K-Precalciners1.pdf

Precalciners

    ‫ محمد عبد الحكيم‬/‫د‬

Learning Objectives Precalciners

 Understand the principle of precalcination.  Know the basic precalciner types  Know the main features of the various precalciner types  Know the advantages of precalcination  Understand the principle of low NOx precalciners

 Know possibilities and limits of lump fuel in precalciners

    ‫ محمد عبد الحكيم‬/‫د‬

Precalciners: Content Content  Principle and theoretical aspects  Precalciner design  ILC precalciners  Pre-combustion chambers

 Low NOx precalciners  Solid AFR in PC: priority and new solutions  Optimization possibilities

 Main Benefits of Precalciner Technology

    ‫ محمد عبد الحكيم‬/‫د‬

Energy Balance of Process Steps for Clinker Burning Endothermic Processes: Dehydration of clays Decarbonisation of calcite Heat of melting Heating of raw materials (0 to 1450 °C) Total endothermic Exothermic Processes: Recrystallistion of dehydrated clay Heat of formation of clinker minerals Crystallisation of melt Cooling of clinker Cooling of CO2 (ex calcite) Cooling and condensation of H2O Total exothermic Net Theor. Heat of Clinker Formation: Endothermic - exothermic

kJ/kg cli 165 1990 105 2050

kcal/kgcli 40 475 25 490

4310 kJ/kg cli 40 420 105 1400 500 85 2550 kJ/kg cli 1760

1030 kcal/kgcli 10 100 25 335 120 20 610 kcal/kgcli 420

    ‫ محمد عبد الحكيم‬/‫د‬

AT (Air Through) and AS (Air Separate) Definitions: PA = Primary Air SA = Secondary Air TA = Tertiary Air

TA

TA PA

SA

PA SA

    ‫ محمد عبد الحكيم‬/‫د‬

Precalciner – Preheater Arrangements 1 or 2 strings

In-Line

Off-Line

2 strings only

Pre-Combustion Chamber

Hybrid

    ‫ محمد عبد الحكيم‬/‫د‬

Separate Line

Comparison of Calciner Arrangements

    ‫ محمد عبد الحكيم‬/‫د‬

Requirements I  Process:

High calcination degree Good control of calcination degree No material drop-out (meal, ashes etc) No build-ups on walls Simple and rapid start-up procedure Forgiving operating behaviour Flexibility regarding fuel ratio BZ / PC Safe regarding equipment overheating Minimum primary air requirement Minimum pressure drop

    ‫ محمد عبد الحكيم‬/‫د‬

Requirements II  Combustion:

High burnout degree of fuels Best mixing of air (O2) with fuel Instant ignition of all fuels Direct return of fuel residues to kiln Optimum combustion monitoring / control  Fuels:

Suitable for all fuel types (high flexibility) Insensitive to changes of mix of fuels Suitable for low reactivity and toxic fuels

    ‫ محمد عبد الحكيم‬/‫د‬

Requirements III  Emissions:

Reduction of pollutants from BZ No (low) generation of pollutants in PC firing Possibility for SNCR  Tertiary Air System:

No dust deposits and dust cycles No hot dust handling Reliable O2-control for BZ and PC firing  Design:

Easy integration in preheater Stepwise upgrading possible     ‫ محمد عبد الحكيم‬/‫د‬

Precalciner Control  Via Fuel Rate

Normally 45% to 60% of total fuel  According to Calcination Degree

of bottom cyclone hot meal (via LOI); Normally 85% to 95% apparent calcination degree  According to Gas Temperature at exit of bottom

cyclone; Normally 840°C to 890°C

    ‫ محمد عبد الحكيم‬/‫د‬

True and Apparent Calcination Degree  True calcination degree:

Degree to which the calcination is completed, i.e. extent to which the CO2 is dissociated from the CaCO3. Extremes: Raw meal 0% (LOI=35%) Clinker 100% (LOI= 0%)  Apparent calcination degree:

The calcination degree determined from a hot meal sample taken from the meal duct of the bottom cyclone

