waste to energy system based on solid oxide fuel cells...

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


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


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


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


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


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


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


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


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


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


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


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]


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


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

�&


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.


Thank you for your attention.

waste to energy system based on solid oxide fuel cells...

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