Kiln Audit H M Balance Calculation: Complete Guide & Downloa

The kiln audit with the heat and the mass balance calculation is the complete diagnostic examination of the kiln system: the measurements of the flows, the temperatures, the pressures, the gas compositions and the compositions of the materials, organized into the mass balance (what goes into the kiln equals what comes out) and the heat balance (where the thermal energy goes), and reported with the findings and the recommendations that the plant implements. The workbook of this article is a full kiln audit calculation tool from the year 2012: a large working file (2.54 MB) of the audit campaign of the period, carrying the complete calculation structure of the heat and the mass balance of a kiln line, the audit data sheets, the computed balances and the comparison rows that the audit engineer of the 2012 practice used to examine the kiln system.

This article rebuilds the complete methodology of the kiln audit: the scope of the audit, the measurement campaign and the instruments, the mass balance of the kiln system (the feed, the fuel, the air, the clinker, the dust and the gas streams), the heat balance with the seven standard terms and their formulas, the worked numbers of a complete audit example, the interpretation of the closing errors, the audit report structure and the action plan. The Complete Cement Technical Package (931 files: the handbooks, the courses, the Excel tools and the audit workbooks, $249.99 one-time, instant download through the secure PayPal payment) delivers the kiln audit workbook together with the complete library of the kiln process tools.

1. The Scope of the Kiln Audit

The kiln audit is the diagnostic examination of the whole pyro-processing line, and its scope covers the complete chain from the kiln feed to the clinker: the preheater, the calciner, the rotary kiln, the burner and the clinker cooler. The audit of the 2012 practice was the systematic campaign: the plant invites the audit team (the process engineers of the technical services, often with the equipment suppliers), the measurements run for the 48–72 hours of the stable operation, and the balances and the findings follow in the weeks after:

• The process audit: the performance of the preheater and the calciner (the cyclone efficiencies, the heat exchange, the degree of the calcination), the kiln (the flame, the burning zone temperature, the coating, the retention time, the kiln loading), the cooler (the recuperation, the air distribution, the clinker temperature) and the burner (the momentum, the primary air, the flame shape);
• The energy audit: the heat and the mass balance of the system: the specific heat consumption, the loss terms and the efficiency: the core calculation of the audit workbook: the fuel consumption against the production, the losses ranked and quantified;
• The mass audit: the material flows around the system: the raw meal in, the clinker out, the dust returned and emitted, the bypass flow: the reconciliation of the weighing and the conveying systems;
• The equipment audit: the mechanical condition of the kiln (the alignment, the tyres, the shell ovality, the drive), the refractories (the residual brick thickness, the coating), the cooler grates and the fans: the condition part of the audit;
• The control audit: the control loops, the instrument calibrations, the operator practices: the human and the automation part of the performance.

The audit delivers the three deliverables: the balances (the numbers), the findings (the deviations from the design and the best practice) and the recommendations (the ranked actions with the expected effects). The workbook of the package is the calculation engine of the first deliverable and the evidence base of the other two.

2. The Measurement Campaign and the Instruments

The quality of the audit stands on the measurement campaign, and the campaign of the 2012 practice used the combination of the plant instruments (calibrated for the audit) and the temporary specialist instruments (installed for the campaign):

• The flow measurements: the kiln feed on the calibrated weighers (the belt weighers of the kiln feed with the check against the silo levels), the fuel flow (the coal weigher and the fuel density for the liquids), the gas flows by the pitot tube traverses in the ducts (the preheater exit, the cooler exhaust, the bypass): the flow measurements are the foundation of the mass balance;
• The temperature measurements: the thermocouples and the pyrometers of the process (the preheater stages, the kiln inlet, the nose, the secondary air), the surface temperatures by the IR scanner (the kiln shell), the clinker temperature at the cooler exit: every heat term of the balance needs its temperature;
• The gas analysis: the portable and the fixed analyzers of the O2, the CO2, the CO and the NOx at the preheater exit, the kiln inlet, the calciner and the cooler: the gas analysis gives the excess air, the completeness of the combustion and the nitrogen balance basis of the gas flows;
• The material sampling: the raw meal, the kiln feed, the hot meal at the stages, the clinker, the dust and the coal: the chemical analyses (the oxides, the LOI, the sulfur, the alkalis, the calorific value of the fuel): the composition data of the mass balance and the quality check of the process;
• The pressure measurements: the draft at the preheater stages, the kiln inlet and the cooler: the pressure profile reveals the blockages, the false air and the fan performance: the complementary diagnostics of the campaign.

