CoalGen Paper Manuscript(1) Modified Coal Combustion Reduces NOX and Fuel Consumption

ABSTRA
This art
combus
altering
combus
increasi
making
conditio
nitrogen
is analy
improve
cuts op
month.
Veri
RET
ACT.
ticle prese
tion proce
g combusti
tion prom
ing and m
coal par
ons predo
n. Integrat
yzed, whe
ement of a
perational

itask Ene
THINK
ents a sci
ess that
ion kinetic
motes react
maintaining
rticles to
minantly
tion of the
ere more
a plant he
costs and
ergy Sys
TRADI
ientific an
expands c
cs. In a p
tions respo
g particle
act as a
converts
e modified
stringent
eat rate, i.
d delivers
tems, In
ITION
nd engine
capabilitie
presence o
onsible for
porosity a
catalyst,
fuel‐N an
d combusti
t NOx re
e. reduced
return on
c.,
NAL
eering bas
es of in‐fu
of a super
r NOx sup
and its su
which u
nd NOx in
ion into po
egulations
d fuel burn
n investm
sis for a
urnace NO
rheated st
ppression b
urface acti
under sub‐
nto a sta
ower gene
can be
rn rates. Th
ment in ab
modified
Ox contro
team mod
by significa
ivity, there
‐stoichiom
able molec
eration pro
met with
This fuel sa
bout 10 to
coal
ol by
dified
antly
efore
metric
cular
ocess
h an
aving
o 15

I
 I
E
 I
B
 I
R
I
 H
S
 H
P
 H
G
 H
C
IF YOU
S THER
EMISSIO
S THER
BOILER?
S THER
RATE BY
IF YOU
HOW CA
STACK B
HOW CA
PLANT E
HOW CA
GAS OR
HOW C
COMBIN
ARE A
RE AN
ONS?
RE AN E
?
RE AN E
Y 3% TO
U ARE A
AN ENE
BE CONV
AN CO2 B
EFFICIEN
AN CO2 R
STEAM
AN A
NED CYC
N OPER
ECONO
CONOM
ECONOM
O 5%?
AN OE
ERGY L
VERTED
BE SEQ
NCY?
RATE PE
CYCLES
GAS C
CLE?
RATING
MIC WA
MIC WAY
MIC WAY
EM ASK
LOSSED
D TO ELE
UESTER
ER MW
S?
CYCLE
G COMP
AY TO
Y TO REC
Y TO IM
K VESI
TO A
ECTRICI
RED WIT
BE ESS
BE MO
VESI-R
PANY A
REDUCE
COVER
MPROVE
I:
STEAM
ITY?
THOUT T
SENTIAL
ORE EFF
RETHIN
ASK VE
E MY P
ENERGY
E MY PL
M COND
THE LO
LLY RED
FICIENT
NK TRA

ESI:
PLANT N
Y LEAV
LANT HE
ENSER
OSS OF T
DUCED F
T THAN
ADITION
NOX
VING
EAT
OR
THE
FOR
N A
NAL

Modified Coal Combustion Reduces NOx Compliance Cost and Fuel Consumption
A.Kravets, A.Favale, J.Barba, D.Ginzburg, (all Veritask Energy Systems, Inc.)
1 | P a g e
1. Introduction.
The steady reduction of power generated by coal and the new tighter environmental regulations
are bringing serious challenges for this power sector and coal market. Operating companies are
facing difficult business/strategic decisions in response to such trends. Never before has there been
a need to rethink current practices of the Best Available Retrofit Technologies (BART) as critical
as they are today.
VESI is a technology company that does exactly that. It offers a wide spectra of cost effective near
term and long term solutions for fossil fuel market. These solutions allow meeting current and
future regulations on emissions and fuel utilization efficiency through innovative and cost-
effective integration of the fossil power system while utilizing existing technologies. Unlike
BART the solutions presented below deliver a reduction of all types of emissions and fuel
consumption. Solutions are tailored to specific application and provide return on investment (ROI)
based on the reduction of fuel and substantial reduction of operating expenses related to existing
AQCS equipment.
In this article we describe one simple, near term solution for NOx reduction for coal-fired power
plants. The solution is patented and derived from experiences collected over several decades of
coal gasification and coal processing industries.
2. Costs of NOx Compliance and Penalties.
The most common means of NOx compliance today include Ultra- and Low NOx Burners (LNB),
Combustion System/Burner Modifications, Selective Catalytic Reduction (SCR), Selective None-
catalytic Reduction (SNCR).
Traditional Low and Ultra-Low NOx technology include sub-stoichiometric combustion of fuel in
burner zone (StBZ) with the balance of air required for complete combustion added through
separate air ports (OFA). This approach has reached its maximum physical potential. Figure 1
illustrates typical trends of NOx and Unburned Carbon variation versus burner zone stoichiometry
for high and medium-volatile bituminous coals
[1]. It was found that NOx reduction trend slows
down with most fuels to a specific optimum
level and then the NOx trend vs. furnace
stoichiometry reverses. The trend for unburned
carbon (CIA - Carbon In Ash) rises up
monotonously while StBZ reduces. Typically
minimal NOx level indicated in the Figure 1
cannot be reached in practice due to multiple
penalties associated with it. Among those are
increase of a plant Heat Rate due to a) increase
of CIA and Carbon monoxide (CO) above
acceptable operating values, b) Increased
parasitic power losses with combustion air
supply to OFA ports, c) excessive water-wall slagging that may cause boiler over-firing and/or
increase of reheater water spray due to high temperatures leaving furnace.
Figure1. Typical NOx and UBC Trends for Ultra Low
NOx Combustion
Burner Zone Stoichiometry, %
100 1208060

