1. Petr Stehlik Technical University of Brno, Czech Republic
SOME ASPECTS CONTRIBUTING TO WASTE-TO-ENERGY AND ENVIRONMENTAL PROTECTION
Petr Stehlik Technical University of Brno, Czech Republic

2. INTRODUCTION Present situation:
Energy saving and pollution prevention = priorities
Sustainability concepts = complex problem
Renewable energy sources   e.g. Waste-to-Energy

3. Combustion of wastes (incineration)
WASTE-TO-ENERGY
Waste-to-energy (WTE) technology = = thermal processing of wastes including energy utilization
WTE systems  clean, reliable and renewable energy
Combustion of wastes (incineration)
generation of heat
steam  
sold
electricity
sold

4. WASTE-TO-ENERGY Environmental Benefit: Economic Benefit:
WTE prevents the release of greenhouse gases (CH4, CO2, NOX, VOC)
Dual benefit: clean source of electricity and clean waste disposal
Economic Benefit:
Renewable energy
Reduction of need to landfill municipal waste

5. WASTE-TO-ENERGY Reasons for Investment to WTE
Sources of renewable energy for electric generation
Note: Source - Renewable Energy Annual U.S. Department of Energy, Energy Information Administration

6. SUSTAINABLE DEVELOPMENT, EFFICIENT DESIGN AND RENEWABLE ENERGY SOURCES IN THE PROCESS INDUSTRY
The following criteria can play a decisive role:
economic and efficient process design
global heat transfer intensification (design of heat exchanger network for maximum energy recovery)
efficient selection of utilities including combined heat and power systems (co-generation) wherever possible
using waste-to-energy systems and/or their combination with conventional ones as much as possible

7. SUSTAINABLE DEVELOPMENT, EFFICIENT DESIGN AND RENEWABLE ENERGY SOURCES IN THE PROCESS INDUSTRY
Criteria (continued):
design of efficient equipment (reactors, separators, heat exchangers, utility systems etc.)
local heat transfer intensification (selection and design of individual heat exchangers including heat transfer enhancement)
and various other criteria

8. PROCESS, WASTE AND ENERGY

9. IMPROVED PROCESS AND EQUIPMENT DESIGN
Research domains in improved process and equipment design

10. IMPROVED PROCESS AND EQUIPMENT DESIGN (continued)
EXPERIENCE IN DESIGN AND OPERATION
SOPHISTICATED APPROACH
(ADVANCED COMPUTATIONAL METHODS)
IMPROVED DESIGN + =
Improved Process Design
Process integration (e.g. Pinch Analysis)
MER design
Utilities selection
Total Site Integration

11. adding a few more heat exchangers increased pressure losses
IMPROVED PROCESS AND EQUIPMENT DESIGN (continued)
Improved Equipment Design
Examples
New type of Shell-and-Tube Heat Exchanger
Retrofit of an industrial process:
adding a few more heat exchangers
energy saving
increased pressure losses
greater pumping power
FIND A SOLUTION !

12. IMPROVED PROCESS AND EQUIPMENT DESIGN (continued)
Conventional heat exchanger (segmental baffles)
Helixchanger
(helical baffles)
Comparison
Example:
p = 44 kPa
(crude oil preheating,1 MW, 90t/hr)
p = 17 kPa
Result: 60% reduction of operating cost
6.3% reduction of total cost

13. IMPROVED PROCESS AND EQUIPMENT DESIGN (continued)
Optimization of Plate Type Heat Exchanger
Minimization of total cost
(utilizing relation „p - h.t.c.”)
Obtaining optimum dimensions
Example:
Industrial unit for the thermal
treatment of polluting hydrocarbons
of synthetic solvents contained
in air (4.52 MW)
Result: up to 14% reduction of annual
total cost can be achieved

