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Metal hydride hydrogen storage and supplysystems for electric forklift with low-temperatureproton exchangemembrane fuel cell powermodule

Mykhaylo V. Lototskyy a,*, Ivan Tolj a,b, Moegamat Wafeeq Davids a,Yevgeniy V. Klochko a, Adrian Parsons a, Dana Swanepoel c,Righardt Ehlers c, Gerhard Louw c, Burt van der Westhuizen c,Fahmida Smith d, Bruno G. Pollet a, Cordellia Sita a, Vladimir Linkov a

a HySA Systems Competence Centre, South African Institute for Advanced Materials Chemistry (SAIAMC),

University of the Western Cape, Bellville, South Africab University of Split, Faculty of Mechanical Engineering and Naval Architecture, Department of Thermodynamics and

Heat Engines, Split, Croatiac TF DESIGN (Pty) Ltd., Stellenbosch, South Africad Impala Platinum Ltd, Springs, South Africa

a r t i c l e i n f o

Article history:

Received 23 October 2015

Received in revised form

10 January 2016

Accepted 29 January 2016

Available online 28 February 2016

Keywords:

Hybrid hydrogen storage

Metal hydride

Compressed gas

Refuelling

Fuel cell forklift

Fuel cell power module

* Corresponding author. HySA Systems CompWestern Cape, Robert Sobukwe Road, Privat

E-mail address: mlototskyy@uwc.ac.za (Mhttp://dx.doi.org/10.1016/j.ijhydene.2016.01.10360-3199/© 2016 Hydrogen Energy Publicati

a b s t r a c t

A novel hydrogen storage system for a RX60-30L 3-tonne electric forklift (STILL), equipped

with a GenDrive 1600-80A fuel cell power module (Plug Power) has been developed. The

system combines a compressed H2 composite cylinder (CGH2) and a liquid-heated-cooled

metal hydride (MH) extension tank which is thermally integrated with a power module.

The MH extension tank comprises a MH bed formed according to an advanced solution to

provide easy activation of the MH material and fast H2 charge/discharge. The system has

the same hydrogen storage capacity (~19 Nm3 H2 or 1.7 kg) as the separate CGH2 tank

charged at P ¼ 350 bar, but at a lower H2 charge pressure (�185 bar). A 15 min cycle

refuelling provides the forklift with full-load operation (according to VDI-60 protocol)

during >3 h, or 2 to 4 working shifts in a real industrial environment. The work also pre-

sents a hydrogen refuelling station (dispensing pressure up to 185 bar) with integrated MH

compressor which has been developed for forklift refuelling.

© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Introduction

A promising option for small/medium sized distributed

renewable energy systems is in adopting electrochemical

etence Centre, South Afre Bag X17, Bellville 7535,.V. Lototskyy).48ons LLC. Published by Els

energy storage in hydrogen driven fuel cells. Hydrogen and

fuel cell technologies offermaximumenergy storage densities

varying from 0.33 to 0.51 kWh/L, depending on the hydrogen

storage method, while the highest value achieved for

rechargeable Li-ion batteries does not exceed 0.14 kWh/L [1].

ican Institute for Advanced Materials Chemistry, University of theSouth Africa. Tel.: þ27 21 9599314; fax: þ27 21 9599312.

evier Ltd. All rights reserved.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 1 3 8 3 1e1 3 8 4 213832

Recently, fuel cells and batteries have been considered as

counterparts of advanced hybrid energy storage systems,

rather than competing technologies [2].

Currently, the use of Proton Exchange Membrane fuel cells

(PEM FC) in the transportation sector is of great interest

worldwide for the R&D sector, industry, business and public

structures. PEM FC have a number of attractive properties,

including low environment impact (only by-products are pure

water and heat), high efficiency, low operating temperature,

high power density, fast start-up time and response to load

changes, simplicity, long life etc. As a result of these prom-

ising attributes, PEM FC have been successfully demonstrated

in various applications, including: automobiles, scooters and

bicycles, golf carts, utility vehicles, distributed power gener-

ation, backup power, portable power, airplanes, boats and

underwater vehicles [3].

A brief overview of PEM FC powered electric vehicles, with

peak power varying from <0.4 to 40 kW, was published by the

authors in 2013 [4]. Due to non-uniform power consumption

during operation, when the peak power can be significantly

higher than the average one, the vehicular power systems

usually have a “hybrid” layout. In doing so, the FC stack rated

power is close to the average system power, and the peak

power consumption by vehicle motors, as well as the quick

start-up of the system, are provided by batteries and/or super-

capacitors. Apart from the rated power and power train

layout, the main distinguishing features of the vehicular

power systems include: (i) vehicle bus voltage, (ii) type of the

fuel cell stack (either liquid or air-cooled), and (iii) hydrogen

storage method (compressed gas or metal hydride).

