FOR VERTICAL        ROLLER MILLS      by Matthias Authenrieth, Thomas Hyttrek and                          Andreas Reintke...
PROCESS CONTROL        I LM-Master for VRMs          by Matthias Authenrieth,                       Loesche is launching i...
PROCESS CONTROL               timely, accurate and rapid               control actions to address               issues wit...
PROCESS CONTROL                                                                                                           ...
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LM-Master for Vertical Roller Mills


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Loesche is launching its new LM-Master for advanced vertical roller mill (VRM) control. This automation solution stabilises the VRM to allow operation with lower vibration. It also optimises mill performance by making accurate control actions several times per minute and offers continuous monitoring of the milling circuit for improved operational visibility.

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LM-Master for Vertical Roller Mills

  1. 1. FOR VERTICAL ROLLER MILLS by Matthias Authenrieth, Thomas Hyttrek and Andreas Reintke, Loesche GmbH, Germany, and Steven McGarel, Senior Consultant, USALMmaster_forVRMs.indd 1 19.06.12 11:46
  2. 2. PROCESS CONTROL I LM-Master for VRMs by Matthias Authenrieth, Loesche is launching its new LM-Master for advanced vertical roller mill Thomas Hyttrek and (VRM) control. This automation solution stabilises the VRM to allow Andreas Reintke, operation with lower vibration. It also optimises mill performance by Loesche GmbH, Germany, making accurate control actions several times per minute and offers and Steven McGarel, continuous monitoring of the milling circuit for improved operational Senior Consultant, USA visibility. V RMs have become the grinding circuit of choice in cement plants for raw meal, clinker and coal grinding due to their lower capital cost and energy consumption compared to ball mills. Loesche GmbH, Germany, has been a leading supplier of roller mills for over 100 years and in more recent times, has expanded by adding a subsidiary automation company for both hardware and software delivery and project management. The latest addition to the automation software portfolio, which already includes mill simulator and SCADA solutions, Figure 1: reducing process is an advanced mill controller called variability improves performance LM-Master. This provides fully-automatic control and real-time optimisation of the mill process through precise control allow for some margin of error due to requirements for production rate, product of mill behaviour according to defined mill process variations, eg, from feed consistency and energy consumption, the objectives of throughput, energy materials. The development of the optimal combination of set points can efficiency and mill availability. The LM-Master solution reverses this situation be calculated on a high-frequency cycle software platform is installed on a PC and by monitoring and controlling more to drive the process to the economic interfaces with common PLC systems. frequently than any operator and allows optimum continuously. With high controller availability the mill for operation at higher capacity and levels is continuously operated close to physical of stability than can be achieved by an Reduction of vibration levels limits yet also with improved stability and operator alone (see Figure 1). Roller mills are constructed of major reduced vibration levels, ensuring high mill mechanical components that can be efficiencies for low capital expenditure. easily damaged by high mill vibrations. It New-generation optimisers such is very important that a mill is operated LM-Master mill optimiser as LM-Master use a dynamic in a stable manner and that corrective Loesche has unique knowledge of all model of the actual mill, resulting actions are taken to prevent damage aspects of roller mill design, operation and in improved regulatory control to mechanical equipment and mill automation, allowing the development of and set points closer to the outages that result in lost production. detailed and accurate mill control models. Unfortunately, high-vibration scenarios physical limits of the process. These have been incorporated into an arise very rapidly and a mill may trip advanced control software platform which before an operator even has time to allows the mill control functionality to be The control solution monitors multiple assess the situation and take corrective configured and held in-house to protect process variables and calculates new set action. LM-Master is valuable in these proprietary knowledge and intellectual points several times a minute to maintain situations in that, not only does a mill property. mill performance at very high levels. operate at generally lower vibration levels The kiln is the equipment that demands Operating at an economic optimum under LM-Master control – reducing the most attention from operators in a is a challenging control problem since wear on gearboxes and other major cement plant, hence mills are generally this constantly varies. However, by components – but the continuous operated below optimum capacity to specifying the overall – and competing – monitoring of the mill process allows for INTERNATIONAL CEMENT REVIEW MAY 2012LMmaster_forVRMs.indd 2 19.06.12 11:46
  3. 3. PROCESS CONTROL timely, accurate and rapid control actions to address issues with high vibration and prevent mill trips. Requirements of VRM operation Safe, reliable and productive use of a mill plant requires consideration of the following: • high production rates in the presence of potential limitations in: – mill table power – mill differential pressure via the mill fan – external recirculation system via bucket elevator or other conveyors – drying capacity via mill exit temperature control Figure 2: control structure diagram • low product size variability: – balance throughput with stability of mill regulatory and operational safety as Control (MPC) which calculates the – adjust for changes in feed hardness to primary objective. Without coupling of optimum combination of set points to promote consistent grinding the dynamic relationship between loops, meet multiple objectives of throughput, • low specific power consumption: holistic optimisation across the process is product quality and process limits – reduce variability in the load parameters