fgd and scr retrofits in aboño 2 power plant“n vanesa hernÁndez… · • to prevent the dew...

JULHO 2016

Development of clean coal technologies

FGD and SCR Retrofits in Aboño 2 Power Plant

Vanesa Hernández RodríguezManager of Engineering Department,Aboño Power Plant, Asturias, EDP España

Challenges for the coal industry in the EUKatowice, May 8th, 2018

Outline

Introduction

FGD – Flue Gas Desulphuration System (DeSOx)

SCR – Selective Catalyst Reactor System (DeNOx)

4

Location of Aboño 2 within the EDP Spain generation plants

Introduction

Aboño 2

MW

MW

Introduction

Main aspects of Aboño Power Plant

KEY FEATURESTotal power: 922 MW

Aboño 1 : 366 MW, year 1974

Aboño 2: 556 MW, year 1985

Multifuel: coal, Blast furnace gas (BFG), Diesel and Fuel Oil (replaced in 2018 by Natural Gas).

Boiler: Foster Wheeler, steam 1.700t/h

MAIN OPERATING PARAMETERSAboño 2

Operating hours: 253.000 h

Gross generation: 118.000 GWh

Availability: > 97 %

Yearly operating: > 8.000 h

Net efficiency: >35%

Heat rate: 2.520 kcal/kWh

DISTINCTIVE FEATURESNear the harbour (Gijón). “Easy” coal management

Near a Steel Industry (Arcelor-Mittal). Supply of BFG (400.000 Nm3/h) – BFG provides the 30% of the total thermal power generated

Near the biggest Asturian industries, to guarantee a reliable electrical supply

Aboño is one of the largest coal and BFG fired power stations within the

Iberian peninsula and probably one of the most efficient coal fired power

plants in the world.

Introduction

Main flue gas cleaning retrofits in Aboño 2 Power Plant

Aboño and the environmental regulation:

It applies the European Directive 2010/75/EU (ED) on

industrial emissions (integrated pollution prevention

and control).

From 1 January 2016 to 30 June 2020: Aboño is running

based on the Transitional National Plan (TNP) being

granted the Authority permit with the emissions limit

values established before that date whenever the

company doesn’t exceed the maximum tons of emissions

per year according to the ED. Once this period finishes, it

will be applied the individual emissions limits.

ELV [mg/Nm3]

AAI = Local Authority permit

ED = European Directive

ELV = Emission Limit Value

Introduction

Main flue gas cleaning retrofits in Aboño 2 Power Plant

• Low NOx Burnes (LNF) & Over Fire Air (OFA) (FW) 2006 NOx reduction achieved from above 1.800 mg/Nm3 up to 400 mg/Nm3

• FGD (Hitachi) 2007Wet limestone-gypsumSO2 reduction achieved from above 1.600 mg/Nm3 up to 150 mg/Nm3

• SCR (MHPS) 2016High-dust SCRNOx reduction achieved from above 650 mg/Nm3 up to 150 mg/Nm3

• Replacement of Fuel Oil by Natural Gas Burners (FW) 2018For the start-up of the unit

Outline

Introduction



FGD – Flue Gas Desulphuration system

Origin of SO2

• Combustion of fossil fuels (coal) acid rain

Technologies to reduce SO2

• Before-combustion: Fuels with low quantity of sulphur (S)- 1% S in coal 1.800 mg/Nm3 in flue gases- Typical range:

Sudafrican/Colombian coal: 0,6-0,8 %SUSA coal: 0,6-2,5 %SNational coal: 1,0-2,5 %SIndonesia coal: 0 % S

Limited due to priceand availability

• After-combustion:

Limited to sorbentavailability

- Several technologies: dry, wet (>85% in theworld)

- Several kinds of sorbents (alkalines): sea water, MgO, NH3, Na2CO3, CaO, Ca(OH), CaCO3

(limestone) (limestone >85% in the world)


Selection of the technology in Aboño 2

• Taking into consideration

• The FGD technology implemented was the wet system type with injection of limestone slurry produced directly at the plant from local mined raw limestone which is available on this area and getting synthetic gypsum as derivative product

Wet scrubber

- Investment cost- Sorbent cost/availability- Desulphuration efficiency- Generated residue management cost


