Combustion Gasflows And Gas Composition: Complete Guide & Do

Combustion, gasflows and gas composition form the invisible machinery of the cement plant: the gas that heats the kiln, the draft that moves it, the oxygen that burns the fuel and the analyzer that guards the whole chain: for the kiln operator, the gas circuit is the nervous system of the process: the flame shape, the back-end temperature, the cyclone pressure and the oxygen at the kiln inlet all speak the same language, and whoever reads that language controls the clinker cost: this guide walks the complete system: the chemistry of the fuel, the paths of the air, the behavior of the draft and the interpretation of the gas analysis: the honest engineer of the package treats this document as the field reference of the combustion quarter: the numbers, the tables and the recipes of the daily operation.

The Complete Cement Technical Package (931 files including the process courses, the books, the Excel tools and the operating manuals: $249.99 one-time: instant download via the PayPal payment) includes the full Combustion, Gasflows and Gas Composition file with its tables, the worked gas balances, the fan calculations and the analysis charts: the beginner finds the basics of the flame, the experienced engineer finds the tricky corrections of the gas volumes: both find the honest framework of the package: the combustion knowledge, measured.

This article is organized the way the file is: the fundamentals of combustion first, the air system second, the gas paths of the preheater and the kiln third, the measurement and the interpretation of the analysis last: every section carries the lists, the tables and the numbers of the plant floor: the reader can work with the article beside the operator screen: the intention of the document.

1. The Gas Circuit as the Nervous System of the Kiln System

The cement plant is a heat engine: fuel burns in the kiln and in the calciner, and the products of combustion carry the heat from the flame through the sintering zone, the transition zone, the chain section, the preheater cyclones and the conditioning tower to the baghouse: roughly 200 to 260 standard cubic meters of dry gas accompany every ton of clinker at the stack, and the plants that control these flows control the largest economic lever of the pyro line: the gas circuit is its own anatomy: the draft is the pressure, the velocity is the pulse and the temperature is the fever: the trained operator reads all three.

• The fuel in: coal, petcoke, oil or alternative fuel enters the burner with the primary air: the feed rate and the calorific value set the thermal field of the kiln;
• The air supply: primary air carries the fuel, secondary air preheated in the clinker cooler enters the kiln hood, tertiary air feeds the calciner: the three streams of the combustion;
• The combustion zone: the mixture burns with the flame at 1800 to 2000 °C: the volatiles release quickly, the fixed carbon burns slower, the ash splits between the clinker and the gas;
• The heat exchange: the rising gases meet the descending material in the cyclones and the chains: temperature drops stage by stage while the material warms: the counter-current exchange;
• The draft: the induced-draft fan at the cold end pulls the whole column: the kiln run keeps negative pressure at the kiln hood, roughly minus 20 to 100 Pa, to stop the hot smoke leaking into the hall;
• The analysis: the oxygen, carbon monoxide and carbon dioxide at the kiln inlet and the preheater exit are the verdict on the mixing, the fuel rate and the air leakages.

The plant burns about 90 to 140 kg of standard coal equivalent per ton of clinker: the air to burn one ton of clinker is 1.8 to 2.4 tons: the gas that travels through the system is about 2.5 to 3.2 tons per ton of clinker: the discipline of the operator moves tens of millions of dollars of energy per year around this tube: the combustion file in the package is the map of that tube.

2. The Fundamentals of Combustion: Stoichiometry, Excess Air and the Lambda Number

Combustion is chemistry: the carbon of the fuel combines with oxygen to carbon dioxide, the hydrogen to water vapor, the sulfur to sulfur dioxide: the stoichiometric air is the exact amount of oxygen needed to burn the fuel completely: for the typical plant coal, this is about 8 to 10 kg of dry air per kg of fuel, depending on the volatile matter and the calorific value: no industrial burner can burn completely at the exact stoichiometric ratio, because the fuel and the air never mix perfectly: the plant therefore supplies excess air.

