FGD retrofit - a techno economic case study

Prof. Dr. W.A. BeneschDirector Energy Technologies

STEAG Energy Services Germany

Overview

• The power station

• The flue gas treatment system

• Used FGD technology

• Wet stack• Wet stack

• Technical data and features

• Material recommendations

• Costs

• Major messages

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Voerde power plantHistory of a site

1970/71 Commissioning of units 1 and 2 of the power plant West, 350 MW each

1975 Forming of the special purpose company “Kraftwerk Voerde STEAG-

RWE oHG”;RWE Power AG 25 %, Steag 75 %

1982 Commissioning of unit A of the Voerde power plant (710 MW) with flue

gas desulfurization system

1985 Commissioning of unit B of the Voerde power plant (710 MW) with flue

gas desulfurization system

1987 Retrofitting of the power plant West with a flue gas desulfurization

systemsystem

1989 Retrofitting of both power plants with nitrogen oxide reduction

systems

2005 Partial modernization of flue gas desulfurization system,

with capacity increase (2 x 50 MW)

2006 Retrofitting of the power plant West with capacity increase (2 x 6 MW)

2017 The entire plant will be shut down in April due to the “Energy

Turnaround “

At Voerde site, STEAG operates the power plants West and Voerde.

2 pulverized-coal fired Benson slag tap boilers ( 980 t/h each),

2 pulverized-coal fired Benson boilers – dry ash removal (2,160 t/h each),

4 turbine-generator sets (2 x 350 MW, 2 x 761 MW in total 2222MW)

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General layout of the site

1. Coal conveyor belt

2. Boiler

3. Turbine hall

4. SCR

5. Ammonia storage5. Ammonia storage

6. ESP

7. FGD

8. ID-Fans

9. Stack

10. Cooling tower

11. Coal storage

Power Station Voerde Unit A/B

Boiler and turbine generator set

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Background

The units Voerde A/B had been equipped stepwise with flue-

gas treatment installations.

• Originally 30% of the flue gas had been cleaned of SO2.

• Later on, this had been extended to 100% of the flue-gas

stream.

• 1989 also the SCR technology had been implemented for

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• 1989 also the SCR technology had been implemented for

NOx reduction after

• exhaustion of all primary NOx measures before.

Over the years, especially the complicated FGD installation

caused high maintenance costs and OPEX which led to the

wish of a related cost reduction.

A study on a simple improvement of the FGD system did not

show the desired reduction of maintenance costs.

Units Voerde A/B, FGD – retrofit

Before retrofit

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Units Voerde A/B, FGD – retrofit

Retrofit without Bypass

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FGD-plant units Voerde A/BDesign data

Full load operating hours / year 2,000 to 7,000

Start up time (cold) 180 min

Ramp rate 7% / min

Primary Fuel: hard coal

LHV 25.5 to 30 MJ/kg

sulphur content 0.3 to 1.3 %

Flue gas data (110% load)

Volume 2,677,180 m³/h (st. wet)

SO2 content 640 to 2,635 mg/m³

HCL max 230 mg/m³

Dust max 100 mg/m³

Inlet temperature 130 to 180°C

Temperature in case of failure 220°C (max. 15 min)30.1.2017

FGD-plant for the units A/BPerformance dataEmissions (referring to dry flue gas, standard conditions, 6% O2 )

SOX as SO2 < 150 mg/m³

85 % sulphur reduction at the lowest

SO2 concentration in raw gas of 640 mg/m³ < 96 mg/m³

SO2 distribution in the flue gas downstream of the scrubber:

admissible deviations of the SO2 clean gas value

over the measuring section based on100 mg/m³ ± 30 % over the measuring section based on100 mg/m³ ± 30 %

Change of emission and performance values at

a concentration range in the flue gas of 10 % / min

HCl < 10 mg/m³

Content of dust < 10 mg/m³

Content of droplets in the flue gas downstream

of the mist eliminator < 20 mg/m³

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FGD-plant for the units A/BSpecial performance characteristics:

