A new waste to energy plant near completion in Ethiopia is set to showcase the opportunities for cleaner energy and a cleaner environment across sub-Saharan Africa’s rapidly expanding urban centres.
On the outskirts of the Ethiopian capital Addis Ababa, Africa’s first energy from waste project is close to completion. The so-called Reppie project is set to transform waste disposal for the rapidly expanding city’s population, but is also expected to serve as a waste management blueprint for the whole of sub-Saharan Africa.
Being developed and constructed as a turnkey project by an Engineering, Procurement, Construction (EPC) contracting consortium, upon completion Reppie will be owned by the national power utility Ethiopian Electric Power (EEP). The facility will supply some 50 MW of electricity to the national grid, supporting about a quarter of the city’s power demand.
The EPC consortium conducting the development includes China’s Cambridge Industries Limited (CIL) together with China National Electric Engineering Co. Ltd (CNEEC). Cambridge Industries Ltd was formerly a subsidiary of biomass combustion specialists DP Cleantech Ltd. Denmark’s Ramboll is acting as the owner’s engineer on behalf of EEP.
Africa’s mixed municipal waste stream is characterised by its relatively low calorific value and high moisture content in comparison with that typically found in Europe. However, the unique nature of African waste has enabled the creation of the CIL-CNEEC consortium, which aims to design, construct and in some cases own extremely cost-competitive and scalable facilities customised for sub-Saharan Africa, the group says.
Building a unique WtE project
Under construction since September 2014, the Reppie project is being developed on a 53,120m2 plot of reclaimed land adjacent to the 37 hectare Koshe dumping site. For the past 40 and more years this open site has seen some 900 tonnes of untreated mixed waste dumped daily and is home to a multitude of people who eke out a living hunting for metals, plastics and other commodities in the city’s waste.
Upon completion though, the Reppie plant will process around 1400 tonnes of municipal waste per day, close to three quarters of the typical waste generated by the Addis Ababa Metro Area population of more than 4.6 million. With an annual waste-disposal capacity of around 438,000 tonnes, Reppie is expected to supply some 185 GWh of electricity annually for export to the grid during its roughly 300 days or 7200 hours of operations per year.
To meet the demands of EEP in terms of ensuring increased plant availability and reliability, the project will use two process lines and twin boilers, each with an air-cooled step grate of the SITY2000 model from Martin GmbH and made under license by Chongqing Sanfeng Covanta Environmental Industry Co., Ltd. Each grate line, which measures 9.7m by 10.6m, has a nominal daily combustion capacity of 640 tonnes of waste and is designed to accept a calorific value range of 5.5 – 9.5 MJ/kg of waste.
Unsorted Municipal Solid Waste (MSW) will be delivered via two 50 tonne weigh bridges to the waste reception hall by the Municipality’s 16 tonne compactor IVECO trucks operated by the Addis Ababa City Administration (AACA). EEP is said to be working in collaboration with Addis Ababa’s City administration to ensure waste collection is streamlined to secure feedstocks. There are six tipping platforms in the 75.6 metre-long and 24 metre-wide tipping hall and a maximum bunker capacity of 22,000 m3. The facility uses magnets to recover steel and other ferrous metals for recycling before two semi-automatic grab cranes mix the waste ahead of combustion.
The two single drum natural circulation boilers feature four vertical gas ducts plus one horizontal gas duct and each produces more than 54 tonnes per hour of superheated steam at 420°C and some 60 bar.
Throughput per line can range from 471 tonnes per day to a maximum of 678 tonnes per day while each boiler has an output of between 36.3 MWth and 55 MWth to make a total maximum thermal capacity of 110 MWth.
Designed and manufactured by China’s Hangzhou Boiler Group (HBG), each boiler has a claimed efficiency of above 80%. The high pressure steam in turn drives two 25 MWe condensing steam turbines.
The Reppie Facility has also adopted modern back-end flue gas treatment technology using selective non-catalytic reduction (SNCR) as well as semi-wet and dry scrubbing together with powder activated carbon (PAC) injection and baghouse filtration. The plant is designed to meet the European emission standards under the EU 2000/76/EC Directive. This ensures that almost all of the nitrogen oxides (NOx), sulphur dioxide (SO2), heavy metals and dioxins produced by the plant are eliminated. Both on-site and online flue gas emission monitoring is featured.
Any residues leftover from the flue gas treatment is recycled or safely disposed of whilst the scrubbed and cleaned flue gas is released into the atmosphere through the plant’s twin stacks.
More than 80% of the daily volume of 220m3 of mixed solid waste is expected to be combusted and what remains is converted into ash. An estimated 100,400 tonnes of bottom ash are expected to be produced annually, along with around 15,210 tonnes per year of fly ash. The bottom ash will be sold as a building material to the local construction industry or used as landfill cover in the new Sendafa Landfill site.
