Specific Mill Volume And Power Demand: Complete Guide & Down

The specific mill volume and the specific power demand are the two numbers that summarize the grinding machinery of a cement plant: the volume of the mill per tonne of the hourly production, and the kilowatts per tonne per hour: the ratio of the machine to the money: when the engineers discuss a proposed mill, these are the first two ratios they quote: the specific volume says how much steel drum the plant is buying for the tonne that must flow, and the specific power demand says how many kilowatt-hours each tonne of the finished cement will consume: the entire economy of the grinding department is folded into these two small numbers.

The Complete Cement Technical Package (931 files including the books, the courses, the Excel tools and the presentations: $249.99 one-time: instant download via the PayPal payment) includes this guide to the specific mill volume and the power demand with its tables, the example calculations, the comparison charts and the design rules of the industry: this article walks the document: the definitions, the arithmetic, the data of the industry, the scaling laws and the practical use of both numbers in the design, the audit and the upgrade of the mills of the plant.

The beauty of the specific numbers is their durability: the specific volume and the specific power survive the scale: a 40 tonne-per-hour mill and a 400 tonne-per-hour line can be compared fairly with the same two ratios: the operator judges his plant, the consultant benchmarks the industry and the designer picks the machine: this page follows the document through the definitions first, the formulas second, the tables third and the applications last: the numbers in the hands of the engineer.

1. The Definitions: The Volume and the Power, Both Made Specific

The two “specific” quantities are the foundation of the grinding economy, and the document begins by pinning the definitions:

• The specific mill volume: the internal volume of the mill (or the total volume of the mill department) divided by the production rate: expressed in cubic metres per tonne per hour (or the inverse): a 4.2 by 13 metre mill of 180 cubic metres making 130 tonnes per hour defines a specific volume of about 1.4 m3 per t/h of the mill body;
• The specific power demand: the power consumed by the mill (or the whole department) per tonne of the material ground or per tonne per hour of the production capacity: the kilowatt-hours per tonne of the ground product: the energy bill of the single tonne: the 25 to 45 kWh per tonne of the finish grinding;
• The deferral of the definition: the strict-boundary of the specific accounts: the mill effective volume only, or the full circuit: the driven power of the motor shaft, or the metered electricity at the switchboard: the document states the boundaries so all the numbers of the different plants can be compared;
• The unit conventions: the metric tonnes and the kilowatt-hours: the short tons of the old literature and the horsepower-hours: the conversion factors in the appendix of the file: the units quoted explicitly, so the figures never lie silently;

The definitions be given, the entire industry comparison becomes possible: the specific volume and the specific power are the grammar of the grinding conversation: the plants of the package report their balancing data in these same terms, and the file instructs the exact boundaries so a number from one plant can be honestly set against the next: the meterology of the mill floor: the discipline of the ratios.

2. The Specific Volume of the Mill: The Steel per the Tonne

The volume of the mill body per unit of the throughput is a fingerprint of the design, and the document paints the distribution:

• The classical range: the finish mill ball grinds occupy the 1.0 to 2.0 cubic metres of the internal volume per tonne per hour of the final cement: the closed circuit and the fine products tend to the lower ratio, the open circuit the higher;
• The raw mills: the raw and the cement differences: the specific volumes of the raw mills in the 1.2 to 2.5 m3 per t/h with the drying chambers occupying a part of the drum: the specific value of the module;
• The coal mills: the dedicated pulverizing follows its own standard: 1.5 to 2.5 m3 per t/h of the fine pulverized fuel, the metallurgy of the grinding kinetics;
• The versatile factor: the feed grindability and the target fineness move the ratio within the band: the harder the clinker, the higher the volume per tonne needed: the finer the product, the higher the volume: the specific volume is the mirror of both factors;
• The vertical machines: the vertical roller mills sit at the small specific volumes of 0.3 to 0.6 m3 per t/h: the concentrated grinding zone, the small compactness of the design: the comparison of the families on the same specific line;

The specific volume answers the layout and the capital: the steel and the building about the moving volume: the financial question of the project, the same two numbers: the file tabulates the industry ranges for each family, each circuit, each fineness class: the engineer looks at his required tonnes, multiplies the specific and obtains the envelope of the mill volume: the complete first cut of the design on one line of arithmetic.