Chemical process


Basic diagram

Limestone slurryDerivative product: gypsum

IDF

ESP

Boiler GGH


Design conditions: Guarantee values

• SO2 emissions, GGH leakages and desulphuration efficiency• Flue gas conditions at the outlet of FGD: Temperature and humidity• Pressure drop in FGD• Consumption of energy and reactives (limestone and water)• Gypsum quality (“Eurogypsum” regulation)• Noise level• Availability


Flue Gas System - ductsCFD study: Optimization of the flue gas ducts to minimize the pressure drop


Flue Gas System – Gas Gas Heater (GGH)

85

ºC1

40

ºC

45

ºC9

6ºC

Absorber

ID FAnChimney

• To improve the desulphuration processefficiency

• To prevent the dew point at the FGD outlet• To improve the chimney gas draught


Absorber

16

• Where chemical process happens. Limestone slurry sprays / Mist eliminator toretain droplets and prevent acid condensations in chimney


Gypsum slurry system

17

• Where gypsum is dewatering. It must work properly to getEurogypsum criteria and sell the gypsum.


Limestone slurry system

18

• To grind limestone to the proper size (hammer mills, ball mills, hydrociclons)


Control of the process

19

Monitoring of process signals in DCSLaboratory AnalysisMaterial Balance

PLANTA DE DESULFURACIÓN ABOÑO 2 Theoretical material balance

Item KKS value Unit Calculation Remarks

IDF 10 HNC10CF901 316 m3N/sec

IDF 20 HNC20CF901 240 m3N/sec

FGD inlet glue gas flow 2.001.600 m3N/h wet =(316+240)x3600

H2O in flue gas 4,35 %

FGD inlet glue gas flow 1.914.530 m3N/h dry =2001600x(1-4,35/100)

Inlet SO2 HTA10CQ001 769 mg/m3N dry

Outlet SO2 HTA21CQ001 22 mg/m3N dry

SO2 removal efficiency 97,1 % =(769-22)/769x100

Absorbed SO2 1430 kg/h =(769-22)x1914530/10 6̂

22,34 kmol/h =1430/64 * SO2=64g/mol

Limestone

Limestone purity 96 %

Limestone slurry concentration 25 wt%

Limestone slurry density HTK33CQ001 1195 kg/m3

Required CaCO3 22,34 kmol/h =Absorbed SO2

2234 kg/h =22,34x100 *CaCO3=100g/mol

Required Limestone 2327 kg/h =2234/(96/100)

Required limestone slurry 9308 kg/h =2327/(25/100)

Limestone slurry flow HTK34CF001 7,8 m3/h =9308/1195

Gypsum

Gypsum purity 95 %

Gypsum slurry concentration 25 wt%

Gypsum slurry density 1128 kg/m3

Gypsum moisture 10 wt%

Produced CaSO4 2H2O 22,34 kmol/h =Absorbed SO2

3842 kg/h =22,34x172 *CaSO4 2H2O=172g/mol

Produced Gypsum 4044 kg/h dry =3842/(95/100)

Produced Gypsum with moisture 4,5 t/h =4044/(1-10/100)/1000

Produced gypsum slurry 16176 kg/h =4044/(25/100)

Gypsum slurry flow HTL12CF001 14,3 m3/h =16176/1128

IDF 10 316 m3N/sec

IDF 20 240 m3N/sec

Inlet SO2 769 mg/m3N dry

Outlet SO2 22 mg/m3N dry

7,8 m3/h

14,3 m3/h

4,5 t/h

Gypsum BleedPumps

M

Vacuum BeltFilter

M

Limestone SlurryPumps

Limestone Slurry Tank

M

Absorber

Atmosphere

to Gypsum Silo

• The control system is DCS (Melody –ABB)

• A material balance “on-line” has beenimplemented in order to detectdeviations between the real processand the theoretical balance (forexample, limestone blinding)

• Once known the flue gas flow, theSO2 at the inlet and the desired SO2 at the outlet (from DCS), it iscalculated the theoretical flow oflimestone slurry to supply and thetheoretical flow of gypsum slurry toproduce.


