PERFORMING A CEMENT PLANT OPERATIONS AUDIT
The cement plants and process engineer (due to training and job title) is frequently asked to examine the “big picture” in a production/operations environment. This can be a formal request for a diagnostic review or a vague request from top management to see what’s wrong or what kind of improvements can be done with production/operations. Operations audit is a procedure that helps the industrial and process engineer determine not only what is wrong, but more importantly, what is right in an operations activity.
Operations audit is the first step in conducting a general and objective assessment of a production/operations area. It is called by many other names, such as diagnostic review, general survey, operations exam, etc. It can be done as a stand-alone project, but is often part of a larger project, such as reducing costs or improving productivity. The technique is based on a logical evaluation of the current factors that control the operating environment.
The audit can be performed by a person or by a team, depending on the complexity of the operation under examination and the need for skills outside the training of the industrial and process engineer. The audit can range from two days to several weeks, depending on the size and complexity of the operation under review.
The audit should result in a concise written statement of the operation’s strengths and weaknesses and support functions. It should also contain diagrams of the interactive features that contribute to the product or service being provided and any comments on areas for improvement and any specific areas for further analysis. The audit will be based on data, numerous interviews, field visits, and the objectivity and past experience of the systems.
WHEN DO YOU DO ONE?
An operations audit should be carried out whenever important changes of a general nature are considered. Some important changes may include: a plant-wide cost reduction effort, the installation of a productivity program, thermal energy efficiency program, electrical energy efficiency program, chemistry and operations strategy, the introduction of new products, changes in the management information system, new plant acquisitions, prior to relocations of plants, etc.
An audit is usually the first step by a management consultant who has been given a broad objective by senior management to improve the profitability of an operation. The consultant may conduct a portion of the audit before the formal proposal is submitted, to ensure that the correct issues are addressed in their proposed work plan. Likewise, the plant’s process engineer or internal consultant will often find that the audit is a necessary first step in ensuring that they address control issues and not just some of the symptoms.
Most operations undergo enough change for an audit to be beneficial every three years, and more often if a major change has occurred or is planned since the last audit.
WHAT TOOLS DO YOU USE?
A variety of tools are used during the conduct of the operations audit and the emphasis will vary based on the complexity of the audit and the time available. One of the most important tools will be the industrial and process engineer’s ability to conduct the audit as a project, with a written objective, defined tasks, expected deliverables, listing of work steps, and a schedule. If other team members are used, then their efforts will be directed and coordinated as well.
Other important tools are the ability of the industrial and process engineer to conduct meaningful interviews at all levels of the organization, and to document findings and draw clear, concise, conclusions. The handling and gathering of data necessary for the conduct of the audit is a particularly important task, since the time usually allotted to the audit will require not only care in analyzing data, but in making realistic data requests of key departments.
The operations tour and related field trips can be an important source of general information, and the tour can be augmented with product flow charts, equipment location drawings, and facility expansion plans. The observations and answers to key questions during operation tours and related visits can become a useful part of the data gathering stage of the operation audit for confirmation and verification at a later date.
Organization charts, job descriptions, budget plans, financial statements, operations records, and written operating procedures can be useful information to be obtained during the conduct of the audit.
STEPS FOR PROCESS AUDITS
Plant operating and shutdown data need to be collected for the past two or more years. The reasons, duration and frequency to identify the causes in order of severity of the stops are analyzed and their classification:
Plant performance is also analyzed by department. Often, the best performance of a department does not occur at the same time as the best performance of the plant as a whole. If we choose the best throughput times for each department and make them occur at the same time, the throughput of the plant will show a significantly higher level of efficiency. Attempts are being made to make them happen at the same time, which is not an unrealistic goal, as the departments had indeed done so at that level in the past.
Through a systematic approach, all departments are made to function at the highest possible level, increasing overall equipment effectiveness.
Modern dry-process cement plants with an efficient grinding and pyro processing system, typically consume less than 700 kcal/kg-cl of thermal energy and 100 kWh/mt of electrical energy. Older plants with inefficient systems, combined with operational and maintenance failure, tend to have much higher energy consumption. Based on the specific plant conditions and requirements, a general benchmarking is conducted to set goals. Plant audits evaluate the performance of a cement plant against the appropriate benchmark. After a detailed evaluation, recommendations are made for optimizing the plant at three levels of capital investment:
- Level 1: no or very little capital investment, making adjustments to operating protocols and improving maintenance.
