3. Production of Hydrogen

3.1 Primary and secondary energy sources for hydrogen production

As hydrogen is only found in nature in compound form, it must first be produced through the use of energy, before hydrogen itself becomes available for energetic purposes. In this case, one can distinguish between production using a primary energy carrier and production using a secondary energy carrier.

Primary energy production presently means hydrogen production from fossil fuels via natural gas reforming as well as the partial oxidation of heavy fuel oil (or Diesel) and coal. Along with these further processes are in the research and development phases. The leader among these is the gasification of biomass, but also worth mentioning is the direct production of hydrogen from algae subjected to solar radiation. It is however only the biomass gasification process whose development phase is so developed, such that a transformation into a market competitive product within the next few years can be expected. 

The idea and principle of the gasification process or related principles can be applied to the disposal/recycling of organic waste and to some extent to all carbon containing waste matter. Therefore it can be expected that processes for the production of hydrogen from waste matter will be developed in the medium term. Commercialization thereof however, will probably not occur until several years after the introduction of biomass produced hydrogen.  

Electricity is presently the only secondary energy carrier used to produce hydrogen, either by the electrolysis of water or as a by-product resulting from the chlorine-alkaline electrolysis. Water electrolysis is independent of primary energy use and as such is seen as the essential element of a hydrogen based energy sector. As another secondary energy based production method, the reforming of methanol in mobile applications could play a role in the near future.

 

3.2 Production from fossil fuels

Of the approximately 500 Bil. Nm3 of hydrogen [4] traded worldwide, the vast majority originates from fossil fuel sources (natural gas, oil) as a by-product in the chemical industry (e.g. Hüls chemical works in Marl, Dow Chemical in Stade) during the manufacture of PVC (e.g. chlorine-alkaline electrolysis) or from crude oil refining processes. All in all, the production of hydrogen as by-product accounts for 190 Bil. Nm3 worldwide (38%), of which about 2% or 10 Bil. Nm3 stems from chlorine-alkaline electrolysis (or in Germany, 4.5% of the total 19 Bil. Nm3 of hydrogen produced there).

 Should in the medium to long term hydrogen achieve a significant share of the energy market, then considering present environmental goals (fewer emissions, CO2-reduction), it will not be possible to produce hydrogen on a large scale using traditional steam reforming of natural gas. Modern processes (Plasma arc process of Kværner Engineering) do however offer the potential, through the use of electricity, of C02 free hydrogen production. 

 

3.2.1 Present state of the art

 - Steam reforming of natural gas

Process description: steam reforming refers to the endothermic, catalytic conversion of light hydrocarbons (Methane to Gasoline) with water vapor. Industry scale processes of this kind are normally carried out at temperatures of 850°C and pressures in the order of 2.5 MPa, according to:

CnHm + n H2O -> n CO + (n + m/2) H2.

Exothermic catalytic conversion (shift reaction) of the resulting carbon monoxide produces pure hydrogen according to :

 CO + H2O -> CO2 + H2.

The energy released from this reaction can however not be directly used for the reformation. Using absorption or membrane separation, the carbon dioxide is removed from the gas mixture, which is further cleaned to remove other unwanted components. The leftover gas consisting of approx. 60% combustible parts (H2, CH4, CO) is, along with a portion of the primary gas itself, used to fuel the reformer.

The industrial scale production of hydrogen is carried out in steam reforming plants with usual capacities in the order of 100,000 Nm3 H2/h. The process is technically well-proven.

What is the cost of such a plant? The investment costs alone for a steam reformer (inc. Desulphurisation, CO-conversion, cleaning and exhaust gas usage) with a yearly capacity of 800 Mil. Nm3 H2 from 340 Nm3/a natural gas, are approx. 200 Mil. DM. Taking into account all capital and operating costs gives a hydrogen production cost of about 20 Pf/Nm3, whereby this price is strongly dominated by labor and primary energy related costs.

 

Who sells steam reformers? Steam reformers are manufactured by large plant engineering companies (e.g. Uhde, Linde, KTI).

- Partial oxidation of heavy hydrocarbons

Process description: Partial oxidation refers to the exothermic or autothermal conversion of heavy hydrocarbons (e.g. residual oil from the treatment of crude oil) with oxygen and steam. The quantities of oxygen and water vapor are controlled such that gasification continues without the need for external energy input, hence autothermal. The following net reaction represents the process:

CH1,4 + 0,3 H2O + 0,4 O2 -> 0,9 CO + 0,1 CO2 + H2.

The industrial scale production of hydrogen is carried out in partial oxidizers with usual capacities in the order of 100 000 Nm3 H2/h. The process is technically well-proven.

