Building Capacities for the Improvement of the Air · PDF fileBuilding Capacities for the Improvement of the Air Quality ... Cement Kiln with De-NOx . ... Flame front Fast formation

Dr. Hubert Baier General Manager - Europe

Building Capacities for the

Improvement of the Air Quality

NOx – Abatement Lima, 22.06.2016

For clarification

It is mandatory to know the sources and options of

prevention of man made and ground based emissions

which effect human health and environment directly.

2

Process Emission of NOx

NO

x-E

mis

sio

n

Temperature

molten glass

Melting boiler

CFB with De-NOx

Dry bottom furnace

Cement Kiln with De-NOx

Formation of NOx

Nitrogen source Reaction partner Mechanism of

formation

N2 from air Exhaust gas thermal NOx

|N≡N|

N2 + O ↔ NO + N

N + O2 ↔ NO + O

„Zeldovich-Mechanism“

strongly related to

temperatures >1.250°C

prompt NOx

Flame front Fast formation reaction;

little relation to

temperature

Nx from fuel fuel NOx

i.e. pyridin from oil C5H5N N2 + CH ↔ N + HCN

HCN → NHx + Ox ↔ NOx

Fast reaction >800°C;

without correlation to the

temperature

4

Burning carbon based fuels

(coal, lignite, oil or solid

alternative fuel) results in

radiant heat for the

clinkerization process

C(s) + O2 (g) → CO2(g)

ΔHo= -393 kJ/mol

T=25°C

Flames in a combustion process

Source: PROCESS // Optimization - ZKG 02 2012

Simplified Kinetics of the Combustion

Measures to reduce NOx emissions

Primary measures are usually correspond with reduction for the

NOx formation influencing factors:

- Combustion temperature

- Oxygen supply (i.e. fuel-air ratio)

- Dwell time

- Temperature profile

(as higher T in on

the first level, as better

the reduction)

- Quantity of volatiles (only

highly volatile lignite

achieves an emission

level <200 mg/Nm3)

7


Primary measures - in the combustion chamber

8

1 Combustion Chamber

2 Main burner zone

3 NOx-reduction

4 after burner

5 flue gas

6 air-coal mix injection

7 coal-air mix injection

8 air injection

9 coal-flue gas mix

10 flue gas recyculation

11 flue gas outlet to cleaning


Secondary measures

9

Scrubber

Process

Deposition designation reactant Reaction

conditions

product Advantage/

dis-

advantage

Dry

NOx SNCR NH3 900-1000°C H2O, N2 Well

established,

waste free

NOx SCR NH3 300-450°C H2O, N2 Well

established,

waste free

SO2, NOx Electron

beam

NH3 50-100°C Fertilizer Not proven

under real

conditions

wet

SO2, NOx Walther O3, NH3 40-50°C Fertilizer No sales of

final product

SO2, NOx Saarberg-

Hölter-Lurgi

FeII-EDTA 40-50°C N2, gypsum Not proven

under real

conditions


Secondary measures are always applied in reduction of already

formed NOx to elemental nitrogen. Until only two principles are

established under daily conditions

SNCR ("selective non catalytic reduction")

reacting with urea or Ammonia:

4NO + 4NH3 + O2 → 4N2 + 6H2O + heat

2NO + (NH2)2CO + ½ O2 → 2N2 + 2H2O + CO2 + heat

Disadvantage:

- NOx-reduction potential 50%

- Ammonia slip

- Requires the exact

reaction temperature/

best reaction temperature

at ~950°C

10

Credit: SandeNOx


Secondary measures are always applied in reduction of already

formed NOx to elemental nitrogen. Until only two principles are

established under daily conditions

SCR ("selective catalytic reduction")

reacting with Ammonia and a catalyst:

4NO + 4NH3 + O2 → cat. → 4N2 + 6 H2O + heat

2NO + 4NH3 + O2 → cat. → 3N2 + 6 H2O + heat

- High reduction efficiency (90%)

- No Ammonia slip

Disadvantage:

- SOx + O2 → 2SO3

- NH3 + SO3 + H2O → NH4HSO4 (sticky salt)

- 2NH3 + 2SO3 + H2O + ½ O2 → 2NH4SO4 (sticky salt)

- Catalysts sensitive against temperature fluctuation > 370°C

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12

Hybrid SNCR/ SCR system from REDECAM© for power plants


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Staged Combustion

In this NOx reducing method, only a portion of the fuel is burned in

the main chamber. All of the fuel is eventually burned, producing

the same amount of energy, but this method greatly reduces the

temperature in the main chamber. As temperatures decreased, the

amount of thermal NOx is reduced.

