Babcock & Wilcox 1

Henry S. Taylor

Public Service Company of New Mexico (SJGS)

Waterflow, New Mexico, U.S.A.

Walter Nischt

Babcock & Wilcox

Barberton, Ohio, U.S.A.

San Juan Generating Station FGD Retrofit Project Update

Presented to: BR-1667

Power-Gen International ’98

December 9-11, 1998

Orlando, Florida, U.S.A.

Background

San Juan Generating Station (SJGS) is an 1800 MW coal

fired plant located in the northwest corner of New Mexico. The

station has two 350 MW Foster-Wheeler boilers and two 550

MW Babcock & Wilcox boilers with three General Electric turbine/generators and one Westinghouse turbine generator. The

plant is located close to large deposits of subbituminous coal

with low sulfur content, 0.9%, and high ash, over 24%. Sulfur

dioxide emissions were originally controlled with a WellmanLord (W-L) regenerative system and particulates are removed

by hot side electrostatic precipitators. SJGS must meet New

Mexico air emission regulations that have always been more

stringent than federal regulations. Cooling water and service

water are supplied from the San Juan River to the plant. SJGS

has been a “zero water discharge” location since 1983. This

means no water discharge is allowed from the plant site. All

waste water must be recycled and the final brine must be stored

in evaporation ponds.

The station is owned by nine different entities including investor owned utilities, municipal utilities and cooperative organizations. Owners are located in New Mexico, Arizona, Utah,

Colorado and California. Power from the generating station is

transmitted to all of those states. Public Service Company of

New Mexico (PNM) is the operating agent.

Prior to the Limestone Conversion Project there were 575

full-time employees at the generating station. After the project,

460 full time employees will be budgeted. Two open pit mines

operated by Broken Hills Properties (BHP) supply coal to the

station. One mine is located next to the plant and a second is

located about twenty miles from the plant. All coal is transported by truck to the plant.

Introduction

In 1994, SJGS owners became concerned over the comparatively high operating and maintenance costs for the flue gas

desulfurization (FGD) system. The 20 year old regenerable

W-L system was originally chosen in the late-sixties because it

was competitive in operating and maintenance (O&M) costs and

because there was concern about sulfur waste being a hazardous waste. Early lime and limestone systems were having many

difficulties in those early years. In the past 20 years, the W-L

system aged until it required comparatively high maintenance

cost while limestone systems have become reliable and efficient.

In early 1995, SJGS contracted a comparison study of costs for

the W-L system with the most common modern systems. The

EPRI FGD Cost Model was used to make the cost comparisons.

Results of this comparison study confirmed the comparative high

cost of the W-L system and indicated that, for the plant location, a limestone forced oxidation system (LSFO) was the best

economic choice.

Babcock & Wilcox (B&W) developed the possibility for

converting the existing W-L system into a LSFO system. The

EPRI FGD Cost Model estimated the cost of a LSFO system for

SJGS at $110 million. Through the collaborative efforts of PNM

and B&W, the budgeted cost of the conversion was reduced to

$80 million. The major items that allowed this to be accomplished were design refinement, utilization of existing equipment, utilization of plant personnel and facilities, value engineering and risk sharing. The LSFO FGD system presented an

opportunity for drastic reductions in O&M and energy costs.

Economic justification based only on the FGD system, however, was not satisfactory. SJGS also has an extremely complicated waste water recovery system in order to meet zero dis-
2 Babcock & Wilcox

charge requirements including sodium waste from the W-L process. The W-L system is based on a sodium sulfite solution while

a LSFO system is calcium carbonate to calcium sulfate. A conversion to LSFO would greatly simplify the waste water treatment system by using cooling tower and boiler blow down directly in the limestone slurry. Direct use of the blowdown water

eliminates the need for more than one-half of the waste water

treatment equipment. The project was justified and approved in

1996 on the basis of savings in the FGD system and waste water treatment. Originally, additional justification was thought

possible with excess emission allowances but fluctuations in

the allowance market have made income from this source uncertain. This conversion project, with the realized savings to

date, is now seen as a $77 million project that will provide a

savings in O&M fuel costs of $16 to $23 million a year depending on the way fuel and power are valued.

The project is unique in three ways. First, it is justified on

the basis of economics with no regulatory requirements. The

new system is, however, more efficient and removes more sulfur dioxide than the old system. Second, it is a true retrofit

project. Much of the existing equipment was converted and the

station remained in compliance with the air emission regulations while it was being converted. A third unique aspect of this

project is that it was designed and constructed under a teaming

or partnership arrangement with B&W. This simplifies organization, reduces cost and involves the operator more deeply in

the project.