2 | P a g e
In addition, LNB cannot meet NOx emissions limits alone and require installation of post
combustion technologies to do so. These technologies incur significant capital and operating cost
and have further distressed unit heat rate. Table 1 provides a quick overview of average retrofit
costs and penalties for coal fired units [2,3]
Table 1. Normalized Costs (2011$) of NOx Compliance and Heat Rate Penalty (Overview)
Technology1)
LNB LNB+OFA SCR SNCR
Low High Low High Low High Low High
NOx Reduction, % 20% 30% 30% 50% 80% 90% 20% 30%
Specific Costs, $US/kW2) $15 $70 $30 $90 $ 250 $350 $15 $60
Heat Rate Penalty, % (Note 3) (Note 3) 0.54% 0.60% 0.78%
Note 1. Low and High costs correspond to unit sizes 1000 MW and 100 MW respectively, and include
Wall-Fired and Tangentially Fired units only
Note 2. Costs information was collected from EIA Form 767
Note 3. No penalties were reported. Operator may choose to trade-off NOx reduction against fuel
efficiency. This would offset heat rate losses but result in increased costs of NOx compliance.
From Table 1 above one can conclude that implementing BART technologies has not only resulted
in substantial capital costs but are damaging to the efficiency of the plant which exacerbates the
operating cost through increased of fuel costs.
It is difficult to evaluate the overall impact on the industry, but according to the capital investment
report [2]
compiled off EIA forms 860/767 the investment into post-combustion NOX control
projects between 2000 and 2016 has exceeded 32B$US. Almost 4B$US is expected to be spent
between now and 2020. The referenced costs do not include LNB replacement and do not account
for the increase in operating costs.
Competitive, cost-effective options for NOx control proposed below will make unit
operation profitable by bringing fuel consumption back to the original (pre-implementation heat
rates, if equipped with SCR/SNCR) or avoiding BACT technology costs all together while
profiting from a reduced fuel consumption.
In order to understand the principles behind the technology a brief review of coal combustion, heat
and material balances of the specific reactions for a steam power plant.
3. Coal Combustion and NOx Formation – Background
The mechanism and effect of the proposed NOx reduction technique depends on fuel type. Its
effect on coals essentially differs from other type of fuels (gaseous and liquid) and alters coal
combustion kinetics at every phase from preheat and volatilization to completed char burnout.
In engineering practice, the level of achievable NOx emissions by primary means of control, i.e.
by combustion system correlates with coal rank or content of Fixed Carbon (FC) and /or Volatile
Matter (VM). For instance, Figure 1 above illustrates substantially higher NOx emissions for mid-
volatile (mvb) vs. high-volatile Class B bituminous coals (hvBb) fired within same combustion
system and conditions, having fuel nitrogen content on as-received basis 1.3% and 1.25%

3 | P a g e
respectively. [1]
In other words, higher rank coal (Anthracite, Semi-Anthracite) inherently generate
more NOx than lower rank Bituminous coals.
In the science of combustion, coal proximate composition FC, VM, as well as, inherent moisture
(IM), have strong correlations with coal porosity or internal surface (S). Original coal porosity and
correspondent initial internal (SO) vs. coal rank is shown in Table 2[10,12].
Here initial particle
surface (S0) is measured by CO2 adsorption. Note SO is expressed in square meters per 1 gram (1g
≈0.002 Lb).
From data in Table 2 an obvious correlation between VM, (FC/VM) with the So or coal porosity
can be made. Numerous combustion and gasification studies concluded that lower rates of NOx
formation can be attributed to coals with higher porosity. This finding demonstrates a major
agreement of scientific and practical experiences; data in Figure 1 illustrates this agreement where
coal with higher VM (i.e. higher porosity) generates less NOx. Most importantly, these findings
open a pass to a deeper understanding of processes affecting coal combustion rates and NOx
emissions formation in particular.
The role of an internal particles surface on chemical reaction for any given coal depends primarily
on oxygen availability, aerodynamic conditions and composition of oxidant (in particular CO2 and
water vapor). There are three distinct zones (regimes) where combustion is controlled by one or
two mechanisms
shown in Figure 2.
It depicts typical
relationship of
combustion
reactions rates vs.
particle temperature
indicating three
distinct zone of
reaction rates
associated with
changes in kinetic
regimes.
 Zone III corresponds to combustion rates of particles exposed to very high temperature.
Due to high temperature chemical reactions between particles and surrounding bulk gas
goes very fast in an immediate vicinity of particles (boundary layer) and on the particles
Table 2. Coal Rank vs. Internal Particles Surface
Coal Rank FC/VM VM, %
So, m2
/g
(by-CO2)
Porosity, %
(ar)
Mid-Volatile Bitum. (mvb) [10] 2.9 25.0 15 - 40 3.0 - 5.0
High-Volatile Bitum. (hvBb) [10] 1.5 37.0 85-150 15.0 – 20.0
High-Volatile Bitum. (Blind Canyon, UT) [12] 1.0 42.0 140 21.5
Lignite (N. Dakota)[12] 0.7 48.0 180 30.6
Figure 2. Three Major Combustion Zones
a) Reaction Rate vs. Particle Temperature,
b) Gaseous species concentration inside and outside the particles for each
Zone

