ORC BOTTOMING OF A GAS TURBINE: AN INNOVATIVE SOLUTION FOR BIOMASS APPLICATIONS

Transcription

1 ORC BOTTOMING OF A GAS TURBINE: AN INNOVATIVE SOLUTION FOR BIOMASS APPLICATIONS Questa memoria è tratta in larga parte dalla presentazione del Prof. M. Gaia al convegno ASME sui sistemi ORC (Ottobre 2015) Convegno "Le Biomasse come vettore energetico: quali prospettive" Milano, 20 Aprile 2016 Cod. 16-A-211-rev.0

2 BIOMASS MAIN RENEWABLE SOURCE (LIKE WIND, SOLAR, GEOTHERMAL AND HYDRO) Nearly carbon neutral Can be stored no alea Ubiquitous most countries

3 THERMAL ENERGY MECHANICAL ENERGY 1 kwh 1 kwh 4810 m 0.4 kg/kwh 76.3 kg Conversion EFFICIENCY h= kwh mech. requires 4-6 heat units

4 Utilisation of biomass for electric power generation (and possibly cogeneration) with a Rankine cycle with direct exchange scheme with indirect (thermal oil) exchange scheme (one /two loops) TURBODEN has about 260 biomass ORC plants all over the world in the MWel range (efficiency: about 15% in cogeneration mode, about 22% in power only mode)

5 HIGH EFFICIENCY PAYS Lower BIOMASS COST per MWh produced typical biomass cost in Europe /kwh thermal if h=0.20 biomass cost 125 /MWh electric if h=0.30 biomass cost 83 /MWh electric Lower required STORAGE VOLUME Lower FLOW OF EXHAUST GASES to be treated Better UTILIZATION of biomass, a limited renewable energy source Higher POWER from a limited biomass source at low cost (e.g. waste wood from a factory)

6 Turboden target: a more efficient, reliable and low O&M cost solution for few MW power range 1) GASIFICATION fixed bed gasifier 2) GAS TURBINE OPRA 2 MW turbine, sophisticated yet simple, rugged, reliable, low emission 1) ORC BOTTOMING easy to operate, reliable, efficient

7 FIXED BED GASIFIER UP-DRAFT DOWN-DRAFT

8 OP 16 GAS TURBINE by Opra Turbines BV - NL

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10 Traditional scheme: atmospheric gasifier, followed by a deep cleaning and compression Syngas compressor ~ 1 bar(a) ~ 11 bar(a) (atmospheric) (deep)

11 Tar problem: thorough gas cleaning required

12 New scheme proposed by Turboden: pressurized gasifier, followed by a simple cleaning Pressurized gasifier Pressurized biomass feeding system ~ 11 bar(a) ~ 11 bar(a) (pressurized) (simple hot filtering)

13 AIR Pressurized Gasifier Tar to GT combustor in vapour state

14 Two solutions are described for the heat recovery downstream the gas turbine (exhaust gases at 575 C) with ORC: 1. Medium temperature, single level ORC 2. High temperature, double level ORC

15 Medium temperature, single level ORC 200 C exhaust gas temperature

16 High temperature (350 C!), double level ORC 130 C exhaust gas temperature 130

17 Standard ORC (medium temp., Single level) Enhanced ORC (high temp., Double level) Fuel power input (rel. To LHV) kw LHV fuel (moisture content wood chips 27.5 wt.% wet bulb MJ/kg Ambient temperature C Temperature syngas out of gasifier C Electric power output turbine - gross kw Thermal power input ORC - from exhaust gas kw Electric power output ORC - gross kw ORC net efficiency/lorenz efficiency % Total electrical power output - net kw Total electric efficiency - net %

18 Power balance for the medium temperature, single level ORC heat recovery case

19 AN INNOVATIVE GASIFIER THE TWINGAS CONCEPT BY TURBODEN

20 ADDITIONAL FEATURES AND CONCLUSIONS RANGE from 2.5 MW (single OPRA turbine + ORC) to 5.0 MW(twin OPRA turbines + single ORC) PERFORMANCE in excess of 30% (and up to some 34%) FAST MODULATION of power produced low POLLUTANT CONTENT in exhaust gas tolerant towards BIOMASS FEED characteristics Further comment: A system featuring reciprocating internal combustion engines has similar performance but the gas cleaning capital and O&M cost are much higher (up to now) and tolerance to different kind/low quality of biomass is low

21 Roberto Bini Turboden srl Brescia - Italy

22 Back up slide Traditionally the solutions are classified according to the following schemes: - fixed bed Updraft in which the descending biomass moves counter-current to the ascending gaseous phase, so that the subsequent steps of the process, from the point of view of biomass, are ordered as Drying, Pyrolysis, Reduction, Oxidation (as reported in fig.1-a) - fixed bed Downdraft in which the descending biomass moves co-current to the descending gaseous phase, so that the subsequent steps of the process, from the point of view of biomass, are ordered as Drying, Pyrolysis, Oxidation, Reduction (fig 1-b) - fluidized bed of various kinds. In many cases the process cannot be divided in zones and it takes place instead on the surface and within each particle of solid biomass, hence all four transitions take place substantially at the same time in parallel.

23 Back up slide

24 Back up slide In fixed bed gasifiers, Reduction is the most characterising step, which takes place in the bed of char resulting from the Pyrolysis. In Downdraft gasifiers reduction involves a given dwell time and interaction between the gases and tars resulting from the pyrolysis. As a consequence, besides the main scope of obtaining a gas composition including high H 2 and high CO, the reduction step is very effective at achieving thermal decomposition of tars. In Updraft gasifiers, the produced gas is substantially clean at the top of the reduction zone, but then it flows through the pyrolysis zone and it becomes heavily loaded with tar and moisture. Apparently, a Downdraft solution is preferable in any case. However in practice the transfer of heat to the upper layers undergoing pyrolysis is rather ineffective and it is difficult to keep a uniform flow through the bed, in particular if the bed has a large cross section. Hence the Updraft solution, though not attractive from the tar content point of view, is preferable for relatively large systems. Moreover so as in fact the counter-current flow of hot gas allows an efficient pre-drying of the biomass before it enters the pyrolysis zone and the separated water is added to the produced gas instead of being put to the high temperature reaction zone, allowing to feed the Updraft gasifier with high moisture biomass (up to 50% vs 20% for the Downdraft). [3] The fluidized bed gasifiers are intermediate, for what concerns both the tar content in the gas point of view and the acceptance of high humidity feed. [4-5] Fixed bed gasifiers are attractive due to the low parasitic power required and their tolerance of uneven quality biomass. However, the required volume of the reactor is large and the quality of the produced gas is less predictable than with fluidized bed gasifiers.