Performance and System Optimisation of Flue Gas ... presentations/4B_… · Performance and System...

1 | FGD for oxyfuel combustion | J. Yan et al., | 2013.09.12

Performance and System Optimisation of Flue Gas Desulphurisation for Oxy-coal Combustion

Jinying Yan*, Rainer Giering, Richard Faber and Uwe Burchhardt Vattenfall R&D Projects Michaela Zennegg and Thomas Schmidt Babcock Noell GmbH The 3rd Oxyfuel Combustion Conference, Ponferrada, Spain, September 9-13, 2013

Agenda

• Long-term performance (2008 to 2012) • FGD system for oxyfuel combustion CO2 capture pilot plant at

Schwarze Pumpe - Sulphur removal efficiency - Achievable clean flue gas - Slurry chemistry and impacts on performance - Impacts of external oxidation - Emission characteristics (to air, liquid and solid streams) • System Optimisation for Oxy-coal combustion (reported by Babcock

Noell GmbH) - Conducted tests - Results

• Conclusions



FGD System (1) - Operation hours from 2008 to 2012

From September 2008 to December 2012 the OxPP was operated with

• air firing:

~ 4 300 h

• oxyfuel combustion:

~ 13 200 h


FGD System (2) General Information

Characteristics:

• Flue gas: approx. 12.000 Nm³/hr wet • Process: lime stone process (wet)

approx. 155 kg limestone/h

• SO2-removal: > 99 % • Variations: up to 3 trays up to 4 spray levels • Gypsum: CaSO4 approx. 100 kg/hr

(used as construction material)

Contractor: Babcock Noell GmbH (Bilfinger)


FGD System (3) Flow Chart

Main difference to „normal“ FGD is the separate oxidation in the reaction tank to avoid air ingress during oxyfuel operation

FGD Performance (1) – for Normal Lignite (2008-2012)

Under design conditions: • SO2 removal efficiency can easily be achieved over 99% (e.g. 99.1 - 99.8 %), • SO2 concentration is in clean flue gas in a range of 15 – 55 mg/Nm3 as the inlet SO2 concentration is in a range of 5000 – 8500 mg/Nm3

FGD Performance (oxyfuel combustion)

0

10

20

30

40

50

60

70

80

90

100

5000 5500 6000 6500 7000 7500 8000 8500

Inlet SO2 (mg/Nm3, dry)

Out

let S

O2

(mg/

Nm

3, d

ry)

97,097,297,497,697,898,098,298,498,698,899,099,299,499,699,8100,0

SO2

rem

oval

(%)

Outlet SO2 SO2 removal


FGD Performance (2) – for Lignite with Higher Sulphur Content

For high sulphur lignite: SO2 concentration up to 20 500 mg/Nm³ dry

Suluhr removal efficiency > 99 %


Slurry Chemistry (1) – pH and Impact on performance

Impacts of slurry pH on SO2 removal and concentration in clean flue gas

(Red lines mark the SO2-removal efficiency and the SO2- value in the flue gas regarding the unit design)

Trend graphs show the impact in oxyfuel operation mode in general


Slurry Chemistry (2) – Impact of Oxidation Process

• Oxidation combined degas reduces the effects of CO2 partial pressure on slurry chemistry; • Impacts of slurry pH on residual limestone contents are similar between oxyfuel and air-firing after the oxidation process; • Slight lower residual limestone could be expected in the slurry for oxyfuel combustion under the same slurry pH



Emission Characteristics (1) – to Air

Depending oxidation air flow H2O: 27 – 28 vol%, CO2:18 – 21 vol%, O2: 15 – 16 vol%,

SO2: near 0, NO: near 0, NO2: near 0

CO2 loss: ~ 0.9 %

Emission characteristics have been changed with

significant reduction of the emissions to air

Emissions to air

Emissions to liquid and solids

Min/out xx-measurement points and data (mass balance)


Emission Characteristics (2) – to Solids (gypsum)

No significant changes in heavy metals contained in the FGD by-products (gypsum) in comparison with the FGD by-products from conventional combustion flue gas treatment