4 | P a g e
surface. The process is controlled primarily by diffusion of oxygen from a surrounding
bulk gas volume. While reaction rates are high, only a small, external surface of a particle
participates in chemical reactions heterogeneously, while homogeneous reactions in a
boundary layer dominate the process. Distribution of any gas component present in a bulk
gas may be as depicted in Figure 2b by line III. Under such kinetic conditions coal/char
particle size and porosity monotonously getting smaller [13]
, due to consumption by
chemical reactions and through a direct surface ablation (evaporation).
The example of equipment operating in Zone III are turbulent burners used in utility boilers
prior to introduction of New Source Performance Standard (NSPS). Then, such burners
produced very high NOx emissions on order of 1 Lb/MMBtu.
 Reactions of coal/char particles in Zone II typically taking place at temperatures above
1000o
C (~1800o
F) are controlled by diffusion of a bulk gases through the boundary layer
and then by pore diffusion/adsorption/chemisorption deep inside particles (refer to line II
on Figure 2b) where they react heterogeneously with an internal particle surface (the latter
is by six orders of magnitude larger than external surface). The products of these
heterogeneous reactions will continue to react with surface upon their exit (desorption)
back to external surface and then react homogeneously in a boundary layer surrounding
particle and beyond. Due to such kinetics, the role of the internal surface in overall burnout
process considerably increases. Moreover, under Zone II condition particles internal
surface for bituminous and subbituminous coals expand, often by 1.5 to 2+ times [11,12, 13]
even for coals with low swell index.
Lower chemical reaction rates in Zone II do not lead to increase in burnout time, as the
reaction rates are compensated by the growth of particles internal surface participating in
the process, as well as, due to catalytic effect on particles surface (see below) resulting in
approximately 50% reduction of activation energy for char oxidation reactions [13]
. The net
effect on overall char consumption rate in Zone II may even result in sizable (~10%)
increase due to other non-oxygen components that are present in a bulk gas [7]
(See below
for more details).
The example of power/industrial application operating under conditions of Zone II are
Entrained gasification, Integrated Gasification Combined Cycle (IGCC), and Low-NOx
pulverized coal combustion. For the latter, in some localized flame/furnace sections
particles may be exposed to temperatures corresponding Zone III [11].
 Within temperature range characteristic for Zone I (less than 600o
C/1100o
F) the chemical
oxidation is slow, which allows oxygen and other oxidant components be absorbed without
reaction with internal surface resulting in about the same bulk gas concentration both inside
and outside of particles. The example of power/industrial application operating under Zone
I condition are fixed bed gasification and fluidized bed boilers.
Coal combustion involves two steps: 1) Thermal decomposition, de-volatilization, and volatiles
burnout; and 2) solid residue (char) burnout. Duration of step 2 in pulverized coal-fired boilers
takes 90%+ of total burnout time. Therefore, under kinetic conditions of Zone II the role of
heterogeneous reactions even further increases due to the intentional delay of the combustion

5 | P a g e
processes taking place in sub-stoichiometric combustion (burner) zone and then in an offset
downstream over-fire air ports (OFAP) zone where a balance of combustion air is supplied.
Often, the perception of engineers is that coal combustion involves two heterogeneous reactions
(R1, R2) and two/three homogeneous reactions (R3, R4, R4a).
+ = , ( 1) + 1
2 = 2 , ( 2)
+ 1
2 = , ( 3) + ↔ + , ( 4) + 1
2 ↔ , ( 4 )
These reactions dominate combustion in kinetic Zone III (see Figure 2a). For Low NOx
combustion in Zone II, two additional heterogeneous reactions (R5, R6) [15]
are significant even
for oxygen-enriched oxidizers [7]
. Only when accounting for these reaction rates the higher
apparent rates of coal/char reactions under kinetic conditions in Zone II could be explained.
+ = 2 , ( 5) + = + , ( 6)
Experience and analyses have shown that homogeneous “water-shift” reaction (R7) is important
in Zone II [15]
.
+ = + , ( 7)
The authors of this article also suggest to include a reforming reaction for hydrocarbons present in
volatile matter (R8), since it was proven important in combustion and NOx formation of other
gaseous hydrocarbon fuels, e.g. steam injection for natural gas combustion (burners/gas turbines).
+ = + ( + 2) 2⁄ , ( 8)
The thermal effects of outlined
above global reactions making
major impact on combustion in
Zone II are shown in Table 3.
Note, these thermal effects are in
reference to the standard
conditions. Effect on thermal
effects under operating
conditions is discussed below.
The study and analysis of internal
particle surface have shown that
its reactivity changes from point to point. Some points exhibit irregularities in chemical and
crystalline structure (geometrical arrangement of carbon corner atoms, inorganic substance
inclusions, presence of oxygen or hydrogen groups). These points generate different molecular
forces (adsorption/desorption) that differentiate reactivity of one part of the surface from another.
The points of higher reactivity are called “active centers” or “active sites”. As mentioned above,
these centers are responsible for acceleration (catalytic effect) of reactions taking place on such
active centers, reducing activation energies of reaction by approximately 50%. Total number of
active centers at any time can be represented by a sum of free [Cf] and occupied [C(O)] centers.
DH, DH,
Btu/lb-mol kJ/kmol
R1 -1.69E+05 -3.94E+05 Exothermic, Heterogeneous
R2 -4.73E+04 -1.10E+05 Exothermic, Heterogeneous
R3 -1.22E+05 -2.84E+05 Exothermic, Homogeneous
R4 (as CH4) -3.48E+05 -8.10E+05 Exothermic, Homogeneous
R5 7.42E+04 1.73E+05 Endothermic, Heterogeneous
R6 5.65E+04 1.31E+05 Endothermic, Heterogeneous
R7 -1.77E+04 -4.12E+04 Exothermic, Homogeneous
R8 (as CH4) 8.86E+04 2.06E+05 Endothermic, Homogeneous
Reaction
Number
Type
Table 3. Thermal Effect of Reaction at 14.696 psia, 77o
F
(0.101 MPa, 298 K)

