This post is being made to 1) explain the technology that is being proposed to produce and distribute hydrogen and 2) to help both my readers and myself understand whether the hydrogen economy is the right choice for our future energy requirements or whether some alternative technologies would make a better choice. The material has been taken from the two resources noted at the end of the post, with very little editing, except to use only the pertinent excerpts. The Program Plan is a very long document and I have tried to use only the portions that will help us understand the technology. Please also see my comments at the end of the post.
There are many long-term options for providing hydrogen as a fuel of the future, but coal is the leading contender to provide a hydrogen source in the near term. In his remarks on the Department of Energy’s (DOE) hydrogen research activities at the National Hydrogen Association Annual Conference in March 2005, Secretary of Energy Samuel Bodman stated “The progress that DOE and the automotive and energy industries have made so far has us on the path to an industry commercialization decision in 2015. If our research program is successful, it is not unreasonable to think we could see the beginning of mass market penetration by 2020.”
"While someday we may be able to produce hydrogen by breaking up water molecules in association with the high-temperature heat from nuclear power reactors, or through renewable energy technologies," said Chris Shaddix, principal investigator for clean coal combustion at Sandia, "right now the most cost-effective way to produce hydrogen is with coal."
Two approaches to burning coal now are under study. The first, oxy-combustion, combines coal with pure oxygen. The second, gasification, burns coal only partially to create a fuel gas.
Oxy-combustion is driven by concern over emissions of CO2 and other pollutants. Burning coal in oxygen is a near-term solution that can produce exhaust streams that are close to pure CO2, Shaddix said. Harmful pollutants like nitrogen oxides, sulfur compounds and mercury are virtually eliminated.
Companies in Japan, Canada, Germany and elsewhere favor oxy-combustion and are building pilot plants. U.S. companies tend to favor gasification technologies, which offer higher efficiency and low pollution formation. Gasification technologies are the only ones described in this post.
The gasification process combines the coal with steam in a hot environment to produce a syngas (synthetic gas) composed mostly of carbon monoxide (CO) and hydrogen. Once the syngas is produced, it can be burned directly in a turbine to produce power, or further reacted with more steam to shift the remaining CO to CO2 and produce more hydrogen. The CO2 can be stored in oil and gas fields and the hydrogen can be used for the many applications that make up the hydrogen economy-- such as to power a car in an engine or a fuel cell, to power a turbine to produce electricity or to power a stationary fuel cell to make electricity.
There are two key hydrogen production pathways for the program – the central production pathway (gaseous hydrogen) and the alternate hydrogen production pathway (hydrogen-rich liquid fuel and substitute natural gas (SNG)).
For the central production pathway the goal is to demonstrate by the end of 2015: 60 percent efficient, near-zero emissions, coal-fueled hydrogen and power co-production facility which reduces the cost of hydrogen by 25 percent compared to current coal-based technology. In this pathway hydrogen is produced at a large, central facility by converting coal into hydrogen. These plants may or may not co-produce electricity or other products, and will be designed to allow capture and ultimately sequestration of CO2.
Parallel to developing the hydrogen production technology, this pathway is to, by the end of 2012 , in collaboration with EERE and the Fossil Energy Office of Oil and Natural Gas, identify, develop, and demonstrate the feasibility of delivering hydrogen, hydrogen-natural gas mixtures, or synthesis gas using existing natural gas pipelines or dedicated, hydrogen-only pipelines.
In the alternate production pathway hydrogen-rich, zero-sulfur liquids and SNG are produced from coal at a central location. Hydrogen-rich liquids and SNG would be transported through the existing petroleum or natural gas pipeline distribution networks to sub-central or distributed locations where they can then be reformed into hydrogen near the end-user.
At sub-central plants, the liquid fuels or SNG would be reformed into hydrogen. This hydrogen would be delivered to the end-user local filling stations by tube trailer where it would be used in fuel cell vehicles (FCVs) or hydrogen internal combustion engine vehicles (ICEVs). At distributed plants, liquid fuels or SNG would be reformed into hydrogen at the refueling station. This pathway is envisioned as an interim pathway until a widespread hydrogen delivery infrastructure is available.
To examine the state of the technology for producing hydrogen from coal and future developmental paths, after examining many possibilities, DOE developed three scenarios to form the basis for going foreword. It should be kept in mind that a kg of hydrogen contains approximately the same amount of energy as a gallon of gasoline.
Today, hydrogen is produced from coal by gasification followed by processing of the resulting synthesis gas, and is used primarily to produce hydrogen for the production of ammonia for fertilizer.
In case 1, present technology, the coal is first gasified with oxygen and steam to produce a synthesis gas consisting mainly of carbon monoxide (CO) and hydrogen (H2), with some carbon dioxide (CO2), sulfur, particulates, and trace elements. O2 is added in less than stoichiometric quantities so that complete combustion does not occur. This process is highly exothermic, with temperatures controlled by the addition of steam. Increasing the temperature in the gasifier initiates devolatilization and breaking of weaker chemical bonds to yield tars, oils, phenols, and hydrocarbon gases. These products generally further react to form H2, CO, and CO2. The fixed carbon that remains after devolatilization is gasified through reactions with O2, steam, and CO2 to form additional amounts of H2 and CO.
Minerals in the feedstock (ash) separate and leave the bottom of the gasifier as an inert slag (or bottom ash), a potentially marketable solid product. The fraction of the ash entrained with the syngas, which is dependent upon the type of gasifier employed, requires removal downstream in particulate control equipment, such as filtration and water scrubbers.
