1

PUBLISHABLE SUMMARY

The principal objective of HYDROSOL‐PLANT (SP1‐JTI‐FCH.2012.2.5/ Contract No:325361) is the

development and operation of a plant for solar thermo‐chemical hydrogen production from water in a

0.750 MWth scale on a solar tower, based on the HYDROSOL technology. The HYDROSOL‐plant consortium

consists of 3 Research Centers from Greece, Germany and Spain (APTL which is the coordinator of the

project, DLR and CIEMAT), 1 SME from the Netherlands (HYGEAR) and 1 Industry from Greece (HELPE).

PROJECT OBJECTIVES FOR THE REPORTING PERIOD: The research programme is organized into eight work‐

packages (WPs), one dealing with the Project Management and coordination (WP1), six (WP2‐WP7) with

the research activities and one with the Dissemination and exploitation activities (WP8). Out of the

research activities related WPs four (WP2, WP3, WP4, WP5) are running within the first 18 months of the

Project. The specific objectives of these WPs are the following:

WP2: • To prepare a detailed design of the complete demonstration plant.

• To provide the basis for the development of system control schemes.

• To enable the final definition of all necessary plant components and

interfaces.

WP3: • Development and manufacture of a complete 750 kWth scale dual

receiver/reactor unit for solar thermochemical splitting of water.

WP4: • To address all ‐ besides the hydrogen production unit ‐ necessary

components’ sizing and detailed design.

• To accordingly manufacture/procure these components.

• To select and procure all necessary sub‐components and equipment

needed for process automation and control.

WP5: • To adapt the solar tower platform to the hydrogen plant operation

requirements.

• To install the fully assembled solar hydrogen production reactor on the

solar tower.

• To install all other necessary plant components.

• To integrate the operation of the whole plant via the implementation of

suitable control software, hardware and plant’s infrastructure.

WORK PROGRESS AND ACHIEVEMENTS DURING THE REPORTING PERIOD:

In WP1, the project website was prepared during the first 3 months of the project and officially launched in

late April 2014. The website was implemented and administered by APTL/CERTH, the coordinating

organization of the project and it can be accessed via the following link: http://hydrosol‐plant.certh.gr . The

website has two levels of accounts, a public area where the public is introduced on the project and the

consortium details and a member area where the user (project partners and EU officers) can log‐in to have

access to all areas. Examples of the website format are shown in the following figures.

Figure 1. Front page of the website. Figure 2. Consortium tab area.

2

In WP2, which deals with the process layout, the process flow‐sheet and P&ID were prepared. The flow

sheet incorporates all process design improvement, identified within the previous Hydrosol project

(HYDROSOL‐3D), mainly concerning heat recovery, water and hydrogen separation and steam generation as

well as the final refinements of the reactor’s design. Furthermore, it contains the main results of the

simulation of the plant, which has been carried out by using the simulation tool Aspen Plus. Based on this

flow sheet, a piping and instrumentation diagram (P&ID) was developed, which provides the piping of the

process flow diagram together with the installed equipment and instrumentation. Additional changes that

were incorporated in the process flowsheet relate mainly to the development of the reactor design and the

incorporation of a 3‐reactors concept instead of the dual‐reactor concept of the former HYDROSOL

projects. The 3‐reactor concept was a product of the parallel investigation that was conducted within WP3

for the design and optimization of the hydrogen production unit. The plant mainly consists of the following

sections:

• Water splitting (Hydrogen production step) and thermal reduction (regeneration step)

sections: includes 3‐reactors in a parallel mode (1 reactor splits water while the other 2

reactors regenerate)

• Feed water evaporation and overheating

• Water separation from the product gas

• Nitrogen separation from the product gas.

The hydrogen purification section serves to upgrade the quality of the hydrogen to a commercial grade,

and hence demonstrate that the produced hydrogen can be usefully applied. It consists of a 4‐vessel

Pressure Swing Adsorption unit (PSA), together with a compressor and storage tanks for the feed, the

hydrogen product and the off‐gas.