6 | P a g e
[ ] = [ ] + [ ( )], ( . 1)
The number of active centers is changing during reaction and could be either destroyed, occupied
or restored. The status of centers could be altered in some control way through thermochemical
processes whereas number of active centers depends on particle temperature, rate of heating, and
composition of bulk gases surrounding particles [9, 13, 14]
. Consequently, the reactivity of a coal
particle could be corrected in more precise way to improve process outputs by maintaining
presence and conditions of such active centers.
A dominant source of NOx emissions in modern Low-NOx coal-fired systems is fuel-bound
nitrogen or (fuel-N), which is responsible for 70% to 80%+ of NOx formation. Depending on
boiler furnace temperature and availability of oxygen NOx also can be formed by thermal
dissociation of N2 and O2 atoms in oxidizer (i.e. thermal NOx). Due to their nature, thermal NOx
could be more or less significant as soon as local flame temperatures exceeding 2400o
F (~1300o
C).
Thermal NOx may contribute 10% to 30% under Low-NOX combustion. Besides the fuel-bound
nitrogen and the thermal NOx, a prompt NOx could be generated during initial stages of fuel
decomposition, when high energy hydrocarbon radicals are braking N2 and O2 atoms, thus causing
nitrogen oxidation at low temperatures [16]
. Prompt NOx in case of coal combustion may reach
~5% of total nitrogen oxides emitted by flame.
It is a common understanding that the main path of fuel-N conversion to NOx could be presented
by the following, yet simplified, scheme [18]
:
− ⇛ ⇛ ⇛ ⇛ ⇛
⇛
(E1)
HCN (hydrogen cyanide) is a main precursor of NOx formation. The rate of HCN/NHi
formation/distraction appears to be directly related to coal rank [18]
. For low rank coals the level of
HCN/NHi is the highest, whereas bituminous and Low-Volatile coal generates less HCN/NHi than
preceding ones in an order of mentioning. As already discussed above NOx emissions vs. ranks of
coals are precisely in a reverse order, i.e. less NOx is generated by low rank coals [19]
. Such
relationship is in agreement with the findings of practice and science. It reinforces existing
understanding of the internal particle surface role on NOx emissions release: coals with higher
internal coal particles surface generate less NOx (See above).
The multi-path of fuel-N conversion to NOx in utility boilers as proposed S.Gil [18]
is presented in
Figure 3. Following coal pyrolysis, fuel-N in VM is released into a boundary layer where an atomic
nitrogen N may undergo either oxidation to NO/N2O or recombines into a stable molecular N2.
Even though the reactions are homogeneous the presence of char surface plays important catalytic
role (see below).
Char-N undergoes similar reactions heterogeneously where bound nitrogen reacts with the active
centers of the particles. Here it has to be underscored that number of free active centers measured
in chars obtained by short time exposure (fraction of a second) to a rapid heating and pyrolysis
was the highest [13]
. Both gasification [20]
and Low-NOx practices [21]
also suggest that higher rates
of fuel-N conversion to stable N2 occur when coal is subjected to pyrolysis at higher temperatures.
These independent results point-out that widely accepted reaction of catalytic NOx reduction

7 | P a g e
(R11) is one of the major mechanism that
minimizing fuel-N conversion to NO in
heterogeneous reactions. Above burner zone
nitrogen oxides NOx and N2O undergo homo-
and heterogeneous reduction with the residual
char while adsorption and desorption of the
bulk gas under reduced oxygen availability
continues to support reduction of NOx to
molecular nitrogen N2.
There is no consensus between scientists on the
contribution of volatile nitrogen and char-N to
a total NOx emissions. In laboratory controlled
experiments it was found that volatile-N and
char-N produce approximately equal shares of NOx [6,19]
. For the conditions of utility boilers [18]
analysis of numerous independent studies suggested that share of VM and char bound nitrogen
varies, and depends on temperature and specifics of combustion system design. This conclusion is
in agreement with experiment work [14]
that confirms significant variation in a number of available
active centers depending on the rate of coal particles heating during pyrolysis.
There are numerous models [6,7,11,17,18]
that include series of reactions describing fuel-N conversion.
Analysis of these models is not an intent of this paper. Here we concentrate only a few common
ones, widely accepted heterogeneous reactions [18.19]
that are catalytic in nature and will help to
explain the mechanism behind the technology presented hereafter:
+ 1
2 + , ( 9) 2 + → + [ ( )] , (R10)
[ ( )] → + ( 11)
As above equations show, presence of CO is essential for NOx reduction providing that internal
particle surface through burn-out and kinetic conditions surrounding particles allow to maintain
activity of the surface. It could be also concluded that should an internal char surface increase due
to changes in the bulk gas parameters and composition it would move the balance of fuel-N
conversion toward production of stable N2.
Summarizing the discussion in this section the following major points must be reiterated:
1. Under Low-NOx combustion the kinetic regime has shifted to Zone II (See Figure 2).
2. In Zone II coal oxidation reactions by CO2 and H2O are very important, especially under
fuel rich conditions. These reactions with char surface provide chemical cooling, maintain
char structure and prevent char surface ablation at high temperatures.
3. Active internal particle surface is greater than it’s external by ~ 6 orders of magnitude and
accelerates coal burnout under lower temperature conditions.
4. Under pyrolysis conditions (Zone II) the internal particle surface grows up to 2.5 times
depending on rank and bulk gas composition until 50% to 60% of particle mass burn-out.

