# Combustion Additives for Control of Phosphorus Effects and Achieving Mercury Reduction Technical Paper
BR-1910

Authors: M. Gadgil, G. Bielawski, and M. Schmeida

Babcock & Wilcox Power Generation Group, Inc. Barberton, Ohio, U.S.A.

Presented to: Power-Gen Europe

Date: June 3-5, 2014

Location: Cologne, Germany1 

## Combustion Additives for Control of Phosphorus Effects and Achieving Mercury Reduction

BR

- 1910 Presented to Power

- Gen Europe 201 4

Mandar Gadgil, G reg Bielawski , Melanie Schmeida Babcock & Wilcox Power Generation Group, Inc

. 20 S

. Van Buren Ave, Barberton , Ohio 44203 USA



### Abstract
Biomass is generally considered CO 2 neutral, so the utilization of biomass fuels for energy production continues to grow. Many European power companies are transitioning to greater biomass use through biomass and coal co

- combusti on and conversion of coal

- fired boilers to biomass firing. The increased use of biomass presents some unique challenges to the operation of both boilers and flue gas treatment equipment. One such challenge involves phosphorus deactivation of the s electiv e c atalytic r eduction (SCR) catalyst.

In addition to these phosphorus issues associated with biomass firing or coal

- biomass co

- combustion, there is a need to reduce mercury emissions from the combustion process . Halogen addition to the fuel is a wi d e l y a c c e p t e d t e c hno l o g y f o r e nh a n ci n g m e rc u ry o xi d at i o n, since oxidized mercury is more readily removed by flue gas cleaning systems. However, under certain operating conditions, halogens are also known to increase fouling and corrosion.

F i e ld d ata will b e p res e n ted demonstrating the use of a patent

- pending combustion additive developed by Ba b c o ck & Wil c o x P o wer G e n erat i o n G r o up, I n c

. (B & W P GG). This additive has been shown to maintain SCR catalyst performance and reduce t h e halogen c o n ce n tr a t i o n r e qu ir e d t o ac h i e v e m e rc u r y oxidation.



### Introduction
Reducing carbon dioxide CO 2 emissions from the power

- generating industry, has led to considerable interest in the utilization of biomass and municipal and industrial waste in power plant boilers. The use of renewabl e energy sources , such as biomass co

- firing with coal or 100% biomass firing in existing coal

fired power plants , represents one option for combined renewable and fossil energy utilization to reduce CO 2 emissions. Biomass is considered CO 2 neutral with re spect to the greenhouse gas balance if the use of fossil fuel in harvesting and transporting the biomass is not considered. Direct co

- firing, i.e. , firing coal and biomass in the same boiler, is the simplest and most widely applied technology for co

firin g biomass.
Biomass and coal have fundamentally different fuel properties. Biomass (and some low

- rank coals) contains larger relative quantities of alkali and alkaline

- earth elements (potassium, sodium, calcium, and2 magnesium ), phosphorus and chlorine tha n coal. Since all the constituents of the biomass enter the boiler during combustion , several technical concerns arise. Higher fuel chlorine content can lead to increased high temperature corrosion in boilers. Accelerated fouling and slagging can occur when fuels containing high potassium levels are utilized

. F or the operation of SCR systems , there are technical challenges associated with co

- combustion of biomass and coal in boilers designed for coal as t he constituents of biomass have the potential to impair the SCR

. SCR catalysts are susceptible to deactivation from several mechanisms resulting in shorter catalyst life. The deactivation mechanisms include c ondensation of volatile inorganic species on the catalyst surface and the reaction of gas

- phase poisons with the vanadium sites. F ormation of the sul fate

- based deposits on the catalyst surface or reaction with the catalyst’s active species can also significantly reduce catalyst life

. Biomass in the form of wastes may also contribute elements such as arsenic , potassium and phosphorus , which are well known catalyst poisons

. [ 1]



### SCR Catalyst D eactivation by Phosphorus
As noted in the introduction, t he SCR catalyst can be deactivated due to the actions of different types of poisons. Some of t hese poi sons include alkali and alkaline earth metals, arsenic and phosphorus. Each

one of the poison s attacks the SCR catalyst in different ways , resulting in the d eactivation

