20.01.2012 Refractory failures at 3x275 TPH Boiler BORL Bina

M/s ACE Calderys Pvt. Ltd. was awarded the work of Refractory supply, application ,Dry Out & Heat Curing of 3X33 MW CFBC Boiler at Bharat Oman Refinery Limited, Bina, Distt: Sagar, Madhya Pradesh. Vide order no. BHE/PW/PUR/BINA-REF/OJ-104/DLOA/43545 Dtd.24/04/2008. AA) With reference of above work order the site was mobilized in the month of March 2009 and the Progress of Refractory application work of unit #1, #2 & #3 including dry out is as follows. BOILER Sub

vendor Work Start Work

Complete Dry out with external burners

Dry-out agency

Unit #1 M/s NCCC & Polycam

16/03/2009 30/11/2009 23/02/2010 M/s Combustion Services

Unit #2 M/s URS 16/12/2009 15/07/2010 23/07/2010 M/s Heat Technologies

Unit #3 M/s URS 15/06/2010 29/11/2010 03/12/2010 M/s BHTL BB) The Boiler light up & coal firing dates are as below: BOILER LIGHT UP DATE COAL FIRING DATE Unit#1 27.05.2010 20.11.2010 Unit#2 30.08.2010 21.12.2010 Unit#3 18.01.2011 09.03.2011 CC) During the operations of the boiler, frequent refractory fall out was observed, the major fall outs are as below:

Stopped

Boiler#1

Started Reason 29/07/10 8/8/2010 During inspection on 1/8/10 combustor refractory

found damage 12/9/2010 25/09/10 During inspection refractory found damage at burner

side & work completed at 16/09/10 25/09/10 1/11/2010 During inspection seal pot -1&2 refractory damage 5/12/2010 2/1/2011 Boiler refractory work 22/4/2011 16/5/2011 Refractory damages at start up burner areas &

surrounding areas 31 05 2011 12 06 2011 Start up Burner Refractory damage 19 06 2011 29 06 2011 Start up Burner Refractory damage 16.08.2011 01.10.2011 Refractory, NMEJ, Tube leakages. Plastic refractory

application carried out during S/D

Boiler# 2

28/4/11 7/6/2011 Refractory damages at start up burner areas & surrounding areas

20/06/2011 08/08/2011 Tube leakages , SUB Refractory fall, NMEJ replacement

Boiler#3

18/4/2011 28/4/2011 Refractory damages at start up burner areas & surrounding areas

28/5/2011 19/06/2011 Refractory damages at start up burner areas & surrounding areas

12/08/2011 26/08/2011 Refractory, tube leakages. 06/11/2011 08/01/211 Clinker formation, refractory damage – plastic

refractory applied. FBHE-4 tube leakages. The above refractory dry out after repairs were done with startup burners as advised by M/s ACE Calderys. Boiler#1 was run for almost 5 months & Boiler#2 for almost 4 months, with coal firing and clinker formation started only after 20.04.2011. BORL had started using their own refinery produced oil, which got mixed up with some other contaminated oil during this time and thereby completely changing the oil properties and resulted into the clinker formation and ultimately refractory fall out in all the boilers.

Cross- section of burner throat area.

REASONS FOR REFRACTORY FALL OUT:

Mostly refractory fall out is observed at BURNER THROAT

area, which results into tube exposure and if it is not attended immediately, there are chances of tube erosion and leakages.

The attending the CFBC tubes in burner throat area is a herculean task, unlike conventional boiler where tubes are easily assessable. In CFBC boiler, tubes are under refractory and whole of refractory are to be removed & seal boxes are to be cut for assessing the tubes.

BURNER THROST AREA, EXPOSURE OF TUBES IS MARKED WITH ARROWS.

ANOTHER BURNER THROAT, WHERE TUBES & ANCHOR EXPOSER CAN BE SEEN CLEARLY.

DESIGN ISSUES:

- The existing burner profile is fouling over the seal box and water tube. The sizes of seal boxes are 1160mm for front side & 1060 mm at rear side. On account of this, the refractory thickness inside the seal box is very less.

- During the discussions with ACE Calderys & Trichy designer, the inner cone diameter is reduced to 986 mm from 1086mm.

