1st Global Cement Electrical Energy Efficiency Conference & Exhibition
14-15 June 2011, Munich, Germany
A review by conference convenor Dr Robert McCaffrey
Global Cement's inaugural attracted delegates from 23 countries, including from Australia, Austria, Croatia, Denmark, Egypt, France, Germany, Hungary, Iran, Japan, Lebanon, Malaysia, Poland, Romania, Spain, Switzerland, Turkey, UK, UAE, the US and Zambia, to hear 15 presentations over two days on methods, technologies and equipment to improve electrical energy efficiency in global cement production. The event was highly rated by exhibitors and by delegates.
Global Cement's Electrical Energy Efficiency Conference took place at the centrally-located Eden Hotel Wolff, in Munich, Germany. There was a 'get to know you' session on the first evening, with the conference starting on the next day.
Following an overview of the global cement industry by Robert McCaffrey, conference convenor, the first technical presentation was given by Kazuki Ao of Kawasaki Heavy Industries (KHI) of Japan and Maarten Holland of Siemens, Germany. Mr Ao explained that KHI has more than 150 references for waste heat recovery systems (WHRS) for power generation around the world, starting more than 30 years ago, including 123 in China. Kawasaki has designed a unique preheater boiler with its boiler tubes located vertically, which can be located in a confined space. Mr Holland then explained that Siemens' high efficiency steam turbine is perfectly matched with the KHI WHRS, since they can operate at low temperatures and low pressures. Siemens also integrates the WHRS into the control and electrical systems of the plant. It is important to look at the altitude of the plant, the ambient temperatures and the availability of cooling water. Mr Ao stated that the WHRS does not influence other equipment at the plant. Operational reliability of the system is high and typically has around 99.5% availability over two years of operation. Mr Holland went through a sample feasibility study, which suggested that a European case would have a benefit of around Euro4.6m per year, leading to a payback in six years, with an Asian case paying back a little more quickly. A net present value for a project was given as Euro61m over 30 years of operation, even without taking into account and CO2 costs. Only preheater exhaust gas and air quenching cooler (AQC) exhaust gas are used, meaning that the power generated is truly 'green.' Using these sources, the German cement industry could generate 230MW, the equivalent of 800 windmills.
Thomas Marx of ABB Switzerland next pointed out that costs of fuels, materials and additives can be reduced by using alternatives - even if these can add problems to cement production. Thomas pointed out that production challenges and business challenges operate on different time-frames and are generally computed using different systems. He suggested that it is sensible to bring them together in a combined management system. ExpertOptimizer is ABB's tool for process control, which incorporates a number of different techniques including fuzzy logic, neural networks and model-based control. The model predicts process behaviour several steps into the future and requires the solution of optimisation problems at every step. The system considers process limits and safety issues, while at the same time applying cost functions to each variable in the process and minimising costs. These combined control models lead to strategies that run the whole cement process and which can include heat recovery parameters: the system is a like an auto-pilot. The system can also cope with inputs of energy cost forecasts and can optimise production scheduling. Mixed Logic Dynamics are used to solve both the production and business sides of this difficult and dynamic equation, while at the same time obeying contractual, environmental and process constraints. Thomas suggested that applying this software to a plant, without any other optimisation, around 3% of energy savings can be achieved each year, as well as production increases.
David Sterling of Schneider Electric promoted the use of ICT (information and communications technology) solutions for energy optimisation in the cement industry. Hover, projects can fail due to cost and time overruns and content deficiencies, where systems don't do what they promised. For an ICT system to be accepted it should be easy to use, it should reduce the amount of manual data entry and should be automated as much as possible, it should be scalable so that it can be expanded if the business or process changes or increases in size and it should be easy to implement. David examined energy use in context, so that energy use should be looked at in terms of comparisons with other plants, the industry as a whole or other industries. He suggested that it is critical to be able to visualise information and that dashboards that give management information can be very useful. The data collected needs to be relevant to the business issues of the cement company, but the most important thing is what is then done with the data. Drilling down into the causes for stoppages and acting on the information, can dramatically reduce the number of stoppages and downtime in a plant. Energy can be wasted when machines are left to run idle during stoppages and this can be a critical area for savings. 'Over-consumption events' where energy usage is much higher than expected, are another area of focus for elimination and David suggested that many of these events were due to people rather than equipment.
Thomas Börrnert of ABB Switzerland stated that an energy consumption of 3-3.5Gj/t is typical for clinker production and that since energy is money, energy efficiency is critical. Reusing the heat in the process should be the priority, since any energy conversion is less than 100% effective. The conversion of low temperature heat, such as is provided at efficient cement plants, can be effected by the use of organic fluids in the Organic Rankin Cycle (ORC). Heat is extracted from the process using water/steam and is then transferred to an organic medium in a separate circuit which is then used to power a turbine. Holcim has installed an ORC system at the Untervaz cement plant in Switzerland. In the first phase a preheater heat source will be used, with a second stage using clinker cooler waste air. The steam turbines used in the project will be very compact indeed - the power plant at the Untervaz plant will be placed on the top of another building. Thomas said that he hoped that his Christmas present this year will be the first production of electricity from the new plant. The two phases combined will provide around 20% of the plant's electrical consumption.
