is the world's largest acrylic fiber manufacturer. AKSA exports products to more than fifty countries worldwide. AKSA has four large cogeneration plants which produce electricity and supply steam to the acrylic fiber plant. In 2012 and 2013, AKSA experienced boiler tube failures on the water side due to overheating caused by iron oxides build up. The unplanned shutdowns directly affected both electricity and the acrylic fiber production which resulted in financial losses for the company. SUEZ provided AKSA with a unique Boiler Water Treatment Solution, which realised a financial saving estimated to be 3.2 M$/year.

challenge

AKSA’s steam production system comprises of four natural gas fired boilers and two coal fired boilers. The natural gas boilers operate at 59 barg and generate a maximum of 450 t/hr of steam. The coal fired Boiler I operates at 86 barg and produces 408 t/h of supeheated steam at 510°C. The coal fired Boiler II operates at 96 barg and produces 230 t/h of supeheated steam at 535°C. The steam generated is used to drive steam turbines to produce electricity and as part of the acrylic fiber production process. The steam condensate is partially recycled without polishing plant; the make-up water is produced via a demineralization plant and mixed bed.

The average total iron level in the boiler feedwater was <20 ppb as Fe, however there where some spot samples which had levels >150 ppb as Fe.

A number of boiler tube failures occurred in both Boiler I and Boiler II. SUEZ conducted several metallurgical studies which confirmed that the failures were due to long-term overheating. Deposit Weight Density (DWD) measurements and elemental analysis confirmed the presence of 9 gr/dm2 of deposited material and the predominant species was iron oxide.

Figure 1 and Figure 2 show a picture of one of the failed boiler tubes and the SEM-EDXA elemental analysis results of the deposit respectively.

Figure 1: View of one of the failure sites; longitudinal failure crack with parallel cracking in an area of tube swelling (bulge).

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Figure 2: Deposit analysis results (SEM-EDXA)

SUEZ solution

Based on the number of boiler tube failures and the confirmation of iron based deposits it was suggested that it would be appropriate to acid clean the boiler to remove the internal deposits and then passivate to restore the required, protective magnetite layer. SUEZ proposed an alternative solution to avoid acid cleaning, the application of HTP-2 polymer technology which had been used previously for on-line cleaning of boilers1.

This unique molecule, named PIPPA (polyisopropenylphosphonic acid), is a superior metal oxide dispersant and is generally applied in high pressure boilers where iron or copper oxide deposits are likely to form on high heat transfer surfaces.

Figure 3: anionic polymer functional group

The PIPPA acts as a dispersing agent rather than a chelant by releasing some orthophosphate from the phosphate radical group off the polymer chain. The

orthophosphate would then form a chemically stable iron or copper-phosphate particle should any soluble iron or copper be present next to the chemically stable metal oxides solids1.

results

SUEZ have been treating the AKSA system since September 2013. The current boiler water treatment regime utilises the following products, CorTrol* OS5614 (carbohydrazide based oxygen scavenger), Steamate* NA0940E (blend of neutralizing amines) and OptiSperse* HTP0453 (internal treatment, cleaning agent).

The on-line cleaning procedure was monitored by measuring the total iron mass balance within the boilers when applying a minimum target of 400 ppm as OptiSperse HTP0453 in the boilers.

Figures 4 and 5 show the base line data and the increase in total iron levels after the treatment start-up. The cleaning effect is clearly observed by the increase in the total iron levels measured in the boiler water samples resulting in an iron transport of >100%, thus proving the effectiveness of the on- line cleaning effects of the HTP-2 polymer.

Figure 4: Boiler I water total iron vs time

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Figure 5: Boiler II water total iron vs time

After six month of OptiSperse HTP0453 treatment, AKSA decided to confirm the effectiveness of the on-line cleaning by cutting out a boiler water tube samples during a scheduled maintenance shutdown. As can be clearly seen in Figure 6 the simple visual examination confirmed the good performance of the HTP-2 on-line cleaning by revealing, for both boilers sample tubes, clean and smooth internal surfaces.

Figure 6: Boiler I, internal water tubes picture before HTP-2 treatment (top) and after (bottom)

Figure 7: Boiler II, internal water tubes picture before HTP-2 treatment (left) and after (right)

In March 2015, during a scheduled maintenance shutdown of Boiler I, a boiler tube sample was removed and submitted for metallographic analysis. The Deposit Weight Density (DWD) analysis confirmed the effectiveness of the OptiSperse HTP0453 internal treatment program to reduce the deposit DWD and thickness, as shown in Figure 8 below.

DWD

(g/dm2)

Deposit tickness

(mm)

Sept 2013 9.0 0.4-1.2

Mar 2015 4.2 0.02-0.12

Figure 8: DWD determination on Boiler I

conclusions

The performance of the OptiSperse HTP0453 treatment program has been confirmed by analytical monitoring and metallurgical analysis. However the most important practical result being the fact that AKSA have not suffered any boiler tube failures on either Boiler I or Boiler II since the treatment started.

By avoiding unscheduled boiler shutdowns and electricity outages the plant saving are estimated at 3.2 M$/yr without taking into account the maintenance costs and health and safety concerns.

The quality of the boiler feed water and the recent DWD determination confirm the on-line cleaning capabilities of using OptiSperse HTP0453.

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SUEZ is working with AKSA to optimize the current condensate corrosion control program. Implementing and monitoring product dose rates in order to reduce the corrosion rate in the complex condensate network of the plant. The reduction in corrosion rates will reduce the total iron content in both the condensate return and the boiler feed water.

references 1. On-line Cleaning of Boilers Using a Novel Polymer

Technology to Avoid Acid; Carter W. Brown, Mark A. Moore, Saleh A. Al-BenHamad, Michel Didden.