8 | P a g e
5. Char surface due to the presence of active centers serves as a catalyst for chemical
reactions; Practice confirmed that internal coal char surfaces with higher share of active
centers has a strong influence on NOx reduction.
6. Activation energies of chemical reactions on active char centers can be reduced by 50%.
4. Modified Coal Combustion Process and In-Furnace NOx Reduction
As follows from above review of coal kinetics further improvement of in-furnace NOx formation
should have a means to modify kinetics in a way that allows increasing coal/char particles porosity
throughout staged combustion under fuel rich conditions, improve char conversion to gaseous
reactants CO/H2 and enhance its reactivity, (i.e. number of active centers) that results in both NOX
and unburned carbon reduction.
This idea of controlling porosity and catalytic properties of the char is not new. For centuries
activated char was produced by subjecting coal to high temperature combustion products
(pyrolysis) whereas steam was added to increase activated char porosity measured in thousands
square meter per gram (i.e. m2
/g based on CO2 sorption). Re-activation of used char also performed
in the high temperature flue gases mixed with steam.
Development of the gasification process early in the 1960s in the USA demonstrated significant
increase in syngas (CO+H2) yield and minimization of residual char (UBC/CIA) by about 60%
after addition of steam to the process [22]
. Later during development of Integrated Gasification
Combined Cycle the effect of steam on syngas combustion was attributed to its effect on HCN
(NOx precursor, See above) reduction due to presence of hydroxyl group OH reaction [22, 23]
. A
“scavenging effect” of steam on HCN was also reported by many experimental studies along with
reduction of thermal and prompt NOx. The latter, is well known fact; steam injection was accepted
by DOE as one of method of nitrogen emissions control in natural gas and oil combustion
applications. As mentioned above, thermal NOx may contribute 10% to 30% during coal
combustion.
Experimental studies [23,24]
of steam effect (i.e. CO2 and H2O gasification) indicated a critical role
of each component on internal particles surface development. Water vapor due to the smaller size
of its molecules and higher diffusion coefficient has a much greater ability to penetrate into small
pores of internal surface (micro-pores). As the result of its higher “mobility” and lesser energy
required by reaction of char with water vapor (See above - Table 3, R6) micro-pores grow to meso-
pores thus allowing larger CO2 molecules to penetrate and react by (R5) deeper inside the particles
(See Figure 2a, and Table 3).
Steam was also successfully used in new technology - fuel cell utilizing coal [26]
. Steam was
introduced into process to improve coal conversion to hydrogen by reactions (R6) and (R7), and
thus improving (3 folds) efficiency of coal utilization in fuel cells [26]
.
At this time practically the only coal application that have not benefited from the use of steam for
more efficient coal utilization is the utility sector.

9 | P a g e
VESI has researched steam injection for steam power cycles for fossil fuels, and developed
solutions that concurrently improve efficiency and reduce NOx emissions. All aspects of
technologies were analyzed – kinetics, heat transfer in boilers, steam cycle material and energy
balances, cost analysis and process economics, and major constrains. A few US patents received
by VESI that cover these solutions; US Patents 7,690,201, 8,453,452 are for steam cycle in
particular.
The NOx reduction portion of VESI’s solution (NOx module – E-NOx) is the first of two add-on
modules that collectively provide substantial increase in plant thermal efficiency and NOx
reduction. The combined effect of two modules is greater than the sum of their individual effects.
In this article the NOx reduction module is presented. It delivers major contribution to NOx
reduction and sizable efficiency improvement, especially for supercritical boilers.
A simplified diagram in Figure 4 depicts
one possible way of E-NOx system
integration into a steam cycle power
plant. Here, a single-reheat, super-critical
plant consisting of an opposed-fired
steam generator equipped with OFA
ports is shown along with the steam
turbine with high, intermediate, and low
pressure sections and feed water heaters.
To maximize work produced by a
turbine, the steam extractions for NOx
control are distributed. A portion of high
pressure steam is taken from HP section
of turbine and low pressure steam is taken
from LP section (lines 1 and 2
respectively). A steam compressor 3 uses high pressure steam 1 as a motive medium to pressurize
steam from line 2 and discharges a mixed steam flow at intermediate pressure into a steam piping
system for distribution into the boiler furnace or burners (injection through burners is preferred).
The piping system design is similar to a soot-blowing piping system, with the exception of flow
control valves, which proportions steam flow to a group of burners by boiler elevations. The
control of Steam-to-Coal ratio and secondary air bias provide flexibility to optimize in-furnace
NOx and UBC reduction. Additional improvements to the process and enhancement in energy
saving is provided by the make-up water preheat by a flue gas leaving the boiler and in a reheater
4 downstream of the steam compressor 3.
The direct injection system as shown in Figure 4 is an open system. It requires larger than typical
make-up water supply. Should high quality feedwater use for NOx control be viewed as a
commercial constrain, VESI offers an indirect steam injection system that does not require high
quality polished feedwater. A much lower quality (e.g. service water) could be used for NOx
control.
Since use of steam for injection affects overall operation of the steam cycle it requires to assess
different aspects of boiler and cycle performance.
Figure 4. E-NOx integration with Steam cycle for in-
furnace NOx reduction: Direct injection arrangement
AHTR
BURNERZONE
REDOX
ZONE
BURN-OUT
ZONE
COND
COMBUSTION AIR
COAL
HP IP LP
ID FAN
FD FAN MAKE-UP WATER
1
2
4
3

10 | P a g e
The brief review and analysis of these aspects are provided below.
Boiler Efficiency. There is a perception of some performance engineers that adding steam to the
combustion would result in decrease of boiler efficiency due to losses with wet flue gas. In this
regard reference to ASME code for boiler performance, PTC 4 is helpful (2008 or later edition).
There are four major energy categories in the code: fuel input (QrF), credits (QpB), energy
outputs (QrO) and losses (QpL). Fuel efficiencies can be determined by two methods: a) Input-
Output Method, and b) Heat Loss Method, as expressed below:
100100100 




 







