New Technology Uprating of Process Compressor and Generator Drive Gas Turbines

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1 THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS 345 E. 47 St., New York, N.Y GT-40 y^ The Society shall not be responsible for statements or opinions advanced in. papers or in dis- L cussion at meetings of the Society or of its Divisions or Sections, or printed in its publications. m Discussion is printed only if the paper is published in an ASME Journal. Papers are available ]^C from ASME for fifteen months after the meeting. Prirrfwri in uee Copyright 1986 by ASME New Technology Uprating of Process Compressor and Generator Drive Gas Turbines R. P. ALLEN H. C. M. SMIT General Electric Co. Dow Chemical Co. Schenectady, NY Terneuzen, The Netherlands ABSTRACT Investment in energy conservation projects can have substantial rates of return, particularly for companies like Dow Chemical which has many plants that are energy intensive. Dow also has many plants that rely on gas turbines for the bulk of their power generation. Thus improvements in efficiency of these gas turbines will contribute significantly to overall plant energy savings. This paper discusses how Dow uprated two of their gas turbines at their Netherlands complex, using retrofit packages developed by the General Electric Company. The justification, the field modifications, and the performance test results are all reviewed. INTRODUCTION By taking advantage of more recent gas turbine technology, General Electric has been able to develop retrofit gas turbine parts to enhance the output and efficiency of older models. The Dow Chemical Company, as part of their worldwide thrust toward energy conservation in their production facilities, decided to upgrade the performance of the MS5001 gas turbines at their plant in Terneuzen, The Netherlands. This paper discusses the implementation and results of the upgrades of the first two modified gas turbine units. UPRATE DESCRIPTION The MS5001 gas turbine was introduced in Until the Model N version was completed in 1969, there had been essentially no changes in the aerodynamic design of the turbine section. Recent developments have produced materials and nozzle and bucket designs that can be retrofitted into earlier turbines to improve their performance. A group of MS5001 models, produced in the late 1960's, are prime candidates for these new designs since they have interchangeable turbine parts and there is a substantial number of them in the field. These are the Models L, LA and M, predecessors of the Model R which is the current production version of the MS5001 with the 16 stage compressor. (Traditionally, changes in General Electric's gas turbine designs are designated alphabetically as a suffix to the basic model series MS3002, MS5001, etc.) This new technology is also applicable to MS5001 N and P units, which have the 17 stage compressor. Overall performance gains are not as great as with the older models, but have been justified for gas turbines in continuous duty applications. The new parts offer improved aerodynamics plus the ability to increase the turbine inlet temperature as much as over the original rated temperature level. Present day materials and coatings, investment cast first and second stage nozzles, a solid first stage bucket and elimination of the tie wired second stage bucket (on Models L, LA, M), should extend parts life and maintenance intervals as well as produce improved thermodynamic performance. Presented at the International Gas Turbine Conference and Exhibit Dusseldorf, West Germany June 8-12, 1986