. The deactivation mechanism for phosphorus is discussed in more detail

. The release mechanism of phosphorus in the gas

- phase during combustion is very different between coal and biomass. In the case of coal, most of the phosphorus is inorganically associated within the coal matrix. During the coal combustion process , especially under a ir

- stag ed combustion conditions, the phosphorus compounds undergo a carbothermic reduction reaction that releases gas

- phase phosphorus . For biomass, almost all of the phosphorus is organically associated in the fuel. The organically bound phosphorus is r eadily released as gas

- phase phosphorus during the combustion process. This release of organically bound phosphorus in the gas phase is similar to the release of the volatile components of the fuel , which are also organically bound in the fuel , and are re leased in the gas phase during combustion, albeit irrespective of staged or un

- staged combustion. The gas

- phase phosphorus can react with the active sites on the surface of the catalyst resulting in chemical deactivation of the catalyst due to formation o f vanadium

- phosphorus bonds. One interesting observation noted with phosphorus deactivation of multilayer SCR catalyst installations is that the second catalyst layer is often more deactivated than the first layer. The possible explanation of this could be due to the suppression of phosphorus adsorption on the catalyst surface in the presence of ammonia. For the first layer , there is much more ammonia present in the gas whereas for the second layer , there is comparatively less ammonia present in the flue gas due to the consumption of ammonia for the nitrogen oxides ( N O x ) reduction reaction

. It may be possible that ammonia gets adsorbed more easily on the active sites than phosphorus and hence , the second layer deactivates more than the first layer

. [ 2 ]3 

### Mitagent TM 

### Combustion Additive Development

B&W PGG initiated the Mitagent TM combustion additive development program to develop a way to reduce the rapid deactivation of SCR catalyst by phosphorous observed on air

- staged Powder River Basin ( PRB ) coal

- fired units in the United States

. T here are two primary sources by which phosph orus can enter the SCR catalyst

. One is in the form of gas

- phase phosphorus; the other is associated with the ash

. The ash

- bound source of phosphorus was investigated first because there was no reliable technique at that time to measure gas

- phase phospho rus concentration in the high dust gas entering the SCR

. Size

separated ash samples were collected from plants that were experiencing rapid catalyst deactivation

. These samples were analyzed to determine the possibility of ash

- bound phosphorus leaching i nto the SCR catalyst and causing a chemical deactivation

. Due to high calcium and low sulfur nature of the PRB coal, t wo pH level s were chosen for this leaching study , with one pH being slightly acidic (pH = 5) and the other pH being slightly alkaline (pH = 9)

. T hese are the two pH conditions most likely present during short (two to three days) or long (two to four weeks ) term u nit outages. Due to the high calcium and low sulfur nature of the PRB coal, the pH values of 5 and 9 were chosen for the leaching study. It was observed that under the se two pH conditions , negligible amounts of phosphorus can leach out ; leading to the conclusion that ash

- bound phosphorus was an unlikely source of SCR catalyst deactivation

. As a result of this analysis , particulate

- bound phosphorus was thus ruled out as the source for SCR deactivation.

F ollowing this analysis, B&W PGG began to investigate whether gas
- phase phosphorus or gas

- phase phosphorus compounds were the primary deactivation agent

. B&W PGG developed a modified procedure to reliably measure gas

- phase phosphorus at high dust locations such as the SCR inlet

. The primary problem with measurement of gas

- phase phosphorus at high dust locations is an interference of the particulate

- bound phosphorus with the impinger solution

. This interference cause d the p rior gas

phase phosphorus measurements determined by standard EPA M ethod 29 to produce highly variable results

. B&W PGG believes that this variability was due to particulate

- bound phosphorus breaking through into t he impingers and being reported as gas
- phase phosphorus. Following numerous investigations, B&W PGG modified the standard EPA Method 29 procedure for gas

- phase phosphorus measurement

. The modifications included installing an in

- stack thimble and a backup filter to collect the ash inside the duct

. The impinger solutions used to collect the gas were also modified

. The first impinger solution was filled with de

- ionized (DI) water because it was observed that ash

- bound phosphorus was insoluble in DI water a nd slightly acidic solutions

. The other two impingers were filled with a mixture of hydrogen peroxide and nitric acid