Two main heat sources can be used- the clinker cooler and the preheater gas flow. The preheater gas flow is perhaps more problematic, since it is generally at a lower temperature and will have a higher moisture and dusty content. Careful design of the heat exchanger is required to avoid problems. In theory a gas conditioning tower will no longer be needed, which may lead to higher production possibilities.
Heat extraction can be effected with either water or with thermal oil and Thomas gave details of the advantages and disadvantages of both: he concluded that thermal oil is less advantageous and so the ABB system uses pressurised water. ABB ORC systems have a one stage turbine with no intermediate superheating, fast start-up times, automatic operation and low maintenance costs. Payback times depend on process characteristics and the specification of the waste heat recovery system, but will depend heavily on the cost of electricity.
York Reichardt of Gebr. Pfeiffer then spoke about electrical energy characteristics of the new MVR roller mill. York pointed out that not all cement plants have enough 'waste' heat (after drying and possible calcination in drying/calcination mills) to make waste heat recovery plants worthwhile. Installing a frequency converter into the mill fans in a coal, cement, or slag mill, can lead to paybacks of only a few months: he suggested that dampers are essentially a terrible idea! Power generation with the co-usage of the heat for drying may become more and more economic, particularly in energy-rich regions. The MVR series of mills are designed to be larger than normal mills and feature built-in redundancy so that with the failure of either a drive or a roller, you can still run at perhaps 80-90% capacity.
Sune Vang Pedersen of Transvision then spoke about a slightly 'left-field' subject for the conference: transport system optimisation. Sune stated that this was potentially (and actually) a real source of energy savings for cement and ready-mix concrete producers. Transport systems also need to take into account the delivery time window of the customers, the optimisation of terminal capacity and loading capacity. They need to be optimised 'on the fly,' since delivery slots may be dynamically changed. Scheduling and dispatching and then delivery and tracking are the two areas where Transvision's software can help. It can also measure stock levels at remote partner sites and can automatically dispatch materials if necessary. Sune also gave a case study of Transvision's software in action at Aalborg Portland in Denmark. A 7% reduction in driving time was achieved, along with a reduction in planning staff from 18 to 4. The centralised planning office has now eliminated late or forgotten deliveries.
Frederic Boeuf of E.On Masdar then spoke on international carbon markets. Around 400Mt of carbon emission credits have previously been issued, but this is dwarfed by future credits: 1.9Gt of carbon credits are due to be issued by 2012, with potentially much more afterwards. There are many barriers to implementing energy efficiency projects., but at the same time there are many companies that will overcome them (for a fee). Frederic's company offers an integrated solution to the problem, including providing project financing, targeting Africa, the Middle East and central and south east Asia. Cement industry waste heat recovery is one of the company's main targets.
After the first day's technical sessions, delegates enjoyed a pleasant walk through the busy streets of the old town of Munich, to finally arrive at the Spatenhaus an der Oper, a cosy restaurant opposite the Munich opera house, for a very convivial evening of drinking, chat and networking.
Second day
On the second day of the conference, Angus Macdonald championed the use of lubricants to lower energy consumption. ExxonMobil forecasts that energy usage will average 200,000btu per person per day by 2030, or 15 billion btu per second worldwide. With these astonishing numbers in mind, it seems imperitive that we reduce our energy usage. The higher the coefficient of friction, the higher the frictional force, but on the other hand, the less work used to overcome friction, the less energy required to make a machine function. But, Angus suggested, oil is not just oil!
Angus stated that there are hundreds if not thousands of different types of lubricants in use around the world. Typically lubricants are composed of a base fluid and additives. Base fluids are either mineral oils derived from refined crude oil or synthesised base fluids. Additives will reduce rusting and wear and may include dispersants, thickeners or many other types of additive. Lubricants, Angus said, are all about reducing metal-to-metal contact. The right lubricant in the right quantities in the correct application must be properly maintained, with proper storage, handling, filtration and analysis. Angus presented a case study of a synthetic oil in a US cement plant gear box, which was experiencing high temperatures, foaming and lubrication breakdown. The old lubricant was replaced with a high-performance mineral oil, which led to a dramatic drop in temperatures in the gear box. Changing lubricants can also lead to lower power consumption, in the region of 3-10%, which can lead to savings of perhaps Euro3000 per year for the operation of a single screw compressor.
