Division Applicability

United Kingdom

In the case of plants dedicated to the incineration of hazardous waste, the applicability may be limited by:

the stickiness of the fly ashes;
the corrosiveness of the flue-gas.

BAT 20. In order to increase the energy efficiency of the incineration plant, BAT is to use an appropriate combination of the techniques given below.

	Technique	Description	Applicability
(a)	Drying of sewage sludge	After mechanical dewatering, sewage sludge is further dried, using for example low-grade heat, before it is fed to the furnace. The extent to which sludge can be dried depends on the furnace feeding system.	Applicable within the constraints associated with the availability of low-grade heat.
(b)	Reduction of the flue-gas flow	The flue-gas flow is reduced through, e.g.: improving the primary and secondary combustion air distribution; flue-gas recirculation (see Section 2.2). A smaller flue-gas flow reduces the energy demand of the plant (e.g. for induced draught fans).	For existing plants, the applicability of flue-gas recirculation may be limited due to technical constraints (e.g. pollutant load in the flue-gas, incineration conditions).
(c)	Minimisation of heat losses	Heat losses are minimised through, e.g.: use of integral furnace-boilers, allowing for heat to also be recovered from the furnace sides; thermal insulation of furnaces and boilers; flue-gas recirculation (see Section 2.2); recovery of heat from the cooling of slags and bottom ashes (see BAT 20(i)).	Integral furnace-boilers are not applicable to rotary kilns or to other furnaces dedicated to the high-temperature incineration of hazardous waste.
(d)	Optimisation of the boiler design	The heat transfer in the boiler is improved by optimising, for example, the: flue-gas velocity and distribution; water/steam circulation; convection bundles; on-line and off-line boiler cleaning systems in order to minimise the fouling of the convection bundles.	Applicable to new plants and to major retrofits of existing plants.
(e)	Low-temperature flue-gas heat exchangers	Special corrosion-resistant heat exchangers are used to recover additional energy from the flue-gas at the boiler exit, after an ESP, or after a dry sorbent injection system.	Applicable within the constraints of the operating temperature profile of the FGC system. In the case of existing plants, the applicability may be limited by a lack of space.
(f)	High steam conditions	The higher the steam conditions (temperature and pressure), the higher the electricity conversion efficiency allowed by the steam cycle. Working at high steam conditions (e.g. above 45 bar, 400 °C) requires the use of special steel alloys or refractory cladding to protect the boiler sections that are exposed to the highest temperatures.	Applicable to new plants and to major retrofits of existing plants, where the plant is mainly oriented towards the generation of electricity. The applicability may be limited by: the stickiness of the fly ashes; the corrosiveness of the flue-gas.
(g)	Cogeneration	Cogeneration of heat and electricity where the heat (mainly from the steam that leaves the turbine) is used for producing hot water/steam to be used in industrial processes/activities or in a district heating/cooling network.	Applicable within the constraints associated with the local heat and power demand and/or availability of networks.
(h)	Flue-gas condenser	A heat exchanger or a scrubber with a heat exchanger, where the water vapour contained in the flue-gas condenses, transferring the latent heat to water at a sufficiently low temperature (e.g. return flow of a district heating network). The flue-gas condenser also provides co-benefits by reducing emissions to air (e.g. of dust and acid gases). The use of heat pumps can increase the amount of energy recovered from flue-gas condensation.	Applicable within the constraints associated with the demand for low-temperature heat, e.g. by the availability of a district heating network with a sufficiently low return temperature.
(i)	Dry bottom ash handling	Dry, hot bottom ash falls from the grate onto a transport system and is cooled down by ambient air. Energy is recovered by using the cooling air for combustion.	Only applicable to grate furnaces. There may be technical restrictions that prevent retrofitting to existing furnaces.

Table 2

BAT-associated energy efficiency levels (BAT-AEELs) for the incineration of waste

BAT-AEEL
The BAT-AEEL only applies where a heat recovery boiler is applicable.
The BAT-AEELs for gross electrical efficiency only apply to plants or parts of plants producing electricity using a condensing turbine.
The higher end of the BAT-AEEL range can be achieved when using BAT 20(f).
The BAT-AEELs for gross energy efficiency only apply to plants or parts of plants producing only heat or producing electricity using a back-pressure turbine and heat with the steam leaving the turbine.
A gross energy efficiency exceeding the higher end of the BAT-AEEL range (even above 100 %) can be achieved where a flue-gas condenser is used.
For the incineration of sewage sludge, the boiler efficiency is highly dependent on the water content of the sewage sludge as fed into the furnace.
(%)
Plant	Municipal solid waste, other non-hazardous waste and hazardous wood waste		Hazardous waste other than hazardous wood waste^f1	Sewage sludge
Plant	Gross electrical efficiency ^f2 ^f3	Gross energy efficiency^f4	Boiler efficiency
New plant	25–35	72–91 ^f5	60–80	60–70 ^f6
Existing plant	20–35	72–91 ^f5	60–80	60–70 ^f6

The associated monitoring is in BAT 2.

Annotations

Footnotes

f1: The BAT-AEEL only applies where a heat recovery boiler is applicable.
f2: The BAT-AEELs for gross electrical efficiency only apply to plants or parts of plants producing electricity using a condensing turbine.
f3: The higher end of the BAT-AEEL range can be achieved when using BAT 20(f).
f4: The BAT-AEELs for gross energy efficiency only apply to plants or parts of plants producing only heat or producing electricity using a back-pressure turbine and heat with the steam leaving the turbine.
f5: A gross energy efficiency exceeding the higher end of the BAT-AEEL range (even above 100 %) can be achieved where a flue-gas condenser is used.
f6: For the incineration of sewage sludge, the boiler efficiency is highly dependent on the water content of the sewage sludge as fed into the furnace.