Operational excellence is a business necessity to achieve and maintain a strong market position within the chemicals industry. One way to gain a higher level of operational excellence maturity is with a well-planned Advanced Process Control (APC) implementation programme. While the goal of APC implementation in the chemical industry is simple, which is to maximise margins while meeting customer expectations, there are a few factors which chemical operators need to consider to ensure a successful implementation.
Understanding the benefits of APC
When APC was originally introduced in the early to mid-80s, it was designed for refineries and petrochemical sites. Since then, this technology has evolved. APC is a process control and optimisation technology that takes into account the multivariable interactive nature of process units to reduce variability and drive the process to an optimum on a minute-by-minute basis. This is done by manipulating variables such as feed flow, temperature settings, pressure settings, and reflux flows, which are normally changed by operators who run the unit.
Due to the multivariable nature of process interactions and variability that is inherent in process units, operations cannot fully optimise the process manually, as this will result in key variables moving out of the desired range of operation from time to time. To be on the conservative side, operations are forced to move the process out of optimum and into a more comfortable operating range. However, this often results in higher costs and/or lower production rates. There is more energy usage, lower yields and lower feed rates compared to operating with APC.
For decades, APC has proven to reduce the variability in the process by actively controlling key process parameters on a minute-by-minute basis. The controlled variables are stabilised and the standard deviation is reduced. Once the key variables are stabilised, the optimising nature of APC is used to move the process to a more optimal point. This results in consistently operating the unit close to the maximum possible profit, day in and day out, safely and reliably.
Identifying APC opportunities
The first step, when implementing an APC programme is to understand what process unit or part of the unit is a good candidate for APC. To be able to quantify benefits and improvement opportunity, it is necessary to first understand the economics of the unit and the production process. It is also necessary to consider the unit by itself or in many cases, its role within the bigger production value chain. If organisations have business or process KPIs, they can serve as a good starting point for analysing the APC opportunities. However, there are other ways in which potential APC benefits can be calculated. Below are some specific examples that can be used to quantify the benefits associated with an APC project.
1. Production increase: Typically, APC projects have proven to increase capacity by 3-5%. By reducing the variability in the process and operating closer to limits, APC debottlenecks the process, or part of the process, allowing for higher production rates. In order for this to happen however, an understanding of how and why the intermediate products affect downstream units is required.
2. Energy savings: Energy savings from APC implementation have been reported to be in the range of 3-15% depending on the process and current operations. Most of the time, utilities management, especially steam, is a complex control issue, which spans across the site and at times also affects the electric grid. APC applications can be designed to manage utility systems effectively by matching steam production to the site’s demand. Benefits come from reducing pressure let-downs and reducing or eliminating vented steam on site. Many companies report a 60-90% reduction in vented steam using APC. After the steam header pressures are stabilised, APC can also be used to optimise energy production. For example, boiler loads, gas turbines or other sources of energy can be adjusted to maximise the efficiency of the overall system while ensuring stable header pressures, day in and day out.
3. Quality improvements: It’s important to reduce variability in the final product quality. Some products, for example, certain types of polymers and specialty chemicals, sell their product at a value, which is dependent on the quality variability of the batch produced. Many companies report a reduction in standard deviation of product qualities of up to 50%.
4. Yield improvement: With APC deployment, many organisations experience a yield improvement of 1-2% through APC deployments. This is typically achieved by optimising the reactor part of the process and/or the separation portion. In almost all cases, the reaction is highly exothermic or endothermic, meaning good reactor temperature control is key. Additionally, good control and optimisation of the ratio of feed components to catalyst is also very beneficial. Well-controlled reactors typically see an increased yield of 0.5 per cent per pass at the same throughput rates, while maintaining safe operating temperatures. In some cases, it has been proven that a well-controlled polymer reactor online time is increased by up to 5% before a shutdown is required to clean out the reactor, resulting in improved yields and throughput. For the non-reaction part of the process, such as distillation columns, maintaining the specifications on the final product can increase the yield of the desired product by increasing impurities up to the contracted specifications. Higher amounts of lower value products (impurities) in the final product are sold as higher value product, while maintaining the specifications and customer expectations.
