Application of Organic Rankine Cycle systems to Anaerobic Digester

Transcription

1 Application of Organic Rankine Cycle systems to Anaerobic Digester Mattia De Rosa 1,2, Thomas Cromie 3, Lionel Macey 4, Roy Douglas 1 1 School of Mechanical and Aerospace Engineering. Queen s University Belfast. 2 Centre of Advance Sustainable Energy. Belfast. Northern Ireland 3 AgriAD Power Ltd. Banbridge, Northern Ireland 4 ThermTech Ltd. Ashton-under-Lyne. England Windsor (UK). April 19-21, 2017

2 Anaerobic Digestion AD is a growing industry in Northern Ireland. 500,000 tons of food waste generated annually in NI: enough biomethane to displace 10% of diesel. Typical feedstocks: pig and cattle, slurry, poultry litter, energy crops and food waste. Map credit 2017 Google 2

3 AgriAD biogas production plant Banbridge (Northern Ireland) Example: AgriAD system Biogas 55% CH4 40% CO2 LHV = 5.48 kwh/m3 Density = 1.25 kg/scm Gas Treatment chimney DIGESTER 1! DIGESTER 2 Exhaust HE 243kW Gas Train Fuel consumption: 1202 kw 470 C 2694 kg/h 97 C 180 C Water HE 97 C 506kW! 78 C 90 C boiler 2016 V2 500kWe ENGINE 70 C 88 C Pump 24 m3/h 78 C! Pump 24 m3/h Radiator 506kW Pump 22.3 m3/h Feedstock heating area 40 C 44 C Pump 10 m3/h Radiator 38kW STREAM LEGEND Biogas Lube oil Exhausted gas flow Water cooler flow List of revisions: PRELIMINARY Water cooler return Client: AD production and consumption Fresh oil tank 1200l Waste oil tank 1200l container CHP area Intercooler flow Intercooler return Secondary water circuit flow Secondary water circuit return Feedstocks flow ORC flow (low pressure) ORC flow (high pressure) Project: CASE WHR Project R3641MEE Title: ORC System for AD plant Drawn: Checked: Queen s University Belfast MDR School of Mechanical and Aerospace Engineering Date: 24/3/16 Sheet: Approved: 1/1 Sheet title: Circuit system - Overall Scale: Drawing number: Ashby Building, Stranmillis Road BT95AH, Belfast. United Kingdom Rev. no.: R3641MEE-01 0 Feedstock consumption ton/y Biogas production MWh t /y CHP engine (eff. 41%) 500 kw e Thermal energy output 4375 MWh t /y Thermal energy recovered 1363 MWh t /y Electricity produced (net) 3526 MWh e /y The system does not exploit all heat generated by the engine. This heat might be used to produce electricity by means of an ORC, increasing the overall performance of the system. 3

4 Organic Rankine Cycle Organic Rankine Cycles (ORCs ) are Rankine cycles using an organic substance as working fluids. ethanol Temperature [ C] ibutene t2butene 1butane dme ipentane c2butane isobutane propane propylen butane propyne neopentane R134a R1234yf cyclopro Entropy [kj/kg-k] Exploitation of low temperature heat sources to produce electricity; Supercritical cycles are achievable without special efforts (<60bar). Advantageous efficiency in a small-scale concept. 4

5 Organic Rankine Cycle 5

6 ORC potential The ORC installation potential is about 2705 MW in Europe, which would lead up to about 21.6 TWh of electricity production, with savings of about 1900M and of over 8.1 Mtonnes of greenhouse gases Campana F et al. ORC waste heat recovery in European energy intensive industries: energy and GHG savings. Energy Conversion and Management. 2013;76: Lemmens S. A perspective on costs and cost estimation techniques for Organic Rankine Cycle System. 3rd International Seminar on ORC Power Systems, October 12-14, 2015, Brussels, Belgium. 6

7 Potential exploitation in the AD market It corresponds to a biogas production of GWh t /y. About 29% of this thermal heat is currently wasted (~47000GWh t ) The exploitation of this heat by using Organic Rankine Cycles in AD plants will increase the electric energy production of GWh e /y. In terms of money, it corresponds to about 900M/y. 7

8 WHR-ORC concept for ADs 8

9 Electricity ORC High Temperature Heat Source Low/Medium Temperature Heat Source How can we collect the heat efficiently to maximise the primary energy saving? 170 C T>350 C 120 C C 9

10 ORC system at QUB ORC 10

11 ORC system at QUB Pump Inlet Pump Outlet REG outlet HE 1 OUTLET HE 2 OUTLET HE3 OUTLET EXP OUTLET REG OUTLET COND OUT STATE 1 STATE 2 STATE 3 STATE4 STATE 5 STATE 6 STATE 7 STATE 8 STATE 9 Pressure kpa Pressure bar Temperature K Temperature C Enthalpy kj/kg Entropy kj/kgk Quality - 0 #Subcooled liquid with p>pc #Subcooled liquid with p>pc #Subcooled liquid with p>pc #Supercritical state (T>Tc, p>pc) #Supercritical state (T>Tc, p>pc) #Superheated vapor #Superheated vapor Density kg/m^ Exergy kj/kg

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13 ORC potential configurations for ADs Based on a 500kWe Biogas Engine 243kWt 470 C 263kWt 88 C CURRENT CONFIGURATION (NO ORC) Production of hot water (97 C) used to heat the digester. 200kWt used 506kWt wasted 13

14 ORC potential configurations for ADs Based on a 500kWe Biogas Engine CONF 1: DIGESTER PRIORITY The thermal demand of the digester has the priority: 243kWt 470 C 95kWt to the digester 148kWt to the ORC 263kWt 88 C 105kWt to the digester 158 kwt wasted 14

15 ORC potential configurations for ADs Based on a 500kWe Biogas Engine CONF 2: Partial ORC priority (EG) All exhaust gas heat is used to feed the ORC: 243kWt 470 C 243kWt to the ORC 263kWt 88 C 105kWt to the digester 158 kwt wasted 95kWt supplied by a gas/oil boiler to reach the desired temperature. 15

16 ORC potential configurations for ADs Based on a 500kWe Biogas Engine CONF 3: Full ORC priority (EG and CW) All heat rejected by the engine (506kWt) is used to feed the ORC. The heat required by the digester is provided by an external gas/oil burner. 243kWt 470 C 263kWt 88 C 16

17 Investment costs 17

18 Analysis of the investment ~15% efficiency 18

19 Analysis of the investment 19

20 Conclusions AD is a growing industry in Northern Ireland with more than 40 operational plants for electricity production. ORC technology would allow to produce even more renewable electric energy by exploiting the heat rejected by the biogas engines. QUB is currently investigating the potential market of AD-ORC systems in Northern Ireland. An experimental system working in transcritical condition is currently under construction at QUB. In the framework of a KCORC grant, a thermoeconomic optimisation of ORC systems for AD plants is ongoing in collaboration with the University of Liege. Preliminary results have shown that PBP between 2.8 and 7.5 years could be achieved depending on the system configuration and on the technology adopted. 20

21 Thanks for your attention 21