1. Criteria for Maximising Output and AFR with Relevant
OH&S Requirements
- Tom Lowes
- John Jones -
2.
3. Cement Production Scenario
In Asia whilst it generally has not suffered as much as the Western World in
terms of downturn and in many areas the market is sold out and production is
still king, the use of Alternative Fuels and Raw Materials (AFR) by the Cement
Industry is becoming an increasingly important part of a Countries Strategy to
resolve it’s recycling and waste production issues.
The Customers Produce Waste, the Pre- Processing entity converts the Waste
to AFR which is then used for Co Processing
The Co Processing of AFR by the Cement Industry has potential bottom line
benefits to its highest cost item, that of Fuel Costs, however there can be
significant issues associated with the use of AFR associated with:-
loss of output
appropriate pre and co-processing and increased OH&S requirements
increased emissions
Even when the market is not sold out, the Plant needs to perform near to
maximum output when it is producing, due to needs of operational efficiency.
When the market is sold out, any loss in output can make a big difference to
the Plant profit.
This paper outlines how to maximise output and minimise emission increase
while using AFR together with the OH&S requirements to achieve it
5. The loss in output can be significant unless the AFR to be used is well
understood in relation to the Plants operational bottlenecks plus impact on
emissions and clinker quality, which results in significantly less being used
than planned or contracted and a poor return on the investment in pre and
co-processing systems.
While the use of AFR generally leads to a drop in NOx, its higher volatility,
variability and size compared to prime fuels, can lead to increased CO and
VOCs and SO3 cycles, leading to emission regulation problems and build up
issues leading to Plant stoppages.
CINAR have the Process Knowledge of the Plant issues associated with the
co-processing of AFR and via its Multi Fuel, Minerals Interactive – CFD,
(which has been customized for the Cement Industry) can resolve any output
or emission issue either at the operational or planning stage.
Our unique MI CFD allows one to go inside the kiln or calciner, have a look
around, find how it is working and try some solutions before implementing it
on a large scale.
However the best analytical tools in the world do not help much unless the
basics of the process are well understood and the pre and co-processing
systems as well as the OH&S are not done well.
Using AFR
6. Needs
Avoid excessive build up
No Significant loss of output
No increased VOC emission
Hit NOx targets
Rules for AFR and Petcoke
VFSO3 < 2
HM Carbon < 0.1%
HM Cl < 1% - 1% by pass per 100mg/kgClk > 300
Eliminate Kiln and Calciner Stratification
Need Tom not 3Ts
M – Temperature
O – Oxygen
T – Micro-mixing
Additional for 500 mg/Nm3
Tom ++
i.e. Volatiles and sub stoichiometric RT
Using AFR Effectively
Combustion in a
very narrow
region
SIGNIFICANT
STRATIFICATION
and waste of
space and hence
need big RT
7. Impact of AFR on Output
There is much myth and folklore surrounding AFR and its impact on
output, let alone emissions and clinker quality.
The output losses are always related to current maximum performance in
sold out market – even if it is not – and hence this is normally a fan
limitation. Hence anything that increases the gas volume, due to H2O,
increased fuel consumption or O2 needs can be seen as a drop in output.
The first major rule to apply is seeking to minimise the impact of AFR on
output is:- %TSR (Thermal Substitution Rate) * Short Terms Thermal
Input Fluctuations = <100%
For example, if the Plant is at 50% TSR the STTIF (one minute) has to be
<2%. If it was for example 7%, up an extra 1.0 % O2 could be needed to
avoid CO and hence potential 6% loss in output.
So to go to the higher AFR rates: good pre-processing, handling, firing
systems are needed, plus of course excellent process knowledge.
The next issues are the impact of H2O, ash, exit temperature and extra O2
have on output. The table on the next shows for a PH/Calciner, where GC-
Giga Cals t-tonnes and fc – fuel consumption.
8. Impact of AFR on Output
The simple one to assess is that impact of H2O and Ash on output with
water being by far the higher. For example a 4000 tpd plant with 50%
of its fuel with 30% water will lose @140 tpd of output or 3.5%.
Poor AFR control needing an extra 1% O2 will lose 6% output.
Poor riser or calciner firing will increase the PH exit temperature by
100C increasing fuel consumption by 50 kcals/kg and losing 2.5% in
output – A CURRENT MI-CFD PROJECT.
The O2 and increased PH temperature can be negated via good process
engineering aided by MI-CFD, however the impact of ash and H2O is
down to the availability of the AFR and various choices as to
preparation, specification and price.
9. Impact of AFR on Output
In addition, with AFR there are many process problems associated with a
longer flame, reducing conditions in the kiln and hot meal due to unburnts
in the hot meal driving the SO3 cycles and build up. They are a function of
the process and the fuels used as well as the level of external help given to
supplement the local process knowledge.
It is imperative for successful AFR use at a Plant that the choice of AFR
quality is made with reference to the Plant co processing and pyro
capabilities.
However to get your Pyro Plant AFR one first has to know your Plants Pyro
State and Eliminate Stratification to avoid significant loss is output and
increased VOC/CO emissions.
While the Calciner performance dominates the AFR TSR potential, the role
of a poor/ good burner cannot be overlooked.
10. Good Kiln Burner Criteria to Avoid Stratification
Kiln Burners Rules forn 75% TSR
11N/ MW
CO < 200 ppm at
1.2% O2
NOx max to 2.5% O2
VF SO3 < 3
Avoid cooler/ kiln
hood SA flow
distortion
These will allow
unburnt C in hot meal
burnout before the
after calcination zone
and 75% Burner TSR
11. 100 % Calciner TSR
Impossible many would say without 8 secs RT, many Asian calciners are < 3
secs, so is 100% TSR impossible?
