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Regional Waste Managment

Introduction

The middle size WtE plant is an example of the integrated approach to waste management. A dedicated MBT facility adjacent to the WtE plant was constructed and installed to process waste from up to 300,000 people in several municipalities and effectively convert the waste from the landfill to renewable energy for the community.

The facility was designed to convert RDF and sewage sludge into renewable heat for the district heating and power for the local community or other purpose. The fully WID-compliant plant can process up to 35,000 t/year of mixed waste (80% of RDF and 20% of sewage Sludge).

Process diagram

 

Process description

- Fuel storage & feeding
RDF is tipped into the reception bunker. An automatic single crane is used to extract the RDF from the bunker.

Sewage sludge is delivered to a storage tank. From there, it is pumped and blended with the RDF prior to feeding into the grate using 4 parallel screw feeders.

- RDF composition

FRACTION

Properties

Fuel composition

Water

Ash (%)

Burnable

Heat value (Mj/Kg)

Average content (%)

Textile

7.56

5.76

86.68

16.65

15

Cardboard

6.85

11.88

81.27

17.49

13.5

Paper

23.99

12.43

63.58

10.1

38

Plastic foil

0.51

13.24

86.25

40.14

13.5

Hard foil

0.4

5.28

94.32

40.12

11

Plastics

0.42

0.15

99.43

21.51

5

Wood

12.52

2.31

85.17

16.32

3

Styrofoam

1.07

9.98

88.95

27.95

1

 

Process scheme

Furnace – Gasification chamber
Primary chamber: hydraulically moving grate design base with primary air cooling; three-point combustion air introduction for gasification and complete combustion (quantity of primary air is 70% of stoichiometric air needed for combustion), flue gas recirculation for fuel drying and primary NOx control. Pyrolytic and gasification process at temperatures from 600 to 850 °C.
Secondary chamber: a standby gas burner is used for temperature boost, if necessary, as the flue gas temperature above 850°C up to 1200 °C has to be maintained for more than two seconds as required by WID.

Steam boiler
A water tube boiler with vertical tubes consists of a radiation chamber – the membrane walls partially lined with refractory to decrease the heat load on the walls, the second and third evaporator pass. The third pass with two super-heaters and evaporators. An economizer is installed as the fifth pass in order to preheat water and increase efficiency. The pressure of live steam is 42 bar and the temperature 410°C.

Boiler cross section

Flue gas cleaning
From the economizer, flue gases are directed to the cyclone to take off a large part of dust load. Sodium bicarbonate and activated carbon are then blown in for dry cleaning. Fine dust, sodium bicarbonate and activated carbon are cleaned in a bag filter. Ammonia water is injected as the secondary measure to lower NOx.

Continuous Emission Monitoring (CEM)
CO, NO, NO2, O2, SO2, HCl, HF, TOC, Hg, NH3, moisture, dust, temperature, pressure, mass flow.

Stack height: 25 m

Steam turbine
The turbine installed can be a backpressure steam turbine (for production a lot thermal energy) or condensing steam turbine with controlled extraction for combined heat and electricity. Condenser solution depends of cooling water availability (water cooled with wet cooling tower, air cooled).

Heat production
Plant can generate 0 - 15 MW of heat for the district heating system or other purpose.

Legislation
WID Compliant, PED compliant (CE mark), IPPC, BREF, BAT

Emissions

 

Unit

Measured

Allowed

CO

mg/m3

3.0

30

TOC

mg/m3

0.56

10

NOx

mg/m3

135.79

180

Dust

mg/m3

1

5

SO2

mg/m3

0.62

40

HCl

mg/m3

2.34

8

HF

mg/m3

0.18

1

Positive environmental and economical benefits:

  • Reduction of landfilled waste
  • 100% disposal of local sewage sludge (40% ash residual)
  • Waste from local population given back as electricity/heat
  • Minimized waste transport and additional environmental pollution
  • Net fossil fuel savings (heating): ~4.000.000 m3 natural gas/year
  • Reduction of greenhouse gases
  • Optimal utilization of heat and electricity

Plant Capacities

  • Minimum plant capacity: 10.000 t/year
  • Maximum plant capacity: 40.000 t/year
  • RDF: Sewage sludge ratio: 80 : 20 %

Additives consumption (for reference plant)

  • Bicarbonate: ~ 18 kg/t RDF+sludge
  • Activated carbon: ~ 1,1 kg/t RDF+sludge
  • Carbon: ~ 1,1 kg/t RDF+sludge
  • Ammonia: ~ 1,3 kg/t RDF+sludge

Remark: Additives consumption primary depends of pollutants content!
Waste production:

  • Inert waste: ~ 125 kg/t RDF+sludge
  • Dangerous waste: ~ 45 kg/t RDF+sludge

Remark: Waste production primary depends of inorganic part in fuel

Flue gas scrubbing

SNCR

Ammonia solution:
reduction of NOX

Dry flue gas scrubbing
Sodium bicarb. powder for reduction of acid gases:
SO2, HCl and HF

Activated carbon powder:
elimination of heavy metals & dioxins/furans

Filters
Ceramic filter
Activated carbon filter

Activated carbon filter, CEMS and stack

Ceramic filter

Ceramic filter:
Particle reduction: ~99,9%
No. of pods: 12
No. of elements: 4800

Fly ash silo:
Volume: 85 m3
Storage cap. for 5-7 days.

Ceramic filter and fly ash silo

Activated Carbon Filter

Activated carbon filter*:
Reduction of TOC, dioxins, furans and heavy metals including Hg.
No. of pods: 21

Activated carbon filter

CEMS and Stack

Flue Gas Fan:
Volume flow: cca. 33.000 Nm3/h
Continuous Emission Monitoring (CEM):
CO, NO, NO2, O2, SO2, HCl, HF, TOC, Hg, NH3, moisture, dust, temperature, pressure, mass flow
Stack:
Height: 25m

CEMS and stack

Input/Output

EXAMPLE PLANT CONFIGURATIONS (informative) for RDF fuel

Plant Size

Gross Power with back-pressure steam turbine

Gross Power with condensing steam turbine

RDF

MWth

MWel

MWth

MWel

MWth

t/year

10

1,2

6,6

2,1 – 1,5

0 – 4,5

18.000

12,5

1,5

8,3

2,6 – 1,8

0 – 5,6

22.500

15

1,8

10,0

3,1 – 2,2

0 – 6,7

27.000

18

2,2

12,0

3,7 – 2,7

0 – 8,1

32.500

20

2,5

13,2

4,2 – 3,0

0 – 9,0

36.000

25

3,0

16,5

5,2 – 3,7

0 – 11,2

45.000