- During the recent meeting with ACE Calderys, they have explained that profile design was followed as provided by BHEL Trichy, which was supplied by burner vendor M/s Coen Bharat. The similar problem was faced for NLC burner also and noticed by using 3D software, which was not available at the time of designing of BORL bina refractory. The 3D model for the same is given below:

- Further M/s ACE Calderys proposed to reduce the angle of the cone of burner profile i.e. instead of two cones, one cone design and also another proposal of providing the SS sleeve in the first tube, so that if any failure in the refractory (as the thickness is very less at the middle of the SUB), tube at the middle will be exposed and protect the puncture. BHEL Trichy did not accept the proposals.

- To avoid the hot spots on seal boxes, now BHEL Trichy proposed to fix the 300X500X1400 boxes (Alloy steel plate 10mm thick, material 387 Gr 12) on both side of seal boxes of SUBs (Front & rear), where hot spots were observed. This modification is to done after initial heat curing and these boxes are filled with 200mm thick castable (Insulyte) and 100mm thick with Accoman-50 with sufficient nos of anchor (20 nos on each box). The sketches are as below:

REFRACTORY MATERIAL ISSUES

Presently, Accmon-50 grade refractory supplied by M/s Ace Calderys has been used at BORL-Bina Boilers, which is having following specification:

As per BHEL Trichy, Accmon-50 has been used for so many CFBC boilers and working properly. The experience of recently commissioned boilers with same refractory is as below:

SLPP experience:

In unit#4, they have used M/s Vesuvies supplied indigenous grade-50 refractory, which has failed frequently. Now they have applied grade-70 refractory, which also not giving satisfactorily service.

M/s SLPP has used grade-50 refractory for unit#3 imported from Germany and it has worked trouble free for more than a year.

PTIBR Indonesia experience

: M/s Calderys has applied Accman-50 on CFBC boiler installed by BHEL Trichy in Indonesia. After frequent failures of refractory, on recommendation of M/s Calderys, Trichy as a special case has agreed for Plastic grade refractory, which is working satisfactorily. The cost of Plastic refractory is 5-6 times of Accman-50.

Gujarat Ambuja

They had discussion with M/s Ace Calderys directly and procured higher grade refractory (Accman-80) for the refractory repairs.

: BORL had discussion M/s Gujarat Ambuja, where they have used Accman-80 for their CFBC boiler and it has run trouble free for a considerable time.

Kutch Lignite

: Refractory Accmon-50 was used by the M/s Ace-Calderys and has run trouble free for a considerable time.

BHEL Trichy did not agree for the use of any other refractory than Accmon-50, as during the tendering stage, M/s Calderys has offered the Accman-50 with the warranty/ Guarantee of 24 months. During the meeting with BORL & Ace Calderys on 03.07.2011, the problem of frequent failure and falling of refractory especially at Start Up Burners (SUB) of each of the boilers was discussed in detail and it was concluded that the specified refractory ACCMON -50 is best suited for this service/application and ACCMON-80 purchased on the recommendation of M/s Ace Calderys is not as much suitable for such type of boiler which are having thermal shocks. BHEL also opined that the anchors were adequate & as per drawing and most possible reason for the refractory falling was attributed to the inadequate refractory dry out procedure adopted by M/s Ace Calderys/ BHEL and later by BORL. Based on the above it was decided that for Boiler#2:

• The refractory would be replaced with ACCMON-50 • Dry out of the repaired refractory would be carried out using external burners

for slow heating and meeting the desired refractory dry out procedure • Protocol would be developed to ensure Quality Assurance during every stage

of application of the refractory • The complete repair of the refractory including dry out would be done under

the supervision of senior people from M/s Calderys and BHEL.

However, M/s ACE Calderys still insisted for the use of plastic grade refractory (ACCPLAST 70 SC) for the better performance & best suited for fuel used at BORL-Bina. A meeting was also arranged by BHEL Trichy on 28.07.2011 with M/s AE&E Lentjas, Germany and ACE Calderys on BORL Bina refractory issues, following is concluded: Lentjas representative informed that, the present refractory grade Accmon-50 used at BORL Bina is in line with their current engineering practice which is also working well in 125MW boilers at SLPP (Stage-I – where refractory was done under collaborator’s supervision) and in many CFBC plants in Germany. Lentjes opined that Accmon-50 refractory as envisaged in the design, is to be applied and cured properly as per recommendation of the supplier for achieving intended life without failures. Lentaj also informed that refractory curing is to be done with external burners/ electrical sources to control the drying at a very slow rate (Unlike done at BORL Bina with startup burners after repairs). Start up burners is never used for curing. Lentjes also informed that plastic refractory is also used for the repair purpose in Germany. M/s ACE Calderys explained the technical reasons for repeated failures of refractory (Accmon-50) in the startup burner areas mainly due to use of unspecified oil and Indonesian coal (which is having high alkali content), resulting into clinker formation/ adherence, impregnation of clinker & low melting compounds in refractory pores, flame impingement & spilling. Considering the various operational issues like clinker formation, fuels used like unspecified oil, Indonesian coal, etc. and to overcome refractory failures, use of plastic refractory (ACCPLAST 70 SC) was proposed, which is having following advantages over the presently castable refractory Accmon-50:

- It is a non cement based refractory so there is no chance of reaction with moisture.