The measurement campaign of the audit collects the data set of the 48–72 hours, the averages of the stable operation periods, and the workbook organizes the data into the input sheets from which the balances compute: the audit is only as good as the campaign, and the campaign is only as good as the instrument discipline.

3. The Mass Balance of the Kiln System

The mass balance of the kiln system is the accounting of the material streams: everything that enters the system (the raw meal, the fuel, the combustion air, the false air) leaves it (the clinker, the exhaust gas, the dust, the cooler air), and the audit computes the balance in the tonnes per hour and the kilograms per kilogram of clinker:

• The solid streams: the raw meal into the preheater, the clinker out of the cooler, the dust returned to the system (the kiln feed dust, the cooler dust), the dust emitted (the bag filter catch or the stack loss) and the bypass dust: the solid balance: the feed, the clinker and the dust reconciled with the clinker factor: the raw meal of 100 tons produces the clinker of the 61–65 tons (the factor of the 1.54–1.64) plus the dust and the emitted fines;
• The fuel stream: the coal, the petcoke or the alternative fuel into the kiln and the calciner burners: the ash of the fuel joins the clinker (the ash absorption: the coal ash of the 10–20 percent at the 90–110 kg coal per tonne of the clinker adds the 10–20 kg of the ash per tonne of the clinker, the part of the raw mix design);
• The gas streams: the combustion air (the primary, the secondary, the tertiary, the cooler air), the combustion products and the calcination CO2 leave as the exhaust gas: the gas mass balance: the exhaust gas of the 1.35–1.55 Nm3 per kg of the clinker at the 1.18–1.25 kg/Nm3 = the 1.6–1.9 kg of the gas per kg of the clinker;
• The nitrogen balance method: the nitrogen enters the system only with the air and the fuel, and leaves only with the exhaust gas: the measured O2 and the CO2 of the exhaust fix the air flow and the gas flow through the nitrogen: the standard method of the audit: the gas flow of the balance is derived, not guessed;
• The closing of the mass balance: the audit tolerance of the ±2–3 percent: the imbalance beyond the tolerance indicates the false air (the air entering without the measurement), the weighing errors or the unaccounted dust: the mass balance audit of the instruments themselves.

The mass balance gives the audit the stream flows that the heat balance needs: the fuel flow and the gas flows of the heat balance come from the mass balance, and the reconciliation of the mass streams is the first diagnostic of the system.

4. The Heat Balance of the Kiln System: The Terms

The heat balance of the audit divides the thermal energy of the system into the standard terms, and the 2012 audit workbook computes each term with the formulas of the industry practice:

Heat term	Typical value (kcal/kg clinker)	Basis of the calculation
Theoretical heat of clinker formation	400–430	Raw meal composition, calcination and clinker phase formation
Sensible heat of preheater exhaust gas	120–160	Gas volume (N2 balance), temperature, mean specific heat
Sensible heat of clinker	15–35	Clinker temperature at cooler exit (100–150°C)
Cooler exhaust air loss	50–90	Excess cooling air flow and temperature
Shell radiation and convection	30–60	Surface temperatures, areas, U-coefficients
Dust loss	5–15	Dust flow, temperature, specific heat
Bypass and unaccounted	0–30	Bypass flow and closing error

• The input side: the heat of the fuel combustion (the fuel flow × the net calorific value, the 85–95 percent of the input), the sensible heat of the fuel, the raw meal and the air: the sum of the inputs;
• The output side: the theoretical heat, the exhaust gas, the clinker, the cooler air, the shell, the dust and the unaccounted: the sum of the outputs;
• The closing error: (the inputs − the outputs) / the inputs: the audit accepts the error below the 3–5 percent and investigates above: the closing error of the 2012 audit workbook is the report card of the measurement campaign;
• The specific heat consumption: the total input per kilogram of the clinker: the headline number of the audit: the 720–800 kcal/kg for the modern five-stage precalciner lines of the period, the 800–900 for the four-stage and the 900–1,200 for the long dry kilns.

The heat balance of the audit is the energy report of the kiln: the terms, the percentages and the comparison with the design and the benchmarks, all computed in the workbook from the campaign data.

