VGB PowerTech 2016-04 Neumann

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Conversion of a Belgium CCGT plant into an open cycle GT VGB PowerTech 4 l 2016

Authors

Kurzfassung

Vilvoorde – Kurzfristiger Umbau zum offenen GT Betrieb – Ein strategischer Schritt

Aufgrund des am Strommarkt gestiegen Anteils regenerativer, aber fluktuierend liefernder Er-zeugungskapazitäten, leidet Belgien wegen der gleichzeitigen wirtschaftlich bedingten Stillle-gung einiger konventioneller Kraftwerke ins-besondere im Winterhalbjahr an Versorgungs-engpässen. Um diese Situation zu entschärfen, trat Anfang 2014 der „Energieplan Wathelet“ der Belgischen Regierung in Kraft, welcher u.a. vorübergehend stillgelegte Gaskraftwerke verpflichtete, an einer Auktion für Reservekapazitäten teilzunehmen. Die Anforderungen an Verfügbarkeit und Leistungsbereitstellung dieser Reserven entsprachen dabei denen eines Spitzenlastkraftwerks. Uniper (vormals E.ON) entschied sich, sein vor-läufig stillgelegtes GuDKraftwerk (V94.3A) in Vilvoorde als Reserve bereitzustellen. Aufgrund der vorgenannten Anforderungen musste das Kraftwerk jedoch vom Kombibetrieb in den of-fenen Gasturbinenbetrieb umgebaut werden. Hierfür war der Einbau eines BypassKamins zur Umfahrung des Kessels erforderlich. Der Kamin musste zudem den lokalen Anforderun-gen insbesondere hinsichtlich der Akustik genü-gen. Aufgrund der Brisanz der Engpässe war der Umbau bis zu Beginn der Winterperiode 2014/2015 durchzuführen. Dabei blieben für Herstellung und Montage des BypassKamins lediglich drei Monate bis zur Sicherung der Be-triebsbereitschaft. Der vorliegende Artikel be-schreibt die Hintergründe, das Umbaukonzept sowie den Umgang mit dem Herstellungs- und Montageprozess unter dem Einfluss außeror-dentlich knapper Terminbedingungen. l

Vilvoorde – Fast track conversion to open cycle GT – A strategic moveÖdön Majoros and Jürgen Neumann

Dipl.-Ing. Univ. Ödön MajorosProjectmanagerUniper Technologies GmbH Gelsenkirchen, GermanyDipl.-Ing. Jürgen NeumannMBA, ProjectmanagerG+H Schallschutz GmbH Ludwigshafen, Germany

Introduction

The Belgian electricity market is currently facing significant structural shortfalls on the security of supply due to the increas-ing share of intermittent power supply and the decreasing wholesale prices, which forced several conventional power plants to shut-down or be mothballed. In order to improve the situation, the Belgium Gov-ernment’s so-called “Energieplan Wathe-let” was put into force at the beginning of 2014. Amongst others, it obliged existing but mothballed gas-fired power plants to participate in an auction for reserve capac-ity, starting with the winter 2014/2015. The requirements on availability and pow-er supply on the reserves were those of a peak load power plant. Uniper (formerly E.ON) decided to pro-vide its mothballed CCGT (V94.3A) in Vilvoorde for strategic reserve. Due to the requirements, the plant needed to be converted from combined-cycle into open-cycle mode. The retrofit of a bypass stack to disconnect the boiler was an essential part of this conversion. The stack needed to fulfil local demand especially concern-ing acoustics. Due to the imminent short-falls the conversion was required to be fin-ished before the next winter. Finally there were only three months left for fabrication and installation until required operability of the plant. This paper describes the back-ground, the concept for conversion and the handling of the fabrication and installation processes under the influence of the very restrictive timeline.