The hydrogen production unit was investigated in WP3. In all solar campaigns conducted so far through the

past HYDROSOL‐project series, three different reactors were constructed that were based on the same

principles, i.e. flat geometry reactors consisting of monoliths coated with the redox material. The reactors

consisted of porous monolithic structures constructed either from re‐crystallized SiC (ReSiC, for the case of

the HYDROSOL project and the single chamber and dual‐chamber 3 kW solar reactors) or from siliconized

SiC (silicon‐infiltrated Si‐SiC, for the case of the HYDROSOL‐II and HYDROSOL‐3D 100 kWth reactor) coated

with the redox material. These monolithic structures were selected because besides their capability of

operating as volumetric receivers/ absorbers of concentrated solar irradiation and achieving and sustaining

the required high temperatures, their multi‐channeled structure provided high gas‐solid contact area and

facilitated the access of the steam to the reaction sites of the redox material. In the HYDROSOL‐3D project,

a point of improvement of the reactor’s design was the change of the geometry of the reactor from flat to

spherical, since the latter provides the most efficient exploitation of the solar flux. However, this reactor

concept had also some disadvantages mainly regarding the shapes of the monoliths and the supporting of

the different segments to achieve the spherical shape of the absorber. Another aspect that was considered

had to do with the fact that the substrate occupies the majority of the reactor volume (and weight)

compared to the active redox material (the amount of the latter used so far on the SiC structures was about

20 %wt). Since the water splitting reaction based on redox materials depends also on the mass of the redox

material on the reactor, the hydrogen yield per reactor volume would be rather low. A solution that would

tackle this limitation was to produce the monolithic segments that constitute the reactor body entirely

from the redox material.

Therefore, in the HYDROSOL‐PLANT project the focus was to finalize the design of the reactor and to

achieve the manufacturing of the reactor body entirely from the redox material. A new reactor design was

developed by DLR based on previous reactor designs that were employed in solar applications. The benefits

from such an approach lie mainly on the know‐how for the construction of such reactors, since such reactor

geometries have been tested under solar radiation.

3

(a) (b)

Figure 3. (a) old HYDROSOL‐II flat reactor, (b) HYDROSOL‐PLANT reactor with the secondary

concentrator

A study was conducted with all necessary calculations for the assessment of the suitability and further

design and improvement of the different components of the reactors (i.e. the vessels, the insulation, the

optical components, the flanges at the inlet and outlet of the reactors as well as the construction of the

support structures of the reactors etc.) to fit the conditions (especially the regeneration temperatures) that

will be applied at the solar platform.

In addition for the finalization of the design of the absorber/reactor, the development of the materials

and the manufacturing of the reactor segments was investigated. Certain issues were addressed that are

listed below:

• use of a more lightweight inert monolith (compared to the SiC monoliths that were employed

in the previous HYDROSOL projects) as a substrate for the redox material

• investigation of the possibility of employing porous structures made entirely from the redox

material instead of using redox coatings on ceramic substrates

• small‐scale monolithic segments development via the extrusion process that consist entirely of

the redox material

• investigation of the possibility to extrude larger monolithic segments into the specific shapes

that were identified in the previous project as well as in the current project

• investigation for the application of foam structures consisting entirely of the redox material.

For the first time it was possible to produce honeycomb monoliths consisting entirely of the redox

material for the splitting of water. Optimization of the extrusion process allowed the production of thin‐

wall extruded monoliths with good structural stability.

(a) (b)

Figure 4. Die drawings and actual extruded redox monoliths with (a) thin and (b) thick walls

4

Additionally foam structures were also developed that consisted entirely of the redox material, while a

third approach was the development of an “alternative” honeycomb‐type structure using an in‐house

developed technique.

All produced redox structures were evaluated under the same protocol that involved an initial

activation step for, followed by a 30 min water‐splitting step at 1100oC and a 30min thermal reduction step

at 1400oC.