In the development of PEM FC vehicles special attention is

paid to materials handling units/forklifts which have been

identified as a promising early market for the fuel cell in-

dustry. In comparison to battery powered forklifts, fuel cell

powered forklifts are characterised by lower total logistics

costs as they require shorter refuelling time and less

maintenance.

A detailed market analysis of the implementation of fuel

cells for forklift applications was presented by Elgowainy et al.

[5] in 2009 and, more recently, Larriba et al. [6] and Ramsden

[7] in 2013. During the past decade the fuel cell forklift market

has been growing, especially in the USA and Canada, with

almost 3000 fuel cell forklifts deployed by 2013 [6]. Between

2003 and 2015, there were more than 6200 fuel cell powered

forklift installations in the USA, including almost 1800 in 2014,

of whichmost (>93%) involved PEM FC power systems [8]. Plug

Power, Inc. controls more than 85% of the materials handling

fuel cell market while other US companies, including: Oorja

Protonics, Infintium Fuel Cells, and Nuvera Fuel Cells share

the remaining 15% of the market [9]. It has been shown that

evenwith the high costs associatedwith fuel cell systems and,

particularly, the accompanying hydrogen refuelling infra-

structure, a deployment of about 60 fuel cell forklifts for 2e3

shifts per day, 6e7 days per week will result in a lower total

cost of ownership than comparable battery forklifts [7].

Information relating to the performance of PEM FC power

modules for electric forklifts is available in the documentation

issued by the OEM's: Plug Power, Inc. (USA) [10,11], Hydro-

genics (Canada) [12], H2Logic A/S (Denmark) [13], and Infin-

tium Fuel Cell Systems, Inc. (USA) [14].

An example of development and testing of a hybrid

drivetrain, comprising a 16 kW PEM FC system, ultracapacitor

modules and a lead-acid battery was published by Ker€anen

et al., in 2011 [15]. Other recently published articles on PEM FC

forklifts were focused on thermal and water management of

the stack Balance of Plant (BoP) [16], performance simulation

and analysis of a hybrid forklift power system (PEM FC þ lead

acid battery) [17], thermal and flow modelling of a PEM FC

system for forklift applications over fast load changes [18] and

numerical analysis of anodic recirculation in a PEM FC system

for forklift applications [19].

Typical hydrogen-fuelled FC-powered forklifts are charac-

terised by a fuel cell output power of about 10 kW, however,

short peak power consumption can be as high as 50 kW for

~10 s. Such systems require a fuel capacity of about 20 Nm3

(1.79 kg) H2 to allow for uninterrupted operation at a rated load

for several hours. Most of the FC-powered forklifts demon-

strated so far have utilised compressed hydrogen stored in gas

cylinders (CGH2) at pressures up to 350 bar, but in some cases

metal hydride (MH) tanks were used [15,20,21].

MH technologies for hydrogen storage are characterised

by compactness (due to the very high volumetric density of

atomic hydrogen accommodated in the crystal structure of

the MH matrix; 100 gH/L), intrinsic safety (originated from

modest hydrogen equilibrium pressures at ambient tem-

peratures in combination with the endothermic nature of

hydrogen release from the MH), simplicity and flexibility

[22e24]. Changing the component composition of hydride

forming alloys allows for extremely wide variations in the

thermodynamics of formation/decomposition of the corre-

sponding MH: from �150 to �45 J mol�1 H2 K�1 for entropy

and from �166 to �6.6 kJ mol�1 H2 for enthalpy [25]. Sub-

sequently, MH hydrogen storage systems are characterised

by tuneable pressure e temperature operating perfor-

mances which can be aligned to the operating conditions of

a specific application by appropriate selection of the type of

MH and adjustment of the composition of the parent hy-

dride forming material. In doing so, the low-grade heat

(T � 60e80 �C) released during low temperature (LT) PEM FC

stack operation can be supplied to the MH, thus promoting

the endothermic process of its decomposition and, in turn,

H2 supply to the stack. This solution has been successfully

verified in numerous portable, mobile and stationary LT

PEM FC applications [26e29].

Hydrogen storage in MH is, therefore, a promising option

which can efficiently solve on-board H storage problems. In

spite of this, the low H storage weight density in commonly

used “low-temperature” MH materials (~2 wt.% H) is consid-

ered as the main obstacle for their use in vehicular applica-

tions [23].We note that such limitations relate to conventional

vehicles like buses and passenger cars; and for utility vehicles,

including light-duty industrial vans [26], underground loco-

motives and dozers [30], and materials handling units

[15,20,21,31,32], this is not the case. Moreover, the utility ve-

hicles should be heavy enough to provide a low centre of

gravity.