• The theoretical air: the computed air for the complete oxidation of C, H and S in the fuel: the base of every calculation in this file;
• The excess air: the air above the theoretical, expressed as a percentage: it guarantees the completeness of the burn and leaves the oxygen in the combustion products;
• The lambda (λ): the ratio of the actual air feed to the stoichiometric air: 1.0 is the neutral point, 1.1 is ten percent excess: the dimensionless soul of the gas balance;
• The combustion products of the air: the oxygen surplus carries away heat on the stack, the correct value is the compromise between burning complete and burning cold;
• The incomplete combustion: too little air, the fuel leaves as CO in the gas and in the worst case as soot: the kiln burns inefficient and the CO alarm sounds;
• The CO2 checks: the instrument, the O2 analyzer and the CO2 reading from the gas measurement verify each other: the redundant channels of the analysis.

The lambda that the kiln plants prefer at the kiln inlet is typically 1.1 to 1.2, which pages 1.5 to 3.5 percent residual oxygen at the preheater entrance: the raw mill requires its own window: the kiln flame requires the smallest excess air, and every extra percent of oxygen in the kiln inlet carries fuel, because the air is heated from the ambient to over 900 °C and the nitrogen carries the heat: the file quantifies this: one percentage point of kiln inlet oxygen can be worth more than ten kilocalories per kilogram of clinker in the waste gas losses: the calculation runs chapter 2 of the document.

The complete balance of one kg of dry coal: the table below summarizes the classical gas quantities that the operator will re-compute from the ultimate analysis:

Gas estimate (per 1 kg dry fuel)	Low volatile coal	High volatile coal	Petcoke
Stoichiometric dry air, Nm³	7.5 to 8.5	9.0 to 10.5	7.0 to 8.0
Wet air at λ = 1.15	9.2 to 10.3	11.0 to 12.5	8.6 to 9.6
Dry flue gas, Nm³	7.9 to 8.9	9.4 to 10.9	7.6 to 8.6
CO2 in dry gas, by volume	16 to 17	15 to 16.5	16.5 to 18
O2 in dry gas at λ = 1.15	2.8 to 3.4	2.8 to 3.4	2.6 to 3.2
Adiabatic flame temperature °C	1950 to 2150	1850 to 2000	2050 to 2200

The table is the estimate of today, the calculation yields the value for tomorrow’s coal: every plant knows its own coal and its own gas: the purpose of the table is the training of the interpretation: the operator recognizes the O2, the flame and the NOx patterns of the shifting fuels.

3. The Combustion of the Plant Fuels: Coal, Petcoke, Oil and Alternative Fuels

Different fuels burn at different speeds, and the gas composition of the plant watches the mixture: coal ignites with the volatiles, the volatile matter 20 to 35 percent in bituminous grade: the flame with a low volatile coal is slow and long, it needs the high secondary air temperature and the long radiation path: petcoke is the material with the highest char content and the sulfur of 5 to 7 percent: petcoke burns as a slow char particle, it requires a hot kiln inlet, the oxygen and a residence time: the flame of the petcoke is brilliant and slow: the oil and the gas burn in the vapor phase and deliver the shortest, hottest, most maneuverable flame: the alternative fuels: tyres, waste-derived, sewage sludge, solvents: burn as the mixture and alter the gas composition with each recipe.

• The volatile yield: the fuel fraction that leaves the particle before the char burns: high volatile coal releases the energy in the kiln early, the flame becomes longer and the calciner fuel management changes;
• The ash chemistry: the ash of the fuel mixes with the kiln feed: the combustion of millions of tons brings the SO3, the chlorine and the alkalis into the gas and the dust: the analyst watches;
• The moisture effect: every percent of fuel moisture inflates the gas volume by the water vapor and carries heat: the dried coal of the plant mills to less than 2 percent moisture, the petcoke similar;
• The sulfur splits: the fuels with the high sulfur form the SO2, partially the SO3, which concentrates the alkalis and chloride released from the feed: the raw gas limit set the emissions;
• The alternative fuel limits: the calorific value, the chlorine content, the heavy metals and the moisture gates: the gas volumes change plus minus 15 percent from the base coal;

The engineering rule of the file: the gas volumes of the plants are always planned for the worst fuel: the flammability of the fuel is the other side of that coin: the coal mill safety, the storage of the fuels: the entire discipline has a dedicated chapter of the package, and the gas composition section quotes it when the volatile content and the O2 minima appear in the flame conversations.

