DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy
Marvin Mikael Rokni
Thermal Energy Section, Technical University of Denmark (DTU)
Waste to Energy System Based on Solid Oxide Fuel Cells: Department Store Case
1
SSMW7 – 2019 Conference, Heraklion, Greece
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy
Motivation
Municipal waste dispose is increasing significantly and must be taken care of. Waste to Energy after basic recycling and producing fuel through waste gasification. Multi generation systems is the most effective way from energetic/exergetic view. Decentralized trigeneration plants for producing electricity, cooling and freshwater.
WasteGasifier
Absorption
FreshwaterSOFC
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy
Introduction
SOFC = Solid Oxide Fuel Cell
Municipal
Waste
GasificationPlant
Syngas
Ash
Air & Steam
Impurities
SOFCPlant
ElectricPower
Air
Heat
Exhaust gases
Freshwater
MembraneDesalination
Absorption chiller
DomesticCool
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy
Gasifier Plant and its Modelling
Waste is dried and pyrolysis and then fed to the gasifier. Drying is made by steam generator (SG) in a steam–loop. Air is preheated in a gasifier preheater (GP) using the product gases from the gasifier. Preheated air and some of the steam from the drying process is fed to the gasifier Gasifier outlet temperature assumed 800C, while inside temperature is around 1300C. Syngas is cleaned in a gas cleaner system (such as sulfur and chlorine).
Scrubber
Ash
Gasifier
Steam loop
Air
GAPWaste
Dryer
SGSyngas
Impurities (Sulfur, chlorine, etc.)
Cleaned gas
SteamBlower
GasPump
Flare
Gas Cleaning System
GAP = Gasification Air PreheaterSG = Steam Generator
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy
Modeling Gasifier (cont.)
Equilibrium condition at outlet. Mixture of perfect gases. Minimizing the Gibbs energy at outlet, as described in Smith et al. (2005). Introduction of a parameter to account for methane bypass without undergoing chemical reactions (about 1%).
Parameter ValueWaste temperature, (˚C) 15Drying inlet temperature, (˚C) 150Gasifier temperature, (˚C) 800 Gasifier pressure drop, (bar) 0.005Gasifier carbon conversion factor 1Gasifier non-equilibrium methane 0.01Steam blower isentropic efficiency 0.8Steam blower mechanical efficiency 0.98Steam temperature in steam loop, (˚C) 150Gas blower isentropic efficiency 0.7Gas blower mechanical efficiency 0.95
Gasifier
inlet
outet
ash
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy
Parameter Waste Parameter SyngasC (vol %) 45.39 H2 (vol %) 29.31
Ash (vol %) 20.26 N2 (vol %) 32.39S (vol %) 0.08 CO (vol %) 25.28
Cl (vol %) 0.08 CO2 (vol %) 5.54O (vol %) 26.56 H2O (vol %) 5.67H (vol %) 6.21 CH4(vol %) 1.07
N (vol %) 1.42 Ar (vol %) 0.38
Moisture 18.12 HCl (ppmv) < 10Cp (kJ/kg) 1.84 H2S (ppmv) < 1
HHV (kW), dry basis 19990
Modeling Gasifier (cont.)
Aij ; element j (H, C, O, N) entering in i (H2, CH4, CO, CO2, H2O, O2, N2 and Ar)Amj: element j of leaving compound m (H2, CH4, CO, CO2, H2O, N2 and Ar)
k
iiii pnRTgnG
1
0 ln
N
j
k
i
w
mmjinmijoutijouttot AnAnG
1 1 1
,,,
kipnRTg
kin
G
nN
jijjoutoutiouti
N
jijj
outi
outtot
outi
,1for 0ln
,1for 0
1,
0,
1,
,
,
A
A
,Njnnw
mmjoutm
k
iijini 1for
1
,
1
,
AA
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy 7
Modelling of SOFC
For planar SOFCs developed by DTU – Risø and TOPSØE Fuel Cell (Denmark). Zero-dimensional model allowing to be used for complex energy systems. Calibrated against experimental in the range of 650 to 800C Keegan et al. (2002), Holtappels et al (1999), Kim and Virkar (1999), Peterson et al.