Technical

The W-L system was based on the chemical reaction of sodium sulfite with sulfur dioxide to form sodium bisulfite, Figure 1. The sodium bisulfite was thermally regenerated and the

resultant sulfur dioxide was used to produce sulfuric acid. The

original SJGS system was designed to produce sulfur but the

process was extremely difficult to operate and was later replaced

with a sulfuric acid plant. W-L absorbers are counter current

multi trays with recirculating solution on each tray. They have

prescrubbers to remove residual flyash and chlorides and to cool

the flue gas. The scrubbing liquid is in the absorber sump and is

separate from the absorbing solution which is drawn off from

the lower tray. They have a set of demisters between the sump

and the lower tray and at the top of the absorber. The product

solution is sent to a regeneration plant which has four sets of

two stage evaporators to produce the sulfur dioxide and regenerate the solution. The process also must remove any oxidized

sulfate solution because it cannot be regenerated. This is done

with chrystallizers and evaporators and sodium sulfate is produced for sale. None of the byproducts are economic to produce. Very high energy costs are involved because of the high

absorber pressure drops and the use of boiler steam to regenerate solution. In addition there are more than 200 pumps used in

the W-L process.

In contrast, the limestone forced oxidation system is simple

and uses much less energy, Figure 2. Limestone slurry is prepared in Svedala ball mills and pumped to the absorbers where

Figure 1 W-L FGD system flow schematic.

Steam

Air

Air

Heater

Clean Flue Gas

Mixer

Absorber

Condenser

Cooling Water

Steam

Purge Stream

SO2

Compressor

SO2

Vapors

Chiller Crystallizer

Steam

Melt

Tank

Steam

Steam

Dryer

Storage

Bin

Centrifuge

Evaporator

Crystallizer

Treated Purge

Stream

Flyash

Purge to Pond

Flue Gas

From Unit

Air Blower

Sodium Carbonate Solution Makeup

Centrifuge

Dried Sulfate

Product

To Sulfuric Acid Plant

Absorber

Surge

Tank

Absorber

Feed

Tank

Dump

Dissolving

Tank

Orifice

Contractor

Evaporator

Crystallizer

Booster Blower
Babcock & Wilcox 3

Figure 2 B&W LSFO FGD system flow schematic.

Limestone

Storage Area

Limestone Silo

Weigh Feeder

Ball Mill

Ball Mill

Product Tank

Limestone Slurry

Transfer Tank

Equipment Being Used

New Equipment

Limestone Slurry

Transfer Pump

Limestone

Slurry

Feed Tank

Limestone

Slurry

Feed Pump

Mist Eliminator

Wash Tank

Mist

Eliminator

Wash

Pump

Mist Eliminators

From Boiler

To Chimney

Oxidation Air

Compressor

Atmosphere

Pump

Service Water

Classifier

Rotary Drum

Vacuum Filter

Filtrate Pump

Purge

To Mine

Gypsum

Storage Area

Filtrate

Tank Filtrate Return Pump

Filter Feed Tank

Filter

Feed

Pump

Units 3 & 4 Cooling Tower Blowdown Water

Units 1 & 2 Cooling Tower Blowdown Water

Absorber

Tower

Ball Mill Product Pump

Absorber Recirculation

Absorber Blowdown Pump

Hydroclone Underflow Transfer Tank

Hydroclone Underflow Transfer Pump

Hydroclone

1

2

3

4

5

6

1

2

3 4

6

5

it is sprayed into the absorbers at two levels. A B&W patented

tray is also in the tower to improve gas liquid contact. Two sets

of demisters are located at the top of each absorber. Spent slurry

in the sumps or reaction tanks is oxidized to gypsum and is drawn

off of the absorber sumps and dewatered. Primary dewatering

is accomplished with hydroclones and secondary dewatering is

done with vacuum drum filters. Dewatered gypsum (85% solids) is conveyed to a pile where it is hauled back to the coal

mine with flyash and bottom ash for disposal. Reduced absorber

pressure results in lower booster blower power and the simpler

process drastically reduces the number of pumps required. No

steam is required for the LSFO system.

