Request for Proposal 

for 

Conceptual SCR Catalyst Design 

 

 

for a 

Low-Dust and Tail-End SCR System 

February 2010
 

Page 2 of 11 February 2010 

Table of Contents 

1. Introduction ......................................................................................................... 3

2. Scope of Supply .................................................................................................. 4

3. Catalyst Design Basis ........................................................................................ 4

3.1 SCR Operating Conditions ................................................................................ 4

3.1.1 Cold-Side Low-Dust SCR Unit A ................................................................... 5

3.1.2 Tail-End SCR Unit B ...................................................................................... 5

3.2 Composition of Particulate Matter .................................................................... 5

3.2.1 Cold-Side Low-Dust SCR Unit A ................................................................... 8

3.2.2 Tail-End SCR Unit B ...................................................................................... 8

3.3 Reagent Composition ......................................................................................... 8

4. SCR Catalyst Design Requirements and Restrictions .................................... 8

5. SCR Catalyst Specification .............................................................................. 10

6. Catalyst Performance Guarantees .................................................................. 10

7. Pricing ............................................................................................................... 11
 

Page 3 of 11 February 2010 

1. Introduction 

This inquiry is intended to generate conceptual design and SCR performance guaranty 

information for the retrofit of either a cold-side low-dust or a tail-end SCR system on two 

different coal-fired electric generating units. 

The unit is intended to have a single SCR DeNOx reactor, which may alternatively be installed 

either in a cold-side low-dust configuration downstream of the air heater and electrostatic 

precipitator and upstream of a wet limestone forced oxidation FGD scrubber or downstream of 

the wet limestone forced oxidation FGD scrubber and before the stack. A regenerative rotary 

gas-gas heater (RGGH) followed by either a natural gas-fired duct burner or a high temperature 

steam coil ensures the necessary flue gas temperature for the SCR process of 290 °C (554 F). 

Each catalyst shall be alternatively designed for NOx removal efficiencies of 90% and 93% 

across the SCR reactor and less than 2 (cold-side low-dust) or 5 (tail-end) ppmvd NH3 slip. The 

relatively high NOx removal efficiency across the SCR reactor is necessary in order to 

effectively compensate for the expected flue gas leakage across the rotary RGGH so that total 

NOx removal efficiencies of at least 85% and 90% for the unit can be achieved. 

The flue gas shall flow vertically downward through the SCR reactor, which is intended to have 

initially two (2) installed catalyst layers and one (1) open spare layer. Each layer shall be 

designed to accommodate the same number of standard size catalyst modules, each with 

installed cross sectional dimensions of < 2 meter in length and < 1 meter in width. 

It is not intended to equip any of the catalyst layers with either sootblowers and/or sonic horns 

unless otherwise requested by the catalyst supplier. 

The flue gas flow distribution at the SCR reactor inlet was designed to be at least within the 

following limits: 

• Molar ratio distribution NH3/NOX: +/- 10% 

• Velocity distribution across 80% of the cross sectional area: +/- 10% 

• Velocity distribution across 100% of the cross sectional area: +/- 15% 

• Temperature distribution: +/- 10 °C 

SCR grade aqueous ammonia is intended to be used as a reagent. Ammonia injection occurs 

only above the minimum SCR reactor outlet temperature of 285 oC (545 F). 

The SCR reactor is not intended to be equipped with a flue gas flow bypass but to be in 

operation at all times when the unit is operating unless otherwise requested by the catalyst 

supplier. In case the catalyst supplier considers a bypass to be advantageous for the catalyst 

deactivation rate/life and/or exchange frequency, please specify the difference in guaranteed 

catalyst life and expected catalyst exchange frequency resulting from the installation of a 

bypass. The SCR system is intended to be in operation on a year round basis. 

Please note that this Request for Proposal for Conceptual SCR Catalyst Design represents an 

actual coal-fired electric utility generating station, which is intended to be retrofitted with an SCR 

system for NOx control. However, it has not yet been decided which SCR arrangement will be 

installed. This will depend to a significant extent upon the proposed performance guarantees 

and particularly the catalyst exchange frequency proposed for either of the two (2) different SCR 

arrangements under consideration. 
 

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Since currently only the catalyst design information, performance and guaranteed exchange 

frequency are of relevance for the decision making process concerning the two (2) different 

types of SCR arrangements, the proposal can be informal and short consisting only of: 

• The completed design data sheet in Section 5. 

• The proposed performance guarantees as per Section 6. 

• The proposed catalyst exchange diagram. 

• Indicative pricing is requested assuming supplier’s normal catalyst delivery leadtime. 

