Keynote Presentation at WASTEENG 2014 Rrio de Janeiro, August 25-28

Comparison of Transport and Reaction Phenomena in Waste-to-Energy (WTE) Power Plants

Prof. Nickolas J. Themelis, Director, and Olivier L.R. Morin, Research Associate

Origin of this study: Comparison of geometry and operating parameters of existing MSW and biomass WTE operations Feedstock

Technology Plant location Starting year Unit capacity, tons/day Height of combustion chamber, Length of grate, m Width of grate,m Grate area, m2 Combustion chamber cross sect. area, m2 Volume of combustion chamber, m^3 Flue gas flow, Nm3/ton Process gas volume, Nm3/hour Assumed ave gas temperature, °C Velocity of gas in comb. chamber, m/s Average minimum residence time, s Grate combustion capacity, tons/h/m2 Heat value of fuel, MJ/kg Heat value of fuel, MWh/ton Thermal flux, MW/m2 of grate area

Shredded MSW MSW MSW2 MSW3

SEMASS Rochester MA 1988 Mass burn Mass burn Brescia Union, NJ 1998 1994 Mass burn Essex, NY 1990 910 30 6 11 66 792 22 8 12.8

102 480 19 7.48

7.8

58 845 20.42

10.7

6.14

66

Wood chips

57% H2O, FB Archangelsk 2001 1584 16.2

6.4

5.8

37

Coal slurry, Shredded MSW4

39% H2O, CFB Karita 2001 48.4%H20, CFB Cixi, China 2012 7318 44.6

9.8

9.8

97 800 16.8

6.94

3.14

21.79

66 1980 5600 212333 950 3.67

8.18

0.57

11.6

3.2

1.9

62 1210 4091 135003 950 2.50

8.79

0.32

11.3

3.1

1.0

38 663 5653 113052 950 3.39

5.60

0.34

11

3.1

1.0

32 1205 5200 183182 950 6.53

3.13

0.54

11

3.1

1.6

37 601 3750 247500 950 7.60

2.13

1.78

8.7

2.4

4.3

97 4326 6100 1860012 950 22 2.04

3.14

10.3

2.9

9.0

21.79

366 2550 85000 950 4.45

3.78

1.53

3.98

1.11

1.69

Fluid bed power plants burning wood chip slurries (40% water): Heat flux of 4-9 MW/m2; Moving Grate power plants burning MSW (30% water: Heat flux of 1-2 MW/m2

+ + 120 kWh,el/ton + 0.6 MW el +0.1

MW el The EEC hierarchy of waste management

Energy recovery from “wastes”(waste-to energy or WTE) is equivalent to recycling

• Today, several countries such as Japan, Austria, Switzerland, Germany, the Netherlands, Korea and Singapore use WTE as the main process for treating post-recycling municipal solid wastes (MSW).

Estimated global disposition of urban post-recycling municipal solid wastes (total: 1.2 billion tons; 2012)

•

Thermal treatment (WTE): 200 mill. tons

• Sanitary landfill, partial CH4 recovery: 200 mill. tons • Landfilled without CH4 recovery: >800 mill. tons

Estimated land use for sanitary landfilling: 10 tons MSW per square meter

There are only two options for managing post recycling wastes: Sanitary landfill or thermal treatment (WTE) WTE advantages:

• Conservation of land near cities • Energy recovery: 0.5 MWh/ton, over LFG recovery • Reduction of Greenhouse Gas (GHG) emissions: 0.5-1 ton CO2 per

ton MSW (vs landfilling)

• Esthetically more acceptable to communities; in fact only

acceptable option in most developing countries.

There are only two options for managing post recycling wastes: Sanitary landfill or thermal treatment (WTE) WTE disadvantages:

• Dissemination of wrong information by some environmental

organizations (“God recycles but devil burns”)

• Some of these organizations were formed at a time (before

1990) when incinerators were major emitters of heavy metals and dioxins. However, their opposition has not changed as the Air Pollution Control systems of WTEs have improved to the point that total toxic emissions of WTEs have decreased by factors of 1000 to 10000. For example total toxic dioxin emissions of U.S. are now <5 grams/year.

• Initial capital investment

Waste-to-Energy (WTE) Facility Reducing the Volume of Waste & Generating Energy 13,000 KWh generated IN 90% volume reduction 100 cubic yards

of waste

E = M x C 2

Energy is mass times a constant

OUT 10 cubic yards

of (inert) ash

The economics of WTE plants – Sources of revenues

• • • Both sanitary landfills and WTE plants need a “gate fee” (e.g., $/ton) to support them.