The practical combustion check of an operator shift: sampling of the fuel, the weigh and the moisture, then the O2 reading at the kiln inlet, then the CO trend: the numbers in the table of section 2 apply: the O2 above the 4.5 percent means wasted heat: below 1.5 percent the CO appears and the flame collapses: the operator keeps the steady band and the plant monitors all three readings at one glance.

4. The Air System: Primary, Secondary and Tertiary Air

The flame is assembled from three air streams, and the gas composition of the kiln is the signature of their proportioning: the primary air is the stream that enters with the fuel: it is cold, one to three percent for the modern low-NOx burners, and in the fluidized and the swirl designs it shapes the recirculation zone at the burner tip: the secondary air is the preheated air from the clinker cooler that enters the kiln hood around the burner pipe: it is the main combustion air of the kiln, 850 to 1100 °C in a modern plant: the tertiary air is the branch that leaves the cooler hood and runs in its own duct to the calciner: the calciner burns 55 to 65 percent of the total heat and depends on that hot air, and its failure starves the whole line.

• Primary air ratio: 5 to 10 percent of the total combustion air: high enough to carry and spread the fuel, low enough to keep the NOx low: the low NOx burners push it back to 3 to 5;
• Secondary air temperature: the first target of the cooler: below 750 °C the flame detaches and the heat transfer to the feed deteriorates, above 1100 °C the burner parts suffer;
• Tertiary air duct: its damper divides the air between the kiln and the calciner: the split is one of the sensitive variables of the whole line: the sensor is the kiln inlet oxygen and the oxygen in the calciner gas;
• The cooler air balance: the cooler receives all the combustion air plus the false air of the cooler seals: the excess leaves through the cooler vent, and the vent air is part of the stack gas of the plant;
• The air leakage: the false air at the kiln seal, the preheater flanges and the mill flaps dilutes the gas and cools the system: each leakage drops the oxygen measured and raises the specific heat consumption: the tight kiln is the cheap flame.

The air split appears in the gas data as two complementary signatures: the kiln inlet oxygen rises when the tertiary damper feeds the calciner and the kiln is starved: the calciner oxygen shows the burn there: the operator steers the ratio until the kiln inlet oxygen holds 2.0 to 3.5 percent, the calciner exit oxygen 1.0 to 2.5 percent, and the CO stays at zero: the file ranks this double check as the first skill of combustion control.

Typical air and gas distribution of a precalciner kiln, 5000 t/d:

Flow	Volume at operating conditions	Share of combustion air	Temperature °C
Primary air	6 to 10 Nm³/min	5 to 9%	ambient to 120
Secondary air	—	55 to 60%	900 to 1100
Tertiary air	—	30 to 40%	800 to 950
Kiln exit gas (wet)	1.6 to 2.0 Nm³/kg clinker	—	850 to 1050
Preheater exit gas (wet)	2.1 to 2.6 Nm³/kg clinker	—	280 to 340
Stack gas (dry)	1.9 to 2.4 Nm³/kg clinker	—	85 to 130

The cold leakages of the conditioning tower and the baghouse inflate the stack flow: the difference between the preheater exit gas and the stack gas is the leakage audit of the plant: the file teaches the measurement of volumes at the three points with the pitot traverses and the calculation of the leakage by the O2 comparison: the leakage target is under 15 percent from the preheater to the stack.

5. The Gas Train of the Preheater: Velocities, Temperatures and Pressures

The gas leaving the kiln at 850 to 1100 °C carries the dust, the alkalies and the heat: it enters the lowermost cyclone stage and climbs against the material: each cyclone is a gas cleaning and heat exchange step: the gas temperature drops by 80 to 160 °C per stage while the material temperature climbs stage by stage: the five-stage preheater of a modern kiln exchanges the gas down to about 300 to 340 °C at the top: the performance of the train is the economy of the plant: every 20 °C of the top gas temperature is worth about 30 to 40 kilocalories per kilogram of clinker.

