Legislation, influenced by the steadily increasing public awareness of the problems and consequences of municipal solid waste, is the most important market driver of demand for waste-to-energy plants worldwide. As economies grow and the GDP/capita increases within developed and developing countries, so does the level of waste production. Waste reduction programmes, such as recycling and composting, offer economical solutions, which help reduce waste volumes.

Unfortunately, large volumes of waste remain. Waste-to-energy plants utilise this waste as a fuel, significantly reducing its volume and using its stored energy to produce steam for industrial processes, district heating or generating electricity. There are two market trends encouraging the development of such plants: they burn waste cleanly and economically, optimising the output of this overly-abundant man-made fuel, and simultaneously reduce consumption of limited natural resources. ABB is developing its products in line with these market trends.

Municipal solid waste takes many forms, including packaging, vegetable waste, and sewage sludge. Converting sewage sludge to a combustible form is an important element, and the technology involved in drying and separating this by-product of human existence is a specialised one.

Market volume trends in the waste-to-energy industry

The annual market volume for waste-to-energy plants sold in western Europe is constant at about 500 tons/hr of incineration capacity. More established markets, such as Germany, Switzerland, the Netherlands and some Scandinavian countries, with significant capacity already installed, have lower demand rates than previously. This is compensated by expanding markets with higher demand rates, such as France, Denmark, Italy, Spain and the UK.

In the long term, European Union directives covering landfills will be implemented as laws within individual countries, and will play a decisive role in increasing demand for waste-to-energy plants over the next 5-8 years.

Market volume in Asia totals approximately 500 tons/hr of capacity sold per year, with the largest country market being Japan. South Korea and Taiwan are quickly growing markets in Asia, with the mega cities in Malaysia, Indonesia, the Philippines, Singapore, India and China offering individual projects, which could develop into national demands in due course.

The markets of eastern Europe, the CIS and South America all have need of waste-to-energy plants. However, these are constrained by the need for economic and political reform, as well as the shortage of available capital. These countries represent long-term future markets within the waste-to-energy industry.

North America, specifically the USA, with its abundant land resources, prefers to use landfills to energy recovery and waste volume reduction systems typified by waste-to-energy plants.

Fulfilling market demands

ABB is developing its “Waste Power Line”, a standardised design for greenfield waste-to-energy plants, or integrated waste lines within existing plants. The concept is based on existing technologies, which have been successfully proven in several plants. ABB Enertech Ltd, the technical lead centre within the ABB Group for waste-to-energy plants, has coordinated optimisation of all the main component groups within the complete plant into a flexible design concept, adaptable to individual customer needs.

Optimum economic performance and plant reliability can only be achieved if well proven systems and components are properly laid-out with regard to each other and with the whole plant in mind. It was for this reason that it was decided that all components for the Waste Power Line should come from ABB.

Standardisation of layout and construction principles made it possible to reduce delivery times and offer financially attractive solutions. The Waste Power Line consists of the following main components: centre-flow furnace, ‘CH’ single pass steam generator and the NID air pollution control unit.

Furnace and combustion concept

ABB Enertech has continuously improved incineration furnaces, especially with respect to the varying heating values of municipal solid waste and stricter environmental legislation. The most frequently supplied combustion design by ABB is the centre-flow furnace, with water-cooled walls and an air-cooled horizontal incineration grate. This fulfils all emission regulations, and minimises investment and operating costs. For these reasons, ABB chose this configuration for its Waste Power Line.

Increases in the heating value of waste as a result of presorting, separation and/or recycling programmes lead to increases in the temperature operating ranges, creating new demands on incinerator maunfacturers.

In response to this trend, ABB introduced its water-cooled grate lining, allowing a complete separation between the control of the combustion process and the cooling of the grate. The advantage of this system lies in the even distribution of the thermal stresses imposed on the surface of the grate. This leads to a reduction in operational wear, to reductions in emissions, and to more complete burnout. To provide optimal cooling of the grate under all operating conditions, a welded construction for the water-cooled grate was developed. The water-cooled grate has been tested under extreme operating conditions, including simulation of a complete loss of cooling water.

The Advanced Combustion Control (ACC) system controls the combustion process within ABB’s furnaces. This system allows a predictable mode of operation, which is determined by permanent on-line monitoring of the waste characteristics, which is utilised to control the combustion parameters. This results in stable production of steam, flue gases and a more efficient burnout.

Steam generator: the ‘CH’ boiler

The CH (Combustion pass and Horizontal pass) concept is characterised below. The concept consists of a boiler with a vertical radiation/combustion pass, directly followed by a horizontal convection pass and its associated bundles. The following features guarantee uninterrupted plant operation with very high temperatures in the convection pass:

  • The initial protective bundle with a large pitch operates as an evaporator.

  • The second protective evaporator bundle reduces the temperature of the flue gases in front of the super-heater to less than 650°C.

  • All of the bundles within the convection pass are free hanging, which permits very efficient cleaning by ‘rapping’ with vibrations at regularly timed intervals.

    With only one bend of 90° in the flue gas direction, very uniform flue gas velocity and consistent temperature distribution over the entire cross section of the convection pass is achieved. This minimises corrosion and fouling.

    Natural circulation

    All boilers from ABB Enertech are cooled by natural circulation, with the boiler layout following these basic principles:

  • Heating surfaces with different temperature levels and elevation are cooled by separately closed cooling loops.

  • Cooling of all heating surfaces is always accomplished by upward flow.

  • All cooling circuits start at the drum and, after running their course, end again at the drum, with no short-cut pipes.

  • The drum is situated above all of the heated surfaces.

  • The down-comers, supplier tubes and risers are flexible and do not support weight. This ensures that cooling of the boiler walls is reliable at all operating loads and conditions.

    Top supported steam generator

    The boiler from ABB is top supported. This concept requires a more rigid support structure. However, it also yields a number of advantages:

  • All components exposed to thermal expansion can freely expand in horizontal and vertical directions.

  • The pressure components are stressed only through their own weight in the vertical axis and are not exposed to horizontal forces which could result in bending.

  • The supports are easily accessible.

  • Improved operational safety, especially in the case of loss of water in the evaporator system.

  • Maintenance work is simplified, such as when a boiler wall requires replacement.

    Air pollution control system: the NID semi-dry process

    The final element in ABB’s Waste Power Line concept is the NID flue gas purification system. This is a compact, low-cost, semi-dry process with a high degree of separation of acid gases through chemical processes, with a reaction time of less than 2 seconds. The reactor is integrated into the inlet duct of fabric filter. It has a volume one tenth of that of a conventional spray absorber. One of the most important components of the NID process is the patented mixer for humidifying the dust. The advantages of the NID technology are:

  • High removal efficiency

  • No pre-collectors required

  • Extremely low dust emission

  • High removal efficiency for SO2, SO3, HCl, HF, HBr

  • Low investment cost

  • Low power consumption

  • Low maintenance resulting from less equipment

  • Integrated humidification and slating

  • Compact design.