MSW Spells Self-Sufficiency for Isle of Wight Residents
U.K. island uses gasification technology to turn municipal solid waste into power , bringing it closer to energy independence.
In operation since February of this year, the gasification technology generates 2.3 megawatts of electricity, enough to power up to 3,000 homes on the island that is home to about 139,000 people. The plant is designed to run on 30,000 tons of fuel annually, produced from 60,000 to 70,000 tons of waste. The biomass plant, which utilizes some of the existing equipment from an old incinerator, runs alongside the Isle of Wight Council's Resource and Recovery Facility in Newport, where the waste is processed.
"The Newport plant will allow the Isle of Wight to become even more self-sufficient in terms of waste," says Steve Boswell, operational manager for the Isle of Wight Council's Environment and Waste division. He adds that the plant has been well-received by residents and the council.
The gasification technology was developed by Energos Ltd., a Norwegian company acquired by Ener-G in 2004. The company has six municipal-solid-waste-to-energy plants operating in Norway and Germany using the same technology, with a total of more than 300,000 operational hours.
The Gasification Process
The Energos waste plant on the Isle of Wight is an ideal model for small, community-based facilities. Drying and gasification of the waste is done in the primary chamber under sub-stoichiometric conditions. The resulting gas is transferred to a separate secondary chamber where high-temperature oxidation occurs. The process is monitored and controlled via a software system.
"We don't separate the syngas out," says Tony Grimshaw, technical director of Energos. "We immediately combust it at 1,000 degrees [Celsius] (1,832 degrees Fahrenheit), which eliminates all the problems that traditional gasification actually has including tar deposition and fouling, and all those kinds of things. We just basically don't allow the tar to condense out." The advantage is that it's a bankable solution and it's reliable, Grimshaw says.
The heat recovery steam generator is connected downstream of the oxidation unit and recovers energy from the flue gas, which is then converted to steam. The resulting energy is supplied directly into the national grid.
Typical measurements of syngas concentrations between the gasification and oxidation stages show 7 percent hydrogen, 3 percent methane, 9 percent carbon monoxide and 14 percent carbon dioxide, Boswell says.
The adjoining Resource Recovery Facility accepts all collected residual household waste from the island. Recyclables such as aluminum, steel and organic fines are extracted and the plastic, cardboard and paper are used to produce a low-densified floc fuel that is baled and transferred to the gasification plant. Previously, it was trucked to the mainland.
The gasification process produces two types of ash: an inert bottom ash and fly ash. The bottom ash is sent to a landfill on the island and used as daily cover. The fly ash is transported off the island for treatment and disposal, according to Ener-G. The Energos research team also developed a new reactor for the Isle of Wight plant that increases combustion efficiency and improves dust removal, increasing availability and enabling fewer interruptions and downtime.
The project is part of the U.K. government's New Technologies Demonstrator Programme managed by the Department for Environment, Food and Rural Affairs (Defra), a government agency that promotes innovative ways to reduce the volume of waste sent to landfills. Defra is contributing £2.7 million (about $4.4 million), 35 percent of the cost of development and operation in the first year, which totals £8 million (about $13.1 million), according to Boswell.
An Excellent Opportunity
The plant uses existing equipment from an incinerator that was closed down, which put the cost of the project development at about $6.6 million. The cost of building a new facility would have been $20 million to $25 million, Grimshaw says. "It was very much an opportunity to do it quickly and do it cheaply." The project uses the existing steam boiler, steam turbine, flue gas cleaning equipment, chimney and water cooling process from the closed incinerator, he says. "All that equipment is being reused and we simply put on a new front end in terms of a gasifier and the oxidizer, put in a new control, added a new building, and a new fuel delivery system."
Many municipal solid waste plants in the past have failed because of poor design and technical base, according to Grimshaw. "The operation is easy to understand, so we're not really taking any step-outs in terms of the technology base and the equipment type," he says.
The simple design was developed by Norwegian petrochemical engineers with Ph.D.'s, Grimshaw says, and the chemistry used in the process is controlled, making emissions low. "It's not a complicated bit of equipment," he says. "The waste industry is not necessarily particularly sophisticated. They're more used to running trucks about and putting waste into holes in the ground. If you try to sell them a solution that is quite sophisticated, they won't have the experience and staff to operate those kinds of facilities. So it seemed for us that it was a relatively simple piece of equipment with unsophisticated controls that would be easy for them to operate."
"This project will deliver significant environmental benefits to Isle of Wight residents," Boswell says. "It is also a localized solution because the energy will be used on the island, and there will be little wastage during the transmission phase." It also supports the island's goal to reduce the amount of biodegradable waste sent to the landfill.
"The Isle of Wight has an objective to be an eco-island-to be carbon neutral-by 2020," Grimshaw says. "What we're doing will contribute to that strategy."
"This is an exciting project, which should enable the Isle of Wight Council, with the support of its partners, Island Waste Services and Waste Gas Technology, to remain one of the leading waste management authorities in the U.K.," Boswell says. "The process will be monitored closely, which will be a factor in enabling the council to develop its long-term waste strategy." The plant also provides nine jobs for islanders.
Incineration is not a popular process in the U.K. because of the pollutants it emits, Grimshaw says. "When you negotiate with a community, it's positive to be able to say the emissions are very low and, because we have six reference plants operating, we can demonstrate that it's real," he says. The communities on the island were consulted and engaged in the decision-making and welcomed the technology, Grimshaw says. "They are satisfied when they can see that a waste stream they were exporting off the island to dispose of is now generating power for up to 3,000 homes," he says. "There's a feel-good factor. On the Isle of Wight, there were no objections whatsoever, but this is better technology than the old plant. They could see it was a better solution than moving waste off the island on a ferry; driving it 100 miles and putting it in a cement kiln."
Some communities are less receptive to building these types of facilities in their neighborhoods, but the facilities are justified because they use only the waste generated by the communities, Grimshaw says. Community-level systems can be more attractive and efficient because bigger facilities produce a large amount of heat and sometimes are unable to find consumers to purchase it, Grimshaw explains. The Isle of Wight system doesn't sell heat, but most of the systems in Norway and Germany do. When developing new projects, Energos is selecting sites near large heat consumers to ensure there is a market, he says.
Another problem with large facilities is the increase in truck movement, he adds. They require more fuel and therefore need more trucks to deliver it, to the dismay of neighbors. "If you have a small facility, you're minimizing truck movement," Grimshaw says. "You're minimizing the amount of miles you have to drive with the waste onboard the truck."
A visitor center also was established at the site to drive development of similar green projects and it has seen heavy traffic thus far, Grimshaw says. Energos' technology and experience has also increased its popularity. "As a company, we have more opportunities than we can easily manage, so we're trying to be selective," he says. "Gasification is attractive at the moment and we're in a position where we have little competition." Legislation in some countries also helps generate business. In Germany for example, laws limit the amount of biodegradable waste that can be landfilled. "The economics are very much in our favor," he says.
Energos is in discussions to build several more waste-to-energy plants, including some in the U.K. and one in Italy, and expects to have another up and running in Norway by the end of the year, according to Grimshaw.
Expansion on the Isle of Wight might be more difficult, though, as there is not enough domestic waste to power the entire island. Energos' contract with island waste management expires in 2015. At that time, the contract will be retendered to procure either an integrated contract or a series of smaller contracts. The arrangement could expand to include commercial waste, but that would only double the capacity of the plant, Grimshaw says. The new arrangements could mean new and bigger equipment, too. "It's that contract that will trigger what we do," he says.
Lisa Gibson is a Biomass Magazine associate editor. Reach her at email@example.com or (701) 738-4952.