• Stage geometry: the cyclone diameter grows towards the top as the gas expands and cools: the inlet velocity of the gas holds 15 to 22 meters per second: the cyclone separator efficiency above 90 percent per stage;
• The pressure profile: every stage draws about 400 to 700 Pa, the full preheater 2000 to 4500 Pa on the exit fan: the delta across each stage is the fixed discipline of the draft;
• The temperatures: stage 5 the gas at 850 to 950 °C; stage 4 at 700 to 800; stage 3 at 550 to 650; stage 2 at 420 to 520; the top at 300 to 360: the curve of the heat exchange;
• The calciner: in the precalciner system the gas of the calciner and the kiln mix above the last stage: the oxygen of the mixture 1.0 to 2.8 percent: the combination of the two flames;
• The dust recirculation: the alkali rich dust travels in the gas and returns with the feed: the cyclone efficiency and the dust load interact, and the blockage pyramids form when the coating teams at 850 to 1100 reach a dead-point;
• The riser duct: the gas accelerates the material in the riser and the pneumatic transport is complete between stages: the velocity must exceed the saltation of the coarse fraction.

Typical pressure and temperature table of the five-stage preheater (wet/gas data, indicative values of a 3000 to 5000 t/d line):

Stage	Gas temperature °C	Pressure Pa (relative inlet)	Material temperature °C
Cyclone 1 (top)	300 to 340	-4300 to -4800	280 to 320
Cyclone 2	440 to 520	-3700 to -4100	400 to 480
Cyclone 3	560 to 650	-3000 to -3400	520 to 610
Cyclone 4	700 to 800	-2200 to -2600	650 to 750
Cyclone 5 (bottom)	850 to 950	-1400 to -1700	800 to 880

The pressure table is the identity card of the preheater: blocked stage, the material avalanches and the pressure collapses: a collapsed cyclone loses the seal and gas short-circuits, the temperature of the exit jumps: the operator who knows the traces of his five stages reads the preheater trouble in seconds: the improvement chapter of the file records the evening cases and their traces.

6. The Draft Management: From the Kiln Hood to the Stack

The draft is the driving force of the gasflows: the induced-draft fan at the baghouse pulls a negative pressure through the whole system, and balanced negative pressures at each stage keep the flows moving and the dust out of the building: the draft is not a constant: it is adjusted live for the fuel changes, the cycl in the cooler, the cleaning of the baghouse and the weather conditions of the stack discharge: the draft management is 90 percent of the “pressure game” of the operator’s shift.

• The draft distribution: ideally the burners operate at the neutral to slightly negative hood pressure: the plant holds -20 to -60 Pa at the kiln hood to protect the seals and the hall;
• The fan curve handling: the ID fan at the damper or the variable speed: each 10°C of the inlet gas temperature changes the fan volume and the pressure: the winter and the summer runs differ;
• The mill pulverizer influence: the raw mill and the cement mill connected to the kiln duct and the preheat duct: the mill running with the kiln direction shares, stops and their flaps change the draft;
• The bypass and the vent: the chloride bypass, the condition tower, the coal mill exhauster: each branch adds and consumes the draft: the war of the pressure;
• The stack discharge: the low exit velocity of the gas with the high moisture risks the downwash: the exit velocity of 12 to 18 m/s and the stack height cover the local environment;
• The draft anomalies: a fouled cyclone, a broken probe, a rattling flap: the draft traces the mechanical health of the chain: the file includes the anomaly catalog with each symptom and its cause.

The control loop of the modern plant sets the kiln hood draft constant and lets the ID fan chase the set point: the plant card typically: kiln inlet oxygen 1.8 to 3.5, kiln exit gas 950 to 1050 saturated, the preheater exit 305 to 345: if the oxygen drops while the draft rises: the calciner has too much fuel: if the oxygen holds and the temperatures drift: the feed or the fuel has changed: the trio of the readings resolves every routine puzzle.

7. The Gas Composition in Operation: O2, CO2, CO and Their Meaning

The gas analysis of the kiln line is the lab report of the combustion: the oxygen tells how much air arrived, the carbon dioxide tells how completely the fuel burned, the carbon monoxide tells the incompleteness of the burn, and the nitrogen oxides tell the temperature history of the flame: each measurement is a witness, and the file trains the operator to read them together and to distrust any one number alone.

