Reducing
KeyPollutants
Janine Keune, Lechler, discusses emission reduction using air
pollution control technologies.

Introduction
For the last few decades, the focus of cement plant
operators and manufacturers has been on increasing
production rates while reducing energy consumption.
The process of increasing efficiency and saving costs
will continue in the future. Additionally, cement plant
operators and OEMs meet the requirements of theincreasingly stringent governmental regulations in regards
to environmental protection. Strict emission requirements
are creating a constant pressure to invest and innovate.
Therefore, air pollution control technologies play animportant role in cement industry.

The main four key pollutant categories are identified
as mercury (Hg), dust, sulfur dioxides (SOX), and nitrogenoxides (NOX). The several applications of gas cooling andconditioning in cement plants support the reduction ofthese pollutants.

Optimisation with gas cooling
Cement dust can adsorb mercury. The dust is captured
in baghouse or electrostatic filters. To protect the filtersfrom damage of high gas temperature and to increase theefficiency of ESP, a gas cooling system is installed upstream
e.g. in a gas cooling tower (GCT) or the downcomer duct.

Gas cooling has some main advantages that increase theefficiency of dust separation and reduce the consumptionof reagents required for emission control of mercury
and sulfur dioxides. Therefore, a cement plant can savethousands of dollars in operating costs.

Engineered solutions

Scheme for the Lechler spillback nozzle.

Scheme for the Lechler VarioJet® nozzle.

Nevertheless, it should not be ignored that gas coolingsystems also present multiple challenges for cement plantoperators. To ensure a stable and trouble‑free operation,
the required spray performance must be achieved, droplet
size and evaporation understood,
and the influence of various operating conditions(mill on/mill off) must be taken into account.
As the dust, mainly consisting of raw material, issensitive to increased humidity, a complete evaporation
within the available evaporation distance is essential.
Otherwise, a wet bottom in the GCT will cause build‑ups,
which in the worst case could lead to damage of theequipment and shutdown of the plant.
As each cooling tower is different, standard solutions
do not always make sense. To find an appropriate solution,
it is recommended to contact gas cooling experts, such asLechler. With detailed knowledge about nozzles and anunderstanding of spray and atomisation processes, Lechler
can provide complete tailor-made solutions from individual
nozzle lances to integrated gas cooling systems.

Selecting the right nozzle

Scheme for the Lechler Laval nozzle.
As temperature is a physical factor that determines
adsorption, the adsorption rate is higher at lower gas
temperatures. The reduction of the temperature alsoreduces the volumetric gas flow rate and therefore
increases the pollutants concentration, as well as theresidence time inside the filter. This is beneficial for theoverall dust removal performance and supports achieving
higher efficiency. Thus, the adsorption of mercury is more
efficient the lower the temperature.
Additionally, the required energy consumption of theID fan is optimised. Lower gas temperature has positiveeffects on ID fan energy consumption by reducing overallgas volumetric flow rates, which decrease with cooler
temperatures.
Furthermore, the gas cooling has further positiveeffects. With temperatures closer to dew point and reduced
actual volume of the flue gas at lower temperatures,the interaction potential between hydrated lime andSO2 molecules is enhanced. Additionally, the increase ofmoisture can reduce lime consumption.

Reprinted from July 2018
World Cement

The purpose of the injection via gas cooling system is toproduce the most liquid surface area for efficient gas‑liquidinteraction for heat and mass transfer by utilising minimum
energy to generate the surface area. Both options,twin‑fluid and spillback, are possible.
Lowest possible operating costs are realised withspillback nozzles, which require no compressed air for
atomisation, but are limited in adjusting the droplet size.
Gas cooling systems with spillback technology are not very
resilient in terms of capacity increase or changing droplet
size, while using same equipment.
Due to limited available space, the market is asking
for small GCTs. This is why twin-fluid nozzles are often
the only possible solution for many projects, as fine water
spray is needed. Additionally, twin-fluid atomisation ismore resilient in terms of retrofit by increasing air flow
capacity to adapt the droplet size. Lechler designed its
twin-fluid nozzles, such as VarioJet® or Laval, to allow anapplication‑optimised fine droplet spectrum at low air
consumption.
Only long‑term comparison of investment,maintenance, and operating costs, based on individual
local parameters of each cement plant (mill operation andreliability, energy prices, etc.), will give the operators a good
position to decide the best system.

Proven technology meets individual design
The VarioCool® gas cooling system is an engineered
solution according to individual customers’ requirements
and process conditions, considering design criteria, such

Gas flow before optimisation.

