How do hydrogen and synthesis gas (syngas) differ? Why are they considered more environmentally friendly than many existing fuel sources?

Hydrogen is considered a future replacement for hydrocarbons in the energy sector because, as well as being a clean fuel that produces low pollution levels when burnt, it also has more energy per unit mass than any other fuel. Among its many uses, hydrogen can be converted into electricity using fuel cells, and is also an important feedstock in the chemical industry and petroleum refining.

Syngas is composed mainly of hydrogen and carbon monoxide. It is used for electricity generation and as an intermediate when producing synthetic petroleum for use as a fuel or lubricant, or directly as a fuel for internal combustion engines.

Could you discuss your fundamental research objectives in the context of hydrogen and syngas production?

Gasification-based systems are often considered efficient and environmentally friendly technologies for the production of low-cost electricity, heat and chemical products. For instance, coal gasification is the process of producing syngas from coal, water, air and/or oxygen as a gasifying agent. We know that inert porous media combustion of rich and ultra-rich mixtures creates a situation in which partial oxidation and/or thermal cracking of

hydrocarbons (gas fuels) takes place. Therefore, we have worked on a combination of inert porous media combustion and the gasification process. Named ‘hybrid filtration combustion’ this is a new technology for hydrogen or syngas production based on partial oxidation of hydrocarbon fuels in porous media composed of inert material and solid fuel particles.

Ultimately, the aim is to create a new industrial reactor for simultaneous conversion of solid and gaseous fuels to hydrogen and syngas. It will be a new commercial gasifier (of wood or coal).

Of this work, can you summarise your most significant discoveries over the past few years?

Our most striking finding to date has been that the combined inert porous media combustion and gasification process technique generates both hydrogen and syngas, as well as heat. This result suggests that hybrid filtration combustion can be used to reform gaseous and solid fuels into hydrogen and syngas. We have also shown that the technique can be used to convert solid and gaseous fuels to hydrogen and syngas simultaneously, and that the method allows solid fuel reforming using air and/or steam as a gasifying agent.

Has your focus shifted over the course of your research?

At first, our research was focused solely on hydrogen and syngas production using inert

Dr Mario Toledo offers a snapshot of his work to improve the production of synthesis gas and hydrogen – two key energy sources for the 21st Century

Hydrogen and syngas: new converts

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DR MARIO TOLEDO

COAL, NATURAL GAS and oil continue to dominate the energy sector, accounting for more than 85 per cent of all energy consumed by modern society. However, this situation cannot continue indefinitely. Fossil fuels are being depleted 100,000 times faster than they are being replenished and are well known to be some of the biggest contributors to global pollution.

Numerous initiatives and regulations at every level of society aim to tackle this energy crisis; from individual organisations pledging to divest from fossil fuels to generous incentives for citizens to build rigorously energy-efficient passive homes. While such measures offer motivation to move away from the current reliance on hydrocarbons, the fact remains that converting to alternative sources wholesale is both complicated and costly.

CLEAN ENERGYAiming to bring the mass move to alternative, renewable energy a step closer to reality is the Research Group in Porous Media Combustion based within the Department of Mechanical Engineering at the Federico Santa María Technical University in Chile. Group Leader Dr Mario Toledo focuses his team’s efforts on two specific clean energy sources: hydrogen and synthesis gas (syngas).

Hydrogen has long been touted as a future replacement for hydrocarbons because it is a clean fuel that produces little pollution when burnt and can be converted into electricity through the benign chemical reactions at the heart of fuel cells. Mainly consisting of hydrogen and carbon monoxide, syngas is a type of biofuel that can be produced from a variety of different materials that contain carbon. Its main current use is in the production of other fuels, specifically methanol and diesel, but in industry, waste gas is often captured and used to produce syngas for various purposes, including as a fuel in internal combustion engines or for cogeneration of heat and electricity. As such, these two gases represent promising clean energy sources.

TODAY’S TECHNOLOGYDespite hydrogen being the most abundant chemical element in the Universe, on Earth

it is mainly found in water molecules and various hydrocarbons. As a result, the extraction of pure hydrogen via simple and cost-effective processes is a priority if it is to be used as the clean energy source of the future. To produce useful quantities of either hydrogen or syngas, the present paradigm relies on methane (natural gas) steam reforming. The central element of this process is a device called a reformer, which reacts steam at high temperatures with methane. However, the technique has significant disadvantages. To achieve high methane conversion, the process has to be carried out at high reactor temperatures, leading to concomitant high energy consumption levels. In addition, carbon dioxide is generated during methane production, contributing to greenhouse gases and subsequent global warming.

Another way to create syngas is through coal gasification. This process mixes pulverised coal feed with an oxidant such as air or steam. The gasifier then partially oxidises the product to produce hydrocarbons that react to generate carbon monoxide and hydrogen. Gasification systems can generally take a variety of carbon-based materials, including coal, petroleum coke, biomass, and municipal and hazardous wastes, and are cheap, efficient and environmentally friendly methods to produce electricity, heat and chemicals.

A HYBRID SOLUTION?Toledo and colleagues have studied the coal gasification process keenly and have struck upon an innovative new method of producing hydrogen and syngas. Combining the benefits of gasification with inert porous media combustion – the process of propagating a chemical exothermic reaction zone in a chemically inert solid under filtration of a gaseous fuel and oxidiser mixture – their new method has been dubbed ‘hybrid filtration combustion’. “The high reaction temperature inside porous media allowed high conversion of different solid fuels into hydrogen and syngas. It is a clean system, compact reactor, low cost and also generates heat,” Toledo enthuses. A crucial advantage of the technique is that it allows the simultaneous conversion of both solid and gaseous fuels to hydrogen and syngas.

