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High efficiency integrated solid waste to energy system


High-Efficiency Integrated Solid Wasteto-Energy System
Kuanrong Qiu and Skip Hayden CANMET Energy Technology Centre-Ottawa Natural Resources Canada

Drivers and Opportunities<

br />? Landfills not a sustainable solution and rising pressure against landfilling. Need for alternatives ? MSW “renewable biofuel”; 65-85% carbon-neutral ? Waste to energy (or Energy from waste): Energy production; Volume reduction and conversion of toxic compounds into less harmful forms via combustion ? Problems with conventional MSW incineration: poor energy recovery efficiency; corrosion; environmental issues ? Alternative: MSW-based hybrid combined cycles for high-efficiency power production; MSW as fuel for bottoming cycle; Gas turbine for topping cycle

Objectives of this work
? Design and optimize combined cycle configurations ? Establish model for combined cycle power plant; Performance simulations ? Assess viability of combined cycles; Evaluate benefits and advantages ? Find out potential for net CO2 emissions reduction ? Economic feasibility ? Provide accurate and scientific information on feasibility and benefits of EfW from proposed combined cycles

MSW as fuel and energy recovery potential
? MSW heating value 8 to 12 MJ/kg (average 10.5 MJ/kg), compared to 19 MJ/kg for dry wood, 15 MJ/kg for lignite or 22 MJ/kg for coal 740 kWh electricity per T MSW if 25% electrical efficiency

?

Problems with power production by conventional MSW incineration
? Aggressive compounds in flue gases are highly corrosive at high temperature ? Low steam temperature has to be used in order to avoid severe corrosion of heat exchangers by flue gases at high temperature. This limits electrical efficiency ? Few extraction points on steam turbine because of low steam parameter thereby limiting feedwater temperature and boiler efficiency

Combined cycle configurations
Air

Natural gas

MSW

Natural gas

Gas turbine Air Steam turbine

MSW

Basic configuration I
Air

Basic configuration II

Benefits of MSW boiler and gas turbine combined cycles Increased power output (1+1>2) Increased efficiency Reduced environmental loading Reduced CO2 emissions High flexibility Eeduced specific investment (less costly than two separate power plants)

Model for MSW/natural gas combined cycle power plants

1 Combustion air; 2 Fan;

Configuration I

3 Air heater; 4 MSW input; 5 MSW boiler; 6 Water pump; 7 Deaerator; 8 Feedwater heater; 9 Makeup/Blowdown; 10 Water pump; 11 Watercooled condenser; 12 Cooling tower; 13 Steam turbine; 14 Superheater; 15 Economiser; 16 Scrubber; 17 Water source; 18 Selective catalytic reactor; 19 Fan; 20 Stack; 21 Air source; 22 Gas turbine; 23 Natural gas input; 24 Superheater; 25 Economiser; 26 Fan; 27 Stack

Configuration II

Summary of modeling results for combined cycle power plants
Power plant summary Conventional MSW power plant Configuration I Configuration II

MSW input, kW Natural gas input, kW Gas to MSW ratio Gross power output, kWe Plant auxiliary, kWe Net power output, kWe Net electrical efficiency, % MSW-based efficiency, % Marginal efficiency, %

126304 0 0 35584 3490 32094 25.41 25.41 0

126122 83741 0.664 85309 (ST55309+GT30000) 5246 80062 38.15 32.1 57.0

127667 83741 0.656 84522 (ST54522+GT30000) 4770 79752 37.72 31.5 56.8

MSW-based efficiency:

Marginal efficiency:

Electrical efficiency as a function of ratio of natural gas input to total energy input
45 Efficiency of combined cycle, % d 40 c a 35

b

30

a: Configuration I; Gas turbine efficiency=32% b: Configuration I; Gas turbine efficiency=35% c: Configuration II; Gas turbine efficiency=32% d: Configuration II; Gas turbine efficiency=35%

25 0.1 0.2 0.3 0.4 0.5 0.6 Ratio of natural gas input to total energy input

Flue gas cleaning systems
? Pollutants from flue gases: particulate matter, cadmium, lead, mercury, dioxin/furan, hydrochloric acid, sulphur dioxide, nitrogen oxides and organic matter State-of-the art flue gas treatment: Removal of fly ash Wet scrubbing or dry lime spray scrubber – remove acid gases such as SO2, HCl and HF Powdered activated carbon (PAC) absorption or activated carbon filtering – remove heavy metals such as mercury aa well as dioxins/furans Baghouse filtering – remove most types of particulate matter Selective catalytic reduction (SCR) – reduce NOx .

? 1. 2. 3.

4. 5.

Emissions from an EfW power facility

Potential for CO2 emissions reduction by EfW and combined cycles
1. Avoided methane credit; CH4 greenhouse factor: 25 more than CO2 2. 65-85% carbon-neutral (CO2 bioderived) 3. Less fuel input or CO2 emissions per unit power due to high efficiency

Net CO2 emissions
1.2 a: MSW power plant b: MSW/gas combined cycles c: Coal-fired power plant d:Gas-fired power plant

1 Net CO2 emissions, kg CO2/kWh

0.8

0.6

0.4

0.2

0 a b c d

Economic analysis
Ccapital + CO & M + C fuel + Cdisposal Pel t

COE =

Ccapital = CRF Cinvestment

CRF

i (1 + i ) n = (1 + i ) n ? 1

Annual capital cost, O&M costs and cost of electricity (COE)*

*MSW tipping fees not considered. MSW tipping fees ($35–$85/ton) provide a large source of income.

Summary
? MSW and natural gas hybrid combined cycles dramatically increase energy recovery efficiency and offer many advantages ? Both MSW and natural gas are used with higher efficiency in hybrid combined cycles compared with separate single-fuel power systems. ? Increased power output ? High flexibility ? Reduced specific investment and lower COE ? Reduced CO2 emissions


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