Gas flow after optimisation.

as available evaporation distance, process conditions (suchas inlet temperature, required outlet temperature, andvolumetric gas flow rates in several conditions [mill on/off]),
optimum spray distribution and coverage of area, and fluegas distribution (ideal for efficient evaporation is less than
20% RMS velocity distribution).
The VarioCool valve skid unit is configured of provencomponents from well-known manufacturers designed
for continuous operation. The most important functional
components are also realised to be redundant. The PLC
control unit ensures an optimum system performanceby adjusting the spray performance according to process
conditions to avoid upset conditions.
In addition to a well-designed injection system,
the inlet parameters are of crucial importance. To
ensure complete evaporation, a homogenous gas andtemperature distribution at the nozzle level is required.
A CFD study can help to detect unequal gas distributions
and turbulences,along with suggestions for solutions withbaffles or perforated plates.
Also, the arrangement of the lances plays a major rolein efficient evaporation. Too much water in the centre, aswell as too much water on the tower wall, increases therequired evaporation distance and can create wet bottom
and build-ups.
All this proves that gas cooling systems are tailor‑madesolutions, which have to be calculated carefully, considering
the individual conditions. The experienced engineering
team from Lechler is aware of the upcoming challenges andsupports cement plants from technical design and detailengineering to commissioning, service within operatingphase, and the supply of spare and wear parts.
A consultation onsite with experts in spray technology
could help cement plant operators to modify the gas
cooling system for more efficiency. With a troubleshooting,it is possible to detect whether the issue of wet bottom
arose e.g. due to changed actual produced droplet size
because of wear over time, interruption of compressed air
supply or improper selection of the droplet size.

Efficient NOX removal

Lechler VarioClean® – NOX.

Overview of gas cooling and conditioning applications
in cement plants.

Not only gas cooling, gas conditioning is also an essential
technology in air pollution control. The process of cement
manufacturing generates emissions of harmful nitrogenoxides (NOX) – mostly thermal. In an effort to reduce these,
many countries have already lowered the respective limit
values – some even to a daily average of 200 mg/Nm³. Inorder to comply with current and future emission limits,
cement plants are constrained to adapt their systems
accordingly.
As more plants substitute fuels that offer higher caloric
values, primary NOX separators (e.g. low NOXburners) areno longer sufficient to meet the demand for lower emission
limits. For this reason, it is necessary to introduce secondary
measures. By injecting aqueous ammonia or urea into theflue gas, the NOX is chemically reduced.
The efficiency of the denitrification process is
significantly dependent on the correct temperature
window, proper residence time in this window, andReprinted from July 2018
World Cementsufficient turbulences to mix reagent with NOX(interaction potential). For optimal use of the reagent
and thus reduction of operating costs, drop size, andvelocity are also of crucial importance.
In order to meet the varying process conditions,as well as local requirements, twin-fluid nozzle lances
equipped with Lechler Laval nozzles are generally used
for the injection of the reagent.
Their great advantage, compared to single-fluid
nozzles, is the adjustability of the droplet size andrealisation of a large flow-rate control range to control
the droplet size and penetration depth, depending on
the duct size and current process requirements. The
nozzles must produce an optimum droplet spectrum toensure penetration deep enough into the flue gas for
optimum distribution of the reducing agent in the fluegas flow and evaporation.
Furthermore, the right control concept can help for
an efficient reaction and keep NH3 slip at a minimum.
Lechler has joined forces with STEAG to provide a
modular deNOX system for different specified limits that
can also be extended at a later time, in line with updated
governmental requirements. The different configurations
help cement plants to adhere to the specified reductionlevels and NH3 slip values, but also lower reducing agent
consumption by 30% and more. Depending on the priceof the reagent, this leads to a significant quicker returnon investment for the injection system.
The injection system VarioClean-NOX can be flexibly
upgraded across the three configuration levels from

Reprinted from July 2018
World Cement

basic to high efficiency SNCR. Each configuration isdefined by the number of lances and injection levels,
as well as in the software and sensor packages for the
successful control of all necessary influencing factors.

Conclusion
Spray nozzles play an important role for efficient gas
cooling and conditioning. For cement manufacturing
operations, it is important for plant operators andOEMs to have a reliable partner that understands boththe spray technology and process. A well‑designed
injection system can reduce maintenance issues and thecost of using expensive reagents required for emission
control. It is very important that cement plant operators
and OEMs ask nozzle manufacturers for assistance ingas cooling and conditioning applications. If design
calculations are carried out correctly and considering
all design conditions, then a gas cooling system should
work reliably 24/7, without unscheduled interruption.
With a wide range of experience – and more than
500 references worldwide for gas cooling in GCT, ducts,
clinker coolers, and gas conditioning, in deNOX as well
as deSOX – Lechler products are used successfully incement industry.

About the author
Janine Keune is the Product Manager for Environmental
Division at Lechler GmbH.