- It has a Phosphate bonding which gives good strength at low temperature of around 260-3000C

- It forms a glassy non sticking surface thus preventing the penetration of alkali inside the refractory.

- It is of ready mixed type and is applied by the pneumatic ramming which avoids the quality issues related to mixing/ installation at sites.

It was also confirmed that Accplast 70 SC refractory application with proper curing, will withstand the service conditions without any failures. BHEL (Corporate R&D) also confirmed that plastic grade refractory proposed is superior to Accmon-50 and is suitable for the service conditions. Finally it was decided to go for the plastic refractory (ACCPLAST 70 SC) in the start- up burner throat area in the combustor in one CFBC boiler at BORL-Bina.

FUEL USED BY THE BORL

The major problem of refractory fall out in Boiler#1&2 observed from 18.04.2011, when BORL started using their own refinery produced oil which was not as per the BHEL specifications. The hot spots on both the side of seal boxes were observed. The analysis of oil (taken immediately from Boiler#1&3 after shut down on 28.04.2011) was carried out at Shriram Institute for Industrial research, Delhi, the report is as below:

From the test report, it can be seen that nothing is conforming the specifications.

Immediately after the receipt of oil report, M/s BORL was advised to drain HSD oil tank and pipelines completely and fill up with fresh HSD oil as per IS:1460-2005 before the boiler light up to avoid recurrence of choking of oil guns and clinker formation. The Boiler#1 was restarted on 16.05.2011, but has to be stopped on 31.05.2011 due to hot spots observed on the burner seal boxes. The oil sample was collected and sent for analysis:

This report was more or less in line with BHEL specifications and cleared by Trichy.

OPERATIONAL ISSUES

Based on the analysis, carried out by our Boiler experts from Trichy, regarding clinker formation (Boiler #1 and #2) and corresponding refractory damage, the following was concluded: a) From the operating data, it is seen that the solid fuel was admitted well below the auto ignition recommended temperature bypassing the operational logics. It is also noticed that combustor middle temperature has exceeded limits whenever higher steam generation was attempted with low combustor bottom temperature with solid fuel addition. Admission of fuel at lower temperatures than limiting value has resulted in heavy clinker in combustor. b) Oil quality: As per IS 1460, HSD is a straight run fuel complying with specific characteristics. However as per the report (enclosed) for the sample collected from CPP area, it is observed that fuel is not meeting the required specification criterion which is major cause of clinker formation. c) It was also seen during burner/ bed lance operation that there existed a condition of oil pressure exceeding atomizing air pressure. This inversion in pressure conditions has resulted in oil dripping on throat as against the desired atomized spray resulting into clinker formation. d) The chemical composition of the clinker indicates that the ash constituents and its contribution (%b wt) are mostly from coal ash. However, the presence of high level of vanadium (1000ppm) and to some extent Nickel (200ppm) are high compared to about 300 ppm Vanadium and 100 ppm nickel normally present in Indian/ Imported coal ashes. Presence of higher vanadium suggests mix up of fuels having high vanadium during the above operation. From above it is concluded that: • Combustor clinker in units #1 and #2 is attributed to admission of solid fuel at much lower temperature than recommended. High vanadium fuel mix up without maintaining operational pre-requisites could have further worsened the operational stability. • Burner throat erosion/ clinker are attributable to non compliance of operational requirements associated with oil of the requisite quality. The above clinker formation & refractory fall out was analyzed with: 1. Boiler operating data collected from Control room. 2. System observation. 3. Laboratory analysis of clinker (collected from Boiler)

REPAIR WORK & APPLICATION OF REFRACTORY:

The following activities involved for the repair of burner throat area: AA) Dismantling and cleaning of old refractory - the photographs during the removal of refractory:

BB) Fixing of the anchors on the tubes and seal box as per drawing and site requirement

CC) Application of Bituminus paint on anchors & Covering of anchor tip with insulation tape.

