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Stationary fluidized bed for the disposal of industrial and sewage sludge

Sewage sludge - the "unpopular residue"

For decades clarification of municipal or industrial waste water to meet increasingly stringent purity standards has become a common and mandatory task. During this period of time the sewage sludge which occurs in this sphere turned from a fertilizer earlier considered a natural one into an "unpopular residue" because

- the use of sewage sludge for agricultural purposes was inhibited to a large extent due to legal provisions and will be fully prohibited in the near future
- in most cases no sufficient dumping areas are at disposal or fit to be approved by local authorities.

These are the reasons why new disposal alternatives had to be found to handle these residual materials. One of those alternatives is provided by the incineration of sludge at temperatures of 850 °C and above in conjunction with a simultaneous utilization of ist energy contents. In this context, the stationary fluidized bed technology proved ist value and became widely accepted. The vast majority of modern incineration plants are equipped with stationary fluidized bed incinerators. They are characterized by the feature of a very efficient heat and individually fitted flue gas cleaning system (dry type, quasi-dry or wet type) compliance with stringent legal provisions is given.

Envirotherm offers fluidized bed technologies designed for the disposal of industrial and municipal (sewage) sludge earlier developed by both companies LURGI and Bamag. Both technologies represent proven and environmentally friendly thermal waste utilization options individually tailored to cope with specific sludge characteristics and provide a high degree of waste disposal security to plant operators. In addition to this, pursuing monoincineration of sludge those operators turn out to be an ideal basis for future activities in the field of phosphorus recovery from produced ashes.
Further development of incineration plants reached a point where, apart from their primary function as sludge disposal units, they are used for electrical power generation and/or district heating purposes without neglecting operational security in this respect. As a rule, those plants can be operated autonomously without external energy supply and, in addition to this, feed electrical energy and/or heat into public or operator's utility networks.

A plant designed to ensure a thermal utilization of sewage sludge basically comprise the following process stages shown in the diagram below:

  • Dewatering / preliminary drying.
  • Incineration within a fluidized bed.
  • Generation of energy (electricity, thermal heat).
  • Wastewater cleaning.
  • Flue gas cleaning.

Envirotherm is in a position to present a significant number of reference plants with a capacity ranging up to 6 tons of dry substance per hours. Examples of sewage sludge incineration plants as well as of plants designed for the disposal of residues from the paper industry are listed in the references chapter.