3. The Specific Power Demand: The Kilowatt-Hours per Tonne

If the volume speaks the capital, the power speaks the operation: the specific power demand is the number the plant lives with every day:

• The finish mandate: the finish grinding in the closed ball circuit consumes the 25 to 42 kWh per tonne for the 3000-4200 Blaine cements: the file’s table, from the soft clinker and the coarse grit to the hard clinker and the fine grit: the boundaries of the money;
• The raw demand: the raw grinding with the drying in the ball circuit runs the 12 to 25 kWh per tonne: with the roller press or the VRM, the 10 to 18: the energy scale of the department:
• The coal: the pulverization of the coal in the vertical mill: the 10 to 25 kWh per tonne: in the ball 20-30: the whole picture of the kiln competition with the separate mills;
• The components: the power of the mill alone, the fans of the circulation and the separator: the specific values of the department mention: the fans can carry the 20 to 30 percent of the department’s total: the metering per machine:
• The reference tables: the cleaning of the section: the file holds the reference tables by type, by size and by fineness: the plant draws its own specific power number on the log: the net point versus the industry code:

The specific power demand is the energy-in-single-note: the modern cement leadership of the plant knows its kWh/t exactly as the pilot knows the fuel consumption: the numbers of the file allow the engineer to see the circuit’s health immediately: the mill recently value: this specific power: in a second: the audit of the grinding, dimensionless.

4. The Arithmetic of the Specifics: The Calculation Workshop

The document runs the calculations of the two specifics with the examples the plant sees, and this section reproduces the logic of the workshop:

• The specific volume: the mill of 4.2 by 13 metres, 180 m3, the measured output 450 t/h: the specific volume: 180 / 450 = 0.40 m3 per t/h: wait and see the tons: re-check the formula: the specific for the total of the circuit including the feed bins and the product:
• The specific power of the mill: the absorbed power by the motor amperage 4,300 kW, the output 145 t/h: the specific power of the mill: 4,300 / 145 = 29.7 kWh per tonne: the number of the line, the pin the comparison:
• The trailing of the department: the total of the metered electricals of the finish corridor: the feed, the elevators, the separator, the fans, the vents: 6,700 kW served 145 t/h: the 46.2 kWh/t of the department: everything-from-the-line accounting of the energy:
• The accumulated view: the plant with the 24 hours: the 3,500 tonnes of the day in the 145: the kWh of the day 166,000: the daily tournapplauded and the weekend totals: the trend of the number: the view of the week and the month:

The examples are deliberately simple: the arithmetic of the specifics is the arithmetic of the field: the document multiplies the examples with the variants: the wet circuits, the pre-grinder, the increased fineness: every variant moves the specific and the tables show exactly how: the reader, armed with the calculator, can audit any mill in the world after an hour of practice with the file.

5. The Scaling Laws: The Power and the Diameter Physics

The specific power of a specific mill is not only a table: it obeys the scaling laws of the grinding physics, and the file outlines the classical relations:

• The Bond power formula: the power of the tonnage mill rises as the diameter to the power of about 2.5: the volume rises only as the diameter squared: the specific power thus climbs with the diameter of the single small machines: the economics of the big mills start in this exponent;
• The linear length: the power of the mill is directly proportional to the length for the same diameter and speed: the doubling of the length doubles the power and the volume; the specific volume of the shell remains the same: the length is the neutral axis of the scaling;
• The speed factor: the power of the mill is the function of the speed as well: the speed factor f of the standard tables (0.85 at 60% of the critical, 1.1 at 78%): the adjusted elements of the calculation: the speed moves the specific numbers within the rage;
• The filling factor: the filling of the charge enters the power as the nearly linear term close to the practical range: a charge of 34 percent instead of 28 raises the draw of the order of the 10 to 15 percent: the specific power attended by the filling: the control handle:
• The practice of the point: the calculated curve against the measured kilowatts: the calibration of the drive constant: the file gives the work formulas of the manufacturer’s pages: the measured validation of every mill:

The scaling laws are the physics of the specific power: the engineer who knows that the power rises with the diameter to the 2.5 knows why the giant mills win on the energy but lose on the flexibility: the file relates each law to the observed practice of the industry’s records: the reader learns the hidden logic under the tables: the charts of the package, the diagrams of the tumbling entrances.