What is the cost of such a plant? The investment costs alone for a partial oxidizer (inc. Air separation, CO-conversion, sour gas separation, sulfur production, methanisation and exhaust gas usage) with a yearly capacity of 800 Mil. Nm3 H2 from 280,000 t/a heavy fuel, are approx. 300 - 350 Mil. DM. Taking into account all capital and operating costs gives a hydrogen production cost of about 25 Pf/Nm3, whereby this price is strongly dominated by labor and primary energy related costs.

Who sells partial oxidizers? Partial oxidizers are manufactured by large plant engineering companies (e.g. Uhde, Linde, KTI).

- Partial oxidation of coal

Process description: Apart from the necessary initial preparation of the coal, the process elements of the plant as a whole are the same as for the gasification of oil. The coal is ground to a fine powder and then mixed with water to create a 50 - 70% solid content suspension suitable for pumping.

The process is only carried out on a commercial basis in the coal rich countries of South Africa and China, while in Germany it is only at the pilot plant stage.

What is the cost of such a plant? The investment costs alone for a plant suitable for partial oxidation of coal with a yearly capacity of 800 Mil. Nm3 H2 from 500,000 t/a of coal, are approx. 450 - 500 Mil. DM. Taking into account all capital and operating costs gives a hydrogen production cost of about 30 Pf/Nm3, whereby this price is strongly dominated by labor and coal costs.

 

3.2.2 What is presently under development:

- CO2-free production of hydrogen and carbon black using natural gas or heavy fuel oil and electricity (Kvaerner process)

Process description: Since the beginning of the eighties, the Norwegian firm KVAERNER ENGINEERING S.A. has been developing a so called plasma-arc process which, at temperatures of 1600°C, separates hydrocarbons into pure carbon and hydrogen. This process, which in itself produces no significant emissions, requires, along with the primary energy source (natural gas, oil), cooling water and electricity. A pilot plant in service since April 1992 produces about 500 kg/h pure carbon (carbon black) and 2000 Nm3/h hydrogen from 1000 Nm3/h natural gas and 2100 kWel. Another by-product is the production of about 1000kW high temperature steam. Considering all potentially usable products, the plant works with almost 100% efficiency, made up of 48% hydrogen, about 10% steam and 40% carbon black. 

This process is in the pilot phase. The next step is the planned construction of a plant capable of producing 100,000 Nm3/h of hydrogen under industrial conditions. The plant is to be built up in a modular form with 20 units of the existing pilot plant.

What is the cost of such a plant ? The price for a plant consisting of 20 modules with a yearly capacity of 6 Mil Nm3 H2 per module is estimated to be somewhere in the vicinity of 300 Mil DM.

Who sells the plant ? The firm KVAERNER ENGINEERING S.A. in Norway.

- Small reformers and partial oxidizers

Small reformers and partial oxidizers are being developed such that the use of hydrogen in systems with fuel cells is also possible in the near future. These systems are particularly intended for mobile applications in vehicles and for small stationary systems. Due to the chemical equation balance, natural gas reformers have to operate at considerably higher temperatures than partial oxidizers of diesel or methanol. Therefore, the inexpensive realization of this process into a marketable process is probably simpler as that for a correspondingly small natural gas reformer.

In mobile applications, it is hoped to make profit of the high energy density and simple handling of a conventional liquid fuel for the supply of a fuel cell. In this respect, the reforming or partial oxidation of methanol and diesel plays an important role. 

Within the next 5 years it is expected that the commercialization of decentralized stationary fuel cells in the range 10 - 250 kWe will occur. In order that these fuel cells can be used with natural gas, small natural gas reformers will be developed.

The first commercial application was the integration of such a reformer into a 200 kWel fuel cell module, with phosphoric acid fuel cell (PAFC), produced by ONSI.

Who sells small reformers? Presently there are still no series-produced small reformers on the market. The only such reformer commercially available is that which is integrated into ONSI's fuel cell module. This is offered in Europe by CLC and up to now on the German market by EES (natural gas version), HGC (natural gas and hydrogen versions) and CONSULECTRA (hydrogen version). The firm KTI is building the reformer for Solarwasserstoff Bayern's 80 kWel fuel cell. 

In Europe development is predominantly being led by the Danish firm Haldor Topsø, with important research work also going on in Germany (e.g. Forschungszentrum Jülich, Fraunhofer Institut für solare Energiesysteme).

How much does a small reformer cost? As there are still no small reformers on the market, there are also no price details available. In American investigations regarding possible costs for mass production, costs for small diesel or methanol reformers with 30 - 35 Nm3 H2/h capacities are quoted at around $30 per Nm3/h production capacity. It can be assumed that the costs in stationary reformers will be lower still. What remains unclear is the question of for what production quantities these costs can be assumed to be relevant.

