In the article, they note:
Reusable, built-for-purpose applications drive costs out of the design, implementation and maintenance efforts, much as pre-fabricated housing takes costs out of building construction. These are simple, straightforward applications that can be put online in a matter of a few weeks, once all the basic instrumentation and control issues have been resolved.
Pete and Gary describe two examples of these pre-engineered APC packages—one for distillation columns and the other for boilers. These units are very large energy consumers. For distillation columns alone: [hyperlink added]:
According to the US Department of Energy, there are more than 40,000 distillation columns in the US alone that consume roughly 19% of all energy used in the processing industries and 6% of the total US energy consumption.
There are a number of similarities between distillation columns across different plants in their instrumentation, control objectives, and operation. Pete and Gary note common operating objectives:
- Maintain overhead and bottoms qualities within target range
- Maximize yield of most valuable product
- Minimize energy usage
- Minimize column pressure (to improve relative volatility)
- Operate within all equipment and process limits
Similarly, boilers have common objectives:
- Generate the target steam demand
- Minimize excess combustion air
- Maximize use of lowest cost fuel
- Control steam-drum level
- Maintain steam supply pressure
- Operate safely within all operational and equipment limits
In both cases, these processes have typical manipulated variables, controlled variables, constraints and key performance indicators.
As we’ve shared in several process optimization-related posts, reviewing the regulatory layer below the advanced control should be a part of the project scope. They note that:
…it is important to address issues with control valves, loop tuning and process measurements to obtain stable, responsive performance in all key control loops. Experience has shown that significant performance and reliability improvements can be obtained just through resolving issues at the regulatory control layer. An APC project is often the driver for fixing problems that may have existed for years.
The authors highlight the reduction in effort and time of a pre-engineered approach as it applies to calculations and control functions, configuration tools, user interface, documentation, and maintenance & support. Projects can also be executed in a modular fashion over time.
Pete and Gary cite some examples where these pre-engineered APC applications were installed:
…a distillation application was implemented for a Midwest US refiner in a total of two weeks and it paid for itself in less than two months. At a site in Texas, a chemicals manufacturer claimed steam reductions and product-recovery savings worth more than $700,000 annually for the first application on its high-purity distillation train. This project was also configured and implemented in only two weeks onsite.
Give the article a read if you’ve got energy-intensive processes such as distillation columns, boilers, fired heaters, cracking furnaces, fractionators, and blenders.