basically impossible. In practice, loops are simultaneously. The structure of the (mill table power, mill differential pressure, de-tuned to maintain process stability and control scheme is shown in Figure 2. mill fan power) do not control the process very effectively. In addition to a cross-coupled – reduce specific power (mill fan and mill In VRMs in particular, highly-interactive multivariable control structure, the table). variables and rapid process dynamics technology has an inherent capability for make PID control difficult while variations disturbance rejection which is desirable in Control technology in the hardness of mill feed represent a grinding circuit control, due to the varying and structure major disturbance to the circuit. nature of feed streams. Traditional PID single input/single output New-generation optimisers such as The main features of MPC technology control has some inherent disadvantages LM-Master use a dynamic model of are: in that each loop operates where a single the actual mill, resulting in improved • a dynamic model as opposed to a variable set point is compared to the regulatory control and set points closer to steady-state model controlled variable. Multiple PID loops the physical limits of the process. • true closed-loop control with built-in are used on a mill circuit, yet these are The technology selected for the control optimisation connected as stand-alone loops with solution is based on Model Predictive • mathematical basis allows optimal solving for control actions in real time Figure 3: system architecture: LM-Master connected to the control network • computationally efficient, allowing controllers to run at high frequency • predictive capability as opposed to reacting to process conditions. The controller will take advantage of stable conditions to increase production, while under upset conditions – such as high vibration – the controller will simultaneously act to reduce vibration, protect process stability, reduce and then restore production while maintaining product quality. Since the controller solves the optimisation problem online, updates can be made to the objective function (to change the operational behaviour of MAY 2012 INTERNATIONAL CEMENT REVIEWLMmaster_forVRMs.indd 3 19.06.12 11:46
  4. 4. PROCESS CONTROL LM-Master-based the process), to the model (to change an interesting challenge in demonstrating parameter values), and to process limits in how a software-based solution could optimisation response to external factors, eg tyre wear deliver additional performance benefits in a VRM. over a mechanically-sound, well-operated advantages These changes are made with the mill. controller running, so the effect of the The project was structured with discrete tuning changes can be evaluated in real steps: time. • historical data was analysed to • Fast process dynamics are Many of the challenges in designing determine mill baseline performance controlled by a control solution controllers which can handle multiple • important control variables were with high frequency. uncertainties are embedded in this online identified for the mill • Multiple inputs and outputs optimisation routine. This results in • process tests of the main variables were are tightly controlled over the controllers which are robust over time conducted to determine mill response complete mill circuit. and which require less maintenance post- • controller was constructed and • Competing objectives of commissioning. connected to the PLC control network throughput, quality and energy The controller resides on a desktop or • calculated control actions were initially consumption are balanced rack server and uses an OPC interface checked in Read-Only mode optimally. to connect to the control network. • variables were activated in Read-Write • Continuous display of control When online, LM-Master writes set mode one by one and tuned performance aids the operators. points directly to the PLC and out to the • multiple variables were activated in • Stable operation reduces mill individual field devices. The architecture is Read-Write mode and interactions tuned vibration problems and allows shown in Figure 3. • run time was accumulated in full closed- operators to focus on kiln A browser-based interface allows loop control to fine tune. operation. multiple users to access the system and By integrating the customer’s operators monitor performance. An operator log-on into the process and promoting close screenshot is shown in Figure 4. teamwork, buy-in of the concept was cent, from 505tph to 528tph achieved and ensured an excellent final • Specific power consumption Project case study solution. was reduced almost five per cent The development and testing of The development and implementation • Mill vibration was reduced by 17 per the LM-Master control solution was was achieved in 2-3 calendar months and cent conducted on a 500tph mill. This was the overall schedule, including planning • Controller utilisation was greater than considered to be already operating well by and post-project evaluation of results was 90 per cent the customer and therefore represented approximately four months as shown in • Operators are freed up to better Figure 5. monitor kiln performance • Reduced CO2 emissions from the plant Project results (produces its own electric power) The project showed • Project Return on Investment was less impressive results, than 12 months. particularly given the customer’s assertion Conclusion that the mill was already The specially-developed roller mill operating well prior controller LM-Master has been to the LM-Master demonstrated to improve the operating implementation. environment for control room operators • Production rate was and increase mill performance. The increased almost five per solution leads to better utilisation of Figure 4: operator log-on screen personnel by automating the routine control of roller mills and freeing operators to focus on kiln operation. On the roller mill, the solution delivers higher production rates, lower specific power consumption, more stable mill operation leading to improved product consistency and lower vibration levels. This can have additional benefits such as avoiding vibration trips with a loss of production time and reducing wear and costly damage to major mechanical Figure 5: project Implementation schedule components such as gearboxes. ____ I INTERNATIONAL CEMENT REVIEW MAY 2012LMmaster_forVRMs.indd 4 19.06.12 11:46