- Email: [email protected]
Biodiesel fuel processor for APU applications
international journal of hydrogen energy 34 (2009) 4495–4499
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/he
Biodiesel fuel processor for APU applications G.J. Kraaija,*, S. Specchiab, G. Bollitoc, L. Mutrid, D. Wailse a
Energy research Centre of The Netherlands, Westerduinweg 3, 1755 ZG Petten, The Netherlands Politecnico di Torino, Materials Science and Chemical Engineering Department, Corso Duca degli Abruzzi 24, 10129 Torino, Italy c Centro Ricerche FIAT, Strada Torino 50, 10043 Orbasssano, Italy d Scandiuzzi Advanced Technologies Department, Viale Dante 78, 38057 Pergine Valsugana, Italy e Johnson Matthey Technology Centre, Blounts Court, Sonning Common, RG4 9NH Reading, United Kingdom b
article info
abstract
Article history:
Tail pipe emission reduction, increased use of renewable fuels and efficient supply of
Received 9 April 2008
auxiliary power for road vehicles using fuel cells have been the main drivers of the Euro-
Accepted 23 July 2008
pean project BIOFEAT (biodiesel fuel processor for a fuel cell auxiliary power unit for
Available online 25 September 2008
a vehicle). Within the project a biodiesel fuelled heat integrated fuel processor for 10 kWe capacity has been designed and constructed. Demonstration tests showed a high quality
Keywords:
reformate with less than 10 ppm of CO and a gross efficiency of 87%.
Biodiesel
ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Fuel processor APU
1.
Introduction
Fuel cell-based auxiliary power unit (FC-APU) systems have attracted growing interest as an alternative technology for onboard electricity generation in vehicles and trucks. The demand for on-board electrical power is expected to grow further while there is increasing pressure to reduce CO2 and the other emissions such as NOx, soot and noise, associated with the use of current engine-generator systems. FC-APU systems offer a promising alternative due to their high potential efficiencies, low tailpipe emissions of NOx, hydrocarbons and CO and their silent operation. The net emission of CO2 can be reduced even further when biodiesel is applied as renewable fuel. In the past decade, biodiesel has been gaining popularity as an alternative energy source worldwide because of its many benefits: this environmently friendly fuel reduces tailpipe emissions (it is practically sulphur-free, <1 ppm), visible smoke and noxious odours. Biodiesel is the alternative fuel that produces basically no emissions during manufacture [1]. Within this context, the FP5 project BIOFEAT [2], has been carried out with the main purpose to demonstrate the concept
of a heat integrated biodiesel fuel processor (FP) delivering the hydrogen for a PEMFC-based APU system. The fuel processor size was chosen equivalent to a power output of 10 kWe as an estimate of future auxiliary power requirements for peripheral systems in road vehicles amongst which are heating, ventilation and air conditioning system, on-board computers, steering by wire, brake by wire and in-car entertainment. The specific objective of the BIOFEAT project was to design, build and demonstrate a laboratory test skid of an on-board biodiesel FP capable of feeding a FC to generate electricity for the auxiliary power needs for a family car or a truck. The project has been carried out by the partners Politecnico di Torino, ECN, CRF, Johnson Matthey, Scandiuzzi, Bekaert and Duisburg-Essen University.
2.