2. Scope of Supply 

This Request for Proposal for a Conceptual SCR Catalyst Design for either a cold-side low-dust 

or tail-end SCR system provides for the catalyst layers the following requirements, which the 

catalyst supplier shall adhere to: 

- Technical design data, catalyst specification and requirements as outlined in Sections 3, 

4 and 5 

- Performance guarantees as detailed in Section 6 

- Catalyst exchange frequency as detailed in Section 6 

The catalyst supplier is requested to provide the following information: standard size catalyst 

modules including but not limited to: 

- Catalyst design and sizing 

- Catalyst manufacturing including: 

- Performance guarantees 

- Catalyst lifetime and exchange frequency projection 

All catalyst modules must be fully and unconditionally: 

• Suitable for the SCR operating conditions as outlined in Section 3 of this Request for 

Proposal for Conceptual SCR Catalyst Design. 

• Designed for the flue gas, fly ash and reagent compositions as specified in Section 3 of 

this Request for Proposal for Conceptual SCR Catalyst Design. 

• In compliance with the technical design requirements and restrictions as set forth in 

Section 4 of this Request for Proposal for Conceptual SCR Catalyst Design. 

• In accordance with the technical information listed on the data sheet to be completed by 

the catalyst supplier as per Section 6 of this Request for Proposal for Conceptual SCR 

Catalyst Design. 

• Performing to the specifications as stated in Section 6 of this Request for Proposal for 

Conceptual SCR Catalyst Design. 

3. Catalyst Design Basis 

3.1 SCR Operating Conditions 

The SCR system will be operated on a year round basis. Typical operation is in a base load 

mode with three (3) to four (4) forced outages per year. Partial load operation down to 

approximately 40% of unit capacity is also possible. Maximum occasional short term load can 

be up to approximately 105%. All catalyst must be unconditionally suitable for the full range of 

operating conditions and shall not impose any restrictions on unit operations. 
 

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3.1.1 Cold-Side Low-Dust SCR Unit A 

The cold-side low-dust SCR catalyst shall be designed for the following operating parameters, 

which shall also serve as the operating conditions where the required performance guarantees 

for the catalyst as detailed in Section 6 shall be met and the proposed catalyst exchange 

frequency shall be based upon: 

 Design value Range 

Flue gas volume flow rate [Nm3/h @ 0 °C, dry]: 1,120,000 450,000 – 1,176,000 

SCR temperature [°C]: 350 340 – 360 

NOX inlet [lb/mmBtu]: 0.5 0.35 – 0.55 

SO2 inlet [lb/mmBtu]: 2.0 1.7 – 2.1 

PM inlet [lb/mmBtu]: 0.0046 0.002 – 0.007 

O2 inlet [%vol. dry]: 6.0 4 – 7 

H2O inlet [%vol.]: 15.8 13 – 18 

3.1.2 Tail-End SCR Unit B 

The tail-end SCR catalyst shall be designed for the following operating parameters, which shall 

also serve as the operating conditions where the required performance guarantees for the 

catalyst as detailed in Section 6 shall be met and the proposed catalyst exchange frequency 

shall be based upon: 

 Design value Range 

Flue gas volume flow rate [Nm3/h @ 0 °C (dry)]: 2,268,000 907,000 – 2,381,000 

SCR temperature [°C]: tbd by supplier tbd -10 K – tbd +10K 

NOX inlet [lb/mmBtu: 0.5 0.35 – 0.55 

SO2 inlet [lb/mmBtu]: 0.1 0.05 – 0.11 

PM [lb/mmBtu]: 0.0066 0.004 – 0.009 

O2 inlet [%vol. dry]: 6.5 5 – 7.5 

H2O inlet [%vol.]: 22.4 20 – 24 

The catalyst supplier is requested to provide a minimum recommended tail-end SCR operating 

temperature given the fact that the flue gas downstream the wet FGD scrubber is fully saturated 

at 60 °C (140 F) as well as in consideration of the concentrations and composition of particulate 

matter leaving the wet FGD scrubber as detailed in section 3.2. 

3.2 Composition of Particulate Matter 

The SCR catalyst of will be continuously exposed to coal combustion flue gases during SCR 

operation. The catalyst supplier shall design the catalyst for the full range of flue gas 

constituents as specified above including various loads of particulate matter remaining present 

in the flue gas downstream of the electrostatic precipitator (ESP) in case of a cold-side low-dust 

SCR or downstream of the wet FGD scrubber in case of a tail-end SCR. 

The following Figure 1 shows the total particulate loading downstream of the ESP (blue) and 

the wet FGD scrubber (red) in four (4) actually measured cases. Figure 2 presents the typical 

particle size distribution of particles with a diameter of less than 14 μm. 
 