This fee ranges from $100/ton MSW, in some highly developed nations, to as low as $20/ton for partially sanitary landfilling in Latin America.

The second source or revenue for WTE plants is the sale of WTE electricity; for Latin America it is projected to be about $50/ton MSW.

The economics of WTE plants – Sources or revenues (cont.)

• Truly sanitary landfills can recover methane gas and use it to produce electricity. Generally, this amounts to about 0.1 MWh/ton MSW, i.e. about $10/ton.

The economics of WTE plants: Revenues

• • According to the numbers presented earlier, future WTE plants in Latin America will enjoy a revenue of $70/ton of MSW, while the revenue of sanitary landfills will be only $30.

However, what tips the balance in favor of sanitary landfilling is the high capital cost of WTE plants.

A WTE problem: Capital investment

• In contrast to landfills, which can be expanded year after year (“cell by cell”), a WTE plant requires an initial, very large investment.

• Therefore, in a less than five years horizon, a community needs to spend a much smaller sum to start a sanitary landfill than a WTE power plant.

The economics of WTE plants – The cost of repaying the capital investment

• • • Modern WTE plants, equipped with Air Pollution Control systems that meet the E.U./U.S. standards cost over $600/ton of annual capacity.

In order to pay this amount back over a period of 20 years (usual contract) requires a capital charge of about $60/ton. Therefore, communities who only pay a “gate fee” of $20/ton MSW cannot afford a WTE plant.

CONCLUSION FOR LATIN AMERICA:

It is necessary to use a WTE technology that requires a lower capital investment than the Moving Grate technologies offered currently

Most common WTE technology: Combustion on moving grate

Over 700 operating plants. I n 2000-1012, there were built over 120 new grate combustion plants (over 25 million tons of new capacity)

Emerging WTE technology: Circulating Fluid Bed

Developed and used mostly in China: Suitable for high organic, high moisture urban wastes (Zhejiang University, Hangzhou: Chinese Academy of Sciences, Beijing)

Reasons for dominance of Moving Grate WTE

• Simplicity of operation • Technology gradually developed over 100 years and constantly advancing • Very high plant availability (>8,000 hours per year • Low personnel requirement (<70 for a one million tons/year plant) and ease of training of personnel of new plants

The Moving Grate technology

Inlet of MSW FB 1 RB 1

Three types of Moving Grate systems

RB n : reciprocating bar FB n : fixed bar Inlet roller Inlet 30 Outlet of Ash

Forward Acting Grate (FAG) -Von Roll type -

RB n : reciprocating bar FB n : fixed bar 30 o Outlet

Roller Grate (RG) - Duesseldorf/Babcock Grate -

FAG Main differences Grate Types RAG RG FB 1 RB 1 26 o

Reverse Acting Grate (RAG) - Martin type -

Outlet Push Forward Reverse Convey in proportion to friction (shear stress) Reciprocation Reciprocation Same direction

MSW Size Distribution and Cumulative Distributions

6 4 2 0 0 14 12 10 8 20 18 16 MSW Particle Size Distribution MSW particle size distribution and cumulative distributions Experimental Data (NYC-MSW) Gamma Distribution 5

D



-

 = 6.4

cm D



=12.8

cm

 0.29

%

10 15

D median

= 11.75

cm D



+

 = 19.2

cm

20 25 30 Particle size (

cm

) 35 40 45 50 Cumulative Distributions MSW particle size distribution and cumulative distributions 0.4

0.3

0.2

0.1

0 0 1 0.9

0.8

0.7

0.6

0.5

Cumulative Density Distribution of Gamma Function F(d): Particle Size Cumulative Density Distribution of Gamma Function F(d Particle Volume

3

): 5 10 15 20 25 30 Particle size (

cm

) 35 40 45 50 Source: M. Nakamura, M.J. Castaldi, and N.J. Themelis, "Numerical Analysis of size reduction of municipal solid waste particles on the traveling grate in a waste-to energy combustion chamber," Proc. 14th annual North American Waste To Energy Conference (NAWTEC14), pp. 125-130, Tampa, FL (2006)

200 180 160 140 120 100 80 60 40 20 0 0 Smaller MSW particle size increases greatly the rates of heat transfer and combustion Wood particle Conversion time vs diameter T=773 K T=973 K T=1173 K 4069.7

3391.4

2713.1

2034.8

1356.6

678.28

( in mm ) 0 866.75

1733.5

2600.3

3467.