The Vilvoorde power plant

The history of the Vilvoorde power sta-tion (formerly Verbrande-Brug) goes back to the late 1950s and early 1960s. The steam power plant located in the vicinity of Brussels Airport (Belgium) was origi-nally built and owned by Engie (formerly GDF Suez) and comprised three coal-fired Units (3 x 125 MWe). Unit 1 and Unit 2 en-tered commercial operation in 1959 and 1961, respectively. Unit 3 followed in 1965. Following a grid accident, the steam tur-bine of Unit 3 was destroyed in 1982 and replaced in 1986 by a new steam turbine (Brown Boveri design, 140 MWe). In the late 1990s, Unit 1 and Unit 2 were demolished, whereas Unit 3 was converted into a combined-cycle gas turbine (CCGT)

power plant. During the conversion, the old coal-fired boiler was removed, the ex-isting steam turbine was refurbished, rel-evant infrastructure (e.g. condenser, cool-ing tower etc.) was overhauled and a new gas turbine (V94.3A) with associated heat recovery steam generator (HRSG) was installed. The repowered Unit 3 entered commercial operation in 2001, with an in-creased net power output of about 385 MW (GT: about 263 MW, ST: about 122 MW) and an increased net electric efficiency of >54 %. The CCGT layout has the typical V94.3A axial arrangement with air-filter and gen-erator upflow the GT and exhaust diffusor and HRSG downflow, all arranged in line. The HRSG is of a vertical type. The CCGT was not equipped with a bypass stack or diverter (F i g u r e 1).In 2009, Engie and Uniper agreed to swap about 1,700 MW of conventional power generation capacity, including the transfer of ownership on the Vilvoorde power sta-tion, which kept on operating until mid-2013. However, since the market condi-tions for gas-fired combined-cycle power stations have changed dramatically due to the increasing share of renewable energies and decreasing wholesale prices, it was decided to mothball this highly efficient plant until an economic operation would become feasible again. As Vilvoorde was not the only shut-off plant, the Belgian electricity market is cur-rently facing significant structural short-falls on the security of supply due to limit-ed back-up capacity for power generation. This will probably get worse until 2017. In order to improve the situation, the Belgium government approved the so-called “Ener-gieplan Wathelet” in July 2013, which was enforced in March 2014 by Belgium’s sen-ior council. This plan includes three pillars:

– Lifetime extension of one nuclear plant (Tihange 1),

– Incentives to install new gas-fired power plants via subsidies and

– Obligation for existing but mothballed gas-fired power plants to remain opera-tional as strategic reserve during three successive winters, starting with the winter of 2014.

In order to reveal the lowest cost for this strategic reserve, the plant owners were obliged to participate in an auction for re-serve capacity with a tendering deadline in


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VGB PowerTech 4 l 2016 Conversion of a Belgium CCGT plant into an open cycle GT

July 2014. Uniper decided to comply with the new law to proactively support secur-ing Belgium’s electricity supply. Thus, ne-gotiations with the Belgium Government, with the Commission for the Regulation of Electricity and Gas (CREG) and with the transmission system operator (Elia) were started.

Amongst others, the framework of Bel-gium’s Strategic Reserve stipulates that the plant operator would be given a 5 hour pre-notification before start-up. It furthermore requests fast load ramps in the order of 10 to 15 MW/min and time from start-up to maximum output of about 2 hours. In ad-dition, the plant operator needs to ensure a high availability during the winter peri-ods (defined as from November 1 to March 31) but with the prospect of maximum 350 operating hours per year. These are clearly the requirements set out for a peak load plant. To comply with them, Uniper was forced to convert Vilvoorde into an open cycle gas turbine (OCGT) power plant, which is ideal to provide the required per-formances of a strategic reserve plant.

The “Belgium Energy Reserve” project was initiated, with the aim to modify the GT’s exhaust gas system by retrofitting a bypass stack and partly re-activating and modify-ing the relevant infrastructure. The steam turbine remained mothballed.

The project was kicked-off in mid July 2014, once CREG and Elia had agreed with this basic concept and had granted an extra month for the conversion, mean-ing that Vilvoorde would have to be ready for operation on December 1, 2014. Thus, the plant operator was facing the situation that he needed to convert and re-commis-sion his mothballed power plant within less than five months. The main challenges

in achieving this ambitious goal will be discussed in the following, both from the plant owner’s and the main supplier’s per-spective.

