Notes from Site Visit at A2A’s Centrale di Monfalcone on April 1, 2011

EPA conducted a site visit at A2A’s Centrale di Monfalcone (Monfalcone) located in 

Monfalcone, Italy on Friday, April 1, 2011 to learn about the operations at the plant, specifically 

the flue gas desulfurization (FGD) system and the FGD wastewater treatment system. Process 

flow diagrams of the FGD wastewater treatment system are included as Attachment 1 to these 

notes. 

These notes describe the information collected during the site visit. Table 1, at the end of these 

notes, identifies the site visit participants.

Plant Overview

• Monfalcone operates four electric generating units. Units 1 and 2 burn both coal 

and fuel oil, while Units 3 and 4 burn only fuel oil. The table below contains some 

general information on the operation of each steam electric generating unit at the 

time of the site visit.

Unit

Installation 

Date

Capacity 

(MW)

Particulate 

Control NOx Control SO2 Control

1 1965 165 Electrostatic 

Precipitator 

(ESP)

Overfire air Wet FGD

2 1970 171 ESP Overfire air Wet FGD

3 1983 320 ESP Overfire air None

4 1984 320 ESP Overfire air None

[QUESTION FOR MONFALCONE: Does the plant operate selective catalytic reduction (SCR) 

or selective noncatalytic reduction (SNCR) systems on any of the units?]

• On average, Monfalcone burns 2,400 to 2,600 tons of coal per day in Units 1 and 

2. Monfalcone burns a Russian bituminous coal with a sulfur content between 0.3 

and 0.4 percent. The maximum sulfur content of the coal is 1 percent. The plant 

stores 30 to 45 days worth of coal on site. The coal pile runoff at the plant is 

collected in sumps and transferred to a physical/chemical precipitation wastewater 

treatment system that receives other stormwater and plant wastewater. The 

effluent from this treatment system is discharged.

• Monfalcone also has the capability to burn biomass, but it can only account for 5 

percent of the fuel used at any given time, based on permit restrictions.

• Fly ash from Units 1 and 2 is handled dry and sent pneumatically to a single silo.

The silo has a capacity of 2,000 tons of fly ash. Monfalcone generates 

approximately 200 to 300 tons of fly ash per day; therefore, the silo has the 

capacity for eight to ten days of storage. Monfalcone currently pays a contractor 

to take the fly ash off site.

• Monfalcone operates a completely dry bottom ash system. Plant personnel stated 

that they used to operate with a wet hopper, but they converted to a completely 

dry system. The bottom ash is pneumatically conveyed to silo (separate silo from 
Page 2

fly ash). According to plant personnel, the plant generates approximately 100,000 

tons of bottom ash each year. Of that, approximately 1,000 tons is disposed of in 

a landfill and the other 99,000 tons is marketed for reuse. [QUESTION FOR 

MONFALCONE: What is the bottom ash marketed for? Is the landfill located 

onsite or offsite?]

• The plant operates a once-through cooling water system.

Flue Gas Desulfurization (FGD) System

• Monfalcone operates double-contact flow limestone forced oxidation FGD 

systems on Units 1 and 2 that were designed by Mitsubishi. A limestone slurry is 

sprayed upward from the bottom of the absorber to react with the sulfur dioxide in 

the flue gas as the slurry is moving upward and as it is falling back down to the 

reaction tank.

• Monfalcone purchases a dry limestone dust and does not use ball mills on site. 

The plant does mix the limestone with well water to generate the slurry used in 

the absorber.

• Monfalcone uses well water as the source of the scrubber make up water.

• The FGD systems operate with a chlorides level between 10,000 and 30,000 ppm. 

The maximum design chlorides level is 50,000 ppm. The FGD system operates 

with approximately 30 percent solids in the absorber.

• The blowdown from the scrubbers is approximately 3 to 4 cubic meters per hour. 