Design of the fuel processor
At the start of the project the final requirements of a commercial PEMFC based APU system for transport applications were established by the industrial partners. The goal
* Corresponding author. Tel.: þ31 224 564569. E-mail address: [email protected] (G.J. Kraaij). 0360-3199/$ – see front matter ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2008.07.108
4496
international journal of hydrogen energy 34 (2009) 4495–4499
of the project was to demonstrate the proof-of-principle of on the one hand the conversion of biodiesel to PEMFC quality reformate and on the other hand the integration aspects by means of the use of heat integrated reactors. For this purpose a specification of the laboratory type skid mounted fuel processor was made as a first step of the development trajectory. The major requirements for the commercial system as well as the BIOFEAT fuel processor are listed in Table 1. As a start of the project various conceptual system approaches have been evaluated resulting in the final choice of the system approach as depicted in the simplified conceptual process flow scheme of the APU system in Fig. 1. Main characteristics of the system are the use of autothermal reforming for primary biodiesel conversion, preferential oxidation as gas-cleanup technology, the use of a lowtemperature PEMFC and the level and approach for heat integration. The requirement of a closed water balance in the system could be fulfilled by operating the PEMFC stack at a pressure of at least 1.5 bar and an off-gas condensation temperature of maximum 50 C. Nevertheless, the cooling duty for condensation of 8 kW requires a large radiator. The net electrical system efficiency at full load is calculated at 30% (incl. BOP losses). For the BIOFEAT project, a fuel processor system excluding a PEMFC was developed. The simplified system design for the fuel processor is provided in Fig. 2. Details of the process design can be found in Refs. [3–5]. Because a PEMFC was not included in the tests, the PEMFC anode off-gas was simulated by feeding part of the reformate to the afterburner, corresponding to a calorific content of the otherwise hydrogen-depleted anode off-gas. Start-up of the
Table 1 – Specification for the biodiesel fuel processor prototype and commercial system. System targets Power (kWe) Durability (continuous) (h) Durability (thermal cycles) Efficiency (ac, net) Fuel processor efficiency Start up time (min) Weight Volume Start-up external electrical energy (kWh) Auxiliaries power (kWe) Working pressure Working temperature CO requirement for a PEM stack
Commercial system
BIOFEAT prototype
10 5000–10000
10 500
>5000
>50
>35%
(>35%) >75%
Fig. 1 – Simplified process scheme for the biodiesel auxiliary power unit.
system was carried out by using an external hydrogen supply. Water was also fed from an external source and not recovered as a condensate. Nitrogen instead of air was used during startup and emergency shut-down in the initial experiments for catalysts’ protection. The biodiesel fuel processor was designed to operate without external heating devices or heat compensation by linking heat sources and sinks internally by proper heat integration and insulation. Steam generation and air preheating is carried out in spiral-wound tubes positioned in the exothermic reactors of the fuel processor and afterburner (AB). This configuration allows maintaining various reactor sections at the desired temperature level. The S/C ratio can be adjusted by variation of the water flow through the afterburner heat exchanger. The autothermal reformer reactor (ATR) is integrated with a steam generator and a water quench in order to reduce the outlet temperature to the required high temperature shift reactor (HTS) inlet temperature, see Fig. 3. Moreover, the wall temperature of the ATR reactor vessel is lowered and low cost stainless steel can be used. For temperature control of the water-gas shift (WGS) and preferential oxidation (PrOx) sections full evaporation of water in the integrated heat exchangers is essential. Therefore these heat exchangers contain a heating section, a boiling section and a superheating section. The concept was successfully validated by using mock-up reactors prior to the integration. The water-fed heat exchanger in the afterburner is designed for
Fuel off-gas (stack simulation)
Flue gas 1 10–20 kg/kW 10–20 l/kW <0.1
<20 <400 kg <500 l <1
AB <2
<2
Stack pressure between 10 C and þ40 C <10 ppm (steady) and <100 ppm (transient)
Stack pressure
Air
ATR
N2 (start-up)
Biodiesel
HTS
H2 (start-up)
LTS
Prox1
Prox2
Water
Fig. 2 – Simplified process scheme of the biodiesel fuel processor.
international journal of hydrogen energy 34 (2009) 4495–4499
4497
Fig. 3 – Autothermal reformer reactor from concept to drawing and realisation.
partial evaporation of the water in order to obtain sufficient cooling capacity in the ATR heat exchanger. The fuel processor is operated as follows: During start-up hydrogen from an external supply and air are fed to the afterburner. As the afterburner ignites at room temperature it supplies the required heat for the air and steam generation that will be used to heat up the rest of the reactors. When the required temperatures in the different reactors are reached, the reformer is started by feeding biodiesel to the ATR reactor where it reacts with air and steam. All reactors are controlled to operate within the operating temperature window by adjusting the water flows. The required CO content is controlled by the air supply in the PrOx. For simulation of stack operation in a truly integrated system, anode off-gas at 80% utilisation is mimicked by feeding a part of the reformate
flow to the afterburner instead, providing the same calorific value and temperature level as determined by integrated system simulations.
3.
Manufacturing of the fuel processor
The fuel processor skid was manufactured by Scandiuzzi and is shown in Fig. 4. As the objective of the project was to demonstrate the feasibility of biodiesel reforming and the principle of heat integrated reactors, the emphasis for the construction is more on manufacturability and easy accessibility in the laboratory rather than a minimized packaging volume. The volume and weight targets were relieved, but the system is designed to run without external heating by means of proper insulation of
Fig. 4 – View of the biodiesel fuel processor mechanical assembly before insulating.