Plant owner’s perspective – Reasons for and benefit of the retrofit

As noted above, the main technical re-quirements and boundary conditions for Vilvoorde’s participation in the strategic reserve are:

– Quick start-up/fast ramp rates, – Highly reliable operation, – Very few operating hours per year and – Competitive electricity cost for peak

power supply.Given the anticipated operating map, it is obvious that the Vilvoorde plant would certainly experience cold starts and may as well experience warm and hot starts. It is well known that the start-up time of a combined-cycle power plant is restricted by the load ramp of the HRSG. For a current Siemens F-class CCGT, this would typically mean 2 to 3 hours (cold), 1 to 1.5 hours (warm) and 30 to 60 minutes (hot) start-up time respectively [1]. At the same time, the typical load ramp would be in the range of 5 %/min. For plant specific reasons at Vilvoorde, however, the start-up from cold to maximum power takes about 9 hours, with the 15 min step response being lim-ited to 3 %/min. Modern OCGT plants on the other hand typically reach maximum output within less than one hour (cold, warm, hot) and achieve load ramps of about 15 %/min [2], while Vilvoorde requires about two hours and can reach ramp rates in the order of 10 to 15 MW/min. Thus, it is clear that an

open cycle configuration offers higher flex-ibility for peak power supply. The down-sides of this configuration are lower elec-trical efficiency and reduced power output.

The second reason for the conversion was the need for very high availability during the winter period. Given the age of the steam turbine (almost 30 years) and some other important systems, a reliable CCGT operation would have required significant investment and time for refurbishing those parts of the power plant. By converting to an open cycle configuration, the number of systems that could potentially fail de-creased, and thus, the risk for unplanned unavailability was reduced.

And last but not least, one main reason was that the technical feasibility of the conversion had been shown in a study [3] conducted in 2013 by Uniper Technologies GmbH, the engineering service provider of the Uniper group. This study had conclud-ed that Vilvoorde was probably one of the most viable sites for this type of conversion. This is mainly due to the excellent acces-sibility, along with a suitable plant layout to be described later on. Furthermore, the study presented a sound cost estimate, pro-viding sufficient confidence that the con-version could be executed with a reason-able investment. However, the study also concluded that such a conversion would typically require about 9 to 12 months from project start to completion. Thus, the only viable option to comply with the demand of the strategic reserve posed an enormous challenge for the conversion time to the power plant owner.

Plant owner’s perspective – Challenges and solutions

From the plant owner’s perspective, the following challenges needed to be over-come within very limited time:

– Setting up a lean and mean proect man-agement structure and management processes. (I.e. ensuring clear responsibilities and avoiding time-consuming decision-mak-ing processes.)

– Putting together an effective project team. (I.e. sourcing the needed experts and en-suring their full commitment to the job.)

– Parallelising as much work as possible, even steps that are usually executed in sequences. (E.g. designing new founda-tions parallel to tendering new exhaust gas system etc.)

– Preparing sound and complete tech-nical specifications for the main lots. (E.g. for new exhaust gas system/addi-tional foundations/emission measure-ment system etc.)

– Preparing and obtaining the relevant permits in time. (I.e. building and envi-ronmental permit, required to start con-struction work 10 m above ground.)

Fig. 1. Plant layout before conversion.


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– Finding and selecting suitable vendors/partners for the main lots on very short notice. (E.g. procure GT exhaust gas sys-tem, from specification to contract, in less than 4 weeks.)

– Getting all the work done required by de-mothballing. (E.g. turbine and generator inspections, modification of the cooling system etc.)

To highlight the enormous challenge of this project with respect to the timeline, the main project milestones are summa-rised in Ta b l e 1. To provide some insight, two cases are shown in the following, which contrib-uted to the overall success of the project. However, these are just two pieces among a dozen others.

New foundationA major challenge was the fact that the pre-sent foundation of the existing exhaust gas system was not designed for carrying ad-ditional loads. Hence there was a need for construction of a new two-part foundation beside the diffuser upstream of the HRSG in such way that the new bypass stack would be properly supported. In a regular project, this foundation would have been designed after the final dimensions and loads had been determined and confirmed by the stack supplier, which is a typical task in the supplier’s engineering phase. In this project, the foundation needed to be de-signed and prepared in parallel to the pro-curement of the new stack in order to gain time for the stack installation. Therefore, the new foundation with 14 vibration-free drilled piles (length 11 m, diameter about

400 mm) on each side of the diffuser was designed with sufficient safety margin to support a stack of 55 m height and 10 m diameter (F i g u r e 2).The stack finally built was indeed some-what lower and smaller, so the foundation was slightly overdesigned but more impor-tantly ready in due time. The pile system was chosen to minimise negative vibration effects on the nearby GT and the diffuser’s foundation.The piling works started just 2 weeks after contracting the new bypass stack, once the stack supplier had confirmed their loads were not exceeding the foundation design-er assumptions. The piling work, which was completed in just one week, was per-formed in sequence, starting with the west side before moving to the east side. Once the piles were finalised on one side, the ex-cavation and foundation works started im-mediately. Due to this seamless transition, the two foundations were even completed ahead of schedule.