VGB Investigation* OxPP measurements

Nature gypsum Hard coal plants Lignite plant Air-firing Oxyfuel

As mg/kg 0,22 - 3,79 0,21 - 2,7 2,04 - 2,6 0,65 0,45

Be mg/kg <0,1 - 0,71 <0,05 - 0,65 0,1 - 0,42 <0,6 <0,6

Pd mg/kg <2,5 - 21,41 0,27 - 22 <3 - 11,1 <0,6 <0,6

Cd mg/kg <0,02 - 0,52 <0,02 - 0,29 <0,02 - 0,15 <0,4 <0,4

Co mg/kg 0,01 - 4,39 0,06 - 2,2 0,49 -0,53 <0,6 <0,6

Cr mg/kg 0,65 - 24,9 1,02 - 9,72 2,75 - 4,8 2,6 3,2

Cu mg/kg 0,01 - 14 1,2 - 8,56 1,1 - 4,65 <0,6 <0,6

Mn mg/kg 4,08 - 195 3,67 - 196 41,7 - 64,9 16,8 13,7

Ni mg/kg 0,3 - 13,4 0,3 - 12,9 1,63 - 3,2 1,3 1,7

Hg mg/kg <0,006 - 0,09 0,1 - 1,32 0,66 - 0,9 0,82 0,85

Te mg/kg <0,1 - <0,2 <0,1- <0,3 <1,3 <1,3

Tl mg/kg <0,05 - 0,2 <0,05 - 0,42 <1,0 <1,0

V mg/kg 0,93 - 26,4 1,22 - 7,7 3,55 - 5,4 1,5 1,5

Zn mg/kg <3 - 41 1,7 - 53,2 24,3 - 43 8,3 8,3

* Based on the VGB report, comparison of nature gypsum and FGD gypsum, VGB-TW 707, VGB, 1990.


Emission Characteristics (3) – to Liquid (FGD blow-down)

Limits Air-firing Oxyfuel

Suspended solids mg/l 30

COD mg/l 80/150 168 109

Nitrogen compounds mg/l - 24,6 3,69

Sulphate mg/l 2000 2012 1898

Sulphite mg/l 20 <0,1 <0,1

Sulphide mg/l 0,2

Cd mg/l 0,05 0,036 0,037

Cr mg/l 0,5 <0,01 <0,01

Cu mg/l 0,5 <0,01 <0,01

Hg mg/l 0,03 0,0089 0,0015

Ni mg/l 0,5 0,325 0,432

Pb mg/l 0,1 <0,01 <0,01

Zn mg/l 1 0,537 0,422

Generally similar wastewater characteristics (FGD blow-down) are expected for the FGD operated for oxyfuel combustion in comparison with air-firing due to similar salt balance required for flue gas cleaning. There may be little differences in specific components between oxyfuel and air-firing in case if there may be small changes in some component distributions in gas phase.

Conducted Tests – Optimising Variables


- Variation of number of spraying levels and recirculation flow

- Variation of number of Trays objective: optimisation of energy consumption

- Variation of material of Trays objective: advantages and disadvantages of different

materials, e.g. corrosion, pressure loss, temperature resistance , accessability etc.

Tray in FGD of Oxyfuel Pilot plant

Operation without Tray

Operation with Tray

Results: Impacts L/G and SO2-Load


Reduction of recirculation

flow resp. L/G

Standard operation

70% of recirc. flow 100 % of recirc. flow, std. operation

60% of recirculation flow 85 % of recirc. flow

SO2-

conc

entr

atio

n in

cle

an g

as [m

g/N

m³ d

ry]

SO2-concentration in clean gas vs. SO2-load

limit value standard plant with lignite

limit value Oxyfuel

SO2-load [kg/h]


Results: Impacts of L/G and Trays SO2-removal efficiency vs. L/G ratio

SO

2-re

mov

al e

ffici

ency

[%]

operation with 1 Tray

operation with 2 Trays L/G [Bm³/h]

100 % 50 %

Results: Variation of Materials of Trays

Comparison of a synthetic material Tray and a stainless Steel Tray:

characteristics synthetic material stainless steel

corrosion resistance + + +

temperature restistance 0 + +

accessability 0 + +

SO2 removal efficiency + + +

pressure loss + + +

expenses + + 0

Tray material



Conclusions for FGD performance

• High SO2 removal efficiency (over 99%) is easily achieved and operation is stable;

• SO2 concentration in clean gas highly depends on the mass transfer and absorption equilibrium, which affected by slurry chemistry (pH) and inlet flue gas concentration. Similar behaviour is expected for oxyfuel combustion in comparison with air-firing;

• Impacts of CO2 partial pressure on slurry chemistry seems to be minimised by the degassing process in the external reaction tank, which makes a similar slurry chemistry between oxyfuel combustion and air-firing;

• In oxyfuel combustion, emissions to air have significantly been reduced in terms of common combustion pollutants. Similar contaminations are expected in FGD wastewater and by-products compared with that from air-firing;

• The long-term performance could be kept in system scale-up due to the similarities in slurry chemistry and absorption mechanisms

between oxyfuel and air-firing flue gas treatments

Conclusions for System Optimisation

• Possibility to achieve SO2-removal efficiency > 99 % by operation with 1 up to 3 Trays, number of Trays depends on pressure reserve of

booster fan and on the maximum recirculation flow possibility to find the optimum balance between SO2-removal

efficiency and energy consumption • Verification tests shown that up to doubled SO2-concentrations can be

removed reliably further test with higher Sulphur content will be conducted • Tray materials used in small scale facilities show influences on SO2-

removal efficieny and pressure loss further tests will be conducted to learn about the dependencies

between different materials


Thank you for your attention !

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