Professional Engineering

The detritus of our economy could have a value beyond that currently ascribed to it. And the environment could benefit, too. This is the message from those promoting waste-to-energy technology as part of the solution of dealing with the UK’s mountains of refuse. 

Britain generates around 300 million tonnes of waste each year – much of which is either incinerated or goes into landfill. This, argues the IMechE, is unacceptable. And the Department for the Environment, Food and Rural Affairs concedes that the institution has a point, saying the situation is “unsustainable”. Waste contributes to climate change
and increases emissions of carbon dioxide, whether it goes into landfill or
is incinerated. 

The government says it has several initiatives to reduce waste under way, including working with businesses on measures to “prevent waste occurring wherever possible” and looking at waste prevention and recycling in certain sectors such as construction. But once waste is created, is there something more useful we could be doing with it?

Generating electricity is one such option. The IMechE argues that waste-to-energy plants are attractive on two fronts: dealing with large volumes of refuse and providing an alternative means of producing power as carbon-intensive power stations are decommissioned. 

There may be something of an image problem to overcome: older incinerators were seen as dirty and they did not use waste as a fuel for providing electricity. Nonetheless, both the incinerator and the modern waste-to-energy plant are sometimes tarred with the same brush, says the institution. There were also concerns about the older plant emitting harmful dioxins into the atmosphere. 

But today’s waste-to-energy plant must comply with the “very stringent” Waste Incineration Directive (WID). The result is that its emissions must be 10 times lower than an equivalent coal-fired power station. Dioxin emissions under WID are limited to one-billionth of a gram per cubic metre. Bearing in mind these factors, the IMechE says it is time that waste-to-energy played a greater role in the government’s energy policy.

Lisa Jordan, business manager for bio-energy, Europe, at Air Products, has been involved in a scheme to build what is claimed to be the world’s largest waste-to-energy plant of its type on Teesside. With a capacity of 50MW, the plant is expected to power up to 50,000 homes in the region. “We have to comply with the WID, and our emissions would be consistent with what we’re required to achieve under WID for our environmental permit,” she says. 

The first construction work has started at the site in the north-east, and the plant is scheduled to come online in mid-2014. Air Products describes the energy that will be created as “renewable”. Jordan says: “It’s going to be on an area that has been designated for industrial development in renewable energy. It’s reclaimed industrial land. When we looked around the country, one of the things that attracted us to Teesside was that it had industrial brownfield land available.”

She says there were no planning objections to the new plant. “Teesside is keen on the inward investment,” she adds, “because that will bring around 700 construction jobs, and then about 50 jobs when we’re up and running. The region needs investment and the creation of jobs to help regenerate the area.”

The plant is known as an “advanced gasification” type, and it is said it will divert 350,000 tonnes of non-recyclable waste from landfill each year. Gasification, which is widely used on industrial sites using fossil fuels to generate electricity, heats waste to high temperatures – without combustion taking place – with oxygen or steam to produce a “syngas”. The gas can then be used in a gas turbine to generate electricity. “We have taken a series of proven technologies for each of these individual steps and bolted them together,” says Jordan.

“One of the things we like about the technology today is its flexibility. We’re talking about producing electricity and supplying it to the grid, but the key is really getting the syngas, which gives you a future-proof energy platform. In future, you could look at using the syngas to produce hydrogen or biofuels, or you could methanate the gas and put it into the grid. You could also use it as a chemical feedstock.” Hydrogen from the plant could one day be used to power vehicles or stationary fuel cells. 

Gasification vies with several other techniques for producing energy from waste, including thermal combustion, in which the waste is used to heat water to drive a steam turbine, pyrolysis and anaerobic digestion. All of these methods have different advantages, but the IMechE says that whatever technique is used, heat from processes should also be captured to heat homes and businesses. Combustion-based power plants inherently produce both heat and electricity, in the ratio of about 3:1. This heat should be captured and used for district or community schemes.

The Teesside plant will feature gasification technology from Westinghouse, which is said to offer a cleaner, more efficient conversion of waste-to-power than some traditional technologies. “The plant will be sourced from all over the world and the gasifier is obviously part of that,” says Jordan. “But there will be input from local engineering and construction firms.”