14. THERMAL TREATMENT OF HAZARDOUS INDUSTRIAL WASTES AND WASTE-TO-ENERGY SYSTEMS
Originally:
disposal of wastes (treatment of wastes)
At present:
waste processing (waste-to-energy systems)
recovering heat (generating steam & electricity
preheating purposes (reduced fuel demand)
processing of residues (vitrification)

15. THERMAL TREATMENT OF HAZARDOUS INDUSTRIAL WASTES AND WASTE-TO-ENERGY SYSTEMS - continued
EXAMPLES
Multi-purpose incinerator for processing solid and liquid wastes

16. INCINERATION VS. GASIFICATION - COMPARISON
Rotary kiln vs. gasification reactor 6 4 7 2
natural gas 3
Incineration 5
Legend: 1 - screw conveyor 4 - heat recovery steam generator
2 - rotary kiln 5 - steam turbine
3 - secondary combustion chamber 6 - off-gas cleaning system
7 – stack
Legend: 1 - screw conveyor 4 - secondary combustion chamber 2 - fluidized bed reactor heat recovery steam generator
3 - cyclone steam turbine off-gas cleaning system
8 - stack 5 6 8 7
flue gas 4
Combustion
solid waste 1 2 3
Gasification
flue gas
superheated steam
feed water
air ~
air
natural gas
Storage waste feeding
Heat recovery
Off-gas cleaning

17. INCINERATION VS. GASIFICATION - COMPARISON
Discussion of comparison Þ in the case of gasification:
Generating gaseous products at the first stage outlet up to 10 times lower Þ aspects influencing operating and investment costs
Considerably lower consumption of auxiliary fuel (natural gas) Þ autothermal regime
Reduced size of the afterburner chamber compared to that necessary for a comparable oxidation incineration plant

18. INCINERATION VS. GASIFICATION - COMPARISON
Discussion of comparison Þ in the case of gasification:
Lower specific volume of gas produced Þ reduction in size of flue gas heat utilization and off-gas cleaning systems Þ reduction of investment and operating costs of the flue gas blower
Lower production of steam (proportional to the volume of flue gas produced)
Disadvantage of gasification technology:
Treatment of wastes by crushing/shredding and by homogenization before feeding into the reactor

19. INCINERATION VS. GASIFICATION - COMPARISON
Comparison of the two alternatives
Auxiliary fuel
consumption
12 Nm3/hr
SCC
Secondary
combustion
chamber
Auxiliary fuel
consumption
602 Nm3/hr
Gas output
3 570 Nm3/hr
Gas output
Nm3/hr
Alternative with a rotary kiln
Alternative with a gasification
reactor

20. THERMAL PROCESSING OF SLUDGE FROM PULP PRODUCTION
Incinerator for thermal treatment of sludge from pulp production

21. Result: Modern up-to-date plant
COPMLETE RETROFIT
Result: Modern up-to-date plant

22. Incinerator capacity vs. dry matter content in sludge
RETROFIT: FIRST STAGE
Incinerator capacity vs. dry matter content in sludge

23. THERMAL TREATMENT OF HAZARDOUS INDUSTRIAL WASTES AND WASTE-TO-ENERGY SYSTEMS - continued
EXAMPLES
Incineration unit of sludge generated in the pulp and paper plant

24. RETROFIT: THIRD STAGE ECONOMICS ASPECTS
Investment return depending on MG/NG ratio
The curve is valid for:
considering depreciation, loan interest, inflation etc.
annual operation 7000 hours
nominal burners duty 6.4 MW (2.4 MW for fluidized bed combustion chamber and 4.0 MW for secondary combustion chamber)
investment of $ 250,000

25. RETROFIT: THIRD STAGE ECONOMICS ASPECTS
Major saving of operational cost
in terms of price of 1MW of energy:
price (MG)  2/3 price (NG)
MG – mining gas NG – natural gas
Possible saving of cost for fuel