    ‫ محمد عبد الحكيم‬/‫د‬

‫د‪ /‬محمد عبد الحكيم ‪   ‬‬

O2 Control for PC/BZ: Tertiary Air Damper pID fan

pC5 exit

Var. Dp1 Dp2 ~pamb     ‫ محمد عبد الحكيم‬/‫د‬

O2 Control for PC/BZ: Kiln Riser Orifice pID fan

pC5 exit

~pamb

Dp1 Var. Dp2     ‫ محمد عبد الحكيم‬/‫د‬

Precalciner Elements  Long tubes “gooseneck type”  Large volume “vessel type”  Tertiary air frontal impact

 Tertiary air tangential inlet  Orifice  Bends, curves and vessels  Multiple burners

 Hot spot with and without control  Precombustion chamber

    ‫ محمد عبد الحكيم‬/‫د‬

Dimensioning Criteria for Precalciners 1. Gas Retention Time (for combustion in pure air)

decisive for complete combustion Fuel Reactivity low medium high

Gas Retention Time > 3.5 sec > 2.5 sec > 2.0 sec

2. Meal Retention Time

decisive for complete calcination Actual meal retention times are 6 to 12 seconds, at the above gas retention times.

Calcination takes much less than that which means that meal retention time is not a decisive design criteria.

Fuel Reactivity Examples: Low: Petrol coke Medium: Bituminous coal, natural gas High: Lignite, fuel oil Inline Calciners: Due to less favourable conditions for combustion (presence of kiln gas, imperfect mixing of tertiary air with kiln gas), the following rule of thumb can be used for sizing this PC type: Recommended gas retention time + 0.5 to 1 sec

    ‫ محمد عبد الحكيم‬/‫د‬

Standard Precalciners In-Line and Off-Line AT FLS, KHD, KSL, Polysius

    ‫ محمد عبد الحكيم‬/‫د‬

In-Line Calciners I

Polysius PREPOL gooseneck type

    ‫ محمد عبد الحكيم‬/‫د‬

In-Line Calciners II

FLS ILC controlled hot spot

    ‫ محمد عبد الحكيم‬/‫د‬

Pre-Combustion Chambers RSP (Technip), FCB, Polysius, FLS

    ‫ محمد عبد الحكيم‬/‫د‬

Calciners with Precombustion Chambers I

Onoda / CLE RSP (~1985)

    ‫ محمد عبد الحكيم‬/‫د‬

Calciners with Precombustion Chambers II

FLS SLC-D Downdraft (~2000)

    ‫ محمد عبد الحكيم‬/‫د‬

Low NOx Precalciners FLS, KHD, Polysius a.o.

    ‫ محمد عبد الحكيم‬/‫د‬

Low NOx Precalciners

Polysius PREPOL MSC (Multi Stage Combustion)

KHD PYROCLON Low NOx-Topair

    ‫ محمد عبد الحكيم‬/‫د‬

Precalciners for Lump Fuels (Tires etc): Future Development FLS, Polysius, KHD, Blue Circle, Ash Grove

    ‫ محمد عبد الحكيم‬/‫د‬

PC for Solid AFR: FLS Hot Disc

FLS Hot Disc

    ‫ محمد عبد الحكيم‬/‫د‬

PC for Solid AFR: BC-Lafarge AFR Ram

Ash Grove Controlled Ram for AFR modules (Patent 2001)

    ‫ محمد عبد الحكيم‬/‫د‬

Pre-Calciner: Typical Problems 1) CO at outlet of PC or cyclone

5) Material build-ups

6) Refractory damage

2) Locally too high temp.

7) Tertiary air damper failure

3) Unburnt fuel particles in hot meal

8) Tertiary air duct blockage (elbow type only)

4) Too high / low calcination degree     ‫ محمد عبد الحكيم‬/‫د‬

Main Benefits of Precalciner Technology 1. More stable kiln operation due to better kiln control via two separate fuel feed/control points 2. More stable kiln operation due to controlled meal conditions at kiln inlet 3. Reduced thermal load of burning zone

4. Lower refractory consumption as a result of 1. to 3. 5. More than double capacities possible with given kiln (10'000 t/d: 6 x 95m) 6. Possibility of increasing capacity of existing kilns

7. Reduced volatilisation of circulating elements 8. Reduction of cycles (S, Cl, Na2O, K2O) with lower bypass rate / losses 9. Makes short kilns possible with 2 stations, L/D < 12 10. Possibilities of NOx reduction 11. Lump fuel (AFR) utilization (in-line only)     ‫ محمد عبد الحكيم‬/‫د‬