. The first impinger , filled with DI water, served as an additional filter to catch any particulate breakthrough

. This technique was tes ted at different power plants burning PRB coal with staged combustion and was found to be a reliable method to measure gas

phase phosphorus

.
Since the deactivation phenomenon was observed only on units with air

- staged combustion or those with known poor co mbustion issues, a mechanism was proposed to explain the release of gas

- phase phosphorus as a result of such stag ing or poor combustion of the PRB fuel

. This mechanism is based on carbothermic reduction of phosphorus

- bearing minerals , resulting in release of gas

- phase phosphorus. Mineral analysis of the PRB coal revealed that the phosphorus was primarily associated with calcium4 (Ca) in the form of calcium phosphate, which is a very stable compound (high melting and boiling point) under un

- staged combustio n conditions

. A coal sequential extraction technique also revealed that a negligible amount of phosphorus was organically associated within the coal matrix

. O rganic phosphorus is readily released into the gas phase

. This is the reason why SCRs on biomas s
- fired units can experience rapid catalyst deactivation from phosphorus

. Formation of vapor phase silicon mono

- oxide (SiO) under reducing conditions due to carbothermic reduction of SiO 2 was explained by Quann

. [ 3 ] Based on that knowledge, B&W PGG propo sed a similar theory involving carbothermic reduction of phosphorus

bearing inorganic compound resulting in the release of gas

- phase phosphorus. The reaction involved is between a phosphorus

- bearing inorganic mineral compound and carbon monoxide and is re presented as follows :

P (compound S ) + CO ( g)  P (g) + CO 2 ( g) Equation (1)
This mechanism could potentially explain increased deactivation of the catalyst by phosphorus under staged combustion con ditions

. The release of gas

- phase phosphorus from E quation 1 is dependent on both carbon monoxide ( CO ) concentration and residence time in a high CO atmosphere. In boilers with staged combustion , the concentration of CO is typically higher in the lower f urnace ( below the over fire air (OFA) ports ) compared to an un

- staged furnace. In addition, due to air staging the phosphorus

bearing coal particles , on an average, spend more time in a high CO atmosphere compared to an un

staged furnace. C ombined , these two conditions result in a significantly higher release of gas

- phase phosphorus compared to an un
- staged combustion process

. Based on this theory, B&W PGG proposed t hat, for a unit using staged combustion to reduce the boiler outlet NO x , there should be m ore gas
- phase phosphorus produced compared to a unit without staged combustion

. This theory was tested at a power plant located in the midwestern United States. The plant has two units that burn the same coal. Unit 1 does not have air staging , whereas u nit 2 does have air staging. Unit 1 is 200 MW generating capacity with SCR and ESP installed, and Unit 2 is 320 MW generating capacity with SCR, circulating dry scrubber (CDS) and fabric filter installed

. Table1: Gas

- Phase Phosphorus Comparison

Paramete r Unit 1 (Un

- s taged Combustion) Unit 2 (Staged Combustion) Boiler Outlet NOx , ppm 300 220 Gas

- phase phosphorus , ppb 14 (9 runs average) 27 (9 runs average) P 2 O 5 % in ash day 1 1.07 0.92 P 2 O 5 % in ash day 2 1.2 0.86

As seen in Table 1, for Unit 1 without air staging , the gas

- phase phosphorus was significantly lower than Unit 2. It is also important to note that for Unit 1, the P 2 O 5 content in the ash was significantly higher than Unit 2. This supports the theory that gas
- phase phosp horus is released as a result of carbothermic reduction reaction. Due to air staging, Unit 2 is expected to have higher CO concentration than U nit 1. As a result of higher CO concentration, it was expected that Unit 2 will have more gas

- phase phosphorus5 as compared to Unit 1. The test results from B&W PGG’s testing support the hypothesis that significantly more gas

- phase phosphorus is produced as a result of air staging.
Based on the theory of a carbothermic reduction reaction causing release of gas