InputFuel
CreditsLosses
InputFuel
Output
Efficiencyfuel
, (1)
or QrFQpBQrFQpLQrFQrOfEf f //100)/(100  , (1a)
Among several credits considered there are two of importance to us: a) “energy supplied by
additional moisture” (e.g. steam for liquid fuel atomization), and b) “moisture in entering air”.
As (1a) shows these sources (credits) do not contribute to the losses associated with wet flue gas,
and therefore do not affect boiler losses. Indeed, any moisture that enters boiler in the form of
steam does not consume fuel energy for vaporization. Therefore, in accord with Heat-Loss Method
the moisture losses at a boiler exit shall be corrected by amount of the latent heat introduced at a
boiler input. Moreover, if steam enters the boiler in a superheated state then available heat or
sensible heat in the input increases. For example, for boiler firing bituminous coal (HHV=11,000
Btu/lb) with 0.4 pounds of steam supplied at
800o
F and 50 psia (h=1,432 Btu/lb) and flue gas
leaving boiler at 300o
F (h=1,192,7 Btu/lb) the
heat input increase is equivalent to 0.87% per
each pound of coal.
Another saving comes due to reduction of
unburned fuel losses (UBC/CIA). From
gasification experience we already learned that
addition of steam considerably reduces residual
char. CFD modeling by an independent company
have shown that introduction of steam for NOx
control in Tangentially-fired boiler lead to 60% -
90% CIA reduction at moderate steam injection
rates (Figure 5). Considering an average, losses
in power sector due to UBC(CIA) are on the order of 0.4% to 1.0%, the equivalent fuel saving
with steam injection will range between 0.2% to 0.9% of fuel input.
Gathering from above one now can conclude that addition of superheated steam to coal combustion
will lead to 1% to 2% of heat input increase per unit of fuel burnt. This energy will result in extra
steam generation and, in turn, to higher power output generated per pound of fuel burnt.
Heat Transfer. Furnace water wall slagging under sub-stoichiometric Low-NOx combustion
conditions often leads to firing rate increase (fuel losses). Steam wall blowers are one typical
Figure 5. Predicted CIA: Parametric case 1 is
the only one without steam injection.

11 | P a g e
method that provides effective resolution to furnace slagging. Sootblowers are also the most
common equipment for fouling control of heat recovery surfaces in coal-fired boilers.
CFD modeling by an independent
company confirmed the expected
trend in furnace slagging. The
results for moderate rates of steam
injection (Figure 6) indicate about
30% reduction in furnace slagging
intensity to be expected,
Several years of coal-fired utility
units’ study [27]
suggested that
reduced furnace slagging leads to
additional fuel saving and about
~10% NOx reduction. The later can
be attributed to a reduced
contribution of the thermal NOx
indicated by a lower furnace exit gas exit temperature (FEGT) at reduced furnace slagging.
In Table 3 above the main reactions in kinetic Zone II – (R6), (R7), (R8) are endothermic. There
were some inquiries concerning their impact on furnace temperature and on heat transfer. It must
be underscored that the thermal effect of (R6), (R7), (R8) depends on operating temperature at
which reactants enter the process. According to Hess’s law of thermodynamic the standard effect
of reactions is determined by a difference of standard energies of formation for substances present
in products and reactants of a reaction are expressed in reference to standard conditions (14.696
psia and 77o
F):
= ∑ ∆ ( ) ∑ ∆ ( , (2)
For reactants participating in reaction (i=1, 2,…k) at temperatures other than standard, thermal
effect of same reaction is changing and is determined by Kirchhoff’s law of thermodynamic that
in terms of Hess’s law could be written as
( ) = + ∑ ∆ ( ), (2a)
Depending on value of the sum in (Eq 2a) the thermal effect of reactions tabulated in Table 3
would change accordingly.
Kirchhoff’s law is used in our daily practices; firing a fuel with combustion air temperature at 77o
F
vs. combustion air temperature greater than 77 o
F results in greater energy released in the furnace,
i.e. greater thermal effect vs. one calculated at standard conditions. This example is for exothermic
reaction. The same is true for endothermic reactions (R6), (R7), (R8), where any excess of energy
above standard conditions will reduce negative thermal effects indicated in Table 3. In other words,
energy used for preheating of reactants will minimize energy requirement to generate the products.
Therefore, submitting products of (R6), (R7), (R8) for combustion by reactions (R3) and (R4a)
Figure 6. Reduced furnace slagging with (Module 1) and
without steam injection (Base Line)

12 | P a g e
will resulting in greater thermal effects than those indicated in Table 3, i.e. thanks to reduction in
energy of formation of the reactants CO and H2.
The effects explained above known to industry as thermochemical recuperation and is presently
utilized in gas turbines and natural gas-steam reforming processes. Similar processes and
equipment were also promoted across the world for various applications due to more effective
waste heat energy utilization, e.g. comparing to air preheater.
It should be noted that the thermal effect of reactions also depends on the presence of catalyst. In
studies referenced above a substantial about, 50% reduction, of the activation energy on char
surface is observed. Consequently, the energy of formation in Table 3 would be affected in addition
to thermal effect or reactant preheat explained above. VESI did not evaluated potential impact of
char catalytic properties on rates of CO and H2 formation, but expects that such catalytic effects
would be important for the overall process effect on NOx and efficiency. The effects will be site-
specific depending on composition coals, and mineral matter in particular.
Gathering from above facts no significant
changes in furnace temperature profile were
expected under steam injection conditions
specified for NOx reduction process. Results of
CFD modeling in Figure 7 showed that under
preferred operating conditions (other than
Case-1_VESI) gas temperature may be lower
by about 50o
F at some elevations or may even
exceed operating temperature without steam
injection (Parametric Case 1).
Emissivity of flue gas gases is determined by
partial pressure of tri-atomic gases (CO2, SO2 and
H2O) and by ash/char particles. VESI used radiant
heat calculations adopted by OEM companies for
boiler design [28]
. This methodology accounts for
furnace slagging, location of flame ball in the
furnace, partial pressure of individual triatomic
gases, radiation bands/spectra overlap, furnace size
and mass-average size of fuel particulates based on
grinding practices. This methodology was verified
in utility boilers for many decades.
Figure 8 shows incident heat flux emitted by
products of bituminous coal combustion with and
without steam injection. For both cases the boiler
water walls assumed to have same slag
accumulation. As the results show the same heat
flux can be achieved by the flue gas produced with and without steam injection as soon as the
Fig 7. Gas temperatures by furnace elevation
Figure 8. Steam injection effect on radiant heat
flux

