GLOBAL CEMENT: ENVIRONMENTDr Ullrich Speer, Global Division Leader (Environmental Division) at Lechler GmbH

High-efficiency SNCR injection systems
Within the last decade the de-nitrification of flue-gas has become an essential topic for all
cement, power and waste incineration plant owners. Here Lechler GmbH’s global division
leader, Ullrich Speer, describes options for NOx removal within the cement industry.

To comply with current and future emissions
requirements, it is important that equipment
suppliers remain ‘in-the-know,’ so that they can offer
the most appropriate solutions. Even within the EU,
the differences in NOx emissions limits from cement
plants are significant and Germany will introduce a
new 200mg/Nm³ limit in 2019. However, the government is keen for all plants to meet the new limits
within a much shorter time-frame.
A cement plant offers multiple possibilities forflue gas conditioning systems at the raw mill, thecooling tower, the duct, the pre-heater, the alkalibypass and at the clinker cooler. Within long kilns
there are additional applications relating to burnerlances. Dedicated NOx reduction equipment canbe applied to calciners and dry and wet long kilns.
In both locations, selective non-catalytic reduction(SNCR) technology is a fundamental technique toreduce NOx emissions.

NOx reduction and ammonia slip
When fuel is burned pollutants are emitted in the fluegas. One of the main pollutants is NOx. Once emitted, NOx reacts with other atmospheric components
to produce ozone (O3). Other products generated
during combustion, such as nitric acid (HNO3), react
in the atmosphere and fall as acid rain, which negatively affects people, plants and animals.
SNCR technology currently involves the injectionof ammonia (NH3) or urea (CH4N2O) solutions. The
reaction of ammonia or urea with gaseous nitrousoxide (NOx) is transformed by thermal decomposition into steam (H2O) and nitrogen (N2).
When ammonia is used, a solution is injected
directly into the duct in several positions/levels, atapproximately 900-1000°C. The ammonia reacts withnitrogen monoxide (NO) to produce nitrogen (N2)and steam:
4NO + 4NH3 + O2 → 4N2 + 6H2O
Adding urea solution is simpler and safer and you
don’t need explosion protection. In the SNCR application, urea reacts like ammonia but with carbon
dioxide (CO2) as a by-product:
NH2CONH2 + H2O → 2NH3 + CO2

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During the injection of ammonia or urea, ammonia slip will appear in the exhaust gas. The amount
can be reduced via process adjustments, but it cannot be eliminated. At high temperatures, ammonia
creates •NH2 radicals. These are a result of the reaction between ammonia with hydroxyl radicals andoxygen radicals, which are usually created in hot gas
streams by other reactions. The •NH2 radicals reduce
nitrogen monoxide to dinitrogen:•NH2 +NO → N2 + H2O
In the overall reaction, the radical formation reactions appear twice and the reduction reaction fourtimes. This results in the following overall equation:
4NO + 4NH3 + O2 → 4N2 + 6H2O
When urea is used it forms •NH2 and the resulting carbon monoxide (CO) is oxidised by oxygen.
The reduction of NOx by ammonia or urea isbased on many partial reactions, the balance of
which is determined by the temperature and concentration of the reagents. Therefore, with a theoreticalover-stoichiometric injection relationship between
ammonia and NOx, the NO cannot be completelyremoved. Additionally, some of the reducing agent isregenerated as NH3 from the reaction.
For a maximum reduction rate of nitrogen monoxide leading to low ammonia and NOx emissions, atemperature window must be complied with (Figure1). In addition, nozzles are often installed at several
levels throughout the whole duct. Based on temperature measurements and calculations, those nozzles
closest to the injection point with the optimum reaction temperature will be activated.
Sophisticated single-nozzle control systems thatoffer independent injection-level sprays alreadyexist. If they could be combined with a local andtimely highly-resolving temperature calculation (likean online computational fluid dynamics - CFD), thebest NOx removal results could be achieved. Furthermore, minimum ammonia slip will be achieved.

Challenges to be managed by the plant
There must be a clear strategy to meet changing
NOx and ammonia emissions limits, with different
requirements for different plants. Some plants can

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proceed step-by-step with multiple small investments, but others find it better to invest in a fullpackage. How are such decisions made?
1. Emissions limits are different in different jurisdictions. Could production costs be optimised evenwith tighter values?
2. P lants must determine (and understand) thecomplexity of the influencing variables of NO
production and NOx reduction, such as: Flue gas
temperature in the injection area; Flue gas speed
in the injection area; Flue gas speed in other partsof the system; Fuel properties; Raw NOx load fromthe sintering zone and possibly from the calciner.
3. 
The process choice will influence current andfuture investments. There are many options atdifferent prices with varying future adaptability.
Some of Lechler’s solutions will be discussed later.
Unfortunately the parameters listed under point
2 must be controlled as well as known. Each of theinfluencing factors must be controlled separately andconsidered in the final calculation that will decide on
the type of control system. Within the plant there arethree different influencing groups:• Unknown variables: These include the raw NOx
value, temperature, gas speed and gas composition in the injection area and must be measured tobe known.
• Difficulty factors: These include temperaturefluctuations in the injection area, high dust loads
within the system, up to five minute delays between
the measurement point(s) and stack, the riser duct

