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Project Description and Objectives: |
The project is organized in two phases.
Plant subsystems of Phase 1
The following plant subsystems were realized in Phase 1 of the project: Solar generators employing monocrystalline and polycrystalline silicon technology with rated field capacities of 135 kWp (10.5 and 11 % efficiency at standard test conditions STC), referred to module surface area including cable losses and 131 kWp (8.6 % efficiency). Electric power conditioning units (DC/DC converters DC busbar electrolysis power supplies AC/AC converters AC busbar DC/AC converters). Two advanced low-pressure water electrolyzers employing different technologies rated at 111 kWel and 100 kWel capacity with a total maximum hydrogen output of 47 m/h. Hydrogen and oxygen gas systems for compression, purification, drying and storage of the electrolytically generated gases (purity 99.9 vol% H2 and O2 or better) Two gas-fired heating boilers of calorific-value design working with different oxidizers (oxygen and air), Capacity each 20 kWth, burning natural gas/hydrogen fuel mixtures
of practically random ratio. Two fuel cell plants employing different technologies: alkaline type of 6.5 kWel, phosphoric acid type of 79.3 kWel and 42.2/13.3 kWth output Automated liquid hydrogen (LH2) filling station for testing automobile fuelling systems Plant subsystems of Phase 2.
New or advanced plant subsystems added in Phase 2 of the project are:
Solar generators of advanced technology together with electric power conditioning
[amorphous silicon type of 25 kWp and 24 kWp rated field capacity] (4.5 % and 5.1 % efficiency at STC, referred to module surface area including cable losses) ; advance monocrystalline structure types with AS hybrid cell of 11.3 kWp capacity (12.9 % efficiency) ; two HE fields of 6.1 kWp capacity each on tables manually adjustable between 20 and 70 degrees elevation (13.3 % efficiency) ; MIS field of 11 kWp capacity (11.5 % efficiency) ; BSF field of 11.8 kWp capacity (13.1 % efficiency). Investigation of alternative foundation and support construction designs Installation of guyrope supporting structures with 10.3 kWp monocrystalline cells (12.6 % efficiency). Alkaline pressure-type electrolyzer, 100 kWel, 32 bar working pressure. Catalytic heater of calorific-value design (10 kWth boiler output fuelled with natural gas and mixtures of natural gas/hydrogen 90/10 to 50/50 vol% with air as oxidizer). This heater is integrated into the on-site building heating system, Catalytically heated absorption-type refrigeration unit (rated burner output 32.6 kWth, rated refrigeration capacity 16.6 kWth) with hydrogen as fuel and air as oxidizer. This unit supports the conventional chilled water circuit. Fuel cell plant with proton-exchange membrane operating with air as oxidizer, rated power output 10 kWel.
For mobile application: electric forklift truck with hydrogen supply from metal hydride storage. Optimization of the Phase 1 automated liquid hydrogen filling station to reduce vehicle fuel tank filling time and boil-off losses as well as the number of steps involved in the filling procedure. Comparison of two clean-break coupling systems of new design, operation of cryogenic pump system and testing of vehicle fuel tank system without cryovalves .
Peripheral systems
In fact several additional peripheral systems are essential for plant operation. While not mentioned specifically in this report, they include particularly the various utility and auxiliary systems control system, safety systems and extensive test data acquisition system.
Safety concept
It may be noted that no fundamentally new safety risks had to be considered when drafting and subsequently implementing the safety concept in force at the Neunburg vorm Wald solar Hydrogen facility Certainly in industrial applications the existing codes and regulations are adequate for safe working with hydrogen, a gas that has been established in industry for decades both in gaseous and liquid form. Long-term operating experience to date has given no cause to amend the concept for a still higher level of safety. Stipulations have been fulfilled that injury to persons present at the facility, damage to property and harm to the environment must be prevented.
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Preliminary or Final Results: |
Electrolysers:
The two low-pressure electrolyzers installed in Phase 1 for the generation of H2 and O2 are advanced technology systems (zero gap geometry, absence of asbestos diaphragms, activated electrodes increased current density) and exhibit significantly lower specific energy consumption than conventional designs (4.5 kWh/m H2 at rated current). Problems occurring with the alkaline electrolyzer, notably inadequate purity of the product gases were eliminated in August 1992 by installing polysulphone diaphragms reinforced on the cathode side to replace the previous plain type The membrane electrolyzer had to be shut down in June 1995 because of increasingly deficient product gas purities (above all H2 in product O2).