An anaerobic leachate treatment system with a membrane bio-reactor (MBR) will be supplied by Hong Kong-based waste to energy project developer China Everbright International for the Reppie project.
At an investment cost of more than US$120 million, the Reppie project is being financed by the Ethiopian government. The lead design firm is the CNEEC affiliate China Urban Construction Design and Research Institute Co., Ltd. China’s national design institute has been responsible for designing dozens of such facilities across China, a country with a waste stream composition very similar to that found in Africa.
Scheduled for completion in 2017, according to Ethiopia’s Ministry of Water, Irrigation and Electricity, at present more than 87% of the construction work on the project has been carried out, including the installation of the two turbine generators and power control units.
Major civil and electro-mechanical works are close to completion together with much of the balance of plant. Civil works of the leachate treatment site and access roads within the site area are being finalised. Roofing of the waste bunkers has been completed, installation of turbine hall crane and the steel structure of the boiler is being completed. Materials and equipment for the power house are also currently being transported from the port to the project site. In addition, excavation of three ground water wells with a depth of about 180 metres each and installation of two 48 metre-high flue stacks, a 132 kV transformer, two 10.5 kV generators, two steam condensers, two oil tanks, steam turbines, and the erection of the lower case have also been carried out.
Preconstruction preparations for the erection and installation of a 132 kV substation and a 3 km power export transmission line to link with the Mekanissa – Sabetta grid network are also underway.
“The project will be finalised within the schedule unless we face unforeseen challenges going beyond our capability,” Bizuneh Tolcha, director at Ethiopia’s Ministry of Water, Irrigation and Energy is reported to have said.
Some 189 Ethiopians and 87 expatriates are currently employed on the project.
Waste to Energy Showcase
According to its developers, Reppie will be the first major waste to energy facility in Africa. By diverting waste from landfill and by adhering to the strict European environmental standards for this kind of project, the facility will be a showcase for other cities and countries across Africa.
Indeed, Cambridge Industries suggests the development is part of a programme for seven city waste to energy plants across Africa and thus represents the first phase of a wider rollout of multiple waste to energy plants across sub-Saharan Africa’s major cities. This chimes with a preliminary government report which indicates the project could be the first of 35 such facilities, according to local media outlet Capital Ethiopia.
Located about 10 km south-west of Addis Ababa at 2300 metres above sea level and with average temperatures of 14-25 oC, the project presents some unique challenges. But at only 7 km from the African Union (AU) headquarters and in the city home of the United Nations Economic Commission for Africa (UNECA), Reppie forms a key part of Ethiopia’s Climate Resilient Green Economy strategy.
Under the terms of this strategy, the Ethiopian government plans to be a carbon neutral economy by 2025. This is a huge challenge. According to the World Bank, Ethiopia has experienced rapid economic growth in recent years, with GDP expanding at an average of close to 11% between 2004 and 2014. From being the second poorest in the world in 2000 it is now set to become a middle income country by 2025. Increasing urbanisation is also seeing the city’s population expand rapidly as it accelerates towards mega-city status.
Rural migration into Addis Ababa has resulted in a high rate of population growth and the city is expected to have some six million residents within 20 years. Indeed, Dr Tewolde Berhan Gebre Egziabher, director general of Ethiopia's Environmental Protection Authority, reportedly noted that when the Koshe site was created decades ago it was well beyond the city limits, today it is home to many, becoming part of the city's landscape due to expanding urbanisation. This has had tragic results. In mid-March it was reported that a ‘landslide’ of hundreds of tonnes of rubbish at the Koshe site killed more than 110 people with dozens more still missing.
Cleaning up Africa’s environment
Though Ethiopia’s domestic electricity demand is currently relatively modest - according to USAID figures the country only has an installed generation capacity of approximately 2300 MW for its population of above 95 million people – urbanisation is set to change that. Furthermore, government investment in infrastructure has been significant.
Some 6000 towns and cities have been electrified and current overall access to electricity is above 50%, a rapid increase from the less than 20% with access a little more than a decade ago. There are also significant power export opportunities for Ethiopia, largely but not exclusively associated with its potential hydropower resources. The next few years are expected to see a number of large hydropower plants come on stream that will close to quadruple the national installed electricity generation capacity.
Waste to energy plants like Reppie are also expected to make a significant contribution, not just to Addis Ababa’s burgeoning electricity demand, but also in reducing greenhouse gas emissions such as carbon dioxide and methane, as well as improving water quality by preventing leachate entering the water course. According to Nicholas Halias, deputy head of the project, Reppie will eliminate the equivalent of 46,494 tonnes of CO2 annually from methane emissions alone.
This project is just one step in Ethiopia’s clean energy supply plan, but it is a huge leap for Africa’s waste management story.
David Appleyard is a freelance journalist focused on energy and the environment.
