The Cryostar Magazine NÂ°3 : pdf file

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ENERGY-RECOVERYThe reaction turbine is of a radial type and theconstruction is based on a proven design for easymaintenance. But the use of a synchronous generatoris new in the energy recovery business.Previously, asynchronous generators were favouredpurely for simplicity of use. But, in comparison,the combination of a synchronous generator andexpansion turbine produces no reactive current,drastically elevating the ER-unit’s profitability.Such ER-units utilise the potential energy of naturalgas being delivered under high-pressure. Thegas is only expanded when it reaches the pressurelet down station, and it is here ER-units come intotheir own.To reduce the gas pipeline pressure of 55-bar tomeet the low pressure of 5.5-bar of the local gasdistribution networks, a pressure drop is needed.In other words, the gas is allowed to expand andduring this process drives the Cryostar turbinewithin the ER-unit.The resulting electricity recovered in this way isthen supplied to local electricity suppliers. Theefficiency of these units is about 85 per cent, vastlysuperior value when compared to BHKWs, to gasandsteam-turbines or even fuel cells.The new ER-unit in Arlesheim is quite revolutionary.It uses a two-stage expansion turbine,equipped with a synchronous generator, to ensureeach stage produces the same power.It allows 35,000 Nm3/h of natural gas to expandfrom 55-bar to 5.5-bar at full capacity, generating1,800 kW. The expanded gas volume canalso be reduced in summer time from 35,000 to15,000 Nm3/h, and the inlet pressure of 55-barcan decrease to 30-bar on very cold days.The turbine system consists of the dual stageexpansion turbine, a turbo-gearbox, low speedcoupling and the synchronous generator. The wholeunit, including the seal gas and lube oil system ismounted on a rigid base frame.And for simplicity of use, control of the turbine andthe auxiliary systems is performed by a programmablelogic controller (PLC). The PLC controlsa constant outlet pressure (pressure control) ora constant gas flow (flow control) through theturbine.In other words, under pressure control, the outletpressure is adjusted to a set point by opening orclosing of the adjustable inlet nozzles. In turn, thegas flow through the turbine will change so thatthe actual downstream gas pressure will adjust tothe set point. In case of flow control, the adjustableinlet nozzles will supply a constant flow, and willbe opened or closed only by higher or lower flowdemand.To use the energy for the new ER-unit in the mostefficient way, all heating losses (waste heat ofall auxiliary systems) is recycled to preheat thenatural gas. Therefore the ER-unit is equipped notonly with a high temperature heating system, butalso with a low temperature heating system. Thisrecycles all heat losses from the turbine coolersand BHKW’s exhaust gases. Each turbine stage isequipped with a preheater fed by the low temperatureheating system and with a second preheater fedby the high temperature heating system. This heatsthe natural gas up to 30ºC (LT system) respectivelyup to 78ºC (HT system).Where a plant operates in low-flow conditions, thehigh temperature heating system is fed from theBHKWs, At high-flow it is fed from the BHKWsin combination with the existing heating boilers,which also supply the heating system of an adjacentoffice building.4Spring 2004
ENERGY-RECOVERYThe electricity from the synchronous generators(BHKW 400V, Turbine 6.3kV) is fed into the electricitygrid and delivered to local consumers. Forthis the expansion turbine as well as the BHKW’sare equipped with a transformer.The whole plant is controlled by a master PLC,which sends all necessary information fordispatching. It operates in separate system groups,and each group is equipped with a PLC (slave) tocontrol their own auxiliary system. This arrangementallows independent operation of each group,and gives better plant redundancy.The big advantage of ER-units is that they supplyabsolutely clean energy, and therefore fulfil allregulations regarding environmental protection.ER-units are not only more efficient and profitablebut meet the environmental criteria – no emissionsof sulphur dioxide, nitrogen oxide or carbondioxide.And even though the investment in such plant isrelatively high, demand is increasing year-on-year.This mirrors the increasing pressure on the energygeneration sector to produce clean, environmentally-friendly,electricity.Use of natural gas is a step in this direction and,with reasonable reserves available worldwide,looks to have a bright future.Certainly no one can afford to ignore the shorttermvalue of coal and oil to produce energy, butthe production of clean electrical power is growingin importance.Already, where possible, many household consumersand trade and industry companies are movingto heating by natural gas instead of coal or oil. Thereasons are simple: not only is it ‘greener’ thancoal/oil but it’s cheaper.The market is also shifting towards designingER-plants on a smaller scale for villages and smalltowns.And, timely investment in research and developmentmeans Cryostar already has the technologies– solutions like expansion turbines with magneticbearings and/or high frequency generators – toservice this new sector.Spring 2004 5
Page 1 and 2: N°3Spring 2004Clean electricityDo
Page 3: Energy-Recovery withCryostar - Turb
Page 7: BUSINESS CENTRESBelgian filling sta
Page 10 and 11: LIQUID TURBINELiquid turbine genera
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