Whether or not fossil fuels are running out the world is looking for alternative sources of supply because of the effect of burning carbon based fuels on the environment and the climate. Huge efforts have gone into seeking renewable sources and Western governments have handed over vast subsidies to very expensive and unreliable sources like solar and wind. In the UK sunshine hours are too limited, particularly in winter to make solar a viable source except for a limited proportion of our needs. Wind is even more unreliable as it simply does not blow all the time. As I look out my window this autumn afternoon I see only a slight rustle on the autumn leaves still on the trees. If I was dependent on wind I would be very cold this evening eating my sandwiches and missing my favourite TV programmes. So the search goes on.
This year I have done quite a lot of consulting in the set-up of the Advanced Propulsion Centre UK (APC), a new initiative set up with a budget of £1 billion over ten years, half from the automotive industry and half from central government, with a vision to put the UK at the forefront of low carbon propulsion technologies. I intend to write a blog dedicated to the APC when it’s full plans are public but in the meantime wanted to write about a few of the exciting developments I have seen in alternative fuels at some of our universities.
Hydrogen fuel is a zero-emission fuel which uses electrochemical cells, or combustion in internal engines, to power vehicles and electric devices. It can potentially be mass-produced for passenger vehicles and aircraft. Hydrogen is the lightest element in the universe. Since hydrogen gas is so light, it rises in the atmosphere and is therefore rarely found in its pure form, H2. In a flame of pure hydrogen gas, burning in the air, H2 reacts with oxygen, O2, to form water H2O as ‘every skuleboy know’ and releases heat.
Combustion heat enables hydrogen to act as a fuel. Nevertheless, hydrogen is an energy carrier, like electricity, not an energy resource. Energy first must first produce the hydrogen gas, and that production induces environmental impacts. Hydrogen production always requires more energy than can be retrieved from the gas as a fuel later on. Because it does not occur naturally on Earth in large quantities it takes a substantial amount of energy in its industrial production. It can be produced using electrolysis where electricity is run through water to separate the hydrogen and oxygen atoms. This may prove to be a viable way of producing at a low cost. The main method used to day is steam-methane reforming. Here the hydrogen is extracted from methane, itself plentiful, but this reaction causes side production of both carbon dioxide and carbon monoxide and we are back to square one.
Once manufactured, hydrogen is an energy carrier. The energy can be delivered to fuel cells or burned to run a combustion engine. In 2009 the Midlands Energy Consortium (Universities of Nottingham, Loughborough and Birmingham), were awarded £5.5 million to deliver the national Centre for Doctoral Training (CDT) in Hydrogen, Fuel Cells and Their Applications. The Centre will run until 2017. In 2013 the MEC universities formed collaboration with UCL and Imperial College London for a new CDT to run in parallel until 2021. Each CDT aims to deliver 50 PhD qualified professionals through industrially driven research and development programmes making it a location for persistent national research and development.
Last week I visited the University of Birmingham Centre for Fuel Cell and Hydrogen research and saw significant capabilities and laboratory facilities for the fabrication and testing of polymer-electrolyte and solid-oxide fuel cells, which can combine to produce hydrogen fuel, supporting companies such as Rolls Royce, Tata motors and Microcab; development of novel alloys for molecular hydrogen storage; and the production of bio-hydrogen. The Centre is actively involved in a number of vehicle fleet demonstration/showcase programmes utilising its on-campus hydrogen fuelling station. While there I had a test ride in a hydrogen-powered Microcab- a conventional vehicle adapted to run on hydrogen power. The experience was very similar to riding in an electric vehicle, the only noise coming from the wheels. On completing our journey I could see that the only emission from the exhaust pipe was water. This vehicle is one of a fleet of five hydrogen cars that will soon be trialled on the streets of Birmingham.
This week I visited the University of Nottingham which has similar facilities and a similar programme as part of the MEC. They have been studying the use of hydrogen for 12 years and are investigating solid state hydrogen storage materials for applications ranging from stationary (e.g. domestic energy) to vehicles (e.g. ICE and fuel cell automobiles) and to portable appliances (e.g. laptops and mobile phones). The research is focused on preparing and testing novel storage materials. World-leading chemists and material engineers are exploring storage systems that either chemically or physically absorb hydrogen and then release it via a change in temperature or pressure.
They are exploring solutions such as metal hydrides and complex hydrides, which chemically bond hydrogen and porous materials such as carbons and metal-organic frameworks, which act as sponges to physically absorb hydrogen. These types of materials are able to hold huge amounts of hydrogen and store it much more compactly and safely than by either liquid or compressed gas technologies. I did not have time for a test drive here but did see their hydrogen and electric vehicle recharging points.
Back at Birmingham they were just putting the finishing touches to a £1 million pound investment to research what may be an even more exciting new technology, Cryogenic Energy Storage or liquid air. This is the first national centre for Cryogenic Energy Storage and related thermal materials research. Air turns to liquid when refrigerated to around -194°C at ambient pressure, and can be conveniently stored in insulated but unpressurised vehicles. Exposure to heat – even at ambient temperatures – causes rapid re-gasification and a 700-fold expansion in volume, which can be used to drive a turbine or piston engine to do useful work. The main potential applications are in electricity storage and transport, and in both, liquid air can provide the additional benefit of waste heat recovery and/or cooling.
A number of engine concepts are being developed, but the focus is on the two closest to commercial deployment: the zero-emissions ‘power and cooling’ engine for truck and trailer refrigeration; and the diesel-liquid air ‘heat hybrid’ engine for buses, lorries and other commercial vehicles. The Dearman Engine Company is developing both applications, and its refrigeration engine begins on-vehicle testing this year and is scheduled for commercialised production from 2016.
One of the reasons for focussing on vehicle refrigeration is its current disproportionate impact on greenhouse gas emissions and local air pollution. In particular, trailer refrigeration units (TRUs) powered by auxiliary diesel engines can emit many times more nitrogen oxides and particulate matter than the lorry’s main drive engine or a diesel car because, it turns out, they are currently unregulated. Proposals to strengthen the regulations are expected to be adopted by the European Commission this year, and may come into force by 2019-21, but will make essentially no difference to the emissions of NOx and PM from TRUs.
The main conclusions of a report on the potential benefits and implications of introducing liquid air engines on commercial vehicles in Britain over the next decade can be summarised as follows:
There is a strong financial, air-quality, energy security and carbon reduction case for developing liquid air-equipped commercial vehicles.
Promising first applications include refrigerated trucks and trailers and heat hybrid buses and Lorries.
Liquid air vehicles could achieve significant cuts in local air pollution.
The rollout of liquid air vehicles could be fuelled entirely from existing spare capacity until at least 2019.
The development of liquid air vehicles would produce substantial economic, industrial and employment benefits.
There is effectively no constraint on liquid nitrogen supply in any British city that would prevent a pilot scheme or really deployment of liquid air vehicles.
There is a major opportunity for the industrial gas producers.[i]
In the case of hydrogen it could be that a combination of hydrogen storage and wind farms would work as the storage of ‘wrong time ‘ low or zero carbon electricity would overcome the downtime of the wind turbines. In the case of cryogenic energy storage I can’t wait to catch a bus operating on such energy in two years’ time.
[i] Liquid Air on the Highway
Liquid Air Energy Network. June 2014
Copyright David C Pearson 2014 All rights reserved