Cold temperature
affords slower reactions

refractory, the gas flow and speed, fouling at the tipof the nozzles and the residence time of the gas.
• Permanent process changes: Most European cement plants (any many elsewhere) use alternative
fuels and each of these changes the gas composition. Ongoing modifications to the kiln line, or evenexisting changes within the process while the kiln isrunning, will also permanently affect the process.
One factor that will affect NOx production isbuild-up in the calciner. This is because the wholeprocess of the production line is based on theoretical
calculations of an optimised new plant. With increasing build-ups in the tower, the internal diameter of
the tower reduces. Assuming the same volume of gas,
but travelling through a smaller diameter, we will seea higher gas velocity. A specific residence time at theoptimum temperature is required to achieve the best
possible NOx reduction. However, increased velocity will shorten the residence time, resulting in an
incomplete reaction and higher NOx levels.
To prevent this, it is necessary to have online control of the build-ups and to be able to predict the next
occurrence ahead of time.

3D-temperature simulation and online CFD
Steag Powitec GmbH (Powitec) from Essen,
Germany has developed a high-efficiency SNCR(heSNCR) software system for NOx reduction incement plants in cooperation with Lechler GmbH,due to the fact that primary measures like staged
combustion will not be able to meet the 200mg/Nm3NOx limit. It is available as a stand-alone solution oras an upgrade to an existing SNCR plant.

Good temperature

Optimum temperature
High temperature induces
generation of extra NO

NO reduction and NH3 slip (%)

100

At 950°C theretention time is 100ms

NH3 slip

Left - Figure 1: The
temperature window for theinjection of the ammonia
solution is vital for good
operations of the SNCR system.

50NO reduction(function of O2)

At 850°C theretention time is 50ms0800900

1000

1100

Gas temperature (°C)

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Above- Figure 2: The Lechler
SNCR lances and twin fluid
Laval nozzles are included in thebasic SNCR, the eSNCR and the
heSNCR systems.

Below - Figure 3: The Lechler
heSNCR system installed in theGerman cement plant.

12The heSNCR technology
enables low NOx emissions while
maintaining tight limits for theammonia slip and reduced reagent consumption. Upgrading toheSNCR from standard SNCR is
attractive because this approachalmost always makes investment
in an SCR system obsolete. The
total costs of the heSNCR system are also lower than those of SCR technology.
The system can also be supported by the advanced
sintering process control system to reduce primaryNOx. The system software comprises: 1. Online CFD
for continuous generation of a highly-resolved timeand spatial model of the flue gas in the rising duct
between kiln and pre-heater (or calciner); 2. Estimation of the build-up thickness in relevant duct wallsthat dominate airstream issues; 3. Online calculationof the ideal spray amount (considering current andfuture levels of NOx, O2, temperature, deposition
rate and slip); 4. Permanent adaptation of control toprocess changes.
An additional special characteristic of the process
is that the NOx reduction efficiency and slip depend
strongly on temperature and O2 distribution. To
achieve the targets, the temperature window must be
determined for spraying the right amount of reducing agent at the right time to the right area. However,this poses another challenge as the optimal temperature window permanently changes, influenced by: 1.
Current cement production volumes; 2. Local fuelloads, fuel types and qualities; 3. Build-ups; 4. Local
gas flow and velocity.
To meet these challenges, Steag Powitec follows
the sense, analyse, predict, control (SAPC) approach:
Sense: Additional temperature sensors are used togain detailed knowledge of the conditions in the area
where reagent is injected. The sensors are installed in
the refractory material of influential ducts, in positions where build-ups tend to occur. At each position
two temperature sensors are used to improve the understanding of the current build-up of the deposits at
this specific point.
Because the sensors are of different lengths, they