4498
international journal of hydrogen energy 34 (2009) 4495–4499
4. 4.1.
Testing of the fuel processor
10.0000
HTS
ATR out
LTS in
HTS out
1.0000 Prox1 in
LTS out
0.1000 Prox2 in
Prox1 out
0.0100
CO Test [%] CO AspenPlus [%]
0.0010
System demonstration tests
Prox2 out
The RME type biodiesel obtained from Oelmu¨hle Hamburg AG was used for the experiments. Chemical analysis revealed that the sulphur content was below 1 ppm and that the actual composition closely resembles that used in the design calculations (C19H36O2). The focus of the tests was to demonstrate the feasibility of the integrated biodiesel fuel processor in terms of heat management, H2 output, and gas quality. A gross fuel processor system efficiency of 87% was reached, the efficiency h being defined as: . 4Biodiesel LHVBiodiesel h ¼ 4H2 in reformate LHVH2 where 4 is the flow rate [kg/s] and LHV is the lower heating value of the fuel. The mimicked anodic offgas flow (20% of the reformate flow), which is used for preheating the air and steam, is not considered in the efficiency calculation. The hydrogen flow used in this calculation is based on the carbon mass balance using the gas analysis results (the sum of the dry gas components being 99.9 0.3%) and equals the efficiency calculated from the ASPENPlus simulation. In these simulations a total heat loss for the reactors of 700 W was assumed and the measured heat loss was 850 W. For every reactor the difference between the assumed and measured heat loss was within 50%. As an example, the measured and calculated dry CO concentration after each of the reactors is shown in Fig. 5. This figure shows that biodiesel can be converted to a reformate gas with a CO concentration lower than 10 ppm, which is suitable for a PEM fuel cell. The measured dry gas composition after each reactor is presented in Table 3.
4.2.
Biofeat 10kW; comparison ASPENPlus design and test results
CO [%]
the (long) connecting tubes and reactors themselves. The control system is designed to control the flows, except the biodiesel flow, by temperature measurements. For evaluation of the performance of the fuel processor all inlet flows are measured. The fuel processor control is PLC based with a SCADA user interface. The specifications of the precious metal based catalyst used in the reactors are shown in Table 2.
Fuel injection system
The turn-down ratio of the fuel processor is 3:1 and is limited by the spraying characteristics of the fuel nozzles. The use of
0.0001 0
100
200
300
400
500
600
700
800
Temperature [°C] Fig. 5 – Comparison of the dry CO composition from the design using AspenPlus and test results for the different reactors and their temperatures.
a simple nozzle limits the turn-down ratio for a single nozzle to 1.6:1. Therefore a double nozzle system has been applied using different nozzle sizes to provide an overall turn-down ratio of 3:1 [4]. A drawback of this solution is that at switchover from one nozzle to the other or to two nozzles, the fuel flow is temporarily reduced. This requires corresponding accurate control of the air flow to the ATR to prevent overheating of the ATR catalyst. The fuel is injected in hot steam (S/C ¼ 2.5) and subsequently air is injected into the gaseous fuel/steam mixture. In the evaporating zone where the fuel is injected coke deposition on the walls is observed. In the zone beyond the air injection no coke is observed. The absence of coke in the section may be due to the operation in the ‘‘cold flame’’ regime in this zone. The presence of cold flames is illustrated by the mixing temperature, which is much higher than can be explained by adiabatic mixing and evaporation.
4.3.
