1. CONCEPTUAL DESIGN OF THE PLANT

1.1 Basis
1.2 Process technology part
1.2.1 Delivery and storage of the waste
1.2.2 Incinerator and boiler
1.2.3 Energy utilisation
1.2.4 Flue gas cleaning
1.2.5 Treatment of residues
1.2.6 Electro and control system
1.3 Buildings and construction

2. ENVIRONMENTAL IMPACT
2.1 Prevention of air pollution
2.2 Odour
2.3 Noise
2.4 Residues

The main goal of today's waste management is an optimised ecological and economical handling of the waste. It is based on the following strategy:

• the production of waste has to be reduced at its source;

• the use of dangerous materials and substances is reduced to the minimum;

• waste is recycled if ever possible;

• for the left over of the waste an ecological way is chosen for a definite disposal.

This description gives in a concise form the conceptual design, the technology and the construction part for the waste treatment plant. Furthermore, information concerning the environmental impact are given under a forthcoming section.

A thermal waste treatment plant based on stoker type grate incineration is according to our experience the most reliable and economical solution. An additional advantage is the production of electricity with good efficiency. A semi-dry flue gas treatment provides the benefit of simple and robust technology combined with little residues to deposit.

The waste will be delivered by road transport and off loaded into the waste pit. The waste pit is sized for a capacity of at least five days in order to guarantee a continuous treatment of the waste even in case of heavy fluctuations in delivery. The incinerator will be fed by specially designed waste crane.

The incineration of the waste takes place on a stoker type grate. The slag produced during this treatment will be removed through a slag quench tank and extractor located underneath the grate. The boiler located above the grate produces live steam by cooling the flue gas from initially minimum of 850°C down to about 230°C at boiler outlet. To guarantee an efficient burnout and the minimum temperature of the flue gas in the post combustion zone at 850°C, this during the start-up phase and temperature fluctuations at normal operation, start up and/or support burners are installed.

The combustion air will be partially drawn from the waste pit, preheated and injected through the grate and the waste layer into the combustion chamber (primary air). Additional air will be drawn above the slag extractor and injected into the combustion chamber above the grate (secondary air), in order to achieve a complete post-combustion of the flue gas. The membrane walls of the boiler around the combustion chamber are protected by refractory lining against corrosive effects of the flame and hot flue gas.

Nitrogen oxides (NO_x) formed during the combustion will be reduced using ammonia (NH₃) injection into the post-combustion chamber by a so called selective non-catalytic reduction (SNCR) process. The fly ash contained in the flue gas falls into the ash hoppers of the boiler and will be transported by a pneumatic or mechanic transport system into the ash silo.

The steam produced in the boiler flows to a condensing turbine which is used for electric power generation. The turbine has steam extraction's at the appropriate pressure stages to cover the internal needs of steam (air preheaters, feed-water turbo pump, feed-water preheater, deaerator etc.).

The electric power generator supplies electricity to all plant internal installations. The surplus production is fed into the public electricity network. In case of a turbine failure as well as during the start-up and shut-down phases, the steam flows through the turbine by-pass directly to the air cooled condenser (ACC).

A semi-dry flue gas cleaning is proposed before the gases are released into the atmosphere. The flue gas cleaning, according to the state of the art, includes the following components:

• semi-dry reactor;

• active carbon injector;

• bag house filter;

• induced draft fan;

• lime preparation plant;

• stack including all necessary ducts.

The slag falls from the grate into the slag quench tank. The quenched slag will be conveyed to a special slag bunker underneath the boiler. By means of a magnetic drum the iron can be separated from the slag which then can be treated externally for further use in road construction.

Optionally, the boiler ash can be washed with process water. After drying on a belt filter, the ash can be used together with the slag. So the extracted hazardous metals would be chemically fixed to the hydrated lime used in the semi-dry reactor.

The plant will be connected to the local public energy distribution network system. An emergency electricity supply using a diesel powered generator (400 V) is foreseen in case of an electrical energy loss. It is used to provide electrical energy for a save operation of consumers being important for process-technical reasons and to important plant equipment (e.g. emergency lightning, fire-fighting pumps) and the security equipment (e.g. rescue equipment in the waste pit).

The incinerator lines and the equipment for energy utilisation can be automated to a large extend. The whole plant can be controlled and supervised from a central control room during normal, continuous operation.

The description applies to the following objects:

solid waste incineration plant (SWIP) including the off-loading place, waste pit, boiler house, flue gas cleaning plant, energy production- and social-/administration buildings.

weigh bridge and infrastructure

The foundation and the wall from the waste pit are of concrete construction. The other buildings are mainly of steel construction.

2. 0 ENVIRONMENTAL IMPACT

The legal local regulations as well as the requirements for the environmental and personal protection, which have to be met by a thermal waste treatment plant, will be fully respected.

The actual emission of the most important air pollutants during normal operation are expected to achieve the concentration limits given by the German regulations (17. BImSchV):

In order to avoid odour emissions from the plant to the environment, the air from the waste off-loading place and the waste pit will be evacuated and used as primary combustion air. A complete destruction of all odour components takes place during the combustion of the gases.

The legal local requirements concerning noise emissions from the plant will be met using different noise reducing measures.

Besides, the noise level in zones or rooms within the plant which require, or are foreseen, for permanent presence of personnel shall comply with the legal regulations.

Three different kinds of residues are obtained. The slag can be reused for mainly road construction after minimal treatment. The boiler ash as well as the residues from semi-dry process should be brought, due to their content of hazardous metals, to a special landfill. The boiler ash could be washed and used after drying together with the slag. The extracted water containing the hazardous metals will be applied in the semi-dry reactor. So these metals will be chemically fixed with lime and carried out with the residues from the semi-dry reactor.

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Longitudinal View

Mass Balance