Test results now gathered over several years indicate that the alkaline low-pressure electrolyzer is working well, Up to the time it was decommissioned the membrane unit also worked well even under conditions of greatly varying power input when directly coupled to a solar generator. Test programs for the alkaline low-pressure electrolyzer have now largely been completed. Further work with this equipment will primarily add to experience of long-term operation. Cyclic recording of basic values (characteristics) is being made. SWB would have gladly furnished the acquired know-how to the manufacturers for use in further development but both have long since abandoned this field of activity. Procurement of spare parts has become very difficult as a result, particularly affecting the Membrane electrolyzer.
After dismantling the cell stack in February 1996 the membranes were found to have deteriorated severely during the five years of test operation with the result that the electrolyzer had to be decommissioned owing to the lack of spare parts although it had performed well over a long period. Advanced pressure-type electrolyzers of the 100 kWel class working at about 30 bar were not available at the time the two low-pressure units were purchased.
Placement of an order for an alkaline electrolyzer of this type (with unitized EDE ceramic diaphragms and nickel electrodes) was delayed until November 1994 and guarantee test run for the unit took place in July 1996. Operating at 135 °C, the specific energy consumption is about the same as for both the low-pressure units but no compression of the product gases is required. Current density is 10 kA/m2 at rated load. The first recording of basic data was interrupted at the end of 1996 when dismantling of the EDE cell stack became necessary primarily due to rising O2 impurity in the product H2.
Under the terms of guarantee it was agreed that the supplier would install a cell stack of different makeup (polysulphone diaphragms activated nickel electrodes, working temperature reduced to 105 °C, new gasket design). This PSU cell stack is to be run for about a year, after which testing will resume with the improved original EDE cell stack. The necessary modifications to the mechanical and control equipment and installation of the PSU cell stack were completed in March 1997. The test program for the pressure-type electrolyzer is due to be resumed at improvement of the safety of the PSU cell stack against short-circuit and better KOH separation from the O2 product gas. A view inside the operating building showing the water electrolyzers is presented in Fig. 4. Pressure storage of H2 and O2 generated by the two low-pressure electrolyzers requires subsequent compression of the product gases where such compression is not required with the pressure-type electrolyzer. Both gases are then cleaned of impurities (the other gas component) by catalytic combustion, dried in regenerated beds of alumina gel/molecular sieves and finally stored in pressure vessels
heating boiler
Although delivering reasonable test results in the past the gas-fired heating boiler operated with oxygen as the fuel oxidizer was unable to reach an acceptable level of availability owing to problems (insufficient stability of the burner head) occurring toward the end. The unit was decommissioned in May 1995. By contrast the heating boiler operated with air as oxidizer continues working satisfactorily. As was to be expected efficiency was better when using oxygen instead of air with other conditions unchanged. Combustion of hydrogen with air resulted in slightly increased emissions of NOx compared to combustion of natural gas (Group H). Significantly increasing the excess of air does enable these emissions to be reduced but at the expense of efficiency. Test programs for the gas-fired heating boiler working with air as the fuel oxidizer have now largely been completed. Further work with this equipment will primarily add to experience of long-term operation. Cyclic recording of basic values (characteristics) is being made.
Catalytic heater
The calorific-value catalytic heater with a boiler capacity of 10 kWth, designed to burn natural gas and also continuously variable mixtures of 10 - 50 vol% H2 in natural gas, was handled as a development project. Air is used as the fuel oxidizer and premixing of fuel gas and air takes place externally. Owing to the reduction of combustion temperature below 900 °C, NOx emissions are less than 20 mg/kWh. Test operation of this unit started in December 1995.
Catalytically heated absorption-type refrigeration unit
Another development contract was placed for the catalytically heated absorption-type refrigeration unit fuelled with hydrogen. A conventional absorption-type refrigeration unit for air conditioning service fired with natural gas, was modified for this application. Running with air as the fuel oxidizer, the unit has a refrigeration capacity of 16.6 kWth. Heat is generated catalytically on diffusion burner structures (without premixing of fuel and oxidizer, which in principle eliminates backfiring). Due to the low burner working temperature of approx. 800 °C, heat transfer in the high-pressure desorber is very efficient. Moreover corrosion problems are reduced by the coolant not being subject to overheating (160°C) in the desorber. NOx emissions are less than 1 vppm. Several improvements had to be made to the refrigeration unit in the beginning due to a number of problems with standard components for example the burner monitor and off-gas sampling piping. The unit is used to support the conventional chilled water circuit.
