Dublin Waste to Energy – the engineering behind the new facility
06 September 2016
The Covanta Dublin Waste to Energy site in July 2016
The Dublin Waste to Energy plant is the capital’s first such facility, which its opponents (and there are many) would prefer to call an ‘incinerator’. According to its operators, Covanta, it will be capable of handling 600,000 tonnes of black-bin waste, the vast majority of which will come from the city and the three Dublin county council areas.
The plant will begin operating in September 2017. Covanta states that it will convert waste from the city’s black bins – most of which would otherwise end up in landfill – into electricity for the grid and reduce our reliance on fossil fuels. I went along to the plant in early August to see how the construction phase is progressing and to have a look at some of the engineering and science that will underpin the plant’s operation.
The Dublin Waste to Energy plant, or incinerator (the depends on your view of it) is a highly contentious project. The story dates back to the late 1990s when the plan was first mooted. At that stage, it had become obvious that Ireland needed to be able to tackle its own waste, rather than simply putting it into landfill or exporting it.
In 2005, Dublin City Council awarded the contract for the plant to a Danish company called Elsam. Elsam was subsequently bought out by DONG energy generation, another Danish company. In 2007, the City Council sent a letter agreeing to engage DONG and Covanta Energy, a US company, to design, build and operate a Dublin waste-to-energy plant as a joint venture.
The Environmental Protection Agency (EPA) gave the plant a licence in 2008 and after the Commission for Energy Regulation gave authorisations to allow the plant to generate and supply energy (via electricity) in September 2009 there was a green light to start building.
It did not happen and construction was suspended because the companies were unable to obtain a foreshore license to allow a development to take place on the coastline. The Minister for the Environment at the time, John Gormley, was opposed to granting the license and represented the local Dublin 4 area.
Finally, the license was granted, and Covanta re-commenced construction in 2014. There is significant progress now at the site, with the main structures in place, and it will began to accept waste from the local area in September 2017.
Covanta is US based, but has built many waste-to-energy plants on this side of the Atlantic and is looking to expand further into Europe. The firm has about 30 years of experience operating 45 such facilities around the world. The company likes to think of itself as being in the recycling business, because it recycles about 500,000 of metals from the residual bottom ash left behind after municipal waste is incinerated or burned.
The majority of Covanta plants are based in the US and the company claims that its facilities there operate up to 90% better than required by US Government standards. In Dublin, it has an almost exclusively Irish management team. It has hired people based in Ireland who have the required expertise, or lured back Irish people that have worked on waste-to-energy plants overseas.
The Poolbeg site for the plant is currently a hive of activity, with construction workers in yellow safety jackets and helmets everywhere to be seen, swarming over the site. There is a sense of purpose, organisation and urgency as the company is working to a tight deadline and it is determined to begin accepting waste in September 2017 from local waste operators, as it is required to do.
There are all manner of specialist construction workers at the site, as the pieces of this gigantic puzzle are put into place. It is like watching a large football stadium or a huge cruise liner being built and it is fascinating to watch.
Most informed observers agree that Dublin, and indeed Ireland, has a major problem with its waste, most of which is being exported. There is very little capacity to deal with the large amount of waste being produced in the Dublin region, and Ireland as a whole, as there are just five landfills operational here that accept waste. In addition, there is little or no likelihood of new landfills being set up as they are a health risk and no-one wants them.
This has been the situation for many years. As a result, Ireland has exported its waste, both its hazardous wastes and the ‘ordinary’ black-bin household waste, overseas by ship. Plants in other countries then burn the waste and recover energy, and dispose of the unusable or dangerous remnants.
The EU wants member states and regions to deal with their waste in their own area, and this is also a key part of national and regional waste policies here. That means that Dublin must deal with its own waste in Dublin, rather than sending hundreds of thousands of tonnes of waste to towns like Drogheda and Arklow, where they are ‘bailed’ and exported by ship. This is wrong in principle and storing waste like this represent a fire and health risk too.