• O2 at the kiln inlet: the combustion air of the kiln, typically 1.5 to 4.0 percent: below 1.5 the reducing atmosphere harms the clinker and melts the chains, above 4.0 the heat is wasted;
• CO at the kiln inlet: the flagship alarm: above 0.5 to 1.0 percent the combustion is incomplete, the flame is starving, and the CO burn-out threatens the baghouse fires: the analyzer at the preheater exit guards the ESP and the filters;
• CO2 by the analyzer: 22 to 28 percent in the kiln inlet gas in the cement process: the CO2 comes from the fuel and the feed decarbonation, and its value checks the O2 measurement: the redundant pair;
• NOx: 200 to 1200 ppm typical from the kiln flame: the high flame temperature, the excess air and the nitrogen of the fuel drive it: the NOx emission limits push the plants to the low-NOx burners and the staged combustion;
• SO2: the sulfur of the fuel and the feed: 10 to 400 mg/Nm³ at the stack after the alkali absorption: the SO2 spikes announce the raw material changes and the kiln atmosphere changes;
• The dew point and the moisture: the water vapor 6 to 12 percent by volume: the dew point of the stack gas drives the acid condensation risk at the cold end: the instrumentation and the duct linings respect the acid dew point.

The interpretation matrix of the combustion analysis:

Symptom	Likely cause	First response
O2 high, CO zero	excess air, false air in the kiln or the preheater	reduce the fuel, hunt the leakages
O2 low, CO rising	fuel excess, poor mixing, flame starvation	raise the primary air, cut the fuel feed
CO2 falls with O2 steady	fuel change to lower carbon, or the feed changes	verify the fuel quality, weigh the feed
NOx spike	hot spot in the burning zone, high excess air	staged air, check the burner, reduce the kiln heat
SO2 sudden rise	raw material with the pyritic sulfur, kiln reducing	check the kiln atmosphere, sample the raw mix
O2 jumps during mill off	flap leakage at the mill branch	close the flaps, re-seal the branch

The matrix is the working table of the shift: it is not the recipe for every plant, because every line has its own offsets: the file instructs the plant engineer to build his own matrix with the site-specific set points after the baseline measurements: the table of the file is the skeleton, the data of the plant the flesh.

8. The Measurement Devices: Probes, Analyzers and Their Maintenance

The gas composition is only as good as the instruments: the cement plant is the harshest sampling environment of the process industry: dust 50 to 500 g/Nm³ at the kiln inlet, temperatures to 1100 °C, and the sticky alkali and chloride coatings: the analyzer reliability is a maintenance discipline of its own, and the file dedicates a full chapter to it.

• The sampling probe: water-cooled or air-cooled lance at the kiln inlet and the preheater exit: the sintered metal or ceramic filter at the tip stops the dust: the back-purge cycles with the compressed air keep it open;
• The gas conditioning: the heated sample line at 160 to 180 °C keeps the water vapor, then the cooler and the membrane dryer drop it: the SO2 dissolves in the condensate, the plant measures SO2 with the hot, wet analyzers or accepts the correction;
• The O2 analyzer: the zirconia cell is the standard: the cell measures the oxygen partial pressure at 600 to 700 °C: the response is seconds and the drift is calibrated weekly with the span gas;
• The CO analyzer: the infrared (NDIR) analyzer is the standard: the CO interferes with the SO2 and the moisture in the IR band: the cross-interference correction is set in the analyzer parameters;
• The NOx analyzer: the chemiluminescence or the NDIR: the sample conditioning must dry before the measurement: the calibration every 2 weeks with the certified bottles;
• The calibration discipline: the zero and span gases daily or weekly, the quarterly audit against the portable analyzer, the record of the drift: the certification of the emission reports depends on it.

Typical analyzer plan of a 5000 t/d line: the kiln inlet probe with O2 and CO: the preheater exit with O2, CO, NOx, SO2: the stack with O2, CO, NOx, SO2, dust: the raw mill inlet and exit for the process and the safety: the bypass with its own gas train: the sample points are the ears of the control room: the file includes the site layout drawing of the typical probe positions and the maintenance schedule of the sample lines, week by week.

