2010 CoalGen Conference – Pittsburgh, PA Aug 10 – 12, 2010 Study of the full implementation of the SmartCleanTM System at SRP Navajo Power Generation Unit 3

Ati Manay, PMP, P.E. - Clyde Bergemann, Inc, Atlanta, GA, USA Danny S. Tandra, Ph.D. - Clyde Bergemann, Inc, Atlanta, GA, USA

ABSTRACT

Reliable power generation and optimum plant heat ra te are the two most im portant targets that will determine the profitability of a coal fired power plant. Uncontrolled fouling and incorrect cleaning strategy in the convection sections will not only in crease the plant h eat rate, but may also lead to costly forced-o utages due to sootbl owing induced tube er osion. Conventional sootblowing systems, which are typically operated with a pre-determined sequence based on past experiences, cannot be efficientl y tuned to keep up with the dyna mic changes in the slagging and fouling conditions inside the boiler. Unlike c onventional systems, Sm artCleanTM Intelligent SootBlowing optimizes the plant h eat rate and prevents heavy fou ling by detecting the location and tenacity of the foul ing in real-time and uses this info rmation to dynami cally manage the sootblower operation. The system al so prevents over cl eaning of the boiler tubes by triggering cleaning operations only when th ere is decay in the heat tran sfer performance of the heat exchangers. This paper discusse s a case study of the full implementation of the SmartCleanTM Intelligent SootBlowing (ISB) system at SRP NAVAJO power generation station Unit 3. The newly installed (i) Super-Heater Fouling Monitor (S HFM) and the Thermo Dynamic Model (TDM) in the convection sections, is used to continuously monitor the cleanliness of the heating surfaces, and to evaluate the effect of sootblowing and resulting plant performance. (ii) 4 Smart USX adjustable cleaning intensity sootblowers are used to reduce the jet progression time on the areas where sootblowing relate d tube erosion has been expe rienced. The decreases in the Economizer Exit Gas Temperature (EEGT) and the re heat spray flow indicate that the thermal efficiency of the boiler was in creased following the implementa tion of the ISB system and the plant heat rate has been improved by approxima tely 0.7%. The corresp onding reduction in the

CO 2 emission was 4.29 tons/hr. The improvements in reliability a nd boiler availability by the SmartCleanTM system implementat ion will be evaluated in the next few years as Unit 3 was reconditioned in February 2009 with a major boiler overhaul.

INTRODUCTION

SRP Navajo Generating Station unit 3 is an 800 MW gross (750 MW net) sub-bituminous coal fired boiler. In the past the plant has experien ced sootblower induced tu be erosion at the nose arch, Superheater and Reheater Pe ndant sections of the boiler. Prior to the installation of the SmartCleanTM ISB system, all of the cleaning devi ces were manually oper ated according to the boiler operator’s discretion and th e plant standard pract ices. The clearance for sootblowing at the

nose arch area between the sootblower nozzle and the tube bank is less than 24” with a required 40 feet travel length. Unit 3 has also experienced tube damage due to condensate purge at the

first few feet of the travel. Forced boiler shut downs took place due to s ootblower related tube damage in the past years. As a result, Unit 3 was reconditioned in February 2009 with a major2010 CoalGen Conference – Pittsburgh, PA Aug 10 – 12, 2010 boiler overhaul. Figure 1 shows th e main challenges that SRP Nava jo Station has dealt with on Unit 3 in the past years.

Extensive research by both university and industry has revealed that over and under cleaning of boilers can significantly increase the risk of prem ature tube failure [1,2]. Over-cleaning causes sootblower-induced-tube erosion, while under-cleaning promotes coal ash corrosion, localized

heat transfer increase and tube overheating. In addition, over and under cleaning will adversely impact the boiler thermal efficiency and most importantly im pose a heavy penalty on the ove rall plant heat rate.