4333.8

Temp, K 5200.5

6067.3

6934.

871 807 743 679 615 551 487 423 359 295 1.51e+003 1.45e+003 1.38e+003 1.32e+003 1.26e+003 1.19e+003 1.13e+003 1.06e+003 1000 935 PROJECT Solid Temperature [K] Thu Nov 14 11:31:52 2002 NewProject 20 hr 00 min 00 sec 000 msec

"Modeling of Waste-to-Energy Combustion with Continuous Variation of the Solid Waste Fuel,"

2003 ASME ICMEE, Washington, D.C. (2003) 5 10 15 Wood particle diameter,

d

(cm)

t

95 = 5.4

´ 10 5 ´ (0.8

´ 10 -3 ´ 1 6 (T-273) 1.39

´ p ´ d 3 ) 0.54

»

d

1.62

20 25 From Masato Nakamura PhD Thesis, Columbia University, 2008:

Rx time for 95% combustion proportional to (d particle ) 1.62

What is a Fluidized Bed?



It is an operation blowing solid particle swarms with gas or liquid, making solid particles turn into fluid-like state .



The gravity on the particles is offset by drag imposed on fluid, so particles are at the state of semi-suspended .

With the addition of airflow speed, solid particles show different flow state.

Types of MSW Fluid Bed furnaces Vertical flow Spiral-shaped Downward spiral-shaped Upward spiral shaped

Circulating fluidized bed is more suitable and originally developed for low heating value waste.

In contrast to MG, CFB requires shredding of the MSW Shredding, as applied in the RDF WTE plants in the 20 th century, was by means of hammermills; it was complex and very costly in construction and operation

Low-speed, high-torque shredders have been developed since the U.S. RDF plants of the early nineties

Cixi WTE advance: Low-Speed, High Torque shredder is part of MSW bunker. Shredder is fed as received MSW by overhead crane and shredded outflow is fed by crane to CFB unit.

Shredder energy: <10 kWh/ton MSW

The CFB technology of Zhejiang University for burning materials of:



Different density



Different size



High moisture



Particles in ZJU CFB are engaged in two flows:r



Heavier particles are reacted in bubbling flow;



lighter, smaller particles are reacted in circulating flow fuel outer cycle Bubbling flow

Exit point of bottom ash

Schematic diagram of CFBI

Comparison of various WTE plants in China (Huang, Chi, and Themelis, 2013) Plant

Technology

Ningbo Fenglin Shanghai Pudong Shanghai Hongqiao

Multistage MG Reverse MG Reverse MG

Cixi, Zhejiang

CFB Unit capacity, t/d 350 364.8

500 800 Grate/Plate area, m 2 Grate/Plate feedstock load, kg/m2/h Thermal energy flux, MW/m2 73.90

197

0.37

61.47

237.24

0.50

86.00

242.25

0.5

10.60

3144.65

3.48

Waste to energy (WTE) plants in China

(ref. Zheng, 2014) • • • • 77 plants use Moving Grate MG) technology 59 plants use Fluidized Bed Combustion technology (Zhejiang, U,; Chinese Academy of Sciences: Tsing Hua U.) Total operating WTE/incineration plants: 136 The Cixi 899 ton/day unit is based on Zhejiang U. technology.

Comparison of some operating parameters of MG and CFB Parameter Reactor type Fly ash amount (as a percentage of waste input) Bottom ash amount (as a percentage of waste input) Average particle residence bubbling bed time in Average gas residence time in combustion chamber Excess air amount Typical results for MG Reactors MG 3% 22% 1 hour 8 seconds 80 - 90% 800 ton/day CFB unit in Cixi plant CFB 12% 16% 54 minutes 3.8 seconds 40%

Very rough capital investment costs

(ref. various sources including Columbia thesis of Ling Qiu (2013)

Technology , location Moving grate expansion, U.S.

Moving grate, greenfield, Canada CFB, China CFB, outside China Capital investment, US$/ton annual capacity 600 700 200-300 ???

If you are interested in learning more about CFB and WTE:

• • Try to attend the ICIPEC International Conference in Hangzhou, China, October 14-17 (www.icipec2014.org) Try to attend the WTERT 2014 Meeting at Columbia University in the City of New York, October 9-10 (www.wtert.org).