5. The Worked Example of the 2012 Audit Balance

Follow the complete worked example of the kiln audit balance in the style of the 2012 practice: the five-stage precalciner line at the 5,000 tons per day of the clinker (208.3 t/h), the coal at the 22 MJ/kg (5,260 kcal/kg), the kiln feed at the 1.60 clinker factor (333.3 t/h), and the measured campaign data of the stable 48 hours:

• The mass balance: the feed of the 333.3 t/h with the factor of the 1.60 gives the clinker of the 208.3 t/h: the measured clinker on the cooler belt weigher at the 210 t/h: the reconciliation at the 0.8 percent, within the tolerance: the dust return of the 12 t/h, the bag filter catch of the 1.5 t/h, the bypass of the 3 percent of the kiln gas: the mass streams of the balance close at the 98.2 percent, the healthy audit number;
• The fuel: the coal flow of the 28.4 t/h at the 5,260 kcal/kg gives the heat input of the 149.4 million kcal/h: the specific input of the 149,400,000 / 208,300 = 717 kcal/kg: the sensible heats of the fuel, the meal and the air add the 12 kcal/kg: the total input of the 729 kcal/kg;
• The theoretical heat: from the raw meal and the clinker composition: the 420 kcal/kg, the 57.6 percent of the input;
• The exhaust gas: the gas flow from the nitrogen balance of the 1.38 Nm3/kg at the exit temperature of the 320°C with the mean specific heat of the 0.32 kcal/Nm3 °C: the 1.38 × 320 × 0.32 = 141 kcal/kg: the largest loss of the line;
• The cooler loss: the excess cooler air at the 65 kcal/kg, the clinker at the 120°C at the 19 kcal/kg, the shell at the 38 kcal/kg, the dust at the 8 kcal/kg, the bypass at the 12 kcal/kg: the total output of the 420 + 141 + 65 + 19 + 38 + 8 + 12 = 703 kcal/kg;
• The closing: the input of the 729 against the output of the 703: the closing error of the 3.6 percent, the accepted audit tolerance, recorded in the unaccounted row of the workbook: the audit reports the balance with the error and the identified causes (the false air at the kiln inlet, the instrument drift of the coal weigher).

The worked example shows the complete method of the audit calculation: the mass streams, the heat terms, the closing and the interpretation, in the exact structure that the audit workbook of the package implements with its 2.54 MB of the 2012 audit data and formulas.

6. The Process Diagnostics of the Audit

Beyond the balances, the audit examines the process performance of each component of the system, and the 2012 audit workbook carries the diagnostic sheets of the line:

• The preheater: the cyclone collection efficiencies (the material balance of each cyclone: the 88–96 percent of the individual cyclones, the 95–99 of the effective separators), the heat exchange profile (the gas and the meal temperatures at the stages), the draft profile and the blockages: the audit findings of the tower (the cyclone fouling, the false air at the flanges) explain the high exhaust temperature;
• The calciner: the degree of the calcination at the kiln inlet (the 90–95 percent in the healthy lines, measured by the LOI of the hot meal), the fuel burn-out in the calciner, the tertiary air flow and its temperature: the calciner findings (the incomplete burn-out, the maldistribution of the meal) affect the kiln stability and the fuel split;
• The kiln: the burning zone temperature (the 1,400–1,500°C by the pyrometer), the shell profile and the coating, the kiln loading (the 4–8 percent of the volume), the retention time (the 20–30 minutes), the secondary air temperature (the 800–1,100°C) and the free lime of the clinker: the kiln findings of the 2012 audit (the coating instability, the burner settings) are the classic causes of the fuel and the quality problems;
• The cooler: the clinker temperature at the exit, the recuperation efficiency (the 65–75 percent), the air distribution across the grate, the fan flows and the pressures: the cooler findings (the over-aeration, the worn grates) show in the cooler loss term of the heat balance;
• The burner: the primary air ratio, the momentum, the flame shape observation: the burner findings of the audit (the low momentum, the asymmetric flame) cause the coating and the refractory issues.

The diagnostics of the audit tie the balance numbers to the process causes: the high exhaust loss is explained by the cyclone findings, the high fuel consumption by the calciner and the burner findings, and the audit report presents the two sides together: the numbers and the causes.