We currently export about 560,000 tonnes of waste from Ireland each year, and the new Covanta plant has a capacity for about 600,000 tonnes.
Scale of Dublin Waste to Energy
Recycling does not appear to be solution to our waste problems: even if we hit the predicted recycling rate here of 45-50% by 2020, there will still be a substantial amount of waste that has to be dealt with. The waste that we produce can, with this plant, be used to produce electricity and reduce the need for fossil fuels, such as gas from Russia and oil from the middle east, which are burned to produce electricity. We need it.
Otherwise, then in the absence of new landfill sites, the EU could decide that Ireland is no longer permitted to export its waste on a massive scale, in contradiction of EU policies and our own national policies. The EU has been very patient with us on this issue, going back almost two decades now.
The plant is huge. Is located at the end of South Bank Road, which is off the roundabout at Ringsend as one heads south onto the coast road past Sandymount, for those that know Dublin. It is next to the Poolbeg Power Plant and beside the Irish Sea, the River Liffey, a sewage-treatment plant and a nature reserve.
its shape is very distinctive; it is very sleek and modern. It reminded me of a streamlined version, without the lifeboats and all the extras, of the kind of large cruise liner that we have grown used to seeing in Dublin Port.
The footprint of Dublin Waste to Energy covers about three football pitches and, at 52 metres at its highest point, it almost identical in height to the nearby Aviva Stadium, which is four metres shorter.
There will be two chimney stacks, which are not yet in place. These will be 100 metres tall. From these will emerge, the company state, mostly water vapour at the end of the waste-to-energy process. That can be compared to the existing Poolbeg stacks, which stand at 207 metres, more than twice as tall.
The facility has a kind of shell like, wrap-around design and the Covanta manager said that about €100 million was spent on design, to make the plant better fit in with its surroundings. They have done a pretty good job in this regard, in that it does not look like a stereotypical ‘dirty power plant’ or industrial factory site.
In terms of the materials, there will be an extraordinary amount put into the construction, such as 6,000 tons of reinforcing steel, enough concrete to fill about 6,500 concrete trucks and enough vertical supporting piles to run – if all the piles were laid out on the ground – the 64km from Poolbeg to Kildare town.
Waste to energy process
When the plant is up and running, it will operate 24/7, although it is not permitted to take waste on a 24-hour basis. As the waste trucks will arrive from around Dublin (mornings are usually the busiest time at these plants), they will be weighed and checked in before they go to a tipping hall, when they unload their waste in a designated ‘bay’.
The waste will be unloaded out onto the floor and then put into a huge storage pit and thoroughly mixed before being lifted with a big mechanical grabber and put into what are called ‘hoppers’. From the hoppers, the waste travels to the combustion area where it is burned.
In the combustion chamber, the waste will be burned at about 2,000F and the combustion a single load of waste from a hopper takes one or two hours. As waste is burned, the heat will convert water in the steel tube-lined walls that rise through ‘boiler tubes’ where it is superheated. The steam will turn a turbine-driven generator to produce electricity. The electricity produced will be exported to the grid for use by homes and business in the immediate area.
Steam from this electricity-generating process will be condensed back into water and returned to the boiler tubes, giving an efficient ‘closed loop’ system. After this process, the volume of waste will be reduced by 90%, according to Covanta, with mainly ash and metal remaining. The ash can be landfilled or re-used. The metal such as iron and steel are recovered for re-use. A separate process recovers other metals like aluminium and copper.
Dublin Waste to Energy has pollution control equipment to ensure, the company states, that emissions are below limits to protect human health. The EPA can come onto the site whenever it wishes and can access Covanta’s emission-monitoring computers. The goal is to have real-time information on emissions available on the company website to whomever is interested.
In terms of air pollution, acid gases will be neutralised using lime and a scrubbing/cleaning, process, and carbon will be injected into the gaseous mixture for better control of heavy metal emissions.
Small particulates – which can cause human health problems, particularly breathing difficulties – are removed as emissions pass through a ‘bag house’. This uses thousands of fabric filter bags to catch and hold particulates.