ATR reactor
The ATR catalyst for biodiesel reforming was developed by Johnson Matthey for this project and the operating conditions were established. At the 10 kWe operating conditions the catalyst converted 99% of the fuel to the components as calculated by thermodynamic equilibrium. Approximately 0.6% of the rest is found as methane that is present in higher concentrations in the reformate gas (0.25–0.3% dry) than
Table 2 – Catalyst specification for the biodiesel fuel processor. Reactor
ATR Afterburner HTS LTS PrOx 1 PrOx 2
GHSV Pressure Tin Tout (bar) ( C) ( C) design (h1) 30000 40000 40000 20000 50000 50000
2.1 1.4 2 1.9 1.8 1.7
450 50 360 265 150 120
730 642 406 272 195 126
Type
Catalyst supplier
Monolith Monolith Monolith Monolith Wire mesh Wire mesh
JM JM JM JM ECN ECN
Table 3 – Measured dry gas composition after each reactor. Biofeat
H2 (%)
CH4 (%)
CO2(%)
CO (%)
N2+Ar (%)
Total (%)
ATR HTS LTS PrOx1 PrOx2
41.65 44.92 46.06 44.91 44.30
0.31 0.35 0.34 0.35 0.39
14.80 19.75 21.61 21.56 21.46
8.62 2.55 0.34 0.059 0.0004
34.34 31.73 32.11 32.61 33.46
99.73 99.30 100.46 99.51 99.64
international journal of hydrogen energy 34 (2009) 4495–4499
4499
stack, the air and fuel feed to the afterburner are mimicked by controlling the energy content and the temperature after the reaction to be identical to the design with the fuel cell. During operation the mixture frequently ignited before the catalyst was reached, leading to rapid changes of the measured temperatures within the reactor. Therefore, flow control of air was used instead of temperature control.
5.
Fig. 6 – Measured CxHy concentration in the reformate gas at 10 kWe power. At the points denoted with ‘‘A’’, the gas analysis was measured after the ATR.
calculated from thermodynamic equilibrium (0.11%) and 0.4% is attributed to non-methane hydrocarbons (NMHC), as shown in Fig. 6. The NMHCs are in the form of C2–C5 alkenes. After the ATR these are fully hydrogenated in the HTS.
4.4.
Shift reactors
A high and a low temperature shift reactor are applied for the conversion of CO to H2 by the water-gas shift reaction. Two shift reactors were chosen since this will provide a higher H2 production and a higher reduction of the CO load to the PrOx reactor compared to a single shift reactor.
4.5.
PrOx reactor
For the PrOx section a double bed reactor with integrated interstage cooling is applied. The PtRu based PrOx catalyst is coated on a wire mesh and has low precious metal content. With this catalyst a CO concentration target of less than 10 ppm was successfully achieved. The lambda value (lambda is 2O2/CO) at 10 kWe operation was 2.6–3 for PrOx 1 and 5–6 for PrOx 2. This catalyst has demonstrated its durability in reforming experiments using natural gas as a fuel for more than 1000 h. Interestingly, this catalyst exhibited significant degradation within 50 h when operated with biodiesel as fuel. Separate small scale experiments confirmed that this catalyst is not well suited for fuel processors with low levels of nonmethane hydrocarbon slip. The concentration of hydrocarbons in the condensed water after the PrOx is below the detection limit of 0.1 mg/kg, as measured by GC.
4.6.
Afterburner
The afterburner design is based on 80% H2 utilisation in a PEMFC stack. In the prototype, lacking an integrated
Conclusions
The experiments with the biodiesel fuel processor showed the proof-of-principle of biodiesel reforming with high gross efficiency of 87% and low CO content (below 10 ppm), providing a reformate gas composition suitable for PEMFC. The design and control of the heat integrated reactors were verified. The significance of inline testing was demonstrated by the degradation aspect of the PrOx, that was not observed by synthetic reformate tests. System packaging and reactor design will require great attention in order to reach the targets for volume, weight and startup time. Independent start-up using only biodiesel and air must be developed. Catalyst durability under real operating conditions requires further research and development.
Acknowledgements Funding of the European Union is gratefully acknowledged (EU project BIOFEAT nr ENK-CT-2002-00612: Biodiesel fuel processor for a fuel cell auxiliary power unit for a vehicle). The support and advice of the partners are greatly acknowledged.
references
[1] Van Gerpen J. Biodiesel processing and production fuel. Process Technol 2005;86:1097–107. [2] EU Commission funded project BIOFEAT. Biodiesel fuel processor for a fuel cell auxiliary power unit for a vehicle, ENK-CT-2002–00612; 2002. [3] Specchia S, Tillemans FWA, Van den Oosterkamp PF, Saracco G. Conceptual design and selection of a biodiesel fuel processor for a vehicle fuel cell auxiliary power unit. J Power Sources 2005;145:683–90. [4] Sgroi M, Bollito G, Saracco G, Specchia S. BIOFEAT: biodiesel fuel processor for a vehicle fuel cell auxiliary power unit; study of the feed system. J Power Sources 2005;149:8–14. [5] Specchia S, Saracco G, Tillemans FWA, Kraaij GJ, Sgroi M, Bollito G. BIOFEAT: biodiesel fuel processor for an APU. EVS-22 2006:2040–9.