2 UPRATE POTENTIALS Original Change with Model Rating (MW) NT Parts (%) (a) (b) L LA M R (a) (b) Retains original larger diameter second stage wheel. Has Model R wheel with long shank bucket and different second stage nozzle. Ratings are on gas fuel at original NEMA conditions of 80F and psia (26.7C and.977 bar), and are for new and clean conditions. Hardware Changes New Technology nozzles and buckets, both stages Model R type second stage wheel Combustion parts Control settings Compressor rotor (refurbished, now new) Projected Performance Gains Output +10% Heat rate -3.9% Fig. 3. Summary of MS5001 Model LA Uprate at Dow Chemical's Terneuzen Plant Fig. 1. Typical Uprates Attainable Through Application of New Technology Turbine Parts, Models L Through M and R. The new technology uprate package for the older models consists of replacement nozzles and buckets for both turbine stages, plus new combustion parts. To obtain the maximum uprate the Model L through N machines need a new second stage wheel to accommodate the long shank shrouded bucket. This version, the Model R New Technology or R/NT, can provide as much as 26% more power and an 8% improvement in heat rate compared to the original Model L ratings. A summary of the power uprate potentials is presented in Figure 1. For the Models N and P, which are produced with the smaller second stage wheel and shrouded bucket, these parts are not replaced. An additional uprate possibility is the installation of current production inlet guide vanes (IGV), which will increase airflow 3 to 4% and power output 2 to 3%. Potential gains for the Models N and P to P/NT are shown in Figure 2. The turbine configurations for the R/NT and P/NT modifications are identical, thus the uprates will result in optimized spare parts stocking.. For the machines at Dow/Terneuzen, Figures 3 and 4 summarize the hardware changes made and the nominal improvements in performance that would be expected. BACKGROUND AND JUSTIFICATION The Dow Chemical Plant at Terneuzen produces chemicals and plastics and employs over 2000 people. It generates 100 MW of its own power by gas and steam generator sets. There are seven gas turbines in the plant, six of the General Electric-designed MS5001 type and one MS3002. Four of the units have in excess of 100,000 operating hours, and the other three are approaching that mark. There are a total of eight steam turbines at Terneuzen, ranging in size from 5000 to HP. Five of the MS5001 gas turbines and one steam turbine produce the 100 MW of electrical power. Process Compressor Drive Application This equipment consists of: a. a large process compressor from Elliott, nominally HP; b. a MS5001-LA-type gas turbine, originally supplied by AEG-Kanis, the GE Manufacturing Associate in West Germany, driving the compressor from one end through a Maag gearbox; c. an AEG--Kanis steam turbine starter and helper driving from the other side; d. an unfired Waste Heat Boiler, generating 35 bar steam for the steam turbine and for various plant headers. The objective of this project was to uprate the gas turbine in shaft output and thermal efficiency and improve its long term reliability. Further, a mechanical clutch coupling was installed between the steam turbine helper and the compressor in order to disengage and re-engage the steam turbine in UPRATE POTENTIALS Original Change with Model Rat ing (MW)NT Parts (%) N P Ratings are on gas fuel at ISO conditions of 59F and 14.7 psia (15C and bar), and are for new and clean conditions. Fig. 2. Typical Uprates Attainable Through Application of New Technology Turbine Parts, Models N Through P. Hardware Changes New Technology nozzles and buckets, first stage and second stage nozzle Combustion parts Control settings Compressor IGV and stator blades Projected Performance Gains Output +6.8% Heat rate -2.7% Fig. 4. Summary of MS5001 Model N Uprate at Dow Chemical's Terneuzen Plant N