9. Gas Flow Corrections: Standard Conditions, Moisture and the Nitrogen Basis

Raw analyzer numbers are the truth of the probe point, but the comparison across the plant needs the corrections: gas volumes are reported in the standard conditions (usually 0 °C, 1.013 bar), the moisture of the sample must be known, and the oxygen and the pollutants are commonly normalized to the reference oxygen of 10 or 11 percent for the emission permits: the uninitiated compare the raw O2 at the kiln inlet with the O2 at the stack and the whole analysis becomes confusing: the file orders the corrections.

• The standard volume: the gas volumes convert with the pressure and temperature factors: V_std = V_actual x (P/1.013) x (273/T): the volume balances of the plant run only in the standard cubic meters;
• The wet and dry basis: the analyzers measure the dry gas after the condenser, the process balances want the wet gas: the moisture 6 to 12 percent shifts every percentage point of the dry measurement;
• The reference oxygen: the emission regulations express the pollutant concentration at the reference O2 (e.g. 10% for the cement kilns in many jurisdictions): C_ref = C_meas x (21-O2_ref)/(21-O2_meas): the comparator of the compliance;
• The nitrogen basis: the fixed nitrogen allows the back-calculation of the excess air from the measured O2: each O2 percent corresponds to a lambda: the operator card in the file lists the O2 to lambda table from 1.0 to 5.0 percent;
• The dilution check: a sudden drop of CO2 in the dry gas with the steady O2 means the false air, not the fuel change: the ratio CO2/O2 flags the leakage before the pressures react: the early warning of the tightness loss.

The correction chapter of the file contains worked examples with the actual plant numbers: the preheater exit measured at 0.9 percent O2 dry, corrected to the wet basis and to the 10 percent reference: the calculations take minutes by hand and seconds in the Excel tool of the package: the corrected numbers are the ones that enter the heat balance and the emission report, and the file is clear: never compare uncorrected measurements across the different points of the line.

10. The Bypass and the Chloride Circuits in the Gas Phase

Alkalis, sulfur and chlorine evaporate in the burning zone, travel in the gas and condense on the colder material: the circuits concentrate them until the coatings, the blockages and the build-ups attack the preheater: the chloride bypass is the plant’s escape valve: a fraction of the kiln exit gas, 3 to 12 percent depending on the raw material, is drawn aside, quenched with the air and cooled, and its dust, the chloride and the alkali-rich fraction, leaves the process: the gas composition at the bypass is the fingerprint of the emerging evil, and the file explains the reading.

• The bypass flow control: the extraction rate balances the chloride removal: the fixed percent depends on the raw material chlorine: 0.01 to 0.02 percent in the raw mix needs 3 to 6 percent, above that 10 to 15 percent;
• The quenching: the hot gas 800 to 1100 °C meets the water mist and the air at 40: the alkali chlorides condense on the dust particles, the sticky compounds solidify, the filters survive;
• The alkali cycle readings: rising chloride and sulfate in the kiln feed dust signals the recirculation: the bypass on, the dust purged, the build-up pressure drops: the pressure swings and the exit gas temperatures interact with the cycle;
• The bypass gas analysis: the O2 in the bypass gas confirms that the false air is not diluting the extraction: the dust concentration 30 to 60 g/Nm³ with the chloride enriched fraction: the sample train of the bypass has its own cleaning schedule;
• The economic balance: the bypass waste gas and the purge dust and the heat cost: the plant runs the minimal bypass that keeps the system clear: the file includes the selection chart of the bypass rate against the raw material chlorine.

The chloride circuit is the most costly invisible loop of the gas phase: the file recommends the weekly dust analyses of the bypass, the preheater stage 5 and the kiln inlet: the comparison of the three dusts is the diagnosis: a growing chloride content in the stage 5 dust means the bypass is too small: the gas analysis alone cannot see the chlorides, but the dust behind the gas tells the whole story: the two disciplines, gas and dust, cross-check.