 

3.3 Production from Biomass

No process for hydrogen production from biomass is presently commercially available. Depending on the method, the processes are in various stages of research and pre-development. The different methods for hydrogen production are: production from solid biomass (e.g. pellets of dedicated energy crops, waste biomass), fermentation of liquid manure and biological hydrogen production. The beauty of direct H2 production from biomass is that renewable energy sources can be utilized without the need for electrolysis thus leading to a higher system efficiency and a more favorable overall result.

- Steam gasification of biomass

Process description: Along with the commercial methods of biomass utilization, this can be used to produce hydrogen via pyrolysis and gasification. Coke, methanol and primary gases are obtained in the first stage. In the second, the reaction with (air) oxygen and/or steam results in a mixture of 20% H2, 20% CO, 10% CO2, almost 5% CH4 and 45% N2. Using pure oxygen or steam only eliminates the nitrogen component. The transformation of this gas mix into a hydrogen rich gas is named, depending on the feedstock, as gasification (solids) or reforming (gas). Endothermic reactions of hydrocarbons with steam create synthetic gasses with high hydrogen content, whereby the so called shift reaction (CO + H2O -> CO2 + H2) can be used to alter the molar CO/H2 ratio. The hydrogen content of the gas is determined by the process parameters pressure and temperature.

 Before the actual gasification, the organic substance breaks up under the application of heat into coke, condensates and gasses. This preliminary stage is known as thermal decomposition or pyrolysis. The presence of oxygen in the reactor leads to partial oxidation of the intermediate products rather than reformation.

When will the process be available? Based on the widespread experience from the gasification of coal, processes for the gasification of biomass could be commercially available within the next 2 - 3 years, with the testing of a prototype expected somewhat earlier. Autothermal wood gasifiers with oxygen injection with varying sizes up to 100 t daily throughput have already been demonstrated. 

Who is developing the process? Since 1977 the firm Batelle has been developing an allothermal gasification process whose commercialization is expected shortly. In Germany, DMT (Deutsche Montan Technologie) is predominantly engaged in the development of a marketable allothermal gasifier, the actual commercialization of which will probably be carried out by others. A third allothermal gasification process is being developed in the USA by MTCI (Manufacturing and Technology Conversion International). Autothermal gasification processes are being developed by many European firms such as Ahlström, Gotaverken, HTW und Lurgi GmbH.

- Biomass fermentation

Process description: From high moisture content biomass or liquid manure Biogas can be produced via methane fermentation. This gas contains high CO and CH4 components. Although it contains hardly any hydrogen, this gas can be used as a fuel for advanced high temperature fuel cells (MCFC), whereby methane reformation takes place directly at the electrode due to the high temperatures (~ 650°C).

Who is developing the process? The fermentation process of biomass is commercially tested and available. The combination of the process for the production of hydrogen has not, as far as is know, been carried out up to now. Only in connection with the molten carbonate fuel cell would such an interesting option appear, as this process offers high electricity generation efficiency with reduced plant complexity. This application is being envisaged by MTU Friedrichshafen among others.

When will the process be available? Biogas plants are already commercially available. The combination with an MCFC will be developed to the point of market readiness in the coming years, whereby a market entry is expected around the turn of the century. The testing of pre-series-production products is however already expected to occur in 1997.

- Biological hydrogen production

Process description: There are various biological processes by which hydrogen is released or appears as an intermediate product. One can basically separate these into two process types: Photosynthesis, for which light is required and fermentation, which occurs in darkness. As there is still no sign of a market in this area, a detailed description will not be given.

When is the Process available? The use of biological processes for hydrogen production is presently at the point of technical system development, whereby there also still remain many unresolved biochemical fundamental questions. At the moment an Algae-bacteria-system seems to be the best candidate for the first technical application. Investigations carried out so far indicate that hydrogen production costs of 25 Pf/kWhH2 or less are achievable. Based on results achieved so far, current research programs plan to be able to demonstrate technical feasibility within the next 2 years, in order to make it possible for interested firms to commence their own involvement . Presently it is expected that within the next 5 to 8 years a market ready concept can be achieved.

 

3.4 Production from electricity by means of electrolysis 

Of the various procedures for the production of hydrogen from water, electrolysis is presently, and for the foreseeable future, the only one of practical importance. Water electrolysis in its conventional form, alkaline electrolysis, has been in commercial use for over 80 years.