The Research Group in Porous Media Combustion at the Federico Santa María Technical University, Chile, has created a hybrid filtration combustion technique that could compete with conventional gasification and catalytic processes to produce alternative and clean energy sources

Creating a better alternative

porous media combustion, but then we refined the technique and generated new porous media composed of uniformly mixed aleatory solid fuel and inert material particles, with promising results.

Under what conditions have you identified maximum syngas production?

Using hybrid filtration combustion of natural gas and coal, we found that the maximum hydrogen conversion for the hybrid coal and alumina bed was ~55 per cent for a volumetric coal content of 75 per cent.

When producing syngas from coal in the presence of steam using filtration combustion, we managed to produce the maximum amount of syngas under the following conditions: 80 per cent steam concentration with 8 l/min of air flow and 50 per cent volume fraction of coal in the hybrid mixture, achieving concentrations of 26.92 per cent of hydrogen and 17.08 per cent of carbon monoxide; 70 per cent volume fraction of coal with 20 per cent steam and 8 l/ min of air flow reaching an 11.81 per cent and 17.12 per cent volume of hydrogen and carbon monoxide, respectively; and 10 l/min of air flow with 50 per cent volume fraction of coal and 20 per cent of steam, achieving 10.13 per cent and 11.60 per cent of hydrogen and carbon monoxide, respectively.

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HYDROGEN AND SYNGAS PRODUCTION

OBJECTIVETo create a new industrial reactor for simultaneous conversion of solid and gaseous fuels to hydrogen and syngas.

KEY COLLABORATORSSebastian Caro, Research Group in Porous Media Combustion, Department of Mechanical Engineering, Federico Santa María Technical University, Chile

Professor Khriscia Utria, Universidad Autónoma Del Caribe, Barranquilla, Colombia

Professor Alexei Saveliev, Department of Mechanical and Aerospace Engineering, North Carolina State University, USA

Professor Janet Ellzey, Department of Mechanical Engineering, University of Texas at Austin, USA

Dipl.-Ing Vojislav Jovicic, Institute of Fluid Mechanics, Germany

Dr Jacques Bingue, Chief Executive Officer, Innovative Energy Solution, USA

FUNDINGFondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT), Chile

CONTACTDr Mario ToledoGroup Leader and Principal Investigator

Federico Santa María Technical UniversityAvenida España 16802390123 ValparaisoChile

T +56 976 971 013

E mario.toledo@usm.cl

www.combustion.mediosporosos.usm.cl

DR MARIO TOLEDO gained experience in mechanical engineering and his PhD in Engineering Sciences from the University of Santiago, Chile.

He has since moved to the Federico Santa María Technical University where he leads the Research Group in Porous Media Combustion and is Head of the Department of Mechanical Engineering.

INTELLIGENCE

The team has experimented with numerous porous media and different wave velocities, combustion temperatures, and hydrogen and carbon monoxide concentrations in an attempt to optimise hybrid combustion of gas and solid fuels. Some of the porous media they tested included uniformly mixed coal and alumina spheres, wood pellets and alumina, and polyethylene pellets and alumina. Different gaseous fuels were used with these media; in these cases, natural gas, butane and propane, respectively.

Results showed that the combustion of all gases inside the various porous media produced a higher syngas yield compared to equivalent filtration combustion in an inert porous medium. Furthermore, the researchers found that a maximum hydrogen conversion of 55 per cent was possible for the hybrid coal and alumina bed at a volumetric coal value of 75 per cent.

FURTHER REFINEMENTFurther to exploring the reformation of gaseous and solid fuels into hydrogen and syngas, the team has also looked into liquid fuels. From these experiments, the researchers achieved maximum conversion of hydrogen of 43 per cent and 30 per cent for methanol and ethanol, respectively. The group will next explore the potential of heavy oil as a liquid fuel in the project ‘Generation of hydrogen from the partial oxidation of heavy fuel oil’.

Now at the stage of refining their processes, another investigation has looked into the

effect of adding steam during filtration combustion of natural gas-air mixtures, finding that hydrogen yield increases with an increase of steam content. Utilising this new knowledge, the researchers have since looked at biomass pellets originating from cereal plantations and the forestry industry – some of the most common residual biomass sources in Chile. Made from oat cane, wheat cane, shining gum (Eucalyptus nitens) and insignis pine (Pinus radiata), the biomass pellets were mixed with alumina spheres and packed into a reactor. Findings suggested that wheat cane was the optimal material, obtaining 50 per cent more hydrogen than the base level.

BACKING UP EXPERIMENTSNot only have the Chilean researchers produced experimental results demonstrating the potential of hybrid filtration combustion, they have also described the process physically and mathematically. Formulating a mathematical model, along with defining assumptions that would allow a computational approach and incorporating adjustable boundary and initial conditions, the team has provided a solid basis for moving forward with hybrid filtration combustion.

The next step will be to seek funding in order to take the Chilean team’s research from the lab bench to a full-scale industrial demonstration reactor: “I am developing a new continuous reactor for solid and gas fuel reforming – a reverse flow burner,” Toledo reveals.

FURTHER READING

S Caro, D Torres and M Toledo, 2015, Syngas production from residual biomass of forestry and cereal plantations using hybrid filtration combustion, International Journal of Hydrogen Energy, 40, 2568-77

R Araya, K Araus, K Utria and M Toledo, 2014, Optimization of hydrogen production by filtration combustion of natural gas by water addition, International Journal of Hydrogen Energy, 39, 7338-45

K Araus, F Reyes and M Toledo, 2014, Syngas production from wood pellet using filtration combustion of lean natural gas-air mixtures, International Journal of Hydrogen Energy, 39, 7819-25

Flame combustion in porous media.

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