Page 6 of 11 February 2010 

Figure 1: Total particulate loading downstream of the ESP (blue) and the wet FGD (red) 

Figure 2: Typical particle size distribution downstream of the ESP (blue) and the wet FGD (red) 

Figure 3 provides a typical particle size distribution of the sulfate particulates with a diameter of 

less than 14 μm downstream of the ESP (blue) and the wet FGD scrubber (red). Table 1

separately details the typical concentrations of total particulates as well as sulfate particulates of 

various size ranges downstream of the ESP (“Inlet” = upstream of the wet FGD scrubber) and 

downstream of the wet limestone forced oxidation FGD scrubber (“Outlet”). The majority of the 

sulfates must be expected to be sodium and potassium sulfates. 
 

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Figure 3: Sulfate particulate size distribution downstream of the ESP (blue) and wet FGD (red) 

Table 1: Particle size distribution of particulate matter 

 
 

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3.2.1 Cold-Side Low-Dust SCR Unit A 

The following data shall be used for catalyst design considerations for a cold-side low-dust SCR 

for Unit A. 

Particulate loading Design value Range 

Total – downstream of the ESP [mg/Nm3, dry] 10.0 4.0 – 11.0 

Particles < 1 μm downstream of the ESP [mg/Nm3, dry]: 3.5 0.5 – 4.0 

Total sulfates downstream of the ESP [mg/Nm3, dry]: 2.0 0.5 – 2.0 

Sulfates < 1 μm downstream of the ESP [mg/Nm3, dry]: 1.0 0.0 – 1.0 

3.2.2 Tail-End SCR Unit B 

The following data shall be used for catalyst design considerations for a tail-end SCR for Unit B: 

Particulate loading Design value Range 

Total – downstream of the wet FGD [mg/Nm3, dry]: 6.0 2.0 – 9.0 

Less than 1 μm downstream of the wet FGD [mg/Nm3, dry]: 3.0 1.0 – 3.0 

Total sulfates downstream of the wet FGD [mg/Nm3, dry]: 2.0 0.5 – 2.0 

Sulfates < 1 μm downstream of the ESP [mg/Nm3, dry]: 1.5 0.0 – 1.5 

3.3 Reagent Composition 

The reagent to be used will be formulated from anhydrous ammonia, mixed with demineralized 

water. The ammonia content is normally 29.4 percent by weight, or 26 degree Baume solution, 

with an acceptable range of 29.0 to 29.9 percent by weight. 

The aqua ammonia product will not contain more than the following limits of impurities: 

Chloride [Cl] Maximum 0.50 ppm 

Total Hardness [as CaCO3] Maximum 0.01 ppm 

Non-Volatile Residue Maximum 0.01% 

Heavy Metals [as Pb] Maximum 1.00 ppm 

Arsenic [as As] Maximum 3.00 ppm 

Total Silica [as SiO2] Maximum 100.00 ppm 

4. SCR Catalyst Design Requirements and Restrictions 

The type, configuration and chemical composition of the catalyst shall be selected based on the 

catalyst supplier’s sole discretion. Nevertheless, the selected catalyst type and module design 

shall comply at least with the following minimum design criteria, requirements and/or limitations: 

• The catalyst supplier is requested to determine the number of standard size modules 

required as well as the catalyst pitch, length and total volume. The module arrangement 

within the SCR reactor will be determined as close to square as permissible by the 

proposed number of catalyst modules. 

• The maximum permissible dimensions of each standard size catalyst module are length 

x width = 1,975 mm x 990 mm 
 

Page 9 of 11 February 2010 

• Any honeycomb module shall be made up of seventy two (72) logs, arranged as six (6) 

logs long and twelve (12) logs wide. Each log shall have cross sectional dimensions not 

exceeding 150 mm x 150 mm (~ 6 inches x 6 inches). 

• Any plate or corrugated catalyst shall not be stacked higher than two (2) boxes (also 

sometimes referred to as elements or cassettes) per module. An arrangement of 

stacking two (2) boxes long, four (4) boxes wide and two (2) boxes high per module is 

preferred. No more than sixteen (16) boxes shall be contained in a separate steel 

module casing. Simply tack or stitch welding the sixteen (16) boxes together to a module 

without a separate steel module casing shall not be considered acceptable. Each box 

shall not exceed a cross sectional area of 467 mm x 467 mm (~18.38 inches x ~18.38 

inches) and shall not be welded to other boxes and/or the steel module casing. 

• Any plate or corrugated catalyst shall not be shorter than 400 mm. Any honeycomb 

catalyst logs shall not be shorter than 500 mm. 