In order to retrofit a LSFO system into the existing W-L system, all equipment had to be evaluated for possible reuse. The

new design was based on the reuse of the existing absorber towers and all of the inlet and outlet ductwork. The absorbers were

stripped inside but the exterior walls remained. The inlet and

outlet ductwork was reused. Since less power was required in

the LSFO system, new smaller motors were added to six of the

absorbers and smaller fan rotors were added to the other six

absorbers. Two new recirculation pumps were added to each

absorber and the old scrubber pumps and tray pumps were removed. The LSFO solution is a less corrosive environment than

the W-L solutions. This results in less expensive materials and

should result in less maintenance problems. Some existing pipe

racks were used to tie in the limestone preparation and dewatering area to the absorbers. Several tanks and a silo were converted to limestone system use. All of the electric power supply

was reused and the switchgear and breakers were converted to

limestone system use. Four control rooms were consolidated

into one with this project and another control room was eliminated. Controls were consolidated and updated to a Distributed

Control System (DCS).

This retrofit project was designed to keep the plant in compliance with State and Federal Regulations which means that

only one absorber per unit could be converted at a time. The

project was constructed in three phases, one absorber per unit

in each phase. It also meant that construction was required to

work around operating equipment without causing downtime.

The design of piping and electrical around the operating system

was extremely difficult.

Teaming Arrangement

PNM and B&W decided that the best approach for this project

was for the two companies to enter into an agreement that allowed both companies to work in a team environment rather

than the traditional supplier purchaser agreement. This arrangement allowed the companies to work closely together toward

the common goal of providing SJGS with a high-quality FGD

system that performs reliably to meet environmental requirements for the lowest possible cost. This type of arrangement

requires a large amount of communication and cooperation. It

also requires a great amount of trust on the part of both companies.

PNM, B&W and some subcontractors participated in formal

team building sessions prior to the start of engineering design

and also prior to the beginning of construction. The team building sessions were a great help in developing the trust required

for this type of approach to a project.

PNM, B&W and the subcontractors held monthly meetings

and weekly conference calls throughout the project to help communications and foster a team environment. These sessions were

attended by individuals from all levels in each organization.

SJGS engineers, mechanics, electricians, instrument journeymen and operators were encouraged to give input on design is-
4 Babcock & Wilcox

sues for cost savings early in the project. This approach greatly

enhanced the “buy in” to the teaming approach. Several brainstorming sessions were conducted in order to solicit ideas for

cost savings early in the project. Many of the ideas that came

from these meetings were incorporated into the project and have

contributed significantly to the cost savings that have been realized to date. A few cost saving ideas could not be incorporated into the project because of the “fast track” nature of the

conversion. A very definite schedule had been established early

in the project and completion dates had been written into the

contracts. Additional savings justified acceleration of Phase II

of the project by working two 50 hour per week shifts. Much

information was transferred in the weekly conference calls to

keep the project on track. Design drawings were reviewed and

approved by SJGS personnel.

The budget for the project was mutually developed by both

companies through a detailed estimate. Once this budget was

established, both companies went to work on value engineering

improvements to lower the cost. All design issues including the

reuse of existing equipment and new equipment selections were

mutually agreed upon. Suggestions for design improvements and

cost savings have come from both parties. The major subcontractors were given incentives to generate ideas for design improvements and cost saving methods also. These subcontractors were invited to team building sessions as well as the monthly

site meetings and conference calls in order to foster teaming.

Construction

The first phase of construction consisted of building the limestone preparation and gypsum dewatering areas in a new building. It also included the conversion of the first absorber on each

unit from the old W-L type to the new LSFO design, Figures 3

and 4. Basically this means removing all absorber internals and

installing B&W’s patented absorber tray and two spray headers

with recirculation pumps in each cell. Most of the power savings for the new LSFO system comes from reduced pressure

drop. The old W-L system had a prescrubber and five sets of

internal trays. Only about 60% of the blower power is required

for LSFO. Additional power savings will be realized because of

the elimination of equipment in the W-L regeneration process

and more than one half of the waste water treatment system.

Overall the auxiliary power requirements are expected to be

reduced by almost 30 MW that translates into increased net capacity of about 30 MW. Since all of the absorber structures are

being reused, the inlet and outlet ductwork is also being reused.

Some tanks, piping and piperacks also are being converted or

used as is. It was found that the electrical power and MCC systems could be converted to the new usage by phases. This saved

the significant cost of new transformers, breakers and switchgear.

Solution Outlet

Solution Outlet

Mist Eliminators

Top Spray Header

Solution Inlet

Solution Outlet

Solution Inlet

Solution Inlet

Solution Outlet

Solution Inlet

Bottom Spray

Header

Mist Eliminators

Solution Outlet

Solution Outlet

Venturi

Figure 3 W-L FGD absorber sideview – before.