20

Absorber and flue gas ducts

Gypsumdewateringsystem

Limestone systemProcess water system

Outline

Introduction



Origin of NOx

• Combustion of fuels (Fuel NOx) + air (Thermal NOx) at high Temp acid rain

Technologies to reduce SO2

• Before-combustion:- Fuels with low quantity of nigrogen (Nx)

It is not effective as the most of Nxcomes from air

• After-combustion:

NOx removalEfficiency SCR>NSCRReagent: following considerations

- SCR (selective catalytic reduction)- NSCR (non-selective catalytic reduction)- Several kinds of reagentsd: anhydrous

ammonia (NH3), ammonium hydroxide(NH4OH), urea (N2H4CO)

SCR - Selective Catalyst Reactor

• During-combustion:- Combustion sequencing (Low Nox Burners)- Air redistribution in boiler (Over Fire Aire)

It has lower DeNOxefficiency

23

Anhydrous ammonia (NH3):

- Lower costs on terms of process product

- Important risks on the handling at the plant of a dangerous product. It implies

special considerations on the storage and on the injection systems.

Injection of Urea (N2H4CO) :

- Only recommended for plants of small size.

- The escalation of a system without sufficient operational references was

considered a high investment risk and consequently not assumed.

Ammonia solution at 24% concentration (NH4OH):

- The handling of the ammonia at this concentration level reduces highly the

environmental risks and the easiness for the workers to handle the product. It has

been considered that the risks associated to the handling of the product can be

assumed and considered the best choice.


Selection of the reagent

Selection of SCR Configuration• High dust: Between Economizer and

air preheater- High temperature (better for the chemical

reaction)- Full dust load from boiler passes through

the SCR reactor (larger catalyst channelsand blowing devices to prevent plugging)

- No heat exchangers required


• Low dust: Between ESP and ID Fan- Lower temperature. It can produce

ammonium bisulphate (undesirable at itplugs the catalyst and air heaters)

- Heat exchanger required- Only for coals with low % S

• Tail end: After FGD

- There is not flue gas ashes but itneed an aditional air heater

Selection of the technology in Aboño 2

• Taking into consideration

Low NOx Burners + OFA + High-dust SCR

- Investment cost- DeNOx efficiency- Operation flue gas temperatures- Risks on the handling of the reagent


SCR• Reagent – ammonia solution 24% conc.• One reactor – 76 m height; independent support structure; 2 + 1 (spare) layers of

catalyst• Plate catalyst (MHPS) – V on a TiO2 matrix over thin inox plates; • Flue Gas: 317 ºC to 475 ºC; rated 2.380.000 Nm3/h; avg velocity < 20 m/s• Pressure drop increase < 10 mbar

Chemical process

SCR - Selective Catalyst ReactorThe basics of the SCR process are the

reduction of the flue gas NOx contents

through its reaction with the ammonia,

reaction enhanced by the presence of the

specific catalyst.

In Aboño it takes place at temperatures on the

flue gas within 317 ºC and 475 ºC

approximately.

If T < 317 ºC and flue gas contains high % of

SO3 (2SO2+O2->2SO3) and NH3 (ammonia slip),

risk of catalyst fouling (ammonium bisulfate)

Basic diagram


28

Major challenges

• Limited space available (“footprint”)

• Complex existing flue gas ductwork

• Wide range of raw flue gas characteristics (flowrate, temperature, ash and SO2

content), depending on fuel mix burnt

• 24 months between Contract Award and SCR Start-up

Ducts to secondary air heater (green)

4 boiler’s outlets

Economizer by-pass (turquoise)

Ducts to pre-economizer (lilac)

Ducts to primary air heater (yellow)


29

Retrofit Summary

• The SCR reactor has been installed in a separated structure with its own foundations, equipped with two ample layers of catalyst and

structure capacity to eventually admit a third catalyst layer in the future. The flue gas path has been equipped with a By-Pass system.

• The Catalyst packages are of free passage type to allow self cleaning, additionally a system of sonic cleaning by means of horns has been

provided to avoid the accumulation of ash.

• The ammonia storage and transfer systems has been located in a reclaimed space outside of the power plant which enables an independent

and convenient handling. The flue gas path diversion has posed a major challenge to the project.

• Different alternatives/different bidders, all of them complex on

terms of construction and implementation and pivoting mainly

on the concept of

Option 1 – Single SCR indep but ducts integrated Option 2 – Twin reactors & ducts indep structure

SCR - Selective Catalyst Reactor- 1 or 2 reactors- Independent or integrated structure- Ducts retrofit concepts- Requiremens of reinforcement on the existing boiler structure/foundations

30

The objectives of the CFD study are: to confirm that the duct arrangement can meet the criteria for DeNOx

performance; to minimize the pressure drop increase imposed on the boiler draft system by the SCR system pressure

drop design recommendations of guide vanes arrangements / locations and to determine the proper location of gas

analysis instrumentation in actual plant.