An on-going development of a FC-powered forklift withMH

hydrogen storage (USA [31,32]) can be mentioned as an

example of such application. The system is expected to be

superior to both battery-driven forklifts (shorter charge time,

1 Reference [36] is a patent application disclosing the technicaldetails of this engineering solution while the detailed systemstudy, including its integration in a light electric vehicle (golf cart)with PEM FC range extender, is presented in Ref. [37].

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 1 3 8 3 1e1 3 8 4 2 13833

longer lifespan) and to the FC-powered ones with CGH2 stor-

age (simpler refuelling infrastructure, higher H2 storage ca-

pacity, less safety issues). The liquid heated/cooled MH

hydrogen storage tank uses a compositeMHmaterial based on

an AB5-type MmNi4.5Al0.5 alloy (Hy-Stor 208) which is charac-

terised by a H absorption capacity up to 1.2 wt.% and H2

equilibrium pressure of ~20 bar at T ¼ 75 �C [31]. The tank has

dimensions 470 mm (L) � 700 mm (W) � 370 mm (H) and is

designed as a staggered array of 40 tubular

(∅50.8 mm � 640 mm) MH containers connected to a common

gas manifold and heated/cooled by circulating liquid. The

heating/cooling system is directly integrated in the LT PEM FC

coolant loop. The hydrogen storage capacity of one of these

containers is estimated to be about 50 g H2, which yields

approximately 2 kg (22.4 Nm3) H2 in total. Though test results

of the H2 charge/discharge performance of the MH tank have

not been presented yet, the H2 refuelling time at the pressure

up to 70 bar was estimated (by modelling) as 30e60 min. The

refuelling dynamics, however, were found to be very sensitive

to the rate of heat rejection from the coolant loop [32],

resulting in significantly longer refuelling time at low (<50 bar)

H2 pressures and high (>1 g/s) H2 flow rates.

The slow charge and discharge of MH hydrogen storage

tanks, as a result of poor heat transfer, is a serious disad-

vantage of these systems and requires special engineering

solutions to be overcome [33]. The H2 charge/discharge rates

dramatically decrease with the size of individual MH con-

tainers; this effect can bemitigated by improving the effective

thermal conductivity of the MH bed, as well as by the inten-

sification of heat exchange between the MH and heating/

cooling fluid [29]. Nevertheless, typical H2 charge times for

large (~1 kg H2) MH containers equipped with heat ex-

changers, are usually not shorter than 90 min [34].

In addition to the technical and economic challenges

hindering the commercialisation of hydrogen fuelled vehi-

cles and, particularly FC forklifts, the lack of hydrogen refu-

elling infrastructure is also a significant problem [7]. Despite

a certain number of hydrogen refuelling stations operating

worldwide, they are not being introduced broadly enough.

This is mainly as a result of their high costs; ranging between

$500,000 and $5,000,000 per installation [35]. The most

expensive H2 refuelling components originate from: (i) on-

site hydrogen production and (ii) hydrogen compression.

The latter problem can be effectively addressed by the

application of MH for hydrogen compression driven by low-

grade heat [24].

Summarising the above-mentioned, we can conclude that

the development of fuel cell powered forklifts, with hydrogen

storage based on metal hydride technologies, can be facili-

tated once the following challenges are addressed:

� Improvement of charge e discharge dynamic perfor-

mances of on-board MH tanks;

� Safe, reliable and cost-effective hydrogen refuelling

solutions.

This paper presents the results of work aimed at over-

coming these issues. Specifically, it involves the development

of MH-based hydrogen storage and supply/refuelling systems

for a commercial electric forklift equipped with a LT PEM FC

power module. The work was undertaken between 2012 and

2015 by HySA Systems Competence Centre in South Africa,

with the involvement of two local industrial partners: Impala

Platinum Ltd (the customer) and TF Design (Pty) Ltd (manu-

facturer of the hardware).

Approach

A novel system concept for fuel cell powered utility vehicles

with on-board MH hydrogen storage has been proposed by

HySA Systems (Fig. 1). The system consists of:

� STILL RX60-30L electric forklift with a 3 tonne lifting ca-

pacity and 80 VDC bus voltage.

� On-board fuel cell power module (A) replacing the forklift

battery. The module is equipped with:

- compressed gas hydrogen storage tank (CGH2), and,

- MH hydrogen storage tank (B).

� Stationary hydrogen refuelling system (C) consisting of a

low-pressure hydrogen supply and a MH hydrogen

compressor.