Second Stage

Mist Eliminators Upper & Lower

Underspray

Headers

Turning

Vanes

First Stage

Mist Eliminators

Lower Underspray Header

Inlet Awning

Absorber

Suction Pump

Agitator

Oxidation Air

Absorber Spray

Headers

Absorber Tray

Figure 4 B&W FGD absorber sideview.
Babcock & Wilcox 5

B&W was released to begin engineering in May of 1996.

Babcock & Wilcox Construction Company (BWCC) mobilized

on the site one year later in May of 1997. This phase was scheduled to last 10 months and was completed by the end of March

1998. The first four LSFO absorbers were started up as a system and were operated in conjunction with two W-L absorbers

per unit for Phase II. Phase II of construction was conversion of

the second absorber on each unit to LSFO absorbers. The second phase schedule was accelerated and completed by April,

1998. After Phase II LSFO completion, two LSFO absorbers

were operated on each unit and the W-L system was shut down.

Existing compliance was met with two limestone scrubbers per

unit because it was possible to pass more flue gas through the

limestone scrubbers than was possible through W-L absorbers

and also dibasic acid (DBA) was added. The final construction

phase was conversion of a third absorber on each unit to limestone. Final construction project completion was October 15,

1998 and New Mexico emission regulations now require approximately 75% SO2 removal or 0.46 lb/million Btu on an annual average. Existing state regulations also require that a station rolling average of 0.65 lb/million Btu be maintained and a

unit 2 rolling average of 72% removal be maintained.

This phased approach to construction complicated the work

considerably as the new equipment was installed throughout an

operating plant that was required to remain in compliance. Also,

many of the piping systems and electrical systems were installed

around and with operating systems. The majority of new equipment was powered from existing power distribution equipment

as it became available from abandoned equipment or absorbers

being converted. This type of installation required a high degree of coordination, communication and team work. The teaming arrangement utilized for this retrofit was ideal for this type

of project.

Seven PNM employees were integrated into the construction site organization. This was done to reduce cost and take

advantage of plant personnel’s knowledge of the plant. This

structure improved the efficiency of the site construction team

dramatically.

PNM is performing some of the design and construction work

with site personnel. This has also reduced cost and has enhanced

SJGS personnel’s sense of ownership in the project. PNM has

the responsibility for design and installation of a new Distributed Control System (DCS) for the LSFO system. This control

system also retrofitted the old controls for the waste water system. Combined DCS allowed for the consolidation of four control rooms into one and the elimination of a fifth. PNM controlled the start-up or commissioning of the system after each

construction phase was complete. PNM in cooperation with

B&W performed all of the training required for Operations and

Maintenance people. This involvement accelerated the learning

curve for operating a new system as well as reducing project

cost.

Results and Economics

This conversion project was justified on the basis of O&M

and power/fuel savings. The reduction of personnel by 110 positions was a large percentage of the savings. The old W-L and

WW systems required 67 people in operations and the new limestone/waste water system will require 26 operations people.

W-L and WW for the old systems required 70 people in maintenance. The new systems will require about 17 people in all crafts.

The high cost for maintenance materials and equipment replacement required for the 20 year-old W-L system will be greatly

reduced with the newer and much less complicated limestone

system. Fuel savings from reduced auxiliary power and elimination of regeneration steam is estimated at almost $5 million

per year. All of these savings are expected to add up to about

$20 million per year. In addition, there could be income from

excess allowance credits if the market allows for it.

The LSFO system is in full operation with three absorbers

on each unit. Removal efficiencies have been measured and

absorbers are performing according to design. The limestone

preparation and gypsum dewatering equipment are operating at

design capacities.

Phase I of the project was under budget and savings of

$6,600,000 was declared. Part of the savings was shared with

B&W and the subcontractors and this shared savings showed

up as project cost. Budgeting has been unusual in applying the

shared percentage of savings as a cost added to the project. Since

the project was constructed in three phases, equipment for each

phase was entered into the accounting books as it was placed in

service. This, along with the nine owners of different units and

different percentages of ownership made accounting extremely

complicated. Additional savings were realized in Phases II and

III through labor efficiency. The teaming arrangement helps

project success and results in lower overall project cost. The

predicted savings are being compared to actual savings as data

is collected on energy and fuel usage. Personnel reductions produce O&M savings and actual budget changes are being compiled. SJGS is much better prepared for the competitive marketplace.