- Level 2: minor capital investments, with ROI within 24 months.
- Level 3: Large capital investments, with ROI within of 3 to 5 years.
A successful thermal energy management program requires energy auditing as its one of the important procedures. The possible approaches of heat recovery from some major heat loss sources by making a detailed analysis of kiln, raw mill, coal mill and grate cooler. To improve the production process, increase the productivity, decrease energy consumption of the plant.
Thermal energy is related to the pyro processing system. For a clinker production of 1 million tons per year, the savings of 10 kcal/kg-cl would result in an annual savings of approximately $92,000.
(1,000,000 tpy * 1,000 kg/year * 10 kcal/year * $ 60/t-coal
(6,500 kcal/kg of coal/1,000 t of coal)
Another significant advantage in most cases is that the reduction in heat consumption can be used to increase production.
Potential savings can also be derived from:
- Cooler optimization
- Stop leakages
- Optimization of operational strategy
The main aim of the energy audit is to provide an accurate account of energy consumption and energy use analysis of different components and to reveal the detailed information needed for determining the possible opportunities for energy conservation.
Large fans and mill units are the main consumers of electrical energy.
Fans: Fan power is linked to specific heat consumption and many operating parameters. Optimizing these parameters will help reduce the fan’s power consumption.
Mills: In the case of ball mills, optimizing the mill load and maintaining the internal parts of the mill will minimize energy consumption. As for the vertical roller mills, the inspection of the internal parts of the mill and the separator, and the adjustments in the operation will bring improvements, both in energy consumption and in increased production.
CHEMISTRY AND OPERATIONS STRATEGY
Problems related to clinker quality are addressed by evaluating chemistry and operating parameters.
HOW IS THE AUDIT PERFORMED?
The operations audit can take a variety of directions and any number of steps can be involved, depending on the complexity of the audit and the size of the operation being examined.
A typical audit may include the following steps:
- Discuss purpose and objective of the operation audit with top management.
- Develop a work plan for the audit and create a project team, as required.
- Determine major data sources and list of key parameters.
- Review detailed plan and data sources with top management.
- Conduct a detailed tour with the operations manager.
- Arrange for interviews starting at the top and going down the organization. Cover all necessary departments such as production/operations, engineering, sales, marketing, finance, information technology, inventory control, etc.
- Make any data requests early in the study to the appropriate department head.
- Conduct interviews and gather departmental information such as sample reports, department goals and challenges, organization charts, etc.
- Analyze data being gathered and develop various diagrams of product flows, information flows, and departmental interactions.
- Develop familiarity with products manufactured (or services provided) and major costs associated with the operation processes.
- Place all data gathered and interview notes in file folders, and keep organized by department. If other team members involved, conduct periodic review sessions and share data.
- Document preliminary findings as a series of un-ranked strengths and weaknesses. List strengths first, so as not to overlook anything when detailing weaknesses.
- Do not discuss preliminary findings with people being interviewed, since comments will not be finalized and final results may be confidential.
- List “unknowns” as well as “knowns” and begin to draft the final report, being careful to include data being developed that substantiates observations.
- Call in all data requests previously made and analyze data with help from the person who prepared the information.
- Develop a prioritized list of major strengths and weaknesses, and describe any specific areas for further analysis or for immediate action that are beyond the scope of the manufacturing audit.
- Review the final report with top management, complete with any appropriate action plans.
- Review copies of the report with department heads, as appropriate.
- Begin to follow up on appropriate action items and develop additional plans, as required.
STACKING AND RECLAIMING
Review: Reliability and Throughput.
- Analysis of machine downtime requires downtime data and maintenance records.
- Frequent stoppages report
- Mechanical inspection of stacker gearbox, rails, turning components, conveyor belts, hydraulic system and boom.
- Mechanical inspection of reclaimer rakes, plows, bogies, rails, drag chains and drag chains.
The evaluation of the process will include chemical data on the input and output streams for the efficiency of the mixture, an annual record of the moisture content and the granulometry of the feed material.
- Moisture content and effectiveness of the machines in the wet season.
