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Cement plant on autopilot: a practical guide to success

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The pressures facing manufacturing industries, such as the cement industry, are well known and often discussed in the pages of trade magazines and industry conferences. Similarly, the benefits of digitalization and Industry 4.0 have been much advertised by suppliers and users, keen to position themselves at the forefront of industry development. Terms such as Internet of Things (IoT), big data, data analytics, artificial intelligence, and cloud technology have become largely familiar – if not fully understood. 

The question has now become not if these digital technologies can bring significant advantages to cement operations but how they are able to achieve ongoing process optimization in practice. This article will take a look at one aspect of that, focusing on the use of advanced process control (APC).  

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Connected, intelligent operations

Figure 1. Driving up the digital value chain.  

When planning and implementing a digitalization strategy, it is important to take a holistic approach. This means moving the process from isolated and discrete functions to one in which processes are connected, via developments in IoT technologies, and then automated. From there, it is possible to transition to autonomous operations, whereby optimization and asset management functions occur largely without human interaction within a secure cyber environment.  

The key therefore to successful digitalization is data, collected directly from connected equipment and processes or derived from soft sensor models. The latter can be used to infer data where no measurement exists, e.g. when real-world measurement would be too expensive, or to increase the frequency of data input and provide backup for unreliable measurements. 

Using this data, it becomes possible to supplement the human operator’s skill and creativity to better control the process and optimize performance. Central to this process is advanced process control (APC). 

The autopilot to an optimized plant 

 Figure 2. APC first stabilises and then optimises the process.

APC - such as ABB Ability™ Expert Optimizer - is best conceptualized as the autopilot that drives a plant to its optimum state. Using model predictive control (MPC), APC is able to reduce process variation and move the process closer to the constraints. It is able to achieve this by first understanding process interactions and delays through data driven empirical models, such as state space models and then making small changes, much more frequently than a human operator could, thereby creating a much more stable process environment than is possible under manual control (Figure 1).

The use of APC therefore offers the potential to overcome a range of customer challenges to:  

1. Minimize costs:  

    • Minimize energy consumption 

    • Minimize consumables  

2. Maximize yield: 

    • Minimize variability 

    • Maximize throughput while minimizing give-away 

    • Minimize shift-to-shift variations 

    • Minimize upstream disturbances 

    • Honor environmental process constraints 

The challenges of APC 

APC as a concept has been around for some time: the first description of the use of MPC to control applications was presented in the 1970s by Jacques Richelet. Despite its potential advantages, however, APC has acquired a mixed reputation. 

A typical APC project starts with the design, installation and commissioning of the applications, at which point the benefits are realized. With the system performing as promised, the user might well decide against the cost of a service-level agreement, preferring to maintain the system via an onsite champion. Over time, however, this onsite champion moves on, while operating conditions, such as raw materials and fuels, gradually change to the point that the predictive model no longer reflects the actual operating conditions. As a result, performance of the application starts to decay and it is eventually turned off.  

The development of new digitalization technologies, such as IoT and cloud computing, offers a solution by moving APC from a CAPEX-led investment with separate software license and maintenance agreements to a collaborative and continuing partnership between APC supplier, such as ABB, and plant, based on the idea of subscription licenses and services. Not only does this mean that the advantages of the system are maintained, but it opens opportunity to achieve enterprise-level multi-site optimization.  

The benefits of this approach can be summarized in three words: collaborative, faster and lower risk:  

  • Collaborative: information is accessible to anyone, anywhere, on any device, at any time. This brings operational visibility to all levels of a business: from a top-level fleet view to compare and benchmark plants, to looking at individual plants to assess critical KPIs, down to viewing individual operations and assets. 

  • Faster: quicker reaction to changes in the process. 

  • Lower risk as a result of lower operational costs and a completely managed environment. The APC is maintained and the benefits sustained and no longer de-activated and then forgotten. 

APC: a guide to success 

As the success of APC implementation has not always been achieved over the long term, ABB offers a three-phase approach to ensure continuous system performance under the banner of ABB Ability™ Performance Optimization for mining and cement (PRISE; see Figure 3): 

  • Evaluate. 

  • Implement.  

  • Sustain.  

Under the first phase, a plant’s needs are assessed via a site study (fingerprint), which helps to define and evaluate a digitalization roadmap based on tangible monetary benefits (ROI), including process stabilization, consumables reduction, throughput increase and quality increase. The goals of the study are:  

  • To identify bottlenecks via data analytics of real plant and process data.  

  • To deduce recommendations to handle the identified issues.  

  • To provide a roadmap for APC applications based on ROI and speed of implementation.  

  • To provide a budgetary costing and resource planning for both parties.  

The analyses and KPIs included in the scope of the study vary from site to site but generally cover raw materials processing, raw mill, calciner, kiln, cooler, and cement mill (Figure 4). It is also recommended that certain preliminary data is provided before the onsite study begins, such as process flowsheet; heat and mass balance (where relevant); process description; standard operating procedure. 

Figure 3. Performance optimization for cement (PRISE)

Figure 4. Analyses and KPIs that can be included in site study. The scope is subject to change during the site visit, depending on plant suitability and information availability.  

Figure 5. Work flow of site study: data understanding and data preparation are critical steps. It is therefore critical that the information collected is as accurate as possible.  

Once the site study has been undertaken and presented to the site and assuming APC implementation moves ahead, the challenge then becomes maintaining the benefits after commissioning. As noted previously, this has been the downfall of APC systems and the reason behind its sometimes less-than-favourable reputation. ABB overcomes this through a process of KPI monitoring. 

The monitoring of KPIs provides a quick overview of application performance and availability with the following goals:  

  • Monitor ongoing application performance.  

  • Highlight areas of concern.  

  • Minimize engineering required to troubleshoot misbehaving controllers.  

  • Maximize application performance.  

KPIs are either predefined and setup during commissioning or can be customized by the client. Predefined KPIs relate to the general performance, effectiveness and utilization of ABB Ability™ Expert Optimizer, or to the manipulated and controlled variables.  

By regular monitoring of the system’s performance, the problems posed by it ‘going out of date’ or a site losing its APC champion are avoided, ensuring the benefits continue to be enjoyed long after commissioning and eliminating the potential for the system to be switched off by operators.  

The benefits of APC 

When implemented and maintained to these best practices, APC becomes a powerful tool for ensuring a cement operation survives and thrives in a competitive business environment. Indeed, typical improvement values delivered by ABB to users of ABB Ability™ Expert Optimizer include: 

  •  Up to 50% use of alternative fuels.  
  •  1%-3% recovery in product.  
  •  Up to 30% reduction in consumables.  
  •  Up to 8% increase in throughput.  
  •  Up to 50% reduction in quality variability.  
  •  Up to 10% reduction in emissions levels.  
  •  Longer equipment lifetimes.  
  •  Improved operational discipline.  
  •  Reduced energy consumption.  

Conclusion: a data-driven revolution 

Data lies at the heart of this revolution. Cutting edge technologies, such as IoT and cloud computing, are connecting equipment and processes to plant operators and company management like never before. With more and better quality data now available, advanced data analytics and artificial intelligence can be applied to enhance process control and bring the concept of an autonomous plant within reach. Boosted by these advances, APC is moving beyond its checkered past to play a leading role in the development of the intelligent cement plant.  

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