NO!!! CINAR has modified a 2 sec RT for £1.5m that can get 100% TSR
Look at the car development
1 litre engines now produce the power of 10 litres 50 years ago
How has the development been done?
Via well customised CFD programmes for Engine combustion for both
diesel and gasoline
A customised CFD programme – MI-CFD – can do the same for a small
calciner
SO Tune the Engine, give it a TOM
What is the Engine
Coal and AFR injection, TA , meal and gas riser.
The micro mixing or O2 and fuels need to be optimised with respect to
combustion and heat transfer to the meal.
The is little point in adding volume at the cold end if the engine is
poorly tuned.
12. 100 % Calciner TSR
CINAR did initially work for this calciner plant to overcome problems of poor coal
burnout and calcination and very bad build up.
This is shown on the next 3 slides, how a low cost modification to the TA inlets
enabled them to overcome the problem and get to @ 70% calciner TSR with an
Engineered Fuel (SRF), however the Plant Manager wanted to get to 100%.
As the calciner has only 2 secs RT this proved to be difficult for them, due to CO,
less of output and elevated PH outlet temperature and we were asked again to
help.
From simulations of the current operations it was identified that:-
The SRF was being quenched too fast to get a good burnout and its path was going
to the lower O2 regions in the calciner and only burning out to 73%.
Simulations of the SRF and coal injection points, plus meal splits and a venturi, a
series of recommendations were made to get potential to 100% TSR.
13. Oxygen Mass Fraction [-]
Original 2
TA inlets,
very poor
mixing with
the coal
Modified
TA to a
Horseshoe
Original Modified
Burnout % 70 93
Calcination % 70 90
14. Oxygen Profiles/ Fuel Trajectories
Coal / O2
O2 [m/ m]
EF / O2
The EF releases
if volatiles
fast, but is then
quenched too
fast by the meal
and then travels
in a low O2
region which
makes the
burnout poor
Near the walls of
there are oxygen
rich areas where
available oxygen
would enhance
the burnout
Case Base Case
Coal Burnout (%) 99
EF Burnout % 73
Total Burnout % 81
Calcination 95
70% TSR increased
CO and kcals/kg and
lower output
15. EF particles in O2 - Meal particles in Temperature
70%
Profuel Axial Sleeve of
EF injectors
100%
Profuel
O2
T (C)
Adding a
lower meal
inlet
Currently
being
implemented
16. Implementation and Feedback
Based on the MI-CFD simulations, modifications were proposed to the SRF
burners, meal split and the installation of the customized venturi design
not only to stop the SRF drop out but to improve the mixing of the O2 with
the EF. The predicted change is below:
So the burners have been modified and part of the Venturi has been
installed, with the change below from the Plant info, which shows already
85% TSR , more output, less CO and better kcals/kg, with a potential
savings of > €1mpa and a pay back on the MI-CFD of 2weeks.
•
Case 70/30 100%
Coal Burnout (%) 99 -
Eng. Fuel Burnout % 73 84
Calcination % 95 97
Exit O2 % 4.2 3.9
Calciner Exit Temperature (C) 865 866
Year Before part Mod After part Mod Percentage
Clinker tpd 2788 2838 2%
EF firing rate tph 6.8 8.2 21%
PH Exit Temperature 431 416 4%
ID fan O2 ppm 7.5 6.6 14%
ID Fan CO ppm 1110 930 19%
Fuel Comsumption kcals/kg 936 896 5%
17. Calciner Modification for AFR and Output
Options
Zero Capex – Process evaluation MI-CFD – calciner burner, AFR injection
and meal location optimised – 100 % TSR possible with specific AFR for
RTs < 3 secs
Low Capex - < $2m US – as above but with TA optimised 100% TSR possible
for a wider range of AFRs
Modest CAPEX < $5m US – SCC recent PMTech/ CINAR develop for most
AFRs up to 75mms and 100% TSR
GIVES @ 6 secs AFR RT with a gas RT volume of 1 sec RT
and fits with the new BMH TSS Concept
18. Generic Calciner for 100% TSR and Low NOx
CINAR customised HOT REBURN
– 0.15 secs at 1300C
SR volatile < 0.9
Non coating refractory (SiC)
plus blasters
Customised Venturi for AFR
Further reburn and stating
section to allow HCN -> N2
with up to 50% meal quench,
at least 0.5 secs
Opposed TA inlets
or horseshoe to
enhance mixing
and avoid
stratifications
Enhanced mixing
and combustion
region – hot spot –
controlled by rest
of meal
2.5 secs RT above TA, for
calcination and burnout
AFR and Coal
burners design
and location
customised as a
function of
specification
20. SRF Residence Time (sec.) Fn Size
Av. RT: 2 s
5 mm 10mm 20mm 30mm 50 mm
Av. RT: 4 s
Av. RT: 5 s
Av. RT: 10 s
Av. RT: 12 s
21. SRF Burnout (%)
Burnout %
Average SRF BO at
SCC exit: 96%
The bigger the SRF the
longer the RT and hence a
good Burnout is assured,
even with only a gas RT of
@ 1sec
The SCC fits nicely with the
BMH TSS concept
The SCC BURNS ALL
and the
TYRANNOSAURUS EATS
ALL
22. Calciner
optimisation
LOI compared to
Temperature
CO < 500 ppm at 2.5%
O2
PH Temperature 350 - 4
stage, 325 – stage, 290 –
6 stage
MI-CFD - O2
stratification
Burners
Meal
TA
SCC
Calciner Rules for 100% TSR
23. All well and good, but major issues are
associated with waste/ AFR platforms and
OH&S before even using AFR at a Kiln.