11. The Combustion Driving: The Flame Pattern and the Operator Recipes

The operator controls the combustion through the fuel rate, the air splits and the feed rate: the goals are the stable kiln inlet oxygen, the zero CO, the steady burning zone temperature and the NOx within the emission limit: the combative game of the modern kiln is the trade-off between the three extremes: starve the flame and the CO rises, overfeed the air and the heat leaks: heat the zone and the NOx climbs: the file presents the classical recipes:

• The normal recipe: kiln inlet oxygen 2.0 to 3.0, primary air 7 to 9 percent, secondary air 900+ °C, fuel finely ground at 90% minus 90 microns: the line runs the hour with the small corrections;
• The low NOx recipe: primary air to 4 to 5 percent, the flame staged, the calciner given the extra fuel: kiln inlet oxygen 1.5 to 2.5: the NOx drops 20 to 40 percent at the same heat;
• The high volatile coal recipe: the long flame: the operator shortens the flame with the higher primary momentum and accepts the slightly higher NOx: the response is the faster temperature in the low zones;
• The alternative fuel recipe: the shredded solids enter at the calciner, the gas volume rises with the moisture: the oxygen set points of the calciner hold, the kiln oxygen may drop: the compensation with the tertiary air;
• The upset recipe: the feeding stops, the load collapses, the flame sees the empty kiln: reduce the fuel immediately, take the O2 up, protect the refractory: the gas analysis is the only real protection in the minutes of the event.

The daily combustion log: the file proposes the one-page shift log: the fuel rate, the calorific value of the blend, the kiln inlet O2/CO/NOx at hours, the preheater exit temperature and the draft, the bypass rate: the shift compares with the previous shift and the best day of the month: the log is the archive where the plant finds the recipe drift before it becomes an outage: the gas tables of the article are the reading keys of that log.

12. The Gas Balance in the Reports: From the Operator Screen to the Heat Balance

The gas data is not only the control of the shift: it feeds the heat balance of the line, the emission report and the plant monthly KPI: the waste gas loss is the biggest single loss of the kiln system, and its calculation is a gas exercise: the sensible heat of the wet gas = the gas volume x the mean specific heat x the temperature: at 320 °C preheater exit, that waste is 100 to 140 kcal/kg clinker, up to 18 percent of the total heat input: the cooler vent and the incomplete combustion add their shares: the sum of the losses is the budget that the efficiency projects attack.

• The waste gas loss calculation: the measured volume at the standard conditions, the mean cp of the CO2, the H2O, the N2 and the O2 mixture: the Excel tool of the package runs it from the analyzer records;
• The unburnt losses: the carbon in the fly ash and the CO in the gas: the CO of 0.1 percent in the preheater exit gas wastes about 3 kilocalories per kg clinker: the small percentages, the large sums at 1.5 million tons a year;
• The radiation and the convection: the kiln shell and the preheater walls: 6 to 12 percent of the heat: the repairs of insulation are repaid by the gas analysis: the fixed loss of the line;
• The temperature record: the exit gas temperature is the monthly KPI: the plants trend it against the production, the season and the fuel: the drift of 10 °C warrants the investigation;
• The CO2 accounting: the scope 1 emissions from the clinker process and the fuel: the gas analysis and the clinker production compute the verified tonnages: the file includes the emission calculation chapter and the sample report structure.

The heat balance table of the file (the gas columns): the waste gas at the top gas 130 to 145, the kiln shell 45 to 60, the cooler vent when wrong 20 to 90, the clinker heat 40 to 55 and the chemical heat of the clinker reaction 1750 while the coal used 3000 to 3400 at the 720 kcal/kg benchmark: the operator and the engineer read one paragraph of this table at the monthly meeting: the gasflows and the gas composition, their numbers in MOTER the whole story: the article closes with the measurement being the memory of the month.

13. The Gas Audit of the Plant: The Annual Measurement Campaign

Once a year, the plant performs the gas survey: the pitot-static traverses across the ducts, the simultaneous gas sampling at the kiln inlet, the preheater exit, the raw mill and the stack, the leakage tests, the temperature profiles: the deliverables of the annual audit in the file: the complete flow map of the line, the oxygen balance with the leakage of each duct, the O2 corrected to the 10% reference at the stack, the heat balance inputs, the recommendations numbered in the order of payback.