Global Cement Magazine November 2014

can measure a specific temperature difference. In thecase of build-ups or a reduction of refractory wall
thickness due to wear, the changes in temperature
difference give information about gas flow velocity.
Analyse: The current build-up deposit situation in
the rising duct is estimated using the data from thetemperature sensors together with the process control system data. Data is continuously analysed andnoise removed.
Predict: The temperature distribution in the risingduct is calculated by dividing the duct into manysmall segments. For each segment, the physical parameters of the flue gas (mass, density, velocity andtemperature) are modelled. Mutual interactions aredescribed by mathematical equations as used in
CFD analysis.
The calculated values are calibrated online withthe values from the process control system. The
temperature distribution is continuously calculated
online with update rates of 10-30s. The permanent
online CFD allows the calculation (prediction) ofthe load- and fuel-dependent change of temperature.
This enables efficient and intelligent system control.
Control: As clinker production is a non-linear
process with significant reaction times andconstantly-changing correlations, controlling an
heSNCR system is a complex task. Different operating conditions generate different emission loads anddifferent temperatures.
The PiT Navigator SNCR technology, part of the
heSNCR system, continuously uses conventional
process data, the additional temperature sensor data
and the results of the online CFD calculations to findand evolve process models automatically over time.
The technique is a system of neural networks, which
are used to estimate important process results. Thus,
the PiT Navigator automatically evaluates the presently-valid model to determine the effect of certain
activities. For example, it simulates slight modifications to the amount of reagent injected through thenozzles to determine the effect on NOx reduction andthe ammonia slip at the stack. The best result derived
from these simulations is used for the control of thelances in the actual plant.
Unlike standard control systems, the PiT Navigator
SNCR system is self-calibrating and auto-optimisingclosed-loop control software. Consequentially, extensive and permanent manual reconfigurations are
not necessary. Additionally, statistical models do not
rely on subjective expert knowledge; they learn fromexisting process data automatically and select thebest control strategy. The system is also fault-tolerant:
If a single measurement fails, it will rely on others.
The heSNCR technology is equipped with a selflearning adaptive process controller that adjusts itself
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optimal quantity of reagent, at the right time, in theright area. This has the effect of continuously achieving significantly lower NOx levels with the lowest
possible reducing agent consumption at the lowest
possible slip. In places where NOx limits are not yet
low, the system still offers significantly lower reagent
consumption rates and protects against further investment costs when NOx limits are lowered.

reduce NOx emissions from 1000mg/Nm³ to 500mg/
Nm³, using 15% less ammonia than the basic SNCR.
High-efficiency SNCR (heSNCR): The heSNCR
consists of the eSNCR system, the build-up detection and the online CFD. Two additional Lechler
twin fluid Laval nozzles are included and the injection takes place on three levels in the calciner. All
outstanding and currently available technologies areincluded, like the NOx prediction, the PiT deposit
detectors and the PiT online CFD tool. A reduction
from 1000mg/Nm³ to 200mg/Nm³ NOx is typicallyachieved, as well as a saving of approximately 30% ofammonia reagent.

SNCR solutions
Lechler GmbH and Powitec provide a variety of NOx
reduction systems. The differences between each system and the anticipated NOx and ammonia reagent
reductions are outlined.

Case study

SmartNOx®: The Lechler SmartNOx system is astandard valve skid for de-NOx using ammonia. Customisation options are limited and the lances (Figure2) are not individually controllable. The system wasdesigned for those that want to gain experience with
de-NOx and is also useful for meeting more relaxedNOx emissions limits.

A case study at a German cement plant in RhinelandPalatinate, Germany, illustrates the excellent results
achieved with the heSNCR technology (Figure 3).
The NOx emissions were measured at the chimney,which is the measuring point for the Federal Environment Agency, as well as directly behind theinjection system at the calciner.
The cement plant has a kiln without a calciner,
which requires NOx limits of 1200mg/Nm3 when themain fuel is coal and 600-800mg/Nm3 when a significant quantity of RDF is used, (which is the normalcase). Using the heSNCR system it was possible toreduce emissions to 300mg/Nm3 on a constant basis(Figure 4) within six minutes of start-up.
The customer was pleased with the reduced NOxemissions, as well as the lower volume of ammonia
required. “By using the heSNCR system on kiln 1 inour Göllheim plant, it was possible to reduce ammonia consumption at the NOx limit of 500mg/Nm³ by
about 35%,” said plant personnel. “During a trial period, it was possible to maintain the NOx limit valueof 200mg/Nm³ at an ammonia slip <30mg/Nm3.”

Basic level SNCR: Basic SNCR is recommended forcustomers seeking long-term equipment that arewilling to upgrade later on. It includes a twin fluid
valve skid with a conventional control system andfour Laval nozzles and lances on one injection level.
It is possible to individually adjust the volume anddroplet size delivered by each lance. Typical reductions in NOx emission levels are from 700mg/Nm³ to500mg/Nm³.
Efficient SNCR (eSNCR): This includes two additional lances with Laval nozzles, giving six lanceson two levels, as well as a second small control rack.
Beside the existing control system, the eSNCR system offers a special NOx prediction. The system can

Chimney NOx

800
600
400200
Right - Figure 4: The NOx
emissions volumes (mg/Nm3)
during a one hour trial on 3 May
2014 at a German cement plant.

1000

PH NOx

800
600
400
200
003.1014

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