The main feature of the on-board hydrogen storage is a

combination of the CGH2 and MH in a “distributed hybrid”

system [36,37]1 consisting of individual MH and CGH2 tanks

with a common gas manifold, and a thermal management

system in which the MH tank is integrated within the cooling

system of the LT PEM FC BoP. This solution allows for; (i) an

increase in hydrogen storage capacity of thewhole gas storage

system and the reduction of H2 charge pressure; (ii) shorter

charging times in the refuelling mode and smoother peaks of

H2 consumption during its supply to the fuel cell stack; (iii) the

use of standard parts with simple layout and lower costs; and

(iv) adding flexibility in the layout and placement of the

components of the hydrogen storage and supply system.

At the first stage of realisation of this concept we intro-

duced a MH tank as an extension of the CGH2 storage (com-

posite cylinder with a 74 L inner volume and operating

pressure of 350 bar) in the commercial fuel cell powermodule,

GenDrive 1000 160X-80CEA, purchased from Plug Power Inc.

The objective of this was to achieve approximately the same

hydrogen storage capacity (1.7 kg, or 19 Nm3 H2) at the lower

refuelling pressure. The required amount of stored hydrogen

should be provided in a reasonable refuelling time, no longer

than 20e30min, and the H2 supply to the fuel cell stack should

be sufficient to provide its uninterrupted operation at the

maximum rated power (~10 kW).

The MH tank uses a low-stability AB2-type MH material

with a H2 equilibrium pressure above 10 bar at room tem-

perature, which provides sufficient pressure driving force for

the H2 supply to the FC stack during operation. In doing so, the

endothermic effect of H2 desorption from the MH is

compensated by its heating to a moderate temperature

(~30e50 �C) using both environmental heat, as well as the heat

Fig. 1 e General system concept: FC power module (A) with on board H2 storage (B) and refuelling (C) systems.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 1 3 8 3 1e1 3 8 4 213834

generated by the stack. In the charge mode, at H2 pressures

between 100 and 200 bar the heat released due to the

exothermic H2 absorption in the MH is dissipated to the

environment. The presence of the CGH2 buffer allows for the

thermal “recovery” of the MH in the discharge mode in the

periods when H2 consumption by the stack drops. In addition,

the CGH2 buffer also allows for the charge time to be short-

ened as a result of the accumulation of moderately high-

pressure H2 in the gas phase, which is further absorbed in

the MH as it is cooled down [37].

Hydrogen refuelling, therefore, requires H2 dispensing

pressures lower than those typically used for the refuelling of

CGH2 storage systems (350 bar). For industrial customers, who

already possess low-pressure pipeline hydrogen, steam and

cooling water, thermally-driven hydrogen compression using

metal hydrides [24] is a promising option, allowing for sig-

nificant reductions in refuelling costs. The high selectivity of

hydrogen absorption/desorption in MH provides a high purity

of the delivered H2, which allows for simultaneous hydrogen

purification within the MH compressor. Since the refuelling

has to be done periodically, the necessary amount of

hydrogen at the pressure higher than the dispensing one can

be stored in a high-pressure buffer, filled from the MH

compressor when necessary.

Metal hydride tank

Metal hydride material

The systems use a MH material based on an AB2-type

hydrogen storage alloy, where A ¼ (Ti,Zr); B ¼ (Fe,Cr,Mn,Ni)

and the Ti:Zr atomic ratio is approximately 0.65:0.35. Ac-

cording to XRD studies (see Fig. 2 and Table 1 for details), the

starting alloy consists of a single intermetallic phase (C14

Laves, MgZn2-type); the values for the hexagonal lattice pe-

riods (a, c) and unit cell volume (V) are presented in Table 1.

Hydrogenation does not change the crystal structure but re-

sults in a lattice expansion, with a relative volume increase

(DV/V0) of approximately 16%. The hydride, AB2Hx, is unstable

at ambient conditions so the XRD pattern of the hydrogenated

material (Fig. 1) also contains the lines of the solid solution of

hydrogen in the parent intermetallic, AB2H~0, as a product of

the hydride decomposition during the XRD measurements.

The XRD data allowed us to calculate the density (r) of the

material in the hydrogenated state. This parameter is very

important to provide a safe filling density of the MH in the

containment, i.e., lower than 61% of the real density of the

hydrogenated material [38].

Fig. 3 shows hydrogen sorption isotherms for the MH ma-

terial. The experimental data taken for H2 absorption (filled

symbols) and desorption (empty symbols) in the range be-

tween T ¼ �25 �C to þ75 �C and P ¼ 0.1 bare200 bar were

further processed by the model of phase equilibria in metal e

hydrogen systems [39]; the calculated isotherms at T ¼ �25 to

þ125 �C are presented as lines. Due to the low hysteresis

observed, the absorption and desorption data were processed

together.

