According to you, what are the noticeable technological advancements in cement manufacturing that have taken place in the last 10 years?
In the last decade, technological advancement in cement industry has taken place with a steady uniform pace. In grinding area, close circuit pre-grinder in combination with close circuit tube mill has gained considerable popularity especially for capacity upgradation. For new grinding installation, vertical roller mill is still the most accepted. Improvement is taking place in this area too. For very high capacity cement grinding, [recently] LOESCHE and RENK together developed COPE (Compact Planetary Electric) drives, especially for powerful vertical roller mills with over 6 MW power. To address exact material friction factor and to stabilise grinding, variable speed (75 per cent to 100 per cent) drive for grinding table is being recommended by a few OEMs with success reference. Development is also being taking place for roller press.
Recently, a lot of research is going on in the field of green cement. In contrast to conventional cement, its production does not involve any burning process. "Slagsrar" is one such cement, produced from granulated slag, sulphate agent and special additives, patented in over 50 countries worldwide.
In fact, improvements are taking place in every area/equipment in a cement plant. In electrical side, use of VFD drive has become a regular feature contributing in saving electrical power consumption. Like every other industries automation, now a days is being applied in any aspect you name like optimisation of process, fuel mix, product mix, power consumption, in laboratory, in condition monitoring and predictive maintenance even from remote, ensuring safety, in cement production accounting and many others.
What is the progress done to reduce overall energy consumption in manufacturing.
In today's date, embracing energy conservation has become an important aspect in any manufacturing process. Since, cement manufacturing sector ranks third in the consumption of energy worldwide, the reduction of energy consumption becomes integral.
Advances in pyro technology have brought down heat consumption of ~1,400 kCal/kG clinker for wet process kilns to <700 kCal/kG clinker for state-of-the-art dry process kilns. Around 400 kCal/kG clinker requires as heat of reaction for clinkerisation. The rest is needed to cover losses from radiation (~60 kCal/kG clinker), cooler (~100 kCal/kG clinker) and preheater exhaust (~160 kCal/kG clinker). About 30 kCal/kG clinker comes from material and fuel. As a standard practice part of heat from preheater/cooler exhaust is utilised for raw material/fuel drying. To conserve thermal energy, alternate avenue of generation of electrical energy from preheater exit gas as well as cooler exhaust air, WHRS, has got enhanced promotion. Cogeneration potential ranging 20-30 kWh/t clinker exists in different plants, saving ~15-25 kCal/kG clinker.
Other than saving of energy directly by improvement of electrical system like VFD system, considerable energy saving could be achieved by introducing pre grinding concept for raw material and cement grinding, reducing idle run of equipment over improved run factor by higher level of plant maintenance and also plant optimisation through respectable application of plant automation and fuzzy logic.
What developments have occurred in pyro processing?
In pyro section, improvements have been observed for using alternate fuel. To tackle difficult situations, separate combustion chamber has been introduced for pre-calciner. Improvements have been noticed in fuel burners too to tackle alternate fuel and reduce NOx generation. Staged combustion in calciner has been proven effective in reducing NOx generation. Probably maximum work has been done on clinker cooler to improve cooler efficiency consistently as well as to reduce cooler maintenance. Almost all frontline OEMs have come out with new coolers claiming the both. Around 2.2 to 2.3 kG cooling air per kG clinker is being used to cool clinker to ambient plus 65 degree Celsius. At the same time, the grate load has typically been increased from ~40 to ~50 TPD clinker per m2, considering the same clinker temperature. Use of mechanical flow regulator for cooling air is another improvement observed in near past.
What are your comments on the use of Fuzzy logic and expert systems in kiln and mill operations and its propagation?
The concept of Fuzzy logic and expert system came into operation in cement industry a long time ago, in the middle of 1980s. However, it did not gain much popularity in India because it requires high degree of plant maintenance especially in instrumentation area. At moment, it is gaining momentum in mainly cement grinding. In pyro section, it is not much accepted.
What are the changes you can point out in grinding process?
In cement plant, a major portion of total consumed electrical energy goes for raw material and cement grinding. Developments have taken place in the last decade in introducing pre-grinder to close circuit tube mill. Various combinations of vertical roller pre-grinder and roller press with close circuit ball mill for grinding in semi finish and finish modes could save ~5-7 kWh/t in cement grinding. Use of VRM in cement grinding gives more saving. Developments are going in ball mill also. Using thinner liner plate with improved metallurgy creates higher chamber volume to accommodate higher grinding media and hence more power.
What is your take on continuous emission monitoring system (CEMS)?
In recent years, online emission monitoring technology has received attention and interest in context of providing accurate and continuous information on particulate matter/gaseous emission from stacks. There are already available systems for monitoring parameters such as PM, HC L, HF, NH3, SO2, CO, O2, CO2, NOx, VOC, etc.