The temperature of the synthesis gas as it leaves the gasifier is generally slightly below 1,900 ºF. With current technology, the gas has to be cooled to ambient temperatures to remove contaminants, although with some designs, steam is generated as the synthesis gas is cooled. Depending on the system design, a scrubbing process is used to remove HCN, NH3, HCl, H2S and particulates that operates at low temperatures with synthesis gas leaving the process at about 72 ºF. H2S, and COS, once hydrolyzed, are removed by dissolution in, or reaction with, an organic solvent and converted to valuable by-products, such as elemental sulfur or sulfuric acid with 99.8 percent sulfur recovery. The residual gas from this separation can be combusted to satisfy process-heating requirements.
This raw clean synthesis gas must be re-heated to 600–700ºF for the first of two water gas shift (WGS) reactors that produce additional hydrogen through the catalytically assisted equilibrium reaction of CO with H2O to form CO2 and H2. The exothermic reaction in the WGS reactor increases the temperature to about 800 ºF, which must be cooled to the required inlet temperature for the second WGS reactor in the range of 250–650 ºF, depending on design. The WGS reaction alters the H2/CO ratio in the final mixture. Overall, about 70 percent of the feed fuel’s heating value is associated with the CO and H2 components of the gas, but can be higher depending upon the gasifier type. Hydrogen must be separated from the shifted gas containing CO2, CO, and other trace contaminants, and polished to remove remaining sulfur, CO, and other contaminants to meet the requirements for various end-uses (e.g., fuel cell vehicles).
The process assumes that a Texaco quench gasification system with conventional acid removal and a pressure swing adsorption (PSA) system for hydrogen recovery are used. All of the CO2 is removed prior to the PSA unit, compressed to 200 bars (2,900 psi), and sequestered for an additional cost of $10 per ton of carbon. In this configuration, 87 percent of the carbon in the feed is sequestered and the required selling price (RSP) of the hydrogen is $8.18/MMBtu ($1.10/kg).
Case 2 represents a process for hydrogen production from coal that uses advanced gasification technology, advanced membrane technology for hydrogen separation with CO2 removal, and carbon sequestration.
In this configuration, advanced E-gas gasification with hot gas cleanup is used in combination with a ceramic membrane system operating at nearly 600 ºC (1,100 ºF), which is capable of shifting and separating hydrogen from clean synthesis gas. It is assumed that 90 mole percent of the hydrogen in the synthesis gas is recovered in this membrane system, assumed to be similar to the diffusion membrane system under development by the Inorganic Membrane Technology Laboratory at Oak Ridge National Laboratory (ORNL).
The hydrogen produced in Case 2 is separated at high pressure, with the hydrogen product produced at low pressure. The hydrogen must be compressed to various pressures depending on its use or storage. The remaining tail gas, containing mostly CO2 with some CO and H2, is combusted with O2 in a gas turbine to provide power for the plant. O2 is used so that a concentrated stream of CO2 is produced for sequestration. Heat is recovered from both the gas turbine exit gas and from the hot hydrogen in heat recovery steam generators (HRSGs), where the steam produced is sent to a steam turbine to provide additional power. This efficiency improvement is due to improved gasifier design combined with hotgas cleanup that eliminates the need to cool and then reheat the synthesis gas, combined with efficient hydrogen membrane separation incorporating the WGS reaction. The capital cost for the facility is $425 million, with the required selling price of hydrogen estimated at $5.89/MMBtu ($0.79/kg). The amount of hydrogen produced is 158 million scfd with 25 MW of excess power.
Case 3, is an example of an advanced co-production concept plant that is expected to be developed by 2015. The concept of this co-production plant is similar to the FutureGen prototype fossil fuel power plant of the future, and produces 153 million scfd of hydrogen and 417 MW of excess power. This case will employ advanced gasification, combustion and turbine systems, membrane separation, and carbon capture and sequestration in a co-production plant producing hydrogen and electric power using technologies similar to Case 2. In Case 3, a separate gasification train is utilized specifically to produce clean electric power. These highly efficient hydrogen and electricity coproduction plants could provide significant additional reductions in the cost of hydrogen, reducing the cost to $4/MMBtu ($0.54/kg) assuming power is sold at $53.6/MW-hr. The use of solid oxide fuel cells to generate electricity from hydrogen also can be introduced in these plants. In this configuration, hydrogen production costs can be reduced to about $3/MMBtu ($0.40/kg), depending on the price of electric power.
The areas of research that are required to support this program are:
- Advanced WGS reaction systems
- Advanced membrane separation systems (for hydrogen separation)
- Advanced CO2 separation systems
- Polishing filters (ultra-clean hydrogen purification systems)
- Advanced adsorption and solvent systems
Details of this research are beyond the scope of this post, but are explained in more detail in the Program Plan document. They are not trivial developments and successful development of these items by 2015 is a challenging goal.
My main concerns have been 1) Is the most efficient use of our coal resources? 2)Is it cost effective? and 3) When is it reasonable to expect that the proposed technologies can be put in place? I see a reasonable pathway to produce enough electrical power from coal, nuclear and renewable energy. The comparison that I would like to see made is to using plug-in electric and all electric cars vs hydrogen fuel cell cars. The ICE's in the plug-ins could be powered by ethanol or synthetic diesel if our fossil supplies are ever that low or if our environmental concerns become so dire as to require not burning fossil fuels in plug-in vehicles. I would like you, my readers, to comment on this for a few days before I make my comments.
Energy Department Examines Hydrogen-Production Benefits of Coal, Bureau of International Information Programs, U.S. Department of State, April 5, 2006
Hydrogen fro Coal Program, Research, Development and Demonstration Plan for the period from 2004 through 2015, US Department of Energy, Office of Fossil Fuels, September 26, 2005