The CFD study was developed by Mitsubishi Hitachi using Fluent 5.4 as software of solver and Gambit as software of

mesh formation. Model scope is from economizer outlet to secondary and primary air heaters and pre-economizer inlet.

SCR - Selective Catalyst Reactor Flue gas systemCFD ANALYSIS

31

- The main conclusion of CFD study was to confirm that design criteria for velocity and temperature, except velocity at AIG

upstream, can be accomplished.

- The gas velocity deviation at AIG upstream is over criteria of the technical specification, however, there is no problem for

SCR process performance because catalyst incoming flow meet the criteria above mentioned and Mitsubishi Hitachi

standard.

- Other study results were that: the design target for NOx and NH3 concentration CV (Coefficient of Variation) can be

accomplished; the gas velocity can be partially over 20 m/s because new duct arrangement has to be adapted to the

existing duct space and the pressure drop increase is lower than 10 mbar.

- The velocity situation in secondary air heaters (rothemülhle type) was studied by CFD under steady state. The conditions

considered are as follows:

- Configuration 1 (C1): Gas flow is blocked by rotating air duct hood

- Configuration 2 (C2): Gas flows into air heater elements directly

CFD ANALYSIS

SCR - Selective Catalyst Reactor Flue gas system

The main conclusions of the study were that:

- Gas flow balance looks no significant difference between each section of the air heater. Therefore, heat input for each

section would be expected same level.

- Velocity distribution at air heater housing inlet looks larger, but it would become smaller at air heater element inlet due

to large pressure loss of the element.

- The velocity distribution level is around 23% CV, therefore no concern is expected.

32

The physical flow model test for the SCR Aboño 2 was performed by NELS consulting services Inc.

A 1/10 scale model was constructed and tested to determine the optimum type, number and location of flue

gas flow correction and gas mixing devices and the optimum ammonia injection system in the ductwork and

reactor. The model was used to ensure uniform gas flow conditions (velocity, temperature, NOx, NH3, fly ash)

and minimize the pressure drop increase imposed on the boiler system by the SCR system pressure drop.

The physical flow model indicated that most of the flow and mixing criteria were acceptable for optimum

operation of the SCR. The main concern with ash deposits was due to accumulations in the bypass to primary

air duct and the economizer bypass ducts. These accumulations were due to the back flow entering the “dead

zones” where the gas velocity was very low.


PHYSICAL MODEL TEST

Flue gas system

33

Before sending the catalyst modules to Aboño site, a bench scale test was conducted in a 3rd Party laboratory (UniperTechnologies – Germany). The bench test is intended to check basically the De-NOx activity and the SO2 to SO3 conversion rate of the catalyst. This test was done in accordance with the VGB guideline “VGB-S-302-00-2013-04-EN Instructions DeNox tests”.

Catalyst plates were sampled after manufacturing process, and the plates were properly cut to fit into a test box with across sectional area of 150x150 mm. The prepared sample was sealed into the bench reactor chamber, heated andexposed to the gas flow under the test conditions. The flue gas composition, velocity and temperature were selected tosimulate the flue gas conditions of the Aboño SCR reactor under two different scenarios

In the Reference Scenario conditions

at 435 °C, the SO2 conversion rate

was determined at 0.33 % and the

activity K at 48.0 Nm/h.

The SO2 oxidation of the catalyst was

measured without ammonia in the

flue gas (α = 0).

For this test, a single test element

was installed to the bench reactor

correlating to a half layer of catalysts

in the full-scale plant.

Outline of bench test facility

SO2/SO3 = 0,33%

K = 48 Nm/h

SCR - Selective Catalyst ReactorCATALYST BENCH TESTS

Flue gas system

34

The construction was planned with two outages of the plant, the first outage was arranged to coincide with a regular

major plant outage which is usually planned every 4 years, this outage took 60 days to dismantle the old conducts and

install new structure and new ducts to establish boiler operation through the by-pass without SCR. A second short

outage of 10 days for tie-in of SCR was performed on August 2016. The complete construction time was approximately

15 months from which the foundation work consumed an important part with more than 5 months to complete the

piling and foundations for new structures only.

View of Boiler original flue gas path and air paths View of new flue gas path to interconnect with SCR

ERECTION WORKS

1.300 tons new ducts

365 tons removed ducts412 tons reinforcement

By-pass


35

Detail of the Ammonia Injection Grid (AIG), with 768 ammonia injection nozzles

ERECTION WORKS


36

- One single reactor has been inserted into the flue gas path between the economizer outlet and the regenerative

secondary air heaters inlet. The contents of flying ashes is very high but the adequate range of flue gas T is maintained.