5. Optimising the polymer production wheel: In polymer production, the production wheel is usually not optimised to market needs, as difficult transitions may be rejected by operations. Without APC, grade transitions take longer and result in low value products produced during these transitions. It's common to see a 20-50% reduction in grade transition time. Through APC, it is possible to “bust the production wheel” and produce grades when they are in demand, while minimising the time when the low-value transition products are produced. Companies using APC in conjunction with supply chain software can exploit the new capabilities to further optimise the production wheel.
6. Emissions control: APC implementation can also help control environmental constraints. By using APC to model and actively control the furnaces and boilers on a steam utility plant through APC, it is possible to operate closer to the emissions limits without violating them. It also helps decrease energy usage and minimise costs to meet NOx and SOx emissions constraints.
7. Exploiting ambient temperature effects: APC has proven to exploit the benefits associated with ambient conditions. Ambient temperature has an effect on compressor performance, condensation capacity, gas turbine operation, cooling water temperature, refrigeration capability, gas volumes and many more process related conditions. Diurnal effects, humidity or even cloud cover have an effect on cooling water temperature, which can result in changes in compressor throughput limits. Operators cannot be expected to exploit the benefits associated with ambient temperature changes. This would mean anticipating the ambient temperature effects on the process and adjusting the process parameters only to reverse all changes as the sun rises in the morning. Units that are affected by ambient conditions can benefit from APC applications as they can anticipate these changes and adjust process parameters accordingly on a minute-by-minute basis.
8. Site-wide optimisation opportunities: Operating units with APC presents a larger scope of optimisation opportunity for the site. Optimising a part of the process as a standalone would mean lost opportunity compared to optimising multi-units together. For example, pushing a reactor to maximum throughput might not make sense if the bottleneck of the unit is the off-gas stripper. If this happens, light materials that should be removed are pushed into either flare or off-gas where they are lost. At some point, this may mean reduced margins. These interactions and constraints are considered in the design of APC systems and can lead to significant benefits for the overall site.
APC deployment and project lifecycle
After identifying the business case for an APC project, the next step is to start building and implementing the APC controller. Traditionally, APC projects have been long and expensive with many defined steps needed for a successful APC commissioning. For example, organisations would be required to go through many phases of step testing, model building, controller development and commissioning before moving onto deployment. As a result, many companies were faced with lost margins during the lengthy deployment phase and disruptions to the process for gathering data to build APC models. Additionally, this process required highly experienced users to build and sustain controllers.
Some companies today have moved beyond the traditional methods to a more advanced technology by integrating Adaptive Process Control with APC technology. With Adaptive Process Control, these four phases have been combined into one, allowing users to experience faster deployments and sustained benefits through continuous model updates in the background with no disruptions to the process. In addition, these tools enable more and less experienced users to deploy and sustain APC controllers, which can save both time and money within the organisation.
Advanced APC technology also helps companies sustain benefits. In the past, any changes to the process or equipment after deployment would require re-identifying the model, which would involve costly step testing and would be handled as a project. However, with Adaptive Process Control technology integrated into today’s APC solutions, sustaining controllers is no longer handled as a project but rather as a continuous process.
Sustainability tools in these advanced APC solutions also include automatic bad-model identification. These models can be calibrated online, in a closed loop with no disruptions to the process. This makes sustaining benefits both easier and cheaper. Additionally, maintaining APC controllers requires fewer resources, and as a result, controllers maintain peak performance which in turn enables companies to deploy and sustain more controllers leading to the best-in-class APC programme.
APC is key to achieving operational excellence
The chemicals market is very competitive, volatile and fast-paced. To maintain a strong market position, companies need to look harder and deeper into their equipment, production and operations to ensure the production chain is optimised. At leading chemical companies, APC is a key strategic tool in the quest to reach higher levels of operational excellence.
The article is written by Tushar Singh, APC Product Marketing Manager, Aspen Technology Inc.
For more details, contact: Tushar.Singh@aspentech.com