DD) Mixing & application of INSULYTE-11 and air drying for 12 hrs. DD) Fabrication of fixing & shuttering of the burner throat area.

EE) Mixing & pouring of castable Accmon-50 refractory in Shuttering stage wise & Vibro-casting FF) Removal of shuttering and allow to set (air drying) the material for 24 hrs. GG) Drying with 6 Halogen in each burner for 24 Hours HH) Heat Curing (Dry out) for 65 Hours as per graph submitted by ACE Calderys. The agency (Heat application (I) pvt Ltd, 3-B, Sun commercial complex, beside Citibank, Gotri road, Vadodara 390007, Phone – 0265-2324340, 2326064, 9979889533) was engaged for heat curing, which took 3 days for completion.

AFTER COMPLETION OF REFRACTORY CASTING

The activities from AA to HH were completed in 14 days.

First Light up burner 1 only and note the temperature. Temperature is to be raise 25°C /hour up to 260°C and after that heat curing curve to be followed up to 60°C and then operation temperature. It means if the temperature shows immediate after start of Burner -1 is 175°C then the raising temperature of next hour will be 200°C and two hours later temperature will be 225°C and so on. Burner no. 2 can be start when it is requiring maintaining the schedule.

After light up, the dry out procedure is as below:

BURNER THROAT SEAL BOX MODIFICATION:

completed by arranging the alloy steel plates size 10mm thick 387 Gr 12 (300X1400 – 4 nos, 500X1400 – 4 nos, 300X500 – 8 nos) from BHEL Bhopal as per last item of design issues.

SEAL POT TO FBHE

: During the inspection of duct connecting to seal pot to FBHE at spies valve joint, no refractory was found as per drawing below:

The following procedure was followed:

- Cut the pockets approx. 200X200mm on the top of the gap minimum 6 nos circumferentially.

- Weld metallic anchors from the pocket. - Cast Insulyte-11 around 150mm thick by tamping method. - After 5-6 hrs, cast Accmon-50 along with refractory binder and apply it by

tamping method and maintain the inner diameter. - Inner face of pocket to be filled with Accmon-50 and outer face of the pocket

around 50mm thick to be filled with 12/25 mm thick cermic fiber blanket. - After setting the castable, close the pocket by welding.

The above work for 4 nos joints took 4 days. BOILER LIGHT UP IS DONE ON 08.08.2011, INITIALLY FOR 48 HRS FOR REFRACTORY DRY OUT PROCEDURE AND PERFORMANCE OF REFRACTORY TILL DATE IS FOUND SATISFACTORILY.

PLASTIC REFRACTORY (ACCPLAST-70SC) APPLICATION

However based on meeting between Director/Power & CMD/BPCL on 14.07.2011 and subsequent meeting on 28th & 29th July’2011 with the vendor M/s Ace Calderys in the presence of M/s AE&E Lentjes and specialist from CTI/corporate R&D, it was decided to apply ACCPLAST-70SC for Boiler#1 burner throat area

- Complete removal of refractory from burner throat areas.

as a confidence built up with the customer BORL. The following decisions were made:

- Modification by extending the seal box of burner throat. - Additional anchor welding on water wall tubes. - Application with a modified drawing - a minimum 200 mm plastic refractory

on the water wall tubes. The engineering specifications prepared based on above was also forwarded to other refractory supplier & applicators - M/s Vesuvius & M/s Tata Refractory, but they did not respond. Finally PO for supply & application was placed on 12.08.2011 on M/s ACE Calderys for Rs 28.22 lakhs including all taxes & duties for BORL Unit#1, which was 4-5 times higher than normal refractory Accmon-50. The tube leakage in the boiler#1 combustor was observed on 16.08.2011 and immediately boiler was taken under shut down. On inspection, SUB#2 (RHS) refractory was found damaged & fallen down and also tube puncture was seen.

The clinker formation was seen on both the SUB areas.

SPECIFICATIONS OF PLASTIC REFRACTORY ACCPLAST-70SC

REFRACTORY ARRANGEMENT IN BURNER FOR COMBUSTOR WITH PLASTIC REFRACTORY

APPLICATION OF PLASTIC REFRACTORY IN BOILER#1

1. Dismantling of exiting refractory. 2. Cleaning the surface to remove the dust particle and old hot surface

refractory over the backup layer by using compressed air. 3. Check and Cut & extend the seal boxes as per fabrication drawing.