Clyde Bergemann, Inc. Sm artCleanTM ISB syst em was installed and commissioned in June 2009 along with 4 Smart USX sootblowers on Unit 3 to reduce tube erosion as a reliability improvement project.

The SmartCleanTM ISB system at SRP Nava jo unit 3 consists of (i) 4 Smart USX adjustable/targeted cleaning intensity sootblower s, 28 conventional retractable sootblowers, 4 SHFM (Zones 1 to 4), and 11 TDM (Zones 5 to 15) cleaning zone s in the convection sections. Figure 2 shows an overvi ew of the system. Figure 1: SRP Navajo Unit 3 Main Challenges2010 CoalGen Conference – Pittsburgh, PA Aug 10 – 12, 2010 Figure 2 SRP Navajo Unit 3 SmartCleanTM ISB System

SHFM (SuperHeater Fouling Monitor) is a network of strain gaug es, mounted on the hanger

rods of a boiler convection sec tion, whose main purpose is to detect the change in the load experienced by the rod due to the accumulation of deposit in the convection section. Every time a sootblower is operated, the SHFM me asures how much deposit is removed, in term of lb deposit removal. This information is then used by the ISB system to manage sootblower operation and to rank them accordi ng to its effectiveness in re moving deposits. SHFM can also provide early detection of clinker formation and prevent it to grow to a larger size by selecting and sending appropriate sootblower s to control the formation.

TDM (ThermoDynamic Model) is a thermodynamic program that uses boiler operating parameters to dynamically calculate the cleanliness fact or (CF) of boiler convection sections. CF is the normalized heat transfer efficiency of the heat exchanger in real time. In other words, CF equals to one is the condition where the heat ex changer is clean and free from deposits. The CF information is used by the SmartCleanTM ISB syst em to determine whether to send sootblowers to clean the exchanger or to let it fouls to a certain level and achi eve balanced heat transfer rate

that benefits the overall boile r and plant performance.2010 CoalGen Conference – Pittsburgh, PA Aug 10 – 12, 2010 ISB PERFORMANCE EVALUATION

A performance evaluation of the SmartCleanTM ISB oper ation was conducted to compare it with that of the conventional SEQUE NTIAL system on the overall boi ler operating condition, thermal efficiency, and plant heat rate . The SEQUENTIAL runtime was sel ected for a 5 day period just before commissioning of the ISB system. The evaluation for the ISB counterpart was conducted for another 5 days period in the following year after 1 year of ISB operations. Similar seasons with similar ambient temperatures were selected to have a fair evalua tion. No heat transfer surface additions or other syst em upgrades took place in betw een the two evaluation periods which can affect plant heat rate and boiler efficiency.

RESULTS & DISCUSSIONS

The convection sections c onsist of (i) SH Pendant Division Pane l, (ii) Platen Superheater, (iii) Final Reheater, (iv) Finishing Su perheater Pendant, and (v) Econo mizer, as depicted in Figure 1. The Final Reheater, and the Fini shing Superheater Pend ant were equipped with both the SHFM

and TDM. The other sections of the boiler were equipped with just the TDM. Figure 3 compares

the CF of the Platen 2 nd Superheater when the boiler was run under ISB and SEQUENTIAL sootblower control. Both Sequen tial and ISB control resulted in similar number of sootblower operations per day. However, ISB initiated 92% of the cleaning operations be low the clean level of 0.9 CF, reducing the risk of ov er cleaning and tube erosion.

Figure 3. SmartCleanTM ISB Preventing Over Cleaning2010 CoalGen Conference – Pittsburgh, PA Aug 10 – 12, 2010 BOILER THERMAL EFFICIENCY AND PLANT HEAT RATE

The improvement of boiler therma l efficiency can be detected through at least two parameters:

 Decrease in Reheat Spray Flow

 Decrease in Economizer Exit Gas Temperature (EEGT) During the performance test period, the Reheat Spray Flow of the ISB system was 9 – 15 KPPH lower than that under SEQUE NTIAL mode (Figure 4).

