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DREWAG - StadtwerkeDresden GmbH Coordinated Unit Control for more Flexibility

With

SiemensUnit

Controlplants

operated underheat extractioncontrol can alsosatisfy the

flexibilityrequire-ments of the

powermarket.

biomass boilers

The PlantThe Cogeneration plant Nossener Brückeis operated by DREWAG, the local utilitycompany for the city of Dresden in Ger-many. With an output of 1,700 gigawatt hours per year, this combined heat and power plant provides up to 80% of the district heat supply to the city.The plant comprises three SGT5-1000(V64.3) Siemens gas turbines withdown-stream heat recovery steam gene-rators. The plant is in operation yearround and regular plant outages are notscheduled.In general the heat requirements of thecustomers in the heat network essential-ly determine the operating mode of theplant. In addition the capabilities of opti-mized operation that are offered bythe use of a thermal storage module arealso employed.

The TaskThe objective is to equip the plant forthe marketing of system services so thatboth primary and secondary frequencyresponse could be marketed in future.

Additional restrictions result from thegas load management plan for the avoi-dance of gas purchase peaks.The stresson the gas turbines shall also be kept ata low level. In addition a low-stresscontrol concept for district heatbalancing had to be elaborated andimplemented.

The SolutionAdjusting the steam turbine inlet valve isa proven method in coal-fired power plants and has been applied in a combined-cycle power plant for the firsttime in this project. This concept involvesusing the main steam system as a steamstorage module which the steam turbinecan use to implement fast load changes.In this case, the gas turbines are onlyoperated slowly and with low plantstressing as a consequence. Siemensimplemented a coordinated unit controlwhich matches the output of the gasturbines with the steam turbine.Up to now, gas turbines have controlledthe output while the steam turbineoperated either with the valves wideopen or in inlet pressure mode.

event of a primary frequency responseevent based on the gas turbines that arein operation and the required PFR quanti-ty. With the future-proof Siemens UnitControl, plants operated under heat ex-traction control can also satisfy the flexi-ble requirements of the power market.

forms the basis for optimizing the combus-tion parameters in real time. The additionalmeasurements of local O2 and CO concen-trations over and above the temperaturedistribution, are an important contributionto the improved use of the SNCR installations.

Combustion optimization is made possibleby the individual adaptation of the existingair-fuel controlled variables, especially theair staging and excess air, in accordancewith requirements. Classic, model-basedcontrol concepts are used here to ensuretransparency and long-term maintainabilityby trained customer personnel.

Published by and copyright © 2018:

Siemens AGPower Generation Services DivisionFreyeslebenstrasse 191058 Erlangen, Germany

Article-No. PSCD-B10014-01-7600Printed in GermanyAL=N, ECCN=N

Subject to changes and errors. The information given in thisdocument only contains general descriptions and/or perfor-mance features which may not always specifically reflect thosedescribed, or which may undergo modification in the course offurther development of the products. The requested perfor-mance features are binding only when they are expresslyagreed upon in the concluded contract.

provider)E–mail: support.ener-gy@siemens.comArticle-No. PGXX-BXXXXX-00-4A00Printed in GermanyDispo 000000000 000000M BR 00000.Subject to changes and er-rors. The information givenin this document only con-tains general descriptionsand/or performance featu-res which may not alwaysspecifically reflect thosedescribed, or which mayundergo modification inthe course of further deve-lopment of the products.The requested performan-ce features are binding on-ly when they are expresslyagreed upon in the conclu-ded contract.

„The new coordinated unit control has pro-ven successful in practice, permitting a dy-namic operating mode which can be adjus-ted in line with the requirements but which is nevertheless stable and incurs low stres-ses. The implemented capabilities and the increase in flexibility have future-proofed the plant and enabled it to adapt better to changing market conditions.“

The Results• Increased plant efficiency

• Flexible adaptation to the regulations of the power market

• Increased flexibility for a future-proof plant

The latter has been retained and the pressure set-point has been piloted such that the steam turbinethrottles and generates the required output in theevent of a primary frequency response (PFR) event.Siemens Performance Optimization models are usedhere which calculate the throttling and the dynamicpressure characteristic in the event of a primary fre-quency response event based on the gas turbinesthat are in operation and the required PFR quantity.With the future-proof Siemens Unit Control, plantsoperated under heat extraction control can also sa-tisfy the flexible requirements of the power market.

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Axel Pechstein, Power Plant Manager, DREWAG - Stadtwerke Dresden GmbH