13 | P a g e
temperature difference of bulk gases with steam injection would not fall below 50o
F (30K) at lower
temperature and 100o
F (60K) – for high temperatures.
Some important details yet to be underscored here; data in Figure 8 is derived for the same
operating conditions at the excess air for cases with and without steam injection. Considering
significant improvement in UBC under steam injection conditions the excess air could be reduced
thus leading to increase of the bulk flue gas temperatures, and therefore incident heat flux. Also
under steam injection condition a burner zone stoichiometry increases compared to Ultra-Low-
NOx operation to achieve superior NOx reduction. As known practice suggests under such
conditions, less slagging would occur when burning the same coal leading to further reduction of
fuel consumption and overall cycle efficiency increase.
Convection heat transfer coefficient also increases with moisture content [20]
. Increase in heat
transfer coefficient and greater energy and mass of the flue gas flowing through the boiler will
compensate some reduction in flue gas temperatures. A lesser degree of a boiler heat recovery area
fouling in case of steam injection is expected, as follows from experience and directions of the
soot blower manufacturers.
Thus, under steam injection conditions as required by the E-NOx performance, slightly lower flue
gas temperature will not result in reduced heat transfer. It will be compensated by improvement in
heat transfer rates due to reduced slagging conditions, lower excess air, and higher burner zone
stoichiometry.
5. Evaluation of E-NOx Performance and Economic benefits.
The evaluation of the E-NOx performance was done by a third party using CFD analysis and by
kinetics modeling using Langmuir–Hinshelwood equations [9,18]
. The latter method has been
successfully applied to and explains the reaction rates for coal combustion in kinetic Zone II[17,19]
.
Based on these studies it was concluded that applying described E-NOx technology will result in
concurrent reduction of NOx, CO and
fuel loss (UBC). There effect depends
on fuel rank and combustion system
arrangement, steam parameters and
steam injection. The expected
concurrent reductions of NOx and
associated components presently
limiting in-furnace NOx control are
summarized in the Table 4.
The effect on coals with lower VM, i.e. smaller internal surface and inherent moisture will benefit
the most.
The CFD analysis has confirmed that E-NOx will bring nitrogen oxides out of the furnace to the
level typically achieved with the help of SCR. As mentioned above the concurrent effects include:
increase in furnace stoichiometry, reduced UBC (CIA) and reduced slagging (See Figure 5 and
Figure 6).
Table 4 . Expected E-NOx Performance
Species
Reduction %
Low VM Mid VM High VM
NOx ~50 40-25 15-25
UBC(fuel loss) 50-60 60-80 70-90
CO 50+ ~40 10-25

14 | P a g e
As it was already discussed above, the injection of steam for NOx control provides additional heat
input. Therefore, the steam generator will produce more steam at the same fuel input in the
proportion to energy of the injected steam which is recovered from the flue gas and regenerative
heaters as shown in Figure 4. Thanks to larger steam throughput through the steam turbine the
electrical output will increase for the same fuel firing rate, i.e. the cycle efficiency increases.
Several studies where performed for subcritical units that indicated the increase in boiler efficiency
by 1.5% to 2.5% depending on fuel fired, steam plant and combustion system arrangement, and E-
NOx configuration applied to specific case. This results in overall cycle efficiency improvement
on the order of 1% or more. For supercritical units the increase in efficiency is greater and relates
to larger share of work performed by HP turbines in the supercritical vs. subcritical cycle.
Table 5. Economic Evaluation of E-NOx and BACT Options
This increase in thermodynamic efficiency provides quick return on investment due to reduction
in fuel consumption, and if used alone will allow to meet regulations for NOx emissions and avoid
significant capital cost associated with available BACT technologies.
E-NOx can also be used together with SCR. In this case it will allow to compensate efficiency
losses associate with the technology (see Table 1) and in addition significantly cut back on variable
cost of reducing reactant. Other benefits and improvements deemed feasible in regard to catalyst
management programs and extension of catalyst life. The latter benefits were not accounted for in
the estimated payback time shown in Table 5.
7. Conclusions
 E-NOx overcomes limitations of Ultra-Low-NOx by controlling internal char surface size
and its chemical activity through burnout process.
 E-NOx makes possible further substantial reduction of NOx by primary means (In-
Furnace).
Retrofit - 600 MWe (Net) PC-fired boiler
Sub-Critical , Low Sulfur Bituminous Coal
Base SCR SNCR
E-NOx
Only
Existing
SCR +
E-NOx
Normalized Cost of Technology, $/kW NA $ 250 $ 21 $ 5 $ 5
Retrofit Cost,M$US $ 150.0 $ 12.6 $ 2.0 $ 2.0
Net Heat Rate(MCR), Btu/kW (HHV) 9,610 9,760 9,830 9,340 9,470
Plant Efficiency, % 35.0 34.5 34.2 36.0 35.5
NOx in Furnace, Lbs/MMBtu 0.25 0.25 0.25 0.08 0.08
NOx In Stack, Lbs/MMBtu 0.25 0.05 0.15 0.08 0.05
- Fuel Cost (Loss)/Savings, M$US*) Base Line ($1.2) ($1.7) $2.1 $1.1
- Variable NOx Control Costs, M$US/yr Base Line ($1.150) ($2.67) ($0.350) ($0.81)
- Fixed O&M (NOx related), M$US/yr Base Line ($0.5) ($0.2) ($0.14) ($0.64)
Total O&M Cost Change (Loss) /(Saving) M$US/yr Base Line ($2.8) ($4.6) $1.6 ($0.4)
Same vs. SCR , M$US/yr Base Line ($1.8) $4.5 2.5$
Pay Back vs. Base, month Base Line Never Never 15 mo NA
Pay Back (Base + SCR), month Base Line NA NA 10 mo