All structures were active water‐splitters especially in the case of the “alternative” monolith. However,

there are some limitations such as the weight of the structure that will define the final choice for the

construction of the reactors in order to comply with the weight limitations of the platform set‐up. The

durability of the redox structures was investigated for the case of the extruded monolith by subjecting the

structure to successive splitting and regeneration cycles. Up to the date of the current report more than

450h of operation were achieved on the monolith without the material showing any significant degradation

of its activity.

0

50

100

150

200

250

300

90cpsi foam "alternative monolith"

H2

μm

ole

/ml

red

ox

Figure 5. Total H2 yield for the honeycomb

monolith, the foam and the “alternative”

monolith structures

Figure 6. Indicative H2 yield consecutive cycles for the

assessment of the durability of the redox monolithic

structure.

In WP4 the BoP and Sub‐BoP components were defined based on the hydrogen production unit designed in

WP3 and the P&ID developed in WP2. With respect to the sizing, the standard conditions as well as

minimum and maximum operational parameters defined or determined in WP2 were used. CIEMAT as the

owner of the solar installation (SPSS‐CRS, small solar power system central‐receiver system at the

Plataforma Solar de Almeria (PSA) in Spain) will contribute to the project by providing a flexible gas N2

supply, the steam generator and the demineralised water unit. The SPSS‐CRS, consists of an autonomous

field of heliostats and a metallic tower 43 meters high. This plant has been used in the past to

accommodate testing of small solar receivers in the range of 200‐350 kW thermal power applications.

Recently, an important effort has been taken to remodel the test facility to turn it in a suitable test‐bed for

hosting (access to research groups) solar hydrogen production projects. In this regard, the SSPS‐CRS tower

is equipped with a large quantity of auxiliary devices that allow the execution of a wide range of tests in the

field of solar thermal chemistry. All test levels have access to pressurized air (29 dm3/s, 8bar), pure nitrogen

supplied by two batteries of 23 standard‐bottles (50 dm3/225bar) each, cooling water with a capacity of up

to 700 kW, demineralized water (ASTM type 2) from a 8 m3 buffer tank for use in steam generators or

directly in the process, and the data network infrastructure consisting of Ethernet cable and optical fibre.

For the needs of the project, in order to ensure that adequate N2 flow can be provided to the plant set‐up

for its operation during the solar thermal and splitting campaigns that will be conducted at the platform, a

preliminary study was undertaken, including the possibility of using a cryogenic plant. Maximum capacity of

the PSA is 90 kg/h N2 based on 2 N2 batteries (in total 46 N2 gas bottles, with 257 kg/battery), with an

autonomy of a few hours. In order to secure that the plant will be able to operate for several days before

the need to refill the N2 tanks, a cryogenic installation would be the choice. The proposed plant will be able

to provide flow rates from 70 kg/hour to 250 kg/hour with an autonomy of several days, or even weeks. In

this plant, liquid N2 is stored in a liquid tank with a 30 TN capacity. This installation is safe and efficient to

operate and it is extremely versatile to provide all the possible variants.

5

Figure 7. Scheme of the cryogenic installation

For feeding the water vapour in the reactors an electric steam generator conceived for very small or

small consumption will be used. The electric steam generator is built with stainless steel AISI‐316L with a

steam production from 6 Kg/h to 50 Kg/h and up to 3.3 Bar of pressure. The evaporator will be equipped

with a feedback control loop to ensure that the required amount of steam is indeed generated. The

evaporator control will be based on measurement of the produced steam flow rate by a flow sensor, which

sends its signal to the PLC. A vortex flow meter with digital signal output may be selected for this purpose.

In addition for Hydrosol‐Plant installation needs, high purity water is essential in preventing the

introduction of impurities into the water circuitry. The existing reverse osmosis unit supplying water for the

PSA uses provides demineralized water with high quality standards for steam generation, cooling needs,

etc. The plant consists of modular compact lines of water treatment for the adequacy of the salty available

water, for services, or with destine to the generation of steam of high quality. This plant incorporates the

last technologies of process as demineralization by means of inverse osmosis and/or electro deionization.