3 FUEL steam consumption on an annual basis is much greater than actually required. In the early days, the plant could benefit from this. With the overall steam savings that have been made, this is no longer true. 1.0 LOSS GAS TURBINE LA-type GEARBOX W.H.B. 75'4 unfired stack Thermal efficiency gas turbine = 23.6%. Fig. 5. Model LA - Pre Uprate Heat Balance STEAM TURBINE to grid + at. tb. Figures 7 and 8 show this situation graphically. Figure 7 depicts the original case, and the relative gas turbine-steam turbine split over the year. Figure 8 shows how the proposal to uprate the gas turbine would allow it to drive the process compressor alone for up to half the year. The mechanical type clutch coupling which can disengage and re-engage the steam turbine in operation, now becomes a beneficial feature. In addition to the stated objectives for this project, Dow wanted to implement computer programs for on-condition performance monitoring. Such a performance analysis program permits understanding the behavior of the gas turbine under all prevailing conditions. This in turn should lead to optimization of equipment use and to energy savings. FUEL CLUTCH LOSS RNT-type (Uprated LA) 78.7 GEARBOX unfired 53.2 Thermal efficiency gas turbine = 24.6%. stack g STEAM TURBINE to rid + St. tb. 25 HORSEPOWER IN THOUSANDS 20 D / STEAM TURBINE _B GAS H Fig. 6. Model LA - Post Uprate Heat Balance operation, depending on the power requirements. This would achieve significant process energy savings and improve operating flexibility. The design point heat balances used by Dow to evaluate the uprate are shown in Figures 5 (before uprate) and 6 (after uprate). These "design points" are for plant process and do not represent the gas turbines operating exactly at their NEMA rating point. The process compressor power demand - at a certain throughput - is dependent on the seawater temperature. Through the cooling circuits, lower water temperatures in the winter reduce the inlet gas temperature to the compressor. Hence, in winter the power demand is lowest and in summer highest. This is contradictory to the gas turbine's capability. As a result, the steam turbine has to supply its maximum power output in the summer, while the gas turbine must operate below its base load capability in winter. The latter condition is required to allow the coupled steam turbine to operate above a certain minimum level in order to run reliably. The exact amount of "derating" (running below baseload capability) for the gas turbine depends on the ambient winter temperature, keeping the process compressor throughput constant. Under "derated" conditions, both the gas turbine and steam turbine perform at lower than design efficiency. Further, 15 -'- WINTER SUMMER ABC - Gas Turbine Input Power DH - Required Compressor Power Shaded Area - Steam Turbine Input Power Fig. 7. Power Split - Before GT Uprate :.: _... D GAS- F 4 STEAM TURBINE HORSEPOWER TURBINE IN B THOUSANDS - G ` ^^ C E 20 A 15 WINTER SUMMER ABC - Gas Turbine Input Power with Steam Turbine Clutched In EFC - Gas Turbine Input Power with Steam Turbine Declutched EFJ - Required Compressor Power Shaded Area - Steam Turbine Input Power Fig. 8. Power Split - After GT Uprate 3

4 Dow started their performance analyses in early Some examples of things learned are: 1. Discovered that several of the seven gas turbines were not performing to capability. 2. Several fuel-meters were measuring low. 3. Compressor inlet differential pressure was not correctly measured. 4. Learned the effects of air extraction from compressor discharge. 5. In one case there was a mismatch in the fuel system between the flow area and the fuel heating value. In other cases, the fuel regulator was no longer in good condition and the fuel and temperature control system were out of calibration. 6. Obtained confidence in use of torquemeter. Approximately eight years of effort went into the development of the strain gage type torquemeter, purchased from Indikon. After three and one half years of operation on the process compressor drive unit, a recalibration indicated that a 3% drift at zero load was the only change. The performance analyses taken prior to the shutdown provided a good guideline for some of the shutdown activities. However, for a reliable performance analyses program, one needs a complete set of reliable instruments installed, preferrably with redundancy. This became a parallel project for the uprate. Thermal efficiency gas turbine = 26.1% Fig. 9. Model N - Pre Uprate Heat Balance losses The described train of turbomachinery was installed and commissioned in 1968 and had accumulated 126,542 operational hours at the time of the uprate in October Generator Drive Applicat ion The second application is in the utilities plant for power generation at Terneuzen. The configuration of the equipment is: a. An MS5001 Model N type gas turbine, sourced from Thomassen, GE's Manufacturing Associate in the Netherlands, driving the generator through a gearbox; LLJ Thermal efficiency gas turbine = 26.8% (2.7% higher). Fig. 10. Model N - Post Uprate Heat Balance FIELD MODIFICATION EXPERIENCES The Process Compressor Drive losses b. A fired Waste Heat Boiler. The objective of this project was to increase efficiency and power output, and reduce purchased power. The modification increases turbine efficiency and thus the power/heat ratio, which fits the site's requirements. The increased amount of waste heat reduces the amount of fuel-gas firing to obtain the required superheat temperature. Again, improved long term reliability was also important. Figures 9 and 10 show the pre- and post-uprate heat balances for this installation. The gas turbine was installed in 1974 and had run 89,500 fired hours at the time of the uprate. This was the first uprate of a process compressor drive for GE and their second New Technology package sold. Dow's schedule - as is most often the case with a large process plant - was extremely tight, and the shutdown date fixed. The schedule called for 15 working days of two shifts of 10 hours each. Weekends served as "spare-time" in case of unexpected delay. To achieve this, Dow had their spare rotor sent to GE's service shop in Basildon, London, to modify it with the new technology parts and have it cleaned and balanced. After return and well before the shutdown, Dow checked the balance in their shop to be certain no changes occurred during shipment. 4

