Controlling Nox

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  • Topic: Ammonia, Nozzle, Nitrogen oxide
  • Pages : 7 (1348 words )
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  • Published : January 10, 2013
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ENVIRONMENTAL SYSTEMS

I Controlling NOx emissions
by Frédéric Blanc,
Lechler France,
France

S

elective Non-Catalytic Reduction
(SNCR) as one proven method to
control nitrogen oxide emissions (NOx)
is used in incinerators, industrial boilers,
utility boilers, process plant heaters, paper
mill recovery boilers, cement kilns and CPI
process exhausts.
The direct injection of ammonia water
(or urea) into hot fumes (850˚C to 1050˚C)
reduces NOx to non-hazardous Nitrogen and
water.
This year, Lechler supplied five injection
systems for ammonia water for French clinker
production lines. Due to higher efficiency
and lower costs compared to urea, ammonia
water was chosen. The systems were part
of a general contract given to the plant
manufacturer ‘Stockage & Systèmes’ which
also included its NH4OH storage, feed and
discharge equipment.
Lechler supplied the following parts:
• twin-fluid nozzle lances for the injection of
ammonia
• pump and regulation skids for ammonia
• components for the regulation of the
compressed air.
For the five different cement lines, two
similar systems were designed due to
comparable process data:
• one system for plants with preheater towers
• four systems for plants using a Lepol grid.
All five systems had the same target
regarding the gas composition in the stack:
• NOx daily average must comply with the
limit of 800mg/Nm3 at 10 per cent O2 dry
• minimising the slipping of ammonia,
according to the temperature conditions
and reaction time available in the different
burning lines.

Pump and regulation unit:
Lechler VarioCool® system
Lechler offers VarioCool, complete gas
conditioning systems, including nozzle lances,
pumps, regulation units and electronic
controls. As the only manufacturer of this
system worldwide, Lechler supplies gas

The latest European regulations regarding NOx emission limit the daily average of NOx to 800mg/Nm3 dry (at 10 per cent O2). In addition to some primary optimisation measures, in order to reduce the production of NOx, several plants in France have recently installed a SNCR DeNOx system to comply with the new regulations.

Figure 1: nozzle lances emit water into the air

conditioning systems equipped with spillback
nozzle lances as well as twin fluid nozzle
lances at the same technical level. The
‘coupled with the engineers’ experience
gained through numerous installations,
enables tailor-made solutions to be designed
and implemented, for gas cooling, DeNOx
applications and other gas conditioning
applications.
The principle of the DeNOx system is
to adapt the quantity of ammonia water
injected as a function of the NOx level and
ammonia slip measured at the stack.
The pump and regulation unit must
therefore be able to regulate the flow rate
of ammonia water with the biggest possible
turn-down ratio and to inject it into the hot
gas stream with the best possible coverage.
Lechler’s target was to supply a reliable and
safe proof solution, with easy maintenance.
Thus, the latest state-of-the-art technology
and components were used and assembled
on a stainless steel valve/pump rack.
The system was designed with the option
to use clear water from the plant network or
ammonia water from the storage tank. The
ability to use clear water as an alternative
is very important for the spray tests on site
during commissioning. It is also necessary to
clean all the pipes and components prior to
doing any maintenance work at the site.

Twin-fluid nozzle-lance for
injection of ammonia water
To meet the process requirements and have
a very flexible system, Lechler has used a
special twin-fluid nozzle that can produce
finer or coarser droplets depending on the
air to liquid ratio. To suit the specific working
conditions Lechler had to take into account
the following aspects to design the nozzle
lances for all systems:
• high temperature range (700-1200˚C)
• high dust load
• variable...
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