Cooling water systemIn combined-cycle configuration, the power plant has a cooling load of about 225 MW (thermal), which is discharged via a natu-ral draught cooling tower. The conversion to open cycle configuration results in a significantly reduced cooling requirement of only about 5 MW. They derive from the generator and the oil coolers of the gas tur-bine package only. Hence a modification of the cooling system became necessary. Given the plant’s limited operating hours, the most efficient way was seen in the re-use of the existing infrastructure with slight modifications. For winter operation, it is advised not to use the evaporative part of the cooling tower at such a low heat load. The risk of icing of the internals and con-sequentially mechanical damage is most likely. It was decided to operate the cooling tower in bypass mode and to use the cooling water’s heat capacity in the basin (approx. 3,150 m3) and the concrete header (approx. 1,350 m3) only. With a maximum design temperature for the GT intercooling system of 28 °C and assuming an initial cooling wa-ter temperature of 8 °C, this would result in an available operation time of 22 hours at full load. After that, make-up cooling water from the nearby canal would be required. In the original layout, however, the loca-tions of the cold cooling water extraction from the basin and warm cooling water return to the basin were very close to each other. In order to avoid a “thermal short-circuit”, the cooling water return pipe was therefore extended by about 40 m to en-sure proper cooling (F i g u r e 3).An additional advantage of the chosen cooling concept was the significant noise reduction by changing from the cooling tower draught into bypass operation mode. A fact that helped keeping low the overall noise emissions from the plant.

Fig. 2. Piling works for the new foundations.

Tab- 1- Project milestones-

No Milestone Date

1 Gate 2 decision to proceed with project 01-07-2014

2 Submit offer for auction of strategic reserve capacity 04-07-2014

3 Technical kick-off 17-07-2014

4 Start of bypass stack tender 04-08-2014

5 Submit environmental and building permits 05-08-2014

6 Place order for bypass stack 22-08-2014

7 Environmental and building permits granted 11-/22-09-2014

8 Foundation for new bypass stack ready/start erection bypass stack 15-10-2014

9 GT and alternator reboot works finished 31-10-2014

10 Cooling water system modification finished 31-10-2014

11 General de-mothballing activities finished 31-10-2014

12 Bypass stack ready for hot commissioning 21-11-2014

13 Hot commissioning completed 29-11-2014

14 Start participation in strategic reserve 01-12-2014


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Supplier’s approach

From the supplier’s perspective, the task was clear: Install a new bypass exhaust gas system in less than half the time usu-ally required. Typically, the cycle time is 7 to 8 months from receipt of order to read-iness for operation. In this case, only three months were granted. Stacks for gas turbines are meanwhile highly standardised regarding their design principles and duct sizes. However, local regulations for emissions like plume spread and noise limits, which influence stack height and silencer design, as well as the vital need to cope with the prevailing en-vironmental loads – mainly wind and seis-mic loads – lead to large varieties of stack layouts even for identical gas turbines. Fur-thermore, diverging engineering standards for different locations (like Eurocode vs. ANSI) and the very specific decision if and where to put platforms to reach emission control measurements, again influencing on the structural design, add up to count-less varieties. When considering all this, it is clear that there is no “one-fits-all-pur-poses” stack available. Nearly each stack is uniquely designed and custom-made for the specific project and it is obvious that there are no stacks produced in advance to be stocked. The variety would simply be too large and there is no economic benefit. In addition, the stack’s cycle period of three-quarters of a year is usually not the limiting factor on a new-build project. Hence, the stack for Vilvoorde also needed to be cus-tomised and fabricated especially for this project before installation could start.