All gases pass through the bags before leaving the stack. The control room monitors emissions through a real-time emissions monitoring system and controls steam flow and other automated processes in the plant.
In Dublin, Covanta is using the nearby Liffey water to act as a coolant in the plant, and it is capturing rainwater and surface water for the same purpose.
Potential benefits and cautions
Dublin Waste to Energy will produce 60 megawatts of electricity per year, enough to heat 80,000 homes and provide district (local) heating for 50,000 homes. It makes use of ‘grey water’ from the nearby sewage treatment plant (which would otherwise require energy to be further treated) to cool the process. This is important, as temperature regulation is central to the safe and efficient operation of the plant.
Most importantly, it has the capacity to take up to 1,800 tonnes of black bin waste per day and up to 600,000 tonnes per year. This will greatly benefit our environment, as some of this waste may have been going to landfill, which has health and safety risks attached.
It will help us to comply with the EU requirement that we deal with our own waste, and it will mean that waste is dealt with close to where it is produced in Dublin – and not stored around the city, or in port towns where it can be a fire or health risk. It should also be remembered that in many places in Europe, plants like this are welcomed by ‘green’ political parties as they help move us away from landfill and promote the idea that waste should be treated as a recoverable resource.
A note of caution was sounded last month, however, when it was reported by The Irish Times that a Covanta-run plant in Canada did not meet emissions targets on dioxins and furans, as set out by the Canadian Ministry of Environment. I asked Covanta how it could reassure people that the Dublin plant was safe and would meet emissions targets.
Covanta responded that they had measures in place in the Canadian plant to shut it down as soon as a problem arose on one of two emissions stacks. This ensured that there was no risk to the environment or health of local residents, and that this was, Covanta told me, confirmed and supported by the Canadian authorities. Furthermore, Covanta said all emissions from the Dublin plant will be independently monitored and verified by the EPA.
Statement in full from Covanta in response to the issue that arose at the Canadian plant:
A stack test in May 2016 at the Canadian plant indicated that the limit for dioxins and furans were exceeded on one line. The emissions exceedance for this unit was not representative of normal operations and previous stack tests and engineering runs have demonstrated compliance. Unit 2 continues to operate without issue with dioxin emissions at only 20% of the permitted levels.
While the emissions for unit 1 exceeded the limit at the stack, ambient air monitoring results of dioxins and furans upwind and downwind of the Canadian plant were well below the air quality standards set by the local environmental regulations. Soil sampling was also done and the testing found no elevated levels of dioxin/furans. The testing regime that Covanta had in place in Canada enabled the shut-down of Unit 1 as soon as the problem arose and thus ensured there was no risk at all to either the environment or the health of local residents which was confirmed by the relevant authorities.
The Dublin plant is technically different from the Canadian plant in many ways and the Poolbeg waste-to-energy process provider has successfully delivered 29 new plants across Europe since 2000 – ten of these in the last five years and without any environmental incident. In addition, Dublin Waste to Energy has invested heavily in experienced management and staff for the Poolbeg plant, which will ensure smooth commissioning, start-up and operations.
The emissions limit values permitted for the Dublin plant have been set out by the EPA in accordance with best practice and EU legislation. In addition, the frequency and testing regime has been set out by the EPA and all emissions (in addition to be monitored by Dublin Waste to Energy) will be independently monitored and verified by the EPA. As an indicator of Covanta’s diligence and commitment to the monitoring of stack emissions to ensure continuous compliance to the EU requirements, the plant has a full CEMS (Continuous Emission Monitoring System) as a stand-by to the two CEMS systems which monitor the emissions from the two lines.http://www.engineersjournal.ie/2016/09/06/dublin-waste-to-energy-covanta/http://www.engineersjournal.ie/wp-content/uploads/2016/08/Covanta-Dublin-July-2016-Pic-1-1024x767.jpghttp://www.engineersjournal.ie/wp-content/uploads/2016/08/Covanta-Dublin-July-2016-Pic-1-300x300.jpgElecDublin,energy,renewables,RPS Group,waste