In the current scenario of limited demand growth and competitive industrial environment, enhancing productivity and reducing the energy consumption has become the need of the hour for survival.
Over the years, Operations Audit has been found to be an effective tool for identifying the measures required to optimise the plant process operations and drawing action plans for exploring the hidden potential for enhancing the capacity through retrofitting route.
This paper discusses case studies to highlight the benefits accrued through conducting operations audit of plants.
Moreover, in view of the fact that cement production is an energy-intensive process, it is important for the cement production units to unleash the plant potential capacity so as to improve the capacity utilization and lower the energy consumption, ensuring reduced unit cost of production.
Process Audit helps in identifying the possibilities to upgrade the available equipment with optimum capital expenditure. A set of action plans are formulated based on identified improvement measures for implementation in the plant covering operational debottlenecking, establishing potential plant capacity, improving key performance indicators etc.
The main objectives of the process optimisation study are to identify the inherent potential in the entire production process starting from mining operations to packing. Each unit operation is studied and analysed including plant stoppages in detail with an objective to identify the potential improvement areas for optimisation of operational practices for sustained operation covering all the aspects.
Case Study - 1
Holtec Consulting Private Limited (HOLTEC) had carried out a Plant Operations Audit for a cement plant in the Kingdom of Saudi Arabia with following objectives:
Plant is operating at specific fuel consumption of about 880 kcal/kg and specific power consumption of about 121 kWh/t cement with about 50% bypass to avoid operational problems caused by presence of excess sulphur present in fuel and raw materials.
HOLTEC suggested the following improvement measures for reducing the bypass extent and reduced specific heat and power consumption:
Plant Capacity Assessment has been carried out based on the process measurements conducted by the HOLTEC team, data collected and discussions held with plant personnel during the site visit. The production capacity can be upgraded to 4,200 tpd clinker at a specific investment of USD 75 Plant implemented some of the above measures in a phased manner. Plant is currently operating at an average production level of about 4,200 tpd clinker at an average specific heat and power consumption of 800 kcal/kg clinker and 100 kWh/t cement.
Case Study - 2
Holtec Consulting Private Limited (HOLTEC) carried out a comprehensive technical audit for cooler optimisation in a cement plant in India having a dry process coal fired kiln with 5-stage suspension pre-heater, Separate Line Calciner (SLC), Grate cooler and Roller Press for Raw, Clinker and Slag grinding.
The target cement plant had operational issues with the cooler, affecting the kiln performance leading to reduced clinker production.
The rated capacity of the plant is 1,650 tpd and has operated at a peak production of about 1,900 tpd in the past. Due to operational issues with the cooler, the clinker production is reduced to 1,300 - 1,400 tpd.
Key Operational Issues
Observations Based on Internal Inspection of Cooler
The phenomenon of burning, faster wear, premature failure of the grate plates is attributable to deformations and misalignment in the support structure/frame which has now led to unwarranted gaps between the plates and cause of clinker fall through as well.
Observations Based on Process Measurement
Mass and Gas balance was done across the clinker cooler system in order to ascertain the present thermal efficiency of the clinker cooler system and cooler losses.
Details of heat balance worked out for clinker cooler is given in Table 2. Following are the observation based on process measurements:
Following actions were suggested for the improvement in cooler performance:
Case Study - 3
Holtec Consulting Private Limited (HOLTEC) had carried out a process optimisation study in a cement plant in Pakistan. The plant was operating at a production level of about 1,800 tpd clinker. The average values of specific fuel consumption and specific power consumption at the time of study were about 977 kcal/kg clinker and about 131.55 kWh/t cement respectively. The major equipments in the plant were a two chambers central discharge ball mill for raw material grinding, a dry process kiln with twin string preheater (PH) and a precalciner (PC) in calciner string, grate cooler and a two chamber, closed circuit ball mill for cement grinding.
Following actions were suggested:
With implementation of above improvement measures and under HOLTEC´s operational supervision, the following were achieved:
HOLTEC assessed the potential capacity of plant as 3,000 tpd clinker. For achieving this capacity, some important recommendations made are as given below:
With HOLTEC´s assistance, the plant implemented some of the above measures. Implementation of these improvement measures were done in a planned manner in consultation and supervision of HOLTEC, in a planned shutdown of about 5 weeks. The plant was able to achieve an average production level of about 2,850 tpd clinker. With complete implementation of the above recommendations, the expected kiln production is 3,000 - 3,100 tpd clinker. At this production level, the expected specific fuel consumption and specific power consumption shall be about 750 kcal/kg clinker and 90 kWh/t cement. Estimated payback period for the capacity upgradation worked out to about 5 months. Moreover, the plant operational consistency has improved a lot as a result the annual production has increased significantly.
The above case studies demonstrate that Operations Audit is an effective tool for identifying the measures required to optimise the plant process operations and drawing action plans for exploring and exploiting the hidden plant potential through retrofit route.
The broad specifications of the grate cooler are furnished below:
Inclined grate cooler
Table: Parameters considered during period of measurement
Table2: Mass and Heat Balance of Clinker cooler