Case Study Qena: Complete Technical Guide

This case study is a complete, worked technical file about the optimization of a dry-process cement plant in the conditions of the Qena region of Upper Egypt: the area of the Nile limestone, the marls of the desert edges and the long summer temperatures: the document follows one plant through the entire engineering cycle: the assessment of the raw materials, the design of the raw mix, the review of the kiln system and the cooler, the energy audit of the mills, the implemented measures and the measured results: the file is written as a real-world case study, and it is also honest about its method: the figures come from the published industry practice, the typical conditions of the region and the calculation tools of the package, and the reader is shown every step of the reasoning so that the same audit can be repeated at his own plant.

The Complete Cement Technical Package (931 files including the process engineering books, the Excel calculation tools, the checklists and the presentations: $249.99 one-time: instant download via the PayPal payment) contains this case study as one of its practical application files: the study is built with the materials and the parameters of the real world of the qena region: the limestone totals and the chemistry, the minerals of the marl, the weather, the fuels available (including natural gas and petcoke), the power prices and the limits of the local cement standards: this article walks the case: the baseline, the audit, the design, the actions and the results, in the language of the numbers.

The case study instructs with a method, not with a miracle: the plant of the study is not presented as the perfect plant but as the plant with the known process problems: high-kiln heat consumption, high finish grinding power, unstable production of CEM I, dust losses, and delayed changes of the new hard fuels: the engineering team of the file applies the classic disciplines: the material balance, the heat balance, the equipment calculations, the sampling programs and the statistical control charts: the improvements follow, and the reader sees which lever produced which saving: this is the study of the numbers, and the numbers are true to the laws of the process.

1. The Location and the Setting: The Raw Materials of the Q is Region

The region of the Q is one of the historic limestone territories of the Upper Egypt: the river cuts through the Eocene limestone of the desert plateau, and the quarries of the region supply the cement factories of the area: the raw materials of the typical Q concept:

• The Nile Valley limestone: the grades of the high-purity CaCO3 that reaches 92 to 97% in the terms of the dominant calcite, used for the main component of the raw mix;
• The marl layers: the carbonate and clay mixtures with the SiO2 total of 15 to 25% and the MgO of 1.5 to 4%, the ideal intermediate of the Egyptian blend;
• The clay correction: the Nile alluvial or the desert clay with the 55 to 65% silica, used as the source of the silica and the alumina, the clay blends 8 to 14% of the raw mix;
• The iron corrective: iron ore or the iron silicate sand (the residue of the associated mineral sands) with Fe2O3 of 50 to 70% to fix the AM of the mix;
• The gypsum: from the neighboring deposits, used in the finish grinding at 3 to 5% by the mass;

The chemical composition of the regional raw materials varies with the geological horizons: the limestone in the case study depths of the quarry has the percentage total of the carbonate between 92 and 97% in the layers of the “white” and of 78 to 88% in the “yellow” beds: the key constants of the design: the LSF (lime saturation factor) of the raw meal 0.92 to 0.98, the silica ratio SM of 2.3 to 2.7, the alumina ratio AM of 1.4 to 1.7: the target values occupy the center of the modern cement production window, and the file computes them for every blend of the quarry block.

2. The Existing Plant and Technical Baseline of the Case Study

The plant of the case, as the typical company of the region, consists of the following lines (the generic capacities scale of the industry):

The measured baseline of the plant: kiln heat consumption of 3,700 kJ/kg clinker including the losses, cooler efficiency 65%, the finish grinding specific power 44 kWh/t, the OPC final fineness 3,400 cm2/g with Blaine 3,700, the clinker factor 62% of the CM emission: the table establishes the reference: the improvement program of the file must beat these baselines with the standard physical and the engineering measures, not with the investment money of the new kiln.

3. The chemical control and the raw mix design of the study

The raw materials are characterized for the design of the mix: the following typical compositions of the raw constituents of the region (the file gives the complete XRF analyses):

The problem: with the compositions above, the raw meal from 46% lime, 13% clay, 10% sand, 31% marl reaches the target: LSF 0.96: the dosage is adjusted on the basis of the daily quarry surveys: the “standard” raw meal target of the plant:

• LSF: 0.96 (the range 0.92-0.98);
• SM (SiO2/Al2O3+Fe2O3): 2.45;
• AM (Al2O3/Fe2O3): 1.55;
• Free lime in the clinker: 1.25% maximum;
• The CaCO3 target (the Tuen): the raw/off 82.0% standard deviation of the raw meal 0.35% after the homogenization:

The study demonstrates the “change the quarry block!” scenario: after 10 years of the operation the deposits of the high-grade limestone dry out, the quarry enters the lower grade, and the plant compensates by raising the marl and the clay shares: the Tuen of the mix falls, the silica rises, the transfer from the vertical furnace expands: the file simulates the new mix design: LSF 0.95, SM 2.55, AM 1.6 with the same raw constituents, and the calculations of the burner drive and the clinker mineralogy of the resulting cement.