Process

Stack customisation and fabrication is a job process that defines a generally known product, which is then uniquely designed and built. Customisation is done in terms of height, acoustics and structural design. It is essential, as for all job processes, that there is a proper product routing and flow of information in order to obtain a good performance [4]. Thus, the mission was to get the processes right to have any chance of meeting the deadline. A closer look on the sub-processes, their sequence and du-ration evolves a clearer picture of the chal-

lenge and shall reveal some ideas of where time savings may be possible (Ta b l e 2. The processes depicted in Table 2 sum up to 31 weeks or 7.2 months in total. Thus, the main question was how to speed-up this process such that the stack could be ready in time. In general, there are the following approaches, which will be dis-cussed later on:

– Local vs. overseas fabrication, – Parallelisation of work sequences, – Increase manpower, – Apply shift work, – Multiple fabrication facilities, – Skip process.

Leveraging the time-line

A basic approach to optimise the overall schedule is to minimise transport time. There were approximately 50 truckloads of bulk material to be loaded and unloaded in total for this project. Overseas fabrication, which is a usual step towards cost effec-tiveness, would imply maritime transport plus trucking to and from the port. Alone this transport would require minimum 6 weeks, which did not seem promising here. Going for local fabrication, the trans-port time can be effectively reduced. How-ever, this requires the place of fabrication to be within one or two days travel distance from the place of installation. Depending on the project, additional time may be gained with parallel execution of sub-processes, which are usually handled in sequence. The overall process can be cat-egorised in a software stage, including de-sign and drawings and in a hardware phase with fabrication and installation. Fabrication of hardware is definitely need-ed as explained above. However, fabrica-tion cannot start without the software being finished first and no installation without prior fabrication. Thus, the option of parallelisation seems to be of limited vi-ability in this case. Next alternative and a typical advice when timelines become tight, is “increase man-power” or “go for shift work”. A standard approach would be to look for doubling workforce or to run at least two shifts per day to make it in half the time. Both the software as well as the hardware stage

would in general be potential candidates for this approach. Unlike for line processes doubling the workforce was not that easy here, as work-ers and staff needed to have a high level of training and understanding for the prod-uct. This understanding is an essential part of a job process. Thus, it was hardly imagi-nable to ramp up the workforce with highly trained externals for just this one job and set them free after it was done. Moreover doubling the workforce would have re-quired to also double the workspace, ma-chinery and tools in order to perform the work, which was not feasible either. Working in double shifts in order to use space and equipment at its best was also not seen as a promising solution. The an-ticipated design and fabrication works are widely complex and require to be executed in specific sequences. This again is an inte-gral part of a job process. These complex and sequenced work could not have been passed from one worker to the other with-out frictions and decrease in efficiency. This along with the commonly known limitations of shift works like lower overall performance and negative implications on safety and quality [5] resulted that the shift options did not get pursued further. Thus, neither doubling workforce nor shift work could be applied here. Another option was to involve two or more workshops to work on different parts in parallel instead of one shop only. This seemed promising, but would have re-quired a high level of coordination, ensur-ing a proper flow of information. Another downside is that misfits on the interfaces will only be found on site during installa-tion, where rectification is very inefficient. In addition, if only one workshop fails in this cooperation, all effort of the others would have become useless. As the hardware stage could obviously not be skipped, the question was raised if cutting the software phase would be a suitable approach. However, how can one produce workshop drawings without engi-neering? Although each stack is unique, there was a small chance to have the suitable produc-tion documents already in hand from pre-vious jobs. A closer look on the key design data revealed: The gas turbine is a Siemens V94.3A, which determines mass flow and exhaust temperature. The stack height

Tab. 2. Sub-processes and their leadtimes.

Engineering and design 2 weeks

Drawings for workshop fabrication and installation

8 weeks

Procurement 2 weeks

Fabrication 10 weeks

Transport 2 weeks

Installation 7 weeks

Fig. 3. Interface of new and existing cooling water pipe.

Fig. 4. Dispersion of the exhaust plume on two V94.2 open cycle stacks.