7. The Mechanical and the Refractory Audit

The kiln audit of the complete practice includes the mechanical and the refractory condition of the equipment, and the 2012 workbook carries the data sheets of the condition survey:

• The kiln mechanics: the shell ovality (the deformation of the rotating shell under the tyres: the standard of the 0.1–0.3 percent of the diameter), the tyres and the rollers (the clearances, the temperatures, the alignment), the kiln axis alignment (the laser survey), the drive (the current, the vibration, the gear wear) and the kiln slope and the rotation speed: the mechanical findings (the ovality beyond the limit, the roller misalignment) increase the refractory wear and the shell temperatures;
• The refractory condition: the residual brick thickness along the kiln (the scanner profile and the inspection at the stops), the coating map of the burning zone, the brick types and the ages of the zones, the hot spots history: the refractory findings of the audit (the thin residual lining of the transition zone) predict the future stops and the shell losses;
• The cooler mechanics: the grate condition, the wear of the plates, the hydraulic drives, the fan and the damper conditions: the cooler findings of the audit (the uneven grate travel, the leaking dampers) degrade the recuperation;
• The fans and the draft: the preheater fan performance (the flow, the pressure, the efficiency from the measured curves), the cooler fans: the fan findings of the audit (the worn impellers, the wrong damper positions) cost the power and the process stability.

The mechanical and the refractory audit closes the loop of the findings: the energy numbers of the balances are the consequences of the mechanical conditions, and the audit report presents the causal chain: the ovality raises the brick wear, the brick wear raises the shell loss, the shell loss raises the fuel consumption: the repair of the mechanical root cause saves the energy.

8. The False Air and the Instrument Findings

The audit of the 2012 practice paid the special attention to the false air and the instrument condition, the two invisible losses of the kiln system:

• The false air measurements: the O2 profile along the preheater tower: the O2 of the exit gas minus the O2 of the kiln inlet gas reveals the air that leaks through the tower: the leak of the 10–20 percent of the gas flow through the flanges, the inspection doors and the sampling ports: each percent of the false air raises the exhaust gas volume, cools the gas and costs the heat: the audit quantifies the false air at each section with the O2 traverses;
• The kiln inlet false air: the air leaking at the kiln inlet seals (the old design with the poor sealing, the worn components) enters the tower directly, bypassing the burning zone and reducing the secondary air temperature: the false air of the 5–10 percent at the kiln inlet is the classic finding of the old kilns: the audit measures it with the O2 at the kiln inlet and the exit;
• The instrument calibrations: the audit checks the feed weighers (the zero and the span calibration, the check weighing), the coal weigher, the thermocouples (the immersion depth, the radiation shields), the gas analyzers (the calibration gases): the instrument findings of the audit (the biased feed weigher at the 2–3 percent, the misplaced thermocouples) explain the discrepancies of the balances;
• The correction actions: the sealing of the flanges, the door repairs, the instrument recalibrations: the low-cost actions with the immediate balance effect: the audit report lists them in the first action batch.

The false air and the instrument findings are the audit’s contribution to the measurement quality of the plant: the balances of the future are only as good as the instruments that feed them, and the audit’s instrument campaign improves both the audit accuracy and the daily process control of the plant.

9. The Audit Report Structure

The audit workbook feeds the audit report, and the report of the 2012 practice followed the standard structure that the package’s workbook supports:

• The executive summary: the one-page view of the audit: the specific heat consumption against the design and the benchmark, the closing errors of the balances, the top findings and the top recommendations with the expected savings: the page that the management reads;
• The balances: the complete heat and the mass balances in the tables and the charts of the workbook: the terms, the percentages, the comparison with the previous audits: the evidence pages;
• The findings: the numbered list of the deviations from the design and the best practice, each with the measured evidence, the location and the effect: the findings sorted by the severity;
• The recommendations: the action list with the priority (the immediate, the short-term, the planned), the responsible department, the investment and the expected saving: the action plan of the audit: the 2012 audit report structure ranks the recommendations by the payback: the false air sealing first (the zero capital, the 2–5 kcal/kg), the cooler optimization second, the preheater improvements and the refractory upgrades next, the WHR projects last;
• The appendix: the raw data of the campaign, the calibration records, the photos of the findings: the documentation of the evidence: the workbook of the package carries the raw data sheets of the 2012 campaign in its 2.54 MB.

The report structure converts the audit numbers into the management decisions: the executive summary gets the approval, the findings and the recommendations get the action, and the workbook provides the evidence and the calculation base of the whole chain.