• Any honeycomb or corrugated catalyst supplied shall not have a thickness of the inner 

walls of less than 0.7 mm. 

• Plate type catalyst shall be supported on a stainless steel base material. The catalyst 

material shall be bonded to the stainless steel base material in such a way as to prevent 

permanent deformation of the support material from stresses imposed by the conditions 

specified above, fly ash loading, or sootblowing and/or other cleaning devices. 

• Each catalyst module shall feature angled deflectors in the bottom of the module on 

either of its two (2) short sides. These deflectors are intended to direct the flue gas flow 

exiting the catalyst module past the I-beam, which the modules’ short sides rest on, thus 

avoiding any ash build-up on said I-beams. The deflectors cannot be angled by less than 

30° or more than 45° off the vertical in order to prevent any fly ash built-up on the 

supporting I-beams. 

• The seal systems installed in order to avoid flue gas bypasses and fly ash intrusion 

between the catalyst modules will be determined in detail at a later point in time. 

• Lifting lugs, which extend past the top surface of the catalyst module are undesirable. 

• Each catalyst module shall be equipped with a protective screen on top, which shall be 

designed to allow for convenient walking on the module as well as for protection of the 

catalyst against intrusion of foreign objects. All protective screens shall be designed for 

easy manual removal and reinstallation without the need for any bolting, grinding, 

cutting, welding or any additional tools. Protective screens shall be designed as part of 

the catalyst module and contained inside the module casing. Protective screens 

extending above the top of the catalyst module casing are undesirable. 

• The catalyst supplier is requested to propose a minimum operating temperature for the 

flue gas composition provided. 

• The catalyst supplier is requested to make recommendations concerning the need for 

sootblower and/or sonic horns for catalyst cleaning. 
 

Page 10 of 11 February 2010 

5. SCR Catalyst Specification 

The catalyst proposed by the catalyst supplier has the following specification: 

Parameter Unit Specification 

(to be completed by 

catalyst supplier) 

Catalyst type 

honeycomb, 

plate or 

corrugated 

Number of initially filled catalyst layers # 

Number of catalyst modules per layer # 

Module dimensions (length x width x height) mm x mm 

x mm 

Module weight lbs / kg 

Number of catalyst logs or boxes per module # 

Number of cells per log (in case of honeycomb) or 

Number of cells per box (in case of corrugated) or 

Number of plates per box (in case of plate) 

# 

Pitch or plate spacing mm 

Wall or plate thickness mm 

Open area per module % 

Total catalyst length per layer (in case of honeycomb) or 

half layer (in case of plate or corrugated), respectively mm 

Catalyst volume per module m3 

Catalyst volume per layer m3 

Catalyst surface area per module m2 

Catalyst surface area per layer m2 

Specific catalyst surface area (physical) m2/m3 

Linear velocity Lv (at actual SCR operating conditions)* m/h 

Minimum permissible operating temperature F / °C 

Maximum permissible operating temperature F / °C 

6. Catalyst Performance Guarantees 

The catalyst supplier is requested to provide at least the following catalyst performance 

guarantees for the proposed catalyst: 

 Desired performance 

values 

Performance guarantees

(to be completed by 

catalyst supplier) 

Catalyst supplier Insert name of bidder 

NOx removal efficiency across SCR ≥ 90% 

Maximum NH3 slip low-dust SCR Unit A ≤ 2 ppmvd @ 3% O2 

Maximum NH3 slip tail-end SCR Unit B ≤ 5 ppmvd @ 3% O2 

Initial pressure drop across two (2) 

initially installed catalyst layers ≤ 2 in. w.c. 
 

Page 11 of 11 February 2010 

SO2/SO3 conversion rate across the 

entire SCR reactor at design conditions 

with NH3 present at 90% NOx removal 

efficiency with two (2) catalyst layers 

initially installed 

≤ 0.5% 

Initial catalyst lifetime with two (2) 

catalyst layers installed ≥ 24,000 hrs. 

Additional catalyst life after the 

installation of the third (3rd) spare layer ≥ 40,000 hrs. 

The catalyst supplier is also requested to provide an expected catalyst exchange diagram (saw 

tooth curve) for up to 100,000 SCR operating hours based on the catalyst design operating 

conditions 

7. Pricing 

The catalyst supplier is requested to provide an indicative firm lump sum price for the initial fill of 

two (2) catalyst layers assuming delivery of the catalyst as early at conveniently possible. The 

firm lump sum price will only be used as an additional decision making indicator for the selection 

between the two (2) alternative SCR arrangements as well as the overall economic viability of 

the cold-side low-dust or tail-end SCR systems as such.