The blowdown is transferred directly to vacuum belt filters; it is not transferred to 

hydroclones prior to dewatering. The plant washes the gypsum as it is applied to 

the belt filters. The moisture content of the gypsum is typically 12 percent. 

Monfalcone does not market the gypsum. The plant pays a contractor to take the 

gypsum from the plant.

• A portion of the filtrate from the vacuum belt filters is recycled back to the FGD 

system. The remainder is sent to the FGD wastewater treatment system.

FGD Wastewater Treatment

• Diagrams of the FGD wastewater flow and treatment system are included as 

Attachment 1.

• The FGD wastewater treatment system uses a two-step process to treat the FGD 

wastewater to achieve zero discharge of wastewater from the system. In the first 

step, the FGD wastewater is pretreated using clarification and softening to reduce 

suspended solids, calcium, magnesium, and heavy metals. The second step 

involves the use of a two-stage evaporation and crystallization system.
Page 3

• The filtrate from the vacuum belt filters is transferred to a reaction tank where the 

plant adds lime to raise the pH to 11 S.U. The plant does not operate an 

equalization tank prior to the reaction tank.

• From the primary reaction tank, the wastewater is sent to a second reaction tank. 

The plant does not add any chemicals to this reaction tank, but some of the sludge 

from the downstream clarifier is recycled to the tank to provide nucleation sites 

for the precipitation of additional solids.

• The effluent from the second reaction tank is transferred to the clarifier where the 

plant adds ferric chloride, polyelectrolyte, and sodium carbonate (soda ash) to the 

wastewater. The soda ash is used to soften the water and reduce the calcium and 

magnesium prior to the evaporation system. Calcium and magnesium lead to 

larger boiling point rise in the system, which requires additional energy.

• The overflow from the clarifier is transferred to the intermediate tank prior to 

being sent to the evaporation system.

• The underflow from the clarifier is transferred to a sludge holding tank and then 

either recycled to the secondary reaction tank or sent to a filter press. The filtrate 

from the filter press is transferred to the intermediate tank. [QUESTION FOR 

MONFALCONE: How does the plant dispose of the filter press solids?]

• From the intermediate tank, some of the wastewater is recycled back to be mixed 

with the sodium carbonate to create the mixture that is used in the clarifier. The 

remainder of the water is transferred to the evaporation system.

• The FGD wastewater first passes through a plate heater where the process 

condensate heats the FGD wastewater. The plant then adds hydrochloric acid to 

the heated water and transfers this stream to the deaerator. The hydrochloric acid 

reacts with the carbonate to generate carbon dioxide, which is vented to the 

atmosphere. 

• The wastewater is then fed to the sump of the falling-film brine concentrator. 

Brine from the sump is pumped to the top of the brine concentrator and enters the 

heat transfer tubes. While falling down the heat transfer tubes, part of the solution 

is vaporized and then compressed and introduced to the shell side of the brine 

concentrator (i.e., the outside of the tubes), along with additional make-up steam. 

The temperature difference between the compressed vapor and the brine solution 

causes the compressed vapor to transfer heat to the brine solution, which flashes 

to a vapor. As heat is transferred to the brine, the compressed vapor cools and 

condenses as distilled water.

• The condensed vapor from the brine concentrator is collected and transferred to a 

condensate tank. Within this tank, some additional steam vapor is returned to the 

system. The remaining condensed water is either recycled back to the 

compression portion of the system to be reused as steam or it is pumped through 
Page 4

the plate heater where it transfers its heat to the incoming FGD wastewater and at 

the same time cooling the condensate stream.

• The concentrated brine slurry from the brine concentrator tubes falls into the 

sump and is recycled with the feed back to the top of the brine concentrator, while 

a small amount is continuously withdrawn from the sump and transferred to the 

crystallizer system.