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/he
Biodiesel fuel processor for APU applications G.J. Kraaija,*, S. Specchiab, G. Bollitoc, L. Mutrid, D. Wailse a
Energy research Centre of The Netherlands, Westerduinweg 3, 1755 ZG Petten, The Netherlands Politecnico di Torino, Materials Science and Chemical Engineering Department, Corso Duca degli Abruzzi 24, 10129 Torino, Italy c Centro Ricerche FIAT, Strada Torino 50, 10043 Orbasssano, Italy d Scandiuzzi Advanced Technologies Department, Viale Dante 78, 38057 Pergine Valsugana, Italy e Johnson Matthey Technology Centre, Blounts Court, Sonning Common, RG4 9NH Reading, United Kingdom b
article info
abstract
Article history:
Tail pipe emission reduction, increased use of renewable fuels and efficient supply of
Received 9 April 2008
auxiliary power for road vehicles using fuel cells have been the main drivers of the Euro-
Accepted 23 July 2008
pean project BIOFEAT (biodiesel fuel processor for a fuel cell auxiliary power unit for
Available online 25 September 2008
a vehicle). Within the project a biodiesel fuelled heat integrated fuel processor for 10 kWe capacity has been designed and constructed. Demonstration tests showed a high quality
Keywords:
reformate with less than 10 ppm of CO and a gross efficiency of 87%.
Biodiesel
ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Fuel processor APU
1.
Introduction
Fuel cell-based auxiliary power unit (FC-APU) systems have attracted growing interest as an alternative technology for onboard electricity generation in vehicles and trucks. The demand for on-board electrical power is expected to grow further while there is increasing pressure to reduce CO2 and the other emissions such as NOx, soot and noise, associated with the use of current engine-generator systems. FC-APU systems offer a promising alternative due to their high potential efficiencies, low tailpipe emissions of NOx, hydrocarbons and CO and their silent operation. The net emission of CO2 can be reduced even further when biodiesel is applied as renewable fuel. In the past decade, biodiesel has been gaining popularity as an alternative energy source worldwide because of its many benefits: this environmently friendly fuel reduces tailpipe emissions (it is practically sulphur-free, <1 ppm), visible smoke and noxious odours. Biodiesel is the alternative fuel that produces basically no emissions during manufacture [1]. Within this context, the FP5 project BIOFEAT [2], has been carried out with the main purpose to demonstrate the concept
of a heat integrated biodiesel fuel processor (FP) delivering the hydrogen for a PEMFC-based APU system. The fuel processor size was chosen equivalent to a power output of 10 kWe as an estimate of future auxiliary power requirements for peripheral systems in road vehicles amongst which are heating, ventilation and air conditioning system, on-board computers, steering by wire, brake by wire and in-car entertainment. The specific objective of the BIOFEAT project was to design, build and demonstrate a laboratory test skid of an on-board biodiesel FP capable of feeding a FC to generate electricity for the auxiliary power needs for a family car or a truck. The project has been carried out by the partners Politecnico di Torino, ECN, CRF, Johnson Matthey, Scandiuzzi, Bekaert and Duisburg-Essen University.
2.