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was specified with 55 m, the acoustic per-formance needed to comply with the local VLAREM II [6] regulation and the design were to be made according to current Eu-rocode. The GT is a common heavy duty machine with a large number of installa-tions worldwide. There was no doubt that there will be some drawings available in the archive. The stack height on the other side was pretty tall for hot GT stacks typi-cally built. As the emissions of GTs are rela-tively low and the stack exit velocities are fairly high compared with other fossil-fired plants, stack heights for these applications usually range between 30 and 35 m. The specified 55 m decrease the chances to find a readily available design. The Vilvoorde plant is located in an indus-trial area with the noise emission measure-ment point in the nearby residential neigh-bourhood. According to the VLAAREM II, a maximum 40 dB (A) sound pressure level was allowed at this area. A calculation showed that this results in an allowable noise emission of 95 dB (A) sound power level at the stack exit. With an emission sound power level of more than 140 dB (A) at the gas turbine exit in mind, this looks as a challenge itself. And last but not least, the stack should be designed for the environmental loads in Belgium which are fairly moderate. How-ever, the structural design was requested to be made according to the latest Eurocode which, as it is relatively new, would finally sort out quite a high number of potential candidates from the archive.

While checking the inventory it became clear that there were no blueprints for a V94.3A stack with height of 55 m avail-able. The tallest ones were in the high forties. The plant owner was consulted to understand the requirement of 55 m. The reasons named were the adjacent HRSG stack with 55 m height and, in about 30 m distance to the potential stack location, the existing building of the formerly coal-fired boiler house with 80 m height. The customer raised concerns that the exhaust plume and heat released through the new stack could have adverse impacts on the buildings and equipment. Based on [7]dealing with plume vertical velocity and spread and own empirical data of exhaust plumes on open cycle stacks, confidence could be gained that a stack height of 45 m is sufficient to save the surroundings (F i g u r e 4).After agreeing on a lower stack height, there was still trouble to find a blueprint for a corresponding V94.3A stack. Espe-cially the VLAREM II requirements caused concerns. Luckily it became obvious that a stack just designed for another but some-what larger turbine could match the re-quired height and acoustic and could easily deal with the mass flow. Fortunately this one crossed the line just at the right time to provide the required data to enable process shortcut without whom the project would otherwise not have been finished on time.

Exhaust systembefore conversion

New bypass stackwith blanking plate

Location of optionalblanking plate

for reconversioninto CC

Flow

Blanking platefor OC operation

Fig. 5. Layout after conversion.

Plant layout and conversion planning

In order to keep the overall footprint small, the HRSG was placed as close as possible towards the GT. Hence there was sim-ply not enough clearance upstream the HRSG inlet to install a standard elbow or a switchable damper system. The HRSG was furthermore not to be removed during the conversion in order to allow for a possible later re-conversion to combined cycle. It re-mained preserved for expected future use.Luckily there was a short rectangular si-lencer duct installed between diffusor exit and HRSG inlet. This is quite common for V94.3A installations built during the turn of the millennium. Those silencers work as a first sound barrier before the flue gases enter the boiler. Diffusor and silencer duct were all internally insulated (“cold cas-ing”) and additionally entirely enclosed for acoustical reasons. The future stack should also be of a cold casing design. The inter-nal liner was agreed to be made of 1.4512 (AISI 409) which is a proven material for exhaust systems on gas-fired plants.The diffusor geometry was not to be modi-fied as it is regarded as a physical part of the GT. It became obvious that the use of the rectangular silencer duct was the only chance to divert the exhaust gases before entering the HRSG. Although this duct was too short to install an aerodynami-cally optimised elbow, it was decided to tie-in at that location, since the pressure loss was regarded to be moderate. The top section of the silencer duct was opened and a vertical blanking plate was installed at its back to divert gases upwards and shut off the HRSG. Although this blanking plate is a fix installation it is designed to be removed once combined cycle process should become economical again. In that case, the bypass stack would be taken out of service by inserting a horizontal blank-ing plate just above the rectangular duct (F i g u r e 5).As size and location of the duct opening was unique, an adapter piece was neces-sary to connect the silencer duct with the already designed stack. This adapter piece as well as the blanking plate needed to be engineered specifically for this project. The new foundations were due to the site requirements outside the standard pitch of the support structure. This asked to en-gineer a modified support as well, which meant another setback for the intended software process shortcut.

Conversion

All processes started right at the time of receiving the order. Procurement and fab-rication of the main stack parts started immediately and as the foundation points were meanwhile agreed on, the modified support structure went into engineering.


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It was essential to provide the foundation loads within very short time in order to en-able the customer to start with piling and foundation works immediately. In parallel the design of the adapter piece and blank-ing plate was pushed.

