wasteWOIMA® – THE MODULAR WASTE-TO-ENERGY POWER PLANT

 

A modular waste-to-energy plant producing:
• Steam 17 tons / h (@400°C / 40 bar) OR
• Electricity 3,4 MWe (gross) / 2,7 MWe (net) OR
• Electricity 2 MWe and thermal energy 10 MWt AND
• Potable water 200 m3 / day

Municipal Solid Waste (MSW) is available in abundance everywhere in the world. It offers several business opportunities in reuse, recycling and incineration for energy. Yet, it remains an under-utilized resource, especially in the developing countries, which would benefit the most of a local energy source. Similarly, the solution reduces the quantity of waste placed in landfills and improves people’s health and general living conditions.

 

1. Waste Incineration

The wasteWOIMA W2E power plant technology is based on the well-proven grate incineration technology, where the fed-in waste fraction moves forward on the reciprocating grate through the combustion phases; drying, pyrolysis and char combustion. Eventually the burn residue, the so called ‘bottom ash’, falls off into a cooling pool. Primary air is fed through the grate to support full combustion. It also acts as a cooling media for the grate reducing the need for maintenance work. Depending on the composition, and thus the calorific value of the waste, the incineration capacity varies between five and seven tons per hour.

The cooled bottom ash is transported to an ash processing system automatically via a system of conveyor belts, where excess water is removed and returned to the cooling pond. The remaining ash is then compacted for landfilling or utilized in e.g. infrastructure construction or cement production.

2. Heat Radiation and Cooling

The furnace opens from the middle to the adiabatic combustion chamber, where the gasified fractions of the incinerated waste burn. Secondary and tertiary air is injected to the upper combustion chamber to help ignite and to ensure full combustion of the gases, which then flow into the radiation / cooling channel, where steam / water in the membrane wall piping absorbs the heat of the flue gas. The steam drum holds the partially evaporated mixture of water and steam, where gravity recirculates the water component back into the membrane walls.

The lengthy channel guarantees the EU-standard residence time (2 sec @ 850°C) for the flue gas, which is required to fully burn out the highly toxic elements; furans and dioxins, in the flue gas. Simultaneously, this radiation channel cools down the flue gas temperature to protect the waste heat recovery boiler from temperature corrosion.

 

3. Waste Heat Recovery

Waste heat from the radiation channel is collected in the recovery boiler, which includes the superheater, evaporator, economizer and air preheater. They are a series of piping arrays designed to collect the remaining heat in the flue gas through convection. The evaporator and superheater convert the steam generated in the membrane walls of the radiation channel into superheated saturated steam for the steam genset. The economizer preheats the water flowing from the water tank into the steam drum, whereas the air preheater heats the primary, secondary and tertiary air for improved incineration efficiency.

The fly ash within the flue gas accumulates on the wall and piping surfaces in the boiler and reduces its heat transfer efficiency over time. Thus, an efficient soot removal process is required to ensure proper functionality of the heat recovery boiler.

4. Air Pollution Control

The air pollution control is based on a dry APC-system. wasteWOIMA power plant is equipped Hydrated Lime, Ca(OH)2 and Activated Carbon dozing systems and reactor, that are combined with fabric filtration system. This APC-system satisfy the World Bank Air Pollution Guidelines and EU Emission Standards. Both systems produce dry ash residue, thus there is no sludge to be treated.

Bottom and fly ashes are ‘clean’ enough to be used in e.g. road construction of cement manufacturing. The APC ash, on the other hand, contains a high proportion of heavy metals and other toxic residues and therefore has to be placed in a landfill or processed further in e.g. a metal extraction plant. The bottom and fly ash quantity is some 15% and the APC ash some 3% of the total incinerated waste amount.

 

5. Power Generation

The saturated and superheated steam (400°C @ 40 bar) is fed to a steam turbine-generator set, which transforms the heat and pressure of the steam through a rotating turbine into electricity. A standard back-pressure of extraction turbine is used, depending on the customer’s requirements. The used steam is then conveyed to the condensing system, where the steam vapour is reduced back to water. This closed circuit ensures efficient operation by maintaining all the plant-generated heat within the system. The power plant production can be utilized in the form of steam, electricity, thermal power, potable water, or a combination of the above.

One standard feature of the plant is an auxiliary diesel generator set, which is used during the start-up and shut-down of the plant to run the conveyor belts and air blowers. During the maintenance period, it can also power the local operations reducing dependence on outside power

Benefits
The proven technology and modular structure ensure that the W2E power plant has

  • simple and robust structure
  • high pre-fabrication rate
  • quick roll-out
  • high efficiency rate
  • good tolerance for heterogenous fuels
  • flexible production scheme
  • low operating and maintenance cost
  • potential for relocation or
  • multiplying capacity cost-efficiently