Dr.Ralf Briest of J. Helmke & Co. next spoke about the use of medium voltage variable speed drives (VSD), compared to slip ring motors. Each MW of power used in a cement plant equates to an electricity bill of approximately US$1m per year. Different types of motors have advantages and disadvantages. Obviously the VSD has variable speed, but it also suffers from lower wear. However, the frequency converter has inherent losses when used in continuous operation, it requires clean ambient air, has limited starting torque, additional hardware costs and potential harmonic interactions. The slip ring motor has simple topology, no additional losses during continuous operation, high starting torque, no harmonic interactions and robust operation. However, on a slip ring motor there is continuous wear on the brushes requiring regular maintenance and higher motor costs. Compared to a simple squirrel cage motor, a slip ring motor might be 245% of the cost, while a VSD might be 750% - but the VSD benefits from an energy saving over the slip ring motor of around 5%, bringing the total cost of operation of the VSD over 20 years down to an equivalent cost of a slip ring motor. In a simple case, a VSD is likely to be best for a fan, a slip ring for a ball mill.
Thomas Becker from EMZ described his company's capabilities in the supply of low and high voltage motors. New IE2 regulations require that new squirrel cage motors are designed and constructed to run at higher efficiencies, using higher specification materials. Thomas pointed out that 95% of the life cycle costs of a motor are energy costs and even higher in the case of higher power ratings.
Robert Part of CE Electric Systems Hungary first gave a short overview of the company, pointing out that it has a deep experience and history of innovation in electrical motors. Robert suggested that a double cage motor can be an effective solution for cement plants. The inner cage is made of high grade copper and the outer 'starter' cage is of a high resistance alloy, with the entire motor built to very high tolerances. A double cage motor has high electrical energy efficiency, has a fast startup time and can avoid resonances and has a long life expectancy, due to its robust construction. "Why is this obvious solution not more widely used?" asked Robert Part.
Gunnar-Marcel Klein, technical director at Intensiv-Filter GmbH, next spoke about the possibility of improving the energy efficiency of bag filters using his company's expert system to reduce delta-P. A typical cement plant might have 100 bag filters in operation, including small 'nuisance' filters and each small improvement in operation can result in large savings over time. Decision matrices can be used to determine the maximum possible filter bag length for jet-pulse bag filters. Even using the most efficient injector nozzles (Coanda-type nozzles) the profile of the excess pressure pulse will modulate over the length of a filter bag, essentially becoming too diffuse to be effective for cleaning at the end of greater lengths of bag. The matrices can be used to find out the minimum impulse pressure that can be accepted for cleaning, which depends on the material being filtered and to find the maximum length of bag which can be applied with the available cleaning pressures. Intensiv-Filter's ProTex needle felt gives a lower residual delta-P after cleaning than other fabrics. In addition, the company's ProExpertise system works out the optimum frequency of filtration cleaning, using 'cake filtration theory:' too frequently and too much compressed air will be used, but too seldom and the delta-P due to the filter cake will be too high. The optimum cycle time will of course vary from case to case.
Hans-Jürgen Scholz for Grace suggested that additives can create benefits that exceed their cost (and if not, he said, then you should stop buying them!). Additives can increase mill output, with a resultant reduction in specific energy consumption and can also improve cement performance in a number of ways. In grinding, additives reduce agglomeration and coating and improve dispersion to allow increased separation efficiency, leading to lower power consumption. Grinding efficiency can be improved by up to 30%. In ball mills, a high circulating load leads to lower mill exit fineness and higher efficiency, but also leads to a higher separator feed rate, higher bypass and lower separator efficiency. Each mill has its optimum level of circulating load, which is determined from operation at different total feed set-points. The use of smaller balls in the mill leads to higher surface area and higher grinding efficiency, but also leads to an increased rate of breakage and increases void filling. The use of an additive can decrease ball coating and can optimise the conditions for using smaller media.
Jörg Schrabback of Sika continued on to expand on the use of additives to reduce grinding energy. Cement grinding can use up to 35-40% of the total electrical energy used in cement production. Increasing production rate can mean that it may be possible to switch off the mill for longer if the market is not sold out. Next-generation polycarboxylate-based additives such as SikaGrind aid in particle dispersion and promote prompt material exit from the mill, increasing throughput. The additive also aids in agglomerate dispersion, which increases the efficiency of the separator and also decreases the coating of the grinding media and the mill internals. One case study at Qassim Cement in Saudi Arabia led to an increase in mill production of 20%, while at the same time reducing the specific energy consumption from 31kWh/t to 26kWh/t. The use of an additive can also increase the quality of the cement such that the cement can be ground to a coarser size, while achieving the same strength: this will also result in a reduction in specific electrical energy consumption.
Awards and prizes
At the end of the conference a number of prizes were given out, based on delegate voting. In third place in the best presentation awards was Thomas Börrnert, head of heat recovery at ABB Switzerland. In second place was Jörg Schrabback of Sika Services, with his paper on energy savings with additives. However, in first place, and winning the award for best presentation, was Angus Macdonald of Lubrication Engineers International AG. Schneider Electric was awarded the 'best exhibition stand' award.
The event was strongly commended by delegates on the conference questionnaire for its technical content, value for money and networking opportunities.