It can be seen from Fig. 3 that the selected MH material

provides high enough H2 pressures (>10 bar) at temperatures

above 0 �C, and at T > 125 �C most of hydrogen is desorbed at

P > 200 bar. The results indicate that the MH is suitable for

both hydrogen storage/supply and hydrogen compression

applications, therefore, both the MH hydrogen storage

Fig. 3 e Experimental (points) and calculated (lines)

hydrogen sorption isotherms for the AB2-type alloy. Curve

labels show the temperatures [�C].Fig. 2 e The refined XRD pattern (Cu-Ka) of the

hydrogenated AB2-type alloy. Before the XRD

measurements the hydride was stabilised by exposing to

air at liquid nitrogen temperature. The pattern contains

lines of the hydride, AB2Hx, as well as of the solid solution

of hydrogen in the parent intermetallide, AB2H~0, formed

during the hydride decomposition.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 1 3 8 3 1e1 3 8 4 2 13835

extension tank and the MH compressor for the refuelling

system for the LT PEM FC forklift use the same AB2-type MH

material.

MH container

Preliminarymodelling of the heat transfer performance in the

MH reactors showed that the optimal layout of a medium-

sized (∅60 mm � 500 mm) cylindrical MH bed is a combina-

tion of external heating/cooling with internal heat conductive

fins. For copper fins (thickness 0.5 mm, pitch 5 mm) and

intensive heat transfer between a heating/cooling fluid

outside the reactor and a metal hydride bed in the reactor

(overall heat transfer coefficient up to 800 W m�2 K�1), the

charge time at a room temperature of the fluid can be as short

as 10 min [40]. This layout was used in the design of the MH

container for the hydrogen storage extension tank (Fig. 4).

The stainless steel container (∅51.3 mm � 800 mm; empty

weight 5.7 kg) was filled with 3.2 kg of MH material (filling

density 3.47 g/cm3, or ~60% of the material density in the

hydrogenated state). The formation of the MH bed was

Table 1 e Summary of the XRD data.

Parameter Parent alloy Hydrogenated alloy

AB2 AB2H~0 AB2Hx

a [�A] 4.9296(3) 4.9340(2) 5.1871(8)

c [�A] 8.0723(9) 8.0858(4) 8.474(3)

V [�A3] 169.88(2) 170.475(9) 197.46(5)

DV/V0 [%] e 0.35 16.23

r [g/cm3] 6.884 6.678 5.765

achieved according to an in-house advanced solution [41],

which provides easy activation of the MHmaterial and fast H2

charge/discharge due to the improved heat exchange between

the MH material and the circulating liquid. Specifically, the

solution involves the minor addition of an easily hydroge-

nated AB5-type MH material, along with expanded natural

graphite (ENG) to the main AB2-type alloy. The latter also

allowed us to achieve a MH filling density close to the

maximum safe value (see above). The container comprises a

number of perforated copper fins, 0.5mm thick, firmly pressed

into the cylindrical part of the container with a pitch of 5 mm.

The gas pipeline in the container is ended by a plugged

stainless steel porous filter (not shown; 6 mm in the diameter,

50 mm in the length, 1 m pore size). The container is also

equipped with a longitudinal gas bypass element, facilitating

H2 transfer along the MH bed.

Fig. 5 shows details and results from the testing of a pro-

totype MH container, made according to Fig. 4, to evaluate its

H2 charge/discharge dynamic performance. The container

was submersed in a water bath where a controlled tempera-

ture of 25e50 �Cwasmaintained. The test rig (Fig. 5A) was also

equipped with a pressure sensor, which enabled monitoring

of the hydrogen pressure in the line, P(line), as well as mass

flow controller for the measurement and limitation of the H2

flow rate (FR). A specially designed gas distribution system

allowed for switching the hydrogen flow to/from the

container, thus providing a unidirectional hydrogen flow

through the mass flow controller.

The prototype MH container was equipped with six ports

for placing K-type thermocouples into for themeasurement of

temperature distribution in the MH bed during absorption/

desorption. The location of thermocouple joints is shown in

Fig. 5B. Four thermocouples (temperatures T1 e T4) were

located in the middle of the container, while the other two

were shifted from themiddle by 158mm towards theH2 input/

output pipeline (T5) and in the opposite direction (T6). The

latter port (TC6/T6) was also equipped with a pressure sensor

Fig. 4 e Assembly drawings of the MH container for the hydrogen storage extension tank (note, all dimensions in mm).