- phas e phosphorus, it

was proposed that for two units with two different boiler outlet NO x levels due to the extent or the degree of staging, not j ust staged or un

- staged, there should be different gas

- phase phosphorus levels. This theory and the modified Meth od 29 technique were tested by performing gas

- phase phosphorus sampling at SCR inlet locations of two plants with different degrees of air staging. Figure 1 shows the results supporting this hypothesis

. P lant A in Figure 1, is the same plant as Unit 2 in Table1. The other plant in Figure 1 is Black Hill Power & Light’s Wygen II unit. The unit has 100 MW generation capacity from a B&W PGG subcritical PRB coal

- fired boiler and is equipped with air

- staged combustion, SCR, spray dryer absorber (SDA) and fab ric filter . Wygen II is a deep

- staged combustion unit with boiler outlet NO x of 150 ppm (0.15 lb/MBtu NO x ) , whereas P lant A has less staging as indicated by boiler outlet NO x of 220 ppm (0.22 lb/MBtu NO x ). Wygen II previously experienced rapid SCR catal yst deactivation by what has been confirmed to be gas

- phase phosphorus poisoning.

Figure1: Gas

- Phase Phosphorus Comparison
In Figure 1, the red columns represent Wygen II measurements and the blue columns represent P lant A measurements. As predicte d , there was more gas
- phase phosphorus at Wygen II than P lant A

. This sampling validated the theory of carbothermic reduction and B& W PGG’s modified M ethod 29 procedure for sampling of gas

- phase phosphorus in a high particulate loading location

. Gas Phase P at Plant A Inlet NOx 0.22 lb/ MBtu

G a s P h a s e P a t W y g e n I I I n l e t N O x 0

. 1 5 l b / M B tu6 

### Mitagent Additive Performance Demonstration for Phosphorus Mitigation
Catalyst samples were obtained and analyzed from Unit 1 mentioned in Table 1

. The analysis showed that there was no appreciable catalyst deactivation due to phosphorus poisoning and the perfor mance
was as predicted . This was not surprising as the gas

- phase sampling at Unit 1 show ed that the phosphorus levels in the gas phase were low (14 ppb ). Catalyst samples were also obtained from the Wy g en II plant. The catalyst samples analyzed from Wy gen II showed the deactivation was caused due to phosphorus poisoning. This also was not surprising as the gas

- phase phosphorus sampling at Wygen II showed the phosphorus concentration to be much higher (36 ppb ) as compared to Unit 1

. Based on the resear ch performed, it was c oncluded that the rapid deactivation of the SCR catalyst was caused by gas
- phase phosphorus poisoning of the catalyst. Therefore, B &W PGG embarked on a developmental program to identify additives and methods that are capable of mitig ating and/or reducing gas
- phase phosphorus compounds

. A novel material was identified that sequestered gas
- phase phosphorus under typical combustion conditions as particulate

- bound phosphorus. This additive and application method lowers the concentratio n of gas

- phase phosphorus and its aerosols entering the SCR

. Detailed studies were performed to investigate the effects of this material on boiler operation and to confirm that there

were no adverse affects , particularly in the areas of boiler slagging an d convection pass fouling and corrosion

. The required addition rate of this material was also analyzed as well as leaching studies to observe stability of this new particulate

- bound phosphorus under standard SCR operating conditions.

B& W PGG’s Mitagent ad ditive technology was first tested at Wygen II in two short

- term (4 to 5 days) injection tests

. The additive was injected at rates less than 0.5% of the total plant coal flow rate using pneumatic conveying

. Gas

- phase phosphorus was measured at baseline c onditions , and during and after the injection test

. It was observed that the gas

- phase concentration decreased by about 50 % during additive injection compared to the baseline conditions

. This injection testing demonstrated the ability of the B&W PGG addit ive to achieve lower gas

- phase phosphorus concentration s entering the SCR. The result of this test is shown in Figure 2.7 Figure 2 : Demonstration of reduction in gas

- phase phosphorus at SCR inlet as a result of additive injection at Wygen II.