The next steps were to install an opening in the roof of the acoustic enclosure and the modification of its substructure to allow the stack to penetrate through the roof. Then silencer duct top was then opened (F i g u r e 6) and the inner wall prepared

for installing the counter bearings for the blanking plate. Meanwhile, the first components left fab-rication from the workshop which was within 1,000 km driving distance from the site. Just 5 weeks from receiving the order, the first parts arrived on site ready for pre-assembly.In order to save installation time and effort, the stack was designed for a flange bolted site assembly. This requires additional work in the workshop, but allows quicker site assembly and installation compared with welded joint design. Furthermore, it allows supplying the individual stack com-ponents as large as possible, without the need for time-consuming oversize loads. The internal insulation system allowed pre-insulation of large-size areas already in the workshop. This also speeded up the installation process. After bolting the duct parts, the internal insulation just needs to be closed at the erection joints to complete the assembly.All parts were delivered to site using stand-ard trucks, with an average shipping time from shop to site of 2 days per load. Proper pre-planning and regular communication between workshop and site facilitated just-in-time deliveries to site. Everything came in to site on time, order and quantity needed. This enabled continuous assembly

Fig. 6. Cut-out in silencer duct top.

Noise Control for Power Generation

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works and avoided wasting resources for either idle waiting time or additional ef-fort to place and remove equipment to and from interim storages on site.

Sub-assemblies were made as far as possi-ble on ground in order to minimise works on height. This facilitates and speeds up the installation process. Nonetheless it re-quires the availability of large lifting capac-ities, which were available in this project. By following this principle, the entire stack – except for its support structure and the silencer baffles (F i g u r e 7) – was erected in 4 lifts only. With creative and pragmatic solutions, well-structured processes, which aim at high levels of prefabrication, fast shipment and just-in-time delivery, skilled personnel and a large portion of luck, this demanding project was completed successfully. It may look simple to pay attention to all these odds and ends. However, it was this focus on the process, which enabled to deliver a new exhaust system of almost 400 tonnes within only 3 months and to re-commis-sion the power plant few days before the deadline (F i g u r e 8).

Summary

The security of electrical power supply is a factor which is often regarded as a given good. With the current market transitions towards an increased share of fluctuating energy production, the wide lack of finan-cial incentives for dispatchability and the quickly changing political frameworks, this good is rather decreasing than enhancing. Fig. 8. Plant after conversion.

It is expected that this situation will con-tinue to present an increasing challenge for energy companies and their suppliers, and ultimately our society. The present article showed that with creative and pragmatic solutions and well-structured processes a combined cy-cle power plant can be converted into an open cycle power plant within 5 months, if the boundary conditions are favourable. This allowed the timely participation in Belgium’s Strategic reserve and with an availability of 100 % during the winter 2014/2015, Vilvoorde made a valuable

contribution, which it will continue to do in the forthcoming winters. However, the price for the higher flexibil-ity was lowering the plant’s electrical effi-ciency. As there is a clear trend that con-ventional power plants need to be operated in a more flexible way [8], such and other conversions that diminish valuable exergy may become more frequent in the future. This might be desirable from an economic and security-of-supply point of view. From a resource point of view, though, exergy maximisation should always be the goal. This aspect seems to be often forgotten in today’s discussions about the energy sup-ply system of the future and it raises the question, how the ideal energy system of the future should look like.

References[1] Schuhbauer, Ch.: Bewertung von Kohlekraft-

werken und Verbesserung ihrer Dynamik in Hinblick auf die zukünftigen Anforderungen, p. 6(2012).

[2] Clipstone, J. et al.: Feasibility assessment of conversion from CCGT to OCGT. Uniper Inter-nal (2013).

[3] Brown, St.et al.: Strategic Operations Man-agement, p 77 (2000).

[4] Monk, T.H.: Maintaining safety and high per-formance on shiftwork (1993).

[5] Vlaams Reglement betreffende de Milieu-vergunning, Titel II, 1 Juni 1995.

[6] Schloss, A. et al.: Plume vertical velocity as-sessment of a proposed gasfired power station at Russel City Energy Center (2007).

[7] Wiese, L. et al.: Flexibility requirements for fossilfired power plants to support the growth of the share of renewable energies, VGB Power Tech 7/2013. l

Fig. 7. Installation of baffles.

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