• The brine is combined with the slurry recirculation from the bottom of the 

crystallizer and transferred to a heat exchanger where the plant uses steam to heat 

the slurry prior to it reentering the crystallizer. The heat from the slurry entering

the crystallizer vaporizes some of the water in the crystallizer. This steam vapor

exits the top of the crystallizer and is transferred to an air condenser, where air is 

used to cool the steam. This cooled steam, along with the condensed steam from 

the heat exchanger, is transferred to a condensate tank. Some of the vapor in the 

tank is combined with the steam exiting the crystallizer to be cooled in the air 

condenser. The remaining condensed water is a process condensate stream.

• Some of the slurry from the bottom of the crystallizer is transferred through the 

heat exchanger where it is heated with steam and fed back to the crystallizer. The 

heat transferred to the slurry allows the water present in the slurry to evaporate 

and exit the crystallizer as steam. The evaporation of the water also concentrates 

the solids present and allows the solids to crystallize. There is a continuous bleed 

of the slurry from the crystallizer that is fed to the Oberlin filter presses where the 

crystallized solids are dewatered. The filtrate from the filter presses is transferred 

to the mother liquor tank and recycled to the crystallizer. The crystallized solids 

are collected in bags. The plant pays a German company to remove these solids, 

which are used as mine fill. Plant personnel stated that, in 2009, the plant 

generated approximately 350 tons of crystallized solids.

• Monfalcone transfers the condensate from the FGD treatment system to the 

demineralizer system. Following treatment in the demineralizer system (reverse 

osmosis), it is used as make up for the boiler.

Sampling

• As part of the site visit, EPA had planned to collect wastewater samples to 

characterize the untreated FGD wastewater and the condensate streams generated 

from the wastewater treatment system. Due to delays in customs, the sampling 

materials were not received at the plant in time for EPA to collect the samples 

during the visit. Therefore, plant representatives collected the samples at a later 

date following instructions provided by EPA (see Attachment 2). The plant 

representatives shipped the samples to the EPA-contract laboratories for analysis.

• Samples were collected from the following waste streams (see Attachment 1 for 

identification of the waste streams in the process flow diagrams):
Page 5

o Influent to FGD wastewater treatment system (process stream 1);

o Condensate from brine concentrator (process stream 35 – after plate 

heater); and

o Condensate from crystallizer (process stream 39).

• Table 2 presents the analytes for which EPA requested Monfalcone to collect 

samples and the analytical methods that were used for the analysis.

• Plant representatives collected the requested samples on April 14, 2011.

• The samples were shipped by the plant representatives, but they did not pass 

customs and were returned to the plant. Because the classical analytes were no 

longer cold by the time they were returned to the plant, EPA coordinated with the 

plant to only reship the metals and mercury samples to the laboratories. 

Therefore, EPA does not have any results for the classical analytes.

• Table 3 presents the analytical results for each of the three waste streams.
Page 6

Table 1. Site Visit Attendees

Name Organization (Representing) Telephone E-mail

Leonardo Mainardis A2A (+39) 0481749269 leonardo.mainardis@a2a.eu

Javier Ceballos HPD (+34) 944914092 javier.ceballos@veoliawater.com

Mikel Garcia HPD (+34) 944914092 mikel.garcia@veoliawater.com

Ron Jordan EPA/Office of Water (202) 566-1003 jordan.ronald@epa.gov

T.J. Finseth ERG (Contractor to EPA) (703) 633-1698 thomas.finseth@erg.com

Tracey Footer ERG (Contractor to EPA) (919) 468-7952 tracey.footer@erg.com
Page 7

Table 2. Analytical Methods

Parameter Method Number

Classicals

Chemical oxygen demand (COD) EPA 410.4

Total suspended solids (TSS) SM 2540 D

Total dissolved solids (TDS) SM 2540 C 

Sulfate EPA 300.0

Chloride EPA 300.0

Ammonia as nitrogen EPA 350.1

Nitrate/nitrate as nitrogen EPA 353.2

Total Kjeldahl nitrogen (TKN) EPA 351.2

Total phosphorus EPA 365.1

Total and Dissolved Metals

Mercury EPA 1631E

Antimony, arsenic, cadmium, chromium, copper, lead, manganese, 

nickel, selenium, silver, thallium, and vanadium

EPA 200.8 with collision cell 

Aluminum, barium, beryllium, boron, calcium, cobalt, iron, magnesium, 

molybdenum, sodium, tin, titanium, and zinc.