26. DUAL BURNER ORIGINAL DESIGN: One fuel
Two stages of fuel and two stages of combustion air
LATER:
Dual burner = mining gas + natural gas (primary fuel) (auxiliary fuel)
INTERESTING APPLICATION:
Secondary combustion chamber in the incineration plant for thermal treatment of sludge from pulp production (see above)

27. DUAL BURNER

28. Utilisation of Alternative Fuels in Cement and Lime Making Industries
Current situation:
alternative fuels (wastes) used mainly in cement kilns
use of alternative fuels in lime production is less applied due to potential impact on product quality
practical issues of the application include waste specification, way of feeding, product quality, and emission levels

29. PERFORMANCE TEST Feeding of alternative fuel:
composition: mixture of crushed plastic, textile, paper
pneumatic conveying into the kiln by special nozzle beside main burner
heating value: 24 GJ/t (compared to 39.5 GJ/t of the baseline fuel)

30. PERFORMANCE TEST Test site: limekiln, production capacity 370 t/d
rotary kiln
baseline feed: black oil (~1.8 t/h)
goal: to feed 0.5 t/h of waste and validate product quality, emission levels, and the potential for savings

31. PERFORMANCE TEST
Alternative fuel

32. PERFORMANCE TEST

33. PERFORMANCE TEST

34. PERFORMANCE TEST
Double-tube
feeder

35. PERFORMANCE TEST
Test evaluation:

36. PERFORMANCE TEST Conclusions:
Substitution of a part of the conventional fuel to cover partially heat supply demands of cement factories
It is possible to achieve 10 to 20% of the overall energy demand of the rotary kilns
In the case of limekilns (where substitution of the noble fuels is often hindered by higher requirements on the final product quality) up to 17% of the primary fuel without notable impact on the lime quality was achieved

37. CEMENT FACTORY
Potential for savings in a cement factory with the same alternative fuel:

38. CEMENT FACTORY
Potential for savings in a cement factory with the same alternative fuel:

39. Waste-to-Energy Plant Structure
THERMAL TREATMENT OF HAZARDOUS INDUSTRIAL WASTES AND WASTE-TO-ENERGY SYSTEMS - continued
Waste-to-Energy Plant Structure
Processing of wastes of wide spectrum
WTE Plant Structure
(mutual interconnection of main units )
WTE utility heat output - for various purposes
(e.g. servicing district heating system, air conditioning, chilled
water production, exporting steam to an industrial plant)

40. Combustion Turbine Heat Recovery Gen - set Steam Generator
Steam Turbine
Heat Recovery
Steam Generator
Heat Exporting Unit
Natural Gas
Air
Flue/Exhaust
Gas
Power to the Grid
Water
Steam from
Flue Gas Heat
Recovery Boiler
Steam
Exported Heat

41. NaHCO3 Injection Assembly Rotary Kiln & Secondary
Ash
Flue Gas
Waste pretreament
Incoming
„Solid“ Waste
Close Coupled
Gasifier Combustor
Waterwide
Flue Gas Heat
Recovery Boiler
NaHCO3 Injection Assembly
& Chemical Reactor
Rotary Kiln & Secondary
Combustion Chamber
Liquid
Waste
Natural
Gas
Air
Water
Steam to
Steam Turbine
Flue Gas to Fly
Ash Separation
Flue Gas
Steam

42. Fluidized Bed Sterilizing
Selective Catalytic
Reduction Facility
Fly Ash Separation
Fabric Filter
Fluidized Bed Sterilizing
- Drying Unit
Flue/Exhaust
Gas
Natural
Air to Rotary Kiln
& Secondary
Combustion
Chamber
Concentrated Waste
Water Treatment Sludge
Separated Fly Ash
Vitrification Unit
Flue / Exhaust
Fertilizers
Fly Ash
Air
Glass Products
Flue Gas

43. CONCLUSION It has been shown how various aspects of a process and
equipment design can contribute to improving economic
and environmental design.
WTE systems provides us with clean, reliable and
renewable energy.
WTE systems = up-to-date technology + experience
(know-how) + theoretical background
Examples