- The reactor with 76 m of height has been disposed on an

independent structure close to the boiler but required a

significant construction of flue gas ducts to deviate the flow at

the economizer outlet discharge it into the reactor inlet and

conduct the reactor outlet into the secondary air heaters. It is

the major challenge to the project in terms of design cost and

work.

- The reactor itself is of vertical type with structure for three

layers of catalyst, of which two layers have been installed at

the initial stage. The flue gas flow is descendent and has

provisions to handle the ash collection with ash hoppers and

extraction system. The rated flow of gas considered is

2.380.000 Nm3/h with average gas velocity of less than 20

m/s.

- The catalyst applied in Aboño is of the shaped plate type, this allows for a relatively smooth discharge of ash, one of

the major concerns on the path considering the head loss which we introduce in the system. Currently the head loss

has been maintained under the 4 mbar through the reactor. The retrofit with the SCR was made without upgrading of

the induced draft fans. Already on 2.006, when the FGD was installed, a prevision on fan capacity was made

considering the future possibility of SCR installation. This prevision has been adequate.

SCR - Selective Catalyst Reactor Reactor

37

View of the sonic horns on the right side of the reactor 4 x 3

View of the additional attenuation boxes currently being installed to reduce the noise impact.

Reactor

View of a sonic horn from inside of the reactor wall


38

- The chemistry of the catalyst is based on a matrix of Titanium Oxide (TiO2) doped with Vanadium applied on a base of

thin inox plates designed by Mitshubishi Hitachy. The catalyst has been tested at laboratory verifying its reactivity,

aging and main characteristics.

- The construction has been integrated into rectangular modules of approximately 1.600 Kg with steel structure and

protecting gratings producing a modular construction with simple erection requirements.

A catalyst module being lifted into the Aboño 2 SCR Reactor

SCR - Selective Catalyst Reactor Catalyst

39

- The chemical life of catalyst is 24.000 hours – 3 years. The expected service life of the catalyst lies somewhere between 6 and 10 years depending on the prevailing operational conditions.

- Due to the relatively high cost of the catalyst, regenerating technics have been developed in the market and usually are very cost efficient but a trade-off between costs vs chemical life has to be analyzed

- When the catalyst ages, the activity is gradually reduced and consequently the ammonia slip increases, this may produce severe impacts downstream of the flue gas path. The typical degradation, regeneration and ammonia slip evolution can be pictured on the following graph which considers the addition of a catalyst layer as it has been considered for Aboño 2.


40

To ensure the removal of ash accumulated on the catalyst layers a system of sonic cleaning has been adopted. Twenty

one (21) Sonic horns of the manufacturer Kockum have been installed. The effectivity on the cleaning seems so far

proven and the head loss through the reactor has maintained constant from the initial stage below 4 mm.

The use of the sonic cleaning has

considerable advantages in respect to other

cleaning processes like the sootblowers, but

the local noise impact is a new factor to be

dealt with. The noise level unprotected at 1

m distance of the horn membrane is above

120 dbA and requires effective attenuation

measures to reduce up to acceptable levels.

On the following pictures the general view

of the sonic horns on one side of the reactor

are shown.

Three levels of sonic horns have been

installed, one for each catalyst layer with

four horns on one side and three horns on

the opposite side.

The additional protective measures which

are still under installation can be seen on

the following picture as well.View of a sonic horn from inside of the reactor wall

SONIC HORNS


41

General view of the completed SCR and the new flue gas path


42

General view of the ammonia unloading, storage and transfer station

Ammonia evaporators

Unloading and transferPumps skids


43

The first flue gas into the reactor was introduced on 25 of August 2016 and the first ammonia injection

was performed on 2ond of September 2016. The first reaction effect of the ammonia injection has been

registered on the following graph when the injection tuning was started.

ERECTION WORKSSCR - Selective Catalyst Reactor

44

Any questions may be addressed to: <[email protected]>

SCRNH3

THANKS FOR YOUR KIND ATTENTIONand

extended thanks to the complete EDP project team and to the contractor, Consortium MHPS-TSK, for the good work performed

fgd and scr retrofits in aboño 2 power plant“n vanesa hernÁndez… · • to prevent the dew...

Documents