Fuel cells
Alkaline fuel cell:
Experience with the alkaline fuel cell plant proved it to be too sensitive for service in elaborate gas systems on account of its complexity. Several replacements of the fuel cell stack became necessary leading to the decision in October 1994 to decommission this plant although it had demonstrated good performance during periods of troublefree operation. Above all, its usability is compromised by the risk of irreversible damage to the nickel anode. The manufacturer relinquished this field of activity some time ago.
Phosphoric acid fuel cell:
Optimized for electric power output the phosphoric acid fuel cell plant is designed to run in a variety of modes for test operation in a (solar) hydrogen demonstration facility. In other words it is not designed as a commercial containerized standard unit. Major problems occurred at the time of commissioning this plant. Most of the difficulties originated in the associate peripheral systems, very few in the fuel cell stack itself. Once the plant was finally taken over by SWB in March 1993, the test program has proceeded at a good pace. The first tests conducted in various modes for recording characteristics were run at the end of 1993. Load following and continuous operation (24 hours a day, five days a week) were investigated in 1994. In the summer of 1995 the plant was used to simulate power requirement of a small hospital in island-site operation. Starting and stopping behavior of the fuel cell plant was investigated more closely in the autumn of 1996 and measurements were made to check emission levels (CO and NOx). Emissions are comparable with other commercially available phosphoric acid fuel cell plants meaning that they are several sortes of magnitude lower than the levels specified for gas engines (German TA Luft specifications 1986 CO, 650 mg/m; NOx, 500 mg/m). Apart from these test periods the phosphoric acid fuel cell plant was operated mainly at rated capacity (fuel cell at 610 Adc). Valuable knowledge relating to long-term stability has been acquired especially under such highly aggravated operating conditions.
PEM fuel cell (since january 1998) and electric forklift truck
The fuel cell plant with proton-exchange membrane now on trial run, was modified by the manufacturer for use of air (instead of oxygen as the fuel oxidizer, which represents a new technology. It has been constructed as a mobile system with a rated power output of 10 kWel and will be employed as an electrochemical power source to drive a standard electric forklift truck at the Neunburg vorm Wald site. The skid-mounted fuel cell plant has been installed in the truck in place of the normal battery pack. Power for all electrical auxiliaries will be supplied by the on-board system using an external battery for startup. Test operation is due to commence when the current trial run is completed and the remaining deficiencies are corrected.
Electric forklift truck and metal hydride
Metal hydride is used for on-board hydrogen storage in the electric forklift truck which is advantageous in this special instance because of its weight. The effective hydrogen capacity of 2 x 13 m3 is designed for 8 hours of forklift truck operation at average power requirement. The envisaged time for charging the hydride is about 10 minutes and the heat generated during the charging will be dissipated by an external cooling water circuit.This system gives SWB the opportunity to undertake practical testing and acquire corresponding experience with a third major hydrogen storage technology complementing the pressurized gas and liquid hydrogen technologies already in use. The metal hydride is to be charged with hydrogen from on-site gas storage at pressures between 10 and 30 bar.
Liquid hydrogen filling station
Work has been proceeding on optimizing the liquid hydrogen fuelling of test cars at Neunburg vorm Wald since 1991 with construction of a LH2 filling station. Through the pressure prevailing in the 3000-litre site tank liquid hydrogen is conditioned according to the vapor pressure curve and can be filled into the vehicle fuel tank either by the site tank pressure or by LH2 pump. The filling line is manually coupled to the vehicle whereas the actual filling operation takes place under program control. Test results acquired to date by SWB have been evaluated to optimize the LH2 filling station insofar as the time for a complete vehicle tank filling cycle has been shortened to approximately 5 minutes at the same time reducing the boil-off losses occurring during filling to less than 8 % of the liquid volume transferred. Successive vehicle tank filling can be achieved within 3 minutes. This was mainly accomplished by using a new design of clean-break coupling systems for connection between the filling station and vehicle fuel tank. Beyond that SWB ordered a 125-litre vehicle tank system without cryovalves which was used during the second half of 1996 to achieve filling in about 3 minutes while eliminating return gas flow . Work on the task of automating operation of the Phase 1 LH2 filling station has been completed. The filling station and the novel vehicle tank system remain on site for coupling Demonstrations using the coaxial coupling system At the same time wearing behavior of components subject to stress remains under observation.
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