The Central Pollution Control Board, in 2014, has issued directions under section 18 (1) of the Water and Air Acts to the State Pollution Control Committees for directing the 17 categories of highly polluting industries for installation of online effluent quality and emission monitoring systems to help tracking the discharges of pollutants from these units.
The direction envisage:
-Installation of online emission quality monitoring system
-Installation of surveillance system
-Ensure regular maintenance and operation of the online system with tamperproof mechanism having facilities for online calibration (onsite/offsite; remote)
At the moment, in cement plants, the parameters required to be monitored in the stack emissions using continuous emission monitoring system are:
-NH3 (as Ammonia)
-SO2 (Sulphur Dioxide)
-NOx (Oxides of Nitrogen)
With rapid industrialisation, it is becoming a necessity to regulate compliance by industries with minimal inspection of industries. Therefore, efforts need to be made to bring discipline in the industries to exercise self-monitoring and compliance and transmit (effluent and) emission quality data to SPCBs/PCCs and CPCB on a continuous basis. CEMS plays a vital role in this aspect.
What are the measures taken to reduce gaseous and dust pollution?
Recently, the Central Pollution Control Board has taken serious steps in reducing gaseous pollution, NOx, in cement industry. Latest norm for NOx emission through chimney is 800 mg/Nm3 and 600 mg/Nm3 for old and new installation respectively while the measurement is corrected for 10 per cent O2 and dry basis. Overnight demands for primary abatement for generation of NOx and SNCR (selective non-catalytic reduction) system have increased considerably. Installation of SNCR system for plants where NOx emission is on higher side has been taken up seriously by plant owners. If not properly installed or operated this system will contribute to ammonia emission to atmosphere. This is also to be taken care of though today there is no limit imposed by the Pollution Control Board.
It is relevant to mention here that at least for new plant installations, the owners should target NOx elimination to match today's norm in European Union and Germany, 200-450 mg/Nm3, keeping in mind the fact that in India, for particulate emission norm started at ~250 mg/Nm3 in 1990s and ultimately came to 30 mg/Nm3 to match the European standard. This is to avoid reinvestment in same area in future.
Dust collection and recycle equipment such as bag house/filter, electrostatic precipitator are commonly used to reduce dust emissions in cement industry. Use of bag house, which ensures uninterrupted and very efficient dust collecting system, is extensively being used for cleaning kiln/raw mill gases. However, for cleaning cooler exhaust air, still the electrostatic precipitator is being preferred, which should be replaced by high reliability bag house/filter in combination with heat exchanger or water cooling system in the system.
How far has been the penetration of robotic labs for quality control? What are your comments specifically on sample collection and real-time analysis.
Advances in automation over the last 10 years are permitting typical cement laboratory to go hi-tech. The use of microprocessor, computer control system, robotics and optics have permitted increased precision and accuracy in testing as well as greater laboratory efficiency. Uniform kiln feed quality is a must for smooth kiln operation and consistent quality of clinker. It requires homogenisation - right from limestone stacking to reclaiming. The next step comes in controlling raw mill feed proportions based on average raw meal sample analysis. The average sample collection from auto sampler on a real-time basis and prompt analysis play a very important role in this aspect. Collection of samples is totally dependent on availability, sincerity, training and also whims of sample boy. In a few cases, it also happens that the sample boy collects sample in one go and then furnishes hourly samples to laboratory from the same lot. The uniformity in analysis misleads kiln operator and makes his life miserable in controlling kiln operations. To avoid such problem and where management understood the importance, robotic lab is gradually started taking its place in Indian cement industry.
A few latest plants set up by industry leaders like Dalmia Bharat, Wonder, JK, Bharati Cements have robotic laboratories.
What about the automation done in the physical testing of cement?
With the increase in plant capacity, a number of units in same plant and a number of testing personnel, it becomes difficult to keep track on sample analysis, analysis procedures followed, maintaining regularity in sampling and storing of data, which has been normally done with the help of plant-generated spreadsheets. To handle this problem, new software are coming into concept, which supports from scheduling and planning, through testing, data acquisition and long-term data storage, to the final conformity report. It ensures one common and uniform interface to all data analysis and test procedures. It supports planning and scheduling of physical tests, collect analytical data, generates works list conformity tests, reports. The data treatment and reporting, operates in accordance with relevant EN/ASTM norms or any other standards, if opted. Ideally a given operator should only see information relevant for him.
What technological gaps you see in plants in India and that in Europe?
Although the Indian cement industry is keeping itself updated with the latest, avant-grade technologies in cement, there is further scope of improvement in certain areas like use of alternate fuel, pre-blending facility of coal, computer operated plant operation and in pollution control seriousness.