Design of the fuel processor
At the start of the project the final requirements of a commercial PEMFC based APU system for transport applications were established by the industrial partners. The goal
* Corresponding author. Tel.: þ31 224 564569. E-mail address: [email protected] (G.J. Kraaij). 0360-3199/$ – see front matter ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2008.07.108
4496
international journal of hydrogen energy 34 (2009) 4495–4499
of the project was to demonstrate the proof-of-principle of on the one hand the conversion of biodiesel to PEMFC quality reformate and on the other hand the integration aspects by means of the use of heat integrated reactors. For this purpose a specification of the laboratory type skid mounted fuel processor was made as a first step of the development trajectory. The major requirements for the commercial system as well as the BIOFEAT fuel processor are listed in Table 1. As a start of the project various conceptual system approaches have been evaluated resulting in the final choice of the system approach as depicted in the simplified conceptual process flow scheme of the APU system in Fig. 1. Main characteristics of the system are the use of autothermal reforming for primary biodiesel conversion, preferential oxidation as gas-cleanup technology, the use of a lowtemperature PEMFC and the level and approach for heat integration. The requirement of a closed water balance in the system could be fulfilled by operating the PEMFC stack at a pressure of at least 1.5 bar and an off-gas condensation temperature of maximum 50 C. Nevertheless, the cooling duty for condensation of 8 kW requires a large radiator. The net electrical system efficiency at full load is calculated at 30% (incl. BOP losses). For the BIOFEAT project, a fuel processor system excluding a PEMFC was developed. The simplified system design for the fuel processor is provided in Fig. 2. Details of the process design can be found in Refs. [3–5]. Because a PEMFC was not included in the tests, the PEMFC anode off-gas was simulated by feeding part of the reformate to the afterburner, corresponding to a calorific content of the otherwise hydrogen-depleted anode off-gas. Start-up of the
Table 1 – Specification for the biodiesel fuel processor prototype and commercial system. System targets Power (kWe) Durability (continuous) (h) Durability (thermal cycles) Efficiency (ac, net) Fuel processor efficiency Start up time (min) Weight Volume Start-up external electrical energy (kWh) Auxiliaries power (kWe) Working pressure Working temperature CO requirement for a PEM stack
Commercial system
BIOFEAT prototype
10 5000–10000
10 500
>5000
>50
>35%
(>35%) >75%
Fig. 1 – Simplified process scheme for the biodiesel auxiliary power unit.
system was carried out by using an external hydrogen supply. Water was also fed from an external source and not recovered as a condensate. Nitrogen instead of air was used during startup and emergency shut-down in the initial experiments for catalysts’ protection. The biodiesel fuel processor was designed to operate without external heating devices or heat compensation by linking heat sources and sinks internally by proper heat integration and insulation. Steam generation and air preheating is carried out in spiral-wound tubes positioned in the exothermic reactors of the fuel processor and afterburner (AB). This configuration allows maintaining various reactor sections at the desired temperature level. The S/C ratio can be adjusted by variation of the water flow through the afterburner heat exchanger. The autothermal reformer reactor (ATR) is integrated with a steam generator and a water quench in order to reduce the outlet temperature to the required high temperature shift reactor (HTS) inlet temperature, see Fig. 3. Moreover, the wall temperature of the ATR reactor vessel is lowered and low cost stainless steel can be used. For temperature control of the water-gas shift (WGS) and preferential oxidation (PrOx) sections full evaporation of water in the integrated heat exchangers is essential. Therefore these heat exchangers contain a heating section, a boiling section and a superheating section. The concept was successfully validated by using mock-up reactors prior to the integration. The water-fed heat exchanger in the afterburner is designed for
Fuel off-gas (stack simulation)
Flue gas 1 10–20 kg/kW 10–20 l/kW <0.1
<20 <400 kg <500 l <1
AB <2
<2
Stack pressure between 10 C and þ40 C <10 ppm (steady) and <100 ppm (transient)
Stack pressure
Air
ATR
N2 (start-up)
Biodiesel
HTS
H2 (start-up)
LTS
Prox1
Prox2
Water
Fig. 2 – Simplified process scheme of the biodiesel fuel processor.
international journal of hydrogen energy 34 (2009) 4495–4499
4497
Fig. 3 – Autothermal reformer reactor from concept to drawing and realisation.
partial evaporation of the water in order to obtain sufficient cooling capacity in the ATR heat exchanger. The fuel processor is operated as follows: During start-up hydrogen from an external supply and air are fed to the afterburner. As the afterburner ignites at room temperature it supplies the required heat for the air and steam generation that will be used to heat up the rest of the reactors. When the required temperatures in the different reactors are reached, the reformer is started by feeding biodiesel to the ATR reactor where it reacts with air and steam. All reactors are controlled to operate within the operating temperature window by adjusting the water flows. The required CO content is controlled by the air supply in the PrOx. For simulation of stack operation in a truly integrated system, anode off-gas at 80% utilisation is mimicked by feeding a part of the reformate
flow to the afterburner instead, providing the same calorific value and temperature level as determined by integrated system simulations.
3.
Manufacturing of the fuel processor
The fuel processor skid was manufactured by Scandiuzzi and is shown in Fig. 4. As the objective of the project was to demonstrate the feasibility of biodiesel reforming and the principle of heat integrated reactors, the emphasis for the construction is more on manufacturability and easy accessibility in the laboratory rather than a minimized packaging volume. The volume and weight targets were relieved, but the system is designed to run without external heating by means of proper insulation of
Fig. 4 – View of the biodiesel fuel processor mechanical assembly before insulating.