EPA 200.7
Page 8

ND – Not detected (number in parentheses is the quantitation limit).

4 – MS and/or MSD did not meet laboratory criteria, but sample concentration is four times greater than the matrix spike amount, so control limits are not applicable.

B – Analyte was found in the blank and sample.

F – MS and/or MSD not within laboratory control limits.

J – Result measured above the MDL, but less than the quantitation limit.

U – Result below the MDL. (Number shown in parentheses is the quantitation limit).

Table 3. Analytical Results, Monfalcone

Analyte Units Method

Influent to FGD 

Wastewater Treatment

Condensate from Brine 

Concentrator

Condensate from 

Crystallizer

Aluminum ug/L 200.7 1600 ND (200) U ND (200) J 

Antimony ug/L 200.8 4.1 ND (2.00) U ND (2.00) U

Arsenic ug/L 200.8 4.7 ND (4.00) U ND (4.00) U

Barium ug/L 200.7 470 ND (20.0) U ND (20.0) U

Beryllium ug/L 200.7 ND (2.00) U ND (2.00) U ND (2.00) U

Boron ug/L 200.7 220000 B, 4 700 B 710 B 

Cadmium ug/L 200.8 100 ND (4.00) U ND (4.00) U

Calcium ug/L 200.7 6400000 4 630 460

Chromium ug/L 200.8 11 ND (8.00) U ND (8.00) U

Cobalt ug/L 200.7 26 ND (20.0) U ND (20.0) U

Copper ug/L 200.8 8.2 ND (4.00) U ND (4.00) U

Iron ug/L 200.7 1300 ND (200) U ND (200) U

Lead ug/L 200.8 3.2 ND (2.00) U ND (2.00) U

Magnesium ug/L 200.7 830000 4 ND (400) J ND (400) J 

Manganese ug/L 200.7 3000 4 ND (20.0) J ND (20.0) J 

Mercury ng/L 1631E 10300 3.76 9.93

Molybdenum ug/L 200.7 ND (40.0) J ND (40.0) U ND (40.0) U

Nickel ug/L 200.8 160 F ND (4.00) U ND (4.00) U

Selenium ug/L 200.8 120 ND (4.00) U ND (4.00) U

Silver ug/L 200.8 ND (2.00) F, U ND (2.00) U ND (2.00) U

Sodium ug/L 200.7 820000 4 32000 36000

Thallium ug/L 200.8 4.7 ND (2.00) U ND (2.00) U

Tin ug/L 200.7 ND (200) U ND (200) U ND (200) U
Page 9

ND – Not detected (number in parentheses is the quantitation limit).

4 – MS and/or MSD did not meet laboratory criteria, but sample concentration is four times greater than the matrix spike amount, so control limits are not applicable.

B – Analyte was found in the blank and sample.

F – MS and/or MSD not within laboratory control limits.

J – Result measured above the MDL, but less than the quantitation limit.

U – Result below the MDL. (Number shown in parentheses is the quantitation limit).

Table 3. Analytical Results, Monfalcone

Analyte Units Method

Influent to FGD 

Wastewater Treatment

Condensate from Brine 

Concentrator

Condensate from 

Crystallizer

Titanium ug/L 200.7 76 ND (20.0) U ND (20.0) U

Vanadium ug/L 200.8 25 ND (10.0) U ND (10.0) U

Zinc ug/L 200.7 270 ND (40.0) U ND (40.0) U