3 Calciner Technology 105 Minutes

Day 1 Pyroprocessing I Calciner _ Process and Technology Diwakar Mishra October 2010

Pyroprocessing I

PRECALCINATION IN PREHEATER

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Pyroprocessing I

PRECALCINATION Another possibility to increase the performance of a Rotary Kiln installation is to add a SECONDARY HEAT SOURCE, upstream, which will fulfil a maximum of reactions. The secondary furnace

dries then Decarbonates

This is PRECALCINATION, that takes place in a cyclone tower.

Pyroprocessing I

Precalciner Mainly: Investment reason  Efficient way to increase capacity of existing plants  Lowest investment cost for a new line Some: Performance Reason  Slightly lower heat consumption compared to preheater kilns  More options for some alternative fuel types  More NOx reduction possibilities

Pyroprocessing I

Air Through (A.T) Meal

Limitations are flame cooling due to excess of draft hearth velocities

Tower

technological limitations on kiln diameter

Fuel 2

Precal

Decarbonated matter

Cooler exhaust Fuel 1 Kiln Clinker

Cooler Clinker

Air

Eventual By-pass

Pyroprocessing I

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Air Through (A.T)

Advantages: System is very simple. Any type cooler can be utilized. Possibility of this system to cope with certain circulating phenomena. Substantial decrease of the thermal load of the burning zone Improved lining life. Disadvantages: Maximum fuel input in the precalciner is not practical. The bypass will be of same size as in conventional preheater kilns. Burning in excess O2.

Pyroprocessing I

Air Separate (A.S.) Meal

With Tertiary air Tower

Fuel 2 Precal

Cooler exhaust

Tertiary air Fuel 1 Kiln

Kiln gas: Before or after precal depending on manufacturers Decarbonated matter Eventual By-pass

Clinker

Cooler Clinker

Air

Pyroprocessing I

Air Separate (A.S.)      

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Advantages: Reduced specific gas quantity through the kiln. Feasible to design production units of large capacity. The thermal load on the burning zone can be reduced. The lining life is substantially increased. More efficient, smaller bypass. Disadvantages: Planetary coolers are ruled out. Some systems air flow has to be regulated (tertiary damper). Slightly higher pressure loss.

Pyroprocessing I

One or two strings Meal

Meal

Precal Tower Fuel 2 Cooler exhaust

Tertiary air

Kiln tower

Precal matter

Fuel 1 Tower Clinker

Cooler Clinker

Air

By-pass

Pyroprocessing I

Calciner Kiln

Pyroprocessing I

Preheater Kiln

Pyroprocessing I

Calcination

Transition

Sintering

Cooling

Calciner

2

6

6

1

Calciner Kiln

Preheater

Preheater

Rotary Kiln Zones

7

3

4

1

Preheater Kiln 0

Kiln Length in D

15

Pyroprocessing I

Type / Basic Design Parameter 

AS / AT

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ILC / SLC or combinations

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Vessel or Riser Type (gas speed)

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High Temperature Zones (hot spot,…)

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O2 rich zone / Reducing Zones (NOx reduction)

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Fuel splitting / Meal splitting / Tertiary air splitting

Pyroprocessing I

Calciner Burn Out / Combustion Efficiency Function of:  Retention Time (Fuel)  Temperature  Oxygen Content  Mixing (Rawmix / Fuel) Additional Target: Low NOx

Pyroprocessing I

Combustion levers: 5 T rules 

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Total O2 content  a higher oxygen content provides a greater driver for the combustion reaction Turbulence  greater mixing of oxygen and fuel Tenuity of fuel particles  greater surface for reaction Temperature of combustion  higher the T° faster the reaction Residence time of fuel particles  increased residence time provide increased burnout

Pyroprocessing I

Calciner gives advantage for AF firing, but

Wood chips Fluff RDF Fluff RDF

Sewage sludge Animal meal

Pyroprocessing I

Important Fuel Properties Size Volatiles N-content Heat Value Moisture Ash content Retention Time in calciner of our region ?