As se en from Figure 2, the average gas

- phase phosphorus before the additive injection was 36 ppb. The average gas
- phase phosphorus was 21 ppb with the addition of the Mitagent combustion additive. M emory effect was observed after the injection of additive was stopped

. The memory effect highlights two points : o ne is that more material was injected than needed and it will be possible to optimize the injection rate in the future , and second , the injected material may have scavenged the gas

- phase phosphorus after it was deposited on walls or economizer tubes, etc., in the upper furnace.

Another short

- term Mitagent additive test was performed at P lant A which was mentioned in Figure 1

. B&W PGG’s additive injection at P lant A reduce d the gas

- phase phosphorus concent ration at the SCR inlet. The baseline gas

- phase phosphorus was 27 ppb and after injection of the Mitagent additive it was reduced to 17 ppb. This testing again demonstrated that by adding Mitagent to the coal, the gas

- phase phosphorus concentration at th e SCR inlet can be reduced.

In a third short

- term test , the Mitagent additive was used along with halogen addition to the coal. Gas

phase sampling was performed at the stack by EPA Method 29 instead of the SCR inlet

. This is also a B&W PGG su b critical boi ler with 250 MW generation capacity , equipped with SCR, ESP, CDS and fabric filter

. Gas

- phase emissions comparisons are shown in Table 2.8 Table2: Gas

- Phase Emission s Comparison

Metal Average b aseline stack gas
- phase emission ( kg /hr )

Two

- day average Average stack gas
phase emission with B&W PGG’s Mitagent additive ( kg /hr) Two

- day Average % Emission s Reduction

Phosphorus 0.0081 0.005 40 Selenium 0.00033 0.00022 25

The results again showed that the combustion additive injection was able t o reduce phosphorus emissions , along with selenium. The gas

- phase phosphorus emissions at the stack were reduced by 40% on average. This was very similar to the reduction in phosphorous observed at Wygen II and P lant A with the Mitagent additive. It wa s also observed that the gas

- phase emissions of selenium and arsenic were also reduced.

T o demonstrate actual impr ovement in catalyst life performance as a result of gas

- phase phosphorus

m itigation using the Mitagent add i tive , a long

- term injection test wa s performed at Wygen II

. The deactivation trend at Wy gen II as a result of the additive injection for 1 3 , 5 00 hours is shown in Figure 3

.

Figure 3 : Actual catalyst deactivation trend for Wygen II with continuous additive injection.
Figure 3 shows thr ee different catalyst deactivation trends. The green curve represents the expected deactivation trend of the original catalyst . The blue curve represents the actual deactivation curve after the catalyst was installed at Wygen II. This very rapid deactiv ation was later confirmed to be due to gas

phase phosphorus pois o n ing of the catalyst. The deactivated catalyst was regenerated and was reinstalled at Wygen II in March 2010. The red curve represents the deactivation curve of this 

### Operating Hours9 regenerated catalyst with the same formulation as the original catalyst along with Mitagent additive injection. The objective of the testing was to determine whether the deactivation of the catalyst could be reduced as a result of the additive injection. As illustrated in Figure 3 , as a result of the B&W PGG additive injection , the actual deactivation of the catalyst ( as shown by the red curve ) was very gradual and closely follow ed the expected deactivation trend (as shown by the green curve )

. This improvement in the catalyst de activation performance was a result of the additive injection process that convert ed the gas

- phase phosphorus into particulate

- bound phosphorus

. The reduced phosphorus deactivation component for the catalyst result ed in slower deactivation. The B&W PGG M itagent additive can be used to reduce phosphorus deactivation for coal , biomass and /or coal

- biomass co
- combustion units because the phosphorus is sequestered in the combustion process . As a result , this additive can be applied to both new as well as rege nerated catalyst and also for any type (plate, honeycomb, corrugated) of catalyst. During the long

- term testing for phosphorus mitigation , some additional interesting effects of Mitagent on halogen chemistry and therefore on mercury removal were also obse rved [ 2 ], which is further expanded upon below.


