IPM Model – Updates to Cost and Performance for APC Technologies

Dry Sorbent Injection for SO2 Control Cost Development Methodology

Final

March 2013

Project 12847-002

Systems Research and Applications Corporation

Prepared by

55 East Monroe Street • Chicago, IL 60603 USA • 312-269-2000
LEGAL NOTICE

This analysis (“Deliverable”) was prepared by Sargent & Lundy, L.L.C. ("S&L"), expressly for the sole 

use of Systems Research and Applications Corporation ("Client") in accordance with the agreement 

between S&L and Client. This Deliverable was prepared using the degree of skill and care ordinarily 

exercised by engineers practicing under similar circumstances. Client acknowledges: (1) S&L prepared 

this Deliverable subject to the particular scope limitations, budgetary and time constraints, and business 

objectives of the Client; (2) information and data provided by others may not have been independently 

verified by S&L; and (3) the information and data contained in this Deliverable are time sensitive and 

changes in the data, applicable codes, standards, and acceptable engineering practices may invalidate the 

findings of this Deliverable. Any use or reliance upon this Deliverable by third parties shall be at their sole 

risk. 

This work was funded by the U.S. Environmental Protection Agency and reviewed by William A. Stevens, 

Senior Advisor – Power Technologies. 
IPM Model – Updates to Cost and Performance for 

APC Technologies

Project No. 12847-002

March 2013

Dry Sorbent Injection for SO2 Control

Cost Development Methodology

Page 1

Technology Description

Dry sorbent injection (DSI) is a viable technology for moderate SO2 reduction on coal 

fired boilers. Demonstrations and recent utility testing have shown SO2 removals greater 

than 80% for systems using sodium based sorbents. The most common sodium based 

sorbent is Trona.

The level of removal for Trona can vary from 0 to 90% depending on the Normalized 

Stoichiometric Ratio (NSR) and particulate capture device. NSR is defined as: 

The target removal efficiency is a requirement from the utility and is independent of unit 

size. The costs for a DSI system are primarily dependent on sorbent feed rate which is a 

function of NSR and SO2 mass feed rate per hour. Therefore, the cost estimation was 

based on sorbent feed rate and not on unit size.

The sorbent solids can be collected in either an ESP or a baghouse. Baghouses generally 

achieve greater SO2 removal efficiencies than ESPs by virtue of the filter cake on the 

bags, which allows for longer reaction time between the sorbent solids and the flue gas. 

For a given removal efficiency with Trona, the NSR is reduced when a baghouse is used 

for particulate capture.

The dry sorbent capture ability is also a function of particle surface area. To increase the 

particle surface area, the sorbent must be injected into a relatively hot flue gas. Heating 

the solids produces micropores on the particle surface which greatly improve the sulfur 

capture ability. For Trona, the sorbent should be injected into flue gas above 275°F to 

maximize the micropore structure. However, if the flue gas is too hot (greater than 

800°F), the solids may sinter and surface area is reduced thus lowering the SO2 removal 

efficiency of the sorbent. 

Another way to increase surface area is to mechanically reduce the particle size by 

grinding the sorbent. Typical Trona is delivered unmilled. The ore is ground such that 

the unmilled product has an average size around 30 m. Commercial testing has shown 

that the reactivity of the Trona can be increased when the sorbent is ground to less than 

30 m. In the cost estimating methodology, the Trona is always delivered in the 

unmilled state. To mill the Trona, in-line mills are continuously used during the Trona 

injection process. Therefore, the delivered cost of the Trona will not change, only the 

reactivity and usage changes as the Trona is milled.
IPM Model – Updates to Cost and Performance for 

APC Technologies

Project No. 12847-002

March 2013

Dry Sorbent Injection for SO2 Control

Cost Development Methodology

Page 2

Ultimately, the NSR required for a given removal is a function of Trona particle size and 

particulate capture equipment. Either as delivered Trona (around 30 m average size) or 

in-line milled Trona (around 15 m average size) can be chosen for injection in the cost 

program. The average Trona particle size and the type of particulate removal both 

contribute to the predicted Trona feed rate.