The quality of the high purity water supplied by reverse osmosis is not sufficient when conductivity below 1

μS/cm is required. For such cases, this plant offers combinations of reverse osmosis with downstream

electrodionisation (EDI). Results from routine usage show that such a combination with this technology

allows product water of less than 0.1 μS/cm to be obtained from 2190 μS/cm raw water. In addition, the

continual self‐regeneration of the high purity mixed bed resins effects a very high microbiological purity of

the ultrapure water produced. The water treatment carried out by the plant close an integral cycle with the

purification and neutralization of the spillages. This plant is able to treat 2300 l/h raw water and produce

1500 l/h of demineralised water within a good quality (ASTM Type II) for process needs at the PSA.

Finally for the product purification unit, as a first step for the sizing of the BoP‐components of the PSA

unit, mass and heat balance calculations were performed, in order to define the stream tables for both day‐

time and night‐time operation of the unit.

Figure 8. Flow diagram of PSA unit

A buffer vessel is required to compensate the fluctuations in the production as well as the pause in the

operation of the plant during no‐sun periods (e.g. over night) was sized on the basis of the flow rates,

6

assuming 6 production hours per day (as agreed by all partners). Its volume will be about 500 l. Calculated

typical pressure variations in the buffer vessel during a week (assuming 5 production days) are shown in

Figure 9. It can be seen that the pressure increases during the day and decreases at night; at the end of the

week the pressure should be equal to the beginning.

0,0

1,0

2,0

3,0

4,0

5,0

6,0

7,0

8,0

9,0

10,0

11,0

12,0

13,0

0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96 102108

Pbuffer [bara]

production time [h]

0,0%

0,5%

1,0%

1,5%

2,0%

2,5%

3,0%

3,5%

4,0%

4,5%

5,0%

0,0%

10,0%

20,0%

30,0%

40,0%

50,0%

60,0%

70,0%

80,0%

90,0%

100,0%

0 2 4 6 8 10 12

xN

2

yie

ld

adsorption time [min]

V=0.8 l, P=13 bar

yield xN2

Figure 9. Pressure fluctuation in buffer vessel Figure 10. PSA model calculation results: yield and

purity vs adsorption time

It was decided to include a drain to the buffer vessel, to account for potential condensation due to low

night‐time temperatures. The PSA vessels were sized on the basis of runs with HyGear’s in‐house PSA

model. An example of calculation results is shown in Figure 10, showing both the hydrogen yield and the

product N2‐content as a function of adsorption time for a certain vessel size. It was decided to size the

vessels to 0.8 l. Besides suitable adsorption times, this also yields acceptable gas velocities.

The definition and procurement of sub‐BoP components includes valves (high temperature, check and

safety valves), pressure and temperature sensors, mass flow controllers and all equipment needed for

process automation and control. For example, valves installed to ensure the switch of different feeds to the

reaction compartment, specific multi‐way high temperature resistant valves to ensure the switching of the

reactor modules from hydrogen production to regeneration mode and vice versa. Regarding, process

automation and control, an intelligent valve control procedure is intended to be applied to minimize or

even avoid mixing of oxygen‐rich and hydrogen rich product gases. All critical components will be

supervised by sensors; in particular the high temperature ones will be well equipped with thermocouples.

In WP5, during the first 18 months, work has been focused in preparing the present solar platform facilities

to house the new plant. The preparation of the solar platform involves improvements not only in structural

works at the 27m height platform but also of the performance of the plant (renovation of the facets, new

control program). In the first 18 months, some actions that have taken place on this task are described

below:

• Improve the communication of heliostats by wiring all heliostats.

• Re‐moderation of control room

• Add some additional functionalities of the control programme

• Renovation of the facets of the heliostat field.

• Conditioning of the platform.