4. The kiln system audit: the preheater, the calciner and the fuel

The hematite: the kiln system is reviewed section by section with two instruments: measurements at the operating point and the heat and the mass balance:

• The preheater: the gas temperatures in the cyclones: exit 320-350 C, cyclone IV at 850-900, the calciner at 870-900, the cyclone III: the pressure losses: the false air of 15-20%, brings the losses and the flow rates: the target false air 8%:
• The calciner: the fuel split: 60% of the fuel to the calciner versus 40% to the kiln is common in the study: the real result: the temperature difference between the bed and the kiln was within 25 K;
• The kiln: the burner zone temperature at 1,450-1,500 C, the specific heat losses through the shell: 150 kJ/kg cl, and the excess air the kiln tail 2.5% – the O2 control:
• The fuel: the baseline used natural gas at 8,200 kcal/m3 then moved to the petcoke (8,100 to 8,300 kcal/kg, ash 1-3%, S 3-4%): the S2O3 cycle and the dust of the alkali cycle;

The heat balance of the kiln in the baseline: heat consumed in the clinkerear actions: raw material heating 25%, decarbonation ~55%, the losses: shell 6%, losses through the gas 10-12%, the cooler losses 5-7%, the dust: total in the order of 3,700 kcal/kg cl: the balance of the file is presented with the complete table and the “finger” of the improvements: a 15 k of the shell loss corresponds to 0.4% of the total: the cooler efficiency of 70% recovers 0.25%: the study quantifies the contribution of the six improvements to the final of 3,400 kcal/kg cl.

5. The cooler and the clinker quality

The clinker cooler of the study was changed from the 3rd to the 4th generation with the following measured effects:

Also the study records the effect of the cooler on the clinker phase: the quick cooling of the clinker at the grate inlet (1,400 to 800 C in 8 seconds) preserves the alite crystals (C3S) of 20-30 micrometer and raises the early strength of the cement: the slower cooling causes the phase reconversion to the belite and the reduction of the sulfate interstitial, degrading the quality: the cooler of the star is therefore the hidden colleague of the quality and colors of the cement plant.

6. The finish grinding: the ball mills and the separators audit

The baseline of the finish grinding is audited with the data of the circuits: the two open-circuit mills produced the cement at 44 kWh/t with the final fineness of 3,400 cm2/g: the study identifies the opportunities:

• The mill internals: liner wave-liner and the charge of 32%: the lift of the liner plates was corroded at 60% of the design and the grinding bodies were removed only every 18 months: the file defines the standard: the wear liners, the correct charge makes 30% of the composition with the 30-40 mm balls, 25% in the 20-25 mm, the end of the compartment;
• The separator: as there is no separator in the single compartment it is the open circuit: the conversion to the closed circuit with the high-efficiency separator and the internal classification (the measurement of the P80 45 order: the typical gain: 6-10% power) is simulated;
• The separator: the seeds: between the classifier bypass 5% and the closed loop: the study demonstrates two configurations with the same mill: the closed, which gives the fineness P80 of 45 the at the rate of 105, and the open which yields 84 t/h
• The water injection: the grinding temperature: 135 C to 115 C control in the summer, and the cement temperature below the 110 C the benefit;

The finish grinding of the study is typical of the region: the mills run on the imported clinker and the imported additives: the results of the audit quantify the total capacity increase: from 84 to 105 t/h at the same 3,400 cm2/g, and the specific power from 44 to 36 kWh/m: the findings of the case are presented in the table of the section and compared with the readings of the plant archive.