4. Marking the location of the metallic anchor as per pitch indicated in the

refractory application drawing.

5. Welding of additional anchors on the water tubes & checking the quality of

welding if any additional/ extension is required weld anchors as per site conditions.

6. Hydro test of the boiler after welding to ensure no tube puncture.

7. Install insulating cast-able on the bottom of the seal box & side walls also as per thickness mentioned in the drawing.

8. Natural curing of 4-5 hrs after insulating cast-able. 9. Plastic is cut into small pieces (~50mm) and apply for a height of 100mm all

along width (thick) and ram that area. 10.The plastic refractory application carried out by using 2 nos of pneumatic

rammer (CP-4117) with steel/ aluminum & rubber buts, hose pipes, compressed air (Min 4-5 Kg/Cm2) and masonry tools & tackles. To ensure the proper compaction, a small (100X100X75mm) mock up test conducted.

11.Plastic thickness built as per burner profile with proper ramming.

12.Trimming the excess plastic as per burner profile. 13.Check the surface of the plastic refractory. In non uniform surface, apply

small piece of plastic refractory and ram the surface slowly by using pneumatic rammer with rubber butt only (no metallic butts are to be used). Level with masonry trowel in the rammed area.

14.Contraction cut provided as per drg on plastic refractory surface. The construction up to half of the thickness of hot face refractory.

15.Provide vent holes dia 2.5mm to 3mm @300mm C/C on hot surface of the plastic refractory for easy removal of moisture during dry-out refractory.

16.Scratching on refractory surface shall be done. Under any circumstances, no toweling on plastic surface is allowed as it will seal the porous surface on the refractory surface if toweling is done. As plastic refractory was done in rainy season, localized heating with the help of heating torch/ gas cutter was required to make the surface enough hardened to avoid any kind of slow setting behavior of the installed plastic due to high humidity in atmosphere.

17.Dry out of refractory as per heating schedule:

The light up of boiler#1 was done on 01.10.2011 and temperature of the combustor was raised @ 500C per hour till it reached to the operating temperature of 5000C on oil firing. After running more than a month, boiler#1 refractory was inspected on 11.11.2011 during the shut-down of the boiler and more or less plastic refractory was found in order.

However during the inspection of boiler#1 on 23.01.2012, the cracks & falling down of plastic refractory were observed as below:

M/s ACE Calderys commented on this refractory fall out as under: “First of all spalling of top layer is not a failure. This has happened at the bottom portion where lining thickness left even after spalling is adequate. This lining will last for another one year or more. Please take the boiler into operation and we will inspect it during next shutdown. The salient feature of this material is “Whenever spalling takes place, the new exposed surface again forms glassy coating and works as a fresh surface taking care of erosion and thermal shock". This material is the best solution for long life where operation is disturbed resulting in Thermal Shock and coating formation. It is proven at several locations time and again.” Boiler was continued to be operated in the same condition. The minor repair work of SUB area was carried out with the left out plastic refractory from Boiler#3 on 17th & 18th Jan’11 during the shutdown of boiler due to refractory fall out in the return leg of combustor. On the insistence of BORL, plastic refractory work in SUB area was also carried out in Boiler#3 also and it was lighted up on 08.01.2012. The process of plastic refractory application took almost 30 days from date of start of refractory dismantling to dry-out.

CONCLUSION: The refractory failure was mainly due to

- Wrong use of the fuel, not as per BHEL specification and use of lances burner & introduction of coal at much less temperature recommended by BHEL. It has resulted into the clinker formation in the combustor, which has damaged the refractory.

- The trajectory of the flame was touching with the refractory & damaging the refractory.

- As it can be seen in the 3D model, the refractory thickness (30-50 mm) on the tubes was very less and getting exposed on the slight refractory damage.

- The heat curing after refractory repair was done with the light up of Boiler, which was resulting into the insertion of small particles of bed material into the refractory and causing the frequent falling down of refractory after rectification.

Following measures were taken to overcome the problem:

- Revision in the refractory application drawing with 3D software. - A clear thickness of 200mm plastic refractory on the tubes. - Modification of seal box. - Fixing of extra anchors on the tubes. - Application of improved plastic refractory ACCPLAST-70SC - Heat curing of the refractory after application with external burners. - Changing of burner tip angle from 550 to 500.

With the application of plastic refractory and modification, it is hoped that refractory will last 1-2 years.