Up until the end of the eighties, only a vanishingly small portion of approximately 0,5 - 1 Bil. Nm3/a that is 0,1-0,2% of the world production of hydrogen, was directly produced by electrolysis, mainly in connection with hydro power. Even this small quantity is declining since the electrolytic production of hydrogen for fertilizer manufacture is no longer competitive with production from natural gas due to falling energy prices. Because electrolytically produced hydrogen is created indirectly via the energy carrier 'electricity', this process is only economically feasible in places where electricity can be extremely cheaply generated. This is generally only possible with large scale hydro systems (Egypt, Brazil, Iceland, Canada, Norway, Zaire), or with excess energy from the primary and secondary control of existing power station capacity with significant nuclear component (France, Belgium, Switzerland, some German Electric Utilities). 

Principle description: The decomposition of water by electrolysis consists of two partial reactions that take place at the two electrodes. The electrodes themselves are separated by an ion conducting electrolyte. Hydrogen is produced at the negative electrode (cathode) and oxygen at the positive electrode (anode). The necessary exchange of charge occurs through the flow of ions. In order to keep the produced gasses isolated, the two reaction areas are separated by an ion conducting separator (diaphragm). The energy for the water separation is supplied in the form of electricity. 

The following section is intended to describe the electrolysis processes specifically optimized for hydrogen production. These processes are the well tested low pressure electrolysis method and two processes still in the development phase, namely the high pressure and the high temperature processes. The chlorine-alkaline electrolysis is not dealt with here as this is a process primarily intended for chlorine production and is therefore not of such interest in the present context.

 

3.4.1 Present state of the art 

- Conventional Water Electrolysis

Process Description : Conventional alkaline electrolysis works with an aqueous alkaline electrolyte. The cathode and anode areas are separated by a micro-porous diaphragm to prevent mixing of the product gasses. Presently in Germany, conventional unpressurised electrolysis utilizes new materials that replace the previously used asbestos diaphragm. With output pressures of 0.2 - 0.5 MPa these processes can reach efficiencies, related to the lower heating value of hydrogen, of around 65%. Newly developed diaphragms and membranes from other materials demonstrate, through their good turn off characteristics, relatively good reliability when subject to fluctuating operating conditions. They are therefore applicable in conjunction with renewable energy technologies.

Who offers Electrolysers? Conventional water electrolysers have been in use commercially for many decades. Units with capacities from 1 kWel to 125 MWel are available. The Electrolyser Corporation Ltd. (Canada) and Norsk Hydro Electrolysers AS (Norway) are well established manufacturers of conventional elctrolysers, offering units with very high capacity. Several manufacturers have also established themselves in the 1 - 100 kW range in Europe (e.g. Ammonia Casale, ELWATEC, Hidroenergia VCST (up to 1 MPa), vHS (von-Hoerner-System; up to 3 MPa but also unpressurised).

What is the cost of such electrolysers? Large commercial electrolysers cost between 500-1000 DM/kWel but smaller plants are considerably more expensive. The smallest 1 kWel electrolysers can cost up to 10,000 DM with the price only falling to the 500 DM/kWel figure in the MW range. Operating efficiencies lie in the 50-60% range for the smaller electrolysers and around 65-70% for the larger plants.

 

3.4.2 What is presently under development

- High pressure water electrolysis

Process description: Through special material choice and optimization, high pressure water electrolysis allows the generation of hydrogen at pressures up to 5 MPa. The processes under development attempt to find an appropriate capacity optimization that will also allow for a problem free connection of the electrolyser with a fluctuating current supply (e.g. Wind or PV connection for isolated plants)

Who offers high pressure electrolysers ? The most important development work to mention is that being carried out by GHW (Gesellschaft für Hochleistungswasserelektrolyseure) for the commercialization of a high performance electrolyser with output pressures up to the 5 MPa level. The goal of these efforts is to reach, along with the high output pressure, an appropriately optimized operating efficiency applicable for strongly varying load. Final commercialization is expected within the next 2 - 3 years. In the field of small capacity units (under 100kW), vHS has the appropriate equipment to offer.

What do such electrolysers cost? The small units from vHS are already available for prices of approx. 10,000 DM/kW. It is expected that the optimised high capacity electrolysers from GWH will be offered at prices around the 2000 - 2500 DM/kW mark. However, no binding statements have been made up to now.

- High temperature water electrolysis

Process description: High temperature electrolysers were under discussion as an interesting alternative several years ago. The main advantage of such a process would be to obtain part of the energy required for water separation in the form of high temperature heat and thus complete the electrolysis with a lower electricity consumption. The discussions focussed on the use of heat from solar concentrators or waste heat from power stations for this purpose. Corresponding investigations were carried out by DLR in Stuttgart. Interest in this method of electrolysis has however declined in the last few years and as such no further discussion at this point is warranted. 

Chapter 4

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