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 1 3 8 3 1e1 3 8 4 213836

allowing for the monitoring of H2 pressure in the container,

P(container) at approximately 560 mm from the H2 entrance/

exit pipeline.

In addition to the temperatures within the MH bed (T1 e

T6), the wall temperature of the container (Tw) was also

measured.

As shown in Fig. 5C, the hydrogen absorption in the pro-

totype container when the temperature of the circulating

water is T0 ¼ 30 �C, H2 line pressure is P0 ¼ 85 bar and

maximum limit of H2 flow rate2 is 40 NL/min, takes no longer

than 15min. In doing so, about 450 NL (40.2 g) H2, or 88% of the

separately determined maximum hydrogen storage capacity

of the container (510 NL, or 45.5 g), is absorbed. The absorption

is accompanied by heating of the MH bed, with the tempera-

ture differences, DT, between the corresponding point and the

circulating water in the range from 12.5 to 17.5 �C. A general

finding was that DT decreased with an increase of radial dis-

tance from the container axis and, to a lesser extent, the

longitudinal distance from the H2 input side. The temperature

difference between the container wall and circulating water

did not exceed 4 �C. Interestingly, it was found that at the

beginning of the absorption process, higher temperatures of

the MH bed (DT up to 20 �C) were observed. This may be a

result of H2 absorption in the small admixture of AB5 alloy,

characterised by a higher hydrogenation heat effect than the

AB2 one (~30 kJ/mol H2 vs. ~20 kJ/mol H2).

During H2 absorption, the measured pressures in the MH

bed, P(container), were found to be lower than the line pres-

sure, P(line), gradually approaching the later value as H2 ab-

sorption at the constant flow rate (40 NL/min) comes closer to

the completion.

Fig. 5D shows an example of the test results in H2 desorp-

tion mode. It was found that a stable H2 supply from the MH

container, whose temperature is maintained at the same level

2 The limitation of maximum H2 flow rate was introduced forthe increase of accuracy of the modelling of heat-and-masstransfer in the MH container (on-going), as well as to avoidexceeding of the upper measurement limit (50 NL/min) of theused mass flow controller.

(T0 ¼ 30 �C), can be provided at a flow rate up to 10 NL/min. At

the rated flow rate (about 7.5 NL/min per container) approxi-

mately 435 NL (38.8 g) of H2 (85% of the maximum H2 storage

capacity) can be delivered. The absolute values of DT during

the desorptionmode are lower than for absorption and do not

exceed 3e7 �C. A similar effect of higher jDTj, possibly due to

the addition of the AB5-type hydride, was observed at the end

of desorption.

Taking into account the limitations onminimumhydrogen

pressure on the high-pressure side of the hydrogen system in

the GenDrive power module, P(min) ¼ 13.5 bar, the amount of

hydrogen available for the delivery from the MH tank will be

lower, corresponding to 360 NL (32.1 g) H2 or 70.5% of the

maximum hydrogen storage capacity. This reduction can,

however, be mitigated by the higher temperatures of the

heating fluid additionally heated from the fuel cell module, as

well as by the presence of CGH2 buffer in the “distributed

hybrid” hydrogen storage system.

Tank assembly

The metal hydride extension tank (Fig. 6) was made as an

assembly of twenty MH containers (1) connected in parallel to

gas manifolds (2) and, further, to a shut-off gas valve (3). The

assembly is held by a cradle (4) submersed in an external

water tank (5) providing thermal control of the MH containers

during their charge and discharge.

The tank has dimensions

950 mm (L) � 120 mm (W) � 700 mm (H), weights approxi-

mately 200 kg and is fitted within the forklift in the space

remaining vacant after the installation of the GenDrive power

module (labelled 1 in Fig. 7). Note that the total weight of the

power module (1) and the extension tank (2) is about 1800 kg

which provides sufficient counter-balance for safe forklift

operation when lifting loads rated up to 3 tonnes.

The tank assembly (shown in Fig. 7) also includes a gas

connector (2.1), in-line tee-type gas filter with pore size 0.5 m

(2.2) and a valve connected to the high-pressure hydrogen line

of the power module (2.3). The thermal management system

Fig. 5 e Details (A, B) and results (C, D) of the tests of the prototype MH container for the hydrogen storage extension tank. A

e experimental test rig; B e location of the thermocouple joints in the container; C e H2 absorption at P0 ¼ 85 bar, T0 ¼ 30 �Cand maximum limit of H2 flow rate of 40 NL/min; D e H2 desorption at T0 ¼ 30 �C and maximum limit of H2 flow rate of

7.5 NL/min.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 1 3 8 3 1e1 3 8 4 2 13837

of the tank also includes a diaphragm circulation pump (2.5;

18.9 kg/min at the head of 2.4 bar), and radiator (2.6) equipped

with three axial fans (5500 rpm). The fans and circulation

pump are powered (24 VDC, 210 W max) from the forklift side

of power connector (1.1), via DC/DC converter and controller

(not shown) and can be switched ON and OFF by the remote

block (2.7).