4498
international journal of hydrogen energy 34 (2009) 4495–4499
4. 4.1.
Testing of the fuel processor
10.0000
HTS
ATR out
LTS in
HTS out
1.0000 Prox1 in
LTS out
0.1000 Prox2 in
Prox1 out
0.0100
CO Test [%] CO AspenPlus [%]
0.0010
System demonstration tests
Prox2 out
The RME type biodiesel obtained from Oelmu¨hle Hamburg AG was used for the experiments. Chemical analysis revealed that the sulphur content was below 1 ppm and that the actual composition closely resembles that used in the design calculations (C19H36O2). The focus of the tests was to demonstrate the feasibility of the integrated biodiesel fuel processor in terms of heat management, H2 output, and gas quality. A gross fuel processor system efficiency of 87% was reached, the efficiency h being defined as: . 4Biodiesel LHVBiodiesel h ¼ 4H2 in reformate LHVH2 where 4 is the flow rate [kg/s] and LHV is the lower heating value of the fuel. The mimicked anodic offgas flow (20% of the reformate flow), which is used for preheating the air and steam, is not considered in the efficiency calculation. The hydrogen flow used in this calculation is based on the carbon mass balance using the gas analysis results (the sum of the dry gas components being 99.9 0.3%) and equals the efficiency calculated from the ASPENPlus simulation. In these simulations a total heat loss for the reactors of 700 W was assumed and the measured heat loss was 850 W. For every reactor the difference between the assumed and measured heat loss was within 50%. As an example, the measured and calculated dry CO concentration after each of the reactors is shown in Fig. 5. This figure shows that biodiesel can be converted to a reformate gas with a CO concentration lower than 10 ppm, which is suitable for a PEM fuel cell. The measured dry gas composition after each reactor is presented in Table 3.
4.2.
Biofeat 10kW; comparison ASPENPlus design and test results
CO [%]
the (long) connecting tubes and reactors themselves. The control system is designed to control the flows, except the biodiesel flow, by temperature measurements. For evaluation of the performance of the fuel processor all inlet flows are measured. The fuel processor control is PLC based with a SCADA user interface. The specifications of the precious metal based catalyst used in the reactors are shown in Table 2.
Fuel injection system
The turn-down ratio of the fuel processor is 3:1 and is limited by the spraying characteristics of the fuel nozzles. The use of
0.0001 0
100
200
300
400
500
600
700
800
Temperature [°C] Fig. 5 – Comparison of the dry CO composition from the design using AspenPlus and test results for the different reactors and their temperatures.
a simple nozzle limits the turn-down ratio for a single nozzle to 1.6:1. Therefore a double nozzle system has been applied using different nozzle sizes to provide an overall turn-down ratio of 3:1 [4]. A drawback of this solution is that at switchover from one nozzle to the other or to two nozzles, the fuel flow is temporarily reduced. This requires corresponding accurate control of the air flow to the ATR to prevent overheating of the ATR catalyst. The fuel is injected in hot steam (S/C ¼ 2.5) and subsequently air is injected into the gaseous fuel/steam mixture. In the evaporating zone where the fuel is injected coke deposition on the walls is observed. In the zone beyond the air injection no coke is observed. The absence of coke in the section may be due to the operation in the ‘‘cold flame’’ regime in this zone. The presence of cold flames is illustrated by the mixing temperature, which is much higher than can be explained by adiabatic mixing and evaporation.
4.3.
ATR reactor
The ATR catalyst for biodiesel reforming was developed by Johnson Matthey for this project and the operating conditions were established. At the 10 kWe operating conditions the catalyst converted 99% of the fuel to the components as calculated by thermodynamic equilibrium. Approximately 0.6% of the rest is found as methane that is present in higher concentrations in the reformate gas (0.25–0.3% dry) than
Table 2 – Catalyst specification for the biodiesel fuel processor. Reactor
ATR Afterburner HTS LTS PrOx 1 PrOx 2
GHSV Pressure Tin Tout (bar) ( C) ( C) design (h1) 30000 40000 40000 20000 50000 50000
2.1 1.4 2 1.9 1.8 1.7
450 50 360 265 150 120
730 642 406 272 195 126
Type
Catalyst supplier
Monolith Monolith Monolith Monolith Wire mesh Wire mesh
JM JM JM JM ECN ECN
Table 3 – Measured dry gas composition after each reactor. Biofeat
H2 (%)
CH4 (%)
CO2(%)
CO (%)
N2+Ar (%)
Total (%)
ATR HTS LTS PrOx1 PrOx2
41.65 44.92 46.06 44.91 44.30
0.31 0.35 0.34 0.35 0.39
14.80 19.75 21.61 21.56 21.46
8.62 2.55 0.34 0.059 0.0004
34.34 31.73 32.11 32.61 33.46
99.73 99.30 100.46 99.51 99.64
international journal of hydrogen energy 34 (2009) 4495–4499
4499
stack, the air and fuel feed to the afterburner are mimicked by controlling the energy content and the temperature after the reaction to be identical to the design with the fuel cell. During operation the mixture frequently ignited before the catalyst was reached, leading to rapid changes of the measured temperatures within the reactor. Therefore, flow control of air was used instead of temperature control.