Figure 4 – Comparison of Reheat Spr ay flow under Non-ISB and ISB modes

Decrease in Economizer Ex it Gas Temperature (EEGT)

Figure 5 compares the ISB and SEQUENTIAL Economizer Exit Gas Temperature (EEGT)

trends. The EEGT of th e boiler run under ISB sy stem is lower than th at of the SEQUENTIAL mode in all boiler MW loads. The temperature under ISB mode was approximately 20 °F lower than the temperature und er SEQUENTIAL mode.2010 CoalGen Conference – Pittsburgh, PA Aug 10 – 12, 2010 Figure 5 – Comparison of Economizer Ex it Gas Temperature under Non-ISB and ISB

Boiler Efficiency

The calculated improvement in the boiler efficiency is approximately 0.6% as a result of the 20

o F improvement in the EEGT.

Plant Heat Rate

The calculated improvement in the plant heat rate is approxima tely 0.7% (67btu/kwh) as a result

of the 20 o F improvement in the EEGT and 15 kpph reduction in the reheat spray flow.

This improvement can be written in terms of energy input savings as

hr Btu ctor CapacityFa MW MWh KWh

KWh Btu 6 10 56

. 45 ) %( 85 800 1 1000 67 =

ENVIRONMENTAL ANALYSIS

CO 2 Reduction by 0.7% Plan t Heatrate Improvement

The reduction in the CO 2 emission can be calculated directly by the reduction in the required energy input to produce the same power output.

The energy input saved by the plant heat rate improvement was calculated to be 45,560,000 btu/hr assuming a 85% capacity factor.2010 CoalGen Conference – Pittsburgh, PA Aug 10 – 12, 2010 For the sub-bituminous fuel, if we use a Car bon content of 61% (as received) and a Higher Heating Value of 10,767 btu/lb (as received), the total reduction in Mass Fu el Carbon Flow Rate can be computed as

hr Tons

lb Tons content carbon btu lb

hr btu 17

. 1 2200

1 ) %( 61 767

, 10 1 000

, 560

, 45 =

Thus, the total reduction in mass CO 2 emission can be derived as:

hr Tons

hr Tons Flow Carbon Fuel Mass in duction Total 29

. 4 17

. 1 12 44 Re C of Mass Molecular CO2 of Mass Molecular

= =

ECONOMIC ANALYSIS

Fuel Savings through Plant Heat Rate Improvement: Figure 6 illustrates the yearly savi ngs in fuel cost by th e 0.7% improvement in the plant heat rate.

Figure 6 –Savings as a result of 0.7% Plant He at Rate Improvement (arranged per Direct Cost of Power Generation)2010 CoalGen Conference – Pittsburgh, PA Aug 10 – 12, 2010 Potential Savings through CO 2 Reduction: Figure 7 shows the potential yearly savings as a result of the reduction of CO 2 emissions with the implementation of the SmartCleanTM ISB System. Th e graph is arranged pe r $ penalty on ton of

CO 2 emission. 4.29 tons/hr CO 2 reduction was used as the baseline for the calculation.

Figure 7 –Potential Savings from CO 2 Reduction

BOILER RELIABILITY AND AVAILABILITY There were no forced outages caused by sootblow er related tube erosio n since June 2009. The improvements in reliab ility and boiler availability by the SmartCleanTM system implementation

will be evaluated in the next few years as Unit 3 was recond itioned in February 2009 with a major boiler overhaul.

REFERENCES

1. Coleman, K., Overcash, D. “ Tube repair and protection from damage caused by

sootblower erosion ”. EPRI, Palo Alto, CA, 2004, Technical Report 1008037

2. “ Steam: Its generation and used ” Edition 41, Babcock & Wilcox Company.2005

3. Tandra, D.S., Shah, S. “ Advanced Intelligent SootBlowing System using

SmartSootblower ” EPRI Sixth Intelligent Sootblowi ng Workshop, May 16 - 17, 2006.