• The traverse grid: the 3 x 4 grid across the circular duct: static and dynamic pressure measured at every point: the flow = the mean velocity x the area: the accuracy of the pitot runs needs the straight duct length;
• The emission run: the simultaneous stack sampling of NOx, SO2, CO, dust by the certified method: the 3 one-hour runs: the average under the limit: the report of the compliance;
• The leakage matrix: the O2 measured before and after every fan: the leakage percent = (O2 after – O2 before) x 21 / (21 – O2 first): the ranking of the leaks:
• The instrumentation audit: the analyzer cell swap, the calibration coefficients, the response times measured: the sample line of the kiln inspected and cleaned;
• The findings book: the leaks at the seal, flap positions, fan blade deposits, baghouse damages: each finding with the value: the investment list for the next overhauls:

The annual campaign is the honest scorecard of the gas management: the file of the package is the instruction manual of the campaign, with the forms, the tables and the checklist: a plant that runs the campaign and fixes ten findings can save 3 to 8 kilocalories per kilogram: the gas knowledge, bought with the measurements: it is the annual review of the combustion work, and the next year’s baseline: the file ends with the blank forms so the plant can photocopy them forever.

13. The Frequently Asked Questions

What oxygen values should I hold at the kiln inlet?

The modern precalciner plant holds 1.5 to 3.5 percent at the kiln inlet with CO at zero: below 1.5 the atmosphere turns reducing, the flame starves and the risk of the CO explosion grows: above 4.0 the heat leaks with the surplus air: the exact window depends on the fuel, the burner and the false air of the plant, and the file shows how to find the own window with the controlled tests.

Why is my CO analyzer always showing a ghost reading?

The NDIR CO reading is cross-sensitive to SO2 and the moisture: the untreated sample gives higher values: the conditioning train with the dryer and the interference correction in the analyzer must be checked first, then the probe purge, then the zero gas: the file includes the troubleshooting tree of the analyzer chain with the eleven most common symptoms.

Is the wet or the dry O2 basis used for the emission reports?

The regulations usually normalize the pollutants to the reference oxygen and the dry basis: the process control of the plant is live on the dry measuring instruments, and the report converts: the conversions are in chapter 9 of the file with the table and the examples: never mix the two bases in one comparison, the error of 1 percent basis is enough to misplace the compliance by a wide margin.

How do I check the tertiary air distribution without the flow meter?

Flow the oxygen at the kiln inlet and the calciner: opening the tertiary damper reduces the kiln inlet oxygen, and the control holds it: the temperature asymmetry of the two flames infers the split: the pitot traverse during the annual campaign verifies the absolute values: the two instruments of the plant are the only flow meters of the tertiary air: the report of the audit includes the calibration.

Does the gas analysis predict the cyclone blockages?

The pressure and the temperature of the blocked stage give the warning first: the exit temperature of the stage above the weaker, the pressure profile distorts: the gas samples at the preheater exit also jump in the O2 when the material shortage lets the hot gas bypass the coldest stage: the file teaches the pattern catalog of the blockages with the combination traces: the weekly database of the plant detects the drift days before the blockage builds.

14. Conclusion

The combustion, the gasflows and the gas composition are the single body of the kiln process: the fuel and the air meet in the flame, the gas carries the heat through the preheated stages, the analyzers report the justice: the operator who reads the O2, the CO and the temperatures like the letters of an alphabet holds the highest economic lever of the plant: the heat is the largest variable cost of the clinker, and the gas is its voice.

The Complete Cement Technical Package includes the Combustion, Gasflows and Gas Composition reference with the full tables, the worked balances and the Excel gas calculation tools: the one-time 249.99: the instant download: the library of the cement plant: the combustion knowledge of the operator: the file of the flame, the kilo of the plant: the professional, steady.

This file is part of the Complete Cement Technical Package (931 files) available from cementequipment.org. Respective rights holders; library copy for the licensed single user.