5.
Fig. 6 – Measured CxHy concentration in the reformate gas at 10 kWe power. At the points denoted with ‘‘A’’, the gas analysis was measured after the ATR.
calculated from thermodynamic equilibrium (0.11%) and 0.4% is attributed to non-methane hydrocarbons (NMHC), as shown in Fig. 6. The NMHCs are in the form of C2–C5 alkenes. After the ATR these are fully hydrogenated in the HTS.
4.4.
Shift reactors
A high and a low temperature shift reactor are applied for the conversion of CO to H2 by the water-gas shift reaction. Two shift reactors were chosen since this will provide a higher H2 production and a higher reduction of the CO load to the PrOx reactor compared to a single shift reactor.
4.5.
PrOx reactor
For the PrOx section a double bed reactor with integrated interstage cooling is applied. The PtRu based PrOx catalyst is coated on a wire mesh and has low precious metal content. With this catalyst a CO concentration target of less than 10 ppm was successfully achieved. The lambda value (lambda is 2O2/CO) at 10 kWe operation was 2.6–3 for PrOx 1 and 5–6 for PrOx 2. This catalyst has demonstrated its durability in reforming experiments using natural gas as a fuel for more than 1000 h. Interestingly, this catalyst exhibited significant degradation within 50 h when operated with biodiesel as fuel. Separate small scale experiments confirmed that this catalyst is not well suited for fuel processors with low levels of nonmethane hydrocarbon slip. The concentration of hydrocarbons in the condensed water after the PrOx is below the detection limit of 0.1 mg/kg, as measured by GC.
4.6.
Afterburner
The afterburner design is based on 80% H2 utilisation in a PEMFC stack. In the prototype, lacking an integrated
Conclusions
The experiments with the biodiesel fuel processor showed the proof-of-principle of biodiesel reforming with high gross efficiency of 87% and low CO content (below 10 ppm), providing a reformate gas composition suitable for PEMFC. The design and control of the heat integrated reactors were verified. The significance of inline testing was demonstrated by the degradation aspect of the PrOx, that was not observed by synthetic reformate tests. System packaging and reactor design will require great attention in order to reach the targets for volume, weight and startup time. Independent start-up using only biodiesel and air must be developed. Catalyst durability under real operating conditions requires further research and development.
Acknowledgements Funding of the European Union is gratefully acknowledged (EU project BIOFEAT nr ENK-CT-2002-00612: Biodiesel fuel processor for a fuel cell auxiliary power unit for a vehicle). The support and advice of the partners are greatly acknowledged.
references
[1] Van Gerpen J. Biodiesel processing and production fuel. Process Technol 2005;86:1097–107. [2] EU Commission funded project BIOFEAT. Biodiesel fuel processor for a fuel cell auxiliary power unit for a vehicle, ENK-CT-2002–00612; 2002. [3] Specchia S, Tillemans FWA, Van den Oosterkamp PF, Saracco G. Conceptual design and selection of a biodiesel fuel processor for a vehicle fuel cell auxiliary power unit. J Power Sources 2005;145:683–90. [4] Sgroi M, Bollito G, Saracco G, Specchia S. BIOFEAT: biodiesel fuel processor for a vehicle fuel cell auxiliary power unit; study of the feed system. J Power Sources 2005;149:8–14. [5] Specchia S, Saracco G, Tillemans FWA, Kraaij GJ, Sgroi M, Bollito G. BIOFEAT: biodiesel fuel processor for an APU. EVS-22 2006:2040–9.