Well-proven technologies vital in race to find sustainable and secure sources of energy
According to a recent report from the Institute of Mechanical Engineers ‘ENERGY FROM WASTE, A WASTED OPPORTUNITY’, waste should not be regarded as problematic but rather as a valuable resource to help the UK meet its national and regional environmental targets and commitments by developing of a network of Energy from Waste (EfW) plants.
The report also outlines how the UK needs to find sustainable and secure sources of energy, using reliable, well-proven technologies. While the conversion of waste-to-energy is controversial and dismissed by some as not commercially viable, a new British venture, Waste2Tricity, has launched to bring cutting-edge technology to market and prove that waste-to-energy is viable – efficient and economical – using a unique combination of new generation alkaline fuel cells with plasma gasification and other existing proven technologies.
Lord Moonie (Dr. Lewis Moonie), chairman elect of Waste2Tricity, said: “Our system will have significant environmental and cost benefits over other methods. We have the technology to change the disposal of waste from being an enormous environmental headache into a commercially viable proposition that provides local authorities or energy sink companies with a revenue stream and increases the amount of renewable electricity, not only in this country but globally as well.”
Waste2Tricity’s unique advantage will be its exclusive rights – within the plasma gasification application – to new generation fuel cells under development by AFC Energy plc, a company with which Waste2Tricity has close links. This unique integration of alkaline fuel cells is projected to increase the net output of electricity by a minimum of 60% over an ICE (internal combustion engine) and by over 130% for a steam turbine. This will result in the most efficient and economic means of converting waste-to-energy, generating 2100kWh of electricity from every tonne of municipal solid waste (MSW) currently sent to landfill. Waste2Tricity estimates that the cost of generating electricity could be less than 3p per KWh (at today’s prices).
The company will take carbon based waste, either MSW or waste from business and industry, and convert it into clean electricity, playing a major role in the reduction of rubbish going to landfill and potentially make a significant contribution to the UK electricity supply. Under Waste2Tricity’s plans, renewable energy plants could be developed at a cost as low as £250,000 per MW of capacity.
Of the 35-40 million tonnes of biomass sent to landfill each year, Waste2Tricity believes it could initially process around 20%. By using waste with a short-cycle biogenic composition, electricity generated by the Waste2Tricity process will be eligible for double ROCs, under legislation effective from April 2009, helping electricity suppliers meet their renewable targets. The company’s initial target is to build a 50 000 tonne pilot plant that will integrate the available technologies in two stages.
Low-risk two-stage approach
Waste2Tricity will develop its process in two stages. Stage one uses known, proven and commercial applications while Stage two will introduce an emerging technology that will increase the efficiency and net output of a waste to electricity facility by 60%+.
First, a homogenised waste stream is obtained, either in conjunction with an existing waste management company, allowing the installation to be established on an existing site, or from an industrial customer, such as supermarket chain, that back hauls its waste to a central depot. Ideally, a mix made up of 35% organics, 35% paper and cardboard, 25% plastic and 5% other materials works best and if sorted in advance, the mix can be checked before entering the gasification process.
The waste stream goes into the first process, the same for both stages, which is plasma gasification. Waste2Tricity is to use a plasma gasification process from Alter-NRG Westinghouse, similar to that used at a plant in Japan.This process uses plasma torches at 8000°C to create a bed of hot gas, which, with limited oxygen, causes the waste to convert to its gaseous components, called syngas. The syngas is H2, CO and CO2, with the energy in the H2 and CO. The remaining by-product is a vitrified slag, an inert material that can be used for aggregates in road building. The syngas is then processed in one of the two stages. “The gasification process has been confirmed by advanced waste treatment technology specialists, Juniper Consulting,” explains lead consultant, Howard White. “We’re also in discussions with US firm Air Products to secure systems to prepare syngas from the gasification process ready for use in fuel cells.”
The syngas is treated to remove certain contaminants and is then put into internal combustion engines where energy in the syngas is converted into electricity at about 30% efficiency. During the second stage, the syngas is cleaned more stringently. The energy in the CO is moved into hydrogen by way of a gas water shift reaction, whereby steam at 200°C is mixed with the syngas. The oxygen in the H2O binds with the CO leaving H2 and CO2.The H2/CO2 mixture is then put through a PSA system (Pressure Swing Adsorption), which splits the H2 into a sufficiently pure stream to operate the next phase.
Alkaline Fuel Cells
AFC Energy’s alkaline fuel cells will then be installed to increase the energy efficiency conversion from the syngas stage to electricity in excess of 60% compared to the ICE stage 1.
White explains: “Alkaline fuel cell technology is the most well-known and proven of all fuel cell technologies, as used today by NASA. Fuel cells developed by AFC Energy offer three unique advantages when compared to other systems. First, as low temperature units standard engineering plastics are used in construction, this and careful engineering design means low cost. Second, the stack has been replaced by a serviceable cartridge, allowing a five-year fit for purpose warranty. Third, at 55%, alkaline fuel cells have the highest conversion efficiency of any fuel cell system so their deployment will produce more electricity than any other system type.
Existing landfill waste streams can be diverted and with less landfill, the future emission of undesirable greenhouse gases can be much reduced from that source. In terms of reducing carbon emissions, it’s a more efficient form of electricity generation than compared to existing coal-fired, most renewable or other waste-to-electricity models such as incineration. In contrast to incineration, plasma gasification emits fewer pollutant gases, and no fly ash or waste ash. Harmful particles, such as dioxins, are destroyed in the process and the by-product, inert vitrified slag, if used as road-building aggregates, will reduce demand for gravel extraction.
“We are launching the company purely from a commercial perspective,” explains Lord Moonie. “As part of our strategy, we have the support of some leading players in their fields. This includes a major waste management company who we hope will supply a homogenous stream of refuse-derived fuel, or a homogenised mix of waste and are also in discussions to establish a pilot plant for 50,000 tonnes of throughput.” The facilities can be built on existing landfill sites, reducing the likelihood of opposition to their construction, and can utilise existing infrastructure such as roads built for waste transport. Ideally this would also be close to electrical energy demand ‘sinks’ to minimise transmission losses via a centralised grid.