10. The Follow-up: The Implementation and the Re-Audit

The audit closes with the follow-up cycle of the implementation and the re-audit, the practice that separates the effective audits from the shelf documents:

• The implementation tracking: the recommendations converted into the project list with the owners and the deadlines: the monthly review of the progress: the energy saving of each implemented action measured against the audit baseline;
• The re-audit: the follow-up audit after the 6–12 months (or after the major implementations) repeats the campaign and the balances: the comparison of the two audits shows the achieved savings: the specific heat consumption after the false air sealing and the cooler work of the example falls by the 20–40 kcal/kg, the measured proof of the audit value;
• The continuous monitoring: the plant adopts the audit’s measurement points as the daily monitoring instruments: the O2 profile, the shell scan, the gas flows: the audit’s campaign becomes the plant’s routine: the numbers of the audit workbook become the daily screens of the control room;
• The audit cycle: the annual audit of the practice: the baseline of the year, the findings of the year, the actions of the year and the re-audit of the next year: the continuous improvement loop of the kiln performance, with the audit workbook of the package as the standing calculation engine of the loop.

The follow-up cycle is the purpose of the audit: the numbers without the action are the archaeology, and the action without the numbers is the guesswork: the audit workbook of the package carries the whole cycle, from the raw data of the campaign to the comparison of the re-audit.

11. Frequently Asked Questions

What is the difference between the heat balance and the mass balance of the kiln audit?

The mass balance accounts for the material streams: the raw meal, the fuel, the air, the clinker, the dust and the gas flows in the tonnes and the kilograms, reconciled against the measured flows. The heat balance accounts for the thermal energy: the fuel heat input split into the theoretical heat of the clinker formation and the losses (the exhaust gas, the clinker, the cooler, the shell, the dust). The audit computes both because the heat balance needs the gas and the fuel flows that only the mass balance establishes: the two balances are the two views of the same campaign.

How long does a complete kiln audit take?

The measurement campaign of the complete audit runs the 48–72 hours of the stable operation, with the preparation (the instrument installation, the calibration) taking the 2–3 days before and the reporting and the analysis the 2–4 weeks after. The plant and the audit team schedule the campaign around the stable production period, and the closing errors of the balances decide whether the campaign needs the repeat measurements.

What is a good closing error for the kiln audit balances?

The mass balance closes within the ±2–3 percent and the heat balance within the ±3–5 percent of the totals in the good audits. The errors above the tolerance force the audit team to revisit the measurements (the flow calibrations, the gas analyses, the temperature sensors) before the findings are signed: the closing error is the quality gate of the audit, and the workbook of the package computes it automatically for both balances.

What are the most common findings of the kiln audits?

The classic findings of the audits across the industry: the false air at the kiln inlet and the preheater flanges (the 10–20 percent of the gas flow), the over-aerated cooler with the high clinker temperature, the degraded refractory with the high shell losses, the biased weighing and the thermocouple errors, the calciner combustion problems, and the burner settings off the design: the same list repeats because the same weaknesses recur, and the audit’s value is the quantified evidence and the ranked actions.

How is the gas flow of the heat balance determined?

By the nitrogen balance method: the nitrogen enters the system with the combustion air and the fuel and leaves only with the exhaust gas, so the measured O2 and the CO2 of the exhaust gas fix the air flow and the gas volume through the nitrogen conservation. The derived gas flow, multiplied by the measured temperature and the mean specific heat, gives the exhaust gas loss term of the heat balance.

Is the kiln audit workbook of 2012 included in the package?

Yes: the Complete Cement Technical Package (931 files) includes the original kiln audit workbook of the 2012 heat and mass balance calculation (the 2.54 MB working file with the audit data sheets and the formulas), together with the heat balance sheets, the shell loss tools and the complete library of the kiln process references: the purchase below delivers the file and the package.

12. Conclusion

The kiln audit with the heat and the mass balance calculation is the complete diagnostic examination of the kiln line: the measurement campaign of the 48–72 hours, the mass balance that reconciles the streams (the feed, the fuel, the air, the clinker, the dust and the gas), the heat balance that splits the energy into the seven terms (the theoretical heat, the exhaust gas, the clinker, the cooler, the shell, the dust and the unaccounted), the process and the mechanical diagnostics, and the report with the ranked recommendations. The workbook of the package carries the complete calculation structure of the 2012 audit practice, and the worked example of the article (the 5,000 t/d line at the 729 kcal/kg input with the 3.6 percent closing error) demonstrates the full method with the concrete numbers.

The audit workbook, the heat balance sheets and the complete library of the kiln process knowledge are part of the Complete Cement Technical Package: the 931 files, the one-time payment of $249.99, the instant download and the lifetime access. The purchase button below delivers the kiln audit calculation workbook and the whole package of the cement engineer in one download.

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.