The integration of the MH extension tank requires only

minor changes to the high-pressure hydrogen system of the

GenDrive power module, as shown in Fig. 8. The piping com-

ponents of the MH tank are assembled using ¼00 OD stainless

steel tubing and include shut-off valves located inside (V1, 3 in

Fig. 6) and outside (V2, 2.3 in Fig. 7) of thewater tank, inline gas

filter (F1, 2.2 in Fig. 7), and tee union (T1) where the main high

pressure gas piping (3/800 OD stainless steel tubing) inside the

power module is connected. The latter includes a hydrogen

receptacle, check valve (CV1), and adapters (A1 & A2) installed

in the gas manifold of the gas cylinder. The check valve (CV1)

was moved from its original position in the gas cylinder (in

place of adapter A1) to provide bidirectional gas flow between

the cylinder and MH tank to improve the performance of the

“distributed hybrid” hydrogen storage system [36,37].

Thermal management of the MH tank is provided by the

circulation of a liquid (50:50 water e glycol mixture) using a

circulation pump and radiator (labelled 2.5 and 2.6, respec-

tively in Fig. 7). During charging, the forklift door is opened

and the fans installed in the radiator (2.6) provide cooling (by

the flow of ambient air) of the circulating liquid which is

Fig. 6 e Hydrogen storage containment of the metal hydride extension tank assembly. 1 emetal hydride containers, 2 e gas

manifolds, 3 e shut-off valve, 4 e cradle, 5 e water tank.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 1 3 8 3 1e1 3 8 4 213838

heated-up due to exothermic hydrogen absorption in the MH

containers.

During operation of the forklift the door is closed, and the

fans installed in the radiator (2.6) capture hot air (T~60 �C)from the cooling system of the unit (1) thus providing the

heating of the MH containers which are cooled down due to

endothermic hydrogen desorption.

The operation of the thermal management system is pro-

vided by the controller powered from the 80 VDC input power

Fig. 7 e An overview of the on-board system. 1 e GenDrive 1000

forklift, 1.2 e gas cylinder manual shutoff valve, 1.3 e remote d

dewatering receptacle, 1.6 e communication connector; 2 e me

filter, 2.3 e manual gas shutoff valve, 2.4 e water tank, 2.5 e ci

control block.

circuit of the forklift (output of the FC module), via remote

display and control block (2.7).

Refuelling station

Figs. 9 and 10 show the layout and general view of the

hydrogen refuelling station. The station includes the

following components:

160X-80CEA power module, 1.1 e power connection to the

isplay and control block, 1.4 e refuelling receptacle, 1.5 e

tal hydride extension tank, 2.1 e gas connector, 2.2 e gas

rculation pump, 2.6 e radiator, 2.7 e remote display and

Fig. 8 e Gas piping diagram of the MH extension tank integrated with GenDrive power module. V1, V2 e gas shut-off valves,

F1 e gas filter, CV1 e check valve, T1 e union tee, A1,A2 e adapters for the connections to gas cylinder manifold.

Fig. 9 e General layout of the hydrogen refuelling station.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 1 3 8 3 1e1 3 8 4 2 13839

Fig. 10 e General view of the refuelling station. 1 e integrated H2 dispenser andMH compressor unit, 2 e dispenser section, 3

e buffer tank, 4 e control block, 5 e refuelling console, 6 e ejector, 7 e venting pipeline, 8 e service pipelines.

i n t e rn a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 1 3 8 3 1e1 3 8 4 213840

� Hydrogen Dispenser, integrated with a thermally driven

metal hydride hydrogen compressor (MH Compressor),

items 1 and 2 in Fig. 10;

� Buffer Storage/Cylinder Pack, item 3 in Fig. 10;

� Control Block, item 4 in Fig. 10;

� A console (item 5 in Fig. 10) holding hydrogen refuelling

nozzle (H2 Nozzle), connector for Water Removal, and

earth clamp;

� Ejector for water removal (item 6 in Fig. 10);

� Hydrogen Venting pipeline, item 7 in Fig. 10.