15 | P a g e
 Technical approach behind E-NOx was used for decades in other energy sectors and now
in Fuel Cells.
 E-NOx utilizes equipment that has been used in Power plants since the 1800s.
 Proper integration of E-NOx into steam plant reduced NOx, allows for fuel savings through
improved thermal efficiency, lowering LOI, and minimizing slagging
 E-NOx if used alone will generate operational profit
 E-NOx with SCR will cut >80% of SCR Operating costs
References:
1. G.A.Richards, C.Q.Money, J.L.Marion, R.Lewis, C.Smith. Ultra-Low NOx Integrated
Systems for Coal Fired Power Plants.
https://www.netl.doe.gov/.../Coal/.../nox/ALSTOM-NOx-IJPGC-Apr11.
2. Capital Investments in Emission Control Retrofits in the U.S. Coal-fired Generating Fleet
through the Years – 2016 Update. Thomas Hewson, Phillip Graeter. Report of Energy
Ventures Analysis, Inc. (Source EIA 767/860 forms)
3. Bin Xu, David Wilson, and Rob Broglio. Lower-Cost Alternative De-NOx
Solutions for Coal-Fired Power Plants, POWER ENGINEERING, 12/21/2015
4. I.W. Smith. The combustion Rates of Coal Chars: A Review. 9th
International Symposium
on Combustion/The Combustion Institute, 1982, pp. 1045-1065
5. D.G.Roberts, D.J.Harris. Akinetic Analysis of Coal Char Gasification Reactions at High
Pressures. Energy and Fuels, 2006,20, pp. 2314 -2320
6. J.F.Spinti, D.W.Pershing. The Fate of Char-N at Pulverized Coal Conditions. Combustion
and Flame 135 (2003) pp. 299-313.
7. M.Geier, et al. On the Use of Single-Film Models to Describe the Oxi-fuel Combustion.
Applied Energy, 93,(2012) 675-679
8. A.Bliek, Gasification of Coal-Derived Chars in Synthesis Gas Mixtures under Intra-
particles Mass-Transfer-Controlled Conditions. Chemical Engineering Science, Vol. 41,
No 7, 1986, pp. 1893-1909
9. S.Gil, P.Mocek, W.Bialik. Changes in Total Active Centers on Particles Surfaces during
Coal Pyrolysis, Gasification, and Combustion. Chemical and Process Engineering 2011,
32(2), pp 155-169
10. J.Thomas, Jr., H.Damberger. Internal Surface Area, Moisture Content, and Porosity of
Illinois Coals. State Geological Survey, CIRCULAR 493, 1976
11. J.F.Unsworth, D.J.Barratt, P.T.Roberts. Coal Quality and Combustion Performance. Coal
Science and Technology, Vol. 19. Elsevier/Shell Research, 1991
12. T.Gale. Effect of Pyrolysis Condition on Coal Char Structure (Thesis), Brigham Young
University, 1994

16 | P a g e
13. T.Gale, C.Bartholomew, T.Fletcher. “Decrease in Swelling and Porosity of Bituminous
Coals during Devolatilization at High Heating Rates. 25th
Symposium (International) on
Combustion, Irvine, California, 1994
14. L.Radovic, et/al. Importance of Active Sites in Coal Char and Carbon Gasification, PSU,
library, https://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/Volumes/Vol28-1.pdf
15. J.Tomaczek, Coal Combustion. Krieger Publishing Co, Malabar, Fl.1994.
16. EPA Technical Bulletin, Nitrogen Oxides. EPA-456/F-99-006R, 11/1999
17. A.Molina, E.G.Eddings, D.W.Pershing, A.F.Sarofim. Char Nitrogen Conversion:
Implications to Emissions from Coal Fired Utility Boilers. Progress in Energy and
Combustion Science 26 (2000) 507–531
18. S.Gil. Fuel-N Conversion to NO, N2O, and N2 during Coal Combustion. Fossil Fuel And
Environment Chemical and Process Engineering 2011, 32(2), pp 155-169
19. A.Molina. Nitric Oxides Destruction During Coal and Char Oxidation Under Pulverized
Coal Combustion Conditions. Combustion and Flame, 136 (2004)303 – 312.
20. Steam Its Generation and Use. Babcock &Wilcox. 40th
edition, 1992.
21. Mitsubishi-Hitachi Low NOx Burners.
https://www.mhps.com/en/products/detail/low_nox_burner.html
22. D.E.Giles, et al. NOx Emission Characteristics of Counter Flow Syngas Diffusion Flames
with Air Stream Dilution. Fuel, 85, 2006, 1729 – 1742
23. J. Ratafia-Brown, L. Manfredo, J. Hoffmann, M. Ramezan “Major Environmental
Aspects of Gasification-Based Power Generation Technologies” U.S. Department of
Energy, Office of Fossil Energy, National Energy Technology Laboratory, December 2002
24. E.F. Aul et al. In-Process Control of Nitrogen and Sulfur in Entrained bed Gasifier. EPA
Project Summary. EPA/600/S7-86/051 Mar. 1987
25. T.K.Gale. Effect of Pyrolysis conditions on Char Properties. Brigham Young University.
Theses. 1994
26. Steam - Cleaning Coal. Mechanical Engineering, June 2016, p.19.
27. E.Levy, T.Elderdge. I&C Enhancement for Low NOx Boiler Operation. Energy Research
Center, Lehigh University
28. A.G. Blokh, R.Viscanta. Heat Transfer in Steam Boiler Furnaces. Taylor & Francis, 1988
29. Xiang Gou, et al. Effect of Water Vapor on Pyrolysis Products of Pulverized Coal. Procedia
Environmental Sciences 12 (2012) 400-407

CoalGen Paper Manuscript(1) Modified Coal Combustion Reduces NOX and Fuel Consumption

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to CoalGen Paper Manuscript(1) Modified Coal Combustion Reduces NOX and Fuel Consumption

Similar to CoalGen Paper Manuscript(1) Modified Coal Combustion Reduces NOX and Fuel Consumption (20)

CoalGen Paper Manuscript(1) Modified Coal Combustion Reduces NOX and Fuel Consumption