### Mitagent Additive A pplication for the Enhancement of Mercury Emission Control
Mercury enters the environment in various ways, such as through volcanic activity, coal combustion, and chemical manufacturing. A s a toxic element, mercury poses ecological threats when it enters water bodies, where small aquatic organisms convert it into its highly toxic form , methyl mercury. This form of mercury may then migrate up the food chain as predator species consume the s maller organisms. Fish contaminated with methyl mercury may pose health threats to people who rely on fish as part of their diet. Mercury can harm fetuses and cause neurological disorders in children, resulting in, among other things, impaired cognitive abilities. As a result , there is a need to control mercury emissions from coal

and biomass

- fired power plants

. [ 4 ] T here are multiple proven technologies available for mercury emission s control. The control technologies include injecting sorbents such as brominated or non
brominated activated carbon or a mended s ilicates, or by a dding halogens to the coal to increase oxidation removal of oxidized mercury in a flue gas desulfurization (FGD) system which is then sequestered in liquid or solid byproducts. Each c ontrol technolog y has its advantages and disadvantages. The advantage of addi ng halogen to the coal for mercury oxidation and removal is that it is a very simple yet effective technology to implement and maintain

. Halogen addition to the coal has b een used for different types of coal with different emissions control equipment downstream of the boiler. Chlorine, b romine and even iodine have been used as halogen add itions to the coal for mercury oxidation. From a cost and effectiveness point of view , the addition of bromine to the coal has been the most successful. The most common method of application of bromine is through the addition of calcium bromide solution to the coal.
The application rate of bromine or any halogen for mercury oxidation depe nds upon the presence o r absence of an SCR system

. When an SCR system is installed, the SCR catalyst reduces the application rate of bromine by 50 to 80% compared to the application rate of bromine when there is no SCR

. On units with higher application r ates of bromine , there have been some cases of negative balance

- of

- plant impacts due to bromine application. The addition of bromi n e to the coal has the potential to increase corrosion at any point along the fuel handling and flue gas path, including the point at which the10 bromine is introduced to the coal, the furnace where the bromine is volatilized, and through the flue gas path to the FGD system and stack. The most commonly observed impact has been on the air heater where cases of c orrosion have been observed in the last several inches of the cold end basket where the coldest temperature s occur within the air heater. In many cases , air heater corrosion occurred very quickly , sometimes within months of the start of the calcium bromide injection process . The rate of corrosion depends upon the operation of the unit (in particular with respect to load swings), whether a steam coil air heater is used to preheat the cold air, material s of construction , and on the application rate of calcium bromide

. There a re different possible mechanisms that can explain the corrosion , but the most likely mechanism is the direct condensation of hydrogen bromide ( HBr ) gas on the metal. Al though t he dew point of HBr is lower than that of SO 3 , when adding a halogen for mercur y oxidation o n low halogen, low sulfur coals, the air heater corrosion is mainly from HBr and not from SO 3 . This is because the concentration of SO 3 in the flue gas is much less than the concentration of HBr. D epending upon the moisture content of the fl ue gas and the HBr concentration in the gas phase , the dew point of H B r can be as low as 125 F. The metal temperature of the cold end of the air heater as it rotates back into the flue gas stream can be below the acid dew point temperature of HBr. T his c an therefore provide the sites for the HBr from the gas phase to condense on the metal. As a result, the possibility of cold end corrosion for air heater baskets increases.

As discussed above , the rate of corrosion depends on flue gas concentration of H Br. Therefore , b y reducing the HBr concentration in the gas , it is possible to reduce the rate of corrosion. In systems with
an SCR , the application rate of bromine for low halogen, low sulfur coals is very low , usually in the range of 1 0 to 4 0 ppm of br omine added to the coal on a dry basis. On units in which no SCR is installed, the application rate is significantly higher , ranging from 100 to 200 ppm of bromine added to the coal on a dry basis. This significant difference in the application rate is a result of HBr gas initially forming when bromine is added to the coal. The HBr gas has to undergo the “ Deacon r eaction ” to be converted into diatomic form be it molecular or other halogen compound

. This reaction is shown by equation 2.