Although the refuelling station is an experimental proto-

type, it complies with South African safety regulations for

operation in a fire and explosion hazardous environment. As

specified in Fig. 9, the main equipment of the refuelling sys-

tem forms a hazardous area (Zone 2; Zone 1 for the end of the

venting line) while the control panel, the console with refu-

elling nozzle, and the water removal connector, as well as the

forklift itself, are located outside the hazardous zone.

The refuelling station utilises the following services sup-

plied by the customer, Impala Platinum Refineries (Fig. 9; item

8 in Fig. 10):

� Low pressure hydrogen (40e60 bar), consumption up to

12 Nm3/h (1.07 kg/h);

� Low grade steam (130e150 �C), consumption up to 33 kg/h;

� Circulating cooling water (supply at �25 �C and return),

consumption up to 15 kg/min;

� Instrument air (5.5e7.5 bar), average consumption below

1 NL/min, peak consumption up to 55.5 NL/min for no

longer than 15 min;

� Electric power (525 or 230 VAC, single phase), consumption

up to 2000 W max.

The necessary amount of dispensed hydrogen is provided

by the Buffer Storage, a pack frame assembly of 18 gas cylin-

ders, with a total (water) internal volume of 900 L and

hydrogen storage pressure up to 200 bar. The buffer is

connected to both hydrogen Dispenser and hydrogen

compressor (MH Compressor); the latter maintains the

maximum hydrogen pressure (195e200 bar) in the buffer

during the operation of the hydrogen refuelling system.

The integrated hydrogen dispensing and compression

unit provides one-stage compression of the low pressure

(~50 bar) hydrogen to the high pressure (200 bar; throughput

7.5 to 12 Nm3/h) using an AB2-type MH material (as

described previously) and steam for the heating and water

for the cooling. The high-pressure hydrogen is supplied to

the Buffer Storage tank, and, further to the Dispenser which

delivers hydrogen (controlled ramping 0e185 bar) to the

dispensing H2 Nozzle when refuelling of the forklift is

necessary. The unit is also equipped with a vent pipeline for

the safe release of hydrogen, as well as with the auxiliary

pipelines for the purging of the gas systems with nitrogen to

provide safety before and after installation and during

servicing.

Independent automated operation of both hydrogen

dispensing and hydrogen compression units is provided by

the Control Block.

The developed hydrogen refuelling station is characterised

by simplicity in design, operation and service; higher safety

and reliability; noiseless operation, and lower capital and

operating costs than existing high-pressure (350e700 bar)

hydrogen refuelling stations available on the market. These

benefits are due to:

� Lower hydrogen dispensing pressure (up to 200 bar) which

enables the use of standard gas service components (fit-

tings, valves, etc.);

� Relatively slow pressure ramping (5e15 min) which pre-

vents overheating of the supplied H2 and, thus, eliminates

the requirement for deep cooling;

� The replacement of a mechanical hydrogen compressor

with the metal hydride compressor which utilises waste

industrial heat, instead of electricity, for the hydrogen

compression.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y 4 1 ( 2 0 1 6 ) 1 3 8 3 1e1 3 8 4 2 13841

The benefits specified above are particularly relevant for

industrial customers who possess the necessary infrastruc-

ture, namely; low-pressure pipeline hydrogen, circulating

cooling water and low-grade steam.

The 15 min refuelling cycle of the forklift with LT PEM FC

power module and MH extension tank at the dispensing

pressure 150e185 bar can provide its full-load operation (ac-

cording to VDI-60 protocol) during more than 3 h. Depending

on the operation schedule at the customer's site, the forklift

requires refuelling after its operation in the real industrial

environment during 2e4 working shifts.

A forklift equipped with a PEM FC power module and a MH

extension tank, along with a hydrogen refuelling station have

recently been put into operation at Impala PlatinumRefineries

in Springs, South Africa as a result of this work. Results of the

detailed field tests of the systemswill be published elsewhere.

Conclusions

� This work describes a novel concept for the integration of

MH in the H storage system on-board an electric PEM FC

forklift by coupling aMH extension tankwith a commercial

PEM FC power module.

� The MH extension tank uses a low-stability MH, based on

an AB2-type alloy, in combination with an advanced engi-

neering solution for the MH container, to provide a high

system dynamic performance.

� H2 refuelling of the PEM FC forklift is provided by a novel

low-pressure refuelling system, integrated with MH

compressor.

Acknowledgements

This work is supported by the Department of Science and

Technology (DST) within theHySA Programme (HySA Systems

projects KP3-S02 and KP3-S03), and Impala Platinum Limited;

South Africa. Investment from the industrial funder has been

leveraged through the Technology and Human Resources for

Industry Programme, jointly managed by the South African

National Research Foundation and the Department of Trade

and Industry (NRF/DTI; THRIP Project TP1207254249).

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