Gypsum dewatering

Residual moisture max. 10 %

Max. gypsum mass flow per filter 32.6 t/h

Absorbent consumption

per absorber (100% load) 10.48 t/hper absorber (100% load) 10.48 t/h

Energy consumption

per absorber (100% load) 2,935 kWh/h

Auxiliary plants 630 kWh/h

Admissible content of chlorine in absorber slurry

due to process and material technology 60,000 ppm

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FGD-plant for the units A/BAbsorber ain data and corrosion protection

Total height 35.8 m

Diameter 17 m

Bottom height 9.5 m

Bottom volume 2,383 m³

Absorber space velocity 3.8 m/sec

Number of nozzle levels 4

Suspension pumps 4 x 8,800 m³/h

Number of nozzles per level 189

Level distance 1.8 m

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Nozzle Level / Raw Gas Inlet

PP-Nozzle

Level

Brombutyl-

caoutchouc

Raw Gas

Inlet

Alloy

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4 single-stage centrifugal pump (mineral cast)

1 pump variable speed

capacity 8.800 m³/h

delivery height max. 21 m

power consumption 900 kW

Circulation pumps FGD VoerdeDetails

iron volute casing (with mineral-cast)

closed impeller (mineral-cast)

axial suction flange

tangential discharge flange

suction-side wear plate (mineral-cast)

single acting mechanical seal

pressure side diffusor / compensator-combination

Units Voerde A/BFGD – retrofit

Reasons for the FGD replacement (2005)

Improvement of the environmental situation

● SO2: from 400 to 200 mg/Nm³

● Dust: from 50 to 20 mg/Nm³

Capacity increase (710 MW ���� 760 MW, 2 x 50 MW) (710 MW ���� 760 MW, 2 x 50 MW)

Reduction of maintenance costs due to deletion of components

● Gas-gas heaters

● Flue gas dampers

● FGD booster fans

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No flue gas reheating• Reduction of the investment

• Reduction of the pressure loss, operating costs

• Reduction of the maintenance costs

Advantages and technical opportunities in case of no lower limit for the exhaust gas temperature

T > 72°C

Opportunities in that case:

Wet Flue gas discharge over

wet Stack

cooling tower

T 50-52°C

T 50-52°C

Decision for a wet stack

Total height 230 m

Diameter Ø 8 m

Reinforced concrete shaft with 2 flues

out of GRP (glass reinforced plastics)

Flue gas velocity < 18 m/s at 110% load

Condensate catching groove at flue gas inlet and exit of the stack

Condensate return in closed vertical channel

Avoidance of any obstacles in the flue gas stream

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• Flow velocity < 18 m/s

• Avoidance of guide vanes

• Avoidance of condensate accumulation

• Optimum hydraulic design for the flue gas duct entry

• Avoidance of vortex flows

Design criteria for „Wet Stacks“in general

• No reinjection of already condensed water into the flue gas stream

• Expansion joints with condensate extraction

• Complete acid resistant stack head

• No flange connection of flue gas ducts

• Condensate catching groove at flue gas inlet and exit of the stack

• FGD with three stage demister

• Acid resistant design of the flue gas duct and of flue gas guide vanes

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• Boiler: utilization of existing reserve capacity

• Turbine: utilization of existing reserve capacity

• ESP: static reinforcement

• Raw gas ducts static reinforcement or new

Units Voerde A/BOverall retrofit measures and costs

• ID – fans: retrofit

• Absorbers: new

• Clean gas ducts: new

• Stack: new wet stack

Investment: 80 Mio €

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The key for the successful, economic solution was the combination of different improvement measures for the entire power plant in one project. So

• the existing boiler margin had been used,

• slight improvements of the turbine had been done,

• the efficiency of the entire plant had been increased,

Major messages

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• the efficiency of the entire plant had been increased,

• the I&C-System had been retrofitted and

• the opportunities of a new regulatory frame work allowing a wet stack without reheating of the flue gases had been used.

• Finally, a simplified FGD system using the latest know-how of FGD technology, meeting also the in the meantime more stringent emission limits could make a successful project out of it, while

• the overall plant capacity had been increased by 2 x 50 MWel .

• At least the maintenance cost had been reduced significantly.