6. The Specific Values of the Common Scale: The Reference Numbers

The document organizes the reference numbers in the tables the field uses daily:

• The 2.6 by 9 meters: about 47 m3, the 550-800 kW, the 20-40 t/h finish: the specific volume 1.2-2.3 m3/t/h, specific power 25-40 kWh/t: the small plant roofs;
• The 3.8 by 12 meters: 136 m3, the 2,500-3,000 kilowatts: 75-100 t/h: the particular volume 1.4-1.8: the particular power 27-38:
• The 4.2 by 13 meters: 180 m3, 3,800-4,400 kW, 90-130 t/h of the cement: the singular volume 1.4-2.0 and the singular power 28-42: the main of the cement:
• The 4.6 by 15 meters: 250 m3, 5,500-6,300 kW, 120-180 t/h: the specific volume 1.4-2.1: the specific power 28-45: precise finish:
• The 5.2 by 17 meters: 350 m3, 7,500-9,500 kW, 165-260 t/h: the gearless or the twin drive: the specific 1.3-2.1, power 28-46 the lines:

The tables show the beautiful constancy: the specific numbers hold almost constant across the whole scale of the plants: a small mill and a giant draw the same power per tonne: this is exactly the message of the specific numbers: the mill trains the same physics of the medium: the only real improvement comes from the circuit, not the scale: the file: the tables: the quick sanity check of every design.

7. The Fineness: The Lever on the Specific Power

The most powerful control of the specific power is the fineness demanded of the product, and the file draws the relationship clearly:

• The Blaine effect: the relationship of the specific power to the Blaine: roughly, each additional 100 cm2/g of the surface on the finish cement costs the 2 to 5 kWh per tonne: the curve steepens as the fine tail grows;
• The asbestos reference: the 3,200 vs 3,800 vs 4,200 cm2/g cements: the specific differences of the order of the 15 to 30 percent of the energy: the quality of the market: the cost of the cement versus the value of the strength:
• The retention of the sieve: the percent retained on the 45, 32 and 24 microns: the control of the enthusiast tail: the separator bypass: the same Blaine with the different tail, the different energy:
• The distribution curve: the steepness of the size distribution: the wide spread grinds cheaper: the uniform distributions cost: the distribution is the science where the separator pays:
• The strength of the concrete: the strength of the cement: the concrete creates the demand: the finish fines offers the strength at the price of the energy: the quality-cost trade of the market: the plotting of the cost lines:

The fineness is the master of the specific power: the sale models the culture: the plant that knows its power-fineness curve can quote the price of the premium cement honestly before the offers: the file prints such curves for the standard cements and instructs the plant on building its own: the premium is paid both in the money and in the kWh:

8. The Circuit Configurations: The Reshaping of the Specific Values

The circuit surrounding the mill reshapes the specific numbers, and the file organizes the comparison:

• The closed circuit versus the open: the closed at the same mill: the production up the 10 to 30 percent: the specific volume down and the specific power drop up to, 10-15 percent: the classification of the efficiency: the standard of the moderns:
• The roller press pre-grinding: the 40 to 60 percent of the energy shifted to the roller press at the lower specific consumption: the specific power of the whole circuit drops the 15-30 percent: the capital increases:
• The vertical mill at the finish: the specific power of the VRM finish at 18-30 kWh/t: the family’s advantage: the product: the response: the different quality: the selection on the specific:
• The semi-finish and the full-finish: the presses and the classifiers: the specific of the whole line: 20-32 finish: the installation of the energy at the limits of the chemistry:

The specific power is the game board on which the engineers play the configurations: the file compares the alternatives in the clean tables: the capacities, the kWh/t, the investments and the paybacks: the reader sees the landscape: the old open ball mill at 40 kWh/t vs the vertical line at 22: the modernization decision: the finance of the plant: the sections of the package: the oracle of the specific: the physics of the loop.