4 HBr+ O 2  2H 2 O+ Br 2 Equation ( 2 )
The reaction of molecular bromine with mercury results in the formation of oxidized mercury. This reaction is as shown by equation 3.
Hg+ Br 2  HgBr 2 Equation ( 3 )

B&W PGG ’s Mitagen t additive allows for the reduc tion in the application rate of bromine or a bromine

containing compound regardless of whether or not an SCR is installed

. The addition of B&W PGG ’s Mitagent catalyzes the bromine Deacon Reaction , resulting in a reduction i n the application rate of bromine for mercury oxidation.
The data presented below from both lab and full

- scale units demonstrates the reduction in bromine usage for units without an SCR. The lab

- scale testing was performed at the Energy and Environmental Research Center (EERC) pilot

- scale test facility. The facility has 560,000 Btu/hr firing capacity and can fire all coal types. T he test facility fires pulverized coal with the c apability for air staging. Different air quality control system (AQCS) equi pment combinations such as SCR, ESP and dry or wet FGD , and fabric filter can be used to mimic the actual plant configuration.11 The objective of the pilot testing was to demonstrate the reduction in the bromine application rate as a result of the Mitagen t additive. Both bituminous and sub bituminous coals were tested . The results demonstrated that the same amount of mercury oxidation could be achieved at 50% of the bromine addition rate when using the M i tagent additive

.
B ased on the pilot

- scale testing , a full

- scale test was performed at a midwestern United States power plant with an 82 MW gross electric generating unit burning PRB coal. This unit has only an ESP as the AQCS equipment. The objective of the field testing was to demonstrate similar or b etter mercury oxidation using B&W PGG ’s Mitagent combustion additive with low er bromine application rate compared to the oxidation obtained with high er bromine application rate s

. For the testing, t he oxidized mercury at the stack was measured by the EPA M ethod 30B (modified for speciation) or the modified sorbent trap method. The injection testing started on December 9 , 2013 , and continued until December 12 , 2013. Table 3 shows the mercury oxidation measured at the stack as a result of the Mitagent additi ve to the coal.

Table 3 : Effect of Mitagent Additive on Halogen Addition and Mercury Oxidation

Br A ddition Rate ( ppm dry ) % Oxidized Hg w ith Mitagent % Oxidized Hg without Mitagent

0 38 37 60 75 46.5 100 83.8 62.5 35 56 Not tested

The data in T able 3 shows that the average mercury oxidation was 38% without addition of halogen and Mitagent to the coal. With the addition of 60 ppm of bromine to the coal, the average mercury oxidation was 46.5%. With addition of 60 ppm of bromine to the coal and Mitagent , the mercury oxidation was improved to 75%. With the addition of 100 ppm of bromine to the coal , the mercury oxidation without Mitagent was 62.5 %, which increased to 8 3.8% with the addition of the Mitagent additive . This showed that , with a ddition of Mitagent to the coal , there was an improvement to the overall mercury oxidation. An i nteresting observation was that even with a much lower bromine addition rate to the coal (35 ppm) with Mitagent , the average mercury oxidation was 56%. This a verage oxidation was higher than the 46.5% oxidation observed with 60 ppm of bromine added to the coal without Mitagent. This testing demonstrated that with the addition of B&W PGG’s Mitagent to the coal, the bromine addition rate can be reduced significa ntly while achieving the same mercury oxidation. The benefits of reducing the bromine addition rate to the coal are both reduction in cost and the reduction in the rate of corrosion.

Pilot

- Scale T esting for Mercury Emission Reduction Testing was also per formed at the EERC pilot

- scale combustion test facility to evaluate the effectiveness of the combined addition of bromine as Ca B r 2 , Mitagent , and S SORB III for mercury emission reduction. S SORB III is a proprietary additive offered by Chem Mod LLC, and has the capability to remove oxidized mercury as particulate

- bound mercury. S SORB III also has the capability to reduce the tendency of particulate

- bound mercury to leach from the ash compared to particulate

- bound mercury removed by powdered activated ca rbon (PAC) injection. Table 4 shows the data from this testing on PRB coal.12 Table 4 : Pilot

- Scale Mercury Emission Results for PRB Coal

Bromine Rate % added to the coal S SORB III % added to the coal Mitagent % added to the coal Hg @ ESP Outlet ug/ s m3 0.0 0.0 0.0 3.41 0.02 0.3 0.0 1.35 0.01 0.175 0.075 1.43