7. The role of the raw meal quality in the cement strength

The tag line of the molecule: “the strength of the cement is decided in the quarry”: the study makes this concrete with the two state variables: the day-to-day LSF stability of the raw meal decides the burning zone stability, and the burning zone stability decides the free lime, the alite distribution and the scatter of the strength: the target runs:

• The raw meal LSF variation ±1.5% is the sector-limit for the clamp low: the measured raw meal of the plant: ±0.6%, after the homogenization improvement ±0.3%;
• The clinker free lime: purpose 90-110% of the batch in the range of 0.8-1.4%: re computes from the wave of the preheater; the quality protocol requires 95% within 1.0 – 1.4;
• The compressive strength: the studied cements: 28.2 MPA at 28 days for CEM I 42.5R (the target based on capacity: 42.5 28 day: the effective 48 MPA including the 92-year: the study’s own ramp:
• The initial strength 2 days: 22 24 MPA
• 7 days: 31-34 MPA
• 28 days: 42-46 MPA

The observed dispersion of the strength (the standard deviation of the 28-day series) fell from 4.8 MPA to 3.1 MPA after the stabilization of the process: this translates directly into the financial optimization of the formula: with the lower dispersion the plant can reduce the excess clinker factor by 2.5% and increase the limestone addition to the blended cement without the unhurried to the standard compliance: the study quantifies the net: the same cement quality per ton of clinker at 4% less clinker: the most direct money of the case.

8. The energy audit and the calculation of the plant electrical balance

The complete electrical balance of the baseline:

The numbers of the regional plant: the electricity consumption target of the modern dry process cement: 105 to 125 kWh per ton of cement (total): the case plant was high at 128 kWh per ton cement; the targets of the action plan: -15% after the projects: raw mill from 21 to 19 kWh/t, finish mill from 44 to 36, the fans of the kiln from 15 to 13.5 per ton of clinker, the cooler fans from 14 to 10: the total fall at 108 kWh/t: the additional 10-15% of the losses determined by the leak survey of 30% false air and the campaigns; the file holds the Excel of the audit of each section.

9. The economic analysis of the case study

Every measure of the program is weighted against the economic reality of the region: the local electricity price (0.06-0.08 USD/kWh), the natural gas price and the cost of the coal, the freight of the clinker and the price levels of the local cement market: the table below collects the assumptions and the results:

Note of the file: the years and the prices are published: the values are: the textbook of the industry and the actual plant numbers vary with the local conditions: the tables of the study have the columns for the plant-reader to fill their own parameters: the Excel model of the file is part of the 931 package and the reader can reload the file with the current price: the reason of the case study: teach the method and let the numbers be the numbers of the reader’s plant.

10. The behavioral audit: the “soft” reasons of a good plant

The case who corrects themselves: the efficiency of the engineering measures is multiplied by the daily discipline, and the study reviews the six head-book operations:

• The daily shake of the mix: the laboratory fills the feed analysis at 3-hour intervals and the mill supervisor confirms the target before the change of the block;
• The “closed the vent” routine: each shutdown:
• The maintenance of the fans: the vibration paths of every fan, the clean of the dirty gases and the belt alignment: the loss of 5% of the flow – the false air 2%;
• The use of the calibration: the belt scales vs the master: the new stock piles indexed monthly;
• The log of the quality: the cement dispatched with the tested strength and the lab results compared at the end of the month;

The study states what the professionalism demands: the same equipment at two plants gives different results in the ratio of the discipline: the present case institutionalizes the hourly routes, the checklists and the review meetings: the file contains the templates of the checklists used.

11. The lessons and the step-by-step plan of the case study

The final plan of the case study is the step plan of the reader’s own plant:

1. Week 1-2: task force, the data of the study: the k (the month’s production hours, the powers by the section, the fuel price);
2. Week 3-4: the energy audit: the wind: the compressor, the kiln, the mills: simple: identify the quick wins and the false air;
3. Month 2: the closure of the false air, the fix of the damaged thermal: expected 2-4% of the total energy;
4. Month 3-5: the mill optimization: the loads, the clm: the separators: their closed loop;
5. Month 6-9: the kiln stability: the raw meal dispersion project, the cooler; (finished the heat)
6. Month 10-12: the economical demolition: the analysis of the annual data:

The study finishes with the “two rounds” of the file: the second iteration of the audit after the implementation: the new baselines: the table of the case’s own numbers: 4,000 kcal/kg → 3,540; 128 kWh/t → 108; 3.4% free lime → 1.2%; the result: the case plant of the study exists in the industry in the same class and the reader can drill his own site into its next round of the improvement.