9. The Wet Circuit Specifics: The Slurry of Another Number

Not all the cement grinding is dry: the wet plants of the world still exist, and the file treats the wet specifics honestly:

• The wet ball mill: the slurry water 30-40% the feed and the pulp of the mill: the specific power of the wet raw grinding 10-20 kWh/t: the energy advantage of the wet route for the raw: the elimination of the drying:
• The slurry rheology: the viscosity of the slip: the solids content: the specific power rises as the viscosity climbs: the optimum solids of the slurry between the 65 and 75 percent by the mass: the dispersing agents:
• The wet finish (the white cement): the white and the specialities grind the wet: the specific numbers 30-50: the smaller world of the plant: the circulating washing and the recovery:
• The choice wet/dry: the total energy when the drying is added: the wet plants avoid the kiln exhaust waste drying, the dry plants the water of the evaporation: the specific including the total: the honest power: the file the given boundary of both:

The wet number is a discipline of its own: the water eases the grinding and electrifies the finances: the file witnesses the complete wet circuits (the jaw, the tube, the separator and the slurry basins) with the specific powers of the tanks: the chapter springs from the closed world of the wet mill: the document: the dry and the wet interleaved: the total power of the plant over both departments, the budget of the energy: the package draws the lines.

10. The Energy Audit of the Mill: From the Specific to the Savings

The specific numbers become instruments of improvement when the plant audits itself against them: the file’s audit chapter:

• The baseline of the audit: the daily specific power of the department: the running average of the 28 days: the reference line: the trend chart: the seasonal and the clay tendencies separated:
• The gap analysis: the plant’s specific versus the industry best of the same feed and fineness: the gap of the 5 kWh/t: the 5 percent: the millions of the electricity: the denominators: the improvement list:
• The meter audit: the sub-meters of the feed, the mill, the separators, the fans and the silos: the share of each: the 15th of the invisible: the identification of the lecs: the fix: the mirrors: the correction: the specific of the deprived:
• The correction actions: the separator speed, the ball charge, the liner profile, the ventilation, the load control: the actions practiced: the measured new specific: the re-audit the following month: the continuous improvement of the energy: the file’s templates: the shift:

The audit makes the specific power a target: the department of the package improved their number with the simple sequence: the baseline, the comparison, the meter, the fix: the documented cases of the mill: the -8 kWh per tonne: the full year bill: the file incorporates all the dead templates the plant needs: the starting of the audit: the meter readings, today afternoon: the specific power, the discipline of the plant.

11. The Design of a New Line From the Specific Numbers

The greenfield design starts with the two best numbers, and the file walks the design path:

• The target rate: the cement production plan of the market: the 5,000 tonnes a day: the 220 tonnes per hour at the 92% availability base: the required line: the cement for the market:
• The specific choice: the precedent of the industry for the same cement: the 30 kWh/t: the chosen common mill: the trained 220 t/h demands the ~7,000 kW of the installed mill: the volume from the specific volume: the dimensions:
• The alternatives screens: the three candidate systems (ball, vertical, press-ball) each with its specific power and its specific volume: the energy the capital the availability: the ranking: the decision with the file’s scoreboard:
• The check of the dimension: the selected mill: the specific of the modules verified: the volume: the loading: the speed: the separator: the balance the complete: the wary: the selected module: the opus of the leave:
• The basis of the design: the safety the market: the availability, the future demand the expanding blend: the design specific of the +5-10% headroom: the project as the bet of the future:

The specific power is the opening move of the design: the number the board remembers: the kilowatt-hours per tonne decides everything after: the file: the systematic screen: the engineers of the package have designed this way dozens of the lines: the resulting paper becomes the chapter of the project: the numbers the owner repeats: the entry of the design chapters: the principle slides in the middle of the mine.

12. The Power of the Existing Plant: The Revamp Books

The most common question is not “the new mill” but the better of the old: the revamp from the specific ledger:

• The power-only revamp: the new motor and the gearbox on the same shell: the power up: the volume stays: the specific power: the higher capacity of the same specific: the rate of the industry: the “power-up” packages:
• The volume revamp: the insertion of the shell section (the lengthening): the +20% of the volume, the same specific power down: the residence increases: the output: the shaft job: the rare, the profitable in the right case:
• The combination: the new separator + the press + the new classifiers: the specific power of the 35 to 25: the output +40-60%: the same shell: the financial analysis of all the options: the casebook:
• The derating option: not every legacy can be scraped: the refit can keep the specific minimum while the capital is held: the energy of the old mill: the “low capex lever”: the file:

The revamp section of the file: the tables: the possible “power-up” of every common mill and its effect on the specific values: the plants of the package: the sequence: the audit, the revamp, the re-audit: the specific number is the report card of the revamp: the meter before, the meter after, and the sentence in the numbers: the file.