Establishment of Cost Basis

For the wet or SDA FGD systems, the sulfur removal is generally specified at the 

maximum achievable level. With those systems, costs are primarily a function of plant 

size and sulfur rate. However, the DSI systems are quite different. The major cost for 

the DSI system is the sorbent itself. The sorbent feed rate is a function of sulfur rate, 

particulate collection device, and removal efficiency. To account for all of the variables, 

the capital cost was established based on a sorbent feed rate. The sorbent feed rate is 

calculated from user input variables. Cost data for several DSI systems was reviewed 

and a relationship was developed for the capital costs of the system on a sorbent feed rate 

basis.

Methodology

Inputs

Several input variables are required in order to predict future retrofit costs. The sulfur 

feed rate and NSR are the major variables for the cost estimate. The NSR is a function 

of:

Removal efficiency;

Trona particle size; and

Particulate capture device.

A retrofit factor that equates to difficulty in construction of the system must be defined. 

The gross unit size and gross heat rate will factor into the amount of sulfur generated.

Based on commercial testing, removal efficiencies with DSI are limited by the particulate 

capture device employed. When the sorbent is captured in an ESP, a 40 to 50% SO2

removal is typically achieved without an increase in particulate emissions. A higher 

efficiency (70 – 75%) is generally achieved with a baghouse. The DSI technology should 

not be applied to fuels with a sulfur content of greater than 2 lb SO2/MMBtu.
IPM Model – Updates to Cost and Performance for 

APC Technologies

Project No. 12847-002

March 2013

Dry Sorbent Injection for SO2 Control

Cost Development Methodology

Page 3

Units with a baghouse and limited NOx control that target a high SO2 removal efficiency

with sodium sorbents may experience a brown plume resulting from the conversion of 

NO to NO2. The formation of NO2 would then have to be addressed by adding adsorbent 

into the flue gas. However, many coal-fired units control NOx to a sufficiently low level 

that a brown plume should not be an issue with sodium-based DSI. Therefore, this study 

does not incorporate any additional costs to control NO2.

The equations provided in the cost methodology spreadsheet allow the user to input the 

required removal efficiency, within the limits of the technology. To simplify the 

correlation, the removal with an ESP should be set at 50% and 70% with a baghouse. 

The simplified sorbent NSR would then be:

For an ESP at the target 50% removal:

Unmilled Trona NSR = 2.85

Milled Trona NSR = 1.40

For a baghouse at the target 70% removal:

Unmilled Trona NSR = 2.00

Milled Trona NSR = 1.55

The correlation could be further simplified by assuming that only milled Trona is used. 

The current trend in the industry is to use in-line milling of the Trona to improve the 

utilization. For a minor increase in capital, the milling can greatly reduce the variable 

operating expenses. It is recommended that only milled Trona be considered in the 

simplified model.

Outputs

Total Project Costs (TPC)

First the base installed cost for the complete DSI system is calculated (BM). The base 

installed cost includes:

All equipment;

Installation;

Buildings;

Foundations;

Electrical; and

Average retrofit difficulty.
IPM Model – Updates to Cost and Performance for 

APC Technologies

Project No. 12847-002

March 2013

Dry Sorbent Injection for SO2 Control

Cost Development Methodology

Page 4

The base module cost is adjusted by the selection of in-line milling equipment. The base 

installed cost is then increased by:

Engineering and construction management costs at 5% of the BM cost;

Labor adjustment for 6 x 10 hour shift premium, per diem, etc., at 5% of the 

BM cost; and

Contractor profit and fees at 5% of the BM cost.

A capital, engineering, and construction cost subtotal (CECC) is established as the sum of 

the BM and the additional engineering and construction fees.

Additional costs and financing expenditures for the project are computed based on the 

CECC. Financing and additional project costs include:

Owner’s home office costs (owner’s engineering, management, and 

procurement) at 5% of the CECC; and

Allowance for Funds Used During Construction (AFUDC) at 0% of the 

CECC and owner’s costs as these projects are expected to be completed in 

less than a year.

The total project cost is based on a multiple lump sum contract approach. Should a 

turnkey engineering procurement construction (EPC) contract be executed, the total 

project cost could be 10 to 15% higher than what is currently estimated.