Example SLC MILAKI

Pyroprocessing I

Example - In Line Calciner Ideal

Pyroprocessing I

Calciner Operation 3

424 °C

1,473 mn /kgcl.

3737 Pa 3,3 %O2

0,099 kg/kgcl.

Calciner operation  Keep exit T by fuel  Keep O2 after calciner by TA damper  Adjust chamber T by meal / fuel splitting  Optimize NOx reduction  Optimize calcination degree  Ensure lifting of meal in tertiary air

TOC 387,3 kJ/kgcl. 1,655 kg/kgcl.

617 °C 2857 Pa

747 °C 2322 Pa

865 °C 1597 Pa 3,0 %O2

261,2 kJ/kgcl. 1315,5 kJ/kgcl. 0,028 mn3/kgcl.

Coal Pet coke

942 °C 0,468 mn3/kgcl.

94 %

1245,5 kJ/kgcl. Coal 247,4 kJ/kgcl. Pet coke 0,0434 mn3/kgcl.

239 °C 1,193 mn3/kgcl.

1202 °C 2,4 %O2

110 °C

2,05 mn3/kgcl. 35 °C

Pyroprocessing I

Good Indicators of calciner operation 

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Exit gas temperature or/and hot meal temperature on target, stable with +/- 5°C. CO calciner exit gas < 500 ppm. TOC (unburned Carbon) in hot meal < 0,2%. Combustion efficiency > 95%. Calcination degree on target. Stable pressure profile – no critical build ups. Stable operation (meal lifting in tertiary air, …). Stable fuel splitting kiln / calciner, with > 50% for the calciner. Stable O2 after calciner, preferable below 2%. Hot meal SO3 / Chlorine in acceptable range. Stable temperature in hot spot area (combustion chamber). Low NOx emission respectively reduction of NO formed in the kiln.

Pyroprocessing I

Design evolution to burn lumpy solid wastes 

High inlet velocity to the precalciner, around 30 m/s 

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Low velocity in main section, 4 m/s 

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allow burnout of CO

High temperature combustion zone 

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increase burn out rate, although negative impact on NOx

Gas residence time > 3.5 secs (4 - 4.5 secs to allow for NOx reduction) 

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increase fuel residence time in the precalciner

High oxygen environment 

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avoid drop out of fuel particles to the kiln inlet

rapid burnout of fuel

Vertically upwards gas stream 

avoid material drop out

Pyroprocessing I

Design evolution to burn lumpy solid wastes 

Good substitution rate achieved in inline vessel type calciner  35 to 75% of calciner fuel replacement

Pyroprocessing I

Calcination Degree (1) Definition: % of kiln feed CO2 which is already calcined in the hot meal.

Pyroprocessing I

Calcination Degree

CD = 100 (% CO2 kf - % CO2 HM) / % CO2 kf = 85,7%

Simple formula should not be used!

Pyroprocessing I

Calcination Degree CO 2kf  CO 2hm   100 *  CO 2kf CD %  100 *    90,23% 100  CO 2hm    

CO2kf:

CO2 of kiln feed

CO2hm:

CO2 of hot meal at bottom stage

CD%:

„Calcination Degree“

Pyroprocessing I

Calcination Degree

Imagine some aspects which can impact the result.

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Pyroprocessing I

Calcination Degree There are many impacts on the result:       

Dust circulation (preheater exit, kiln bottom cyclone) TOC kiln feed and hot meal CO2 or LOI analyzed Formula used Kiln feed analyzed or fixed value used Timing of kiln feed / hot meal sampling Sampling error and analytical error

Pyroprocessing I

Calcination Degree The target for calcination degree remains plant specific, but typically should be 90 – 92%. 

Too low:  Risk of weak kiln

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Too high:  Risk of stabilized phases before entering the sintering zone  Dusty clinker, more difficult to burn  Risk of excessive kiln inlet temperature, esp. when using AF