13. The Monitoring of the Specific: The Daily KPI of the Mill

The plants of the modernity run the specific power as the daily KPI: the file describes the routine:

• The daily report: the sum of the kWh, the tonnes of the day and the kWh/t of the department: the trend in the log: the reds and the greens of the weekly: the chatter of the meeting:
• The shifts: the day of the demand: the time of day: the night shift: the specific of the same grind across the day: the environmental of the temperature: the normal set:
• The quality guard: the kWh/t held at the same Blaine: the effect of the mill on the consumption: the grade of the product by the numbers: the audit: two shifts: the maintenance of the mill?> the tales of the numbers:
• The integration of the energy: the ISO 50001 of the plant: the monitoring of the whole plant with the kWh/t of every department: the target, the deviation and the review: the energy leadership of the cement: the part of the corporate:

The daily KPI bed the energy culture of the plant: the morning meeting opens with the sum of yesterday: the specific power: every attendant: the number known, the deviations ask, the corrective: this book: the file: the template: the daily tour: the monthly: the year: the plant with the culture of the engagements: the annual corporate: the energy of the mill: the competitive of the plant: the team: the specific: the prize.

14. Conclusion

The specific volume and the specific power demand: the two ratios at the center of the grinding economy: the cubic metres of the drum per the tonne of the flow, and the kilowatt-hours per the tonne of the cement: the same two numbers serve the design day and the audit month, the greenfield board and the production meeting: the mastery of the specifics is the discriminator of the modern cement engineering: the numbers do not lie: the machines, the best.

The Complete Cement Technical Package includes this full guide with the industry tables, the calculated examples, the audit templates and the comparison charts: the $249.99 one-time purchase: the instant download: the life-long reference: the thousand pages of the package, the two numbers of the mill inside: the engineer who knows the specific numbers of the plant runs the plant of the numbers: the power: the volume: the tonne: the mission.

The Frequently Asked Questions

What exactly is the specific power demand of a mill?

The specific power demand is the kilowatt-hours consumed per tonne of the product (kWh/t): the plant divides the measured power of the mill (or the whole department) by the tonnage produced in the same hour: the figure for the cement finish grinding usually lies between 25 and 45 kWh/t: the number holds the comparison of the circuits, the audits and the invoices: the simplest powerful metric of the grinding.

Why is the specific volume expressed per tonne per hour?

Because the volume of the mill and the output are independent of the absolute scale: dividing the volume by the hourly tonnage gives a ratio (m3 per t/h) that stays comparable between a 40 t/h and a 400 t/h plant: the same mill family, the same ratio: the capital-ratio: the design first cut: the industry’s rule of thumb for the sizing of the shell.

Does the specific power vary with the fineness?

Yes, and substantially: each additional 100 cm2/g of the Blaine surface commonly costs the 2 to 5 kWh per tonne: the finer the product, the higher the specific: the plant must sell the premium of the fineness against the power of the purchase: the file prints the fineness versus the power curves for the standard cements to quantify the trade-off.

Can two different plants be compared with the specific values?

Yes, but honestly: the definitions must match: the same boundary (mill only or the total department), the same product fineness, the same circuit: a 40 kWh/t at a 4200 Blaine can be better than a 30 kWh/t at 3200: the file insists on the stated boundaries so the comparisons do not lie: the specific is a fair sport with the agreed rules.

Why does a bigger mill seem to need less energy per tonne?

Because the power of a tumbling mill grows with the diameter to the power of about 2.5 while several other losses (the shell friction, the single machine overheads) grow more slowly: the giant mills dilute those fixed costs over more tonnes: the specific power of the big line falls: the reason the newest plants build the biggest mills with the most modern separators.

Is the kWh/t the entire electricity of the cement plant?

No: the raw mill, the kiln fans, the compressors, the conveying and the packing department all draw their own power: but the finish grinding typically carries 60 to 70 percent of the electrical demand of the plant, so its specific number is the dominant single line of the electricity bill: the file places the mill specific in the total picture of the cement, kilowatt by kilowatt.

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.