Another aspect is in philosophy. India is yet to gather confidence level to apply and improve upon well understood technology without case reference in Europe as a matter any western country. Application of SNCR system in cement plants is one example. Once confidence level is established many developments will definitely get start up in India.
What are the steps taken to reduce dust and mitigation of CO2 emission per unit of cement in the present system or by way of development of a new product?
Generation of fine particulates and dusts are inherent in the process of cement manufacturing. The priority in the cement industry is to minimise the increase in ambient particulate levels by reducing the mass load emitted from the stack, from fugitive emissions and other sources.
Serious measures have already been taken by most of the major cement manufacturers to satisfy norms set by the Pollution Control Board.
For control of fugitive dust:
-Ventilation systems are used in conjunction with hoods and enclosures covering transfer points and conveyors
-Drop distances are minimised by the use of adjustable conveyors
-Dusty areas like roads are wetted down on a regular basis to reduce dust generation
For production of OPC, CO2 generation is around 0.82 kg per kg of cement in best operated cement plants. Contribution from process generation is maximum, approximately 65 per cent followed by approximately 27 per cent and approximately 8 per cent from thermal and electrical energy consumed in production, respectively.
CO2 generation can be reduced by following process:
c -Reduction of clinker/cement ratio in cement
-Utilisation of biomass
-Making cement manufacturing more energy efficient
-Utilisation of decarbonated (secondary/waste) raw materials
-Oxy fuel technology
In India, the first process is widely in operation-blended cement has been well accepted and gaining its popularity day by day. In India, R&D/adoption of green cement should be strengthened.
Is use of simulation-based learning for skill upgradation happening in cement? Please give details.
Only blessed professionals passed through stage-wise proper training programme in the beginning of their career not only to become successful in future life but also to enjoy their jobs.
Effective training programme comprises of following three stages:
b)In-plant training; and
Probably, simulation-based training can be put in category b) and then onwards. In India, except for may be a very few plants owned by global cement companies, this facility has not become popular yet. Generally, in most plants, the new comers are put directly in category 'c' training. A big disadvantage in this process is that its success depends largely on trainer. In most of the cases, training does not become effective because of biased concept of trainers based on their past experience.
Well developed training simulators provide a dynamic simulation model of each process units, which is made up of sub-models, allowing for each customisation. A good training programme comprising of simulator-based training will definitely not only increase skill and produce good operators/supervisors but also in the long run the investment will be paid off in improved productivity. Earlier, the plant management understands the fact better it is for the industry.
What about the advancements in bagging and loading to reduce labour intensity?
Bagging and loading processes have always been labour intensive. In the past couple of years, compelling research has been dedicated to tackle this issue. One good example is the cement dispatch system software (FLS Automation and Ventomatic), which provides solution to most of the prevailing issues faced by dispatch operations. Such automated systems along with new age machines are contributing largely in reducing labour requirements.
What is your call on zero water consumption in cement manufacturing?
In recent past, governments around the world and companies have greatly increased their attention to the world's supply of fresh water and have recognised access to safe drinking water and sanitation as a human right. In this context, water has now taken up importance as a sustainability issue. Water conservation, water footprint and water management are having a prominent place on the sustainability agendas of many businesses, ranking next to carbon as a finite global resource that requires meticulous management. Many global cement companies like Holcim, Lafarge, CEMEX are developing methodologies to standardise water measurement and management across all the company's operations.
A modern, dry process cement factory consumes water in three ways:
i)For cooling bearings of large machines;
ii)For injection in process and dust suppression; and
iii)As potable, drinking water.
In total, a 3,000 tpd cement plant might require a bearing cooling flow of 3,600 m3/h. This cooling water is usually recirculated and around 20 per cent is required as make up
Water for injection into the process will vary from one dry process cement factory to another. The major consumers are:
-Dust suppression in crushers;
-Gas cooling tower;
-Cooler exhaust gas temperature control; and
-In grinding systems.
A benchmark value for water consumption in process use for a modern, dry process cement plant would be ~0.2/t of cement produced.
The first step towards water less plant or zero water consumption would be to monitor the current consumption. Once the base line value is determined, targets for reduction can be set and measures can be taken to reduce the water reduce the water consumption in gradual steps. Water management is indeed a need for cement plants today to be sustainable in future.
Jayant Saha holds a Masters Degree in Chemical Engineering from IIT Kharagpur. He worked with L&T for a long time, and was Director and CEO at Penta India Cement and Minerals Pvt Ltd. He is now a freelance consultant.
Titas Saha is a Chemical Engineer from Mumbai, and has obtained her Masters Degree from New York, USA. She did her internship with FLSmidth Inc.