Escalation is not included in the estimate. The total project cost (TPC) is the sum of the 

CECC and the additional costs and financing expenditures.

Fixed O&M (FOM)

The fixed operating and maintenance (O&M) cost is a function of the additional 

operations staff (FOMO), maintenance labor and materials (FOMM), and administrative 

labor (FOMA) associated with the DSI installation. The FOM is the sum of the FOMO, 

FOMM, and FOMA.

The following factors and assumptions underlie calculations of the FOM:

All of the FOM costs were tabulated on a per kilowatt-year (kW-yr) basis.

In general, 2 additional operators are required for a DSI system. The FOMO 

was based on the number of additional operations staff required.
IPM Model – Updates to Cost and Performance for 

APC Technologies

Project No. 12847-002

March 2013

Dry Sorbent Injection for SO2 Control

Cost Development Methodology

Page 5

The fixed maintenance materials and labor is a direct function of the process 

capital cost (BM).

The administrative labor is a function of the FOMO and FOMM.

Variable O&M (VOM)

Variable O&M is a function of:

Reagent use and unit costs;

Waste production and unit disposal costs; and

Additional power required and unit power cost.

The following factors and assumptions underlie calculations of the VOM:

All of the VOM costs were tabulated on a per megawatt-hour (MWh) basis.

The reagent usage is a function of NSR and SO2 feed rate. The gross unit size 

and gross heat rate factor multiplied by the SO2 rate determine the SO2 feed 

rate. The estimated NSR is a function of removal efficiency required. The 

basis for the total reagent rate is a Trona purity of 95%.

The waste generation rate is a function of the Trona feed rate and is adjusted 

for the excess sorbent fed. The waste generation rate is based on reaction 

products of Na2SO4 and unreacted dry sorbent as Na2CO3. Waste product 

adjusted for a maximum of 5% inert in the Trona sorbent.

With the addition of a sodium sorbent that is captured in the same particulate 

control device as the fly ash, any fly ash produced must be landfilled. Typical 

ash contents for each fuel are used to calculate a total fly ash production rate. 

The fly ash production is added to the sorbent waste to account for a total 

waste stream in the O&M analysis.

The user has the ability to remove fly ash from the waste disposal cost to 

reflect the situation where the unit has separate particulate capture devices for 

fly ash and dry sorbent.

When a baghouse is installed downstream of an ESP, the sodium sorbent 

could be injected before the baghouse with no effect on the fly ash collection. 
IPM Model – Updates to Cost and Performance for 

APC Technologies

Project No. 12847-002

March 2013

Dry Sorbent Injection for SO2 Control

Cost Development Methodology

Page 6

In that case, the disposal costs of the sodium only waste should be increased 

to account for the increased difficulty in handling the pure sodium waste 

product.

The additional power required includes air blowers for the injection system, 

drying equipment for the transport air, and in-line Trona milling equipment as 

needed.

The additional power is reported as a percent of the total unit gross 

production. In addition, a cost associated with the additional power 

requirements can be included in the total variable costs.

Input options are provided for the user to adjust the variable O&M costs per unit. 

Average default values are included in the base estimate. The variable O&M costs per 

unit options are:

Trona cost in $/ton;

Waste disposal costs in $/ton that should vary with the type of waste being 

disposed;

Auxiliary power cost in $/kWh;

Operating labor rate (including all benefits) in $/hr.

The variables that contribute to the overall VOM are:

VOMR = Variable O&M costs for trona reagent

VOMW = Variable O&M costs for waste disposal

VOMP = Variable O&M costs for additional auxiliary power

The total VOM is the sum of VOMR, VOMW, and VOMP. The additional auxiliary 

power requirement is also reported as a percentage of the total gross power of the unit. 

Table 1 contains an example of the complete capital and O&M cost estimate worksheet.
IPM Model – Updates to Cost and Performance for APC Technologies Project No. 12847-002

March 2013

Dry Sorbent Injection for SO2 Control

Cost Development Methodology

Page 7

Table 1. Example Complete Cost Estimate for a DSI System
IPM Model – Updates to Cost and Performance for APC Technologies Project No. 12847-002

March 2013

Dry Sorbent Injection for SO2 Control

Cost Development Methodology

Page 8