As seen in Table 4 , the baseline mercury emission was 3.41 ug/ s m 3 ( 2.73 lb/TBtu ) . The mercury emission with application of a 0.02% Ca B r 2 solution to the coal and 0.3% S SORB III to the coal was 1.35 ug/ sm 3 ( 1.08 lb/TBtu )

. This was a reduction of 60% in mercury emissions. With the addition of 0.075% by weight Mitagent additive to the coal, the Ca B r 2 application rate was reduced by 50% from 0.02% to 0.01% while still achieving similar m ercury removal. This result showed that the Mitagent additive can reduce the bromine addition rate and the S SORB III can remove the oxidized mercury in a particulate

bound form.
Field Test for Mercury Emission Compliance
The second objective of the fie ld testing described above was to achieve stack mercury emission s below 1.5 ug/ s m 3 ( 1.2 lb/TBtu ) as a result of addition of bromine as CaBr 2 , Mitagent additive and S SORB III to the coal. The value of 1.5 ug/ s m 3 (1.2 lb/TBtu) is the current gas
- phase mercu ry emission limit in the United States per the Environmental Protection Agency ( EPA)’s Mercury and Air Toxic Standards ( MATS) emission s limit for bituminous and sub bituminous coal

- fired utility electric generating units. S Sorb III was added to the coal along with Ca Br 2 and Mitagent on November 12, 2013 and December 12, 2013

. On November 12 , the average total Hg at the stack was about 0.38 ug/ sm 3 ( 0.3 lb/TBtu )

. On December 12 , only 20 ppm of bromine , Mitagent additive and S Sorb III was tested and the a verage total Hg in the stack was 0.75 ug/ m 3 ( 0.6 lbs/TBtu )

. Figure 4 shows the stack mercury emission fo r December 12, 2013

.13 Figure 4 : Stack Mercury Emission with Additive Injection
As seen from Figure 4 , the stack mercury emission s befor e the start of the injection was approximately 2.25 ug/sm 3 ( 1. 8 lb/TBtu )

. With the injection of the additive to the coal, the stack mercury emission was reduced to an average value of 0.75 ug/sm 3 ( 0.6 lb/TBtu ) during the injection period from 8 :00 AM to 3 : 30 PM. The stack mercury increased back to the baseline mercury values once the injection was stopped. One of the most important advantages of the blended additive (S Sorb III plus Mitagent additive ) injection for mercury control is that it can remove th e mercury in a particulate

- bound form [ 5 ]. This advantage could be very beneficial for units with wet FGD systems , as the removal of the majority of the mercury before the wet FGD will reduce the concerns associated with mercury in the gypsum or wet FGD wa ste water.

Conclusion

Based on the long

- term testing data from Wygen II, B&W PGG demonstrated that the use of the Mitagent additive can significantly reduce the rate of SCR catalyst deactivation by r educing catalyst poisoning by phosphorus. This combustio n additive can be applied to any type of SCR catalyst

. The Mitagent additive can also reduce the application rate of halogen for mercury oxidation for units without an SCR and, along with Chem Mod’s S SORB III additive, can be an inexpensive yet effective mercury control alternative to activated carbon injection

.14 

### References

1) Thogersen , Joakim , et al , “Impact of biomass co

- combustion on SCR DeNox operation , ” p resented at 2009 Power Gen Europe Conference, Cologn e, Germany. 2) Pierson , Larry , et al, “Im provement in the performance of SCR catalyst using combustion additives: technology status update,” Presented at the 2012 Electric Utility Mega Symposium, Baltimore , Maryland, 2012. 3) Quann, R.J., “Ash vaporization under simulated pulverized coal combustion conditions,” PhD thesis , January 1982 , Massachusetts Institute of Technology. 4) Mazyck , David, et al,” Performance of non halogenated impregnated activated carbon for mercury compliance ,” Presented at the 2013 Air Quality IX Conference, Arlington , Virginia, 2013. 5) Gadgil , M andar , et al, “SCR catalyst phosphorus poisoning when firing PRB coal and reducing bromine additive required for Hg control,” Presented at the 2014 Reinhold NOx Conference, Charlotte , Carolina, 2014

.

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