12. The dust collection and the emission control of the case

The emissions limits of the region and of the market place an additional constraint on every improvement of the case: the dust collectors of the plant are audited together with the process: the bag filters of the finish mill, the mill fan of the raw circuit, the kiln main bag filter and the coal mill filter: the audit points:

• The kiln bag filter: the dust content of the cleaned gas below 30 mg/Nm3 at the operating inlet of 50 to 150 g/Nm3: the pressure drop 1,200 to 1,800 Pa, the cleaning cycle 6 to 10 seconds per compartment, the filter bags of the PPS (polyphenylene sulfide) type with the 150 to 160 C of the gas temperature limit;
• The false air in the collectors: the air ingress at the inlet of the ESP and the bag filter changes the dew point and the corrosion: the study repaired the insulation and the sealing of the duct, reducing the false air from 10% to 3%;
• The SO2 and the alkali control: the switch of the kiln to the petcoke of 1.5-2.5% sulfur raised the SO2 at the stack: the limestone injection of 5-8 kg/h reacts in the preheater: the stack SO2 returns under the 200 mg/Nm3 limit:
• The NOx control: the target: under 500, the study runs the staged combustion (calciner) plus the reduction of the excess O2 in the kiln tail from 3.5 to 2.2%; the NOx fell from 780 to 460 mg/Nm3;
• The dust of the roads and the stockpiles: the water spraying of the raw storage and the baghouse by the belt transfer points: the opacity of the local plant remains below the 10% of the correct;

The emissions control of the case is not only a regulatory duty: it is also an engineering tool: the false air fixes the flow of the exhausters, the efficient collectors reduce the pressure drop and thus the fan electricity, and the dust-free gas improves the measuring of the CEM analyzer: the case study demonstrates that the environmental measures of the plant pay back with the maintenance reductions and the fan power savings in 12 to 18 months, before the regulatory audits even start.

13. The people, the skills and the transfer of the knowledge

No improvement program of a plant survives without the people who operate it, and the case study devotes a full section to the human side of the Q project: the training matrix of the package puts five skill boxes for each operator group:

• The raw mill operator: the interpretation of the raw meal every hour: the response to the 0.3% CaCO3 drift: the mill dynamics, the separator settings and the false air checks;
• The kiln operator: the understanding of the clinker exits, the nose of the flame, the heat balance and the braving of the bed, the emergency resumption the preventive measures of the ring:
• The process engineer: the daily heat balance summary, the calculations of the coolers ratio and the separators, the draw of the trend and the cause analysis:
• The maintenance crew: the repairs of the filter bags, the classifier blades, the grinding table, the grate of the cooler: with the book of the standard work for each:
• The shift change discipline: the log shift, the parameter handover, the incident alarm: the “no silo surprise” shift culture;

The implementation of the case program reduced the kiln trouble-shooting time of the shift from 40 to 10 minutes through the organized operator screen: the alarms of the kiln stabilizer from 22 per day to 9: the trainings have a long lasting effect and the study measures the retention with the simulation sessions each year: the companies that adopt the same training plan can count the results in the quality statistics before the year is over, and the files of the training material and the operator manuals are also the parts that the package delivers with its 931 documents.

14. The Frequently Asked Questions

Is this a real case study of a specific factory?

No: it is a composite study with a fair method: no specific company, no names: the geometry, the composition, the tariffs and the rates are representative of the typical conditions of the region, and every line of the data is drawn from the standard public engineering: this is the professional honesty that the package follows: the reader reproduces the method with his own data and receives his own concrete answer.

Which of the sections of the plant produces the largest saving?

In the study: the finish grinding: from 44 to 36 kWh/mt: +18% of the total electric: the cooling (cooler) directly recovers the fuel (the best 2-4% of the kiln heat): yet the order of implementation should follow the payback: the false/air of the repair (very cheap with the immediate quit) first, then the mill, then the cooler.

How much does the real improvement of the region affect the results?

The variations of the fuel and the price affect the absolute sums, not the method: e.g. the natural gas vs coal changing point: the same kiln of the calciner loses 1-0.2% when the coal replaces the gas and 0.5% when the minus: the cooler, however, loses the same: the order of the improvements is correct for any energy mix, and the number of the case demonstrates the methodics of the adaptation: this scale of the values is the law, and the parameters are what the reader edits in the attached worksheet.

How can a small plant (2,000-3,000 t/d) reach the level of the study?

The line capacities of the study (5,000 t/d) do not change the physics: the small plant can: use the same audit: the specific mills the kilns: the same gain percentages apply at 80 – 120%: the file states: capacity 3,000 t/d: 112 kWh/t achievable, 75% of the same absolute gains in the fuel: the load of the 165 or the direct: whatever the size, the first step is the same: measure.

Is the 3,700-3,540 kcal/kg clinker target achievable with coal in the kiln of the region?

Yes, with a 5-stage preheater and the dry system: the modern references reach 3,300-3,500 kcal/kg with the coal: the study with the long wet kiln heritage of the region: the existing 3-stage: the practical: 3,900-4,300 kcal/kg: the kit is the preheater stages: the cooler: the burner: and the false air. The file details these combinations per the configurational lengths.

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.