Half a year before the shutdown, the Dow maintenance and the development rotating equipment groups discussed the planning in detail with GE's service engineer.

5 Half a year before the shutdown, the Dow maintenance and the development rotating equipment groups discussed the planning in detail with GE's service engineer. The maintenance group made up a critical path schedule, and so did the service engineer, independently. The results were thoroughly discussed and presented to plant supervision. Only when Terneuzen was convinced it could be done within 3 weeks was the authorization request issued. The uprate was ordered about two months prior to the scheduled shutdown and both organizations had to get ready for an ultra-quick job. Dow's instruments group had revamped the temperature and fuel systems to replace the original pneumatic systems with more reliable electronics. Transmitters for full redundancy in each function were added along with others for the computer performance program. Two GE service engineers on site really helped, knowing who and where to reach in their factories. The following set of guidelines was derived from this experience, and may be of value to others considering similar uprate programs. 1. A vendor, small or large, needs a project coordinator, free from other functions, with sufficient authority to bridge the interdepartmental borders, coordinate and communicate with the Buyer. 2. Nothing should be taken for granted, such as engineering or inspection documents, hardware, or shipping instructions. Screening should be 100%. The shorter the lead time, the more this rule must be obeyed. Errors discovered at the site become costly. 3. Even so, a few errors will slip through. Therefore, all documents and hardware should arrive at the site at least two weeks before the shutdown. In fact, engineering documents which are required for the planning at the site, should arrive a month before. The success of a tight shutdown depends on the thoroughness of the planning. 4. All instruments, control and protection systems should be checked and calibrated. This saves much time when starting up and assures that safety aspects and also turbine hot parts reliability can be monitored. The instruments group--in fact the last group to finish the job-- must be given due time for this task. Also, when installing control system modifications, it is not uncommon to find the response not exactly as predicted. Real operating conditions will govern the actual settings of the controllers. So, trimming will always be required. 5. This thorough, one hundred percent checking also includes all dimensions and clearances of the mechanical parts. This starts with the "opening checks" made on the machine after casings are lifted and before rotor removal. 6. In case the job advances faster than the schedule indicated in the beginning, this should be ignored instead of permitting any relaxation. The most time-consuming part comes at the end with clearance checking of the newly installed parts. This job in particular must not be rushed. Although there were a few problems, the reassembly of the unit, in general, went smoothly and all compressor and turbine clearances were found to be according to specification. The gas turbine was ready for startup, after the overspeed tests, one weekend later than planned. Generator Drive Application Planning and execution both benefitted from the previous experience. Engineering documents arrived on time. Again, the critical path planning was set up for 15 working days in three weeks. Compared to the process compressor drive, the mechanical changes were simpler, because no new second stage turbine wheel with new type buckets and stationary shroud blocks were required. This was fortunate since for this N-type machine (the only one at Terneuzen), there was no spare rotor. With assistance from a Basildon supervisor, the rotor was modified for the uprate in the Dow shop and also balanced. Extra work on this turbine included modifications to the air inlet system. All compressor blades and vanes, except the last stage and exit guide vanes, and the inlet air path were coated with Sermetel 725. The rotor was coated with blades installed at the site, and the stationary parts were sent to Sermetel's shop in Germany. The target was to have better air filters (high efficiency), less inlet pressure drop, and to replace the worn-off original Nickel-Cadmium coating by a non-sacrificial coating. Relative to instrumentation, this gas turbine was also simpler than the first unit. It has electronic temperature, fuel control and protection systems, using GE's SpeedtronicTM Mark I. The controls modification for the uprate had to be implemented, accompanied by a precise calibration of each instrument and device in each system. Dow replaced the annunciator panels and installed an LED test circuit to enable quick location of any circuit break. Alarms were installed on the compressor bleed valves to preclude operation with them in an open position after startup. The gas fuel system was modified to prevent excessive fuel at startup, and to remove restrictions in the supply line. The uprate modification of this gas turbine was completed in the planned time. Although a few problems were experienced, the planning effort was proven to be extremely worthwhile. TEST RESULTS To establish the incremental improvements in performance associated with the new parts, performance tests of the units were run both before and after the refurbishment. The results of these two tests are tabulated below for the MS5001 Model LA compressor drive unit. Before After Change Predicted Output-HP % 10.0% Heat Rate-Btu/hphr(LHV) % 3.9%