The quality of the mirrors is critical to ensure that the energy reflected by the heliostats is collected in

the receiver and not “spilled” and wasted. PSA has made an effort to improve the efficiency of the heliostat

field by replacing 2/3 of the facets of the present heliostat field. The new facets provide high reflectivity

contributing to improve the efficiency of the solar irradiation on the solar receiver.

7

Figure 11. Aerial view of the experimental SSPS‐CRS facility.

The new control room for the operation, control and monitoring of the plant includes ergonomic

workspaces, a large‐format display wall, new computer equipment, new voice and data lines, improved

analog and video switching systems and many other improvements (Figure 12).

(a) (b)

Figure 12. a. control room b. Heliostat field with new facets

Finally, a new control program has been terminated, the new control program provides much more

information for the design of a supervisory system (monitoring and diagnosis displays, definition of alarms,

meter readings, equipment status reports etc.). Additional features of the control programme are

summarized below:

• Nº heliostats at each foci, coordinates of the foci

• Definition of foci. Implementation of new functionality on the current control software that allows

the management of any number of significant foci, eliminating the current restriction on the

existing foci number. It will be very useful for aiming strategy.

• Each new center will mean a possible new "state" which can be each heliostat, and will be

interpreted from the central control software.

• Information available in real time. Development of a MODBUS‐TCP server type that allows for real‐

time public the current state of the field and other variables of interest. This server will be

integrated into the current control software and other software will serve SCADA who can make

remote requests on published data. On‐line published information includes (Period of time each

heliostat has remained in a given focus, Nº of foci, etc).

The space that will be used at the SSPS‐CRS tower for hosting the HYDROSOL‐Plant installation is located at

26 m. This level also housed the HYDROSOL 3D installation and it was a closed room, two meters high, 40

m2 available for equipment. However, the future platform will be enlarged: It will be a closed room with 60

8

m2 available raising the roof up to 4 m high, distributed according to the following figures: (2.5 + 6.27 ) wide

X 6.27 long = 55 m2.

Besides that, an additional platform to accommodate additional equipment, such as tanks, PSA unit,

etc., will be placed three meters below the main floor. It will be an open area. The receiver‐reactors along

with the other high temperature components, as a fully assembled and fully functional system, will be

mounted to the upper floor. The reactor will be combined with the rest of the peripheral components,

including steam generators, preheaters, reactor arrays, etc. The 2nd floor, located directly under the floor

where the reactors will be placed, will accommodate the rest of the peripheral components.

(a)

(b)

Figure 13. Example of (a) the two levels that will be occupied with the HYDROSOL‐PLANT facilities and (b)

Integration of the receiver array on the tower

On the upper floor, the reactors are assembled on the support structures and connected with pipes to the

high temperature heat exchangers, placed also on this floor to minimize the heat losses between these

components and to reduce the length of the stainless steel pipes, which are quite expensive.

The three reactors are placed to form a triangle, with the two reactors placed on the floor and the

third reactor hanged from the ceiling of the room.

Figure 14. View of the upper floor

9

Another important question solved within discussions between DLR and CIEMAT, relates to the space

between optical axes. This variable is critical because of a limited vertical space available on the tower,

furthermore, final decision influences some aspects like spillage losses and control temperature. For

example: If spacing between modules is small, it would be easier to integrate the system into the tower,

and also reduce the spillage losses. However, temperature control becomes difficult, given that when two

receivers are at regeneration temperature (1400°C) the spillage of these two influences the one which is at

production temperature (1100°C).

A preliminary simulation of the heliostat field will be required with the new reactor design in order to

achieve the best performance (e.g. homogeneous flux, low spillage etc.). This simulation has already been

done and some of problems that remain to be resolved have already been detected.

Figure 15. Trace‐Pro simulations of the receiver array

As starting point the entire heliostat field aims at a single aiming point which is centered in the

aperture center (Figure 15). However, flux directed at the central point of the reactor needs to be

distributed differently to cover the needs of the peripheral points in order to achieve the required

temperature at each module (Figure 15). A special attention will be paid to the validation of our model

through the confrontation of simulated results and experimental measurements.