(2005).
t = thickness, = conductivity
id = current density,ias = anode limiting current
concohmactNernstFC EEEEE
41
x10096.1087.132sinh
254.1001698.0 T
i
FT
RTE d
act
dca
ca
el
el
an
anohm i
tttE
as
d
asOH
dHconc i
i
ip
ipBE 1ln
1ln
2
2
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy 8
Design of SOFC Plant Fed by Syngas
Gas cleaner (Desulfurization) Gas pump Anode preheater (AP) Anode side of SOFC Burner
Air compressor Cathode preheating (CP) Burner
Air
CP AP
Burner
SOFC
GasCleanerOff air Off fuel
Parameter ValueFuel utilization factor 0.7
Number of cells in stack 75Number of stacks 160
Cathode pressure drop ratio, [bar] 0.04Anode pressure drop ratio, [bar] 0.01
Cathode inlet temperature, [C] 600
Anode inlet temperature, [C] 650
Outlet temperatures [C] 780DC/AC convertor efficiency 0.97
A / c m2
Vo
ltag
e
0 0 . 2 0 . 4 0 . 6 0 . 8 1 1 . 2 1 . 4 1 . 6 1 . 8 20
0 . 1
0 . 2
0 . 3
0 . 4
0 . 5
0 . 6
0 . 7
0 . 8
0 . 9
1
1 . 1
6 5 0 C7 0 0 C
7 5 0 C
8 0 0 CExperimentModel
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy 9
Absorption Chiller
LiBr (Lithium Bromide) is used as absorbent.
Refrigerant
(Water/Steam)
Pump
Valve 1
EVAPORATOR
Cooling (return) Cooling (supply)
Hot gas in Hot gas out
DESORBER 1
LiB
r w
ate
r
Wea
kso
lutio
n
SHX
Liquid ine.g. water
ABSORBER
Cooling demand
DE
SO
RB
ER
2
Pump
LiBr water CONDENSER
Liquid outValve 4
Valve 2 Valve 3
Parameter ValueDesorber gas outlet temp. (C) 90
Rich solution (–) 0.6195Week solution (–) 0.548
Condenser outlet temp. (C) 32Pressure after valve 1 (bar) 0.008Pressure after valve 3 (bar) 0.05
Absorber cooling inlet temp. (˚C) 20Absorber cooling inlet pressure (bar) 16Hot side outlet temp. for SHX (˚C) 70
Solution pump pressure high/low (bar) 0.8/0.05
SHX = Solution Heat eXchanger
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy 10
DCMD (Membrane Desalination)
LiBr (Lithium Bromide) is used as absorbent.
Freshwater
DCMD
SwP2
SeaWater
SwP1Pump
Pump
HeatSource
Parameter ValueFiber length 0.4 m
Inner diameter of fiber 0.3 mmMembrane thickness 60 μm
Porosity 75%Membrane conductivity 0.25 W/mK
Shell diameter 0.003 mNumber of fibers 3000Packing density 60%Inlet temperature 80C
Ck (individual contribution of Knudsen diffusion) 15.18 × 10–4 [–]
Cm (individual contribution of Molecular diffusion ) 5.1 × 103 m–1
Cp (individual contribution of Poiseuille flow) 12.97 × 10–11 m
SwP = Sea Water Preheater
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy 11
The Complete Plant
Evaporator
SHX
Absorber
Dstrict Cooling
Condenser
Desorber 1
De
sorb
er
2
Coolingliquid in
Coolingliquid out
Off Gases
Ash
Gasifier
Steam loop
Air
GAPWaste
Dryer andPyrolysis
SGGas
CleanerAP
SOFC
Burner
CP
Air
Off airOff fuel
Freshwater
DCMD
SwP2
SeaWater
SwP1PumpOff Gases
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy 12
Parameter ValueMW mass flow (kg/h) 105.3MW temperature (C) 15
Drying temperature (C) 150
Gasifier outlet temperature (C) 800Gasifier pressure (bar) 1
Gasifier pressure drop (bar) 0.005Gasifier carbon conversion factor 1Gasifier non-equilibrium methane 0.01Steam blower isentropic efficiency 0.8
Steam blower mechanical efficiency 0.98Air temperature into gasifier (C) 15
Syngas blower isentropic efficiency 0.7Syngas blower mechanical efficiency 0.95
Syngas cleaner pressure drop 0.0049Blower air intake temperature (C) 15
Blower isentropic efficiency 0.7Blower mechanical efficiency 0.95
Gas heat exchangers pressure drop (bar) 0.01Cathode preheater pressure drop (bar) 0.04Anode preheater pressure drop (bar) 0.01
Burner inlet-outlet pressure ratio (efficiency) 0.95
Parameter ValuesNet electric production (kW) 146.56 Freshwater production (kg/h) 179.94 Heat input to DCMD, QFW (kJ/s) 125.66 DCMD efficiency (%) 59.30 Cooling production (kJ/s) 145.34Fuel consumption (LHV) (kW) 433.35Total power consumption (kW) 16.394 Off-gases temp. (C) 90Electric efficiency, Eq. (2) (%) 33.82Plant energy efficiency, Eq. (1) (%) 84.55
Plant Performance
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy 13
Effect of SOFC Utilization Factor
There exist a point where plant efficiency and power maximizes.
This optimum value is 0.7.