6 These data are all corrected to identical conditions corresponding to the original NEMA rating (80 F, psia). A 10% increase in power was forecast, along with a 3.9% decrease in heat rate, based on new and clean" condition of the unit. From the analysis of the test data, it was not possible to sort out the effects of the new turbine blading since many other changes were made when the unit was refurbished. These included a different compressor rotor and a different torquemeter coupling, used to measure output. There was also a significant variance in fuel flow and heat value measurements, which contributed to a large uncertainty in the heat rate. For example, the "Before" test heat rate of Btu/hphr is over two percent better than the originally quoted level for the Model LA of 10300, after some 120,000 fired hours operating time. The output, HP, is some 2.4% below the original HP rating, which could be anticipated. The "After" heat rate is about 0.7% better than the rated level for the rebuilt unit, which also could be expected. The pre-uprate heat rate of Btu/hphr result is very questionable, which suppresses the apparent percentage gain in efficiency. For the Model N generator drive unit, the comparable set of test results is shown below. These data are corrected to ISO conditions of 59F, 14.7 psia. The ISO standard became effective in the period between the purchases of these two machines. Before After Change Predi cted Output-kW % 6.8% Heat Rate-Btu/kwhr(LHV) % 2.7% Predicted performance improvements were 6.8% in output and 2.7% in heat rate, comparing equivalent new and clean ratings. New turbine parts, some new compressor stator blades, and new inlet guide vanes were installed, but the compressor rotor blading was not replaced. Minor blade damage was blended out, and a protective coating was applied to both rotor and stator blades. This turbine had just under 90,000 fired hours at time of refurbishment. Compared to its original rating of KW, its output had degraded some 8% over this period. A large portion of the 13.5% power gain is attributed to improved airflow and compressor efficiency. Like the Model LA results, due to the compressor changes the specific effects of the new turbine parts are not discernable from the overall improvement. SUMMARY In summary, both uprates were a success. This is true not only for the basic project objectives, gains in power output and efficiency, but also the field work was completed within the tight schedule. For a project as new as it was for both vendor and buyer, this was quite an achievement. This success resulted from truly close coordination and cooperation between both organizations. Uprating of older model gas turbines offers an incentive to improve power plant operating costs. It also provides an opportunity to modernize controls, improve instrumentation, repair other parts, and generally upgrade the entire installation. These gains should be factored into the justification and planning for the outage scheduled to install the new turbine parts. ACKNOWLEDGMENTS The authors are indebted to the assistance provided by Jan Rajtoral of Dow in Terneuzen, and by Gerrit Van Dalen of Physical Dynamic Research (FDO) in Hengelo. Mr. Van Dalen has been under contract with Dow at Terneuzen for some time.

STEAM TURBINE-GENERATOR & AUXILLIARY SYSTEMS Presentation by: RANA NASIR ALI General Manager, Power Plants Projects, at PITCO November 02, 2017

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