Catalytic Converters

These devices are utilized to lower the toxicity of the emissions of

many combustion processes such as stationary engines, boilers,

heaters and internal combustion engines. Catalytic converters

break down nitrogen oxides into separate nitrogen and oxygen

particles. Some catalytic converters are also used to reduce the

high CO levels produced when reducing NOx, as low CO levels

are important to ensuring complete combustion.


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Flue Gas Recirculation

Flue Gas Recirculation, FGR, is a method of NOx reduction that

lowers the temperature of the flame, and therefore reduces

thermal NOx. A portion of the exhaust gas is re-circulated into the

combustion process, cooling the area. This process may be either

external or induced, depending on the method used to move the

exhaust gas. Flue Gas Recirculation may also minimize CO levels

while reducing NOx levels.

Reducing O2 levels

By reducing the amount of O2 that is available to react with the

nitrogen, NOx is reduced. This is achieved through the use of

oxygen trim controls. To minimize the O2levels, a combustion

analyzer is used to adjust the fuel and air mixture. This method

can reduce the level of NOx produced by up to 10%, but it may

increase the emissions of Carbon Monoxide (CO) very

significantly. This method is widely used in many processes such

as in rich burn engines.


15

Flue Gas Recirculation

Flue Gas Recirculation, FGR, is a method of NOx reduction that

lowers the temperature of the flame, and therefore reduces

thermal NOx. A portion of the exhaust gas is re-circulated into the

combustion process, cooling the area. This process may be either

external or induced, depending on the method used to move the

exhaust gas. Flue Gas Recirculation may also minimize CO levels

while reducing NOx levels.

Reducing O2 levels

By reducing the amount of O2 that is available to react with the

nitrogen, NOx is reduced. This is achieved through the use of

oxygen trim controls. To minimize the O2levels, a combustion

analyzer is used to adjust the fuel and air mixture. This method

can reduce the level of NOx produced by up to 10%, but it may

increase the emissions of Carbon Monoxide (CO) very

significantly. This method is widely used in many processes such

as in rich burn engines.


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Low NOx Burners

By changing the shape and formation of the flame by using plates

to control airflow, a more elongated flame is created in the burner.

The temperature is decreased due to the extended flame and

surface area, and the lower temperature reduces the amount of

thermal NOx. CO levels may be elevated when using low

NOx burners. It is important to monitor CO and True NOx levels to

better control Low NOx burners.

Low Nitrogen Fuel Oil

The use of low nitrogen oils, which can contain up to 15-20 times

less fuel bound nitrogen than standard No. 2 oil, can greatly

reduce NOx emissions as fuel bound nitrogen can contribute

anywhere between 20-50% of total NOx levels.


17

Water/Steam Injection

Water or steam injection reduces the amount of NOx produced by

lowering the temperature of the flame during combustion. The

lower temperature allows for the decrease of thermal NOx.This

method can result in an increase of 3-10% boiler efficiency losses

and excess amounts of condensation may form.Some advanced

designs of steam injection technology do not have significant

impact on boiler efficiency.


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SCR (Selective Catalytic Reduction)

SCR is a process where a reductant, most often ammonia, is

added to the flue. The reductant then reacts with the NOx in the

emissions and forms H2O and N2 (ambient nitrogen). This

process may take place at anywhere between 500°F and 1200°F

depending on the catalyst used. SCR may reduce NOx emissions

by up to 90%. SCRs are mainly used in large industrial and utility

boilers.

SNCR (Selective non-catalytic Reduction)

SNCR is a process that involves a reductant, usually urea, being

added to the top of the furnace and going through a very long

reaction at approximately 1400-1600 °F. This method is more

difficult to apply to boilers due to the specific temperature needs,

but it can reduce NOx emissions by 70%.

Costs of NOx reduction in German power plants

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Primary

measures

NOx

Reduction %

CAPEX

€/kWel

€ct./kWh

Low NOx-Burner 30-50 10-15 0.035-0.045

Air staging

combustion 50 5-20 0.03-0.05

SNCR 50 5-30 0.05-0.13

SCR 70-90 50-80 0.15-0.25

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Building Capacities for the Improvement of the Air · PDF fileBuilding Capacities for the Improvement of the Air Quality ... Cement Kiln with De-NOx . ... Flame front Fast formation