- Final stack chemical deviation in LSF: if correcting the final stack can avoid severe chemical oscillations
- Execution factor throughout the year.
- Performance in the dry and wet season.
- Maximum recovery rate
- Small modifications to improve execution factor and derived ROI
THE DATA AND MEASUREMENTS OF THE AUDIT OF THE VERTICAL ROLLER MILL APPLY TO RAW GRINDING, COAL AND CEMENT
- Maximum production
- Grinding efficiency/power consumption
- System airflow
- Material flow
- Separator performance
Operational variables to be monitored include:
- Temperature, Mill inlet
- Temperature, Mill outlet
- Pressure, Mill inlet
- Differential Pressure
- Power consumption of the fan
- Table Layer thickness
- Mill vibrations
- Power consumption of the mill motor
The following measurements and samples can be taken:
- Temperatures: input and output with handheld thermocouple
- Power readings: mill motor, fan and classifier, by wattmeter totalizer for specific motors and/or manual amplifier probe
- Determination of air flow: inlet and outlet of the mill and bypass by cross pitot
- Gas samples: cyclone inlet, outlet and outlet analyzed for O2 to determine leakage
- Pressure profile: mill inlet, above table/lower body, upper body, classifier inlet, outlet, mill outlet, cyclone outlet, fan inlet and outlet using digital manometer or U-tube
- Verification of calibration of the feeder of weight: all the feeders of raw material by means of test of fall or cut of strap
In addition to the samples and field measurements, the following data from the control room operation must be collected:
Operating Data (from CCR)
- Power – mill motor, classifier, fan
- Mill fan damper and speed
- Mill vibration
- Bleed air damper
- Feed rate
- Pressure – mill inlet, outlet, mill differential, cyclone differential
- Temperatures – mill inlet, outlet
- Classifier speed
- Grinding pressure
- Maximum production
- Fuel efficiency
- System gas flow
- Power Consumption
- Bottlenecks and recommendations for improvement
Operational variables to be monitored include:
- Pyro system temperature profile
- Pyro system pressure profile and differential pressure
- Gas analysis- kiln and PH tower
- Power of major processing fans
- Power of kiln drive
- Cooler drive speed
- Cooler fan flows
- Clinker temperature
- Burner performance
The following measurements and samples can be taken:
- Air flow Measurements by Pitot tube or anemometer
- Temperature Measurements by hand-held thermocouple
- Kiln, cooler, and preheater radiation measured with handheld pyrometer
- Power Data – current and percent output measured with amp probe
- Kiln Dust weighed for a sufficient length of time to determine an average dust loss in tons/hour
- Gas Analysis (CO2 and O2)
- Operation Parameters
BALL MILL AUDIT DESCRIPTION
- Current level of production and power consumption
- Current product quality including all laboratory analysis (Blaine, residue, etc.)
- Feed size and composition;
- Description of any current problems with operation
- Daily operating logs during normal, stable operation for at least one month prior including grinding aid and water spray rates
- Types of liners and screens and other mill mechanical data
- Ball charge history
The mill performance will be evaluated in relation to the following:
- Ball charge and mill grinding efficiency
- Maximum production
- Comparison of actual power consumption (kWh/MT) versus laboratory test
- Separator circulating load and efficiency
- System airflow
- Material flow through the system
The following measurements and samples may be taken:
- Circuit samples for evaluation of separator performance will be taken during operation and analyzed by the plant laboratory for 45µm residue.
- Hourly Blaine and fineness measurements taken on cement mill product.
- Clinker, gypsum and other additive samples taken for grindability tests.
- Determination of air flows through the ball mill system wherever possible
- Logging of all available operating data
The mill may be crashed stopped for internal inspection and sampling:
- Measurement of charge height and internal dimensions in each compartment
- Internal inspection of ball charge, liners and screens
- Measurement of screen slots
- Axial samples of material through the entire mill length. Residues and Blaine determinations to be done by plant laboratory, required sieves from 2mm to 45 µ
- Ball samples at same locations to determine charge composition
A plant audit is the basis for optimizing plant operations and often has the lowest cost/benefit ratio of investment.
The operations audit can be a beneficial first step in aiding the industrial and process engineer in assessing the appropriate focus for later problem-solving efforts and can be used in a variety of circumstances in most production and operations environments.