S O F C u t i l i z a t i o n f a c t o r [ ]
Eff
icie
ncy
& C
ell v
olt
age
Net
po
wer
0 . 6 0 . 6 5 0 . 7 0 . 7 5 0 . 8 0 . 8 50 0
0 . 0 8 1 50 . 1 6 3 00 . 2 4 4 50 . 3 2 6 0
0 . 4 7 50 . 4 8 9 00 . 5 6 1 0 50 . 6 4 1 2 00 . 7 2 1 3 5
0 . 8 1 5 0Cell voltage [V]Electrical efficeincy, Eq. (2)Net power [kW] Increasing utilization factor increases
current density. At a certain current density, the
concentration losses increases exponentially and thereby decreases cell voltage as ell as power.
S O F C u t i l i z a t i o n f a c t o r [ ]
Cu
rren
t d
ensi
ty
Po
lari
zati
on
s
0 . 6 0 . 6 5 0 . 7 0 . 7 5 0 . 8 0 . 8 51 1 0 0 01 1 5 0 0 . 0 31 2 0 0 0 . 0 61 2 5 0 0 . 0 91 3 0 0 0 . 1 21 3 5 0 0 . 1 51 4 0 0 0 . 1 81 4 5 0 0 . 2 11 5 0 0 0 . 2 41 5 5 0 0 . 2 71 6 0 0 0 . 3Current dencity [mA/cm 2]Concentration [V]
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy 14
Effect of SOFC Operating Temperature and Utilization Factor
Opening the valve for chiller increases cooling production (more off-gases to chiller);
Thereby, freshwater production decreases.
Opening the valve beyond 95% , then the freshwater device (DCMD) must be decoupled. This is due to the pinch temp associated with the DCMD heat exchanger.
S p l i t t e r f r a c t i o n [ ]
Fre
shw
ater
an
d C
oo
ling
0 0 . 2 0 . 4 0 . 6 0 . 8 10 5 2
5 0 5 6
1 0 0 6 0
1 5 0 6 4
2 0 0 6 8
2 5 0 7 2
3 0 0 7 6
3 5 0 8 0
Freshwater [kg/h]Cooling [kJ/s]T S w P 2 , h o t i nT S w P 2 , c o l d o u t
Opening the valve for chiller increases plant efficiency because chiller performance is higher than the desalination performance.
Even though desalination performances increases with opening the chiller valve.
S p l i t t e r f r a c t i o n [ ]E
ffic
ien
cy [
] an
d C
OP
[]
0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6 0 . 7 0 . 8 0 . 9 10
0 . 10 . 20 . 30 . 40 . 50 . 60 . 70 . 80 . 9
11 . 11 . 2
D C M DCOPA CCOPD C M D
p l a n t
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy
Effect of Moisture Content
Waste moisture may changes significantly from day to day. Increasing moisture content results in decreasing plant performance. All production
decreases. Higher moisture content means also lower fuel energy (LHV) and therefore plant
performance remains unchanged.
M o i s t u r e c o n t e n t [ % ]
Eff
ect
[kW
]
Fre
shw
ater
[kg
/h]
1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6 2 8 3 01 1 0 1 3 0
1 2 0 1 4 0
1 3 0 1 5 0
1 4 0 1 6 0
1 5 0 1 7 0
1 6 0 1 8 0
1 7 0 1 9 0CoolingFreshwaterNet powerM o i s t u r e c o n t e n t [ % ]
Eff
icie
ncy
[]
Tem
per
atu
re [
C]
1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6 2 8 3 00 4 0 0
0 . 1 4 0 50 . 2 4 1 00 . 3 4 1 50 . 4 4 2 00 . 5 4 2 50 . 6 4 3 00 . 7 4 3 50 . 8 4 4 00 . 9 4 4 5
1 4 5 0Energy efficiency, Eq. (1)Electrical efficiency, Eq. (2)Burner temperature(1) (2)
`
net FWplant
fuel fuel
P Q Cool
m LHV
�& `
netplant
fuel fuel
P
m LHV
�&
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy
Conclusions
The electrical efficiency of the plant is about 34% with a net power of 145 kW. Connecting the absorption chiller and seawater desalination systems in parallel as
bottoming cycle for the fuel cell plant then freshwater and cooling productions will be about 180 liter/hour and 145 kW respectively when waste heat from SOFC plant divides equally between AC and DCMD plants.
The suggested designs offer the possibility to regulate freshwater and cooling productions after demand.
Effect production (electricity, cooling and freshwater) depends on the moisture of the feed waste while plant total efficiencies (electrical and energy) does not change significantly.
DTU Mechanical Engineering26 – 29 June 2019 Dr. M. M. Rokni SSWM7 – 2019 Heraklion Waste to Energy
Thank you for your attention.